Effect of the N/C ratios of ammonia added to process gas mixtures on the morphology and structure of MPCVD diamond films

Abstract

In this study, N-doped diamond films were prepared through microwave plasma chemical vapor deposition withNH3/CH4/H2 gas mixtures. The effects of the ammonia addition to the process gas mixture on the morphology and structure of diamond films were systematically investigated through characterization by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). This work focuses on the ammonia addition to the process gas mixtures in the narrow range of N/C ratios from 0.4% to 1.0%. The results reveal that different N/C ratios can affect the morphology, the preferred crystal orientation, and the sp3/sp2 ratio in the films. When the N/C ratio of the process gas mixture ranges from 0.6% to 1.0%, the XRD and SEM results show that ammonia addition is beneficial for the growth of the (110) faceted grains. When the N/C ratio of the process gas mixture ranges from 0.8% to 1.0%, the XPS and Raman results indicate that the diamond films exhibit a considerable enhancement in the sp3 fraction.