Seishiro Goto

Actively controlled oxidation of Cu{100} with hyperthermal O2 molecular beam

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.

Estimation of the electrical resistivity in field‐reversed configuration plasmas from detailed interferometric measurements

Electrical resistivity at the magnetic axis η(R) and at the separatrix η(rs) of a field‐reversed configuration (FRC) plasma produced by theta pinch machines are estimated from detailed interferometric measurements, assuming that the temperature is uniform within the separatrix. The ratio f0[=η(R)/η(rs)] increases with the beta value at the separatrix βs, which is consistent with the fact that f0 decreases when xs (separatrix radius normalized by the inner radius of a theta pinch coil) increases [Phys. Fluids 28, 888 (1985)]. This tendency is a natural consequence of the transport properties of the FRC plasma when the particle confinement time is nearly equal to the decay time of the trapped reversed magnetic flux, as is normally the case. Theoretical expectations of the anomaly of η(rs) over the classical resistivity η0 increases and decreases slightly with βs for the case of the lower hybrid drift and the low‐frequency drift instability, respectively. On the other hand, the observed η(rs)/η0 decreases su...

Photoemission study of the translational energy induced oxidation processes on Cu(111)

The oxidation processes of Cu(111) with a hyperthermal O2 molecular beam (HOMB) were studied using high-resolution x-ray photoemission spectroscopy in conjunction with a synchrotron radiation source. The O-uptake curves were precisely measured at ∼300 K when irradiating with 2.3 and 0.6 eV HOMB on a Cu(111) surface. A Langmuir-type adsorption model at an oxygen coverage (Θ)⩽0.4 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 Θ⩾0.4 ML. A collision-induced absorption mechanism can interpret the slow oxidation process of Cu(111).

Reduction of the density profile of a field-reversed configuration plasma from detailed interferometric measurements

In order to obtain a detailed density profile of a field‐reversed configuration (FRC) plasma, fast‐response multichannel heterodyne quadrature interferometers are constructed. Using these interferometers and assuming a rigid‐body radial shift motion of the plasma, a spatially fine‐grained line integrated density (∫ n dl) profile at its axial midplane is measured. A radial density profile n(r) is reduced from spline fitting of ∫ n dl. The n(r) is found to be nearly an even function of u(=r2/R2−1, R is the magnetic axis radius) as expected. The n(r) is also obtained by the fitting of a line integral of a model n(r) consisting of a modified rigid rotor (RR) profile which can describe the density steepening near the separatrix of the FRC plasma. When the plasma is fat (xs =separatrix radius/coil inner radius=0.63), the density profile is very near to the RR profile itself given by sech2 (Ku), where K is a constant. When the plasma is slender (xs =0.43), the modification is somewhat pronounced. In both cases n...

New Development of Ultrahigh-Vacuum Oriented-Molecular-Beam Machine and Its Application to Chemical Reactions on Silicon Surface

The stereochemical control of surface reactions is one of the ultimate goals of surface scientists. An oriented-molecular-beam technique based on the Stark effect of a molecule in an inhomogeneous hexapole electrostatic field is a potential tool for achieving such a goal. This technique allows us to select a specific rotational quantum state and also an orientation of a reagent molecule. We have designed, built and tuned up a new UHV-compatible oriented-molecular-beam machine for the elucidation of the reaction dynamics on surfaces and for surface manufacturing application. In the dissociative adsorption of CH3Cl on a Si{100} surface, we found a dynamical steric effect on the initial sticking probability (S0) using the new machine. S0 in Cl-end collision is larger than that in CH3-end collision at an incident energy of 120 meV. To our knowledge, this is the first measurement of the steric effect in the chemisorption of a molecule on a Si surface.