chemical vapour deposition

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Poducherry engineering college

product design and manufacturing M.TECH (first year)

Nanotechnology assignment-1

Submitted by R.RANJITH KUMAR

content

1.0 Chemical Vapor Deposition(cvd)………………………………………………...042.What is CVD?.............................................................................................................052.1 Chemical Vapor Deposition………………………………………………………062.2 Examples of CVD …………………………………………………………….......092.3 Generic CVD Steps ………………………………………………………………092.4Advantages……………………………………………………………………........112.5 Disadvantages……………………………………………………………………..113 Chemical Synthesis …………………………………………………………...……12Definition for chemical synthesis…………………………………………………….123.1 Nano-synthesis Technology……………………………………………………….133.2 Top-down versus Bottom-up………………………………………………..........153.3Bottom-up Process - What to control …………………………………………....163.4Colloids………………………………………………………………………..........173.5 Colloids………………………………………………………………………........18

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4.0 Wetdeposition techniques…………………………………………………...........264.1 Self-Assembly (supramolecular approach) ………………………………….…284.1 Advantages of self-assembly………………………………………………...........314.2 Disadvantages of self-assembly…………………………………………………..324.3 Applications…………………………………………………………………….…345.0 Molecular Design and modeling………………………………………………...43

3.6 Nucleation & Growth………………………………………………………........….............193.7Colloidal stability…………………………………………………………….........…............203.8 Colloidal stability……………………………………………………………........................213.9 Methods for Nanosynthesis…………………………………………………........................223.10 Sol-gel process……………………………………………………………….......................233.11 Advantage & Disadvantage………………………………………………..........................243.12Application…………………………………………………………………............….........25

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1.0 Chemical Vapor Deposition(cvd)Chemical vapor deposition (CVD) is a widely used method for depositing thin films of a large variety of materials. Applications of CVD range from the fabrication of microelectronic devices to the deposition of protective coatings. In a typical CVD process, reactant gases (often diluted in a carrier gas) at room temperature enter the reaction chamber.

The gas mixture is heated as it approaches the deposition surface, heated radiatively or placed upon a heated substrate. Depending on the process and operating conditions, the reactant gases may undergo homogeneous chemical reactions in the vapor phase before striking the surface.

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Near the surface thermal, momentum, and chemical concentration boundary layers form as the gas stream heats, slows down due to viscous drag, and the chemical composition changes.

2.What is CVD?Thin film formation from vapor phase reactants. Deposited films range from metals to semiconductors to insulators.

An essential process step in the manufacturing of microelectronic devices. High temperatures and low pressures are the most common process conditions, but are not necessary.

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All CVD involves using an energy source to break reactant gases into reactive species for deposition.

2.1 Chemical Vapor Deposition

CVD is the formation of a film on a surface from a volatile precursor (vapor or gas), as a consequence of one or more chemical reactions which change the state of the precursor. Many different films can be deposited: elements and compounds, crystalline, polycrystalline, and amorphous. Most films can be deposited from several different precursor systems. Plasma discharges can be used to help things along, or the substrate and/or the gas can be heated or cooled. Different deposition techniques, process conditions, and treatment after deposition produce films with differing

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Molecular self-assembly is a key concept in supramolecular

chemistry since assembly of the molecules is directed through

noncovalent interactions (e.g., hydrogen bonding, metal

coordination, hydrophobic forces, van der Waals forces, π-π

interactions, and/or electrostatic) as well as electromagnetic

interactions.

Molecular self-assembly is the process by which molecules

adopt a defined arrangement without guidance or management

from an outside source. There are two types of self-assembly,

intramolecular self-assembly and intermolecular self-

assembly.

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In every case, CVD processes mustprovide a volatile precursor containing the constituents of the film transport that precursor to the deposition surface encourage or avoid reactions in the gas phase encourage surface reactions that form the film and do it rapidly, reproducibly, and uniformly for industrial applications.

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2.2 Examples of CVD Metals/Conductors - W, Al, Cu, doped poly-SiInsulators (dielectrics) - BPSG, Si3N4, SiO2 Semiconductors - Si, Ge, InP, GaAsP Silicides - TiSi2, WSi2Barriers – TiN, TaN

2.3 Generic CVD Steps Five steps occur during all CVD processes:

Reactants pumped through reactor. Reactants diffuse across boundary layer to surface. Reactants adsorb on surface (adatoms).

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Surface reactions; pos. formation of islands or clusters. Pos. surface diffusion of adatoms. Diffusion of by-products away from surface.

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2.4Advantages:

high growth rates possiblecan deposit materials which are hard to evaporategood reproducibilitycan grow epitaxial films

2.5 Disadvantages

high temperaturescomplex processestoxic and corrosive gasses

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3 Chemical Synthesis

Definition for chemical synthesis

In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions. .

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3.1 Nano-synthesis Technology04/19/23

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3.2 Top-down versus Bottom-up04/19/23

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3.3Bottom-up Process - What to control

• Colloidally stable nanoparticles• Reproducible• Adaptable surface properties• Easy + cheap•(Biocompatible or biodegradable systems)

+

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3.4Colloids04/19/23

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To some the word `colloidal' conjures up visions of things indefinite in

shape, indefinite in chemical composition and physical properties, fickle

in chemical deportment, things infilterable and generally unmanageable.

Hedges, 1931

Application Involved Principles

• Pharmaceutics, cosmetics, inks, paints, foods, foams, chemicals

• Formation and stabilization of end-use products

• Photographic products, ceramics, paper coatings, catalysts, magnetic media

• Formation of colloids for use in subsequent manufacturing processes

• Pumping of slurries, coating technology, filtration

• Handling properties of colloids, rheology, sintering

• Water purification, fining of wines and beer

• Destruction of unwanted colloidal systems

3.5 Colloids

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Nucleation (critical size)

Agglomeration

Clusters

Crystallites

Primary particlesParticles

Growth

Typical precipitation reaction:

Reactant 1 + Reactant 2 Product + By-productT, t

Stabilizer

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3.7Colloidal stability04/19/23

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3.8 Colloidal stability04/19/23

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1) Physical methods: Carbon arc, Laser ablation, Vapour trapping….

2) Chemical methods

Reactant 1 + Reactant 2 Product + …T, p, t

Sonochemistry

Microwave synthesis

Hydrothermal methods

Microencapsulation

Sol-gel methods

Wet chemical co-precipitation

3.9 Methods for Nanosynthesis04/19/23

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3.10 Sol-gel process04/19/23

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3.11 Advantage & Disadvantage04/19/23

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3.12Application04/19/23

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4.0 Wetdeposition techniquesIn wet deposition, there are always some atmospheric hydrometeors which scavenge aerosol particles. This means that wet deposition is gravitational, Brownian and or turbulent coagulation with water droplets. Different types of wet deposition include:

This is where falling rain droplets collide with particles. This is also called "below-cloud scavenging".In-cloud scavenging. This is where aerosol particles collide with the water droplets in clouds. A common example of this type of deposition is inside fog. (e.g. onto a mountain).

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Snow scavenging. This is where falling snow"removes" the material below it.Nucleation scavenging. This is not a physical scavenging process strictly speaking.

It stands for the conceptual representation of aerosol activation to cloud droplets within aerosol computer models. Aerosols and cloud droplets are mostly treated separately within computer models so that aerosol activation to cloud droplets represents a loss process that can be assimilated with aerosol scavenging.

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Most often the term molecular self-assembly refers to intermolecular self-assembly, while the intramolecular analog is more commonly called self-assembly

Molecular self-assembly has allowed the construction of challenging molecular topologies. An example are Borromean rings,interlocking rings wherein removal of one ring unlocks each of the other rings.

4.1 Self-Assembly (supramolecular approach)

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DNA has been used to prepare a molecular analog of Borromean rings. More recently, a similar structure has been prepared using non-biological building blocks

Everyone knows how to assemble things: Just grasp the parts and put them together. Self-assembly, though, doesn’t work at all like this, and as a consequence, it presents special challenges

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Improving methods for making complex structures by self-assembly is an enormously important area of research.I’ve already discussed the near-term promise of nanotechnologies based on composite nanosystems that use biomolecules to organize non-biological components. Here, I’d like to outline some fundamental principles will shape the role of self-assembly as nanotechnology advances.

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4.1 Advantages of self-assembly

Self-assembly has a fundamental advantage over mechanically directed assembly: It requires no machinery to move and orient components, letting random, Brownian motion do the job instead. Selective binding between uniquely matching surfaces compensates for the randomness of the motions that bring components together.

Molecular synthesis methods and self-assembly can be used to produce atomically precise nanosystems by the billions, and even by the ton, thereby establishing a technology base with wide-ranging applications that can drive development forward.

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The architecture of biomolecular fabrication is based on the use of programmable machines to produce the complex parts necessary for self-assembly of complex systems. The same fundamental architecture can be extended to use artificial biomolecular machines (and then non-biomolecular machines), resulting in products made of better and more

4.2 Disadvantages of self-assemblyThe most fundamental disadvantage of pure self-assembly is that for every product, the structure of the parts must encode the structure of the whole. This requires that components be more complex, which tends to make design and fabrication more difficult

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Another consequence is that a self-assembled product will be partitioned by complex internal interfaces that have no operational function. Unless they are strengthened after assembly, these interfaces will weak. These are major constraints.

Mechanically directed assembly avoids these constraints. Because components need not encode the structure of a product, they can be simple and standardized, and they can be chosen for their functional properties with less concern for how they are put together

This will enable more straightforward design and fabrication, but one must make the necessary machinery — and I expect that this will be accomplished by means of self-assembly.

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4.3 Applications

Supramolecular assemblies are being investigated as new materials in a variety of contexts. For instance, Samuel Stupp and coworkers at Northwestern University showed that a supramolecular assembly of peptide amphiphiles in the form of nanofibers could be used to promote the growth of neurons.

Self-assembling dendrons have also been used to generate arrays of nanowires.Electron donor-acceptor complexes comprise the core of the cylindrical supramolecular assemblies, which further self-organize into two-dimensional columnar liquid crystaline lattices. Each cylindrical supramolecular assembly functions as an individual wire. High charge carrier mobilities for holes and electrons were obtained.

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Another example with implications at the biology/materials science interface is of self-assembling dendritic dipeptides, which form hollow cylindrical supramolecular assemblies in solution and in bulk. The cylindrical assemblies possess internal helical order and self-organize into columnar liquid crystalline lattices. When inserted into vesicular membranes, the porous cylindrical assemblies mediate transport of protons across the membrane.

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5.0 Molecular Design and modeling

Molecular Modeling and Design" has a very interdisciplinary character and is intended to provide basic information as well as the details of theory and examples of its application to experimentalists and theoreticians interested in modeling molecular properties and putting into practice rational design of new materials.

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One of the first requirements to initiate the molecular modeling of molecular materials is an accurate and realistic description of the electronic structure, intermolecular interactions and chemical reactions at microscopic and macroscopic scale. Therefore the first four chapters contain an extensive introduction into the latest theories of intermolecular interactions, functional density techniques, microscopic and mezoscopic modeling techniques as well as first-principle molecular dynamics

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In the following chapters, techniques bridging microscopic and mezoscopic modeling scales are presented. The authors then illustrate various successful applications of molecular design of new materials, drugs, biocatalysts, etc. before presenting challenging topics in molecular materials design.

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