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 oxygen with a diamond (110)-oriented surface. Exposure of the hydrogen-free diamond 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 infrared 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 diamond surface was dosed with O 2 at room temperature, no oxygen adsorption was observed by Auger electron spectroscopy (AES) or TPD. In contrast, dosing the surface with O 2 * at 300 K led to oxygen chemisorption. The room-temperature diamond surface was saturated with oxygen after exposures of >2400 L O 2 *. When the oxidized surface was heated, only CO 2 and CO desorption were observed, with peak maxima at 780 and 870 K, respectively. The peak desorption temperatures for CO 2 and CO did not vary with O coverage, implying first-order desorption kinetics. MIRIR spectra of the oxygen-saturated (110)-oriented surface showed weak absorption modes at 790 and 980 cm -1 . The exposure of the surface at 900 K to O 2 * led to (1) an increase in the coverage of oxygen species stable at high-temperature, (2) narrower, more intense, MIRIRS absorption modes ( 16 O, 770, 934, and 980 cm -1; 18 O, 747, 895, 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 etched away, thus favoring the additional adsorption of oxygen into the adsorption sites that are stable at high temperature.