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

Abstract

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.