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UNIT 2 SYNTHESIS BY PHYSICAL AND CHEMICAL METHOD, NAME:JEEVITHA P ROLL…
UNIT 2
SYNTHESIS BY PHYSICAL AND CHEMICAL METHOD
NANOLITHOGRAPHY
Nanolithography is a method of producing structures by using a mold with 3D surface designs that is pressed against a superheated cast.
Lithography is viewed as a physical process involving image transfer.
ADVANTAGES
1.Given the speed with which prints can be made, lithography is the cheapest way to produce large scale commercial print runs.
Long life of lithography plate.
3.Ability to reuse.
4.Time and cost low compared to traditional raised letter printing.
DISADVANTAGES
1.When not properly maintained lithographic degrade over time.
2.Colours can be less bright.
3.Cost is not effective when it comes to smaller amount.
OPTICAL LITHOGRAPHY PROCESS
STEP1:DESIGN
1.There is mask
2.Mask and writer process.
STEP2:ARIAL IMAGE
1.Real image
2.Exposure to arial image to real image.
STEP3:LATENT IMAGE
1.Resist image
2.latent image to resist image RIE pattern transfer.
STEP4:DEVICE LAYER
1.Desire image
2.wavelength used for optical lithography is 0.3nm.
TYPES OF LITHOGRAPHY BASED ON OPTICAL PROPERTIES
X-RAY LITHOGRAPHY
X-ray lithography is a process used in semiconductor device fabrication industry to selectively remove parts of a thin film of photoresist. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist," on the substrate to reach extremely small topological size of a feature. A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist.
ELECTRON BEAM LITHOGRAPHY
Electron-beam lithography often abbreviated as e-beam lithography, is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist . The electron beam changes the solubility of the resist, enabling selective removal of either the exposed or non-exposed regions of the resist by immersing it in a solvent (developing). The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching.
LASER LITHOGRAPHY
laser interference lithography, a coherent UV laser beam goes through a spatial filter for cleanup and expansion . A mirror and a tilted polymer resist-coated substrate are assembled perpendicular to each other. The expanded laser beam strikes a tilted mirror and the tilted polymer resist–coated substrate simultaneously. The reflection from the mirror also strikes the substrate. The incoming light and the reflected light interfere on the substrate creating a standing wave 2-D regular pattern of bright and dark spots. This constitutes a basic setup of the well-known Lloyd’s mirror interferometer.
CHEMICAL METHODS
CHEMICAL VAPOUR DEPOSITION
Chemical Vapor Deposition (CVD) is a process in which the substrate is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired thin film deposit.
CLASSIFICATION
BASED ON PRESSURE
1.Atmospheric pressure CVD
2.Subatmospheric CVD
3.Low pressure CVD
4.Ultra high vacuum CVD
BASED ON GAS PRECURSSOR,FILM STRUCTURE,GROWTH
1.Metal organic CVD
2.Epitaxy or vapour phase epitaxy CVD
3.Non epitaxial growth
4.Atomic layer deposition or atomic layer epitaxy CVD
SOL-GEL METHOD
In this method, the molecular precursor (usually metal alkoxide) is dissolved in water or alcohol and converted to gel by heating and stirring by hydrolysis. Since the gel obtained from the hydrolysis process is wet or damp, it should be dried using appropriate methods depending on the desired properties and application of the gel. After the drying stage, the produced gels are powdered and then calcined.
1)Very important to control
PH of the starting solution.
2)Anything want to grow, we need nucleation.
3)Most disadvantageous is that it couldn't control chemical reaction.
COPRECIPITATION METHOD
It is the settling down of insoluble particles from a solution. It involves in simultaneous occurance of nucleation growth ,coarsening, and agglomeration process.
Typical synthesis method
1)Metal formed from aqueous solution by reduction from non-aqueous solution.
2)Oxides formed from aqueous solution and non-aqueous solution.
PHYSICAL METHODS
PHYSICAL VAPOUR DEPOSITION
In this method, material source is heated to high temperature in vacuum either by thermal or e-beam methods.
Material vapor is transported to the target in vacuum.
DISADVANTAGES
1)Film quality is often not good as sputtering film.
2)When chimney is used vapor gets deposited on chimney.
SPUTTERING
Sputter deposition is a widely used technique to deposit thin films on substrates. The technique is based on ion bombardment of a source material, the target. Ion bombardment results in a vapor due to a purely physical process, i.e., the sputtering of the target material.
ADVANTAGES
1)Better step coverage.
2)Less radiation damage than e-beam evaporation,
3)Easier to deposit alloys
DISADVANTAGES
1)Some plasma damages including implanted argon.
2)Not good for schotkey diodes.
LASER ABLATION
In this method, nanoparticles are generated by nucleation and growth of laser-vaporized species in a background gas. The extremely rapid quenching of vapor is advantageous in producing high purity nanoparticles in the quantum size range.
CONSOLIDATION OF NANOMATERIALS
SHOCKWAVE CONSOLIDATION
Shockwave consolidation is accomplished by surrounding the nanopowder-containing tube with explosives and then detonated. The resulting shock wave causes rapid fusing of the powders without the melt and subsequent grain growth.
SPARK PLASMA SINTERING
In this method known quantity of dried and milled powder sample in cylindrical die with graphite sheet facilitates easy removal of sintered compact is taken. On chiller compressor and machine. Place die containing sample in SPS chamber. Maintain vacuum, argon inside chamber.
NAME:JEEVITHA P
ROLL NO:1961012
SUBJECT:NANOMATRIALS
SUBCODE:18MTE61
