Artificial Cvd Diamond

Although diamond showers are formed routinely on giant gaseous planets in the solar system, humanity has learned the trick and made CVD diamond based on similar principles. Most CVD diamonds are formed by thermally decomposing a carbonaceous gas (e.g. methane) in the presence of an over abundance (e.g. 100X) of hydrogen. The diatomic hydrogen partially dissociates to form

Figure 1.14. Various sizes of CVD diamond films deposited by microwave plasma of hydrogen and methane gas mixture (Aixtron brochure). Note that the blue diamond film contains doped boron so it is semiconducting.

Photon Energy (eV)

Photon Energy (eV)

0.1 1 10 100 ItMKJ

Wavelength (jim) Figure 1.15. The range of transparency for various optical materials.

0.1 1 10 100 ItMKJ

Wavelength (jim) Figure 1.15. The range of transparency for various optical materials.

hydrogen atoms that fly around. When carbon atoms are formed, the hydrogen atoms bombard the detached carbon atoms to maintain carbon's diamond (sp3) bonds until they are joined by other carbon atoms. As a result, diamond is formed by linking dissociated atoms without forming the more stable form of carbon — graphite. Even if graphite is formed, graphitic (sp2) bonds can be converted into diamondoid bonds (sp3) by the continual bombardment of hydrogen atoms. Thus, diamond film can be formed metastably with the protection of hydrogen atoms as the catalyst.

Figure 1.16. A large transparent CVD diamond grown by De Beers. Similar diamond windows can be as large as 16 cm in diameter and more than 2 mm in thickness (e.g. Raytheon). The amount of absorbed energy is less than 1%. The absorption coefficient is less than 0.1 cm-1, and can be as low as 0.027 cm-1.

Figure 1.16. A large transparent CVD diamond grown by De Beers. Similar diamond windows can be as large as 16 cm in diameter and more than 2 mm in thickness (e.g. Raytheon). The amount of absorbed energy is less than 1%. The absorption coefficient is less than 0.1 cm-1, and can be as low as 0.027 cm-1.

The more hydrogen atoms that are present during this process, the faster the growth of diamond without the formation of graphitic carbon or other defects.

Diamond films with low concentration of defects can be excellent optical windows for shielding generators of X-ray (Fig. 1.14), visible light (Fig. 1.15), or infrared electromagnetic radiation. A diamond window can absorb so little of the electromagnetic radiation that even megawatts of microwave can pass through without warming it (Fig. 1.16). This makes diamond windows ideal for igniting hydrogen fusion with a megawatts microwave beam. Diamond windows may also survive high corrosive environments. For example, a natural diamond lens was used to explore the acidic atmosphere of Venus.

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