Chemical vapour deposition or CVD is a generic name for a group of processes which used to produce high quality, high-performance, solid materials which is deposited from a gas onto a substrate and that chemical reactions are involved.
2. What is CVD diamond?
Synthetic diamonds are prepared or produced by CVD techniques and therefore it is called as CVD Diamonds. It is also known as Synthetic diamond, CVD Grown diamond, Man-Made diamond, Cultured Diamond.
3. Why is it difficult to synthesize diamond?
Diamond consists – like coal or graphite – of carbon. The main difference is the arrangement of the carbon atoms in the material (i.e. in the crystal lattice). Unfortunately graphite is the more stable carbon allotype (form) and therefore diamond is very rare in nature. To convert graphite into diamond high pressure and high temperatures (HPHT) must be applied. Under those conditions diamond becomes the more stable carbon allotype. For diamond CVD a carbon containing gas is decomposed and the carbon atoms are deposited on a surface. By proper conditions the growth of diamond crystals can be enhanced and the growth of graphite is suppressed.
4. How does CVD work ?
The CVD process begins with tanks containing an initiator material (red) and one or more monomers (purple and blue), which are the building blocks of the desired polymer coating. These are vaporized, either by heating them or reducing the pressure, and are then introduced into a vacuum chamber containing the material to be coated. The initiator helps to speed up the process in which the monomers link up in chains to form polymers on the surface of the substrate material.
5. What gases are used for CVD DIAMONDS ?
Mostly a mixture of hydrogen and methane gases are used for the making of CVD Diamonds.
6. What are approx growth temperatures require for CVD Diamonds ?
For CVD Diamonds around 700-900°C . Also lower temperatures are possible but at strongly reduced growth rates.
7. How fast does CVD DIAMOND Grows ?
Actually it is a very slow process. At growth rates between 0.1 and 10 micron per hour usually deposited on large areas (>100 cm2) diamond where, much higher growth rates (>100 micron per hour) have been demonstrated for small areas (<1 cm2).
8. What substrate material can be used to make CVD DIAMONDS ?
Materials used in chemical vapor deposition include silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, silicon dioxide, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and diamond. The main requirements are: the material must be able to withstand high temperatures, it must not be attacked by the activated process gas and it must not dissolve carbon.
9. What are typical grain sizes of polycrystalline diamond ?
Usually the grain size is in the sub-micron range at the beginning of diamond growth. With increasing thickness the grains grow larger. Usually the grain size at the growing surface of a diamond film is about 10 % of the film thickness.
10. What is nano-crystalline diamond ?
By enforced re-nucleation during diamond growth the diamond grains can be kept very small. This material is called nanocrystalline or ultra-nanocrystalline diamond (UNCD). This material does not have all the unique properties of diamond (e.g. it is not transparent and the thermal conductivity is low). But it exhibits a pretty smooth surface and there are interesting applications in tribology, micro-mechanics and bio-chemical sensing.
11. What is the surface roughness ?
The surface of an as grown polycrystalline diamond film is pretty rough (like sandpaper). Hence polishing is a very important processing step for many applications. The surface roughness of polished diamond is usually a few nanometers.
12. How does CVD diamond compare to DLC ?
DLC is an acronym for diamond-like carbon. Other denotations are a-C:H or a-C. In this material the carbon atoms do not form a crystal lattice but a random (amorphous) network. It is deposited by bombarding a surface with energetic (hydro-)carbon particles. This can be done at room temperature. DLC films exhibit quite a lot of compressive stress which limits the maximum thickness. It is somehow “diamond-like” as it is chemically stable and hard, however, it is clearly no diamond.
13. How does CVD diamond compare to natural diamond ?
Natural diamonds show a widespread range of properties. A sophisticated system for the categorization of natural diamond stones with respect to color, clarity, defects and so on has been established. High-quality polycrystalline CVD diamond does have similar properties like perfect natural stones. For mono-crystalline CVD diamond properties have been demonstrated that even surpasses those of the best natural stones.
14. Is CVD diamond expensive?
The answer is yes and no. For e.g. large area diamond disk i.e more than 1 mm thickness will be expensive as compare to small area diamond disk are rather cheap. So usually diamond is only used if necessary. This is mainly because the deposition process requires a lot of energy, low growth rate and the equipment expensive.
15. Is CVD diamond a billion market ?
The answer is No as of now. Most of the CVD diamond products serving small niche markets. As natural diamond are expected to reduce and CVD Diamond for several applications may become important in the future.