X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si+1, Si+2, and Si+3 suboxide states at the SiO2/Si interface for (100)- and (111)-oriented substrates with gate oxide quality thermal oxides. The Si+1 and Si+2 states are localized within 6–10 Å of the interface while the Si+3 state extends ∼30 Å into the bulk SiO2. The distribution of Si+1 and Si+2 states shows a strong crystallographic dependence with Si+2 dominating on (100) substrates and Si+1 dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si+1 and Si+2 states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94% and 83% of a monolayer for these (100) and (111) substrates, respectively. We speculate that the remaining interfacial substrate Si atoms that are not associated with bonding to oxygen are bonded to impurity species.

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Results from the Viking biology experiments indicate the presence of reactive oxidants in martian soils that have previously been attributed to peroxide and superoxide. Instruments on the Mars Phoenix Lander and the Mars Science Laboratory detected perchlorate in martian soil, which is nonreactive under the conditions of the Viking biology experiments. We show that calcium perchlorate exposed to gamma rays decomposes in a CO 2 atmosphere to form hypochlorite (ClO -), trapped oxygen (O 2 ), and chlorine dioxide (ClO 2 ). Our results show that the release of trapped O 2 (g) from radiation-damaged perchlorate salts and the reaction of ClO -with amino acids that were added to the martian soils can explain the results of the Viking biology experiments. We conclude that neither hydrogen peroxide nor superoxide is required to explain the results of the Viking biology experiments.

The chemical structures of thin SiO2 films, thin native oxides of GaAs (20–30 Å), and the respective oxide–semiconductor interfaces, have been investigated using high-resolution x-ray photoelectron spectroscopy. Depth profiles of these structures have been obtained using both argon ion bombardment and wet chemical etching techniques. The chemical destruction induced by the ion profiling method is shown by direct comparison of these methods for identical samples. Fourier transform data-reduction methods based on linear prediction with maximum entropy constraints are used to analyze the discrete structure in oxides and substrates. This discrete structure is interpreted by means of a structure-induced charge-transfer model (SICT).

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