We have studied annealing effects on X-ray irradiated single-walled carbon nanotubes (SWNTs) by confocal micro-Raman scattering spectroscopy. The SWNT films irradiated with 1254-eV X-ray were annealed in argon atmosphere with increasing the temperature from 200 degrees C to 500 degrees C by 100 degrees C. We found that a new Raman peak at similar to 1130 cm(-1) came into existence after the annealing at 300-400 degrees C. The 1130-cm(-1) peak was grown by the annealing exclusively in the X-ray irradiated sample. It is presumable that the 1130-cm(-1) peak is ascribed to carbon nanostructure formed by the annealing of the X-ray irradiated SWNT. Based on the comparison of spatial images of Raman intensity, the nanostructure responsible to the 1130-cm(-1) peak is likely formed by aggregation of interstitial carbon atoms diffused on SWNT surface. Because of the comparison of the probe wavelength dependence of the peak frequency with previous reports, we concluded that polyacetylene-like structures are formed by the post-irradiation annealing of SWNT. (C) 2016 Elsevier B.V. All rights reserved.

Nitrogen- and boron-doped graphene layers were grown on copper substrates by alcoholic chemical vapor deposition and characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrical transport measurements. The growth of high-quality monolayer graphene was confirmed by micro-Raman spectroscopy. The G and 2D peaks showed systematic frequency shift and broadening with the impurity concentration. The G peaks showed Fano-like asymmetric line shapes. These behaviors suggested the generation of free carriers by doping. XPS and electrical transport measurements also supported the systematic incorporation of impurities in graphene layers. (C) 2015 The Japan Society of Applied Physics

Diameter-dependent annealing effects of X-ray-induced defects in single-walled carbon nanotubes (SWNTs) were studied by Raman scattering spectroscopy. We found that Xray-induced defects were formed in thin SWNTs at higher density than that in thick SWNTs. The X-ray-induced defects, distant pairs of interstitials and vacancies (I-V), were eliminated by thermal annealing. The recovery temperature of the X-ray-induced defects in the thin SWNTs were higher than that of the thick ones, indicating the thermal stability of the defects in thinner SWNTs are higher. In order to simulate the annealing behaviours of the X-ray-induced defects in SWNTs with diameters of similar to 0.9 and similar to 1.4 nm, we suggested the competitive reactions of diffusion of interstitials, formation of close I-V pairs and their recombination. The simulated results showed that the reaction-rate constant of elimination of close I-V pairs is dependent on tube diameter, which is presumably derived from nano-structure effects of SWNTs.

We have grown high-quality nanographene layers by alcoholic chemical vapor deposition on insulated MgO substrates without catalysts. Typical Raman spectra showed the formation of nanographene layers consisting mainly of sp(2) bonds. Their grain size depended on the flow rate of the carbon source. Planar and triangular nanographenes were formed on MgO(100) and (111) substrates, respectively. The results suggested that the lattice orientation of the MgO substrate determined the morphology of nanographenes. (C) 2014 The Japan Society of Applied Physics

The resonant Raman scattering spectra of X-ray-irradiated single-walled carbon nanotubes (SWNTs) have been measured at 532, 561, 568, 647, and 660 nm. We found that X-ray irradiation induced a marked change in the radial breathing mode (RBM). In order to analyze the X-ray-induced change in the RBM spectra, we drew a map of the RBM peaks showing the relation between the peak position and the probe beam energy by interpolating the spectra measured at the probe wavelengths. We found that shifting the transition energy by 0.05 eV reproduced the RBM spectra of the irradiated SWNTs. This model well explains the results of our optical absorption measurements and previous reports on theoretical and scanning tunneling microscopy studies by other groups. On the basis of these results, we suggest that X-ray irradiation is one of the practical methods of controlling the electronic properties of SWNTs. (C) 2014 The Japan Society of Applied Physics

The formation of X-ray-induced defects changes the spectral shape of the radial breathing mode (RBM) and defect-induced mode (D band) in the Raman spectra of single-walled carbon nanotubes (SWNTs). X-ray-induced defects have been found to be annealed by thermal treatment, indicating that they are Frenkel pairs (vacancy and interstitial pairs). We found that the spectral shape of RBM is not entirely recovered after postirradiation annealing. The temperatures for the complete annealing of X-ray-induced defects were within the range of 200-600 degrees C depending on the tube geometry. From these results, we suggest that the stability of X-ray-induced defects depends on the tube geometry and that the combination of X-ray irradiation and post-irradiation annealing causes a chirality change in SWNTs. (C) 2014 The Japan Society of Applied Physics

X-ray induced defects in single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs) were characterized by Raman scattering spectroscopy. Frenkel defects, interstitial-vacancy pairs, were revealed to form in both SWCNTs and DWCNTs after X-ray irradiation because these defects were entirely healed by thermal annealing. In order to clarify the structure of the X-ray induced defect in SWCNT and DWCNT, isochronal-annealing experiments were performed on the irradiated samples and the activation energy for defect healing was estimated. The intensity of D band (defect induced band) on Raman spectra was used as a measure of the density of X-ray induced defects. The experimental results were in good agreement with the simulated values using second order reaction model, which indicated that the defect healing was determined by the migration energy of interstitials on the carbon layer. We also found that the activation energy for defect healing of SWCNT and DWCNT were around 0.5 eV and 0.32 eV, respectively. The X-ray induced defects in SWCNTs were more stable than those in DWCNTs. Compared these estimated activation energies to previous theoretical reports, we concluded that bridge and/or dumbbell interstitials are formed in both SWCNT and DWCNT by X-ray irradiation. (C) 2013 AIP Publishing LLC.

We have studied double-walled carbon nanotube (DWNT) irradiated by soft X-ray by Raman scattering spectroscopy and the spectral characteristics are compared to single-walled carbon nanotube (SWNT) irradiated under the same condition. We proved that DWNT is more stable for the X-ray induced defect formation than SWNT. Moreover, we found that the outer tube of DWNT was more sensitive on X-ray irradiation than the inner tube. The defect was recovered by annealing in Ar at lower temperature than that of SWNT. Based on these results, we inferred that X-ray irradiation leads to formation of interstitial-vacancy pairs, Frenkel defects, in carbon nanotube. The interstitial-vacancy separation on the inner tube of DWNT is conceivably shorter than that of the outer tube. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

We prepared Al-deopd ZnO (AZO) films by reactive DC sputtering method using metallic target at room temperature. All the tested AZO films (0 < [Al] < 8.9%) with the transmittance above 85% in visible region were successfully grown on quartz substrate. All the AZO films have wurtzite structure with no impurity phase. The AZO films with [Al] < 2.9% have the preferential orientation in c-axis direction, and the orientation became indistinct as increasing in Al content. In the optical measurement, the absorption edge was shifted from 3.30 to 3.66 eV due to Burstein-Moss effect, and the electron densities were roughly estimated at 2.5 x 10(19) to 1.5 x 10(21) cm(-3), respectively. On the other hand, the high transmittance in infrared region suggested low electron mobility. Since this gives rise to the high electric resistivity, the further improvements and optimization of the growth conditions are required for the realization of AZO based transparent conductive. (C) 2013 The Japan Society of Applied Physics

Few-layer epitaxial graphenes grown on vicinal 6H-SiC (0001) were characterized by confocal Raman imaging. In the beginning of the growth, the surface of SiC substrate was covered with monolayer graphene. Next, few-layer graphenes started to grow toward directions perpendicular to [11-20] of the SiC substrate. The shift in the G-peak was not straightforward with the increase in number of graphene layers. This result can be interpreted that the in-plane compressive stress from the substrate depends on the domain size of graphene. The 2D-peak frequency shifted to higher frequency side due to strong compressive strain from the substrate with increasing of the growth times. (C) 2012 Elsevier B.V. All rights reserved.

Improvement of hexagonal InN film quality grown by metal-organic vapor phase epitaxy has been challenged by changing the ambient-gas pressure in 87320?kPa (similar to 13?atm.). The growth temperature and the source-gas supply ratio, the so-called V/III ratio, were optimized at each ambient-gas pressure to improve the film quality. Raman scattering characterization of InN phonon spectra showed great improvement in crystalline quality by increasing the pressure from 87 to 213?kPa, and furthermore to 320?kPa. This tendency was also confirmed by a structural characterization by X-ray diffraction.

An longitudinal-optic-phonon-plasmon coupled mode (LOPC) has been clearly observed by Raman scattering in n-type Al(x)Ga(1-x)N films with x similar to 0.67 and different carrier densities n - 1 x 10(17)-9 x 10(17) cm(-3). The A(1)-LO-phonon mode showed a systematic frequency shift and broadening with increasing n. This is a characteristic behavior of LOPC as previously observed in n-type binary semiconductors. A theoretical line-shape fitting analysis was conducted for the LOPC profile using n and plasmon-damping rate as adjustable parameter. Assuming m*/m(0)-0.28 for the longitudinal effective mass of electron, the analysis well reproduced carrier density and mobility deduced by Hall measurement. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3670338]

Raman scattering spectra were observed for a series of AlxGa1-xN film samples to evaluate the Al molar fraction x from phonon frequencies using published data for calibration. Comparison with a precise quantitative measurement of x by electron-probe microanalysis (EPMA) showed systematic deviations from the Raman analysis up to about 6 similar to 15%. The molar fraction was also deduced by x ray diffraction (XRD), assuming elastic deformation of the lattice and Vegard's law for the lattice constant. The XRD analysis agreed well with that of EPMA to suggest that the Raman analysis is sensitively affected by lattice distortion due to residual stress. (C) 2011 American Institute of Physics. [doi:10.1063/1.3610525]

Several PbZr1-xTixO3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr1-xTixO3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions. Copyright (C) 2010 John Wiley & Sons, Ltd.

ZnO thin films were prepared by sol-gel spin-coating method with thermal annealing in O-2 atmosphere. The annealing temperature was varied in the range of 150 degrees C to 550 degrees C. ZnO thin films with wurtzite structure were synthesized in all the samples. The sample annealed at low temperature showed the smooth surface morphology, and it gradually became rough with increase in annealing temperature. Finally, the sample had porous structure due to the aggregation of ZnO grain. As this result, the transmittance decreased in the visible region by annealing at high temperature. Furthermore, Raman analysis indicated that the lattice defects such as O vacancy could be suppressed by annealing at low temperature. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ZnO/Zn0.85Mg0.15O heterostructure thin films were prepared by sol-gel spin-coating method on sapphire (0001) substrate with different thickness of ZnO layer. X-ray diffraction patterns showed that all the samples were preferentially oriented in [0001] direction with no phase separation. Optical transmission spectra showed the clear band-edge absorption of ZnO and Zn0.85Mg0.15O layer, and the thickness of each layer was roughly estimated. Also, two UV emission peaks originated from each layer at 3.2 eV and 3.55 eV were observed in photoluminescence measurement. And, the emission peak at 3.2 eV of ZnO layer shifted to higher energy side with decrease in the thickness of ZnO layer. This result indicates that Mg ions slightly diffused to the ZnO layer in several nanometers of ZnO/Zn0.85Mg0.15O interface by thermal treatment in growth process. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Few layer epitaxial graphenes (1.8-3.0 layers) grown on vicinal 6H-SiC (0001) were characterized by deep ultraviolet Raman spectroscopy. Shallow penetration depth of the probe laser enabled us to observe G-peak of graphene without subtraction of the SiC substrate signal from observed spectra. The G-peak was greatly shifted to higher frequency compared to that of graphite due to in-plane compressive stress deriving from the substrate. The frequency shift decreased with the number of graphene layers because of stress relaxation from layer to layer. Our experiment suggests that the stress is completely relaxed within five to six graphene layers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3466150]

Mg-doped AlxGa1-xN layers were characterized by micro- scopic Raman scattering to study the activation process of dopant by thermal annealing and behavior of H impurities. Two types of samples, a monolayer and a device-like (laser diode) structure, were prepared for this study. Local vibrational modes (LVMs) related to H and Mg were clearly observed in the monolayer sample. The LVMs evidenced activation of Mg in Ga site with the release of H. Electronic Raman signal due to free hole was also observed in the annealed sample. In the device-like structure sample, the Mg-doped AlxGa1-xN clading layer showed similar results, though the signal was weaker than the monolayer sample. Interactions with neighboring layers may have influenced the layer properties. Composition of Al in the AlxGa1-xN layer was also determined from phonon frequencies in both samples, and the result well agreed with that of X-ray diffraction analysis. © 2010 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

We report microscopic Raman scattering studies of epitaxial graphene grown on SiC substrates using a deep-ultraviolet (UV) laser excitation at 266 nm to elucidate the interaction between the graphene layer and the substrate. The samples were grown on the Si-face of vicinal 6H-SiC (0001) substrates by sublimation of Si from SiC. The G band of the epitaxial graphene layer was clearly observed without any data manipulation. Increasing the number of graphene layers, the peak frequency of the G-band decreases linearly, while the peak width and the intensity increase. The G-band frequency of the graphene layers on SiC is higher than those of exfoliated graphene, which has been ascribed to compression from the substrate.

BiFeO3thin films were grown by chemical solution deposition using precursors with different elemental ratios, Bi/Fe = 1.1/1.0, 1.0/1.0 and 1.0/1.1. All the samples consisted of two easily distinguishable components of crystalline and amorphous phases. We have found that the electric properties of BiFeO3thin films are closely connected to the crystallinity of the films.

Thin films of chiral porphyrin J-aggregates have been studied by vibrationally and electronically doubly resonant sum frequency generation (SFG) spectroscopy. It was revealed that the chiral supramolecular structures of porphyrin aggregates in solutions were retained in the thin film samples, and their chirality was determined by using chiral vibrational SFG spectroscopy. Electronic resonance profiles of some vibrational bands in achiral and chiral SFG were different from each other, and both were distinct from electronic absorption spectra. To account for these peculiar profiles, we have proposed interference effects of Raman tensor components in achiral and chiral SFG susceptibilities, which is analogous to that of resonance Raman scattering.

Zn(1-x)Co(x)O samples were prepared by a standard solid- state reaction method. Zn(1-x)Co(x)O crystals in the wurtzite structure were obtained with a Co composition of up to 22.1%. The a- and c-axis lengths increased and decreased, respectively, with an increase in Co composition. Raman spectra showed systematic broadening of the E(2) (high) phonon mode associated with the increase in Co composition, and electronic transitions of Co in the oxygen tetrahedron were observed in optical absorption measurement. These results indicated systematic substitution of Co into the Zn sites. Furthermore, an additional broad absorption band at 2.4-3.3 eV corresponding to the charge transfer (CT) process (Co(2+) -> Co(1+)) was also observed. The Raman spectra showed strong enhancement of the LO phonon due to a resonant Raman process induced with the coupling of the LO phonon and a photo-excited carriers mediated CT gap. These results suggest the possibility of carrier-induced ferromagnetism based on double exchange interaction in Zn(1-x)Co(x)O by visible light irradiation.

Ho3Fe5O12 crystallizes in a body-centered cubic lattice and shows no ferroelectricity because of its highly symmetric (centrosymmetric) crystal structure. However, in heteroepitaxially grown thin films, Ho3Fe5O12 may exhibit ferroelectricity because of lattice strains induced by the substrate. In this work, heteroepitaxial films of Ho3Fe5O12 were grown with different thicknesses of 50-160 nm and studied by x-ray diffraction and Raman scattering. The results were compared with those of bulk polycrystals to characterize residual strains. At room temperature, Raman spectra of films revealed a phonon frequency shift from those of bulk samples, showing lattice distortion. There was a difference in the lattice distortion scheme between the thinner and thicker films. Results of x-ray diffraction were well correlated with the Raman data. Raman measurements at 300-800 K showed the existence of lattice strain up to similar to 650 K. This suggests a remanent-polarization character of Ho3Fe5O12 films up to this temperature. Closeness between the magnetic ordering temperature T-N = 567 K and T-C similar to 650 K may bring us the ideal multiferroic material with an enhanced magnetoelectric effect at room temperature.

Hexagonal YbMnO3 bulk polycrystals were prepared and studied by Raman scattering in the temperature range of 15-300 K. A total of 15 phonon modes of A(1), E-1 and E-2 type were identified. Some E-2 phonon modes showed anomalous temperature variations in frequency at T-N similar to 80 K, suggesting a coupling between the spin and phonon systems below T-N. As another evidence of spin-phonon coupling, softening of an A(1)-phonon mode for the O-Mn vibration was observed at similar to T-N. Substitution of Mn by Al suggests this view.

TiO2 nanocrystals were synthesized by a hydrolysis method combined with a thermal treatment. TiO2 nanocrystals with rutile and anatase structure were selectively synthesized by controlling the pH level in the precursor solution, and the crystallite size was controlled by changing the reaction temperature. Moreover, Co-doped TiO2 nanocrystals with rutile structure were also synthesized by means of the addition of Co to the precursor solution. Secondary phases such as Co precipitates and Co oxide were not present in the sample tested, with [Co] < 10 mol%. With an increase in the Co doping level, the Eg-phonon signal at 447 cm(-1) was broadened and shifted to a lower frequency, indicating the incorporation of Co into the rutile TiO2 host lattice and lattice expansion. Optical absorption spectra showed that the absorption edge at similar to 3.0 eV corresponded to the band gap of rutile TiO2 and shifted to the lower energy side upon Co doping. These results indicated the possibility of band gap engineering of rutile TiO2 via Co doping. On the other hand, the charge transfer gap between O 2p and Co 3d orbitals was also observed for samples with Co, suggesting the possibility of photo- induced magnetism in rutile TiO2 nanocrystals, obtained by visible light irradiation.

ZnO nanocrystals doped with Co were synthesized by co-precipitation method combined with post-thermal treatment. The synthesized crystals formed high-quality wurtzite ZnO crystal lattice with the dimension about 10 nm, substituting Co ions into Zn sites in the composition range of [Co] < 3.0%. The position of Co2+/1+ charge transfer (CT) level composed by O 2p and Co 3d orbitals was observed at 3.0 eV by optical absorption measurements. Raman spectra showed the enhancement of LO phonon due to resonant Raman effect caused by photo-excitation of free carriers mediated the CT level. And, Photoluminescence spectra showed UV emission at similar to 3.3 eV suppressed and shifted to higher energy side with increase in Co doping level, indicating increase in nonradiative recombination centers and the possibility of band-gap engineering in Zn1-xCoxO nanocrystals, respectively. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We have presented a combined method of microscopic measurements between Raman scattering and polarizing optical microscope to characterize inhomogeneous residual stress distributions around dislocations in 4H- and 6H-SiC wafers. First, stressed portions were found in wafers by an optical polarizing microscope under a crossed Nicole arrangement. Then, the portions were examined by Raman-imaging technique for lateral variations of phonon spectra. The residual stresses were quantified from the phonon-peak frequency shift using a known frequency-shift rate for 6H-SiC. Characterization to the depth direction was also conducted by surface etching with molten KOH. The stresses typically amounted to the order of 100 MPa. In a 4H-SiC homoepitaxial wafer sample, we observed threading dislocations transferred from the substrate to the epitaxial layer, and found that larger stress fields existed in the epitaxial layer than the substrate. We also observed stress distributions around compressively stressed sub-grain boundaries.

We have compared catalytic activity of Co and Fe in a growth process of single-walled carbon nanotube (SWNT) by chemical vapor deposition using ethanol as a carbon source and SiO2 as a catalyst-supporting material. Changes of the catalyst precursors (Co- and Fe acetate) in the growth process were carefully observed at three different stages: (i) after oxidation in air at 400 degrees C but before heating to the growth temperature (800 degrees C), (ii) after heating to the growth temperature in flowing Ar and H-2 but before starting the nanotube growth and (iii) after the growth process is over. During the growth of SWNT, the Co catalyst took the form of beta-Co, resulting in a high yield growth. On the contrary, the Fe catalyst formed a silicate, Fe2SiO4, showing a poor catalytic ability. Our result shows that chemical reactions between the catalyst precursors and their supporting materials sensitively affect the catalytic ability. (c) 2008 Elsevier B. V. All rights reserved.

Double-walled carbon nanotubes (DWCNTs) with a purity higher than 99% were synthesized by chemical vapor deposition, and their Raman spectra were observed at different excitation wavelengths lambda(ex). The spectra had a unique feature compared with single-walled carbon nanotubes (SWCNTs): the G-band shape was distinctly different from that of SWCNTs and showed a clear lambda(ex) dependence. The pure DWCNT samples showed complex radial breathing modes (RBM) spectra. The mode peaks were unambiguously classified into those for the inner and outer tubes by applying a simple analytic model considering the interwall interaction. After isolation treatment of the pure bundled samples, we observed RBM signals of DWCNTs having an identical inner tube with different outer tubes. The peculiar behavior of the G-band shape was interpreted by resonance enhancement of the outer tube. (C) 2008 American Institute of Physics.

Single-walled carbon nanotubes (SWNTs) grown on Si(100) were irradiated with X-ray having the spectrum with a peak at 277 eV. We measured Raman scattering spectra of the samples before and after the irradiation at various fluences and found that the relative intensity of the defect-related band, D band, to the band of the tangential shear modes of the carbon atoms in a graphene sheet, G band, was enhanced by the irradiation. The fluence dependence of this intensity ratio, DIG, took a peak around the fluence of 7 x 10(13) cm(-2). Further X-ray irradiation reduced the DIG to around half of the maximum. Detail inspection of the low frequency Raman spectra revealed that the radial breathing modes of the SWNTs were modified by the irradiation. The result suggests that the X-ray irradiation gives rise to not only defect formation but also modification of the SWNT structure. (c) 2008 Elsevier B.V. All rights reserved.

Single-walled carbon nanotubes (SWNTs) were grown by catalytic chemical vapor deposition on SiO2 substrates. By thinning the substrate before growth, the morphologies of the SWNTs and their seed catalyst particles were simultaneously observed in the as-grown state by plan-view transmission electron microscopy (TEM). Analysis over a wide area of the substrate showed that the diameters of the SWNTs d and those of the catalyst particles D had different distributions. The catalytic activity was size-dependent: fine particles (D less than or similar to 4 nm) yielded the same diameter SWNTs (d similar to D), and intermediate sizes (similar to 4 < D less than or similar to 6 nm) yielded finer tubes (d < D), while larger particles (D greater than or similar to 6 nm) had no catalytic activity. We also found that the small catalyst particles with D of less than 5 nm that appeared during the growth process by chemical reactions with the carbon source mainly contributed to the growth of SWNTs.

Nanometre-sized ZnO crystals doped with Co were synthesized by a co-precipitation method combined with a thermal treatment. By changing the reaction temperature, we can control the crystallite size from roughly 10 nm particles to 20 nm x 200 nm nm rods grown along the hexagonal c-direction. X-ray diffraction and Raman scattering showed growth of high-quality wurtzite ZnO crystals incorporating Co systematically in the ZnO host lattice in the tested range of [ Co] < 3.0 mol%. Electronic transitions of Co in the oxygen tetrahedron were also observed in optical absorption, giving supporting evidence for systematic substitution of Co into the Zn site.

We have grown BiFeO3 bulk single crystals by a flux method and characterized the phonon spectra in detail by Raman scattering in the temperature range 4-1100 K. All the 13 Raman-active phonon modes predicted by group theory, 4A(1) + 9E, were observed at low temperature and successfully assigned by a polarized Raman measurement. Moreover, drastic spectral changes in the Raman spectra were observed at temperatures 600-700 K and 1000-1100 K. These features are discussed from the viewpoint of phonon coupling with the magnetic ordering and the structural phase transition, respectively.

YMnO3 is a multiferroic material in which ferroelectric and antiferromagnetic ordering can coexist. We have studied a YMnO3 bulk crystal in detail by Raman scattering in a wide temperature range of 15-1200 K, with comparison to a previous experiment at room temperature and a theoretical prediction for Raman- active phonon modes. In the low- temperature ferroelectric phase, the observed phonon spectra showed anomalous temperature variation at the Neel temperature, T-N similar to 80 K, suggesting a coupling between the spin and phonon systems below T-N. Furthermore, spectra for the high- temperature paraelectric phase, reported here for the first time, showed a sudden change at the Curie temperature T-C > 900 K, suggesting an abrupt structural phase change from the ferroelectric to the paraelectric phase.

We have grown single walled carbon nanotubes (SWNTs) by catalytic chemical vapor deposition and optically characterized them after dispersing in an aqueous solution with centrifugal purification. Defect-induced band observed in Raman spectra drastically decreased in intensity after the centrifugal process, showing a good separation of by-products such as defective nanotubes and amorphous carbons. Radial breathing modes of the dispersed SWNTs showed frequency up-shift by 2-3 cm(-1) from those of bundled SWNTs as an evidence of isolation. The effect of inter-tube interaction on the electronic transition energy was traced by time-resolved PL measurement. The effect of aggregation process was much smaller than that estimated previously for bundling. It suggests that the aggregated samples are still well dispersed like those in aqueous solution. (c) 2007 Elsevier B.V All rights reserved.

Almost 100% pure double-walled carbon nanotube (DWNT) was successfully synthesized by optimizing the catalyst composition of Co/Fe/ Mo in a chemical vapor deposition (CVD) growth system with a post-growth purification process. The Raman scattering spectra of the product showed characteristic features of DWNT. The radial breathing modes were analyzed well by a simple analytic model considering the interwall interaction. (c) 2006 Elsevier B.V All rights reserved.

Raman scattering spectra of bulk BiFeO3 single crystals have been measured in the temperature range of 4-1200 K. All Raman active phonon modes predicted by the group theory were observed at 4 K and assigned by a polarized measurement. Moreover, we have found drastic changes of Raman spectra at 600-700 and 1000-1100 K. These changes were discussed in combination with magnetic ordering and structural phase transition. (c) 2006 Elsevier B.V. All rights reserved.

YbMnO3 epitaxial thin films were investigated by Raman scattering in the temperature range of 15-300K. We successfully observed some phonon modes (5A(1)+6E(2)) at 15K with mode assignment based on polarized Raman study. Furthermore, an E-2 mode at 253 cm(-1) which affected Mn-O-Mn bond angles showed anomalous temperature variation in frequency at temperature below similar to 80K. It suggested a spin-phonon coupling that occurred below T-N.

Blue-violet GaN-based laser diodes have been characterized by microscopic Raman scattering to obtain temperature distributions in the chip during operation. The local temperature increased steeply in the vicinity of the light-emitting layer at distance < similar to 20 pun. At injection current I = 120 mA with laser output of 150 mW, the local temperature at the light emitting layer was about 50 degrees C higher than that of the chip mount, 25 degrees C.

Single-walled carbon nanotubes (SWCNTs)were grown on Si/SiO2 substrates by catalytic chemical vapor deposition using ethanol as a carbon source. We found that a bimetallic catalyst, Fe-Co, worked efficiently in growing SWCNTs in contrast to Fe or Co catalyst only. The underlying mechanism was carefully studied by observing the catalyst-substrate interactions by transmission electron microscopy. It is shown that preferential diffusion of Fe into a SiO2 layer occurs in the bimetallic case, which suppresses aggregation of nanometer-sized Co particles that play key roles in growing SWCNTs. (c) 2006 American Institute of Physics.

We investigated the impact of the growth morphology of single-walled carbon nanotubes (SWNTs) on gas sensing performance. An SWNT film was directly synthesized on alumina substrate by thermal chemical vapour deposition. Different morphologies of the SWNTs in terms of density, diameter distribution and orientation were obtained by varying the growth temperature. Vertically aligned SWNTs with a high density were grown at 750°C, while horizontally lying SWNT networks with a low density were grown in the temperature range 800-950°C. The sensor response of the resultant SWNTs to NO2 was characterized at room temperature. It was found that the density of SWNTs strongly dominates sensor performance
the SWNT networks with the lowest density exhibited the highest sensor sensitivity. This was evidenced by characterization of density-controlled SWNTs synthesized using different thicknesses of an Fe/Al multilayer catalyst. The high sensor sensitivity for low-density SWNT networks is likely to be attributed to suppression of the formation of SWNT bundles and reduction of narrow-band-gap conduction paths, resulting in the enhancement of the adsorption probability and chemical gating efficiency of gas molecules on SWNTs. © IOP Publishing Ltd.

We demonstrated the direct growth of single-walled carbon nanotubes (SWNTs) on a W tip by Fe/Al catalyst-assisted chemical vapor deposition (CVD). A high-purity network of SWNTs with diameters of 0.9-3.7 nm was grown on the W tip. Under optimum CVD conditions, the growth of isolated SWNTs protruding from the W tip apex was achieved. We found that the circumference of the tip region affected the morphology of the resultant SWNTs. The direct growth method provides a potential application of SWNTs to a novel tip for scanning tunnelling microscopy (STM). © 2006 The Japan Society of Applied Physics.

Precise control of fabrication processing is a key point for future integration technology of Si devices. Reliable characterization of Si wafers at each fabrication process is indispensable. Raman scattering has high-potential as a technique for non-contact and nondestructive characterization which yields valuable information on Si-based materials. Here, a patterned Si wafer for a modern electronic device is characterized by Raman microprobe to study the effect of different processes on residual stress, as well as other physical aspects. © 2006 IEEE.

We have performed Raman scattering experiments on high quality In0.2Ga0.8N/GaN superlattices(SLs). The A(1) LO phonon mode from the In0.2Ga0.8N layer was observed in the Mg doped SL. This was attributable to manifestation of a resonance enhancement via acceptor levels formed by magnesium doping. The peak frequency of the A, LO mode shifted to high frequency side with the excitation energy. The frequency shift suggested that the composition of indium was fluctuated along the growth direction in the InGaN layer. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We explored structural and electrical properties of single-walled carbon nanotube (SWNT) networks directly grown on alumina substrates. The netlike SWNTs were uniformly grown on the substrate at a high quality. From the Raman spectroscopy analysis it was found that the as-grown SWNT networks were a mixture of metallic and semiconducting SWNTs, while the SWNT networks after their electrical breakdown exhibited a predominance of the semiconducting property. The direct growth method and subsequent electrical breakdown facilitated high-throughput production of practical ultrasensitive sensors for pollutant gases with a high sensitivity, which was demonstrated by NO 2 detection. © 2005 The Japan Society of Applied Physics.

We explored the growth of single-walled carbon nanotubes (SWNTs) from nanoparticle array made of an Fe/Al multilayer catalyst by thermal chemical vapor deposition. Fe nanoparticles with a high number density and a narrow size distribution (1-5 nm) were efficiently formed by annealing the Fe/Al thin layer, resulting in the high-yield growth of SWNTs. Moreover, it was found that isolated SWNTs are rooted from patterned Fe/Al islands. The SWNTs bridged between electrodes exhibited semiconducting and metallic properties.

ZnO layers doped simultaneously with Ga and N (codoping), and magnetic elements (V, Co) were characterized by Raman scattering to study their structural stability. Five impurity modes were observed in range 200-900 cm(-1) in the doped samples, and showed characteristic variation with the doping level. It is shown that these modes can be used as a good measure of lattice defects induced by doping. The Raman spectra showed that the magnetic elements were incorporated up to 5 mol% without serious deterioration in crystallinity.

Structural properties of GaN layers doped with magnetic impurities (Mn, Cr) were investigated by Raman scattering. In the case of Mn-doping, an impurity mode was observed at around 585 cm(-1) with concentrations of Mn up to 1-2%. This mode was assigned to a local vibrational mode of Mn substituting the Ga site, and interpreted as spectral evidence of a uniform solid solution in the samples. For Cr-doping, good crystalline quality was also confirmed up to [Cr] = 3-5%. Cr is more miscible in GaN than Mn. Resonance enhancement of LO phonon signal was observed in GaCrN layers when excited by a deep UV laser at 266 nm (4.7 eV). This indicates generation of photo-carriers.

Single-walled carbon nanotubes (SWNTs) were grown on both the Si- and C-faces of a 6H-SiC substrate by catalytic chemical vapor deposition (CCVD) using ethanol as the carbon source. Raman scattering measurements showed that uniform SWNTs grew on the Si face. Furthermore, SWNTs grown on the Si face showed larger intensity ratio of G-band to D-band (G/D ratio) than those grown on the C face. These results mean that growth of high quality SWNTs is promoted on the Si face in SiC substrates. This is probably attributed to the more reactive nature of the C face with the catalyst compared to the Si face. (C) 2004 Elsevier B.V. All rights reserved.

Ohmic contact formation on a p-GaN layer with a specific contact resistance of rho(c) = 5 x 10(-4) Omegacm(2) has been achieved using a Pd/Mo electrode without the use of an alloying process. rho(c) was reduced to 2 x 10(-4) Omegacm(2) by annealing in vacuum at 500degreesC. The Pd/Mo electrode showed much improved ohmic-contact characteristics than the Ni/Mo electrode. Characterization by micro-Raman scattering revealed that the hole concentration increased in the p-GaN layer just under the Pd/Mo electrode with increasing annealing temperature. This cannot be explained by the removal of hydrogen. A decrease in the density of hole traps and an increase in the density of active acceptors, such as Ga vacancies, are considered to be the most significant contributing factors.

C-13 NMR spectra at room temperature and the temperature dependences of H-1 T-1 in the solid state were measured in [Ni1-xPdxX(chxn)(2)]X-2 (X: Cl, Br; chxn: 1R,2R-cyclohexanedianline; 0.0 less than or equal to x less than or equal to 1.0), where anti ferromagnetically coupled paramagnetic -X-Ni3+-X-Ni3+-X- chains were formed at x = 0.00, while the mixed-valence -X-Pd2+-X-Pd4+-X- state was made at x = 1.00. C-13 signals at alpha-carbons in chxn coordinating to Pd atoms showed a doublet assignable to Pd2+ and Pd-4+ in x = 1.00, while, with a slight decrease of x from 1.00, a clear broadening and a shift to low-field of signals, indicating conversion into the averaged Pd3+ state, were observed. This can be explained by the fluctuation of the Pd valency caused by neighboring paramagnetic Ni3+ sites introduced in small amounts in the 1-D chain. The x dependences of the chemical shifts of beta- and gamma-carbons are also attributable to the effect from a partial mixing of the paramagnetic Pd3+ sites. The values of H-1 T-1 and its temperature dependence observed in the ranges of 100-300 K and x less than or equal to 0.13 for [Ni1-xPdxBr(chxn)(2)]Br-2 could be explained by a model of strong exchange interactions between Ni3+ and Pd3+ as well as Ni3+ sites. Gradual changes in the T-1 value and slope with increasing x from 0.00 to 0.93 are attributabte to the variation of the exchange interaction value, which depends upon the number of Ni-Ni pairs.

Spectroscopic observations of high-quality wurtzite InN have shown that oxygen is easily incorporated in the crystal by thermal treatments in the air. Incorporation of oxygen may play a key role in determining the apparent properties of InN including the bandgap and the lattice constant. It is shown that Raman scattering is a sensitive tool to probe the oxygen incorporation process and associated deterioration in crystallinity. (C) 2004 American Institute of Physics.

LO-phonon-plasmon coupled modes in n-type 15R-SiC bulk crystals with free carrier concentration of n = 10(16) similar to 10(18) cm(-3) were observed by Raman scattering. The axial-type mode for which the plasma oscillation and atomic displacements occur along the c-axis, and the planar-type mode for which these oscillations occur in the c- plane, were separately observed. A spectral line-shape analysis was done using three adjustable parameters for free carrier concentration, plasmon damping rate and phonon damping rate. Carrier mobilities parallel and perpendicular to the c-axis (mu(perpendicular to) and mu(ll), respectively) were evaluated from the results, showing a weak anisotropy mu(perpendicular to)/mu(ll) = 1.8 +/- 0.3. This result is in agreement with a previous Hall measurement, and is qualitatively similar to the case of n-type 6H-SiC.

We suggest on approach including lattice dynamics calculations and Raman measurements of individual phonon modes in hexagonal GaN/AlN and GaN/AlGaN superlattices, which can prove to be a valuable tool in quantitative characterization of these nanostructures. © 2003 WILEY-VCH Verlag GmbH &amp
Co. KGaA.

We suggest on approach including lattice dynamics calculations and Raman measurements of individual phonon modes in hexagonal GaN/AlN and GaN/AlGaN superlattices, which can prove to be a valuable tool in quantitative characterization of these nanostructures. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Intrinsic localized vibrational modes in a halogen-bridged Pt complex were studied by Raman spectroscopy. We compared the peak frequency of the overtone of Pt-Cl stretch vibration between that excited by an Ar+ and that by a near infrared (NIR) lasers. The decrease in the overtone peak frequency of the NIR excitation were larger than that of the visible excitation. We interpreted that the charge transfer led to weaken the bond strength and that the anharmonicity of the system became weak. (C) 2001 Elsevier Science B.V. All rights reserved.

In femtosecond pump-probe experiments on antimony, we have detected coherent oscillations that exhibit phase-dependent noise. The Fourier transforms of the coherent amplitude and its variance show that the two fluctuate at different frequencies, suggesting that the phonons created in the pump-probe experiment are of a squeezed nature. (C) 2000 American Institute of Physics. [S0003-6951(00)02608-5].

We have investigated the temperature dependence of the optical reflectivity at femtosecond scale in YBa2Cu3O7-x superconductors. In both normal and superconducting states, we detect the oscillations associated with two A(1g) metal-ion modes and compare the phonon dynamics to those obtained by frequency-domain (Raman) spectroscopy. Apart from the considerable increase of amplitude for low-frequency mode in the superconducting state, we observe that its initial phase in the time domain is approximately pi/4 shifted by the superconductivity, whereas for the high-frequency mode the initial phase shift is almost two times larger. Even though similar lattice anomalies are observed in both time and frequency domains, the systematic analysis shows that the coherent lattice dynamics is different from the ordinary (thermal state) dynamics probed by frequency-domain spectroscopy.

The surface of the misfit-layer compounds (LaSe)(x)NbSe2 and (PbSe)(x)NbSe2 is studied by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in air and nitrogen, in the range of 0.5 to 10 mu m(2). The cleaved surface of (LaSe)(x)NbSe2 presents flat non-stepped surfaces which crack and react. Inner layers do not appear to crack. The dynamic process taking place in the superficial layers produces pieces which arrange in a self-similar way and eventually gives rise to discrete islands which self-organize periodically in one direction. On the other hand, the cleaved surface of (PbSe)(x)NbSe2 is stepped and shows no reactivity. The influence of the cleavage, the strain, the strength of the interlayer and intralayer bonding, and the misfit of the compounds are discussed as reasons for the mesoscopic behaviour of these materials, (C) 1999 Elsevier Science B.V. All rights reserved.

We report an optical study of the superconducting transition in the YBa(2)Cu(3)O(7-x) films on MgO substrate carried out by femtosecond pump-probe spectroscopy. In both the normal and the superconducting state, we have observed the transient time-resolved reflectivity caused by the oscillations associated with two A,, metal-ion modes. Temporal interference between the modes is modified below the phase transition, which also appeared in an altered relative intensity of the modes in the Fourier transformed spectra. (C) 1999 Elsevier Science B.V. All rights reserved.

We studied the pump power dependence of the coherent phonon amplitude in the CDW and the normal states of eta-Mo4O11, which undergoes two CDW phase transitions at T-c1 = 105 K and T-c2 = 35 K. Femtosecond time-resolved pump-probe measurements were conducted at room temperature, 80 K (< T-c1), and 20 K (< T-c2). Unlike Raman spectra, the coherent phonon amplitudes showed a strong pump power dependence below T-c1 and T-c2. We found coherent phonons of which amplitudes were not proportional to the pump power. (C) 1999 Elsevier Science B.V. All rights reserved.

We report an optical study of the Mott transition in V2O3 carried out by time- and frequency-domain spectroscopies. We have observed time-resolved spectra through the Mott transition with oscillations in reflectivity associated with the fully symmetric phonon modes. Raman spectrum also shows an abrupt change of both the phonon and electronic excitations through the phase transition. We notice that although the phonon spectra obtained by the time- and frequency-domain spectroscopies are essentially similar, there are distinct differences in the phonon lineshape. (C) 1999 Elsevier Science B.V. All rights reserved.

Atomic images of the misfit layer compounds (LaSe)(x)NbSe2 and (PbSe)(x)NbSe2 were obtained with a scanning tunneling microscope (STM) operating in constant height mode in air. It was possible to record pictures of only the NbSe2 layers of both compounds, the LaSe and PbSe layers could not be observed. Formation of stage-2 portions embedded in the stage-1 crystal and instability of the LaSe and PbSe layers under the scanning conditions are discussed as possible causes. Comparing with the NbSe2 crystal, the lattice of the NbSe2 layers of the misfit layer compounds appear deformed. Nonperiodic Moire-like structures have been observed in the (LaSe)(x)NbSe2 surface. We consider that this feature is caused by the STM tip pushing down the surface where it is softer. The nonperiodicity of the patterns might be due to the strain conditions of the crystal growth that would give rise to dislocations and defects.

We report the results of an optical study of the Mott transition in V2O3 carried out by time- and frequency domain spectroscopies. We have observed time-resolved spectra through the Mott transition with oscillations in reflectivity associated with the fully symmetric modes. As a consequence of the phase transition, the Raman spectrum also shows an abrupt change of both the phonon and electronic excitations. Most notable are (i) disappearance of the electronic continuum, which is very strong and broad in the metallic state, and (ii) altered coupling of a fully symmetric phonon to the electronic subsystem, which is shown to be temperature dependent even above the transition. We notice that although the spectra obtained by the time- and frequency-domain spectroscopies are similar, there are distinct differences in phonon line shape. [S0163-1829(98)04743-2].

STM has been used to investigate the variety of processes taking place in the surface of NbSe(2) in air and N(2). Induced surface layer by layer etching and formation and evolution of surface reaction sites both in air and N(2), are discussed. Residues removed and transported by the tip were found in N(2) but they seemed to get dissolved in air. Rests of chemicals (and/or surface defects) have been observed to be left in the edges of pre-existing terrace steps in N(2), providing a preferential place for the formation of new reaction sites when air was re-introduced. In places where apparently no defects were present, the tip induced etching process was not possible, but focusing in a pre-existing small depression, the etching proceeded fast not only in that layer but also in the layers beneath. We propose that the processes taking place at the surface of NbSe(2) are due to mechanical and chemical interactions that unsaturated bonds which are present in surface defects and step edges have with the environment and the tip. (C) 1998 Elsevier Science B.V. All rights reserved.

Low temperature structure was investigated on infinite-layered Sr1-xLaxCuO2 (0 less than or equal to x less than or equal to 0.12, La-IL) superconductor by X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and Raman spectroscopy. XAFS showed that Cu-O bond distance slightly expanded with lowering temperature down to 20 K, and the expansion was remarkable below T-c(onset) = 43 K. Tetragonal lattice parameters shrank with lowering temperature but the shrinkage of the a-parameter seemed to be almost saturated below T-c(onset). Resonance Raman peaks were observed at 151 cm(-1) and 304 cm(-1) in the La-doped samples, although the ideal IL structure should be Raman inactive. The peak intensities increased with lowering temperature. The variation may be related to the change observed with both XAFS and XRD in local structure with temperature. It is assumed that the CuO2 plane may buckle with shifting oxygen ion positions above and below the CuO2 plane, as reported in another electron-doped superconductor Nd2-xCexCuO4 (T'-214). (C) 1997 Elsevier Science B.V.

We have performed optical reflectivity measurements on the mixed crystals of misfit layer compounds (MxLa1-xS)NbS2 (M: metal = Sn, Pb; 0 less than or equal to x less than or equal to 1) to estimate the carrier density in conducting NbS2 layers. The carrier density monotonically increases with the metal content x. The variation of the carrier density with x can be explained in terms of the charge transfer from MxLa1-xS to NbS2 layers. The influence of the charge transfer on the vibrational properties in the mixed crystals is studied by Raman scattering measurements. The peak frequencies of the A modes confined to the NbS2 layer shift to the higher energy side with decreasing x. The frequency shifts of the phonon modes suggest that the inter-and intralayer interactions increase with increasing the degree of the charge transfer. (C) 1997 Elsevier Science Ltd.

In the misfit layer compounds of metal-dichalcogenides (MX)(TX2), there are two intense Raman bands, which have been ascribed as their origins to the in-plane and the out-of-plane vibrations in the host layer compounds. It is commonly observed that the frequency of the in-plane mode is appreciably increased, while that of the out-of-plane mode is almost unchanged, in the misfit layer compounds. The mechanism is investigated by means of the classical lattice dynamics. It is found that competition between increasing central forces and decreasing noncentral forces in the host layer is the cause of this change. In the misfit layer compounds, electrons are donated to the host layer, further filling the conduction band. Filling that band makes the distribution of the valence electrons more spherical, which eliminates the angle dependence on the adiabatic potential. (C) 1997 Elsevier Science Ltd.

We have measured Raman scattering from SiC crystals containing stacking disorders. Raman intensity profiles are calculated for models of disordered structures and compared with the observed spectra.

Misfit layer compounds (RS)(x)NbS2 (R = rare earth; x approximate to 1.2) are made of two types of layers: RS and NbS2. Polarized Raman spectra have been measured on (RS)(x)NbS2 (R = La, Ce, Pr, Nd, Sm, Dy, Yb) in order to study the interlayer interaction between the RS and the NbS2 layers and the effect of the charge transfer from the RS layer to the NbS2 layer, The behavior of the intralayer E mode of the NbS2 layer in (RS)(x)NbS2 is sensitive to the charge transfer and shifts considerably to higher frequency compared with that of the pristine compound 2H-NbS2. Two Raman bands whose peak frequencies depend on the mass of the R atoms appear below 200 cm(-1). These bands are attributed to the mode relevant to the RS layer.

Misfit layer compounds (MS)(NbS2)(n) (M = Sn,Pb; n = 1, 2) are composed of two types of layers MS and NbS2. Raman spectra of these compounds have been measured for stage-1 (n = 1) and stage-2 (n = 2) compounds and compared with those of pristine NbS2 and other misfit layer compounds. The intralayer E modes of the NbS2 layer for (MS)(NbS2)(n) shifts upwards relative to 2H- and 3R-NbS2 and the amount of the shift is larger for the stage-1 compounds than the stage-2 compounds. This result is interpreted in terms of the charge transfer (CT) from the MS layer to the NbS, layer. The extra phonon modes observed for (RS)(NbS)(2) (R = La,Ce) which become Raman active by the breakdown of the mirror symmetry of the NbS2 layer are not observed for (PbS)(NbS2)(2) because the amount of CT is considerably smaller for the Pb compounds than the La and Ce compounds.

Polarized Raman scattering experiments on misfit layer compounds (RS)(x)TaS2 (R = La, Ce, Sm or Gd; S = sulphur; x similar or equal to 1.2) have been carried out in order to investigate the effect of the charge transfer (CT) from an RS layer to a TaS2 layer on the vibrational motion. The mode assignment is made by comparing the spectra of(RS)xTaS(2) with those of 2H-TaS2 and (RS)(x)NbS2. The modes at frequencies below about 200 cm(-1) are ascribed to the intralayer modes of the RS layer and the main peaks higher than 200 cm(-1) are ascribed to the intralayer modes of the TaS2 layer. The E mode relevant to the TaS2 layer shifts upwards by about 40 cm-1 relative to the corresponding mode in 2H-TaS2 while the A mode hardly shifts. In addition to the intralayer modes of each layer, extra modes which show an anisotropy in the basal plane are observed at 360-370 cm(-1). These observations indicate that the restoring forces for intralayer and interlayer interactions strengthen owing to the CT. The two-phonon Raman band is observed at higher frequencies than that of 2H-TaS2. The comparison with the spectra of (RS)(x)NbS2 shows that the amount of the CT in (RS)(x)TaS2 is less than that in (RS)(x)NbS2.

Polarized Raman scattering experiments on misfit layer compounds (RS)xTaS2 (R identical to La, Ce, Sm or Gd
S identical to sulphur
x approximately=1.2) have been carried out in order to investigate the effect of the charge transfer (CT) from an RS layer to a TaS2 layer on the vibrational motion. The mode assignment is made by comparing the spectra of (RS)xTaS2 with those of 2H-TaS2 and (RS)xNbS2. The modes at frequencies below about 200 cm-1 are ascribed to the intralayer modes of the RS layer and the main peaks higher than 200 cm-1 are ascribed to the intralayer modes of the TaS2 layer. The E mode relevant to the TaS2 layer shifts upwards by about 40 cm-1 relative to the corresponding mode in 2H-TaS2 while the A mode hardly shifts. In addition to the intralayer modes of each layer, extra modes which show an anisotropy in the basal plane are observed at 360-370 cm-1. These observations indicate that the restoring forces for intralayer and interlayer interactions strengthen owing to the CT. The two-phonon Raman band is observed at higher frequencies than that of 2H-TaS2. The comparison with the spectra of (RS)xNbS2 shows that the amount of the CT in (RS)xTaS2 is less than that in (RS)xNbS2.

Raman spectroscopy has been applied to identification of longer-period SiC polytypes. The stacking structures of 5 1 R and 1 3 2R polytypes have been examined, the result of which is consistent with electron- and x-ray-diffraction analyses. The possibility is discussed for Raman determination of the period and stacking structure of longer period polytypes. It is demonstrated that Raman scattering is useful for the determination of the structure of SiC polytypes.

Phonon spectra of A 1(LO), E 2(high) and B 1(high) modes were observed in a series of hexagonal In x Ga 1-xN alloy films (x = 0.11-0.54) by Raman scattering using a deep-UV laser at 266 nm for excitation. The A 1(LO) and E 2(high) modes both showed one-mode type variation with x. The B 1(high) mode, which is Raman-forbidden in ideal binary wurtzite compounds, has been first observed in In x Ga 1-xN alloy in a clear manner. Its frequency variation is in line with a theoretical prediction of one-mode type behavior. © 2012 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

We have estimated the longitudinal effective mass (m//) of electron in n-type InN films by Raman scattering. The samples were grown by MOVPE (metal organic vapor phase epitaxy) with free carrier concentration of n=6.7×1018 -9.9×1018 cm-3 according to Hall measurement. A weak Raman signal observed at ∼430 cm-1 at room temperature was sharpened and shifted to higher frequency toward the A 1(TO)-phonon mode at 447 cm-1 with increasing n. This mode was assigned to the lower branch (L-) of the longitudinal-optic-phonon-plasmon- coupled (LOPC) mode. The line shape was carefully analyzed by a semi-classical line-shape fitting analysis assuming deformation potential and electro-optic coupling mechanisms for the light scattering process. A line-shape fitting analysis was conducted by adjusting three major parameters
electron density, effective mass and plasmon damping rate. The analysis well reproduced values of electron density and mobility deduced by Hall measurement. Electron effective mass of m//*/m0 = 0.05 (±0.01) was also obtained as the best-fit parameter. The result agrees well with previous data obtained by other optical methods. © 2010 Wiley-VCH Verlag GmbH &amp
Co. KGaA.

BiFeO3 is a multiferroic material showing antiferromagnetic ordering and ferroelectric behavior simultaneously. Here, Mn-doped BiFeO 3 nanoparticles were synthesized up to 10% of Mn composition by a, sol-gel process. The samples showed high crystallinity with no secondary phase up to 2% of Mn doping. A phonon peak at 1250 cm-1 in undoped BiFeO3 showed anomalous intensity enhancement in the magnetically ordered phase below TN = 643 K due to a spin-phonon coupling. This behavior was less pronounced in the Mn-doped samples, suggesting a suppression of magnetic ordering between Fe3+ spins by Mn doping.

Low-temperature formation processes of Ni suicide were studied by Raman scattering and cross-sectional transmission electron microscopy (TEM) using Si wafer samples deposited with thin Ni layers. Comparisons were made between two annealing methods
cold wall, lamp based rapid thermal process (lamp RTP) and a hot wall chamber RTP system. . The TEM and Raman observations showed good agreement on the Ni silicidation scheme at the Ni/Si interface. It is shown that Raman scattering spectroscopy is a convenient, non-contact and non-destructive characterization tool to probe and investigate the Ni-silicide formation process in the top nm-order surface of metal/Si contact, as well as to monitor the grain size variation of the suicides and residual stress in the Si wafer. © 2006 IEEE.

The charge-density-wave (CDW) phase transition in (Formula presented) is studied by femtosecond time-resolved reflection. We observed coherent optical phonons in the reflectivity signal in both the normal and the CDW states. Below the transition temperature (Formula presented) six vibrational modes were clearly detected. Four of them, centered at 64, 78, 85, and (Formula presented) were enhanced below (Formula presented) We conclude that the generation of these coherent phonon modes are closely related to the CDW state. © 1998 The American Physical Society.

Local structure of infinite layered superconductor Sr<SUB>1</SUB>-xLa<SUB>x</SUB>CuO<SUB>2</SUB> in low temperature was investigated by EXAFS, X-ray diffraction and Raman spectroscopy. EXAFS showed that the Cu-O bond distance slightly expanded in a range <0.1Å with lowering temperature down to 20K.<BR>The expansion was remarkable below Tc(onset)=43K. Tetragonal lattice parameters shrank with lowering temperature but the shrinkage of a-parameter seemed to be almost saturated below Tc(onset). Oxygen atoms may slightly shift their positions above and below the CuO<SUB>2</SUB> plane. Raman spectrum of Sr<SUB>1</SUB>-xLa<SUB>x</SUB>CuO<SUB>2</SUB> superconductors were Raman active although infinite layered structure should be Raman inactive from its symmetry. Resonance Raman peaks were observed at 151cm<SUB>-1</SUB> and 304cm<SUB>-1</SUB> in a usage of 4880Å Ar ion laser. Its energy of 2.54eV almost corresponds to that of the exitation between lower and upper Hubard bands. The peak intensities increased with lowering temperature even above Tc(onset). The intensity change may also be related to the change observed with both X-ray absorption and diffraction in local structure with temperature. The CuO<SUB>2</SUB> plane may buckle as reported in atomic pair distribution function refinement of neutron diffraction data on (Nd.Ce)<SUB>2</SUB>CuO<SUB>4</SUB> in low temperature.

査読

The Journal of Physical Chemistry に投稿された論文の審査

非常勤講師

京都工芸繊維大学工芸科学部にて「物理学Ⅰ」「物理学Ⅰ演習」「物理学Ⅱ」「物理学Ⅱ演習」の講義を行う。

講演講師等

講師,任期:2019年12月～

講演講師等

講師,任期:2019年8月～

非常勤講師等

平成31年度非常勤講師,任期:2019年4月～2020年3月

学術雑誌等の編集委員・査読・審査員等

査読

学術雑誌等の編集委員・査読・審査員等

論文査読

非常勤講師等

非常勤講師,任期:2018年4月～2019年3月

講演講師等

講師,任期:2017年１２月～

非常勤講師等

非常勤講師,任期:2017年４月～2018年３月

講演講師等

講師

非常勤講師等

非常勤講師,任期:2016年4月-2017年3月

学術雑誌等の編集委員・査読・審査員等

APEXに投稿された論文の査読

小・中・高校生を対象とした学部体験入学・出張講座等

同授業と実験を行った,日付:12月１4日

小・中・高校生を対象とした学部体験入学・出張講座等

物理分野担当,日付:12月10日

非常勤講師等

非常勤講師,任期:2015/03/11～2016/03/31

学術雑誌等の編集委員・査読・審査員等

論文査読

学術雑誌等の編集委員・査読・審査員等

論文の査読

小・中・高校生を対象とした学部体験入学・出張講座等

物理分野を担当した．,日付:2014年12月10日

学術雑誌等の編集委員・査読・審査員等

論文査読

公開講座・講演会の企画・講師等

電磁誘導

小・中・高校生を対象とした学部体験入学・出張講座等

物理分野担当

公開講座・講演会の企画・講師等

自然エネルギー,日付:平成21年8月20日

小・中・高校生を対象とした学部体験入学・出張講座等

物理学分野を担当した。

公開講座・講演会の企画・講師等

環境物理学

公開講座・講演会の企画・講師等

光に関する工作と実験