Search Results - (Author, Cooperation:Y. Sugimoto)

2018-01-25

BMJ Publishing Group

0022-2593

1468-6244

Medicine

Genetics

2014-10-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Binding Sites ; Cryoelectron Microscopy ; Humans ; Mitochondria/genetics/*metabolism ; Mitochondrial Proteins/chemistry/ultrastructure ; Mutation ; Nucleic Acid Conformation ; Protein Conformation ; RNA, Transfer, Val/analysis/*chemistry ; Ribosome Subunits/*chemistry/genetics/*ultrastructure

2015-03-25

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

3' Untranslated Regions/genetics ; Base Sequence ; Cytoplasm/genetics/metabolism ; Cytoskeletal Proteins/*metabolism ; DNA-Binding Proteins/genetics ; Humans ; *Nucleic Acid Conformation ; Polymorphism, Single Nucleotide/genetics ; RNA Splicing ; RNA Stability ; RNA, Messenger/*chemistry/genetics/*metabolism ; RNA-Binding Proteins/*metabolism ; Transcription Factors/genetics

2018-06-01

The American Society for Microbiology (ASM)

0099-2240

1098-5336

Biology

2018-04-06

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

1089-7550

AIP Digital Archive

Physics

Electron-beam (EB)-induced pattern etching of AlxGa1−xAs (0≤x≤0.7) is described. An ultra-thin GaAs oxide at the surface of a GaAs/AlGaAs heterostructure wafer is used as a resist film. The GaAs oxide resist can be selectively removed by EB irradiation in a Cl2 ambient, which results in pattern etching of GaAs/AlGaAs. The etch rate of AlGaAs is examined as functions of substrate temperature, AlAs mole fraction, and EB flux. The results indicate that pattern etching is realized in the AlAs mole fraction range of 0≤x≤0.7

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Damage in GaAs induced by Ga+ focused-ion-beam-assisted Cl2 etching is studied by photoluminescence (PL) intensity measurements as functions of ion energy, ion dose, and substrate temperature. By decreasing the ion energy from 10 to 1 keV, the damage depth decrease to 1/5, where damage depth is taken as the thickness at which the PL intensity recovers by wet etching. The damage depth is shallower when the etching yield is larger with the same ion energy. By increasing the ion dose, the normalized PL intensity decreases, but damage depth is nearly constant. Over 1015 ion dose, the normalized PL intensity shows a constant value. By increasing the sample temperature, the damage depth becomes shallower. At 150 °C with ion energy of 1 keV, the damage depth is less than 0.5 μm, which is the detection limit of the PL measurement in GaAs substrate.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Pattern formation on GaAs by Ga+ focused-ion-beam (FIB) irradiation and subsequent Cl2 gas etching was carried out. A higher etch rate at the FIB-irradiated area compared with that not irradiated under Cl2 gas allows pattern construction without a mask process. The degree of residual crystal damage was evaluated using photoluminescence (PL) intensity measurements. The PL intensity in the etched region was one order of magnitude stronger than that of FIB sputtering, and was several times stronger than that of Ga+ FIB-assisted Cl2 etching. Etch depths of the order of 100 nm, which is five times deeper than that obtained by FIB sputtering, were efficiently performed using moderate Ga+-ion doses.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The first demonstration of in situ electron-beam (EB) lithography is reported, where a photo-oxidized surface thin layer of GaAs is used for a resist. The in situ EB lithography sequence consists of five processes, i.e., preparation of a clean GaAs surface, photo-oxidation for a resist film formation, direct patterning of the oxide resist by EB-induced Cl2 etching, Cl2 gas etching of GaAs surface for pattern transfer, and thermal treatment in an arsenic ambient for resist removal and surface cleaning. The GaAs wafer is never exposed to air throughout all of the above processes to avoid an unintentional surface contamination. The minimum electron dose required for patterning of the GaAs oxide resist is about 5×1016 cm−2. An overgrown layer on the patterned GaAs surface shows a good surface morphology, which strongly indicates that this technology makes it possible to repeat crystal growth and surface patterning.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A new method for in situ pattern etching of GaAs was demonstrated by using an electron-beam (EB)-stimulated-oxidized surface layer as a mask for subsequent Cl2 gas etching. This process is based on the experimental results that GaAs oxide prepared by EB irradiation under an oxygen atmosphere is resistive to Cl2 gas etching, whereas GaAs oxide without an EB can be easily etched. The resistance of the oxide mask against Cl2 gas etching varies depending on the EB dose with which the oxide of GaAs is formed. A fine pattern, such as a 1 μm linewidth in a 5-μm pitch line-and-space, is obtained.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Electrical characteristics associated with radiation detection were measured on single-crystal natural type-IIa diamond using two techniques: charged particle-induced conductivity and time-resolved transient photoinduced conductivity. The two techniques complement each other: The charged particle-induced conductivity technique measures the product of the carrier mobility μ and lifetime τ throughout the bulk of the material while the transient photoconductivity technique measures the carrier mobility and lifetime independently at the first few micrometers of the material surface. For each technique, the μτ product was determined by integration of the respective signals. The collection distance that a free carrier drifts in an electric field was extracted by each technique. As a result, a direct comparison of bulk and surface electrical properties was performed. The data from these two techniques are in agreement, indicating no difference in the electrical properties between the bulk and the surface of the material. The collection distance continues to increase with field up to 25 kV/cm without saturation. Using the transient photoconductivity technique the carrier mobility was measured separately and compared with a simple electron-phonon scattering model. The general characteristics of carrier mobility, lifetime, and collection distance at low electric field appear to be adequately described by the model.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The reaction of oxygen with H2S-treated GaAs (001) surfaces was studied using Auger electron spectroscopy and reflection high-energy electron diffraction. GaAs surfaces in situ treated with H2S gas were exposed to pure oxygen gas with and without simultaneous light illumination of a halogen lamp. It was shown that the oxygen uptake on a H2S-treated surface is much less than that on an untreated bare GaAs surface. Surfaces exposed to oxygen were heated in an ultrahigh-vacuum environment in order to study the desorption of the reacted oxygen. The oxygen Auger signal was found to easily disappear when the surface was heated to 520 °C, leaving sulfur atoms on the surface. The oxide formed on a bare GaAs surface with light illumination was found to be relatively thick; it did not desorb completely until it was heated to about 550 °C. These results indicate that oxide on a H2S-treated surface is formed only on the top surface.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A novel multichamber system for beam-assisted etching, in situ lithography, and molecular-beam epitaxy (MBE) has been constructed and proved to be usable with full functions. This system comprises seven ultrahigh-vacuum (UHV) chambers connected by UHV tunnels. A specially designed gun column, which can be used for a focused-ion-beam (FIB) gun or an electron-beam gun, and an introduction system of Cl2 gas have been installed in a UHV chamber for beam-assisted Cl2 gas etching. In order to evaluate the induced damage by ion irradiation, the FIB gun with a novel retarding system was installed. An in situ Auger electron spectroscopy apparatus and an in situ photoluminescence unit were attached to the analysis chamber in order to evaluate the surface composition and the induced damage, respectively. Examples of GaAs/AlGaAs heterostructure grown on in situ patterned substrates showed good surface morphology, indicating the usefulness of this technique for microfabrication.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Sixty-degree-bent defect waveguides (DWGs) in an AlGaAs-based air-bridge-type two-dimensional photonic crystal (2D PC) slab were fabricated, and the resulting optical transmission spectra and the plan-view image of the optical beam propagating along the bent DWG were measured in the wavelength range between 850 and 1100 nm. Using the two output ports of the stripe waveguides, one aligned to and another offset from the output edge of the bent DWG, the guided mode specific to the DWG and the slab mode in the defect-free PC slab were experimentally observed with the same sample. These results were verified using the calculated band structure and transmission spectra. © 2002 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

This is the demonstration of "in-situ masking'' concept. In situ patterning of GaAs is carried out by using a photo-oxidized surface layer as a mask for subsequent Cl2 etching. Clean GaAs surface provided by molecular beam epitaxy is exposed to pure oxygen and is simultaneously irradiated with an Ar+ ion laser of the 514.5 nm line for photo-oxidation of the surface. Subsequent Cl2 gas etching of the photo-oxidized sample reveals that the GaAs oxide fills the role of an etching mask. The resistance of the oxide mask against Cl2 etching varies depending on the laser fluence with which the oxide of GaAs is formed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Pattern etching of GaAs at submicron size is carried out by in situ electron beam (EB) lithography using a computer-controlled pattern generator. GaAs oxide on the wafer surface is used as a resist film in EB-induced Cl2 etching. A 0.5 μm linewidth in a 1 μm pitch line-and-space pattern with flat top surface is obtained. Observations of the pattern edge with a scanning electron microscope show that the boundary between the etched area and the oxide mask area is abrupt and that the undulation of the pattern edge is less than about 30 nm.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The high-repetition switching capabilities of a recently developed symmetric Mach–Zehnder (SMZ) all-optical switch are experimentally investigated. Using a series of four control pulses at intervals of 100 or 25 ps, nearly full switching is achieved at the corresponding intervals. The results experimentally show that the repetition rate, as well as the switching speed, of the SMZ all-optical switch is not restricted by the slow relaxation of the utilized high-efficiency band-filling effect. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A GaAs/AlGaAs quantum well structure is in situ patterned by irradiating a thin (50 A(ring)) epitaxial In0.2Ga0.8As mask layer with an electron beam (EB) while exposing the mask to Cl2 gas. This simultaneous EB/Cl2 exposure increases the resistance of the mask to Cl2 etching. However, the parts of the mask only exposed to Cl2 are easily etched off, resulting in a negative-type pattern formation. The etching resistance of the EB/Cl2-exposed area depends on the In content in the InGaAs mask. Possible causes of this are discussed. Using this method, a GaAs/AlGaAs quantum well is fabricated into a dot-matrix pattern.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the results of a high-speed all-optical switching experiment in Mach–Zehnder configuration using a GaAs waveguide. The all-optical switching is based on the nonlinear refractive index change induced by the band-filling effect in the GaAs waveguide. To achieve high-speed operation without being limited by the slow carrier relaxation time, a dc electric field is externally applied to the nonlinear waveguide to sweep carriers away from the light guiding region. The FWHM (full width at half maximum) of the switching waveform without the externally applied electric field is about 800–900 ps. As the electric field is increased, the FWHM is reduced to about 80–90 ps.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Buried GaAs/AlGaAs single quantum-well structures have been fabricated for the first time by in situ electron beam (EB) lithography. The process includes the molecular beam epitaxy of a GaAs/AlGaAs single quantum well, electron-beam direct writing, Cl2 gas etching, and overgrowth of an AlGaAs layer. A thin GaAs oxide layer was used as the etching mask, which was selectively formed on a clean GaAs surface by EB irradiation under an O2 ambient. Subsequent Cl2 gas etching resulted in the formation of isolated quantum wells. Prior to the overgrowth, thermal cleaning with atomic hydrogen was employed for removing the oxide mask. The cathodoluminescence image of the buried quantum well demonstrates the high quality of the resultant structure formed by in situ EB lithography.

Electronic Resource