The oxidation of Cu{100} with a hyperthermal O2 molecular beam (HOMB) was investigated using x-ray photoemission spectroscopy in conjunction with a synchrotron light source. The efficiency of oxidation with HOMB is higher than that with ambient thermal O2. Further oxidation under oxygen coverage (Θ)⩾0.5 ML occurs rather inefficiently even for the 2.3-eV-HOMB irradiation. We found that such slow oxidation of Cu corresponding to the initial stage of the Cu2O formation can be interpreted in terms of a collision-induced-absorption mechanism. The kinetics of the dissociative adsorption under Θ⩽0.5 ML is well described using the first-order kinetics in a simple Langmuir-type adsorption model.

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We report results of a study on the incident energy and the surface-temperature dependence of the steric effects in the dissociative adsorption of CH3Cl on a Si{100} surface. Data presented here show that the initial sticking probability for the Cl-end collision is larger at an incident energy of 120 meV than that in the CH3-end collision. Furthermore, this steric preference is quite sensitive to the kinetic energy and the rotational state of CH3Cl and the surface temperature. This study shows that the nonequilibrium surface trapping plays a key role in the initial step of the decomposition of CH3Cl on Si{100}.

Alloying Pd with Au has remarkable features of enhancement of hydrogen solubility compared to Pd and catalytic activity for reactions such as partial hydrogenation of unsaturated hydrocarbons. A key to understanding these phenomena is clarification of hydrogen behavior in the near-surface region. In the present work, by applying nuclear reaction analysis for high-resolution depth profiling of hydrogen in combination with thermal desorption spectroscopy, we show that hydrogen substantially accumulates in the near-surface region and is absorbed in the bulk of a single-crystal Pd70Au30(110) alloy. We also demonstrate a molecular cap effect of CO, where a small amount of CO adsorption greatly changes the hydrogen absorption and desorption behavior by blocking the entrance/exit channel for hydrogen. These findings lead to understanding and controlling the catalytic activity of the Pd–Au alloy and Pd-related surfaces and also open up a new method to control hydrogen transport across metal surfaces.

This paper reports a study on the surface reconstruction on Cu(111) induced by a hyperthermal oxygen molecular beam (HOMB) at room temperature (RT). HOMB incidence at translational energies (E i ) g 0.5 eV induced surface reconstruction to the | -1 3 2 2 | structure for an O coverage (Θ) g 0.27 monolayer (ML). On the other hand, long-range-ordered structures were not formed even at Θ ≈ 0.4 ML for the backfilling of thermal O 2 at RT. No surface reconstruction was induced at E i e 0.23 eV where the attainable Θ value was 0.27 ML for the O 2 exposures below 10 18 molecules/cm 2 . Translational energy above 0.5 eV is required for the dissociative adsorption of O 2 and the resulting surface reconstruction at Θ g 0.27 ML. The O-1s XPS peak for HOMB incidence at RT was resolved into two components, 529.4 and 528.9 eV, at Θ g 0.27 ML, which can be assigned to the O atoms occupying the three-fold hollow sites on unreconstructed Cu(111) and four-coordinated sites on the | -1 3 2 2 | structure, respectively. Annealing the | -1 3 2 2 | reconstructed surface at 620 K decreased Θ to ∼0.27 ML and induced (√13R46.1°× 7R21.8°), the so-called "29" superstructure.

Articles you may be interested in 1,2-Dibromoethane on Cu(100): Bonding structure and transformation to C2H4Kinetics of the CO oxidation reaction on Pt(111) studied by in situ high-resolution x-ray photoelectron spectroscopyThe oxidation processes of Cu͑111͒ with a hyperthermal O 2 molecular beam ͑HOMB͒ were studied using high-resolution x-ray photoemission spectroscopy in conjunction with a synchrotron radiation source. The O-uptake curves were precisely measured at ϳ300 K when irradiating with 2.3 and 0.6 eV HOMB on a Cu͑111͒ surface. A Langmuir-type adsorption model at an oxygen coverage ͑⌰͒р0.4 ML describes the kinetics of dissociative adsorption in the HOMB incidence. On the other hand, further inefficient oxidation occurs even for the 2.3 eV HOMB irradiation at ⌰у0.4 ML. A collision-induced absorption mechanism can interpret the slow oxidation process of Cu͑111͒.

Oxidation of Cu3Au(100) using a hyperthermal O2 molecular beam (HOMB) was investigated by x-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident energy dependence of the O-uptake curve, it was determined that the dissociative adsorption of O2 implies a higher activation barrier and therefore less reactivity compared to Cu, owing to the Au alloying. The dissociative adsorption progresses with the Cu segregation on the surface. No prominent growth of Cu2O even for 2eV HOMB suggests that the Au alloying of Cu can serve as a protective layer against further oxidation into the bulk.

We studied the oxidation of Cu(410) using high-resolution electron energy loss spectroscopy and X-ray photoemission spectroscopy performed with synchrotron radiation. Cu2O formation starts above half a monolayer oxygen coverage, and the oxidation rate is larger,than for the parent low Miller index Cu(100) surface. Open steps favor therefore the process by opening pathways for subsurface migration and oxygen incorporation. Oxidation occurs only above 500 K when dosing O-2 by backfilling, but the ignition temperature can be lowered to room temperature by dosing O-2 Via a supersonic molecular beam at hyperthermal energy indicating the opening of a different pathway. The oxidation rate is maximal at normal incidence; at grazing incidence, it is higher when O-2 impinges nearly normal to the (100) nanofacets than when it hits the surface close to the normal to the step rises. A collision induced absorption mechanism can explain the experimental findings