“alexandru ioan cuza” university of iasi faculty of ......dan gheorghe dimitriu who, through...
TRANSCRIPT
1
“Alexandru Ioan Cuza” University of Iasi
Faculty of Physics
Alexandru COCEAN
PHD THESIS SUMMARY
Contributions to the study of laser induced
physico - chemical phenomena in controlled atmosphere
PhD supervisor
Prof. PhD. Felicia IACOMI
Iași ‐ 2019
2
3
Universitatea ”Alexandru Ioan Cuza” din Iași,
Facultatea de Fizică
În atenția: ................................................................................................................. .....
Vă facem cunoscut că în ziua de 26 august 2019, orele 12:00, în Sala L1,
domnul Alexandru C. COCEAN va susține, în ședință publică, teza de doctorat
intitulată:
“Contributions to the study of laser induced physico - chemical phenomena
in controlled atmosphere”
în vederea obținerii titlului științific de Doctor în domeniul fundamental Științe Exacte,
domeniul Fizică.
Comisia de doctorat are următoarea componență:
Președinte:
Conf. univ. dr. Sebastian POPESCU Universitatea ”Alexandru Ioan Cuza” din Iași
Conducător științific:
Prof. univ. dr. Felicia-Dacia IACOMI Universitatea ”Alexandru Ioan Cuza” din Iași
Referenți:
Prof. univ. dr. Cristina STAN Universitatea Politehnica București
Prof. univ. dr. Shashi PAUL
De Montfort University, Leicester, UK
Conf. univ. dr. Silviu-Octavian GURLUI Universitatea ”Alexandru Ioan Cuza” din Iași
Vă invităm pe această cale să participați la ședința publică de susținere a tezei de
doctorat. Teza poate fi consultată la Biblioteca Facultății de Fizică.
4
5
Acknowledgements
This thesis was developed under the supervision of Prof. PhD Felicia IACOMI
and under the guidance of the Doctoral Advisory Committee formed by Assoc. Prof.
Habil. PhD Silviu Octavian GURLUI, Prof. Habil. Dr. Liviu LEONTIE, Assoc. Prof.
PhD. Dan Gheorghe Dimitriu who, through their expertise, evaluation of the annual
reports and the provision of documentation resources, led to the improvement of this
study.
The experimental work and numerical simulation and modeling related to the
present work were carried out in Atmosphere Optics, Spectroscopy and Lasers
Laboratory (LOASL: http://spectroscopy.phys.uaic.ro) Faculty of Physics of
Alexandru Ioan Cuza University of Iasi, Romania, under the experimental and
theoretical scientific coordination of the head of laboratory, Assoc. Prof. PhD Silviu
Octavian GURLUI, who encouraged and supported my ideas, also contributing to their
improvement and finding solutions for my experimental work, including but not
limited to use of laser systems for pulsed laser deposition and LIBS, DARLIOES –
LIDAR system for atmospheric investigation and all devices and apparatus available
in the laboratory.
During all these years of study, I have had all the support of my family: my
parents, Cezar and Cristina Cocean, my paternal grandmother, Ortansa Cocean, my
sister Georgiana Cocean and my maternal grandparents, Aurel and Didina Biali, as
well as many others.
A real and competent support and advice came from MD. PhD. Daniel Alexa.
In my grandfather’s memory, Gheorghe Cocean, who encouraged me to
always climb the heights.
6
Table of contents
Introduction 7
I Laser matter interaction. Laser induced breakdown spectroscopy
(LIBS)
11
I.1 Fundamentals 11
I.2 Theoretical models: COMSOL simulation technics 12
II Modelling of LIBS in vacuum. Applications 20
II.1 Laser ablation. Experimental set-up 20
II.2 Pulsed Laser Deposition – PLD. Study in COMSOL of ablation
and deposition phenomena
23
II.2.1 Target Heating under Pulsed Laser Irradiation 24
II.2.2 Film Deposition model setup in COMSOL 28
II.3 Non-homogeneous target influencing physico - chemical thin
layer map dispersion, morphology and fluorescence properties
32
II.3.1 Pulsed Laser Deposition from Silver target with Iron and Nickel
impurities
33
II.3.2 COMSOL compiling for phase change during ablation of material
from the target
37
II.3.3 Chemical interaction of ablated material on the deposition
substrate
40
II.3.4 Physico – chemical behavior of nonhomogeneous material under
UV laser beam
42
III Modelling of LIBS in free atmosphere and non-homogeneous
materials
44
III. 1 Pulsed Laser Inducing Thermal Effects in limestone covered by an
impurity layer
44
III. 2 Damage threshold behavior of silver target unpurified with iron
and nickel
49
IV Study of physicochemical processes of the environmental
atmosphere by spectroscopic and numerical methods
54
IV.1 Optical instruments and techniques 54
IV.2 Study of some critical physicochemical phenomena in the
terrestrial atmosphere
55
V. General Conclusions 61
VI. Reference 66
VII List of publications 82
7
Introduction
The fundamental mechanisms underlying the interaction of laser radiation
with matter are topics in continuous research. The complexities of the processes and
phenomena that occur in the context of the photon interaction with various material
have not yet been fully understood. However, the applications of the devices based on
coherent light began a long time after the construction of the first laser system. Thus,
if the first laser was built in 1960, laser spectroscopy immediately followed as Laser-
Induced Breakdown Spectroscopy (LIBS) in 1963 and Laser- Induced Fluoresnce
(LIF) in 1968 [Anabitarte et al, 2012; Kim et al, 2012; Tango (1968); Zare (2012)].
Spectroscopic analysis techniques (LIBS) have been added to the deposition of thin
layers based on laser ablation, namely Pulsed Laser Deposition (PLD) when, with the
same laser pulse resulted in material ablation, both producing thin films and spectral
analysis are accomplished.
The theoretical context in which the studies of this paper were conducted will
be presented in the two sections of the first chapter (I. Laser matter interaction. Laser
induced breakdown spectroscopy (LIBS)) where laser interaction with the matter and
LIBS fundamentals are presented in a first section (I.1. Fundamentals), followed by a
general presentation of Finite Element Method (FEM) and COMSOL software basics
(I.2 Theoretical models: COMSOL simulation technics). The schematic installations
and principles, specific parameters and set-ups of laser system in PLD, LIBS and
LIDAR mode, as well as work with COMSOL, modeling and applications to assist the
laboratory experiments, will be subject for the next chapters.
Four main research topics have been subjects for studies of computing
models and simulations applied and confirmed within the experiments that are
presented in this thesis in the chapters from II to IV. In this regard, the chapter II of
the thesis (II. Modelling of LIBS in vacuum. Applications) presents in section II. 1.
Laser ablation. Experimental set-up the experimental installation for PLD, LIBS and
LIF from LOASL. The next two sections from chapter II refers to setting – up a
numerical model to complete the existing mathematically description in COMSOL of
heat transfer in solids process with the laser interaction with matter as the heating
ignition mode (II. 2 Pulsed Laser Deposition – PLD. Study in COMSOL of ablation
and deposition phenomena) followed by experimental work (II. 3 Non-homogeneous
target influencing physico - chemical thin layer map dispersion, morphology and
fluorescence properties) with pulsed laser deposition of thin layers from non-
homogeneous target of silver with iron and nickel impurities (II.3.1. Pulsed Laser
Deposition from Silver target with Iron and Nickel impurities), assisted by simulation
in COMSOL (II.3.2 COMSOL compiling for phase change during ablation of material
from the target) to explain different phenomena observed during PLD and based on
analysis of plasma dynamics and elemental mapping and morphology of both target
and thin deposited layer (analyzed in SE-EDX and AFM). In the section II.3.3
Chemical interaction of ablated material on the deposition substrate a study of
8
interaction of the plasma of ablation with the citrate from the substrates (hemp fabric
and glass slab) is presented with the aim to find a method to produce silver citrate for
further applications in medicine and also in other fields for antibacterial and antifungal
purposes. The section II.3.4 Physico – chemical behavior of nonhomogeneous
materials under UV laser beam presents a study of a polyacrylic textile material dyed
with curcumin extracted from turmeric powder in aqueous alcoholic and non-alcoholic
solution using LIF methode.
Chapter III. Modelling of LIBS in free atmosphere and non-homogeneous
materials comprises two sections: III. 1 Pulsed Laser Inducing Thermal Effects in
limestone covered by an impurity layer which is a study that continues the modeling
and simulation work in COMSOL with regards to laser ablation, this time for
application in cleaning buildings and other civil and/or historical constructions
exposed to deposition of different particles from the atmosphere which contribute to
“aging” phenomena and III. 2 Damage threshold behavior of silver target unpurified
with iron and nickel that analysis both in a simulation in COMSOL and experimentally
the damage threshold of the thin layer of silver with iron and nickel impurities and
both experiments refer to ablation process conducted in free atmosphere. In chapter
IV.Study of physicochemical processes of the environmental atmosphere by
spectroscopic and numerical methods, dynamic of chemical compounds detected in
the atmosphere with DARLIOES-LIDAR installation from LOASL (installation
presented in section IV. Study of physicochemical processes of the environmental
atmosphere by spectroscopic and numerical methods) is reported and analyzed from
a physicochemical point of view and, simulating in COMSOL the conditions in the
atmosphere at the time when measurements were made, it is evidenced that water
dissociation during nighttime, detected with LIDAR system, is due to the artificial
streets lights (IV.2 Study of some critical physicochemical phenomena in the terrestrial
atmosphere). Chapter V. General Conclusions will underline the achievements
resulted from the studies presented and it will evidence the importance of numerical
simulation for the experimental work and the compatibility of the results received
during the two methods of study.
The quality of thin films and their functionality resulting from this requires the setting
of working parameters by varying them until the properties that are desired to be
obtained. This often means a considerable number of attempts / repetitions of the
experimental work and here the important role of the numerical simulations begins
[Bechtel, 1975; Franklin et al, 2004; Gurlui et al, 2006; Stafe et al, 2008; Gurlui et al,
2008, Pop et al, 2001; Dascalu et al, 2013; Cocean et al, U.P.B. Sci. Bull., 2017; A.
Cocean et al, Appl. Surf. Sci., 2017, Cocean et al, May 2019].
The mathematical model to be presented in this paper applies to the Heat
Transfer in Solids module of COMSOL Multiphysics, completing its equations and
functions, and establishing the conditions of the studied physical process, while
allowing its further development and expansion, anticipating other possibilities for
9
use. The two-dimensional models previously purposed in literature for laser
interaction with matter in COMSOL [Poulain et al, 2010; Rühl et al, 2012; Rogers et
al, 2007; Beltramo et al, 2009] are limited only to symmetrical geometry while the 3
D geometry and improved mathematical models that we reported later [Cocean et al,
U.P.B. Sci. Bull., 2017; A. Cocean et al, Appl. Surf. Sci., 2017; A. Cocean et al, 2018]
and which is also developed in this thesis, allows a better and more flexible simulation
method with more possibilities of application to a variety of materials and structures.
The model is complex and requires consistent computing resources, but this is where
the role of the mesh in the Finite Element Analysis comes in the picture, optimizing
the system for reducing the calculation to the essential and of interest regions. This is
the advantage to working with the Finite Element Method. In the simulation, multiple
parameters can be varied until the optimum matrix is found, but also when physical
parameters values cannot be directly measured, the simulation can calculate those –
such as temperature during pulse irradiation but also its evolution in time of pulse
width duration (ns) [Cocean et al, U.P.B. Sci. Bull., 2017].
On the quality of thin silver layers, previous published studies have been
performed with regards to their smoothness and consistence, characteristics that are
also of interest for the laser mirrors. Research on PLD of thin silver layers and
compounds has led to conclusions regarding morphology as well as their
characteristics important to those. In this regard, published studies present conditions
of 10-2 Torr pressure in deposition chamber and low energy for ablation as suitable
for a smooth layer reported as 0.36 nm roughness on a quartz substrate with 0.3 nm
roughness, using a buffer layer of Yttrium oxide [Kuznetsov et al, 2013]. Quality of
deposited layer is also connected to the number of pulses, when for a YAG:Nd laser
at 355 nm wavelength, a number of 15.000 pulses was necessary for obtaining a
consistent silver layer, while from 500 to 10.000, a discontinued film was formed,
rather an agglomeration of particles than a film, the particles sizes growing with the
number of pulses [Alonso et al, 2008]. A COMSOL simulation of layer deposition
confirmed the mathematics that governs the growth of a silver layer during PLD
[Cocean et al, U.P.B. Sci. Bull., 2017]. Other papers report changes in optical
properties between metal nanoparticles and bulk material [McFarland et al, 2003;
Cazzaniga et al, 2013].
Among optical changes, considerable alteration of refraction and extinction
index that take place when the incident photon resonates with the conduction band
electrons and it is known as LSPR – localized surface Plasmon resonance [McFarland
et al, 2003].
Plateau - Rayleigh instability [Saifi et al, 2017; Xuan et al, 2017; Hokmabad
et al, 2014], but also crown splash [Zhang et al, 2010] and Richter – Meshkov
instability are considered in the discussions on the droplets formation during thin
layers deposition by means of PLD method. Previous papers extended Plateau –
Rayleigh instability theory from liquids in dielectric elastomer films [Saifi et al, 2017],
10
in solids as simple phase separation [Xuan et al, 2017], during reorganization of silicon
macro pores process [Garín et al, 2017] and with the work presented herein was found
experimental evidence that Plateau – Rayleigh instability is also induced by
perturbation produced during plasma expansion shortly after its laser ablation.
The model implemented in COMSOL is also aimed for laser application in
procedures in free atmosphere such as damage threshold of the metallic thin films and
procedures of cleaning the crust formed by deposition of different particles from the
atmosphere on buildings and other civil constructions and historical monuments
exposed [Cocean et al, Appl. Surf. Sci., 2017] when particle of pollutants form a crust
on the surface of buildings and other civil and historical constructions [Sabbioni, 1995;
Pouli et al, 2008; Pouli et al, 2012].
Air pollution episodes have been subject to research, an important number of
studies being focused on the sink and sources of the pollutants, their chemistry and
dynamic in the atmosphere [Schlager et al, 2012; Chameides et al, 1982; Smith et al,
2008; Zhao et al, 2014; X. Xia et al, 2015; Dubovik et al, 1998; Papayannis et al, 2014;
Ciuraru et al, 2011]. Therefore, a LIDAR detection in the atmosphere of Iasi city was
of interest and the role of simulation in COMSOL has become important to supplement
the explanation of phenomena such as water dissociation in nocturnal and humidity
conditions [Cocean et al, 2018]. The information has been completed after that, when
rain waters were studied and compounds with the groups detected with DARLIOES
LIDAR in the atmosphere have been found in the water collected during rainfalls
[Cocean et al, April 2019]
Within the thesis chapter that will follow, a contribution to the study by
means of numerical simulation of laser interaction with matter will be presented and
the results that complete the experimental work in a manner that is aimed to lead to a
better understanding of the phenomena and also to anticipate optimum parameters and
conditions, as well as damage threshold for application of the LIBS method in
laboratory but also in other processes and practical procedures that can also involve
chemical processes and the model for simulation of laser interaction with matter is
aimed to address that as well.
11
I. Laser matter interaction. Laser induced breakdown
spectroscopy (LIBS)
I.1 Fundamentals
Laser-Induced Breakdown Spectroscopy (LIBS) is based on the atomic
emission spectroscopy where the electrons from lower level are excited by laser
irradiation to a higher level of energy. The electrons return to their fundamental state
thus reemitting photons. A spectrum can be made and analyzed. LIBS as the name
suggests uses a laser for the excitation and breakdown [Kim et al, 2012]. Emission of
the atom depends highly on the environment conditions. In not to dense plasma the
shape and line of the spectra changes due to temperature. In high density plasmas Stark
effect broadens and changes the shape of the spectral lines. This effect happens due to
the electric fields made by fast electrons and slower ions which split and shift the
energy levels that change the shape and intensity. The intensity, shape and continuous
spectra are used in determining the plasma parameters, electron temperature, pressure,
and electron density [Cremers et al, 2006; J. P. Singh, 2007]. These parameters are
necessary for quantitative analysis because they are important in LTE conditions for
calibration for the set-up. Laser induced plasma has three stages in its lifetime:
The first stage is ignition. It depends on laser pulse characteristics. Ignition
includes bond breaking and plasma shielding depending the laser pulse, type and
duration.
The next phase of plasma lifetime is expansion and cooling. It is a crucial stage
for LIBS as it depends on the emission caused by cooling. After ignition the
plasma continues expanding and cooling, electron temperature and density
changes. Plasma cooling and expansion depends on the environment (state of the
sample, pressure, etc.), spot size, ablated mass, energy.
The last step in plasma life, condensation, is not interesting for LIBS. The ablated
material becomes cold and does emit any radiation. It is characterized by
particles which creates condensed vapor, liquid sample ejection, and solid sample
exfoliation [Anabitarte et al, 2012].
In the first stages of recombination in plasma life the spectra emitted is
continuum due to the recombination process and Bremsstrahlung effect. In the
recombination process electrons from a free state passes to the upper bound and then
the ion cascades to a fundamental level emitting photons. The Bremsstrahlung is
caused by electrons passing through an ion’s field slowing down also emitting
photons. In a femtosecond laser this radiation is in X-ray. The continuum radiation
hides the emission spectrum that interests us. However it doesn’t last for the entire
period of the recombination process. It depends on temperature and plasma density.
And in the initial stages of plasma generation especially the ignition stage plasma
density and temperature are too high therefore a delay is necessary. For a femtosecond
laser the delay should be higher than 1 nanosecond, as the continuum emission was
12
noticed to be this long [Cremers et al, 2006; Singh, 2007; Angel et al, 2001]. For
nanosecond lasers the delay should be 1 microsecond and for molecules should be later
[Cremers et al, 2006; Singh, 2007; Angel et al, 2001]. The parameters shown above
are optimal for acquiring ion emission lines. The parameters depend on sample,
environment and experimental conditions. It is better to take measurements in the in
initial stages of the plasma despite the continuum emission. The parameters shown
above serve as a starting point for each kind of laser [Castle et al, 1998].
The laser ablation plasma dynamics are mainly influenced by the
characteristics of incident laser radiation (fluency, wavelength, repetition rate,
duration of the laser pulse), the nature of the target, the pressure and the nature of the
gas and diagnosis methods will raise a lot of difficulty, Since lasers provide the ability
to accurately supply large amounts of energy in a reduced volume and in a short time,
the fundamental aspects of the ablation phenomenon, as well as the process of thin
layer deposition (PLD), are of particular practical importance [Gurlui et al, 2006,
Gurlui et al, 2008, Cocean et al, U.P.B. Sci. Bull., 2017, Cocean et al, May 2019].
The quality and thickness of thin layers deposited by the PLD technique
depend on a number of factors: laser radiation (laser pulse duration, repetitive
frequency, wavelength, fluence), type of target material, type of substrate on which
the thin film is deposited, the surface of the substrate, the temperature of the substrate,
the distance between the target and the substrate, the working gas pressure, the nature
of the working gas, the irradiation time, the speed of rotation of the target and the
support relative to the direction of laser radiation, as well as others) [Bulai et al, 2018;
Bulai et al, 2016; Dascalu et al, 2015; Cocean et al, Appl. Surf. Sci., 2017, Cocean et
al, U.P.B. Sci. Bull., 2017, Cocean et al, May 2019].
Laser ablation plasma containing the macroscopic particles (droplets) is the
main disadvantage of the PLD technique and can seriously damage both the quality of
the deposited thin layer and the morphology [J.P. Singh et al, 1998]. While particles
formed from the solid target tend to have an irregular shape, those formed in the liquid
phase and vapor phase tend to have a spherical shape. The droplet sizes depend on the
phase state and may have micrometric dimensions in the case of solid and liquid phases
reaching up to nanometric dimensions for droplets formed in the vapor phase. To
eliminate large droplet deposition, several techniques are used, taking into account the
geometry of the PLD configuration, the laser type, the properties of the materials and
the working gas. Generally, to reduce particle number density, the simplest technique
involves decreasing laser fluency.
I.2 Theoretical models: COMSOL simulation technics
The approach by numerical computation of the theoretical and experimental
studies leads to a better understanding and explanation of the physical phenomenon,
to a more elaborate data processing and even to the anticipation of the conditions for
13
an experiment to lead to the expected results [Poulain et al, 2010; Rühl et al, 2012;
Rogers et al, 2007; Beltramo et al, 2009; Cocean et al, U.P.B. Sci. Bull., 2017;
Cocean et al, Appl. Surf. Sci., 2017; Cocean et al, 2018].
The study of physical processes by numerical simulation is carried out both
in the sense of assisting the experiment – with the purpose to reduce the number of
experimental attempts – and in completing or calculating values of parameters that
vary at a very high speed or are of short duration, or the environmental conditions and
existing devices do not allow their measurement [Cocean et al, Appl. Surf. Sci., 2017;
Cocean et al, 2018].
COMSOL Multiphysics is finite element software to analyze physical
processes and phenomena with large possibilities to add mathematical models and
geometry with the purpose to be applied in a large range of applications while
providing large possibilities to build various geometrical systems. In order to do that,
the software has a number of modules AC/DC, Acoustics, Chemical Species Transport,
Electrochemistry, Fluid Flow, Heat Transfer, Optics, Plasma, Radio Frequency,
Structural Mechanics, Semiconductor, Mathematics and each of these modules has
implemented the differencial formulae needed. For example the Heat Transfer in
Solids module has implemented the heat transfer equation and all its conditions and
boundarys that need to be selected properly, in accordance with the system studied.
COMSOL as a finite element method (FEM) software with the strong
advantage of flexibility and multiple possibilities to add mathematical models,
materials with their parameters, geometry, interconnect modules and other and other
ways to improve the proposed simulation. Its key fundaments are logical which makes
it an attractive method. The importance of understanding the basic concepts comes
from the fact that this concepts have hypothesis, simplifications and generalizations
that, if ignored, would result in grave errors in the modeling and finite element
analyses (FEA).
FEM Basic Concept
Finite Element Method (FEM) has been developed from the need to solve
differential problems and to address a variety of engineering and physics problems,
same as the Finite Difference Method (FDM). The first addressed problem in FEM
was stress analysis in 1960. The method was extended to heat transfer, fluid flow,
electromagnetism, mass transport, as well as others [Evan Mitsoulis et al, 1984].
Finite Element Method uses less complicated codes, but complex enough that
users do not write their own codes. That leaded to an important “industry” of
commercial codes compatible with various computing machines from microcomputers
to supercomputers. Most of the Finite Element Method codes are written in
FORTRAN but also in C programs. The method presents the advantage to solve
problems in an irregular/asymmetric geometry when non-homogeneous media can be
modeled as well as homogeneous ones. The main disadvantage consists in a
complicated formulation. [Evan Mitsoulis et al, 1984].
14
The basic concept will be further explained based on the stress analysis that
can be extended and applied to different other fields named before.
In order to have an increased efficiency FEA uses a concept of a general
structure and a simpler one than usual. Usually in FEA by resistance structure it is
understood as beams, plates and solid volumes. For example the frame of a parallel
lathe, landing gear of a plane, the arm of a Libra, the housing of a nuclear reactor, the
hull of a submarine, a network of pipes, and so on. An example of structure defined in
the geometry of COMSOL (a finite element analyzer software) is presented in Figure
1.1.
Figure 1.1. Geometry in COMSOL (FEM software)
Mathematical model
In order to have an analysis with finite elements of a structure, the important
bit is the creation of a mathematical model of said structure.
FEM models approximate mathematical models of structures which are about
to be analyzed. For the passing from the real structure to its model there is no general
algorithm or general method to ensure a unique model, which approximates with a
pre-established error the structure that is being modeled. Generally, it is possible that
for a structure more models to be established, all of them correct but with different
performances. The mathematical models for the structural resistance are made based
on intuition, imagination, and previous experience of the one who makes the model.
Discretization
The mathematical model of a structure that is about to be analyzed through
the finite element, in general, is made up of lines, which are the axes to the bars of the
structure, from plane surfaces and curves, which are middle surfaces of the component
plates of the structure and volumes, which are massive bodies of the structure. Finite
element method usually defines the unknown variables (movement or stresses) in the
nodes and computes the variable values in those points. In this condition discretization
must be made so that a sufficient number of points are defined in the zone of interest,
the resting conditions and load conditions, to be satisfactory for the purpose of FEA.
15
Discretization or mesh in COMSOL (a finite element analyze software) is presented
in Figure 1.2.
Figure 1.2. Discretization/Mesh in COMSOL (FEM software)
Node
The points defined by the discretization network are called nods. In nods the
primary nod variables are defined computed by FEA. The unknown variables
associated with nods can be movement in which the FEM is called a moving model,
or stresses, the FEM is called a equilibrium model. Mixt models are rarely used. For
the moving model a deformation of a structure because of a force applied is defined
by the movement of the nods compared to the network of nods before, every node can
have 6 maximum movement directions, named nodale movements, compared to global
reference: three components u, v, w linear displacement and three rotations jx, jy, jz.
Finite element
The discretization process divides the structure model in a random number of
fragments or elements just like a building being seen as being made of bricks. A
structure can be divided or discretized in a number of quadrilateral and triangular
elements, finite elements. These elements thigh together in common nodes, edges of
the quadrilaterals and triangles (there are elements that have nodes on the lines). A
finite element can be seen as a piece that only interacts with other elements in nodes.
Discretization in finite element is similar to a function and its linear approximation -
similitude with differential calculation (Figure 1.3).
16
Figure 1.3. The function (blue line) and its linear approximation (the red lines)
The finite element can be classified by different criteria, the most important
being:
Type of analysis: On a discretization grid there can be defined elements that
have mathematics procedures intended for various analyses like: linear elastic,
nonlinear, heat transfer, fluid mechanics, electro-magnetism, high frequency electro-
magnetism, and so on.
Functional role: The finite elements used to modeling a structure must
ensure the functional role as best as possible, for example for a truss, the elements are
bars, a thin plate cover must be modeled out of plates, a foundation must be modeled
out of brick like elements, and so on. The elements used can be dot type (mass element
or arc element), line type (straight or curbed bars, in plane or in space), surface type
(plate elements plane or curbed, thin or thick, in plane or in space, axial symmetric
elements, membranes, and so on), volume type (spatial elements, -3D- for solid
structures, composites, with variable nods, for fluids, piezoelectric, magnetic, and so
on). Every element type listed above have several tens of types. They also have
elements with special functioning role, for example: contact rigid, friction rigid,
linking rigid, defined by the rigidity matrix, and so on.
Geometric shape. The finite elements have simple shapes generally as for
example a line, arc of a circle, triangle, and quadrilaterals. Also some geometric
characteristics can be constant or variable, like the section of beams or thickness of
plates [Roylanceet al, 2001; Hrabok et al, 1984; Pian et al, 1969; Barkanov, 2001].
Number of nodes. For some elements, a certain geometric shape, for
example a triangle, can have a number of ways involving number of nodes, because
except the nodes at the tips they can be added to the side of the triangle and also inside
it. Nodes can be added inside for results. Nods can be also variable in number - for
example on thick plates - and can be from 8 to 48 nods [Roylanceet al, 2001; Hrabok
et al, 1984; Pian et al, 1969; Barkanov, 2001].
Degrees of freedom. The nods of elements have attached to them a DOF of
which 6 are possible, so it can operate with the total number of DOF for an element,
17
which is the number of nods multiplied with the DOF per element [Roylanceet al,
2001; Hrabok et al, 1984; Pian H.H. et al, 1969; Barkanov, 2001].
The interpolation polynomial degree. Each finite element has implemented
interpolation polynomials of a certain degree, starting from first degree. The more the
degree increases, the more the quantity of information increases for the element to
operate and the model is better [D. Roylanceet al, 2001; Hrabok M.M. et al, 1984; Pian
H.H. et al, 1969; E. Barkanov, 2001].
Material characteristics. In FEA the material of the finite element can be
homogenous and isotropic or whit a type of anisotropy. Also the elastic and physical
properties of the material can be dependent on temperature and strain. The mention
must be made that the description above for finite elements explains only certain
important aspects used in FEM. In conclusion it is noted that every finite element is
an ensemble of conditions and hypotheses and it should be seen as a whole and only
used as such, after the documentation linked to it is studied [Roylanceet al, 2001;
Hrabok et al, 1984; Pian et al, 1969; Barkanov, 2001].
For example from the parameters that define the element that show the strain,
the tension, its interactions with other elements, and so on, it results the behavior of
the body. FEM programs that are used in FEA have huge libraries with finite elements
to which new elements are added. To show the dynamics of development of FEM
article [Hrabok M.M. et al, 1984] is cited, in which from year 1984, 88 finite elements
for plates are found.
Efficiency of Finite Element Method
The model made for a structure for a FEA analysis must be precise and efficient.
The main conditions for a model to be efficient:
The model must have a reasonable amount of load;
Volume of information obtained by FEA to be large enough and an acceptable
error considering the purpose, destination of the information and the way they are
being used [Hrabok et al, 1984; Pian et al, 1969]. For satisfying those requirements
the user has at its disposal numerous ways and means, the most important being as
follows [Roylanceet al, 2001; Zienkiewick et al, 2000; Larson et al, 2010; Bathe,
2014; Nikishkov, 2004; Barkanov, 2001] :
Discretization configuration. It is convenient and rational that the
discretization mesh to be as simple and uniform. This is in contradiction with
efficiency and that’s why finer mesh will be added for the regions where the
important data and results will be collected, meaning the regions of interest
for the phenomena and processes subject to the simulation.
Number of nodes. It is better that a model has as many nodes because FEA
results are more precise and the volume of information is higher. The
requirement of making the mesh as fine with as many nodes as possible needs
to be analyzed critically, with a lot of deliberation and discerning because the
18
unreasonable increase of the number doesn’t lead to a better solution. Usually
increasing the number of nodes is efficient for a model with a relative small
number of nodes. After a certain threshold is attained increasing the number
of nodes doesn’t improve the FEA solution. Concerning the number of
elements of the model this has a linear dependency depending on the number
of nodes, if the elements do not change.
Dimensions of the finite element. An alternative requirement to that of the
number of nodes is the dimension of elements the two aspects being closely
interconnected. For the structure subjected to FEA analysis depending on
configuration and purpose the minimum and maximum size of the finite
elements of the model. Of course this operation presumes that the elements
to be used are chosen and that the user knows very well their properties and
performances. The maximum dimensions will be established considering that
bigger elements estimate more poorly the geometry and stresses than smaller
elements, but those have the disadvantage that they become too numerous. In
conclusion intuitively a compromise solution needs to be found concerning
maximum and minimum elements and those for different regions of the
model. It is mentioned that for various procedures of automated discretization
implemented in FEM software have defined as parameters either number of
nodes, either maximum and minimum dimensions.
Automatic generation. In order that the generation of the model to be made
with minimum of work or that the procedure to be efficient FEM software
have a generated steering procedure of nodes and elements others than the
ones of automated discretization. After some the nodes and elements are
defined the user can use them as seeds to which he has a number of commands
with which he can generate new nodes and elements. The most used
commands for automated generation are:
- For nodes and elements:
o copying, repositioning, moving, pasting; operations that consist in
modifying the position of nodes and source elements using operations
of translation and rotation for obtaining the wanted nodes and
generated elements desired;
o symmetry from a point, a direction or a plane; nodes and elements are
generated symmetrical to a source;
o changing scale; consists of multiplication by a factor of the values of
coordinates of nodes and source elements.
- Only for elements:
o extrusion, slipping, copying, creeping; operations that lead to
covering of surfaces and filing of volumes with elements and nodes
generated
19
Synthetizing the application of FEM for the modeling and simulation in COMSOL,
the steps are reviewed and schematically represented in Figure 1.3.
Figure 1.3. Schematic representation of FEM application in COMSOL
20
II. Modelling of LIBS in vacuum. Applications
Numerical study of physical phenomena offer an important support for the
experimental work, reducing the number of trials, measurements and analysis,
focusing the experiment in an estimated range and also can anticipate or complete the
information regarding some parameters that cannot be directly measured during the
process. The software COMSOL Multiphysics provides with basic mathematical
models on modules as described in section I.2, graphic interfaces with the possibility
to develop the mathematical model adding analytic functions, parameters and
variables. The Material Library consists in a large database of constants and
parameters and their functions when those change based on an external parameter. The
database can be completed by adding new materials and their constants and
parameters.
In order to model LIBS in vacuum it is important to choose the right model
based on the phenomena induced by the process of interaction of matter with the laser
beam. As the process is the laser ablation that consists in heating and phase change of
the material from solid to liquid and to gas and plasma phases, the Heat Transfer in
Solids is the suitable model and for the deposition, when the fluid phases (liquid, gas
and plasma) coexist, Fluid Flow is the most appropriate module to simulate the
process. Geometry and mesh (discretization proper to the Finite Element Method) are
important and they will be described in the next sections. The variables formulae,
parameters, analytical functions, their connections with the existing mathematics and
boundary conditions added to the existing equations and conditions will complete the
model.
II. 1. Laser ablation. Experimental set-up
The experimental work was carried out on an installation for laser ablation
consisting of the laser system, the lens and mirrors system, the vacuum chamber
serviced by vacuum pumps, the spectrometer and the intensified CCD camera as seen
in Figure 2.1a-h and schematically represented in Figure 2.2.
This installation allows the fixation of a target from the ablate material placed
in the focal plane of a lens with a focal length of about 25 cm, the radiation being at
an angle of 45 degrees. The irradiation of the target is performed with a laser beam
comprising various spectral domains (UV, VIS, IR). The target is placed horizontally
and can move automatically, in three directions, by means of a computerized
micrometric system. The major advantage is that the action of a particular species can
be recorded at any distance at different times. The installation also has an upper
furnace on which special specimens can be used for thin layer coatings. Both the thin-
film substrate and the target can be isolated from the vacuum enclosure and electrically
polarized to provide thin layers of superior quality. The spatio-temporal evolution of
21
charged species from plasma is further analyzed by Langmuir probes and space-time
resolved spectroscopy techniques.
Figure 2.1. Different images of the experimental set-up
The installation was configured and set up in the laboratory LOASL
(Atmosphere Optics, Spectroscopy and Lasers Laboratory) from Faculty of Physics of
the “Alexandru Ioan Cuza” University. There are two laser systems at LOASL, both
Nd:YAG (neodymium-doped yttrium aluminum garnet; Nd:Y3Al5O12) high power
lasers: a Brilliant EaZy laser system with ranges of 1064 nm, 532 nm wavelength, 330
mJ, 165 mJ energy and 5 ns pulse width and a YG981E/IR – 10 Hz laser system with
ranges of 1064 nm, 532 nm, 355 nm, 266 nm wavelength, 1600 mJ, 820 mJ, 490 mJ,
150 mJ, 330 mJ, 165 mJ energy and 10 ns pulse width and pulse repetition frequency
of 10 Hz. The laser used for the experiments in this work is the YG981E/IR – 10 Hz
(Figure 1a, c).
22
The vacuum chamber (Figure 1 a-e) is a spherical vacuum enclosure and can
work both at low pressure and in free atmosphere. The vacuum from the depositing
chamber may achieve 10-8 Torr using two pumps system - dry rotary pump and turbo-
molecular pump.
Figure 2.2. Experimental set-up.
The spectral installation comprises a dual diffraction grating spectrometer
and a CCD intensifying chamber (Figure 1g) with an integration time of up to 2ns. In
this way, optical phenomena (temporal evolution of excited species) can be traced over
very small time intervals, ensuring a very good time resolution. The laser ablation
plasma plume was analyzed using lenses - spherical or cylindrical lenses - and an
original complex mechanical device that provides an optical space resolution of up to
0.2 mm on the axis of the laser ablation peak, by micrometric displacement of the
target along three directions.
Optical analysis was possible by using the same spectroscope in which one
of the diffraction networks was replaced by a mirror and the image of the plume was
projected onto the ICCD chamber aperture. The spectrometer can perform both spatio-
temporal plasma movement and elemental analysis (LIBS). For temporal analysis of
excited species (atoms and ions) in the 0.2 mm thick plasma section, two experiments
were imagined. Both experiments use the spectrometer and ICCD camera.
23
The main drawback of rapid imaging technique is that it records only global
optical emission at a given time, i.e. individual information on excited species present
in plasma ablation laser cannot be obtained. The ICCD imaging technique is used in
addition to other optical and electrical diagnostics, such as space-time resolved optical
emission spectroscopy, laser-induced fluorescence, Langmuir probe, etc.
One of the advantages is that, depending on the experimental conditions, the
plume of laser ablation may even be optically highlighted as being structured in several
formations (optically excised particles) with different evolution rates [Nica et al,
2012].
II. 2. Pulsed Laser Deposition – PLD. Study in COMSOL of ablation and
deposition phenomena
Pulsed laser deposition (PLD) consists in two processes to be addressed in a
simulated study: ablation, vaporization and melting of the target material and transport
to the support and deposition. The theoretical approach in COMSOL involves using
Heat Transfer in Solids module in order to determine the heating of a silver slab
(target) and though different phases generate based on achieved temperatures, under
laser irradiation. Then the temperature is used to determine the deposition on an inert
material: silica glass or silicon. To model the laser ablation and vaporization, laser
parameters were taken into account: energy or fluence, pulse width, spot size and also
material characteristics and constants needed for the heat transfer calculation taken
either from COMSOL library or added from different specific sources. The second
model used was Free Molecular Flow module in order to simulate the deposition. The
model takes into account the average temperature on the silver slab surface, the
distance between target and support, the number of pulses, material parameters: silver
density, molecular mass and vapors pressure. The entire model constructs the
simulation for PLD deposition from laser ablation to the deposition of material.
Cylinder geometry in COMSOL was used for both target and deposition
substrate. The mesh system is the discretization of the geometry for the finite element
unit. There are several preset meshes, namely coarse (maximum element size and
minimum element size) extremely coarse (maximum element size 12.7 mm, minimum
element size 1.78 mm), extra coarse (maximum element size 7.62 mm, minimum
element size 1.37 mm), coarser (maximum element size 4.83 mm, minimum element
size 1.02 mm), coarse (maximum element size 3.81 mm, minimum size 0.711 mm),
normal (maximum element size 2.54 mm, minimum element size 0.457 mm), fine
(maximum element size 2.03 mm, minimum element size 0.254 mm), finer (maximum
element size 1.4 mm, minimum element size 0.102 mm), extra fine (maximum element
size 0.889 mm, minimum element size 0.0381), extremely fine (maximum element
size 0.508 mm, minimum element size 0.00508 mm).
The mesh in this simulation was made accordingly to the following setup: an
extremely fine mesh on the spot, a coarse mesh for the surface area and a normal mesh
24
for the remaining geometry (Figure 2.3). The study used in simulation is time -
dependent. The domain is set automatically based on the geometry.
Figure 2.3. Finite Element Discretization (Mesh)
The results of the studied variables (either based on the equations that are
already implemented in COMSOL to describe the phenomenon, or declared in the
Variable section of each module) are presented as plots that are automatically
generated by the software or plots that are generated based on specific set-ups. To
generate a custom plot, few aspects need to be addressed: the parameter on which the
variable is being studied, the coordinates, the time and other specific conditions in
relation with the study.
The domains where data results are of interest need to be declared for
generating the plots. The software makes plots in accumulating domains which may
be points, lines and planes, named as “cut points”, “cut lines” and “cut planes”. They
can be either 2 D (except for cut planes) when they refer to a data selection from a
planar or 3 D when the data selection refers to a volumetric. In order to make graphs,
the cut point, cut lines and cut planes must be declared in terms of coordinates and
vectors. After they are declared, plots can be generated to easily see the results.
II.2.1. Target Heating under Pulsed Laser Irradiation
The model needs to be setup for heating under laser irradiation and that is
possible using the specific laser formulas to model laser pulse, irradiation time and
heat source in order to simulate the heating effect that is of interest when ablation is
studied. The geometry for the target is a cylinder 26 mm diameter, 13 mm height,
dimensions that can be changed either in the geometry mode or introducing as
parameters. Silver is selected from the software library of COMSOL, material for
25
which the library has all the constants necessary for the simulation. However, the
parameters – such as thermal conductivity, heat capacity at constant pressure, density
- are temperature dependent and are calculated based on specific functions. COMSOL
provides the said functions only up to 1235 K for Silver (Silver melting point), with
the possibility to extrapolate when apply “nearest function” setting, and extrapolate to
a higher temperature the parameters calculation.
Starting from the heat - transfer equation (2.1), that COMSOL provides, in
Heat transfer in Solids module, a heat source, Q(W/m3), must be defined, which is the
laser irradiation in this specific study [Cocean, U.P.B. Sci. Bull., 2017].
𝜌(𝑇)𝐶𝑝(𝑇)𝛿𝑇
𝛿𝑡= ∇[Ҡ(𝑇)𝛻𝑇] + 𝑄 (2.1)
where ρ(T), CP(T) and Ҡ(T) are the material constants: density, the specific heat at
constant pressure and the thermal conductivity, as functions of temperature T.
The heat source Q needs to be mathematically formulated in accordance with
the laser irradiation and the specific phenomena and processes must be addressed. To
define it, variables and analytic functions must be defined.
The irradiant energy of the laser beam which is absorbed into the material
will transform into heat by interaction with matter and the thermal effect due
to laser irradiation will develop inside the material as deep as the absorption
coefficient allows, and that is the optical length: 𝛿(𝑚) = 1
𝛼 (𝑚−1) (2.2)
where α is the absorption coefficient and δ, the optical length.
For high enough energy, the heating will lead to phase change of the material
from solid to liquid, gas and plasma, resulting in ablation. The incident laser beam of
radius r (m), pulse width τ(s), and energy E(J) will develop during one pulse the power
𝑃0(𝑊) = 𝐸(𝐽)
𝜏(𝑠) (2.3)
and fluence
𝐹 (𝐽
𝑚2) = 𝐸(𝐽)
𝐴(𝑚2) (2.4)
where 𝐴 =1
2∙ 𝜋 ∙ 𝑟2 (2.5)
is the standardized area as per ISO 21254-2:2011 and ISO 21254-3:2011.
Thus, the heating source is a function of space coordinates and time,
𝑄 = 𝑄(𝑥, 𝑦, 𝑧, 𝑡) (2.6)
with the following component analytic functions:
a. The density of power on the target surface or incident laser beam
intensity,
𝐼0 (𝑊
𝑚2) = 𝑃0(𝑊)
𝐴 (𝑚2) (2.7)
in terms of physical phenomena represents the power for ablation
ignition, introduced in the Parameters section from Global Definitions
[Cocean et al, U.P.B. Sci. Bull, 2017];
b. Gaussian distribution in space,
26
𝑔1(𝑥, 𝑦) = 𝑒−
(𝒙−𝒙𝟎)
𝟐∙𝒓𝟐
𝟐
−(𝒚−𝒚𝟎)
𝟐∙𝒓𝟐
𝟐
(2.8)
for circular laser spot with r the spot radius at FWHM (full width at half
maximum) and
𝑔1(𝑥, 𝑦) = 𝑒−
(𝒙−𝒙𝟎)
𝟐∙𝝈𝒙𝟐
𝟐
−(𝒚−𝒚𝟎)
𝟐
𝟐∙𝝈𝒚𝟐
(2.9)
for elliptical laser spot with σx and σy as laser standard deviation,
introduced as function an1 in Global Definitions/Functions/Analytic
[Cocean et al, U.P.B. Sci. Bull, 2017; G. Poulain et al, COMSOL
Conference 2010 Paris]; c. Gaussian distribution in time
𝑔2(𝑡) = 𝑒−𝟑.𝟓∙(𝒕−𝝉
𝝉)
𝟐
(2.10)
introduced as analytic function an2 in Global
Definitions/Functions/Analytic [Cocean et al, U.P.B. Sci. Bull, 2017],
with τ as pulse width;
d. Relative intensity of the laser beam through the material, along z-
coordinate, based on Beer – Lambert law, where the attenuation of
relative intensity is an expression of absorption coefficient and z-
coordinate, representing an exponential decay:
𝐼(𝑧) = 𝑒−𝛼(𝑇)∙|𝑧| (2.11)
introduced in Component/ Definitions/ Variables [Cocean et al, U.P.B.
Sci. Bull, 2017].
Because Heat Transfer in Solids module does not have the formula for laser
heating, the formula consists of the heat source per unit volume dependent on absorbed
laser power (Q). In the software it was introduced as a variable in Component/
Definitions/ Variables section [Cocean et al, U.P.B. Sci. Bull, 2017]:
𝑄(𝑥, 𝑦, 𝑧, 𝑡) = 𝐼0 ∙ (1 − 𝑅(𝑇)) ∙ 𝛼(𝑇) · 𝑎𝑛1 · 𝑎𝑛2 · 𝐼𝑧 (2.12)
where R(T) is the reflectivity coefficient and α(T) is the absorption coefficient of the
material used as target (the material in interaction with the laser beam). I0, Iz, an1 and
an2 are incident laser beam intensity, exponential decay of laser beam due to
absorption and analytic functions for Gaussian distribution of laser beam in space and
time as described before.
The reflectivity coefficient depends on wavelength (λ), refractive index (n)
and extinction coefficient (k) and it’s given by the formula:
𝑅(𝑇) =(𝑛(𝑇)−1)2+𝑘2(𝑇)
(𝑛(𝑇)+1)2+𝑘2(𝑇)
(2.13)
As for the absorption coefficient, it has the formula:
𝛼(𝑇) =4𝜋𝑘2(𝑇)
𝜆 (2.14)
27
Reflectivity and absorption coefficients need to be introduced and defined
with the equations (2.13) and (2.14) in the Parameters section from Global Definitions
[Cocean et al, U.P.B. Sci. Bull., 2017].
Thus, the equation (2.12) accumulates all the mathematics in connection with
laser interaction with the matter, resulted in heat due to laser beam absorption.
Transcription of equation (2.12), with all its components detailed as per equations
(2.3), (2.5), (2.7), (2.8) or (2.9), together with (2.10), (2.11), (2.13), (2.14), will result
into equations (2.15) for circular laser spot and (2.16) for elliptical laser spot, as it
follows:
𝑄(𝑥, 𝑦, 𝑧, 𝑡) = 2
𝜋∙
𝐸
𝑟2𝜏∙ (1 −
(𝑛(𝑇)−1)2+𝑘2(𝑇)
(𝑛(𝑇)+1)2+𝑘2(𝑇)) ∙
4𝜋𝑘2(𝑇)
𝜆∙ 𝑒
−(𝒙−𝒙𝟎)
𝟐∙𝒓𝟐
𝟐
−(𝒚−𝒚𝟎)
𝟐∙𝒓𝟐
𝟐
∙
𝑒−𝟑.𝟓∙(𝒕−𝝉
𝝉)
𝟐
∙ 𝑒−4𝜋𝑘2(𝑇)
𝜆∙|𝑧|
(2.15)
𝑄(𝑥, 𝑦, 𝑧, 𝑡) = 2
𝜋∙
𝐸
𝑟2𝜏∙ (1 −
(𝑛(𝑇)−1)2+𝑘2(𝑇)
(𝑛(𝑇)+1)2+𝑘2(𝑇)) ∙
4𝜋𝑘2(𝑇)
𝜆∙ 𝑒
−(𝒙−𝒙𝟎)
𝟐∙𝝈𝒙𝟐
𝟐
−(𝒚−𝒚𝟎)
𝟐
𝟐∙𝝈𝒚𝟐
∙
𝑒−𝟑.𝟓∙(𝒕−𝝉
𝝉)
𝟐
∙ 𝑒−4𝜋𝑘2(𝑇)
𝜆∙|𝑧|
(2.16)
The formula (2.12) - same as (2.15), (2.16) - describes the heat generated by
direct effect of the laser irradiant energy that will be absorbed into the volume and
within nanoseconds the heat will be conducted by diffusion into the material as per the
heat-transfer equation (1), process that depends on the constants of material.
COMSOL materials library provides temperature dependent polynomial functions for
the material parameters up to a maximum temperature (e.g. 1235 K for Silver, material
that was used for the work presented in the herein thesis). However, pulsed laser
sources induce heating that develop very high temperatures (up to 104 K and more),
and for calculating the parameters for temperatures exceeding the maximum for which
the soft provides the characteristic functions, an extrapolation is used based on the
nearest function, selected in COMSOL. The latent heat was not used in this model,
but phase change is taken into account based on the temperature dependent variation
of material parameters, including plasma phase.
Ablation results in COMSOL simulation
Temperatures obtained in simulation are according to reality. The silver
vaporization point is 2435 K, the temperatures obtained in simulation was around 104
K. This shows the formation of plasma which is according to literature for laser
irradiation and temperatures [Gurlui et al, 2006].The simulation shows that there is a
vaporization in thickness as much as 10μm as per experimental data too [Stafe et al,
Rom. Rep. Phys., 2008].
To have a representation of the time - dependent graph, solutions need to be
calculated in each time. The number of data would have been too large for each
specific time so only 25 were used to store solutions. Consequently, the time step =
28
τ/25, where τ is the pulse width was chosen mathematically. This provides 50 solutions
for two times pulse width (2τ) which is the end time for simulation. The solutions are
represented graphically below in Figure 2.6 a - c and they have a Gaussian shape for
the Temperature profile in time. As the ablation consists of the liquid, gas and plasma
phases, the plots in Figure 2.6 a-c are phase diagrams showing the evolution of phases
in time based on the melting point and boiling point which are 1234 K and 2435 K,
respectively for Silver as material used in this case.
Average temperature calculation is based on the formula:
𝑇𝐴𝑉 =1
2𝜏∫ 𝑇(𝑡)𝑑𝑡
2𝜏
0 (2.21)
where τ is the pulse width, T is the temperature in Kelvin and t is the time. The integral
represents the area under the Gaussian curve and the results are listed in Table 2.1 for
each of the laser energies. [Cocean, et al, U.P.B. Sci. Bull., 2017]
II.2.2. Film Deposition model setup in COMSOL
In order to simulate the deposition, Free Molecular Flow module in
COMSOL was used. The high temperatures achieved during ablation are enough to
vaporize silver and make the deposition possible. The energies used of 50 mJ, 100 mJ,
150 mJ are sufficient to have those temperatures, as evidenced in the simulation of
target heating under laser irradiation. Following the ablation, deposition takes place.
The ablated plume cools down after the initial expansion and formation of plasma into
vapors that deposit on the substrate by cooling down even further into solids [Pop et
al, 2001; Gurlui et al, 2006; Gurlui et al, 2008]. The simulation is a stochastic model
which is the best assumption for this case because the target is a monoatomic material
with the same molar mass for the ions, clusters, atoms generated during ablation.
The geometry consists of a cylinder with 26 mm diameter and 15 mm height,
as distance between target and support. The materials virtually added to the geometry
were silver for target (upper surface) and silica glass for the support that is placed on
the bottom of the cylinder from the setup geometry with the same diameter of 26 mm.
The mesh was selected extremely fine for the deposition surface and course for the
rest (Figure 2.4)
29
Figure 2.4. Geometry and mesh for the model used in film deposition simulation
The deposition temperature taken into account is the average of the one
obtained by simulating the ablation (Table 2.1) and the support temperature is room
temperature (293.15 K). The important parameters used in module (model/simulation)
are the molar mass of silver, 0.108 kg/mol and the silver density, 10490 kg/m3
[Cocean, et al, U.P.B. Sci. Bull., 2017]
The formula describing the deposition is
𝑑ℎ𝑓𝑖𝑙𝑚
𝑑𝑡=
𝑀𝑛𝐺
𝑁𝐴𝜌𝑓𝑖𝑙𝑚
(2.22)
where hfilm is the film thickness, Mn molecular weight, G incident molecular flux, NA
Avogadro number, ρfilm silver density. The formula describes that the incoming flux
at the surface G [1/m2·s] is the number of molecules dN that intersect (cross) a unit of
surface in one direction during a unit of time [Dmitry Garanin, 2012, Gerd M.
Rosenblatt, 1976]. When integrating equation (2.22), a time linear dependence is
noticed for the thickness of the layer. The reservoir of particles is determined in this
case by the spot on the target where the laser brings the temperature up to silver
vaporization and ablation. The chamber pressure is considered 100 kPa [Rühlet al,
COMSOL Conference 2012 Milan] because of the silver vapors and because the
deposition took place in vacuum. Incident molecular flux, number density and pressure
are calculated by the module Free Molecular Flow where the formulae are
implemented.
Film Deposition Results in COMSOL
The simulation is similar to experimental values ones and is listed in Table 2.1.
30
Table 2.1. Physical properties of PLD thin films obtained at different laser energies
Energy (mJ) Average Temperature (K) Thickness of the
deposited film (nm)
50 mJ 8102 K 2.17 nm
100 mJ 1.5·104 K 1.60 nm
150 mJ 2.364·104 K 1.27 nm
The thickness of the film varies with the laser energy. The deposited film
becomes thinner with increase of energy, in accordance with literature [Beltramo et al,
2009)]. The 3D plot in Figure 2.5 represents the deposited layer. The layer shows non-
uniformities. The film deposition starts after 18000 pulses as reported in literature
[Bechtel, 975], and as can all be seen in the plot [Cocean et al, U.P.B. Sci. Bull., 2017].
Figure 2.5. Film deposition process and thickness
Figure 2.6 a, b, c represent the plots where the film thickness deposition in time is
studied for the different energies used for the laser heating simulation. A linear shape
of the deposition growth with time, as per equation (2.22) is obtained.
31
(a)
(b)
(c) Figure 2.6. The variation in time of film thickness in (x, y, z) = ( -0.5 mm, -0.05 mm, 0
mm) for different laser energies: (a) E= 50 mJ; (b) E = 100 mJ; (c) E = 150 mJ
32
II.3. Non-homogeneous target influencing physico - chemical thin layer
map dispersion, morphology and fluorescence properties
Study of non-homogeneous targets in the Pulsed Laser Deposition (PLD)
method for producing thin layers is of practical importance because in the everyday
work and industrial applications, materials of high purity are not only expensive, but
also difficult to acquire.
The disk shaped target of 20 mm diameter and 2 mm thickness (Figure 2.10)
was produced starting from silver jewelry by classical heating and mechanic
procedures and chemical thermal purifying in the presence of sodium tetra - borate
(Na2Bo4O7·10H2O) or sodium borohydride (NaBH4).
Figure 2.10. Silver target: (a) before irradiation; (b) after 9 PLD processes; (c) after
many PLD processes and exposure in the atmospheric air
Other chemical reactions of silver, such as combination with halides –
especially with fluor (AgF2), oxidation with potassium dichromate K₂Cr₂O₇ when
silver oxides result, the reaction of nitric acid when silver nitrate is formed (AgNO3),
are of low probability to occur in conditions of normal atmosphere. Yet, slow ion -
release oxidation of silver (Ag+) takes place in time. It is why silver is used as
antibacterial and antifungal in disinfection and preserving.
EDX analyze using Bruker AXS Microanalysis GmbH system shows a non -
homogenuoeous initial composition of the target in atomic percentage of 81.84 %
Silver, 17.40% Nickel, 0.76% iron on some area, 88.26 % Silver, 10.32 % Nickel, 0.44
on other area and even 100% Silver on some areas. EDX evidenced an important
change after ablation on irradiated zone when elemental composition in atomic
percentage became 64.56% Silver, 27.01% Nickel, 8.43% Iron on some region or
77.20 % Silver, 17.56 % Nickel, 5.20 % Iron on other analyzed region of the target.
The increase of Ni and Fe atoms on irradiated area of the target after ablation is the
result of different processes and phenomena during ablation such as re-deposition of
33
the lighter elements (atomic mass, A, and atomic number, Z, of each component being
𝑁𝑖2858.69 where ANi = 58.69, 𝐹𝑒26
55.845 where AFe= 26 and 𝐴𝑔47108 where AAg = 108) that
may be due to their elastic collision with heavier atoms, ions and clusters, but also to
other perturbing phenomena including but not limited to electromagnetic field
influence on the charged particles (ions). The re-deposition on the target is also
evidenced in the SEM image in Figure 2.11.
Figure 2.11. Ablated zone of the target with re-deposition structures
II.3.1. Pulsed Laser Deposition from Silver target with Iron and Nickel impurities
For pulsed laser deposition (PLD) a laser system YG 981E/IR-10 was used
and the parameters of 532 nm wavelength (λ), 10 ns pulse width (τ) with pulse
repetition of 10 Hz (ν), 168 μm as average standard deviation (σx, σy) and incident
angle 450 (α). The pressure in the vacuum chamber was 3·10-2 Torr. A number of
experiments have been conducted at different energies and distances target – support
to observe the quality and topography of the films received and how these parameters
influence those. The films in discussion herein have been deposited on glass slab at
energies (E) of 100 mJ, 150 mJ and 180 mJ, respectively and distances of 2 cm, 3 cm
and 6 cm respectively. For gathering information on the topography of the layer,
analysis in SEM (Scanning Electronic Microscopy) and AFM (Atomic Force
Microscopy) have been performed. Three samples are in discussion regarding the
influence of energy on the silver film pulsed laser deposited. The first sample, A,
obtained by PLD using 180 mJ energy with target – support distance of 2 cm shows,
in SEM images (Figures 2.12 a - d), ring – shaped droplets on the surface of a
continuous layer. The size of the droplets varies from 0.50 μm or less to 2.95 μm.
34
Figure 2.12. SEM images with the ring – shaped droplets formation at 180 mJ
laser energy during PLD (sample A) at different magnitudes: 500 x (a); 5kx (b);
10kx (c); and 3 D 10kx (d)
In Figure 2.13a - d, AFM images evidence the layer roughness, including
craters that are associated to the ring – shaped droplets formed on the film surface.
Figure 2.13. AFM image of the layer deposited with 180 mJ laser energy (sample A
35
Actually, the literature reports that in experimental applications, it was
noticed that the deposition takes place at the beginning as discontinuous layer, and
only after more than 15000 pulses the continuous layer is achieved, noticing an
enhancement of nano-particles in diameter with the number of pulses [Bechtel, 1975]
also confirmed in numerical simulation in COMSOL where the required number of
pulses for a continuous layer was found to be as 18000 [Cocean et al, U.P.B. Sci. Bull.,
Series A, 2017].
The composition of the droplets that consists preponderantly of silver will be
explained further down. X-Ray diffraction analysis on the silver layer evidenced the
crystalline specific sharp peaks and Miller indices as (111), (200), (220) and (311), as
in literature [Jyoti et al, 2016; Bagherzade1 et al, 2017, Karthik et al, 2013, Hajakbari
et al, 2016 ], showing polycrystalline structure of the layer. The next sample, B, is a
silver layer obtained at a lower energy, 100 mJ and the substrate was placed at 3 cm
distance from the target.
Though the laser energy was not reduced to minimum for the experiment B, a change
in layer topography is expected in the direction of obtaining a smoother layer. An
improvement of the topography is noticed with SEM images (Figure 2.15). Less
droplets are formed when we compare SEM image for 500 x magnifying from Figure
2.12a with that from Figures 2.16, 2.17. This time, sample B, the droplets are pearl –
shaped with sizes between 0.52 μm and 2.72 μm comparable with those from sample
A. Another deposition, namely C, used 150 mJ energy and 6 cm distance target –
substrate. Ring – shaped droplets formation for this intermediate energy between the
energy used for sample A and the one used for B shows that the shape of the droplets
is influenced by the energy. The mitigation in number of droplets on the surface of
sample C may be in this case due to the increased distance between target and
substrate. The surface of the layer C is shown in the SEM images from Figure 2.16
Figure 2.15. SEM images with the pearl – shaped droplets formation at 100
mJ laser energy during PLD (sample B) at different magnitudes: 500 x (a); 5kx (b);
10kx (c)
36
Figure 2.16. SEM images with the ring – shaped droplets formation at 150 mJ
laser energy during PLD (sample C) at different magnitudes: 200x (a); 500x (b);
1kx (c). The image is after the layer was irradiated for damage threshold
evaluation. On a side of the damaged area, ring-shaped droplets can be observed.
SEM images are for the sample C after it was laser irradiated for another experiment
where damage threshold was studied and that it will be presented in section III.2
Damage threshold behavior of silver target unpurified with iron and nickel.
Droplets that form on the film surface during PLD have been associated with
high laser fluences [Alonso et al, 2008], as also was noticed during the experiments
presented herein. Low fluences have been reported to favor smooth layers [Kuznetsov
et al, 2013]. The aim of the study presented herein is to formulate the mechanism and
processes during pulsed laser deposition of silver films that are responsible to produce
droplets.
J. H. Bechtel [Bechtel, 1975] reported that the silver layer deposited by PLD
method is discontinuous at the beginning and only after a number of pulses it becomes
a continuous layer. They notice that deposition is in fact generation of particulates or
nano-particles that accumulate on the substrate until they form the film. They also
noticed that the particulates grow in size with the laser fluence. During the experiments
conducted for the work presented herein, the same phenomenon was observed. The
ablated material behaves during deposition like it was sprayed and that leads to the
idea that Plateau – Rayleigh instability is applicable when, under a perturbation, the
fluid (plasma plume in this case, but also liquid state of ablated material) tends to
minimize its surface area due to surface tensions and to break –up into smaller,
spherical droplets.
This phenomenon explains the pearl – shaped droplets evidenced for sample
B. The ring – shaped droplets observed on the surface of sample A are the results of
another phenomena, namely crown – splash [Zhang et al, 2010] that describes two
phenomena: the break-up of the stream of fluid (plasma plume) in the atmosphere and
a second break –up, of the spherical droplets into small rings or crowns at the impact
37
with the substrate, in a splash. The evidence of these two phenomena consists of
comparable sizes of the droplets from the surface of sample A (as rings) with the sizes
of the droplets from surface of sample B (as pearls). Also, for sample B, both shapes
of the droplets are evidenced – pearls and rings – that may be explained as result of
the intermediate energy (150 mJ which is between the energy of 180 mJ for producing
sample A and energy of 100 mJ used for producing sample B), but also to the higher
distance target – substrate (6 cm) that leads to attenuation of the splash effect.
Getting back to the Plateau – Rayleigh instability that is evidenced in the
droplets formation, the analysis of the phenomena should start from the phases that
co-exist in the ablated material, namely “plasma plume”. Pulse laser ablation is a
photothermal process where the incident laser beam heats the target surface following
a Gaussian function and then the heat is transferred on the surface and in volume based
on thermal diffusion [Cocean et al, U.P.B. Sci. Bull., Series A, 2017]. That means that
different temperatures are achieved during laser irradiation on the surface of the target,
temperatures that correspond to melting, evaporation and plasma formation. The liquid
phase is susceptible to Plateau – Rayleigh instability when a perturbation takes place
in the system [Seifi et al, 2017, Xuan et al, 2017, Vajdi Hokmabad et al, 2014]. Plateau
– Rayleigh instability could also occur on the gas phase more than during its travel
from target to the substrate partial or total condensation takes place and the same phase
transformation happens with plasma phase. However, the phase conditions for Plateau
– Rayleigh instability are fulfilled mostly in the target vicinity and substrate vicinity
where there is a significant quantity of liquid phase, resulting into redesposition on the
target in the form of droplets, on the one hand and droplets formation during deposition
on the target.
Regarding perturbing phenomena, that may be sourced in the electrical field
associated to the diffusion current caused by the charged carriers from the plasma of
ablation that moves towards the substrate. The diffusion current propagates through
the plasma media and arrives in the neighborhood of the substrate where is responsible
for the perturbation induced in the liquid phase resulted from plasma and gas phases
cooling, inducing Plateau - Rayleigh instability.
II.3.2 COMSOL compiling for phase change during ablation of material
from the target
For the simulation in COMSOL a geometry consisting of 3D squares was
chosen to construct the interaction between different component elements of the target
(Figure 21).
38
Figure 2.21. Geometry and materials to simulate the elements found in the target
used in experiment
Mathematics and boundary conditions and mesh are as described in section
II.2.1 Target Heating under Pulsed Laser Irradiation, using the formulae (2.1), (2.16)
to model the heating due to laser irradiation, (2.19) for thermal insulation for the
exterior sides of the slab, less the top that receives the radiation and (2.20) for the top
of the slab but also the inside edges of each component modeling the heat flux. The
materials are selected from Materials Library and they are silver, nickel and iron
disposed like a layer on a slab entirely made of silver in an approximation of the non-
homogeneous composition of the target where silver is the main material and nickel
and iron are the impurities as evidenced in EDX analysis of the target. The thermal
effect is studied at different energies and for that purpose, a parametric sweep of 50
mJ, 100 mJ and 150 mJ is used. Plots based on 3D Cut Lines across diagonal D1 and
diagonal D2 (Figure 2.21) have been generated as phase change diagrams T(d) (Figure
2.22 a, b, c, d). Conditions of ablation are meat on an average distance of 1.23 mm –
1.55 mm, depending on the components in the ablated area
Figures 2.22 a, b, c, d and Figure 2.23 reflect the influence of non-
homogeneous composition of the irradiated material over the diffusion of the thermal
effect generated by its interaction with the laser beam when beside optical properties
of each component, i.e. absorbance and reflectivity, other effects and processes take
place, such as thermal equilibrium at contact regions of the components where heat
exchange occurs with thermal diffusion effects. [Cocean et al., 2017].
39
Figure 2.22 Phase diagrams (temperature profile indicating various phase change
starting in the spot center): Silver on target surface (a); Silver ablated phases -
liquid, gas and plasma represented as patterned surfaces (b); Iron and Nickel
impurities on target surface (c); Iron and Nickel impurities ablated phases -
liquid, gas and plasma represented as patterned surfaces.
Figure 2.23. 2D Plots of target surface in the region where phase change and ablation
conditions are met: (a) during irradiation interaction with the material (τ = 10 ns) and
(b) after τ = 20 ns.
40
II.3.3. Chemical interaction of ablated material on the deposition
substrate
The same target of silver with impurities of iron and silver was used in a
pulsed laser deposition on hemp fabric support - sample D, as well as on the same
quality of hemp fabric but previously soaked in saturated aqueous solution of citric
acid – sample E, and on a glass slab that was previously covered with supersaturated
aqueous solution of citric acid – sample F. Laser parameters were set to 87 mJ on a
spot of 336 μm, 10 ns pulse width, 10 Hz repetition rate, 532 nm wavelength, 45o
incident angle. The pressure in the deposition chamber was 3.5·10-2 Torr pressure and
the deposition time was 30 minutes (18·104 pulses). SEM images (500 x magnifying)
of the three samples of Silver film deposition are presented in Figure 2.23.
Figure 2.23. SEM images 500 x of the samples (a) Sample D (silver deposited on
hemp fabric), (b) Sample E (Silver deposited on hemp fabric previously soaked in
saturated aqueous solution of citric acid), (c) Sample F (Silver deposited on the glass
slab previously covered with supersaturated aqueous solution of citric acid).
The pictures in Figure 2.23 show the droplets of silver resulted during the
laser deposition as also presented in section II.3.1. Pulsed Laser Deposition from
Silver target with Iron and Nickel impurities.
The copper from the samples D and E elemental composition, same as carbon
are due to the hemp fabric.
However, the aim of these depositions with the related procedures is to study
if interaction of citric acid with the ablated silver in its final plasma stage before hitting
the support and under the conditions of vacuum chamber could lead to a chemical
reaction resulting in citrate formation. It is known that silver does not react with citric
acid unless one of the reactants is in ionic state (inorganic compounds of silver –
AgNO3 for instance – would enter into reaction with citric acid or sodium citrate would
enter in reaction with silver). Also silver does not react with cellulose in its metallic
41
state. In order to react with cellulose, “silver seeds”, i.e. silver nitrate (AgNO3), and
reagents are required [Zeng et al, 2011]. Other methods utilized for producing silver
nanoparticles synthesis in ionic state for medical purposes are based on so called
“green synthesis” that is based on different biological organisms or extracts of those
in a photochemical or chemical process [Bera et al, 2013; Butch et al, 2013; Homan et
al, 2012; Zhang et al, 2014]. The aim of the research on producing compounds where
silver is in ionic state is for its proven benefits regarding its antibacterial and antifungal
properties. Researchers are also concerned about studies on possible application of
gold nanoparticles in cancer treatment where gold nanoparticles in ionic state are
supposedly the active form against cancer cells. In this respect, synthesis of gold
nanoparticles has been produced as gold citrate but also gold ionic bonded to polymers
like polyethylene imine [Mohan et al, 2013]. Starting from the fact that PLD technique
is based on laser ablation where different phases co-exist including plasma phase and
because plasma is a state of matter where ions, electrons, atoms and clusters exist at
the same time, named also as ionized gas, it means that silver ions should arrive on the
target surface and react with the citric acid. Therefore, in order to determine if the
reaction took place, powder of the deposited layers was collected by scraping it off the
surface of the samples and FTIR results are presented in Figure 2.24.
4000 3500 3000 2500 2000 1500 1000 500
0
50
100
150
200
250
300
350
Tra
nsm
itance (
%)
(cm-1)
AgFilm/Hemp (D)
AgFilm/CA/Hemp (E)
Sodium Citrate
AgFilm/CA/glass (F)
Citric Acid (CA)
Figure 2.24. Compared FTIR spectra of samples D (AgFilm/Hemp), E
(AgFilm/Hemp AcC), F(AgFilm/glass) and the sodium citrate and citric acid
The FTIR spectra (Figure 2.24) show the change of citric acid after silver thin
film deposition when silver citrate formation is noticed. For both types of hydroxyl
groups associated to carboxyl from citric acid (free 3500 cm-1 and H- bounded 3283
cm-1) it is evidenced that they are transformed into ionized groups COO- involved into
42
ionic bonds with Ag+, indicated by the carbonyl bands from 1638 cm-1 and 1760 cm-1.
The bands from about 3500 cm-1 are the alcoholic groups for citric acid spectrum (CA),
but also in the sample of PLD films spectra for citrate when the peak becomes broader
due to Hydrogen bonding. It results that the silver ions from plasma of ablation that
still exist when arriving on the substrate surface enter into reaction with the citric acid
on the surface and may form trisilver citrate but also mono- and disilver citrate.
However, the physico – chemical process is more complex than just citric
reaction with silver plasma ions. Intermolecular H-bonds between hydroxyl groups of
citrate are indicated in the broad spectra from 3500 cm-1 for sample E. Furthermore,
the partially ionized oxygen from the carbonyl groups will enter into hydrogen bonds
with hydroxyl goups from other molecules, but also intramolecular, as the peak from
1638 cm-1 could indicate. H-bonding could also form between citrate and cellulose.
The spectrum for sample E (hemp impregnated with citric acid before
deposition) evidences the citrate formation. As for the silver deposited directly on
citric acid (sample F), the spectrum indicates that some of the citric acid has reacted
with silver plasma ions, while some still exists as citric acid or only part of the
carboxylic groups have been transformed into carboxylates.
Due to the environmental conditions in the vacuum chamber, a further
ionized structure of the silver citrate could form and such structures may interact
through ionic and H-bonding and form aggregates and complex structures, the most
evident being for the citrate formed on the glass slab. The very broad band between
3560 and 2598 cm-1 indicates that both carboxyl and carboxylate groups coexist,
meaning that part of the citric acid transformed into citrate and part remained as citric
acid. The broad band also indicates H-bonds, intermolecular ionic bonds and other
intermolecular interactions, such as Van Der Waals interactions.
Also, Van Der Waals interactions between ionized and/or partially ionized
atoms will occur in both films (E – film on hemp treated with citric acid and F – film
deposited on citric acid). Adsorption of silver atoms on carbonyl groups is also part of
the complex interactions in the thin film system.
As noticed analyzing FTIR spectrum for silver deposited by PLD technique
on the citric acid, not all the citric acid was transformed into citrate and that is because
of the quantity of citric acid in excess compared to the quantity of silver ions formed
in plasma. Based on that, a method to measure the quantity of ions of metals that arrive
on the substrate, and further a PLD method of “titration” could be developed to analyze
different intermediary compounds formed during plasma travel on the path from the
target to the substrate.
II.3.4. Physico – chemical behavior of nonhomogeneous material under
UV laser beam Fluorescent dyes in textile industry is of practical interest and polyacrylonitril
copolymers with fluorescent dyes had been tested [Grabchev and Bojinov, 2000]
43
before the study presented with my co-authors [Popescu et al, 2019] when the
photostability of curcumin dye applied on acrylic fiber was tested. Two types of acrylic
material, Dralon L and Melana were used as support and curcumin extracted from
turmeric powder with water and alcohol was applied under microwave procedures
[Popescu et al, 2019].
The photostability was studied comparatively as response to UV radiation of
the initial substance - turmeric powder, curmeric extracted in aqueous solutions
without and with alcohol - alcohol increases the dissolution of turmeric and of the two
materials – Dralon L and Melana - dyed with turmeric.
The study was conducted with the installation presented in section II.1 Laser
ablation. Experimental set – up in Figures 2.1 – 2.2. The pulsed laser irradiation was
conducted in free atmosphere, and the laser beam parameters were 10 ns pulse width,
355 nm excitation wavelength 10 Hz repetition and 150 mJ energy. The emitting
wavelengths (500 – 700 nm) provide information as to the fluorophore from the
molecule of curcumin and its interaction with different solvents and other compounds
added to the solution of curcumin as well as treatments applied during the process.
[Popescu et al, 2019]. Other conditions referring to preparation of solution and dyeing
method influenced the fluorescence intensity as well. In this regard, it is noticed that
the intensity of the emission spectra proves to be influenced by the solvent used
(aqueous solution or in ethanol) for the solutions and the composition of the support
material for the fabrics dyed with curcumin. Also, the microwave exposure in time,
proves to enhance the fluorescence of the curcumin dye in the exhausted dyeing bath.
It is to understand that the increased excitation is more related to the curcumin
fluorophore and its exposure to the microwave cook than to the exposure to microwave
of the whole system resulted from interaction of polyacrilic fibers with the curcumin.
The study of fluorescence presented herein for the polyacrilic fibers covered
by curcumin with a dye-bath procedure under microwave exposure, offers information
about interaction mechanism between fiber and curcumin dyestuff, as being more a
“dissolution” into a nonpolar solvent (polyacrylic fibers) than an electrostatic
interaction between fiber and curcumin dyestuff due to the wide shift to blue of the
maximum peak of curcumin. [Popescu et al, 2019].
Laser induced fluorescence as spectroscopic method of analyze provides
information related not only to the fluorophore structure in the analyzed sample, but
also about other phenomena such as photochromism, interactions between the
constituents of the material and also chemical reactions and radical formation [Cocean
et al, May 2019]. Taking into account the high fluence of the laser beam (37 J/cm2),
thermal effect should be taken into consideration, and the shift to blue of the maximum
peak may also be a different heating effect influenced by the acrylic support and its
thermal conductivity and thermochromism could be considered as well. Also, the
optical properties change with the thickness of the irradiated material.
44
III. Modelling of LIBS in free atmosphere and non-homogeneous
materials
If producing thin films and nanoparticles, as well as for spectroscopic
purposes for fundamental research of laser irradiation interaction with the matter,
requires controlled atmosphere as it was the case for the experiments and numerical
simulations described in section II, other applications and spectroscopic measurements
need to be conducted in free atmosphere. LIBS is a method with technical application
in industry, including operations used to determine the composition of natural deposits
during the aging process of some architectural and art objects, as well as their cleaning
by removing the material deposited as a crust on their surface. The study of the
removal of crust deposited on rocks, architectural and civil constructions, as well as
on statues, was accomplished by the numerical simulation method in the COMSOL
software, from the point of view of the physical interaction of the laser beam with the
material of the crust, to which was added the interpretation of the chemical processes
placed in the given temperature and humidity conditions.
III. 1. Pulsed Laser Inducing Thermal Effects in limestone covered by an
impurity layer
` Analysis on the rock was performed using LIBS – Laser-Induced Breakdown
Spectroscopy – with an Acton 2750i high resolution spectrometer (750 mm focal
length) coupled with the Roper Scientific PIMAX3 ICCD camera 1024x1024 pixels
with a minimum gate time of 2 ns was fitted with one mirror and two diffraction
gratings (600 l/mm, blaze at 300 nm, and 2400 l/mm, blaze at 240 nm) mounted on
the same three-position turret, which allowed an easy switching between imaging,
low-resolution and high-resolution spectroscopy experiments.
The rocks used for analysis were oolitic calcareous limestone (Repedea
Limestone). These rocks are indigenous to Iasi area. They were collected from “Podul
de Piatră” (Stone Bridge) intersection, after aging naturaly. The aerosol particles
investigated are the black crust formed by gravimetric deposition. The study was
conducted on the crust as well as inside the rock keeping the same experimental
conditions. Laser used in this study was a Nd:Yag laser (Quantel Brilliant Eazy) with
532 nm wavelength and 10 ns pulse at 50 mJ energy, spot diamete2r 1.4 mm, fluence
3.2 J/cm. Data in Figure 3.2 shows an overview of 200 to 350 mm spectral range where
the difference between crust and limestone was noticed. The graph indicates the
presence of Saharan dust – represented by Si in elemental composition - and also
metallic compounds such as iron and magnesium that are part of urban industrial
aerosols. To determine the surface geometry and an elemental composition a
SEM/EDX (Scanning Electron Microscopy coupled with Energy Dispersive X-ray
Spectroscopy, Vega II LSH – Tescan, coupled Quantax QX2 – Bruker – Roentec) was
used.
45
For the simulation a geometry (Figure 3.3) consisting of a square slab with a
thin layer on was made as for the materials chosen: limestone for the slab and iron (Fe
I) and magnesium (Mg I) for the thin layer. Iron and magnesium are the elements found
in the elemental composition that heat the most under laser irradiation therefore they
have been chosen.
Figure 3.1. Aerosol particle size distribution using
IASI LOASL – AERONET data
210 225 240 255 270 285 300 315 330 345
outside
inside
Inte
ns
ity
[a
.u.]
Fe I
I 317.9
5 n
m
Fe I
I 315.9
1 n
m
Na I
I 309.2
nm
Fe I
I 308.3
0 n
m
Fe I
300.8
1 n
mF
e I
300.0
4 n
m
Si
I 288.1
5 n
m
Fe
II 2
80
.34
nm
Fe I
I 279.6
6 n
mO
V 2
78.1
0 n
m
Fe I
I 263.1
3 n
mF
e I
I 259.8
3 n
m
Fe I
252.4
2 n
mS
i I
252.8
5 n
m
Fe I
I 251.7
1 n
mF
e I
I 250.7
5 n
m
Fe I
I 243.3
9 n
m
Fe I
I 238.2
0 n
m
Fe I
I 234.3
5 n
m
Fe I
I 227.6
0 n
m
Fe I
I 221.1
1 n
m
Fe I
I 212.3
8 n
m
Fe I
I 211.4
nm
Mg
I 2
85
.2 n
m
Fe I
I 210.4
5 n
m
wavelength [nm]
Figure 3.2. The spectral composition of the aged using LIBS technic.
46
The top thin layer was split in two in order to simulate both elements.
Limestone was not considered for staying on top because it does not interact with laser
irradiation. The heat transferred through diffusion can affect the limestone and degrade
it; thus this simulation is necessary for choosing the right energy for the laser.
Figure 3.3. 3 D geometry with materials disposal in the layer and x, y, z – axis
system [Cocean et al, Appl. Surf. Sci. (2017)]
Mathematics and simulation model are as per II.2.1 Target Heating under
Pulsed Laser Irradiation section. The module Heat Transfer in Solids is used, where
the governing equation is the heat - transfer equation (2.1) and heat source is
mathematically modeled based on equations (2.15), (2.16). The difference between the
two models – the previous from II.2.1 Target Heating under Pulsed Laser Irradiation
section and the one from this section - consists in the model of the irradiated surface.
If the model in section II.2.1 Target Heating under Pulsed Laser Irradiation refers to
one component as irradiated surface, for the model in discussion herein, a non-
homogeneous surface is the target laser irradiated. Boundary conditions are set for heat
exchange between the two materials that form the layer and heat exchange between
each component of the layer and the limestone slab. The heat transfer from the hot
source to the cold source is simulated based on thermal diffusivity equation (3.1)
[Bechtel, (1975)].
𝐷 =𝑘(𝑇)
𝜌(𝑇)𝐶𝑝(𝑇) (3.1)
In equation 3.1, k(T), ρ(T), Cp(T) are thermal conductivity, material density and the
specific heat at constant pressure temperature dependent. As the soft provides
temperature dependent functions for materials constants only up to a certain level,
which is usually the melting or vaporization point, the nearest function selected in
47
COMSOL is used for extrapolation as also mentioned in II.2.1 Target Heating under
Pulsed Laser Irradiation section. Diffusivity coefficient (3.2), applied to equation
(2.1) will describe heat diffusion from laser irradiated areas to the rest of the surface
and in volume, taking into account the specific materials of each of the components
(layer with magnesium and iron and slab of limestone). 𝜕𝑇
𝜕𝑡= 𝐷∇2𝑇 (3.2)
COMSOL provides the constants and parameter for a large range of materials stored
in the Materials Library, and also allows introduction of new materials and their
constants and parameters.
The model consider an element of basic material, limestone as a slab of 50.8
mm diameter (D) and 2.54 mm thickness, covered by a layer (the crust of impurities)
of 10 nm thickness with the specific parameters for each of the materials. For the
irradiated side, nfe = 2.8954 as refractive index of Fe, nmg = 0.29776 as refractive index
of Mg, kfe = 2.9179 as the extinction coefficient of Fe, kmg = 4.8550 as the extinction
coefficient of Mg were introduced. An energy of 50 mJ (E) and 532 nm wavelength,
pulse width of 10 ns (τ), together with the pulse coordinates (x0, y0) = (0,0) and
standard deviation describing the circular spot of the laser beam (σx = σy) of
(1.3/2)[mm] are the laser parameters. The initial temperature was set as T0 =
293.15[K].
The results are presented in 1D plots. The plots represent the temperature
distribution along x-axis and along diagonal (at 45 degrees), on the surface and at 1
mm depth in limestone. The information given by the plots is that the conditions for
laser ablation are met or not and if the temperature is high enough for chemical
reactions to take place. The simulation also gives information about heat diffusion by
conduction after the laser pulse interaction with the matter. The 1D plots at the surface
of the layer along x-axis consisting of Mg and Fe shows that there are conditions for
ablation.
The temperatures for ablation in the simulation are on about 1.5 mm width in
for iron and on about 1 mm width for magnesium. The plasma usually forms in the
range of 104 K. The temperatures for Mg is about 2·104 K at the surface and 2104 K -
4.5104 K for Fe as predicted by the simulation in COMSOL and both temperatures
resulted in simulation are in accordance with expected temperature of 104 K order,
suggesting plasma formation. Literature based on experimental results gained with
Langmuir probe shows that the condition for plasma formation is met in similar pulsed
laser irradiation [Gurlui et al, 2006].
The plots that this software generates are equally important. They offer
information about temperature variation between different materials in contact, which
are very small in size, so they can be assimilated with non-homogeneous systems. The
interpretation of the plots is based on different laser heating and different thermal
diffusion of each material.
48
0.0 0.4 0.8 1.2 1.6 2.0 2.4
0
1x104
2x104
3x104
4x104
5x104
z = 0 mm
Mg (over x axis
Fe (over x axis)
Mg (profile at 45 degree)
Fe (profile at 45 degree)
Te
mp
era
ture
[K
]
Distance [mm]
Figure 3.4 Temperature variation along x-axis and along diagonal (45 degrees)
on Mg and on Fe (on layer surface) [Cocean et al, Appl. Surf. Sci. (2017)]
The picture above, Figure 3.4, represents the surface temperature variation
on x - axis and across the diagonal, at 450. The thermal equilibrium is reached in x=0
between Fe and Mg where the temperature is 2.5104 K. The two irradiated sides meet
in the middle where the two temperatures are at equilibrium from both sides Fe and
Mg border, along y axis, which is both the geometric and thermal border (Fig. 3.4). In
the x-axis representation the two meet in x=0. The temperature increases up to over
4.5104 K and mitigation takes place.
The maximum temperature of 4.5104 K on iron side corresponds to a
minimum of 3000 K for magnesium and those temperatures only correspond to the
laser heating effect on the two components of the layer, the iron absorbs more radiation
than magnesium which causes it to heat more. From the plot can be deduced that at
about 0.18 mm from spot center (the distance is within the spot standard deviation σx
= 1.3/2 mm) the thermal effect is due to laser heating and thermal equilibrium hasn’t
taken place. The thermal effects beyond 0.18 mm are because of laser heating and also
because of thermal conduction and of the tendency of thermal equilibrium in
limestone. Consequently, enhancement of temperature on magnesium and temperature
mitigation on iron, corresponding to the coordinate of 0.25 mm, is supposedly
reflecting the heat transfer through the limestone area from beneath iron to the
limestone area beneath magnesium and then to magnesium until thermal equilibrium
is reached.
A new thermal maximum for iron side is observed at about 0.5 mm
corresponding to a minimum for magnesium followed by temperature mitigation on
49
both sides until thermal equilibrium is established at 2 mm with both sides of the
remaining geometry reaching room temperature.
Based on the temperatures achived in the numerical simulation conducted for
the process of cleaning the crust by laser ablation, a number of chemical reactions can
be anticipated [Beral et al, 1977; Cocean et al, Appl. Surf. Sci. 2017].
The limestone – calcium carbonate – a powder of white color decomposes
resulting calcium oxide (lime), which is of trigonal crystal structure and white color.
The other reaction product is carbon dioxide, which is released in the gaseous phase.
Ca CO3 CaO + CO2 ↑ (773K – 873K)
Calcium oxide, lime, reacts with carbon resulting into calcium carbide, which
is a white powder of grey/black crystals, and carbon dioxide gas is released.
CaO + 5C 2CaC2 + CO2 ↑
Calcium oxide – lime – may also react with sulfur dioxide to make solid
calcium sulfite which in the presence of air turns into hydrated calcium sulfate,
CaSO4∙2H2O colorless, white, but may also be yellow, tan, blue or pink due to different
impurities.
CaO + SO2 CaSO3 CaSO4
Mineral pigments used in slaked lime (Ca(OH)2) or limestone for painting
reasons, are susceptible to reactions under laser irradiation effect or the reactions may
take place anaerobically with impurities. Such chemical processes refer to dehydration
of limonite (yellow ochre) with formation of hematite (red ochre) when water
vaporizes due to thermal effects. Another chemical transformation may take place for
the pigment of ferrous hydroxide (green) which decomposes into magnetite of black
or grey color – more stable – caused by the anaerobic corrosion, resulting also
hydrogen and water:
Fe2O3∙H2O Fe2O3 + H2O
3Fe(OH)2 Fe3O4 + H2 +2H2O
These possible reactions together with others – depending on the pigments or
impurities – may take place during laser cleaning process and will result into color
change, but also in physical structure of the construction material. The information
provided by the numerical simulation can be used for laser parameters selection,
environmental conditions of work (such as humidity, atmosphere composition, etc).
III. 2 Damage threshold behavior of silver target unpurified with iron
and nickel
Deposition by PLD method using the silver target unpurified with iron and
nickel with the composition as presented in Table 2.2, section II.3 Non-homogeneous
target influencing physico - chemical thin layer map dispersion, morphology and
fluorescence properties, it resulted in a thin film with the characteristics as per the
same section II.3 where it was named as “sample C”. After deposition, on the thin film
50
of sample C, laser irradiation was performed with τ =10 ns pulse width, λ=532nm
wavelength, α=45° incident angle, ν = 10 Hz pulse time repetition, D=336μm spot
diameter, and different energies E of 20 mJ, 25 mJ, 35 mJ, 40 mJ, 45 mJ, 60 mJ, 65
mJ, 80 mJ. The irradiation was conducted with a single shot in a straight line as can
be seen on the image below (Figure 3.5) to facilitate comparing the different damage
effects.
Figure 3.5. SEM images of the laser irradiated damaged
areas on the Silver layer surface
To determine the damaged spots where the irradiation took place, radius of
the spots was measured in SEM images using VegaTC software.
A simulation in COMSOL was conducted to compare with the damage thresholds
analyzed in SEM and find if that can be numerically predicted. The mathematics,
geometry, module Heat Transfer in Solids in COMSOL, boundary conditions and all
the specific set-up for the simulation used for damage threshold estimation are the
same as described in section II.2.1 Target Heating under Pulsed Laser Irradiation for
laser heating effects on a target. Geometry was set up consisting of a cylinder. Then
the mesh was built as Figure 3.6 – b shows.
51
Figure 3.6 Geometry (a) and mesh (b)
The parameters are same as used in the experiment, as it follows: spot radius
r = 168 μm, wavelength λ = 532 nm, repetition f = 10 Hz, pulse width τ = 10 ns, time
step to store solutions equal τ/25, end time 20 ns, refractive indexes for silver, iron and
nickel of 0.054007, 2.8954 and 1.8775 respectively
[http://refractiveindex.info/?shelf=main&book=CaCO3&page=Ghosh-o], extinction
coefficient k for silver, iron and nickel of 3.4290, 2.9179 and 3.4946 respectively
[http://refractiveindex.info/?shelf=main&book=CaCO3&page=Ghosh-o], slab
diameter D= 20 mm, slab thickness Lz = 2 mm, silver layer thickness of 240 nm and
initial temperature Ti= 293.15 Kelvin. In order to conduct the simulation for different
energies, energy parametric sweep in the range of 20 mJ, 25 mJ, 35 mJ, 40 mJ, 45 mJ,
60 mJ, 65 mJ, 80 mJ was added as for experimental conditions. The silver layer is
virtually deposited on a glass slab of 50.8 mm diameter and 20 mm thickness (Figures
3.6 a-b). In order to measure the computed damaged spot, the distance is measured as
corresponding to a temperature higher than melting point of Silver (1239 K). The
melting point is considered the starting temperature when the conditions for the
ablation are met.
52
25.2 25.3 25.4 25.5 25.6
1x103
2x103
3x103
4x103
5x103
Te
mp
era
ture
(K
)
Width (mm)
20 mJ
25 mJ
35 mJ
40 mJ
45 mJ
50 mJ
60 mJ
65 mJ
80 mJ
a)
25.2 25.3 25.4 25.5 25.6
300
310
320
330
340
350
360
370
380
390
Te
mp
era
ture
(K
)
Width (mm)
20 mJ
25 mJ
35 mJ
40 mJ
45 mJ
50 mJ
60 mJ
65 mJ
80 mJ
(b)
Figure 3.7 COMSOL results of layer heating under pulsed laser irradiation: (a)
phase change temperature conditions on laser irradiated surface at different laser
irradiation energies; (b) thermal effects on layer back side surface under laser
irradiation at different energies
The melting condition is not met on the back side of the layer and the damage does
not go through all the layer thickness.
Discussion of the compared experimental and numerical results
The experimental and simulated results fit very well as shown on the graph bellow
(Figure 3.8).
53
40 60 80 100 120 140 160 180 200
-40
0
40
80
120
160
200
240
280
Damage measured with SEM
Damage calculated in COMSOL
Density of energy (J/cm2)
Da
ma
ge
me
as
ure
d w
ith
SE
M (m
)
-40
0
40
80
120
160
200
240
280
Da
ma
ge
ca
lcu
late
d in
CO
MS
OL
(m
)
Figure 3.10. Damages magnitude (μm) versus laser irradiation density of energy
(mJ) compared experimental and simulated in COMSOL
Threshold starts right after 45.11 J/cm2 density of energy. Magnitude of
damages evolution with density of energy would be the fitting exponential line
described by the equation𝑦 = 𝑦0 + 𝐴 ∙ 𝑒𝑅0∙𝑥, where y0 = 305.41307, A = -396.31276,
R0 = -0.03514.
54
IV. Study of physicochemical processes of the environmental
atmosphere by spectroscopic and numerical methods
IV.1. Optical instruments and techniques
Figure 4.1 is a schematic diagram of the experimental installation that
contains the following components: optical excitation source (laser), Optical
Parametric Oscillator - HR-UV/V-OPO, beam expander, optical telescope, optical
polarizers, and high resolution spectral spectroscope coupled with ICCD camera with
intensifier and integration time of 2 ns. The system can detect a large range of chemical
compounds organic and inorganic and their distribution in space and time. The
information is important to understand the physical interactions and chemical reactions
during different episodes in the atmosphere. Investigation of the atmosphere with the
advanced LIDAR – DARLIOES is based on laser induced RAMAN and breakdown
spectroscopy. The system was developed in LOASL Laboratory. The laser used for
the investigation of the atmosphere was Quantel Brilliant EaZy Q-switched Nd:YAG
and the range of irradiating wavelength was 205 – 700 nm.
Figure 4.1. Schematic DARLIOES experimental set-up: the fast LIDAR resolved
spectroscopy
55
The installation and its components is presented in the pictures of Figure 4.2.
Figure 4.2. Subassemblies that make up the installation for atmospheric probing with
space-time solution DARLIOES (Detection and Ranging Laser Induced Optical
Emission Spectroscopy)
IV.2. Study of some critical physicochemical phenomena in the
terrestrial atmosphere
Various chemical reactions take place in the atmosphere, and the most
important studied during daylight involve ozone and radicals resulted under the
interaction with UV radiation. The humidity plays an important role in wet removal of
oxides and different other compounds soluble or miscible with water. The variation in
concentrations of gases and other compounds is linked with air currents, humidity,
electrical discharge and also chemical reactions. The evolution of concentration of
substances will be analyzed further, considering night time and consequently, absence
56
of the photolytic processes. Humidity, caused by fog and snow flacks will be taken in
consideration.
Figure 4.3 RAMAN spectra recorded with DARLIOES System for atmosphere
chemical composition [Cocean et al, 2018]
Trace gases and particles behavior and changes will be the main goal of
investigation. The concentration of different species is represented by the spectral
57
bands intensities. The data was collected on 27 January 2017, between 6:47 pm 18:47
and 20: 58 pm hours are presented in Figure 4.3. The system used was DARLIOES
that was described in the previous section, IV.1 Optical instruments and techniques.
The data was collected during intense snowfall and high humidity. The reason for this
is to studying atmosphere self-cleaning, because in conditions of humidity the oxides
and particles interact with water droplets and fall to the ground and the atmosphere
becomes cleaner. The atmosphere is a place where molecules interact in a complex
manner so this only complicates matters. The variation of the sources, air currents, and
electrical discharge has an important contribution to the chemical composition of the
atmosphere. The concentration of the pollutants was measured as spectral bands
intensities. Due to the presence of water in the atmosphere, this needs to be taken into
consideration. Figure 4.3a through 3h shows different concentration of different
compounds. The detected compounds are only those that reemit light in the range
measured and time frame. In the same range and time frame, those that reemit at the
same wavelength but at lower intensity are not detected. The wet removal is important
as a sink for gases and particles. Surfactants increase the number of removed
substances and quantity. Surfactants are substances that reduce the local tension, thus
allowing for substances to disperse in water easier due to their amphophilic structure
– having both hydrophilic and hydrophobic parts. Sulfonic acids, 𝑅 − 𝑆𝑂3−𝑁𝑎+ and
sodium sulfonates, 𝑅 − 𝑆𝑂3−𝑁𝑎+ were detected in the spectra. The surfactant will
increase the absorption and adsorption of chemicals. It will help to form emulsions in
water of fats and other hydrophilic compounds that are not ordinarily soluble in water.
Solubility in water also depends on electronegativity and capacities to bond with H.
Hydrogen bonding is what facilitates many gases being absorbed no liquids. The
presence of water in various phases can be a sink for many gases; the atmospheric
conditions must be taken into account (nighttime, winter season, mixt precipitation,
snowfall with dense fog). The measurements were made at 500 meters [Cocean et al,
2018]. Another consequence of humid atmosphere is the decrease of CO2 evidenced
as reduction in intensity in the spectra (Figure 4.3 a, b, c). The reaction is listed below:
𝐶𝑂2(𝑔) + 𝐻2𝑂(𝑙) → 𝐻22−𝐶𝑂3(𝑎𝑞)
2−
The carbon dioxide is transformed in carbonic acid, of course not all of it.
The carbonic acid dissolves in water and falls to the ground. The presence of carbon
monoxide was also found. That proofs a more complex mixture of oxides, carbon
monoxide forming because of the reactions taking place in the atmosphere. This cycle
takes place in the presence of light and involves free hydroxyl radicals, azote oxides
and aldehydes. This also explains various oxides found. Sulfur trioxide, SO3 becomes
sulfuric acid in the presence of water sulfuric acid. The reaction is listed below:
𝑆𝑂3(𝑔) + 𝐻2(𝑙) → 𝐻22+𝑆𝑂4
2−
The enthalpy of reaction is ΔHf = −200 kJ mol-1 which indicates a
spontaneous reaction. The sulfuric acid will reach the earth due to ionic bonding with
water from the atmosphere that will transport it. The spectra from Figure 4.3 show the
58
presence of other substances too. Among those, nitric oxides NO3 at 1050 cm-1, Figure
3c and NO2 at 1320 cm-1 in Figure 4.3b and Figure 4.3d, are specific for the night time,
in absence of photodisociation and only these two nitric oxides are usually present in
the atmosphere. In literature they are grouped as odd oxygen or Ox (nocturnal) that is
defined as being O3 (ozone), NO2, 2NO3, 3N2O5. The increase of NO2 concentration
from 18:47 hours (Figure 4.3b) to 19:02 hours (Figure 4.3 c) can be explained by NO3
reaction with peroxy radicals:
𝑁𝑂3 + 𝑅𝑂2 → 𝑁𝑂2 + 𝑅𝐻𝑂 + 𝐻𝑂2 [Brown et al, 2006; Ingold, 1969; Hakiki
et al, 2015]. Nitrogen dioxide, NO2, is also sourced in the car emissions (fuel burn).
Between 19:14 hours and 20:25 hours - as in Figure 4.2d and Figure 4.3b – the
reduction of NO2 occurs because of its association with NO3 and formation of N2O5
which, mixed with humidity, forms nitric acid HNO3. The decrease in concentration
leads to a diminished intensity observed in the spectral bands for NO2 which led to this
conclusion. The reactions associated to this process are listed below [Cocean et al,
2018]:
𝑁𝑂2 + 𝑁𝑂3 + 𝑀 → 𝑁2𝑂5 + 𝑀
𝑁2𝑂5 + 𝐻2𝑂 → 2𝐻𝑁𝑂3 [Brown et al, 2006; Ingold et al, 1969; Thompson
et al, 1982]
The 𝐻+𝑁𝑂3− ions are attached to the water droplets and that way the nitric
acid is cleaned from the atmosphere. Increase of nitrogen dioxide NO2 concentration
from 20:25 hours to 20:36 hours – Figure 4.3b and Figure 4.3d – is considered due to
traffic and it is observed a reduction in regeneration after 20:30 hours caused by the
drop in traffic [Brown et al, 2006]. Hydrogen cyanide is a very stable chemical
compound and cannot be easily chemically react with other species nor be dissociated
under normal physical interactions that may exist in the atmosphere. The breakdown
of HCN is about 2 years so decrease in intensity in the lines of the spectra cannot be
explained that way. Instead, the change in concentration can be explained through
water cleaning. HCN is miscible in water droplets as seen in the drop of intensity of
bands in Figure 2 d and Figure 4.3a. The time frame was 19:14 to 19:34. HCN can
react with Cl and OH [Li et al, 2000; Breton et al, 2013; Akagi et al, 2011; Li et al,
2009; Giménez-López et al, 2010; Thompson et al, 1982] but considering its long
lifetime, the decrease in concentration could not have been explained in another way
more than the detection was in nocturnal conditions. The further increase of the
intensity of the spectra from 20:22 hours to 20:36 hours are due to different sources
like burnt fuel, wood but also dye activities, transport and air currents. Another
compound called sulfonic acid could be the result of a chemical reaction. This reaction
is known as sulfonation, a reaction between alkyl benzenes and sulfur trioxide (SO3).
Sulfonation is less likely to take place in the atmosphere due to conditions and an
anthropogenic source is more likely. Industrial and urban activities lead to the
formation of salts from sulfonic aid with metals with sodium hydroxide. They will act
as surfactants, detergent like in the water droplets making possible the absorption of
59
substances that are not soluble in water including gases and particles [Y. Yuan et al,
2013; F. Hakiki et al, 2015; M. J. Rosen et al, 2012]. The reaction of etherification is
listed below.
𝑅 − 𝑆𝑂3𝐻 + 𝑁𝑎𝑂𝐻 → 𝑅 − 𝑆𝑂3𝑁𝑎 + 𝐻𝑂𝐻 The transformation of alcohols into ethers could explain the reduction of
intensity in the appropriate spectra bands of secondary alcohols. This is seen in Figure
3d in the time frame 19:14 to 20:36 hours. An increase in intensity of the two isomers
cis and trans of vinyl alkyl ethers has been noticed between 18:47 and 19:34 as can be
seen in Figure 4.3b and Figure 4.3a. The concentration of vinyl alkyl ethers remains
constant after 19:34. The reaction of alcohol etherification cannot be met in the
atmosphere especially at night so another source is more plausible.
The source in question could be house-hold sprays, especially dye ones and
industrial sprays. As a sink for them wet removal is to be considered due to their –OH
polar group. Also traces of industrial activity were detected especially those of
pharmaceutical industry. The N-H groups were detected in the spectra which lead
towards the amides as part of the main chain of proteins or drugs like paracetamol,
penicillin and others. The N-H groups show a decrease of intensity in the spectra from
19:14 hours to 20:36 hours, as shown in Figure 3d and considering the conditions of
fog and snow the phenomenon is probably due to wet removal. This happens because
of the property of amides to form –OH bonds, Table 4.1, with water which even if
amides have a small solubility it still can decrease in concentration due to falling to
the ground attached to water drops. Another functional group detected was carboxyl,
C=O, specific to amides, aldehydes, ketones and carboxylic acid. The decrease
detected (presumably because H bonds shown in Table 4.1) from 19:14 hours to 20:36
hours of carbonyl and N-H indicates that the carbonyl groups were more likely from
amides [Cocean et al, 2018].
Water photodisociation simulated in COMSOL
Nocturnal conditions raised the question on water dissociation in absence of
sun light. The water dissociation was observed in the bands spectra from Figure 4.3h.
In order to understand the phenomena, a simulation in COMSOL was conducted. The
source of energy is considered as the photons energy that is provided to the water as
reaction enthalpy [Poulain et al, 2010; Rühl et al, 2012; Stafe et al, 2008; Stafe et al,
2010; Cocean et al, U.P.B. Sci. Bull, 2017; Cocean et al., Appl. Surf. Sci., 2017]. The
model takes into account the two existing phases of water during spectroscopic
measurements, gas and liquid. Thus, the Heat Transfer in Solids in COMSOL was
used where analytical functions are added to the module and the variable as heat source
provided by the laser beam as per formulae (2.15), (2.16) from section II.2.1. Target
Heating under Pulsed Laser Irradiation [Cocean et al, U.P.B. Sci. Bull, 2017, A.
Cocean et al., Appl. Surf. Sci., 2017].
60
The system used for the Finite Element Method applied to the studied model consists
of a sphere (Figure 4.4a) – representing the snowflake – enclosed in a cylinder that
represents a finite element from the atmosphere (Figure 4.4b). Water in solid state is
selected from Materials Library for the sphere (snowflake) and wet air for the
environmental atmosphere and the constants for each material are provided by
COMSOL library
Figure 4.4. Geometry to model the environmental system of snowflake into wet
atmosphere (a-Snowflake representation [Cocean et al, 2018]; b- The system of
snowflake in wet air environment [Cocean et al, 2018]
Finite element discretization – mesh – is represented in Figure 4.5. A time –
dependent study is selected and the range is 0 s, 300 s and 12400 s. The parameters
introduced are 550 nm wavelength and 250 W input power to simulate the artificial
light. Initial temperatures of 273 K for the snowflake (the sphere in the modeled
system) and 273 K for the environmental atmosphere (the cylinder enclosure in the
modeled system) are introduced and the heat transfer is considered as a transfer of
energy from the photons to the system in Figure 4.4. An extremely fine mesh on the
ice grain and coarse mesh for the rest of the system are set as in Figure 4.5. The results
are generated as temperatures in eV and represented in the plots from Figure 4.6.
61
Figure 4.5. The Mesh geometry used in the COMSOL simulation model [Cocean
et al, 2018]
In the plots from Figure 4.6, maximum of energy is reached within 300 s,
being constant after that. The amount of energy of 4.85 eV through the middle of the
snowflake equals 466.99 kJ/mol and the amount of energy of 4.92 eV on the bottom
of the snowflake equals 474.71 kJ/mol. As for water dissociation the required energy
is of 458.9 kJ/mol, the simulation shows that the artificial light irradiating the two co-
existing phases of the water (solid – snowflakes and liquid – fog) may represent
conditions to dissociate water molecules [Cocean et al, 2018]. The simulation, together
with the measured spectra (Figure 4.3h) confirms that water can dissociate during
night time, under artificial light.
V. General Conclusions
In order to deepen the fundamental studies regarding the physico - chemical
processes that take place during the interaction of the laser irradiation with the matter
and to evaluate the possibility of applying the LIBS technology, a simulation model
was developed in the COMSOL software based on the finite element method to assist
and complete the information acquired during experimental work. Adding specific
formulae and boundary conditions to Heat Transfer in Solids module of COMSOL,
the model achieved proves to be reliable and provides valuable information about
heating, temperature, phase change – including plasma formation, processes and
phenomena in connection with laser ablation. Thin films deposition simulated based
on the Fluid Flow module completes the study in a model that provides a good
representation of the Pulsed Laser Deposition.
62
The plots illustrating the phase change processes in a time dependent and
space dependent profile, together with plots illustrating the deposition of the ablated
material provide important and accurate information to describe the phenomena.
Results obtained in COMSOL fitting literature reported experimental studies also
complete the information regarding the thermal effect influence on the ablation
through the phases generated during the transfer of energy from the laser beam to the
matter with which it interacts.
Although in the COMSOL module Heat Transfer in Solids that I selected to
simulate the laser ablation, the governing equation is for heat – transfer only, I have
added the optical components of laser beam as the ignition source for heating and
ablation, which are the laser fluence and implicitly its intensity and density of power,
to describe the entire process. The parameters with all the specific optical parameters
such as refractive index (n), extinction coefficient (Ҡ) and laser beam wavelength (λ)
and formulae for reflexive and absorption coefficients are also part of the model that I
set – up together with analytical functions to describe the Gaussian shape for pulse
width and for the effect on the surface, as well as the beam intensity as variable
described by Beer – Lambert Law for beam attenuation. Finally, all this contributes to
the essential variable of the model I have implemented, namely the one for initiating
laser ablation, respectively the power density described by the formulas (15) and (16)
from section II.2.1. Target Heating under Pulsed Laser Irradiation of this thesis. The
plots generated with the simulation results provide information about thermal effects
as temperature in space and during pulse width, which are actually phase diagrams,
indicating time ranges and/or space areas where a certain phase may exist based on the
temperature resulted from simulation and due to material properties covered in the
mathematical and parametrical model and simulation.
Although this first model for the interaction of laser radiation with matter has
been conceived for a symmetric geometry and uniform composition target, I designed
it to be used in various work situations and that is why I worked on entire 3D geometry.
That makes possible studies on non – homogeneous targets as well on asymmetric and
layered geometry and provides information about process evolution on the surface, in
depth, as well as at interfaces and on regions of the surface or volume of the target. In
this respect, the model was extended and supplemented to assist by simulating the
ablation in the study of thermal effects on a non-homogeneous target of silver with
iron and nickel impurities. The non-homogeneous composition of the target resulted
in non-uniform phenomena with respect to the heat dispersion through the regions with
different components, the thermal equilibrium tendency at interfaces being evidenced
influencing at the same time all process of heat dispersion observed mainly on surface
due to low thermal length and optical length.
During Pulsed Laser Deposition, the droplets formation was observed, but
also the change in their shape from pearl for lower laser energy/fluency to rings when
the laser energy/fluence is increased. For experiments conducted for three laser
63
energies of 100 mJ, 150 mJ and 180 mJ, the change was obvious from pearl shaped
droplets at 100 mJ laser energy to ring shaped at 180 mJ and also the number of
droplets increased a lot with the laser energy. As for the laser energy of 150 mJ,
intermediary results among the other two were obtained. For a better visualization and
compilation of the data, the simulation was conducted for all three energies in the same
model where a parametric sweep on energy was added.
Taking into account the information from the simulation in COMSOL for the
ablation of the target made of silver unpurified with iron and nickel, where co-existing
phase is evidenced for the ablated material (gas and plasma, but also liquid phase), the
droplets are explained based on Plateau – Rayleigh instability developed by a
sinusoidal perturbation given by the diffusive electric field from plasma and by the
pressure waves generated during plasma travel with extremely high velocity in the
deposition chamber. The consistent amount of liquid phase in the plume of ablation as
per the phase diagrams COMSOL supports the statement that Plateau – Rayleigh
instability may be the explanation for droplets formation during PLD. The other
element is the high speed of the plasma that is in connection with the energy and that
is responsible for the crown splash effect, where the droplets break under the high
speed at the impact with the deposition support.
Another phenomenon observed during laser ablation experiments, was the
redeposition on the target, preponderantly of the lighter elements iron and nickel
leading to an increase of these two elements in the target elemental composition and
low to almost absent in the deposited thin layer composition. As the simulation in
COMSOL revealed liquid phase resulted in ablation preponderantly for silver, and as
liquid phase is the one most susceptible to redeposit, as well as due to the droplets
evidenced on the target around the ablated region, it must follow that the redeposition
is the result of collision between the lighter liquid micro-droplets of the three metals
constituting the target when the lighter ones – i.e. iron and nickel, almost twice lighter
than silver - will return on the target.
More investigation about how Rayleigh instability and crown splash induced
by the laser parameters, but also by the conditions of vacuum and temperature in the
deposition chamber, could lead to a better control of the PLD and make it more
efficient and with a wider range of application. Controlling the conditions in the
vacuum chamber in a way that mitigates Rayleigh instability or the opposite, enhances
it, a variety of studies on the solid films and nanoparticles but also applications for
technology could be developed.
In the context of an increased interest in medicine but also for other
applications where silver is required to be in the ionic state, a study of pulsed laser
deposition of silver on hemp fabrics previously impregnated with citric acid and on
citric acid deposited as supersaturated aqueous solution of citric acid on a glass slab
was conducted and FTIR spectra of the powder obtained from the surface of deposited
64
films evidenced silver citrate formation and also H-bonds inter- and intramolecular, as
well as Van Der Waals interactions are revealed in the said spectra.
Based on the findings resulted from FTIR analyze of the silver thin film deposited on
the citric acid when broad band between 3560 cm-1 and 2598 cm-1 indicates both citrate
and citric acid, possibility to develop a PLD method of “titration” to determine the
quantity of silver ions from plasma of ablation arrived to the substrate within specific
conditions and parameters of the laser irradiation and pressure in the deposition
chamber is purposed. The method could be extended for other materials too.
Laser induced fluorescence used on polyacrylic fibers in textile textures
coated with curcumin by dyeing under microwave procedure, offered information
about physico – chemical interactions and processes in the nonhomogeneous system
and shift of the maximum peak of fluorescence to blue region provided information
that the the curcumin fluorophore recorded changes due either to the interaction with
the acrylic substrate or due to thermal effects with thermocromism. More
investigations are to be continued to elucidate the mechanism behind the noticed shift
in fluorophore emission after curcumin is deposited on the polyacrylic fiber.
A similar model in COMSOL for laser irradiation of non – homogeneous
materials was conducted for the study of laser cleaning of buildings, monuments and
civil constructions. For the restoration / reconditioning method of laser cleaning of
mineral rocks and constructions based on lime, such simulation can provide
information about optimum parameters and conditions so that laser irradiation does
not affect the substrate. Deposited layer as crust was investigated on limestone based
rocks from Podul de Piatra in Iasi, area exposed to urban and industrial pollution, but
also to the episodes of Saharan dust. The elemental analysis of the rock included LIBS
and SEM-EDX. The results in the generated plots offer an image about efficiency of
ablation of crust constituents, and also the effects on the substrate, i.e. limestone for
this specific case. Beside direct thermal effect to cause damages to the substrate subject
for cleaning, the temperatures resulted in the simulation indicated possible chemical
reactions that may change the chemical formula of the substrate, but the dimension of
such modified chemical composition is insignificant. The parameters and conditions
for laser cleaning of materials based on limestone were set up with this simulation.
As one of the important studies on laser interaction with matter refers to laser
mirrors threshold, the simulation in COMSOL was conducted using again a parametric
sweep on the energy to calculate when damage of the silver thin layer starts and to find
the magnitude of the damaged area. It resulted that the results of the simulation are
almost identical with the results from the experiments proceeded for same conditions
and parameters as in COMSOL. It was found that the first damage appears at 25 mJ
laser beam energy and 336 μm laser beam spot diameter which corresponds to a
fluence of 28 J/cm2. The same was noticed in the simulation in COMSOL.
The model in COMSOL set up for laser beam interaction with the matter was
adapted for interaction of artificial light emitting at 550 nm wavelength with a system
65
consisting of liquid and solid phase of water to simulate the effects of artificial light
provided by street lighting in an atmosphere saturated in water as fog and snowflakes.
Detection with DARILOES – LIDAR system of water dissociation during nighttime
required to find out the mechanism of such transformation and COMSOL simulation,
based on a model presented at section IV.2 Study of some critical physicochemical
phenomena in the terrestrial atmosphere of this thesis evidenced a transfer of energy
from the photons sourced by street lamps cumulating 250 W input power and emitting
at 550 nm in amount of 4.85 eV and 4.99 eV, equivalent to 474.71 kJ/mol and 474.71
kJ/mol, respectively, enough to ensure conditions to water dissociation that requires
458.9 kJ/mol. The simulation in COMSOL completed a more extended experimental
study with information needed to explain chemical transformation in specific
conditions.
The measurements in the atmosphere at 500 meters had the purpose to
monitor an episode of urban pollution in special conditions, nocturnal and high
humidity. The data acquired with DARLIOES – LIDAR system leaded to the
conclusion that the evolution and changes of the different detected chemical species
are part of a wet removal process, namely “atmosphere self-cleaning under humidity
conditions” [Cocean et al, 2018] and later was re-confirmed based on specific analysis
of water collected after severe rainfalls from the same area [Cocean et al, April 2019].
Since chemical processes can occur during the interaction of laser radiation
with matter, they can also be either anticipated or explained by the temperatures
developed as a result of the energy transfer between the photons of the laser radiation
and the chemical molecules of the irradiated substance, and this results from the
simulations made in COMSOL through the model for laser irradiation heating [Cocean
et al, 2018].
All studies presented in this thesis evidence the important role of numerical
modeling and simulation to assist and complete the experimental work in LIBS for a
better understanding of the processes and phenomena that take place during light
interaction with the matter and for developing applications where such interaction may
be involved. The results of the simulations proved to be according to the experimental
data and that makes the modules used from COMSOL and its data base together with
the mathematical formulae and equations as well as boundary conditions introduced
to develop further models reliable and applicable with possibilities to extend for
implementation in even more experimental and theoretical studies.
66
Reference
[Abderrahim et al, 2015] Benarbia Abderrahim, Elidrissi Abderrahman, Aqil
Mohamed, Tabaght Fatima, Tahani Abdesselam, Ouassini Krim, Kinetic Thermal
Degradation of Cellulose, Polybutylene Succinate and a Green Composite:
Comparative Study, World Journal of Environmental Engineering, 2015, Vol. 3, No.
4, 95-110, DOI:10.12691/wjee-3-4-1
[Aguilera et al, 1998 ]: J. A. Aguilera, C. Arag ´ on, and F. Pe˜nalba, “Plasma shielding
effect in laser ablation of metallic samples and its influence on LIBS analysis,”
Applied Surface Science, vol. 127–129, pp. 309–314, 1998
[Akagi et al, 2011]: S. K. Akagi, R. J. Yokelson, C. Wiedinmyer, M. J. Alvarado, J. S.
Reid, T. Karl, J. D. Crounse, and P. O. Wennberg, Emission factors for open and
domestic biomass burning for use in atmospheric models, Atmos. Chem. Phys., 11,
4039–4072, 2011
[Alonso et al, 2008]: J.C. Alonso, R. Diamant, P. Castillo, M.C. Acosta–Garcia, N.
Batina, E. Haro-Poniatowski, Thin films of silver nanoparticles deposited in vacuum
by pulsed laser ablation using a YAG:Nd laser, Applied Surface Science, 2009, v.
255(9); p. 4933-4937, http://dx.doi.org/10.1016/j.apsusc.2008.12.040
[Anabitarte et al, 2012]: F. Anabitarte, A. Cobo, and J.M. Lopez-Higuera, Laser-
Induced Breakdown Spectroscopy: Fundamentals, Applications, and Challenges,
ISRN Spectroscopy, Volume 2012, Article ID 285240, doi:10.5402/2012/285240
[Anabitarte et al, 2012]: F. Anabitarte, J. Mirapeix, O. M. C. Portilla, J. M. Lopez-
Higuera, and A. Cobo, “Sensor for the detection of protective coating traces on boron
steel with aluminium-silicon coveringby means of laser-induced breakdown
spectroscopy and support vector machines,” IEEE Sensors Journal, vol. 12, no. . 1,
Article ID Article number5722011, pp. 64-70, 2012
[Angel et al, 2001]: S. M. Angel, D. N. Stratis, K. L. Eland, T. Lai, M. A. Berg, and
D. M. Gold, “LIBS using dual- and ultra-short laser pulses,” Fresenius’ Journal of
Analytical Chemistry, vol. 369, no. 1, pp. 320–327, 2001
[Anzano et al, 2006]: J. M. Anzano, M. A. Villoria, A. Ru´ız-Medina, and R. J.
Lasheras, “Laser-induced breakdown spectroscopy for quantitative spectrochemical
analysis of geological materials: effects of the matrix and simultaneous
determination,”Analytica Chimica Acta, vol. 575, no. 2, pp. 230–235, 2006
[Aragon et al, 1993]: C. Aragon, J. Aguilera, and J. Campos, “Determination of carbon
content in molten steel using laser-induced breakdown spectroscopy,” Applied
Spectroscopy, vol. 47, pp. 606– 608, 1993
[Bagherzade et al, 2016] Ghodsieh Bagherzade, Maryam Manzari Tavakoli,
Mohmmad Hasan Namaei, Green synthesis of silver nanoparticles using aqueous
extract of saffron (Crocus sativus L.) wastages and its antibacterial activity against six
bacteria, Asian Pacific Journal of Tropical Biomedicine,
http://dx.doi.org/10.1016/j.apjtb.2016.12.014
67
[Bagherzade et al, 2017]: Ghodsieh Bagherzade, Maryam Manzari Tavakoli,
Mohmmad Hasan Namaei, Green synthesis of silver nanoparticles using aqueous
extract of saffron (Crocus sativus L.) wastages and its antibacterial activity against six
bacteria, Asian Pac J Trop Biomed 2017; 7(3): 227–233,
http://dx.doi.org/10.1016/j.apjtb.2016.12.014
[Balika et al, 2012]: L. Balika, C. Focsa, S. Gurlui, S. Pellerin, N. Pellerin, D. Pagnon
and M. Dudeck, Laser ablation in a running hall effect thruster for space propulsion,
Appl. Phys A, DOI 10.1007/s00339-012-7211-0, (2012)
[Balika et al, 2012]: L. Balika, C. Focsa, S. Gurlui, S. Pellerin, N. Pellerin, D. Pagnon,
M. Dudeck, Laser-induced breakdown spectroscopy in a running hall effect thruster
for space propulsion, Spectrochim. Acta B 74-75 (2012) 184-189.
[Barkanov, 2001] Evgeny Barkanov, Introduction to the finite element method,
Institute of Materials and Structures Faculty of Civil Engineering Riga Technical
University, 2001
[Bassiotis et al, 2001]: I. Bassiotis, A. Diamantopoulou, A. Giannoudakos, F.
Roubani-Kalantzopoulou, and M. Kompitsas, “Effects of experimental parameters in
quantitative analysis of steel alloy by laser-induced breakdown spectroscopy,”
Spectrochimica Acta Part B, vol. 56, no. 6, pp. 671–683, 2001;
[Bauer et al, 1998]: H. E. Bauer, F. Leis, and K. Niemax, “Laser induced breakdown
spectrometry with an echelle spectrometer and intensified charge coupled device
detection,” Spectrochimica Acta Part B, vol. 53, no. 13, pp. 1815–1825, 1998
[Bechtel et al, 1975]: J. H. Bechtel, Heating of solid targets with laser pulses, J.
Appl.Phys. 46(4) (1975) 1585-1593.
[Becker et al, 2006]: Holger Becker, Herbert Vogel, Phenothiazine as Stabilizer for
Acrylic Acid, Chem. Eng. Technol. 2006, 29, No. 8, 931–936
[Bekrisa et al, 2011]: N. Bekrisa, J.P. Coadb, C. Grisoliac, J. Likonend, A. Semeroke,
K. Dylstf, A. Widdowsonb, Fusion Technology related studies at JET: Post-mortem
tile analysis with MKII-HD geometry, In situ laser detritiation and Molecular Sieve
Bed detritiation, Journal of Nuclear Materials, Volume 417, Issues 1–3, Pages 1356–
1360, 1 October 2011
[Belegante et al, 2011]: L. Belegante, C. Talianu, A. Nemuc, D. N. Nicolae, Detection
of local weather events from multiwavelength lidar measurements during the
EARLI09 campaign, Rom. J. Phys. 56(3-4) (2011) 484-494.
[Beltramo et al, 2009]: P. J. Beltramo, C. L. Bodarky, H. M. Kyd, Design and Control
Using Stochastic Models of Deposition Reactors, Senior Design Reports (CBE),
University of Pennsylvania Scholarly Commons, Department of Chemical &
Biomolecular Engineering (4-14-2009)
[Bera et al, 2013] Raj Kumar Bera, C. Retna Raj, A facile photochemical route for the
synthesis of triangular Ag nanoplates and colorimetric sensing of H2O2, Journal of
Photochemistry and Photobiology A: Chemistry 270 (2013) 1– 6,
http://dx.doi.org/10.1016/j.jphotochem.2013.07.005
68
[Beral et al, 1977]: E. Beral, M. Zapan, Iorganic Chemistry, Forth Edition, Technical
Editor, Bucharest, 1977
[Brown et al, 2006]: S. S. Brown, J. A. Neuman, T. B. Ryerson, M. Trainer, W. P.
Dube, J. S. Holloway, C. Warneke, J. A. de Gouw, S. G. Donnelly, E. Atlas, B.
Matthew, A. M. Middlebrook, R. Peltier, R. J. Weber, A. Stohl, J. F. Meagher, F. C.
Fehsenfeld, A. R. Ravishankara, Nocturnal odd-oxygen budget and its implications
for ozone loss in the lower troposphere, Geophysical Research Letters, VOL. 33,
L08801, doi:10.1029/2006GL025900, 2006
[Bulai et al, 2016]: G. Bulai, I. Dumitru, M. Pinteala, C. Focsa, S. Gurlui, Magnetic
nanoparticles generated by laser ablation in liquid Digest Journal of Nanomaterials
and Biostructures, 11 (1), pp. 283-291 (2016)
[Bulai et al, 2018]: G. Bulai, O. Rusu, MM Cazacu, F. Tudorache, B. Chazallon, C.
Focsa, S. Gurlui, Structural, magnetic and humidity sensing properties of rare earth
doped cobalt ferrite thin films synthesized by pulsed laser deposition, JOURNAL OF
OVONIC RESEARCH Volume: 14 Issue: 2 Pages: 119-128 Published: MAR-
APR 2018
[Busser et al, 2018]: Benoit Busser, Samuel Moncayo, Jean-Luc Coll, Lucie Sancey,
Vincent Motto-Ros, Elemental imaging using laser-induced breakdown spectroscopy:
A new and promising approach for biological and medical applications, Coordination
Chemistry Reviews 358 (2018) 70 – 79, http://doi.org/10.1016/j.ccr.2017.12.006
[Butch et al, 2013] Christopher Butch, Elizabeth D. Cope, Pamela Pollet, Leslie
Gelbaum, Ramanarayanan Krishnamurthy, Charles L. Liotta, Production of Tartrates
by Cyanide-Mediated Dimerization of Glyoxylate: A Potential Abiotic Pathway to the
Citric Acid Cycle, J. Am. Chem. Soc. 2013, 135, 13440−13445,
dx.doi.org/10.1021/ja405103r
[Carranza et al, 2003]: J. E. Carranza, E. Gibb, B. W. Smith, D. W. Hahn, and J. D.
Winefordner, “Comparison of nonintensified and intensified CCD detectors for laser-
induced breakdown spectroscopy,”Applied Optics, vol. 42, no. 30, pp. 6016–6021,
2003
[Castle et al, 1998]: B. C. Castle, K. Talabardon, B. W. Smith, and J. D.bWinefordner,
“Variables influencing the precision of laserinduced breakdown spectroscopy
measurements,” Applied Spectroscopy, vol. 52, no. 5, pp. 649–657, 1998
[Cazzaniga et al, 2013]: Andrea Cazzaniga, Rebecca Bolt Ettlinger, Stela Canulescu,
Jørgen Schou and Nini Pryds, Nanosecond laser ablation and deposition of silver,
copper, zinc and tin, Appl. Phys. A DOI 10.1007/s00339-013-8207-0, 10 December
2013 © Springer-Verlag Berlin Heidelberg 2014
[Chameides et al, 1982]: W. L. Chameides and D. D. Davis, The Free Radical
Chemistry of Cloud Droplets And Its Impact Upon the Composition of Rain, Journal
Of Geophysical Research, Vol. 87, No. C7, Pages 4863-4877, June 20, 1982
[Chen et al, 2010]: Shuang Chen, Xinrong Ren, Jingqiu Maoa, Zhong Chen, William
H. Brune, Barry Lefer, Bernhard Rappenglu, James Flynn, Jennifer Olson, James H.
69
Crawford, A comparison of chemical mechanisms based on TRAMP-2006 field data,
Atmospheric Environment 44 (2010) 4116–4125
[Ciuraru et al, 2011]: R. Ciuraru, S. Gosselin, N. Visez, D. Petitprez, Heterogeneous
reactivity of chlorine atoms with sodium chloride and synthetic sea salt particles, Phys
Chem Chem Phys. 2011 Nov 21;13(43):19460-70
[Cocean et al, 2018]: A.Cocean, I.Cocean, M.M. Cazacu, G.Bulai, F.Iacomi, S.Gurlui,
Atmosphere self-cleaning under humidity conditions and influence of the snowflakes
and artificial light, Applied Surface Science 443 (2018) 83–90, DOI:
10.1016/j.apsusc.2018.02.156
[Cocean et al, Appl. Surf. Sci., 2017]: Alexandru Cocean, Vasile Pelin, Marius Mihai
Cazacu, Iuliana Cocean, Ion Sandu, Silviu Gurlui, Felicia Iacomi, Thermal Effects
Induced By Laser Ablation In Non-Homogeneous Limestone Covered By An Impurity
Layer, Applied Surface Science Volume 424, Part 3, 1 December 2017, Pages 324-
329, http://dx.doi.org/10.1016/j.apsusc.2017.03.172
[Cocean et al, April 2019] I. Cocean, A. Cocean, V. Pohoata, F. Iacomi, S. Gurlui,
City water pollution by soot-surface-active agents revealed by FTIR spectroscopy,
Applied Surface Science, https://doi.org/10.1016/j.apsusc.2019.04.179
[Cocean et al, May 2019]: I. Cocean, A. Cocean, C. Postolachi, V. Pohoata, N.
Cimpoesu, G. Bulai, F. Iacomi, S. Gurlui, alpha keratin amino acids behvior under
high fluence laser interaction. Medical applications, Applied Surface Science 2019,
DOI: 10.1016/j.apsusc.2019.05.207
[Cocean et al, U.P.B. Sci. Bull., 2017]: A. Cocean, I. Cocean, S. Gurlui, F. Iacomi,
Study of the pulsed laser deposition phenomena by means of Comsol Multiphysics,
U.P.B. Sci. Bull., Series A, Vol. 79, Iss. 2, 2017
[Cremers et al, 1995]: D. Cremers, J. Barefield, and A. Koskelo, “Remote elemental
analysis by lase induced breakdown spectroscopy using a fiber-optic cable,” Applied
Spectroscopy, vol. 49, pp. 857–860, 1995
[Cremers et al, 2006]: D. A. Cremers, L. J. Radziemski, and J. Wiley, Handbook of
Laser-Induced Breakdown Spectroscopy, John Wiley & Sons, 2006.
[Cremers et al, 2007]: D. A. Cremers, L. J. Radziemski, and J. Wiley, Handbook of
Laser-Induced Breakdown Spectroscopy, John Wiley & Sons, 2006., J. P. Singh,
Laser-Induced Breakdown Spectroscopy, Elsevier Science, 2007
[Cristoforetti et al, 2006]: R Gabriele Cristoforetti, Stefano Legnaioli, Vincenzo
Palleschi, Azenio Salvetti, Elisabetta Tognoni, Pier Alberto Benedetti, Franco
Brioschi and Fabio Ferrario, Quantitative analysis of aluminium alloys by low-energy,
high-repetitionrate laserinduced breakdown spectroscopy,J. Anal. At. Spectro.
2006,21 607-702
[Cu˜nat et al, 2005]: J. Cu˜nat, S. Palanco, F. Carrasco, M. D. Sim´ on, and J. J.
Laserna, “Portable instrument and analytical method using laser-induced breakdown
spectrometry for in situ characterization of speleothems in karstic caves,” Journal of
Analytical Atomic Spectrometry, vol. 20, no. 4, pp. 295–300, 2005
70
[Dascalu et al, 2013]: G. Dascalu, O. Pompilian, B. Chazallon, V. Nica, O. F. Caltun,
S. Gurlui, C. Focsa, Rare earth doped cobalt ferrite thin films deposited by PLD,
Applied Physics A, 110 (4), pp.: 915-922 (2013)
[Dascalu et al, 2015]: G. Dascalu, G. Pompilian, B. Chazallon, O. F. Caltun, S. Gurlui,
C. Focsa, Femtosecond pulsed laser deposition of cobalt ferrite thin films, Applied
Surface Science, Volume 278, p. 38-42 (2013) 10.1016/j.apsusc.2013.02.107
[David et al, 2010]: David W. Hahn, Nicolo´ Omenetto, Laser-Induced Breakdown
Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological
Approaches to Material Analysis and Applications to Different Fields, Vol 64, Issue
12, 2010
[Demetriosanglos et al, 1997]: Demetriosanglos, Stelion Couris, Costas Fotakis, Laser
diagnostics of painted artworks: Laser-Induces breakdown spectroscopy in pigment
identification, Appl. Spectrosco, 81(7),1997 1025-1030
[Drogoff et al, 2001]: B. Le Drogoff, J. Margot, M. Chaker et al., “Temporal
characterization of femtosecond laser pulses induced plasma for spectrochemical
analysis of aluminumalloys,” Spectrochimica Acta Part B, vol. 56, no. 6, pp. 987–
1002, 2001
[Dubovik et al, 1998]: O. Dubovik, B. N. Holben, Y. J. Kaufman, M. Yamasoe, A.
Smirnov, D. Tanré, I. Slutsker, Single-scattering albedo of smoke retrieved from the
sky radiance and solar transmittance measured from ground, J. Geophys. Res. Atmos.
103(D24) (1998) 31903-31923.
[Duttaa et al, 2004]: Srabasti Duttaa, James Glimma, John W. Grovec, David H.
Sharpd and Yongmin Zhanga, Spherical Richtmyer-Meshkov instability for
axisymmetric flow, 0378-4754/$30.00 © 2004 IMACS,
doi:10.1016/j.matcom.2004.01.020
[Eberhardt et al, 1994]: Eric S. Eberhardt and Ronald T. Raines, Amide–Amide and
Amide–Water Hydrogen Bonds: Implications for Protein Folding and Stability, J Am
Chem Soc. 1994 March 9; 116(5): 2149–2150.
[El-Diasty et al, 2011]: Fouad El-Diasty, Coherent anti-Stokes Raman scattering:
Spectroscopy and microscopy, Vibrational Spectroscopy 55 (2011) 1–37
[Fantonia et al, 2013]: R. Fantonia, S. Almavivaa, L. Canevea, F. Colaoa, A. M.
Popovb, G. Maddalunoc, Development of Calibration-Free Laser-Induced-
Breakdown-Spectroscopy based techniques for deposited layers diagnostics on ITER-
like tiles, Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 87, Pages 153–
160, 1 September 2013
[Fornarini et al, 2005]: L. Fornarini, F. Colao, R. Fantoni, V. Lazic, and V.
Spizzicchino, “Calibration analysis of bronze samples by nanosecond laser induced
breakdown spectroscopy: a theoretical and experimental approach,” Spectrochimica
Acta Part B, vol. 60, no. 7-8, pp. 1186–1201, 2005
[Francisco et al, 2012]: Francisco J. Fortes, Javier Moros, Patricia Lucena, Luisa M.
Cabalín, and J. Javier Laserna, Laser-Induced Breakdown Spectroscopy, 2012
71
American Chemical Society, dx.doi.org/10.1021/ac303220r | Anal. Chem. 2013, 85,
640−669
[Franklin et al, 2004]: S.R. Franklin, R.K. Thareja, Simplified model to account for
dependence of ablation parameters on temperature and phase of the ablated material,
Appl. Surf. Sci. 222(1-4) (2004) 293-306.
[Franklin et al, 2004]: S.R. Franklin, R.K. Thareja, Simplified model to account for
dependence of ablation parameters on temperature and phase of the ablated material,
Appl. Surf. Sci. 222(1-4) (2004) 293-306.
[Garanin, 2012]: Dmitry Garanin, Molecular theory of ideal gases, Statistical
Thermodynamics, October 1, 2012
[Garín et al, 2017]: M. Garín, C. Jin, D. Cardador, T. Trifonov, R. Alcubilla,
Controlling Plateau-Rayleigh instabilities during the reorganization of silicon
macropores in the Silicon Millefeuille process, Scientific Reports volume 7, Article
number: 7233 (2017), https://doi.org/10.1038/s41598-017-07393-4
[Giles et al, 2012]: D. M. Giles, B. N. Holben, T. F. Eck, A. Sinyuk, A. Smirnov, I.
Slutsker, R. R. Dickerson, A. M. Thompson, J. S. Schafer, An analysis of AERONET
aerosol absorption properties and classifications representative of aerosol source
regions, J. Geophys. Res. Atmos. 117 (2012) D17203.
[Giménez-López et al, 2010]: J. Giménez-López, A. Millera, R. Bilbao, M.U. Alzueta,
HCN oxidation in an O2/CO2 atmosphere: An experimental and kinetic modeling
study, Combustion and Flame 157 (2010) 267–276
[Gonz´alez et al, 2009]: R. Gonz´alez, P. Lucena, L. M. Tobaria, and J. J. Laserna,
“Standoff LIBS detection of explosive residues behind a barrier,” Journal of Analytical
Atomic Spectrometry, vol. 24, no. 8, pp. 1123–1126, 2009
[Gothard et al, 2014]: M. Gothard, A. Nemuc, C. Radu, and S. Dascalu, An intensive
case of saharan dust intrusion over south east Romania, Rom. Rep. Phys. 66(2) (2014)
509-519.
[Govarthanan et al, 2014] Muthusamy Govarthanan, Thangasamy Selvankumar,
Koildhasan Manoharan, Rajiniganth Rathika, Kuppusamy Shanthi, Kui-Jae Lee, Min
Cho, Seralathan Kamala-Kannan, Byung-Taek Oh, Biosynthesis and characterization
of silver nanoparticles using panchakavya, an Indian traditional farming formulating
agent, International Journal of Nanomedicine, 2014,
http://dx.doi.org/10.2147/IJN.S58932
[Grasu et al, 2002]: C. Grasu, M. Branzila, G. C. Miclaus and I. Bobos, Sarmatian
System of Foreland Basin of the Eastern Carpathians, Technical Publishing,
Bucharest, 2002, pp. 287-297.
[Grisoliaa et al, 2007]: C. Grisoliaa, A. Semerokb, J.M. Weulersseb, F. Le Guernc, S.
Fomichevb, F. Brygob, P. Fichetb, P.Y. Throb, P. Coadd, N. Bekrise, M. Stampc, S.
Rosanvallonc, G. Piazzac, In-situ tokamak laser applications for detritiation and co-
deposited layers studies, Journal of Nuclear Materials, Volumes 363–365, , Pages
1138–1147, 15 June 2007
72
[Guo et al, 2010]: Q. J. Guo, H. B. Yu, Y. Xin, X. L. Li, and X. H. Li, “Experimental
study on high alloy steel sample by laserinduced breakdown spectroscopy,” Guang Pu
Xue Yu Guang Pu Fen Xi, vol. 30, no. 3, pp. 783–787, 2010
[Gurlui et al, 2006]: S. Gurlui, M. Sanduloviciu, M. Strat, G. Strat, C. Mihesan, M.
Ziskind, C. Focsa, Dynamic space charge structures in high fluence laser ablation
plumes, J. Optoelectron. Adv. M. 8(1) (2006) 148-151.
[Gurlui et al, 2008]: S. Gurlui, M. Agop, P. Nica, M. Ziskind, C. Focsa, Experimental
and theoretical investigations of a laser produced aluminum plasma, Phys. Rev. E
78(2) (2008) 026405 part 2.
[Gurlui et al, 2011]: S. Gurlui, C. Focsa, Plasma Science, Laser Ablation Transient
Plasma Structures Expansion in Vacuum, IEEE Transactions on Volume: PP, Issue:
99 , DOI: 10.1109/TPS.2011.2151884, Publication Year: (2011).
[Gurlui et al, 2013]: S. Gurlui, G. O. Pompilian, P. Nemec, V. Nazabal, M. Ziskind,
C. Focsa, Plasma Diagnostics in Pulsed Laser Deposition of GaLaS Chalcogenides,
Appl. Surf. Science, 278, Pages 352-356 (2013)
[Hajakbari et al, 2016] F. Hajakbari, M. Ensandoust, Study of Thermal Annealing
Effect on the Properties of Silver Thin Films Prepared by DC Magnetron Sputtering,
ACTA PHYSICA POLONICA A, Vol. 129 (2016), No. 4, DOI:
10.12693/APhysPolA.129.680
[Hajakbari et al, 2016]: F. Hajakbari, M. Ensandoust, Study of Thermal Annealing
Effect on the Properties of Silver Thin Films Prepared by DC Magnetron Sputtering,
ACTA PHYSICA POLONICA A, Vol. 129 (2016), DOI:
10.12693/APhysPolA.129.680
[Hakiki et al, 2015]: Farizal Hakiki, Dara Ayuda Maharsi, Taufan Marhaendrajana,
Surfactant-Polymer Coreflood Simulation and Uncertainty Analysis Derived from
Laboratory Study, J. Eng. Technol. Sci., Vol. 47, No. 6, 2015, 706-724
[Hakkanen et al, 1995]: H.J. Hakkanen, J.E.I. Korppi-tommola, UV-Laser Plasma
study of elemental distribution of paper coating. Appl. Spectrosc, v49,(12) 1995,p1721
[Hamzaoui et al, 2011]: S. Hamzaoui, R. Khleifia, N. Ja¨ıdane, and Z. Ben Lakhdar,
“Quantitative analysis of pathological nails using laserinduced breakdown
spectroscopy (LIBS) technique,” Lasers in Medical Science, vol. 26, no. 1, pp. 79–83,
2011
[Harrad et al, 1992]: S.J. Harrad, K.C. Jones, A source dioxins inventory and budget
for chlorinated and furans in the United Kingdom environment, The Science of the
Total Environment, 126 (1992) 89-107, Elsevier Science Publishers B.V., Amsterdam
[Hernandeza et al, 2009]: C. Hernandeza, H. Rochea, C. Pocheaua, C. Grisoliaa, L.
Gargiuloa, A. Semerokb, A. Vatryc, P. Delaportec, L. Mercadierc, Development of a
Laser Ablation System Kit (LASK) for Tokamak in vessel tritium and dust inventory
control, Fusion Engineering and Design, Volume 84, Issues 2–6, Pages 939–942, June
2009
73
[Homan et al, 2012] Kimberly A. Homan, Michael Souza, Ryan Truby, Geoffrey P.
Luke, Christopher Green, Erika Vreeland, Stanislav Emelianov, Silver Nanoplate
Contrast Agents for In Vivo Molecular Photoacoustic Imaging, ACS Nano. 2012
January 24; 6(1): 641–650. doi:10.1021/nn204100n
[Hrabok et al, 1984]: Hrabok M. M., Hrudey T. M., A review and catalogue of plane
bending finite elements. Comput. Structures, 19 (3), 479-495 (1984).
[Hrdliˇcka et al 2009]: A. Hrdliˇcka, L. Zaor´alkov´a, M. Galiov´a et al., “Correlation
of acoustic and optical emission signals produced at 1064 nm and 532 nm laser-
induced breakdown spectroscopy (LIBS) of glazed wall tiles,” Spectrochimica Acta
Part B, vol. 64, no. 1, pp. 74–78, 2009
[Hrivíkovä et al, 1973]: J. Hrivíkovä, V. Kellö, Inhibition effect of phenothiazine on
the oxidation of natural rubber, Chem. zvesti 27 (2) 249-254 (1973)
[Ingold et al, 1969]: K.U. Ingold, Peroxy Radicals, Accounts of Chemical Research,
Vol.2, No. 1, January 1969, DOI: 10.1021/ar50013a00
[ISO 21254-2:2011; ISO 21254-3:2011]: ISO 21254-2:2011, Lasers and laser-related
equipment – Test methods for laser-induced damage threshold – Part 2: Threshold
determination; ISO 21254-3:2011, Lasers and laser-related equipment – Test methods
for laser-induced damage threshold – Part 3: Assurance of laser power (energy)
handling capabilities.
[James et al, 1969]: J. F. James and R. Sternberg, The Design of Optical
Spectrometers, Chapman & Hall, London, UK, 1969;
[Jyoti et al, 2015] Kumari Jyoti, Mamta Baunthiyal, Ajeet Singh, Characterization of
silver nanoparticles synthesized using Urtica dioica Linn. leaves and their synergistic
effects with antibiotics, Journal of Radiation Research and Applied Sciences, 2015,
http://dx.doi.org/10.1016/j.jrras.2015.10.002
[Karthik et al, 2013] L. Karthik, Gaurav Kumar, A. Vishnu Kirthi, A. A. Rahuman, K.
V. Bhaskara Rao, Streptomyces sp. LK3 mediated synthesis of silver nanoparticles
and its biomedical application, Bioprocess Biosyst Eng, 2013, DOI 10.1007/s00449-
013-0994-3
[Kasem et al, 2011]: M. A. Kasem, R. E. Russo, and M. A. Harith, “Influence of
biological degradation and environmental effects on the interpretation of archeological
bone samples with laserinduced breakdown spectroscopy,” Journal of Analytical
Atomic Spectrometry, vol. 26, no. 9, pp. 1733–1739, 2011.
[Khan et al, 106 (2015)]: M.A.H. Khan, M.C. Cooke, S.R. Utembe, A.T. Archibald,
R.G. Derwent, M.E. Jenkin, W.C. Morris, N. South, J.C. Hansen, J.S. Francisco, C.J.
Percival, D.E. Shallcross, Global analysis of peroxy radicals and peroxy radical-water
complexation using the STOCHEM-CRI global chemistry and transport model,
Atmospheric Environment 106 (2015) 278e287
[Khan et al, 112 (2015)]: M.A.H. Khan, M.C. Cooke, S.R. Utembe, A.T. Archibald,
P. Maxwell, W.C. Morris, P. Xiao, R.G. Derwent, M.E. Jenkin, C.J. Percival, R.C.
Walsh, T.D.S. Young, P.G. Simmonds, G. Nickless, S. O'Doherty, D.E. Shallcross, A
74
study of global atmospheric budget and distribution of acetone using global
atmospheric model STOCHEM-CRI, Atmospheric Environment 112 (2015) 269e277
[Khan et al, 164 – 165 (2015)]: M.A.H. Khan, M.C. Cooke, S.R. Utembe, A.T.
Archibald, R.G. Derwent, P. Xiao, C.J. Percival, M.E. Jenkin,W.C. Morris, D.E.
Shallcross, Global modeling of the nitrate radical (NO3) for present and pre-industrial
scenarios, Atmospheric Research 164–165 (2015) 347–357
[Kim et al, 2012]: Taesam Kim and Chhiu-Tsu Lin, Northern Illinois University,
Illinois, USA, Laser-Induced Breakdown Spectroscopy , InTech,2012,
http://dx.doi.org/10.5772/48281
[Klaus-Jurgen Bathe, 2014] Klaus-Jurgen Bathe, Finite Element Procedures Second
Edition, 2014, ISBN 978-0-9790049-5-7
[Kosswig et al, 2012]: Kurt Kosswig, Sulfonic Acids, Aliphatic, 2012 Wiley-VCH
Verlag GmbH & Co. KGaA, Weinheim, DOI: 10.1002/14356007.a25_503
[Kowalczyk et al, 2010]: J. M. D. Kowalczyk, J. Perkins, J. Kaneshiro et al.,
“Measurement of the sodium concentration in CIGS solar cells via laser induced
breakdown spectroscopy,” in Proceedings of the 35th IEEE Photovoltaic Specialists
Conference (PVSC ’10), pp. 1742–1744, June 2010
[Kuznetsov et al, 2013]: I. A. Kuznetsov, M. Ya. Garaeva, D. A. Mamichev, Yu. V.
Grishchenko, and M. L. Zanaveskin, Formation of Ultrasmooth Thin Silver Films by
Pulsed Laser Deposition, ISSN 1063_7745, Crystallography Reports, 2013, Vol. 58,
No. 5, pp. 739–742. © Pleiades Publishing, Inc., 2013. Original Russian Text © I.A.
Kuznetsov, M.Ya. Garaeva, D.A. Mamichev, Yu.V. Grishchenko, M.L. Zanaveskin,
2013, published in Kristallografiya, 2013, Vol. 58, No. 5, pp. 725–729.
[Larson et al, 2010] Mats G. Larson, Fredrik Bengzon, The Finite Element Method:
Theory, Implementation, and Practice, Springer, 2010
[Laserna et al, 2003]: J. Laserna and S. Palanco, “Spectral analysis of the acoustic
emission of laser-produced plasmas,” Applied Optics, vol. 42, no. 30, pp. 6078–6084,
2003;
[Lazic et al, 2005]: V. Lazic, F. Colao, R. Fantoni, and V. Spizzicchino, “Recognition
of archeological materials underwater by laser induced breakdown spectroscopy,”
Spectrochimica Acta Part B, vol. 60, no. 7-8, pp. 1014–1024, 2005
[Lazic et al, 2010]: V. Lazic, A. Palucci, S. Jovicevic, M. Carapanese, C. Poggi, and
E. Buono, “Detection of explosives at trace levels by Laser Induced Breakdown
Spectroscopy (LIBS),” in Chemical,Biological, Radiological, Nuclear, and Explosives
(CBRNE) Sensing XI, vol. 7665 of Proceedings of SPIE, April 2010
[Le Breton et al, 2013]: M. Le Breton, A. Bacak, J. B. A. Muller, S. J. O’Shea, P.
Xiao, M. N. R. Ashfold, M. C. Cooke, R. Batt, D. E. Shallcross, D. E. Oram, G.
Forster, S. J.-B. Bauguitte, and C. J. Percival, Airborne hydrogen cyanide
measurements using a chemical ionisation mass spectrometer for the plume
identification of biomass burning forest fires, Atmos. Chem. Phys., 13, 9217–9232,
2013
75
[Lee et al, 1995]: Y.-N. Lee, X. Zhou, L. I. Kleinman, L. J. Nunnermacker, S. R.
Springston, P. H. Daum, L. Newman, W. G. Keigley, M. W. Holdren, C. W. Spicer,
V. Young, B. Fu, D. D. Parrish, J. Holloway, J. Williams, J. M. Roberts, T. B. Ryerson,
and F. C. Fehsenfeld, Atmospheric chemistry and distribution of formaldehyde and
several multi-oxygenated carbonyl compounds during the 1995 Nashville/middle
Tennessee ozone study, BNL-64861-98/10-Rev.
[Li et al, 2000]: Qinbin Li, Daniel J. Jacob, Isabelle Bey, Robert M. Yantosca,
Yongjing Zhao, Yutaka Kondo, Atmospheric Hydrogen Cyanide (HCN)-Biomass
Burning Source, Ocean Sink?, Geophysical Re Search Le Tters, Vol. 2 7,No. 3, Pages3
57-360, February 1 ,2000
[Li et al, 2009]: Q. Li, P. I. Palmer, H. C. Pumphrey, P. Bernath, and E. Mahieu, What
drives the observed variability of HCN in the troposphere and lower stratosphere?,
Atmos. Chem. Phys., 9, 8531–8543, 2009
[Liu et al, 2008]: X. Y. Liu and W. J. Zhang, “Recent developments in biomedicine
fields for laser induced breakdown spectroscopy,”Journal of Biomedical Science, vol.
1, pp. 147–151, 2008
[Loebe et al, 2003]: Klaus Loebe, Arnold Uhl, and HartmutLucht, Micro analysis of
tool steel and glass with laser-induced breakdown spectroscopy, applie optics 2003,
42(30) 6166-6173
[Lohmann et al, 1998]: Rainer Lohmann, Kevin C. Jones, Dioxins and furans in air
and deposition: A review of levels, behaviour and processes, The Science of the Total
Environment 219 1998. 53]81
[Lyu et al, 2014]: Fuzhen Lyu, Hanok Park, Soo-Hyoung Lee, and Youn-Sik Lee,
Synthesis and Characterization of Phenothiazine-Isoindigo Copolymers for
Photovoltaic Applications, Bull. Korean Chem. Soc. 2014, Vol. 35, No. 6
[M. Stafe et al, 2010]: M. Stafe, C. Negutu, N. N. Puscas, I. M. Popescu, Pulsed laser
ablation of solids, Rom. Rep. Phys. 62(4) (2010) 758-770
[Maravelaki et al, 1997]: P. V. Maravelaki, V. Zafiropulos, V. Kilikoglou, M.
Kalaitzaki, and C. Fotakis, “Laser-induced breakdown spectroscopy as a diagnostic
technique for the laser cleaning of marble,” Spectrochimica Acta Part B, vol. 52, no.
1, pp. 41–53, 1997
[McFarland et al, 2003]: Adam D. McFarland and Richard P. Van Duyne, Single
Silver Nanoparticles as Real-Time Optical Sensors with Zeptomole Sensitivity, Nano
Letters 2003 3 (8), 1057-1062 DOI: 10.1021/nl034372s
[Melessanaki et al, 2002]: K. Melessanaki, M. Mateo, S. C. Ferrence, P. P. Betancourt,
and D. Anglos, “The application of LIBS for the analysis of archaeological ceramic
and metal artifacts,” Applied Surface Science, vol. 197-198, pp. 156–163, 2002
[Mercadiera et al, 2011]: L. Mercadiera, J. Hermanna, C. Grisoliab, A. Semerokc,
Analysis of deposited layers on plasma facing components by laser-induced
breakdown spectroscopy: Towards ITER tritium inventory diagnostics, Journal of
76
Nuclear Materials, Volume 415, Issue 1, Supplement, Pages S1187–S1190, 1 August
2011
[Mitsoulis et al, 1984]: Evan Mitsoulis, John Vlachopoulos, The Finite Element
Method for Flow and Heat Transfer Analysis, Advances in Polymer Technology,
1984, DOI: 10.1002/adv.1984.060040203
[Miziolek et al, 2006]: Miziolek, A. W., Palleschi, A., Schechter, I. “Laser induced
Breakdown Spectroscopy”2006, Cambridge
[Mohan et al, 2013] JithinC.Mohan, G.Praveen, K.P.Chennazhi,
R.JayakumarandS.V.Nair, Functionalised gold nanoparticles for selective induction of
invitro apoptosis among human cancer cell lines, Journal of Experimental
Nanoscience, 2013 Vol. 8, No. 1, 32–45,
http://dx.doi.org/10.1080/17458080.2011.557841
[Multari et al 1996]: R. A. Multari, L. E. Foster, D. A. Cremers, and M. J. Ferris,
“Effect of sampling geometry on elemental emissions in laser-induced breakdown
spectroscopy,” Applied Spectroscopy, vol. 50, no. 12, pp. 1483–1499, 1996
[Nica et al, 2009]: P. Nica, P.Vizureanu, M. Agop, S. Gurlui, C. Focsa, N. Forna, P.
D. Ioannou, Z. Borsos, Experimental and theoretical aspects of aluminum expanding
laser plasma, Japanese Journal of Applied Physics, 48 (6), art. no. 066001 (2009);
[Nica et al, 2010]: P. Nica, M. Agop, S. Gurlui and C. Focsa, Oscillatory Langmuir
probe ion current in laser produced plasma expansion, Epl-Europhys LETT 89, 6 Art
no: 65001 (2010)
[Nica et al, 2012]: P. Nica, M. Agop, S. Gurlui, C. Bejinariu, C. Focsa,
Characterization of Aluminum Laser Produced Plasma by Target Current
Measurements, Jpn. J. Appl. Phys. 51, 106102 (2012)
[Nikishkov, 2004] G. P. Nikishkov, INTRODUCTION TO THE FINITE ELEMENT
METHOD, Lecture Notes. University of Aizu, Aizu-Wakamatsu 965-8580, Japan
[email protected], 2004
[O. C. Zienkiewick et al, 2000] O. C. Zienkiewick, R. L. Taylor, The Finite Element
Method Fifth edition Volume 3: Fluid Dynamics, Butterworth-Heinemann, 2000,
ISBN 7506 5050 8
[O. Hill et al, 1997]: K. O. Hill and G.Meltz, “Fiber Bragg grating technology
fundamentals and overview, Journal of Lightwave Technology, vol. 15, no. 8, pp.
1263–1276, 1997
[Ohring, 2001]: M. Ohring (2001). Materials Science of Thin Films (2nd ed.). Boston:
Academic Press. ISBN 9780125249751.
[Papayannis et al, 2014]: A. Papayannis, D. Nicolae, P. Kokkalis, I. Binieroglou, C.
Talianu, L. Belegante, G. Tsaknakis, M. M. Cazacu, I. Vetres, L. Ilic, Optical, size and
mass properties of mixed type aerosols in Greece and Romania as observed by synergy
of lidar and sunphotometers in combination with model simulations: A case study, Sci.
Total Environ. 500 (2014) 277-294.
77
[Parigger et al, 2012]: Christian G. Parigger, Atomic and molecular emissions in laser-
induced breakdown spectroscopy, http://dx.doi.org/10.1016/j.sab.2012.11.012]
[Pathak et al, 2010] D. Pathak, R.K. Bedi, D. Kaur, Characterization of laser ablated
AgInSe2 films, Materials Science-Poland, Vol. 28, No. 1, 2010
[Pelin et al, 2016]: V. Pelin, I. Sandu, M. Munteanu, C. T. Iurcovschi, S. Gurlui, A.V.
Sandu, V. Vasilache, M. Branzila, I. G. Sandu, Colour change evaluation on UV
radiation exposure for Paun - Repedea calcareous geomaterial, IOP. C. SER: Mat. Sci.
Eng. 133 (2016) 012061.
[Pian et al, 1969]: Tong P., Basis of finite element methods for solid continua. Int. J.
Numer. Meth. Engng. 1 (1), 3-28 (1969).
[Pop et al, 2001]: V. Pop, I. Chicinas, N. Jumate, Physics of Materials. Experimental
Methods, Universitary Press, Cluj, 2001.
[Pop et al, 2001]: Viorel Pop, Ionel Chicinaş, Nicolaie Jumate, Fizica materialelor.
Metode experimentale, Presa Universitară Clujeană, 2001, ISBN 973-610-036-7
[Popescu et al, 2019]: Vasilica Popescu, Dragos-George Astanei, Radu Burlica,
Andrei Popescu, Corneliu Munteanu, Florin Ciolacu, Mariana Ursache, Luminita
Ciobanu, Alexandru Cocean, Sustainable and cleaner microwave-assisted dyeing
process for obtaining ecofriendly and fluorescent acrylic knitted fabrics, Journal of
Cleaner Production (2019), doi: https://doi.org/10.1016/j.jclepro.2019.05.281
[Poulain et al, 2010]: G. Poulain, D. Blanc, A. Kaminski, B. Semmache, M. Lemiti,
Modeling of Laser Processing for Advanced Silicon Solar Cells, COMSOL
Conference 2010 Paris.
[Pouli et al, 2008]: P. Pouli, C. Fotakisa, , B. Hermosin, C. Saiz-Jimenez, C. Domingo,
M. Oujja, M. Castillejo, The laser-induced discoloration of stonework; a comparative
study on its origins and remedies, Spectrochim. Acta A 71 (2008) 932–945.
[Pouli et al, 2012]: P. Pouli, M. Oujja, M. Castillejo, Practical issues in laser cleaning
of stone and painted artefacts: optimisation procedures and side effects, Appl. Phys. A
106 (2012) 447–464.
[Prefetti et al, 1994]: Prefetti, B. M. Metal Surface Characteristics Affecting Organic
Coatings, Federation Series on Coating Technology, FSCT, Blue Bell, PA, 1994
[Rai et al, 2003]: A. K. Rai, F. Y. Yueh, and J. P. Singh, “Laser-induced breakdown
spectroscopy of molten aluminum alloy,” Applied Optics, vol. 42, no. 12, pp. 2078–
2084, 2003
[Rai et al, 2008]: N. K. Rai and A. K. Rai, “LIBS-An efficient approach for the
determination of Cr in industrial wastewater,” Journal of Hazardous Materials, vol.
150, no. 3, pp. 835–838, 2008
[Ralchenko et al, 2005]: Y. Ralchenko, “NIST atomic spectra
database,”MemorieDella Societa Astronomica Italiana Supplementi, vol. 8, p. 96,
2005
[Ravi Chandra Raju et al, 2009] N. Ravi Chandra Raju, K. Jagadeesh Kumar, A.
Subrahmanyam, Physical properties of silver oxide thin films by pulsed laser
78
deposition: effect of oxygen pressure during growth, J. Phys. D: Appl. Phys. 42 (2009)
135411, 2009
[Reddy et al]: J. N. Reddy, D. K. Gartling, The Finite Element Method in Heat Transfer
and Fluid Dynamics Third Edition, CRC Press ????
[Rogers et al, 2007]: E. Rogers, E. Gutierrez-Miravete, An Analysis of the Thermal
Effects of Focused Laser Beams on Steel, Proceedings of the COMSOL Conference
2007, Boston
[Rosen et al, 1986]: Milton J. Rosen, Joy T. Kunjappu, Surfactants and Interfacial
Phenomena, John Wiley & Sons, Inc. , Publications, Hoboken, New Jersey, 2012
[Rosenblatt, 1976]: Gerd M. Rosenblatt, Effect of incident flux on surface
concentrations and condensation coefficients when growth and vaporization involve
mobile surface species, Published by the American Institute of Physics, 1976, doi:
10.1063/1.432010
[Roylanceet al, 2001]: David Roylance, Finite Element Analysis, 2001
[Rühl et al, 2012]: M. Rühl, G. Dietrich, E. Pflug, S. Brau and A. Leson , Heat and
Mass Transfer in Reactive Multilayer System (RMS), COMSOL Conference 2012
Milan
[Sabbioni, 1995]: C. Sabbioni, Contribution of atmospheric deposition to the
formation of damage layers, Sci. Total Environ. 167 (1995) 49-55.
[Sadeghian Maryan et al, 2016] A. Sadeghian Maryan, M. Gorji, Synthesize of nano
silver using cellulose or glucose as a reduction agent: the study of their antibacterial
activity on polyurethan fibers, Bulgarian Chemical Communications, Volume 47,
Special Issue D, (pp. 151 – 155) 2016
[Sall´e et al, 2005]: B. Sall´e, D. A. Cremers, S. Maurice, and R. C. Wiens, “Laser-
induced breakdown spectroscopy for space exploration applications: influence of the
ambient pressure on the calibration curves prepared from soil and clay
samples,”Spectrochimica Acta Part B, vol. 60, no. 4, pp. 479–490, 2005;
[Sall´e et al, 2005]: B. Sall´e, D. A. Cremers, S. Maurice, R. C. Wiens, and P. Fichet,
“Evaluation of a compact spectrograph for in-situ and stand-off Laser-Induced
Breakdown Spectroscopy analyses of geological samples on Mars missions,”
Spectrochimica Acta Part B, vol. 60, no. 6, pp. 805–815, 2005
[Salthammer et al, 2016]: Tunga Salthammer, Formaldehyde in the Ambient
Atmosphere: From an Indoor Pollutant to an Outdoor Pollutant?, Angew. Chem. Int.
Ed. 2013, 52, 3320 – 3327, DOI: 10.1002/anie.201205984
[Sarkar et al, 2009]: A. Sarkar, V. M. Telmore, D. Alamelu, and S. K. Aggarwal,
“Laser induced breakdown spectroscopic quantification of platinum groupmetals in
simulated high level nuclear waste,” Journal of Analytical Atomic Spectrometry, vol.
24, no. 11, pp. 1545–1550, 2009
[Schlager et al, 2012]: Hans Schlager, Volker Grewe, Anke Roiger, Chemical
Composition of the Atmosphere, U. Schumann (ed.), Atmospheric Physics, Research
79
Topics in Aerospace, Springer-Verlag Berlin Heidelberg 2012, DOI: 10.1007/978-3-
642-30183-4_2
[Sedov et al, 1977]: L. Sedov, Similarity Methods and Dimensional Analysis in
Mechanics, Izdatel Nauka, Moscow, Russia, 1977
[Seifi et al, 2017]: Saman Seifi and Harold S Park, Electro-elastocapillary Rayleigh-
Plateau Instability in Dielectric Elastomer Films, DOI: 10.1039/C7SM00917H , Soft
Matter 13(23), May 2017
[Seshan, 2012]: K. Seshan, ed. (2012). Handbook of Thin Film Deposition (3rd ed.).
Amsterdam: Elsevier. ISBN 978-1-4377-7873-1
[Shameli et al, 2012] Kamyar Shameli, Mansor Bin Ahmad, Ali Zamanian, Parvanh
Sangpour, Parvaneh Shabanzadeh, Yadollah Abdollahi, Mohsen Zargar, Green
biosynthesis of silver nanoparticles using Curcuma longa tuber powder, International
Journal of Nanomedicine, 2012, http://dx.doi.org/10.2147/IJN.S36786
[Singh et al, 2007]: J. P. Singh, Laser-Induced Breakdown Spectroscopy, Elsevier
Science, 2007,
[Singh et al, 2014] Reena Singh, Sunil Kumar Sahu, and Muthusamy Thangaraj,
Biosynthesis of Silver Nanoparticles by Marine Invertebrate (Polychaete) and
Assessment of Its Efficacy against Human Pathogens, Journal of Nanoparticles,
Volume 2014, Article ID 718240, 7 pages, http://dx.doi.org/10.1155/2014/718240
[Smith et al, 2008]: J. N. Smith, M. J. Dunn, T. M. VanReken, K. Iida, M. R.
Stolzenburg, P. H. McMurry, and L. G. Huey, Chemical composition of atmospheric
nanoparticles formed from nucleation in Tecamac, Mexico: Evidence for an important
role for organic species in nanoparticle growth, GEOPHYSICAL RESEARCH
LETTERS, VOL. 35, L04808, Doi:10.1029/2007GL032523, 2008
[Stafe et al, 2008]: M. Stafe, I. Vladoiu, C. Negutu, I.M. Popescu, Experimental
investigation of the nanosecond laser ablation rate of aluminum, Rom. Rep. Phys.
60(3) (2008) 789-796.
[Stahl et al, 1986]: Neil Stahl and William P. Jencks, Hydrogen Bonding between
Solutes in Aqueous Solution, J. Am. Chem. SOC. 1986, 108, 4196-4205
[Stamenkovic et al, 2004]: Stamenkovic, J., Cakic, S., Konstantinovic, S., Stoilkovic,
S. ”Catalysis of the Isocyanate-Hydroxyl Reaction by Non-Tin Catalysts in Water
borne Two Components Polyurethane Coatings”, Working and living environmental
protection 2004, 2, 243-250
[Stull, 1972.]: Stull, D., in American Institute of Physics Handbook, Third Edition,
Gray, D.E., Ed., McGraw Hill, New York, 1972.
[Sweetman et al, Nature communications]: A.M. Sweetman, S.P. Jarvis, Hongqian
Sang, I. Lekkas, P. Rahe, Yu Wang, Jianbo Wang, N.R. Champness, L. Kantorovich
& P. Moriarty, Mapping the force field of a hydrogen-bonded assembly, NATURE
COMMUNICATIONS/ 5:3931 / DOI:
10.1038/ncomms4931/www.nature.com/naturecommunications
80
[Tango, 1968]: Tango, William J. (1968). "Spectroscopy of K2 Using Laser-Induced
Fluorescence". The Journal of Chemical Physics. 49 (10): 4264.
Bibcode:1968JChPh..49.4264T. doi:10.1063/1.1669869. ISSN 0021-9606
[Thompson et al, 1982]: Anne M. Thompson, Ralph J. Cicerone, Clouds and Wet
Removal as Causes of Variability in the Trace-Gas Composition of the Marine
Troposphere, Journal Of Geophysical Research, Vol. 87, No. C11, Pages 8811-8826,
October 20, 1982
[Torrisi et al, 2010]: L. Torrisi, F. Caridi, L. Giuffrida et al., “LAMQS analysis applied
to ancient Egyptian bronze coins,” Nuclear Instruments and Methods in Physics
Research, Section B, vol. 268, no. 10, pp. 1657–1664, 2010
[Trevizan et al, 2009]: L. C. Trevizan, D. Santos, R. E. Samad et al., “Evaluation of
laser induced breakdown spectroscopy for the determination of micronutrients in plant
materials,” Spectrochimica Acta Part B, vol. 64, no. 5, pp. 369–377, 2009
[Ursu et al, 2009]: C. Ursu, S. Gurlui, C. Focsa, G. Popa, Space- and time-resolved
optical diagnosis for the study of laser ablation plasma dynamics, Nucl. Instrum.
Meth. B 267 (2) (2009) 446-450.
[Ursu et al, 2010]: C. Ursu, O. G. Pompilian, S. Gurlui, P. Nica, M. Agop, M. Dudeck
and C. Focsa, Al2O3 ceramics under high-fluence irradiation: plasma plume dynamics
through space- and time-resolved optical emission spectroscopy, Applied physics a:
materials science & processing, Volume 101, Number 1, 153-159, (2010), DOI:
10.1007/s00339-010-5775-0
[Vadillo et al, 1999]: J. M. Vadillo, J. M. Fern´andez Romero, C. Rodr´ıguez, and J.
J. Laserna, “Effect of plasma shielding on laser ablation rate of puremetals at reduced
pressure,” Surface and Interface Analysis, vol. 27, no. 11, pp. 1009–1015, 1999,
[Vajdi Hokmabad et al, 2014]: B. Vajdi Hokmabad, S. Faraji, T. Ghaznavi Dizajyekan,
B. Sadri and E. Esmaeilzadeh, Electric field-assisted manipulation of liquid jet and
emanated droplets, Inernational Journal of Multi phase Flow, DOI:
10.1016/j.ijmultiphaseflow.2014.03.009, 31 March 2014
[Vosmanská et al, 2018] Vosmanská V, Kolářová K, Pišlová M, Švorčík V, Reaction
parameters of in situ silver chloride precipitation on cellulose fibres, Mater Sci Eng C
Mater Biol Appl. 2019 Feb 1;95:134-142. doi: 10.1016/j.msec.2018.10.070. Epub
2018 Oct 22, DOI: 10.1016/j.msec.2018.10.070
[Whitehouse et al, 2001]: A. I. Whitehouse, J. Young, I. M. Botheroyd, S. Lawson, C.
P. Evans, and J. Wright, “Remote material analysis of nuclear power station steam
generator tubes by laser-induced breakdown spectroscopy,” Spectrochimica Acta Part
B, vol. 56, no. 6, pp. 821–830, 2001
[Xia et al, 2015]: X. Xia, H. Che, J. Zhu, H. Chen, Z. Cong, X. Deng, X. Fan, Y. Fu,
P. Goloub, H. Jiang, Q. Liu, B. Mai, P. Wang, Y.Wu, J. Zhang, R. Zhang, X. Zhang,
Ground-based remote sensing of aerosol climatology in China: Aerosol optical
properties, direct radiative effect and its parameterization,
81
doi.org/10.1016/j.atmosenv.2015.05.071, 1352-2310/© 2015 Published by Elsevier
Ltd.
[Xuan et al, 2017]: Chen Xuan and John Biggins, Plateau-Rayleigh instability in solids
is a simple phase separation, Phys. Rev. E 95, 053106, 11 May 2017
[Yuan et al, 2013]: Yuehua Yuan and T. Randall Lee, Contact Angle and Wetting
Properties, Surface Science Techniques, Springer Series in Surface Sciences 51, DOI
10.1007/978-3-642-34243-1_1, Springer-Verlag Berlin Heidelberg 2013
[Zare, 2012]: Zare, R. N. (2012). "My Life with LIF: A Personal Account of
Developing Laser-Induced Fluorescence". Annual Review of Analytical Chemistry. 5:
1–14. Bibcode: doi:10.1146/annurev-anchem-062011-143148. PMID 22149473
[Zel’Dovich et al, 2002]: Y. B. Zel’Dovich and Y. P. Raizer, Physics of ShockWaves
and High-Temperature Hydrodynamic Phenomena, Dover, 2002
[Zeng et al, 2011] Jie Zeng, Jing Tao, Weiyang Li, Jennifer Grant, Phyllis Wang,
Yimei Zhu, Younan Xia, A Mechanistic Study on the Formation of Silver Nanoplates
in the Presence of Silver Seeds and Citric Acid or Citrate Ions, Chem. Asian J. , 6, 376
– 379, 2011, DOI: 10.1002/asia.201000728
[Zhang et al, 2010]: Li V. Zhang, Philippe Brunet, Jens Eggers, and Robert D. Deegan,
Wavelength selection in the crown splash, PHYSICS OF FLUIDS 22, 122105, 19
November 2010, doi:10.1063/1.3526743
[Zhang et al, 2014] Tong Zhang, Yuan-Jun Song, Xiao-Yang Zhang, Jing-Yuan Wu,
Synthesis of Silver Nanostructures by Multistep Methods, Sensors 2014, 14, 5860-
5889; doi:10.3390/s140405860
[Zhao et al, 2014]: F. Zhao, N. Zeng, Continued increase in atmospheric CO2 seasonal
amplitude in the 21st century projected by the CMIP5 Earth system models, Earth
Syst. Dynam., 5, 423–439, 2014, doi:10.5194/esd-5-423-2014
82
List of publications
1. ISI Papers
1. A. Cocean, V. Pelin, M. M. Cazacua,, I. Cocean, I. Sandu, S. Gurlui, F. Iacomi,
Thermal effects induced by laser ablation in non-homogeneous limestone covered by
an impurity layer, Appl. Surf. Sci. (2017),
http://dx.doi.org/10.1016/j.apsusc.2017.03.172 [AI = 0.671]
2. A. Cocean, I. Cocean, S. Gurlui, F. Iacomi, Study of the pulsed laser deposition
phenomena by means of Comsol Multiphysics, U.P.B. Sci. Bull., Series A, Vol. 79,
Iss. 2, 2017, [AI = 0.094]
3. A. Cocean, I. Cocean, M.M. Cazacu, G. Bulai, F.Iacomi, S. Gurlui, Atmosphere
self-cleaning under humidity conditions and influence of the snowflakes and artificial
light, Applied Surface Science 443 (2018) 83–90, DOI: 10.1016/j.apsusc.2018.02.156
[AI = 0.671] 4. I. Cocean, A. Cocean, V. Pohoata, F. Iacomi, S. Gurlui, City water pollution by
soot-surface-active agents revealed by FTIR spectroscopy, Applied Surface Science,
https://doi.org/10.1016/j.apsusc.2019.04.179 [AI = 0.671]
5. I. Cocean, A. Cocean, C. Postolachi, V. Pohoata, N. Cimpoesu, G. Bulai, F. Iacomi,
S. Gurlui, alpha keratin amino acids behvior under high fluence laser interaction.
Medical applications, Applied Surface Science 2019, DOI:
10.1016/j.apsusc.2019.05.207 [AI = 0.671]
6. V. Popescu, D. G. Astanei, R. Burlica, A. Popescu, C. Munteanu, F. Ciolacu, M.
Ursache, L. Ciobanu, A. Cocean, Sustainable and cleaner microwave-assisted dyeing
process for obtaining ecofriendly and fluorescent acrylic knitted fabrics, Journal of
Cleaner Production (2019), doi: https://doi.org/10.1016/j.jclepro.2019.05.281 [AI =
0.863]
I = 0.671 x 4 + 0.094 + 0.863 = 3.641
2. Conferences
1. A. Cocean, V. Pelin, M. M. Cazacu, S. Gurlui, F. Iacomi, Thermal doping
effect on the limestone under laser irradiation, 11th International Conference
On Physics Of Advanced Materials (ICPAM-11), Babes-Bolyai University
of Cluj-Napoca, Romania, from 8th to 14th of September, 2016 – Oral
presentation Alexandru Cocean
2. A. Cocean, S. Gurlui, F. Iacomi, Dual-Pulsed Laser Induced Non-Linear
Thermal Effects, 11th International Conference On Physics Of Advanced
Materials (ICPAM-11), Babes-Bolyai University of Cluj-Napoca, Romania,
from 8th to 14th of September, 2016 – Poster presentation Alexandru
Cocean 3. A. Cocean, I. Cocean, M. M. Cazacu,V. Pohoață, D. Pricop, S. Gurlui, F.
Iacomi, Effects of silver interaction with light over textile dyestuffs
chromophore groups in the reaction with hemp fabrics, International
83
Photocatalysis Workshop AdvPhotoCat-E2017, Heraklion, Greece. 14-16
July 2017 – Poster Presentation Alexandru Cocean
4. I. Cocean, A. Cocean, M. M. Cazacu, V. Pohoață, D. Pricop, D. Țîmpu, S.
Gurlui, F. Iacomi, Dyeing process for recovery of textile reactive dyestuffs
from wastewaters using photocatalytic ability of garnet and turquoise
gemstones, International Photocatalysis Workshop AdvPhotoCat-E2017,
Heraklion, Greece. 14-16 July 2017 – Oral presentation Iuliana Cocean
5. I. Cocean, A. Cocean, L. Cojocaru, V. Pohoata, N. Cimpoesu, G. Bulai, F.
Iacomi, S. Gurlui, Study of horn and wool keratin and shell chitosan PLD,
film properties and its effects on hemp fabrics, International Conference On
Physics Of Advanced Materials (ICPAM-12), Technological Educational
Institute of Crete, Heraklion, Greece, from 22nd of September to 28th of
September, 2018 – Poster presentation Iuliana Cocean
6. I. Cocean, A. Cocean, V. Pohoata, L. Cojocaru, F. Husanu, S. Gurlui, F.
Iacomi, Effect of soot – surface-active agents composites on air and water
pollution, International Conference On Physics Of Advanced Materials
(ICPAM-12), Technological Educational Institute of Crete, Heraklion,
Greece, from 22nd of September to 28th of September, 2018 - Oral
presentation Iuliana Cocean 7. A. Cocean, I. Cocean, L. Cojocaru, N. Cimpoesu, G. Bulai, F. Iacomi, S.
Gurlui, Damage threshold of special mirrors obtained by pulsed laser
deposition under high fluence irradiation. Experimental and theoretical
overview in COMSOL, International Conference On Physics Of Advanced
Materials (ICPAM-12), Technological Educational Institute of Crete,
Heraklion, Greece, from 22nd of September to 28th of September, 2018 – oral
presentation – Oral presentation Alexandru Cocean
2. Member in Research Projects
1. Extreme Light Induced Ablation Plasma Jet And Nano-patterning,
ELI-NP, CAPACITIES / RO-CERN E03/30.06.2014 (Project
Manager, Assoc. Prof. Habil. PhD Silviu Octavian GURLUI)
2. SATY: Satellite hybrid micro-thrusters, Romanian Space Agency
(ROSA), 2017- 2018 (Project Manager, Assoc. Prof. Habil. PhD
Silviu Octavian GURLUI), Position: Research Assistant
3. AiRFRAME: Aerosol properties retrieval from remote sensing
spectroscopic measurements (partner UAIC), (ROSA), 2017-2018
(Project Manager, Assoc. Prof. Habil. PhD Silviu Octavian
GURLUI), Position: Research Assistant
4. LEO: LOASL’s Earth Observatory, Romanian Space Agency
(ROSA), ID 499/2016-2017 (Project Manager, Assoc. Prof. Habil.
PhD Silviu Octavian GURLUI