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The morphology of active material particles has a significant impact on the charge–discharge cycle performances of lithium-ion batteries because each crystal surface constructed by different elemental arrangements indicates various surface energies. The surface properties of each facet affect the stability of the interface between the facets of particles and electrolytes. In this study, we applied microscopic resonant photoelectron spectroscopy with a spatial resolution of 100 nm (3DnanoESCA system) to reveal the electronic structure of each facet of prototypical layered LiCoO2 cathode particles, where the characteristic facets are (001), (104), and (012). We detected the difference in an electronic structure near the valence-band maximum (around 1–3 eV) on different LiCoO2 facets, where the dominant Co 3d bands at the valence band of the (001), (104) and (012) facets showed binding energies of 2.48, 2.25 and 2.02 eV, respectively. The closer Co 3d band of the (012) facet to the Fermi level makes it easier to lose electrons than the other facets, suggesting its more reactive property than the other facets. This technique, which provides the electronic structure of each crystal facet, is useful for designing active materials with excellent charge–discharge cycle performances. [ABSTRACT FROM AUTHOR]

Drastic electronic-structure changes in an Fe2O3 thin film anode for a Li-ion battery during discharge (lithiation) and charge (delithiation) processes were observed using operando Fe 2p soft X-ray emission spectroscopy (XES). The conversion reaction forming metallic iron due to the lithiation reaction was confirmed by operando XES in combination with the analysis using full-multiplet calculation. The valence of Fe at the open-circuit voltage (OCV) before the second cycle was not Fe3+, but Fe2+ with a weak p–d hybridization, suggesting a considerable irreversibility upon the first discharge–charge cycle and a weakened Fe–O bond after the first cycle. Moreover, we revealed that the Fe 3d electronic-structure change during the second cycle was to some extent reversible as Fe2+ (2.7 V vs. Li/Li+: open circuit voltage) → Fe0 (0.1 V vs. Li/Li+: discharged) → Fe(2+δ)+ (3.0 V vs. Li/Li+: charged). This operando Fe 2p XES in combination with the full-multiplet calculation provides detailed information for redox chemistry during a discharge–charge operation that cannot be obtained by other methods such as crystal-structure and morphology analyses. XES is thus very powerful for investigating the origin and limitation of the lithiation function of anodes involving conversion reactions. [ABSTRACT FROM AUTHOR]

We have investigated the transport properties and electronic states of W-doped anatase TiO2 (Ti1-xWxO2) fabricated by pulsed-laser deposition. Based on transport and photoemission spectroscopy (PES) measurements, we discuss the conduction mechanism of Ti1-xWxO2, focusing on the valence state of W. The Ti0.95W0.05O2 film deposited under optimized conditions showed a resistivity of 2×10-3 Ω cm at room temperature, which is approximately ten times higher than that of Ti0.94Nb0.06O2. This is mainly due to the lower carrier density in Ti1-xWxO2 films. From PES measurements of Ti0.91W0.09O2 films, we observed the finite density of states originating from O 2p hybridized with W near the top of the valence band. However, we could not find any states at the same position in the Ti0.94Nb0.06O2 films. In addition, the density of states near the Fermi level [N(EF)] was found to be quite low in the Ti0.91W0.09O2 films. Indeed, this is in sharp contrast to Ti0.94Nb0.06O2, which indicates a remarkably high N(EF) value assigned to the bottom of the Ti 3d conduction band. The difference in transport properties between Ti1-xWxO2 and Ti1-xNbxO2 can be attributed to the existence of impurity states that trap carriers associated with doped W atoms. [ABSTRACT FROM AUTHOR]

We have investigated the effect of HfO2 layer thickness on crystallization in thin HfO2 films using photoemission spectroscopy and x-ray absorption spectroscopy (XAS). O K-edge XAS spectra depending on annealing temperature indicate that crystallization in thin HfO2 films is suppressed upon annealing for thin HfO2 film, which in turn has a beneficial effect on the performance of devices. The annealing-temperature dependence of the depth profile of HfO2 films suggests that diffusion of Si atoms into the HfO2 layer plays only a minor role in the suppression of crystallization, indicating that HfO2 films can restrain a decrease in dielectric constant. [ABSTRACT FROM AUTHOR]

GaAs(111)B surfaces grown by molecular-beam epitaxy have been investigated in situ using synchrotron radiation photoemission spectroscopy. For the GaAs(111)B-2×2 phase, the Ga 3d core-level spectra consists of one dominating component while the As 3d spectra are decomposed into four components. This analysis is fully consistent with an As-trimer model where As-trimers in T4 or H3 position exist on top of As atoms in the uppermost double layer. On the other hand, the core-level spectra for the 19×19 surface disagree with the hexagonal ring structural model. [ABSTRACT FROM AUTHOR]

The generalized grazing-incidence-angle x-ray scattering technique has been developed for analysis of near-surface structures, namely, the anisotropy of the structure in the directions perpendicular and parallel to its surface, and its change within the depth. In this method, a specimen is irradiated by an x-ray beam with a grazing-incidence angle as small as the critical angle of the surface, and both in- and out-of-plane scattering are analyzed simultaneously. The technique has been applied to investigate the structures of InAs quantum dots grown on Si with a diameter of 37 nm and a surface coverage of 11%. It has been found that the InAs dots were dilated by 1.7% along the direction perpendicular to the surface and compressed by 1.4% in the lateral direction. The compression in the lateral direction shows a maximum value at the interface, and decreases as the distance from the interface increases. The existence of 1.7% compressive strain means that most of the 11.7% lattice mismatch between the InAs dots and the Si substrate was relaxed during the growth. [ABSTRACT FROM AUTHOR]

Ferromagnetic nanoscale zinc-blende MnAs dots were successfully fabricated on a sulfur-passivated GaAs (001) surface by molecular-beam epitaxy. Transmission electron microscopy and selected area electron diffraction showed that the crystalline structure was not the same as that of bulk MnAs with NiAs-type hexagonal crystalline structure, but of zinc-blende type. In in situ photoemission spectroscopy of the zinc-blende MnAs dots, the Fermi edge was not clearly observed and the Mn 3 d partial density of states was similar to that of the diluted ferromagnetic semiconductor Ga[sub 1-χ]Mn[sub χ]As, which also supports the fabrication of zinc-blende MnAs in the nanoscale. [ABSTRACT FROM AUTHOR]

We have quantitatively investigated how boron segregates to regions close to the surface, and what controls this phenomenon, using x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and backside secondary ion mass spectrometry measurement techniques. We found that, contrary to the equilibrium segregation, the pileup of boron is mainly on and within 0.6 nm of the Si side of the interface, and that there is no difference between the kind of encapsulation. This also suggests that the pileup of boron is mainly on the Si side, and implies that the main factor in this segregation is the existence of the Si surface. From the viewpoint of device fabrication, this result seems to be useful in terms of the fabrication of sidewalls. The possibility of boron pileup to occurring in the interstitial state was also shown. Our results suggested a way of looking at dopant profiles by predictive computer modeling. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the chemistry of the (NH4)[sub2]S[subx]-treated n-gallium arsenide (GaAs) (100) surfaces. Use of synchrotron radiation photoemission spectroscopy; Schottky barrier heights of the diodes; Analysis of the binding energy for the GaAs surfaces.

Examines the radio frequency (rf)-plasma oxidation process of lead alloy performed using oxygen isotope observed by secondary ion mass spectroscopic analysis. Overview of previous studies on the structure of oxides formed by rf-plasma oxidation; Details of experimental procedures; Transport processes which affect oxidation.

Presents a study that investigated the initial stages of indium (In)-arsenic (As) deposition on europium-barium-copper-oxygen thin film superconductors with a strontium-fluorine interlayer. Use of synchrotron-radiation photoelectron spectroscopy; Background on high-temperature superconducting thin-film technology; Information on the surface morphology of an InAs grown sample.

With the rapid depletion of communication-frequency resources, mainly due to the explosive spread of information communication devices for the internet of things, GaN-based high-frequency high-power transistors (GaN-HEMTs) have attracted considerable interest as one of the key devices that can operate in the high-frequency millimeter-wave band. However, GaN-HEMT operation is destabilized by current collapse phenomena arising from surface electron trapping (SET), which has not been fully understood thus far. Here, we conduct quantitative mechanistic studies on SET in GaN-HEMTs by applying element- and site-specific photoelectron nanospectroscopy to a GaN-HEMT device under operation. Our study reveals that SET is induced by a large local electric field. Furthermore, surface passivation using a SiN thin film is demonstrated to play a dual role: electric-field weakening and giving rise to chemical interactions that suppress SET. Our findings can contribute to the realization of high-capacity wireless communication systems based on GaN-HEMTs. [ABSTRACT FROM AUTHOR]

We report on the epitaxial growth of semipolar InAlN (1...03) on yttria-stabilized zirconia (YSZ) by pulsed sputtering deposition (PSD). Unlike the direct growth of InAlN on YSZ that resulted in c-plane InAlN, the insertion of an InN buffer layer favored the growth of InAlN in the semipolar direction. Phase separation of semipolar InAlN taking place in the films with intermediate indium contents can be suppressed by low-temperature (less than 400°C) PSD growth. These semipolar InAlN films grown at low temperatures possessed sufficient optical quality to demonstrate photoluminescence at room temperature. [ABSTRACT FROM AUTHOR]

The characteristics of CO adsorption sites on a nitrogen-doped graphite model system (N-HOPG) were investigated by X-ray photoelectron and absorption spectroscopy and infrared reflection absorption spectroscopy. Adsorbed CO was observed lying flat on N-HOPG, stabilized by a charge transfer from the substrate. This demonstrated that Lewis base sites were formed by the incorporation of nitrogen via low-energy nitrogen-ion sputtering. The possible roles of twofold coordinated pyridinic N and threefold coordinated valley N (graphitic N) sites in Lewis base site formation on N-HOPG are discussed. The presence of these nitrogen species focused on the appropriate interaction strength of CO indicates the potential to fine-tune the Lewis basicity of carbon-based catalysts. [ABSTRACT FROM AUTHOR]

The electronic structures of nitrogen species incorporated into highly oriented pyrolytic graphite (HOPG), prepared by low energy (200 eV) nitrogen ion sputtering and subsequent annealing at 1000 K, were investigated by X-ray photoelectron spectroscopy (XPS), angle-dependent X-ray absorption spectroscopy (XAS), and Raman spectroscopy. An additional peak was observed at higher binding energy of 401.9 eV than 400.9 eV for graphitic1 N (graphitic N in the basal plane) in N 1s XPS, where graphitic2 N (graphitic N in the zigzag edge and/or vacancy sites) has been theoretically expected to appear. N 1s XPS showed that graphitic1 N and graphitic2 N were preferably incorporated under low nitrogen content doping conditions (8 × 1013 ions cm−2), while pyridinic N and graphitic1 N were dominantly observed under high nitrogen content doping conditions. In addition, angle-dependent N 1s XAS showed that the graphitic N and pyridinic N atoms were incorporated into the basal plane of HOPG and thus were highly oriented. Furthermore, Raman spectroscopy revealed that low energy sputtering resulted in almost no fraction of the disturbed graphite surface layers under the lowest nitrogen doping condition. The suitable nitrogen doping condition was discovered for realizing the well-controlled nitrogen doped HOPG. The electrochemical properties for the oxygen reduction reaction of these samples in acidic solution were examined and discussed. [ABSTRACT FROM AUTHOR]

Graphene exhibits unusual electronic properties, caused by a linear band structure near the Dirac point. This band structure is determined by the stacking sequence in graphene multilayers. Here we present a novel method of microscopically controlling the band structure. This is achieved by epitaxy of graphene on 3C-SiC(111) and 3C-SiC(100) thin films grown on a 3D microfabricated Si(100) substrate (3D-GOS (graphene on silicon)) by anisotropic etching, which produces Si(111) microfacets as well as major Si(100) microterraces. We show that tuning of the interface between the graphene and the 3C-SiC microfacets enables microscopic control of stacking and ultimately of the band structure of 3D-GOS, which is typified by the selective emergence of semiconducting and metallic behaviours on the (111) and (100) portions, respectively. The use of 3D-GOS is thus effective in microscopically unlocking various potentials of graphene depending on the application target, such as electronic or photonic devices. [ABSTRACT FROM AUTHOR]

The characteristics of InO x N y alloy films prepared via thermal oxidation of InN epitaxial films with In- or N-polarities grown on nearly lattice-matched, yttria-stabilized zirconia (YSZ) substrates are investigated. The InN films were oxidized to InO x N y with a gradual change in O/N composition by annealing in air. Structural analysis revealed that the temperature for phase transition from wurtzite structure depends on the polarity of InN, and N-polar InO x N y films can retain their wurtzite structure even at higher temperatures compared with the case of In-polar films. Furthermore, changes in the valence band structure and optical characteristics of the InO x N y alloys take place via thermal oxidation. These results indicate that InO x N y grown via thermal oxidation of N-polar InN on YSZ can be considered as an alloy semiconductor for optoelectronic devices. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

High-quality AlN epilayers were grown via pulsed sputtering deposition on thermally nitrided sapphire $(11\bar 20)$ with precise control of the N/Al ratio. Under slightly Al-rich growth conditions, the growth of AlN epilayers on the thermally nitrided sapphire proceeded in a two-dimensional mode from the initial stage of growth, and their surfaces were atomically flat stepped and terraced structures. The FWHM values of the X-ray rocking curves were as low as 87 arcsec and 339 arcsec for the 0002 and $1 \bar 102$ diffractions, respectively, at a film thickness of 400 nm. The present approach is therefore quite promising for the low-cost fabrication of AlGaN-based UV optical devices. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The observation method of photoemission electron microscopy (PEEM) on insulating samples has been established in an extremely simple way. Surface conductivity is induced locally on an insulating surface by continuous radiation of soft X-rays, and Au films close to the area of interest allow the accumulated charges on the insulated area to be released to ground level. Magnetic domain observations of a NiZn ferrite, local X-ray absorption spectroscopy of sapphire, high-resolution imaging of a poorly conducting Li0.9CoO2 film surface, and Au pattern evaporation on a fine rock particle are demonstrated. Using this technique, all users' experiments on poorly conducting samples have been performed successfully at the PEEM experimental station of SPring-8. [ABSTRACT FROM AUTHOR]

Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our '3D nano-ESCA' (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over ∼500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO2-substrate interface. [ABSTRACT FROM AUTHOR]

We report angle-resolved photoemission spectroscopy (ARPES) on a GaAs thin film protected by an amorphous As layer with thickness exceeding the typical probing depths of vacuum-ultraviolet rays up to ∼100 eV. Increasing the probing depth by increasing photon energy into the soft x-ray (SX) region of several hundred eV clearly exposes the bulk band dispersion of the GaAs underlayer without any surface treatment. Our results demonstrate that the use of SX-ARPES enables access to the three-dimensional band dispersion of buried underlayer through an amorphous overlayer. This opens frontiers in diagnostics of authentic momentum-resolved electronic structure of protected thin-film heterostructures. [ABSTRACT FROM AUTHOR]

We have found that polarity of epitaxial InN layers has been controlled by choice of a capping material during high-temperature annealing of yttria-stabilized zirconia (YSZ) (111) substrates in air. Angle-resolved X-ray photoelectron spectroscopy has revealed that the amount of segregation of Y atoms to the YSZ surface depended on the capping material of the substrates. In-polar and N-polar InN have been reproducibly grown on Y-segregated and Y-segregation-free YSZ surfaces, respectively. We have also found that the growth of the first monolayer (ML) of N-polar InN proceeds in a step-flow mode which then switches to layer-by-layer mode after the coverage by 1-ML-thick InN. [ABSTRACT FROM AUTHOR]

We have characterized the electronic structure of FeSe1-xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe. [ABSTRACT FROM AUTHOR]

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE < 100 meV and/or an E/ΔE ∼ 10 000 are expected for the energy range of 350 eV - 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively. [ABSTRACT FROM AUTHOR]

The authors have investigated the effects of Al doping and annealing on the photoemission spectra and thermal stability of Y2O3/Si gate stacks by photoemission spectroscopy and x-ray absorption spectroscopy. They have found that the SiO2 components diffuse into the Y2O3 layer by annealing, resulting in the formation of Y silicate; however, the formation of metallic Y silicide is not observed. The changes in valence- and conduction-band offsets by doping Y2O3 with Al with respect to both Al concentration and annealing temperature have been systematically investigated. With an increase in the Al concentration, the band offsets and band gaps increase and the conduction-band edges change nonlinearly. [ABSTRACT FROM AUTHOR]

An undulator-radiation-excited x-ray fluorescence analysis system for light elements has been developed and tested on the 26-period multipole wiggler/undulator beamline at the Photon Factory. An entrance-slitless optics with a variable-spacing grating was devised for a fluorescent x-ray dispersion system to achieve spectroscopic analysis with high efficiency and high resolution. Both soft x-ray emission (SXE) spectra and x-ray absorption near-edge structure (XANES) spectra with fluorescent x-ray detection were obtained by this system, taking advantage of the high brightness and quasimonochromatic character of the incident undulator beam. The analysis system was evaluated by measuring the B Kα SXE and fluorescence XANES spectra of B, BN, and B2O3. [ABSTRACT FROM AUTHOR]

An ultrahigh vacuum compatible goniometer system has been developed for use in angle-scan standing-wave experiments in a soft x-ray region. This system uses a horizontal two-axis (theta and two-theta) goniometer for the x-ray diffractometer. The theta axle used for sample rotations is inserted into the vacuum chamber through a differentially pumped rotary feedthrough and is driven by a stepping motor. To detect x-ray fluorescence excited by x-ray standing waves, a three-element linear-army Si(Li) detector is equipped for this system. SKα fluorescence angular yield from monolayer-order sulfur atoms on a GaAs (111) surface could be measured for the first time by the angle-scan standing-wave experiment. This result demonstrates that this goniometer system can be used for angle-scan standing-wave experiments in the soft x-ray region. [ABSTRACT FROM AUTHOR]

An ultrahigh vacuum compatible x-ray detector has been developed for measuring the extended x-ray absorption fine structure (EXAFS) of low-Z elements (C,N,O) by fluorescence yield detection. The detector is a type of gas scintillation proportional counter, with a better energy resolution than conventional gas proportional counters. Two Mylar windows of 0.6 μm thickness and 36 mm diameter in series, in combination with a differential pumping system, were utilized for the entrance of ultrasoft x-ray fluorescence. The energy resolution (full width half maximum) of 46% at 183 eV was confirmed by measuring the boron Kα pulse height distribution curve. Fluorescence yield EXAFS spectra, with high signal-to-background ratios, were obtained above O and N K edges of thin SiO2 and Si3N4 films for the first time by using this detector. These results demonstrate that the newly developed detector with improved energy resolution is extremely useful for fluorescence yield EXAFS measurements of low-Z atoms on the surface and in the bulk. [ABSTRACT FROM AUTHOR]

P-type doping of GaN by pulsed sputtering deposition (PSD) at a low growth temperature of 480 °C and dramatic reduction in the growth process temperature for InGaN-based light-emitting diodes (LEDs) were achieved. Mg-doped GaN layers grown on semi-insulating GaN at 480 °C exhibited clear p-type conductivity with a hole concentration and mobility of 3.0×1017 cm-3 and 3.1 cm² V-1 s-1, respectively. GaN/In0.33Ga0.67N/GaN LEDs fabricated at 480 °C showed clear rectifying characteristics and a bright electroluminescence emission near 640 nm. These results indicate that this low temperature PSD growth technique is quite promising for the production of nitride-based light-emitting devices on large-area glass substrates. [ABSTRACT FROM AUTHOR]

Determination of the polarity of insulating semipolar AlN layers was achieved via atomic scattering spectroscopy. The back scattering of neutralized He atoms on AlN surfaces revealed the atomic alignment of the topmost layers of semipolar AlN and the ZnO substrate. Pole figures of the scattering intensity were used to readily determine the polarity of these wurtzite-type semipolar materials. In addition, we found that +R-plane AlN epitaxially grows on -R-plane ZnO, indicating that the polarity flips at the semipolar AlN/ZnO interface. This polarity flipping is possibly explained by the appearance of -c and m-faces on the -R ZnO surfaces, which was also revealed by atomic scattering spectroscopy. [ABSTRACT FROM AUTHOR]

We have investigated the crystal plane alignment at m-plane GaN/ZnO heterointerfaces prepared by a room temperature epitaxial growth technique. Coaxial impact-collision ion scattering spectroscopy was used to show that the +c directions for GaN and ZnO are aligned at the GaN/ZnO ([formula]) hetero interface, which makes a striking contrast to polar c-plane GaN (0001)/ZnO ([formula]) interfaces, where polarity-flipping always occurs. Theoretical calculations revealed that an atomic alignment at the m-plane GaN/ZnO interface that maintains the +c direction across the interface is energetically favorable, although there could be an in-plane shift in the positions of the anions and cations at the interface. [ABSTRACT FROM AUTHOR]