bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical InGaAs Channel Metal–Insulator–Semiconductor Field Effect Transistor with High Current Density
Authors: Saito Hisashi , Matsumoto Yutaka , Miyamoto Yasuyuki , Furuya Kazuhito
Published: January 2011

A high-speed transistor operation is expected from using an undoped channel region. We propose a vertical InGaAs-channel metal–insulator–semiconductor field effect transistor (MISFET) with an ultra-narrow mesa structure, an undoped channel, and a heterostructure launcher. According to a Monte Carlo simulation, a cutoff frequency of 1.5 THz is expected when a 20-nm-wide mesa structure, a 60-nm-long channel, and a 5 MA/cm2 drain current density are achieved. We fabricated an ultra-narrow mesa structure by using selective undercut etching. In the fabricated device, the channel mesa was 15 nm wide, and the observed drain current density was 0.95 A/mm. Because the channel mesa width was 15 nm, the drain current density per unit area was 6.3 MA/cm2. A high current density was achieved for a short charging time. By comparing the drain current density of the 60-nm-long channel device with that of a 100-nm-long channel device, we inferred that quasi-ballistic transportation can be achieved in our devices.
Pinch-Off Voltage Lowering in Polycrystalline Silicon Thin-Film Transistors
Authors: Ikeda Hiroyuki , Sano Nobuyuki
Published: January 2011

Pinch-off voltage (V
p) lowering phenomenon in the output characteristics of polycrystalline silicon thin-film transistors (poly-Si TFTs) is reported and investigated by measurement and device simulation. As the trap density increases, the observed V
p becomes smaller than the ideal V
p while maintaining a linear relationship with the gate–source voltage (V
gs). The device simulation analysis revealed two mechanisms for V
p lowering. One is current saturation due to the increase in onset gate–drain voltage (V
gd), causing the drain region to become highly resistive, which originates from the gradual increase in surface potential with V
gs. This is interpreted as an expansion of the conventional pinch-off concept. The other is the current limitation, controlled by grain boundary (GB) and intragrain conductance at the drain edge, which is peculiar to poly-Si TFTs. On the basis of the above analysis, a GB-conductance-limited carrier transport model is proposed. Its good agreement with the measurements suggests the suitability of this model for describing V
p lowering.
Effects of Flow Transport of the Ar Carrier on the Synthesis of ZnO Nanowires by Chemical Vapor Deposition
Authors: Choi Joon Hyock , Seo Ju Seok , Cha Seung Nam , Kim Hyun Jin , Kim Seong Min , Park Young Jun , Kim Sang-Woo , Yoo Ji-Beom , Kim
Published: January 2011

ZnO nanowires were synthesized by the chemical vapor deposition (CVD) and heating of ZnO powders under Ar gas flow. The effect of the carrier gas (Ar) on the growth region inside the CVD chamber was systematically investigated. The transport of Zn vapor was assisted by the Ar gas flow, producing a spatial distribution of the growth of the ZnO nanowires (in this case, the longer nanowires grown in a certain region show better crystallinity). A simple model of a parabolic transport of Zn vapor (caused by the Ar flow) was, thus, proposed to explain these effects. Field-effect transistors (FETs) were also fabricated using ZnO nanowires and the device performance was determinded, showing a mobility of 20 cm2 V-1 s-1.
Gate-Induced Cross-Over between Fabry–Perot Interference and Coulomb Blockade in a Single-Walled Carbon Nanotube Transistor with Double-Gate Structure
Authors: Kamimura Takafumi , Matsumoto Kazuhiko
Published: January 2011

The gate-induced cross-over between Fabry–Perot interference and Coulomb blockade characteristics in a single-walled carbon nanotube (SWNT) transistor are observed. The behaviors of Fabry–Perot interference and Coulomb blockade are controlled by the control-gate and observed by the sweep-gate. When a negatively high voltage is applied to the control-gate electrode, the SWNT transistor showed a resonant tunneling transistor (RTT) characteristic, e.g., a Fabry–Perot quantum interference pattern. However, when a negatively low voltage is applied to the control gate electrode, the SWNT transistor showed a single-hole transistor (SHT) characteristic, e.g., a Coulomb diamond characteristic. The transition between RTT and SHT is achieved by modulating the coupling strength between the source and drain electrodes and the quantum island using control-gate voltage change. Schottky barriers at the contact between the SWNT and the source and drain electrodes act as tunneling barriers. The thicknesses of the tunneling barriers are modulated by the control-gate voltage change, and the strength of the coupling between the source and drain electrode and the quantum island is also modulated.
Lateral Manipulation of Single Defect on Insulating Surface Using Noncontact Atomic Force Microscope
Authors: Yi Insook , Nishi Ryuji , Abe Masayuki , Sugimoto Yoshiaki , Morita Seizo
Published: January 2011

A single atomic defect on an ionic crystal surface was manipulated at the atomic level using an atomic force microscope. During raster scanning, the defect was manipulated at near the tip–sample distance and at room temperature. The defect, which is imaged as a sharp half-moon shape, moves continuously if the tip is close to the sample surface. The defect randomly moves along a zigzag or straight path or jumps long distances. The movement of the defect on an insulator is complex in contrast to that on semiconductors. The defect moves suddenly owing to the tip approaching the surface when the distance feedback is overshot under the condition of a large difference in frequency shift between the feedback set point and a weak interaction on the defect.
Study of the Reflectivity of Silver Films Deposited by Radio Frequency and Direct Current Coupled Magnetron Sputtering
Authors: Goto Tetsuya , Seki Nobuaki , Shirai Yasuyuki , Ohmi Tadahiro
Published: January 2011

Silver films are deposited on a SiO2 surface and a cyclo-olefin polymer surface by radio frequency and direct current (RF–DC) coupled magnetron sputtering to realize light reflectors with high reflectivity in the visible light region. Because the reflectivity of silver is relatively low, especially in the short-wavelength region less than 500 nm owing to a slight increase in the refractive index of silver, deposition conditions are studied with emphasis on maximizing the reflectivity in this region. Also, protection film depositions of Si3N4 on a silver surface by microwave-excited-plasma-enhanced chemical vapor deposition were carried out to improve the durability of silver films, which are easily oxidized and/or sulfurized, resulting in the degradation of the reflectivity of the films. It is found that a high reflectivity in the short-wavelength region can be obtained by Xe plasma sputtering and/or Ar plasma sputtering at a relatively high working pressure, i.e., the conditions with a low ion bombardment energy at the substrate surface. At the same time, a normalized ion flux supplied to the substrate surface at approximately 2 is optimum, where the normalized ion flux is defined as the ratio of plasma-ion flux to deposited-atom flux on the growing film surface. Under such optimized deposition conditions, a silver film with a low resistivity and a smooth surface is obtained. Furthermore, it is found that a Si3N4 film with a thickness of 8 nm on a silver surface serves as a good protection film without serious degradation of reflectivity, and the reflectivity can be maintained even after the immersion of the sample in the boiling water (100 °C) for 2 h.
Measurement of Ions Penetration Pattern in Point to Grid Atmospheric Corona Discharge
Authors: Haghdel Ali , Abiri Habibollah , Eskandari Mohammad Reza , Zibaeinejad Hasan
Published: January 2011

Atmospheric plasma which has many scientific and engineering applications is a complicated phenomena because of interaction between ions, fields and neutrals. For more accurate modeling and better use of corona phenomena which is a kind of atmospheric plasma, some experimental measurements have been done in the case of point to grid corona problem and relative ion penetration pattern behind the grid has been measured. Also the measurement probe is discussed and some simple models are introduced for the pattern, then a one dimensional simulation result based on statistical equations has been presented to be compared with measurements.
Model of Reactive Microwave Plasma Discharge for Growth of Single-Crystal Diamond
Authors: Yamada Hideaki , Chayahara Akiyoshi , Mokuno Yoshiaki , Shikata Shin-ichi
Published: January 2011

Distributions of species during microwave plasma discharge under elevated power density have been studied numerically. Calculations are conducted for an axisymmetric two-dimensional system, where the effects of the thermal diffusions of the constituent species and some of their chemical reactions are taken into account. While the model is simple, several qualitative characteristics of the obtained results are consistent with those obtained by experimental observations and other numerical simulations. The dependences of the distributions of the radicals on the power density and the mass-flow-rate of methane are shown. Results show that the variation of power density contributes to the increases in the amounts of both the atomic hydrogen and hydrocarbon radicals, which may be related with the simultaneous improvements of growth rate and crystal quality in experiments.
Effect of Excitation Frequency on the Spatial Distributions of a Surface Wave Plasma
Authors: Muta Hiroshi , Nishida Satoshi , Kuribayashi Shizuma , Yoshikawa Naoki , Komatsu Ryota , Uchino Kiichiro , Kawai Yoshinobu
Published: January 2011

Using different frequencies of 2.45 GHz and 915 MHz, the effect of excitation frequency on the spatial distributions of a surface wave plasma for 450 mm wafer processing was experimentally investigated at a medium pressure of 1 Torr. As a result, it was found that the mode number of standing waves which the surface waves form in the radial direction has great influence on the radial distribution of plasma density. Consequently, the plasma uniformity in the downstream region at 915 MHz was better than that at 2.45 GHz. On the other hand, the electron temperature was roughly constant and below 1.5 eV except in the vicinity of the quartz window at both frequencies.
Structural Change of InGaN Nanostructures Grown by Mixed-Source Hydride Vapor Phase Epitaxy
Authors: Ok Jin Eun , Jo Dong Wan , Jeon Hun Soo , Lee Ah Reum , Lee Gang Suok , Kim Kyung Hwa , Ahn Hyung Soo , Yang Min
Published: January 2011

We determined the effect of the type of substrate on the growth of InGaN nanostructures by mixed-source hydride vapor phase epitaxy (HVPE). InGaN nanostructures were formed on c-plane, r-plane sapphire, and undoped GaN substrates at various growth temperatures. Also, we looked into the changes in the structural and optical characteristics of InGaN nanostructures when antimony (Sb) is used as a surfactant during the growth of InGaN nanostructures. The samples were characterized by scanning electron microscopy (SEM) and photoluminescence (PL) measurement. The density of the nanostructures on the surface and the indium composition of the InGaN layer varied depending on the type of substrate and growth temperature. The aligning direction of the nanostructures markedly changed and the indium composition increased when Sb was used as the surfactant during the growth of the InGaN nanostructure, compared with the results of the InGaN nanostructures grown without Sb addition.
Metal Organic Chemical Vapor Deposition Growth and Characterization of AlInN-Based Schottky Ultraviolet Photodiodes on AlN Template
Authors: Sakai Yusuke , Morimoto Tomohiko , Egawa Takashi , Jimbo Takashi
Published: January 2011

AlInN-based Schottky ultraviolet photodiodes on AlN template are demonstrated. AlInN/GaN structures are grown using metal organic chemical vapor deposition. AlInN layer on AlN template exhibits high crystal quality and good surface morphology as it was confirmed respectively through X-ray diffraction (XRD) and atomic force microscope (AFM). The fabricated Schottky photodiodes on AlN template have the leakage current of 16 nA at a reverse voltage of 5 V and the cut-off wavelength around 260 nm. A zero-bias peak responsivity of 33 mA/W is achieved at 230 nm, corresponding to the quantum efficiency of 17%. This efficiency for AlInN-based photodiode on AlN template is superior to the photodiode grown on sapphire with low temperature buffer layer (LT-BL). It is possible to realize a high-performance AlInN-based Schottky photodiode by using AlN template as a substrate.
Deep-Level Characterization of n-GaN Epitaxial Layers Using Transparent Conductive Polyaniline Schottky Contacts
Authors: Nakano Yoshitaka , Matsuki Nobuyuki , Irokawa Yoshihiro , Sumiya Masatomo
Published: January 2011

We have successfully investigated surface-related deep levels in n-GaN epilayers with high carrier concentrations by using transparent conductive polyaniline Schottky contacts. High quality Schottky barrier diodes fabricated showed a typical capacitance dispersion phenomenon at ∼10 kHz, which is characteristic of conductive polyaniline films with polarization capacitance and resistance components. Steady-state photocapacitance spectroscopy measurements at over this cutoff frequency revealed five photoemission states with their onsets at ∼1.40, ∼1.70, ∼2.08, ∼2.64, and ∼2.90 eV below the conduction band, being identical with the deep levels commonly observed in GaN and AlGaN/GaN. Particularly, the concentrations of the ∼1.70 and ∼2.90 eV levels were found to increase significantly with decreasing their probing depth range to the near-surface region of the n-GaN layers. Therefore, these levels are probably subject to the surface conditions of the n-GaN layers.
High-Temperature Operation of Normally Off-Mode AlGaN/GaN Heterostructure Field-Effect Transistors with p-GaN Gate
Authors: Sugiyama Takayuki , Amano Hiroshi , Iida Daisuke , Iwaya Motoaki , Kamiyama Satoshi , Akasaki Isamu
Published: January 2011

We demonstrated the high-temperature operation of normally off-mode heterostructure field-effect transistors (HFETs) with a p-GaN gate. The HFETs with a p-GaN gate were operated in the normally off mode at 350 °C. The temperature dependence of their performance was compared with the results of simulation.
Improvement in the Light Output Power of GaN-Based Light Emitting Diodes by One-Step Current Blocking Design
Authors: Tsai Chun-Fu , Su Yan-Kuin , Lin Chun-Liang
Published: January 2011

This paper presented the InGaN/GaN light-emitting diodes (LEDs) using one-step design of indium–tin-oxide (ITO) layer as the current blocking layer (CBL) structure was fabricated successfully and the optoelectronic properties were also measured. The ITO CBL LEDs exhibit higher light output power (16.3% at 20 mA) compared with that of the reference LEDs without CBL. As for the usual current blocking process, the one-step design of ITO CBL as the current blocking structure was demonstrated in our experiment and proved to be an effective, feasible and inexpensive way, with fewer steps and less cost, to improve the LEDs' performance.
Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum
Authors: Lee Ah Reum , Jeon Hunsoo , Lee Gang-Seok , Ok Jin-Eun , Jo Dong-Wan , Kim Kyoung Hwa , Yi Sam Nyung , Yang Min , Ahn Hyung Soo , Cho Chae-Ryong , Kim Suok-Whan , Lee Jae-Hak , Ha Hong-Ju
Published: January 2011

We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 µm. After the growth, the InGaN/GaN MQW LED of 200 µm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-µm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.
Growth, Fabrication, and Characterization of InGaAsN Double Heterojunction Solar Cells
Authors: Wu Tzung-Han , Su Yan-Kuin , Lin Yi-Chieh , Wang Yu-Jen
Published: January 2011

In this paper, we have demonstrated fabrication and characterization of p-GaAs/i-InGaAsN/n-GaAs double heterojunction solar cells (DHJSCs). The intrinsic InGaAsN absorption layers which were lattice-matched to GaAs substrate with photoresponse to 1 eV were grown by the metal organic chemical vapor deposition method. The samples were studied experimentally by varying the growth temperature of intrinsic InGaAsN absorption layers. By adjusting the indium and nitrogen content, we have grown InGaAsN epilayers which were lattice-matched to GaAs substrate at various growth temperatures. Among three intrinsic layer growth temperatures, it was found that the InGaAsN DHJSC with the intrinsic layer growth temperature of 550 °C can get the largest absorption region. Under the AM 1.5 direct spectrum, the DHJSCs with absorption layer which were grown at 550 °C have open-circuit voltages ranging from 0.295 V, short-circuit currents of 14.4 mA/cm2, and fill factor of 51.2%. The conversion efficiency of InGaAsN double heterojunction solar cells achieves 2.38%, and the absorption wavelength region would extend to 1200 nm.
Growth of Two-Dimensional Carbon Nanostructures and Their Electrical Transport Properties at Low Tempertaure
Authors: Wu Yihong , Wang Haomin , Choong Catherine
Published: January 2011

We report on a systematic electrical transport study of carbon nanowalls using both the normal metal and superconducting electrodes. The nonlinear transport and corresponding anomalous d
I/d
V versus bias curves below ∼2 K observed in samples with both Ti and Nb electrodes is accounted for by the formation of charge density waves due to enhanced density of states at the Fermi level at edges or extended defects. This phase competes with superconducting instability at very low temperature, as manifested by distinctive resistance-temperature behaviors and associated d
V/d
I characteristics observed in different samples.
Effect of Hydrogen on Carbon Nanowall Growth by Microwave Plasma-Enhanced Chemical Vapor Deposition
Authors: Suzuki Seiya , Chatterjee Anindita , Cheng Chia-Liang , Yoshimura Masamichi
Published: January 2011

The effect of hydrogen on the growth of carbon nanowalls (CNWs) with different hydrogen-to-carbon (H2/CH4) flow ratios in chemical vapor deposition was investigated using scanning electron microscopy (SEM) and Raman spectroscopy. The CNWs were synthesized on catalyst-free substrates (Si or SiO2) by microwave plasma-enhanced chemical vapor deposition (MPECVD). At low H2/CH4 flow rate ratios (0–2), the wall size increased with increasing H2/CH4 flow rate ratio while the I
G/I
D remained constant; however, at high H2/CH4 flow rate ratios (2–4), the wall size decreased and I
G/I
D increased with increasing H2/CH4 flow rate ratios. This indicates that hydrogen plays different roles in the two ranges: reduction of nucleation density resulting in the larger CNWs for the former range and removal of amorphous carbon resulting in a higher I
G/I
D for the latter range. Note that the present growth method provides an extremely high growth rate of CNWs reaching 23 µm/h.
Morphology and Size of Ion Induced Carbon Nanofibers: Effect of Ion Incidence Angle, Sputtering Rate, and Temperature
Authors: Yusop Mohd Zamri , Yamaguchi Kohei , Suzuki Takahito , Ghosh Pradip , Hayashi Akari , Hayashi Yasuhiko , Tanemura Masaki
Published: January 2011

Graphite surfaces were bombarded with oblique Ar+ ions at 1 keV to induce the carbon nanofiber (CNF) growth at room temperature and at high temperature (300 °C), and their dependence of length, diameter and number density on ion-incidence angle and sputtering rate was investigated in detail. The sputtered surface ion-irradiated at normal incidence produced huge cones and rod-like structures. It was found that some of the cones possessed the non-aligned thick carbon fibers on the top. By contrast, obliquely ion-irradiation induced the formation of densely distributed CNF-tipped cones. The higher ion-incidence angle produced CNF of smaller diameter and high fabrication temperature favors the formation of longer fiber with higher numerical density. In addition, the number density of the CNF-tipped cones strongly depended upon the ion-incidence angle rather than the sputtering rate. Thus, the diameter, length and number density of CNFs were strongly dependent upon the ion-irradiation parameters. It is believed that myriad of applications is possible with ion-induced CNFs by selecting the suitable ion-irradiation parameters.
Removal of Diamond-Like Carbon Film by Oxygen-Dominated Plasma Beam Converted from Filtered Carbon-Cathodic Arc
Authors: Tanoue Hideto , Kamiya Masao , Suda Yoshiyuki , Takikawa Hirofumi , Oke Shinichiro , Hasegawa Yushi , Taki Makoto , Tsuji Nobuhiro , Ishikawa Takeshi , Yasui Haruyuki
Published: January 2011

Diamond-like carbon (DLC) film is sometimes removed using oxygen plasma in order to reuse workpieces such as cutting tools and press molds. In this study, an oxygen-dominated plasma beam was generated by converting the cathodic carbon arc plasma beam formed in T-shaped filtered-arc-deposition (T-FAD) in order to investigate the feasibility of using the plasma beam for the removal of DLC film. When the oxygen (O2) gas flow rate was relatively high (50 ml/min) and the substrate was biased (DC -500 V), the plasma beam in front of the substrate was confirmed to contain a considerable amount of excited oxygen atoms, since an atomic oxygen spectral line (777 nm) emitted from the plasma beam had relatively strong radiation intensity. The plasma beam was irradiated on a tetrahedral amorphous carbon film, a hydrogen-free sp3-rich DLC film, prepared on a hard alloy (WC with 6 wt % Co binder) substrate. It was found that a plasma beam generated with an appropriate O2 gas flow rate and applied substrate bias was able to etch the DLC film proportionally to the treatment time. The surface was not roughened when the treatment time was 1.5 times longer than the intended time to remove a given thickness of DLC film.
Fabrication of the CuInGaSe Pellet and Characterization of the Thin Film
Authors: Jeon Hunsoo , Lee Ahreum , Lee Gang-Seok , Jo Dong-Wan , Ok Jin-Eun , Kim Kyoung Hwa , Yang Min , Yi Sam Nyung , Ahn Hyung Soo , Cho Chae-Ryong , Kim Suck-Whan , Ha Hong-Ju
Published: January 2011

CuInGaSe (CIGS) mixed-source was prepared by hydride vapor transport method (HVT). The new source synthesis method was attempted by mixing several metals such as Cu, In, Ga, and Se with 3:5:1:4 mass ratios. This mixed-source was soaked at 1090 °C for 90 min in nitrogen atmosphere. Then, the CIGS was grinded up and formed the state of powder and the CIGS pellet was made by pressure machine. The diameter of pellet is 10 mm. The CIGS thin film was deposited on soda lime glass with evaporated molybdenum layer by e-beam evaporating this CIGS pellet. For crystallization of CIGS thin film, we measured scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). High intensity X-ray peaks diffracted from (112), (204)/(220), (116)/(312), and (400) of CIGS thin film and from (110) of Mo were confirmed by XRD measurement.
Formation of Metallic Nanostructure by Helium Plasma Irradiation
Authors: Kajita Shin , Saeki Tsubasa , Hirahata Yuki , Ohno Noriyasu
Published: January 2011

Morphology changes on various metals by helium irradiation are shown experimentally. It has been revealed that a whisker-like nanostructure was formed on tungsten and molybdenum surfaces by the exposure to a helium plasma. After helium irradiation to titanium and stainless steel, many dots in several hundreds of nanometers cover the surface. The morphology change may be caused by the growing process of helium bubbles in the sub-surface region.
Growth of Single-Crystalline Nanorods in Atmospheric Plasma
Authors: Guo Ying , Xu Jinzhou , Ding Ke , Yang Ping , Nakamura Keiji , Zhang Jing
Published: January 2011

Single-crystalline fluorocarbon polymer nanorods are synthesized by oriented atmospheric plasma polymerization. It is found that the nanorods have a high length-to-width ratio of more than 25 and the tadpole structure is formed after annealing. The discharge is characterized experimentally by the waveforms of applied voltage and discharge current. The potential gradient in the discharge volume and electric field gradient the around anode are demonstrated by particle-in-cell (PIC) numerical simulation and are considered to play an important role on the formation of one-dimensional nanorods by driving most of the CF clusters to the tip of nanorods. With the particle charging theory, the “one-dimensional activated growth model limited by an electrical field gradient” is proposed for the growth mechanism of nanocrystalline film in atmospheric plasmas.
Static Water Contact Angle Analysis of Cyclonic Atmospheric Pressure Plasma-Activated Polycarbonate
Authors: Huang Chun , Wu Shin-Yi , Liu Yu-Chia , Chang Ya-Chi , Tsai Ching-Yuan
Published: January 2011

Polycarbonate (PC) films were activated using cyclonic atmospheric pressure plasma. The experimentally measured gas phase temperature was from 30 to 95 °C, demonstrating that this cyclonic atmospheric pressure plasma can treat heat-sensitive polymeric materials at the low temperatures. The surface hydrophilicity changes of cyclonic atmospheric pressure plasma-treated PC films were determined by water contact angle analysis. The activation effects of plasma operational parameters including treatment time, plasma power, and distance of nozzle to substrate on the PC surface features were investigated. The glow feature and luminous plasma species in the cyclonic atmospheric pressure plasma were identified by optical emission spectroscopy (OES). Cyclonic atmospheric pressure plasma-activated PC films showed a significant decrease in water contact angle. In this investigation, we developed an innovative technique for chamberless polymeric surface activation by this atmospheric pressure plasma processing.
Development of Atmospheric Pressure Plasma Jet with Slit Nozzle
Authors: Oshima Nobuaki , Takada Ryuji , Kubota Yusuke , Abraha Petros , Hara Tamio
Published: January 2011

A wide flame atmospheric pressure plasma jet has been developed by using a slit nozzle for large area treatment of surfaces. The width of the plasma treated surfaces has been broadened to more than 5 times that obtained by conventional nozzle. The proper function of the slit nozzle towards surface treatment is confirmed by evaluating contact angles of water on polyethylene (PE) surface upon treatment by nitrogen atmospheric plasma jet. A thin film has also been deposited on a glass substrate by introducing hexamethyldisiloxane (HMDSO) into the plasma. The width of the thin film matched with the width of the slit confirming the success of our approach towards attaining a viable large area atmospheric plasma jet for various surface treatments.
Magnetostructural Property of a Twisted Bis(µ-hydroxo) Dicopper(II) Core and Its Relevance to Formation of an Active Dioxygen Intermediate
Authors: Funahashi Yasuhiro , Toyama Tomoaki , Yoshii Kotaro , Nishikawa Tomohide , Kishida Mitsumi , Kajita Yuji , Inomata Tomohiko , Ozawa Tomohiro , Wasada-Tsutsui Yuko , Masuda Hideki
Published: January 2011

A precursor compound of a dioxygen adduct, [CuII
2(Sp)2(µ-OH)2](ClO4)2·CH2Cl2 (Sp = (-)-sparteine) (1·(ClO4)2·CH2Cl2), has been investigated by X-ray structural analysis, magnetic measurement, and molecular orbital calculations. The crystal structure of 1·(ClO4)2·CH2Cl2 showed that the coordination structure is spirally twisted and both of the two edged CuN2 planes with ligating nitrogen atoms of Sp are almost orthogonally crossed, the dihedral angle being 84°. The magnetic susceptibility measurement of 1·(ClO4)2·CH2Cl2 showed an ineffective antiferromagnetic coupling interaction between the two copper(II) centers (2J = -260 cm-1). The density functional theory (DFT) calculation confirmed that the spirally twisted coordination of Sp-nitrogen atoms in 1 contributed to a decrease in energy gap between the two singly occupied molecular orbitals (SOMOs), making the magnitude of antiferromagnetic coupling smaller.
Three-Dimensionally Ordered Macroporous ZrO2:Tb3+ Films: Synthesis, Characterization, and Photoluminescence Properties
Authors: Qu Xuesong , Yang Hyun Kyoung , Moon Byung Kee , Choi Byung Chun , Jeong Jung Hyun
Published: January 2011

Three-dimensionally ordered macroporous (3DOM) ZrO2:Tb3+ films on glass were successfully prepared using a polystyrene (PS) colloidal crystal template in combination with a sol–gel method. Microstructure of as-prepared 3DOM ZrO2:Tb3+ films were examined by field emission scanning electron microscopy (FE-SEM). The results indicated that the material featured closely packed three-dimensional ordering of pores structure with (111) plane parallel to the surface of glass substrate. In addition, photoluminescence (PL) spectra showed a dominating green emission corresponding to 5D4–7F
J
(J = 3, 4, 5, 6) transitions of Tb3+ under UV light excitation. Due to the presence of oxygen vacancies the PL peak from ZrO2 host matrix was also observed.
Evaluation of Polar Anchoring Energy Based on Symmetric Oblique Incident Transmission Ellipsometry Method: the Voltage Diminution by Alignment Films
Authors: Tachibana Kazuya , Goda Kazuya , Kaneko Yoshiyuki , Inoue Masaru , Kimura Munehiro , Akahane Tadashi
Published: January 2011

Polar anchoring energy coefficient is one of the important parameters to improve the performance of liquid crystal displays (LCDs). To determine the polar anchoring energy coefficient with high accuracy, the symmetric oblique incident transmission ellipsometry (SOITE) method with voltage correction is proposed. As a result, the polar anchoring energy coefficients are found to be little affected by the voltage diminution at the alignment film and can be determined by the SOITE method. However, the reduced elastic anisotropy κ was not fixed by changing the thickness of the alignment film. These results indicate a possibility that the SOITE method with voltage correction can be used to determine the device parameters with high accuracy. Consequently, it may contribute to the technological development of high-performance LCDs.
Development of Ultraviolet Crosslinking Glucose-Based Resist Materials for Advanced Electronic Device Applications Using Nanoimprint Lithography
Authors: Takei Satoshi
Published: January 2011

An ultraviolet crosslinking glucose-based resist material in nanoimprint lithography was studied for environmental applicability and 65 nm dense line patterning. In this study, the applyication of a glucose derivative as an ecofriendlier compound to the resist material in an advanced nanopatterning process was demonstrated. It was found that the developed glucose-based resist material with an epoxy group in cationic polymerization had the properties of high-crosslinked polymer networks for step and flash nanoimprint lithography and created 65 nm rectangular dense line patterns. In addition, an elemental analysis was carried out to evaluate resist material shrinkage in ultraviolet irradiation and the resistance of a crosslinked film. This desirable concept using a glucose derivative with an epoxy group in the resist material is one of the most promising processes ready to be incorporated into the mass production of advanced electronic device applications.
Manipulation of Work Function and Surface Free Energy of Tungsten Oxide Hole Injection Layer Modified with a Self-Assembled Monolayer
Authors: Kim Seong-Ho , Otsuka Hanae , Shin Hyea-Weon , Tanaka Kuniaki , Advincula Rigoberto C. , Usui Hiroaki
Published: January 2011

As a hole injection layer for organic devices, a tungsten oxide (WO
x
) thin film was vapor-deposited on an indium–tin oxide (ITO) substrate, on which a self-assembled monolayer (SAM) of either 3-aminopropyltrimethoxysilane (APS), phenyltrimethoxysilane (PTMS), or octadecyltrimethoxysilane (ODS) was prepared to modify the surface characteristics. The deposition of WO
x
substantially increased the ionization potential (I
p) of the substrate surface, which was effective in enhancing hole injection. The formation of SAM on WO
x
reduced I
p, but enabled the control of the surface free energy so as to modify the growth morphology of an organic film deposited on its surface. A hole-only device was prepared using a hole transport material of N,N '-diphenyl-N,N '-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD). In the space-charge-limited region, a high current was drawn by using an anode that has a high I
p. At low driving voltages, however, the current flow was considerably influenced by the surface free energy. It was found that the PTMS-SAM on WO
x
gives a satisfactory accommodation of both the work function and the surface energy.
High Current-Gain Cutoff Frequencies above 10 MHz in n-Channel C60 and p-Channel Pentacene Thin-Film Transistors
Authors: Kitamura Masatoshi , Arakawa Yasuhiko
Published: January 2011

The current-gain cutoff frequencies for bottom contact n-channel C60 and p-channel pentacene thin-film transistors (TFTs) with channel lengths of 2–10 µm have been investigated. The cutoff frequency was estimated by direct measurement of the gate and drain modulation currents. The measured cutoff frequencies for both C60 and pentacene TFTs increase consistently with reducing channel length. Cutoff frequencies of 27.7 and 11.4 MHz were obtained from C60 and pentacene TFTs with a channel length of 2 µm, respectively.
Study of the Characteristics of Organic Thin Film Transistors with Plasma-Polymer Gate Dielectrics
Authors: Cho Sang-Jin , Bae In-Seob , Seol Young Gug. , Lee Nae-Eung , Park Yong Seob , Boo Jin-Hyo
Published: January 2011

The effects of gate dielectrics material in organic thin film transistors (OTFTs) were investigated. The gate dielectrics were deposited by plasma enhanced chemical vapor deposition (PECVD) with cyclohexane and tetraethylorthosilane (TEOS) respectively used as organic and inorganic precursors. The gate dielectrics (gate insulators) were deposited as either organic plasma-polymer or organic–inorganic hybrid plasma-polymer thin film by using cyclohexane or cyclohexane with TEOS, respectively. Additionally, hydrogen and argon were used as precursor bubbler gases. A polyimide (PI) substrate was used in the fabrication of pentacene OTFTs with a plasma-polymer gate insulator, an Au source–drain (S/D), and Cu gate electrodes. Different gate dielectrics were investigated. The as-grown plasma-polymer thin films were first analyzed using Fourier-transform infrared (FT-IR) spectroscopy. Also, they were analyzed by nano-indentation and capacitance measurements. The electrical properties, such as mobility and threshold voltage of the pentacene field-effect transistors with the plasma-polymer gate-dielectrics were investigated. Transistor with cyclohexane gate dielectric had a higher field-effect mobility, µFET = 0.84 cm2 V-1 s-1, and a smaller threshold voltage, V
T= -6.8 V, than the transistor with the hybrid gate-dielectric.
Ti-Doped VO2 Films Grown on Glass Substrates by Excimer-Laser-Assisted Metal Organic Deposition Process
Authors: Nishikawa Masami , Nakajima Tomohiko , Kumagai Toshiya , Okutani Takeshi , Tsuchiya Tetsuo
Published: January 2011

V1-x
Ti
x
O2 films were prepared on glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) and thermal MOD processes. The VO2 phase was successfully formed in the range of x = 0–0.35 at 300 °C in air using the ELAMOD process. This is a big advantage in terms of fabrication process for glass or organic substrates. It was also confirmed that dense films were obtained by preparing TiO2 buffer layers on glass substrates. Furthermore, the detailed effect of Ti content in VO2 films on metal–insulator (MI) transition properties was examined. As Ti content increased, the broadening of MI transition and the decreasing of the hysteresis width occurred. At x = 0.14, the hysteresis disappeared. The temperature coefficient of electrical resistance (TCR) value of the film (x = 0.14) remained at approximately -3%/K from 300 to 340 K and was more than -4%/K from 340 to 350 K.
Ferromagnetism Induced by Vacancies in Bulk and the (1010) Surfaces of ZnO: Density Functional Theory Calculations
Authors: Chae Kisung , Chung Yong-Chae , Kim Hanchul
Published: January 2011

We studied the vacancy-induced ferromagnetism in bulk and at the (1010) surface of wurtzite ZnO using density functional theory calculations. It is found out that surface vacancies are energetically favored to bulk vacancies and that the ferromagnetism is induced by Zn vacancies but not by O vacancies. Moreover, local magnetic moments induced at O atoms adjacent to the Zn vacancy are calculated to be larger on the surface than in bulk. These findings indicate that Zn vacancies at surfaces are responsible for the experimentally observed room-temperature ferromagnetism in undoped ZnO thin films and nanoparticles.
Atomic-Scale Investigation on the Ti/Fe(001) Interface Structure: Molecular Dynamics Simulations and Ab initio Calculations
Authors: Choi Heechae , Yoon Geunsup , Chung Yong-Chae
Published: January 2011

The structure dependent magnetism and intermixing characteristics of Ti/Fe(001) thin films were investigated using molecular dynamics simulations and ab initio calculations. Through density functional theory based ab initio calculations, sharply decreased demagnetization energy of Fe(001) substrate by the interface intermixing was observed. The intermixing at the Ti/Fe(001) interface was limited within only the topmost layer of the Fe(001) substrate at temperatures ranging from 300 to 600 K with incident energies of a Ti atom from 0.1 to 5 eV. Both the high deposition temperature and the high incident energy of the Ti adatom inproved the surface smoothness of the deposited Ti films. The elevated temperature significantly increased the amount of Ti/Fe interface intermixing, while the incident energy dependency was negligible. The extremely low atomic intermixing ratio and short diffusion length of Ti/Fe system compared to other transition metal thin films could be explained by comparing the local acceleration and incorporation energy barrier effects.
Dependence on Annealing Temperature of Properties of Cu2ZnSnS4 Thin Films Prepared by Sol–Gel Sulfurization Method
Authors: Maeda Kazuya , Tanaka Kunihiko , Fukui Yuki , Uchiki Hisao
Published: January 2011

Cu2ZnSnS4 (CZTS) thin films were fabricated using a rapid thermal process in 5% H2S+ N2 atmosphere from precursors prepared by the sol–gel method. The precursors were preheated at 250 °C for 10 min and then sulfurized at different temperatures from 300 to 600 °C for 10 min. XRD studies showed that the samples sulfurized at 500–600 °C had a CZTS structure. With increasing sulfurization temperature, the chemical composition ratio of sulfur/metal and the grains size of CZTS increased. From the (αh ν)2–hν plot, the CZTS films had a band gap of ∼1.5 eV.
High-Pressure Synthesis of CuBa2Ca3Cu4O10+δ Superconductor from Precursors Prepared by a Polymerized Complex Method
Authors: Aoba Tomoya , Bizen Takeshi , Suzuki Tsuneo , Nakayama Tadachika , Suematsu Hisayuki , Katsumata Tetsuhiro , Inaguma Yoshiyuki , Niihara Koichi
Published: January 2011

Samples of a CuBa2Ca3Cu4O10+δ superconductor were synthesized under a high pressure of 5 GPa at 1100–1200 °C for 30 min using precursors produced by solid-state reaction and polymerized complex methods. Compared with the precursors prepared by the solid-state reaction method, the precursors produced by the polymerized complex method have low grain sizes. The superconductive transition temperature of the samples prepared using precursors made by the polymerized complex method was found to be 113 K. The volume fractions of the superconducting phase in the samples prepared using precursors made by the solid-state reaction and polymerized complex methods were 49 and 36%, respectively. From these results, precursors made by the polymerized complex method can be used in the high-pressure synthesis of superconductors similarly to those made by the solid-state reaction method.
Preparation of Ce-Doped CaGa2S4 by Mechanochemical Solid-State Reaction
Authors: Ohta Takumi , Tanaka Kunihiko , Uchiki Hisao
Published: January 2011

CaGa2S4:Ce crystallites were synthesized by the mechanochemical reaction of CaS, Ga2S3, and Ce2S3 source powders. The growth process was studied by observing X-ray diffraction (XRD) patterns and Raman scattering spectra of the synthesized powder as a parameter of reaction time. Ce doping of CaGa2S4 was studied in terms of its photoluminescence (PL). The approximate crystallite size calculated by a Williamson–Hall plot was 59 (+5, -3) nm.
Effect of Pt and Al Electrodes on Resistive Switching Properties of Sputter-Deposited Cu-Doped SiO2 Film
Authors: Li Chia-Jen , Jou Shyankay , Chen Wei-Ling
Published: January 2011

A copper-doped silica (Cu-SiO2) film of 50 nm thickness was prepared by cosputter deposition of Cu and SiO2 targets. A metal–oxide–metal (MOM) cell comprising a Cu-SiO2 layer sandwiched between a Cu top electrode and a Pt or Al bottom electrode was utilized to characterize resistive switching behavior. Both cells exhibited bipolar switching behavior. Electric conduction of the cell in the high-resistance state prepared using the Pt bottom electrode followed the space-charge-limited-current mechanism, whereas the cell prepared using the Al bottom electrode exhibited Schottky emission. An intermediate oxide layer was observed and attributed to the Schottky emission in the cell prepared using Al bottom electrode.
Cu2ZnSnS4 Thin Film Solar Cells Utilizing Sulfurization of Metallic Precursor Prepared by Simultaneous Sputtering of Metal Targets
Authors: Momose Noritaka , Htay Myo Than , Yudasaka Takuto , Igarashi Shigeo , Seki Takuro , Iwano Shota , Hashimoto Yoshio , Ito Kentaro
Published: January 2011

Cu2ZnSnS4 (CZTS) thin films were prepared by simultaneous sputtering of metallic targets and sulfurizing a metallic precursor under elemental sulfur atmosphere in a sealed tube. Subsequently, they were applied to the fabrication of thin film solar cells. The precursors with desired compositional ratio and thickness were obtained by controlling the area ratio of sputtering targets and also sputtering parameters. We have succeeded in obtaining high-quality polycrystalline CZTS thin films by sulfurization under a sulfur vapor pressure higher than atmospheric pressure. A CZTS-based solar cell with 3.7% conversion efficiency was obtained from CZTS films sulfurized at 590 °C for 7 min.
Structural and Electrical Characterization of Three-Dimensional Superlattices of Organic Monolayer Protected Gold Nanocrystals
Authors: Sato Seiichi , Matsuda Ayumi , Sugimoto Tatsuya , Kimura Keisaku
Published: January 2011

Micrometer-sized three-dimensional superlattices were fabricated by assembling Au nanocrystals modified with mercaptosuccinic acid in aqueous suspensions. Each superlattice formed a single crystal arrangement with a hexagonal close-packed structure where a=5.1 nm. The superlattices were densely deposited on a glass substrate and their electrical properties were investigated. The superlattice-assembled film showed ohmic behavior in the temperature range from 20 to 285 K. The absolute value of the resistivity was in the semiconductor region, but the resistivity slightly decreased as the temperature decreased. The temperature coefficient of the film was one order of magnitude smaller than that of bulk Au.
Strain Effects on Optoelectronic Characteristics of Laterally Arrayed Silicon Nanowires on a Flexible Substrate
Authors: Choi Jinyong , Cho Kyoungah , Kim Sanging
Published: January 2011

In this study, we array n-type silicon nanowires (SiNWs) on a flexible plastic substrate and investigate the effects of tensile strain on the optoelectronic characteristics of the laterally arrayed SiNWs under the illumination of 633-nm-wavelength light in air at room temperature. The unstrained SiNW array has an efficiency of approximately 5.3 µA/W at a bias voltage of 5 V. When the plastic substrate suffers from a tensile strain of up to 2.2% in parallel to the channels of SiNWs, dark current and photocurrent increase markedly owing to the change in their band structure caused by the tensile strain.
Formation and Structural Characteristic of Perpendicularly Aligned Boron Nitride Nanosheet Bridges in Polymer/Boron Nitride Composite Film and Its Thermal Conductivity
Authors: Cho Hong-Baek , Nakayama Tadachika , Suzuki Tsuneo , Tanaka Satoshi , Jiang Weihua , Suematsu Hisayuki , Niihara Koichi
Published: January 2011

The anisotropic alignment of boron nitride (BN) nanosheets was performed in polysiloxane/BN nanosheet composite film under a DC electric field with a change in polarity. The hexagonal BN nanosheets were dispersed by sonication in a prepolymer mixture of polysiloxane followed by high-speed mixing. The homogeneous suspension was cast onto a spacer of microscale thickness and applied to a high DC electric field while changing polarity before the mixture became cross-linked. Analysis revealed that linearly aligned BN nanosheet (LABN) bridges were fabricated in the composite film while connecting the film planes as bridges. This is for first report on the fabrication of linearly aligned nanosheet bridges inside organic–inorganic hybrid films. The fabricated LABN bridges were attributed to the enhancement in the thermal conductivity of the composite film, and the mechanisms underlying the formation of LABN bridges and heat conduction were discussed.
Interfacial-Force-Controlled Placing Technique of Microstructures of Sub- to One Hundred Micrometer Size Using Blade Coating
Authors: Nakagawa Tohru , Arase Hidekazu
Published: January 2011

The surface mounting technology of electronic devices using pick-and-place machines is commonly used to fabricate functional electronic appliances, such as motherboards, flat panel displays, and mobile phones. However, the pick-and-place method begins to encounter difficulties in mounting electronic devices when devices shrink to a few hundreds of micrometers or less. We propose a new blade-coating method of placing microstructures smaller than several hundreds of micrometers on a substrate. The method comprises three steps: (1) preparing a microstructure dispersion consisting of chemically modified microstructures and a water-insoluble organic solvent, (2) continuous blade-coating of water and the dispersion on a chemically patterned substrate on which hydrophilic areas are surrounded by a hydrophobic self-assembled monolayer, and (3) spontaneous placing of the microstructures on the hydrophilic areas by a water/solvent interfacial force that acts on the microstructures. Using this method, we have been able to place microstructures ranging in length from submicrometer to one hundred micrometers, including silicon nanowires and SiO2 microstructures of various sizes. However, our blade-coating method for placing microstructures can be realized with successful combinations of chemical modifiers for the microstructures and water-insoluble solvents. We present a simple method of assessing dispersion using a chemically modified glass test tube filled with water and a solvent for the dispersion.