Electrical diamond-like carbon

The next point to realize is that the best emitter is a metal. Many forms of carbon initially studied are semiconductors or even insulators, including nanodiamond [8-11] and diamond-like carbon (DLC) [12-13,4]. Combine this with local field enhancement means that there is never uniform emission from a flat carbon surface, it emits from local regions of field enhancement, such as grain boundaries [8-11] or conductive tracks burnt across the film in a forming process akin to electrical breakdown [13]. Any conductive track is near-metallic and is able to form an internal tip, which provides the field enhancement within the solid state [4]. Figure 13.2 shows the equipoten-tials around an internal tip due to grain boundaries or tracks inside a less conductive region. 

Reports on man-made diamond obtained by HPHT synthesis were first published in 1955 by General Electric [4]. Usually, metals able to dissolve carbon under HPHT conditions are used as catalysts and increase growth rates. Diamond crystals of several millimeters in size can be obtained in this way, but usually small grains for abrasives are produced. Direct conversion of graphite to diamond without catalyst in HPHT apparatus is possible, but uneconomical for industrial application. Direct transformation can be done by the detonation method and produces nanosized powders of diamond and diamond-like carbon [5]. 

By using chemical vapour deposition (CVD) technology at a relatively low temperature, Nissin Electric, Kyoto, Japan, claims it is able to apply diamond-like carbon coatings to materials such as plastics and rubber, improving their properties of friction, abrasion resistance and insulation. 

Hard-coating materials range from ultra-hard materials such as diamond-like carbon through the refractory compounds to alloys. However, the transition-metal carbides and nitrides have achieved by far the highest level of commercial success. Perhaps, the most important property of this group of carbides and nitrides is their defect structure. Ideal stoichiometry is generally not found in these phases deviations from the stoichiometry are found to be far more common. The transition-metal carbides and nitrides are typically metallic in their electrical, magnetic and optical properties. 

Wear resistance Cutting tools, machine parts Electric parts, optical parts TiC, TiN, Ti(C, N), (Ti, A1)N CrN, Cr,C3, AI2O3, SiOj W2C, TiB2, diamond Diamond-like carbon Cemented carbide Quenched and tempered steel, stainless steel, Ti alloy, A1 alloy, PET film Plastic lens... 

Mechanical properties, electrical properties, thermodynamic stability, surface chemical activity, and other important parameters can all be discussed relative to the structure of the carbon network, composed of both aromatic layers and 3D-arranged (diamond-like) phases. 

Soga, T. Hyashi, Y. Solar photovoltaic application of diamond-like a-C. In Properties of Amorphous Carbon Silva, S.R.P., Ed. EMIS Data Review Series No. 29 INSPEC, The Institution of Electrical Engineers U.K., 2003 355 pp. 

Metals conduct electricity extremely well. Many solids, however, conduct electricity somewhat, but nowhere near as well as metals, which is why such materials are called semiconductors. Two examples of semiconductors are silicon and germanium, which he immediately below carbon in the periodic table. Like carbon, each of these elements has four valence electrons, just the right number to satisfy the octet rule by forming single covalent bonds with four neighbors. Hence, silicon and germanium, as well as the gray form of tin, crystalhze with the same infinite network of covalent bonds as diamond. 

Another application for diamond films depends on the possibility of producing the material for microelectronic components by building up layers of carbon atoms on a diamond film. Although diamond is an electrical insulator, like silicon and other materials, it becomes a conductor when small quantities of other substances, such as boron, are added to it. We say that the diamond has been doped and behaves as a semiconductor. (We will discuss semiconductors in Section 13.5.) In principle, diamond could supplant silicon as the material for constructing microelectronics devices, and theoretically these devices would be much faster than ones constructed from silicon. 

Kuznetsov, V.L., Butenko, Yu. V., Chuviln, A.L., Romanenko, A.I., Okotrrub, A.V., 2001, Electrical resistivity of graphitized ultra-disperse diamond and onion-like carbon, Chem. Phys. Lett. 336, 397-404. 

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