The oxidation is one of the major corrosion processes of metals. Copper and copper alloys have wide industrial applications, and therefore are of interest for studies of oxidation mechanism, particularly in the Cu₂O formation. We proposed the collision-induced absorption (CIA) mechanism for the oxidation of Cu with hyperthermal O₂ molecular beam (HOMB) in our early studies. Here, we introduce our recent studies of the oxidation of Cu(410) and Cu(511) stepped surfaces and various Cu₃Au surfaces with HOMB. On the Cu stepped surface, we discuss the role of defects on the CIA mechanism in the oxidation. The Cu-Au alloys are an ideal system for investigating the formation of protective layer against further oxidation into bulk. On the various Cu₃Au surfaces, we demonstrate how the protective layer against the CIA oxidation is formed. Finally, we introduce shortly the steric effects in the reaction of NO on Si(111).

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  A single spin-rotational state-selected [(J,M)=(2,2)] O₂ beam developed recently allows us to define the alignment of an O₂ molecule with respect to the defining magnetic field. A fully alignment-resolved O₂ sticking experiment on a single domain Si(100) has provided the first experimental evidence that the reactivity of O₂ depends on both the polar and azimuthal angles of the molecular axis relative to a surface. The analysis of the observed steric effects has clarified the followings. (1) Side-on collision is much more favorable than end-on collision for O₂ dissociation on Si(100). (2) In case of side-on collision, an O₂ molecule perpendicular to the dimer on Si(100) is about 40% more reactive than that parallel to the dimer. No steric effect was observed for the precursor-mediated process. O₂ dissociation on the double-layer step was found to proceed nearly barrierlessly.

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  Germanium oxide (GeO₂) is one of the key materials in Ge-based transistors. However, GeO₂ is permeable and soluble in water, unlike the more familiar silicon oxide (SiO₂). This implies that GeO₂ films will react with water vapor in air. In this review, water growth on ultrathin GeO₂ films on a Ge(100) substrate as well as the effect of water layers on the electronic properties of GeO₂ films are investigated by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at relative humidities (RHs) from 0% to approximately 45%. After the basic concept of AP-XPS, as well as its experimental setup, is explained, I show that water adsorbs at low RHs and continues to grow gradually up to approximately 1% RH, and probably forms hydroxyls. Water grows rapidly above 1% RH, indicative of the formation of a molecular water film. In addition, AP-XPS spectra reveal anomalous positive charging of the GeO₂ film starting at a very low RH of around 10⁻⁶%, and its mechanism is discussed.

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  In this paper, the evaluation methods of the degradation and dielectric breakdown of ultrathin SiO₂ thermally grown on Si, which are one of most superior dielectric films, are introduced along with some examples. SISuR (Stress-Induced oxide Surface Roughness) method with using a reaction between SiO₂ films with trapped charges and etching solution is available to clarify that the degradation in SiO₂ film under high electric field stress is not uniform. Furthermore, it is indicated that thermal oxidation of the atomically-flat Si terrace surface does not progress two-dimensionally uniformly, strictly speaking. The non-uniform oxidation is one of the origins of the wide lifetime distribution of dielectric breakdown of the ultrathin SiO₂ films.

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