Properties of CVD diamond

C. E. Nebel, Transport and Defect Properties of Intrinsic and Boron-Doped Diamond MiloS Neslddek, Ken Haenen and Milan VanSSek, Optical Properties of CVD Diamond Rolf Sauer, Luminescence from Optical Defects and Impurities in CVD Diamond... 

The crystal structure of diamond combined with the strong interatomic chemical bonding accounts for most of its unique properties. Although the properties of CVD diamond are slightly inferior to those of natural single crystal diamond (due to the presence of nondiamond... 

Table 1. Properties of CVD Diamond and Single-Crystal Diamondf ...

Considerable progress has been achieved in recent years on improving the optical properties of CVD diamond and in making this material available in large sizes and with reproducible and consistent properties [4,5,35] so that its use in actual laser systems has become a practical reality [48]. This section reviews the technical issues relevant to the performance of windows for high power lasers comparing the specific case of CVD diamond and ZnSe for the transmission of CO2 laser beams. 

Measurements of the effect of radiation on the dielectric properties of CVD diamond have been reported using neutron irradiation experiments with fast neutron fluences up to at least lO nm (energy >0.1 MeV) [65]. Differences before and after irradiation were found to be more pronounced at lower frequencies. At 145 GHz specimens that started with values of tan 5 of 2 x 10 maintained these levels (or even showed a decrease in loss). Further experiments to extend radiation fluencies to 10 nm are in progress [68]. 

The chemicai properties of CVD diamond are similar to those of the singie-crystai materiai reviewed in Ch. 11, Sec. 11.0. 

The thermal conductivity of CVD diamond substrates can vary by as much as 50 percent, apparently depending on deposition conditions. Table 1.25 shows the properties of CVD diamond available from various suppliers. 

The compact structure of diamond accounts for its outstanding properties. It is the hardest of all materials with the highest thermal conductivity. It is the most perfectly transparent material and has one of the highest electrical resistivities and, when suitably doped, is an outstanding semiconductor material. The properties of CVD and single-crystal diamonds are summarized in Table 7 2.[1][18]-[20]... 

The properties of DLC are summarized and compared with those of CVD diamond in Table 7.5.[44]-[47]... 

With such properties, it could be the ideal material for many semiconductor applications, such as high-power and high-frequency transistors and cold cathodes, or in the harsh environment found in internal-combustion and jet engines. With the advent of CVD diamond, it is now possible to take advantage of these properties. 

Table 3. Comparison of properties between CVD diamond and ZnSe...

The current standard material for optical elements in CO2 lasers is ZnSe [27] because of its very low intrinsic absorption at 10.6 pm [14,15,34]. Table 3 compares the critical parameters of CVD diamond and ZnSe showing that CVD diamond, for the reasons discussed above, has the potential to handle much greater beam powers. This has been long recognized [51] and the thermal effects in diamond laser windows have been theoretically modelled in previous work [27,51-53]. Some of the earlier results [51-53] were derived before reliable data were available on the properties of polycrystalline diamond and were therefore very speculative. The following is an up-date of the predicted thermal effects in optical grade CVD diamond and ZnSe windows where some of the earlier calculations are revisited. 

Measurements of dielectric loss in high quality CVD diamond at millimetre wave microwave frequencies, reported in 1993 [2], furnished for the first time clear evidence that the loss tangent of CVD diamond could be comparable or lower than conventional dielectrics such as sapphire or boron nitride. This initial data and subsequent first dedicated dielectric property studies [61] intensified the considerable amount of interest that had already existed in the nuclear fusion community for CVD diamond as a high power window material [62] especially for the development... 

Limited data is available on the wear rate of CVD diamond [90,91]. A recent study has been conducted in order to investigate the basic tribological properties of bulk and thin-film CVD diamond. The sliding wear characteristics of a number CVD diamond materials have been evaluated using a modified Denison T62 abrasion [92] pin-on-disc test rig, operated in dry and lubricated sliding wear conditions, and compared with a typical hardened steel which is often used for wear part components. 

The ability to deposit single-crystal diamond, or at least a material with a high degree of crystalline orientation and with properties equal to the high-purity single crystal material, would be an important factor in the development of CVD diamond in electronic, semiconductor, optical, and other applications. 

DLC can be considered as a metastable carbon produced as a thin coating with a broad range of structures (primarily amorphous with variable sp /sp bonding ratio) and compositions (variable hydrogen concentration) DLC coatings alter the surface properties of a substrate in a manner similar to that of CVD diamond (see Table 13.2, Ch. 13). 

Plano, L.S., Growth of CVD diamond for electronic applications, in Diamond Electronic Properties and Applications, Pan, L.S., Kania, D.R., eds., Kluwer Academic Publishers, Boston, Dordrecht, London, 62, 1995. 

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