Oxidation and Etching of CVD Diamond by Thermal and Hyperthermal Atomic Oxygen

Abstract

The chemical bonding and morphology of chemical vapor deposited (CVD) diamond films exposed to thermal (∼0.04 eV) and hyperthermal (5 and 7.5 eV) atomic oxygen (AO) were studied by using high resolution electron energy loss spectroscopy (HREELS), atomic force microscopy, and theoretical simulations. Although exposure to thermal AO caused subtle changes to the surface morphology, hyperthermal AO resulted in selective etching of the diamond facets: (100) facets remained essentially unaffected, whereas (111)-oriented and other facets were severely etched. HREELS reveals that hydrogen is removed from the diamond surfaces during both thermal and hyperthermal AO exposures. By using isotopic labeling in the CVD growth procedure, it is observed that exposure to ambient conditions after the AO exposure leads to adsorption of adventitious hydrocarbons on the surface. The high background in the HREEL spectrum of samples exposed to hyperthermal AO suggests the presence of a graphitic layer. Simulations of the interaction between hyperthermal AO and (100) and (111) diamond surfaces were conducted by using direct dynamics based on density-functional-based tight binding methods, in an attempt to elucidate relevant reaction mechanisms. They suggest mechanisms for the partial graphitization of the (111) surface and for etching of this surface by way of CO 2 desorption. Such damaged graphitic layers have been previously shown to erode easily when exposed to a hyperthermal AO beam. The simulations also suggest that the (100) surface, fully covered with ketones, is inert to carbon removal upon exposure to hyperthermal oxygen atoms, which scatter inelastically from this surface without reaction. The simulations suggest that a nearly full ketone coverage is the steady-state configuration for a (100) diamond surface exposed to AO.