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The insertion effect of an interface NiO layer on magnetism in Fe/BaTiO3 is investigated by X-ray absorption spectroscopy (XAS). From X-ray magnetic circular dichroism (XMCD) analysis, the enhancement of remanent magnetization in Fe is observed with increasing NiO thickness. We also find that the NiO layer is partially composed of metallic Ni, and its thickness is estimated to be ~0.4 nm from the NiO-thickness dependence of the Ni XAS intensity by assuming that Ni is localized at the interface between Fe and NiO. Moreover, extended X-ray absorption fine structure data shows that the Ni–O distance of the interface NiO layer is shorter than that of bulk NiO, which leads to the pseudomorphic growth of NiO on BaTiO3. We thus suppose that the improved Fe growth promoted by the interface NiO layer enhances the magnetic moment in Fe.

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.

The magnetic properties of ferromagnetic Ni thin films grown on a Cu(001) single crystal are modified by the growth of a NiO overlayer, as well as by the voltage application through the NiO/Ni interface. A spin reorientation transition from in-plane to perpendicular magnetization is induced with increasing NiO thickness, and the coercive field significantly increases by further growth of the NiO overlayer. The remanent magnetization of the films is found to be modulated by the voltage application. Moreover, a small exchange-bias effect arising from the ferromagnetic–antiferromagnetic interaction at the interface is observed, and the amplitude of the effect is modified by the applied voltage.

Ferromagnetism with perpendicular magnetic anisotropy (PMA) was observed at room temperature in cobalt nanoparticles (NPs) grown on hexagonal boron nitride (h-BN) on a Pt(111) surface. It was shown that the Co NPs have planar hexagonal shapes with a mean diameter of ∼20 nm and a mean height of ∼1.6 nm. The depth-resolved analysis of X-ray magnetic circular dichroism at the Co L2,3-edges revealed that in the ferromagnetic Co NPs, the ratio of the orbital magnetic moment to the spin magnetic moment in the out-of-plane direction becomes larger at the Co NP/h-BN interface than the ratio in bulk Co. The B and N K-edge near edge X-ray absorption fine structures showed the orbital hybridization between the π orbitals of h-BN and d orbitals of Co at the interface, as an origin of the orbital magnetic moment enhancement possibly giving rise to PMA in the Co NPs.

The reaction mechanism of ammonia formation on a Rh(111) surface was investigated by means of dispersive near-edge X-ray absorption fine structure (dispersive-NEXAFS) spectroscopy. Nitrogen-covered Rh(111) surfaces were exposed to gaseous hydrogen (1.0−5.0 × 10−7 Torr) at constant surface temperatures (330−390 K) to form ammonia which desorbs immediately from the surface. Continuous data acquisition of nitrogen K-edge NEXAFS spectra enables us to monitor coverage changes of surface species during the progress of the reaction. The obtained NEXAFS spectra were well reproduced by summation of the standard spectra for N and NH. We found that the NH species, which is considered as a stable intermediate, is not only hydrogenized to NH3, but also decomposed into N and H under H2-lacking conditions. The reaction-order analyses indicate that the NH decomposition occurs at periphery of 2-dimensional islands of NH while the NH3 formation takes place most likely over the entire NH islands. We propose a two-step react...

We studied the mechanism of the N + NO reaction on Rh(111) surfaces by means of near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Atomic nitrogen layers on Rh(111) were titrated with NO at various temperatures. Below 350 K, the chemisorbed NO monomer does not react with N, while the NO dimer formed in the second layer acts as an extrinsic precursor to the reaction: N(a) + (NO)2(a) → N2O(g) + NO(a). Because of a dominant role of the precursor-mediated mechanism, the reaction proceeds slower with an increase in temperature. Above 350 K, the reaction switches to a different path: N(a) + NO(a) → N2(g) + O(a).

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.

Development and potential applications of a three-dimensional X-ray absorption fine structure (XAFS) technique are described showing some preliminary data. By combining an X-ray microbeam with a depth-resolved XAFS technique, one can observe atomic, electronic and magnetic structures of thin film samples with a three-dimensional spatial resolution. A 3-5 μm beam size was achieved by adopting a two-step focusing mirror system, and two-dimensional magnetic images for a wedge-shaped Fe/Ni/Cu(100) thin film were obtained. On the other hand, the surface and interface components of XAFS spectra were extracted by applying the depth-resolved XAFS technique to a Ni/Cu(100) thin film. These results indicate that the three-dimensional XAFS measurements are now possible. Future prospects of this novel technique are also described.

A new version of synchrotron-radiation-based x-ray spectroscopy, wave-length-dispersive near-edge x-ray absorption fine structure (dispersive-NEXAFS), and fast x-ray photoelectron spectroscopy have been applied to mechanistic studies on several surface catalytic reactions on platinum-group-metal surfaces. In this review, our approach using above techniques to understand the reaction mechanism and actual application studies on three well-known catalytic surface reactions, CO oxidation on Pt(111) and Pd(111), NO reduction on Rh(111) and H2O formation on Pt(111), are introduced. Spectroscopic monitoring of the progress of the surface reactions enabled us to detect reaction intermediates and analyze the reaction kinetics quantitatively which provides information on reaction order, rate constant, pre-exponential factor, activation energy and etc. Such quantitative analyses combined with scanning tunneling microscopy and kinetic Monte Carlo simulations revealed significant contribution of the adsorbate configurations and their dynamic changes to the reaction mechanisms of the above fundamental catalytic surface reactions.

Molecular adsorptions affect on the magnetism of magnetic thin films. We have observed anomalous magnetic states in gas adsorbed Fe thin films. In this report, we present the CO or NO adsorption effects on the magnetism of 2-4 ML Fe thin films on Cu(001), which are typical magnetic thin films. The Fe(2 ML)/Cu(001) film does not change its magnetic structure upon CO adsorption, whereas the CO/Fe(3 and 4 ML)/Cu(001) films turned their easy axes of magnetization to in plane. Depth resolved XMCD measurements give us detailed information on the depth profile of the magnetic structures. The surface two layers of the CO/Fe(4 ML)/Cu(001) film lose the magnetization, and only the bottom two layers keep the magnetization. NO adsorbed Fe films have the in-plane easy axes of magnetization. Moreover, the magnetization of the topmost layer of the NO/Fe/Cu(001) films aligns in the opposite direction to the other layers. Thus, the antiferromagnetism in the surface layers has appeared in the NO/Fe/Cu(001) films.

The surface reactions of iodine ions on nearly atomically flat, H-terminated Si(111) surfaces, when immersed in 7.6 M HI in a temperature range of −20 to 63 °C, were investigated by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and core-level shift spectra. It was revealed that the following two reactions simultaneously occurred, which were competitive with each other: (1) substitution reaction of Si−H bonds with Si−I bonds and (2) cluster formation by the condensation of SiHxI4−x or their oligomer species, which were generated by surface etching reaction. The ratio of those competitive reactions was strongly dependent on the temperature of the HI solution. At the high temperature, the former reaction was enhanced, whereas the latter reaction was suppressed. Inversely, at the low temperature, the latter reaction was relatively enhanced, resulting in that the ordered rodlike clusters were formed on the Si(111) surface. These results were explained by the fact that the forme...

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.

XAFS (X-ray Absorption Fine Structure) is a powerful technique, which provides element-specific information on atomic and electronic structures even for samples without long-range periodic structure. Owing to the recent developments of synchrotron radiation facilities, it has become possible also for non-expert researchers to obtain such information using XAFS. In this lecture, the basic concept and analytic procedures are presented including the utilization of X-ray polarization and time-resolved measurements.

Effects of CO adsorption on the magnetic properties of Fe films on Cu(001) were studied at 100 K as a function of the film thickness. CO adsorption does not affect the magnetic property of 2 ML Fe film but induces the spin reorientation transition from perpendicular to in-plane magnetization for 4 ML Fe film. It also causes the apparent decrease of magnetization, which is attributed to the reduction in surface magnetization by analyses of depth-resolved XMCD spectra. The reduction of the magnetization can be originated from a reconstruction of the surface structure of the films. It was suggested that the surface structures of the 4 ML Fe film are changed to a bcc-like structure upon CO adsorption, while the structure of the 2 ML Fe film could not change by CO adsorption because its magnetization is unchanged. [DOI: 10.1380/ejssnt.2008.233]

Photon Factory and Condensed Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki 319-1106, Japan Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan

Catalytic CO oxidation reaction on a Pd(100) single-crystal surface under several hundred mTorr pressure conditions has been studied by ambient pressure X-ray photoelectron spectroscopy and mass spectroscopy. In-situ observation of the reaction reveals that two reaction pathways switch over alternatively depending on the surface temperature. At lower temperatures, the Pd(100) surface is covered by CO molecules and the CO2 formation rate is low, indicating CO poisoning. At higher temperatures above 190 °C, an O–Pd–O trilayer surface oxide phase is formed on the surface and the CO2 formation rate drastically increases. It is likely that the enhanced rate of CO2 formation is associated with an active oxygen species that is located at the surface of the trilayer oxide.

Carbon contamination of a chromium-coated mirror was removed by exposure to oxygen activated with non-monochromated synchrotron radiation. Higher-order harmonics of the chromium-coated mirror are much smaller than those of a gold-coated mirror in the carbon K-edge region., Carbon-free chromium-coated optics are ideal in the carbon K-edge region (280–330 eV) because the reflectivity of first-order light is larger than that of gold-coated optics while the second-order harmonics (560–660 eV) are significantly suppressed by chromium L-edge and oxygen K-edge absorption. Here, chromium-, gold- and nickel-coated mirrors have been adopted in the vacuum ultraviolet and soft X-ray branch beamline BL-13B at the Photon Factory in Tsukuba, Japan. Carbon contamination on the chromium-coated mirror was almost completely removed by exposure to oxygen at a pressure of 8 × 10−2 Pa for 1 h under irradiation of non-monochromated synchrotron radiation. The pressure in the chamber recovered to the order of 10−7 Pa within a few hours. The reflectivity of the chromium-coated mirror of the second-order harmonics in the carbon K-edge region (560–660 eV) was found to be a factor of 0.1–0.48 smaller than that of the gold-coated mirror.

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 adsorption structure of NO on the reconstructed Pt(110)-(1 x 2) surface was studied with X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), low-energy scanned-angle photoelectron diffraction (LESA-PD), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The experiments were performed at 180 K, where no surface lifting from (1 x 2) to (1 x 1) takes place after NO adsorption. XPS indicates that the (1 x 2) unit cell of the Pt(110) surface contains 1.5 NO molecules at the saturated coverage. XPD and LESA-PD analyses allow us to propose a structural model for the NO adlayer, where two-thirds of the NO molecules in the (1 x 2) unit cell are adsorbed on the atop site of the close-packed Pt rows (ridges) along the [10] direction with an inclined geometry and one-third of the NO molecules adsorb on the bridge site between the Pt ridges with an upright configuration. This model is supported by the N K-edge NEXAFS experiments and is consistent with the recently reported model based on the density functional theory (Orita, H.; Nakamura, I.; Fujitani, T. J. Phys. Chem. B 2005, 109, 10312).

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.

X-ray magnetic circular dichroism (XMCD) is a powerful method to study the magnetic properties of magnetic thin films. However it provides depth-averaged information. Recently, we have developed a simple but effective depth-resolved technique in XMCD by using an imaging type microchannel plate detector. The performance of this method is demonstrated by applying to the depth-resolved analyses of Ni/Cu(100) and the effect of CO adsorption on Ni/Cu(100), Fe/Cu(100) and Fe/Ni/Cu(100) magnetic thin films. For Ni/Cu(100), magnetic orbital moments of the surface and internal layers are extracted to give deep insight for the spin reorientation transitions. For 7 ML Fe/Cu(100), the surface two layers are ferromagnetically coupled, while the inner layers are non-magnetic at 200 K and are in the spin density wave (SDW) state at 130 K. For Fe/Ni/Cu(100), magnetically live surface layers and some thickness-dependent magnetic coupling between the Fe surface and Ni film have been observed.

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.

A novel design concept is presented for a variable-included-angle Monk-Gillieson mounting monochromator with a varied-line-spacing (VLS) plane grating, in which the grating is illuminated by converging X-rays. The energy resolution for a beamline with a typical undulator source is estimated by means of the ray-tracing method. It is shown that the source-size or slope-error limited resolution is achieved in a wide energy range by properly changing the included angle. Moreover, relatively high resolution is maintained even if one scans the photon energy with a fixed included angle, which is a great advantage over the previous VLS grating monochromator with diverging illumination on the grating. A design example for a bending-magnet beamline is also presented, indicating that the new design concept is valid even for high-emittance sources.

The catalytic water formation reaction was investigated by the energy dispersive near-edge x-ray absorption fine structure (dispersive NEXAFS) spectroscopy. An oxygen covered Pt(111) surface with the (2×2) structure was exposed to gaseous hydrogen (5.0×10−9 Torr) at constant surface temperatures (120–140 K). O K-edge NEXAFS spectra were measured during the reaction with a time interval of 35 s. Quantitative analyses of the spectra provided the coverage changes of the adsorbed species (O, OH, and H2O). The reaction is composed of three steps, which are characterized by an induction period (I), fast increase in coverage of OH and H2O with consuming O (II), and slow conversion of OH to H2O after the complete consumption of O (III). It was also found that the maximum OH coverage becomes smaller at a higher temperature. The kinetic Monte Carlo simulation has reproduced the three characteristic reaction steps; in the first step OH domains are created through two-dimensional aggregation of H2O (I), after the nuc...

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.

A depth-resolved technique is applied in the x-ray magnetic circular dichroism (XMCD) method by controlling the probing depth of the electron yield XMCD spectra. The usefulness of this technique is demonstrated for the study of magnetic structures of 4 and 8 ML Fe films grown on Cu(100), which are known to exhibit peculiar magnetic depth profiles. It was directly shown that the 4 ML film is uniformly magnetized, while the magnetic moment is localized at the surface in the case of the 8 ML film. The XMCD spectrum for each layer of the 4 ML film was separately extracted. All the extracted spectra were almost identical to each other, confirming the ferromagnetic coupling over the whole film. As for the 8 ML film, it was suggested that the surface two layers are ferromagnetically coupled, while the inner layers are in a spin density wave state with a wavenumber q = 2π/2.4d.

Spin reorientation transitions (SRTs) of ultrathin Co/Pd(111) films induced by adsorption of atoms and molecules have been investigated by means of Co LIII,II-edge x-ray magnetic circular dichroism (XMCD). We have examined CO, NO, O and H as chemisorbed species. We observed the adsorbate-induced SRT from surface parallel to perpendicular magnetization at 200 K in the cases of CO and NO on 4.5 ML Co/Pd(111), while O or H adsorption has been found not to lead to the transition on 4.5 ML Co. We have investigated the detailed Co-thickness dependence in the case of CO and have found that the critical thickness of the SRT in CO-adsorbed Co is ~6.5 ML, which is greater by ~3 ML than that of clean Co (~3.5 ML). From the sum rule analysis, it has been found that the surface parallel orbital moment is reduced after CO adsorption, while the surface normal orbital moment is left unchanged. We can conclude that the observed stabilization of perpendicular magnetic anisotropy due to adsorption is ascribed to quenching of the surface parallel magnetic orbital moment.

Magnetic anisotropy of alternately layered FeNi thin films grown on Ni(3--21 ML)/Cu(001) is investigated by means of the X-ray magnetic circular dichroism (XMCD). Perpendicular magnetic anisotropy is observed when the substrate Ni is thicker than 15 and 20 ML for 4 and 6 ML FeNi films, respectively, while in-plane magnetic anisotropy appears at the thinner substrate Ni region. By comparing with the magnetic phase diagram calculated from the magnetic anisotropy energies, which are obtained by the XMCD study [M. Sakamaki and K. Amemiya, Appl. Phys. Express 4, 073002 (2011)], we show that the phase boundary of the present samples shifts so as to prefer the in-plane magnetic anisotropy. This might be caused by the structural relaxation in the substrate Ni. [DOI: 10.1380/ejssnt.2012.97]

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.

N K -, O K - and Co L III,II -edge X-ray magnetic circular dichroism (XMCD) was investigated for NO adsorbed on ultrathin fcc -Co(001) films which show both in-planar and perpendicular magnetic anisotropies. Large suppression of spin and orbital magnetic moments of Co was observed upon NO adsorption. Both N and O K -edge XMCD spectra show negative signs at the NO 2π * resonance, irrespective of in-plane and perpendicular magnetic anisotropies. This finding implies the parallel alignment of the NO 2π * orbital magnetic moments with the total magnetization. The results are comparatively discussed with the previous works on CO on Co and Ni films and are interpreted by a simple chemical bonding scheme.

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.

The electronic structure of Na2[Fe(CN)5NO]·2H2O (sodium nitroprusside: SNP) was investigated by using soft X-ray absorption (XA) spectroscopy. The Fe L2,3-edge XA spectrum of SNP exhibited distinct and very large satellite peaks for L3 and L2 regions, which is different from the spectra of hexacyanoferrates and the other iron compounds. A configuration-interaction full-multiplet calculation, in which the ligand molecular orbitals for the C4v symmetry were taken into account, revealed the Fe(2+) low-spin state with very strong effects of metal-to-ligand charge-transfer from the Fe 3d to NO 2p orbitals.

A twisted magnetic structure in Ni ultrathin films attached to antiferromagnetic FeMn is revealed by a combination of the depth-resolved x-ray magnetic circular dichroism (XMCD) and the polarized neutron reflectivity (PNR) techniques. The depth-resolved XMCD at remanent magnetization shows that the perpendicular magnetization component in the Ni film decreases around the interface to FeMn when the film exhibits perpendicular magnetization, whereas the in-plane component is kept constant through the whole film in the case of in-plane magnetization. Moreover, the PNR data shows that when a weak in-plane magnetic field is applied to a film, which exhibits perpendicular magnetization at the remanent state, an in-plane magnetization component is induced in Ni around the interface to FeMn. These results are reasonably interpreted by assuming that the magnetic moment in the Ni layer is twisted from the perpendicular to the in-plane directions towards the interface to FeMn. Such a magnetic structure is supposed to be induced by a magnetic anisotropy interaction at the interface between ferromagnetic Ni and antiferromagnetic FeMn, which makes the Ni magnetic moment around the interface rotate towards the in-plane direction.

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.

The ferromagnetic oxide ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$ has been studied by magnetic circular x-ray dichroism (MCXD) in core-level absorption. In the Co ${2p}_{3/2,1/2}$ absorption, the orbital and spin magnetic moments of the Co $3d$ are deduced with the use of magneto-optical sum rules and compared with magnetization measurements. In the O $1s$ absorption, large negative MCXD structures are observed, showing that the O $2p$ orbitals are heavily mixed with the Co $3d$ orbitals and that the orbital magnetic moment of O $2p$ is parallel to the orbital magnetic moment of Co $3d$ and the total magnetic moment. The relative magnitudes of the spin and orbital magnetic moments are most consistently interpreted based on the intermediate-spin states of Co $3d$ within the ionic model, although the absolute values of the spin and orbital magnetic moments are found to be smaller, probably indicating that the itinerant electron description of the Co $3d$ states is more appropriate in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}.$

The atomic and electronic structures of the methoxy $({\mathrm{CH}}_{3}\mathrm{O})$ adsorbate formed on the Cu(111) and Ni(111) surfaces have been studied by NEXAFS (near-edge x-ray-absorption fine structure) and SEXAFS (surface extended x-ray-absorption fine structure) with a newly constructed soft x-ray beamline in the Photon Factory. The transition from the O $1s$ core to the $2e$ level of the methoxy species was found to be noticeably stronger on Ni(111) than on Cu(111), indicating that the methoxy adsorbate on Cu(111) is more anionic. The C-O bond lengths of the species on Cu(111) and Ni(111) were estimated using the ${\ensuremath{\sigma}}^{*}(\mathrm{C}\ensuremath{-}\mathrm{O})$ resonance to be $1.46\ifmmode\pm\else\textpm\fi{}0.05$ and $1.43\ifmmode\pm\else\textpm\fi{}0.05\AA{},$ respectively. The polarization-dependent NEXAFS measurements showed that the C-O axis of the methoxy adsorbate is nearly perpendicular to the surface on both Cu(111) and Ni(111). From the SEXAFS analysis on Cu(111), it was revealed that the oxygen atom of the methoxy species locates on a threefold hollow site and the nearest-neighbor O-Cu distance was determined to be $2.00\ifmmode\pm\else\textpm\fi{}0.03\AA{}.$

Structure and magnetic anisotropy of alternately layered FeNi thin films grown on Ni ($x=3$--21 ML)/Cu(001) are investigated by means of reflection high-energy electron diffraction (RHEED) and x-ray magnetic circular dichroism (XMCD). From the RHEED analysis, we find that $n$ ML FeNi films grow with a similar in-plane lattice constant, $a$, to that of Cu up to the total film thickness, $n+x$, of $\ensuremath{\sim}$13 ML, from which the decrease in $a$ occurs. For the Ni-sandwiched Fe layer, we find from the XMCD analysis that the perpendicular component of the orbital magnetic moment increases and the in-plane component decreases as the in-plane lattice constant gets smaller. This suggests that perpendicular magnetic anisotropy is enhanced when the compressive strain in the in-plane direction is applied to the Fe layer. On the other hand, in the case of the Fe-sandwiched Ni layer, the orbital magnetic moment in both directions shows a small dependence on $a$. The change in magnetic anisotropy of Ni as a function of the structural strain is within the error margins.

A depth-resolved technique in the x-ray magnetic circular dichroism (XMCD) has been developed and applied to Fe/Cu(100) and Fe/Ni/Cu(100) in order to observe the magnetic depth profile directly. It was confirmed that the surface two layers of the 7 ML Fe/Cu(100) are ferromagnetically coupled, while the inner layers are in the spin density wave (SDW) state at 130 K. The technique enables one to extract the XMCD spectra from the surface ferromagnetic (FM) and inner SDW regions separately, indicating that the FM/SDW interface has an antiparallel magnetic coupling, and that the SDW region has the bulk-like feature. For Fe/Ni/Cu(100), we have observed magnetically live surface layers and some thickness dependent magnetic coupling between the Fe surface and Ni film.

A depth-resolved X-ray magnetic circular dichroism (XMCD) technique has been developed in the soft X-ray region by combining a multi-anode microchannel plate detector with polarization switching between right and left circular polarizations. A simultaneous measurement for 30-channel anodes has been achieved with a continuous data acquisition rate of 1 kHz, which is fast enough for 10 Hz polarization switching. This enables us to realize the layer-resolved XMCD analysis with a high signal-to-noise ratio.

Ga${}^{+}$ irradiation-induced changes in magnetic anisotropy and crystalline structure of a Pt/Co/Pt ultrathin film are investigated by means of x-ray magnetic circular dichroism (XMCD) and extended x-ray absorption fine structure (EXAFS) techniques. The XMCD analysis shows a large orbital moment difference between out-of-plane and in-plane directions, which corresponds to perpendicular magnetic anisotropy (PMA), at moderate Ga${}^{+}$ fluences, while further increased fluences reduce the orbital moment difference resulting in in-plane magnetization. From the EXAFS analysis, enhancement of PMA is directly related to an in-plane lattice expansion caused by ion irradiation and Co-Pt intermixing, which results in a large lattice distortion. Thus, the origin of the ion irradiation-induced changes in magnetic anisotropy is successfully explained.