High temperature studies of diamond and CVD diamond thin films

[摘要] The extreme hardness, thermal conductivity and molar density of diamond make it an important technological and industrial material. For some applications, thin films of diamond are desired, but the low quality of such films prevents them from achieving their full potential. This dissertation includes the characterization of diamond at high temperatures, which is necessary for understanding the chemical vapor deposition (CVD) of diamond, and a new process designed to produce higher quality films.The UV absorption edge of diamond was examined from room temperature to 1000$spcirc$C for three different samples. For all of the samples, the edge shifted to lower energy at higher temperature, but both the position of the edge and the magnitude of the shift depended on the sample. The absorption edge of the Type IIa diamond shifted from 224 to 270 nm. For the colorless Type Ia sample the shift was from 304 to 344 nm, while for the brown Type Ia sample it was from 264 to 285 nm. Temperature can be measured with a calibrated diamond probe by measuring the position of the absorption edge of the diamond.The laser ablation threshold of diamond with the 248 nm KrF excimer laser was investigated. Since it was shown that Type IIa diamond is transparent to 248 nm radiation at room temperature, but strongly absorbing at 1000$spcirc$C, the threshold was measured at 1000$spcirc$C as well as at room temperature. The room temperature threshold was 4.0 J/cm$sp2,$ and the 1000$spcirc$C threshold was 6.6 J/cm$sp2.$ Diamond exhibits a transition from a two-photon absorption process to a one-photon absorption process over this temperature range. Using a fluence which was above the ablation threshold of graphite but below the ablation threshold of diamond to irradiate the substrate surface during homoepitaxial CVD had no effect on the deposition.The change in the refractive index of diamond with temperature, dn/dT, was measured from room temperature to 1000$spcirc$C. Although dn/dT was slightly wavelength dependent, it was independent of the sample type. Use of dn/dT as a simple, noncontact temperature measurement technique is presented. The change in the Penn gap of diamond with temperature is calculated.

[发布机构] Rice University

[效力级别] chemistry