Evolution and properties of nanodiamond films deposited by direct current glow discharge

Abstract

Nanocrystalline carbon films possessing a prevailing diamond character are deposited by a direct current glow discharge chemical vapor deposition method using a 9:91 vol % methane to hydrogen gas mixture. In the present work the evolution and properties of nanodiamond films deposited by this method onto silicon substrates as a function of time were studied by various complementary techniques. Our analysis showed that prior to formation and growth of continuous films of a predominantly nanodiamond character, a graphitic phase is formed. After the nanodiamond phase is stabilized, near edge x-ray adsorption fine structure measurements proved the predominant diamond character of the film to be about 80%. By electron energy loss spectroscopy analysis the sp2-like character of the nanodiamond grain boundaries has been determined. The nanodiamond films were found to be thermally stable up to temperatures of ∼950 °C as established by vacuum heating. By scanning electron microscopy and atomic force microscopy the morphology of the films was examined showing that the formation of the nanodiamond phase is initially accompanied with an increase in surface roughness which decreases with film growth. By high-resolution transmission electron microscopy it was determined that the continous nanodiamond films are composed of diamond nanocrystallites, 3–5 nm in diameter.