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This paper reports, for the first time, on a low-temperature growth technique for obtaining crystalline InAs and InSb on a EuBa 2 Cu 3 O 7- y (EBCO) film with a SrF 2 interlayer preventing disruption of the underlying EBCO. Firstly, the InAs layer has been grown on the SrF 2 -coated EBCO by molecular beam epitaxy with a two-step growth procedure. An initial InAs layer was grown at room temperature with a thickness of more than 20 nm. A top InAs layer was then grown at 200°C. Consequently, (111) oriented crystalline InAs can be obtained by using this growth process. Cross-sectional transmission electron microscopy (TEM) studies show that the SrF 2 film completely covers the EBCO surface and that the interface between SrF 2 and EBCO is very sharp. Secondly, InSb has been grown on SrF 2 -coated EBCO by a two-step process. Synchrotron-radiation photoemission spectroscopy and X-ray photoemission spectroscopy studies demonstrate that InSb deposition reduces the amount of EBCO surface disruption as compared with InAs deposition. This is attributed to the fact that InSb is more easily grown at lower temperatures than InAs. Furthermore, cross-sectional TEM analysis for an InSb-grown sample indicates that InSb deposition is promising for growing better epitaxial layers on SrF 2 -coated EBCO.

The influence of crystal defects near the surface on horizontal Bridgman-grown GaAs(001) surface is investigated by photoluminescence (PL) and synchrotron radiation photoelectron spectroscopy (SRPES). PL measurements reveal that after heating to 500°C a layer with lower defect concentration exists just under the thermal degraded one. SRPES shows that the surface Fermi level (E FS ) moves to the conduction band minimum when this thermally degraded layer is removed by chemically etching and the etched surface is heated in ultra-high vacuum after rinsing with the deoxygenated and deionized water. These results suggest that the position of E FS for GaAs(001) surface is strongly affected by crystal defects near the surface.

In-situ synchrotron radiation photoelectron spectroscopy is used to study the surface chemical bonding structures on InAs(001) with and without Se passivation and to determine changes in the surface Fermi level ( E F ) position as a result of Se treatment. Analysis of the As 3d and In 4d core-levels for the epitaxially grown InAs and reflection high-energy electron diffraction pattern observations are found to be almost the same as those for GaAs (001)-(2 × 4), showing that a well-ordered InAs (001)-(2 × 4) surface is achieved. The results of As 3d and In 4d spectra for the Se-passivated InAs show that a Se-terminated surface is formed where the topmost Se atoms bond to In. Anomalous downward band bending, where the E F position is located at about 0.5 eV above the conduction band minimum, is observed for the first time at the Se-passivated InAs (001)-(2 × 1), in contrast to the well-known results for Se-passivated GaAs.

Effects of a Se treatment on the work function of epitaxially grown GaAs surfaces were measured by photoemission spectroscopy. Although the Se treatments reduced the band bending of n-type GaAs, the work function increased. This result indicates that the surface component of the work function increased and that the surface dipole moment, whose direction was from the surface to the bulk (outer layer: -, inner layer: +), was formed at the Se-treated GaAs surface. On the other hand, qualitative analysis based on the electron counting model revealed that the direction of the surface dipole in the previously proposed structural model of Se/GaAs(001) was completely opposite to that obtained in our experimental results. It is suggested that this discrepancy is due to the vacancies in the internal Ga layer in the structural model.

The electronic structure and chemical states of the overlayer and substrate in epitaxially grown Co films on Se-treated GaAs(001) 2×1 are investigated by photoemission spectroscopy (PES) using synchrotron radiation. Adatom (Co)-substrate (Ga) intermixing is found at the initial stages of Co deposition. The intermixed layer is then buried and epitaxial growth is achieved following further deposition. During the intermixing, Se is floated over the surface of Co overlayers. A small amount of As-segregation is also observed in the thicker Co films.

The effect of post-annealing on InSb island-crystal formation on Se-terminated GaAs, which is used to improve the composition ratio of Sb to In, was examined by using high-resolution scanning electron microscopy and cross-sectional transmission electron microscopy. Post-annealing after InSb growth on Se/GaAs reduces the density of nanocrystals by a factor of about 10 compared with as-grown InSb on Se/GaAs. It also increases island separation. The InSb island-crystal has a smooth terrace with edges a little higher than the inner region. The stoichiometry of nanocrystals was evaluated for the first time by using in situ synchrotron radiation photoelectron spectroscopy. Using this technique, we demonstrated that Sb incorporation occurs during post-annealing and that this drastically improves the stoichiometry of InSb nanocrystals grown on Se-terminated GaAs. As a result, we were able to obtain stoichiometric InSb nanocrystals on Se-terminated GaAs.

A system has been developed for realtime crystal-growth analysis by photoelectron spectroscopy, using vacuum ultraviolet (VUV) light from synchrotron radiation. This system consists of a VUV synchrotron radiation beamline and growth/analysis apparatus in which photoelectron spectroscopy is performed. A “non-scanning” photoelectron spectroscopy measurement method that uses only electron energy dispersion on a multi-channel detector achieves sub-second resolution. This system was used to monitor the GaSb-growth process by alternately supplying Ga and Sb molecular beams; the changes in the chemical state were analyzed with sub-second resolution. The Ga supply resulted in a Ga-full surface; Ga droplets formed on this surface, in which the Sb atoms remained lying on the Ga layer. The Sb supply did not change the ratio of Ga and Sb atoms at the surface from the initial value. These results show that, exposure to an Sb flux causes a crystal surface to once again become an Sb-rich surface although Ga droplets were previously formed during exposure to a Ga flux a GaSb surface was thus successfully grown.

The Sb desorption process from Sb-terminated GaAs(001) substrates has been analysed by time-resolved core-level photoelectron spectroscopy to investigate the influence of the substrate on the desorption. From the time dependence of the Ga 3d intensity, and the spectrum changes of Ga 3d and Sb 4d under Sb flux and during Sb desorption, three series of time constants for Sb desorption were found and activation energies of 2.5 eV and 1.1 eV were obtained for two of the desorption series. Spectrum analysis clarified that Sb double layers lie on the surface under Sb flux exposure and that Sb atoms corresponding to activation energies of 2.5 and 1.1 eV desorb from the topmost site of the Sb double layers. This is the same in the case of GaSb (001) substrate without the activation energy and shows that the bonding strength between the Sb atoms of the topmost layer site and the second layer site depends on the substrate materials.

We employed surface sensitive photoelectron spectroscopy (PES) using synchrotron radiation to investigate the strain of both deposited InAs and GaAs substrates with and without Se-termination. The two distinct chemical components comprising GaAs bonding and InAs bonding states in the As 3d spectrum are clearly observed for the first time, which indicates that the strain in both the deposited InAs and GaAs substrates can be separately evaluated using the core-level energy difference between the respective core-level chemical components. This difference between the chemical components of Ga 3d and As 3d levels for both two kinds of samples is found to be independent of InAs deposition time, and to be almost the same as that of a bulk GaAs, implying that no strain is generated in both two type GaAs substrates. On the other hand, in the case of the deposited InAs, this value increases with an increase in the layer thickness of InAs for the InAs/GaAs system and approaches to a bulk InAs value, whereas, there exits only a slight change for the InAs/Se/GaAs system at the very early stages of InAs growth and is almost the same as a bulk InAs value. These results suggest that the driving force for the formation of InAs nanocrystals in the InAs/GaAs system is the elastic strain, whereas, in the InAs/Se/GaAs system, passivation-induced self-organizing mechanism is crucial.

The throughput of a Schwarzschild objective using undulator synchrotron radiation was measured. Conventionally, the throughput was estimated from the squared reflectivity of one multilayer mirror and from the obstruction ratio. However, we evaluated the transmission ratio from the input and output photon flux using a precisely calibrated monochromatic beam from an undulator light source. It was found that the objective has a maximum throughput of 8.5% at a wavelength of 13.9 nm.

Rejuvenation of the oxidized Se/GaAs surface has been realized by deposition of a thin Al layer. The results provided by synchrotron radiation photoelectron spectroscopy show that upon Al deposition, oxygen originally bound to Ga segregates to the surface and forms a more thermodynamically stable Al oxide species. In addition, a reduction in band bending is realized suggesting that this method may be useful as a means of fabricating a wide range of passivated overlayer/Se/GaAs interfaces.

Using atomic force microscopy and scanning electron microscopy, we demonstrate that a Co epitaxial film surface grown on S-passivated GaAs(001) is smoother than one grown on bare GaAs(001) and establish that the surfactant nature of sulfur plays a vital role in the formation of a smooth surface. Synchrotron radiation photoemission spectroscopy results confirm that S passivation greatly reduces the segregation of substrate atoms during film growth on a S-passivated surface. It was also found that methanol rinsing after chemical S passivation provides an even smoother surface.

The process of Sb desorption from GaSb(001) and Sb-terminated GaAs(001) was investigated by using a real-time analysis system that uses time-resolved core-level photoelectron spectroscopy. From the photoelectron intensity analysis, two competing processes with fast and slow time constants were found on the Sb desorption from both substrates and the activation energies were determined to be 0.71 eV and 0.90 eV for GaSb(001) and 1.1 eV and 2.5 eV for Sb-terminated GaAs(001). We investigated the relationship between the activation energies and surface bonding structure using spectrum differences based on the assignment of conventional core-level photoelectron spectroscopy of the surfaces whose Sb coverage is well controlled. This indicated that the activation energy of the desorption related to the transition from 2×8 to 2×4 of an Sb-terminated GaAs(001) is larger than the other desorption processes and it can be explained that the large potential barrier for bonding structure rearrangement between 2×8 superstructure and 2×4 superstructure exist in addition to Sb atoms desorption.

Bonding at heterointerfaces between InAs nanocrystals and Se-terminated GaAs is investigated by in situ synchrotron radiation photoelectron spectroscopy (SRPES). The binding energy separation between Ga and GaSe bonding doublet components in the Ga 3 d spectrum for the Se-terminated GaAs surface was estimated for the first time to be 0.3 eV. A distinct spin-orbit component, composed of only the GaAs bulk bonding states, in the As 3 d spectrum for the Se-terminated GaAs surface was also observed. Comparing the core-level SRPES spectra before and after InAs growth, shows that the Se-terminated surface is not disrupted upon InAs epitaxial growth. Furthermore, from the evolution of the peak area ratio of In 4 d to Ga 3 d upon InAs deposition, it is found that, during InAs heteroepitaxial growth on the Se-terminated surface, self-organization of InAs is drastically enhanced compared with the case of As-rich surfaces.

A submicrometre-area photoelectron spectroscopy system that uses a multi-layer-coated Schwarzschild objective as the soft X-ray microbeam optics has been developed. The system is located at an undulator beamline (BL-16U) at the Photon Factory in the High Energy Accelerator Research Organization. By knife-edge measurement, the microbeam size was estimated to be 160 nm at the sample position using a 25–75% criterion. Photoelectron spectral measurements revealed that the Fermi edge width was 0.12 eV, which means that the instrumental resolution was 0.05 eV, after removing the natural broadening of the Fermi edge at room temperature. This system offers both high energy resolution and high spatial resolution.

Ultraviolet photoemission spectra of high-T c superconductor (La1-x Sr x )2CuO4-δ, (x=0.075 and δ≤0.04) are presented. The experimental result was compared with the band calculations of La2CuO4 by Mattheiss and Takegahara et al. It was found that as regards the valence-band width (about 7 eV) the experiment and the calculations are in good agreement with each other, but the position of the calculated valence bands contributed mainly by weakly bonding Cu(3d)-O(2p) states are shiftd toward the lower binding energy by about 1 eV with respect to the experiment. The possible origins for this discrepancy were discussed.

Photoelectron measurements made on the high-T c superconductor single crystals of Bi2(Sr, Ca)3Cu2O x using synchrotron radiation of 35–120 eV revealed a valence band satellite due to the two-hole bound state, which indicated considerable large intra-atomic Coulomb energy between Cu-3d electrons. The density of states on the Fermi level was clearly observed. This feature is quite different from those of the La-Sr-Cu-O and Y-Ba-Cu-O systems.

Electronic structure and chemical state of high-Tc superconductor (La1-xSrx)2CuO4-δ (x=0.075 and δ≦0.04) were studied by photoelectron spectroscopy. Resonant photoemission with synchrotron radiation snowed that the copper atom in the La–Sr–Cu–0 system is mostly divalent. The experimental results were compared with the band calculations performed for La2CuO4.