Influence of CO2 addition on hydrogen and oxygen surface bonding onto nanostructured diamond thin film surfaces deposited at low substrate temperatures

Abstract

In this work, hydrogen and oxygen chemisorption onto nanocrystalline diamond films deposited using CH4/H2/CO2 precursor gas mixture by hot-filament chemical vapor deposition were investigated. The deposition was carried out with a specially designed substrate force-cooling setup at back substrate temperatures (Tb) of 200, 450 and 730 °C. For a similar gas phase activation and composition, high-resolution scanning electron microscopy shows that films deposited at Tb = 200 °C display nanostructure morphology while the increase in Tb results in an increase in grain size. Raman scattering, X-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy analyses revealed that addition of CO2 influences the surface composition and bonding configuration of the diamond films. CO2 addition in the gas mixture resulted in improving the quality of the films by reducing CC carbon during the growth process nonetheless it also substantially increases the CO bonds at the grain boundaries and on the diamond crystallites surfaces and reduces their CH concentration.