curs 6 new

8/13/2019 Curs 6 new

1/28

Procese tehnologice avansate

Titularul de disciplin:Prof. Dr. Ing. Dan Dasclu

Cerc.st. gr. I, dr. Ing. Mircea Dragoman

Dr. Emil Mihai Pavelescu (IMT).

[email protected]

Cursul 6

Metode de autoasamblare

Metode de crestere prin matrite (template)

8/13/2019 Curs 6 new

2/28

Semiconductor doping is a key technological process in microelectronics andaccompanies the deposition processes. It is well known that p- or n-doping of asemiconductor changes significantly the electrical, chemical and mechanicalcharacteristics of semiconductors. These changes are often referred to as thefunctionalization or engineering of the material. The electrical changes areused to produce almost any active electronic component, such as transistors anddiodes, while the mechanical changes create MEMS devices with prescribed

mechanical characteristics. Impurities ofp- or n-type are controllable introducedin intrinsic silicon via diffusion into furnaces at high temperatures from liquid or solidsources or via ion implantation techniques, which are more accurate with respect tothe amount of impurities/area and the prescribed impurity profile.

The variety of functionalization techniques at nanoscale is much richercompared to that of microscale transistors, diodes and integrated circuits.The doping is still used, for example, for nanotube transistors, but the

functionalization of nanowires or dots can be done via oxygenation,hydrogenation, adsorbing of molecules, biomolecules etc

Semiconductor doping

Doping by diffusion

Typical doping

concentration

1015-1019atoms/cm3


8/13/2019 Curs 6 new

3/28

8/13/2019 Curs 6 new

4/28

Feature size (nm)

1000 100 10 1 0.1

SUBMICRON

TECHNOLOGYNANOTECHNOLOGY ATOM TECHNOLOGY

EB

FIB

EUV

Optical

AFM, STM

Atom lithography

Nanoimprint

Next lecture


8/13/2019 Curs 6 new

5/28

Self-Assembly Techniques

The self-assembly process refers to the spontaneous organization of various components (molecules or

various nanosize objects such as nanoparticles) into a single, ordered aggregate. The organization process is

made into a desired structure via physical, chemical, or biochemical interactive processes involving, for

example, electrostatic and surface forces, hydrophobic and hydrophilic chemical interactions. All these

processes, irrespective of their origin, are very selective and reject defects so that the resulting desired

structure is characterized by a high degree of perfection

The Langmuir-Blodgett (LB)technique dedicated to thin film realization is a well spread self-

assembly technique in which the organized aggregate is built by growing one monolayer at a

time. A monolayer of a desired material, which is initially adsorbed at a gas-liquid interface, is

transported to a substrate on which the self-assembly structure will be grown. For example, a

monolayer of some molecular species, such as a fatty acid, is spread over the surface of the water.In the water there is a glass microscope slide, which plays the role of the self-assembly substrate.

If we pull out the glass slide the monolayer will be attached to it. If we then pass the glass slide

several times through the water surface we will deposit on it a monolayer at each passing .The

LB technique is implemented with specialized instruments comprising a Langmuir trough, a

dipping device for the substrate that will be raised or lowered, and a movable barrier controlled

by a pressure sensor, which slides on the gas-liquid interface to maintain a certain surfacepressure


8/13/2019 Curs 6 new

6/28

Water

Fat acid

Monolayer Glass plate

LB technique

Although 2D gold, nanoparticle arrays,

semiconducting quantum dots and

polymeric films were realized usingthe LB technique, the method is quite

difficult and requir esexpensive

instrumentation


8/13/2019 Curs 6 new

7/28

The electrostatic self-assemblyis realized through the electrostaticinteraction between molecules or nanoparticles. This self-assembly technique

originates from the fabrication of multilayer films where each layer is composed of

positive- and negative-charged colloid particles such as Si and Al. The method is

widespread in the implementation of nanostructured films containing metals,

semiconductors, magnetic materials, polymers, or organic molecules. The resulting

film is uniform and stable due to strong ionic bonds between negative- andpositive-charged particles, and the defects are minimized due to the repulsive

force between the particles involved in the process. The utilization of polymers

in combination with layers of charged nanoparticles is the best way to minimize

the defects. The electrostatic self-assembly process starts with the immersion of

a clean substrate into a cationic solution, followed by a dip of the substrate

coated with cations into an anionic solution where the adsorption of anionicmolecules takes place at a molecular level.For example, positively charged gold

nanoparticles are self-assembled on a negative glass substrate by immersion into 4-

ATP(aminotiophenol)-capped gold solution with pH = 4. A layer of negatively charged

Ag nanoparticles can be further deposited by immersion of the glass coated with Au

particles into a 4-CTP(carboxythiophenol)-capped silver solution with pH = 8.5 Thus, it

is possible to obtain a heterostructure consisting of successive layers of Au and Agnanoparticles.


8/13/2019 Curs 6 new

8/28

Cationic

solutionAnionic

solution

Water

water

RINSE DRY RINSE DRY

Water


8/13/2019 Curs 6 new

9/28

The chemical self-assembly methods are the most commonly used

techniques. Among them, SAM (self-assembled monolayers) and MPC(monolayer-protected clusters) are the most prominent. SAM deals withthe spontaneous formation of monolayers via immersion of a suitablesubstrate into a solution, while MPC refers to nanoclusters whose surface isderivatized by ligand molecules with the help of chemisorption

Biomolecular self-assembly uses DNA or proteins as basic constituents to

realize: 1) biomolecular-metal complexes such as DNA-Au complexes, 2)self-assembly of semiconducting nanoparticles such as CdSe quantum dotensembles, or 3) functionalized metallic nanoparticles.

Au substrate Au

nanoparticleAlkanethiol

molecules

SAM MPC


8/13/2019 Curs 6 new

10/28


8/13/2019 Curs 6 new

11/28

8/13/2019 Curs 6 new

12/28


8/13/2019 Curs 6 new

13/28


8/13/2019 Curs 6 new

14/28


8/13/2019 Curs 6 new

15/28


8/13/2019 Curs 6 new

16/28


8/13/2019 Curs 6 new

17/28


DNA origami

8/13/2019 Curs 6 new

18/28

Nanoparticles

The physical properties, and especially the electronic structure of metal nano-

particles, are very different from those of bulk metals and are strongly dependenton their size. For example, the conduction band of bulk metals is replaced by

discrete energy states in a metal nanoparticle. Thus, the metal particle behaves like

a quantum dot, in which electrons are confined in all directions, in contrast with thefree electrons of bulk metals. Metal particles covered with organic molecules such as

thiols are able to self-organize in 1D, 2D and 3D arrays. The discreteness of

electronic states in a metal nanoparticle is characterized by the Kubo gap (i.e., the

average spacing between successive quantum levels)

nE 3/4 Fwhere EFis the Fermi energy, and nis the number of electrons in the nano-

particle. The nanoparticle is metallic if :

TkB

For example, a silver particle with a diameter of 3 nm, for

which = 10 meV, is metallic at room temperature sincekBT

=25 meV for T= 300 K.


8/13/2019 Curs 6 new

19/28

CdS (semiconductor nanoparticles)

Gold substrate

CdS (semiconductor nanoparticles)

Gold substrate

There are not only metal nanoparticles, but also semiconductor nanoparticles

such as silicon nanoparticles, III-V nanoclusters, elemental II-VI semiconductorquantum dots in solution or gaseous phases.


8/13/2019 Curs 6 new

20/28

Nanowires

A nanowire is a metallic, semiconducting, superconducting or magnetic physical system,which is confined in two dimensions. The nanowire has a transverse area of a few nm and

can attain 100300 nm in length, although longer nanowires, up to 1 m, have also been

fabricated. Nanowires can be realized via many methods.

Aluminium

Anodized aluminaSourcematerial

Template synthesis

SiO2

Si Si Si

MetalCracksNanowire array Top

view

Self assembly


8/13/2019 Curs 6 new

21/28

Nanowires with ultra-small diameters are grown using CVD or MOCVD. The nanowire

precursor material is heated to produce vapors that penetrate the nanopores of thetemplate, which is then cooled to get the solidified nanowires. Nearly single-crystal

nanowires are obtained with the CVD method, while in the rest of the above-mentioned

methods mainly polycrystalline nano-wires are fabricated. Single-crystal nanowires of Bi,

GaN, GaAs, and InAs, with diameters less than 10 nm, can be grown with the CVD

techniques. Carbon nanotubes (CNTs), are also grown in alumina templates via CVD

techniques. CNTs with very small diameters, of a few nm, can be grown by replacing the

alumina template with a zeolite template.The vapor-liquid-solid (VLS) nanowire growthmethod is based on the fact that the vapors (V) of the source material can be absorbed into

a liquid (L) droplet of a catalyst. The nanowire is obtained due to the solidification (S) of the

source material as a result of the saturation of the liquid alloy followed by a nucleation

process, which creates a preferential site for further deposition at the liquid boundary.

Growth

direction

Vapors (V)

Liquid catalyst

(L)

Nanowire (S)


8/13/2019 Curs 6 new

22/28

Millions of CNTs can be aligned and integrated using a large-scale assembly technique

inspired from biomolecular self-assembly processes . In this method, chemically

functionalized patterns on a surface are first realized, on which millions of CNTs spread

in a solution are then aligned. Two distinct regions coated via direct deposition with polar

groups and nonpolar groups, respectively, create the functionalization of the surface. By

placing the functionalized surface into a liquid suspension containing millions of CNTs

the nanotubes are attracted by the polar regions and millions of CNTs are aligned in less

than 10 s, The electrostatic attraction force rotates the CNTs towards the polar regionand confines them only in this region. The efficiency of alignment is very high, of about

90%.

Polar region

Gold surface

Rotationtowards polar

region

Nonpolar

region


8/13/2019 Curs 6 new

23/28

Dielectrophoresis(or DEP) is a phenomenon in which a forceis exerted

on a dielectricparticle when it is subjected to a non-uniform electricAll

particles exhibit dielectrophoretic activity in the presence of electric fields.

However, the strength of the force depends strongly on the medium and

particles' electrical properties, on the particles' shape and size, as well as

on the frequency of the electric field. Consequently, fields of a particular

frequency can manipulate particles with great selectivity. This has allowed,

for example, the separation of cells or the orientation and manipulation ofnanoparticles and nanowires.

http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Dielectrichttp://en.wikipedia.org/wiki/Electric_fieldhttp://nanotechweb.org/articles/journal/5/10/2/1http://nanotechweb.org/articles/journal/5/10/2/1http://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Dielectrichttp://en.wikipedia.org/wiki/Force

8/13/2019 Curs 6 new

24/28

CNT

interconnect


8/13/2019 Curs 6 new

25/28


8/13/2019 Curs 6 new

26/28


8/13/2019 Curs 6 new

27/28

Al template

Si nanowire

ZnO

GaN CNT


8/13/2019 Curs 6 new

28/28

curs 6 new

Documents