Investigation of structural perfection of SiC ingots grown by a sublimation method

Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-2500 ⁰C at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour in the C-axis direction. At growth time of about 15 hours we obtained the ingots with 35 mm useful diameter. To determine the polytype composition of SiC ingots the Raman scattering technique was used. The structural defects were investigated by means of reflection and transmission light microscopy and by selective etching. In the best ingots the dislocation density did not exceed 102 cm⁻², the micropipe density - 10-20 cm⁻², and blocks were absent

Micro-Raman study of CNx composites subjected to high pressure treatment

CNx films were deposited by reactive ion-plasma sputtering of a graphite target in an argon-nitrogen-acetone vapor atmosphere onto molybdenum substrates. After deposition the CNx composites were cut from substrates, formed in pellets of 6 mm in diameter, and subjected to a high pressure-high temperature treatment at 7.7 GPa and 2000⁰C for 60 seconds. Micro-Raman spectroscopy, microhardness and X-ray diffraction were used for the sample characterization. After treatment the CNx material leads to the formation of a number of highly ordered diamond crystals showing an extraordinarily low broadening of the 1332 cm⁻¹ Raman-line (∆n = 2.43 cm⁻¹). Besides, the Raman spectra of the matrix surrounding the diamond crystals show an additional band at ~1621 cm⁻¹ with a Raman intensity that strongly depends on the distance from the crystals. We propose that this band is related to the formation of rombohedral graphite in the treated sample and the corresponding effect of puckering of the graphite layers. The double-well potential model earlier proposed to describe diamond-like amorphous carbon has been used here for a qualitative description of the graphite-diamond phase-structural transformation