BY,PRATHUL NATH P P15PH62R06M.TECH SSTIIT KHARAGPUR

DIAMOND THIN FILMS

Diamond : Biggest and Best

Allotrope of carbon .

Highest hardness and thermal conductivity.

Optical Transparency (bandgap =5.4 eV).

Resistant to chemical corrosion.

High Melting Point.

Source: Wikipedia

Methods of Creating Artificial Diamond

Heating carbon under extreme pressure.

High-pressure high-temperature (HPHT) growth technique.

Graphite compressed to tens of thousands of atmospheres at 2000 K in the presence of metal catalyst, and left until diamond crystallizes.

Limits the range of applications.

Chemical Vapor Deposition

Thermal decomposition of carbon-containing gases under reduced pressure to grow diamond on the surface of natural diamond crystals at 900 ◦C.

Deryagin and Spitsyn independent reasearch to grow diamond on non-diamond substrates.

Lots of advancements afterwards like ‘Hot filament reactor’ and ‘Microwave plasma reactor’.

A gas phase chemical reaction occurring above a solid surface, which causes deposition onto that surface.

Methods of production of Diamond CVDa)Hot filament, b) NIRIM type microwave plasma reactor, c) ASTEX type microwave reactor, d) DC arc jet

Source: Paul W May, University of Bristol

CVD techniques require a means of activating gas phase carbon-containing precursor molecules.

This activation can involve thermal methods (e.g. a hot filament), electric discharge (e.g. DC, RF or microwave), or a combustion flame.

Precursor gas (usually CH4) is diluted in excess of hydrogen, in a typical mixing ratio of 1%vol. CH4. Also, the temperature of the substrate is usually greater than 700 ◦C

The chemistry of CVD diamond growth

Source: Paul W May, University of Bristol

• Gases first mix in the chamber before diffusing toward the substrate surface.

• They pass through an activation which provides energy to the gaseous species.

•This activation causes molecules to fragment into reactive radicals and atoms, creates ions and electrons,and heats the gas.

• Undergoes a complex set of chemical reactions until they strike the substrate surface. •At this point the species can either adsorb, react, desorb or diffuse until an appropriate reaction site is found.

Nucleation

Once individual diamond crystallites have nucleated on the surface, growth proceeds in three dimensions until the crystals coalesce.

Resulting film is polycrystalline with many grain boundaries and defects, and exhibits a columnar structure extending upward from the substrate.

As the film becomes thicker, the crystal size increases while the number of defects and grain boundaries decreases.

SEM/ TEM images

(a) individual diamond crystalisation.

b) a randomly oriented film; (c) A (111) triangular-faceted film.

(d) a (100) square-faceted film.

(e) a large grained epitaxially.

grown diamond film .

(f ) A nanocrystalline

diamond film grown by HFCVD at high CH4 concentration.

Source: W Professor John Wilson, Heriot Watt University, UK.)

Substrate Material

Little or no solubility or reaction with C Eg: Cu, Sn, Pb, Ag and Au, as well as non-metals such as

Ge, sapphire, alumina.

Substantial mutual solubility or reaction with C Eg: Metals where this is significant include Pt, Pd, Rh, Ni, Ti and Fe.

Carbide formation These include metals such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,

W, Co, Ni, Fe, Y, Al, and certain other rare-earth metals.

Applications

Cutting tools.

Thermal management.

Optics.

Electronic devices.

Field emission displays.

Patterned diamond film

Diamond-coated tungsten wire

Diamond wafers on Si

Source: Professor John Wilson, Heriot-Watt University, UK

Conclusion

The biggest challenge is cost and therefore commercialization of this amazing material is still in its infancy.

We are still some way from diamond becoming the engineer’s dream of being ‘the ultimate engineering material’.

Since familiarity with diamond as just another common place material might remove some of the glamour and mystique surrounding the world’s most sought-after gemstone.

References

Diamond thin films: a 21st-century material By Paul W. May, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK

Growth and Characterization of Thin Films, Robert J. Nemanich Department of Physics, North Carolina State University, Raleigh, North Carolina

Thin Film Diamond by Chemical Vapour Deposition Methods, M. N. R. Ashfold, P. W. May, and C. A. Rego, School of Chemistry University of Bristol.

A REVIEW ON THE MORPHOLOGY OF DIAMOND THIN FILM COATING ON VARIOUS TYPES OF SUBSTRATE MATERIALS:, Esah Hamzah, Agung Purniawan, Mohd. Radzi Mohd, Department of Materials Engineering, Teknologi Malaysia.

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