Synchrotron X-ray photoemission study of NiTi surface oxidation with hyperthermal oxygen molecular beam

Yamazaki, Daichi*; Sowa, Makoto*; Okada, Michio*; Teraoka, Yuden; Kasai, Toshio*

Journal of the Vacuum Society of Japan, 54(5), p.307 - 312, 2011/05

https://doi.org/10.3131/jvsj2.54.307

The Study of oxidation on TiAl surface with photoemission spectroscopy in conjunction with synchrotron radiation

Hashinokuchi, Michihiro*; Sumimoto, Yuichi*; Tode, Mayumi; Harries, J.; Okada, Michio*; Teraoka, Yuden; Kasai, Toshio*

Denki Gakkai Rombunshi, C, 130(10), p.1723 - 1729, 2010/10

https://doi.org/10.1541/ieejeiss.130.1723

The oxidation processes on a TiAl surface induced by a hyperthermal O molecular beam (HOMB) with a translational energy of 2.2 eV was studied by X-ray photoemission spectroscopy in conjunction with synchrotron radiation. At a surface temperature of 300 K, the simultaneous growth of Al and Ti oxides accompanied with the segregation of AlO near the surface was observed. The efficiency of oxidation for the HOMB incidence was smaller than that for O backfilling (25 meV). Furthermore, the chemical compositions of oxide species (AlO, TiO, TiO) on the TiAl surface were independent of the translational energy of incident O molecule. The present results suggest that the oxidation on TiAl surface proceeds via precursor molecular states.

Fabrication of Cu oxides on single crystal Cu surfaces using hyperthermal O molecular beams

Okada, Michio*; Moritani, Kosuke*; Vattuone, L.*; Savio, L.*; Teraoka, Yuden; Kasai, Toshio*; Rocca, M.*

Metal Oxide Nanostructures and Their Applications, 1, p.205 - 237, 2010/03

The use of hyperthermal O molecular beams may improve the quality of thin film growth, for example, for organic films, and allow the production of oxide layers at lower crystal temperatures, avoiding contamination problems and reducing film defects. Collision-induced absorption and local heating of the substrate were shown to be indeed effective in inducing oxide nucleation, opening up new possibilities for the production of nanostructured metal oxides. Herein we offer an overview on recent detailed studies of oxygen adsorption and of the initial stages of CuO and CuO formation on low Miller index and vicinal Cu surfaces. We introduce the hyperthermal molecular beam technique and give some details on the experimental apparatuses. We discuss the available data for Cu(100), Cu(410) and Cu(110) and Cu(111), respectively.

Kinetics of oxygen adsorption and initial oxidation on Cu(110) by hyperthermal oxygen molecular beams

Moritani, Kosuke*; Okada, Michio*; Teraoka, Yuden; Yoshigoe, Akitaka; Kasai, Toshio*

Journal of Physical Chemistry A, 113(52), p.15217 - 15222, 2009/10

https://doi.org/10.1021/jp905564m

Oxygen adsorption and subsequent oxide formation on Cu(110) using a hyperthermal oxygen molecular beam (HOMB) has been investigated using SR-XPS. The O-uptake curves, which were determined from the evolution of O-1s peaks, indicate that simple Langmuir type kinetics can describe dissociative adsorption of O with an incident energy (Ei) below 0.5eV under oxygen coverage of 0.5 ML. The reaction order dependence on Ei implies two competing dissociation mechanisms, trapping-mediated and directly-activated adsorption. Oxidation at oxygen coverage larger than 0.5 ML proceeds rather effectively using highly energetic HOMB at Ei larger than 1.0 eV. The surface CuO formed with highly-energetic HOMB incidence decomposes with desorbing subsurface oxygen even at room temperature. This indicates that HOMB can induce a meta stable surface structure that cannot be produced in the thermal equilibrium process.

Reconstruction of Cu(111) induced by a hyperthermal oxygen molecular beam

Moritani, Kosuke*; Okada, Michio*; Teraoka, Yuden; Yoshigoe, Akitaka; Kasai, Toshio*

Journal of Physical Chemistry C, 112(23), p.8662 - 8667, 2008/06

https://doi.org/10.1021/jp800713u

This paper reports a study on the reconstruction at Cu(111) surface induced by a hyperthermal oxygen molecular beam (HOMB) at room temperature. The HOMB incidence at translational energies larger than 0.5 eV induced surface reconstruction in the oxygen coverage larger than 0.27 ML. On the other hand, long-range-ordered structures were not formed even at the oxygen coverage of 0.4 ML for the backfilling of thermal O at room temperature. The O1s XPS peak for the HOMB incidence at room temperature was resolved into two components, 529.4 and 528.9 eV, at the oxygen coverage larger than 0.27 ML, which can be assigned to the O atoms occupying the threefold hollow sites on the unreconstructed Cu(111) surface and four-coordinated sites on the reconstructed structure, respectively. Annealing the reconstructed surface at 620 K decreased the oxygen coverage to 0.27 ML and induced so-called "29" superstructure.

New oriented-molecular-beam machine for surface stereochemistry with X-ray photoemission spectroscopy

Okada, Michio*; Hashinokuchi, Michihiro*; Moritani, Kosuke*; Kasai, Toshio*; Teraoka, Yuden

Japanese Journal of Applied Physics, 47(5), p.3686 - 3691, 2008/05

https://doi.org/10.1143/JJAP.47.3686

An oriented-molecular-beam technique based on the Stark effect of a molecule in an inhomogeneous hexapole electrostatic field is a potential tool for stereochemical control of surface reactions. This technique allows us to select a specific rotational quantum state and also an orientation of a reagent molecule. We have developed a new UHV-compatible oriented-molecular-beam machine. This apparatus is equipped with components for X-ray photoemission spectroscopy (XPS) in order to detect surface-reaction products. In the dissociative adsorption of NO on an Si(111) surface, we found a steric effect in the reactivity by monitoring the products on the surface with the new machine. The N-end collision is more reactive than the O-end collision at an incident energy of 58 meV. To our knowledge, this is the first measurement of the steric effect appearing in the reaction products on the surface.

Unravelling the role of steps in CuO formation via hyperthermal O adsorption at Cu(410)

Okada, Michio*; Vattuone, L.*; Gerbi, A.*; Savio, L.*; Rocca, M.*; Moritani, Kosuke*; Teraoka, Yuden; Kasai, Toshio*

Journal of Physical Chemistry C, 111(46), p.17340 - 17345, 2007/11

https://doi.org/10.1021/jp074520t

We report a study on the oxidation process of Cu(410) using high-resolution electron energy loss spectroscopy and X-ray photoemission spectroscopy using synchrotron radiation. We demonstrate that a hyperthermal O molecular beam (HOMB) is an efficient tool to fabricate CuO thin film also at room temperature. The efficiency of the CuO formation in the initial stages depends on the angle of incidence of HOMB. Step roughening, acting as a source of mobile precursor Cu adatoms and opening channels for bulk diffusion of the O atoms, is a key feature in determining the CuO formation rate.

Effects of vibrational and rotational excitations on the dissociative adsorption of O on Cu surfaces

Moritani, Kosuke*; Tsuda, Muneyuki*; Teraoka, Yuden; Okada, Michio*; Yoshigoe, Akitaka; Fukuyama, Tetsuya*; Kasai, Toshio*; Kasai, Hideaki*

Journal of Physical Chemistry C, 111(27), p.9961 - 9967, 2007/07

https://doi.org/10.1021/jp0718496

We report an X-ray photoemission study of the dissociative adsorption of O at Cu(111), (001), and (110) surfaces with an O molecular beam generated with a variable temperature nozzle. The O-uptake curves, which are produced from precisely measured O-1s peaks, indicate that the dissociative absorption is enhanced as the nozzle temperature is increased up to 1000 K for the normal incidence of O at a kinetic energy of 0.5 eV. However, further increasing the nozzle temperature to 1400 K reduces the probability of dissociativeadsorption. These results suggest that vibrational excitations of incident O assist dissociative adsorption while rotational excitations hinder it.

Protective layer formation during oxidation of CuAu(100) using hyperthermal O molecular beam

Okada, Michio*; Hashinokuchi, Michihiro*; Fukuoka, Masayuki*; Kasai, Toshio*; Moritani, Kosuke*; Teraoka, Yuden

Applied Physics Letters, 89(20), p.201912_1 - 201912_3, 2006/11

https://doi.org/10.1063/1.2390672

Oxidation of CuAu(100) using a hyperthermal O 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 O implies a higher activation barrier and therefore less reactivity due to the Au alloying. The dissociative adsorption progresses with the Cu segregation on the surface. No prominent growth of CuO even for 2 eV HOMB suggests that the Au-alloying of Cu can serve as a protective layer against further oxidation into the bulk.

The Azimuthal dependent oxidation process on Cu(110) by energetic oxygen molecules

Moritani, Kosuke; Okada, Michio*; Fukuyama, Tetsuya*; Teraoka, Yuden; Yoshigoe, Akitaka; Kasai, Toshio*

European Physical Journal D, 38(1), p.111 - 115, 2006/04

https://doi.org/10.1140/epjd/e2006-00041-3

We report a study on the oxidation process induced by a hyperthermal oxygen molecular beam (HOMB) on Cu(110) using X-ray photoemission spectroscopy in conjunction with a synchrotron radiation source. The oxidation process induced by energetic O beams on Cu(110), depending on the azimuthal angle of incidence, suggests that the -Cu-O- added row structure has a role in inhibiting adsorption as a steric obstacle for incident O molecules.