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In situ X-ray absorption spectroscopy (XAS) was applied to investigate the Sn underpotential deposition (UPD) on Ni surface from 0.2 M HClO 4 solution containing 10 −3 M Sn 2+ with relation to the inhibition effect of Sn on aqueous corrosion of Ni. The periodical emersion method under potentiostatic polarization, using the surface-roughened Ni plate (surface roughness S r = 78.3) as a working electrode was employed to detect sensitively the sub-monolayer coverage of Sn on Ni. The Sn K-edge absorption spectra in a scanning XAS mode were measured by monitoring the Sn K α1 fluorescence line. The Sn K-edge absorption near-edge structure (XANES) in the Sn-UPD potential region has revealed that the Sn-UPD layer on Ni is oxygenated. The extended X-ray absorption fine structure (EXAFS) analysis was performed with a two shell fit of the nearest neighbor Sn-Ni and Sn-O interactions, assuming that the uppermost Ni surface exposed to the solution is mainly oriented to the (111) plane. The results have indicated that Sn atoms are substituted like a surface alloy at face-center-cubic sites in the first Ni layer and further bonded with oxygen atoms. The strong inhibition effect of Sn on aqueous corrosion of Ni is ascribed to the bond between Sn and O atoms in addition to the bond between Sn and Ni atoms. The formation of metal monolayer on a foreign metal electrode at potentials more noble than the equilibrium potential of bulk electrodeposition is termed underpotential deposition (UPD). The UPD of Sn on Pt 1-4 has been investigated with relation to electrocatalysts for electro-oxidation of CO, 5 HCOOH 6 or methanol 7-10 while Sn-plating has been widely used in steel industry due to the corrosion prevention of iron and steels by Sn.11-14 Our recent study 15 has revealed that 10 −3 M Sn 2+ added in 0.2 M HClO 4 inhibits completely the anodic dissolution of pure Ni, suggesting the participation of Sn-UPD in corrosion inhibition of Ni. We reported previously that the addition of Pb 2+ in acidic perchlorate solution suppresses the anodic dissolution of Ni and the suppression of Ni corrosion is ascribed to the Pb-UPD. 16 Moreover, it was confirmed by in situ surface X-ray absorption spectroscopy (XAS) that the Pb species deposited on Ni are in metallic state. 17The following differences, however, are distinct between inhibition effects of Pb 2+ and Sn 2+ on anodic dissolution of Ni. In the case of Pb 2+ , although the Pb atoms deposited on Ni in the UPD potential region suppress the anodic dissolution of Ni, the anodic dissolution of Ni is re-activated due to anodic stripping of the deposited Pb atoms as the potential shifts to the noble direction and Ni is subsequently passivated. 16 In contrast in the case of Sn 2+ , no anodic dissolution of Ni is observed in the wide potential region exceeding the Sn-UPD region.15 The X-ray photoelectron spectroscopy (XPS) analysis has showed that in the case of Pb 2+ , any Pb species are not detected on the passive surface of Ni, 16 while in the case of Sn 2+ , Sn species are detected on the pa...

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It is widely recognized that, in comparison with conventional Ar + sputter etching, Argon gas cluster ion beam (Ar-GCIB) sputtering provides mild etching of a sample surface because of its low energy per atom and lateral sputtering effect. X-ray photoelectron spectroscopy (XPS) combined with Ar-GCIB has become established as an in-depth analysis technique for organic materials. Considering such advantages, Ar-GCIB irradiation conditions were investigated for removal of organic contaminations on inorganic material surfaces. The bonding state of the native oxide on the Si-substrate surface was employed as an indicator of surface damage. It was found that the incident angle of Ar-GCIB irradiation strongly affects the roughness and damage to the surface. It was also found that the surface contamination layer can be removed without affecting the native oxide film on the Si-substrate when the incident angle is 85° for Ar 1000 + and 80° for Ar 2000 + , respectively.