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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.

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]

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 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]

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]

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]

We have grown a semipolar Al0.83Ga0.17N/AlN heterostructure on ZnO ([formula]) substrates and investigated the optical polarization characteristics of the near-band-edge (NBE) emission of Al0.83Ga0.17N experimentally and theoretically. Reciprocal space mapping measurements revealed that AlN is fully relaxed with respect to ZnO, and Al0.83Ga0.17N grows coherently in both of the in-plane orthogonal directions on AlN. The NBE emissions of coherently grown Al0.83Ga0.17N ([formula]) at 5.4 eV were clearly polarized with E||X2. The polarization ratio of the surface emission was as high as -0.66 at room temperature. This phenomenon is consistent with a large crystal splitting energy, which was clarified by theoretical investigations based on the k · p method. [ABSTRACT FROM AUTHOR]

We have grown m-plane InxGa1-xN (x = 0.24-0.43) commensurately on m-plane ZnO by the use of a low temperature epitaxial growth technique and investigated its optical properties. We found that the critical thickness for strain relaxation in the InGaN films prepared by the present technique is at least one order of magnitude larger than those reported by the other techniques. Polarized optical absorption measurements revealed that the allowed optical transition between the conduction band and the topmost valence band in m-plane InxGa1-xN (x = 0.24-0.43) on ZnO is for light polarized along c-axis. We found that the valence band splitting energy strongly depends upon the In composition. The values of the deformation potentials of InN were determined as D3 = 2.4 eV, D4 = -6.3 eV, and D5 = -1.2 eV, by fitting the experimental results with theoretical calculations based on the k·p approach. [ABSTRACT FROM AUTHOR]

The transport and photoluminescence properties of interfaces between amorphous CaHfO3 films and SrTiO3 single crystal substrates were investigated. Although both materials are band-gap insulators, the interfaces were metallic. The sheet carrier density was found to depend strongly on the laser fluence used during the CaHfO3 layer fabrication by pulsed laser deposition, indicating the presence of oxygen vacancies at the interface. The Hall mobility of the heterostructures saturated at 2000 cm2/V s at low temperature. Photoluminescence spectra showed an oxygen vacancy-related emission band at around 420 nm. [ABSTRACT FROM AUTHOR]

Epitaxial AlN films have been grown on atomically flat 6H-SiC (0001) and 4H-SiC (0001) substrates at room temperature (RT), and their growth mechanisms have been investigated. It has been revealed that the growth of AlN at RT proceeds in a layer-by-layer mode from the initial stage. During the growth, AlN nucei have an equilateral triangular shape probably due to the anisotropy in growth rates. The triangular AlN nuclei at the adjacent terraces formed on the 6H-SiC substrates are rotated by 60°, whereas the triangular AlN nuclei on the 4H-SiC were formed in the same direction on all of the terraces. This phenomenon can be explained by the difference in the arrangement of the atoms for the topmost layers. [ABSTRACT FROM AUTHOR]

We have investigated nitrogen-doping effects into HfSiOx films on Si and their thermal stability using synchrotron-radiation photoemission and x-ray absorption spectroscopy. N 1s core-level photoemission and N K-edge absorption spectra have revealed that chemical-bonding states of N–Si3-xOx and interstitial N2-gaslike features are clearly observed in as-grown HfSiOxNy film and they decrease upon ultrahigh vacuum (UHV) annealing due to a thermal instability, which can be related to the device performance. Annealing-temperature dependence in Hf 4f and Si 2p photoemission spectra suggests that the Hf-silicidation temperature is effectively increased by nitrogen doping into the HfSiOx although the interfacial SiO2 layer is selectively reduced. No change in valence-band spectra upon UHV annealing suggests that crystallization of the HfSiOxNy films is also hindered by nitrogen doping into the HfSiOx. [ABSTRACT FROM AUTHOR]

A gas scintillation proportional counter has been developed for measuring ultrasoft fluorescence x rays. This counter is high-vacuum compatible for connecting to the ICF-70 flange of a vacuum chamber. A Mylar window of 0.6-µm thickness and 12-mm diameter is utilized for the entrance of the ultrasoft x rays. The counter has a large entrance window of approximately 100 mm² and an energy resolution high enough to separate C Kα and O Kα radiations. This counter is applicable to not only x-ray fluorescence analysis, but also to fluorescence-yield extended x-ray absorption fine structure measurement of ultralow-Z elements. [ABSTRACT FROM AUTHOR]

An In-polar InN ultrathin film with high electron mobility was grown on an insulating yttria-stabilized zirconia (YSZ) (111) substrate via precise control of growth conditions for initial monolayers. It was found that the first several monolayers of InN on YSZ can be grown in a two-dimensional mode using extremely N-rich (ex-N-rich) conditions. Although the growth of more than several InN monolayers under these conditions results in rough surfaces, probably because of the suppressed migration of In atoms on the surface, the combination of ex-N-rich growth for the first few monolayers with subsequent conventional In-rich growth leads to the successful formation of InN films with smooth surfaces. The electron mobility of 11-nm-thick InN on YSZ with two-dimensionally grown initial layers was 170 cm2 V-1 s-1, which is much higher than the best reported value for InN ultrathin layers grown on GaN substrates. These results indicate that the structural quality of the InN/YSZ heterointerface and a smooth surface are inherently important for obtaining InN ultrathin films with good transport properties. [ABSTRACT FROM AUTHOR]

The detailed cross-sectional structure of InGaAs quantum dots fabricated by a heterogeneous droplet epitaxy method was investigated by means of cross-sectional transmission electron microscopy observation. It was confirmed that concave disks without any dislocations or wetting layer were formed at the upper part of the flat surface. This result was consistent with the change of photoluminescence intensity and peak position. The sizes of the disks were estimated to be 30 and 12 nm in lateral and vertical directions, respectively. From this estimation, the occurrence of a phase-separation effect is suggested. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]