bluuebunny/crossref_metadata_2025 huggingface dataset:
EXAFS Study of Orientational Glasses
Authors: Yagi Kenichiro , Sakaue Kiyoshi , Terauchi Hikaru
Published: March 2014

The extended X-ray absorption fine structure (EXAFS) study of K1-x
(NH4)
x
I and KBr1-x
(NO2)
x
mixed crystals was performed to elucidate the local structure of their glassy state associated with the reorientational freezing of molecular ions without any long-range order. The magnitude of EXAFS spectra of K1-x
(NH4)
x
I was reduced with increasing ammonium ion concentration, while that of KBr1-x
(NO2)
x
exhibits no anomalous changes with increasing nitrite ion concentration even below the glass transition temperature T
g. The results indicate that the local distortion which breaks the symmetry of fcc lattice is induced by the short-range antiferroelectric order of ammonium ions in K1-x
(NH4)
x
I and the local structure is retained by the short-range ferroelectric order of nitrite ions in KBr1-x
(NO2)
x
. The temperature dependence of mean-square displacement of bromine-potassium pair-distribution in KBr1-x
(NO2)
x
obeys the Debye approximation even below T
g, which conflicts the result of previous X-ray diffraction studies that the mean-square displacement deviates largely from the Debye approximation.
EXAFS Study of Densified GeO2 Glasses
Authors: Ohtaka Osamu , Kikuchi Motohiro , Nakajima Kenji , Yoshiasa Akira , Yamanaka Takamitsu
Published: March 2014

Glasses of composition GeO2 and Li2O-3GeO2 were compressed up to 30 GPa at temperatures from 300 to 773K where sixfold coordination of Ge is stable. Densification of 10 and 15 % was achieved for GeO2 and Li2O-3GeO2 glasses, respectively. Ge EXAFS measurements of Li2O-3GeO2 glasses retrieved from high pressure indicated that the coordination number of Ge is 4. The second and third neighbor distances (Ge-Ge1 and Ge-Ge2) determined by EXAFS show that the densification mechanism is explained by more distorted packing of GeO4 tetrahedra than that in ambient glass. Coordination change by compression in the present Li2O-3GeO2 and GeO2 glasses is reversible. The quenchability of the sixfold coordination of Ge in germanate glass is discussed.
Optically Controlled Alignment of Liquid Crystal on Polyimide Films Exposed to Undulator Radiation
Authors: Shitomi Hiroshi , Ibuki Toshio , Matsumoto Setsuko , Onuki Hideo
Published: March 2014

Liquid crystal (LC) alignment properties on photo-exposed polyimide films were studied in the UV and VUV regions using linearly polarized synchrotron radiation from the Onuki-type polarizing undulator installed in the electron storage ring NIJI-II in ETL. It was found that the LC alignment uniformity depends on the UV and VUV exposure conditions, especially on the wavelength of the radiation. The photoabsorption spectrum of polyimide films was also measured in both UV and VUV regions. It was concluded that at least two mechanisms exist in the photo-induced alignment of LC molecules on the polyimide films.
Low-Temperature High-Resolution Resonant Photoemission Study of Kondo Insulator Ce3Bi4Pt3
Authors: Takeda Yukiharu , Arita Masashi , Okamura Yoshihiro , Sato Hitoshi , Shimada Kenya , Mamiya Kazutoshi , Namatame Hirofumi , Taniguchi Masaki , Katoh Kenichi , Iga Fumitoshi , Takabatake Toshiro
Published: March 2014

High-resolution Ce 4d-4f resonant photoemission spectroscopy has been performed on the Kondo insulator Ce3Bi4Pt3 at 12 K. By subtracting the off-resonance spectrum (hν=114 eV) from the on-resonance spectrum (hν=122 eV), a measure of Ce 4f partial density of state is obtained. Temperature-dependent Ce 4f spectra very close to EF are measured with ultrahigh-energy resolution (ΔE∼6 meV) and a clear depression of intensity is observed at 6 K, indicating a (pseudo)gap opening at low tempera tures.
Si 2p Spectra of Initial Thermal Oxides on Si(100) Oxidized by H2O
Authors: Enta Yoshiharu , Shoji Daisei , Shinohara Masanori , Suemitsu Maki , Niwano Michio , Miyamoto Nobuo , Azuma Yoshiro , Kato Hiroo
Published: March 2014

Initial stage of wet thermal oxidation of Si(100)2×1 surfaces using water has been investigated by high-resolution Si 2p core-level measurements with synchrotron radiation at substrate temperatures of room temperature (RT) - 800 °C. Water was found to dissociatively adsorb at RT, forming Si-H and Si-OH bonds. At elevated temperatures, the four oxide components that are identical with those in dry oxidation also appeared in the spectrum in addition to the Si-H component. The Si-H component showed a peak shift toward higher binding energies with temperature, which suggests transformation from the monohydride to the dihydride at higher temperatures.
X-Ray Interference and Crystal Truncation Rod Observation of GaN and GaInN Layers Grown on Sapphire with AlN Buffer Layer
Authors: Tabuchi Masao , Takeda Yoshikazu , Matsumoto Nobuhiro , Amano Hiroshi , Akasaki Isamu
Published: March 2014

X-ray CTR measurement was conducted for GaN and GaInN layers grown on sapphire substrates with low-temperature grown AlN buffer layers. It is to study the crystalline structure of the GaN and GaInN layers formed on the sapphire substrates with the buffer layers. The GaN and GaInN/GaN layers on the sapphire substrates with the low-temperature grown AlN buffer layers had the Al polarity ((0001)A). The surfaces were found to be covered with N. The thicknesses of the GaInN layers were measured accurately to be 4.02nm and 40.5nm for the samples designed to have 4nm and 40nm-thick GaInN layers, respectively. Indium compositions for 4nm- and 40nm-thick GaInN layers were determined to be 8.8% and 11%, respectively.
Application of XANES Spectra to Supported Catalysts
Authors: Tanaka Tsunehiro , Yamamoto Takashi , Kohno Yoshiumi , Yoshida Tomoko , Yoshida Satohiro
Published: March 2014

XANES spectroscopy is applied to the characterization of surface species of supported catalysts. In case of vanadium oxide supported on silica (V2O5/SiO2) at low loadings, comparison of the vanadium K-edge XANES spectrum with the spectra of the authentic samples allowed the determination that the surface species is a VO4 tetrahedron where three oxygen atoms of the four are linked to silica support. The coordination environment changed easily by adsorption of water molecules, indicating the direct attachment of water molecules to vanadium atoms. A platinum particle of Pt-sulfated ZrO2, known as a catalyst promoting super acidic reactions, consists of a core of platinum metal particle and surface layers of platinum oxide. The analysis of XANES spectrum of the catalyst sample by using those of Pt metal and α-PtO2 goves the fraction of α-PtO2. Fe ions in Fe, Mn-sulfated ZrO2 catalyst, knowing as a catalyst promoting super acidic reactions, were found to be present inside the ZrO2 as a solid solution and the ions does not directly participate in the super acidic reaction. Mn ions are the site of adsorption of reactant gas molecules. The in situ XANES spectra at Fe K-edge did not change throughout the reaction and those at Mn K-edge were affected by introduction of reaction gas. Europium amide complex in zeolite is a mixture of trivalent and divalent Eu species. Eu divalent species is an active species for abase-catalyzed reaction. The fraction of Eu divalent species could be determined by danalysis of XANES spectra of Eu L3-edge. The analysis applied to Pt XANES spectra can be applied to the XANES spectra of Rh/TiO2 at Rh K-edge. In the case of a Rh/TiO2 photocatalyst, the reactivity of the catalyst varies with the loading amount of Rh. XANES analysis of the Rh/TiO2 catalysts showed that surface rhodium species are a mixture of Rh metal and highly dispersed Rh2O3 and the fraction of Rh2O3 varies with the loading amount. We found that Rh atoms are present as an oxide form at low loadings even after heating the catalyst in the presence of hydrogen at 673 K.
Photon Stimulated Ion Desorption of Polymer Thin Films Following Core Excitation
Authors: Fujii K. , Tomimoto H. , Isshiki K. , Tooyama M. , Sekitani T. , Tanaka K.
Published: March 2014

We have studied the photon stimulated ion desorption of poly-isopropenyl-acetate (PiPAc) and poly-vinyl-acetate (PVAc) thin films from the viewpoint of site-specific bond scission. PiPAc is the structural isomer of PMMA, which shows site-specific bond scission. The structures of PiPAc and PVAc are different in the substitutional group of the side-chain, a methyl group or hydrogen. H+, CH+, CH2
+, CH3
+ and COCH3
+ are mainly desorbed from PiPAc and PVAc thin films following the oxygen core excitation. The near edge X-ray absorption fine structure (NEXAFS) spectra of these thin films are assigned through a comparison to the inner shell electron energy loss spectra of the related molecules. The features of the partial ion yield (YPi) spectra of CH3
+ and COCH3
+ ions are different from that of the total electron yield (Ye) spectrum. This indicates that the efficiencies of desorption of these ions depend on the primary excitation and these ions are consequently desorbed site-specifically. The most remarkable difference in the YPi is seen in the YPi(CH3
+) and YPi(COCH3
+) spectra. In YPi(CH3
+) and YPi(COCH3
+) spectra, the peak is assigned to the O 1s(C=O) → σ*(C-C) with the help of this result.
Magnetic Dichroism and High Resolution Photoemission Study of Materials
Authors: Suga Shigemasa , Imada Shin , Sekiyama Akira
Published: March 2014

Magnetic dichroism in photoemission and core absorption provides detailed information on electronic states in magnetic materials. High resolution resonance photoemission spectroscopy is a powerful tool to probe correlated electronic states. We report some results of Ni, pyrite compounds FeS2 and NiS2, Ce compounds CeNiSn and CePdSn, and perovskite Mn oxides Nd1-xSrxMnO3 with x=0.5 and 0.47.
Magnetic Moments in (Cr and Ni) Doped CMR Manganites as Seen by Soft X-ray Magnetic Circular Dichroism
Authors: Studer Francis , Toulemonde Olivier , Goedkoop Jeroen , Barnabe Antoine , Raveau Bernard
Published: March 2014

Soft X-ray Magnetic Circular Dichroism (SXMCD) at Transition Metal (TM) L2,3-edges was used to investigate the existence and orientation of magnetic moments at the B site of doped manganites Ln0.5Ca0.5(Mn1-xBx)O3 (Ln = Pr, Sm; B = Cr, Ni; 0.02 ≤ x ≤ 0.10). In this series of substituted compounds, the undoped compounds are antiferromagnetic and insulating because of charge ordering. Upon doping, the manganites exhibit a ferromagnetic ordering at TC ranging from 50K to 150K and, depending on the doping amount up to x = 0.1, an insulator-metal transition and Colossal Magneto-Resistant (CMR) properties. It is shown that all doping TM bear a magnetic moment below TC but with various orientations: Cr aligns antiparallel to the Mn sublattice whereas Ni aligns parallel to the manganese moment in an applied magnetic field of 0.6 T. Moreover magnetic moment intensities on Cr and Mn increase with doping in agreement with the increase of the total magnetization.
Temperature Dependence of Magnetic Compton Profiles of Ni
Authors: Tanaka Yoshikazu , Matsumoto Isao , Adachi Hiromichi , Kawata Hiroshi
Published: March 2014

The temperature dependence of the magnetic Compton profile of Ni [100] was measured for the first time. It was found that there is a significant difference in shape between the MCPs at room temperature and at 640 K. The result shows that the MCP of Ni above the T
C (628 K) has much smaller ratio of the magnetic moment of the s, p-like electrons to that of the 3d magnetic electrons than the MCP at room temperature. This indicates that the spin moment of the s, p-like electrons disappears more rapidly than that of the localized moment due to thermal excitations when temperature approaches to the Curie temperature.
Infrared Magnetic Circular Dichroism of Strongly Correlated 4f Electron Systems with Synchrotron Radiation
Authors: Kimura Shin-ichi
Published: March 2014

Magnetic circular dichroism (MCD) experiment in the infrared region using synchrotron radiation has been done for the first time. Since the off-axis component of the synchrotron radiation is circular polarization by itself, a MCD spectrum in wide energy range can be measured easily by using the infrared synchrotron radiation. The experimental method is suitable for the investigation of strongly correlated electron systems because the electronic structure, which is made by magnetic many-body interactions, is located in the wide energy region near the Fermi level. The experimental apparatus and a result of the MCD experiment of CeSb are reported.
Importance of Measurements of Small MCD Signals at Temperatures Higher than Tc: Distinction between Itinerant and Localized Magnetism
Authors: Miyahara Tsuneaki , Ishii Hiroyoshi , Imada Shin , Saitoh Yuji , Jung Rang-J. , Kimura Hiroaki , Suga Shigemasa , Sugawara Hitoshi , Sato Hideyuki
Published: March 2014

CeFe4P12 is a non-magnetic semiconductor which might include both “strongly correlated” and “weakly correlated” systems, also being a reference material to investigate the interesting property of LaxCe1-xFe4P12. In order to check the above expectation we tried to measure small MCD signals in the Ce 3d-4f and Fe 2p-3d excitation regions. It was found that the MCD signal intensity per atom at Fe atomic site is much smaller than that in Ce atomic site, suggesting that the empty Fe 3d states would be a “weakly correlated” or a very itinerant system. It is also suggested that the MCD spectrum of Ce 3d-4f excitation region reflects some polarization induced by the externally applied magnetic field both in the ground and the excited states.
Electronic States of fcc Fe/Co(001) of 5-11 Monolayers Probed by Spin-Resolved Photoemission Spectroscopy
Authors: Kamakura Nozomu , Kimura Akio , Hayashi Kei , Harasawa Ayumi , Kakizaki Akito
Published: March 2014

We have measured spin- and angle-resolved photoemission spectra of Fe/Co(001) of 5-11 monolayers thickness range by using photon energy of 44.5, 69 and 101 eV, in which Fe forms face-centered cubic structure. The finite spin-polarization has been found for fcc Fe at room temperature, which indicates the existence of the ferromagnetic surface layer. In addition we have clearly observed a temperature dependence of the spin polarization, and observed the exchange splitting peaks of Δ5 symmetry band as well as the peaks of the non-magnetic state in the spectra excited by 44.5 eV.
X-ray Diffraction Studies of Expanded Fluid Mercury Using Synchrotron Radiation at SPring-8
Authors: Tamura Kozaburo , Inui Masanori , Nakaso Ichiro , Oh'ishi Yasufumi , Funakoshi Ken'ichi , Utsumi Wataru
Published: March 2014

The energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for expanded fluid Hg were carried out in the wide density range from the liquid to the dense vapour region including the metal-nonmetal (M-NM) transition region. Density ranges from 13.6 to 1.9 gcm-3. We obtained the structure factor S(k) and the pair distribution functions g(r). The density variations of the obtained interatomic distance and coordination number were discussed in relation to the M-NM transition in fluid Hg.
The Local Structure of Amorphous Gd80Si12B8
Authors: Nakai Ikuo , Maeda Hironobu , Ishio Shunji
Published: March 2014

We report the local structure of an amorphous alloy Gd80Si12B8 determined from an extended x-ray absorption fine structure (EXAFS) measurements near the Gd LIII edge. Analysis is made using an asymmetric pair distribution function. The distances from the Gd atom are 2.55 Å to B, 2.96 Å to Si and 3.50 Å to Gd. The interatomic separation between Gd atoms is rather consistent with one for 12-coordinated metals, while the distances of Gd-B and Gd-Si are close to ones estimated from radii of atoms in tetrahedral covalent bonds rather than metallic radii. A central Gd atom has 11.4 nearest neighbors which consist of 0.9 B, 1.4 Si and 9.1 Gd atoms.
Recent Progress in X-ray Topography for Silicon Materials
Authors: Kawado Seiji
Published: March 2014

The present paper reviews recent synchrotron x-ray topographic studies on minute fluctuations of impurity- and point-defect concentration in CZ and FZ silicon crystals, and studies on microdefects such as oxygen precipitates and dislocation clusters in CZ silicon crystals. Plane wave x-ray topography enables us to determine the degree of strain with a sensitivity of 108 and to clarify the relationship between oxygen-concentration fluctuation and lattice-spacing variation. Ultra-plane wave x-ray topography and Lang topography using high-order reflection of high-energy x-rays give some information about microdefects, but the identification of defect images is not easy. The possibility of topographic observation of nearly strain-free microdefects such as octahedral voids in as-grown CZ crystals is briefly discussed.
EXAFS Study of Ti, Fe and Ga Substituted Silicalites
Authors: Lamberti Carlo , Palomino Gemma Turnes , Bordiga Silvia , Arduino Diego , Zecchina Adriano , Vlaic Gilberto
Published: March 2014

The local environment of isomprphous substituted Ti, Fe and Ga metal atoms in silicalite (hereafter indicated as TS-1, Fe-S and Ga-S respectively) has been studied by means of EXAFS spectroscopy. Measurements have been carried out on the samples in presence of template and after template removal at increasing temperatures in order to follow the evolution of the local environment of the metal heteroatoms. Ti(IV) atoms in (TS-1) show a great stability, while Ga(III) and particularly Fe(III) atoms have propensity to migrate from framework into extraframework positions, forming small oxide particles trapped inside the MFI channels upon increasing the template burning temperature. The established stability scale is Ti(IV) > Ga(III) > Fe(III). These conclusions are qualitatively supported by UV-Vis, IR and Raman data.
Preliminary Spectromicroscopic Measurements of Self-Organized InAs Nanocrystals by SPELEEM
Authors: Watanabe Y. , Heun S. , Schmidt TH. , Prince K. C.
Published: March 2014

Preliminary Spectromicroscopic measurements of self-organized InAs nanocrystals by soft x-ray photoemission electron microscopy (XPEEM) are presented. The InAs nanocrystals were fabricated on Se-terminated GaAs(100) surfaces by molecular beam epitaxy (MBE) in a dedicated chamber in Tsukuba, Japan. The measurements were performed with the Spectroscopic Photo Emission and Low Energy Electron Microscope (SPELEEM) of the Technical University of Clausthal at beamline 6.2LL at the synchrotron radiation light source ELETTRA in Trieste, Italy. The samples were protected during transfer in air to ELETTRA by an As capping layer deposited in-situ in the MBE chamber. The capping layer was desorbed in the SPELEEM sample preparation chamber. We performed tests on As-capping and decapping of InAs nanocrystals by synchrotron radiation photoelectron spectroscopy at the Photon Factory, Tsukuba, Japan. We found that the electronic properties of the sample were not changed by capping and decapping. Low energy electron microscopy and XPEEM measurements proved the feasibility of Spectromicroscopic experiments on InAs nanocrystals.
Angular Dependence of Al-2p X-ray Yield Spectra of GaAs/AlAs/GaAs Heterostructures
Authors: Inoue Koichi , Agui Akane , Shin Shik
Published: March 2014

The X-ray emission yield by the Al-2p core-exciton excitation in GaAs/AlAs/GaAs heterostructures is studied theoretically: especially the angular correlation between absorbed and emitted X-rays are discussed. It becomes clear that the angular dependence of the X-ray emission yield is drastically changed according to the excitation character whether 2p → s or 2p → d transitions.
Structural Study of Poly-Molybdate Ions in Acid Mo–Ni Aqueuous Solutions
Authors: Matsubara Eiichiro , Shinoda Kozo
Published: March 2014

Structures of poly-molybdate ions in acid Ni-Mo aqueous solutions have been investigated by the anomalous x-ray scattering (AXS), EXAFS and small angle x-ray scattering (SAXS) methods. In a solution containing only molybdenum ions, molybdenum ions form a poly-molybdate ion consisting of seven edge-sharing MoO6 octahedra. In a solution containing both Mo and Ni ions, there exists another poly-molybdate ion consisting of 6 edge-sharing MoO6 surrounding a Ni ion. The coordination number of Mo-Mo pairs decreases by half by adding citric ions. This indicates that the large poly-molybdate ion is decomposed to smaller molybdate ions due to formation of citric complexes. This is also confirmed by the SAXS measurement. Since molybdenum-nickel alloys are not electrodeposited from the solutions without citric ions, we expect that the decomposition of large poly-molybdate ions in the solution is closely related with the mechanism of the induced codeposition of molybdenum and nickel alloy.
Si1-xGex Laterally Graded Crystals as Monochromators for X-Ray Absorption Spectroscopy Studies
Authors: Veldkamp Markus , Erko Alexei , Gudat Wolfgang , Abrosimov Nikolai V. , Alex Volker , Khasanov Salavat , Shekhtman Veniamin , Neissendorfer Frank , Pietsch Ullrich
Published: March 2014

Using the BESSY I wavelength shifter (WLS) beamline we have examined the energy resolution of a laterally graded Si1-xGex crystal in the full divergent, white synchrotron beam. At the Fe-K absorption edge (E = 7112 eV) we have measured an energy resolution of E/ΔE=7.1·104 for the (440) reflection and a vertical divergence of 0.63 mrad. For a pure Si(440) reference crystal and the same divergence we found E/ΔE=7.1·103 which means a factor of 10 improvement in the case of the laterally graded crystal. Similar results have been obtained at the Co-K absorption edge (E = 7710 eV) with an increase of 2.6 for E/ΔE. We present the experimental set-up and a method for the characterization of the absolute lattice parameter with a precision of Δd/d=2·10-5. In addition, we discuss the application of the laterally graded Si1-xGex crystals in the crystal monochromator KMC-2 at the BESSY II storage ring.
Design of Surface Chemistry End-Station of BL23SU in SPring-8
Authors: Teraoka Yuden , Yoshigoe Akitaka
Published: March 2014

An experimental apparatus for surface reaction research has been designed as an end-station of a soft x-ray beamline, BL23SU, in the SPring-8. The soft x-ray with intense flux density is provided by a variable-polarizing undulator and is monochromized by using a varied line-spacing plane grating with grazing-incidence. A supersonic molecular beam technique is applied to obtain translational-energy control of incident molecules. Owing to keeping low pressure in the surface reaction chamber during molecular beam operation, the analysis of translational-energy-induced surface reactions is achieved by simultaneous application of the photoelectron spectroscopy. The end-station will promote research activities on new atomic layer reactions induced by the kinetic energy of incident molecules as well as new photofragmentation of monolayer due to the inner-shell selective photoexcitation.
X-Ray Fluorescence Analysis with a Johansson-type Spectrometer
Authors: Sakurai Kenji , Eba Hiromi
Published: March 2014

A new age is dawning in X-ray fluorescence spectrometry with the advent of 3rd-generation synchrotron radiation, especially undulator radiation in the X-ray region. Not only a brilliant source, but also a high-performance spectrometer is indispensable to realizing advanced analysis, which has been almost impossible so far. The present paper describes experimental feasibility tests of a Johansson-type spectrometer performed with monochromatic undulator radiation at SPring-8. A Ge (220) analyzing crystal (Rowland radius 350 mm) and a NaI:Tl detector with a 0.15 mm receiving slit were employed. The energy resolution obtained is 8eV for Cu Kα1 line (8.04 keV), and is sufficient to separate signals from unnecessary scattering and other fluorescent X-rays. The resonant X-ray fluorescence spectra were obtained in a reasonably short time as well. Further optimization of detection efficiency is now under way for application to trace systems.
XAFS Study on Metal Particle Formation in Noble Metal Cation Loaded Synthesized Smectite Containing Several Divalent Cations during Hydrogen Reduction
Authors: Shirai Masayuki , Torii Kazuo , Arai Masahiko
Published: March 2014

A platinumloaded nickel-substituted smectite catalyst (Pt/Ni-SM) showed high activity for n-butane hydrogenolysis. XAFS analysis showed that the Pt/Ni-SM catalyst has active small nickel metal particles. The reduction mechanism of nickel divalent cations in the lattice was discussed. It has been shown that noble metal (platinum or palladium) particles are first produced and then nickel divalent cations in lattice are reduced to metal particles in noble metal cation loaded nickel-substituted smectite catalyst during hydrogen reduction.
XAFS Study on the Structure of Mo Species in NaY Zeolite Derived from Mo(CO)6
Authors: Asakura Kiyotaka , Noguchi Yoshiaki , Iwasawa Yasuhiro
Published: March 2014

We carried out XAFS characterization on Mo species in the supercage which was prepared in the supercage of NaY zeolite by cycles of saturation adsorption of Mo(CO)6 at room temperature and subsequent thermal decomposition at 573 K. XAFS analysis revealed that Mo dimer with the Mo-Mo distance of 0.285 nm was formed in the supercage, the structure of which was unchanged during the saturation adsorption/thermal decomposition cycles.
Combining in situ XAFS, XRD and SAXS to Follow the Synthesis of Cadmium Oxide from a Hydroxyl Gel
Authors: Alétru C. , Greaves G. N. , Sankar G. , Kempson V.
Published: March 2014

Starting with a hydroxyl gel, the synthesis of cadmium oxide has been charted using combinations of in situ X-ray Diffraction (XRD), X-ray Absorption Fine Structure (XAFS) spectroscopy and Small Angle X-ray Scattering (SAXS). The crystallography, particle size and local structure have been quantified from XRD and XAFS, as the gel converts into cadmium oxide close to 182°C. The associated microstructure has been deduced from SAXS, which reveals how cadmium oxide initially grows dendritically in a fractal geometry of nanoparticles, before finally densifying between around 550°C.
Photoreflectance of a High Quality CuInSe2 Single Crystal
Authors: Chatraphorn Somphong , Yoodee Kajornyod , Songpongs Pong , Chityuttakan Chanwit
Published: March 2014

A melt growth CuInSe2 bulk single crystal was shown to be very high quality from its sharp and strong photoluminescence (PL) emissions. Photoreflectance (PR) measurement on a selected sample were performed from 12 K to room temperature. The PR line shape depends on surface treatment of the sample. Sharp features of PR spectra were obtained from bromine-methanol etched surface. PR spectra measured from 12 K to 140 K were analyzed by using both the well known Aspnes' relation and the confluent hypergeometric function suitable for exciton with Gaussian line shape. Result of the line-shape analysis shows that transitions involved are derived from two excitons with Gaussian line shape. By comparison with excitonic emission from its PL result, the two excitons are identified as the A- and the B-exciton which result from the splitting of the uppermost of the valence band. The energy difference of the two excitons computed from the PR spectrum at 12 K is 3.7 meV which agrees fairly well with 3.2 meV from PL result. The Gaussian exciton line shape at low temperature also indicates that the exciton-phonon coupling in a high quality CuInSe2 bulk single crystal is strong. PR spectra measured from an as-polished surface are weak and exhibit broader spectral lines which are well fitted by two excitons with the Lorentzian line shape. In addition, by carefully etching and polishing, the PR spectrum at 40 K exhibits a spectral line which can be interpreted as a superposition of the two spectra of different line shapes. The spectrum is well fitted by two Gaussian excitons and two Lorentzian excitons with two sets of transition energies. The presence of Lorentzian excitons indicates that excitons near the as-polished surface are weakly coupled to phonon which may be a result of residual strain left over by mechanical polishing.
Observation of Biexciton Luminescence from CuGaS2 Bulk Single Crystals
Authors: Tanaka Kunihiko , Uchiki Hisao , Iida Seishi , Terasako Tomoaki , Shirakata Sho , Isomura Shigehiro
Published: March 2014

Excitation intensity dependences of time-integrated and picosecond time-resolved excitonic photoluminescence from CuGaS2 bulk single crystals were studied. Under high excitation broad and fast decay luminescence appeared at the lower energy side of free exciton luminescence. The new luminescence is attributed to the radiative recombination of biexcitons. The shape of the time-resolved spectrum of this luminescence at 0–20 ps after excitation fits quite well with “reverse” Boltzmann distribution for the biexciton temperature of ∼54 K at the excitation level of 42 MW/cm2 and binding energy of the biexciton of 4.5±0.5 meV. This is, to the best of our knowledge, the first observation of biexciton luminescence in CuGaS2.
Decay Properties of Photoluminescence Lines in CuGaS2 Crystals
Authors: Terasako Tomoaki , Umiji Hiroshi , Tanaka Kunihiko , Shirakata Sho , Uchiki Hisao , Isomura Shigehiro
Published: March 2014

Decay properties of sharp zero-phonon photoluminescence (PL) lines at 2.460 eV, 2.457 eV, 2.417 eV, 2.404 eV, 2.397 eV and 2.295 eV have been studied for CuGaS2 single crystals grown by an iodine transport method. These PL lines exhibited biexponential decay. The relationship between the decay time of the fast component (τ
f
) and the exciton localization energy (E

loc
) can be given by τ
f
∝E

loc

1.25. On the other hand, the decay times of the slow components (τ
s
) have been classified into two groups having different trends τ
s
∝E

loc

2.7 and E

loc

0.5.
Luminescence of Eu2+ in CaGa2S4 Mono and Polycrystals
Authors: Benalloul Paul , Barthou Carlos , Benoit Jacques , Georgobiani Anatoly , Lepnev Leonid , Gruzintsev Alex , Tagiev Bakhadur , Tagiev Oktay , Dzhabborov Rasim
Published: March 2014

Luminescence, decay and thermal quenching under photonic excitation of CaGa2S4:Eu2+ mono and polycrystals were measured. The thermal quenching of the emission centered at 562 nm is only 10% at room temperature. Decays under 420 nm excitation are exponential but varies with T due to two different traps.
Quaternary Sulfospinels in the System Cu-Mn-In-S
Authors: Garbato Andrea , Garbato Lelio , Marrocu Pasqualino , Sedda Franca
Published: March 2014

We report the results on synthesis process and structural characterisation of quaternary phases in the mixed system CuIn5S8–MnIn2S4 SEM and XRD investigations show that these ternary sulfides are mutually soluble over the whole concentration range, forming a continuous series of solid solutions with the cubic (disordered, Fd3m) spinel structure. The composition variation of lattice parameter is discussed in correlation with the cation distribution determined by integrated intensity analysis.
Synthesis and Characterization of the Ternary Compound Ag2SnS3.
Authors: Belandria Edgar , Avila Rosario , Fernández Braulio J.
Published: March 2014

The structural determination, the thermal properties and the microscopic chemical analysis for the characterization of the ternary compound Ag2SnS3 are reported. The thermal differential analysis curves show a majority phase at about 640 °C, other thermal arrests are negligible. We consider that the melting point is at 640 °C; the melting point derived agrees quite well with an estimate obtained by extrapolation of previous reported values for other compounds from the same family. The chemical analysis from X-ray spectrometry by energy dispersion and scanning microanalysis gave averaged stoichiometry ratios near to the expected values. From the X-ray diffraction patterns it is deduced that the compound belongs to the monoclinic system and averaged lattice parameters of: a= 8.03 Å, b= 10.815 Å, c= 5.085 Å, β=108.28 °. These results agree reasonably well with JCPDS-ICDD file PDF-2 set (PDF: 39-140) assigned to Ag2SnS3.
Phase Transitions Induced by Hydrostatic Pressure in II-III2-VI4 Compounds
Authors: Ursaki Veacheslav V. , Burlakov Igor I. , Tiginyanu Ivan M. , Raptis Yannis S. , Anastassakis Evangelos , Anedda Alberto , Corpino Riccardo
Published: March 2014

II-III2-VI4 compounds with different crystal structures have been studied by Raman spectroscopy (RS) under hydrostatic pressure up to 30 GPa. The phase transition characteristics induced by hydrostatic pressure i.e. the path of the phase transformation, the pressure value of phase transition and the structure of the high pressure phase, were found to depend on the initial crystal lattice parameters such as parameters of cations, tetragonal distortion, bond length and bond ionicity. At high pressures a general property for most of these compounds is the phase transition to the Raman inactive rocksalt-type structure. Another common feature is related to the order-disorder phase transition in the cation sublattice occurring at low and intermediate pressures.
Control of Intrinsic Defects in CuInSe2 Films for Device Applications
Authors: Niki Shigeru , Suzuki Ryoichi , Ishibashi Syoji , Ohdaira Toshiyuki , Fons Paul J. , Yamada Akimasa , Oyanagi Hiroyuki , Wada Takahiro
Published: March 2014

Effects of Cu2-xSe and air-annealing on the growth and properties of CuInSe2 films have been investigated in terms of control of intrinsic defects. Enhanced two-dimensional growth and suppression of the Cu-Se divacancy formation (suppression of Se-vacancies) imply that under Cu-excess growth conditions a thin Cu-excess surface layer controls the growth of CuInSe2. The presence of the Cu-Se phase made possible to grow high-quality CuInSe2 epitaxial films at temperatures well below the melting point of any Cu-Se compound. Post-growth air-annealing of the CuInSe2 films showed a significant change in PL spectra and positron lifetime. A decrease in donor concentration and in positron lifetime indicated Se-vacancies were annihilated by oxygen. A decrease in twin density was simultaneously observed after the air-annealing; the control of Se-vacancy is a key issue to be addressed for improving the electrical and structural properties of CuInSe2 films.
Investigations on the Emergence of the Bandgap Anomaly between II-VI and their analogous I-III-VI2 Compounds on the Basis of the Zn2-2xCuxInxS2 Solid Solution System
Authors: Luck Ilka , Eyert Volker , Fieber-Erdmann Martin , Holub-Krappe Elisabeth , Scheer Roland
Published: March 2014

The Zn2-2xCuxInxS2 solid solution system has been investigated with respect to the emergence of the bandgap anomaly between II-VI and IB-Ill-VI2 compounds. Cation-S bond lengths and bandgap Eg have been determined as a function of the sample composition x. The bond lengths are found to be constant over the whole composition range in first approximation. Band structure calculations were applied to simulate the highly non-linear Eg(x). The appearance of Cu3d states at the top of the valence band was shown to cause this dependence in the course of intermixing. The cation-S bond lengths, however, determine the degree of the bandgap anomaly.
MOVPE Growth and Characterization of AlInAsSb/GaInAsSb multiple-quantum-well structure
Authors: Wu Jeng-Shian , Su Yan-Kuin , Chang Jia-Rong , Lin Chuing-Liang , Wang Hsin-Chuan , Jaw Duen-Hwa
Published: March 2014

We have grown unstrained Al0.66In0.33As0.85Sb0.15/Ga0.64In0.36As0.84Sb0.16 multiple-quantum-well structure on Fe-doped InP substrate by metalorganic vapor phase epitaxy. Double crystal X-ray diffraction, secondary ion mass spectrometry, and low-temperature photoluminescence were used to characterize the multiple-quantum-well structure.
Electrical Transport Mechanisms for Cu2GeSe3
Authors: Marcano G. , Bracho D. , Fernandez B.
Published: March 2014

In the present work results of transport properties of p-Cu2GeSe3 measured in the temperature range 80-300 K are reported. The analysis of hole concentration p allows to deduce a shallow energy level EA < 10 meV, which can be attributed to selenium atoms in interstitials sites or germanium vacancies. Considering the case of a current carriers by both electron and hole, the two band model is used to explain the temperature dependence of the Hall coefficient. The temperature dependence of the Hall mobility is analysed using termally activated, ionized impurity and acoustic deformation potential scattering processes.
Change of Optical Absorption by Application of Electric Field in Al-CuAlS2-Au Diode
Authors: NlshI Takao , Ishibashi Naohiro , Hayashi Naoyuki , Furuhashi Chihomi , Sato Katsuaki
Published: March 2014

Planer type Schottky-type metal-semiconductor diodes were prepared using CuAlS2 single crystal with evaporated metal contacts of Al and Au. It is found that optical absorption spectra can be changed by application of the electrical field to the Al-CuAlS2-Au diode. This change in the absorption is attributed to the change in the valence of the transition atom impurities due to the movement of Fermi level caused by electric field.
The Absorption by Free Carriers in n-type AgCuSe
Authors: Alekperova Sh. , Abdul-Zade N. N. , Akhmedov I. A. , Hajiyeva G. S.
Published: March 2014

In the ternary compound of n-type AgCuSe the absorption by free carriers in the range 2.5-25 µ was observed. There are two processes of absorption on the spectrogram α∼(hν). The coefficient of optical absorption by free carriers of a charge, corresponds to the classical Droode-Lowrens theory. The spectral dependence of electronic losses -Jm
ε
-1(ω), dielectric constants ε
1 and ε
2 have been estimated
Molecular Modes in Vibration Spectra of CaGa2S4
Authors: Iida Seishi , Mamedov Nazim , Aoki-Matsumoto Tamao , Yamamoto Nobuyuki , Yamazaki Makoto , Kato Ariyuki , Iwai Kazutoshi , Yasunaka Atsushi
Published: March 2014

Polarization dependence of the effective phonon density-of-states (DOS), and the depolarization ratio were investigated on amorphous CaGa2S4 by means of Raman spectroscopy at room temperature in ∥- and ⊥-configurations of the scattered light vector with respect to the scattering plane. It was found that the structures are more intense in the DOS derived from the Raman spectra in ∥-configuration. Position of the DOS maximum is moved away from its location at 360.7cm-1 in one phonon spectra by -20cm-1 and +20 cm-1 for ∥- and ⊥-configurations, respectively. The depolarization ratio exhibits a plateau and a clear-cut minimum at around 220cm-1 and 290cm-1, respectively The minimum comes to the intense 284.7cm-1 mode in the one-phonon spectra of CaGa2S4. The intense 360.7 cm-1 mode in the one-phonon spectra falls in the region of a drastic increase in depolarization ratio. Vibration modes in the orthorhombic CaGa2S4 can be classified as \varGammaν(Raman-active)=19A

g
+22B
3g
+222g
+21B

l
g
and \varGammaν(IR-active)=21B
3u
+21B
2u
+20B
1u
, respectively. However, the obtained experimental results point to the molecular character of some modes in the vibration spectra of CaGa2S4.
Structural Properties of CuIn3Se5 and Influence of Growth Conditions
Authors: Vidales Jose Luis Martín De , Charbonnier Helene , Díaz Raquel , Merino José Manuel , Rueda Fernando , León Máximo
Published: March 2014

Polycrystalline samples of CuIn3Se5 have been synthesized by reaction of stoichiometric mixture of the constituents in evacuated quartz ampoules, in a vertical furnace and in an horizontal one. The composition has been studied by EDAX and Atomic Absorption Spectroscopy. Important deviations in composition have been measured. The structure has been analyzed by X-ray Powder Diffraction, existing mainly single phase. Two spatial groups (SG) have been attributed to CuIn3Se5 by the Rietveld refinement: I 4̄2m (Stannitetype structure) and P 4̄2c (P-chalcopyrite). However, only the refinement in the SG P 4̄2c provides occupation numbers in the lattice that are coherent with the composition determined by EDAX. The discrepancy index, especially the goodness of fit, are smaller for the SG P 4̄2c.
Applications of InGaP “Insulator” for High-Breakdown and Low-Offset Voltage Heterostructure Bipolar Transistor
Authors: Cheng Shiou-Ying , Liu Wen-Chau , Chang Wen-Lung , Wang Wei-Chou , Pan Hsi-Jean , Chen Jing-Yuh , Thei Kong-Beng
Published: March 2014

In this work, a new InGaP/GaAs heterostructure transistor with a □-doped wide-gap collector structure has been fabricated successfully and demonstrated. A near-ideal breakdown characteristic and good transistor performance are obtained. These good characteristics are mainly due to the complete elimination of potential spike at emitter-base (base-collector) heterojunction and the employment of wide-gap InGaP material as collector layer. Consequently, the studied device shows a promise for high-speed and large input signal circuit applications.
Comments on Surface Studies and Surface Alteration of CuInSe2 Polycrystalline Thin Films
Authors: Cheng Yu-Han , Soo Yun-Liang , Huang Shiwen , Kioseoglou George , Kim Soon-Seok , Kao Yi-Han , Tseng Bae-Heng , Dann Hsueh-HsingHung , Hwang Huey-Liang
Published: March 2014

The effects of surface alteration on CuInSe2 thin films by KCN etching and subsequent (NH4)2Sx sulfur passivation as well as the formation of higher bandgap CuIn(S,Se)2 layer were investigated. After these chemical treatments, no oxygen uptake was observed and a significant number of sulfur atoms were found to diffuse into the Sb-incoporated CuInSe2 thin films to form a stable and higher bandgap CuIn(S,Se)2 layer. A model is proposed to explain how Sb atoms in CuInSe2 thin films can create a pathway for fast replacement of Se by S atoms. Also, Cu segregation from Cu-rich CuInSe2 thin films was directly verified for the first time by the experiments of angular dependence of x-ray fluorescence.
Millimeter Wave Reflection Measurement of Secondary Battery Substance LiNiO2
Authors: Ohta Hitoshi , Ueda Atsushi , Ono Shunsuke , Ikeuchi Youji , Nanba Takao , Hirano Atsushi , Kanno Ryouji
Published: March 2014

A superionic conductor LiNiO2 is a promising candidate for the positive electrode material of secondary Li ion battery. We have performed the reflection measurements of the nearly stoichiometric LiNiO2 in the millimeter wave region from 6 to 60 cm-1. The reflectivity has almost the constant value of 0.25 in the observed spectra region below 197 K. However, the reflectivity starts to rise at 300 K and changes its value significantly from about 0.25 to 0.8 in the low energy region below 10 cm-1 as the temperature is increased. This is the first observation of such a phenomena and the possible origin of this significant phenomena is discussed.
Modulation Frequency Dependence of the Photoacoustic Signal Intensities for Multinary Compound CdInGaS4 with a DC Electric Field
Authors: Toyoda Taro , Yamamuro Masamichi , Shen Qing
Published: March 2014

Photoacoustic (PA) spectroscopy is used to study the heat generated by nonradiative processes of CdInGaS4 with an external dc electric field transverse to the light path in order to study the correlation between carrier diffusion processes and nonradiative processes. Maxima are observed on PA spectra at 2.7 and 2.3 eV, the amplitude of which values are proportional to the square of the applied voltage. The peak at 2.7 eV shifted toward higher energy region when the modulation frequency increased. That at 2.3 eV did not shift. The PA signal intensity at 2.7 eV changes from f-1.0 to f-1.5 with the increase of dc electric field. On the contrary, that at 2.3 eV changes suddenly from f-1.5 to f-2.0 with the increase of dc electric field.
Cyclotron Resonance in CdMnTe/CdMgTe Diluted Magnetic 2 Dimensional Electron Gas at High Magnetic Fields
Authors: Imanaka Yasutaka , Takamasu Tadashi , Kido Giyuu , Karczewski Grzegorz , Wojtowicz Tomasz , Kossut Jacek
Published: March 2014

Far-infrared studies of the 2D electron gas were performed in CdMnTe/CdMgTe single quantum well at magnetic fields up to 14T. We observed an anomalous magnetic field dependence of the resonant width and the effective mass. These anomalies are special features in the 2D electron system of the diluted magnetic semiconductor.
Magnetic and Electrical Resistivity Studies of Pr1-xTiO3
Authors: Yoshii Kenji , Nakamura Akio , Abe Hideki
Published: March 2014

Magnetic, electrical and structural properties were investigated for the lanthanide deficient perovskite Pr1-x
TiO3 (0≤x≤0.1). The crystal structures were refined to the orthorhombic perovskite type (Pnma; GdFeO3 type). The end compound PrTiO3 exhibited a two-step magnetic transition at T
N=120 K and T'N∼60 K, as reported previously. The ordering temperatures and ordered magnetization below T
N decreased monotonically with increasing x. Finally, magnetic order almost disappeared at x=0.1. Corresponding to the disappearance in magnetic order, the system changes to a paramagnetic metal from a magnetic insulator between x=0.05 and 0.1. A resistivity-temperature (ρ-T) curve of x=0.05 exhibited a characteristic plateau at 100-170 K, while semiconductive behavior was observed above and below this region. In addition, magnetization-field (M-H) curves with x≤0.05 showed spin-flop and/or metamagnetic transitions around 1 5,000 Oe below T'N, and discontinuous jumps of magnetization at 2 K.
Effect of CuO Addition on the Magnetic and Microwave Properties of YIG
Authors: Song Young Yeal , Min Seong-Gi , Yu Seong-Cho , Kim Won-Tae , Kim Cheol-Gi
Published: March 2014

The structure, magnetic and microwave properties of polycrystalline YIG prepared by a conventional ceramic method with the addition of a small quantity of CuO as a sintering agent, were studied using X-ray diffractometry, magnetometry and ferromagnetic resonance experiments. Samples sintered with the sintering agent consisted of mainly a cubic YIG structure. Small amounts of Cu ferrite and grain boundary phase were formed in specimens with CuO content above 1.5 wt% during sintering. Saturation magnetization and Curie temperature of specimens were almost independent of the content of CuO. Sintering temperature for YIG can be reduced by about 100 K by adding 0.5-1.0 wt% CuO without any change in saturation magnetization and Curie temperature. The specimen prepared with CuO showed improved microwave property.
Structure and Magnetic Properties of Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12
Authors: Min Seong-Gi , Song Young Yeal , Yu Seong-Cho , Kim Won-Tae , Han Gee Pyeong , Paek Mun Chel
Published: March 2014

Polycrystalline Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12 (0 ≤ z ≤ 1.2) were prepared by the conventional ceramic method. The structure, magnetic and microwave properties were characterized by using scanning electron microscopy, X-ray diffraction (XRD), magnetization and ferromagnetic resonance experiments. The Ca-V-In-Si substituted polycrystalline specimens consist of a single cubic garnet phase. The lattice constant of the specimens decreased linerly from 12.457 Å to 12.348 Å and also the Curie temperature of the specimens decreased from 477 K to 329 K with increasing z from 0 to 1.2. Spontaneous magnetic moment per formula unit of Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12 samples, measured at 5 K decreased with increasing z. The ferromagnetic resonance linewidth of the samples showed a maximum at z=0.8, which may be explained by the relatively large anisotropy field contribution to ferromagnetic resonance linewidth.
Possibility of Charge Density Wave Transition in Tellurium Molybdenum Oxide TeMo5O16
Authors: Negishi Hiroshi , Negishi Saiko , Sasaki Minoru , Inoue Masasi , Takase Kouichi , Kubota Yoji , Takano Yoshiki , Sekizawa Kazuko
Published: March 2014

Electrical resistivity ρ, specific heat C, and magnetic susceptibility χ have been measured over 4.5 K - 300 K for the ternary molybdenum oxide TeMo5O16 grown by a chemical vapor transport method. The temperature dependence of ρ and C shows an anomalous behavior around 170 K and a remarkable peak at 179 K, respectively. Furthermore, the magnetic susceptibility, subtracted by a Curie-Weiss component from the observed values, shows a decrease below 180 K. These results suggest that in TeMo5O16 the charge density wave transition occurs at T
c=179 K due to a reduction of the Fermi surface.