17th technological plasma workshop · 12:00 – 12:20 black diamond as an antibacterial surface:...
TRANSCRIPT
17th Technological Plasma Workshop
Programme and Book of Abstracts
Theatre 8, Lounge North, Ricoh Arena, Coventry, UK
9th and 10th October 2019
Notes
There are more notes pages at the back of this booklet
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Contents
TPW Background
Conference Dinner Arrangements
Conference Schedule
Abstracts for Invited presentations
Abstracts for Contributed Presentations
Abstracts for Poster Presentations
TPW Background
The Technological Plasma Workshop (TPW) is principally a UK‐based international forum on the
science and technology of plasmas and gas discharges. Delegates from all countries are very
welcome to participate in this workshop.
Since the EPSRC Technological Plasma Initiative in 1997, technological plasmas have found
applications in diverse fields ranging from nano‐science energy, through biomedicine and
environment, to space exploration. They offer major collaboration opportunities for academic
and industrial communities and exciting career prospects for younger scientists and engineers.
To support a full realisation of these opportunities, TPW aims to foster academic‐industry
collaboration and to engage young plasma scientists with a scientific programme anchored by
leading plasma scientists. The workshop will comprise invited talks, contributed presentations
and a poster session.
In 2011, TPW became a conference of the Institute of Physics (IOP) Plasma Physics Group and
since 2014 TPW has been held in conjunction with the Vacuum Expo and the Vacuum Symposium.
The conference is currently sponsored by the IOP Plasma Physics Group.
Scientific Committee
Professor Adrian Cross
University of Strathclyde
Chairman
Dr Felipe Iza
Loughborough University
Co‐chairman
Professor Timo Gans
University of York
Dr Kirsty McKay
University of Liverpool
Dr Simone Magni
Edwards Limited, Clevedon, UK
Mr John Simmons
RF Services, UK
Organising Committee
Dr Felipe Iza
Loughborough University
Dr Alex Shaw
Loughborough University
Professor Adrian Cross
University of Strathclyde
Conference Dinner Arrangements
The conference dinner will be held at Café Rouge. A 3‐course meal is included in your conference
registration. If you have not registered for this and wish to attend the dinner, then please speak
to one of the organising committee as soon as you can. You have already chosen your menu
choices in your registration. Red and white wine will be provided on the table, if you want more
drinks then please purchase these yourself.
The table is booked for 18:30.
Please make your own way from the conference venue to the restaurant, Café Rouge – Coventry,
Belgrade Plaza, Upper Well Street, Coventry, CV1 4BF.
If you have any problems getting to the restaurant then you can call the organising committee
on 07949 851738.
A number of transport options are available:
If you are driving then there are several car parks located close to the restaurant
Taxi‐ the address for the restaurant is Belgrade Plaza, Upper Well Street, Coventry, CV1
4BF
o www.allenstaxis.com or 02476 55 55 55
Bus‐ there is several buses that can get you to the restaurant. A google maps search is the
most efficient way of finding the next bus, however the 20, 20B or 48 gold bus routes go
from near the arena to near the restaurant.
Conference Schedule
Wednesday 9th October 2019
10:00 – 12:00 Registration, hang posters and visit Vacuum Expo
12:00 – 12:10 Welcome and opening remarks ‐ TPW Chairman, Adrian Cross
Session 1 Chair: Professor Adrian Cross, University of Strathclyde, UK
12:10 – 12:50 Characterization of Ablation Plasma in Pulsed Electron Beam Deposition
(invited)
Magdalena Nistor, National Institute for Lasers, Romania
12:50 – 13:10 Cross sections estimations for molecular collisions with electrons for FEBIP and
plasma processing
Maria Pintea, University of Kent, UK
13:10 – 13:30 Fault modelling in HVDC systems at different pressures
Igor Timoshkin, University of Strathclyde, UK
13:30 – 14:40 Coffee break and Visit Vacuum Expo
Session 2 Chair: Dr Felipe Iza, Loughborough University, UK
14:40 – 15:20 The Role of Diagnostics in Plasma Etch Reactors in Enabling the Information
Age (invited)
Alex Paterson, LAM Research, USA
15:20 – 15:40 Plasma deposition of ‘fluffy’ carbon aggregates as analogues for dust in space
Ionut Topala, IPARC, Romania
15:40 – 16:00 Turbulence‐induced entrainment in plasma jets
Mohammad Hasan, University of Liverpool, UK
16:00 – 17:00 Poster session (poster prize presentation – 16:30)
18:30 Conference dinner – Café Rouge, Upper Well St, Coventry, CV1 4BF
Thursday 10th October 2019
Session 3 Chair: Dr Mohammad Hasan, University of Liverpool, UK
09:00 – 09:20 Pseudospark plasma‐sourced sheet electron beam for the generation of high‐
power millimetre waves
Adrian Cross, University of Strathclyde, UK
09:20 – 19:40 Gas‐plasma jet interaction with liquids: modelling and experiments
Chinasa Ojiako, Loughborough University, UK
09:40 – 10:00 Study of Molybdenum Plasma by HIPIMS
Daniel Loch, Sheffield Hallam University, UK
10:00 – 11:00 Coffee break and visit Vacuum Expo
Session 4 Chair: Dr Simone Magni, Edwards Limited, UK
11:00 – 11:40 Plasma Techniques for Nanostructured Materials (invited)
Claudia Riccardi, University of Milano‐Bicocca, IT
11:40 – 12:00 Use of Atmospheric Pressure Plasma to Improve Solid Oxide Cell Performance
Ann Call, University of Sheffield, UK
12:00 – 12:20 Black Diamond as an antibacterial surface: interplay between chemical and
mechanical bactericidal activity
Paul May, University of Bristol, UK
12:20 – 12:40 Plasma‐driven Organic Synthesis: Waste‐free Epoxidation
Felipe Iza, Loughborough University, UK
12:40 – 13:50 Lunch, visit Vacuum Expo and Poster session (poster prize– 13:30)
Session 5 Chair: Professor Paul May, University of Bristol, UK
13:50 – 14:30 Chasing convergence: Plasma application at the nanoscale? (invited)
Geoff Hassall, Oxford Instruments, UK
14:30 – 14:50 Increasing control of electron, ion and neutral heating in radio‐frequency
hollow cathode microthrusters
James Dedrick, University of York, UK
14:50 – 15:00 Closing remarks – TPW Chairman, Adrian Cross
15:00 Depart
Posters
P1 A helicon plasma apparatus for fundamental wave‐plasma experiments
Kevin Ronald, University of Strathclyde, UK
P2 Metrology for in‐situ industrial plasma processing
Michael Mo, University of York, UK
P3 Atmospheric pressure microplasma as synthesis method for nitrogen doped
carbon quantum dots applied to third‐generation solar cells
Slavia Deeksha Dsouza, Ulster University, UK
P4 Time resolved electron properties measured by laser Thomson scattering in a
HiPIMS plasma
Marcus Law, University of Liverpool, UK
P5 Plasma‐driven epoxidation using a He+O2 atmospheric pressure COST plasma
jet
Han Xu, Loughborough University, UK
P6 An integrated microfluidic chip for generation and transfer of reactive species
using gas plasma
Oladayo Ogunyinka, Loughborough University, UK
P7 Plasma cathode electron beam for high‐integrity materials processing
Andrew Sandeman, TWI, UK
P8 Enhanced Fuzzy Tungsten Growth in the Presence of Tungsten Deposition
Patrick McCarthy, University of Liverpool, UK
P9 Investigation of a Capacitively Coupled RF Allylamine Discharge
Michael Barnes, University of Liverpool, UK
P10 Power controlled Atmospheric‐pressure Plasma Treatment System
Junchen Ren, Loughborough University, UK
P11 Electro carboxylation of Alkene with Carbon Dioxide in the presence of Plasma
Muhammad Shaban, Loughborough University, UK
P12 Microwave emission due to kinetic instabilities in an over‐dense mirror‐
confined plasma
Kevin Ronald, University of Strathclyde, UK
Technological Plasma Workshop 2019
Abstracts for Invited Presentations
Characterization of Ablation Plasma in Pulsed Electron Beam Deposition
M. Nistor, F. Gherendi and N.B. Mandache
National Institute for Lasers, Plasma and Radiation Physics (NILPRP),
Plasma Physics and Nuclear Fusion Laboratory,
P.O.Box MG‐32, 077125, Bucharest‐Magurele, Romania
The field of oxide thin films has a rapid growth driven by the demand for a wide range of
applications in photovoltaics, optoelectronics, energy, nanotechnology. In particular, thin
films made from transparent conducting oxides are used for solar cells, touch screens
sensors, light emitting diodes, flat panel displays and smart windows due to their high
electrical conductivity and high transparency in the visible spectral range. Satisfying these
competing demands is challenging but technological plasmas are ideally placed in this field
due to the processes involved that can be carefully tailored to the specific application.
The pulsed electron beam deposition (PED) is a low‐cost plasma technology for the
deposition of stoichiometric, smooth, amorphous or crystalline oxide thin films with tunable
physical properties [1‐3]. PED has features in common with the pulsed laser deposition but
uses a pulsed electron beam instead of a laser beam for ablating a target material and
formation of a plasma plume that mediates the growth of thin films on substrates at around
10‐2 mbar gas pressure. The knowledge about the propagation of the ablation plasma plume
is crucial due to the influence of the kinetic energy and density of the species emitted from
the target over the quality of the films (composition, structure, surface morphology and
physical properties).
Langmuir probes have been widely used for investigation of the nanosecond laser ablation
plume in different gases [4]. In this work we report on the plasma plume characterization by
Langmuir probes during ablation of an oxide target in PED. The probe was placed in the
substrate position at various distances to the target and the measurements were performed
in the same working conditions as those used for the thin film deposition. From the current‐
voltage probe characteristics the electron temperature and the electron density were
determined as function of the gas pressure and pulsed electron beam parameters. The
probe signals were recorded with temporal resolution at different bias voltages and used for
determining the ion energy by the time of flight method. These results are discussed in the
frame of existing models for ablation plasmas. A correlation between the morphological,
structural and functional physical properties of oxide thin films and kinetic energies of the
plasma species is also presented. Some examples include undoped and doped zinc oxide
and indium oxide thin films with tunable physical properties.
[1] M. Nistor, N.B. Mandache, J. Perrière, J. Phys. D: Appl. Phys. 41, 165205 (2008) [2] M. Nistor, L. Mihut, E. Millon, C. Cachoncinlle, C. Hebert, J. J.Perrière, RSC Adv. 6, 41465‐41472 (2016) [3] M. Nistor, F. Gherendi, J. Perrière, Mater. Sci. Semicond. Process. 88, 45 (2018) [4] B. Doggett, J.G. Lunney, J. Appl. Phys. 105, 033306 (2009)
The Role of Diagnostics in Plasma Etch Reactors in Enabling the Information
Age
Alex Paterson1, Saravanapriyan Sriraman1, John Holland1, Harmeet Singh1, Vahid Vahedi1
1Lam Research Corp
Over the last decade, semiconductor industry growth has been driven chiefly by the demand
for consumer electronics and the advent of the data economy: the move to mobile smart
devices such as phones and tablet PC’s and the proliferation of Artificial Intelligence. It is
now common place for hand‐held mobile devices to have 512 Gb of memory and processor
speeds of over 2 GHz, a truly remarkable feat that would have been unthinkable 10 years
ago. This capability has been enabled by the continuation of IC scaling to smaller and
smaller features sizes with the present technology being mass produced by 14 nm node
technology and smaller nodes down to 3 nm currently being developed by IC
manufacturers. For example, the latest Apple® iPhone® 11 uses an A13 Bionic CPU with 8.5
billion transistors fabricated with 7nm technology. The limitations of lithography to keep up
with the decrease in dimensions required for these smaller nodes has resulted in new
challenges for plasma etch to enable patterning at these small feature sizes. Device
performance requirements also drive critical dimension (CD) non‐uniformity to less than
one nanometre across the entire 300 mm wafer for sub‐20 nm features and yield
requirements extend this pattering region to within 1.5 mm of the wafer edge. Wafer
fabrication production also relies on plasma etch solutions to be stable at these levels across
long periods of time and capable of flexibility in multiple applications. The realization of all
of these goals has been greatly facilitated by a much better understanding of the basic
chemical, physical, and electromagnetic processes that occur during the plasma etch of
semiconductor devices.
In this paper we will discuss the crucial role diagnostics play in achieving this understanding
and in the development of state‐of‐the‐art plasma etch chamber technology that allow the
continuation of Moore’s Law. Diagnostics are essential not only to understand etch
mechanisms and chamber characteristics but to also accelerate hardware development in
order to meet customer time critical needs. We will review the different types of diagnostics
commonly used in plasma etch chamber development with reference to findings from
literature and augment this with diagnostic work undertaken at Lam Research. Finally, we
will discuss the suitability of diagnostics in main stream production and give some thoughts
on future diagnostics that may be required for production enhancement and angstrom level
etching.
Plasma Techniques for Nanostructured Materials
Claudia Riccardi Dept of Physics University of Milano‐Bicocca
Nanostructured materials are revolutionizing many fields of science and technology and are finding
their way in many commercial products. Their interest is due to the fact that nanostructured films
present functional (tribological, biological, electrical, optical) properties which are new, or of
superior quality, compared to nonnanostructured ones.
Indeed, plasma sources are essential for the synthesis of new molecules yielding very high purity
materials, allowing in addition the control of formation and transport of the synthesized building
blocks for the nanofabrication of thin layers and multilayer composited films, as well as the synthesis
of nanoparticles (NPs). A large variety of nanostructured materials and their applications have been
already demonstrated in different fields. So far, plasma‐based methods have been employed for the
precursor dissociation, the most relevant of which is the expanding thermal jet (1995) enabling
purity control of the growth process, and more recently, the Pulsed Laser Deposition (PLD)
technique working at ultra‐high vacuum has been developed to control both purity and
nanostructured morphology. A novel technique was designed to assemble high purity materials at
the nanoscale over a larger area and higher flexibility, allowing to work with many kind of chemicals,
and less severe operational conditions due to the possibility of working at higher pressures. The
method is based on a non‐thermal supersonic plasma jet where independent control over plasma
chemistry, dissociation and molecule aggregation, nanoparticle assembly and film growth, are
achieved by fluidodynamic segregation of the two processes in a unique remote plasma
configuraton. The method for producing nanostructured films and NPs with controlled morphology,
particularly of a hierarchically organized type, is suitable to a scale‐up for industrial processing. The
technique denominated
Plasma Assisted Supersonic Jet Deposition (PA‐SJD) is the segmentation of the gas phase material
synthesis in two separate steps: Chemistry control in a reactive cold plasma environment of several
precursors; and secondly, nucleation and assembling of the building blocks by means of a supersonic
inseminated plasma jet where particle collisions can be controlled. The former is performed in a
vacuum chamber where a gas or vaporizable precursor is employed as the source of nanosize seeds
by a non‐thermal plasma. In a second, lower pressure chamber, the plasma expands into a
supersonic jet containing seeds of NPs. By acting on the jet parameters, the active control of the
synthesis of NPs is able to produce cluster sizes varying from few nm to 100 nm, as well as their
assembling in an organized nanostructure on a given substrate with the desired film porosity. The
deposition rate of thin films ranges from 10 nm/min up to about 500 nm/min. By operating with two
plasma jet sources simultaneously it was also possible to produce NPs shells of different oxides and
to deposit multicomponent thin films. These nanomaterials (NPs and films) have a broad range of
applications in diverse fields such as photovoltaics, photoelectrochemistry, energy storage,
photonics and biomedicine.
E.Dell’Orto, S.Caldirola, A.Sassella, V.Morandi, C. Riccardi (2017), “Growth and properties of nanostructured titanium dioxide deposited by supersonic plasma jet deposition” Applied Surface Science 425 (2017) ‐407‐415
Chasing Convergence: Plasma application at the nano‐scale?
Hassall G
Oxford Instruments Plasma Technology, North End, Yatton, Bristol
This year, Oxford Instruments (OI) celebrates its 60th birthday. In the years since it was
founded, we have seen an extraordinary development of technology that to many is still in
the realms of science fiction. Oxford Instruments Plasma Technology (OIPT) has been part of
the OI story for over 30 years and provides compound semiconductor processing tools and
expertise to a broad range of sectors. In support of the demands of our customers,
companies like ours must adapt our technology and understanding of the interaction of
plasma and surfaces to enable the creation of devices that continue to push performance
limits.
The inspiration for this talk came from the diagram shown below, first published over a
decade ago. It illustrates the idea that we have been approaching a convergence of
previously disparate scientific disciplines to bring about a very real industrial revolution that
will impact everyone in one way or another. The suggestion is that the nature of the
semiconductor manufacturing world we inhabit today is changing and indicates the source
of many of the future issues we must consider to adequately address the needs of our
Customers in the decades to come. There are clear examples that tell us the convergence is
happening now. From the plasma perspective, we have seen a growth in the importance of
“surface‐driven” process technology in contrast to conventional “flux‐driven” systems. This
change has become a significant enabler in supporting this convergence.
Figure 1. Convergence is happening now. This graphic is from a paper by Uwe [1].
In this talk, conventional surface processing is reviewed (briefly) to provide the context for
how processing has evolved at the nanoscale. We will look at how these techniques must be
adapted to meet the requirements of modern production‐driven process technology.
[1] Uwe B. Sleytr (2006). NANOBIOTECHNOLOGY, An Interdisciplinary Challenge. Center for NanoBiotechnology, Vienna.
Technological Plasma Workshop 2019
Abstracts for Contributed Presentations
Cross sections estimations for molecular collisions with electrons for FEBIP
and plasma processing
1Maria Pintea, 1,2Nigel Mason and 3Maria Tudorovskaya 1School of Physical Sciences, University of Kent, Canterbury, CT2 7NH, UK, 2School of Physical
Sciences, The Open University, Milton Keynes, MK7 6AA, UK, 3Quantemol Ltd, London, UK
Characterized by the dissociative ionization phenomenon, the fragmentation of the
molecules in the molecular collisions with electrons, is determined from the reaction rates
and cross sections, the proximity, the incident electron energies and kinetic energies of the
molecules.
Irradiation induced chemistry is one of the most important processes in the new
developments in nanotechnology with application to focused electron beam induced
deposition (FEBID) and Extreme Ultraviolet Lithography (EUVL). The challenges in this newly
adapted techniques for induced chemistry of molecules on particular substrates, come with
the creating high purity high metal content structures of certain shapes, heights, widths.
Correlation between gas phase studies with ultra‐high vacuum surface science bring to FEBID
information for the designing of new precursors and deposition parameters optimization for
the processes induced by low‐energy electrons such as dissociative electron attachment,
dissociative ionization, neutral dissociation and dipolar dissociation.
Quantemol‐N was employed to study and determine the effects on the molecules at certain
energy ranges. The simulations were run on molecules such as Fe(CO)5, Co(CO)3NO for FEBID
applications and CH4, CF4 and SF6 for plasma processing at low electron energies, 0 ‐ 25eV.
With the use of Quantemol‐N simulation package, information on collision processes of low‐
energy electrons with Fe(CO)5 molecules and the interaction processes governing this
reactions, such as elastic cross‐sections, electronic excitation cross‐sections, electron impact
dissociation, scattering reaction rate, rotational excitation cross sections to dissociative
electron attachment (DEA) is presented. [2], [3]
[1] A V Solov’yov et al, Eur. Phys. J. D (2016) 70 [2] J R Hamilton et al, Plasma Sources Sci. Technol. 27 (2018) 095008 [3] J R Hamilton et al, Plasma Sources Sci. Technol. 26 (2017) 065010 [4] Z Wang et al, Applied Surface Science 257 (2011) 9082‐9085 [5] Resnik et al, Materials 2018, 11, 311 [6] Laricchiuta et al, Plasma Phys. Control Fusion 61 (2019) 014009 [7] John B Boffard et al, 2004, J. Phys. D: Appl. Phys. 37 R143 [8] Yoon et al, J Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010 [9] Ingolfsson et al, Beilstein J. Nanotechnol. 2015, 6, 1904‐1926 [10] van Dorp et al, J. Appl. Phys. 104, 081301 (2008)
Fault modelling in HVDC systems at different pressures
I. Timoshkin1, M. P. Wilson1, S. J. MacGregor1,
N. Bonifaci2, R. Hanna2
1Department of Electronic and Electrical Engineering, University of Strathclyde,
204 George Street, Glasgow, UK 2G2Elab, 21 rue des Martyrs, Grenoble, France
The development of advanced transportation systems such as electric vehicles and more electric aircraft requires electrical insulation that can operate in low pressure, high humidity, environments, and over a wide range of temperatures. The use of high DC voltages in electrical avionic systems serves to minimise conduction losses and to achieve transmission of increased power levels over longer distances. Correspondingly the diameter and therefore the weight of wires and cables used in aircraft could be reduced, which is an important factor for the aero‐space industry. It is recognised that with higher electric stress, damage to dielectric materials providing electrical insulation within harsh environmental operating conditions may result in failure of the electrical system. Thus, insulation coordination in more electric aircraft is critical to avoid catastrophic damage of their electrical systems.
The work reported in the present paper, investigates the electric field distribution around undamaged electrical wiring and around wiring with “soft” faults and is used in the analysis of gas discharge and breakdown processes, at lower pressures relevant to avionic applications. This analysis will underpin an insulation coordination strategy, which will be used to enable the optimisation of avionic insulation systems.
Acknowledgement This work is supported by The British Council‐Alliance Hubert Curien Programme
Plasma deposition of ‘fluffy’ carbon aggregates as analogues for dust in space
I.C. Gerber1, I. Mihaila2, L.V Soroaga2,3, A. Chiper1, V. Pohoata1, I. Topala1 1Faculty of Physics, Iasi Plasma Advanced Research Center (IPARC); 2Integrated Center of
Environmental Science Studies in the North‐Eastern Development Region (CERNESIM); 3Faculty of Chemistry, Alexandru Ioan Cuza University of Iasi, Carol I No. 11, Iasi, Romania
Various physico‐chemical methods have been developed to deposit carbon and silicon based
materials as analogues for dust in space: condensation, physical vapour deposition, plasma
enhanced chemical vapour deposition, combustion and pyrolysis, pulsed laser deposition. We
discuss in this paper a new plasma method, based on high power impulse dielectric barrier discharge
in helium and hydrocarbon gas mixtures, to obtain at low temperature carbon dust analogues, in
form of both non‐aromatic thin films and ‘fluffy’ aggregates.
The carbon interstellar dust analogues were deposited using a dielectric barrier discharge, hosted by
a stainless steel chamber. The dielectric barrier discharge uses a 5 mm gas gap, and nanosecond high
voltage pulses are used to excite the plasma (positive pulses of 7 kV amplitude, 1 kHz frequency and
500 ns duration), in gas mixture of He (85%) ‐ Hydrocarbons (15%, methane, butane) at 600 Torr , for
6 hours.
The samples obtained from this deposition process, presented in Fig. 1, are composed out of
inhomogeneous carbon aggregates, incompletely covering the substrates. Microscopic voids visible
at mesoscale and a large internal surface area, were observed during the scanning electron
microscopy investigations, using various magnifications and regions of the sample.
The 3.4 micron feature (assigned to aliphatic −C−H stretching band), as well the CH2/CH3 ratio and
the H/C value show a variability that is influenced by synthesis method, the pulsing regime and the
experimental parameters of a specific technique [1‐4].
The dielectric barrier discharge in helium and hydrocarbon gas mixtures is a new method suitable for
low temperature deposition of carbon dust analogues. The ‘fluffy’ carbon aggregates exhibits
morphological features of recent observations of interplanetary, asteroidal and cometary dust. The
spectroscopic features of the carbon dust analogues are in good agreement with observational data
for sources presenting high column density of sp3 hybridized carbon atoms (Sgr A*, IRAS
08572+3915, IRAS 19254–7245, NGC 1068 and NGC 5506).
[1] Hodoroaba B, Gerber IC, Ciubotaru D, Mihaila I, Dobromir M, Pohoata V, Topala I, “Carbon fluffy aggregates produced by helium ‐ hydrocarbon high pressure plasmas as analogs to interstellar dust”, Mon Not R Astron Soc, 481, 2, pp. 2841‐2850 (December, 2018).
[2] Mennella V, Brucato JR, Colangeli L, Palumbo P, “CH bond formation in carbon grains by exposure to atomic hydrogen: The evolution of the carrier of the interstellar 3.4 micron band”, Astrophys J, 569, 1, pp. 531 (April, 2002)
[3] Peláez RJ, Maté B, Tanarro I, Molpeceres G, Jiménez‐Redondo M, Timón V, Escribano R, Herrero VJ, “Plasma generation and processing of interstellar carbonaceous dust analogs”, Plasma Sources Sci Technol, 27, pp. 035007 (March 2002)
[4] Godard M, Féraud G, Chabot M, Carpentier Y, Pino T, Brunetto R, Duprat J, Engrand C, Brechignac P, d’Hendencourt L, Dartois E, “Ion irradiation of carbonaceous interstellar analogues ‐ Effects of cosmic rays on the 3.4 μm interstellar absorption band”, Astron Astrophys Suppl Ser, 529, pp. A146 (May, 2011)
Turbulence‐induced entrainment in plasma jets
Y. Morabit1, M. I. Hasanoror1, R. D. Whalley2, and J. L. Walsh1
1 Centre for Plasma Microbiology, Department of Electrical Engineering and Electronics,
University of Liverpool, L69 3GJ, United Kingdom
2 School of Mechanical and Systems Engineering, Newcastle University, NE1 7RU, United
Kingdom [email protected]
Low temperature atmospheric pressure plasma jets generate a highly reactive and targeted
stream of chemical species that have found application in a number of materials processing
and healthcare applications. Understanding the complex interactions between the discharge
and the downstream gas is the key to understanding and potentially controlling how
reactive species are produced and transported to a downstream sample. One aspect of such
interactions is the onset of turbulence when the plasma is ignited in a laminar helium jet,
which significantly changes the gas composition downstream, thus altering the generated
mixture of chemical species [1,2].
In this investigation, particle imaging velocimetry (PIV), laser induced fluoresce (LIF) and
numerical modelling were used to provide quantitative insights into the air’s entrainment in
the helium jet as a result of the plasma‐induced turbulence. Utilising statistical analysis of
PIV velocity profiles and numerical modelling, it was possible to quantify the entrainment of
air in the helium jet for different plasma powers. LIF was subsequently used to confirm this
quantification by detecting the variation of OH density. It is shown that air entrainment not
only occurs in the turbulent region of the jet, but also in its laminar region. Moreover, it is
shown that an increase in the plasma power results in a larger entrainment and a higher
density of OH due to entrained water vapour. Ultimately it is shown that the plasma‐
induced shear layer perturbations were the dominant mechanism of air entrainment in the
laminar region of the plasma jet.
[1] Li et al. (2009) Applied Physics Letters 95, 141502 [2] R D Whalley et al (2016) Scientific Reports 6, 31756
Pseudospark plasma‐sourced sheet electron beam for the
generation of high power millimetre waves
A.W. Cross1, L. Zhang1, C.R. Donaldson1, J. Xie2, H. Yin1, J. Zhang3, X. Chen3, Yasir Alfadhl3 J. Zhao3, K. Ronald1 and A. D. R. Phelps1
1Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 ONG, UK 2School of Electronic Science and Engineering, University of Electronic Science & Technology of China,
Chengdu, 610054, China 3Department of Electronic Engineering, Queen Mary University of London, London, UK
4School of Electrical Engineering, Xi’an Jiaotong University, Xi’an, 710049, China
A plasma‐sourced sheet electron beam generated by a pseudospark (PS) discharge is presented. The advantages
of using a PS discharge to generate an electron beam includes: high current density, ion‐channel assisted beam
focusing, long life and simplicity with no external guiding magnetic field needed for beam transportation. A
pseudospark‐sourced sheet electron beam of dimensions: 2.0mm x 0.25mm in size with peak current in the
range of 20‐30A (~104 A/cm2 beam current density) and peak voltage of ~32 kV was successfully measured after
propagating a distance of 10‐mm without the need of an external focusing magnetic field.
A PS discharge basically evolves through three stages, 1) Townsend discharge; 2) hollow cathode discharge; 3)
final conductive stage [1]. Electron beams with moderate beam current and high energy can be obtained in the
second hollow cathode stage for direct applications. The beam current reaches its maximum in the final
conductive discharge stage, while the beam energy rapidly decreases due to the breakdown between the gaps.
Post‐acceleration of the PS beam generated can result in a desirable beam of combined high beam current and
energy.
As shown in Fig.1, the PS sheet beam generation consisted of a pseudospark discharge section and a post‐
acceleration unit [2]. Attached with the anode is a collimator disc with slot dimensions to form a sheet beam,
Fig 2. Because of the gas background in the beam drifting area, a high energy beam front from the second hollow
cathode stage would ionize the gas along its path to form an ion‐channel for later beam electrons to propagate.
Therefore, there is no need for an external guiding magnetic field for beam transportation. Recent results on
the use of a sheet electron beam to produce high power millimetre wave radiation will be presented [3].
Figure 2 Pseudospark plasma‐sourced sheet electron beam generation experiment
Figure 2 Cross section image of the sheet beam of
2.0 mm×0.25 mm
[1] Frank, K., Boggasch, E., Christiansen, J., et al.: IEEE Trans. Plasma Sci., 1988, 16, (2), pp. 317‐323. [2] J. Zhao, H. Yin, L. Zhang, G. Shu, W. He, Q. Zhang, A. D. R. Phelps, and A. W. Cross, Phys. Plasmas 24,
023105 (2017). [3] Yin H., Zhang L., Xie J. et al, IET Microwaves, Antennas & Propagation, March 2019
Beam shape
Correspond to
Gas‐plasma jet interaction with liquids: modelling and experiments
Chinasa J. Ojiako1,2, Hemaka Bandulasena2, Roger Smith1, Dmitri Tseluiko1 1Department of Mathematical Sciences, Loughborough University, Loughborough, LE11 3TU,
UK, 2Department of Chemical Engineering, Loughborough University, Loughborough, LE11 3TU,
Gas‐plasma interactions with liquids find applications in industries and medicine. We aim to model the interaction of an air‐plasma jet with a liquid accounting for hydrodynamics, electro‐hydrodynamics and chemical kinetics. This involves the calculation of the deformation of the surface of the liquid and flows generated in the gas and in the liquid [1], the rate at which the generated long‐lived plasma species are transferred to the liquid as well as the associated chemical reactions. When a plasma strikes a liquid, there is also an associated electric field and the plasma itself can also be quite hot. These two effects are decoupled and analysed separately. We start by using the generated long lived plasma species [2,3] determined from experiment as the initial conditions for the plasma jet striking a liquid surface and quantify the plasma species that are transported into the liquid and the rates of chemical reactions, taking into account the motion of the fluid. The problem is solved using the Computational Fluid Dynamics package in COMSOL and the numerical results are compared with experiments. [1] C.J.Ojaiko et al, Deformation of Liquid Film by an impinging Gas Jet: Modelling and Experiments, Proceedings of the 6th International Conference on Fluid Flow, Heat and Mass Transfer (FFHMT’19). Avestia Publishing FFHMT 171. [2] Z. C. Lui et al, Physicochemical processes in the indirect interaction between surface air plasma and deionized water, J. Phy. D: Appl. 48, 495201 [3] A. Wright et al, Microbubble‐enhanced DBD plasma reactor: Design, characterisation and modelling, Chem. Eng. Research & Design, 144, 159‐173
Study of Molybdenum Plasma by HIPIMS
Daniel A. L. Loch, Arutiun P. Ehiasarian
HIPIMS Technology Centre, Sheffield Hallam University, Sheffield, UK,
Molybdenum is a good candidate as back contact for CIGS cells, due to the appropriate bandgap, low
resistivity and good reflectivity of Mo thin films. Compared to conventional PVD processes, HIPIMS
offers more control over the thin film properties due to the metal ion dominated plasma. The
behaviour of gas species and their influence on the coating properties is not well understood.
A complete understanding of the HIPIMS plasma can support the tailoring of better‐performing back
contacts.
In this study we report the findings of the plasma being analysed by current‐voltage (I‐V) waveform
evaluation, time‐resolved plasma sampling energy‐mass spectroscopy and optical emission
spectroscopy. A voltage‐pulse time matrix was devised varying the voltage from 800 ‐ 1500V and the
pulse time was increased from 60 ‐ 1000μs in 5 steps. Processes were operated at 0.22Pa and 0.44Pa.
The increase and drop of the current within the pulse resulted in a change in Ar2+/Ar1+ flux. Mass
spectroscopy measurements were taken half‐way through the pulse. The Ar1+ IEDF exhibits a low
energy peak representing thermalised ions at 1.5eV. With increasing pulse time, the peak intensity
increases by 2 orders of magnitude and a higher energy tail up to 15eV develops. Ar2+ IEDF displays a
broad peak between 5‐15 eV, with a higher energy tail to 25eV. With increasing pulse time the tail
disappears and the peak reduces by an order of magnitude (Fig.2). The ratio of the Ar2+/Ar1+ intensity
is larger for shorter pulses and higher currents, and reduces with increasing pulse time where the
current reduces to a plateau. This indicates that due to gas rarefaction in the beginning of the pulse,
a significant fraction of double‐charged gas ions is created that can sustain high currents and higher
sputter rates on account of the higher charge and energy of bombardment.
To get further insight into the excited atom evolution with pulse time and voltage, we will also be
discussing the OES results. The presented results reveal new details of the gas rarefaction process and
illustrate the control potential for HIPIMS plasma in support of the development of better performing
back contacts.
Figure 1 IEDF's of Ar1+ at 800V and 0.22Pa for
pulse widths of 60‐1000µs.
Figure 2 IEDF's of Ar2+ at 800V and 0.22Pa for
pulse widths of 60‐1000µs.
Keywords: HIPIMS, Plasma Analysis, CIGS, Back contact
Use of Atmospheric Pressure Plasma to Improve Solid Oxide Cell Performance
Ann V. Call1, Thomas D. Holmes1, Pratik D. Desai2, William B. Zimmerman1,
Rachael H. Rothman1
1The University of Sheffield, Sheffield, United Kingdom
2 Perlemax, Sheffield, United Kingdom
The reduction in carbon emissions required to meet the 2°C scenario (2DS) and the resultant
necessary decarbonisation of energy generation require an increased focus on renewable
energy sources. Solid Oxide Cells (SOCs) are widely seen as a leading technology for future
clean power generation and chemicals production, whether operated in fuel cell (SOFC) or
electrolysis (SOEC) mode. However, SOCs have a number of performance limitations,
including the energy associated with dissociative ionisation and the comparatively low
density of reaction sites to facilitate this process. Improvements can typically be made via
surface catalysis, but this in turn is limited by the cost and scarcity of catalysts, typically
comprised of precious or rare earth metals.
Improvements to cell geometry and composition have been used to incrementally improve
performance, however increasing performance through the incorporation of atmospheric
pressure plasma (APP) sources has the potential to reduce the operating cost of the system
by removing the need for costly catalysts and increasing the density of available ions. The
ability of APP’s to enable high temperature chemistry to occur at low bulk gas temperatures
offers a higher efficiency option for providing the necessary activation energy for ion
formation by dissociation. Applied specifically to CO2 plasmas, this has the potential to
improve the efficiency of SOC’s to form O2‐ ions from CO2. As part of this work, a novel
bespoke rig was used to combine electrocatalysis and atmospheric pressure CO2 plasma.
The experimental design and progress to date will be covered.
Black Diamond as an antibacterial surface: interplay between chemical and
mechanical bactericidal activity
May, P.W. 1, Dunseath, O.1, Smith, E.J.W.1, Al‐Jeda, T.1,
Smith, J.A.1, Nobbs, A.2, Hazell, G.2 & Welch, C.C.3
1School of Chemistry, University of Bristol, Bristol, U.K.
2Bristol Dental School, University of Bristol, Bristol, U.K.
3Oxford Instruments Plasma Technology, Yatton, Bristol, U.K.
‘Black silicon’ (bSi) samples with surfaces covered in nanoneedles of length ~5 μm were fabricated
using a plasma etching process and then coated with a conformal uniform layer of diamond using
hot filament chemical vapour deposition to produce ‘black diamond’ (bD) nanostructures1,2. The
diamond needles were then chemically terminated with H, O, NH2 or F using plasma treatment, and
the hydrophilicity of the resulting surfaces were assessed using water droplet contact‐angle
measurements.
The effectiveness of these differently terminated bD needles in killing the Gram‐negative bacterium
E. coli was semi‐quantified by Live/Dead staining and fluorescence microscopy, and visualised by
SEM (see Fig.1). The total number of adhered bacteria was consistent for all the nanostructured bD
surfaces at around 50% of the value for the flat diamond control. This, combined with a chemical
bactericidal effect of 20‐30%, shows that the nanostructured bD surfaces supported significantly
fewer viable E. coli than the flat controls.
The bD surfaces were particularly effective at preventing the establishment of bacterial aggregates –
a precursor to biofilm formation. The percentage of dead bacteria also decreased slightly as a
function of hydrophilicity, with superhydrophobic F‐terminated bD killing 50% of the adherent
bacteria. These results are consistent with a predominantly mechanical mechanism for bacteria
death based on the stretching and disruption of the cell membrane, combined with a smaller
additional effect from the chemical nature of the surface.
Figure 3. An E. coli bacterium lying uncomfortably on top of a black diamond needle surface.
[1] P.W. May, M. Clegg et al., "Diamond‐coated ‘black silicon’ as a promising material for high‐surface‐area electrochemical electrodes and antibacterial surfaces", J. Mater. Chem. B. 4 5737‐5746 2016.
[2] G. Hazell, P.W. May, P. Taylor, A.H. Nobbs, C.C. Welch, B. Su, "Studies of black silicon and black diamond as materials for antibacterial surfaces", Biomater. Sci. 6 1424‐1432 2018.
[3] O. Dunseath, E.J.W. Smith, T. Al‐Jeda, J.A. Smith, S. King, P.W. May, A.H. Nobbs, G. Hazell, C.C. Welch, B. Su, "Studies of Black Diamond as an antibacterial surface for Gram Negative bacteria: the interplay between chemical and mechanical bactericidal activity", Sci. Rep. 9 (2019) 8815.
Plasma‐driven organic synthesis: Waste‐free epoxidation
Xu H1,3, Wang S1,3, Shaban M1, Montazersadgh F1, Alkayal A2, Liu DX3, Kong MG3,
Buckley BR2, Iza F1 1Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough
University, Leics. LE11‐3TU; 2 Dept. Chemistry, Loughborough University, Leics. LE11‐3TU; 3
Center for Plasma Biomedicine, Xi’an Jiaotong University, Xi’an 710049, P. R. China
Advancements in non‐thermal plasmas operating at atmospheric pressure have made possible novel
processing of liquids that were not conceivable in conventional vacuum systems due to vapor
pressure limitations. In addition to their rapidly growing use in medicine, agriculture and food
industries, catalysis, nanoparticle synthesis and water treatment, the interaction of plasmas with
organic liquids opens up new opportunities in organic synthesis.
Despite the limited success of early studies of plasma‐driven organic synthesis in low‐pressure
systems in the 70’s, direct treatment of liquids at atmospheric pressure provides a new paradigm for
the interaction of plasma species with organic molecules. In particular, these reactions often create
excited intermediates and when generated in the liquid phase, these intermediates undergo many
collisions, which lead to the rapid removal of excess energy and favour chemical pathways different
from those observed in low pressure gaseous systems.
Of particular interest, are novel synthetic processes that eliminate waste streams. In this study we
focus on the synthesis of epoxides, key building blocks in the chemical industry that are used as
intermediates in the preparation of many products (drugs, paints, adhesives, sealants, plastics, etc).
Epoxides are typically synthesized by oxidizing alkenes and the ultimate oxygen donor would be
molecular oxygen (O2) because it is readily available and once incorporated into the target molecule
it generates no oxidant waste stream. Unfortunately, owing to the lack of reactivity of small
molecular oxygen donors (e.g. O2, H2O2) with alkenes, catalysts and peracids (i.e. organic compounds
with an O=C‐O‐OH functional group that can readily donate an oxygen atom) are often used to drive
epoxidation reactions. A widely used peracid is m‐chloroperbenzoic acid (mCPBA), which although
effective, is also corrosive and explosive, leads to chlorinated waste products and even under
optimum epoxidation conditions, it produces more than 10 kg of waste stream per kg of oxygen
transferred.
As an alternative, here we report on the use of reactive oxygen species generated in an oxygen‐
containing atmospheric‐pressure plasma to drive the epoxidation of alkenes in solution, in a process
that produces epoxide without generating oxidant waste‐streams, runs at room temperature and
atmospheric pressure, and requires no catalyst. [1] The reactions between different reactive oxygen
species generated in the plasma and the target alkene, trans‐stilbene in this study, have been
identified and optimization of the plasma conditions within the constraints of the current
experimental set‐up have led to yields of ~70%, which are of preparative interest.
[1] Xu, H et al., Plasma Process Polym. 2019; e1900162
Increasing control of electron, ion and neutral heating in radio‐frequency hollow cathode microthrusters
Scott J. Doyle1, Andrew R. Gibson1, Sid Leigh1, Gregory J. Smith1,
Rod W. Boswell2, Christine Charles2, Mark J. Kushner3 and James P. Dedrick1
1York Plasma Institute, Department of Physics, University of York, Heslington,
York, YO10 5DD, UK 2Space Plasma, Power and Propulsion Laboratory, Research School of Physics and
Engineering, The Australian National University, ACT 0200, Australia 3University of Michigan, Department of Electrical and Computer Engineering, 1301 Beal Ave.,
Ann Arbor, MI 48109‐2122, USA
Low‐power, compact and charge‐neutral propulsion sources are of significant interest for
meeting the increasingly demanding challenges of space missions [1]. Radio‐frequency (rf)
hollow cathode microthrusters operate by heating the neutral gas propellant. To maximise
thrust‐power efficiency, it is important to control the spatial and temporal deposition of
electrical power into the plasma. In this study, we investigate control strategies for electron,
ion and neutral heating in the recently developed Pocket Rocket microthruster [2], operating
in argon at 1.5 Torr plenum pressure, via 2D fluid‐kinetic simulations and phase‐resolved
optical emission spectroscopy. Electron power deposition, and the ion and neutral‐gas
heating this underpins, is investigated across the α‐γ mode transition and on‐axis pressure
gradient for single‐frequency [4] and ‘tailored’ voltage waveform excitation [4]. Strategies for
enhancing control of the charged and neutral particle dynamics, e.g. structured ion energy
distribution functions at the radial wall [5], via the applied voltage waveform are also
discussed.
We wish to thank J. Flatt, R. Armitage, K. Niemi and P. Hill for their technical assistance and acknowledge financial support from the Engineering and Physical Sciences Research Council (EP/M508196/1). The participation of M. J. Kushner was supported by the US National Science Foundation and the US Department of Energy Office of Fusion Energy Science. 1. I. Levchenko et al. Space micropropulsion systems for Cubesats and small satellites: From proximate
targets to furthermost frontiers. Applied Physics Reviews 5 011104 (2018) 2. C. Charles and R. W. Boswell. Measurement and modelling of a radiofrequency micro‐thruster. Plasma
Sources Science and Technology 21 022002 (2012) 3. S. J. Doyle, A. R. Gibson, J. Flatt, T. S. Ho, R. W. Boswell, C. Charles, P. Tian, M. J. Kushner and J. Dedrick.
Spatio‐temporal plasma heating mechanisms in a radio frequency electrothermal microthruster. Plasma Sources Science and Technology 27 085011 (2018)
4. S. J. Doyle, A. R. Gibson, R. W. Boswell, C. Charles and J. Dedrick. Control of electron, ion and neutral heating in a radio‐frequency electrothermal microthruster via dual‐frequency voltage waveforms. Plasma Sources Science and Technology 28 035019 (2019)
5. S. J. Doyle, A. R. Gibson, R. W. Boswell, C. Charles and J. Dedrick. Inducing locally structured ion energy distributions in intermediate‐pressure plasmas. Physics of Plasmas 26 073519 (2019)
Technological Plasma Workshop 2019
Abstracts for Poster Presentations
A helicon plasma apparatus for fundamental wave‐plasma experiments
K. Ronald1, B. Eliasson1, A.W. Cross1, K. Wilson1, R. Bingham3,1, C.G. Whyte1,
A.D.R. Phelps1, R.A. Cairns2,1, M.E. Koepke4,1, D.C. Speirs1, C.W. Robertson1, P. MacInnes1,
and R. Bamford3
1 Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, Scotland
2 School of Mathematics and Statistics, University of St Andrews, KY16 9SS, Scotland
3 STFC Rutherford Appleton Laboratory, Harwell, Oxford, Didcot, OX11 0QX, England
4 Department of Physics, West Virginia University, Morgantown, WV 26506‐6315, USA
In a wide range of interesting plasma physics scenarios, electromagnetic (EM) waves are key to
providing energy. Plasmas support and enable complex interactions between multiple EM
signals. Raman and Brillouin coupling of two EM waves by Langmuir oscillation or through ion‐
acoustic waves respectively are important in laser plasma interactions. It is possible to achieve
normalised intensities comparable to those used in some laser plasma interactions at microwave
frequencies. The plasmas required to couple such microwave beams are relatively tenuous coo
and accessible. This enhances the diagnostic opportunities to characterise the physics of these
processes. Magnetic confinement fusion physics may directly benefit from multifrequency
microwave interaction in plasma to excite cyclotron and upper hybrid resonances in dense
plasma, either for heating or current drive.
Building on earlier research investigating geophysical cyclotron wave emissions [1,2], a new
linear plasma experiment, figure 1, is being developed to test multifrequency microwave
interactions in magnetised plasma. The magnetic field will reach up to 0.085T, with the plasma
created by a helicon wave launched from an RF antenna. This will produce a large, dense, cool
plasma. Fixed frequency, and wideband sources and amplifiers will provide microwave beams for
the multi‐signal interaction experiments. The paper will present progress on this apparatus.
Figure 1: Perspective model of the apparatus
The authors gratefully acknowledge support from the EPSRC (EP/R004773/1), MBDA UK Ltd
and TMD Technologies Ltd.
[1] Ronald K., Speirs D.C., McConville S.L., Phelps A.D.R., Robertson C.W., Whyte C.G., He W., Gillespie K.M.,
Cross A.W., Bingham R., 2008, Phys. Plasmas, 15, art.056503
[2] Speirs D.C., Bingham R., Cairns R.A., Vorgul I., Kellett B.J., Phelps A.D.R., Ronald K., 2014, Phys. Rev. Lett.,
113, art 155002
Metrology for in‐situ industrial plasma processing
Michael Mo1, Andrew R. Gibson2, Chris Bowman3, Timo Gans1, Deborah O’Connell1 1 York Plasma Institute, Department of Physics, University of York, York, YO10 5DQ, UK 2 Institute for Electrical Engineering and Plasma Technology, Ruhr‐Universität Bochum,
Universitätsstr. 150, Gebäude ID 1/517, Bochum, 44801, Germany 3 Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxford, OX14 3EB, UK
Real‐time monitoring of plasma parameters is highly desirable in industry to improve the efficiency of manufacturing processes. These include the atomic oxygen density and the mean electron energy; atomic oxygen helps to drive many plasma processing applications [1] while the latter shapes the Electron Energy Distribution Function (EEDF), which in turn determines the chemistry of the plasma [2]. Both are pivotal in controlling plasma‐surface interactions, such as the etch rate of semiconductors. While advanced diagnostics can obtain these plasma parameters to a high degree of accuracy, they are incompatible with industrial machines due to their experimental complexities. Optical Emission Spectroscopy (OES) offers a non‐intrusive approach to infer these and has been used to estimate electron temperature for argon containing plasmas [3, 4]. Consequently, the development of a sensor that only uses light emitted from argon‐oxygen plasmas to obtain the mean electron energy and atomic oxygen density in real‐time is investigated. A Bayesian approach is employed where theoretical excitation ratios are compared against experimental emission intensity ratios for a range of admixtures, powers and pressures up to several hundred millitorrs to infer the plasma parameters. Plus, due to the presence of molecular oxygen, quenching effects will also be considered. These are benchmarked against results obtained through Energy Resolved Actinometry where the mean electron energy and dissociation degree are simultaneously resolved [1, 5]. [1] Tsutsumi et al. 2017 Journal of Applied Physics 121, 143301 [2] DeJoseph et al. 2005 Physical Review E 72 036410 [3] Siepa et al. 2014 J. Phys. D: Appl. Phys. 47 445201 [4] Chung et al. 2012 Phys. Plasmas 19, 113502
[5] Greb et al. 2014 Appl. Phys. Lett. 105, 234105
Atmospheric pressure microplasma as synthesis method for nitrogen doped
carbon quantum dots applied to third‐generation solar cells
Slavia Deeksha Dsouza1, 2, Atta Ul Haq1, Paul Brunet1, Bruno Alessi1, Ruairi McGlynn1,
Chiranjeevi Maddi1, Paul Maguire1, Vladimir Svrcek2, Davide Mariotti1 1Nanotechnology & Integrated Bio‐Engineering Centre (NIBEC), Ulster University,
Jordanstown, Newtownabbey, Co. Antrim, BT37 0QB, United Kingdom
2National Institute of Advanced Industrial Science and Technology (AIST)
Central 2, Umezono 1‐1‐1, Tsukuba, Ibaraki, 305‐8568, Japan
Dsouza‐[email protected]
Atmospheric pressure microplasmas form an easy and precise method for synthesis of
nanoparticles and for controlling the optical and electronic properties [1]. Carbon
nanoparticles are a promising alternative to semiconductor nanocrystals as next generation
green nanomaterials due to excellent biocompatibility, low cytotoxicity and solution
processability which results in ease of production and incorporation in devices [2]. In the
current work, we describe how direct current microplasmas serve as a reliable and highly
reproducible synthesis method for tuning the optical properties of nitrogen doped carbon
quantum dots in colloid form which result as being highly stable and environmentally‐
friendly. The outcome of precursors and discharge current of the microplasma affecting the
particle morphology and optical properties are studied using various characterization
techniques. An attempt is made towards explanation of the synthesis and luminescence
mechanism by studying the electron interaction taking place at the liquid‐plasma interface.
The synthesized quantum dots are non‐toxic and water dispersible and hence there is good
potential for their implementation as absorber materials in solar cells. Since the method
gives rise to solution‐processable quantum dots, incorporation into solar cell devices is
relatively easy and does not require high‐temperature methods or complex chemical
reactions.
[1] Davide Mariotti, Jenish Patel, Vladimir Svrcek, Paul Maguire, Plasma–Liquid Interactions at Atmospheric Pressure for Nanomaterials Synthesis and Surface Engineering, Plasma Process. Polym., 9 (2012) 1074–1085.
[2] L. Lin, M. Rong, F. Luo, D. Chen, Y. Wang, X. Chen, Luminescent graphene quantum dots as new fluorescent materials for environmental and biological applications, TrAC ‐ Trends Anal. Chem. 54 (2014) 83–102.
Time resolved electron properties measured by laser Thomson scattering in a
HiPIMS plasma
Marcus A. Law1, Mark D. Bowden1 and James W. Bradley1 1Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill,
Liverpool l69 3GJ, United Kingdom
High Power Impulse Magnetron Sputtering (HiPIMS) belongs to a group of plasma‐based deposition
techniques called Ionised Physical Vapour Deposition (IPVD) [1]. The process creates dense plasmas
and produces large amounts of metal ions through sputtering of the cathode (target), which is
achieved by applying a large negative voltage pulse to the target. To stop the target from melting,
these pulses are short and of the order 10‐100µs with low duty cycles of about 1%. An advantage of
this is that by biasing the substrate, the direction and energy of the ions can be controlled and hence
the films created are superior, being harder, denser and smoother in comparison to DC operation.
This however poses a challenge as an experimentalist, as the high flux of sputtered materials creates
a difficult environment for most plasma diagnostics.
At the University of Liverpool, Department of Electrical Engineering and Electronics we have
designed an experiment such that time resolved measurements can be made by laser Thomson
scattering on the HiPIMS waveform, both in the active‐glow and after‐glow. Results have been
published in [2] by P.J. Ryan and presented here is an example of the time evolution of the electron
temperature and density at the magnetic null point.
A disadvantage to this technique is the lower deposition rate in comparison to DC operation. Further
work will include the addition of a positive “kick” pulse after the active glow to counter this lower
deposition and electron properties will be measured throughout. The study will also incorporate
probes and comparisons between both diagnostics will be done.
[1] U. Helmersson, M. Lattemann, J. Bohlmark, A. P. Ehiasarian, J. T. Gudmundsson, Thin solid films 513, 1 (2006)
[2] P. J. Ryan, J. W. Bradley, M. D. Bowden,Physics of Plasmas26, 040702 (2019).
Plasma‐driven epoxidation using a He+O2 atmospheric pressure COST plasma jet
H. Xu1,2, S. Wang1,2, M. Shaban1, D.X. Liu2, B.R. Buckley3, F. Iza1
1 Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, Leics LE11‐3TU, UK
2 State Key Laboratory of Electrical Insulation and Power Equipment, Center for Plasma Biomedicine, Xi’an Jiaotong University, Xi’an 710049, P. R. China
3 Department of Chemistry, Loughborough University, Loughborough, Leics LE11‐3TU, UK [email protected]
Being rich sources of reactive oxygen species, plasmas are found to be effective in oxidizing
organic compounds and in particular, it has recently been reported that plasma‐generated
atomic oxygen readily dissolves in water and directly oxidises organic solutes [1]. This opens
the possibility to a new plasma‐driven catalyst‐free epoxidation process that eliminate the
oxidant waste‐stream of conventional approaches [2]. In this paper, we report on a
systematic study of the epoxidation of trans‐stilbene solutions treated with a He+O2 COST
plasma jet. The experimental set‐up is shown in Figure 1 and different oxygen
concentrations, electrode voltages and gap distances were used to unravel the role of
atomic oxygen (O), ozone (O3) and singlet oxygen O2(alAg) in the oxidation of trans‐stilbene.
Experiments with photosensitized singlet
oxygen indicate that O2(alAg) leads to the
production of very little epoxide and more
abundant cis‐stilbene, and two additional
products that are not observed in typical
plasma experiments. As a result, it can be
concluded that singlet oxygen plays a
minor role in the oxidation of trans‐
stilbene in the current system. This leaves
ozone and atomic oxygen as the main
reactive species leading to the production
of the observed benzaldehyde and
epoxide. By varying the concentration of
oxygen in the gas and the distance
between the plasma and the liquid, it is possible to vary the ratio of atomic oxygen and
ozone reaching the liquid. These experiments indicate that ozone leads to the production of
benzaldehyde with virutally no other product. Therefore, to maximize the epoxide
production, the plasma should be engineered to maximize the ratio of atomic oxygen to
ozone. With the experimental setup used in this study and under optimum conditions, a
maximum yield of epoxide of 70% is achieved.
[1] J. Benedikt et al. Phys. Chem. Chem. Phys. 20, 12037 (2018). [2] J. Golda et al. J. Phys. D. Appl. Phys. 49, (2016).
Figure. 1 (a) A photograph of the COST jet with He+O2 plasma and (b) the schematic of the experimental system
for plasma-driven epoxidation of trans-stilbene.
An integrated microfluidic chip for generation and transfer of
reactive species using gas plasma
O. Ogunyinka, A. Wright, G. Bolognesi, F. Iza, H. Bandulasena 1Wolfson School of Mechanical, Electrical and Manufacturing Engineering
2Department of Chemistry
Loughborough University, Loughborough LE11 3TU, United Kingdom
Reactive species produced by atmospheric pressure plasma (APP) are useful in many applications including disinfection, pre‐treatment, catalysis, detection and chemical synthesis. Most highly reactive species produced by plasma, such as ∙OH, 1O2 and ∙ , are short‐lived; therefore, in‐situ generation is essential to transfer plasma products to the liquid phase efficiently. A novel microfluidic device that generates a dielectric barrier discharge (DBD) plasma at the gas‐liquid interface and disperses the reactive species generated using microbubbles of ca. 200 µm in diameter has been developed and tested. As the bubble size affects the mass transfer performance of the device, the effect of operating parameters and plasma discharge on generated bubbles size has been studied. The mass transfer performance of the device was evaluated by transferring the reactive species generated to an aqueous solution containing dye and measuring percentage degradation of the dye. Monodisperse microbubbles (polydispersity index between 2 ‐ 7%) were generated under all examined conditions. The generated microbubble size increased by up to ~ 8% when the device was operated with the gas plasma in the dispersed phase compared to the case without the plasma due to thermal expansion of the feed gas. At the optimal operating conditions, initial dye concentration was reduced by ~60% in a single pass with a residence time of 5‐10 s. This microfluidic chip has the potential to play a significant role in lab‐on‐a‐chip devices where highly reactive species are essential for the process such as organic synthesis.
Plasma cathode electron beam for high‐integrity materials processing
Andrew Sandeman1,2,3, Sofia del Pozo2, Felipe Iza1 1Loughborough University, Leicestershire LE11 3TU
2TWI Ltd., Granta Park, Abington, Cambridge CB21 6AL
3NSIRC, TWI Ltd., Granta Park, Abington, Cambridge CB21 6AL
Conventional thermionic electron sources have been used in electron beams since the 1950s for
welding, additive manufacturing, and surface modification. However, beam quality and reliability
has remained an issue due to wear and sensitivity of thermionic cathodes, especially for processing
which requires high‐integrity. Characterisation and optimisation of a plasma cathode is currently
being done to offer an alternative to the thermionic cathode and provide a more consistent electron
beam.
The design of the plasma cathode is based on a hollow cathode geometry using Ar gas (see Fig. 1).
Fig. 2(a) shows the pressure dependence of the Ar+ flux energy distribution at the centre of the
hollow cathode. At pressure = 7e‐2 mbar, the Ar+ ions reach the walls with the full energy from the
field as they transition the sheath without undergoing collisions. As the pressure increases the ions
lose energy due to collisions in the sheaths and reach the cathode wall with lower energy. As the
pressure increases from 7e‐2 to 14e‐2 mbar, the ion flux to the cathode decreases and yet the
plasma density (Fig. 2(b)) increases, which suggests that electrons are ionising the gas more
efficiently (expending their energy in ionisation collisions before being lost to the anode). As the
pressure increases further, the ion flux increases which leads to more secondary electrons being
emitted, more ionisation and a higher plasma density.
Figure 1. Plasma chamber and axisymmetric simulation domain. Ion bombardment of the hollow cathode releases electrons via secondary emission, which then perform a pendular motion between opposing cathode sheaths.
Figure 2. Simulation diagnostics at the centre of the hollow cathode: (a) flux energy distribution of Ar+. (b) e‐ density.
[1] Verboncoeur, J. P., Langdon, A. B., & Gladd, N. T. (1995). An object‐oriented electromagnetic PIC code. Computer Physics Communications, 87(1–2), 199–211. https://doi.org/10.1016/0010‐4655(94)00173‐Y
Enhanced Fuzzy Tungsten Growth in the Presence of Tungsten Deposition
P. McCarthy1, D. Hwangbo2, M. Bilton3 and J. Bradley1 1Department of Electrical Engineering and Electronics, The University of Liverpool, Liverpool,
L69 3GJ, UK 2 Graduate School of Engineering, Nagoya University, Furo‐cho, Nagoya 44‐8603, Japan
3 Imaging Centre at Liverpool, The University of Liverpool, Liverpool, L69 3GL, UK
[email protected] or [email protected]
A major concern for the safe operation of the thermonuclear fusion device ITER is the production of
surface nanostructures on tungsten components due to helium plasma irradiation [1]. These
nanostructures, known as fuzz, consist of nanoscale tendrils interlocking across the W surface,
changing both optical and mechanical properties of the material [2]. Worryingly, fuzz growth has
been observed to be easily removed from W components in fusion environments [3], posing
concerns about the poisoning of fusion plasma with W material.
In this study we investigate the evolution of fuzzy tungsten growth for a temperature and helium ion
fluence range, whilst also depositing a significant auxillary source of tungsten. This will be important
with respect to ITER’s operation since a considerable flux of ablated or sputtered tungsten is
expected to deposit on tungsten first wall components that are meeting the conditions (of
temperature, helium ion fluence ) for fuzz to form [4].
Here, through the use of a DC magnetron sputtering device, we are able to deposit tungsten atoms
at a controlled rate on to tungsten samples as they transition to fuzz. Importantly, this is done with
surface temperatures, helium ion energies and tungsten flux densities relevant to those expected at
the ITER divertor [5]. We study the effect of tungsten deposition on the growth rates and
morphology of the resulting fuzz for helium ion fluences in the range of 4 x 1023 – 1 x 1025 m‐2. The
magnetron grown fuzzy tungsten surfaces were compared and contrasted with those produced in a
deposition‐free environment of the linear plasma device NAGDIS II (across a similar ion fluence
range).
Our findings show that fuzz formation during deposition of tungsten results in significantly enhanced
fuzz growth rates. We have also observed that the enhancement in the growth rates is accelerated
for increases in the surface temperature and tungsten atom‐to‐helium ion arrival rate ratio.
[1] S. Kajita et al, “Formation process of tungsten nanostructure by the exposure to helium plasma under fusion relevant plasma conditions,” Nucl. Fusion, 49, 9, 095005, 2009
[2] S. Kajita et al, “Degradation of optical reflectivity of in‐vessel mirror materials by helium bombardment,” J. Nucl. Mater., 417, 1–3, 838–841, 2011
[3] F. W. Meyer, H. Hijazi, M. E. Bannister, K. A. Unocic, L. M. Garrison, and C. M. Parish, “Flux threshold measurements of He‐ion beam induced nanofuzz formation on hot tungsten surfaces,” Phys. Scr., vol. 2016, no. T167, 2016
[4] K. Schmid, K. Krieger, S. W. Lisgo, G. Meisl, and S. Brezinsek, “WALLDYN simulations of global impurity migration in JET and extrapolations to ITER,” Nucl. Fusion, vol. 55, no. 5, 2015
[5] G. De Temmerman et al, “The influence of plasma‐surface interaction on the performance of tungsten at the ITER divertor vertical targets,” Plasma Phys. Control. Fusion, 60, 044018 2018
Investigation of a Capacitively Coupled RF Allylamine Discharge
M. J. Barnes1, A. Robson2, R.D. Short2, J. W. Bradley1 1University of Liverpool, 2University of Lancaster.
Polymer films deposited through the plasma polymerisation of organic compounds have found a wide variety of applications including biosensors [1], cell attachment [2], nanoparticle attachment [3], and fabrication of non‐fouling surfaces [4]. Allylamine is one of the most commonly utilised monomers in the production of aminated films, due to the retention of primary amines in the polymer surface. Polymer films containing high concentrations of primary amine groups are of particular interest due to their ability to covalently or electrostatically bind biomolecules to surfaces [5]. In this study in situ mass spectrometry (RGA and positive ions) of RF capacitvely coupled allylamine plasmas across a gas pressure range of 2‐80 Pa with powers of 5‐20 W was carried out. The resulting spectra demonstrated a dominance of the protonated monomer at higher pressures and lower input powers, as well as suppression of higher mass molecules and diligomers. Ion energy distribution measurements also provide insight into the origin of the protonated monomer signal, and the importance of the sheath at high pressures. At low pressures the flux is almost entirely determined by high energy molecules originating from the plasma bulk accelerated through the sheath. Low energy molecules which are either formed in the plasma sheath or undergo collisions as they propagate to the grounded substrate dominate the measured energy distributions when operating at higher pressures. Langmuir probe measurements will also provide additional understanding of changing mass spectrum intensities across the measured pressure range. [1] L‐Q. Chu, W. Knoll, R. Förch, in Surface Design: Applications in Bioscience and Nanotechnology, R. Förch, H. Schönherr, A. T. A. Jenkins, Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, Germany 2009.
[2] P. Hamerli, Th. Weigel, Th. Groth, D. Paul, Biomaterials 2003, 24, 3989
[3] R. V. Goreham, R. D. Short, K. Vasilev, J. Phys. Chem. C 2011, 115, 3429.
[4] A. Michelmore, P. Gross‐Kosche, S. A. Al‐Bataineh, J. D. Whittle, R. D. Short, Langmuir 2013, 29, 2595.
[5] D. E. Robinson, A. Marson, R. D. Short, D. J. Buttle, A. J. Day, K. L. Parry, M. Wiles, P. Highfield, A. Mistry, J. D. Whittle, Adv. Mater. 2008, 20, 1166
Power controlled Atmospheric‐pressure Plasma Treatment System
J. Ren a, A. Wright b, A. Shaw a, H. Bandulasena b and F. Iza a a Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough
University, Loughborough, Leicestershire, UK, LE11 3TU b Dept of Chemical Engineering, Loughborough University, Leicestershire, LE11 3TU, UK
Recently, cold atmospheric‐pressure plasmas (CAPs) have become an emerging technology with great potential in many applications cover a broad spectrum of topics including medical, surface modification and environmental protection systems. Many experimental results suggest that the performance of the plasma reactor depends on the power delivered to the discharge, and the key challenges in all plasma systems are the stabilisation, repeatability and control of the discharge [1]. With this brings increased focus on the Power Supply Units (PSU) required to generate the necessary electrical field for dielectric barrier discharge plasmas and to control the power for a long time and stable plasma treatment. In this project a novel plasma water treatment system has been developed with a power controlled high AC voltage PSU.
The PSU design proposed in this work solves many existing issues that related to output waveform control. The system is based on the conjunction of a full‐bridge DC‐AC inverter and a high turn ratio step‐up resonant transformer. The control signals of the inverter, pulse‐width modulation (PWM), are all produced by a specific microcontroller. This design can achieve a specific voltage (10~40kVp‐p) with a specific frequency (1~100kHz) from input DC voltages (60~300V), allowing for greater flexibility. Further to this, the system should allow the user to configure the run time frequency, on‐time and duty cycle of the signal through an intuitive user interface.
The experiment set up in figure 1 includes a power control PSU, a DBD microbubble plasma reactor,
diagnostic equipment, and a computer for data storage and analysis. The power supply provides a
high voltage at variable frequency to sustain the plasma, which forms between a metallic membrane
and an array of columnar electrodes. The latter are encapsulated in glass tubes, providing a DBD
arrangement. Typical operation conditions of this device require 12 kV peak to peak at 38 kHz.
Compressed air is used to force an air flow through the membrane and a mass flow controller is used
to maintain a constant flow even if there are variations in the pressure of the compressed air line.
The starting average power delivered to the plasma was evaluated using Q‐V Lissajous and it was found to be ~15 W which decrease 20% after 2 hours treatment without power control. It also leads to a lower ozone concentration (650 ppm) in water compare to the ozone concentration (850 ppm) of the power control plasma treatment after two hours.
Air outlet / FTIR
Drafttube
AirInlet
Flow Meter
HVGround
Membrane
Plasma
Spectrum
Electrode Power supply
Oscilloscope
Airsupply
High speed camera
UV light
Computer
pH and conductivity
meter
Figure 1: The schematic diagram of the experimental set up
[1] P. Vadym, R. Alonso, and K. Konstantin, “On the measurement of Single‐Electrode Low‐Power Ar Plasma Jets,” Brazilian Journal of Physics, vol. 46, no. 5, pp. 496‐502, 2016.
Electro carboxylation of Alkene with Carbon Dioxide in the presence of
Plasma
M. Shaban1, A. Randi1,2, A. Alkayal2, B.R. Buckley2 and F. Iza1 1 Wolfson School of Mechanical, Electrical and Manufacturing Engineering
2Department of Chemistry
Loughborough University, Loughborough LE11 3TU, United Kingdom
Atmospheric CO2 concentration have been increasing from 280 ppm since the beginning of the
industrial revolution to 400 ppm in 2014 [1]. With high certainty, it can be said that it is this increase
that has led to the current adverse global environmental climate changes, which have a growing
detrimental effect on our climate and environment, and that represent a severe threat to our current
society and future generations in general. Therefore, the conversion of this main greenhouse gas into
value‐added chemicals and liquid fuels is considered as one of the main challenges for the 21st
century. The aim is not only to tackle climate change, but also to provide an answer to our dependence
on fossil fuels.
By generating useful products out of CO2, we create the possibility to effectively close the carbon loop.
This has already resulted in a booming interest in technologies that can convert CO2 into value‐added
products, since they can effectively convert waste into new feedstocks following the cradle‐to‐cradle
principle [2]. Besides the traditional thermal CO2 conversion, a novel approach considered to have
great potential in recent years, which is the approach based on plasma. From a chemical point of view,
reduction of CO2 simply requires an electron donor and in principle, electrons can be provided by
plasma. In this work, we have developed a DC plasma reactor to investigate the feasibility of plasma‐
driven electrochemical reduction of CO2 and demonstrated that carboxylation of both alkenes and
alkynes are possible in a flow reactor operating at atmospheric pressure.
The system utilises DC plasma jets that act as a source of electrons to electrochemically drive the
carboxylation of alkenes present in a flowing solution saturated with CO2. Using Gas Chromatography
Mass Spectrometry (GCMS), we show that CO2 is selectively incorporated into the alkene trans‐
stilbene to form 2,3‐diphenylpropanoic acid. The efficacy of the process depends on the plasma
conditions and current efficiencies of up to 80% have been observed to date.
[1] R. K. Pachauri and L. A. Meyer, IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Geneva, Switzerland, 2014.
[2] W. McDonough, M. Braungart, P. Anastas and J. Zimmerman, Environ. Sci. Technol., 2003, 37, 434A–441A.
Microwave emission due to kinetic instabilities in an over‐dense mirror‐
confined plasma
M. Viktorov1, B. Eliasson2, S. Golubev1, D.C. Speirs2, D. Mansfeld1, A.D.R. Phelps2, R.
Bingham2,3, A.W. Cross2, K. Ronald2
1Institute of Applied Physics of Russian Academy of Sciences (IAP RAS), Nizhny Novgorod,
603950, Russian Federation
2Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, United Kingdom
3STFC Rutherford Appleton Laboratory, Harwell, Oxford, Didcot, OX11 0QX, United Kingdom
[email protected]‐nnov.ru, [email protected]
The kinetic instabilities of a microwave plasma confined in an open magnetic trap are relevant to
understanding various types of radio emission in space plasma, for example, in the magnetospheres
of the Earth and the planets, the Sun, and certain types of stars. The high efficiency of the kinetic wave
generation mechanism is due to the low group velocity of plasma waves (in comparison with
electromagnetic waves), which ensures they enjoy an extended interaction time with nonequilibrium
particles resulting in a high integral gain. Emission from the plasma is observed due to various
mechanisms for the transformation of plasma waves into electromagnetic waves, for example, as a
result of scattering by thermal ions. In view of the universality of the physical mechanisms of radiation
generation, essential aspects of natural systems can be reproduced in laboratory magnetic traps under
controlled and reproducible conditions. Hitherto the excitation of plasma waves in open magnetic
traps has been carried out with the use of electron beams. The technique reported here exploits a
plasma generated by irradiating a mirror confined plasma using mm‐waves from a gyrotron under
electron‐cyclotron resonance conditions, a technique also potentially of interest for technological
applications. In such a discharge, a two‐component plasma is created with a dense cold (background)
fraction with an isotropic particle velocity distribution and a less dense high‐energy fraction of
nonequilibrium electrons with an anisotropic distribution function. In these experiments, bursts of
powerful electromagnetic radiation at a frequency close to the upper hybrid resonance and to the
second harmonic of the electron gyrofrequency were observed for the first time, accompanied by
synchronous precipitation of fast electrons from the trap. The observed bursts were associated with
the instability of plasma waves under conditions of a double plasma resonance, with subsequent
transformation of the plasma waves into electromagnetic waves.
This poster focusses on a theoretical and experimental study of wave generation in a dense
magnetoactive plasma at the harmonics of the electron gyrofrequency. In the experiments at the IAP
RAS, a detailed study of the fine structure of dynamic spectra using ultra‐wideband oscilloscopes with
a bandwidth of up to 59 GHz is reported. Theoretical and numerical analysis at relevant plasma
parameters is underway at the University of Strathclyde. Comparison of experimental and theoretical
data will lead to an understanding of the mechanisms of electromagnetic radiation generation in
magnetic traps and the features of the radio emission spectra observed in natural conditions.
The authors would like to acknowledge the funders of the research. In Russia the project is funded by
the RFBR and К under project № 19‐52‐10007. In the UK the project is enabled by funding from the
Royal Society, award IEC\R2\181158 and the UK EPSRC under grants EP/R034737/1, EP/R004773/1,
EP/M009386/1, EP/G04239X/1.
Notes ________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Notes ________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Notes ________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
________________________________________________________________________________________________________
