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INTRODUCTION This study is motivated, in large measure, by recent discoveries that have permitted the growth of crystalline diamond by chemical vapor deposition at practical growth rates. Chemical vapor deposition of diamond has enormous technological potential in areas as diverse as electronics, optics, biomedical implants, abrasives, cutting tools, bearing surfaces, and heat sinks. The related diamond-like materials show great potential for tribological surfaces, corrosion protection, passivating layers, and diffusion barriers as well as in photolithography. By way of background, annual world production of natural rough diamonds is about 94 million carats (18.7 tons). Synthetic production in weight terms is much larger, possibly 66 tons. Imports of industrial-quality artificial diamonds amount to about 51 million carats (10 tons). Sale price is slightly over $1 /carat. Vapor-grown diamond and diamond-like materials may play an important role in a wide range of industries. Their ultimate economic impact may well outstrip that of high-temperature superconductors. However, despite this promise, there are relatively few applications currently being realized. Many of the most exciting applications of both diamond and the diamond-like materials arise from their extreme properties, or combinations of properties, with hardness sometimes unimportant or of secondary importance. SCOPE This report reviews the present status of vapor-grown diamond, the diamond-like materials, and related solids such as SiC and cubic BN. Current developments are considered in a broad context, and directions for future work are recommended. The field of superhard materials is rapidly evolving and has diffuse and expanding boundaries. It is not an exaggeration to say that there has been an explosion of interest in the subject. Figure 1-1 shows the trend in numbers of scientific papers published in the past 20 years. The curve is sharply upward, with no indication of peaking. At the risk of incompleteness, it was necessary to make some arbitrary judgments about topics to include. This inevitably reflects the experiences of the members of the committee an should not necessarily be regarded as a value judgment about the relative importance of topics. s
6 200 150 co a: llJ cry ~ 100 o cr: Lid a: is 50 o hi- T ~ ~ ~ 11 ~ ~ I I I I I I 74 76 78 80 82 84 86 88 YEAR 68 70 72 FIGURE 1-1 Number of papers published in scientific journals on low-pressure growth of diamond and diamond-like materials. (Source Yalamanchi and Thutupalli, 1988) The types of materials considered may be categorized by their elemental composition. Most of the materials considered fall in the "composition tetrahedron" shown in Figure 1-2 and are compounds or solid solutions involving the elements boron, carbon, nitrogen, and silicon. These low-atomic-weight elements also form strong covalent bonds with hydrogen, which leads to a class of hydrogenated, typically amorphous, solids discussed later. si / 1 \ 1 Sic ~ ~ Si3N4 ~~ 1 `N 1 \ "A 1 \ / N ~ ~ / , BCN ? _` / ,~ ~ _ ~ _ ~ ~ it_ i` . ~ CN ~l B4C B C DIAMOND- LIKE CARBONS B12C2.8Si O.35 FIGURE 1-2 Hard materials in the composition tetrahedron C-B-N-Si. Other hard materials not shown include amorphous hydrocarbons and compounds with other B/C ratios, B-O compounds, and C-N compounds.
The major emphasis is on crystalline diamond and the so-called diamoncl-like materials. For the latter the categorization method proposed by Angus and Hayman (1988) is used; coverage is restricted to carbons and hydrocarbons with atomic number densities greater than approximately 0.19 g-atom/cm3. The amorphous diamond-like materials have higher number densities than other carbonaceous materials and have a significant fraction of sp3-bonded carbon sites. Cubic BN and both hexagonal and cubic SiC are considered because they are structurally related to diamond and have overlapping areas of application. Other recently reported hard materials in the C-N and B-O systems are noted but not discussed. The committee has arbitrarily chosen not to include BeO, Al2O3, BP, A1N, Si3N4, and the garnets. No doubt these materials will compete for many of the same applications discussed in this report. NOMENCLATURE A confusing and inconsistent nomenclature has arisen to describe the diamond-like materials. The committee made an arbitrary choice of terms for use in this report. The generally accepted generic term, ~diamond-like materials," is used to describe all carbon and hydrocarbon solids with atomic number densities greater than approximately 0.19 g-atom/cm3. It is accurate in that the diamond-like phases have exceptional hardness, a significant proportion of Sp3 carbon atom sites, and atomic number densities between those of crystalline diamond and the adamantanes. There appear to be two main classes of diamond-like solids (i.e., nonhydrogenated and hydrogenated). These are referred to in this report as diamond-like carbons and diamond-like hydrocarbons respectively. In some cases the abbreviations a-C (amorphous carbon) and DLC are also used to refer to the diamond-like carbons and a-C:H and DLHC to refer to the diamond- like hydrocarbons. A summary of the principal terms used to describe the diamond-like materials is given in Table 1-1. TABLE 1-1 Nomenclature for Diamond-Like Materials Nonhydrogenated Hydrogenated Used in This Report Diamond-like carbons a-C DLC Not Used in This Report Dense carbons a-D i-C Hard carbons Diamond-like hydrocarbons a-C:H DLHC Dense hydrocarbons
8 BACKGROUND Hardness is one of the oldest and yet most poorly understood of all the physical properties of solids. The theory of hardness has remained essentially a semiempirical science, at least until very recent years. Relatively few studies are available that attempt to relate hardness to basic notions of bonding and structure (Cohen, 1986; Zhogolev et al., 1981; Goble and Scott, 1985) There are useful empirical correlations of wear resistance versus lattice energy per unit volume (Plend! ant! Gielisse, 1962) and bulk modulus versus some function of interatomic spacing (Cohen, 1985~. Similarly, hardness correlates strongly with atomic number density and with bond energy density. This is shown in Figure 1-3, which is a plot of microhardness versus atomic number density for diamond-cubic and zinc-blend solids (Angus et al., 1988~. The extreme values of hardness of diamond, cubic BE, and a-C:H are clearly evident. ~ 0,000 ~ C'J 8,000- E `~, 6,000- cn he G I o 4,000 - 2,000 ~ o · 25 g load O 50 9 load · 100 g load O Unknown load DIAMOND 0/ too / O o ~ BN a-C:H / siC 1 0. 00 0.05 0.1 0 0.1 5 0.20 0.25 0.30 0.35 ATOMIC NUMBER DENSITY (g atom/cm3) FIGURE 1-3 Microhardness versus atomic number density
9 High-Pressure Synthesis of Diamond and Cubic BN The General Electric Company was the first to reveal a successful process for growth of diamond at high pressure and high temperature (Bundy et al., 1955~. Graphitic carbons in the presence of a liquid metal solvent-catalyst are brought into the temperature-pressure range where diamond is the thermoclynamically stable phase and crystals spontaneously nucleate and grow (Figure 1-4~. Since 1955 the growth of abrasive grain up to about I mm at high pressures and temperatures has matured to become a routine manufacturing procedure. About 90 percent of industrial diamond abrasives are now synthesized. In terms of size, shape, and toughness, the process provides a reproducibility and tailorability not found in natural materials. General Electric, DeBeers, Sumitomo, and the Soviet Union now provide high-pressure grit on the world market. PT 80 ; 60' - y 40 - 20 o Diamond . _ o / RH PD)/ Ni FEW ,~BERMAN-SIMON EXTRAPOLATION Graphite - - - 1000 2000 3000 T (K) FIGURE 1-4 Equilibrium phase diagram for the carbon system. The P-T curves for several diamond-liquid metal eutectics are cross-plottec! on the diagram. These curves define the minimum P-T conditions for high- pressure diamond synthesis by the solvent-catalyst method. The region for vapor-growth of diamond is located at pressures less than ~ bar and temperatures less than 1400 K. The pressure range for high-pressure synthesis is generally 50 to 65 kb; the temperature range is from 1300 to 17000C. The reaction mixture contains carbon (usually as graphite) in combination with the Group ~ elements, iron, nickel, and cobalt; manganese, aluminum, and boron are principal secondary elements. At the reaction conditions these systems exhibit a diamond-liquid two-phase region. Nucleation of diamond is rapid once the metal-carbon eutectic temperature is exceeded. ;
10 High-pressure diamond synthesis is a batch operation. The time cycle is determined by the desired grain size and optimization of die life. Growth rates can be very fast, but 1000 M/hour is a useful average rate for grain sizes in the range of 50 to 1000 ~m. The process becomes prohibitively expensive for sizes larger than about ~ mm, with the possible exception of crystals larger than 1 carat. Sistered materials are produced for cutting tools, wire-drawing cites, and well-~rilling bits. Polycrystalline pieces up to about 50 mm in diameter, usually on a carbide base or within a carbide ring, are available. It is possible to grow large gem-quality single crystals by a high-pressure thermal gradient process. Diamond crystals as large as 11 carats with a maximum dimension of 17 mm have been reported (Shigley, 1987~. Crystals doped with either boron or nickel can also be prociucecI. Sumitomo Corporation sells N-doped crystals at least 6 to 7 mm in maximum dimension for fabrication into cutting tools, microtome and scalpel blades, wire dies, anvils, and heat sinks. Similar processes are used for cubic BN synthesis. The principal solvent-catalysts are alkali and alkaline earth metal nitrides and metal solvents similar to those used for growing diamond. Although cubic BN abrasive grain has been available since 1957, the first optically and electrically useful crystals were synthesized in 1987 (Mishima et al., 1987~. Metastable Diamond Growth Metastable phases can form from precursors with high chemical potential if the activation barriers to more stable phases are sufficiently high. As the precursors fall in energy they can be trapped in a metastable state. For metastable diamond synthesis the undesired competing processes are nucleation of graphitic carbons and graphitization of existing diamond. The possibility of making diamond in the pressure-temperature range where it is thermodynamically unstable has been recognized for many years (Bridgman, 1955; Lander and Morrison, 1966), however, accomplishing practical low-pressure processes has taken decades to accomplish. The first documented successful effort to grow diamond from vapor was initiated in 1949 by William G. Eversole at the Linde Laboratories of Union Carbide Corporation (Kiffer, 1956; Eversole, 1962~. Eversole's work was contemporaneous with the earliest studies of high-pressure diamond growth. Angus in the United States (Angus et al., 1968) and Deryagin in the Soviet Union (Deryagin et al., 1968) continuer! these efforts, which ultimately led to proof that diamond could be grown by chemical vapor deposition from hydrocarbon gases and to some under- standing of the role of hydrogen in the process. Although relatively rapid transient growth rates (0.1 um/hour) of diamond were achieved in these early studies, graphitic carbons eventually nucleated on the diamond seed crystals, suppressing further diamond growth. Average growth rates were too low to be of commercial significance. Several reviews describing the history of low-pressure diamond growth are available (Devries, 1987; Badzian and Devries, 1988; Angus and Hayman, 1988~. These papers provide extensive bibliographies. VAPOR GROWTH OF DIAMOND The first reports of rapid low-pressure growth of diamond crystals on nondiamond substrates were by Deryagin's group in the Soviet Union (Deryagin et al., 1977; Spitsyn et al., 1981~; however, the method of growth was not revealed. Worldwide interest in low-pressure diamond growth was stimulated by a series of remarkable papers published by workers associated with the National Institute for Inorganic Materials (NIRIM) in Japan (Matsumoto, 1985;
11 Matsumoto et al., 1982a,b; 1987a,b). Yaichiro Sato and Nobuo Setaka were leading figures in this effort. Methods for growth of diamond at rates of 10 M/hour were described, and convincing characterization evidence was given. The de novo growth of faceted diamond without the necessity of a seed crystal was a significant advance over earlier methods. Crystalline diamond can be grown by an astonishingly large variety of energetically assisted chemical vapor deposition processes. These may be conveniently, if somewhat arbitrarily, divided into two broad categories: . Thermally-assisted chemical vapor deposition, for example, hot-filament-assisted processes. . Plasma-assisted chemical vapor deposition (PACVD), for example, microwave- assisted processes. These methods are described in detail later in this report. They can produce polycrystalline diamond films on a wide variety of substrates without the necessity of a diamond seed crystal. Although detailed molecular mechanisms are not known with certainty, all of the processes have elements in common; namely, the presence of atomic hydrogen and the production of energetic carbon-containing fragments under conditions that support high mobilities on the diamond surface. Average growth rates of polycrystalline diamond films are tens of micrometers per hour, but growth rates on the order of hundreds of micrometers per hour have been reported in high- energy systems. (Kurihara et al., 1988~. Indeed, a growth rate of 30 to 40 am per hour has been achieved with an acetylene torch (Hirose and Kando, 198S, Hirose, and Mitsuizumi, 1988~. Diamond-on-diamond epitaxy has been reported (Spitsyn et al., 1981; Fujimori, 1987) but the epitaxial layer is not of high quality, with stacking faults, twins, and even microcracks along (111) planes. It is expected that heteroepitaxy of diamond will be accomplished in the near future. The uncontrollable nucleation of diamond nuclei has prevented the growth of large (i.e., greater than 1 mm) single crystals by vapor deposition. DIAMOND-LIKE MATERIALS Related research has led to the discovery of a new class of materials, the diamond-like solids. The diamond-like phases are distinguished by unusual hardness and chemical inertness. These properties apparently arise from the high proportion of Sp3 carbon sites. Several recent review articles give access to this literature (Angus and Hayman, 1988; Tsai and Bogy, 1987; Angus et al., 1986~. There appear to be two classes of diamond-like phases: the diamond-like hydrocarbons (a-C:H) and the diamond-like carbon (a-C). More is known about the diamond-like hydrocarbons than the diamond-like carbons. The diamond-like carbons may, in fact, include several different types of structures ranging from microcrystalline diamond to complex, amorphous materials containing significant amounts of both sp2 and Sp3 carbon sites. The diamond-like materials are made by energetically assisted deposition processes--for ~ ~ .. . . . . ~ . , . A ~ . ~ . . . example, from rf plasmas--by direct deposition from low-energy (~100 eV) ion beams or by condensation from plasma arcs. As in the case of vapor growth of diamond, detailed molecular mechanisms are not known with certainty. However, evidence from several sources suggests that the metastable, amorphous diamond-like structures may be stabilized by the quenching due to the cold substrate.
1 12 APPLICATIONS Applications of Diamond The applications of diamond will stem from its extreme properties. Diamond has the highest values of atomic number density, hardness, thermal conductivity at 298 K, and elastic modulus of any known material (Table 1-2~. It is the most incompressible substance known and has a thermal expansion coefficient lower than Invar. Diamond also has a high refractive index and optical dispersion. If nitrogen is absent, diamond is extremely transparent from 230 nm to at least 40 '`m in the infrared (apart from a few intrinsic absorption bancis from 2.5 to 6.0 ~m). Applications of diamond as an abrasive or as a cutting tool arise from its extreme hardness and high thermal conductivity. The ability to deposit diamond films over large areas will greatly expand these applications and should lead to many others as well. Diamond films may find application as wear-resistant coatings, wire-drawing dies, coatings for drills, and bearing surfaces. It may also be possible to employ diamond coatings as impact-protection coatings for rain erosion and small-particle impact. TABLE 1-2 Some Properties of Natural Type IlA Diamond and Vapor-Grown Diamond Properties Type IIA Vapor-Grown Hardness, GPa Go* So - >90 Mass density, g/cm3 3.515 2.S - 3.5 Molar density, g-atom/cm3 0.293* 0.23 - 0.29 Specific heat at 300 K, J/g 6.195 Debye temperature, 273-1100 K 1860 ~ 10 K Thermal conductivity at 198 K, =20* 10 - 20 W/cm/K Bulk modulus, N/m2 4.4-5.9x0* Compressibility, cm2/kg 1.7xl 0-7*$ Linear thermal expansion coefficient o.8xIO~6*~* at 293 K, K-i Refractive index at 589.19 nm 2.41726 ~2.4 Dielectric constant at 300 K 5.7 ~ 0.05 ~5.7 *Higher than any other known material. **Lower than any other known material. ***Lower than Invar. The high thermal conductivity, low expansion coefficient, and strength of diamond provide high resistance to thermal shock. Windows for very-high-power lasers may take advantage of this combination of properties. Crystallume for example, has announced the commercial availability of 6-mm diameter x-ray windows. The high thermal conductivity has led to the use of diamond as a heat sink material in electronic applications. This application, and many others, will likely be expanded by the availability of large-area diamond films.
13 Natural and high-pressure synthetic diamonds are already used as instrument windows in specializes! research applications. This is a natural application of vapor-grown diamond films; optical elements and diamond-coated optics are long-range possibilities. However, some applications require significant reductions in surface roughness and in optical absorption. Diamond electronics is another long-range possibility. Diamond is a wide-band-gap semiconductor (5.5 eV) and, furthermore, has a high breakdown voltage (~107V/cm) and a saturation velocity (2.7 X 107 cm/see), higher than silicon, GaAs, or InP. Electron and hole mobilities are approximately 1900 and 1200 cm2/V-sec respectively. However, the use of vapor- grown diamond as an active electronic component will require greater crystalline perfection than is now available. Many electronic applications will also require growth of heteroepitaxial diamond films, which at this time has not been achieved. Applications of Cubic BN. SiC' and Other Materials Cubic BN has a hardness second only to diamond and is unreactive with alloys of iron, nickel, and cobalt. These properties have led to important applications as an abrasive. It has potential applications as an active semiconductor device (it can be doped both n- and p-type) and as a heat sink material. Silicon carbide is a commercially important abrasive material that can be made in tonnage lots at 1 atm pressure. Recent advances in the growth of large single crystals of SiC may lead to applications as an active electronic device material, as a heat sink, and possibly as a substrate for the heteroepitaxial growth of diamond from the vapor. Boron carbide is used as an abrasive (although never achieving its initial promise in this application), as an energy-absorbing material in armor, and as a moderator in nuclear reactors. It is under serious study and shows promise for high-temperature thermal electric applications. Applications of Diamond-Like Materials As with crystalline diamond, the applications of the diamond-like materials stem from their extreme properties. Of particular importance are their hardness, chemical inertness, smoothness, and apparent impermeability. Also, these films can be deposited on cold, temperature-sensitive substrates (e.g., hardened steel), which opens up other potential applications. The properties of the diamond-like hydrocarbons can be "tuned" by adjusting the hydrogen composition and by adding other functional groups. It may be possible to exploit this behavior to tailor the properties for specific applications. The diamond-like materials may find principal applications as a wear-resistant coating and as a diffusion barrier and corrosion-resistant coating. Coatings on magnetic and optical disks are the most immediate possibilities. Hermetic coatings to protect optical fibers and high- temperature superconductors are other potential applications. These materials have been used as antireflection coatings on germanium optics because of their hardness and the ability to control their refractive indexes by varying the carbon/hydrogen ratio. Diamond-like materials are being actively developed for high-resolution submicrometer- scale lithography. Excimer laser etching has been used to produce structures as small as 0.13 ~m. These materials can also be employed as a bottom layer in a two-layer resist system.
14 Other potential applications of diamond-like films include ultraviolet-absorbing coatings and coatings for photothermal energy conversion and photoreceptors. INTERNATIONAL ACTIVITIES It is difficult to make an accurate assessment of the relative positions of the various countries known to be doing research in diamond and diamond-like materials. Groups in Japan are leading in practical applications of this new technology. Whether or not they have any greater insight into the fundamental issues of nucleation and growth is much less clear. According to an article in the New York Times (October 20, 1988), American experts acknowledge that Japan now holds a commanding lead in CVD diamond technology. Statistics from industry sources provide a comparison: in the past 5 years, of 573 patents granted in the new diamond technology, 488 were awarded to Japanese companies and only 28 were awarded in the United States. Soviet workers, particularly Deryagin's group, have a long history in low- pressure diamond research (Badzian and DeVries, 1988~. However, the committee is aware of no applications of this technology in the Soviet Union. This may, of course, be due to the unwillingness of Soviet researchers to divulge detailed descriptions of their efforts. DeBeers has supported low-pressure diamond synthesis, at least sporadically, since the early 1970s and currently is supporting work on CVD growth of diamond in both England and South Africa, but apparently not at the intensity of the Japanese effort. Leadership in diamonci-like technology appears to be more evenly diffused. There are leading research groups in Japan, the Federal Republic of Germany, Australia, Great Britain, and the United States. RESEARCH AND DEVELOPMENT ISSUES The new diamond science and technology transcend the boundaries of traditional materials science. Fundamental developments in this field will require contributions from organic chemistry, surface chemistry, plasma physics and chemistry, theoretical quantum chemistry, thin-film mechanics, and solid-state physics. A host of engineering and applied disciplines will be involved in applications work. The basic molecular mechanisms involved in both nucleation and growth of diamond are not well understood. Special attention should be paid to those surface spectroscopies that can give insight into species and processes on the growing crystal surface. It is unlikely that high- rate growth of optical- and semiconductor-grade diamonds can be achieved without better understanding of the molecular mechanisms involved in both nucleation and growth. Virtually all current research efforts involve growth of diamond from the vapor. Other low-pressure processes--for example, growth from liquicls--should be explored as alternative avenues for growth of large, high-quality diamond crystals. The vapor growth of diamond for sophisticated optical and electronic applications by current techniques is limited by two factors: (a) the uncontrolled formation of independent diamond nuclei during growth and (b) the appearance of growth errors during extension of the lattice. The first leads to polycrystalline films with a typical crystal size of 1 to 10 am and surfaces that are faceted. The second leads directly to defect structures within the diamond lattice.
15 Diamond-on-diamond epitaxy has been achieved, and the epitaxial layers are approaching electronic-grade quality. The relationships between growth parameters and the types of defect structures procluced should be explored. Heteroepitaxy on silicon, SiC' or other sacrificial substrates would also be highly desirable but has not been achieved yet as far as the committee knows. Also, achieving substitutional e-type doping in diamond is still problematical. Fundamental theoretical studies of the types of molecular structures that lead to "hardness and basic studies of the atomic-scale processes during inelastic deformation are appropriate. This research could lead to new superhard materials and to designed modifications of existing superhard materials. The scale-up and engineering of plasma processes for production of diamond and d~amond-like films is important for the development of practical, large-scale applications. Rapid growth of uniform, high-quality films over large areas that exhibit good adhesion to their substrates will be required for many applications. Here the application of fundamental concepts of plasma chemistry and plasma physics is in order. The deposition of crystalline diamond films at low temperatures (<300OC) would permit a host of applications involving temperature- sensitive substrates. Deposition on steel or other metals, of strongly adherent films would be a major achievement in saws, drills, and similar tools. Growth of diamond at high pressures will continue to be an important commercial process. Basic research in the synthesis of diamond and related materials at high pressures should be supported. The diamond-like phases should be recognized as a new class of materials. Much work on the influence of elemental composition and process variables on the structure anti properties of the diamond-like hydrocarbons (a-C:H) is required before these materials can be fully exploited. Current a-C:H films are highly compressively stressed and are thermally unstable above 400 C. The structure and properties of the diamond-like carbons (a-C) and their relationship to microcrystalline diamond should be explored. Assuming solutions to adhesion problems, the largest impact of the diamond-like phases may be in tribological coatings and as diffusion barriers. However, the influence of additional elements, functional groups, and ambient gases on friction and wear characteristics is not known. The permeability of diamond-like hydrocarbons is expecter! to be very low. However, careful measurements of permeability as a function of process conditions and film composition have not been made. REFERENCES Angus, I. C., and C. C. Hayman. 1988. Low-pressure, metastable growth of diamond and "diamond-like~ phases. Science, Vol. 241, pp. 913-921. Angus, J. C., C. C. Hayman, and R. W. Hoffman. 1988. Diamond Optics, SPIE Symposium 969, August 16-17, 198S, San Diego, California. Bellingham, Washington: SPIE-International Society for Optical Engineers. Angus, I. C., P. Koidl, and S. Domitz. 1986. Carbon thin films. Chapter 4 in Plasma Deposition of Thin Films, I. Mort and F. Jansen, eds. Boca Raton, Florida: CRC Press. Angus, J. C., H. A. Will, and W. S. Stanko. 1968. J. Appl. Phys., Vol. 39, p. 2915.
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17 Matsumoto, S., Y. Sato, M. Kamo, and N. Setaka. 1982a. Vapor deposition of diamond particles from methane. Ipn. I. Appl. Phys., Part 2, Vol. 21, p. 183. Matsumoto, S., Y. Sato, M. Tsutsumi, and N. Setaka. 1982b. Growth of diamond particles from methane-hydrogen gas. I. Mat. Sci., Vol. 17, p. 3106. Mishima, O., J. Tanaka, S. Yamaoka, and O. Fukunmaga. 1987. High-temperature cubic boron nitride pen junction diode made at high pressure. Science, Vol. 23S, pp. 181-183. PlendI, J. N., and P. I. Gileisse. 1962. Phys. Rev., Vol. 125, pp. 828-832. Shigley, I. E., et al. 1987. The gemological properties of the DeBeers gem-quality synthetic diamonds. Gems and Gemology, Vol. 23, pp. 187-206. Spitsyn, B. V., L. L. Bouilov, and B. V. Deryagin. 1981. Vapor growth of diamond on diamond and other surfaces. I. Cryst. Growth, Vol. 52, p. 219. Tsai, H., and D. B. Bogy. 1987. Characterization of diamondlike carbon films and their application as overcoats on thin-film media for magnetic recording. ]. Vac. Sci. Tech., Vol. A5, p. 3287. Yalamanchi, R. S., and G. K. M. Thutupalli. 1988. Investigatians of R. S. plasma-deposited diamond-like carbon coatings. I. Thin Solid Films, Vol. 164, pp. 103-109. Zhogolev, D. A., O. P. Bugaets, and I. A. Marushko. 1981. Zh. Struktur Khim. Vol. 22, No. 1, pp. 46-53.
