bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the Symmetry Breaking in the Surface Molecular Structures of One- and Two-Dimensional Bis(ethylenedithio)tetrathiafulvalene Compounds
Authors: Takeuchi Masahiko Ishida , Takehiko Mori Takehiko Mori , Hidemi Shigekawa Hidemi Shigekawa
Published: October 2002

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were performed on the cationic molecular surfaces of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)-based organic conductors with one-dimensional (β-(BEDT-TTF)2AsF6) and two-dimensional (κ-(BEDT-TTF)2Cu(NCS)2) conductivity. For the β-(BEDT-TTF)2AsF6 surface, highly similar STM/AFM images to those of β-(BEDT-TTF)2PF6 were observed. Two types of alternately aligned molecular rows existed in the direction of the crystal a-axis; one is characterized by bright and distinct protrusions, and the other is a little darker with less distinct rows forming a zigzag structure. On the other hand, in the case of κ-(BEDT-TTF)2Cu(NCS)2, similar one-dimensional modulation was confirmed by AFM for the first time in addition to the STM observation. However, the observed difference in the molecular images was only in their brightness, and their shapes were quite similar. Since the surface structures were confirmed by both STM and AFM, the obtained results indicate that the observed modulations are associated with the structural changes in the surface molecular arrangements. The modulations were discussed in relation to the crystal structures.
Nanometer-Scale Characterization of Ferroelectric Polymer Thin Films by Variable-Temperature Atomic Force Microscopy
Authors: Fukuma Takeshi , Kobayashi Kei , Horiuchi Toshihisa , Yamada Hirofumi , Matsushige Kazumi
Published: October 2002

The morphological changes of ferroelectric polymer thin films during the annealing process were directly imaged
by variable-temperature atomic force microscopy (AFM).
The growing process of the crystallites underlying the surface amorphous layer was observed as well as the morphological changes
using intermittent-contact AFM.
We found that fine structures appeared in the rod like grains at a temperature corresponding
to the Curie point of the bulk copolymer in the cooling process.
In addition, local piezoelectric response was mapped in order to investigate the relationship between the structural change and the ferroelectric phase transition.
The local polarization prepared at room temperature disappeared after the film was heated above 120°C,
which agreed with both the Curie temperature and the temperature of the observed structural change.
Location-Control of Large Si Grains by Dual-Beam Excimer-Laser and Thick Oxide Portion
Authors: Ishihara Ryoichi , Burtsev Artyom , Alkemade Paul F. A.
Published: October 2002

An array of large Si grains was placed at a predetermined position by dual excimer-laser irradiation of a multi-layer structure of silicon (Si), silicon dioxide (SiO2) with an array of bumps and metal on a glass substrate. We have investigated the effects of irradiating energy density and the topology of the structure on the grain size and crystallographic structure by scanning electron microscopy (SEM) and electron back-scattering pattern (EBSP) analysis. In the low-energy-density regime, numerous small grains and petal shaped grains formed on top of the SiO2 bumps. The number of small grains on the bumps decreased with increasing irradiating energy density. At sufficiently high energy densities, one single Si grain as large as 3.5 µm was positioned at the center of the bumps. Although most of the area of the large Si grain has a single crystallographic orientation, twins and low-angle grain boundaries are often formed at the periphery of the grain. There was no preferred crystallographic orientation in the center of the location-controlled Si grain. Numerical analysis of the temperature profile showed that a temperature drop occurs at the center of the bump, during and immediately after laser irradiation. The diameter of the location-controlled Si grain increased with total thickness of the intermediate SiO2 layer, and took the maximum value of 6.2 µm.
Characterization of CdS Thin-Film in High Efficient CdS/CdTe Solar Cells
Authors: Tsuji Miwa , Aramoto Tetsuya , Ohyama Hideaki , Hibino Takeshi , Omura Kuniyoshi
Published: October 2002

Cadmium sulfide (CdS) thin films are the most commonly used window materials for high efficient cadmium telluride (CdTe) and chalcopyrite polycrystalline thin-film photovoltaic devices. High efficient CdS/CdTe solar cells with thin CdS films have been developed using ultrathin CdS films with a thickness of less than 0.1 µm. CdS films were deposited on transparent conductive oxide (TCO)/glass substrates by the metal organic chemical vapor deposition (MOCVD) technique. CdTe films were subsequently deposited by the close-spaced sublimation (CSS) technique. The screen printing and sintering method fabricated carbon and silver electrodes. Cell performance depends primarily on the electrical and optical properties of CdS films. Therefore we started to develop higher-quality CdS films and found clear differences between high- and low-quality CdS films from the analyses of scanning electron microscope (SEM), atomic force microscope (AFM), secondary ion mass spectroscopy (SIMS), thermal desorption spectrometry (TDS) and Fourier transforms-infrared spectrometry (FT-IR) measurements. As a result of controlling the quality of CdS films, a photovoltaic conversion efficiency of 10.5% has been achieved for size of 1376 cm2 of the solar cells under the Air Mass (AM) 1.5 conditions of the Japan Quality Assurance Organization.
Annealing of GaN-InGaN Multi Quantum Wells: Correlation between the Bandgap and Yellow Photoluminescence
Authors: G. Eliseev Saulius Juodkazis , Mitsuru Watanabe Mitsuru Watanabe , Hong-Bo Sun Hong-Bo Sun , Shigeki Matsuo Shigeki Matsuo , Tomoya Sugahara Tomoya Sugahara , Shiro Sakai Shiro Sakai , Hiroaki Misawa Hiroaki Misawa
Published: October 2002

We report experimental data on photoluminescence (PL) annealing of metalorganic chemical vapor deposition (MOCVD) grown GaN-InGaN multi quantum wells (MQWs). The formation of phase separation in the InGaN quantum well layer was confirmed by PL mapping when the MQW was grown at 675°C. Spatial distribution of the yellow (Y)-band PL correlated with the dislocation network in that the intensity of the PL was lowest at the grain boundaries. The activation energy of thermal quenching of the InGaN PL at 400 nm was found to be equal to that of the increase of Y-band PL at 550 nm. The origin of the Y-band is explained as a radiative donor-acceptor recombination.
Analysis of Magnetization State of Recording Head Tip with Narrow Track
Authors: Shimizu Yusuke , Shiiki Kazuo
Published: October 2002

Three-dimensional micromagnetic simulation coupled with electromagnetic calculation of continuous medium was carried out to investigate the magnetization state of the narrow track recording head tip. The entire recording head is treated as a macroscopic magnetic material. The effect induced by the recording current is incorporated into the micromagnetic simulation of the head tip as the boundary condition. First, the magnetic flux density in the entire head and the external magnetic field are calculated by the magnetic moment method. Then the micro-magnetization states of the head tip are solved using the Landau-Lifsitz-Gilbert equation under the boundary condition of the magnetization in external magnetic fields. Closure domains of which the magnetization direction of the main domains is the bit direction, are formed in the head tip in the case of track direction easy axis. As the recording current increases, the induced magnetic field parallel to the bit direction moves the 180° domain wall in the tip. This problem cannot be overcome either by changing the easy axis or by increasing the anisotropy strength. The laminated magnetic film tip with nonmagnetic spacers is able to suppress the domain wall motion.
Electron Spin-Relaxation Times in p-type δ-doped GaAs/AlGaAs Double Heterostructures
Authors: Endo Toshihiro , Sueoka Kazuhisa , Mukasa Koichi
Published: October 2002

Optically pumped GaAs is a promising material for probes of spin-polarized
scanning tunneling microscopy. To increase the accuracy of the measurement, it is
necessary to increase the spin polarization of excited electrons and their
spin-relaxation time. A δ-doped GaAs/AlGaAs double heterostructure shows a
larger spin-relaxation time than bulk GaAs. It has been reported that in this structure
the effect of the exchange interaction between the electrons and excitons can easily be
reduced by spatially separating the electrons and holes. However, the dependency of the
relaxation time on the structural details has not been experimentally examined. In this
study, we determine the optimum well width of the δ-doped double
heterostructure which yields a long spin-relaxation time using time-resolved
photoluminescence measurement. Spin-relaxation times of the
e0→hh1 recombination and
e0→lh1 recombination are individually characterized.
The e0→hh1 recombination has the longer
spin-relaxation time, and the longest relaxation time of
τs\fallingdotseq20 ns is observed for the structure with a well
90 nm in width.
Tunable Cr:YSO Q-Switched Cr:BeAl2O4 Laser: Numerical Study on Laser Performance along Three Principal Axes of the Q Switch
Authors: Lin Yen-Kuang Kuo , Chen Horng-Min
Published: October 2002

Numerical simulation of the Cr:YSO Q-switched Cr:BeAl2O4 tunable laser is studied along the three principal axes of the Cr:YSO saturable absorber. The n
1 axis has the best Q-switching performance when compared to the n
2 and n
3 axes. Theoretical expressions of important parameters such as the laser population inversion at various stages, the peak photon number inside the laser resonator, and the output energy and the pulsewidth of the Q-switched laser pulses are derived and used to evaluate the characteristics of the Cr:YSO Q-switched Cr:BeAl2O4 laser system.
Optical Memory Media Based on Excitation-Time Dependent Luminescence from a Thin Film of Semiconductor Nanocrystals
Authors: Maenosono Shinya , Dushkin Ceco Danov , Saita Soichiro , Yamaguchi Yukio
Published: October 2002

We describe the increase of photoluminescence intensity from densely packed semiconductor nanocrystals (quantum dots) with excitation time, which is clearly observed by the naked eye under ambient conditions. This enabled the invention of the first luminescence-based optical memory media feasible for practical applications. Bright luminescent images are stored and then read out by exciting the medium, a thin film of cadmium selenide nanocrystals, with blue or UV light. The increase in emission intensity is attributed to the trapping and accumulation of photo-generated electrons in the matrix of organic molecules capping the nanocrystals.
Efficient Reduction of Fringe Noise in Trace Gas Detection with Diode Laser Multipass Absorption Spectroscopy
Authors: Wu Shang-Qian , Kimishima Tetsuya , Kuze Hiroaki , Takeuchi Nobuo
Published: October 2002

The combination of a diode laser source and a multipass cell is attractive for the detection of trace gases. The sensitivity achievable with this system, however, is often limited by etalon fringes arising from path length difference among the optical components. In this paper, we describe a sensitive detection method that minimizes the effect of the fringes. In accordance with the expected widths of the 2f (second-harmonic of the modulation frequency) absorption signals of the target molecule, the base length of a multipass cell is chosen so that the free spectral range of the fringes becomes much narrower than the signal widths. Then, the 2f signal is subjected to multistage smoothing to remove the fringe noise by exploiting its periodicity. As a demonstration of this method, trace moisture in nitrogen is detected using a near-infrared, distributed-feedback diode laser and a multipass cell of 20 m absorption length. The detection limit of the system is found to be about 2.3 ppb, two orders of magnitude better than the limit before fringe elimination.
Role of Processing Solvents in Photocarrier Transport of Polyanilines
Authors: Pandey Shyam S. , Wataru Takashima Wataru Takashima , Keiichi Kaneto Keiichi Kaneto
Published: October 2002

Transient photoconductivity measurements have been performed on polyaniline (PAN), poly(2-methoxyaniline) (PMA) and poly(2-fluoroaniline) (PFA) films by means of the time-of-flight technique. The effect of processing solvents such as N-methylpyrrolidinone (NMP) and dichloromethane on the nature of transient photocurrent signals is discussed. In the NMP-cast PAN, PFA and PMA films, the photocurrent was composed of only short-lived components, which did not show the sign of transit time. On the other hand, the PMA film cast from dichloromethane showed a long-lived component of photocurrent with the presence of a field-dependent kink due to the transit time. PAN and PFA are least soluble in dichloromethane. The room-temperature hole mobility of PMA cast from dichloromethane solution has been found to be 1.2 ×10-5 cm2/V·s at an applied field of 1.0×106 V/cm.
Gate-Oxide-Integrity Characteristics of Vacancy-rich Wafer Compared with Crystal-Originated-Pits-free Wafer as a Function of Oxide Thickness
Authors: Ki-Sang Lee Ki-Sang Lee , Won-Ju Cho Won-Ju Cho , Bo-Young Lee Bo-Young Lee , Hak-Do Yoo Hak-Do Yoo
Published: October 2002

The dielectric breakdown of oxides with various thickness between 5–70 nm on Czochralski (CZ)-grown silicon wafer had been investigated. To observe the effects of crystal-originated-particle (COP), vacancy-rich wafers and COP-free wafers were compared. In breakdown voltage (BV) measurement, breakdown fractions of vacancy-rich wafers were increased with the increase of oxide thickness (t
OX) and showed a maximum value at the t
OX range of 10–20 nm. On the other hand, COP-free wafers showed few breakdowns over all the range of t
OX. Furthermore, time dependent dielectric breakdown (TDDB) of the vacancy-rich wafers showed higher extrinsic breakdowns than that of the COP-free wafers in the t
OX below 20 nm. For the intrinsic breakdown, two groups showed the same charge-to-breakdown (Q
BD) along the strength of injection current over all the range of t
OX. Especially, only in case of vacancy-rich wafer, abnormal increase of current, i.e., hump phenomena, was observed in the range of electric field below the Fowler-Nordheim (F-N) tunneling.
Asymmetric Switching of Ferroelectric Polarization in a Heteroepitaxial BaTiO3 Thin Film Capacitor
Authors: Kazuhide Abe Kazuhide Abe , Naoko Yanase Naoko Yanase , Takashi Kawakubo Takashi Kawakubo
Published: October 2002

Asymmetric switching of ferroelectric polarization was measured and analyzed for a heteroepitaxial BaTiO3 thin film of 58 nm thickness. The BaTiO3 film prepared on a SrRuO3/SrTiO3 substrate by radio-frequency magnetron sputtering has a c-axis oriented normal to the surface which is 3% longer than that of the bulk due to lattice misfit between SrRuO3 and BaTiO3. When positive and negative voltage pulses of the same amplitude were sequentially applied, asymmetric responses were observed in the transient current. Although the switching charge densities Q
sw were the same for both the polarities, the switching time t
s was longer and the peak current i
max was smaller for the positive response. From the analyses of the transient current, the asymmetric switching of polarization was attributed to the discrepancy in coercive voltages V
c between polarities.
Field-Ion Microscopic Observation of Surface Silicide Formation and Substrate Metal Interfaces
Authors: Okuno Kimio , Tanaka Hiroaki
Published: October 2002

Surface silicide formation and semiconductor-metal intermixing phenomena have been investigated using atomic capability field-emission and field-ion microscopy (FEM-FIM). When silicon is vapor-deposited onto a tungsten tip surface at low temperature (50 K), interfacial reactions between silicon and tungsten atoms do not occur, and silicon adatoms on the W{011} plane assume a special pseudomorphic structure. Initial silicide reactions are particularly favorable on and around W{001}, W{111} and W{112} planes. The work function for the various silicide reaction stages and for various coverages was also evaluated. The silicide layers which cover the entire W tip surface were observed after a few hundred layers of silicon were vapor-deposited and thermally heated to around 950 K. A region in which the atomic structure of the substrate tungsten is invisible appears locally due to preferential hydrogen diffusion in the tungsten matrix. This phenomenon was observed specifically on and around the W{111} plane and in a mismatch zone which appears because of the epitaxial growth of silicide layers from the W{001} plane. This result indicates that the depth of silicide formation varies locally over several atomic layers of the tungsten substrate.
Effects of Ion-Beam-Irradiation on Morphology and Densification of CeO2 Films Prepared by Ion-Beam-Assisted Deposition
Authors: Shimizu Ippei , Setsuhara Yuichi , Miyake Shoji , Saitou Hidenori , Kumagai Masao
Published: October 2002

Cerium oxide (CeO2) films were prepared by ion-beam-assisted deposition (IBAD). The films were synthesized on Si wafers by depositing CeO2 vapor under simultaneous bombardment with O2, Ar and Xe ions in the energy range of 1.0 to 5.0 keV. Film characterizations were performed using field-emission-type scanning electron microscopy (FE-SEM) for cross-sectional observation of film morphology and film crystallization was examined by X-ray diffractometry (XRD). Rutherford backscattering spectrometry (RBS) was used for measuring the film composition and the packing density. Refractive indices of the films were measured by ellipsometry to investigate their optical properties. With increasing the transport rate ratio of ions to CeO2 vapor, the morphology of the specimens prepared with O2 and Xe ion beams was changed from columnar to granular structure. The increase in the transport ratio also had a significant effect on the enhancement of the film densification, leading to an increase in the refractive index.
Infrared Observations of the Interface Electric Current along the Methyl Alcohol-Silica Interface
Authors: Osuga Toshiaki , Kitagawa Shinya , Sakamoto Hideo , Tsuda Takao
Published: October 2002

The existence of the interface current at the methyl alcohol-silica interface was confirmed by infrared observations of the thermal boundary layer (TBL) formed due to Joule heat at the interface. Since the current estimated using the electric conductivity of the bulk phase of the methyl alcohol was 1/10 of the current actually observed, the existence of an interface current flowing in the electric double layer formed at the liquid-solid interface, where the excess cations carry the electric current more effectively than the bulk phase, was confirmed. Since the electric conductivity of the methyl alcohol is extremely low, the infrared rays from the TBL were observed without being impeded by the Joule heat of the bulk phase. Despite the fact that the heat conduction is capable of expanding the TBL, the steady thickness of the TBL was found to be maintained due to radiation loss.
Donor Compensation and Carrier-Transport Mechanisms in Tin-doped In2O3 Films Studied by Means of Conversion Electron 119Sn Mössbauer Spectroscopy and Hall Effect Measurements
Authors: Yamada Naoomi , Yasui Itaru , Shigesato Yuzo , Li Hongling , Ujihira Yusuke , Nomura Kiyoshi
Published: October 2002

Donor compensation and carrier-transport mechanisms in tin-doped indium oxide (ITO) thin films were investigated, from the viewpoint of chemical state of tin atoms, by conversion electron Mössbauer (CEM) spectroscopy and Hall effect measurement. Carrier density (n
e) and Hall mobility (µH), changed with the post-deposition anneals. The carrier density decreased with air-anneal and increased with reducing atmosphere. Analyses of the CEM spectra indicated that the decrease in n
e with air-anneal was attributed to the compensation of tin donors by excess interstitial oxygen (tin-oxygen complex). Also, we could explain the increase in n
e with reducing atmosphere in terms of the dissociation of the tin-oxygen complex. From the analyses of µH, we arrived at the possibility that the tin-oxygen complex behaved as the screened dipole scattering center.
Structure Analysis of SrTiO3/BaTiO3 Strained Superlattice Films Prepared by Atomic-Layer Metalorganic Chemical Vapor Deposition
Authors: Wang Zaiyang , Oda Shunri , Karlsteen M. , Södervall U. , Willander Magnus
Published: October 2002

Ferroelectric films of SrTiO3/BaTiO3 with strained superlattice structures, prepared by atomic layer metalorganic chemical vapor deposition, are investigated by the X-ray diffraction spectroscopy, transmission electron microscopy and secondary ion mass spectrometry. Stress is evident in a strained superlattice grown heteroepitaxially. In order to relax the stress in the superlattice film, dislocations are formed as well as atomic displacement which results in enhanced dielectric properties.
0.13 µm Metal-Oxide-Nitride-Oxide-Semiconductor Single Transistor Memory Cell with Separated Source Line
Authors: Fujiwara Ichiro , Aozasa Hiroshi , Nakamura Akihiro , Komatsu Yasutoshi , Hayashi Yutaka
Published: October 2002

A 0.13 µm metal (conductive gate) oxide nitride oxide semiconductor
(MONOS) single transistor memory cell is proposed and demonstrated. The three main
limiting factors and their solutions in a 0.13 µm MONOS single transistor memory
cell with a separated source line are clarified. The first issue is the reduction in the
margin of program inhibit voltage due to a short channel effect. This problem can be
improved by applying a positive bias voltage to unselected wordlines. The second issue
is the leakage current from unselected cells. This problem can be reduced by the use of
a source bias read technique. The third issue is the read disturb of a selected cell. This
problem can be improved with a thicker tunnel insulator without increase in program
time. An experimental 0.13 µm MONOS memory cell is obtained with satisfactory
results. A small cell size of about 6F
2 (F: feature size) is proposed by the use of
winding source lines.
Molecular-Beam Epitaxial Growth of (001) Cr/Al/Cr/Al Quadrilayer Superlattice Containing One-Monolayer-Thick Cr Layers
Authors: Toshiki Kingetsu Toshiki Kingetsu , Yasuhiro Kamada Yasuhiro Kamada , Masahiko Yamamoto Masahiko Yamamoto
Published: October 2002

We studied the growth behavior and structures of a molecular-beam-epitaxy-grown (001) Cr/Al/Cr/Al quadrilayer superlattice that contains one-monolayer-thick Cr layers, using in situ reflection high-energy electron diffraction and ex situ X-ray diffraction. We found that the quadrilayer superlattice grows epitaxially through many quadrilayer depositions to the top layer of the superlattice, in contrast to the previous finding that epitaxial growth is unstable upon deposition of (001) Al/Cr bilayer superlattices that contain Cr layers whose thickness is two monolayers or less.
Photochemical Decomposition of Co Phthalocyanine Films Using Ultraviolet Excimer Lamp
Authors: Naoki Ohta Naoki Ohta , Manabu Gomi Manabu Gomi
Published: October 2002

Structural and compositional changes of Co phthalocyanine (CoPc) films irradiated by ultraviolet (UV) light of 7.21 eV using an excimer lamp and the corresponding photo-oxidation process have been investigated. Optical absorption and X-ray photoelectron spectroscopy (XPS) measurements showed that the CoPc molecules in the films are completely decomposed by the light irradiation and resultant photo-oxidation, so that only Co oxides remain on the substrate surface. The C–N bonds which form the main frame of the Pc molecule were found to be broken with a high probability at an earlier stage of the dissociation process, as compared to the C=C bonds. The organic species with the bonds cleaved by photo-oxidation were finally removed from the substrate surface.
Removal of NOx in Oxygen-Mixed NO(=200 ppm)/N2 Gas by Pulsed Electron Beam Irradiation
Authors: Nakagawa Yoshiro , Kawauchi Hiroshi
Published: October 2002

By injection of a pulsed electron beam (kinetic energy: ≤160 keV; current: ∼140 A; current density: ∼2 A/cm2; pulse width: ∼700 ns; electron beam energy in one pulse: 12.6 J) into a NO(=200 ppm)/N2 gas mixture containing 20% O2, the oxidation of NO was sufficiently activated as to convert 85% of the NO into NO2 after 6 shots without decrease of NO
x
(=NO+NO2). The oxidation efficiency was 200 nmol/J. When water (2.6%) was added to the gas mixture, NO
x
was removed with the efficiency of 400 nmol/J, which was rapidly decreased at removal ratios greater than 50%. When the internal surface of the gas chamber was covered with a wet cloth and then the pulsed electron beam was irradiated into the gas mixture, NO2 was converted to HNO3 in the gas phase and simultaneously absorbed by the wet cloth. The total NO
x
removal efficiency increased to 570 and 300 nmol/J at the removal ratios of 40% and 84%, respectively. When ammonia was added to the gas mixture, NO
x
was removed with a constant low efficiency of 160 nmol/J at the removal ratio of 95%. The removal efficiency of NO
x
by the pulsed electron beam seems to depend strongly on the initial concentration of NO
x
, amount of water, amount of NH3, and parameters of the pulsed electron beam.
1/f Fluctuation in a Discrete One-Dimensional Diffusion System
Authors: Akabane Hideo , Okamoto Yoshiwo , Agu Masahiro
Published: October 2002

A one-dimensional diffusion system is considered to be a convenient tool to generate 1/f fluctuations by a computer, since its frequency response to the driving force concentrated at one point is proportional to 1/√f. However, the frequency response of a discrete diffusion system depends not only on the spatial increment and time step but also on the type of finite difference used to approximate the derivative. In the present paper, we specify the conditions under which a discrete diffusion system has a frequency response strictly proportional to 1/√f.
Construction of a New-Type Tuning Fork Vibratory Gyroscope Using a Single Resonance Mode
Authors: Sugawara Sumio , Tomikawa Yoshiro
Published: October 2002

The development of a flat-type vibratory gyroscope is expected in the near future. The new vibratory gyroscope using only a single resonance mode, which is entirely different from the conventional construction, is proposed here as such a structure. The characteristic of this type of vibratory gyroscope is that the mass is added asymmetrically to the top of the arm of a 2-arm-type tuning fork. The amplitude of the driving mode is increased or decreased by the Coriolis force that occurs in the mass part. This structure is used as an angular rate sensor by detecting the change of amplitude. The resonance frequency and displacement are analyzed by the finite-element method. Moreover, the influence on the resonance frequency by clamping the base end for support is also calculated, and the base form which is not affected by clamping, is clarified. Furthermore, it is investigated experimentally that this vibratory gyroscope acts as an angular rate sensor.
Molecular Adsorption on Ultrafine Precious Metal Particles Studied by Density Functional Calculation
Authors: Ohashi Nobumoto , Endou Akira , Takami Seiichi , Kubo Momoji , Miyamoto Akira
Published: October 2002

The microscopic adsorption behavior of molecules including SO2 and NO on ultrafine precious metal particles was investigated by the density functional quantum chemical calculations. The precious metals particles, which are the sites of activation in the catalyst, were modeled by Pt5, Rh5 and Pd5 clusters. The adsorption energies (E
ads) of the molecules calculated on the metal clusters were calculated. Three geometries of SO2 on the apex of Pt5 cluster (X) were considered: (a) two O atoms interact with X (C2v symmetry; model-1), (b) one S atom interacts with X (C2v symmetry; model-2), and (c) one O atom interacts with X (Cs symmetry; model-3). The order of E
ads values for the SO2 adsorption states on Pt5 clusters can be described as model-2>model-3>model-1. This result revealed the adsorption state of SO2 in which one Pt–S bond formed is the most stable energetically. The order of E
ads for the SO2 adsorption state on different metal clusters can be described as Pt>Pd>Rh. It was also determined that the adsorption state of SO2 on metal clusters is less stable than that of NO and the order of adsorption stability on metal clusters is different for SO2 and NO molecules.
Adsorption Properties of CH3OH on Al (111) and Fe (100) Surfaces: A Periodic First-Principles Investigation
Authors: Zhou Hui , Tamura Hiroyuki , Takami Seiichi , Kubo Momoji , Zhanpeisov Nourbosyn , Miyamoto Akira
Published: October 2002

The molecular adsorption of CH3OH on different metal surfaces including Al (111) and Fe (100) is reported. We present the results of a density functional theory (DFT) study on the mechanism of the molecular adsorption of methanol by applying the generalized gradient approximation (GGA) to a three-dimensional supercell representing aluminum and iron crystal planes. It has been observed that the molecular adsorption of CH3OH on the Fe (100) surface occurs more easily than that on the Al (111) surface. The on-top adsorption of the O atom of CH3OH is found to be more energetically favorable on the Al (111) surface. The different orientations of the CH3 group of CH3OH have almost the same adsorption energies.
Ab Initio Study for Si–H Bond Vibration on the Surface of Silicon Vacancy
Authors: Nimura Mikihiko , Yamada Aruba , Takami Seiichi , Kubo Momoji , Miyamoto Akira
Published: October 2002

Si–H bond vibrational frequency on the surface of silicon multivacancies and platelets is estimated by the ab initio molecular dynamics method. There are two forms of hydrogen molecules considered whose vibrational frequencies agree with the experimental ones, one is in silicon multivacancies and the other is in silicon platelets which are planar vacancies. In this work, we identify that the experimental peak frequency is due to hydrogen molecules in platelets, from the information of Si–H bond vibrational frequency, particularly its difference in broadness that is also observed in the experiment.
Effect of Steps on Structural Phase Transitions of Si(111) 7×7 Surfaces
Authors: Kato Tomohiko , Takajyo Tomonori , Tochihara Hiroshi , Shimada Wataru
Published: October 2002

The effect of steps on the structural phase transition for the Si(111)
7×7 structure dimer-adatom-stacking fault (DAS) structure is investigated
using a cell model. This model describes the state of the Si(111) surface in units of
7×7 triangular halves. In the previous work, the subject of which was an
infinite terrace, the result calculated for the temperature dependence of the DAS order
parameter exhibited much larger hysteresis than in the experiments, although the main
features of the phase transition were consistent with experiments. The presence of
steps is expected to suppress hysteresis. Calculations for the temperature dependence
of the order parameter are performed using a Monte Carlo simulation in the presence of
steps. By assuming reasonable values of the formation energy of the DAS cell at the
step edges and the intervals between the steps, the calculated result agrees with the
experimental results in terms of hysteresis.
Structural Properties of LixMn2O4 as Investigated by Molecular Dynamics and Density Functional Theory
Authors: Suzuki Ken , Oumi Yasunori , Takami Seiichi , Kubo Momoji , Miyamoto Akira , Kikuchi Masahiro , Yamazaki Nobuyuki , Mita Muneo
Published: October 2002

We performed density functional calculations and molecular
dynamics (MD) simulations to study the structural properties of
LiMn2O4. The periodic density functional calculations
revealed that LiMn2O4 had a locally distorted structure
due to the different local structures around Mn3+ and
Mn4+. The trajectory plots of Mn3+ in
Li0.4Mn2O4 at 300 K obtained by MD simulations
indicated that Mn3+ ions moved easily from the 16d site, which
is the original position of Mn3+ ion in the spinel
structure. It was observed that the Mn3+ ions moved with
greater ease at low lithium concentrations, resulting in unstable
Li
x
Mn2O4 structures.
Adsorption of Methanol on Oxygen-Modified ZrC(100) and (111) Surfaces
Authors: Edamoto Kazuyuki , Inoue Hideyuki , Nakane Takuji , Ozawa Ken-ichi , Otani Shigeki
Published: October 2002

Adsorption of methanol on clean and oxygen-modified ZrC(100) and (111) surfaces
at room temperature has been studied by ultraviolet photoemission spectroscopy (UPS).
It is determined that methanol adsorbs molecularly on the (100) surface while it
dissociates on the (111) surface; methoxy species and completely dissociated atomic
species are coexistent on the (111) surface. As the (100) surface is precovered with
oxygen (≦20 L), methanol is dissociated on the surface to form methoxy
species and the sticking probability in the initial stage is enhanced, indicating
that the preadsorbed oxygen acts to facilitate dissociative adsorption. On the other
hand, the preadsorbed oxygen is found to inhibit methanol adsorption due to site
blocking on the (111) surface.
Two-Dimensional Hydrogen Analysis on Solid Surfaces by Time-of-Flight Electron-Stimulated Desorption Microscope
Authors: Ueda Kazuyuki , Ogai Keiko , Ishikawa Ken'ichi , Yoshimura Masamichi
Published: October 2002

Hydrogen analysis on a solid surface has been performed using the electron-stimulated desorption (ESD) method. ESD is a highly sensitive technique for hydrogen analysis due to an isotope effect of desorbed ions. The scanning system of the ESD method which used a finely focused electron gun, reveals a two-dimensional hydrogen distribution on the surface. The spatial resolution is smaller than 1 µm. The degradation of petterning on the hydrogen terminated surface (a kind of radiation damage) by repeated scanning on the lithographed lines, related to the cross section of ion desorption, is discussed.
Surface Order Evaluation of the Heteroepitaxial Diamond Film Grown on an Inclined β-SiC(001)
Authors: Kono Shozo , Goto Tadahiko , Abukawa Tadashi , Wild Christph , Koidl Peter , Kawarada Hiroshi
Published: October 2002

The surface order of a heteroepitaxial diamond (001) film grown on an inclined β-SiC(001) has been evaluated with a micro-electron beam in ultra-high-vacuum. It was determined that the range of order of surface dimer-rows of the heteroepitaxial diamond film is ∼15 Å.
Effect of Relaxation of Secondary Electrons and Holes on Time-Resolved Two-Photon Photoemission from Cu(111)
Authors: Mamoru Sakaue Mamoru Sakaue , Hideaki Kasai Hideaki Kasai , Ayao Okiji Ayao Okiji
Published: October 2002

We investigate the time-resolved two-photon photoemission (time-resolved 2PPE, TR2PPE) spectrum of the image state on Cu(111) by nonequilibrium perturbation theory. We show that, in the 2PPE process, the scattering of photoexcited quasiparticles (electrons and holes) due to Coulomb interactions between electrons causes excitation of secondary quasiparticles in the vicinity of the Fermi level as well as electron transitions to the image state. We demonstrate quantitatively on the basis of numerical results how the effect of relaxation of secondary quasiparticles is manifested in the TR2PPE spectrum.
Oxygen Distribution and Site Switching for CO2 Formation on Pd(100), Pd(110) and Pt(113): An Angular and Velocity Distribution Study
Authors: Matsushima Tatsuo , Wako Sugio , Moula Md. Golam , Cao Gengyu , Kobal Ivan , Ohno Yuichi
Published: October 2002

The working site providing reactive oxygen was examined from the angular and velocity distributions of the desorbing product, CO2, on Pd(100), Pd(110), and Pt(113) by means of cross-correlation time-of-flight techniques. Around a critical CO pressure where the rate-determining step of CO oxidation shifted from CO adsorption to O2 dissociation, site switching was confirmed for CO2 formation on Pt(113) and Pd(110). On the other hand, no site switching was found on Pd(100) although clear changes were observed in the chemical kinetics for CO2 formation.
In-Situ Transmission Electron Microscopy and Electron Energy Loss Spectroscopy Observation of TiN Grown by N-Implantation
Authors: Yoshitaka Kasukabe Yoshitaka Kasukabe , Hiromitsu Tani Hiromitsu Tani , Hiroaki Abe Hiroaki Abe , Yukio Yamada Yukio Yamada
Published: October 2002

Nitrogen ions (N2
+) with 62 keV were implanted into evaporated-Ti films in the 400 kV analytical and high resolution transmission electron microscopy (TEM) combined with ion accelerators at JAERI-Takasaki. Observations by in-situ TEM equipped with electron energy loss spectroscopy, along with the discrete variational Xα molecular orbital calculations, revealed changes in the crystallographic and electronic structures of evaporated-Ti films due to N-implantation. A (001)-oriented NaCl-type TiNy is epitaxially formed by the transformation of (03·5)-oriented hcp-Ti to (001)-oriented fcc-Ti and by the occupation of N in the octahedral (O-) sites, whereas a (110)-oriented TiNy is formed by nitriding a (110)-oriented TiHx. The release of H from the TiHx occurs preferentially rather than the occupation of N in the O-sites of fcc-Ti sublattice. The loss peak due to volume plasmon of areas where TiHx has grown in the as-grown Ti film shifts to lower loss energy in the early N-implanting stage, while that of areas, where hcp-Ti has grown, gradually shifts to higher loss energies with increasing N dose. Analysis of Mulliken bond overlap populations determines that occupation of N in the O-sites gives rise to weakening Ti-Ti bonds and formation of Ti-N covalent bonds. The growth process of TiNy accompanied by changes of the crystallographic and electronic structures of Ti films due to N-implantation is discussed.
Investigation of Thermal Annealing Process of GaN Layer on Sapphire by Molecular Dynamics
Authors: Onozu Takayuki , Miura Ryuji , Takami Seiichi , Kubo Momoji , Miyamoto Akira , Iyechika Yasushi , Maeda Takayoshi
Published: October 2002

Molecular dynamics (MD) calculations have been performed to
simulate the heteroepitaxial growth process of GaN on sapphire
(0001) substrates and the thermal stability of the low-temperature
GaN layer during the annealing process has been investigated. The MD
simulations indicated that the surface morphology and the
crystallinity of GaN thin layers grown on sapphire at low
temperature of 800 K was amorphouslike and very rough. The surface
atomic morphology of the low-temperature GaN layer was improved
after the thermal annealing MD simulations at 1100 and 1200 K and
showed atomically hexagonal structures. The crystallinity of the GaN
epitaxial layer on the sapphire (0001) substrate is found to be
strongly dependent on the temperature of annealing.
Novel Transition Mechanism of Surface Electromigration Induced Step Structure on Vicinal Si(111) Surfaces
Authors: Suga Nobuo , Kimpara Junya , Wu Nan-Jian , Yasunaga Hitoshi , Natori Akiko
Published: October 2002

The step structure transition between a regular step and a bunched step structure on Si(111) induced by DC is studied, using a terrace-adatom-step-kink (TASK) model in which the mass transport of Si adatoms is taken into account explicitly. The step structure transformation dynamics were calculated by the dynamical Monte Carlo simulation in the TASK model, and the adatom flux was analyzed by the generalized Burton-Cabrela-Frank (BCF) theory. The step bunching was generated by the step-down directed force in capture-limited regime and by the step-up directed force in diffusion-limited regime. For a regular step structure in the diffusion-limited regime, in-phase wandering of steps was induced by the step-down force.
Frustrated Nanodomains on O/Cu(100)
Authors: Ishimaru Yasuyuki , Wu Nan-Jian , Yasunaga Hitoshi , Natori Akiko
Published: October 2002

The formation of nanometer-scale c(2×2) domains and their dynamical fluctuation have been observed on O/Cu(100) surface around 0.3 ML oxygen coverage. We study the origin of both the formation of nanometer-scale domains at 450 K and their fluctuation at room temperature, using the dynamical Monte Carlo simulation of the lattice gas model of
adsorbed oxygen atoms. We show that the competition between the attractive short-range interaction and the repulsive long-range interaction between adsorbed oxygen atoms brings about frustration between antiphase c(2×2) domains. This
frustration causes the suppression of domain size and the dynamical fluctuation of the domain boundaries. The simulated c(2×2) double domain structure and the fluctuation behavior of the domain boundaries agree with the properties observed by scanning tunneling microscopy and reproduce well the four-spot pattern around the ½-order positions observed by low energy electron diffraction.
The Effect of Surface Cleaning by Wet Treatments and Ultra High Vacuum Annealing for Ohmic Contact Formation of P-Type GaN
Authors: Waki Ichitaro , Fujioka Hiroshi , Ono Kanta , Oshima Masaharu , Miki Hisayuki , Fukizawa Akira
Published: October 2002

The effect of surface cleaning techniques on the properties of the metal/p-GaN contacts has been studied using X-ray photoelectron spectroscopy (XPS) and I–V measurements. It has been clarified that the contact resistance strongly depends on the amount of the surface residues such as oxygen and carbon just before the electrode deposition. We have also found that the annealing in ultra high vacuum (UHV) is effective to reduce the residues. It has turned out that the combination of the hydrochloric acid and sulfuric acid hydrogen peroxide mixtures cleaning followed by the UHV annealing is promising for the improvement in the contact characteristics.
High Resolution Photoemission Study of Low-temperature Oxidation on the Si(001) Surface
Authors: Yeom Han Woog , Uhrberg Roger
Published: October 2002

High-resolution photoemission is applied to the oxygen
adsorption on the Si(001) surface at 120 K and the subsequent
evolution of the adsorbates upon annealing. Si 2p components due
to the Si2+ and Si3+ species are observed from the very
early stage of adsorption at ∼120 K, which grow linearly
with the oxygen coverage. This indicates an active agglomeration of
oxygen adsorbates even for the submonolayer adsorption at low
temperature. Annealing above 500 K enhances the agglomeration by
mostly converting the Si1+ species into Si3+ and then into
Si4+. In addition, the annealing changes the Si 2p binding
energies for the Si2+ and Si3+ species by 0.14 and
0.23 eV, respectively. These shifts are attributed to the
structural relaxation (strain relief) of the metastable
oxygen-adsorbate complex formed at low temperature.
Reduction and Removal of Thin Al Oxide Film from Cu Substrate by Focused Electron Beam
Authors: Rar Andrei , Yoshitake Michiko
Published: October 2002

The electron-stimulated reduction of alumina deposited on Cu was studied by Auger electron spectroscopy (AES) and electron-energy-loss-spectroscopy (EELS). The reduction behavior of alumina films with different thicknesses, 3, 6, 9, and 80 nm was observed under electron-beam irradiation in the energy range from 0.5 to 10 keV at various temperatures from 300 to 670 K. It was determined that the reduction rate was higher for thinner alumina film and at higher surface temperatures. Alumina was not completely reduced to metallic aluminum even after a long electron irradiation and reached a steady state in which Al3+ and Al0 coexisted. Until this steady state was reached, the oxygen concentration decreased monotonically to about 55% of the initial value. This reduced value did not depend on the thickness of alumina film, beam energy or sample temperature below 535 K. At temperatures higher than 550 K, reduced Al disappeared from the surface, possibly by dissolving into the Cu bulk.
Anisotropic Initial Stage of Laser-Induced Chlorine Reaction on Si(111) Observed by Surface-Sensitive Optical Methods
Authors: Haraichi Satoshi , Sasaki Fumio
Published: October 2002

We investigate chlorine chemisorption and the initial stage of laser-induced reaction on Si(111) using second-harmonic generation (SHG) and reflectance difference spectroscopy (RDS). SHG signals that originate from direct bulk transition, generated by 1.6 and 1.7 eV probe light, show good threefold symmetry reflecting the symmetry of bulk Si, and SHG signals that originate from the surface, generated by 2.0 eV probe light, show threefold symmetry that intensifies in the [211] direction after chlorine chemisorption. The difference in reflectivity between the [211] direction and the [011] direction in the initial stage of the reaction is observed. In both clean Si surface and chlorinated Si surface, the RDS signal gradually changes with the progress of etching reaction, and the anisotropic initial stage of the reaction that depends on the direction of the atomic steps is observed.
Surface Oxidation Kinetics of GaAs Oxide Growth by Liquid Phase Chemical-Enhanced Technique
Authors: Wang Hwei-Heng , Chou Dei-Wei , Wu Jau-Yi , Wang Yeong-Her , Houng Mau-Phon
Published: October 2002

The initial stage of GaAs oxidation
by a near-room-temperature liquid phase chemical-enhanced technique
has been studied.
Based on the experimental results of X-ray photoelectron spectroscopy,
a complete model illustrating the chemical composition
of the grown oxide film has been established.
To clarify the kinetics of oxide growth in a liquid solution in more detail,
we have also performed selective oxidation and surface profile measurements.
Unusual features of the oxide growth kinetics have been observed
by investigating the physical structure of oxide
at the edge of mask in the selective oxidation.
Oxidation of Si(001) Surfaces Studied by High-Resolution Rutherford Backscattering Spectroscopy
Authors: Kaoru Nakajima Kaoru Nakajima , Yasutaka Okazaki Yasutaka Okazaki , Kenji Kimura Kenji Kimura
Published: October 2002

The feasibility of high-resolution Rutherford backscattering spectroscopy (HRBS) to study the initial stage of Si(001) oxidation is examined. It is shown that HRBS provides oxygen depth profiling with depth resolution at an atomic level. After oxidation of Si(001) at room temperature under 2 ×10-6 Torr oxygen partial pressure for 20 min, the coverage of oxygen was determined to be 1.2 ±0.3 ML.
Frictional Force Microscopic Anisotropy on (001) Surfaces of Alkali Halides and MgO
Authors: Namai Yoshimichi , Shindo Hitoshi
Published: October 2002

In frictional force microscopic measurement of anisotropy at
(001) surfaces of NaCl, NaF, KCl, LiF and MgO crystals,
significantly lower friction was observed when the probe was scanned
in the [110], rather than the [100] direction in air at 25%
relative humidity. In more humid conditions, the anisotropy was lost
with NaCl, KCl and NaF, most probably due to lubrication by water
which condensed beneath the tip. The anisotropy was explained by
corrugation in charge-dipole interaction potentials between the ions
at the sample surface and the probe. Due to much larger corrugation
along the [100] direction where anions and cations alternate,
greater horizontal force is required to scan the stylus in that
direction. A good correlation was recognized between the ratio of
potential gradients and the ratio of frictional coefficients in the
two directions.
Detection Mechanism of S–O Tilt Directions on CaSO4(100) by Frictional Force Microscopy
Authors: Shindo Hitoshi , Shitagami Kozo , Sugai Takashi , Kondo Sei-ichi
Published: October 2002

Tilted S–O bonds on a CaSO4(100) surface exhibit asymmetry under frictional force microscopic observation. The detection mechanism of the directional bonds was explained as being an interaction between the probe surface and an array of tilted mass-spring systems at the sample surface. When the scan speed of the probe was changed in the range of 5–91 µm/s under 40% relative humidity, the asymmetric component of friction increased linearly with the speed, while the total friction signal remained constant at speeds higher than 25 µm/s. A higher scan speed is more suitable for the detection of the tilted bonds. At lower scan speeds, the total friction signal decreased in intensity and the asymmetry signal became unstable. This is due to the condensation of water beneath the tip. A similar experiment under 60–65% relative humidity yielded much smaller signals for both the total friction and the asymmetry component.