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Actual knowledge of the intrinsic electronic characteristics of p-type oxide semiconductors should help guide the design of innovative electronic devices. The electronic characteristics of oxide semiconductors in thin-film form potentially differ from those in the bulk form owing to lattice strain. In this Letter, we report on the empirical band structure of stannous oxide (SnO) film, which has been shown to have a higher hole mobility than the theoretically expected values for SnO in the bulk form. In vacuo angle-resolved photoemission spectroscopy measurements reveal that the uppermost valence band is anisotropic between the out-of-plane and in-plane directions, and more dispersive than the theoretical predictions. Our findings unveil the underlying mechanism of the semiconductor properties of SnO films and suggest a suitable device structure based on the electronic characteristics.

We demonstrate that hole carrier density of α-SnWO4 can be tuned by controlling the annealing process. Hole carrier density increased by two orders of magnitude and achieved a value close to 1019 cm−3 at an optimum O2 gas concentration.

Diodes, memories, logic circuits, and most other current information technologies rely on the combined use of p- and n-type semiconductors. Although oxide semiconductors have many technologically attractive functionalities, such as transparency and high dopability to enable their use as conducting films, they typically lack bipolar conductivity. In particular, the absence of p-type semiconducting properties owing to the innate electronic structures of oxides represents a bottleneck for the development of practical devices. Here, bipolar semiconducting properties are demonstrated in α-SnWO4 within a 100 °C temperature window after appropriate thermal treatment. Comprehensive spectroscopic observations reveal that Sn4+ is present in p-type α-SnWO4 in a notably greater quantity than in n-type. This result strongly suggests that the Sn4+ substitutional defects on the W6+ sites contribute to hole-carrier generation in α-SnWO4. We also find that oxygen vacancies are initially formed in Sn-O-W bonds and migrate to W-O-W bonds with changes in semiconducting properties from p-type to n-type. These findings suggest useful strategies for exploring p-type oxide semiconductors and controlling their carrier type by utilizing the octahedral structure.

A high-precision XYZ translator was developed for the microanalysis of electronic structures and chemical compositions on material surfaces by electron spectroscopy techniques, such as photoelectron spectroscopy and absorption spectroscopy, utilizing the vacuum ultraviolet and soft X-ray synchrotron radiation at an undulator beamline BL-13B at the Photon Factory. Using the high-precision translator, the profile and size of the undulator beam were estimated. They were found to strongly depend on the photon energy but were less affected by the polarization direction. To demonstrate the microscopic measurement capability of an experimental apparatus incorporating a high-precision XYZ translator, the homogeneities of an SnO film and a naturally grown anatase TiO2 single crystal were investigated using X-ray absorption and photoemission spectroscopies. The upgraded system can be used for elemental analyses and electronic structure studies at a spatial resolution in the order of the beam size.

Beamline 13 of the Photon Factory has been in operation since 2010 as a vacuum ultraviolet and soft X-ray undulator beamline for X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and angle-resolved photoelectron spectroscopy (ARPES) experiments. The beamline and the end-station at branch B have been recently upgraded, enabling microscopic XPS, XAS, and ARPES measurements to be performed. In 2015, a planar undulator insertion device was replaced with an APPLE-II (advanced planar polarized light emitter II) undulator. This replacement allows use of linear, circular, and elliptical polarized light between 48 and 2000 eV with photon intensities of 109–1013 photons s−1. For microscopic measurements, a toroidal post-mirror was renewed to have more focused beam with profile sizes of 78 µm (horizontal) × 15 µm (vertical) and 84 µm × 11 µm at photon energies of 100 and 400 eV, respectively. A high-precision sample manipulator composed of an XYZ translator, a rotary feedthrough, and a newly developed goniometer, which is essential for microscopic measurements, has been used to control a sample specimen in six degrees of freedom, i.e. translation in the X, Y, and Z directions and rotation in the polar, azimuthal, and tilt directions. To demonstrate the performance of the focused beams, one- and two-dimensional XPS and XAS scan measurements of a copper grid have been performed. It was indicated from analysis of XPS and XAS intensity maps that the actual spatial resolution can be determined by the beam size.

Obtaining semiconducting properties that meet practical standards for p-type transparent oxide semiconductors is challenging due to the balance between the defects that generate hole and electron c...

Stannous oxide, SnO, is a promising material for practical applications as a p-type transparent oxide semiconductor. However, in its thin-film form, the reported semiconducting properties of SnO are unfortunately insufficient for the development of oxide devices. In this work, we report that the hole mobility of SnO epitaxial films grown by pulsed laser deposition can be improved by reducing the growth temperature. The hole mobility is estimated to be approximately 10 cm2 V−1 s−1 at room temperature, which is nearly four times higher than the one originally reported for epitaxial films fabricated at the conventional growth temperature. In addition, the observed carrier density of the fabricated SnO films is slightly lower compared with that of the ones fabricated at the conventional growth temperature. This suggests that the Sn vacancy formation as a hole carrier dopant is suppressed by the reduction in the growth temperature. This result offers the key for the improvement of the performance of oxide thin-film devices.

Local distortion in the conduction pathway has a significant influence on the conducting properties of oxides. The electronic states induced in the band gap of SrTiO3 by La doping were investigated using photoemission spectroscopy (PES) and soft X-ray emission spectroscopy (SXES); moreover, the local distortion in the conduction pathway was examined using extended X-ray absorption fine structure (EXAFS). An itinerant state and a localized state were observed as a metallic state and an in-gap state, respectively, in the PES spectra and as inelastic peaks in the SXES spectra. This implied that the itinerant state and the in-gap state coexisted within the bulk. From EXAFS results, it was observed that La doped into SrTiO3 substituted Sr and locally distorted the conduction pathway. The results showed that some electrons doped by La-on-Sr substitution are trapped/localized by the local distortion in the conduction pathway, whereas the remaining doped electrons itinerate in the pristine conduction pathway with no distortion.

Diodes, memories, logic circuits, and most other current information technologies rely on the combined use of p- and n-type semiconductors. Although oxide semiconductors have many technologically attractive functionalities, such as transparency and high dopability to enable their use as conducting films, they typically lack bipolar conductivity. In particular, the absence of p-type semiconducting properties owing to the innate electronic structures of oxides represents a bottleneck for the development of practical devices. Here, bipolar semiconducting properties are demonstrated in α-SnWO

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ reveals a distinct oxygen isotope shift near the electron-boson coupling ``kink'' in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.

Wide-gap oxides with their valence band maximum (VBM) composed of s orbitals are essential for realizing practical p-type transparent oxide semiconductors. We prepared a new p-type wide-gap oxide, SnNb2O6 foordite, with its VBM composed of Sn 5s orbitals. To discuss carrier generation, we prepared both p-type and n-type SnNb2O6 by controlling the annealing conditions. The carrier mobility and density were 3.8 × 10–1 cm2 V–1 s–1 and 3.7 × 1018 cm–3, respectively, for the p-type sample and 9.9 cm2 V–1 s–1 and 7.5 × 1015 cm–3, respectively, for the n-type sample. The crystal structure of SnNb2O6 foordite consists of two types of alternating layers, Sn and Nb2O6 octahedra, where three nonequivalent oxygen sites exist. Six oxygens in the chemical formula of SnNb2O6 are distributed at the three sites in pairs, where the oxygens in three nonequivalent sites were named O1–O3. Hole and electron carriers were considered to be generated by Sn4+-on-Nb5+ substitutional defects (SnNb′) and oxygen vacancies of O1 and O2...

The competition between itineracy and localization of electrons doped into the near-surface region of anatase TiO2 (a-TiO2) is examined by photoemission spectroscopy. Since a-TiO2 samples used in this study are naturally grown single crystals, some electrons derived from oxygen vacancies are inherently present within the bulk and result in both a metallic state just below the Fermi level (EF) and a localized state tightly trapped by the oxygen vacancies (deep-trap state) within the energy gap. Additional electrons were doped to the surface by in situ deposition of potassium and by irradiation with high-intensity synchrotron radiation (SR). The potassium deposition does not cause a direct disturbance in the conduction pathway of the doped electrons, whereas the SR radiation produces oxygen vacancies in the pathway. Most of the doped electrons produced by depositing potassium contribute to a metallic state just below EF and behave as the carriers responsible for the surface conductivity. The remaining fract...

Semiconductor La0.67Sr0.33CoO3 thin films has been investigated as function of oxygen atmosphere during film growth in pulsed laser deposition. While amount of oxygen greatly depends on an oxygen atmosphere during film growth, in condition of oxygen atmosphere from 4 Pa to 100 Pa, the carrier in La0.67Sr0.33CoO3 thin films were found to be positive, exhibiting p-type conduction. Furthermore, we prepared (p)-La0.67Sr0.33CoO3/(i)-CeO2/(n)-InGaZnOx heterostructure devices and investigated electrical properties. These results showed rectifying behavior was clearly observed in heterostructure at room temperature. The sharp increase of current with voltage, when voltage exceeds diffusion potential, indicates the conductive resistance was small. p-type semiconductor La0.67Sr0.33CoO3 thin films and their p–n heterostructure devices with rectifying behavior may aid in the development of various semiconductor devices such as three terminal transistors, light emitted diode (LED) and solar cell.

We have developed a laser-based scanning angle-resolved photoemission spectroscopy system (µ-ARPES) equipped with a high precision 6-axis control system, realizing not only high-resolution photoemission spectroscopy in energy and momentum, but also spatial resolution of a µm scale. This enables our µ-ARPES system to probe fine details of intrinsic electronic states near the Fermi level such as the superconducting gaps and lifetime broadening.

The electronic structure of ternary tin oxide with pyrochlore structure, Sn2Nb2O7, which has the contribution of the Sn 5s orbitals in the valence band, is examined by synchrotron-radiation-excited photoelectron spectroscopy and X-ray absorption spectroscopy together with ab initio calculations. The empirical spectra are qualitatively consistent with the calculated density of states with the exception of a striking discrepancy in the electronic structure around the valence band maximum (VBM). The band calculation suggests the presence of a sharp peak around the VBM, mainly due to dispersionless bands that are derived from hybridization of Sn 5s orbitals and O 2p orbitals close to the Sn atom. However, the photoelectron spectra show no such characteristic spectral feature. From the theoretical prediction about the orbital origin of the localized VBM and the experimental estimation of the elemental composition by chemical analysis, it seems reasonable to conclude that the discrepancy of the electronic struc...

Local distortion in the conduction pathway has a significant influence on the conducting properties of oxides. The electronic states induced in the band gap of SrTiO3 by La doping were investigated using photoemission spectroscopy (PES) and soft X-ray emission spectroscopy (SXES); moreover, the local distortion in the conduction pathway was examined using extended X-ray absorption fine structure (EXAFS). An itinerant state and a localized state were observed as a metallic state and an in-gap state, respectively, in the PES spectra and as inelastic peaks in the SXES spectra. This implied that the itinerant state and the in-gap state coexisted within the bulk. From EXAFS results, it was observed that La doped into SrTiO3 substituted Sr and locally distorted the conduction pathway. The results showed that some electrons doped by La-on-Sr substitution are trapped/localized by the local distortion in the conduction pathway, whereas the remaining doped electrons itinerate in the pristine conduction pathway with no distortion.

Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique in materials science, as it can directly probe electronic states inside solids in energy (E) and momentum (k) space. As an advanced technique, spatially-resolved ARPES using a well-focused light source (high-resolution ARPES microscopy) has recently attracted growing interests because of its capability to obtain local electronic information at micro- or nano-metric length scales. However, there exist several technical challenges to guarantee high precision in determining translational and rotational positions in reasonable measurement time. Here we present two methods of obtaining k-space mapping and real-space imaging in high-resolution ARPES microscopy. One method is for k-space mapping measurements that enables us to keep a target position on a sample surface during sample rotation by compensating rotation-induced displacements (tracing acquisition method). Another method is for real-space imaging measurements that significantly reduces total acquisition time (scanning acquisition method). We provide several examples of these methods that clearly indicate higher accuracy in k-space mapping as well as higher efficiency in real-space imaging, and thus improved throughput of high-resolution APRES microscopy.

Quantum mechanics tells us that the hopping integral between local orbitals makes the energy band dispersive. In a lattice with geometric frustration, however, dispersionless flat bands may appear due to quantum interference. Several models possessing flat bands have been proposed theoretically, and many attracting magnetic and electronic properties are predicted. However, despite many attempts to realize these models experimentally, compounds that are appropriately described by this model have not been found so far. Here we show that pyrochlore oxides ${\mathrm{Sn}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Sn}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{7}$ are such examples, by performing first-principles band calculation and several tight-binding analyses. Moreover, spin-polarized band calculation shows that the hole-doped systems ${\mathrm{Sn}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}\mathrm{N}$ and ${\mathrm{Sn}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{6}\mathrm{N}$ have complete spin polarization, and their magnetic moments are mostly carried by Sn-$s$ and N-$p$ orbitals, which are usually nonmagnetic. These compounds are not only candidates for ferromagnets without a magnetic element, but also will provide an experimental platform for a flat-band model which shows a wide range of physical properties.

By controlling lattice defects through the annealing condition during crystal growth, a wide-gap and $p$-type semiconductor ${\mathrm{Sn}}_{2}({\mathrm{Nb}}_{2\text{\ensuremath{-}}x}{\mathrm{Ta}}_{x}){\mathrm{O}}_{7}$ $(x=$ $0--2)$ was developed. The band gap is variable in the range from 2.4 eV for ${\mathrm{Sn}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ $(x=0)$ to 3.0 eV for ${\mathrm{Sn}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{7}$ $(x=2)$, respectively. The carrier density and the hole mobility were estimated to be $0.20--1.4$ $(\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$ and $0.28--1.9$ $(\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$, respectively. From the mutual relation between the defect content and the electrical properties, we concluded that the hole carriers in the $p$-type semiconducting ${\mathrm{Sn}}_{2}({\mathrm{Nb}}_{2\text{\ensuremath{-}}x}{\mathrm{Ta}}_{x}){\mathrm{O}}_{7}$ are generated by ${\mathrm{Sn}}^{4+}$-on-${\mathrm{Nb}}^{5+}/{\mathrm{Ta}}^{5+}$ substitutional defects in (Nb,${\mathrm{Ta})}_{2}{\mathrm{O}}_{6}$ octahedral chains.

The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = −∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm−1 shifts to 341 cm−1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction.

The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = −∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm−1 shifts to 341 cm−1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction.

We have investigated the Au-SrTiO3(100) interface as a function of the Au evaporation using the photoemission spectroscopy. In the valence band of SrTiO3, the broad state originating from O 2p electrons and a state from Ti 3d electrons were observed between 3-9 eV and at 1 eV below the Fermi level (EF), respectively. With increasing the Au evaporation, the decrease in intensity of the state at 1 eV was observed. In the Ti 3p core-level, the decrease of the Ti3+ states was observed after Au evaporation. These results indicate that the electrons transfer from the Ti3+ states of the SrTiO3(100) surface to the evaporated Au. In addition, with increasing the Au evaporation, the larger shift of the peak in the Au 4f core-level to lower binding energy side was clearly observed as compared to that of the Sr 4p, O 2s, Ti 3p, and Sr 3d core-levels. Based on the results of the photoemission spectroscopy of the valence band and core-levels, we will discuss the electronic structures of the Au-SrTiO3(100) interface.

We have re-examined the oxygen isotope effect in high-temperature superconductors Bi 2 Sr 2 CaCu 2 O 8+ δ using high-precision angle-resolved photoemission spectroscopy with low-energy photons in order to elucidate the origin of the kink. The results taken with a much improved energy and momentum resolution showed the absence of the reported unusual oxygen isotope effect.

High-resolution angle-resolved photoemission spectroscopy (ARPES) has been conducted to study the Shockley state (SS) in ferromagnetic Ni(1 1 1) located at the Γ ¯ point of the surface Brillouin zone. We have determined the Fermi wave vector and Fermi energy of the state with excitation photon energies of hν = 6.9–27.5 eV. On the basis of ARPES spectral shape analyses, we have found significant electron–electron interaction in the SS.

The adsorption process and valence band structure of Ag on ZnO(1010) have been investigated by angle-resolved photoelectron spectroscopy utilizing synchrotron radiation. The coverage-dependent measurements of the Ag 4d band structure reveal that the Ag bands with a dispersing feature are formed even at low coverages and that the basic structure of the bands is essentially the same throughout the submonolayer region. These results indicate that the Ag atoms aggregate to form islands with an atomically ordered structure from the low coverages. Upon annealing the Ag-covered surface at 900 K, the Ag 4d band undergoes only a minor change, suggesting that the ordered structure within the Ag islands is persistent against mild annealing. From the dispersive feature of the Ag 4d states, we propose that the atomic structure has locally rectangular symmetry with a good lattice matching with the ZnO(1010) surface.

Transparent p–n junctions composed of zinc oxide, copper-aluminum oxide and indium-tin oxide films were fabricated by pulsed laser deposition on glass substrates at temperatures as low as 400 °C. Diode characteristics in the current–voltage response and the photovoltaic effect were observed for the junctions fabricated. The photovoltaic junction had an optical transparency of more than 43% for the wavelengths λ>500 nm, and exhibited photovoltage as large as 80 mV when it was illuminated by a LED of λ≈470 nm. The properties of the photovoltaic transparent junction seemed to be degraded by the inadequate crystallinity of the copper-aluminum oxide layer. The ZnO/CuAlO/ITO/glass structure developed in this study has demonstrated a possible application of transparent solar cells.

Using angle-resolved photoemission spectroscopy we have performed a detailed study of bilayer splitting in Bi2Sr2CaCu2O8+δ as a function of doping level and temperature. In heavily overdoped samples where the splitting is the clearest, we extract an intracell coupling t⊥∼55 meV. As a function of photon energy the intensity ratio of the bonding and antibonding bands varies, allowing us to detect the bilayer splitting effect in the optimal and underdoped regimes. Surprisingly, with reduced doping the intracell coupling is not measurably reduced. Upon cooling to the superconducting state, a gap Δ opens in both bands yet the magnitude of the splitting remains unchanged.

The behavior of the metallic state of lightly electron-doped SrTiO3 has been studied using angle-integrated ultraviolet photoemission spectroscopy (UPS) and angle-resolved photoemission spectroscopy (ARPES). Two states in the bulk band gap of stoichiometric SrTiO3 are shown by doping electron carriers: a metallic state with a sharp Fermi cut-off and a broad state centered at ∼1.3 eV below the Fermi level. By slight oxygen exposure, the UPS spectra showed a rapid decrease in the spectral intensity of the metallic state followed by a sudden energy shift of the valence band. These changes are explained in terms of the band-bending effect due to the formation of a thick charge depletion layer when the adsorbed oxygen atoms attract the free electrons from the bulk to the surface. Normal-emission photoelectron spectra before the oxygen exposure showed that the spectral intensity of the metallic state is remarkably enhanced at the photon energy of 28 and 45 eV whereas its energy position is almost independent of the photon energy. Off-normal-emission spectra showed that the spectral intensity of the metallic state is drastically reduced with increasing emission angle. From a comparison between the calculated band structure and ARPES results, we conclude that the metallic state is qualitatively explained by the Fermi liquid behavior based on the band theory.

We have investigated the electronic structures of metal-to-insulator transitions (MIT) due to charge-density-wave phase transition in 1T- TaS x Se 2-x by angle-resolved photoemission spectroscopy. In the insulating phase of the sample with x = 1.5, we observe a gap formation at the Fermi energy (E F ), while in the metallic phase of the sample with x = 1.2, we do not observe a drastic change in the spectra between at room temperature and at low temperature. We observe a peak originating from the lower Hubbard band in the insulating phase of the sample with x = 1.5. In the metallic phase of the sample with x = 1.2, the peak intensity is smaller and the peak energy shifts near E F , but the lower Hubbard band peak still remains. These results suggest that MIT in 1T- TaS x Se 2-x is due to the Mott localization.

A Fermi arc is a disconnected segment of a Fermi surface observed in the pseudogap phase of cuprate superconductors. This simple description belies the fundamental inconsistency in the physics of Fermi arcs, specifically that such segments violate the topological integrity of the band. Efforts to resolve this contradiction of experiment and theory have focused on connecting the ends of the Fermi arc back on itself to form a pocket, with limited and controversial success. Here we show the Fermi arc, while composed of real spectral weight, lacks the quasiparticles to be a true Fermi surface. To reach this conclusion we developed a new photoemission-based technique that directly probes the interplay of pair-forming and pair-breaking processes with unprecedented precision. We find the spectral weight composing the Fermi arc is shifted from the gap edge to the Fermi energy by pair-breaking processes. While real, this weight does not form a true Fermi surface, because the quasiparticles, though significantly broadened, remain at the gap edge. This non-quasiparticle weight may account for much of the unexplained behavior of the pseudogap phase of the cuprates.

We have prepared oxygen isotope exchanged crystals of impurity-free ${\text{YBa}}_{2}$${\text{Cu}}_{3}$${\text{O}}_{y}$ with various oxygen contents, and examined pure doping ($p$) dependence of isotope effect on superconducting transition temperature. With decreasing oxygen contents, the isotope exponent $\ensuremath{\alpha}$ monotonously increases without any anomaly around $p=1/8$. The monotonous increase in $\ensuremath{\alpha}$ indicates that phonons are involved in the mechanism which causes the monotonous ${T}_{c}$ suppression with underdoping.

The electronic structure of CaVO3 is studied on single-crystalline samples cleaved in ultrahigh vacuum by means of ultraviolet photoelectron spectroscopy (UPS). In the UPS spectra of the V3d-band region, a sharp peak near the Fermi level (EF) and a broad one centered at 1.4 eV below EF are shown. The former is assigned to the coherent band, whereas the latter is to the precursor of the lower Hubbard band, or the incoherent band. As the cleaved surfaces are exposed to oxygen, the ratio of the spectral weight of the coherent band to that of the incoherent band increases. At the same time, the spectral width of the coherent band enlarges. We conclude that the UPS spectra of the cleaved surfaces are partially caused by the electronic structure characteristic of the surface for which the correlation effect is expected to be more profound compared with that for the bulk.

In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a highresolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-1C of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-controlled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(0 0 1) surfaces were measured with high-resolution and bulk and surface components are clearly resolved. r 2001 Elsevier Science B.V. All rights reserved.

The effect of surface defects on the electronic structure of CaVO3 has been studied by ultraviolet photoemission spectroscopy (UPS). We used flat surfaces obtained by in situ fracturing of single-crystalline samples in an ultrahigh vacuum, and rough surfaces obtained by scraping, which are presumed to contain many surface defects. It is shown that the UPS spectra of CaVO3 are very sensitive to the surface structures, which depend on the cleaning procedure. In addition, the oxygen-exposure dependence of the UPS spectra was investigated in order to evaluate the influence of those surface defects on the UPS spectra. We conclude that the UPS spectra observed on the CaVO3 surfaces (both fractured and scraped) are strongly influenced by the electronic structure characteristic of the surface.

An in situ conduction measurement of metallic electronic states on the SrTiO3 (110) surface is reported. The electronic states were observed on the SrTiO3 (110) surface in our previous work after annealing in ultrahigh vacuum (UHV) at relatively low temperature, 800 °C, based on a sharp Fermi edge detected by ultraviolet photoemission spectroscopy and finite zero-bias differential conductance by scanning tunneling spectroscopy. The electric conductance measurement is performed in order to verify the metallic feature of the surface as a macroscopic property. For the measurement, a sample holder is designed which enables both annealing in UHV by electron beam and four-probe electric conduction measurement with uniform electric field. Conductance contributed by bulk is separated by measuring the decrease of total conductance by adsorption of oxygen at room temperature, which is supposed to modify only the surface electronic states. Surface conductance is deduced between 150 to 300 K and showed a metallic fea...

A straightforward method to deduce sample local density of states (LDOS) from the current–voltage characteristics (I–V) raw data in scanning tunneling spectroscopy (STS) is presented. The method is based on the relation between the I–V spectrum and the LDOS, both of which are treated as one-dimensional vectors: the I–V is generated from the LDOS by operating a triangular transfer matrix M. Then the LDOS is readily calculated from the I–V by operating the inverse matrix M−1, which is also triangular. The method is an alternative for the conventional method to take (dI/dV)(V/I), which often causes artificial peaks in LDOS at the onsets of I–V. Each row of M is determined by the tip density of states (DOS) and the barrier profile for the corresponding bias voltage. The tip DOS will be calculated from the I–V values measured at different tip-to-sample distances if the tip and sample have the same DOS and the barrier profile is symmetrical. As an example, the LDOS is calculated for the reduced SrTiO3 (110) on which the electronic states show metallic character depending on the annealing condition and sites.

Using angle-resolved photoemission spectroscopy (ARPES) with low-energy tunable photons, we studied the oxygen isotope effect in optimally doped Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212). We found the oxygen isotope shift in the real part of the electron self-energies [ReΣ( ω )s] along the nodal direction derived not only from the momentum distribution curves (MDCs) but also from the energy distribution curves (EDCs). Present results indicate straightforwardly the coupling between the nodal electrons and the phonons.

We have performed angle-resolved photoemission (ARPES) experiments on a variety of Bi-Sr-Ca-Cu-O (BSCCO) samples. By applying a stricter set of FS crossing criteria as well as by varying the incident photon energy outside the usual range, we have found very different behavior from that previously observed. Instead of being centered around the X or Y points and having hole-like character, we argue that the FS is centered around the Γ point and contains electron-like portions. In addition, the flat bands just below EF around [Formula: see text] are not observed at the photon energy of 33eV, raising questions about the origin of these states.

We present a reexamination of the electronic structure and Fermi surface (FS) topology of Bi-Sr-Ca-Cu-O (BSCCO) as obtained from angle-resolved photoemission experiments. By applying a stricter set of FS crossing criteria as well as by varying the incident photon energy outside the usual range, we have found very different behavior from that previously observed. In particular, we have found a FS that is centered around the $\ensuremath{\Gamma}$ point and contains electronlike portions, and we observe a depletion of spectral weight around $\overline{M}$. The flat bands observed at other photon energies may indicate the presence of two electronic components in the cuprates.

A high-resolution angle-resolved photoemission spectroscopy (ARPES) study of Fe(110) single crystal was conducted to elucidate many-body interactions between quasi-particles at the Fermi level at low-temperature. Two kink structures were observed in the energy-band dispersion at the binding energies of similar to 40 meV and similar to 270 meV for the bulk-derived band on the majority-spin Fermi surface around the F point. Based on analyses of the experimentally obtained real parts of the self-energy, these kink structures are derived from electron-phonon and electron-magnon interactions.

Using photoemission (PES) spectroscopy and a first-principles band-structure calculation, we have investigated the electronic structure of perovskite-type Ti-Cr oxides Sr 1 - ( x + y ) La x + y Ti 1 - x Cr x O 3 , in which the charge and spin density can be controlled. It was found that the near-Fermi level ( E F ) electronic structure consisted of a Cr 3d localized state and a Ti 3d itinerant state that were well separated in energy. The spectral weight of the Cr 3d state was proportional to x , demonstrating a controllable spin density. In contrast, the near- E F spectral weight exhibited different behavior. The band theory has reproduced the essential features of the Cr and Ti 3d states as well as the O 2p ones, but failed to predict the location of the Cr 3d and O 2p states. Implications of this discrepancy have been discussed in connection with calculated magnetic moments.

A high-resolution angle-resolved photoemission spectroscopy study of an Fe (1 1 0) single crystal has been conducted to clarify the role of many-body interactions acting on the quasi-particles at the Fermi level at low temperatures. We have evaluated the real and imaginary parts of the self-energy for the bulk-derived majority-spin Fermi surface around the Γ point, and found two characteristic energy scales, at ∼40 and ∼270 meV. The former corresponds to the energy scale of the Debye temperature. As for the latter, we found that it is close to the cut-off energy of the calculated magnon density-of-states. This correspondence indicates that the energy scale is related to the magnetic excitation.