Post on 13-Aug-2015
transcript
NANO MATERIALSPRESENTED BY: ANJANA JAYASHRIBRANCH:CHE ‘A’
CONTENTS
PULSE LASER DEPOSITION
CHEMICAL DEPOSITION
PROPERTIES
Pulsed Laser Depositiona) principleb) Experimental Setup
c)workingd) Advantages and
DisadvantagesTarget: Just about anything! (metals, semiconductors…)Laser: Typically excimer (UV, 10 nanosecond pulses)Vacuum: Atmospheres to ultrahigh vacuum
CCD /PMT
spectrometer
Target
Substrates or Faraday
cup
laser beam
PRINCIPLE: The laser pulse of high intensity and energy is used to evaporate carbon from graphiteThese carbon atoms are condensed to form nanotubes.DESCRIPTION:A quart tube contains a graphite target is kept inside a high temperature muffle furnace filled with argon gas and heated at 1473 K. A water cooled copper collector is fitted at other end.The target material contains small amount of Ni-Co to catalyse the formation of nano tubes.
PROCESSES IN PVD:
LASER PULSE
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LATTICE
· Flexible, easy to implement · Growth in any environment· Exact transfer of complicated materials
(YBCO)· Variable growth rate · Epitaxy at low temperature· Resonant interactions possible (i.e.,
plasmons in metals, absorption peaks in dielectrics and semiconductors)
· Atoms arrive in bunches, allowing for much more controlled deposition
· Greater control of growth (e.g., by varying laser parameters)
Advantages of PLD
CHEMICAL VAPOUR DEPOSITION
INTRODUCTION Chemical Vapour Deposition (CVD) is a
chemical process used to produce high purity, high performance solid materials.
In a typical CVD process, the substrate is exposed to one or more volatile precursors which react and decompose on the substrate surface to produce the desired deposit.
During this process, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.
Transport of reactants by forced
convection to the
deposition region
Transport of reactants
by diffusion from the main gas stream to
the substrate surface.
Adsorption of reactants in the wafer (substrate)
surface.
Chemical
decomposition and other
surface reactions
take place.Desorption
of by-products from the surface
Transport of by-products by diffusionTransport of
by-products by forced
convection away from
the deposition
region.
STEPS INVOLVED IN CHEMICAL VAPOUR DEPOSITION
SCHEMATIC DIAGRAM - THE STEPS INVOLVED IN CVD
CVD’s are classified into two types on the basis of Operating Pressure. 1. Atmospheric Pressure CVD 2. Low Pressure CVD Plasma Enhanced CVDPhotochemical Vapour DepositionThermal CVD
TYPES OF CVD
Variable shaped surfaces, given reasonable access to the coating powders or gases, such as screw threads, blind holes or channels or recesses, can be coated evenly without build-up on edges.Versatile –any element or compound can be deposited. High Purity can be obtained. High Density – nearly 100% of theoretical value. Material Formation well below the melting point Economical in production, since many parts can be coated at the same time.
ADVANTAGES OF CHEMICAL VAPOUR DEPOSITION
APPLICATIONS OF CHEMICAL VAPOUR DEPOSITION
CVD has applications across a wide range of industries such as: Coatings – Coatings for a variety of applications such as wear resistance, corrosion resistance, high temperature protection, erosion protection and combinations thereof.Semiconductors and related devices – Integrated circuits, sensors and optoelectronic devicesDense structural parts – CVD can be used to produce components that are difficult or uneconomical to produce using conventional fabrication techniques. Dense parts produced via CVD are generally thin walled and maybe deposited onto a mandrel or former.
Properties of Nano Materials
The melting point decreases dramatically as the particle size gets below 5 nm
Melting Point
Band gap
The band gap is increases with reducing the size of the particles
Surface Area
The total surface area (or) the number of surface atom increases with reducing size of the particles
• For semiconductors such as ZnO, CdS, and Si, the bandgap changes with size
- Bandgap is the energy needed to promote an electron from the valence band to the conduction band
- When the bandgaps lie in the visible spectrum, changing bandgap with size means a change in color
• For magnetic materials such as Fe, Co, Ni, Fe3O4, etc., magnetic properties are size dependent
- The ‘coercive force’ (or magnetic memory) needed to reverse an internal magnetic field within the particle is size dependent
- The strength of a particle’s internal magnetic field can be size dependent
Size-DependentProperties of semiconductor and magnetic materials
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