bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin Relaxation of Electrons in Strained-GaAs-Layer Photocathode of Polarized Electron Source
Authors: Horinaka Hiromichi , Ono Daisaku , Zhen Wendong , Wada Kenji , Cho Yoshio , Hayashi Yoshikazu , Nakanishi Tsutomu , Okumi Shoji , Aoyagi Hideki , Saka Takashi , Kato Toshihiro
Published: October 2002

The luminescence polarization method using a mode-locked Ti:sapphire laser and a streak camera is applied to the measurement of the spin relaxation time and the lifetime of electrons in the strained-GaAs-layer photocathode of a polarized electron source. The spin relaxation time and the electron lifetime are 105 ps and 45 ps at room temperature, respectively. Electron-hole scattering is thought to be the main mechanism of the spin relaxation of our strained-GaAs photocathode.
Simultaneous Analysis of Total Reflection X-Ray Diffraction and Fluorescence from Copper-Phthalocyanine Thin Films during Evaporation Process
Authors: Hayashi Kouichi , Horiuchi Toshihisa , Kazumi Matsushige Kazumi Matsushige
Published: October 2002

A newly developed X-ray measuring system, capable of simultaneously conducting total-reflection X-ray diffraction (TXRD) and total-reflection X-ray fluorescence (TXRF) analyses, was utilized to follow the adsorption and structural changes in copper phthalocyanine (CuPc) thin films during an evaporation process. The intensities of Cu Kα fluorescent X-rays provided precise data on the amount of CuPc molecules adsorbed on the substrate of SiO2, and thus the difference in adsorption coefficient of CuPc molecules on the SiO2 substrate and the oscillator surfaces of Ag could be evaluated in the first place. Moreover, by combining these fluorescent data with the diffraction data we could follow the exact changes of molecular orientation with the increase of film thickness. The data on the film thickness variations of the X-ray profiles revealed that the structural change in the CuPc molecular crystal occurred at about 9 nm thickness of the evaporated film.
Preparation and Evaluation of Direct Current Glow Discharge Plasma-Polymerized Films of Naphthalene and Octafluoronaphthalene
Authors: Suwa Toshihiro , Jikei Mitsutoshi , Kakimoto Masa-aki , Yoshio Imai Yoshio Imai
Published: October 2002

The plasma polymerization of naphthalene and octafluoronaphthalene using a DC glow discharge was performed. The prepared films were characterized by FT-IR and Raman spectroscopies, ESCA, ellipsometry, and contact angle measurements. The deposition rates of all of the plasma-polymerized films were high under general conditions (1-10 W). The applied voltage was found to strongly influence the structure of the deposited films. The ESCA profiles indicated that the deposited films were composed of a highly oxidized surface and a carbon-rich bulk region. This technique is also applicable to the preparation of hydrogen-free carbon films.
Mixing and Matching Deep-UV Step-and-Scan with I-Line Step and Repeat
Authors: Harry Sewell Harry Sewell
Published: October 2002

This paper reviews all the major aspects of successfully implementing a “mix and match” (Deep-UV/I-line, stepper/scanner) strategy. The resolution and linewidth-control limits of I-line are quantified for a number of the process levels and compared with the capabilities of Deep-UV step-and-scan. This analysis predicts the typical mix of steppers and scanners in a 256 MBit production line for 250 nm lithography. A step-by-step procedure to achieve and monitor successful matching is reviewed. The procedure begins by defining a “golden system”, which is used to produce reference wafers for the setup and monitoring of all the systems being mixed and matched. The reference wafers are used to ensure that the pre-aligners of the systems are calibrated and that offsets are adapted to allow the transfer of wafers between systems. The wafers are also used to match both wafer-stage grid and exposure-field distortions. The matching of both wafer-grid and stepper-field distortions are reviewed. The implementation of stage correction-tables is demonstrated. It is indicated that grid matching to better than 10 nm is achievable. It is also indicated that the dynamic scanning of a step-and-scan system allows the monitoring and correction of such typical stepper problems as field magnification and rotation. The critical aspects of multi-field matching between stepper and scanner are analyzed. The key factors that allow the successful overlaying of large, single, scanned fields with multiple, small, stepped fields are reviewed. The total overlay accuracy achieved using step-and-scan, and “mix-and-match” is analyzed and demonstrated.
Active Vibration Correction in Electron Beam Lithography System
Authors: Nagata Kouji , Ohta Hiroya , Morimura Toshiyuki , Okumura Masahide , Norio Saitou Norio Saitou
Published: October 2002

In an electron beam (EB) lithography system, beam positional vibration is one of the most influential factors of positioning accuracy degradation. We propose a new correction method for improving this accuracy and investigate its effectiveness by applying it to a nanometer EB system. In our method, first, the correction signal is generated by detecting the beam positional vibration as the variation of the backscattered or the transmitted electron signal and then extracting one period of this signal. Then, the correction signal is added to that of the beam deflection control. The effectiveness of this correction is evaluated by measuring beam positional vibration and stitching accuracy of the delineated pattern between subfields with size of 8 µ m×8 µ m. As a result, both an amplitude of the beam vibration of less than 10 nm and a stitching accuracy of less than 8 nm (3σ) are achieved, which confirms that the beam vibration has been actively corrected, and the positioning accuracy has been improved. The above results indicate that this correction method is very valuable for the EB lithography system.
Accuracy Evaluation of Representative Figure Method for Proximity Effect Correction
Authors: Nakasugi Tetsuro , Abe Takayuki , Satoshi Yamasaki Satoshi Yamasaki
Published: October 2002

The correction accuracy of the representative figure method is studied. In order to evaluate pattern size deviation using the small area size as a parameter, we carry out a systematic experiment using a 0.2 µ m line-and-space pattern. It is found that the small area size of an element and a reference rectangle can be maximized at 5 µ m and 15 µ m, respectively, to suppress the pattern size deviation below 10%, or 0.02 µ m. The large area sizes obtained here result in the reduction of calculation time for correction. The correction time itself can be reduced to 1/16 of that in our previous work. When a 4 CPU (50 MIPS per CPU) computer is used, the total calculation time can be completed in less than 15 min for a chip of 15×15 mm2 size.
Effects of Mask Line-and-Space Ratio in Replicating near- 0.1-µm Patterns in X-Ray Lithography
Authors: Kikuchi Yukiko , Nomura Hiroshi , Kondo Kenzo , Higashikawa Iwao , Yoshio Gomei Yoshio Gomei
Published: October 2002

In replicating line-and-space ( L/S ) patterns by X-ray proximity printing, optimizing the mask duty together with mask contrast is crucial to obtain high resolution in the 0.1 µ m region. We have successfully replicated L/S down to the pitch of 0.18 µ m, and evaluated the effects of mask L/S ratio. It was confirmed that the mask L/S ratio is transferred to the replicated pattern more faithfully as the proximity gap becomes narrower, and the ratio should be about 1:1 to achieve large exposure latitude together with wide dose margin. The results of our calculation agreed well with the experimental results upon introducing novel criteria to estimate replicated pattern width. Exposure latitude for 0.1±0.01 µ m L/S replication using the gaps of 10 and 15 µ m was within ±12% with feasible pattern profiles, although the specification of measured mask L/S differed from the ideal one. Even for the gap of 20 µ m the exposure latitude remained within ±6%.
Analysis of Deformation of X-Ray Mask Membrane in Aligner Motion
Authors: Mitsui Ryuji Takaki , Tohru Itoh Tohru Itoh , Nobufumi Atoda Nobufumi Atoda
Published: October 2002

Deformation of X-ray mask membrane is analysed theoretically based on the viscous fluid dynamics in the case where a solid boundary (wafer) placed adjacent to the membrane moved perpendicular to the membrane. It is assumed that the membrane and its support are axisymmetric and the gap between the membrane and the wafer is so thin that the Hele-Shaw flow theory can be applied. It is shown that the center of the membrane is deflected in the same direction as the wafer motion and that the maximum deflection depends on the membrane tension and the final gap. The results of analysis agree well with the experiment.
Improving X-Ray Mask Pattern Placement Accuracy by Correcting Process Distortion in Electron Beam Writing
Authors: Uchiyama Shingo , Ohki Shigehisa , Ozawa Akira , Oda Masatoshi , Matsuda Tadahito , Tetsuo Morosawa Tetsuo Morosawa
Published: October 2002

A new correction method named PAT (previous analysis of distortion and transformation of coordinates) has been developed for improving the pattern placement accuracy of completed X-ray masks. PAT compensates for total-process distortion in the electron beam writing step. In PAT, overall pattern position shifts are estimated using a send-ahead mask in advance of making working masks. Then the pattern position shifts obtained from the send-ahead mask are compensated for during electron beam writing. In an experiment, the pattern placement error of a completed X-ray mask represented by 3σ was reduced to below 0.07 µ m. This confirmed that highly accurate X-ray masks could be fabricated using PAT.
Nanofabrication of Multilayer Zone Plates by Helicon Plasma Sputtering
Authors: Koike Masaki , Isao H. Suzuki Isao H. Suzuki
Published: October 2002

Multilayer zone plates whose outermost zone widths are less than 100 nm have been fabricated. Alternate deposition of Ag and Al layers has been performed using a helicon plasma sputtering technique, in which Ar gas pressure was less than 1×10-3 Torr, which is one order lower than in conventional magnetron sputtering. More than 100 Ag/Al layers were deposited, with the thickness of each layer being monitored and controlled by a computer. The multilayered plane was sliced vertically and thinned after the deposition. The multilayer zone plate combined with a crystal acts as a monochromatizing and focusing device for hard X-rays, i.e., a Bragg-Fresnel lens.
Nanofabrication of Fresnel Zone Plates for X-Ray Focusing
Authors: Baciocchi Marco , Fabrizio Enzo Di , Gentili Massimo , Grella Luca , Maggiora Romano , Mastrogiacomo Luigi , Daniela Peschiaroli Daniela Peschiaroli
Published: October 2002

In this paper E-beam nanolithography and gold electroplating on very thin silicon nitride membranes, are combined for fabrication of amplitude soft X-ray Zone Plates (λ=40 Å) with resolution down to 50 nm and external diameters up to 200 µ m. In particular, challenges to the lithographic process introduced by advanced and non-standard requirements, such as large external diameters together with a very high resolution external zones pitch, and ring-to-space ratio optimization for higher order focusing (2nd order), will be studied in detail. The mechanism of image formation and control is studied by means of Monte Carlo electron scattering modelling, and a self consistent proximity effect routine is specifically developed for the case of Zone Plates. Some of the fabricated ZPs were tested at a dedicated synchrotron microscopy beam line working at 3.7 nm, showing 1st-order efficiencies up to 9.5% (against a theoretical 10%) and resolutions down to 50 nm for the second order.
Real Time Monitoring of NH3 Concentration Using Diffusion Scrubber Sampling Technique and Result of Application to the Processing of Chemically Amplified Resists
Authors: Park Jungchul , Bae Eunyoung , Park Chungeun , Han Woosung , Koh Youngbum , Lee Moonyoung , Jonggil Lee Jonggil Lee
Published: October 2002

The application of chemically amplified resist is known to cause a problem in the accurate measurement of the concentration of basic gas species ( NH3, N-methylpyrrolidone (NMP)) in a clean room environment because it is sensitive to its environment. Among various methods of measurement, diffusion scrubber sampling method was selected and tested. The environmental sensitivity of a commercial chemically amplified resist, APEX-E, was also tested. For the concentration measurement, the method proved to be suitable for automation and good for measuring NH3 concentration as low as the sub ppb level (limit of detection ∼0.08 ppb). Some measurement results concerning various aspects of application are presented. Test results of the environmental stability of chemically amplified resists showed that NH3 concentration should be controlled to at least under 7.5 ppb for maintaining the process stability.
Negative Tone Dry Development of Si-Containing Resists by Laser Ablation
Authors: Yamaguchi Atsuko , Tachibana Hiroaki , Oizumi Hiroaki , Soga Takashi , Tanaka Toshihiko , Ogawa Taro , Matsumoto Mutsuyoshi , Eiji Takeda Eiji Takeda
Published: October 2002

A new negative tone dry development process is proposed. This process consists of area selective oxidation of a Si-containing layer with soft X-ray exposure and removal of the unoxidized areas by KrF laser ablation. Polysilane and Si-containing polystyrene have been investigated as resist polymers. Laser ablation rates of the polymers have been measured. The unexposed areas of a polysilane film have a high ablation rate while exposed areas cannot be ablated. Measurement done in air, O2-, and N2-gas atmospheres show that oxidation of Si atoms suppresses ablation. A bilayer resist using a polysilane film as a surface-imaging layer has been patterned using this dry development process and 0.4-µ m patterns have been replicated. This dry process has the potential to be used in sub-half micrometer lithography.
Role of Oxygen in Poly-Si Etching by Cl2/O2 Plasmas
Authors: Ozawa Nobuo , Matsui Takayuki , Jun Kanamori Jun Kanamori
Published: October 2002

The increase in poly-Si etch rate at low O2 concentration (1-5%) in Cl2/O2 plasmas was investigated using optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS). The OES spectrum indicates that the Cl (837.5 nm) intensities increase at low O2 concentration during the poly-Si etching but the dissociation of Cl2 is not promoted by the addition of O2 to Cl2. SiCl (287 nm) intensities decrease in the range of O2 concentration where poly-Si etch rate increases. The result of XPS shows that by increasing O2 concentration from 0% to 3%, the amount of Cl and O adsorbed onto poly-Si surface decreases and increases, respectively. In Cl2/O2 plasmas, a cause of the poly-Si etch rate increase may be that oxygen atoms adsorb more easily on the poly-Si surface than chlorine atoms, and this weakens the Si-Si back bonds.
Aluminum Reflow Behavior in Via-Hole Filling Investigated by Molecular Dynamics Simulation and Computer Graphics
Authors: Yamauchi Ryo , Endou Akira , Katagiri Masahiko , Kubo Momoji , Stirling Aandras , Miyamoto Akira , Ohta Tomohiro
Published: October 2002

We have performed molecular dynamics simulation to study the fine structure of Al thin layer and Al reflow behavior in a temperature range of 300 K-1400 K. We have shown that at 300 K the Al atoms on the insulator surface do not migrate toward the via-hole. With increasing the temperature, the mobility of all the Al atoms increased and the via-hole was completely filled with the Al atoms at 1400 K. This acceleration of Al reflow behavior due to the rise of the temperature is in qualitatively good agreement with the experimental result. Furthermore, we clarified the dynamic transformation process of an Al thin-layer on SiO2surface to an Al plug filling in the via-hole on an atomic scale. Hence, the effectiveness and the applicability of the molecular dynamics method to investigate the Al reflow behavior related to the fabrication of an electronic device were strongly confirmed.
Molecular Dynamics Simulations of Metal Clusters and Metal Deposition on Metal Surfaces
Authors: Katagiri Masahiko , Kubo Momoji , Yamauchi Ryo , Miyamoto Akira , Nozue Yasuo , Terasaki Osamu , Coley Terry R. , Li Yongsheng Sean , Newsam John M.
Published: October 2002

The geometries and energies of Pd
n
clusters (n=2-15) and the deposition of Pd atoms on the Cu(110) surface at several temperatures have been studied by molecular dynamics using embedded-atom type potentials. Compact structures were obtained for the small Pd
n
clusters; these geometries are compared with results for Many-Body Alloy (MBA) and Lennard-Jones potentials. For Pd atoms on the Cu(110) surface, the simulations indicate no substantial Pd penetration into the bulk, but unconstrained thin slab models do exhibit surface-driven melting and Pd penetration. The motion Pd adatoms on the surface is influenced by the surface dynamics, which manifests anharmonicity and roughening.
Atomic Control of Ultrafine Gold Particles on MgO(100) as Investigated by Molecular Dynamics and Computer Graphics
Authors: Kubo Momoji , Miura Ryuji , Yamauchi Ryo , Katagiri Masahiko , Vetrivel Rajappan , Broclawik Ewa , Akira Miyamoto Akira Miyamoto
Published: October 2002

The applicability of our new molecular dynamics code to the design of highly dispersed ultrafine Au particles on an MgO(100) plane, which is essential for the maximum catalytic performance, was demonstrated. Although only a single large Au cluster was formed on a smooth MgO(100) plane, two Au clusters were formed on an MgO(100) plane with either two point defects or two monoatomic steps at 300 K, since a single trapped Au atom in each defect site played a role of the nucleation center. These results suggested that the artificial construction of defects on the MgO(100) plane is desirable for realizing the ultrafine dispersion of Au particles. Furthermore, two Au clusters just over the surface step sites did not aggregate even at high temperatures, such as 700 K.
Thus, it was also revealed that the surface defects are effective for inhibiting the sintering of Au clusters on the MgO(100) plane, which is essential for preventing catalyst deactivation.
Observation Technique of Surface Magnetic Structure Using Type-I Magnetic Contrast in the Scanning Electron Microscope
Authors: Kotera Masatoshi , Katoh Misao , Hiroshi Suga Hiroshi Suga
Published: October 2002

The type-I magnetic contrast in the scanning electron microscope is simulated. The magnetic flux that leaked from the surface magnetic domain is calculated based on the Maxwell equation. Trajectories of secondary electrons emitted from the surface are traced considering this magnetic field and the electric field generated by the secondary electron detector. On the basis of the characteristic variation of the spatial deviation of electrons arriving at the detector, the original domain structure at the specimen surface is estimated.
New Challenges for Deltalike Confinement of Impurities in GaAs
Authors: Ploog Klaus H. , Lutz Däweritz Lutz Däweritz
Published: October 2002

We review some aspects of deltalike confinement of isoelectronic and dopant impurities in (001) GaAs. Nucleation, redistribution and relaxation are the important processes for achieving structural perfection and hence the resulting electronic properties for both the generation of quantum dots and wires by self-organized molecular beam epitaxy (MBE) growth and high-density incorporation up to one monolayer. In detail, we discuss the fabrication and properties of InAs quantum dots and wires, of Si doping wires in GaAs, and of Si-delta-doped GaAs with highly improved free-carrier density. The most important issue in our experiments is that the impurity species must be deposited not continuously, but in pulses to ensure ordered incorporation on lattice sites along step edges.
Self-Aligned Fabrication of Extractor for Cone-Shaped Metal-Insulator-Semiconductor Electron Tunneling Cathodes
Authors: Gotoh Kazunori Inoue , Hiroshi Tsuji Hiroshi Tsuji , Junzo Ishikawa Junzo Ishikawa
Published: October 2002

An extractor, which is expected to play a significant role in the improvement of the electron emission efficiency of a cone-shaped metal-insulator-semiconductor (MIS) cathode, has been successfully fabricated using self-aligned photolithography. The present method requires the mask patterning to be carried out only once. Also, sharpening of the cone apex was achieved by retaining the SiO2 mask during the oxidation process. The fabricated devices at each step of the process were observed with a scanning electron microscope (SEM) and formation of preferable structure for electron emission was confirmed. The diode characteristics of the fabricated MIS cathode were similar to those of the previously fabricated cathodes without the outside electrode. It was also observed that the external electric field decreased the threshold voltage of the electron emission.
Ultra-Shallow and Abrupt Boron Profiles in Si by δ-Doping Technique
Authors: Kujirai Hiroshi , Murakami Eiichi , Shin'ichiro Kimura Shin'ichiro Kimura
Published: October 2002

Ultra-shallow and abrupt boron (B) profiles in Si are achieved by molecular beam epitaxy, and the thermal stability of these profiles is closely examined. Oxidation-enhanced diffusion of a B-δ-doped Si layer is observed at 700-850° C. However, broadening of the δ-doped layer during gate oxidation can be minimized by wet O2 oxidation owing to the shorter oxidation time than that of dry O2. The sheet resistance of heavily δ-doped layers with ultra-shallow junctions is 1 kΩ /sq which is almost constant even after thermal annealing. This value is about 1/10 of the reported value obtained by solid-phase diffusion from boron-silicated glass film, in which solid solubility limits the maximum carrier concentration.
Real-Time Monitoring of Surface Reactions during Plasma-Enhanced CVD of Silicon
Authors: Miyazaki Seiichi , Shin Hidetoshi , Miyoshi Yasutoshi , Masataka Hirose Masataka Hirose
Published: October 2002

Reacting silicon surfaces in contact with a SiH4 glow discharge have been studied by a real-time, in situ Fourier-transform infrared attenuated total reflection (FT-IR-ATR) technique. In the early stages of silicon deposition at a substrate temperature of 200° C, SiH2 is the major surface species although ( SiH2)
n
chains and SiH3 also exist, while at room temperature, SiH3 and ( SiH2)
n
chains are the dominant surface products. At a temperature of -95° C, polymerization reactions among adsorbates proceed on the surface to form polysilanes consisting of ( SiH2)
n
chains terminated with SiH3.
Low-Temperature Drain Current Characteristics in Sub-10-nm-Thick SOI nMOSFET's on SIMOX (Separation by IMplanted OXygen) Substrates
Authors: Omura Yasuhisa , Masao Nagase Masao Nagase
Published: October 2002

This paper describes specific features in low-temperature drain current and transconductance characteristics of thin silicon-on-insulator n-channel metal-oxide-semiconductor field effect transistors (SOI nMOSFET's) with a sub-10-nm-thick silicon layer and presents some simple analyses based on quantum mechanics. It is suggested that these features originate from the two-dimensional subband system in the thin SOI layer and its local deviation based on the local-deviated silicon layer thickness reflecting the buried oxide layer surface morphology of high-temperature-annealed SIMOX substrates.
Characterization of Ultrathin Dielectrics Grown by Microwave Afterglow Oxygen and N2O Plasma
Authors: Chen Po-ching , Hsu Klaus Yung-jane , Lin Jian-yang , Huey-liang Hwang Huey-liang Hwang
Published: October 2002

Ultrathin dielectrics, oxides and oxynitrides were grown using microwave afterglow oxygen and N2O plasma at low temperature. N2O plasma annealing and pretreatment improved the breakdown properties of O2 plasma oxides. From secondary ion mass spectroscopy (SIMS) analysis, nitrogen was found to be incorporated into oxides effectively by this low-temperature method. Nitrogen content was highest at the oxide surface and decreased toward the oxide/Si interface. This indicates a nitridation mechanism different from the conventional N2O gas annealing or oxidation processes. The relationships among interface state densities, tunneling current and nitrogen profiles were also investigated by C-V and I-V measurements.
Self-Aligned Rapid Thermal Nitridation of TiSi2 in NH3 Ambient as a Diffusion Barrier Layer for Selective CVD-Al Contact Plug Formation
Authors: Sinriki Hiroshi , Komiya Takayuki , Takeyasu Nobuyuki , Tomohiro Ohta Tomohiro Ohta
Published: October 2002

Diffusion barrier properties and selectivity required for selective chemical vapor deposition (CVD)-Al contact plug formation are remarkably improved by the self-aligned rapid thermal nitridation (RTN) of TiSi2 layer in NH3 ambient at 865° C for 30 s. This treatment enables the formation of a nonstoichiometric TiSi
x
layer with a low concentration of nitrogen within 10-20 nm below its surface. However, nitridation is thought to occur particularly along the grain boundaries, resulting in high diffusion-barrier integrity against aluminum diffusion through the grain boundaries. In addition, this treatment provides favorable selective growth from the bottom of contact holes by reducing the number of nucleation sites on the inner side of contact holes. Therefore, our newly developed process is very promising for contact plug formation of complementary metal-oxide-semiconductor (CMOS) using the salicide process.
Al Growth on Si(111)(√ 3×√ 3)-Ga Surfaces at Room Temperature
Authors: Maehashi Kenzo , Katsuki Hiroyuki , Hisao Nakashima Hisao Nakashima
Published: October 2002

The initial stages of Al growth on Si(111)(√ 3×√ 3)-Ga surfaces at room temperature (RT) have been studied by reflection high-energy electron diffraction and X-ray photoemission spectroscopy. The Al-Ga exchange reaction takes place, resulting in the formation of Al-Si bonds at the interface. Al films contain both (111)- and (100)-oriented structures. Most of the Ga atoms segregate at surfaces of the Al overlayer from the very initial stage, even at RT.
Thermally Activated Electric Conduction in Carbon Nanotubes
Authors: Nakayama Yoshikazu , Akita Seiji , Yoshihito Shimada Yoshihito Shimada
Published: October 2002

Thermally activated electric conduction has been measured for carbon nanotubes lying on coplanar electrodes. Linear current-voltage characteristics suggest that the measured activation energies ranging from 0.03 to 0.13 eV reflect the characteristics of semiconducting nanotubes. The activation energies are discussed in terms of the diameters of nanotubes with high yields.
Peculiarity of an Oblique Liquid Crystal Alignment Induced by a Photosensitive Orientant
Authors: Dyaduysha Andrey , Khizhnyak Anatolii , Marusii Tatyana , Reshetnyak Victor , Reznikov Yuriy , Park Woo-Sang
Published: October 2002

The distribution of the director of a nematic liquid crystal (NLC) in a cell with photosensitive aligning layers has been studied. It is shown that a doubly degenerate easy orientation axis is induced on the interface between the nematic and orienting surface. It was also found that the degeneracy of the easy axis orientation can be removed by NLC molecules flow during LC cell filling and an oblique liquid crystal orientation is realized.
New Magnetic Regenerator Materials with Broad Peaks of Magnetic Specific Heat
Authors: Makuuchi Hidekazu , Aikawa Toshiharu , Matsumoto Kohichi , Hashimoto Takasu , Li Rui , Onishi Atsushi , Satoh Toshimi , Kanazawa Yoshiaki
Published: October 2002

The materials of the Er1-
x

Dy

x

Ni system are proposed as new magnetic regenerator materials for use in a 2-stage Gifford-McMahon refrigerator. We produced a series of solid solutions, Er1-
x

Dy

x

Ni, by mixing two substances, ErNi and DyNi. These two substances have the same crystal structure and their easy axes of magnetization are perpendicular to each other. The peak in the temperature dependence curve of the magnetic specific heat was observed to broaden, as the concentration, x, of the Dy ions increased above x=0.075. We have demonstrated that mixtures of ErNi and DyNi, which have different easy axes of magnetization, lead to materials with broad peaks in the temperature dependence curve of the magnetic specific heat.
High-Accuracy X-ray Reflectivity Study of Native Oxide Formed in Chemical Treatment
Authors: Awaji Naoki , Sugita Yoshihiro , Ohkubo Satosi , Nakanishi Toshiro , Takasaki Kanetake , Satoshi Komiya Satoshi Komiya
Published: October 2002

High-accuracy X-ray reflectivity measurements using synchrotron radiation have been carried out to study native oxides formed during various chemical-cleaning processes on Si wafer. Clear differences in the density of native oxides between various chemical treatments were obtained from the normalized reflectivity for the first time. Native oxides formed by HCl and NH4OH solutions have a low density, in contrast to the oxides formed by H2SO4 solution and UV/O3 whose densities are close to that of thermal oxide. These results are closely related to the results of chemical studies and the etching characterization of native oxides.
Carbon Ion Implantation in GaAs
Authors: Hara Tohru , Takeda Satoru , Mochizuki Akira , Oikawa Hirokazu , Higashisaka Asamitsu , Kohzu Hideaki
Published: October 2002

Atom and carrier concentration profiles in carbon-ion-implanted GaAs have been measured. Ion implantation of carbon is performed at 300 keV with dose of 1.0×1014 ions/cm2. Carbon concentration profile obtained by secondary ion mass spectrometry measurement is in good agreement with the profile obtained by Monte Carlo simulation. The implanted carbon does not diffuse markedly with annealing at 900° C because the diffusion coefficient is below 4×10-16 cm2/ s for the ion-implanted carbon. Therefore, a shallow carrier concentration profile is formed after annealing. Activation efficiency is 17% at the surface (depth less than 0.47 µ m). However, this efficiency is as low as 4% in deeper regions. The lower activation efficiency in deeper regions is due to the suppression of activation by the precipitation of carbon after the annealing.
Surface Morphologies of Hydrogenated Amorphous Silicon at the Early Stages of Plasma-Enhanced Chemical Vapor Deposition
Authors: Deki Hidenori , Fukuda Masatoshi , Miyazaki Seiichi , Masataka Hirose Masataka Hirose
Published: October 2002

Ultrathin hydrogenated amorphous silicon (a-Si:H) films have been deposited on atomically flat, hydrogen-terminated Si(111) surfaces. The film morphologies have been studied by atomic force microscopy (AFM) with a vertical resolution of 0.01 nm. The film surfaces of 1.0-5.0 nm thick a-Si:H deposited at 200° C on flat Si(111) substrates reveal terraces and biatomic steps of the initial Si(111) 1×1: H surface and the average microroughness remains unchanged regardless of the film thickness. In the case of a-Si:H deposition on 1.7-nm-thick SiO2 thermally grown on flat Si(111) or 2.0-nm-thick a-Ge:H on Si(111), the a-Si:H surface morphology also maintains the atomic step structure of the substrate. This indicates that a-Si:H deposition occurs via a layer-by-layer mechanism.
Superconductivity in Conducting Polymer/Fullerence Composite Doped by Alkali Metal
Authors: Araki Hisashi , Saiki Anvar A. Zakhidov , Yamasaki Nobuo , Yakushi Kyuya , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

Superconductivity in poly(3-alkylthiophene)- C60 composite (PAT- C60) is found upon doping by potassium from vapor phase. The superconducting (SC) transition at T
C=17 K is detected by superconducting quantum interference device (SQUID), which showed 0.8% of SC fraction for C60 content of 5 mol%. An exceptionally strong low-field microwave absorption (LFMA) implies the existence of granular SC phase. A rather small hysteresis of LFMA indicates the important role of the Josephson weak link network, probably formed between SC K

x

C60 clusters separated by conductive K

x

PAT barriers. ESR of PAT(C60)

y

K

x

composite shows two types of lines: one from negative polarons P
- in PAT chains, and another assigned to K

x

C60 clusters and C1-
60 radical.
A Narrow-Linewidth Dye Laser Pumped by a High-Repetition-Rate, Long-Pulse Nd:YAG Laser
Authors: Maruyama Yoichiro , Kato Masaaki , Ohba Masaki , Takashi Arisawa Takashi Arisawa
Published: October 2002

Using a high-repetition-rate Nd:YAG laser with the pulse duration of about 250 ns as a pumping light source, characteristics of a dye laser oscillator and a dye laser amplifier are studied. As a result, a linewidth of around 20 MHz is generated by the dye laser oscillation using a dye jet. For the dye laser amplifier, the energy conversion efficiency of 20% is obtained by using a dye jet as an amplifier.
Generation of a Surface-Wave-Enhanced Plasma Using Coaxial-Type Open-Ended Dielectric Cavity
Authors: Kimura Tadashi , Yoshida Yoshikazu , Shin-ichi Mizuguchi Shin-ichi Mizuguchi
Published: October 2002

A high-density and uniform plasma source which utilizes surface waves is described. Microwaves propagated through a coaxial waveguide are introduced circularly into the circumferential side of the dielectric disk, which is set at the open end of the coaxial-type cavity. A surface wave is launched from the dielectric surface and generates a plasma. The plasma density and electron temperature are 8×1011 cm-3 and 4.5 eV, respectively, at Ar gas pressure of 50 mTorr and microwave power of 800 W.
The ashing rate without substrate heating of photoresist is 0.6 µ m/min at the O2 gas pressure of 50 mTorr and the microwave power of 500 W.
Determination of Interstitial Oxygen Concentration in Oxygen-Precipitated Silicon Wafers by Low-Temperature High-Resolution Infrared Spectroscopy
Authors: Saito Hiroyuki , Hiroshi Shirai Hiroshi Shirai
Published: October 2002

The low-temperature high-resolution infrared absorption spectra have been measured on oxygen-precipitated Czochralski-grown silicon wafers in the 1100 cm-1 range at approximately 13.8 K, using the p-polarized Brewster angle incidence configuration. The multiple peaks due to interstitial oxygen have been successfully observed without interference fringes. It has been verified that the interstitial oxygen concentration in oxygen-precipitated wafers is precisely determined by low-temperature high-resolution p-polarized Brewster angle incidence infrared spectroscopy.
New Fabrication Process for Small Junctions Using a Selective Etch-Back Technique
Authors: Kodaira Shinji , Shoji Akira , Kohjiro Satoshi , Kiryu Shogo
Published: October 2002

A new process for fabricating small junctions from a full-wafer junction sandwich has been developed, in which a dry-etching technique is used for selectively etching an SiO2 insulating layer deposited on a junction. Using this new process and a deep-uv photolithography technology, we fabricated NbC

x

N1-
x

/MgO/NbC

x

N1-
x

junctions with dimensions of 0.8×1.1 µ m2.
Multiloop Superconducting Quantum Interference Devices with Nb/Al-AlOx-Al/Nb Edge Junctions
Authors: Mizutani Naoki , Uehara Gen , Takada Youichi , Adachi Akira , Kado Hisashi
Published: October 2002

We have fabricated multiloop superconducting quantum interference devices (SQUIDs) of 4×4 mm2 total size using sub-µ m Nb/Al-AlO

x

-Al/Nb edge junctions. We obtained very large voltage swing and gradient ∂V/∂Φ of 0.95-1.53 mV/Φ0, because it was possible to increase the shunt resistance due to the small junction capacitance. This advantage enabled us to achieve very low flux density noise of 1.9 fT/Hz0.5 for white noise by using a readout circuit in which the voltage noise of the amplifier was 1.4 nV/Hz0.5. The low-frequency noise was also very low (7.3 fT/Hz0.5 at 1 Hz). These noise results are half and one-third, respectively, compared with noise before the improvement achieved by this study. We obtained very low flux density noise for the small SQUID using only an inexpensive, compact readout circuit.
Preparation of Device-Quality Cu(In, Ga)Se2 Thin Films Deposited by Coevaporation with Composition Monitor
Authors: Kohara Naoki , Negami Takayuki , Nishitani Mikihiko , Takahiro Wada Takahiro Wada
Published: October 2002

The chemical composition of Cu(In, Ga)Se2 (CIGS) thin film was monitored in real time during the physical vapor deposition. The temperature of growing CIGS film was found to depend on the composition ratio of Cu/(In+Ga) when the film was deposited under constant heating power. The composition monitoring system can be easily applied to a 3-stage deposition process of the CIGS films. The solar cells (active area: 1 cm2) fabricated by using the obtained CIGS absorber layer showed an efficiency of 15.4% under standard AM 1.5 illumination.
Optical Second Harmonic Generation in Si1-ninxGex Film Epitaxially Grown on Si(100)
Authors: Mizutani Goro , Sonoda Yasuyuki , Ushioda Sukekatsu , Maeda Takahiro , Murota Junichi
Published: October 2002

We have observed the optical second harmonic generation (SHG) from Si1-
x

Ge

x

epitaxial films for the first time. The SH intensity was measured as a function of Ge fraction x and the azimuthal angle of rotation of the film about the surface normal. The SH intensity has a maximum around x=0.8∼0.9. The SH intensity curve as a function of the azimuthal angle shows a four-fold pattern for the Ge fraction x=0.8∼0.9. The enhancement in the SH intensity and the signal anisotropy are believed to be due to the resonance of the incident and second harmonic photon energies with the E
0 and E
1 band gaps of Si1-
x

Ge

x

, respectively.
Optical Kerr Shutter Response of Organic Microcrystals
Authors: Kasai Hitoshi , Kanbara Hirohisa , Iida Rieko , Okada Shuji , Matsuda Hiro , Oikawa Hidetoshi , Hachiro Nakanishi Hachiro Nakanishi
Published: October 2002

Optical Kerr shutter responses of both polydiacetylene and J-aggregated merocyanine microcrystals dispersed in water were measured for the first time, using the gate beam at 1064 nm and the probe beam at 813 nm. The χ(3) values based upon optical Kerr effect for these microcrystals were on the order of 10-13 esu, and these physical quantities normalized by concentration (1 M) were approximately 10-9 esu/M, of which order is very large even in the nonresonant wavelength region.
Alkali-Metal Doping of Langmuir-Blodgett Films of C60 Studied by ESR
Authors: Ikegami Keiichi , Kuroda Shin-ichi , Matsumoto Mutsuyoshi , Nakamura Takayoshi
Published: October 2002

Various doping methods were used in order to realize the charge transfer between C60 molecules and alkali-metal atoms in the Langmuir-Blodgett structure. ESR measurements have clearly indicated the charge transfer in the samples heated with RbN3 powder. The development of the metallic region in these films, possibly in the form of o-Rb1C60, has been indicated, for the first time, by the obtained Pauli-like spin susceptibility and the Elliott-like ESR linewidth. Furthermore, hysteresis was observed in the low-magnetic-field microwave absorption signal (LFS) for a sample, showing the appearance of the superconducting phase with T
c≈23 K in the sample tube.
Non-Approximate Evaluation of Macroscopic Quantum Tunneling of Charge for the Two-Junction Case at Arbitrary Temperatures and Bias Voltages
Authors: Christoph Wasshuber Christoph Wasshuber , Kunihiro Asada Kunihiro Asada
Published: October 2002

Inelastic macroscopic quantum tunneling of charge (q-MQT) is non-approximately evaluated, in the case of two tunnel junctions in series at arbitrary temperatures and bias voltages, to our knowledge for the first time. In the Coulomb blockade regime at low temperature q-MQT dominates the overall tunnel rate. For equal junctions one resonance of the tunnel rate was found. For different junctions the resonance splits in two. This resonance decreases with increasing temperature. For T=0 K the resonance is a logarithmic pole. The evaluation shows that inelastic q-MQT cannot in general be neglected in comparison with the normal tunnel rate.
Metal (CoSi 2)/Insulator (CaF 2) Hot Electron Transistor Fabricated by Electron-Beam Lithography on a Si Substrate
Authors: Wataru Saitoh Wataru Saitoh , Takashi Suemasu Takashi Suemasu , Yoshifumi Kohno Yoshifumi Kohno , Masahiro Watanabe Masahiro Watanabe , Masahiro Asada Masahiro Asada
Published: October 2002

We fabricated a small-area metal (CoSi2)/insulator (CaF2) hot electron transistor using electron-beam lithography. The transistor is composed of a CoSi2/CaF2 (1.9 nm)/CoSi2 (1.9 nm) tunnel emitter and a CaF2 (5 nm) collector barrier on an n-Si(111) substrate. The emitter mesa area is 0.9 × 0.9 µm2. Although the measured characteristics show, for the first time, clear transistor action with a curve similar to those of semiconductor HETs, the collector current increases without saturation due to leakage current through the SiO2 film under the external electrode pads. The intrinsic device characteristics (zero leakage current) exhibited saturation, and a current gain β ≥ 36 was obtained at 77 K.
In Situ Transmission Electron Microscopy Observation of Single Crystallization of Filled Aluminum Interconnection
Authors: Wada Jun-ichi , Toyoda Hiroshi , Kaneko Hisashi , Hayasaka Nobuo , Yasuda Hidehiro , Mori Hirotaro , Okano Haruo
Published: October 2002

In situ transmission electron microscopy (TEM) observation was carried out to clarify the aluminum single-crystallization mechanism. Aluminum filling into the grooves formed on an amorphous insulator completed at 903 K, which was 30 K below the melting point of pure aluminum. It was found that aluminum remained in the liquid state even at temperatures more than 80 K below its melting point. It is concluded that this supercooled aluminum state is essential to the fabrication of single-crystal aluminum lines, because this state enables fast solidification and suppresses polynucleations.
Third Harmonic Generation Measurements for Halogen-Doped One-Dimensional Nickel Complexes
Authors: Kamata Toshihide , Kubota Shinya , Fukaya Toshio , Matsuda Hiro , Mizukami Fujio , Uchida Tokiko
Published: October 2002

Halogen doping effects on the third-order nonlinear optical properties of bis(dimethylglyoximato)nickel(II), Ni(dmg)2, which has a one-dimensional backbone of metal chains, were examined. Ni(dmg)2 showed 10-12 esu order of the third-order nonlinear susceptibility χ(3) by three-photon resonance at the d

z

2-p

z
transition band. Exposing the Ni(dmg)2 film to chlorine or bromine gas induced a red shift of the d

z

2-p

z
transition band and considerable enhancement of the optical nonlinearity. In particular, chlorine doping led to two-odd orders of enhancement of the χ(3) values (10-10 esu order). The doping effects are discussed in relation to the electron delocalization in the linear metal chains.
1.55 µm InGaAs/InAlAs/InP Quantum Wells with Mass-Dependent Width for Polarization-Independent Optical Modulation
Authors: Hamakawa Atsushi , Ishihara Kiyoteru , Yamaguchi Takeharu , Nakano Yoshiaki , Tada Kunio , Nishikata Kazuaki , Irikawa Michinori
Published: October 2002

We describe a new quantum well structure in 1.55 µ m materials where the effective width of the well is mass-dependent. This is advantageous for polarization-independent modulation of 1.55 µ m optical waves. An InGaAs/InAlAs multiple quantum well p-i-n diode with such a structure on an InP substrate has been fabricated for the first time, and its photocurrent spectra have been measured. We have observed a larger Stark shift for light-hole exciton than that for heavy-hole exciton, which never occurred in conventional quantum wells. Therefore, the same amount of Stark shift for both holes should be possible by adjusting such a quantum well structure with mass-dependent width.
Efficient Fiber Gratings Formed on High NA Dispersion-Shifted Fiber and Dispersion-Flattened Fiber
Authors: Komukai Tetsuro , Masataka Nakazawa Masataka Nakazawa
Published: October 2002

A wavelength separation as wide as 7 nm has been achieved between the Bragg wavelength and the onset wavelength of radiation mode coupling in highly reflective fiber gratings by using a high NA dispersion-shifted fiber (DSF) and a dispersion-flattened fiber (DFF). We have used this technique to fabricate highly reflective chirped gratings with a bandwidth of 8 nm. These types of fibers are also suitable for fabricating highly reflective multi-wavelength filters.
Influence of the Piezoelectric Effect on the Energy Levels of InGaAs/GaAs Strained Quantum Wells Grown on (311)A GaAs
Authors: Vaccaro Pablo O. , Takahashi Mitsuo , Fujita Kazuhisa , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

The built-in electric field generated by the piezoelectric effect in In0.2Ga0.8As/GaAs strained quantum wells (SQWs) grown on (311)A GaAs substrates was studied. In contrast to SQWs grown on (100) GaAs substrates, the photoluminescence excitation spectrum shows transitions that are forbidden in the absence of an electric field and the emergence of new energy levels confined by the tilted barrier in the hole bands. The observed features agree with the calculated built-in electric field of 80 kV/cm. Because the high quality of these SQWs, (311)A GaAs substrates come forth as an alternative for investigating the piezoelectric effect in SQWs.
Lattice Continuity at Interface of Alumina-Coated Transition Metals
Authors: Saito Tomohiro , Ikuhara Yuichi , Shibuki Kunio , Suzuki Tetsuya
Published: October 2002

Interfaces of alumina-coated transition metals were studied by cross-sectional high-resolution electron microscopy (HREM) to investigate the lattice continuity across the interface. α-alumina films 2-3 µ m in thickness were coated on vanadium, niobium and tantalum polycrystals by the sputtering method. Cross-sectional HREM observations showed that there was a three-dimensional orientation relationship (3-D OR) between α-alumina films and substrate transition metals. The 3-D OR is discussed based on the coincidence of reciprocal lattice points of two adjoining crystals.
Photo- and Electroluminescence from Electrochemically Polished Silicon
Authors: Matsumoto Takahiro , Mimura Hidenori , Kanemitsu Yoshihiko
Published: October 2002

Visible photoluminescence has been obtained from surface-etched silicon fabricated with high-current-density anodization on the order of 1000 mA/cm2 (electrochemical polishing mode). Anodization at this current density makes silicon mirror-like with blue or yellow color. Photoluminescence intensity is almost equal to that of porous Si even for a thin layer on the order of a nanometer. Using such a layer, we have fabricated light-emitting diodes by indium tin oxide evaporation. Schottky-type junctions formed in this way have a large rectifying ratio on the order of 104 at ±15 V and show visible electroluminescence at a threshold bias voltage of less than 5 V.
Recombination Dynamics in ZnxCd 1-xS Single Quantum Well Grown by Photoassisted Metalorganic Vapour Phase Epitaxy by Time-Resolved Photoluminescence Spectroscopy
Authors: Hervé Dumont Hervé Dumont , Yoichi Kawakami Yoichi Kawakami , Shizuo Fujita Shizuo Fujita , Shigeo Fujita Shigeo Fujita
Published: October 2002

A higher zinc composition of illuminated epilayers (Zn0.38Cd0.62S) was employed to form the barrier whereas unilluminated growth sequences were adopted to grow the well (Zn0.30Cd0.70S) in the photoassisted metalorganic vapour phase epitaxy (MOVPE). Time-integrated photoluminescence spectra clearly show two peaks at 437 nm (2.83 eV) and 443 nm (2.80 eV) attributed to the barrier and to the well respectively. The time evolution of these spectra shows an increasing intensity of emission from the well with a time delay due to the confinement and recombination of carriers in the well. Time-resolved measurements have shown a time delay of 60 ps between the barrier and the well. These results indicate the formation of type-I band structure.