Phase Transformation of Nanocrystalline Diamond Films: Effect of Methane Concentration

Abstract:

Ultra-nanocrystalline diamond films were prepared by a microwave plasma-enhanced chemical vapor deposition reactor using CH₄/H₂ gas mixture with a power as low as 650 W. The effects of CH₄ concentration on nanostructure of the films and gas-phase species in plasma were investigated. The CH₄ concentrations of 1.5%, 3.0%, 3.5%, and 4.0% were used and balanced with H₂ to a total flow rate of 200 sccm. Morphology and composition of the films were characterized by SEM, Raman spectroscopy and Auger spectroscopy. The gas-phase species and electron density in the plasma were explored by optical emission spectroscopy and plasma-impedance measurement. The increasing CH₄ concentration from 1.5% to 4.0% increased C₂H_x species and decreased electron density. Phase of the film transform from nano- into ultranano- diamond phase but the growth rate revealingly decreased from 300 to 210 nm/h. Raman spectra indicate the higher CH₄ concentration promted phase of the film transiton from NCD to UNCD. While Auger spectra revealed that UNCD film deposited with 4.0%CH₄ was composed of 90.52% diamond phase but only 9.48% of graphite phase. The relation between phase transformation of the films and growth mechnism controlled by gas-phase species in the plasma will be dissused.

• Periodical: Key Engineering Materials (Volume 831)
• Pages: 127-131
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.831.127
• Online since: February 2020
• Authors: S.Tipawan Khlayboonme*, Warawoot Thowladda
• Keywords: Auger Spectra, Nanocrystalline Diamond Film, Plasma Impedance, Raman Spectra

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