The interaction of oxygen molecules with amorphous Ge, Ge:H, and some Ge:C:H alloys

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Abstract
The interaction of oxygen molecules with Ar+ sputter-etched (amorphized) Ge(100) and rf sputter-deposited amorphous germanium carbides (a-Ge1−xCx:H), 0≤x≤0.5, was investigated using Auger measurements and core-level, valence-band, and high-resolution electron energy-loss spectroscopies (EELS). A film covered with native oxide was also studied. Samples were exposed to oxygen following surface cleaning by Ar+ etching. This procedure, as previously reported, preferentially removed hydrogen bonded to Ge in a-Ge:H and a-Ge1−xCx:H films. High-resolution EELS indicated dissociative chemisorption of oxygen on Ge in all Ar+-etched samples used in this study. The oxygen appears to be bonded to Ge mainly in an isolated bridge form (+1 oxidation state) at the early stages of oxidation. Even when the surface was pre-exposed to 104-L O2, subsequent exposure to hydrogen atoms indicated the existence of a high density of bonds available for hydrogen bonding, contrary to observations at Ge(111). Under these conditions the Ge–H stretch loss split into two features separated by ∼8 meV. Possible bonding configurations, including oxygen bridging between the first and second layers, are discussed. Valence-band EEL spectra exhibited a single oxygen induced loss at an energy loss similar to that observed for single crystals of Ge. Core-level shifts due to oxidation were not observed as was the case for room-temperature adsorption on single crystals. In addition, no change in the Ge(MVV) Auger line shape was induced by oxygen chemisorption, in contrast to previously observed hydrogen related changes. These results are compared to those reported for single crystals of Ge.

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