A novel growth model for depositing ultrananocrystalline diamond films in CH4/H-2 chemistry

Q Lin and SL Chen and Z Ji and ZW Huang and ZN Zhang and B Shen, SURFACE & COATINGS TECHNOLOGY, 419, 127280 (2021).

DOI: 10.1016/j.surfcoat.2021.127280

For more than twenty years, the synthesis of ultrananocrystalline diamond (UNCD) films is typically realized by the well-known Ar-rich atmosphere. In the present study, we demonstrate that the deposition of UNCD films can be achieved in CH4/H-2 chemistry without Ar in a hot- filament chemical vapor deposition (HFCVD) apparatus. In this case, the high re-nucleation rate for the deposition of UNCD films is realized through the combination of high kinetic energy and high local concentration of the growth species (CHx, x = 0, 1, 2, 3). By synergistically tuning the gas pressure and carbon concentration (CH4/H-2), the kinetic energy and local concentration of the growth species can be specifically regulated for adjusting the re-nucleation rate. In this paper, a novel kinetic growth model was established to interpret the UNCD growth mechanism with CH4/H-2 chemistry, and the atmospheric window of the gas pressure and CH4/H-2 ratio for the deposition of UNCD films was obtained. High growth rate, high surface finish and superior tribological performance of the UNCD films were demonstrated. This study provides significant insights into the UNCD growth mechanism without Ar content, and renders the gas strategy simpler, more controllable and more flexible.

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