THERMAL-CONDUCTIVITY AND STRUCTURE OF DIAMOND FILMS

We have studied two mechanisms that enable us to describe, using the Debye theory, the temperature dependence of thermal conductivity of diamond films in the range 10-300 K, previously measured experimentally by Morelli et al. The first mechanism accounts for boundary scattering of phonons, allowing for specular phonon reflection. The microcrystallites have a calculated size of 1.6-mu-m, which is similar to the results obtained by Morelli et al., and the magnitude of the boundary roughness is H = 9-10 angstrom. The second mechanism is a phonon scattering mechanism for isometric inclusions which possess different density and elasticity, compared with the diamond matrix. The former can be a non-diamond phase zone. The calculations show that the films contain 1.1 x 10(18) cm-3 of the material of diameter a = 12 angstrom, which corresponds to the volume of the non-diamond phase concentration, and is almost-equal-to 0.1%. Due to the fact that the values of H and a are almost equal, it is possible to suggest that the non-diamond carbon phase is concentrated close to the microcrystallite boundaries. This makes the two approaches fully complementary.