bluuebunny/crossref_metadata_2025 huggingface dataset:
Coaxial Impact-Collision Ion Scattering Spectroscopy and Time-of-Flight Elastic Recoil Detection Analysis for In Situ Monitoring of Surface Processes in Gas Phase Atmosphere
Authors: Katayama Mitsuhiro , Fujino Toshiaki , Yamazaki Yujin , Inoue Shin-ichi , Ryu Jeong-Tak , Oura Kenjiro
Published: October 2002

Based on conventional coaxial impact-collision ion scattering spectroscopy (CAICISS) and time-of-flight elastic recoil detection analysis (TOF-ERDA), we have developed a novel ion scattering and recoiling spectrometer equipped with a differential pumping system for in situ monitoring of surface processes in gas phase atmosphere in the pressure regime up to 10-4 Torr. In order to demonstrate the performance of this apparatus, we have applied it to real-time monitoring of Ge thin film growth on a Si(001) surface in atomic hydrogen (H) atmosphere. The morphology of Ge thin films and H coverage on the growth front during the growth in H atmosphere were successfully observed.
1.3–1.6-µm-Wavelength Quantum Dots Self-Formed in GaAs/InAs Short-Period Superlattices Grown on InP (411)A Substrates
Authors: Matsuda Satoshi , Asahi Hajime , Mori Jun , Watanabe Daisuke , Asami Kumiko
Published: October 2002

(GaAs)2(InAs)2 short-period superlattices (SLs) were grown on InP (411)A substrates by gas-source molecular-beam epitaxy. Scanning tunneling microscopy observations revealed that the lateral-composition-modulated quantum dot structures were self-formed. They were aligned periodically along two perpendicular lateral directions with a lateral density of approximately 1011 cm-2. Multilayer quantum dot structures sandwiched between InP barrier layers showed strong photoluminescence emission with wavelengths of 1.3–1.6 µm depending on the SL period.
Inhomogeneous Contact Potential Image of AlGaN/GaN Grown on Sapphire Substrate Measured by Kelvin Probe Force Microscopy
Authors: Eguchi Yasuyuki , Kishimoto Shigeru , Mizutani Takashi
Published: October 2002

The contact potential of AlGaN/GaN on sapphire substrate grown by metalorganic chemical vapor deposition (MOCVD) was measured by Kelvin probe force microscopy (KFM). A clear correlation was observed between the topographic image and the contact potential image. The potential around the surface pits was about 100 mV lower than that in the surrounding region. This suggests the existence of an effect of the pits on the electrical properties of the epitaxial layer. Even though the diameters of the pits were 20–60 nm, the diameter of the affected low-potential region was as large as 0.3–0.7 µm.
Direct Bonding of Epitaxial GaAs Film on Si Substrate with Improved Optical Properties
Authors: Guolin Yu Guolin Yu , Hiroshi Ebisu Hiroshi Ebisu , Md. Mosaddeq ur Rahman Md. Mosaddeq ur Rahman , Tetsuo Soga Tetsuo Soga , Takashi Jimbo Takashi Jimbo , Masayoshi Umeno Masayoshi Umeno
Published: October 2002

In this Letter, we describe a new approach for the direct bonding of the epitaxial GaAs film on a Si substrate, namely, a thick GaAs/Si film grown by molecular-beam epitaxy (MBE) is transplanted onto another Si substrate on which a thin GaAs film has been grown, by heating for 1 h at 700°C. A reflection high-energy electron diffraction (RHEED) measurement from such a transplanted film indicates its single-crystalline nature. The double-crystal X-ray diffraction shows a full-width at half maximum (FWHM) of 481 arcsec in the case of the as-transplanted sample and decreases to 254 arcsec when followed by thermal cycle annealing (TCA) repeated five times. Compared to the non transplanted film, the transplanted film exhibits very good photoluminescence properties with very weak deep-level emission.
Nondestructive Detection of Delamination in Carbon-Fiber-Reinforced Plastics Using Superconducting Quantum Interference Device*
Authors: Hatsukade Yoshimi , Kasai Naoko , Ishiyama Atsushi
Published: October 2002

The use of carbon-fiber-reinforced plastic (CFRP) in aircraft and space structures is recently increasing. We investigated the possibility of nondestructively detecting a delamination in CFRP using a low-T
c first-order gradiometric superconducting quantum interference device (SQUID) loop. A CFRP plate including a thin insulator sheet between the central layers was prepared. The injected current method was adopted. The magnetic field due to the sheet was measured by a SQUID nondestructive evaluation system using the lock-in detection technique. The position and size of the sheet were successfully detected by mapping the measured field. The result agreed with that by ultrasonic testing. Future application of this method for detecting deep-lying flaws was discussed.
YBaCuO/PrBaCuO/YBaCuO Trilayer Junctions on Vicinal Substrates
Authors: Kuroda Ken'ichi , Takami Tetsuya , Nishi Kazuhisa , Wada Yukihiko , Ozeki Tatsuo
Published: October 2002

Trilayer junctions with c-axis oriented YBaCuO/PrBaCuO/YBaCuO films were fabricated. We used vicinal substrates in order to improve the surface morphology of YBaCuO base electrodes. Junctions with PrBaCuO barrier thickness of 15 nm showed resistively shunted junction (RSJ)-like I–V curves with a small excess current of below 10% at 4.2 K. The spreads (1σ) of I
c and R
n were 11% and 8.8%, respectively, for 14 junctions on a chip. These values are markedly small considering the trilayer junctions. The flattening of the interfaces between YBaCuO and PrBaCuO layers may improve the uniformity of the barrier thickness.
Carrier Transport across a Few Grain Boundaries in Highly Doped Polycrystalline Silicon
Authors: T. Tan Yoshikazu Furuta , K. Durrani Toshio Kamiya , Haroon Ahmed Haroon Ahmed , Kenji Taniguchi Kenji Taniguchi
Published: October 2002

We have fabricated nanometer-scale point-contact devices in 50-nm-thick poly-Si films with a grain size of from 150 nm to 20 nm. Both linear and nonlinear I
ds-V
ds characteristics were observed in these devices, corresponding to a channel without a grain boundary (GB) and that with a single or a few GBs, respectively. The temperature dependence of resistivity indicated that the effective potential barrier height q
V
B of the GBs for the devices which show the nonlinear I
ds-V
ds characteristics ranges from 30 meV to 80 meV. We discussed percolation conduction of electrons through a few GBs due to nonuniform GB properties in heavily doped poly-Si films.
Experimental Studies on Acoustic Energy Loss in Surface Acoustic Wave Filters Using Grating Waveguides
Authors: Tsutsumi Jun , Ikata Osamu , Satoh Yoshio
Published: October 2002

The acoustic energy loss in surface acoustic wave filters using grating waveguides is investigated experimentally. The propagation loss in the waveguide formed on a ST-cut quartz with aluminum grids, which have the period detuned from that of the Bragg condition, is evaluated to be small as 2×10-3 dB/wavelength. However, it is revealed that the extra energy loss arises with a short waveguide length and before surface acoustic waves (SAWs) launched by the interdigital transducer (IDT) enter the waveguide. Based on the experimental studies on these extra energy losses, the insertion loss in the reflector filter using a SAW grating waveguide is reduced by 2 dB by increasing the aluminum film thickness.
Temperature Dependence of the Near-IR Emission and Its Absorption in Oxygen-Doped BaFBr Crystals
Authors: Toshio Kurobori Toshio Kurobori , Min Liu Min Liu , Yukio Hirose Yukio Hirose
Published: October 2002

The enhancement of the near-IR emission intensity at 200 K excited at the F(Br-) band in oxygen-doped BaFBr was observed. It was found from the corresponding absorption spectra that the origin is attributed to a thermal dissociation between F(Br-) centers and O- ions. The role of the oxygen-defect centers was investigated at temperatures of 77–300 K in BaFBr single crystals containing oxygen impurities.
In Situ Gravimetric Monitoring of Decomposition Rate from GaN (0001) and (0001̄) Surfaces Using Freestanding GaN
Authors: Miho Mayumi Miho Mayumi , Fumitaka Satoh Fumitaka Satoh , Yoshinao Kumagai Yoshinao Kumagai , Akinori Koukitu Akinori Koukitu
Published: October 2002

Polarity dependence on GaN decomposition has been investigated by an in situ gravimetric monitoring (GM) method using freestanding GaN (0001). In the H2 carrier gas ambient, the decomposition rate of both GaN (0001) and GaN (0001̄) increased with increasing substrate temperature. The decomposition rate of GaN (0001̄) was faster than that of GaN (0001̄) at temperatures below 820°C, whereas the decomposition rate of GaN (0001) was faster than that of GaN (0001) in the temperature range above 850°C. The decomposition rate as a function of the hydrogen partial pressure (P
H2
) has been observed. The rate-limiting reaction of the GaN decomposition on both surfaces is shifted from N(surface) + 3/2H2(g)→NH3(g) to Ga(surface) + 1/2H2(g) →GaH(g) with increase of temperature.
Comparative Study of Schottky Diode Characteristics in Ni, Ta and Ni/Ta Metal Contact Schemes on n-GaN
Authors: Chen Gin-Liang , Chang Fu-Chin , Chuang Wang-Cheng , Chung Hao-Ming , Shen Kun-Ching , Chen Wen-Hsiung , Lee Ming-Chih , Chen Wei-Kuo
Published: October 2002

We have reported current–voltage characteristics of Ta/- and Ni/Ta/n-GaN Schottky diodes under various thermal treatments. Experimental data indicate that the electrical characteristics of Ni/Ta diodes are controlled by the interfacial properties of the Ta and GaN heterointerface for the as-deposited samples and strongly affected by the presence of an oxide layer (Ta2O5) in those high-temperature-annealed diodes. In regard to Ta/Ni diodes, probably because of thermal stability and wide-band-gap properties of tantalum oxide, dramatic improvement in Schottky diode performance was resulted after annealing at high temperatures. The corresponding barrier height and ideality factor values can reach 1.17 eV and 1.09, respectively, even at an annealing temperature of 800°C.
Modeling the Post-Breakdown I–V Characteristics of Ultrathin SiO2 Films with Multiple Snapbacks
Authors: Chen Tupei , Tse Man Siu , Fung Steve
Published: October 2002

Multiple conduction states in ultra-thin SiO2 films after hard breakdown could be observed when the oxides exhibited the behavior of multiple snapbacks. Although the I–V characteristics seem very complicated when the snapbacks occurred with multiple conduction states involved, a careful modeling indicates that each conduction state was well defined. The I–V characteristic of each conduction state can be well modeled by the power law, and a convincing linear dependence is observed for each state when the I–V characteristics are plotted in log
-log
scale. These findings consist with the percolation model.
Generation of THz Radiation from Resonant Absorption in Strained Multiple Quantum Wells in a Magnetic Field
Authors: Liu Tze-An , Huang Kai-Feng , Pan Ci-Ling , Ono Shingo , Ohtake Hideyuki , Sarukura Nobuhiko
Published: October 2002

Optically excited THz-radiation from ten molecular-beam epitaxy (MBE)-grown strained multiple quantum wells (MQWs) on a (100)-oriented semi-insulating GaAs substrate is studied in a 1-T magnetic field. Wavelength-dependent THz-radiation clearly exhibits a resonance behavior at the excitation wavelength near 830 nm, the peak wavelength of photoluminescence (PL). We also observe and explain an emission spectrum from the MQW with slightly enhanced higher-frequency components compared to that of bulk GaAs. In the thin MQW sample, the THz emission is still significant. This indicates the possibility of designing MQWs as efficient THz emitters in the future.
Brewster Angle Microscope Imaging of Surface Inhomogeneity in Liquid Crystal Alignment Polyimide Layers
Authors: Park Byoungchoo , Wu J. W. , Jung Chi-Sup
Published: October 2002

The surface structure of the polyimide alignment layer has been probed by various tools, but a direct visualization of the treated layer surface over a sizable area is lacking. We demonstrate Brewster angle microscope imaging of the micro-grooves formed on a rubbed polyimide alignment layer, compared with the flat surface image of a photo-aligned polyimide surface. Textures of cholesteric liquid crystal on these alignment layers showed that the rubbing causes a nonuniform orientational alignment of liquid crystals, in contrast to a uniform orientation in the photo-aligned cell. This tool enables early detection of surface defects in alignment layers, which would significantly reduce the failure in liquid crystal display fabrication.
Improved Electrochromic Response Time of Nickel Hydroxide Thin Film by Ultra-Thin Nickel Metal Layer
Authors: Jeong Do Jin , Kim Woo-Seong , Sung Yung-Eun
Published: October 2002

Improvements in the optical switching properties of electrochromic nickel hydroxide/nickel/glass thin film are reported. Nickel metal film was deposited on glass by e-beam evaporation prior to following electrochemical redox cycling to form nickel hydroxide for electrochromic activation. In the absence of the indium tin oxide (ITO) layer as an electrical conductor, this electrode showed a more rapid coloration rate than a nickel hydroxide film on ITO substrate in terms of change in electric voltage and optical transmittance. X-ray photoelectron spectroscopy analysis confirmed the existence of ultra-thin nickel metal layer between the electrochemically grown nickel hydroxide and the glass substrate. We conclude that the nickel metal nano-layer can be attributed to the conduction layer and the enhanced response time.
Energy Dispersive Near Edge X-Ray Absorption Fine Structure in the Soft X-Ray Region: A New Technique to Investigate Surface Reactions
Authors: Kenta Amemiya Kenta Amemiya , Hiroshi Kondoh Hiroshi Kondoh , Akira Nambu Akira Nambu , Masaoki Iwasaki Masaoki Iwasaki , Ikuyo Nakai Ikuyo Nakai , Toshihiko Yokoyama Toshihiko Yokoyama , Toshiaki Ohta Toshiaki Ohta
Published: October 2002

A novel technique, energy dispersive near edge X-ray absorption fine structure (NEXAFS) spectroscopy, has been successfully developed by using a position sensitive electron analyzer and a new soft X-ray beamline constructed at the bending magnet in the Photon Factory. It was revealed that the NEXAFS spectra can be obtained even for submonolayer adsorbates with an accumulation period of ∼ 30 s. As the first application of the new technique, coverage dependence of C-K-edge NEXAFS spectra were recorded in situ for thiophene adsorption on Au(111).
Molecular Beam Epitaxy of Wurtzite GaN-Based Magnetic Alloy Semiconductors
Authors: Seiji Kuwabara Seiji Kuwabara , Tsuyoshi Kondo Tsuyoshi Kondo , Toyohiro Chikyow Toyohiro Chikyow , Parhat Ahmet Parhat Ahmet , Hiroo Munekata Hiroo Munekata
Published: October 2002

The preparation of hexagonal GaN:Mn and GaN:Fe epilayers has been studied by RF-plasma-assisted molecular beam epitaxy. GaN:Fe epilayers exhibit superparamagnetic behavior, presumably due to ferromagnetic inclusions. GaN:Mn epilayers can be expressed in the form of Ga1-x
Mn
x
N with x up to 0.02, indicating the successful preparation of the GaN-based magnetic alloy semiconductor for the first time. The epilayers are primarily paramagnetic and highly resistive. For epilayers with very high Mn concentration (∼ 1021 cm-3), analysis of the paramagnetic component has revealed the effective spin number S ≈2.5 together with the positive paramagnetic Curie temperature. This suggests the presence of ferromagnetic spin exchange between Mn ions.
Enhanced Efficiency of a Dye-Sensitized Solar Cell Made from MgO-Coated Nanocrystalline SnO2
Authors: Tennakone Kirthi , Bandara Jayasundara , Bandaranayake Priyangi Konara Mudiyanselage , Kumara Gamaralalage Rajanya Asoka , Konno Akinori
Published: October 2002

Nanocrystalline SnO2-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325–375 mV and efficiencies of ∼ 1%. However, on coating the SnO2 crystallites with a thin film of MgO, the voltage and efficiency are increased to 650–700 mV and ∼ 6.5%, respectively. Evidence is presented to show that the photoexcited dye on the outer MgO shell could tunnel electrons to SnO2 and that the low probability of reverse tunneling suppresses recombinations, thus increasing the efficiency. An explanation is also given as to understand why dye-sensitized TiO2 cells are more efficient than those made from SnO2 alone.
An Improved Method for Obtaining Single-Phase Sr2MoO4 under Controlled Ultralow Oxygen Partial Pressure
Authors: Shirakawa Naoki , Ikeda Shin-Ichi , Matsuhata Hirofumi , Bando Hiroshi
Published: October 2002

We investigated a method for obtaining a sintered bulk sample of single-phase Sr2MoO4, which has recently increased in importance due to its similarities to superconducting Sr2RuO4. We discovered that with the aid of Ti2O3 as a p(O2) buffer, high-purity Sr2MoO4 is successfully synthesized in a sealed tube. We confirmed the space group and determined the exact elemental composition of the compound in order to establish its stoichiometry. The guideline for the rational choice of a p(O2)-buffer material is discussed.
Focusing Hard X-Ray with a Single Lens
Authors: Zhang Yanping , Katoh Takanori , Kagoshima Yasushi , Matui Junji , Tsusaka Yoshiyuki
Published: October 2002

We show that a 10 keV X-ray has been focused into 3.4–8.4 µm at a focal length F=0.4–1.5 m with a single refractive lens and such X-ray microbeams can be generated in array. For the beam from a synchrotron radiation source, which typically had a diameter φ=100 µm, transmissions of our lenses were measured to be T=54–85%. X-ray imaging of a copper mesh was carried out with a magnification of about 5 in one dimension and the imaging resolution was evaluated to be 0.9 µm. Our lenses have performed well under a flux of 1.1×1011 photons·s-1·mm-2, showing no visible damage due to the X-ray exposure.
Transition of Infrared Absorption Peaks in Thermally Annealed GaInNAs
Authors: Kitatani Takeshi , Kondow Masahiko , Kudo Makoto
Published: October 2002

We measured the infrared absorption of GaInNAs to clarify the origin of the large bandgap shift induced by thermal annealing. In the as-grown sample, an absorption peak due to the transverse-optical (TO) mode of Ga–N bonds was clearly observed at 469 cm-1. At higher annealing temperatures, the peak intensity decreased, and a new peak with an increased intensity appeared at 489 cm-1. Because the total absorbance of both peaks after the annealing was almost the same as that before the annealing, this peak transition resulting from thermal annealing is probably due to the alternation of the Ga–N bonding state. Because absorption peaks of larger bandgap semiconductors are generally observed in the higher wavenumber region, the observed transition of the peaks to the higher wavenumber side is consistent with the increased bandgap of GaInNAs. Therefore, we found that the variation in bonding causes the blue shift in the bandgap of GaInNAs during thermal annealing.
Improved Luminous Efficiency of Organic Light-Emitting Diodes by Carrier Trapping Dopants
Authors: Hamada Yuji , Matsusue Noriyuki , Kanno Hiroshi , Fujii Hiroyuki , Tsujioka Tsuyoshi , Takahashi Hisakazu
Published: October 2002

We propose a carrier trapping (CT) dopant method to improve the luminous efficiency of organic light-emitting diodes (OLEDs). The CT dopant did not emit light itself, but adjusted the charge balance in the OLEDs. The cell structure of the OLED in the experiment was as follows: Indium tin oxide (ITO)/hole transport layer (50 nm, 2TNATA)/emitting layer (20 nm, NPB+5% rubrene)/electron transport layer (30 nm, Alq+4% CT dopant)/MgIn. (2TNATA: 4,4′,4′′-Tris(N-(2-naphthyl)-N-phenyl-amino)-triphenylamine, NPB; N,N′-Di(naphthalen-1-yl)-N,N′-diphenyl-benzidine). 4,4′-Bis(carbazol-9-yl)-biphenyl (CBP) was used as a CT dopant. This cell had a yellow emission originating from the rubrene with the luminous efficiency of 8.7 cd/A at a current density of 10 mA/cm2. On the other hand, when the CT dopant was not used, the luminous efficiency was 7.5 cd/A. The luminous efficiency was improved by the CT dopant method.
Linear Birefringence along the (010) Direction of (NH3C3H7)2MnCl4
Authors: Kim Dal-Young , Glazer A. Michael
Published: October 2002

The newly-developed tilter method was used to measure the linear birefringence behaviour of (NH3C3H7)2MnCl4 in the temperature range between 50 K and 300 K. The birefringence along the (010) direction was measured for the first time. We observed the δ-ε and ε-ξ phase transitions in birefringence behaviour. It is shown that the tilter method can measure the birefringence along the direction normal to the incident laser beam.
Homeotropic Alignment Properties of Nematic Liquid Crystal on UV-Exposed Alignment Film
Authors: Akiyama Hidenari , Iimura Yasufumi
Published: October 2002

We have studied the homeotropic alignment properties of nematic liquid crystal (NLC) on UV-exposed alignment films of polyamic acid having alkyl branches, where the surface density of the alkyl branches is systematically reduced by the irradiation of UV light at the wavelength of 254 nm. We show that the UV irradiation of the alignment film reduces the surface density of alkyl branches. This reduction results in the decrease of the polar anchoring energy of NLC with a larger temperature dependence. These results are interpreted by considering two competing surface anchoring forces, which also promote the anchoring transition phenomenon in a highly UV-exposed sample.
Simple Measurement of Quantum Efficiency in Organic Electroluminescent Devices
Authors: Okamoto Shinji , Tanaka Katsu , Izumi Yoshitaka , Adachi Hironori , Yamaji Takayuki , Suzuki Takeo
Published: October 2002

A simple method of measuring the external quantum efficiency of organic electroluminescent (EL) devices has been investigated. Assuming a perfectly diffusive EL emission surface, this method enables the external quantum efficiency to be calculated from the conventionally measured parameters: luminance, EL spectrum, and current. Its use is limited to EL emission in the visible wavelength range.
Ultraviolet GaN Single Quantum Well Laser Diodes
Authors: Nagahama Shin-ichi , Yanamoto Tomoya , Sano Masahiko , Mukai Takashi
Published: October 2002

The ultraviolet laser diodes (LDs) whose active layers consisted of binary GaN were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. For the first time, we observed the lasing emission from binary GaN active layer by current injection. The emission wavelength of GaN single quantum well LDs was 366.9 nm under pulsed current injection and 369.0 nm under continuos-wave (cw) operation at room temperature. The threshold current density and voltage of these LDs under the 25°C cw operation were 3.5 kA/cm2 and 4.6 V, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.
Characteristics of Ultraviolet Laser Diodes Composed of Quaternary AlxInyGa(1-x-y)N
Authors: Nagahama Shin-ichi , Yanamoto Tomoya , Sano Masahiko , Mukai Takashi
Published: October 2002

Ultraviolet (UV) laser diodes (LDs) whose active layers were composed of quaternary Al
x
In
y
Ga(1-x-y)N were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We investigated the Al and In mole fractions dependence of LD characteristics in the UV region. The emission wavelength of the LDs whose active layers consisted of Al0.03In0.02Ga0.95N single quantum well (SQW) was 366.4 nm under pulsed current injection at room temperature. The lasing wavelength was the shortest ever reported for III-V nitride-based LDs. The Al0.03In0.03Ga0.94N SQW UV LDs were demonstrated under 25°C continuous-wave (cw) operation. The threshold current density and voltage of these LDs were 3.5 kA/cm2 and 4.8 V, respectively. The estimated lifetime was approximately 500 h under 25°C cw operation at an output power of 2 mW.
Efficient 1.5-µm-Band MgO-Doped LiNbO3 Quasi-Phase-Matched Wavelength Converters
Authors: Zhou Bing , Xu Chang-qing , Chen Bo , Nihei Yasukazu , Harada Akinori , Yang Xiu Feng , Lu Chao
Published: October 2002

1.5-µm-band wavelength converters based on cascaded χ(2) in periodically poled MgO:LiNbO3 (PPMGLN) waveguides are fabricated and studied for the first time. A conversion efficiency of -26 dB is obtained with the pump power of only 16 mW, which is compatible with the highest reported value of the PPLN wavelength converters based on nondoped substrates. The 3 dB conversion bandwidth is found to be as large as 68 nm for a 45-mm-long device.
Generation of Heralded Twin-Photons in a Series-Coupled Mesoscopic Light-Emitting Diode System
Authors: Hiroyuki Sumitomo Hiroyuki Sumitomo , Masamichi Yamanishi Masamichi Yamanishi , Yutaka Kadoya Yutaka Kadoya
Published: October 2002

A two-coupled mesoscopic single-junction light-emitting diode (LED) system is proposed to generate heralded twin-photons with a strong positive correlation, which have different energies. Monte-Carlo simulations demonstrate that the two photons are generated per modulation cycle with a regulated time interval due to the Coulomb blockade and quantum confinement effects, when the two-coupled LED system is driven by an alternating voltage source.
Synthesis of Heavy Carbon Clusters by Laser Ablation in Vacuum
Authors: Kanji Shibagaki Kanji Shibagaki , Koichi Sasaki Koichi Sasaki , Noriharu Takada Noriharu Takada , Kiyoshi Kadota Kiyoshi Kadota
Published: October 2002

It has been found that heavy carbon clusters can be produced by laser ablation in vacuum with no ambient gases. The synthesis of heavy clusters is obtained when a copolymer of ethylene and tetrafluoroethylene is employed as the target material for laser ablation. Time-of-flight mass spectrometry was used for analyzing ionic species produced by laser ablation. The significant temporal evolution of carbon cluster ions was observed even though no ambient gases were injected into the vacuum chamber. At ∼ 10 µs after the irradiation of the laser pulse, we detected a large amount of carbon cluster ions Cn
+ with n up to 400.
Vacancy Formation Energy of Silicon Determined by a New Quenching Method
Authors: Fukata Naoki , Kasuya Atsuo , Suezawa Masashi
Published: October 2002

By applying a new quenching method, we determined the formation energy of vacancies in high-purity silicon. Specimens were heated in H2 gas at high temperatures for 1 h followed by quenching in water. By this method, vacancies are quenched in the form of complexes with hydrogen and the vacancy formation energy can be determined from the quenching temperature dependence of the intensity of the optical absorption peak due to the complexes. The vacancy formation energy of silicon was determined to be about 4.0 eV. This value is in good agreement with results of recent theoretical calculation.
Spectral Analyses of the Impact of Nanotopography of Silicon Wafers on Oxide Chemical Mechanical Polishing
Authors: Park Jea-Gun , Katoh Takeo , Yoo Hyung-Chul , Park Jin-Hyung
Published: October 2002

The purpose of this study is to investigate quantitatively how the height change of silicon wafer surfaces (nanotopography) impacts on the variation of removal rate during oxide chemical mechanical polishing (CMP). We have analyzed the spatial power spectral densities (PSD) of both nanotopography and thickness variation of oxide film after CMP. We defined a transfer function as the ratio of PSD for the oxide film thickness variation to that for nanotopography. The transfer function decreased with increase of the wavelength and this result quantitatively indicates that longer wavelength of nanotopography influence relatively less on the oxide thickness variation after CMP.
High Frequency Operation of Nanoelectronic Y-Branch at Room Temperature
Authors: Worschech Lukas , Fischer Frank , Forchel Alfred , Kamp Martin , Schweizer Heinz
Published: October 2002

Nanoelectronic Y-branches have been fabricated using electron beam lithography and wet etching on modulation doped GaAs/AlGaAs heterostructures. The output voltage of the devices measured at the stem shows clear rectification characteristics as the input voltage of one branch is varied. The high frequency properties of rectification are investigated at room temperature. The second harmonic of a microwave injected into the right branch is observed at the stem up to 20 GHz.
Experimental Analysis of Classical Arago Point with White-Light Laser
Authors: Uno Katsuhiro , Suzuki Masahiro , Fujii Kan-ichi
Published: October 2002

The Arago point is a bright spot that appears at the center portion of the shadow of an obstacle such as a ball or a disk as the result of diffraction. Using this Arago point, we can judge the sphericity of a ball and the circularity of a disk, but it is difficult to distinguish the ball or the disk. To solve this problem, it is also necessary to observe the z coordinate component. As a method for doing this, we rotated the disk and observed its diffraction pattern as a function of the rotation angle. By employing the white-light laser as the light source and a three charge coupled device (3-CCD) camera as the detector, we have observed novel phenomena, for instance the deformation of the Arago point and the distortion of the circular fringes. Also, the color (wavelength) dependence of the diffraction angle could be directly understood in a visible sense.
Low-Threshold Continuous-Wave Lasing in Photopumped GaInAsP Microdisk Lasers
Authors: Masayuki Fujita Masayuki Fujita , Kousou Teshima Kousou Teshima , Toshihiko Baba Toshihiko Baba
Published: October 2002

We demonstrated continuous-wave lasing at room temperature in a photopumped GaInAsP microdisk laser fabricated by Cl2/Xe inductively coupled plasma etching. The minimum threshold pump power was as low as 30 µW. This value is 0.7 times the lowest threshold in the current injection device due to the uniform carrier distribution by photopumping. Higher thermal resistance and odd-order azimuthal mode lasing as a result of a narrower pedestal and no upper post structure were observed.
Ultrahigh Scanning Speed Optical Coherence Tomography Using Optical Frequency Comb Generators
Authors: Lee Seok-Jeong , Widiyatmoko Bambang , Kourogi Motonobu , Ohtsu Motoichi
Published: October 2002

A novel optical coherence tomography system without any moving parts for depth scanning was proposed and demonstrated. It was accomplished using two optical frequency comb generators, as broad-band spectrum generators, instead of moving parts for depth scanning. A high scanning speed of more than 12.5 km/s and also a high repetition rate of 500 kHz were achieved in a long scan range of 25 mm. The resolution was about 100 µm.
Virtual Space Charge Model for a Frequency-Based Characterization of Insulators
Authors: Jean-Luc Franceschi Jean-Luc Franceschi , Cédrick Biellmann Cédrick Biellmann , Laurent Berquez Laurent Berquez , Didier Marty-Dessus Didier Marty-Dessus
Published: October 2002

As insulators are stressed with a strong electric field, they store electric charges that can be represented as space charge distributions. We propose a simple equivalent model of these distributions in order to characterize the internal residual field in a thin polymeric insulator using a frequency-based technique called focused laser intensity modulation method (FLIMM). This approach shows its ability to follow simple evolutions resulting for example from an increasing of stressing field or of the poling duration time, avoiding in a first approximation the use of complex mathematical algorithms.
Observation of Optical Near-Field as Photo-Induced Surface Relief Formation
Authors: Fukuda Takashi , Sumaru Kimio , Kimura Tatsumi , Matsuda Hiro , Narita Yoshihito , Inoue Tsutomu , Sato Fuminori
Published: October 2002

The spatial distribution and the polarization condition of the optical near-field has successfully been visualized for the first time. It is realized in connection with the photo-induced surface relief formation on the azobenzene functionalized polymer film that had been reported so far only on the optical far-field condition. In this study, the observation was performed for linear and circular polarized light irradiation. The proposed technique is considered to be as a simple and an effective method to analyze the optical near-field.
High-Efficiency Oscillation of 170 GHz High-Power Gyrotron at TE31,8Mode Using Depressed Collector
Authors: Hiroaki Shoyama Hiroaki Shoyama , Keishi Sakamoto Keishi Sakamoto , Kenichi Hayashi Kenichi Hayashi , Atsushi Kasugai Atsushi Kasugai , Masaki Tsuneoka Masaki Tsuneoka , Koji Takahashi Koji Takahashi , Yukiharu Ikeda Yukiharu Ikeda , Tsuyoshi Kariya Tsuyoshi Kariya , Yoshika Mitsunaka Yoshika Mitsunaka , Tsuyoshi Imai Tsuyoshi Imai
Published: October 2002

Stable 1.1 MW oscillation was achieved by a 170 GHz high power gyrotron. The oscillation mode capable of the CW operation is TE31,8. The efficiency was 32%, which was enhanced to 57% by a depressed-collector operation. The parasitic oscillation in a beam tunnel (a beam drifting tube between an electron gun and a cavity) that degraded the oscillation efficiency was suppressed by installing an RF absorber. This result has a large impact on the development of a 1-MW-long-pulse gyrotron that is required for fusion devices.
Growth of High-Electron-Mobility InN by RF Molecular Beam Epitaxy
Authors: Saito Yoshiki , Teraguchi Nobuaki , Suzuki Akira , Araki Tsutomu , Nanishi Yasushi
Published: October 2002

We succeeded in growing InN films two-dimensionally by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE), using a low-temperature-grown InN buffer layer. From the results of reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction (XRD) measurement, it was found that a single crystal of InN films with a wurtzite structure was obtained. Moreover, from the results of Hall effect measurement, it was found that the InN films had quite high electron mobilities. The best electron mobility at room temperature obtained in this study was 760 cm2/V·s and the corresponding carrier density was 3.0×1019 cm-3. To our knowledge, this electron mobility is the highest value ever reported for single crystal InN films.
Influence of Oxygen on Formation of Hollow Voids at SiC/Si Interface
Authors: Yong Sun Yong Sun , Toyotsugu Enokida Toyotsugu Enokida , Hiroyasu Hagino Hiroyasu Hagino , Tatsuro Miyasato Tatsuro Miyasato
Published: October 2002

Influences of oxygen on the formation of hollow voids at the SiC/Si interface are studied by electric current heating of the Si substrate in the temperature range of 650°C to 1000°C. By changing the thickness of the SiC film and the concentration of residual oxygen in the Si substrate, we found that the formation of hollow voids depends on the concentration of residual oxygen, and the formation reaction of hollow voids is enhanced around the oxygen-related defects in the Si substrate.
Proposal of Optically Pumped Tunable Surface Emitting Laser
Authors: Murakami Ayako , Sekiguchi Shigeaki , Sakaguchi Takahiro , Miyamoto Tomoyuki , Koyama Fumio , Iga Kenichi
Published: October 2002

A tunable laser is a key device for providing flexibility and functionality in future Wavelength Division Multiplexing networks. We propose a novel optically pumped tunable surface emitting laser. The lasing wavelength of the device can be varied by changing the photo-pumped position of a vertical cavity with a spatial gradient in the cavity length. A possibility of mode-hop-free wide wavelength tuning is presented over current existing tunable lasers. We fabricated a GaInAsP/InP short cavity and measured the resonant spontaneous emission of an optically pumped cavity with spatial gradient. The change of the resonance peak is as large as 40 nm. The obtained result shows the possibility of large continuous wavelength tuning.
Spontaneous Polarization and Piezoelectric Effects on Inter-Subband Scattering Rate in Wurtzite GaN/AlGaN Quantum-Well
Authors: Park Seoung-Hwan , Ahn Doyeol , Lee Yong-Tak
Published: October 2002

Spontaneous (SP) and piezoelectric (PZ) polarization effects on the inter-subband scattering rate for wurtzite (WZ) GaN/AlGaN quantum-well (QW) are investigated theoretically as functions of the sheet carrier density and the well thickness. This is also compared with the data obtained without the SP and PZ polarization effects. The SP polarization constant for AlN estimated from a comparison with the experimental results is about -0.060 C/m2, which is lower than the value (-0.081 C/m2) calculated by theoretically. The SC model shows that scattering rates are largely reduced compared with those for the FB model. This is mainly due to the increase of the inverse screening length with inclusion of the PZ and SP polarization. The inverse screening length is obtained by assuming that electrons and holes exist in the well simultaneously. The intra-subband scattering rate at the subband edge increases with increasing carrier density and gradually decreases when the carrier density exceeds 10×1012 cm-2. On the other hand, the inter-subband scattering rate gradually decreases due to the increase of the inverse screening length with increasing carrier density.
Organic Light-Emitting Diode with TiOPc Layer–A New Multifunctional Optoelectronic Device
Authors: Jingping Ni Jingping Ni , Takanori Tano Takanori Tano , Yoshiro Ichino Yoshiro Ichino , Takeshi Hanada Takeshi Hanada , Toshihide Kamata Toshihide Kamata , Noriyuki Takada Noriyuki Takada , Kiyoshi Yase Kiyoshi Yase
Published: October 2002

An organic light-emitting diode containing titanyl phthalocyanine (TiOPc) and tris-(8-hydroxy quinoline) aluminum (Alq3) layers has been fabricated. The device exhibits green emission from the Alq3 emissive layer under ambient conditions. Below the turn-on voltage, the green emission is instantaneously switched on by laser irradiation at 650 nm, indicating that the device can be used as a red-to-green light converter. Above the turn-on voltage, the green emission is greatly enhanced by laser irradiation, while the current-voltage characteristics are significantly modified. Amplification factors of the emission intensity as well as the current density upon laser irradiation are found to greatly depend on the TiOPc layer thickness. The TiOPc layer acts as a hole generation layer rather than as a buffer layer.
Measurements of the Nonlinear Refractive Index of an Er3+-Doped Bi2O3-Based Glass Fiber
Authors: Hiroshi Kitano Hiroshi Kitano , Akira Tokuhisa Akira Tokuhisa , Masaaki Doi Masaaki Doi , Soichi Owa Soichi Owa
Published: October 2002

A nonlinear refractive index n
2 determines the spectral broadening of optical pulses due to self-phase modulation. We report on the generation of kilowatt peak power optical pulses by an Er3+-doped Bi2O3-based glass fiber amplifier. We estimate n
2 of a Bi2O3-based glass fiber by measuring the spectral broadening of output pulses from the fiber amplifier. The obtained value of n
2 is (4.9±0.6)×10-19 m2/W at 1.55 µm wavelength. To our knowledge, this represents the first evaluation of n
2 in an Er3+-doped Bi2O3-based glass fiber.
Morphology and Visible Ray Reflection of Aventurine Glass Including Cr2O3 Microcrystals
Authors: Takahashi Shinichi , Nishimura Yuji , Tabata Hiroshi , Shimizu Tadao
Published: October 2002

Aventurine glass is a colored glass that has been utilized as art glass. We studied the morphology and the reflective property of Cr2O3 microcrystals in SiO2–B2O3–Na2O glass. An increase in B2O3 content and Cr2O3 addition rate increases the number of microcrystals in aventurine glass. The aventurine glass fiber that was packed Cr2O3 microcrystals into the base glass with high density shows a higher reflectance at the peak wavelength than the glass fiber colored by Cr3+. Moreover, the reflectance of the aventurine glass fiber is correlated with the number of Cr2O3 microcrystals in aventurine glass.
Refractive Index Control and Grating Fabrication of 4′-N,N-dimethylamino-N-methyl-4-stilbazolium Tosylate Crystal
Authors: Cai Bin , Hattori Toshiaki , Deng Hui Hua , Komatsu Kyoji , Zawadzki Crispin , Keil Norbert , Kaino Toshikuni
Published: October 2002

The refractive index of nonlinear optical ionic crystal 4′-N,N-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) was controlled by a photobleaching technique. The ellipticity of the DAST refractive index ellipsoid decreased after the irradiation of a 532 nm laser. By means of the photobleaching effect we fabricated a grating on DAST single crystals by two-beam interference. The calculation based on the diffraction efficiency indicates that the depth of refractive index change can be extended to 5.75–7.38 µm by 2.08 W/cm2 irradiation power. This result is promising for the fabrication of DAST waveguides by photobleaching.
Possibility of Two-Step As-Desorption from (001) InP Using Surface Photoabsorption
Authors: Young Seong Tae-Wan Lee , Young-Dong Kim Young-Dong Kim , Heedon Hwang Heedon Hwang , Sukho Yoon Sukho Yoon , Euijoon Yoon Euijoon Yoon
Published: October 2002

We present an in situ investigation of As-desorption from the (001) InP surface using surface photoabsorption (SPA). At 470°C, we observed that the SPA signals along [110] remained unchanged even after the AsH3 supply was turned off, while the SPA signal along [110] showed a sharp increase as reported previously. We also measured SPA spectra at several stable states and found that the surface after AsH3 was turned off could not reach that of an In-stabilized surface. We interpret these results in terms of As-desorption occurring possibily as a two-step process, in contrast to P-desorption of a one step process.
Emission Properties from Carbon Nanotube Field Emitter Arrays (FEAs) Grown on Si Emitters
Authors: Yoshimoto Tomomi , Iwata Tatsuo , Minesawa Ryuutaro , Matsumoto Kazuhiko
Published: October 2002

Electron emission properties of carbon nanotube field emitter arrays (CNT FEAs) having carbon nanotube emitters on the top of Si emitters were investigated under the ultrahigh-vacuum (UHV) condition. The emission pattern from the CNT FEAs was confirmed on a phosphor screen. The emission current followed the Fowler-Nordheim relationship under the high emission current condition. With the emission current of 0.5 mA, the fluctuation of the emission current was 3% or lower at the background pressure of ∼ 10-7 Pa.
Large-Area Optical Coatings with Uniform Thickness Grown by Surface Chemical Reactions for High-Power Laser Applications
Authors: Shin-ichi Zaitsu Shin-ichi Zaitsu , Shinji Motokoshi Shinji Motokoshi , Takahisa Jitsuno Takahisa Jitsuno , Masahiro Nakatsuka Masahiro Nakatsuka , Tatsuhiko Yamanaka Tatsuhiko Yamanaka
Published: October 2002

We prepared optical thin films using an atomic layer deposition (ALD) procedure in order to apply this coating method to optical components for high-power and large-scale lasers. Film thickness shows a proportional relationship to the number of operation cycles even in the case of room-temperature growth, and the distribution is uniform with a thickness error of less than 1% over an area of 240 mm diameter. We examined the laser damage thresholds of the films with 1 ns laser pulses at 1.064 µm. The highest thresholds (TiO2: 5 J/cm2, Al2O3: 5.2 J/cm2) are obtained in the amorphous films grown at low growth temperatures (25–50°C). Results from the analysis of film structure and composition, and measurement of optical absorption reveal that the decrease in laser damage threshold as the growth temperature rises is caused by the crystallization of films.
Dynamic Pattern Formation and Beam-Steering Characteristics of Cholesteric Gratings
Authors: Fuh Andy Ying-Guey , Lin Chi-Huang , Huang Chi-Yen
Published: October 2002

The dynamic pattern formation and the beam-steering characteristics of cholesteric gratings were studied. Films with a planar cholesteric texture and various thickness to pitch length ratios (d/p) were fabricated. An optical microscope was used to observe the stripe patterns of the cholesteric gratings formed by applying a voltage to the planar films. The micrographs showed that the cholesteric gratings were formed in two different ways, depending on the sample'sd/pratio. For samples with 1/2≤d/p≤1.0, the grating stripes simultaneously appeared across the whole sample, and the contrast of the stripes increased with time during formation. For films withd/p≥1.5, the stripes were initiated near the edges, and near the defects on the substrates, and then slowly extended to the whole sample along the rubbing direction. The diffraction measurements showed that the diffracted beams could be steered either electrically or optically only for the latter type of film. These results can be well explained theoretically.
Low-Resistivity Phosphorus-Doped Polycrystalline Silicon Thin Films Formed by Catalytic Chemical Vapor Deposition and Successive Rapid Thermal Annealing
Authors: Morimoto Rui , Izumi Akira , Masuda Atsushi , Matsumura Hideki
Published: October 2002

Low-resistivity phosphorus (P)-doped polycrystalline silicon (poly-Si) thin films were prepared from amorphous silicon (a-Si) films deposited by catalytic chemical vapor deposition (Cat-CVD) and successive rapid thermal annealing (RTA). RTA was carried out at 1000°C for crystallization of heavily P-doped a-Si prepared by Cat-CVD. The films are suitable for the solid-phase crystallization (SPC) process because of their low hydrogen (H) content. It is revealed that both the crystallization and low resistivity of 0.001 Ω·cm are realized by RTA at 1000°C for only 5 s. Even after high-temperature RTA processes, perfect surface-flatness is maintained and neither peeling nor bubbling due to H atoms in the films is observed.
Book reviews
Authors: Sutherland Karen
Published: October 2002

If you are interested in reviewing books for

intelligence

, please contact book review editor Karen Sutherland at intelligence_book-reviews@acm.org.
One Foot in the Furrow: Implications to One's Career in Plant Pathology
Authors: Mathre D.E.
Published: October 2002

Most of us want to be successful in what we do—either financially or programmatically. For me, being a good, well-respected plant pathologist is what motivated me throughout my professional career. After being trained as a plant pathologist at the University of California-Davis, an institution that prides itself in solving problems, I spent the majority of my career in population-sparse Montana—“the last best place.” And best place it has been for me as I became involved in researching a number of plant disease problems and solving a few. J.C. Walker's philosophy of keeping “one foot in the furrow” has stood by me, and I encourage young plant pathologists to adopt it as well to ensure a productive and satisfying life in agricultural science.
Coronary Flow Velocity and Disturbed Flow Predict Adverse Clinical Outcome After Coronary Angioplasty
Authors: Kinlay Scott , Grewal Jasmine , Manuelin Deborah , Fang James C. , Selwyn Andrew P. , Bittl John A. , Ganz Peter
Published: October 2002

Objective—

Laminar flow becomes disturbed at high velocities, reducing shear stress and augmenting vascular inflammation and proliferation, processes that are pivotal in restenosis and atherogenesis. We hypothesized that disturbed blood flow after coronary angioplasty is associated with adverse long-term clinical outcome.

Methods and Results—

The cineangiograms from 97 patients undergoing laser-assisted coronary angioplasty were analyzed. Coronary blood flow velocity, the residual lesion dimensions, and the Reynolds number (an index of disturbed flow) were measured by using a frame-counting technique and quantitative coronary angiography. Cox proportional hazards were used to assess the relative risk of adverse events (target-vessel revascularization, myocardial infarction, or death) over a mean 2.5 years after the index procedure. There were 41 adverse events during 245 patient years of follow-up (17% per year of follow-up). The risk of an adverse event was increased for patients with a high flow velocity (>250 mm/s; relative risk 2.5, 95% CI 1.3 to 4.7) or a high Reynolds number (>200) at the stenosis inlet (relative risk 2.1, 95% CI 1.1 to 4.1) at the end of the procedure. Adjustment for other factors did not alter these results.

Conclusions—

High Reynolds numbers, indicating disturbed blood flow after coronary angioplasty, increase the risk of adverse clinical events, potentially through shear-stress–related molecular mechanisms that promote restenosis and atherogenesis.