Effect of frequency on low temperature synthesis of diamond by pulsed discharge MPCVD

Abstract

Low-temperature synthesis of diamond has broader application prospects compared to traditional diamond synthesis, but it faces issues such as low deposition rate and poor diamond quality. In this study, CH4–CO–H2 were used as reaction gases, and a pulsed discharge MPCVD apparatus was used to deposit diamond films at a substrate temperature of 400 °C and different frequencies were investigated. The results showed that the deposition rate of the pulse discharge was faster than that of continuous microwave discharge. The fastest deposition rate was observed at 500Hz, and crystal size became finer with increasing frequency, while the crystal orientation changed from (100) to (111). A diamond peak at 1333 cm−1 was observed in the Raman spectrum, and the diamond grain size was found to be biggest at 750Hz based on the measured half-width of the peak. Plasma OES analysis revealed that the brightness of CO increased gradually with increasing frequency, while the brightness of H showed an initial increase followed by a decrease. Comparison of emission spectra during low-temperature deposition with a single carbon source showed that CO participated in the reaction for low-temperature diamond synthesis.