A. Imanishi

Surface structures and electronic properties of SO2 adsorbed on Ni(111) and Ni(100) studied by S K-edge X-ray absorption fine structure spectroscopy

Surface structures and electronic properties of submonolayer sulfur dioxide, SO2, molecularly adsorbed on Ni(111) and Ni(100) at ∼ 170 K have been investigated by means of S K-edge surface extended X-ray-absorption fine structure (SEXAFS), near-edge X-ray-absorption fine structure (NEXAFS) and S 1s X-ray photoelectron spectroscopy (XPS) measurements. NEXAFS and SEXAFS have clarified that on both surfaces the SO2 molecule adsorbs with the molecular plane parallel to the surface and the elongated intramolecular Sue5f8O bond lengths. The S atom directly interacts with substrate Ni, located at the bridge sites on both surfaces. Such adsorption geometries for submonolayer SO2 on metal surfaces have never been reported before. Comparing to other SO2metal systems the determined surface structures are discussed in terms of chemical bonding.

Adsorption of acetylene and ethylene on the Si(001)2×1 surface studied by NEXAFS and UPS

Abstract The adsorption of acetylene (C 2 H 2 ) and ethylene (C 2 H 4 ) on the Si(001)2×1 surface has been investigated by near edge X-ray adsorption fine structure (NEXAFS) and ultraviolet photoemission spectroscopy (UPS) using synchrotron radiation. Upon molecular adsorption, a drastic decrease of the π* resonance (C 2 H 4 ) and an energy shift of the σ* resonance (both C 2 H 2 and C 2 H 4 ) were observed in the NEXAFS spectra. The intensity of dangling bond states of Si in the UPS spectra diminished significantly by adsorption of both molecules. These results provide firm evidence for the structure model with Si dimers preserved and the di-σ bonding between the adsorbed molecules and Si dimers.

Structural studies of adsorbed alkanethiols on Cu(111) by use of S and C K-edge X-ray absorption fine structures

Surface structures of submonolayer alkanethiol CH3(CH2)n−1SH (n=6,12) adsorbed on Cu(111) at room temperature (0.3 ML) were investigated by means of S K-edge surface extended X-ray absorption fine structure (EXAFS) and S, C K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopies. Polarization dependence of the C K-edge NEXAFS spectra revealed that alkanethiol molecules adsorb with the tilt angle of 12 ± 10° from the surface normal. The S K-edge surface EXAFS determined that the Sue5f8Cu distance is 2.31 ± 0.02 A and that the S atoms locate at a deep three-fold hollow site with significant lateral outward movements of the nearest neighbor Cu atoms.

Structural and electronic properties of adsorbed C4H4S on Cu(100) and Ni(100) studied by S K-XAFS and S-1s XPS

Abstract Surface structures and electronic properties of submonolayer thiophene C4H4S adsorbed on Cu(100) (0.07 ML, 220 K) and Ni(100) (0.10 ML, 43 K) have been investigated by means of S K-edge surface extended X-ray-absorption fine structure (SEXAFS), near-edge X-ray-absorption fine structure (NEXAFS) and S 1s X-ray photoemission spectroscopy (XPS) measurements. It is revealed that the C4H4S molecules adsorb with the molecular plane parallel to the surface and the S atom locates at the bridge site on both surfaces. The distances of S-substrate atoms, and of the Sue5f8C bond in C4H4S, as well as the degree of charge transfer from the substrate to the C4H4S π ∗ orbital were determined. These results indicate that C4H4S interacts more strongly with the Ni substrate than with the Cu substrate.

Surface structure of SO2 adsorbed on Ni(110) studied by S K-edge X-ray absorption fine structure spectroscopy

Abstract Surface structure and electronic properties of submonolayer sulfur dioxide SO2 molecularly absorbed on Ni(110) have been investigated by means of S K-edge surface-extended X-ray absorption fine structure (SEXAFS), near-edge X-ray absorption fine structure (NEXAFS) and S 1s X-ray photoemission spectroscopy (XPS) measurements. The SO2 molecule was found by SEXAFS and NEXAFS to adsorb with the molecular plane parallel to the surface and an elongated Sue5f8O bond distance compared to that of a free molecule. The S atom was revealed to locate on the long- and short-bridge sites with almost equal probabilities. No azimuthal-angle dependence was detected as for the Sue5f8O bond direction. A significant amount of charge transfer from the substrate to the SO2 π∗ orbital was found by NEXAFS and XPS. Such structural and electronic properties are essentially similar to those of SO2 on Ni(100) and Ni(111).

Thiophene adsorption on Pd(111) and Pd(100) surfaces studied by total-reflection S K-edge X-ray absorption fine-structure spectroscopy

Abstract The total-reflection grazing-incidence technique has been applied to measure the S K-edge soft X-ray absorption fine structure spectra of submonolayer thiophene on Pd(111) and Pd(100) surfaces. The total-reflection mode allows us to obtain reliable spectra with a much higher signal-to-background ratio compared to that given by the conventional non-total reflection method. Similar surface structures of adsorbed thiophene are consequently determined on both surfaces. Thiophene molecules are found to lie flat accompanied by slightly elongated S–C bonds due to the charge transfer of 1.1–1.2 electrons from the Pd valence bands to the thiophene π* orbital. The S atom in the thiophene adsorbate is located at an intermediate position between bridge and atop sites. The displacement is estimated to be 0.61±0.05xa0A away from the bridge site towards the atop one. The structural and electronic properties of adsorbed thiophene on Pd(111) and Pd(100) are discussed in comparison with the previous results on Ni(100) and Cu(100).

Electronic properties of SO2 adsorbed on Ni(100) studied by UPS and O K-edge NEXAFS

Abstract Surface electronic properties of submonolayer sulfur dioxide SO2 molecularly adsorbed on Ni(100) have been investigated by means of ultraviolet photoelectron spectroscopy (UPS) and O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS has confirmed that the SO2 molecule is lying flat on the surface and significant charge transfer occurs from the substrate to the π ∗ orbital. UPS has directly clarified a partial occupancy of the π ∗ level, and correspondingly the π level was found to shift to a lower binding energy more significantly than other orbitals. It has been clearly elucidated that the SO2 molecule acts as a π acceptor upon adsorption on the Ni(100) surface.

Structural and electronic properties of molecularly adsorbed CS2 on Cu(111) studied by X-ray absorption and photoelectron spectroscopies

Abstract The surface structure and the electronic properties of submonolayer carbon disulphide CS 2 molecularly adsorbed on Cu(111) at 92 K were investigated by means of S K-edge surface extended X-ray absorption fine structure (SEXAFS), near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements. The CS 2 molecule is found by NEXAFS to lie nearly flat and linearly on the surface with a tilt angle of the molecular axis of 8 ± 5°. NEXAFS and XPS suggest that the adsorbed species is in a state close to CS 2− 2 . SEXAFS has clarified the adsorption geometry of the CS 2 molecule, where one S atom locates at the three-fold hollow site and the other S is at the bridge site with a slightly longer S-Cu distance. The determined surface structure is discussed comparing to other molecular adsorbate systems.

Asymmetric adsorption of CS2 on Cu(100) studied by S K-edge X-ray absorption fine structure spectroscopy

Abstract The surface structure and the electronic property of submonolayer carbon disulfide CS 2 adsorbed molecularly on Cu(100) at 106 K were investigated by means of S K-edge surface extended X-ray absorption fine structure (SEXAFS), near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements. The CS 2 molecule is found by NEXAFS to lie nearly flat on the surface with a small tilt angle of the molecular axis from the surface. The π∗ resonance intensity in NEXAFS suggests that the adsorbed species is in the state of CS 1.3− 2 . SEXAFS has clarified the adsorption geometry of the CS 2 molecule; the molecule adsorbs asymmetrically with the two S atoms respectively locating at the fourfold hollow site and closely to the bridge site. Such an adsorption structure is quite similar to submonolayer CS 2 on a Cu(111) surface.

Adsorption and decomposition of SiH4 and surface silicide formation on Cu(111) studied by X-ray absorption fine structure spectroscopy

Abstract Adsorption and thermal decomposition of silane (SiH 4 ) on Cu(111) were investigated by Si K-edge X-ray absorption fine structure spectroscopy. It is found that the molecule is adsorbed on the hcp site retaining some of the Siue5f8H bonds at 110 K. After heating the sample to 230 K, Siue5f8Si bonds were recognized in the EXAFS spectra which indicates cluster formation on the surface. Further annealing at 600 K forms a silicide-like structure by substituting some surface Cu atoms by Si ones.