Abstract
In this study, N-doped diamond films were prepared through microwave plasma chemical vapor deposition with NH3/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.
Highlights
Nitrogen (N)-doped diamond films have been studied for their many applications, such as in semiconductor devices [1], thermionic electron emission [2], photoelectron emission [3], field emission [4], electrochemical biosensing [5], sterilization [6], and N-V color centers for quantum communications [7]
When the N/C ratio increases from 0.6% to 0.8% and 1.0%, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that the (110) facet grains gradually increase
The Raman spectra demonstrate an improvement in the diamond phase quality, while the deconvolution profile from the X-ray photoelectron spectroscopy (XPS) spectra illustrates the increase of the sp3 fraction in the deposited film
Summary
Nitrogen (N)-doped diamond films have been studied for their many applications, such as in semiconductor devices [1], thermionic electron emission [2], photoelectron emission [3], field emission [4], electrochemical biosensing [5], sterilization [6], and N-V color centers for quantum communications [7]. Many different results have been reported regarding the influence of N addition on the film morphology and the diamond quality, with reports of N addition benefiting the growth of the (100) facet surface [9,11,13,14,15,16,17,18], producing films without any preferred orientation of the surface facets [12,19,20] and improving diamond quality [13,16,21] or leading to a higher sp fraction in the deposited material [19,20] These different results are highly dependent on the process parameters and the N/C atomic ratio in the process gas mixture. Drawing on the experience of previous studies of a broad range of N/C atomic ratios (0.1%, 1.0%, 10.0%, and 40%) [11] and of very low N/C ratios (from 0.02% to 0.32%) [19], this work focuses on the ammonia addition to process gas mixtures in a narrow N/C ratio range from 0.4% to 1.0%
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