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Thermal dehydrogenation of long n-alkane on Au(111) and Pt(111) surfaces is investigated by near the carbon K-edge X-ray absorption fine structure spectroscopy (C K-NEXAFS) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV). On Au(111), dehydrogenation and formation of unsaturated bonds start at temperatures above 480 K, ending at 650 K. This is confirmed by the decrease in the 1 s → σ*CH/R resonance (σ*CH/R resonance) and the evolution of the π*CC resonance in the C K-NEXAFS spectra. The aliphatic or non-aromatic unsaturated bonds are generated at the early stage of the dehydrogenation on the Au(111), which is examined by the reaction with bromine. The dual peaks of the π*CC resonance at 284–286 eV suggest the formation of polycyclic aromatic hydrocarbons (PAHs). These PAHs exhibit a ribbon or rosary and planer shape by heating at 800 K, which is observed by the STM. In contrast, dehydrogenation begins at RT on Pt(111), and is almost completed at 480 K. π*CC resonance exhibits a main peak at 286 eV, which corresponds to a graphene skeleton, with a sub peak or a shoulder at 284.6 eV, which is attributed to a carbon atom at an edge or defect. The main peak intensity increases as the temperature is raised up to 820 K. STM images obtained after heating at 820 K show nanodots having a diameter of ca. 2–3 nm. The final products upon heating to 1000 K on Pt(111) are graphene nanoflakes with a size of tens of nanometers. The difference between the products is related to the difference between the reaction pathways on Au(111) and Pt(111) surfaces.

Graphene growth on a Pt(111) substrate exposed to benzene was studied at substrate temperatures between 800 K and 1100 K. The effects of the substrate temperature during benzene exposure and post-annealing were examined. It was revealed that the substrate temperature during benzene exposure determined the graphene size, which was measured using scanning tunneling microscopy (STM). Nanographenes (NGs) of ~10 nm in size. were obtained by exposing the substrate to benzene at 800 K and post-annealing at 1100 K. The presence of a C–Pt bond, which may fix the carbon atoms on the Pt(111) surface and suppress any further growth of graphene, was confirmed by the carbon K-edge near-edge X-ray absorption fine structure spectroscopy (C K NEXAFS) and X-ray photoelectron spectroscopy (XPS) for the NG. Angle resolved photoemission spectroscopy (ARPES) performed on the NG has a reduced density of states at the Fermi level.

X-ray photoelectron spectroscopy (XPS) is useful for in situ analysis of catalytically active surfaces under reaction conditions. We conducted in situ observations of CO oxidation on Pd single-crystal surfaces with different orientations under near ambient pressure (NAP) conditions with XPS. In this short review we compare catalytically active surfaces of Pd with the different orientations. Both surface oxides and atomic oxygen chemisorbed on metallic surfaces can be active for CO oxidation depending on surface geometric structure. We propose similarity between the surface oxides and the chemisorbed oxygen from a viewpoint of availability of active oxygen. Catalytic activity of the metallic surface under NAP condition is also compared with that under ultrahigh vacuum conditions.

Surface ferromagnetic state of FeRh thin films irradiated with 1 keV Ar ion-beam has been investigated by using soft X-ray Magnetic Circular Dichroism (XMCD). It was revealed that the Fe atoms of the samples were strongly spin-polarized after Ar ion-beam irradiation. Due to its small penetration depth, 1 keV Ar ion-beam irradiation can modify the magnetic state at subsurface of the samples. In accordance with the XMCD sum rule analysis, the main component of the irradiation induced ferromagnetism at the FeRh film surface was to be effective spin magnetic moment, and not to be orbital moment. We also confirmed that the surface ferromagnetic state could be produced by thermal annealing of the excessively ion irradiated paramagnetic subsurface of the FeRh thin films. This novel magnetic modification technique by using ion irradiation and subsequent annealing can be a potential tool to control the surface magnetic state of FeRh thin films.

A graphene nanoribbon is formed by the dehydrogenation reaction of n-alkane adsorbed on a Au(111) surface. The X-ray absorption spectra at the near carbon K-edge show the appearance of the out-of-plane 1s → π⁎ resonance upon heating the n-C44H90 monolayer with the simultaneous disappearance of the 1s → σ⁎CH/R (R: Rydberg state) resonance. The π⁎ resonance located at 284.6 eV reflects a high edge density and is consistent with the ribbon shape, which was observed by scanning tunneling microscopy, and the C 1s XPS peak at 284.0 eV.

We investigated the interactions of CO and O2 with Ru( 10 1 ¯ 0 ) single crystal surfaces, and studied the in-situ catalytic oxidation reaction of CO on the surface under near realistic pressure conditions by using a combination of near-ambient-pressure x-ray photoelectron spectroscopy and differential pumping mass spectroscopy. At lower temperatures (T

We show from the depth-resolved X-ray absorption analysis that the degree of surface oxidation of Fe70Co30 thin films is reduced by Ar+ ion milling even if the film is exposed to air after ion milling. The milled film has thinner surface oxide layer and smaller ratio of Fe oxide component in the surface layer than those of the as-deposited film. It is also indicated that selective oxidation of Fe proceeds accompanied by the movement of Fe atoms toward the surface. The suppression of oxidation is explained by the obstruction of Fe movement toward the surface by the milling-induced disorder.

We report molecular CO and NO adsorption structures on Pd(100) single crystal surfaces under sub-Torr pressure conditions at room temperature. A combination of ambient pressure X-ray photoelectron spectroscopy and density functional theory based calculations indicates that CO molecules adsorb at 2-fold bridge sites with (2√2 × √2)R45°, (3√2 × √2)R45° and (4√2 × √2)R45° structures under the CO gas pressures at room temperature. Furthermore a higher-density adsorption structure is reversibly formed at 0.5 Torr CO, where all the CO molecules keep sitting on the bridge sites. In case of NO adsorption, at 10 − 7 Torr, a (2√2 × √2)R45° structure with occupying bridge sites is formed, which is the same as the case of CO. However, subsequent gas introduction up to 0.5 Torr causes additional site occupation of on-top sites. Furthermore NO molecules partially dissociate into atomic N and O species but they disappear from the surface due to further reaction with NO under ambient conditions.

Spectral separation methods for X-ray absorption fine structure spectroscopy at the near carbon K-edge are examined for an n -C 36 H 74 monolayer adsorbed on a monolayer graphene grown on a Pt(1 1 1) surface. The spectra of n -C 36 H 74 and the monolayer graphene are separated by fitting decay curves obtained for all photon energies by detecting photoelectrons as a function of the ejection angle. The results are discussed in comparison with separation results obtained by subtracting the independently measured graphene spectra as a background.

We report x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements of both paramagnetic and ferromagnetic Ti 1 − x Fe x O 2 − δ thin films. Fe L 3 , 2 edge XAS spectra showed that the Fe ions in our samples were in mixed valence states and that the Fe2+/Fe3+ ratio decreased with increasing oxygen partial pressure. Finite XMCD signals were observed only for the Fe2+ state in the ferromagnetic sample. These findings indicate that the observed ferromagnetism in Ti 1 − x Fe x O 2 − δ originates from ferromagnetic interactions between Fe2+ local spins.

Depth analysis using X-ray absorption fine-structure spectroscopy at the near carbon K-edge (C K-NEXAFS) was performed for self-assembled monolayers of 4-methylbenzenethiol (4-MBT) and 4-ethylbenzenethiol (4-EBT) on Au(1 1 1). On the basis of the polarization dependence of π * resonance intensity, the benzene rings of 4-MBT and 4-EBT were found to be tilted by 30 ± 10° and 60 ± 5° with respect to the Au(1 1 1) surface, respectively. The spectra were separated into two components according to their depth by fitting the intensity decay curves of the electrons emitted by X-ray absorption. The spectra for lower segments exhibited bands at almost identical energies with different intensities depending on the polarization between 4-MBT and 4-EBT. In contrast, the spectra for upper segments including the alkyl groups showed a marked difference in the location of the σ CC * resonance. The σ CC * resonance of the ethyl group predominantly observed in the 15° incidence spectrum of 4-EBT indicated that the ethyl group was directed perpendicularly.

Formation process of carbon nanocaps, which are formed at the beginning of carbon nanotube (CNT) growth by surface decomposition of SiC, was investigated by scanning tunneling microscopy (STM) and in situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. As Si atoms were desorbed, carbon nanoparticles 1–2 nm in diameter were accumulated on SiC(000-1) surfaces. At around 1200 °C, these were coalesced and crystallized to carbon nanocaps. In addition, just before the crystallization, majority of C–C bonds were directed nearly parallel to the surface. Based on these experimental results, we proposed a model for carbon nanocap formation, which plays an important role to determine the CNTs.

Near edge X-ray absorption fine structure spectra at the carbon K-edge (C K-NEXAFS) of n-C12H26 films grown on graphite (0 0 0 1) were measured under ultrahigh vacuum conditions. In the normal incidence spectra, the 1 s → σ CH * / R resonance of n-alkane was identified at a lower energy than the absorption edge of graphite. The σ CH * / R resonance directed along the CH bond was observed at 286.9 eV for the first layer of the n-C12H26 film on graphite. This indicates that the CCC plane of the molecule is parallel to the surface (flat-on orientation). As the film thickness increases, another peak assigned to σ CH * / R ⊥ grows at 288.0 eV, suggesting an increase in the number of molecules with the CCC plane perpendicular to the surface in a multilayer film.

The electronic and atomic structures of a 4-cyano-4′-iodobiphenyl (CIB) thin film on a GeS(0 0 1) substrate were studied by atomic force microscopy (AFM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. CIB molecules exhibit high crystallinity owing to halogen bonding and are grown as a microcrystal at a nominal thickness of 80 A. NEXAFS measurements suggest that, at a thickness of 0.4 A, the molecular plane tilts away from the surface plane at an angle of 12°, and the molecular axis tilts away from the GeS [0 1 0] direction by 35°. At a thickness of 80 A, the molecular plane tilts away from the surface plane by 51°, and the molecular axis tilts away from the GeS [0 1 0] direction by 43° on average. NEXAFS spectra show a drastic reduction in the π C C * and π C N * resonances in the thicker film. This is interpreted as electron transfer, which is induced by halogen bonding, from the halogen atom.

The electronic and atomic structures of 4-cyano-4′-iodobiphenyl (CIB) during the growth of a molecular crystal on a GeS(001) substrate were studied by ultraviolet photoemission spectroscopy (UPS), atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy. AFM images suggest that the CIB molecule grows as a microcrystal at a nominal thickness of 80 A. The microcrystal grows with the crystal plane parallel to the surface and isotropic crystal axis orientation. EXAFS analysis suggests that a CIB crystal forms by strong N···I interaction, called halogen bonding. The formation of the intermolecular N···I bond was demonstrated by EXAFS analyses in which the N–I distance was determined to be 3.29 A. An upward shift of the highest occupied molecular orbital level was observed by UPS and can be attributed to the aggregation of CIB molecules caused by halogen bonding.

Proton transfer in water–hydroxyl mixed overlayers on a Pt(1 1 1) surface was studied by a combination of laser induced thermal desorption (LITD) method and spatially-resolved X-ray photoelectron spectroscopy (micro-XPS). The modulated pattern OH + H 2 O/H 2 O/OH + H 2 O was initially prepared by the LITD method; vacant area with a 400 μm width was first formed in the mixed OH + H 2 O overlayer by irradiation of focused laser pulses, and followed by refilling the vacant area with pure H 2 O. Spatial distribution changes of OH and H 2 O were measured as a function of time with the micro-XPS technique, which indicated that H 2 O molecules in the central region flow into the OH + H 2 O region. From quantitative analyses using a diffusion equation, we found that the proton transfer in the mixed overlayer consists of at least two pathways: direct proton transfer from H 2 O to OH in the nearest site and the proton transfer to the next-nearest site via H 3 O + formation. The time scale of first and second path was estimated to be 5.2 ± 0.9 ns and 48 ± 12 ns at 140 K, respectively. In the presence of water capping layer, however, the rate of proton transfer is reduced by an order of magnitude, which would be explained by peripatetic behavior of proton into H 2 O capping layer.

Spin-reorientation transitions of Co/Pd(1 1 1) magnetic thin films induced by chemisorption of molecules have been investigated by the magneto-optical Kerr effect. The magnetic hysteresis curves during the phase transitions induced by CO adsorption were recorded with the polar and longitudinal Kerr geometries. Essential differences in the variations of the coercive field and the remanent magnetization were observed between the in-plane and perpendicular magnetization processes. It was found that the larger the area of perpendicular magnetization is, the larger the perpendicular coercive field becomes. On the contrary, as the area of in-plane magnetization is smaller, the in-plane coercive field becomes larger, although the enhancement is much less significant than in the perpendicular case. This difference is explained in terms of the different character of domain walls. NO adsorption has also been investigated. Similarities and dissimilarities between CO and NO adsorption indicate that NO stabilizes perpendicular magnetization even from the initial stage of adsorption, while the stabilization of perpendicular magnetization by CO adsorption occurs only at the second stage where the atop-site adsorption is completed and the bridge-site adsorption starts.

In this work we theoretically study magnetic EXAFS based on relativistic scattering theory. So far Fourier transform of magnetic EXAFS has been believed to give no peak for the backscattering from nonmagnetic atoms. We carefully study this problem for two examples, Gd L 23 -edge EXAFS for Gd 3 Fe 5 O 12 and Mn K-edge EXAFS for Ni 1− x Mn x alloys, and find that even nonmagnetic nearest neighbors can give a prominent peak in Fourier transform of magnetic EXAFS as far as the X-ray absorbing atom is strongly spin polarized. We also investigate the effect of the integral region in the Fourier transform.

The spin reorientation transition (SRT) of Ni / Cu ( 0 0 1 ) induced by Fe deposition was investigated using the X-ray magnetic circular dichroism (XMCD) method. In-plane magnetized Ni films ( ⩽ 9 ML ) undergo the SRT twice; first, a small amount ( 1 ML ) of Fe deposition causes a transition to perpendicular magnetization. Second, further Fe deposition (1–2 ML in total) causes a return to in-plane magnetization. Perpendicularly magnetized Ni films ( ⩾ 10 ML ) also exhibit a transition to in-plane by 1–2 ML Fe deposition. A precise magnetic anisotropy phase diagram was obtained using a combination of wedge-shaped Ni samples and stepwise Fe deposition. Magnetic anisotropy energies in the bulk, surface and interface layers of Ni films were separately determined using the depth-resolved XMCD technique, while values in the 1 ML and 2 ML portions of the Fe films were obtained from the conventional XMCD measurements. The origin of the SRTs is successfully explained with a simple phenomenological layer model using the obtained magnetic anisotropy energies.

Surface and interface magnetization of Fe/Ni/Cu(1 0 0) thin films was observed with the probing depth-dependent X-ray magnetic circular dichroism technique, in which the probing depth is controlled by changing the electron detection angle. An oscillatory behaviour of the surface magnetization dependent on the Fe thickness was directly revealed, while simple analyses indicated that the interface (bottom) Fe magnetization stays almost unchanged independent of the Fe thickness, and that the inner layers are basically nonmagnetic. These results suggest an oscillatory interlayer magnetic coupling between the surface and interface of the Fe film via the nonmagnetic inner layers. It was indicated that the observed oscillation can also be attributed to a rotatory interlayer coupling between the surface and interface. A temperature-dependent experiment indicated that the surface magnetization is reversed depending on the temperature, which might be attributed to the magnetic structural change in the inner layers.

We have studied the structure of the ‘striped’ (flat-lying) phase of hexanethiolate on Au(1 1 1) by using X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure and scanned-energy photoelectron diffraction. Combined results of these techniques indicate that gaseous hexanethiol adsorbs as hexanethiolate in the ‘striped’ phase with the alkyl chain lying down onto the surface and the S head group occupying an atop site. The S–Au distance was determined to be 2.40 ± 0.05 A. The present experiments clearly exclude both the multiple-site model and the dimer model.

We have studied the magnetic states of Au/2-monolayer Co clusters/Au(1 1 1) by angle-, field-, temperature-, and cluster-size-dependent magnetic circular X-ray dichroism (MCXD) measurements in the longitudinal geometry with full use of a magic angle of 54.7°. The absolute magnitude of the normal-incidence MCXD provides evidence for a single domain of clusters and for a phase transition from ferromagnetism (FM) to superparamagnetism (SPM) with decreasing cluster size. The spin, in-plane and out-of-plane orbital, and in-plane and out-of-plane magnetic dipole moments of almost purely interfacial Co atoms were directly determined. The interfacial spin moment is strongly enhanced and the interfacial orbital and magnetic dipole moments are highly anisotropic and enhanced as compared with those in bulk Co, verifying theoretical predictions. We argue the implications of the results in particular relation to their physical origin and to a potential technological application of the nanoclusters.

The adsorption behavior of thiophene on Au(1 1 1) surface has been extensively studied as a function of coverage by two inner-shell spectroscopies; X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Thiophene was adsorbed on Au(1 1 1) at about 130 K with several exposures. It was revealed that the growth of thiophene film on Au surface has three processes: (1) growth of a flat-lying monolayer; (2) growth of a “compressed(inclined)” monolayer; (3) growth of a standing multilayer. Photochemical reactions induced by X-ray irradiation on the thiophene film have also been studied. The yield of the reaction products drastically increases above the coverage at which the compressed monolayer is formed. XPS and NEXAFS results suggest that the photochemical products are oligothiophenes and thiolates. X-ray energy dependence on the yield shows that the yield is significantly enhanced above the C K-edge, which means that the core hole creation of the carbon atom plays an important role for these reactions.

Interaction between C 60 molecules and Si surfaces at room temperature has been investigated by near-edge X-ray absorption fine structure (NEXAFS). The NEXAFS spectra of 1.0 monolayer (ML) C 60 films adsorbed on Si(001)-(2 × 1) and Si(111)-(7 × 7) surfaces show the same spectral profile as those of C 60 solids. At 0.25 ML, the full-width at half-maximum's of the unoccupied molecular orbitals increase, the energy levels of the lowest unoccupied molecular orbital (LUMO) shift, and the intensities of the LUMO + 1 decrease on both Si surfaces. These results indicate that C 60 molecules are chemisorbed at 0.25 ML, and 75% of C 60 molecules are physisorbed and 25% are chemisorbed at 1.0 ML on both Si surfaces. Further, we conclude that the character of the chemisorption is covalent, to which the LUMO + 1 contributes on both Si(001)-(2 × 1) and Si(111)-(7 × 7) surfaces.

A new soft X-ray (50–1500 eV) beamline has been constructed at a bending magnet station at the Photon Factory in order to perform photoemission spectroscopy (PES), X-ray absorption fine structure (XAFS), photoelectron diffraction (PED) and X-ray magnetic circular dichroism (XMCD) experiments in surface chemistry. Approximately 10 11 photons/s can be obtained with a medium resolution ( E /Δ E ∼1000), while E /Δ E ∼8000 can be attained at the N K edge with a photon flux of ∼10 9 photons/s. In addition to conventional XAFS, a novel technique ‘energy dispersive NEXAFS (near-edge X-ray absorption fine structure)’ has been successfully developed. The performance of the new beamline is reported and typical examples of its application to surface chemistry are demonstrated.

Using Co L 2,3 resonant soft X-ray scattering measurement, we reveal that the magnetic orderings with q = (1/2, 0, 1/2) and (1/2, 0, 1) originate from different magnetic domains. Temperature dependence of the magnetic ordering peaks clearly shows that there is a finite difference between the transition temperatures of these magnetic orderings.

We have measured the unoccupied electronic structures of a C 60 monolayer film adsorbed on a Si(1 1 1)-(7×7) surface at 300 and 500 K, using inverse photoemission spectroscopy (IPES) and near edge X-ray absorption fine structure (NEXAFS). At 300 K, both IPES and NEXAFS spectra reveal that most of C 60 molecules interact with the Si surface by van der Waals force at a coverage of 1.0 monolayer. After annealing the sample at 500 K, the full-width at half maximum of the unoccupied molecular orbitals becomes broader indicating the chemisorption at this temperature. Moreover, the NEXAFS spectrum shows the shift of the lowest unoccupied molecular orbital (LUMO) to the higher photon energy side and the decrease in intensity of the LUMO+1. These results suggest that the strong interaction induced at 500 K has a covalent character, to which the LUMO+1 contributes.

We observed O K-edge X-ray magnetic circular dichroism (XMCD) of molecular CO adsorbed on Co and Ni epitaxial films grown on a Cu(001) substrate. The films examined are 6 ML Ni, thick (>100 ML) Ni, 4 ML fcc Co which show in-plane magnetic anisotropy, while the others, 10 ML Ni and ∼2 ML Co on 30 ML Ni, exhibit perpendicular magnetic anisotropy (PMA). In the PMA films, negative XMCD signals were observed at the O 1s→CO 2π* transition, while in the in-plane magnetization films, positive XMCD signals were detected at the same transition. These findings imply the presence of orbital magnetic moments at the CO 2π* levels since the CO 2π* orbitals are partially filled due to hybridization of metal 3d levels, in spite that CO is inherently diamagnetic in a gas phase. The observed XMCD signs indicate parallel and antiparallel alignments of the CO 2π* orbital magnetic moments for the PMA and in-plane magnetization films, respectively. The direction of the orbital moments is tried to interpret within a framework of chemical bonding between CO and metal atoms.

We have investigated the interaction between metastable molecular oxygen and the adatom dangling bonds modified by the adsorption of atomic oxygen into the back-bonds of a Si(111)-(7×7) surface. Ultraviolet photoelectron spectroscopy shows that the metastable states increase in intensity faster but with a decrease in its saturated intensity as the coverage of atomic oxygen increases. This result suggests that the number of modified dangling bonds is not the only important factor for the adsorption process of metastable oxygen. Taking into account the observation of modified dangling bonds with different density of states in scanning tunneling microscopy, we conclude that the adsorption of the metastable oxygen species correlates closely with the density of states of the dangling bond.

Progress in the commissioning of the new soft X-ray beamline 11A at the Photon Factory is reported. Highly pure soft X-rays down from 70 up to 1900 eV were found to be obtainable with two holographically recorded varied-line-spacing gratings and a novel harmonic-rejection double-mirror system. The wide photon energy availability is quite useful to measure EXAFS spectra on B, C, N, O, F, Na, Mg, or Al K-edge.