We have been studying correlation between thermal desorption of hydrogen and chemical bonding states of overlayer on the surface of hydrogen storage metals because desorption and absorption of hydrogen take place through the overlayer. Poly-crystalline Vanadium and VCrTa alloy are important as candidates for fuel cells of automobiles. In this study, native oxides, their thermal instability and artificial oxides formation via supersonic oxygen molecular beams (SSOMB) have been investigated using photoemission spectroscopy with synchrotron radiation (SR-PES). Various photon energies ranging from 600 eV to 1800 eV were used to investigate depth distributions in the native overlayer. All experiments have been performed at the surface chemistry end-station (SUREAC2000) of BL23SU in the SPring-8. Although carbon contamination was observed in the overlayer of both metals, nitrogen was negligible. C1s and O1s photoemission peaks decreased with increasing surface temperature. Especially, a new C1s peak appeared in the low binding energy side in the poly-Vanadium case. The peak strength moved from the original peak to the new peak. The native overlayer could be removed by heating up to 1273 K. The bare Vanadium surface was irradiated by SSOMB with the translational energy of 0.4 eV until saturation. This pure oxide overlayer could be removed by the same heating procedure. We verified again the oxidation of the surface using SSOMB with 2.3 eV. The saturated oxygen was larger than that of 0.4 eV case and an oxidation rate in the early stage was also large compared to the 0.4 eV case. Translational-energy–induced oxidation was found in the poly-Vanadium oxidation. In other words, we can control artificially the surface oxide thickness at room temperature using kinetic energy of oxygen as a parameter.

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