High resolution electron energy loss studies of O2, H, N, NO, and N2O adsorption on germanium surfaces

Abstract

The first high resolution electron energy loss spectroscopy (HREELS) studies of the oxidation and nitridation of germanium surfaces are reported. Both single crystal Ge(lll) and disordered surfaces were studied. Surfaces were exposed to H, O2, NO, N2O, and N, after cleaning in ultra-high vacuum. The Ge surfaces were found to be non-reactive to molecular hydrogen (H2) at room temperature. Exposure to atomic hydrogen (H) resulted hydrogen adsorption as demonstrated by the presence of Ge-H vibrational modes. The HREEL spectrum of the native oxide of Ge characteristic of v-Ge02 was obtained by heating the oxide to 200*C. Three peaks were observed at 33, 62, and 106 meV for molecular oxygen (O2) adsorbed on clean Ge(lll) at room temperature. These peaks are indicative of dissociative bonding and a dominant Ge-O-Ge bridge structure. Subsequent hydrogen exposure resulted in a shift of the Ge-H stretch from its isolated value of 247 meV to 267 meV, indicative of a dominant +3 oxidation state. A high density of dangling bonds and defects and deeper oxygen penetration at the amorphous Ge surface result in a dilute bridge structure with a predominant +1 oxidation state for similar exposures. Molecules of N2O decompose at the surfaces to desorbed N2 molecules and chemisorbed oxygen atoms. In contrast, both oxygen and nitrogen are detected at the surfaces following exposure to NO molecules. Both NO and N2O appear to dissociate and bond at the top surface layer. Molecular nitrogen (N2) does not react with the Ge surfaces, however, a precursor Ge nitride is observed at room temperature