Abstract
AbstractPolycrystalline CVD diamond has been annealed in vacuum at temperatures tan = 1550 °C–1690 °C to investigate an influence of modifications of grain boundaries (GB) and defects on thermal conductivity and optical properties of originally optical quality material. While the sample was converted by this heat treatment to “black diamond”, excitons still could be observed in cathodoluminescence spectra. Photoluminescence spectra revealed an aggregation of nitrogen (formation of H3 optical center) after annealing at 1690 °C. In‐plane thermal conductivity k (T) measured by a heated bar method in the temperature range T = 5–410 K shows a strong (up to 5 times) and monotonic decrease at T < 45 K upon annealing, while room temperature k (298 K) value remains almost constant (ca. 19.0 W/cm K) till tan = 1650 °C, rapidly degrading at higher tan. The experimental data on thermal conductivity are analyzed in the framework of full Callaway theory taking into account three‐phonon scattering processes, phonon scattering on point defects, sample boundaries, and GB. The proposed model reproduces well the observed k (T) behavior, the phonon scattering on the modified GB playing an important role. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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