Oxygen adsorption on the (110)-oriented diamond surface

Multiple internal reflection infrared spectroscopy (MIRIRS) and temperature -programmed desorption (TPD) were used to investigate the interaction of ox ygen with a diamond (110)-oriented surface. Exposure of the hydrogen-free d iamond surface at 90 K to room-temperature O-2 or thermally excited oxygen, O-2* (produced with a heated iridium filament) resulted in a sharp infrare d absorption at 657 cm(-1), which disappeared on heating to 300 K. The 657 cm(-1) absorption may indicate a surface peroxide. When the hydrogen-free d iamond surface was dosed with O-2 at room temperature, no oxygen adsorption was observed by Auger electron spectroscopy (AES) or TPD. In contrast, dos ing the surface with O-2* at 300 K led to oxygen chemisorption. The room-te mperature diamond surface was saturated with oxygen after exposures of > 24 00 L O-2*. When the oxidized surface was heated, only CO2 and CO desorption were observed, with peak maxima at 780 and 870 K, respectively. The peak d esorption temperatures for CO2 and CO did not vary with O coverage, implyin g first-order desorption kinetics, MIRIR spectra of the oxygen-saturated (1 10)-oriented surface showed weak absorption modes at 790 and 980 cm(-1). Th e exposure of the surface at 900 K to O-2* led to (1) an increase in the co verage of oxygen species stable at high-temperature, (2) narrower, more int ense, MIRIRS absorption modes (O-16, 770, 934, and 980 cm(-1); O-18, 747, 8 95, and 936 cm(-1)) and (3) a sharp, intense CO desorption peak at 1025 K. These observations imply that the low-temperature adsorption sites were etc hed away, thus favoring the additional adsorption of oxygen into the adsorp tion sites that are stable at high temperature.