1. SPECIALIZED TECHNIQUES (14 hours)
Unit:4
SPECIALIZED TECHNIQUES (14 hours)
Electrophoretic deposition
Chemical Vapour deposition: Wet and Dry oxidation process
Dip and Spin coating process
Successive ionic layer adsorption and reaction (SILAR)
Spray and Flame spray pyrolysis
Self assembly

2. Electrophoretic deposition (EPD)

3. Electrodeposition is a process that assembles solid materials from molecules, ions or complexes in a solution.
These are images of gold nanostructures produced by controlling the electrodeposition process.
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5. Electrophoretic deposition (EPD)
Characteristics
There is a stable dispersion of particles in a solvent (a colloid).
The particles gain a surface charge as a result of an electrostatic interaction with the molecules of the solvent.
The particles are capable to move in the suspension towards the work part under the influence of a voltage imposed between the work part and the counter electrode (the phenomenon called electrophoresis).
A rigid deposition composed of condensed particles is built up on the work part surface in contrast to dip coating - a painting process in which the concentration of particles in the layer adhered to the work part is the same as the concentration of the particles in the bulk suspension.
The deposited coating is adhered to the surface of the work part.

6. Electrophoretic deposition (EPD)
Characteristics
When a voltage is applied between the electrophoretic electrodes the charged particles start to migrate towards the electrode with the opposite electric polarity.
The particles are deposited first of all at the surface areas with the highest electric potential. The formed coating decreases the potential of such areas and equalizes the potential distribution over the part surface.
As a result a uniform and even film forms over the whole part surface including the surface of cavities, edges and corners.
The coating thickness is determined by the voltage value which is typically V. After a coating of a certain thickness is built the deposition process stops.

7. Electrophoretic deposition (EPD)
Electrophoretic deposition EPD is a method of coating a conductive part with particles suspended in a fluid dispersion under the influence of an electric field applied between the work part and the counter electrode.
Similar to Electroplating coating, electrophoretic deposition utilizes electrically charged particles moving between two electrodes (an anode and a cathode) immersed in a liquid media.
However in contrast to conductive electrolytes used in electroplating, the fluids of electrophoretic dispersions are dielectric.
In addition, the electroplating coatings are built from metallic ions converted into atoms when discharged at the cathode, whereas in electrophoretic process the coating is formed by a deposition of relatively large powder particles which may be polymeric, ceramic or metallic.

8. Electrophoretic deposition (EPD)
Provides a low-temperature method to deposit nanoparticles into patterned films
Compatible with traditional micro fabrication processes
Offers high deposition rates using a simple apparatus that is easily scalable for production
Utilizes the mobility of charged particles in solution upon exposure to an applied electric field to deposit those particles on an electrode that acts as a substrate
Processing parameters of importance for EPD are
Particle mobility,
Bath solution (i.e., solvent),
Applied electric field,
Deposition time

9. Electrophoretic deposition (EPD)
If the Electrophoretic dispersion is aqueous, the voltage applied between the immersed electrodes, causes water molecules to decompose.
At the anode Oxygen is generated according to the oxidation reaction:
2 H2O = O2 + 4 H+ + 4e-
The reduction reaction at the cathode results in a formation of Hydrogen:
2 H2O + 2e- = H2 + 2 OH-
As a result of electrolysis the solution surrounding the anode becomes acidic and in the cathode region - alkaline.
Changes of the solution PH destabilize the colloid causing the particles to coagulate and deposit on the electrode surface.

10. Electrophoretic deposition (EPD)
Polarity of electrophoretic deposition
The electric charge of the dispersed particles may be either positive or negative. The positively charged particles are attracted to the cathode. The process of a deposition of positively charged particles is classified as cathodic electrophoretic coating in contrast to anodic electrophoretic coating related to the deposition of negatively charged particles.
Anodic electrophoretic process is less expensive. It produces coatings of good aesthetic appearance. However the anode metal slightly dissolves in the solvent producing metallic ions which are incorporated in the coated film. The metallic contamination of anodic coatings decreases their corrosion resistance. Therefore anodic electrophoretic coatings are mostly used in indoor applications.
Cathodic electrophoretic process results in a deposition of coatings with very low metallic contamination. Cathodic coatings are characterized by high corrosion resistance and durability in both indoor and outdoor applications.

11. Electrophoretic deposition (EPD)
Electrophoretic coating process:
The industrial applications of electrophoretic deposition are referred to as e-coating, electrocoating, electrophoretic painting or electrophoretic coating. Stages
Hanging the work parts
Alkaline cleaning
Rinsing
Acid cleaning
Immersion in adhesion promoter (wetting agent)
Electrophoretic deposition
Rinsing and dispersion recovery
Rinsing in de-ionized water
Dehydration oven
Curing
The most popular applications of electrophoretic deposition are cathodic coating of automotive parts with epoxy, acrylic and polyurethane films. The coatings have excellent scratch resistance and corrosion resistance. Acrylic and polyurethane coatings are also resistant against ultra-violet light.

13. Teapots can be suspended in a solution so that a thin layer of silver atoms is electrodeposited on a more rigid metal to give the teapots an attractive and durable finish.

14. References:
Adsorption
Desorption
Diffusion
Aerosol
Plasma
Combustion
Carrier gas and source gas
Pyrolysis
Epitaxy

15. Adsorption
Adsorption is a surface process that leads to transfer of a molecule from a fluid bulk to solid surface. This can occur because of physical forces or by chemical bonds.
Desorption
Usually it is reversible (the reverse process is called desorption); then it is responsible not only for a subtraction of substances but also for release.
Diffusion
Diffusion is the net movement of atoms, ions, molecules, energy generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. 
Aerosol
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas
Plasma
Plasma is called the fourth state of matter after solid, liquid, and gas.  It contains a significant portion of charged particles – ions and/or electrons.  It is the most abundant form of ordinary matter in the universe,[2] being mostly associated with stars,[3] including the Sun. The presence of charged particles makes plasma electrically conductive.  is a state of matter in which an ionized substance becomes highly electrically conductive to the point that long-range electric and magnetic fields dominate its behaviour.[19][20] Plasma is typically an electrically quasineutral medium of unbound positive and negative particles (i.e. the overall charge of a plasma is roughly zero)

16. Combustion
 The original substance is called the fuel, and the source of oxygen is called the oxidizer. The fuel can be a solid, liquid, or gas, although for airplane propulsion the fuel is usually a liquid. The oxidizer, likewise, could be a solid, liquid, or gas, but is usually a gas (air) for airplanes. For model rockets, a solid fuel and oxidizer is used. uring combustion, new chemical substances are created from the fuel and the oxidizer. These substances are called exhaust. Most of the exhaust comes from chemical combinations of the fuel and oxygen. When a hydrogen-carbon-based fuel (like gasoline) burns, the exhaust includes water (hydrogen + oxygen) and carbon dioxide (carbon + oxygen). 
Carrier gas and source gas
Pyrolysis
Epitaxy

17. Chemical Vapor Deposition (CVD)

18. Introduction
CVD is a chemical process used to produce high-purity, high-performance solid materials.
This technique is suitable for the manufacture of coatings, powders, fibers and monolithic components.
This technique is often used in many thin film applications.
By varying the experimental conditions—substrate material, substrate temperature, composition of the reaction gas mixture, total pressure gas flows, etc.— materials with different properties can be grown.

19. Definition and Types
Chemical vapour deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapour phase. It belongs to the class of vapour-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination of these.
Schematic of a simple thermal CVD reactor

20. Sequence of events during deposition

21. Classified by operating pressure:
Atmospheric pressure CVD (APCVD) – CVD at atmospheric pressure.
Low-pressure CVD (LPCVD) – CVD at sub-atmospheric pressures.
Ultrahigh vacuum CVD (UHVCVD) – CVD at very low pressure, below 10−6 Pa (~10−8 torr).
Classified by physical characteristics of vapour:
Aerosol assisted CVD (AACVD) – CVD in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically.
Direct liquid injection CVD (DLICVD) – CVD in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors. The precursor vapours are then transported to the substrate as in classical CVD.

22. Atomic-layer CVD (ALCVD)  Metalorganic chemical vapor
Plasma methods:
Microwave plasma-assisted CVD (MPCVD)
Plasma-Enhanced CVD(PECVD) – CVD that utilizes plasma to enhance chemical reaction rates of the precursors.
Remote plasma-enhanced CVD (RPECVD) – Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region.
Atomic-layer CVD (ALCVD)  Metalorganic chemical vapor
deposition (MOCVD)
Combustion Chemical Vapour Deposition (CCVD)
Hot filament CVD (HFCVD)
Hybrid Physical-Chemical Vapour Deposition(HPCVD)
Rapid thermal CVD (RTCVD)
Vapour-phase epitaxy
Photo-initiated CVD (PICVD)

23. Historical perspective
1960: Introduction of the terms CVD and PVD to distinguish “chemical vapour deposition” from “physical vapour deposition.”
1960: Introduction of CVD in semiconductor fabrication.
1960: CVD TiC coating on cemented carbide tools introduced and development of CVD tungsten.
1963: Introduction of plasma CVD in electronics.
1968: Start of industrial use of CVD coated cemented carbides.
1980s: Introduction of CVD diamond coatings.
1990s: Rapid expansion of metallo-organic CVD (MOCVD) for ceramic and metal deposition.
1990s: Development of cluster tools combining CVD, PVD and other processing steps in a single tool for semiconductor fabrication. Major development of CVD in optics and optoelectronics.

24. Classification of CVD reactions
Thermal decomposition (pyrolysis) reactions

25. Hydrogen reduction reactions
Co-reduction reactions

26. Metal reduction of halides
Oxidation and hydrolysis reactions
Carbidization and nitridation

27. CVD system The reaction gas dispensing system.
The reactor, including components for defining the gas flows.
The exhaust system containing a
total pressure controller, pump, scrubber and/or
vacuum reactant
recycle system.

28. Applications In semiconductor and microelectronic industries
In metallurgical coating industries
Optical fibers for telecommunications
Wear resistant
coatings, corrosion resistant
coatings, heat-resistant coatings etc.
Preparation of high temperature materials