bluuebunny/crossref_metadata_2025 huggingface dataset:
Advantages of Phase Measurement over Amplitude Measurement of Surface Acoustic Wave Using Optical Probing Method
Authors: Ohki Michio , Shima Naomi , Kita Toshihiro , Shiosaki Tadashi
Published: October 2002

The advantages of phase measurement of acoustic waves over amplitude measurement by the optical probing technique are discussed. Phase measurement has the advantages of less variation due to external disturbance, specification of the direction of energy flow, and possibility of more precise calculation of the standing wave ratio. Measurement results of distributions of the amplitude and the phase of surface acoustic waves confirm these advantages.
Brillouin Scattering Experiment under Strong Background Light
Authors: Sakai Keiji , Hattori Koichiro , Kenshiro Takagi Kenshiro Takagi
Published: October 2002

We constructed a new system for optical beating Brillouin spectroscopy designed especially for slightly opaque samples or samples with scatterers. The undesired effect of stray light was successfully eliminated by a new optical lock-in detection device, in which modulation of the polarization of light is employed instead of the current method of intensity modulation, a large shot-noise component of the stray light can be filtered out with a lock-in amplifier. The usefulness of the system was demonstrated by a Brillouin scattering experiment in ethanol containing a small obstacle, and also by an experiment of thermal phonon resonance in a microcavity.
Estimation of Sound Velocity Distribution of Scattering Medium by Simulated Annealing
Authors: Goto Masahito , Tabei Makoto , Mitsuhiro Ueda Mitsuhiro Ueda
Published: October 2002

A method for estimating sound velocity distribution of a scattering medium is developed. The sound velocity is estimated by iterating the WKB (Wentzel, Kramers and Brillouin) approximation for the calculation of the scattered field. The iterative procedure incorporates “simulated annealing” for determining of the optimal distribution of sound velocity. Estimations for the cylinder and 2-layer cylindrical shell models are carried out numerically and experimentally. The estimated sound velocity agrees well with the original distribution.
Fundamental Investigation of Shear and Surface Elastic Waves in Soft Biological Tissues by Numerical Simulation
Authors: Masahiro Sato Masahiro Sato
Published: October 2002

To investigate the possibility of applying a shear or surface wave to ultrasonic diagnosis, fundamental examination of wave generation and propagation characteristics in soft biological tissues is performed by means of numerical analysis. Assuming that tissues are isotropic, the elements of the elastic constant tensor [c] and the viscosity coefficient tensor [η] of tissues are chosen as c
11=109 N/m2, c
44=105 N/m2, and η11=1.0 N· s/m2 and η44=0.01 N· s/m2, respectively. The constants are assumed to be independent of frequency. By the finite-difference time-domain method formulated in an explicit manner, the generation and propagation of the shear and surface waves at low frequency (50 kHz) are confirmed in a 2-dimensional homogeneous medium surrounded by a free boundary in a region in which a vibrational source exists.
Quantitative Estimation of the Amount of Fibrosis in the Rat Liver Using Fractal Dimension of the Shape of Power Spectrum
Authors: Kikuchi Tsuneo , Nakazawa Toshihiro , Furukawa Tetsuo , Higuchi Toshiyuki , Maruyama Yukio , Sojun Sato Sojun Sato
Published: October 2002

This paper describes the quantitative measurement of the amount of fibrosis in the rat liver using the fractal dimension of the shape of power spectrum. The shape of the power spectrum of the scattered echo from biotissues is strongly affected by its internal structure. The fractal dimension, which is one of the important parameters of the fractal theory, is useful to express the complexity of shape of figures such as the power spectrum. From i
n
v
i
t
r
o experiments using rat liver, it was found that this method can be used to quantitatively measure the amount of fibrosis in the liver, and has the possibility for use in the diagnosis of human liver cirrhosis.
Tissue Displacement Measurement Using Ultrasonic Wave Adaptive Digital Detection Method
Authors: Otaki Hajime , Yoshiki Yamakoshi Yoshiki Yamakoshi
Published: October 2002

We have developed an internal small-displacement measurement system based on the ultrasonic wave pulsed Doppler technique. In the system, the ultrasonic wave Doppler frequency shift due to tissue movement is detected by using either an analog-type quadrature detector or digital detection algorithm. In this paper, we propose an adaptive digital detection algorithm which can derive a Doppler frequency shift signal with higher precision and with higher signal-to-noise ratio than the conventional method. The comparison between the proposed method and the conventional method is shown through both numerical analysis and basic experimentation.
Estimation of Measurement Characteristics of Ultrasound Fetal Heart Rate Monitor
Authors: Noguchi Yasuaki , Mamune Hideyuki , Sugimoto Suguru , Yoshida Atsushi , Sasa Hidenori , Kobayashi Hisaaki , Kobayashi Mitsunao
Published: October 2002

Ultrasound fetal heart rate monitoring is very useful to determine the status of the fetus because it is noninvasive. In order to ensure the accuracy of the fetal heart rate (FHR) obtained from the ultrasound Doppler data, we measure the fetal electrocardiogram (ECG) directly and obtain the Doppler data simultaneously. The FHR differences of the Doppler data from the direct ECG data are concentrated at 0 bpm (beats per minute), and are practically symmetrical. The distribution is found to be very close to the Student's t distribution by the test of goodness of fit with the chi-square test. The spectral density of the FHR differences shows the white noise spectrum without any dominant peaks. Furthermore, the f
-n
(n>1) fluctuation is observed both with the ultrasound Doppler FHR and with the direct ECG FHR.
Thus, it is confirmed that the FHR observation and observation of the f
-n
(n>1) fluctuation using the ultrasound Doppler FHR are as useful as the direct ECG.
Wide View-Angle Imaging Obtained by Compounding Multidirection Images through a Narrow Window
Authors: Kiyokazu Shikano Kiyokazu Shikano , Masasumi Yoshizawa Masasumi Yoshizawa , Norio Tagawa Norio Tagawa , Tadashi Moriya Tadashi Moriya , Shinichi Minohara Shinichi Minohara
Published: October 2002

This study evaluates the error in locating the region of interest in cancer therapy using a commercially available sector scanner, and describes a method for improving lateral resolution using a compound image obtained by pointing a sector scanner in several directions.
Three-Dimensional Dynamic Imaging by Spherical Pulsed Wave of Ultrasound
Authors: Tojo Hirofumi , Oshiro Osamu , Matani Ayumu , Chihara Kunihiro , Asao Masato , Furukawa Toshiyuki
Published: October 2002

We developed an ultrasonic dynamic imaging system to obtain a three-dimensional echogram in a blood vessel. The method makes it possible to detect the echo signal from objects instantaneously without scanning an ultrasonic beam using a ring array probe. First, we examined the spatial resolution. Second, we performed experiments using a butter block and a copper plate. The results show that this system has a spatial resolution below 1.0 mm, and also that a butter block in a plastic tube and a moving copper plate can be detected by this system.
Observation of Oxidation-Induced Stacking Faults by Electron-Acoustic Microscopy
Authors: Hiroshi Takenoshita Hiroshi Takenoshita
Published: October 2002

A high-power npn Tr-chip ( 5×5×0.2 mm3) fabricated by high-temperature heat treatments on a dislocation-free Si (111) wafer was investigated using electron-acoustic microscopy (EAM). Part of the specimen was angle-lapped (3°) to partially expose the emitter and base layers, and the mechanically damaged layer was removed by chemical polishing with CP-4A.
From the scanning electron microscopy and EAM images of the same site, right triangles with each side measuring about 30 µ m in length, arranged in the <101> direction, were observed at the selected area. These images are oxidation-induced stacking faults (OSF) observed for the first time by EAM.
These right triangles were distributed within the specimen and OSF existed not only on the specimen surface but also at depths of about 6 µ m from it.
Strain-Imaging Observation of Pb(Zr, Ti)O3 Thin Films
Authors: Takata Keiji , Kushida Keiko , Torii Kazuyoshi
Published: October 2002

This paper describes Strain-Imaging observation, using a tunneling acoustic microscope, of lead-zirconate-titanate (PZT) thin films. Strain Imaging detects fine strains generated by the tip voltage in piezoelectric films. This method reveals piezoelectric properties nondestructively with high spatial resolution and is suitable for the characterization of PZT materials for microelectric devices. In Pb(Zr0.5Ti0.5)O3 grown by rf magnetron sputtering, we have observed different properties between round grain structures, so-called “rosettes”, where PZT crystallines have grown from the same cores. This fact shows that not only grain size but also the size of rosettes and the fluctuation of its composition are important factors in the production of homogeneous PZT films.
Measurement of Thermal Diffusivity of Transparent Adhesives by Photoacoustic Microscope
Authors: Tokunaga Yoshiaki , Minamide Akiyuki , Naotaka Nakada Naotaka Nakada
Published: October 2002

In this paper, we describe a method by which thermal diffusivity of transparent epoxy adhesive on a substrate can easily be measured from the frequency dependence of a photoacoustic (PA) signal. In order to eliminate the influence of the substrate, the phase difference between a PA signal of the adhesive on the substrate and a PA signal of only the substrate was measured. This method was tested for cases of thermally thin and thick graphite (high thermal conductivity) substrates and a polypropylene (low thermal conductivity) substrate. It has the advantage that the thermal diffusivity of a transparent adhesive on a substrate can be measured regardless of the thickness and the thermal properties of the substrate.
Generation of Oxidation-Induced Stacking Faults in Czochralski-Grown Silicon Crystals Exhibiting a Ring-like Distributed Stacking Fault Region
Authors: Marsden Kieran , Sadamitsu Shinsuke , Yamamoto Toshiro , Tatsuhiko Shigematsu Tatsuhiko Shigematsu
Published: October 2002

The radial density distribution of oxidation-induced stacking faults (OSFs) and bulk micro defects (BMDs) in Czochralski-grown silicon crystals having a ring-like distributed OSF (ring-OSF) region was characterized after low-temperature pre-annealing followed by high-temperature oxidation, using optical microscopy, IR light scattering tomography and Fourier transform IR spectroscopy. Stacking faults were observed to have grown during oxidation in various radial regions of the crystal other than the ring-OSF region, depending on the radial distributions of BMDs determined by the pre-annealing conditions. The ability of these BMDs grown during pre-annealing to nucleate OSFs with subsequent oxidation is determined by the strain surrounding them. However, to realize OSF nucleation, the strain must lie within specific limits controlled by the size of the BMD.
Dislocation Density Reduction in SIMOX (Separation by Implanted Oxygen) Multi-Energy Single Implantation*1
Authors: Hamaguchi Isao , Fujita Tetsuo , Yano Takayuki , Hayashi Shun-ichi , Kenji Kajiyama Kenji Kajiyama
Published: October 2002

SIMOX (Separation by IMplanted OXygen) dislocation density in the surface-Si layer was reduced by a multi-energy single implantation process. In this process, implantation energy was reduced from 200 keV to 150 keV midway through a 1.6×1018/cm2 oxygen dose. After annealing at 1300° C for 6 h, threading-dislocation density was 1.5 orders of magnitude lower than under single-energy 200 keV implantation, and 3 orders of magnitude lower than under upward energy-change 150 keV→200 keV implantation. Under the new process, the oxygen-concentration depth profile was more diffuse than when upward-stepped implantation was used, as revealed by SIMS (secondary ion mass spectroscopy) and XTEM (cross-sectional transmission electron microscope) measurements.
A pH-Controlled Chemical Mechanical Polishing Method for Thin Bonded Silicon-on-Insulator Wafers
Authors: Sugimoto Fumitoshi , Horie Hiroshi , Arimoto Yoshihiro , Takashi Ito Takashi Ito
Published: October 2002

A pH-controlled chemical mechanical polishing (CMP) method for fabricating largearea ultrathin silicon-on-insulator (SOI) layers with uniform thickness was developed. Using a polishing reagent with the pH and colloidal silica concentration lowered, together with grooves fabricated on the SOI layer to expose the insulating oxide, the polishing rate clearly decreased leaving a uniform 0.1-µ m-thick SOI layer. An SOI layer with superior thickness uniformity (±0.01 µ m) across 5-by-5-mm SOI-Si islands was obtained. The thickness uniformity across the wafers was decreased to ±0.07 µ m. In this technique, the end point for polishing was controlled to form thin SOI layers with uniform thickness.
H2Partial Pressure Dependences of CH3Radical Density and Effects of H2Dilution on Carbon Thin-Film Formation in RF Discharge CH4Plasma
Authors: Susumu Naito Susumu Naito , Nobuei Ito Nobuei Ito , Tadashi Hattori Tadashi Hattori , Toshio Goto Toshio Goto
Published: October 2002

Both the CH3radical density and carbon thin-film formation were investigated in an RF-discharge CH4/H2plasma. In this plasma, although CH3radical density was almost constant, the deposition rate decreased markedly with increasing H2partial pressure. These results suggested that the surface loss of the radicals was decreased due to the change in surface composition of the film, and also the film etching was enhanced with increasing H2partial pressure. Therefore, the deposition rate of the carbon thin film decreased.
Nitrogen Ion Implantation into 6H-SiC and Application to High-Temperature, Radiation-Hard Diodes
Authors: Yaguchi Seiji , Kimoto Tsunenobu , Ohyama Naoki , Hiroyuki Matsunami Hiroyuki Matsunami
Published: October 2002

Ion implantation of nitrogen (N) into 6H-SiC{0001} epilayers was systematically investigated. The N profiles simulated with a TRIM (transport of ions in matter) program showed good agreement with experimental results when the tilt angle was set larger than 5°. The sheet resistance of implanted layers decreased with increasing annealing temperature, and a low sheet resistance of 820 Ω/\Box was obtained by annealing at 1600° C. The implanted p-n junction diodes showed a small reverse leakage current of 2.9×10-9 A/cm2 at a bias voltage of -10 V, and a high breakdown voltage of 446 V at room temperature. The diodes operated with good rectification at a high temperature of 350° C. The characteristics of the diodes showed very little change after gamma-ray irradiation with total doses up to 10 Mrad.
Iron-Induced Negative Charge in Thermally Grown Oxide of Silicon Wafers
Authors: Shimizu Hirofumi , Shigeaki Saitou Shigeaki Saitou
Published: October 2002

An ac surface photovoltage (SPV) is investigated in the thermally-grown silicon (Si) wafers, which are pretreated with an iron (Fe)-contaminated alkaline solution composed of ammonia hydroxide, hydrogen peroxide, and water. The ac SPV appeared in the cleaned and oxidized p-type Si is reduced by the incorporation of Fe into the thermal oxide, which causes the ac SPV being on the rise in n-type Si, depending on Fe concentration. These results prove that a negative charge due to Fe incorporated in the native oxide survives in the thermal oxide.
Iodine Treatment of GaAs Surface
Authors: Yoshio Hashimoto Yoshio Hashimoto , Jun-ichi Sakurai Jun-ichi Sakurai , Isamu Minemura Isamu Minemura , Kentaro Ito Kentaro Ito
Published: October 2002

The GaAs (100) surface treated with an aqueous solution of NH4I has been studied by X-ray photoemission spectroscopy. After the NH4I treatment, peaks due to the I 3d core level appear, and signals originating from Ga-I bonds are also detected in the Ga 3d spectrum. The oxide-related peak of the As 3d level is almost removed by the treatment. The NH4I treatment is a possible candidate for surface passivation of GaAs.
Operation of Rhodamine 6G Dye Laser in Water Solution
Authors: Shimamoto Kaoru Igarashi
Published: October 2002

The ethanolic solution of Rhodamine 6G is used for dye lasers in the atomic vapor laser isotope separation (AVLIS) system. However, the water solution is preferable from the standpoint of easy treatment and safety. In this paper, we systematically investigated the laser efficiency of a Rhodamine 6G dye laser pumped by a frequency-doubled Nd:YAG laser, for various water-based solutions with surface-active agents and alcohols. By adding an appropriate amount of surface-active agent (Triton X or Emulgen) or alcohol (ethanol or propanol), we obtained almost the same level of laser efficiency as in the pure ethanolic solution. The improvement in the laser efficiency with these additives was attained by the deaggregation of nonradiative dimers. It was also confirmed that the water-based solution showed better performance against thermal distortion than the ethanolic solution, and was suitable for copper vapor laser (CVL) pumping.
Photoluminescence of ZnS 1-xSex:Te Prepared by Solution Growth Using Sb-Chalcogenides as Solvent
Authors: Hiroyuki Araki Hiroyuki Araki , Hisashi Kanie Hisashi Kanie , Masatoshi Sano Masatoshi Sano
Published: October 2002

Photoluminescences due to Te isoelectronic traps were investigated for Te-doped ZnS1-x
Se
x
crystals (0 ≤x ≤1) grown from Sb-chalcogenide solutions. The optical depths of the isolated Te atom center and the nearest-neighbor Te–Te pair center were determined from the emission spectra and the excitation spectra at 77 K. These depths decreased monotonically with increasing Se composition x. The theoretical relation between the optical depth and the composition x on the basis of the Koster-Slater one-band one-site approximation was best fitted to the experimental data by assuming the values of the matrix element of the impurity potential J
ZnS:Te = 2.41 eV, J
ZnSe:Te = 1.27 eV, and the effective width of the valence band T
ZnS = 6.02 eV, T
ZnSe = 6.21 eV. According to the criteria in the theory, excitons bound to the isolated Te atoms exist in ZnS1-x
Se
x
:Te for 0 ≤x < 0.85 and excitons bound to the Te–Te pairs exist throughout the entire composition range. The emission band observed at 2.61 eV in ZnSe:Te was shown to be due to the excitons bound to the Te–Te pairs.
Enhancement of Third-Order Optical Nonlinearity of Poly(aryleneethynylene)s by Introducing an Intramolecular Charge Transfer Interaction into Their π-Conjugation
Authors: Ooba Naoki , Tomaru Satoru , Kurihara Takashi , Kaino Toshikuni , Yamada Wataru , Takagi Masakazu , Yamamoto Takakazu
Published: October 2002

Poly(aryleneethynylene) type π-conjugated polymers (PAEs) are synthesized and the third-order optical susceptibility χ(3) of their thin films is evaluated. There is a red-shift in the electronic absorption of the PAE caused by an intramolecular charge transfer (CT) interaction when π-electron excessive heteroaromatic rings are introduced into the π-conjugation. The χ(3) value of the PAEs is enhanced by increasing the CT interaction and reaches more than 10-11 esu in the near resonant region. The increase in the π-electron delocalization caused by the CT interaction is found to be the main factor enhancing χ(3). This introduction of a CT interaction into a π-conjugation is an effective concept for the design of large χ(3) materials.
Ferroelectric and Dielectric Characteristics of (Pb1-yLay)[Mg(x+2y)/3Nb(2x+y)/3Ti1-x-y]O3 Thin Films Prepared by RF Magnetron Sputtering
Authors: Jiang Ming-Chrong , Wu Tai-Bor , Jenn-Ming Wu Jenn-Ming Wu
Published: October 2002

Ferroelectric thin films having compositions of xPb(Mg1/3Nb2/3)O3+(1- x- y)PbTiO3+ yLa(Mg2/3Nb1/3)O3 (PLMNT) with x=0.37-0.78 and y=0.03-0.13 were prepared on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering deposition at 520° C. Pure perovskite films were obtained for all compositions. The 0.5-µ m-thick films having a constant La(Mg2/3Nb1/3)O3 content of y=0.03 showed a ferroelectric-hysteresis characteristic with the remanent polarization and coercive field decreased from 8.5 µ C/cm2 and 46 kV/cm to 4.2 µ C/cm2 and 29 kV/cm, respectively, for changing the composition from x=0.645 to 0.78. Dielectric constant (k) of 1200-1300 and dielectric loss (tan
δ) less than 0.04 were also measured at 1 kHz. The temperature of dielectric peak decreased to near room temperature for an increase of Pb(Mg1/3Nb2/3)O3 content to x=0.78, which corresponded to a composition at the rhombohedral/cubic phase boundary of the PLMNT system. For films having composition lying along this phase boundary but containing La(Mg2/3Nb1/3)O3\geqslant7 mol%, the dielectric peak became much more broadened (flattened), which provided a good dielectric stability against variation of temperature. Good dielectric stability against frequency up to 1 MHz was also observed. The films also showed weak ferroelectric-hysteresis characteristic.
Wavelength Characteristics of Birefringent Film Refractive Index Anisotropy for a Black and White Film Supertwisted Nematic Liquid Crystal Display with a High Contrast Ratio
Authors: Hirakata Jun-ichi , Nagae Yosiharu , Kikuchi Naoki , Kando Yasuhiko
Published: October 2002

Film supertwisted nematic liquid crystal displays (F-STN-LCDs) with a single birefringent plastic film can be used for monochromatic black and white (B/W) LCDs, but their contrast ratio is inferior to that of double-layered (D-) STN-LCDs. We optimized the wavelength characteristics of the birefringent film refractive index anisotropy (Δn) through calculations and experiments to increase the contrast ratio of F-STN-LCDs. It was found that the wavelength characteristics of the Δn should be large at shorter wavelength regions and small at longer wavelengths. Moreover, the main axis in exit elliptical polarized light of the film must be crossed perpendicular to that of the STN-LC cell in all wavelength regions to obtain a high contrast ratio of the B/W F-STN-LCD.
Laser Dew-Point Hygrometer
Authors: Matsumoto Shigeaki , Toyooka Satoru
Published: October 2002

A rough-surface-type automatic dew-point hygrometer was developed using a laser diode and an optical fiber cable. A gold plate with 0.8 µ m average surface roughness was used as a surface for deposition of dew to facilitate dew deposition and prevent supersaturation of water vapor at the dew point. It was shown experimentally that the quantity of dew deposited can be controlled to be constant at any predetermined level, and is independent of the dew point to be measured. The dew points were measured in the range from -15° C to 54° C in which the temperature ranged from 0° C to 60° C. The measurement error of the dew point was ±0.5° C which was equal to below ±2% in relative humidity in the above dew-point range.
A Method for Determination of Rotational Viscosity and Pretilt Angle from Transient Current in Twisted Nematic Liquid Crystal Cells
Authors: Masahiro Imai Masahiro Imai , Hiroyoshi Naito Hiroyoshi Naito , Masahiro Okuda Masahiro Okuda , Akihiko Sugimura Akihiko Sugimura
Published: October 2002

A method for the determination of rotational viscosity γ1 and pretilt angle θ° in twisted nematic liquid crystal cells is proposed. The method is based on the analysis of transient current of a cell excited by a dc voltage pulse. The accuracy of γ1 and θ° values determined by the method is demonstrated by means of numerical calculation of exact basic equations. Experimental results for a ZLI2293 (Merck) cell are presented, and the γ1 values obtained are found to be in excellent agreement with values in the literature.
Macrostructure of Melt-Crystallized Vinylidene Fluoride /Trifluoroethylene Copolymers (37/63, 65/35, 73/27 mol%)
Authors: Sunao Sasaki Sunao Sasaki , Akira Funato Akira Funato , Kohji Kubo Kohji Kubo , Akio Chiba Akio Chiba
Published: October 2002

Macrostructures of melt-crystallized vinylidene fluoride/trifluoroethylene (37/63), (65/35) and (73/27) mol% copolymers have been studied using a scanning electron microscope (SEM) and small-angle X-ray scattering (SAXS). The SEM images show stacks of lamellar crystals with thicknesses of about 1000 Å. However, experimental SAXS intensities do not show diffraction peaks that are sufficiently distinct to suggest the presence of the lamellar stacks; rather, they decrease almost monotonically as the scattering angle increases. Two structural models are introduced to calculate theoretical SAXS intensity, and the degree of agreement between theoretical and experimental SAXS intensities is examined for each model. The first model is the finite lamellar stack model, which presents a good approximation of the macrostructures shown in the SEM images. However, this model yields poor agreement in higher angular regions, which indicates that the lamellar stack model is not valid for analyzing the experimental SAXS intensities of melt-crystallized copolymers. Thus, a second model is proposed: crystalline blocks cohere and constitute quasi lamellae, which are then stacked. The theoretical SAXS intensity based on the second model gives a satisfactory description of the experimental SAXS intensity.
Conformational Characteristics of Poly-ether-ether-ketone and Poly-ether-nitrile
Authors: Shirouzu Shigenori , Yoshida Masahiro , Senda Norio
Published: October 2002

Conformational analyses of poly-ether-ether-ketone (PEEK), poly-ether-nitrile (PEN) and their related polymers were performed using a semi-empirical molecular orbital method with the Austin Model 1 Hamiltonian (AM1 method in MOPAC). The minimum energy conformations were in good agreement with those in crystal structures of PEEK and PEN.
The calculated characteristic ratios C
∞ of the unperturbed end-to-end distance according to the rotational isomeric state theory were 3.93 for PEEK and 6.73 for PEN.
Numbers of repeating units between adjacent entanglements were also estimated.
The Relationship between the Bending Stress in Silicon Wafers and the Mechanical Strength of Silicon Crystals
Authors: Tetsuo Fukuda Tetsuo Fukuda
Published: October 2002

Silicon wafers horizontally stacked in a vertical furnace bend downward due to their weight. Using a linear elastic theory, we calculated the shear stress caused by the wafer bending and investigated the mechanical strength by comparing the shear stress with the upper yield stress of silicon crystals. We concluded that the maximum shear stress increased with the increase in the wafer diameter, 0.20, 0.30, and 0.55 MPa for 6, 8, and 12 inch wafers. In bending the 12 inch wafers, oxygen precipitates, lowering the upper yield stress, caused serious wafer warping because the shear stress exceeded the lowered yield stress.
Observation of Topography and Optical Image of Optical Fiber End by Atomic Force Mode Scanning Near-Field Optical Microscope
Authors: Chiba Norio , Muramatsu Hiroshi , Ataka Tatsuaki , Fujihira Masamichi
Published: October 2002

A scanning near-field optic/atomic force microscope (SNOAM) was improved using a novel optical fiber probe. The optical fiber probe has a mirror grounded on the ridge for the optical lever of AFM. The resonant characteristics of the optical fiber probe were adequate for a noncontact AFM cantilever: the typical Q factor and resonant frequency were 574 and 10.9 kHz, respectively. The topographical and optical resolution of the SNOAM was better than 100 nm for a standard sample of chromium patterns on a quartz substrate. The SNOAM successfully provided topographies and optical images of optical fiber ends simultaneously. These images indicated that the optical pattern of the core was markedly influenced by the surface roughness of the optical fiber end.
Theoretical Study of Step Coverage and Comparison with Experimental Results from Low Pressure Chemical Vapor Deposition Process of Tungsten Film
Authors: Yun Jong-Ho , Sang-Kyu Park Sang-Kyu Park
Published: October 2002

As the feature size of trench or via hole decreases below 1 µ m, a void formation caused by nonconformal step coverage leads to serious problems in the reliability of integrated circuits. In this work, the numerical simulation for the microscopic feature scale model was performed to study the step coverage in low pressure chemical vapor deposition processes by using Monte Carlo method and string algorithm. Several mechanisms such as direct deposition, re-emission, and surface diffusion were included in the model. Dependence of step coverage on aspect ratio, sticking coefficient, surface diffusion coefficient, initial trench shape, and various re-emission mechanisms was investigated and discussed in detail. Then comparison was made with experimental results from SiH4-reduced LPCVD of tungsten film for various substrate temperatures and carrier gases. The activation energy of sticking coefficient and deposition rate on the flat surface at the top of the trench were 13.0 and 6.4 kcal/mol, respectively. Sticking coefficient for Ar, H2, and He at 275° C, 0.3 mbar, WF6/SiH4/carrier gas=10/10/200 sccm was 0.04, 0.10, and 0.29, respectively, implying that a low temperature process using Ar carrier gas is preferred for better step coverage.
Photo-Generation of Linearly Polymerized Liquid Crystal Aligning Layers Comprising Novel, Integrated Optically Patterned Retarders and Color Filters
Authors: Schadt Martin , Seiberle Hubert , Schuster Andreas , Stephen M. Kelly Stephen M. Kelly
Published: October 2002

For the first time photo cross-linking of linearly polymerizable polymers (LPPs) is shown to induce uniaxial planar alignment in adjacent liquid crystal polymer (LCP)-layers on single substrates. Ways and novel materials allowing integration of LPP-aligning layers with optical retarders in patterned, hybrid LPP-LCP-configurations with freely adjustable optical axes are presented. The novel multifunctional, anisotropic photopolymer configurations are shown to render in-situ optical retarders and polarization interference filters for black-white and color liquid crystal displays (LCDs) feasible. The molecular mechanisms inducing the anisotropic film properties and their thermal and optical stabilities are outlined. The photo-patternable, high resolution hybrid configurations are shown to exhibit excellent thermal and light stability.
Structure of Self-Assembled Monolayers from Amphiphilic Diacetylene Derivatives on Indium-Tin Oxide
Authors: Tanaka Toshihiko , Honda Yoshiaki , Sugi Michio
Published: October 2002

Self-assembled monolayers (SAMs) of amphiphilic diacetylene derivatives CH3(CH2)

n

C≡C-C≡C(CH2)8COOH (n=9, 11, 13, 15) were prepared on an indium-tin oxide (ITO)/glass substrate by chemisorption from the solution. Infrared transmission spectra, visible transmission spectra, and contact angles of water revealed that the SAMs of the diacetylenes are sparse monolayers on the substrate, while the Langmuir-Blodgett monolayer is a condensed one: density of the molecules on the SAMs was approximately estimated to be one molecule/nm2.
Feasibility of Reflection Electron Energy Loss Spectroscopy with a Small Scattering Angle for Research in Surface Science
Authors: Hayashi Toshinori , Araki Kiyoaki , Takatoh Shuji , Enokijima Toru , Yikegaki Tetsurou , Futami Toru , Kurihara Yoshifumi , Tsukajima Jun'ichi , Takamoto Kiichi , Fujikawa Takashi , Usami Seiji
Published: October 2002

A reflection electron energy loss spectroscopy (R-EELS) system has been developed to investigate local surface atomic structures around light atoms such as C, N, and O. In this system, the primary electrons are incident on a surface at a grazing angle, and the electrons scattered inelastically at a small scattering angle are energy-analyzed to make the momentum transfer from the primary electrons to the scattered ones as small as possible. With this system, one can measure an energy loss near edge structure (ELNES) and an extended energy loss fine structure (EXELFS), compared with an X-ray absorption near edge structure (XANES) and an extended X-ray absorption fine structure (EXAFS). The feasibility of the system in surface science is examined by measurements of ELNES and EXELFS for oxygen-adsorbed Ni(100) surfaces.
Measurements of Tritiated Water by Microwave Spectroscopy for the Monitoring of Discharge Cleaning
Authors: Mushiaki Motoi , Kubota Yusuke , Funato Yasuyuki , Miyahara Akira , Sakuma Yoichi
Published: October 2002

The rotational spectrum of monotritiated water (THO) was measured with a Stark modulation spectrometer at 16.625 GHz. It was verified that the spectrum intensity was proportional to the pressure of THO. This result showed that the method was applicable to the monitoring of discharge cleaning under a tritium environment. Radioactivity of exhaust gases was kept below 0.56 Bq/cm3during the experiment in compliance with statutory requirements.
Independent Characterization of Density and Interface Roughness of Multilayers Using X-Ray Standing Waves
Authors: Tomoaki Kawamura Tomoaki Kawamura , Hisataka Takenaka Hisataka Takenaka , Takayoshi Hayashi Takayoshi Hayashi
Published: October 2002

X-ray standing waves were used to characterize the density and the interface roughness of multilayers. To include the interface roughness effect into consideration, the X-ray wave amplitude in the multilayers was described in terms of a modified optical matrix. Simulation results show the possibility of determining both roughness and density of multilayers, independently. Analysis of a Ni/C multilayer with a period of about 54.6 Å showed the interface roughness was 10 Å and the density of the nickel layer was equal to the bulk value. The uniqueness of the roughness and the density was confirmed by calculating standing wave profiles for various roughnesses and nickel layer densities.
High Field Effects and Methods Useful for Transferring Atoms in Scanning Tunneling Microscope
Authors: Tien T. Tsong Tien T. Tsong , Chia-Seng Chang Chia-Seng Chang
Published: October 2002

Some of our recent work on atom transfer processes between the tip and the sample in scanning tunneling microscope is summarized. A modified field evaporation model is used to explain the atom transfer process in ultra-high-vacuum. We show that this model is valid with the normal imaging tip-sample separation or longer distances, whereas the first principle theories of Lang, Hirose and Tsukada are valid under a near-contact tip-sample separation. Our model indicates that Au and Si favor negative field evaporation whereas Pt favors positive field evaporation. Available UHV data are consistent with these conclusions. We also show that in air and in an insulating liquid, atom transfer due to mechanical contact is an important mechanism, but other mechanisms may also occur. The actual mechanism depends very much on how an atom transfer experiment is carried out.
Theoretical Simulation of Atomic Force Microscope Based on Cluster Models
Authors: Naruo Sasaki Naruo Sasaki , Masaru Tsukada Masaru Tsukada
Published: October 2002

The theoretical simulation of atomic force microscope (AFM) images is performed using a model of a multiple-atom diamond tip scanned on a graphite substrate surface. It is clarified how the AFM images and the force distributions change as the load varies. The effect of the tip apex structure is examined by tilting the tip and by using two different tips. In the cluster models, the interatomic potential within the tip and the surface is assumed to be harmonic, and that between the tip and the surface is taken as Lennard-Jones type. It is clearly shown that AFM images are influenced not only by the geometrical structure of the surface, but also by microscopic elastic properties of the tip and the surface as well as the tip structure.
Self-Assembly of 2-Thiocytosine Molecules Adsorbed on Au(111) Surface
Authors: Shunji Katsumata Shunji Katsumata , Atsushi Ide Atsushi Ide
Published: October 2002

We have studied self-assembly of 2-thiocytosine, a substituent of deoxyribonucleic acid (DNA) bases, adsorbed on a Au(111) surface by scanning tunneling microscopy (STM) under ambient conditions in air. STM images always obtained under ambient conditions are similar to those of an ordered array of cytosine on a Au substrate in solution. However, two kinds of STM images have been obtained in this work, one of which was observed for the first time.
Scanning Tunneling Imaging of Bio-Organic Molecules and Their Tunneling Properties: Fatty Acids, Their Derivatives and Cholesteryl Stearate
Authors: Kousei Yoshimura Kousei Yoshimura , Hideo Arakawa Hideo Arakawa , Atsushi Ikai Atsushi Ikai
Published: October 2002

Scanning tunneling microscopy imaging was applied to long-chain fatty acids, their derivatives and cholesteryl stearate in the adsorbed state at the liquid-solid interface between phenyloctane and highly oriented pyrolytic graphite. Cerotic acid, lignoceric acid, stearic acid, sodium stearate, stearoyl amide, and stearoyl anilide all produced regular arrays of dark and bright bands. Bright bands in the images of all execept the last compound were assigned as side-by-side alignment of hydrocarbon chains based on the variation of the band width between the three fatty acids. In the case of stearoyl anilide, the bright part was assigned to aromatic ring structure and the wider dark area to the hydrocarbon part.
Scanning Capacitace Microscope/Atomic Force Microscope/Scanning Tunneling Microscope Study of Ion-Implanted Silicon Surfaces
Authors: Hideto Tomiye Hideto Tomiye , Hiroshi Kawami Hiroshi Kawami , Michiyoshi Izawa Michiyoshi Izawa , Masamichi Yoshimura Masamichi Yoshimura , Takafumi Yao Takafumi Yao
Published: October 2002

We have investigated the local electrical properties of ion-implanted Si using a combined scanning capacitance microscope (SCaM)/atomic force microscope (AFM)/scanning tunneling microscope (STM) with special attention paid to the effect of annealing. The STM image shows that the as-implanted area is insulating, while the unimplanted area is conductive, in an unannealed sample. Both STM and SCaM images clearly indicate that the implanted area is conductive with n-type behavior after annealing. However, the unimplanted area did not show p-type behavior but slightly n-type behavior due to the diffusion of P impurities during annealing.
Hydrogen-like Ultrashallow Thermal Donors in Silicon Crystals
Authors: Akito Hara Akito Hara
Published: October 2002

I investigated the electrical properties of annealed carbon- and nitrogen-rich Czochralski-grown silicon crystals using optical absorption and electron spin resonance, and I discovered the formation of a new kind of hydrogen-like donors,ultrashallowthermaldonors(USTDs), made up of carbon, nitrogen and oxygen, and having very shallow energy levels. The donors' central-cell corrections are very small, with some of them having a negative central-cell correction peculiar to large cluster size defects. Based on the similarities between nitrogen-oxygen donors (D(N, O)s) and USTDs, I propose a formation mechanism and an atomic configuration for the USTDs. The USTDs are defects caused by interstitial carbons diffusing into the core of D(N, O) and modifying its electronic structure.
Temperature Dependence of the Viscosity of Molten Silicon Measured by the Oscillating Cup Method
Authors: Sasaki Hitoshi , Tokizaki Eiji , Huang Xin Ming , Terashima Kazutaka , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

The viscosity of molten silicon was measured using a oscillating cup made of SiC. In the temperature range, from the solidification point of about 1,415° C to about 1,600° C, the viscosity ranged from 0.7 to 0.9 mPa· s. The activation energy estimated from the data was 0.20 eV. An anomalous increase in the viscosity with decreasing temperature was observed for temperatures lower than about 1,430° C. In this temperature range, an anomalous temperature dependence of the density and surface tension have been observed. Our results thus indicate that the anomalous behavior of different properties occurs simultaneously, reflecting a kind of essential variation in the melt.
Effect of Post-Thermal Annealing on the Various Sulfur Passivations of GaAs
Authors: Sakata Minoru , Hayakawa Masaki , Nakano Noriyuki , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

Effects of post-thermal annealing on the various sulfur passivations of GaAs were investigated using X-ray photoelectron spectroscopy (XPS) and electrical measurements of the Schottky diode. The P2S5/NH4OH, ( NH4)2S

x

and Na2S solutions were used as sulfur sources. The XPS data showed that thermal annealing after any of the passivations studied here, substantially decreased the amounts of both elemental arsenic ( As0) and unstable As-S bonds (probably incomplete compounds such as AsS). On the other hand, the amount of stable Ga-S bonds increased after post-thermal annealing for all the sulfur passivations studied here. These findings show that unstable As-S bonds were converted to stable Ga-S bonds during post-thermal annealing. This behavior was the most marked in the Na2S passivation. Elemental arsenic, As suboxides such as AsO and incomplete As-S bonds are considered to be detrimental to the formation of stable GaAs surface, whereas the full-oxides of both As and Ga ( As2O3 and Ga2O3) and probably the full-sulfide ( As2S3) are not so detrimental. The electrical characteristics were also observed to be considerably improved by the post-thermal annealing. Degradations of electrical characteristics were smallest for the sample annealed after P2S5/NH4OH passivation (and cleaning in deionized water). The P2S5/NH4OH treatment leads to the most robust surface passivation of GaAs among those studied here.
Composition Analysis and Distributed Feedback Lasers of Strained InGaAsP Quantum Wells with Constant As/P Ratio
Authors: Kuphal Eckart , Burkhard Herbert , Armin Pöcker Armin Pöcker
Published: October 2002

Multi-quantum well 1.55 µ m lasers using compressively strained InGaAsP wells and tensile-strained InGaAsP barriers with the same As/P ratio are advantageous with respect to thermal stability and ease of metalorganic vapor phase epitaxial (MOVPE) growth. The composition of strongly strained (≤±1.3%) quaternary layers with As content y=0.75 but different Ga contents x is analyzed using X-ray diffraction and photoluminescence, and also, for the first time, electron probe microanalysis. It is found that x and y can be determined from the mismatch and a gap energy function E
g(x, y), as well as from a vapor-solid relation, which formerly were established to hold only for nearly lattice-matched layers. Thermal treatment of laser structures only negligibly shifted the emission wavelength. Nearly strain-compensated 2-well lasers on n- and p-substrates reveal extrapolated threshold current densities of 190 and 730 A/cm2, respectively, which are the lowest values reported so far for a constant-y material. Constricted-mesa 2-well DFB lasers on p-substrates show threshold currents of 10 to 20 mA and a modulation capability of 8 Gb/s.
Strain Distribution Measurement in Stainless Steels by Convergent-Beam Electron Diffraction
Authors: Saito Masakazu , Aoyama Takashi , Nakata Kiyotomo , Takaya Suzuki Takaya Suzuki
Published: October 2002

A convergent-beam electron diffraction technique was utilized to measure local strain distributions in stainless steels. Electron beams were focused into {210} crystal planes and the higher order Laue zone (HOLZ) lines diffracted from {375} and {119} planes were characterized by measuring the distances between the intersections of these HOLZ lines. Four parameters, including strains in three directions and one magnification factor, were calculated based on the least squares method. Strain distributions near a chromium carbide precipitate were measured in sensitized SUS 304 and it was confirmed that parallel tensile strain and vertical compressive strain to the edge of the precipitate existed and that they decreased with the distance from the edge of precipitate.
High-Efficiency Intracavity Frequency-Doubled CW and Tunable Ti:Sapphire Laser
Authors: Zhou Wang-Long , Mori Yusuke , Sasaki Takatomo , Nakai Sadao , Nakano Kouichi , Niikura Shinji
Published: October 2002

An efficient and stable intracavity frequency-doubled cw and tunable Ti:sapphire laser has been developed using a critically phase-matched, temperature-tuned lithium triborate crystal. Ultraviolet coherent radiation tunable from 400 nm to 395 nm has been obtained with maximum output power of 460 mW. The frequency-doubling efficiency, the ratio of the converted second-harmonic power to the fundamental output capability, is over 70%. The effects on the conversion efficiency of the fundamental oval-shaped beam, multimode structure and harmonic-reflection-mirror enhancement are analyzed. The temporal stability of the harmonic output power and the crystal coating damage are examined and discussed.
Second-Harmonic Generation of a Picosecond Laser Pulse at High Intensities with Time Predelay
Authors: Zhang Tiejun , Daido Hiroyuki , Kato Yoshiaki , Sharma Lalit Bhushan , Izawa Yasukazu , Sadao Nakai Sadao Nakai
Published: October 2002

We describe an experiment on second-harmonic generation of a picosecond laser pulse with time predelay at intensities of up to 200 GW/cm2. Duration of the second-harmonic pulse was reduced to 0.6 ps from the 1.5 ps width of the fundamental pulse at an optimum intensity of 50 GW/cm2. The spatial profile of the laser beam is not degraded by self-focusing at an input intensity of near 50 GW/cm2.
Wavefront Spread of Hot Electrons Generated by Planer Tunnel Emitters
Authors: Matsuura Hiroshi , Kazuhito Furuya Kazuhito Furuya
Published: October 2002

For realization of quantum coherent devices which use the wavefront of the electron wave, the wavefront spread is important. To investigate the wavefront spread, the double-slit diffraction of hot electrons from a planer tunnel emitter is analyzed. Due to the statistical spread of the transverse momentum of electrons in the emitter electrode, the visibility of the diffraction pattern is less than unity. The wavefront spread is defined as the maximum spacing of the double-slit which provides visibility higher than 1/e. Dependencies of the wavefront spread on various parameters are derived. It increases when the temperature and/or the Fermi energy decreases. For example, when the Fermi energy is 5 meV, spread is 60 and 27 nm at 4 and 77 K, respectively.
Crystallographic Orientation Dependence of Dielectric Constant in Epitaxially Grown SrTiO3 Films
Authors: Komatsu Shuichi , Kazuhide Abe Kazuhide Abe
Published: October 2002

Dielectric constants were compared between SrTiO3(STO) (100) and (110) films, which were epitaxially grown on Pt-deposited MgO (100) and MgO(110) single crystals, respectively. Epitaxial STO films with different orientation were prepared by rf sputtering. The relations between crystallographic orientation of the dielectric films and the substrates were confirmed to be (100) STO||
(100) Pt||
(100) MgO and (110) STO||
(110) Pt||
(110) MgO. The dielectric constant of the (100) oriented STO film was greater than that of the (110) oriented one. The orientation dependence of the dielectric constant is discussed from the viewpoint of thermodynamic phenomenology. It is clarified that the difference in interface energy between the dielectric and the electrode has an important role in determining the difference in the dielectric constant.