General Expressions for Ellipsoidal-Valley Quantum Transport in Arbitrary Growth Direction: Non-Equilibrium Green's Function

Chun-Nan Chen, Wei-Long Su, Meng-En Lee, Jen-Yi Jen, and Yiming Li — 2011-06-06T09:00:00+09:00

Authors: Chun-Nan Chen, Wei-Long Su, Meng-En Lee, Jen-Yi Jen, and Yiming Li
A theoretical method for the calculation of quantum transport in an ellipsoidal valley is presented. This method is developed using a non-equilibrium Green's function framework. Importantly, it is instructive that k_{z} is separated into two parts so that the wrong figure shape of the transmission coefficients does not exist. The L-electron effect on AlAs–GaAs–AlAs double barrier structures oriented in the [001], [111], and [110] growth directions is explored using the proposed method.

Estimation of Fermi Level Changes Caused by Changes in Ambient Conditions around Organic Semiconductors by Seebeck Effect Measurement

Kouji Suemori, Ryuuto Yamamoto, and Toshihide Kamata — 2011-06-06T09:00:00+09:00

Authors: Kouji Suemori, Ryuuto Yamamoto, and Toshihide Kamata
By using the Seebeck effect measurement, we investigated changes in the Fermi level of pentacene caused by changes in ambient conditions. Since, measurement of Seebeck voltage is not accompanied with current flow, this measurement is not affected by contact resistance of devices. Thus, we can measure Fermi level change caused by ambient change without influence of contact resistance.

Effects of Phase-Separation Direction of Monomers on Polymer Wall Formation and Electrooptical Properties of Flexible Smectic Liquid Crystal Cell

Ji-Hoon Lee and Tae-Hoon Yoon — 2011-06-06T09:00:00+09:00

Authors: Ji-Hoon Lee and Tae-Hoon Yoon
We examined the effects of the phase-separation direction of monomers on the polymer wall formation and the electrooptical properties of a chiral smectic C liquid crystal. Monomers are more clearly phase-separated when polymer walls are formed in the layer normal direction rather than in the layer parallel direction. The anisotropic phase-separation property of monomers is considered to be related to the layered structure of the smectic liquid crystal. The tilt angle and contrast ratio of the cell with the layer-normal polymer walls are larger than those of the cell with the layer-parallel polymer walls.

Flexible Ferroelectric Liquid Crystal Cell Stabilized by Column Spacer and Polymer Wall: Influence of Bending and Pressing on the Mechanical Stability

Ji-Hoon Lee, Min-Ki Choi, Tong-Kun Lim, and Tae-Hoon Yoon — 2011-06-06T09:00:00+09:00

Authors: Ji-Hoon Lee, Min-Ki Choi, Tong-Kun Lim, and Tae-Hoon Yoon
We prepared a flexible ferroelectric liquid crystal cell stabilized by column spacers and polymer walls. The column-shaped spacers were built on a plastic substrate and a liquid crystal-reactive monomer mixture was printed on it. The polymer walls were formed perpendicular to the column spacers by a polymerization-induced phase-separation technique, and the polymer networks were formed in the pixel area by an additional UV curing. The change of the liquid crystal orientation was examined vs the bending and pressing of the plastic substrates.

Extremely High Purcell Factor of Plasmonic Modes in Thin Nano-Metallic Cylinders

Jin-Kyu Yang — 2011-06-06T09:00:00+09:00

Authors: Jin-Kyu Yang
We numerically study the ultrahigh Purcell factor (>10^{4}) of plasmonic modes in thin metallic nanodisk and nanoring structures by fully three-dimensional (3D) finite-difference time-domain (FDTD) simulation. Because of their extremely small mode volume (∼10^{-5} λ_{0}^{3}, λ_{0} is the resonant wavelength in vacuum), plasmonic modes with a large radiative loss can have a high decay rate. Because of a uniform field enhancement inside their rings, nano-metallic ring structures show high potential for controlling high-extraction efficiency and single molecular sensing utilized in surface-enhanced Raman scattering.

Uncooled InAsSb Photoconductors with Long Wavelength

2011-06-06T09:00:00+09:00

Authors: Yu Zhu Gao, Xiu Ying Gong, Guang Hui Wu, Yan Bin Feng, Takamitsu Makino, and Hirofumi Kan
High-sensitivity uncooled InAsSb photoconductors with long wavelength were successfully fabricated. The detectors are based on InAsSb epilayers with the thickness of 100 µm grown on InAs substrates by melt epitaxy (ME). Si optical lenses were set on the photoconductors without any antireflective coatings. At room temperature, the peak detectivity D_{λp}^{*} (6.5 µm, 1200) reaches 5.3 ×10^{9} cm Hz^{1/2} W^{-1} for InAsSb immersion photoconductors. The detectivity D^{*} at the wavelength of 8 µm is 1.5 ×10^{8} cm Hz^{1/2} W^{-1}, and that at 9 µm is 1.0 ×10^{7} cm Hz^{1/2} W^{-1}. The excellent performance of the detectors indicates the potential applications for infrared (IR) detection and imaging at room temperature.

Color Reproduction of Multi-Wavelength Digital Holography Using a Color Correction Algorithm

Han-Yen Tu, Xin-Ji Lai, Chau-Jern Cheng, and Li-Chien Lin — 2011-06-06T09:00:00+09:00

Authors: Han-Yen Tu, Xin-Ji Lai, Chau-Jern Cheng, and Li-Chien Lin
This work describes color reproduction of multi-wavelength digital holographic recording and reconstruction of real objects based on color correction procedures. Color correction primarily consists of tone correction and chromaticity correction for reconstructed images from a multi-wavelength digital hologram. With recording and reconstruction knowledge from a standard ColorChecker chart, a color profile can be generated to characterize the color properties of the multi-wavelength digital holography system and then use this profile for color reproduction of different target images. The color accuracy of reconstructed images via the proposed method is demonstrated experimentally.

Analytical Investigation of an All-Optical T-Type Flip-Flop Using a Semiconductor Optical Amplifier Mach–Zehnder Interferometer with Push–Pull Configuration

Satoshi Shimizu and Hiroyuki Uenohara — 2011-06-06T09:00:00+09:00

Authors: Satoshi Shimizu and Hiroyuki Uenohara
To achieve an optical regenerator for a differential phase-shift keying signal based on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI), we need an all-optical T-type flip-flop (T-FF) for encoding. We propose an all-optical T-FF consisting of an SOA-MZI with push–pull configuration and a feedback mirror to overcome the speed limitation of the previously proposed counter-faced configuration. Numerical simulation reveals its possibility of stable operation in 10 Gbps with a 2^{7} - 1 pseudo random binary sequence (PRBS) signal even by using a conventional SOA with a slow carrier recovery of 100 ps, and the possibility of 40 Gbps operation is also investigated.

Kinetics Study on Initial Growth Stage in Vapor Deposition of Organic Thin Film Using Quartz Crystal Microbalance

Takaya Ito, Shinya Onoda, Masaaki Kino, Kiyoshi Hagihara, and Atsushi Kubono — 2011-06-06T09:00:00+09:00

Authors: Takaya Ito, Shinya Onoda, Masaaki Kino, Kiyoshi Hagihara, and Atsushi Kubono
The deposition behavior of stearic acid evaporated in vacuum was observed using a quartz crystal microbalance technique, and the time evolution curves of the amount of admolecules in the initial growth were compared with a theoretical curve calculated using a rate equation proposed on the basis of physisorption. From the results, it was demonstrated that the proposed rate equation for the early stage of film formation well described the experimental results and the growth kinetics of organic thin films was dependent on the substrate temperature. Basic parameters for thin-film growth, such as the mean stay time on the substrate of deposited molecules, can be estimated from the fitting of the theoretical equation to the experimental results at each substrate temperature. It should be noted that the basic parameters were sensitive to a small change in substrate temperature.

Fabrication of Epitaxial Interface between Transition Metal Cyanides

Yutaro Kurihara and Yutaka Moritomo — 2011-06-06T09:00:00+09:00

Authors: Yutaro Kurihara and Yutaka Moritomo
Nanoporous materials are currently attracting the interest of materials scientists, because nanopores can transfer and accommodate guest cations. We may realize a rapid cation transfer from one material to another through an epitaxial interface. In this study, we fabricated bilayer films of nanoporous transition metal cyanides by an electrochemical deposition technique. Scanning electron microscopy (SEM) images as well as X-ray diffraction patterns strongly suggest that the cyanide layers are epitaxially connected to each other. We compared the current–voltage (I–V) properties of the epitaxial bilayer films with those of the monolayer films.

Current–Voltage Characteristics of Discharge with Water–Ceramic Electrode

Mikio Deguchi and Toru Niki — 2011-06-06T09:00:00+09:00

Authors: Mikio Deguchi and Toru Niki
Current–voltage characteristics of discharge with a water–ceramic electrode were measured under various conditions. The existence of the incandescent ceramic component in the discharge gap reduces the discharge voltage and sustains the discharge in a low current range. Discharge voltage reduction is more notable in the case that the water is positively biased. The closer to the water surface the incandescent ceramic component is positioned, the more notable its effects become. These effects can be attributed to the thermoelectronic emission from the incandescent ceramic component and the intense irradiation onto the water surface from it.

Origin Investigation of a Nitrogen-Related Recombination Center in GaAsN Grown by Chemical Beam Epitaxy

2011-05-20T09:00:00+09:00

Authors: Boussairi Bouzazi, Jong-Han Lee, Hidetoshi Suzuki, Nobuaki Kojima, Yoshio Ohshita, and Masafumi Yamaguchi
The origin of a N-related recombination center (E1), at around 0.33 eV below the conduction band minimum (CBM) of chemical beam epitaxy (CBE) grown GaAsN, is discussed based on effect of H implantation and dependence of E1 density to As flow rate (TDMAAs). After H implantation, E1 disappears completely whereas two new defects are recorded. The first one (HP1) is a hole trap at around 0.11 eV above the valence band minimum, similar to a N-related hole trap in unintentionally doped p-type GaAsN grown by CBE and expected to be N–H–V_{Ga}. The second level (EP1) is an electron trap at around 0.41 eV from CBM, identical to EL5 native defect in GaAs and expected to be V_{Ga}–As_{i} or As_{Ga}–V_{Ga}. The atomic structure of E1 is discussed from that of HP1 and EP1 and it is expected to be the split interstitial (N–As)_{As}. This expectation is supported by the peaking behavior of E1 density with As source flow rate.

Band Alignment at the Cu_{2}O/ZnO Heterojunction

Masaya Ichimura and Ying Song — 2011-05-20T09:00:00+09:00

Authors: Masaya Ichimura and Ying Song
The band offset at the Cu_{2}O/ZnO heterojunction was estimated both experimentally and theoretically following the procedure of core-level spectroscopy. The heterojunction was fabricated by electrochemical deposition, and the band offset was determined by X-ray photoelectron spectroscopy. For the theoretical calculation of the band offset, the first-principles, density-functional, pseudopotential method was used. It was predicted from both the experimental and calculation results that the valence band maximum of Cu_{2}O is located higher than that of ZnO. The experimentally obtained valence band offset ΔE_{v} was 1.7 eV, and the theoretically obtained ΔE_{v} was 1.3–1.6 eV; both results agreed fairly well.

Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

2011-05-20T09:00:00+09:00

Authors: Lynda Saci, Ramdane Mahamdi, Farida Mansour, Jonathan Boucher, Maéva Collet, Eléna Bedel Pereira, and Pierre Temple-Boyer
The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B–N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

Comparison of Ferroelectric and Insulating Properties of Mn-Doped BiFeO_{3} Films Formed on Pt, SrRuO_{3}/Pt, and LaNiO_{3}/Pt Bottom Electrodes by Radio-Frequency Sputtering

Jeong Hwan Kim, Hiroshi Funakubo, and Hiroshi Ishiwara — 2011-05-20T09:00:00+09:00

Authors: Jeong Hwan Kim, Hiroshi Funakubo, and Hiroshi Ishiwara
Mn-doped BiFeO_{3} (BFMO) films were deposited on Pt(111), SrRuO_{3}(SRO)/Pt(111) and LaNiO_{3}(LNO)/Pt(111) bottom electrodes by radio-frequency (RF) sputtering. <111> and <100>-oriented BFMO films were formed on the SRO/Pt and LNO/Pt bottom electrodes, respectively. The remanent polarization (P_{r}) in a <111>-oriented BFMO film on the SRO/Pt bottom electrode was 80 µC/cm^{2}, which was twice larger than that in a <100>-oriented BFMO film on the LNO/Pt bottom electrode. However, the coercive field (E_{c}) of the BFMO film on LNO/Pt bottom electrode (242 kV/cm) was much lower than that of the BFMO film on SRO/Pt (407 kV/cm). Furthermore, improved leakage current, breakdown field, and fatigue endurance characteristics were obtained in the <100>-oriented BFMO film on LNO/Pt.

Evaluation and Reliability Improvement Investigation of Electrical Characteristics of Ba_{0.9}Sr_{0.1}TiO_{3} Dielectric Films Prepared by Electrophoretic Deposition Method

2011-05-20T09:00:00+09:00

Authors: Naohiko Abe, Masahiko Hoshino, Naoto Kitamura, Akira Ichiryu, and Yasushi Idemoto
Ba_{0.9}Sr_{0.1}TiO_{3} (BST) thin films were deposited by the electrophoretic deposition (EPD) method for an embedded capacitor for printed circuit boards (PCBs). When the dielectric properties were evaluated in air, the leakage current densities were large, from 1×10^{-2} to 1×10^{-5} A/cm^{2} applied at 40 V. On the other hand, when the condition was dry Ar, they greatly decreased to be 5×10^{-8} A/cm^{2} at an applied voltage of 40 V. From Fourier-transform infrared (FT-IR) evaluation, the change in dielectric properties caused by changing the measuring atmosphere was attributed to the absorption of moisture in the air. These leakage currents were decreased by coating resin onto the EPD films, even when the measurement was carried out in air. When a resin varnish with 2 wt % concentration was coated onto the film with 1.91 µm thickness annealed at 900 °C for 30 min in N_{2}, the dielectric constant remained almost the same as that of without coating, 221, and the leakage current was 4×10^{-8} A/cm^{2} or less at 50 V. The resistance of the resin-coated sample was 10.2 MΩ/cm^{2} after 1000 h under 85 °C and 85% humidity with a 3.5 V bias.

Approximate Analysis of Cylindrical Ferroelectric Capacitor and Derivation of Drain Current Characteristics in Ferroelectric Gate-All-Around Carbon Nanotube Transistor

Masakazu Ibata and Hiroshi Ishiwara — 2011-05-20T09:00:00+09:00

Authors: Masakazu Ibata and Hiroshi Ishiwara
Drain current vs gate voltage and drain current vs drain voltage characteristics have been derived in a ferroelectric gate-all-around carbon nanotube (CNT) transistor. An approximate analysis to derive the polarization characteristics in a cylindrical ferroelectric capacitor is first presented. It has been found that the characteristics can be approximated by those of a parallel-plate capacitor having the same area as the inner electrode of the cylindrical capacitor and the same thickness as the ferroelectric cylinder. Then, the drain current characteristics of the ferroelectric gate-all-around CNT transistor are derived by combining the analysis on the cylindrical capacitor and the ballistic transport theory on CNT transistors. The gate structure is assumed to be such that CNTs with diameters of 1 and 2 nm are surrounded with a 5-nm-thick poly(vinyliden fluoride–trifluoroethylene) [P(VDF–TrFE)] film. It has been found that, in this structure, the CNT transistor can operate as a memory transistor with an appropriate voltage margin.

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

2011-05-20T09:00:00+09:00

Authors: Martin Weis, Wei Ou-Yang, Tetsuya Yamamoto, Yohei Matsuoka, Takaaki Manaka, and Mitsumasa Iwamoto
Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

Hybrid Alignment Induced by Asymmetric Photopolymerization of Liquid Crystal-Reactive Mesogen Composition between Two Plastic Substrates

Kyoung-Sun Kim and Ji-Hoon Lee — 2011-05-20T09:00:00+09:00

Authors: Kyoung-Sun Kim and Ji-Hoon Lee
A hybrid aligned liquid crystal layer was prepared between plastic substrates by the asymmetric photopolymerization of the reactive mesogen. The planar alignment of liquid crystal molecules was induced on the top substrate facing the UV light by the predominant photopolymerization at this substrate, whereas a homeotropic orientation was induced on the bottom substrate. The extinction ratio of the hybrid aligned samples vs the polymer concentration and the thickness of the liquid crystal layer was examined.

Relation between Monomer Structure and Image Sticking Phenomenon of Polymer-Sustained-Alignment Liquid Crystal Displays

Yohei Nakanishi, Kazutaka Hanaoka, Masakazu Shibasaki, and Kenji Okamoto — 2011-05-20T09:00:00+09:00

Authors: Yohei Nakanishi, Kazutaka Hanaoka, Masakazu Shibasaki, and Kenji Okamoto
We investigated the image-sticking phenomenon of polymer-sustained-alignment liquid crystal displays (PSA-LCDs) by the evaluation of residual DC and the difference in tilt angle. Experimental results indicate that the difference in tilt angle affects the image sticking of PSA-LCDs more than the residual DC. We also found that the difference in tilt angle is strongly dependent on the chemical structure of the monomer that forms the polymer layer between the alignment layer and the liquid crystal layer by photopolymerization.

Nanosize-Induced Optically Isotropic Nematic Phase

Satoshi Aya, Khoa V. Le, Fumito Araoka, Ken Ishikawa, and Hideo Takezoe — 2011-05-20T09:00:00+09:00

Authors: Satoshi Aya, Khoa V. Le, Fumito Araoka, Ken Ishikawa, and Hideo Takezoe
We fabricated, in a polymer matrix, liquid crystal (LC) nanosized droplets with a correlation length ξ of about 140 nm, which appear as an optically isotropic film. Differential scanning calorimetry (DSC) and light scattering measurements gave unambiguous evidences of an existence of nematic LC (NLC) order and fluctuation over a wide temperature range. The correlation length obtained by light scattering was consistent to the droplet size determined by a scanning electron microscope (SEM). The dynamic electro-optic (EO) response in such an isotropic NLC (IsoN) phase was found to be very fast, tens of µs, in a confined geometry because of the local short-range nematic order in the IsoN phase. This type of EO effect is very attractive for next-generation LC displays and light waveguides because of (1) very dark view in the absence of a field, (2) very fast response being independent of temperature and applied electric field, (3) gray-scale display capability with a constant response time, and (4) unnecessity of any surface treatment.

N-Polar III–Nitride Green (540 nm) Light Emitting Diode

Fatih Akyol, Digbijoy N. Nath, Emre Gür, Pil Sung Park, and Siddharth Rajan — 2011-05-20T09:00:00+09:00

Authors: Fatih Akyol, Digbijoy N. Nath, Emre Gür, Pil Sung Park, and Siddharth Rajan
We report the demonstration of a N-polar InGaN based green light emitting diode (LED) grown by N_{2} plasma-assisted molecular beam epitaxy (PAMBE). High quality multiple quantum well LEDs with In_{0.29}Ga_{0.71}N quantum wells were grown at a temperature of 600 °C by applying a new growth model. LED structures exhibited green emission, and electroluminescence measurements on the test structure showed peak emission wavelengths varying from 564.5 to 540 nm. The full width at half-maximum reduced from 74 to 63 nm as the drive current was increased to 180 A/cm^{2}. This work is the first demonstration of an N-polar LED with emission in the green wavelength range.

High Extraction Efficiency of GaN-Based Vertical-Injection Light-Emitting Diodes Using Distinctive Indium–Tin-Oxide Nanorod by Glancing-Angle Deposition

Min-An Tsai, Hsun-Wen Wang, Peichen Yu, Hao-Chung Kuo, and Shiuan-Huei Lin — 2011-05-20T09:00:00+09:00

Authors: Min-An Tsai, Hsun-Wen Wang, Peichen Yu, Hao-Chung Kuo, and Shiuan-Huei Lin
The enhanced light extraction and reduced forward voltage of a GaN-based vertical injection light emitting diode (VI-LED) with an indium–tin-oxide (ITO) nanorod array were demonstrated. The ITO nanorod array was fabricated by the glancing-angle deposition method. The employment of ITO nanostructures amplified not only the broadband transmission but also the current spreading. The optical output power of GaN-based VI-LEDs with ITO nanorods was enhanced by 50% compared with a conventional VI-LED at an injection current of 350 mA. The extraction efficiency was dramatically raised from 62 to 93% by the surface ITO nanorods. We also optimized the extraction efficiency of the GaN-based VI-LED with an ITO nanorod array by tuning the thickness of the n-GaN top layer via three-dimensional finite difference time domain (3D-FDTD) simulation.

Multi Junction Solar Cells Stacked with Transparent and Conductive Adhesive

2011-05-20T09:00:00+09:00

Authors: Toshiyuki Sameshima, Jun Takenezawa, Masahiko Hasumi, Takashi Koida, Tetsuya Kaneko, Minoru Karasawa, and Michio Kondo
We propose a polyimide transparent adhesive layer dispersed with In_{2}O_{3}–SnO_{2} (ITO) conductive particles (polyimide-ITO) to be used in the mechanical stacking of solar cells. A 20-µm-thick polyimide-ITO layer had a high transmissivity from 78 to 80% for wavelengths ranging from 500 to 1000 nm and a low connecting resistivity of 2.3 Ω cm^{2} at minimum. The fabrication of stacked cell consisting of a top hydrogenated amorphous silicon (a-Si:H) p–i–n cell and a bottom hetero-junction with an intrinsic thin-layer (HIT)-type silicon cell was demonstrated using an intermediate polyimide-ITO layer. A high open circuit voltage of 1.34 V was experimentally obtained. Simultaneous electric power generation from the top and bottom solar cells was achieved.

Effect of Excitons in AlGaAs/GaAs Superlattice Solar Cells

2011-05-20T09:00:00+09:00

Authors: Jiro Nishinaga, Atsushi Kawaharazuka, Koji Onomitsu, Klaus H. Ploog, and Yoshiji Horikoshi
The effect of excitonic absorption on solar cell efficiency has been investigated using solar cells with AlGaAs/GaAs superlattice active regions. Numerical calculations reveal that excitonic absorption considerably enhances the overall absorption of bulk GaAs. Excitonic absorption shows strong and sharp peaks at the absorption edge and in the energy region above the band gap. Absorption enhancement is also achieved in the AlGaAs/GaAs superlattice. The measured quantum efficiency spectra of AlGaAs/GaAs solar cells are found to be quite similar to the calculated absorption spectra considering the excitonic effect. The miniband structures of the superlattice and the electric field of the p–i–n junction enhance the dissociation of excitons and the extraction of separated carriers. These results suggest that the enhanced absorption by excitons can increase the quantum efficiency of solar cells.

Ion-Irradiated Laterally Graded Ni/C Multilayers: A Combined X-ray Standing Wave and X-ray Reflectivity Analysis

2011-05-20T09:00:00+09:00

Authors: Bhupendra Nath Dev, Sumalay Roy, Sambhunath Bera, Yuzuru Tawara, Norbert Schell, Jörg Grenzer, Johannes von Borany, and Rainer Grötzschel
An X-ray standing wave (XSW) experimental facility was set up at the Rossendorf Beam Line (ROBL) at the European Synchrotron Radiation Facility (ESRF). Using this facility, the microstructures and ion-beam induced microstructural modifications of a nanoscale laterally graded Ni/C multilayer systems have been studied by the combined X-ray reflectivity (XRR) and XSW technique. The multilayer stack with 15 Ni/C layer pairs was fabricated on a glass substrate by ion beam sputtering. A 2 MeV Cu^{2+} ion beam was rastered on the samples to obtain uniformly irradiated strips with fluences from 1×10^{14} to 7×10^{14} ions/cm^{2}. We have observed that X-ray reflectivity at the first order Bragg peak gradually increases due to increase in multilayer period in the virgin samples. The multilayer period has expanded and interfaces broadened due to ion irradiation. X-ray standing wave analysis indicates that, during deposition, a significant amount of Ni diffuses into C layers. Up to a certain fluence, we have observed that more and more Ni atoms are incorporated into C layers. At higher fluences, Ni is progressively segregated from the C layers. These mixing and demixing phenomena of Ni in C layers as a function of ion fluence have been explained in terms of two competitive processes including ballistic mixing and chemically guided atomic movements.

Dynamics of Magnetostatically Coupled Vortices Observed by Time-Resolved Photoemission Electron Microscopy

2011-05-20T09:00:00+09:00

Authors: Kuniaki Arai, Taichi Okuda, Keiki Fukumoto, Masato Kotsugi, Takuo Ohkouchi, Kenji Kodama, Takashi Kimura, Yuichi Haruyama, Tetsuya Nakamura, Tomohiro Matsushita, Hitoshi Osawa, Takayuki Muro, Shinji Matsui, Akito Kakizaki, YoshiChika Otani, and Toyohiko Kinoshita
The dynamics of magnetostatically coupled vortices in a pair of ferromagnetic micron-sized disks has been observed in real space by pump–probe time-resolved photoemission electron microscopy. It is found that the dynamics of paired vortices is affected by a magnetic dipolar interaction. The displacement of a vortex core from its equilibrium position in the paired vortices during the supply of a magnetic field pulse is smaller than that in the isolated vortex, which is in qualitative agreement with micromagnetic simulation results. Unexpectedly, two eigenfrequencies of the paired vortices are different from each other. When the separation distance between the paired disks is shorter, the difference between the two eigenfrequencies is larger.

Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La_{0.85}Ca_{0.15}Mn_{0.95}Fe_{0.05}O Manganates

Wiqar Hussain Shah and Abdullah Al Jaffari — 2011-05-20T09:00:00+09:00

Authors: Wiqar Hussain Shah and Abdullah Al Jaffari
Linear and non-linear dynamic properties of a re-entrant ferromagnetic polycrystalline bulk La_{0.85}Ca_{0.15}Mn_{0.95}Fe_{0.05}O_{3} sample are studied using AC susceptibility. The Fe doped La_{0.85}Ca_{0.15}Mn_{0.95}Fe_{0.05}O_{3} undergoes a ferromagnetic transition at T_{C} = 174 K and to spin glass (SG) at T_{g}∼100 K, and a decrease in the AC susceptibility as well as zero-field-cooled (ZFC) magnetization measured using very low DC magnetic fields. The dynamic behavior is investigated in the intermediate temperature range (T_{g}<T<T_{C}). A prominent non-linear susceptibility is observed in this range, signifying the decomposition of the FM network into clusters by a random magnetic field which is expected to be generated by PM spins in the FM region. The results are supported by a study of the AC frequency and DC field effect on the non-linear susceptibility.

Substrate Dependence of Structural and Transport Properties in FeSe_{0.5}Te_{0.5} Thin Films

2011-05-20T09:00:00+09:00

Authors: Masafumi Hanawa, Ataru Ichinose, Seiki Komiya, Ichiro Tsukada, Takanori Akiike, Yoshinori Imai, Tatsuo Hikage, Takahiko Kawaguchi, Hiroshi Ikuta, and Atsutaka Maeda
In order to clarify the best condition for the growth of iron chalcogenide superconductor thin films, we investigated the effect of the substrate on the transport and structural properties of films. Thin films of FeSe_{0.5}Te_{0.5} grown by pulsed laser deposition were characterized by DC electrical resistivity, Hall effect, X-ray diffraction measurements, and transmission electron microscopy (TEM) observation. The c-axis length of the FeSe_{0.5}Te_{0.5} thin films revealed a non-systematic change with the cell constants of the substrates. In the films with poor or no superconductivity, we found the occurrence of oxygen penetration to the film and the formation of amorphous layer between the film and the substrate. The origin of the oxygen penetration and the amorphous layer was the chemical properties of substrate. From the chemical viewpoint, LaAlO_{3} and MgO substrates were confirmed to be appropriate to grow FeSe_{0.5}Te_{0.5} films.

Quantification of Superiority of Broad-Buffer Diodes

Michio Nemoto, Takashi Yoshimura, Haruo Nakazawa, and Kousuke Yakubo — 2011-05-20T09:00:00+09:00

Authors: Michio Nemoto, Takashi Yoshimura, Haruo Nakazawa, and Kousuke Yakubo
We have quantitatively shown the superiority of broad-buffer (BB) diodes over conventional p–i–n diodes, especially with regard to fast and soft reverse recovery, by measuring a new quantity, Γ, signifying the degree of reverse recovery oscillation (RRO). The performance of switching devices has been evaluated in terms of the forward voltage drop V_{F} and the reverse recovery loss E_{RR} up to now, but these quantities cannot assess the inhibition of the RRO, which is another important property of switching devices. The quantity Γ, defined as the difference between the voltage rating and the RRO threshold power-supply voltage, represents how well the RRO is inhibited. We evaluated the performance of diodes having a variety of doping profiles in the n-drift region by numerically calculating V_{F}, E_{RR}, and Γ and plotting these quantities in a three-dimensional evaluation space. Our device simulation results clearly show that the values of Γ as well as V_{F} and E_{RR} for BB diodes are significantly lower than those for conventional diodes, and that BB diodes should be classified as a new category of diodes in view of their superior reverse recovery characteristics.

Theoretical Investigation of Effect of Side Facets on Adsorption–Desorption Behaviors of In and P Atoms at Top Layers in InP Nanowires

Tomoki Yamashita, Toru Akiyama, Kohji Nakamura, and Tomonori Ito — 2011-05-20T09:00:00+09:00

Authors: Tomoki Yamashita, Toru Akiyama, Kohji Nakamura, and Tomonori Ito
We investigate the adsorption and desorption behaviors of In and P atoms on the (111)A top layer of InP nanowires by an ab initio-based approach. Our calculated results reveal that In adatoms occupy the lattice sites of the wurtzite structure as well as the zinc blende structure in the central area of the (111)A top layer. On the other hand, the wurtzite structure is found to be feasible when In adatoms are located near the side facets. The wurtzite structure is preferentially formed for nanowires with small diameters, when most of the top layer consists of side facets. The difference in adsorption behaviors between the surfaces at the central and near the side facet on the top layer of nanowires is one the of factors determining the crystal structure of InP nanowires.

Effects of Concentration of Nanoscale Tin-Doped Indium Oxide on Electrical Breakdown of High-Resistance Liquid Crystal

Bau-Jy Liang, Don-Gey Liu, Chih-Yuan Chang, and Wun-Yi Shie — 2011-05-20T09:00:00+09:00

Authors: Bau-Jy Liang, Don-Gey Liu, Chih-Yuan Chang, and Wun-Yi Shie
According to our previous study, a high concentration of nanoscale tin-doped indium oxide (ITO) may be beneficial for protecting liquid crystal (LC) against attacks by electrostatic discharge (ESD). In this study, the influence of high-voltage stresses in an ESD test was investigated for cells doped with different concentrations of ITO. It was found that nano-ITO with a concentration of 0.4% in weight ratio deteriorated the physical properties of LC of transparency transition and charge retention. However, our experiment showed that the capability of ESD protection for the doped LC was still improved at the ITO concentration of 0.4 wt %. This finding supports the proposed model in our previous report. The role of ITO in the LC is not always beneficial, as discussed in this paper.

Effect of Pd Reactant on One-Dimensional Growth of ZnO on Si Substrate by Thermal Evaporation Method

2011-05-20T09:00:00+09:00

Authors: Kyoung-bum Kim, Young Hun Jeong, Chang-il Kim, Young-jin Lee, Jeong-ho Cho, and Jong-hoo Paik
ZnO nanostructures were developed on a Si(100) substrate from the powder mixture of ZnO and x mol % Pd (ZP-x) as reactants using a thermal evaporation method. The effect of Pd on the growth characteristics of one-dimensional ZnO nanostructures was investigated. High temperature X-ray diffraction patterns obviously revealed that Pd assisted the reduction of ZnO at temperatures higher than 1000 °C. Needle-like ZnO nanorod array, developed from ZP-x (x≥2) mixture, was well aligned vertically on the Si substrate at 1100 °C while nano-crystalline ZnO layer was only obtained from pure ZnO powder. Thus, it is considered that Pd is responsible for the growth of ZnO nanorod on the Si substrate at 1100 °C by providing the Zn vapor for the Zn/ZnO_{x} droplets with reducing ZnO in the reactant. The developed ZnO nanorod exhibited growth direction along [001] with defect-free high crystallinity.

Carrier Gas Dependence at Initial Processes for a-Plane AlN Growth on r-Plane Sapphire Substrates by Hydride Vapor Phase Epitaxy

2011-05-20T09:00:00+09:00

Authors: Jumpei Tajima, Chikashi Echizen, Rie Togashi, Hisashi Murakami, Yoshinao Kumagai, Kazuya Takada, and Akinori Koukitu
The influence of the carrier gas used during the thermal cleaning of r-plane sapphire substrates and the subsequent first AlN layer growth at 1050 °C on two-step growth of a-plane AlN layers by hydride vapor phase epitaxy (HVPE) was investigated. When hydrogen (H_{2}) was used as the carrier gas, the decomposition of r-plane sapphire occurred during the thermal cleaning, and unintentional nitridation of the sapphire surface occurred at the beginning of the growth of the first AlN layer, which resulted in the occurrence of misoriented AlN grains in the second AlN layer grown at 1450 °C. When a mixture of H_{2} and nitrogen (N_{2}) was used as the carrier gas, nitridation of the sapphire surface occurred during the thermal cleaning, which also resulted in the occurrence of misoriented AlN grains. A single-crystalline a-plane AlN layer free of misoriented grains could be obtained by using only N_{2} as the carrier gas during the thermal cleaning and the growth of the first AlN layer to prevent nitridation of the sapphire surface.

Properties of Si-Doped a-Plane GaN Grown with Different SiH_{4} Flow Rates

2011-05-20T09:00:00+09:00

Authors: Keun Man Song, Chang Zoo Kim, Jong Min Kim, Dae Ho Yoon, Sung Min Hwang, and Hogyoung Kim
Nonpolar Si-doped a-plane GaN layers were grown using metal organic chemical vapor deposition (MOCVD) with different silane (SiH_{4}) flow rates. The on-axis full width at half maximum (FWHM) of X-ray rocking curves (XRCs) along the c- and m-axis directions showed that Si doping barely affected the anisotropy of a-plane GaN. A decrease in the edge threading dislocations (TDs) with increasing Si doping was confirmed by the decreased off-axis FWHM values of the XRCs. With increasing SiH_{4} flow rate, both the carrier concentration and mobility increased through a reduction in the edge dislocation density. The photoluminescence (PL) spectra revealed that the PL peak positions were first slightly redshifted and then blueshifted with increasing carrier concentration.

High-Throughput Characterization Method for Crystallization Temperature of Integrated Thin Film Amorphous Alloys Using Thermography

Yuko Aono, Junpei Sakurai, Akira Shimokohbe, and Seiichi Hata — 2011-05-20T09:00:00+09:00

Authors: Yuko Aono, Junpei Sakurai, Akira Shimokohbe, and Seiichi Hata
We introduce the high-throughput characterization of the crystallization temperature T_{x} of thin film amorphous alloys integrated into a thin film library. This characterization is achieved using thermography. A new thin film library is designed and fabricated using photolithography and a lift-off process. Using a homogeneous composition thin film library, the validity of the proposed method is confirmed. The crystallization of all samples can be detected simultaneously, and the measured T_{x} distribution is about 8 K. Three compositionally distributed thin film libraries of the Pd–Cu–Si alloy system were then fabricated using combinatorial arc plasma deposition (CAPD), and the T_{x} values of the samples on the three libraries were measured. In the three libraries, T_{x} for 285 amorphous samples could be measured, and there was an obvious distribution in T_{x} depending on the sample composition. At two selected compositions, the measured T_{x} values agree with differential scanning calorimetry (DSC) results within 8 K. In terms of throughput, the proposed method achieves a measurement time reduction of 66% compared with a conventional method using DSC. Consequently, the proposed method enables the high-throughput combinatorial characterization of the T_{x} of thin film amorphous alloys.

Effect of Lithium Absorption at Tetrahedral Site and Isomorphic Substitution on Montmorillonite Properties: A Density Functional Theory Study

2011-05-20T09:00:00+09:00

Authors: Triati Dewi Kencana Wungu, Wilson Agerico Diño, Hermawan Kresno Dipojono, and Hideaki Kasai
This study deals with the effect of the isomorphic substitution on the sorption of two Li atoms on montmorillonite using density functional theory (DFT). The isomorphic substitution is carried out by modifying the atomic composition of the upper tetrahedral layer of the montmorillonite by replacing one Si atom with one Al atom on the said position. Note that in the conventional structure, Si atom is located at the upper tetrahedral layer of montmorillonite. Results show that one Li atom is likely to be situated in the vacant tetrahedral site and the other one is in the vacant octahedral site, for both of the two montmorillonite systems (isomorphic substitution and conventional structure). The sorption energy was found to be -6.31 eV at the most stable configuration, that is for the isomorphic substitution.

Density Functional Theory Study on the Interaction of O_{2} Molecule with Cobalt–(6)Pyrrole Clusters

Hermawan K. Dipojono, Adhitya G. Saputro, Susan M. Aspera, and Hideaki Kasai — 2011-05-20T09:00:00+09:00

Authors: Hermawan K. Dipojono, Adhitya G. Saputro, Susan M. Aspera, and Hideaki Kasai
We have investigated the interaction between cobalt–(6)pyrrole [Co–(6)Ppy] clusters and O_{2} molecule, including the adsorption and dissociation of O_{2} molecule using the density functional theory (DFT) calculations. We found that O_{2} molecule is adsorbed on Co–(6)Ppy clusters with side-on configuration and the O–O bond length elongated around 10%. The elongation of the O–O bond when O_{2} is adsorbed on the clusters will weaken the O–O bond and increase the reactivity of the molecule. The calculated dissociation energies of O_{2} molecule on Co–(6)Ppy clusters span from 0.89 to 1.23 eV. The order of the dissociation energy is affected by the amount of the charge transferred from Co–(6)Ppy clusters to the O_{2} molecule in the transition state.

Effect of the Soft X-rays on Highly Hydrogenated Diamond-Like Carbon Films

2011-05-20T09:00:00+09:00

Authors: Kazuhiro Kanda, Kumiko Yokota, Masahito Tagawa, Mayumi Tode, Yuden Teraoka, and Shinji Matsui
The effect of soft X-ray irradiation of diamond-like carbon films in vacuum was investigated using synchrotron radiation (SR). Etching and the desorption of hydrogen upon SR exposure in vacuum occurred in highly hydrogenated diamond-like carbon (H-DLC) films; these processes were not observed in the irradiation of a low-hydrogenated DLC film. The extent of decrease in hydrogen content due to SR exposure was found to decrease with increasing the etching ratio of the H-DLC film. This indicates that hydrogen desorption from the H-DLC films competed with the etching process. Namely, the modified surface, in which hydrogen content was decreased by SR exposure, was immediately removed from the H-DLC film that had a high etching rate.

Effect of K_{0.5}Na_{0.5}NbO_{3} on Properties at and off the Morphotropic Phase Boundary in Bi_{0.5}Na_{0.5}TiO_{3}–Bi_{0.5}K_{0.5}TiO_{3} Ceramics

2011-05-20T09:00:00+09:00

Authors: Eva-Maria Anton, Wook Jo, Joe Trodahl, Dragan Damjanovic, and Jürgen Rödel
Lead-free (1-y)(Bi_{1/2}Na_{1/2}TiO_{3}–xBi_{1/2}K_{1/2}TiO_{3})–yK_{0.5}Na_{0.5}NbO_{3} [(1-y)(BNT–xBKT)–yKNN] (0.1≤x≤0.6 and 0≤y≤0.05) ceramics were prepared with compositions both at as well as off the morphotropic phase boundary (MPB) of x=0.2 and y=0. It was found that KNN addition destabilizes a ferroelectric order in BNT–BKT at zero electric-field, resulting in low remanent polarization, remanent strain and effective small signal d_{33eff} [23 pC/N for (x,y)=(0.2,0.05), 60 pC/N for (0.2, 0.02)], while it does not affect the maximum polarisation and strain at high fields and thus enhances large signal piezoelectric coefficient, d_{33}^{*} [200 pm/V for (0.2,0.05), 217 pm/V for (0.2,0.02)]. This effect of KNN was found to be independent from the MPB and thus equally high d_{33}^{*} values were obtained for compositions at and far off the MPB. Thus, adding KNN to BNT–BKT removes the restriction to remain at exactly MPB position and provides more flexibility while offering equal or even improved strain.

Ionic Conductivity in Uniaxial Micro Strain/Stress Fields of Yttria-Stabilized Zirconia

2011-05-20T09:00:00+09:00

Authors: Kazuhisa Sato, Ken Suzuki, Ryo Narumi, Keiji Yashiro, Toshiyuki Hashida, and Junichiro Mizusaki
The influence of uniaxial compressive strain/stress on the O^{2-} ion conductivity of an yttria-stabilized zirconia (YSZ) sample was investigated by using electrochemical measurement. The conductivity was investigated by the AC four-probe method and molecular dynamics simulation. The applied compressive strain/stress ranged from 0 to 0.0003 (stress: 1.5–55 MPa) for the specimen in air at 873, 973, and 1073 K. To clarify the reason for the phenomenon of the decline in conductivity, the relaxation time for the conductivity after the application of strain/stresses was measured. The experimental result revealed that as the applied compressive strain/stress increases, the carrier concentration remains steady, whereas the mobility decreases. The conductivity was decreased with increasing compressive strain, and this trend agreed with that of the simulation results. Therefore, the decrease in mobility was considered to be the reason for the decline in conductivity under compressive strain/stress conditions.

High Temperature-Coefficient of Resistance at Room Temperature in W-Doped VO_{2} Thin Films on Al_{2}O_{3} Substrate and Their Thickness Dependence

Hidefumi Takami, Kenichi Kawatani, Teruo Kanki, and Hidekazu Tanaka — 2011-05-20T09:00:00+09:00

Authors: Hidefumi Takami, Kenichi Kawatani, Teruo Kanki, and Hidekazu Tanaka
The temperature coefficient of resistance (TCR) in V_{1-x}W_{x}O_{2} (VWO) with various W-doping levels and thicknesses were investigated on Al_{2}O_{3}(0001) single crystal substrates. The VWO thin films with an appropriate doping level (x=0.015) showed high TCR over 10%/K just at room temperature (300 K), which was larger than that in other reported high TCR materials. Moreover, no significant change of the TCR property was found based on their thickness dependence, meaning effective enhancement of the sensing performance for bolometric application.

Optical Properties of Ultrathin Copper Thin Films Sandwiched between Nb-Doped TiO_{2} Films Studied with Spectroscopic Ellipsometry

2011-05-20T09:00:00+09:00

Authors: Hosuk Lee, Hosun Lee, Jun-Hyuk Park, Han-Ki Kim, Bo Hyun Kong, and Hyung Koun Cho
Cu thin films sandwiched between Nb-doped TiO_{2} (NTO) thin films were grown on glass substrates using tilted-dual target DC magnetron sputtering deposition. The thicknesses of the top and bottom NTOs were nominally 30 nm, and the thicknesses of the Cu films (t) varied between 1.5 nm and 50 nm. We measured the ellipsometric angles (Ψ,Δ) of the NTO/Cu/NTO/glass by using spectroscopic ellipsometry and estimated the thicknesses and dielectric functions of the Cu films by using a multi-layer model analysis. Transmission electron microscopy measurements showed that the Cu layers evolved from aggregates of Cu nanoparticles to coalesced Cu thin films as the Cu film thickness increased. Sheet resistance data also showed that the t = 8 nm film was near the percolation threshold, suggesting that films thinner than 8 nm were aggregations of Cu nanoparticles that were not well-connected. The films thicker than 8 nm were above the percolation threshold. From the Drude model, we estimated the plasmon frequency (ω_{p}) and the electron relaxation time (τ), which were found to increase with increasing film thickness. By applying standard critical point analysis to the second derivatives of the dielectric function spectra, we found several peaks near 1.5, 2.1, 2.5, 3.5, and 4.3 eV, and attributed to interband transitions. The peak energies (except 1.5 eV) matched to the band structure calculations of bulk Cu found in the literature.

Spatial Distributions of Electron, CF, and CF_{2} Radical Densities and Gas Temperature in DC-Superposed Dual-Frequency Capacitively Coupled Plasma Etch Reactor Employing Cyclic-C_{4}F_{8}/N_{2}/Ar Gas

2011-05-20T09:00:00+09:00

Authors: Tsuyoshi Yamaguchi, Tetsuya Kimura, Chishio Koshimizu, Keigo Takeda, Hiroki Kondo, Kenji Ishikawa, Makoto Sekine, and Masaru Hori
On a plasma etch reactor for a wafer of 300 mm in diameter, the spatial distributions of the absolute densities of CF and CF_{2} radicals, electron density (n_{e}), and the gas temperature (T_{g}) of N_{2} were measured employing the dual frequency of negative dc voltage superposed to a very high frequency (VHF) of 60 MHz capacitively coupled plasma (DS-2f-CCP) with the cyclic- (c-)C_{4}F_{8}/Ar/N_{2} gas mixture. The dc bias was superposed on the upper electrode with a frequency of 60 MHz. The distributions of electron and radical densities were uniform within a diameter of about 260 mm, and took a monotonic decay in regions outside a diameter of 260 mm on the reactor for 300 mm wafers in the reactor. It was found that only CF_{2} density at the radial position between 150 and 180 mm, corresponding to the position of the Si focus ring, dropped, while CF density took a uniform distribution over a diameter of 260 mm. Additionally, at this position, the rotational temperature of N_{2} gas increased to be 100 K larger than that at the center position. CF_{2} radical density was markedly affected by the modified surface loss probability of the material owing to coupling with surface temperature.

Gallic Acid as a Complexing Agent for Copper Chemical Mechanical Polishing Slurries at Neutral pH

Yung Jun Kim, Min Cheol Kang, Oh Joong Kwon, and Jae Jeong Kim — 2011-05-20T09:00:00+09:00

Authors: Yung Jun Kim, Min Cheol Kang, Oh Joong Kwon, and Jae Jeong Kim
Gallic acid was investigated as a new complexing agent for copper (Cu) chemical mechanical polishing slurries at neutral pH. Addition of 0.03 M gallic acid and 1.12 M H_{2}O_{2} at pH 7 resulted in a Cu removal rate of 560.73±17.49 nm/min, and the ratio of the Cu removal rate to the Cu dissolution rate was 14.8. Addition of gallic acid improved the slurry performance compared to glycine addition. X-ray photoelectron spectroscopy analysis and contact angle measurements showed that addition of gallic acid enhanced the Cu polishing behavior by suppressing the formation of surface Cu oxide.

Characterization of Bistable Hybrid-Twisted Nematic Liquid Crystal Mode by Means of Renormalized Transmission Spectroscopic Ellipsometry

2011-05-20T09:00:00+09:00

Authors: Kazuya Goda, Yasuo Toko, Ryouhei Takahashi, Taiju Takahashi, Munehiro Kimura, and Tadashi Akahane
We report on how to determine asymmetrical director distribution throughout a liquid crystal layer such as a bistable hybrid-twisted nematic (BHTN) liquid crystal device by means of renormalized transmission spectroscopic ellipsometry. The advantage of the plural oblique incidence spectroscopic ellipsometry (POISE) is that the azimuthal angle as well as the tilt angle with a relatively high zenithal angle can be determined simultaneously without using a special cell with a coupling prizm. It was demonstrated that five device parameters, namely, cell gap, pretilt angles of upper and lower surfaces, twist angle of the director alignment, and azimuthal angle of the entrance liquid crystal director, can be determined uniquely. It is experimentally confirmed that each bistable state has an opposite twist sense and the twist angle difference between two stable states is approximately 180°.

Optimization of Bandwidth and Signal Responses of Optically Pumped Atomic Magnetometers for Biomagnetic Applications

Keigo Kamada, Shuji Taue, and Tetsuo Kobayashi — 2011-05-20T09:00:00+09:00

Authors: Keigo Kamada, Shuji Taue, and Tetsuo Kobayashi
Recently developed ultrasensitive optically pumped atomic magnetometers are promising for biomagnetic measurements such as magnetoencephalograms and magnetocardiograms. The magnetometer's bandwidth and amplitude of signal response are important factors for biomagnetic measurements. These factors depend on various operating parameters such as power density and wavelengths of laser beams. By focusing on the transverse spin relaxation time, we theoretically and experimentally studied the change in the bandwidth and amplitude of the signal response. By considering the effect of the attenuation of a pump beam inside a cell, we showed good agreement between theoretical and experimental results. Furthermore, the magnetometer's integrated performances for the factors were evaluated by changing the power density of the pump beam. Measured data indicated that the bandwidth of signal response depended on the power density of the pump beam and that the bandwidth could be tuned to a desirable frequency range.

Evaluation of a Delay-Line Detector Combined with Analog-to-Digital Converters as the Ion Detection System for Stigmatic Imaging Mass Spectrometry

2011-05-20T09:00:00+09:00

Authors: Hidetoshi Yoshimura, Hisanao Hazama, Jun Aoki, Michisato Toyoda, Yasuhide Naito, and Kunio Awazu
In addition to identifying analytes from the time-of-flight of ions, stigmatic imaging mass spectrometry (IMS) realizes microscopic and high-throughput imaging of multiple mass-resolved molecules. However, practical applications require a fast position- and time-sensitive ion detector. We have developed a delay-line detector combined with analog-to-digital converters (ADCs), and evaluated its performance as an ion detector for stigmatic IMS using electron ionization. The system shows spatial and temporal resolutions of 230 µm and 24 ns (4.2 ×10^{7} frames per second), respectively. We speculate that the timing jitter of the signals limits the spatial resolution due to the signal processing devices. At a 20-fold ion optical magnification and m/z of 10,000, the estimated spatial resolution and mass resolving power m/Δm using this ion detection system with a stigmatic imaging mass spectrometer, which we are currently developing, are 12 µm and 15,000, respectively.

Pulse Analyzing System Using Optical Coherence Tomography for Oriental Medical Application

2011-05-20T09:00:00+09:00

Authors: Unsang Jung, Mansik Jeon, Changho Lee, Namhyun Cho, Hyosang Jeong, Changsu Na, and Jeehyun Kim
In oriental medicine, the pulse wave of a radial artery is a critical diagnosis factor. An oriental doctor puts a finger on the radial artery to sense the pulse wave of a radial artery. The pulse wave plays an important role because its shape, pressure, and duration determine the pathological status of a patient. Chongumaekbeop, which is a traditional technique for measuring the pulse by using a finger, is sometimes believed to be not reproducible due to the subjective judgment of the measurement location and pulse signal, so we performed a clinical experiment with a developed diagnosis equipment to produce quantitative and reproducible results. In this study, we measured the pulse wave of the radial artery and quantified the speed, intensity, and power of the pulse wave using optical coherence tomography (OCT). We confirmed the applicability of the developed system through an analysis of the pulse wave. We used two OCT systems whose measurement parameters are different because of the measurement limitation and analysis of vector components of pulse movement. We gathered 25 volunteers, compared and analyzed the experiment results with four oriental medicine doctors' diagnosis. The results showed an agreement of 88% in pulse speed, 64% in pulse intensity, and 72% in pulse power when comparing traditional measurements with the system using OCT. We confirmed the dynamical motion detection through the two-dimensional image to ensure the reproducibility of the developed system. Thus, if the OCT system is applied to pulse measurement systems in oriental medicine, it may partially substitute for traditional measurement methods.

Tip to Side Welding of Ultrathin Pt Wires by Joule Heating

Satoru Fukui and Hironori Tohmyoh — 2011-05-20T09:00:00+09:00

Authors: Satoru Fukui and Hironori Tohmyoh
This paper demonstrates welding the tip of an ultrathin Pt wire to the side of a similar wire by Joule heating. The tip of the wire, with a diameter of 600–800 nm, is brought into contact with the side of another wire, and they are welded together into a complex form by supplying a constant direct current through the parts in contact. The conditions for tip to side welding of Pt wires are compared to those of tip to tip welding using a parameter that was proposed previously for the tip to tip welding of two wires. The parameter depends on the current, the length and cross-sectional area of the wires and comprises a function with respect to the thermal boundary conditions. Although the successful welding conditions of tip to side welding are located in the range of those for tip to tip welding, the lower limit of the conditions for tip to side welding was slightly higher than that in tip to tip welding. Finally, a three-dimensional micrometer-scale structure was created by repeating the tip to side welding process.

Deflections of Magnetic Actuator under Different Directions of External Magnetic Field

2011-05-20T09:00:00+09:00

Authors: Yi-Ping Hsieh, Yun-Jui Li, Zung-Hang Wei, Wei-Yuan Chen, Jung-Shao Chang, Hong-Ren Shiao, Chen-Chi Huang, Hui-Chun Hung, and Mei-Feng Lai
A magnetic actuator consisting of a 70×0.525×1 µm^{3} silicon oxide microcantilever and a 70×5×1 µm^{3} silicon oxide plate deposited on a 50×1×0.09 µm^{3} ferromagnetic thin film is successfully fabricated using electron beam lithography and electron beam evaporation, and placed in various magnetic fields to observe its flexure. The magnetic actuator is bent using a magnetic torque produced by a ferromagnetic thin film under an external magnetic field owing to the fabrication of a highly sensitive microcantilever and the design of a high magnetic shape anisotropy. In this study, the magnetic actuator is placed in three magnetic field directions to investigate its diversity of deflections; the angles between the easy axis of the ferromagnetic thin film and the direction of the external magnetic field are 90, 80, and 45°.

Implications of the Differential Equations of the X-ray Free-Electron Laser

Tae-Yeon Lee — 2011-05-20T09:00:00+09:00

Authors: Tae-Yeon Lee
Differential equations governing the X-ray free-electron laser are complicated and it is not straightforward to see all the information they have other than the fitting formula for the radiation power gain. Using the equations and the fitting formula but not solving the equations completely, some useful information is obtained including the radiation beam size and the saturation value of the bunching parameter.

Characteristics of La_{2}O_{3}- and Al_{2}O_{3}-Capped HfO_{2} Dielectric Metal–Oxide–Semiconductor Field-Effect Transistors Fabricated on (110)-Oriented Silicon Substrates

2011-05-06T09:00:00+09:00

Authors: Ryosuke Iijima, Lisa F. Edge, John Bruley, Vamsi Paruchuri, and Mariko Takayanagi
The influence of the crystal orientation difference between (100) and (110) silicon substrates on characteristics of La_{2}O_{3}- and Al_{2}O_{3}-capped HfO_{2} dielectric metal–oxide–semiconductor field-effect transistors has been investigated. We observed that the equivalent oxide thickness of the capped devices varies according to the crystal orientation, indicating that the two substrates are not equal in the gate stack scalability within a sub-nanometer regime. We found that the mobility dependency on the crystal orientation is reduced by additional scattering associated with the capping films, suggesting the difficulty to derive maximum benefit from an inherent difference in the mobility depending on the crystal orientation.

Organic Electrodes Consisting of Dianthratetrathiafulvalene and Fullerene and Their Application in Organic Field Effect Transistors

Takuji Kato, Chikako Origuchi, Masato Shinoda, and Chihaya Adachi — 2011-05-06T09:00:00+09:00

Authors: Takuji Kato, Chikako Origuchi, Masato Shinoda, and Chihaya Adachi
A double layer of dianthratetrathiafulvalene (DATTF) and fullerene (C_{60}) on an n^{++}-Si wafer pretreated with n-octyltrichlorosilane exhibited a high electrical conductivity of σ= 0.12 S/cm and was used as source–drain electrodes in organic field effect transistors (OFETs). A simplified OFET device architecture composed of an organic semiconducting active layer and an organic electrode layer was easily fabricated by successive vacuum deposition of organic donor and acceptor layers. It was confirmed that this device configuration is applicable for both p- and n-type FET operation.

Reverse-Tilt-Domain Boundary Wall in a Polymer-Encapsulated Flexible Liquid Crystal Display

Sun-Kyoung Kim and Ji-Hoon Lee — 2011-05-06T09:00:00+09:00

Authors: Sun-Kyoung Kim and Ji-Hoon Lee
A reverse-tilt-domain boundary wall in a polymer-encapsulated nematic liquid crystal was examined. A boundary wall in which the liquid crystal director was nearly planar midway through the wall was formed during UV polymerization; it remained stable even though the liquid crystal molecules in neighboring domains are nearly vertically aligned. The formation of the boundary wall was found to be suppressed by the oblique irradiation with linearly polarized UV light.

Power Dependent Micro-Photoluminescence of Green-InGaN/GaN Multiple Quantum Wells

Sang-Youp Yim, Joon Heon Kim, Mun Seok Jeong, Seung-Han Park, and Jongmin Lee — 2011-05-06T09:00:00+09:00

Authors: Sang-Youp Yim, Joon Heon Kim, Mun Seok Jeong, Seung-Han Park, and Jongmin Lee
We report the excitation-power-dependent micro-photoluminescence (micro-PL) of green-InGaN/GaN multiple quantum wells grown on a sapphire substrate. By using a micro-PL imaging technique based on laser scanning confocal microscopy, bright luminescent centers emitting blue, green, and yellow bands were clearly resolved at a low excitation power. With increasing power, in addition, the strong blue-shift of PL bands from all luminescent centers was observed, with a much stronger blue-shift for initial yellow band. We show that the band-tail filling model qualitatively agrees well with our microscopic study revealing the origin of apparent bandwidth-narrowing in macroscopic ensemble PL spectra.

Moving Picture Recording and Observation of Visible Femtosecond Light Pulse Propagation

2011-05-06T09:00:00+09:00

Authors: Takashi Kakue, Masayuki Aihara, Tetsuya Takimoto, Yasuhiro Awatsuji, Kenzo Nishio, Shogo Ura, and Toshihiro Kubota
We succeeded in recording and observing a spatially and temporally continuous moving picture of visible femtosecond light pulse propagation by using light-in-flight recording by holography, for the first time. We applied second-harmonic generation (SHG) to a NIR femtosecond light pulse from a mode-locked Ti:sapphire laser to generate a visible femtosecond light pulse. The center wavelength and duration of the generated light pulse were 400 nm and ∼100 fs, respectively. We acquired a moving picture of a visible and collimated femtosecond light pulse that propagated on a diffuser plate for 145 ps.

Highly Scalable Vertical Channel Phase Change Random Access Memory

Kyung Soo Kim, Jongho Lee, and Il Hwan Cho — 2011-05-06T09:00:00+09:00

Authors: Kyung Soo Kim, Jongho Lee, and Il Hwan Cho
A novel vertical channel phase change random access memory (PCRAM) for application in high-density PCRAM technology with high scalability and small unselected cell current is proposed. The channel of the select transistor and the phase change material are integrated in a vertical structure. A side wall process for the self-aligned phase change material is suggested and memory operation is verified by three-dimensional (3D) device simulation. In addition, memory characteristics are compared for different types of select metal–oxide–semiconductor field-effect transistor (MOSFET).

Fabrication and Piezoelectric Property of Highly Textured CaBi_{2}Nb_{2}O_{9} Ceramics by Tape Casting

Huanbei Chen, Fang Fu, and Jiwei Zhai — 2011-05-06T09:00:00+09:00

Authors: Huanbei Chen, Fang Fu, and Jiwei Zhai
Textured high-Curie-point lead-free piezoelectric ceramics, CaBi_{2}Nb_{2}O_{9} (CBN), were prepared by the tape casting method. Highly textured ceramics with a single phase and 95% Lotgering factor were obtained by the templated grain growth (TGG) technique. The textured CBN ceramics had a higher piezoelectric constant (d_{33} = 17.8 pC/N) than their non textured counterparts (d_{33} = 6.2 pC/N) prepared by a conventional solid-state sintering process. Furthermore, they had excellent thermostable of piezoelectric properties from room temperature to near Curie temperature. This type of textured CBN ceramic that can be prepared using the low-cost and scalable tape casting technique should be a promising candidate for high-temperature piezoelectric applications.

Recent articles in Jpn. J. Appl. Phys.

General Expressions for Ellipsoidal-Valley Quantum Transport in Arbitrary Growth Direction: Non-Equilibrium Green's Function

Estimation of Fermi Level Changes Caused by Changes in Ambient Conditions around Organic Semiconductors by Seebeck Effect Measurement

Effects of Phase-Separation Direction of Monomers on Polymer Wall Formation and Electrooptical Properties of Flexible Smectic Liquid Crystal Cell

Flexible Ferroelectric Liquid Crystal Cell Stabilized by Column Spacer and Polymer Wall: Influence of Bending and Pressing on the Mechanical Stability

Extremely High Purcell Factor of Plasmonic Modes in Thin Nano-Metallic Cylinders

Uncooled InAsSb Photoconductors with Long Wavelength

Color Reproduction of Multi-Wavelength Digital Holography Using a Color Correction Algorithm

Analytical Investigation of an All-Optical T-Type Flip-Flop Using a Semiconductor Optical Amplifier Mach–Zehnder Interferometer with Push–Pull Configuration

Kinetics Study on Initial Growth Stage in Vapor Deposition of Organic Thin Film Using Quartz Crystal Microbalance

Fabrication of Epitaxial Interface between Transition Metal Cyanides

Current–Voltage Characteristics of Discharge with Water–Ceramic Electrode

Origin Investigation of a Nitrogen-Related Recombination Center in GaAsN Grown by Chemical Beam Epitaxy

Band Alignment at the Cu_{2}O/ZnO Heterojunction

Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

Comparison of Ferroelectric and Insulating Properties of Mn-Doped BiFeO_{3} Films Formed on Pt, SrRuO_{3}/Pt, and LaNiO_{3}/Pt Bottom Electrodes by Radio-Frequency Sputtering

Evaluation and Reliability Improvement Investigation of Electrical Characteristics of Ba_{0.9}Sr_{0.1}TiO_{3} Dielectric Films Prepared by Electrophoretic Deposition Method

Approximate Analysis of Cylindrical Ferroelectric Capacitor and Derivation of Drain Current Characteristics in Ferroelectric Gate-All-Around Carbon Nanotube Transistor

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

Hybrid Alignment Induced by Asymmetric Photopolymerization of Liquid Crystal-Reactive Mesogen Composition between Two Plastic Substrates

Relation between Monomer Structure and Image Sticking Phenomenon of Polymer-Sustained-Alignment Liquid Crystal Displays

Nanosize-Induced Optically Isotropic Nematic Phase

N-Polar III–Nitride Green (540 nm) Light Emitting Diode

High Extraction Efficiency of GaN-Based Vertical-Injection Light-Emitting Diodes Using Distinctive Indium–Tin-Oxide Nanorod by Glancing-Angle Deposition

Multi Junction Solar Cells Stacked with Transparent and Conductive Adhesive

Effect of Excitons in AlGaAs/GaAs Superlattice Solar Cells

Ion-Irradiated Laterally Graded Ni/C Multilayers: A Combined X-ray Standing Wave and X-ray Reflectivity Analysis

Dynamics of Magnetostatically Coupled Vortices Observed by Time-Resolved Photoemission Electron Microscopy

Cluster Co-Existence and DC Field Effect on Re-entrant Spin Freezing Behavior in La_{0.85}Ca_{0.15}Mn_{0.95}Fe_{0.05}O Manganates

Substrate Dependence of Structural and Transport Properties in FeSe_{0.5}Te_{0.5} Thin Films

Quantification of Superiority of Broad-Buffer Diodes

Theoretical Investigation of Effect of Side Facets on Adsorption–Desorption Behaviors of In and P Atoms at Top Layers in InP Nanowires

Effects of Concentration of Nanoscale Tin-Doped Indium Oxide on Electrical Breakdown of High-Resistance Liquid Crystal

Effect of Pd Reactant on One-Dimensional Growth of ZnO on Si Substrate by Thermal Evaporation Method

Carrier Gas Dependence at Initial Processes for a-Plane AlN Growth on r-Plane Sapphire Substrates by Hydride Vapor Phase Epitaxy

Properties of Si-Doped a-Plane GaN Grown with Different SiH_{4} Flow Rates

High-Throughput Characterization Method for Crystallization Temperature of Integrated Thin Film Amorphous Alloys Using Thermography

Effect of Lithium Absorption at Tetrahedral Site and Isomorphic Substitution on Montmorillonite Properties: A Density Functional Theory Study

Density Functional Theory Study on the Interaction of O_{2} Molecule with Cobalt–(6)Pyrrole Clusters

Effect of the Soft X-rays on Highly Hydrogenated Diamond-Like Carbon Films

Effect of K_{0.5}Na_{0.5}NbO_{3} on Properties at and off the Morphotropic Phase Boundary in Bi_{0.5}Na_{0.5}TiO_{3}–Bi_{0.5}K_{0.5}TiO_{3} Ceramics

Ionic Conductivity in Uniaxial Micro Strain/Stress Fields of Yttria-Stabilized Zirconia

High Temperature-Coefficient of Resistance at Room Temperature in W-Doped VO_{2} Thin Films on Al_{2}O_{3} Substrate and Their Thickness Dependence

Optical Properties of Ultrathin Copper Thin Films Sandwiched between Nb-Doped TiO_{2} Films Studied with Spectroscopic Ellipsometry

Spatial Distributions of Electron, CF, and CF_{2} Radical Densities and Gas Temperature in DC-Superposed Dual-Frequency Capacitively Coupled Plasma Etch Reactor Employing Cyclic-C_{4}F_{8}/N_{2}/Ar Gas

Gallic Acid as a Complexing Agent for Copper Chemical Mechanical Polishing Slurries at Neutral pH

Characterization of Bistable Hybrid-Twisted Nematic Liquid Crystal Mode by Means of Renormalized Transmission Spectroscopic Ellipsometry

Optimization of Bandwidth and Signal Responses of Optically Pumped Atomic Magnetometers for Biomagnetic Applications

Evaluation of a Delay-Line Detector Combined with Analog-to-Digital Converters as the Ion Detection System for Stigmatic Imaging Mass Spectrometry

Pulse Analyzing System Using Optical Coherence Tomography for Oriental Medical Application

Tip to Side Welding of Ultrathin Pt Wires by Joule Heating

Deflections of Magnetic Actuator under Different Directions of External Magnetic Field

Implications of the Differential Equations of the X-ray Free-Electron Laser

Characteristics of La_{2}O_{3}- and Al_{2}O_{3}-Capped HfO_{2} Dielectric Metal–Oxide–Semiconductor Field-Effect Transistors Fabricated on (110)-Oriented Silicon Substrates

Organic Electrodes Consisting of Dianthratetrathiafulvalene and Fullerene and Their Application in Organic Field Effect Transistors

Reverse-Tilt-Domain Boundary Wall in a Polymer-Encapsulated Flexible Liquid Crystal Display

Power Dependent Micro-Photoluminescence of Green-InGaN/GaN Multiple Quantum Wells

Moving Picture Recording and Observation of Visible Femtosecond Light Pulse Propagation

Highly Scalable Vertical Channel Phase Change Random Access Memory

Fabrication and Piezoelectric Property of Highly Textured CaBi_{2}Nb_{2}O_{9} Ceramics by Tape Casting