bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Analysis of AlN/GaAs(001) and AlN/Ge/GaAs(001) Metal–Insulator–Semiconductor Structures
Authors: Kudo Masahiro , Shih Hong-An , Akabori Masashi , Suzuki Toshi-kazu
Published: February 2012

Using sputtering-deposited AlN insulator films, we fabricated and analyzed AlN/GaAs(001) and AlN/Ge/GaAs(001) metal–insulator–semiconductor (MIS) structures; the former is obtained by the direct deposition of AlN on GaAs, while the latter includes a Ge interlayer between AlN and GaAs. By current–voltage (I–V) measurements, we obtained similar good insulating properties for both MIS structures. On the other hand, we observed rather different frequency dispersions in the capacitance–voltage (C–V) characteristics of the MIS structures; the AlN/Ge/GaAs(001) MIS structure exhibits a significantly smaller dispersion than the AlN/GaAs(001) MIS structure, attributed to a smaller interface state density, as confirmed by analysis using the conductance method. From the X-ray photoelectron spectroscopy analysis results of the MIS interfaces, we found that, in comparison with the AlN/GaAs(001) interface, the AlN/Ge/GaAs(001) interface exhibits suppressed As deficiency and Ga–O bonding, with an indication of their relation to interface states.
InGaAs/InAlAs Multiple Quantum Well Mach–Zehnder Modulator with Single Microring Resonator
Authors: Kaneshige Hiroki , Ueyama Yuta , Yamada Hitoshi , Yajima Hideki , Arakawa Taro , Kokubun Yasuo
Published: February 2012

We propose and a novel InGaAs/InAlAs multiple quantum well (MQW) Mach–Zehnder (MZ) modulator with a single microring resonator, and a significant reduction of driving voltage is demonstrated for the first time. The modulator is driven by the quantum-confined Stark effect (QCSE) in the MQW and the driving voltage of the proposed modulator is expected to be significantly reduced by the phase-shift-enhancement effect in the microring. A waveguide structure was grown by solid-source molecular beam epitaxy and fabricated by inductively coupled plasma etching. A directional coupler with a shallow gap is employed to control the coupling parameters between a busline and the microring waveguide. An asymmetrical splitter was used as an input coupler to prevent the degradation of the extinction ratio of the MZ modulator. The extinction ratio of the fabricated microring MZ modulator was approximately 17.5 dB. The product of half-wave voltage and phase shifter length V
π
L was 2.0 Vmm in static modulation. This value was one-third that of a conventional MZ modulator with the same waveguide structure.
Highly Sensitive Gate/Body-Tied P-Channel Metal Oxide Semiconductor Field Effect Transistor-Type Photodetector with an Overlapping Control Gate
Authors: Jung Joontaek , Jo Sung-Hyun , Seo Sang-Ho , Bae Myunghan , Shin Jang-Kyoo
Published: February 2012

In this paper, a highly sensitive gate/body-tied p-channel metal oxide semiconductor field effect transistor (PMOSFET)-type photodetector with an overlapping control gate is proposed. The proposed photodetector has an overlapping control gate that makes it possible to control the sensitivity of the proposed photodetector. This sensitivity controllability extends the dynamic range and provides a high sensitivity in a low-light environment. The body of the proposed gate/body-tied PMOSFET-type photodetector is connected to the floating gate, and the control gate is placed on top of the floating gate. The proposed device was fabricated using a 0.35 µm standard complementary metal oxide semiconductor (CMOS) process. The amplified photocurrent of the proposed device was more than 100 times larger than that of a conventional n+/p-sub photodiode with the same area. The area of the proposed photodetector is 3.8×4.4 µm2, which is 24% smaller than that of a conventional gate/body-tied PMOSFET-type photodetector with a transfer gate. Therefore, the proposed photodetector can be suitable for high-sensitivity active pixel sensors (APSs) because of its much higher responsivity than that of a conventional n+/p-sub photodiode.
Effect of Deposition Temperature on the Opto-Electronic Properties of Molecular Beam Epitaxy Grown InAs Quantum Dot Devices for Broadband Applications
Authors: Majid Mohammed A. , Hugues Maxime , Childs David T. D. , Hogg Richard A.
Published: February 2012

The effect of the quantum dot (QD) deposition temperature is discussed for dot-in-a-well (DWELL) structures with a view to their optimization for broadband applications. Atomic force microscopy (AFM) analysis allows the measurement of the quantum dot and the defective island density. The reduced QD growth temperature results in broad emission spectrum and increased defective island density. Reduced electroluminescence efficiency, higher reverse leakage currents, and lower reverse breakdown voltage could be correlated to the presence of the defective island density. Maximal output power is obtained for devices with a QD growth temperature of 500 °C, whilst the preferred spectral shape and QD density is obtained at the lowest temperature, 470 °C. To benefit from broad emission bandwidth, the growth conditions need to be further optimized to avoid, or at least reduce, the defective island density.
Characterization of the Oxide Film Obtained by Wet Oxidation of Al-Rich AlGaAs
Authors: Hirai Yuichiro , Yamada Takahiro , Kondow Masahiko , Ishikawa Fumitaro
Published: February 2012

We investigate the characteristics of oxide film obtained by wet oxidation of Al
x
Ga1-x
As with its Al concentration x between 0.55 and 0.99. 300-nm-thick Al
x
Ga1-x
As grown on GaAs substrate by molecular beam epitaxy is wet-oxidized in a furnace at 410 °C for 120 min. Samples having x greater than 0.8 are confirmed to be oxidized from their observation, examined by X-ray diffraction showing the vanished crystallographic diffraction peaks. Scanning electron microscopy, X-ray reflectivity, and spectroscopic ellipsometry study determines the thickness, density and refractive index of the oxide films.
Growth and Characterization of MnAs Nanoclusters Embedded in GaAs Nanowires by Metal–Organic Vapor Phase Epitaxy
Authors: Yatago Masatoshi , Iguchi Hiroko , Sakita Shinya , Hara Shinjiro
Published: February 2012

The authors report on the fabrication of MnAs/GaAs hybrid nanowires by combining selective-area metal–organic vapor phase epitaxy of GaAs nanowires and “endotaxy” of MnAs nanoclusters. MnAs nanoclusters are embedded in the six ridges of hexagonal GaAs nanowires as a result of endotaxy. From the cross-sectional characterizations by transmission electron microscopy, the average width of MnAs nanoclusters with the hexagonal NiAs-type crystal structure and the average depth in GaAs nanowires are estimated to be about 10 and 8 nm, respectively. The magnetic responses detected from the reference samples grown on planar GaAs (111)B layers show that ferromagnetic MnAs nanoclusters are formed. The diameter of nanoclusters grown in GaAs nanowires increases with decreasing growth temperature and/or increasing distance between the GaAs nanowires, while the density of nanoclusters increases with increasing growth temperature. It is found that the diameter and density of nanoclusters are strongly influenced by the gas supplied during the decrease in temperature after the nanocluster growth.
Impact of Rapid Crystallization of Si Using Nickel-Metal-Induced Lateral Crystallization on Thin-Film Transistor Characteristics
Authors: Nagata Sho , Nakagawa Gou , Asano Tanemasa
Published: February 2012

Metal-induced lateral crystallization (MILC) of amorphous Si using a nickel disilicide catalyst at temperatures up to 770 °C is investigated to produce high-quality polycrystalline Si films in a short period, while 670 °C is the maximum temperature allowed for processing using non alkaline glass substrates. Investigation of crystallization kinetics by isothermal annealing experiments provides activation energy values of 2.3 and 3.6 eV for MILC growth and spontaneous nucleation of amorphous Si, respectively. These values indicate that a MILC region of about 30 µm, which is large enough to place transistor circuits, can be grown by annealing for 15 min at 670 °C, which almost agrees with experimental results. N-channel thin-film transistors are fabricated on MILC films. An average carrier mobility of about 200 cm2·V-1·s-1 is obtained from the MILC film crystallized at 670 °C.
Fabrication of High-Performance Thin-Film Transistors on Glass Substrate by Atmospheric Pressure Micro-Thermal-Plasma-Jet-Induced Lateral Crystallization Technique
Authors: Fujita Yuji , Hayashi Shohei , Higashi Seiichiro
Published: February 2012

Amorphous silicon (a-Si) films deposited by plasma-enhanced chemical vapor deposition (PECVD) were patterned to strips with a width ranging from 1 to 50 µm, and irradiated with an atmospheric pressure micro-thermal-plasma-jet (µ-TPJ) to induce high-speed lateral crystallization (HSLC). From electron backscattering diffraction patterns (EBSPs), the growth of ∼20-µm-long single grains was observed in a narrow line of 1 µm width under a µ-TPJ scan speed as high as 4000 mm/s. TFTs with a large channel length (L)/width (W) of 40 µm/50 µm show a field-effect mobility (µFE) of 284 cm2 V-1 s-1, whereas decreasing W monotonically increased µFE to 477 cm2 V-1 s-1 at W = 2 µm. By applying µ-TPJ to strip a-Si films, we can form single-crystalline Si at predetermined positions and obtain TFTs with reasonably high performance. We confirmed that HSLC is applicable to a-Si films on conventional glass substrates without crack generation by either inserting a buffer layer underneath a-Si films, or heating the samples during µ-TPJ irradiation. A new positioning method using a Si slit mask is also demonstrated. TFTs fabricated on glass with a buffer layer inserted underneath the a-Si films show a high µFE of 267 cm2 V-1 s-1.
Theory of Resonant Tunneling through a Donor State
Authors: Mori Nobuya , Patanè Amalia , Eaves Laurence
Published: February 2012

We present a theoretical model for electron tunneling through a single Si-donor state in a resonant tunneling diode with a Si δ-doped layer in the central plane of the quantum well, under tilted magnetic field B. The tunneling current is calculated with a transfer Hamiltonian method by assuming that the current is limited by the emitter barrier. Through a variational calculation of the donor state, we show that the component of B parallel to the direction of current, B
||
, provides us with a means of compressing the donor wavefunction in the quantum-well plane. We also show that by measuring the current as a function of the perpendicular component B
⊥ one can probe how the magneto-compression induced by B
||
affects the spatial form of the donor wavefunction. We compare the theoretical results with the experiment.
Bottom Electrode Modification of ZrO2 Resistive Switching Memory Device with Au Nanodots
Authors: Lee Dai-Ying , Yao I-Chuan , Tseng Tseung-Yuen
Published: February 2012

The resistive switching properties of the ZrO2 memory devices with bottom electrode modification by using Au nanodots are investigated in this study. The regular arrays of Au nanodots are fabricated on Pt bottom electrode by nanosphere lithography. Due to the tip of the Au nanodots on the Pt bottom electrode, it causes the higher electric field within the ZrO2 film above the nanodots due to reduced effective film thickness and induces the localized conducting filaments easily. The operation parameters' variation for switching devices is, therefore, suppressed with lower operation voltage and resistance ratio. Long retention time (>106 s) and stubborn nondestructive readout test (>104 s) at room temperature and 150 °C are also demonstrated in this device.
Wavelength Tunable Quantum Dot Single-Photon Source with a Side Gate
Authors: Nakaoka Toshihiro , Tamura Yugo , Miyazawa Toshiyuki , Watanabe Katsuyuki , Ota Yasutomo , Iwamoto Satoshi , Arakawa Yasuhiko
Published: February 2012

We demonstrate photon antibunching from a wavelength controlled quantum dot single-photon source with a side gate. The photoluminescence peaks from the quantum dots embedded in the side-gate structure are clearly identified as a neutral exciton and a neutral biexciton by the studies of excitation-power dependence, polarization dependence, and photon correlation. The neutral exciton energy is controlled by the side gate via the quantum confined Stark effect. Measurement of the second-order autocorrelation function indicates g
(2)(0) = 0.07 at 0 V, 0.14 at 0.8 V, and 0.24 at 0.9 V. The results show g
(2)(0)s are below the 0.5 limit necessary for classification as a single photon source even under applied gate voltage. We also show a biexciton-exciton cascade which can be used to create entangled photon pairs.
Series-Coupled Triple Quantum Dot Molecules
Authors: Amaha Shinichi , Hatano Tsuyoshi , Izumida Wataru , Teraoka Soichiro , Ono Keiji , Kono Kimitoshi , Tarucha Seigo , Aers Geof , Gupta James , Austing Guy
Published: February 2012

We present the electronic properties of a triple quantum dot molecule embedded inside a sub-micron mesa, made from a quadruple-barrier triple-quantum-well structure, and surrounded by a single gate electrode. We outline the design principles of the quadruple-barrier triple-quantum-well structure and calculate the energy of the three lowest states as a function of center well thickness. We observe regular and irregular shaped Coulomb diamond regions similar to those for double quantum dot devices. Variation in the Coulomb blockade region shape is introduced by fluctuation in the offset energies between the quantum dots likely associated with device processing and random impurity potential in the material. We also present Coulomb blockade patterns calculated with a constant interaction model for sequential tunneling through the three series-coupled quantum dots.
Correlation of 1/f Noise between Semiconductor Point Contacts with a Common Lead
Authors: Yamagishi Masakazu , Hashisaka Masayuki , Muraki Koji , Fujisawa Toshimasa
Published: February 2012

We investigate cross spectral density between tunneling currents through closely spaced point contacts (PCs) in a semiconductor heterostructure. Analysis of 1/f noise, which originates from background charge fluctuations, is expected to reveal the characteristics of a charge detector and screened Coulomb potential in the device. However, the common resistance in the measurement circuit and the leads of the PCs causes a significant negative correlation. We find that this negative correlation is enhanced when the common electrical channel becomes so narrow that it has only a few one-dimensional conductive modes. Our finding suggests the importance of the circuit environment in integrating multiple charge detectors.
A Multi-Purpose Electrostatically Defined Silicon Quantum Dot Structure
Authors: Sulthoni Muhammad Amin , Kodera Tetsuo , Kawano Yukio , Oda Shunri
Published: February 2012

Small size and good coupling control between dots are the key parameters for useful coupled quantum dot devices. Using a new approach of electrostatically defined silicon double quantum dot device recently proposed, we design and simulate a silicon quantum dot structure that exhibits multi functionality. Control on potential tunnel barrier using side gates, as well as the preparation of series-coupled and parallel-coupled double quantum dot structure are demonstrated and explained by numerical simulation on electron distribution profile.
Analysis of Anomalous Discharging Processes in Pentacene/C60 Double-Layer Organic Solar Cell
Authors: Chen Xiangyu , Taguchi Dai , Lee Keanchuan , Manaka Takaaki , Iwamoto Mitsumasa
Published: February 2012

Optical electric-field-induced second-harmonic generation (EFISHG) measurement was employed for studying interfacial processes in pentacene/C60 double-layer organic solar cells (OSCs). Results showed that charging and discharging on the double-layer interface by photoillumination were nonreversible, and a recharging process continued after the illumination stopped. The Maxwell–Wagner model analysis revealed that the photoconductance change is responsible for this anomalous interfacial recharging. The results of impedance spectroscopy (IS) analysis supported this conclusion.
Work Function Controlled Zn:Cu Electrode for All-Printed Polymer Diode
Authors: Yoshida Manabu , Suemori Kouji , Uemura Sei , Hoshino Satoshi , Takada Noriyuki , Kodzasa Takehito , Kamata Toshihide
Published: February 2012

We have developed a pressure annealing technique for fabricating low-work-function metal patterns on plastic substrates. The pressure annealing technique can destroy the metal oxide layer and can form a conductive layer on printed metal patterns. Furthermore, we have confirmed that a binary solid solution is easily formed on metal patterns including two kinds of metal particles by using the pressure annealing technique. Changing the composition ratio of the binary metal paste led to the work function control of the pressure-annealed metal patterns. The formation of the binary solid solution was confirmed by X-ray diffraction (XRD) analysis, and work function was measured by photoelectron emission spectroscopy. In the case of the binary metal paste of Cu and Zn, we have succeeded in controlling work function from 3.8 to 5.0 eV. Since the Cu–Zn paste is composed of relatively cheap metals, this would be applicable to large-scale flexible electronic devices.
Channel Formation as an Interface Charging Process in a Pentacene Field Effect Transistor Investigated by Time-Resolved Second Harmonic Generation and Impedance Spectroscopy
Authors: Zhang Le , Taguchi Dai , Masada Hiroshi , Manaka Takaaki , Iwamoto Mitsumasa
Published: February 2012

The channel formation process in a pentacene field effect transistor was studied by directly probing the carrier motion along the channel in the time domain and the capacitance changes in the frequency domain. With the source and drain electrodes short circuited and the voltage applied only to the gate electrode, the carrier injection from both top electrodes and its motion along the channel was still observable, implying an interface charging process driven by a self-induced electric field. In addition, it was found that when the source and drain electrodes were short circuited, the capacitance of the device was larger than the geometric capacitance and proportional to the channel length, which also supported the interface charging model. The relationship between the two approaches was also discussed.
Solvent Dependence of Vacuum-Dried C60 Thin-Film Transistors
Authors: Kang Woogun , Kitamura Masatoshi , Kamura Masakazu , Aomori Shigeru , Arakawa Yasuhiko
Published: February 2012

We demonstrated solution-processed C60 thin-film transistors with high electron mobility. C60 solutions in various organic solvents were dried in a vacuum chamber to obtain uniform thin films. While C60 solution dried under atmospheric pressure produced a large number of crystals, vacuum-dried C60 solution provided flat and uniform thin films of sufficiently high quality to fabricate thin-film transistors. In spite of amorphous-like thin-film formation, C60 transistors showed strong solvent dependence. High performance C60 thin-film transistors with field-effect mobility of 0.86 cm2 V-1 s-1, threshold voltage of 1.5 V, subthreshold slope of 0.67 V/decade and a current on/off ratio of 3.9 ×106 were obtained from 1,2,4-trichlorobenzene C60 solution.
Improved Power Conversion Efficiency of Organic Photovoltaic Cell Fabricated by Electrospray Deposition Method by Mixing Different Solvents
Authors: Fukuda Takeshi , Takagi Kenji , Asano Takashi , Honda Zentaro , Kamata Norihiko , Shirai Hajime , Ju Jungmyoung , Yamagata Yutaka , Tajima Yusuke
Published: February 2012

A smooth surface of the poly(3-hexylthiophene) (P3HT)-doped-(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) thin film was achieved by mixing different solvents for the electrospray deposition method. As a result, the high power-conversion efficiency (PCE) of the bulk-heterojunction organic photovoltaic cell (OPV) was comparable to that obtained in the case of the spin-coating method. By optimizing the additional solvent in o-dichlorobenzene, the P3HT/PCBM active layer with the root-means-square roughness of 2.23 nm and the PCE of 2.2% was fabricated employing acetonitrile as the additional solvent.
Fabrication of Inverted Bulk-Heterojunction Organic Solar Cell with Ultrathin Titanium Oxide Nanosheet as an Electron-Extracting Buffer Layer
Authors: Itoh Eiji , Maruyama Yasutake , Fukuda Katsutoshi
Published: February 2012

The contributions and deposition conditions of ultrathin titania nanosheet (TN) crystallites were studied in an inverted bulk-heterojunction (BHJ) cell in indium tin oxide (ITO)/titania nanosheet/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methylester (PCBM) active layer/MoO
x
/Ag multilayered photovoltaic devices. Only one or two layers of poly(diallyldimethylammonium chloride) (PDDA) and TN multilayered film deposited by the layer-by-layer deposition technique effectively decreased the leakage current and increased both open circuit voltage (V
OC) and fill factor (FF), and power conversion efficiency (η) was increased nearly twofold by the insertion of two TN layers. The deposition of additional TN layers caused the reduction in FF, and the abnormal S-shaped curves above V
OC for the devices with three and four TN layers were ascribed to the interfacial potential barrier at the ITO/TN interface and the series resistance across the multilayers of TN and PDDA. The performance of the BHJ cell with TN was markedly improved, and the S-shaped curves were eliminated following the the insertion of anatase-phase titanium dioxide between the ITO and TN layers owing to the decrease in the interfacial potential barrier.
Relationship between Work Function of Hole Collection Electrode and Temperature Dependence of Open-Circuit Voltage in Multilayered Organic Solar Cells
Authors: Itoh Eiji , Shirotori Toshiki
Published: February 2012

We have investigated the photovoltaic properties of multilayered organic photovoltaic devices consisting of indium tin oxide (ITO)/(NiO)/donor/C60/bathocuproine (BCP)/Al structures. Open circuit voltage (V
OC) increases with the decrease in temperature between 40 and 350 K. The V
OC was, however, pinned at approximately 0.6 V for the device without NiO, probably owing to the insufficient work-function difference between ITO and Al electrodes. The hole injection was also markedly suppressed at the ITO/donor interface in the device with large IP donor materials without the buffer layer and abnormal S-shaped current density–voltage (J–V) characteristics were observed. On the other hand, the value of V
OC increases with the increase in ionization potential (IP) of donor materials in the device with NiO buffer layers owing to the enhanced work-function difference of about 1 eV, and the S-shaped curves disappeared at the high temperatures above 200 K. The V
OC is further improved to nearly 1.2 V by the UV–ozone treatment of the NiO surface. We have therefore concluded that the increment of work function of the anode caused by the insertion of an oxide buffer layer and the surface treatment of the electrode by UV–ozone treatment are essentially important for the improvement of V
OC and charge transport/injection properties in the multilayered organic solar cell applications.
Climbing Rates of Microtubules Propelled by Dynein after Collision with Microfabricated Walls
Authors: Ashikari Norihiko , Shitaka Yuji , Fujita Kosuke , Kojima Hiroaki , Oiwa Kazuhiro , Sakaue Hiroyuki , Takahagi Takayuki , Suzuki Hitoshi
Published: February 2012

We proposed a method to characterize the effect of micrometer-scale walls on the motion of microtubules propelled by dynein, a motor protein. The walls were made of resist polymers, such as OEBR1000, SAL601, and PMGI, using e-beam lithography. The pattern of the walls was designed to make microtubules collide with the wall perpendicularly and the number of microtubules crossing over the wall was counted from sequential images obtained with a fluorescence microscope. It was found that the wall, which was higher than approximately 800 nm, stops microtubules from crossing over the wall. The wall made of OEBR1000 prevents microtubules from crossing it more effectively than that made of SAL601 and the overhang is also useful for guiding the microtubule motion.
Time-Resolved Switching Characteristic in Magnetic Tunnel Junction with Spin Transfer Torque Write Scheme
Authors: Iga Fumitaka , Yoshida Yasuhiro , Ikeda Shoji , Hanyu Takahiro , Ohno Hideo , Endoh Tetsuo
Published: February 2012

The time-resolved switching characteristics of 100×200 nm2 size CoFeB/MgO/CoFeB-based magnetic tunnel junction (MTJ) are investigated by using the 20 GHz sampling measurement technique. We focused on the physical quantities of the time-resolved characteristics such as incubation time t
A, transit time t
B, and the standard deviations σV's of the period of the switching waveform. Furthermore, the dependencies of t
A and t
B on the applied pulse waveforms are analyzed. We found t
A exponentially decreases as the applied voltage to MTJ increases, while t
B remains less than two nano seconds regardless of the applied voltage. Furthermore, it is observed that the standard deviations of the waveform during t
A is larger than that of the other periods. Finally, we discuss the switching characteristics with proposed toy model based on spin transfer torque (STT) phenomena.
Estimation of Height of Barrier Formed in Metallic Carbon Nanotube
Authors: Okigawa Yuki , Ohno Yutaka , Kishimoto Shigeru , Mizutani Takashi
Published: February 2012

We have estimated the height of barriers against carriers formed in the metallic carbon nanotube (m-CNT) grown by plasma-enhanced chemical vapor deposition. The result shows that the heights of the barriers against both electrons and holes are about 300 meV. The existence of the barrier in the m-CNT was confirmed by local current modulation using scanning gate microscopy and by the potential drop obtained by Kelvin probe force microscopy.
Electrical Characterization of Bilayer Graphene Formed by Hydrogen Intercalation of Monolayer Graphene on SiC(0001)
Authors: Tanabe Shinichi , Sekine Yoshiaki , Kageshima Hiroyuki , Hibino Hiroki
Published: February 2012

Quasi-free-standing bilayer graphene was grown by hydrogen intercalation of epitaxial monolayer graphene on SiC(0001). A larger size of stacking domains compared to that of epitaxial bilayer graphene grown on SiC(0001) was observed in a low-energy electron microscopy analysis of its morphology. By evaluating its electronic transport characteristics in top-gated devices, we found that the quasi-free-standing bilayer graphene is p-doped at zero-gate voltage. Further, an increase in mobility was found compared to that of epitaxial bilayer graphene. As a result of the higher mobility, Shubnikov–de Hass oscillations were observed. We attribute the improved quality of the quasi-free-standing bilayer graphene to its structural properties.
Electronic Structure of Corrugated Graphene Sheet
Authors: Okada Susumu , Kawai Takazumi
Published: February 2012

We study the geometries, energetics, and electronic structures of free-standing graphene with long range structural undulations. Our calculations, which are based on density functional theory, show that the energy cost to induce the structural corrugation is about a few tens of meV per C atom which is similar to the total energy of the C atoms in carbon nanotubes. Our tight-binding molecular dynamics simulations confirmed that graphene exhibits long-range structural undulation at temperatures above 400 K. Moreover, our detailed analysis of the electronic energy band near the Fermi level shows that the linear dispersion band is sensitive to these structural undulations, which leads to semiconducting properties with an energy gap of a few meV.
Observation of n-Type Conduction in Carbon Nanotube Field-Effect Transistors with Au Contacts in Vacuum
Authors: Imaeda Hideki , Ishii Satoshi , Kishimoto Shigeru , Ohno Yutaka , Mizutani Takashi
Published: February 2012

The change in the conduction type of carbon nanotube field-effect transistors (CNT-FETs) with Au contacts from p-type to n-type by annealing in vacuum was observed. The result was explained by the local work function change of the Au contacts based on the measurement of the surface potential of the Au/CNT contact by Kelvin probe force microscopy (KFM). This work function change became prominent due to the desorption of oxygen by annealing. The degree of the conduction-type change was found to be dependent on the devices. The CNT-FETs with small OFF current showed clear conduction-type change. However, the devices with large OFF current did not show clear conduction-type change. This device dependent behavior was explained by the energy gap difference among devices, in which suppression of OFF current is not sufficient for the devices with thick CNTs with small bandgap.
Development of the Transparent Conductive Oxide Layer for Nanocrystalline Cubic Silicon Carbide/Silicon Heterojunction Solar Cells with Aluminum Oxide Passivation Layers
Authors: Irikawa Junpei , Miyajima Shinsuke , Watahiki Tatsuro , Konagai Makoto
Published: February 2012

We developed an In2O3:H/indium–tin oxide (ITO) stack as the front transparent conductive oxide (TCO) layer of nanocrystalline cubic silicon carbide/crystalline silicon heterojunction solar cells with Al2O3 passivation layers. We investigated the solar cell performance and optical and electrical properties of this layer with various annealing temperatures. The solar cells with In2O3:H and In2O3:H/ITO layers show a higher short circuit current density (J
sc) than that with an ITO layer owing to their lower surface reflection and lower free carrier absorption. The solar cell with the In2O3:H/ITO stack shows a higher fill factor (FF) than that with the In2O3:H layer. The solar cell with the In2O3:H/ITO stack shows an aperture area efficiency of 16.8% (V
oc = 0.638 V, J
sc = 34.5 mA/cm2, and FF= 0.762). These results indicate that the In2O3:H/ITO stack has good optical and electrical properties after annealing.
Dynamic-Carrier-Distribution-Based Compact Modeling of p–i–n Diode Reverse Recovery Effects
Authors: Nakashima Junichi , Miyake Masataka , Miura-Mattausch Mitiko
Published: February 2012

This paper presents a compact model of the diode reverse recovery effect for the simulation program with integrated circuit emphasis (SPICE) simulation. We found that the reverse recovery effect can be described with the dynamic carrier distribution within the lightly-doped N- drift layer of a p–i–n power diode. The proposed model is verified with two-dimensional (2D) device simulation results and compared with a lumped-charge-based conventional model.
Metal-Assisted Chemical Etching Using Silica Nanoparticle for the Fabrication of a Silicon Nanowire Array
Authors: Kato Shinya , Watanabe Yuya , Kurokawa Yasuyoshi , Yamada Akira , Ohta Yoshimi , Niwa Yusuke , Hirota Masaki
Published: February 2012

30-nm-diameter silica nanoparticles with a carboxyl radical (COO-) were successfully dispersed on an amino-treated silicon wafer at about 20 nm intervals owing to the repulsion among nanoparticles with negative charges. The dispersed silica nanoparticles were used as the mask for the preparation of silicon nanowire (SiNW) arrays by metal-assisted chemical etching (MAE). The diameter of the prepared SiNWs was approximately 30 nm from their transmission electron microscope image.
Laser Annealing to Form High-Temperature Phase of FeS2
Authors: Umehara Mitsutaro , Takeda Yasuhiko , Azuma Hirozumi , Motohiro Tomoyoshi
Published: February 2012

We fabricated single-phase pyrite thin films of FeS2 by laser annealing of multi-phase FeS2 films. Sputter-deposited FeS films followed by sulfurization in sulfur vapor at high temperatures were mainly composed of the high-temperature phase (pyrite) but contained a small amount of the low-temperature phase (marcasite) that likely grew when the samples were naturally cooled after the sulfurization. We applied the rapid cooling feature of laser annealing to preventing the marcasite phase formation. No trace of marcasite phase was observed in Raman spectra and X-ray diffraction patterns of the laser-annealed samples. We analyzed temporal evolution of the sample temperature during the laser-annealing processes to confirm that the laser heating induced phase change of the small amount of marcasite to pyrite and the rapid cooling prevented marcasite regrowth.
Genetic ablation of Slc4a10 alters the expression pattern of transporters involved in solute movement in the mouse choroid plexus
Authors: Damkier Helle Hasager , Praetorius Jeppe
Published: February 2012

Mutational changes of one transporter can have deleterious effects on epithelial function leaving the cells with the options of either compensating for the loss of function or dedifferentiating. Previous studies have shown that the choroid plexus epithelium (CPE) from mice lacking the Na+-dependent Cl−/HCO3− exchanger (NCBE) encoded by Slc4a10 leads to retargeting of the Na+/H+ exchanger 1 (NHE1) from the luminal to the basolateral plasma membrane. We hypothesized that disruption of NCBE, the main basolateral Na+ importer in the CPE, would lead to a compensatory increase in the abundance of other important transport proteins in this tissue. Aquaporin-1 (AQP1) abundance was 42.7% lower and Na,K-ATPase 36.4% lower in the CPE of Slc4a10 knockout mice, respectively. The NHE1 binding ezrin cytoskeleton appeared disrupted in Slc4a10 knockout mice, whereas no changes were observed in cellular polarization with respect to claudin-2 and appearance of luminal surface microvilli. The renal proximal tubule constitutes a leaky epithelium with high transport rate similar to CPE. Here, Slc4a10 knockout did not affect Na,K-ATPase or AQP1 expression. CPE from AQP1 knockout mice has a secretory defect similar to Slc4a10 mice. However, neither NCBE nor Na,K-ATPase expression was affected in CPE from AQP1 knockout mice. By contrast, the abundance of Na,K-ATPase and NBCe1 was decreased by 23 and 31.7%, respectively, in AQP1 knockout proximal tubules, while the NHE3 abundance was unchanged. In conclusion, CPE lacking NCBE seems to spare the molecular machinery involved in CSF secretion rather than compensate for the loss of the Na+ loader. Slc4a10 knockout seems to be more deleterious to CPE than AQP1 knockout.
Real-time differential labeling of blood, interstitium, and lymphatic and single-field analysis of vasculature dynamics in vivo
Authors: Sarkisyan Gor , Cahalan Stuart M. , Gonzalez-Cabrera Pedro J. , Leaf Nora B. , Rosen Hugh
Published: February 2012

Lymph nodes are highly organized structures specialized for efficient regulation of adaptive immunity. The blood and lymphatic systems within a lymph node play essential roles by providing functionally distinct environments for lymphocyte entry and egress, respectively. Direct imaging and measurement of vascular microenvironments by intravital multiphoton microscopy provide anatomical and mechanistic insights into the essential events of lymphocyte trafficking. Lymphocytes, blood endothelial cells, and lymphatic endothelial cells express sphingosine 1-phosphate receptor 1, a key G protein-coupled receptor regulating cellular egress and a modulator of endothelial permeability. Here we report the development of a differential vascular labeling (DVL) technique in which a single intravenous injection of a fluorescent dextran, in combination with fluorescent semiconductor quantum dot particles, differentially labels multiple blood and lymphatic compartments in a manner dependent on the size of the fluorescent particle used. Thus DVL allows measurement of endothelial integrity in multiple vascular compartments and the affects or pharmacological manipulation in vascular integrity. In addition, this technique allows for real-time observation of lymphocyte trafficking across physiological barriers differentiated by DVL. Last, single-field fluid movement dynamics can be derived, allowing for the simultaneous determination of fluid flow rates in diverse blood and lymphatic compartments.
Differential regulation of a CLC anion channel by SPAK kinase ortholog-mediated multisite phosphorylation
Authors: Miyazaki Hiroaki , Strange Kevin
Published: February 2012

Shrinkage-induced inhibition of the Caenorhabditis elegans cell volume and cell cycle-dependent CLC anion channel CLH-3b occurs by concomitant phosphorylation of S742 and S747, which are located on a 175 amino acid linker domain between cystathionine-β-synthase 1 (CBS1) and CBS2. Phosphorylation is mediated by the SPAK kinase homolog GCK-3 and is mimicked by substituting serine residues with glutamate. Type 1 serine/threonine protein phosphatases mediate swelling-induced channel dephosphorylation. S742E/S747E double mutant channels are constitutively inactive and cannot be activated by cell swelling. S742E and S747E mutant channels were fully active in the absence of GCK-3 and were inactive when coexpressed with the kinase. Both channels responded to cell volume changes. However, the S747E mutant channel activated and inactivated in response to cell swelling and shrinkage, respectively, much more slowly than either wild-type or S742E mutant channels. Slower activation and inactivation of S747E was not due to altered rates of dephosphorylation or dephosphorylation-dependent conformational changes. GCK-3 binds to the 175 amino acid inter-CBS linker domain. Coexpression of wild-type CLH-3b and GCK-3 with either wild-type or S742E linkers gave rise to similar channel activity and regulation. In contrast, coexpression with the S747E linker greatly enhanced basal channel activity and increased the rate of shrinkage-induced channel inactivation. Our findings suggest the intriguing possibility that the phosphorylation state of S742 in S747E mutant channels modulates GCK-3/channel interaction and hence channel phosphorylation. These results provide a foundation for further detailed studies of the role of multisite phosphorylation in regulating CLH-3b and GCK-3 activity.
Na delivery and ENaC mediate flow regulation of collecting duct endothelin-1 production
Authors: Pandit Meghana M. , Strait Kevin A. , Matsuda Toshio , Kohan Donald E.
Published: February 2012

Collecting duct (CD) endothelin-1 (ET-1) is an important autocrine inhibitor of Na and water transport. CD ET-1 production is stimulated by extracellular fluid volume expansion and tubule fluid flow, suggesting a mechanism coupling CD Na delivery and ET-1 synthesis. A mouse cortical CD cell line, mpkCCDc14, was subjected to static or flow conditions for 2 h at 2 dyn/cm2, followed by determination of ET-1 mRNA content. Flow with 300 mosmol/l NaCl increased ET-1 mRNA to 65% above that observed under static conditions. Increasing perfusate osmolarity to 450 mosmol/l with NaCl or Na acetate increased ET-1 mRNA to ∼184% compared with no flow, which was not observed when osmolarity was increased using mannitol or urea. Reducing Na concentration to 150 mosmol/l while maintaining total osmolarity at 300 mosmol/l with urea or mannitol decreased the flow response. Inhibition of epithelial Na channel (ENaC) with amiloride or benzamil abolished the flow response, suggesting involvement of ENaC in flow-regulated ET-1 synthesis. Aldosterone almost doubled the flow response. Since Ca2+ enhances CD ET-1 production, the involvement of plasma membrane and mitochondrial Na/Ca2+ exchangers (NCX) was assessed. SEA0400 and KB-R7943, plasma membrane NCX inhibitors, did not affect the flow response. However, CGP37157, a mitochondrial NCX inhibitor, abolished the response. In summary, the current study indicates that increased Na delivery, leading to ENaC-mediated Na entry and mitochondrial NCX activity, is involved in flow-stimulated CD ET-1 synthesis. This constitutes the first report of either ENaC or mitochondrial NCX regulation of an autocrine factor in any biologic system.
Proteomic profiling of the effect of metabolic acidosis on the apical membrane of the proximal convoluted tubule
Authors: Walmsley Scott J. , Freund Dana M. , Curthoys Norman P.
Published: February 2012

The physiological response to the onset of metabolic acidosis requires pronounced changes in renal gene expression. Adaptations within the proximal convoluted tubule support the increased extraction of plasma glutamine and the increased synthesis and transport of glucose and of NH4+and HCO3−ions. Many of these adaptations involve proteins associated with the apical membrane. To quantify the temporal changes in these proteins, proteomic profiling was performed using brush-border membrane vesicles isolated from proximal convoluted tubules (BBMVPCT) that were purified from normal and acidotic rats. This preparation is essentially free of contaminating apical membranes from other renal cortical cells. The analysis identified 298 proteins, 26% of which contained one or more transmembrane domains. Spectral counts were used to assess changes in protein abundance. The onset of acidosis produced a twofold, but transient, increase in the Na+-dependent glucose transporter and a more gradual, but sustained, increase (3-fold) in the Na+-dependent lactate transporter. These changes were associated with the loss of glycolytic and gluconeogenic enzymes that are contained in the BBMVPCTisolated from normal rats. In addition, the levels of γ-glutamyltranspeptidase increased twofold, while transporters that participate in the uptake of neutral amino acids, including glutamine, were decreased. These changes could facilitate the deamidation of glutamine within the tubular lumen. Finally, pronounced increases were also observed in the levels of DAB2 (3-fold) and myosin 9 (7-fold), proteins that may participate in endocytosis of apical membrane proteins. Western blot analysis and accurate mass and time analyses were used to validate the spectral counting.
The hormone melatonin stimulates renoprotective effects of “early outgrowth” endothelial progenitor cells in acute ischemic kidney injury
Authors: Patschan D. , Hildebrandt A. , Rinneburger J. , Wessels J. T. , Patschan S. , Becker J. U. , Henze E. , Krüger A. , Müller G. A.
Published: February 2012

Endothelial progenitor cells (EPCs) protect the kidney from acute ischemic injury. The aim of this study was to analyze whether pretreatment of murine “early outgrowth” EPCs (eEPCs) with the hormone melatonin increases the cells' renoprotective effects in the setting of murine acute ischemic renal failure. Male (8–12 wk old) C57Bl/6N mice were subjected to unilateral ischemia-reperfusion injury postuninephrectomy (40 min). Postischemic animals were injected with either 0.5×106 untreated syngeneic murine eEPCs or with cells, pretreated with melatonin for 1 h. Injections were performed shortly after reperfusion of the kidney. While animals injected with untreated cells developed acute renal failure, eEPC pretreatment with melatonin dramatically improved renoprotective actions of the cells. These effects were completely reversed after cell pretreatment with melatonin and the MT-1/-2 antagonist luzindole. In vitro analysis revealed that melatonin reduced the amount of tumor growth factor-β-induced eEPC apoptosis/necrosis. Secretion of vascular endothelial growth factor by the cells was markedly stimulated by the hormone. In addition, migratory activity of eEPCs was enhanced by melatonin and supernatant from melatonin-treated eEPCs stimulated migration of cultured mature endothelial cells. In summary, melatonin was identified as a new agonist of eEPCs in acute ischemic kidney injury.
Angiotensin AT1receptor-associated protein Arap1 in the kidney vasculature is suppressed by angiotensin II
Authors: Doblinger Elisabeth , Höcherl Klaus , Mederle Katharina , Kattler Veronika , Walter Steen , Hansen Pernille B. , Jensen Boye , Castrop Hayo
Published: February 2012

Arap1 is a protein that interacts with angiotensin II type 1 (AT1) receptors and facilitates increased AT1receptor surface expression in vitro. In the present study, we assessed the tissue localization and regulation of Arap1 in vivo. Arap1 was found in various mouse organs, with the highest expression in the heart, kidney, aorta, and adrenal gland. Renal Arap1 protein was restricted to the vasculature and to glomerular mesangial cells and was absent from tubular epithelia. A similar localization was found in human kidneys. To test the hypothesis that angiotensin II may control renal Arap1 expression, mice were subjected to various conditions to alter the activity of the renin-angiotensin system. A high-salt diet (4% NaCl, 7 days) upregulated Arap1 expression in mice by 47% compared with controls (0.6% NaCl, P = 0.03). Renal artery stenosis (7 days) or water restriction (48 h) suppressed Arap1 levels compared with controls (−64 and −62% in the clipped and contralateral kidney, respectively; and −50% after water restriction, P < 0.01). Angiotensin II infusion (2 μg·kg−1·min−1, 7 days) reduced Arap1 mRNA levels compared with vehicle by 29% ( P < 0.01), whereas AT1antagonism (losartan, 30 mg·kg−1·day−1, 7 days) enhanced Arap1 mRNA expression by 52% ( P < 0.01); changes in mRNA were paralleled by Arap1 protein abundance. Experiments with hydralazine and epithelial nitric oxide synthase−/− mice further suggested that Arap1 expression changed in parallel with angiotensin II, rather than with blood pressure per se. Similar to in vivo, Arap1 mRNA and protein were suppressed by angiotensin II in a time- and dose-dependent manner in cultured mesangial cells. In summary, Arap1 is highly expressed in the renal vasculature, and its expression is suppressed by angiotensin II. Thus Arap1 may serve as a local modulator of vascular AT1receptor function in vivo.
Connecting tubule glomerular feedback mediates acute tubuloglomerular feedback resetting
Authors: Wang Hong , D'Ambrosio Martin A. , Garvin Jeffrey L. , Ren Yilin , Carretero Oscar A.
Published: February 2012

Tubuloglomerular feedback (TGF) and connecting tubule glomerular feedback (CTGF) are mechanisms that control afferent arteriole (Af-Art) tone. TGF, initiated by increased NaCl at the macula densa, causes Af-Art constriction. Prolonged activation of TGF leads to an attenuation or “resetting” of its constrictor effect. The mechanisms of TGF resetting remain incompletely understood. CTGF is initiated by increased NaCl in the connecting tubule and Na+ entry via epithelial sodium channels (ENaC). Contrary to TGF, CTGF dilates the Af-Art. Here, we hypothesize that CTGF, in part, mediates TGF resetting. We performed micropuncture of individual rat nephrons while measuring stop-flow pressure (PSF), an index of glomerular filtration pressure and Af-Art tone. Increases in Af-Art tone cause PSF to decrease. TGF responses, measured as the decrease in PSF induced by switching late proximal tubule perfusion from 5 to 40 nl/min, were elicited before and after a 30-min period of sustained perfusion of the late proximal tubule at a rate of 40 nl/min designed to induce TGF resetting. TGF responses were 7.3 ± 0.3 and 4.9 ± 0.2 mmHg before and after resetting was induced ( P < 0.001, n = 6). When CTGF was inhibited with the ENaC blocker benzamil (1 μM), TGF responses were 9.5 ± 0.3 and 8.8 ± 0.6 mmHg (NS, n = 6), thus resetting was abolished. In the presence of the carbonic anhydrase inhibitor acetazolamide (10 mM), TGF responses were 8.8 ± 0.6 and 3.3 ± 0.4 mmHg before and after resetting ( P < 0.001, n = 6). With both acetazolamide and benzamil, TGF responses were 10.4 ± 0.2 and 8.4 ± 0.5 mmHg ( P < 0.01, n = 6), thus resetting was attenuated. We conclude that CTGF, in part, mediates acutely induced TGF resetting.