bluuebunny/crossref_metadata_2025 huggingface dataset:
ON THE STOCHASTIC DEPENDENCE STRUCTURE OF THE LIMIT LOGNORMAL PROCESS
Authors: OSTROVSKY DMITRY
Published: March 2011

The distribution of a single increment of the limit lognormal process of Mandelbrot, several representations of its Mellin transform, and an explicit analytic continuation of the Selberg integral are reviewed. The intermittency invariance of the limit lognormal construction is used to establish a functional Feynman–Kac equation that captures the entire stochastic dependence structure of the limit process. This equation is a general rule of intermittency differentiation that quantifies how the joint distribution of an arbitrary number of increments of the limit process evolves as a function of intermittency. The solution is represented by means of a formal intermittency expansion and shown to be an exactly renormalized expansion in the joint centered moments of the limit process. The expansion coefficients are related to a novel extension of the Selberg integral.
EIGENFUNCTIONS AT THE THRESHOLD ENERGIES OF MAGNETIC DIRAC OPERATORS
Authors: SAITŌ YOSHIMI , UMEDA TOMIO
Published: March 2011

Discussed are ±m modes and ±m resonances of Dirac operators with vector potentials HA= α · (D - A(x)) + mβ. Asymptotic limits of ±m modes at infinity are derived when |A(x)| ≤ C〈x〉-ρ, ρ > 1, provided that HAhas ±m modes. In wider classes of vector potentials, sparseness of the vector potentials which give rise to the ±m modes of HAare established. It is proved that no HAhas ±m resonances if |A(x)| ≤ C〈x〉-ρ, ρ > 3/2.
Ternary AlGaN Alloys with High Al Content and Enhanced Compositional Homogeneity Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Fellmann Vincent , Jaffrennou Périne , Sam-Giao Diane , Gayral Bruno , Lorenz Katharina , Alves Eduardo , Daudin Bruno
Published: March 2011

We have studied the influence of III/N flux ratio and growth temperature on structural and optical properties of high Al-content, around 50–60%, AlGaN alloy layers grown by plasma-assisted molecular beam epitaxy. In a first part, based on structural analysis by Rutherford Backscattering Spectroscopy, we establish that a III/N flux ratio slightly above 1 produces layers with low amount of structural defects. In a second part, we study the effect of growth temperature on structural and optical properties of layers grown with previously determined optimal III/N flux ratio. We find that optimal growth temperatures for Al0.50Ga0.50N layers with compositional homogeneity related with narrow UV photoluminescence properties are in the low temperature range for growing GaN layers, i.e., 650–680 °C. We propose that lowering Ga adatom diffusion on the surface favors random incorporation of both Ga and Al adatoms on wurtzite crystallographic sites leading to the formation of an homogeneous alloy.
Stress Relaxation in Low-Strain AlInN/GaN Bragg Mirrors
Authors: Moser Pascal , Bläsing Jürgen , Dadgar Armin , Hempel Thomas , Christen Jürgen , Krost Alois
Published: March 2011

The structural behaviour of lattice mismatched AlInN/GaN-based multilayer structures grown on sapphire substrates by metal organic vapour phase epitaxy has been studied in-situ by curvature and real-surface temperature measurement, and ex-situ by atomic force microscope, field-emission secondary electron microscope, Nomarski microscope and various X-ray diffraction techniques. Samples grown with AlInN layers obtaining a slightly lower and a higher indium concentration compared to the lattice matched samples show a strong degradation of the AlInN/GaN double layers. The degradation of the multilayer structures both on a microscopic and on a macroscopic scale is investigated, revealing a much stronger roughening of the AlInN surfaces with higher indium concentration. The roughening is attributed to a Stranski–Krastanov transition from two-dimensional to three-dimensional growth mode.
Effect of Growth Mode on Eu-Incorporation and Luminescence of Eu-Doped GaN Epitaxial Film Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Park Ji-Ho , Wakahara Akihiro , Okada Hiroshi , Sekiguchi Hiroto , Tiwari Ajay , Kim Yong-Tae , Song Jonghan , Lee Jong-Han , Jhin Junggeun
Published: March 2011

The growth mode of europium (Eu)-doped GaN epitaxial films grown on a GaN template by rf plasma-assisted molecular beam epitaxy (PAMBE) was investigated with different III/V ratios under a constant Eu beam equivalent pressure ratio [P
Eu/(P
Eu+P
Ga)]. The reflection high-energy electron diffraction (RHEED) patterns and atomic force microscopy (AFM) images revealed the transition of the growth mode from three-dimensional (3D) to step-flow/two-dimensional (2D) by increasing the III/V ratio. When the films were grown in the 3D growth mode, Eu concentrations estimated by Rutherford backscattering spectrometry/channeling (RBS/channeling) were almost constant, although the III/V ratios varied. However, when the growth mode was transferred from 3D to step-flow/2D, precipitates on the surface abruptly increased while the Eu concentration abruptly decreased, indicating the abrupt degradation of Eu-incorporation in the film. Luminescence sites of Eu3+ were sensitive to the III/V ratio, and Eu atoms have different luminescence sites in both growth modes. Furthermore, luminescence efficiency abruptly increased when the growth mode was transferred from 3D to step-flow/2D.
Influence of a GaN Cap Layer on the Morphology and the Physical Properties of Embedded Self-Organized InN Quantum Dots on GaN(0001) Grown by Metal–Organic Vapour Phase Epitaxy
Authors: Ivaldi Francesco , Meissner Christian , Domagala Jarosław , Kret Sławomir , Pristovsek Markus , Högele Michael , Kneissl Michael
Published: March 2011

Self-organized InN quantum dots were grown on GaN(0001) by metal–organic vapour phase epitaxy. Transmission electron microscopy (TEM) measurements found no wetting layer, i.e., the dots grow directly in Volmer–Weber growth mode. The dots were capped with GaN by three different procedures. Direct overgrowth at the same temperature as the dot formation produced the smoothest surfaces. Cubic and hexagonal GaN was observed in the cap layer, as well as strong indium intermixing. The dot size and volume was reduced during overgrowth. The dots were ∼90% relaxed with many dislocations at the interface from GaN to InN. The photoluminescence of the dots was very weak due to the dislocation.
Effect of Indium Mole Fraction on the Diode Characteristics of ZnO:In/p-Si(111) Heterojunctions
Authors: Lee Jong Hoon , Jang Bo Ra , Lee Ju Young , Kim Hong Seung , Jang Nak Won , Kong Bo Hyun , Cho Hyung Koun , Bae Ki Ryeol , Lee Won Jae , Yun Young
Published: March 2011

We investigated the effect of indium (In) doping (0.6, 1, 5, and 10 at. %) on the diode characteristics of heterostructures consisting of In-doped ZnO films on p-Si(111) substrates. In-doped ZnO films were deposited by pulsed laser deposition with an In-doped ZnO target, and heterojunction diodes were fabricated by photolithography and a lift-off method. The electrical properties of ZnO films were altered by In doping, with the In (10 at. %)-doped ZnO film having the highest electron concentration (3.0×1019 cm-3) and lowest resistivity (1.5×10-2 Ω·cm) of the analyzed ZnO films. In doping also had a strong effect on diode characteristics. In particular, In-doped ZnO/p-Si diodes show a very low reverse current density of approximately 2.8×10-6 A/cm2 (In 10 at. %) at -5 V and a high on–off ratio (In 10 at. %) of about 2.5×10-6 at ±5 V. The heterostructure diodes exhibited typical current–voltage characteristics with turn-on voltages in the range 1.2–2.4 V and series resistances in the range 37–99 Ω. The modified diode characteristics may be related to changes in the ZnO film structure induced by In doping. We also discuss the effect on diode characteristics of In doping of ZnO films.
Grain Boundary Character Distribution on the Surface of Cu(In,Ga)Se2 Thin Film
Authors: Minemoto Takashi , Wakisaka Yoichi , Takakura Hideyuki
Published: March 2011

In general, defects in grain boundaries (GBs) in polycrystalline materials form effective recombination centers. However, this is not the case for polycrystalline Cu(In,Ga)Se2 (CIGS) thin films used in solar cells. It is difficult to determine GB properties by electron backscatter diffraction (EBSD) and electron-beam-induced current (EBIC) measurements because of the surface roughness of as-grown CIGS films. In this study, the CIGS film surface was flattened by ion milling, and then the GB character distribution and spatial distribution of electronically active defects were determined by EBSD and EBIC measurements, respectively. Results suggested that flattening the CIGS film surface enabled the measurements of intrinsic GB properties. Moreover, the results revealed that the GB character distribution on the CIGS film surface hardly changed in the band gap energy range less than 1.28 eV.
Thermoelectric Properties of Single-Crystalline SiC and Dense Sintered SiC for Self-Cooling Devices
Authors: Fukuda Shinji , Kato Tomohisa , Okamoto Yoichi , Nakatsugawa Hiroshi , Kitagawa Hiroyuki , Yamaguchi Satarou
Published: March 2011

We investigated the thermoelectric properties of 4H-SiC substrates and dense sintered SiC, which are expected to be candidate materials for use in self-cooling devices because of their high Seebeck coefficient, low electrical resistivity, and high thermal conductivity. The carrier concentration of 4H-SiC samples doped with nitrogen is in the range of 1016 to 1019 cm-3. The sintered SiC samples of the α-type and β-type contain less than 1000 ppm of cation impurities and have a relative density higher than 98% with respect to single-crystalline SiC. 4H-SiC with a carrier concentration of 1019 cm-3 has the highest power factor of 2.7 ×10-3 W·K-2·m-1 and a high thermal conductivity of 260 W·K-1·m-1 at room temperature. One-dimensional calculations for heat distribution indicate that a Si chip in a self-cooling device, which consists of 4H-SiC with a carrier concentration of 1019 cm-3, could be refrigerated more strongly than one on a copper plate under specific operating conditions.
Ultraviolet Light-Induced Conduction Current in Silicon Nitride Films
Authors: Kobayashi Kiyoteru , Ishikawa Kokichi
Published: March 2011

We have investigated current conduction in silicon nitride films subjected to 4.9 eV ultraviolet (UV) illumination at room temperature. By exposure of silicon nitride single-layer and silicon nitride–silicon dioxide double-layer films to UV illumination, paramagnetic defects were generated in the nitride layers in both films, which were identified to be neutrally charged silicon dangling bonds (K0 centers). UV illumination also induced a substantial increase in conduction current in both films. The increase in current was clearly dependent on the density of the UV-induced paramagnetic defects. We discuss the mechanism of the UV-induced current increase and suggest that the generation of paramagnetic defects is likely responsible for the current increase.
Interfacial Dipole at High-k Dielectric/SiO2 Interface: X-ray Photoelectron Spectroscopy Characteristics
Authors: Zhu Li Qiang , Kita Koji , Nishimura Tomonori , Nagashio Kosuke , Wang Sheng Kai , Toriumi Akira
Published: March 2011

Band bending at both the SiO2 side and the high-k side of the high-k/SiO2 interface has been investigated using X-ray photoelectron spectroscopy (XPS). This band bending is not understandable on the basis of silicate formation or the fixed charges in high-k/SiO2/Si stacks if we do not consider dipole formation at the high-k/SiO2 interface, which in turn confirms the dipole formation at the HfO2/SiO2 interface and at the Y2O3/SiO2 interface. By investigating band bending behavior, the opposite dipole directions have been evaluated between these two interfaces, and the relative difference in dipole magnitude has been demonstrated between the HfO2/SiO2 interface and the Y2O3/SiO2 interface. Although the band bending of SiO2 is underestimated and that of high-k is overestimated, the estimation of relative dipole magnitude is not affected. The relative difference in dipole magnitude is estimated to be ∼0.6 eV between the HfO2/SiO2 interface and the Y2O3/SiO2 interface, which is consistent with relative flatband voltage shifts of ∼0.5 V.
Evolution of Linear Moduli and Remanent State Variables during Polarization Reversal in a Lead Zirconate Titanate Wafer at Various Temperatures
Authors: Kim Yong Soo , Kim Sang-Joo
Published: March 2011

A poled lead zirconate titanate (PZT) wafer is subjected to electric field loading of pulse type whose magnitude is increasing until polarization direction is completely reversed. Then it is subjected to the same type of electric field loading in the opposite direction to return to initial state. During the complete cycle of polarization reversal, electric displacement in thickness direction and in-plane strain are measured in both loaded and unloaded states. The same measurement is made at four different temperatures. From the measured data, permittivity and piezoelectric coefficient are evaluated and fitted as linear functions of remanent polarization and temperature. Reference remanent polarization-reference remanent in-plane strain plots are drawn and switching processes at different temperatures are compared with each other. The present observations will be helpful in constructing constitutive models for nonlinear thermo-electro-mechanical behavior of ferroelectric ceramics.
Vertical Liquid Crystal Orientation on Amorphous Tantalum Pentoxide Surfaces Depending on Anisotropic Dipole–Dipole Interaction via Ion Beam Irradiation
Authors: Lee Jong-Jin , Kim Hyung-Jun , Kang Young-Gu , Kim Young-Hwan , Park Hong-Gyu , Kim Byoung-Yong , Seo Dae-Shik
Published: March 2011

We achieved vertically aligned (VA) liquid crystals (LCs) on amorphous tantalum pentoxide (Ta2O5) alignment films deposited by radio frequency (rf) magnetron sputtering using ion beam (IB) irradiation. By analyzing measurements by X-ray photoelectron spectroscopy (XPS), we confirmed the bond breaking, as detected from the O 1s spectra, which caused an isotropic dipole–dipole interaction between the LC molecules and the Ta2O5 alignment film to uniformly align the vertical LC molecular orientation as a function of IB energy density. Moreover, by examining the electro-optical (EO) characteristics of the Ta2O5 surfaces compared with those of the polyimide (PI) alignment layer, we confirmed that Ta2O5 has a low threshold voltage and a low power consumption when used as an LC alignment layer.
Output Power Enhancement of GaN-Based Light-Emitting Diodes Using Circular-Gear Structure
Authors: Wu Chan-Shou , Liang Tsair-Chun , Kuan Hon , Cheng Wei-Chih
Published: March 2011

In this study, we investigated the characteristics of circular-gear light-emitting diodes (LEDs) and compared them with those of triangular and rectangular LEDs. The emission optical powers of the circular-gear, triangular, and rectangular LEDs at an injection current of 20 mA are 4.6, 5.9, and 7.9 mW, respectively. The total radiant flux from the circular-gear LED was increased by 73 and 34% compared with those of the rectangular LED and triangular LED, respectively. Then, we fabricated a periodic-textured structure on the surface of a circular-gear LED, and it increased the light output power by 32% at an input current of 20 mA. We discovered a leakage current in the triangular sidewall. Therefore, the circular-gear structure demonstrated better extraction efficiency and an improvement in the leakage current. Furthermore, owing to the circular periphery of the circular-gear sidewall, the current was spread evenly. We also achieved a lower driver voltage than that of the triangular LED, which is about 0.68 V at 20 mA.
Refractometric Sensor Based on a Birefringent Silica Waveguide Using a Tapered Cladding
Authors: Son Geun-Sik , Lee Sang-Shin , Kim Woo-Kyung , Lee Han-Young
Published: March 2011

An integrated photonic refractometric sensor was proposed and accomplished based on a birefringent silica rib waveguide incorporating a tapered cladding, which is overlaid with a uniform high-index film. A sensing region is free of the cladding so that the modification of the birefringence incurred by an analyte could be maximized, whereas input/output sections are not subject to it. And a shadow mask was taken advantage of to produce the tapered upper cladding in the light propagation direction. The variation in the refractive index of the analyte was in situ monitored via a polarimetric interference scheme by observing the accumulated phase difference between the transverse-electric (TE) and transverse-magnetic (TM) mode. The fabricated sensor provided a phase difference of 4814 degrees for a variation of 0.015 in the refractive index of the analyte, which is equivalent to an interference count of 13.3 times, and its sensitivity was accordingly 5.2 ×10-6 refractive index unit (RIU) per degree. Finally, the resolution was estimated to be 0.73 ×10-6 RIU for a phase measurement resolution of 0.14°.
Oxidization Process of Fe–Ni Mixed Prussian Blue Analogue Investigated by Valence-Differential Spectroscopy
Authors: Omura Ayako , Kurihara Yutaro , Ishizaki Manabu , Kurihara Masato , Moritomo Yutaka
Published: March 2011

The oxidization process of the Fe–Ni mixed Prussian blue analogue (Fe0.2Ni0.8)[Fe(CN)6]0.67·zH2O was investigated by means of valence-differential spectroscopy. The spectroscopy revealed that the oxidization process selectively starts from the intermediate clusters. With a further increase in the oxidization level, all intermediate clusters are oxidized, and then Fe-rich clusters begin to be oxidized. On the basis of these results, we will discuss the redox process of the Ni–Fe cyano mixed crystal.
Optimization of a Broadband Visible or Near-Infrared Antireflection Coating Design Using Recurrent Circling Search Algorithm
Authors: Liou Yeuh-Yeong , Chen Yan-Ping , Wang Shau-Kuei , Jaing Cheng-Chung , Liu Wen-Long
Published: March 2011

A synthesis method based on a recurrent circling search algorithm is proposed for obtaining a very low loss normal-incidence broadband visible (vis) or near-infrared (NIR) antireflection (AR) coating design. Its design algorithm is quite simple and straight, and a fairly high resultant AR performance can also be achieved. It is shown that the mean residual reflectance of a broadband vis AR coating design in the range of 400–750 nm and a broadband NIR AR coating design in the range of 800–1600 nm, obtained by the recurrent circling search method using a two-material system, can be reduced to below 0.035 and 0.063%, respectively.
Brightness Enhancement with a Fingerprint Chiral Nematic Liquid Crystal
Authors: Lee King-Lien , Wu Jin-Jei , Chen Tien-Jung , Wu Yeong-Shiun , Chen Fu-Chen , Chen Shu-Hsia
Published: March 2011

We demonstrate a brightness enhancement element that can be laminated to a linear polarizer for increasing the optical efficiency of a liquid crystal display device. The device structure is a chiral nematic liquid crystal (CNLC) with a fingerprint texture. For an unpolarized incident light, our experimental results show that the combination of a CNLC film and a conventional linear polarizer can achieve a transmittance of over 50%. The CNLC film increases the optical efficiency of a conventional polarizer by 21.7%. The detailed mechanism of such a CNLC-polarizer system is analyzed.
Numerical Study on Depth Gauging of Surface Breaking Defects Using Laser-Generated Surface Acoustic Waves
Authors: Guan Jianfei
Published: March 2011

Laser-generated surface acoustic waves scattering from surface cracks of various depths and widths have been calculated by the finite element method, where a surface notch is introduced to represent a fatigue crack for the convenience of modeling. The bipolar Rayleigh waves have been captured clearly using this model, as the laser line source close to the surface crack. In addition, the numerical results demonstrate that there exist clear oscillation signals following the reflected Rayleigh waves, the temporal cycles of which are found to be dependent on only notch depth, the arrival time of which is related mainly to the width of the notch. Therefore, a new crack evaluation method based on the temporal characteristics of surface acoustic wave signals has been proposed and discussed in this paper, which is helpful for measuring the depth of surface cracks accurately.
Microwave Magnetic Field Heating of a Cobalt-Based Amorphous Ribbon
Authors: Kato Tomotsugu , Yoshikawa Noboru , Taniguchi Shoji , Terakado Yutaro , Ito Naoki , Ohta Motoki , Yoshizawa Yoshihito
Published: March 2011

The relationship between the magnetic properties of a Co-based amorphous ribbon and its heating by a microwave magnetic field (h
f) was investigated by using a 5.8-GHz single-mode applicator. The amorphous ribbon has a magnetic anisotropy in the ribbon plane. Heating efficiency of h
f which was applied in the direction perpendicular to the casting direction was better than that of it applied along the casting direction. The contribution of magnetic loss to the h
f heating was evaluated quantitatively when the h
f was applied to both directions. The contribution of magnetic loss was more than 80% when the microwave h
f was applied perpendicular to the casting direction, and less than 20% when it was applied parallel to the casting direction.
New Bidirectional T-Shaped Triple-Gate n-Type Polycrystalline Silicon Thin-Film Transistors Formed by Low-Temperature Sequential Lateral Solidification Process to Reduce of Kink Effects
Authors: Choi Sung-Hwan , Han Min-Koo
Published: March 2011

A new bidirectional T-shaped triple-gate device structure, which suppresses the kink effect of sequential lateral solidification (SLS)-processed polycrystalline silicon thin film transistors (poly-Si TFTs), is proposed and fabricated without any additional process. The proposed poly-Si TFTs have a lateral grain growth in channels, similar to TFTs fabricated by SLS or continuous wave (CW) laser crystallization. The whole current flow of the proposed device is mainly affected by the grain boundaries of lateral grain growth. The bidirectional T-shaped triple-gate structure has incorporated a channel located parallel to the lateral grain growth direction, and the another channel located vertically to the lateral grain growth direction. It is verified from experimental and simulation results that the proposed bidirectional T-shaped triple-gate TFT effectively suppresses the kink current of poly-Si TFT with anisotropic mobility in the triple-gate structure. Our experimental results show that the proposed bidirectional T-shaped triple-gate TFT can suppress the kink effect more effectively than the conventional dual-gate TFT, and L-shaped dual-gate TFT and can improve reliability under the high drain bias condition. The proposed device demonstrates that bidirectional operation is possible for integrated circuits compared with the L-shaped dual-gate structure that shows only fixed one-directional behavior. The proposed device exhibits a very low output conductance in the saturation regime, and this result indicates that higher output resistance is obtained in the proposed bidirectional T-shaped triple-gate TFT.
Accelerated Degradation of High Power Light-Emitting Diode Resulted from Inhomogeneous Current Distribution
Authors: Yang Shih Chun , Lin Pang , Fu Han Kuei , Lee An Tse , Chen Tzung Te , Wang Chien Ping , Huang Sheng Bang , Chou Pei Ting
Published: March 2011

The uniformity of current spreading is one of the key points to inspect the reliability and endurance of InGaN-based light-emitting diodes. In this paper, we propose an effective circuit model to analyze the phenomenon of premature turn-on diodes in the active layer. With the aging tests and novel investigation of failure analyses, the simulating results are good agreement with experimental data. It is found that an inhomogeneous distribution of forward current in light-emitting diode chips, as measured by conductive atomic force microscopes, provides the evidence that V-shaped defects and the associated threading dislocations are electrically active. Furthermore, the results of emission microscopy images and transmission electron microscope reviews support the assumption that the threading dislocations associated with V-shaped defects behave as very small shunt resistors connected across p–n junction. This study provides a degradation mechanism to realized one of the failure modes of high power light-emitting diodes.
Synthesis of Highly Tetragonal BaTiO3 Nanopowders Using Acetone as a Solvent by Alkoxide–Hydroxide Route
Authors: Joung Mi-Ri , Seo In-Tae , Kim Jin-Seong , Choi Jae-Hong , Nahm Sahn , Choi Chang-Hak , Sung Tae-Hyun
Published: March 2011

BaTiO3 (BT) nanopowders were synthesized in acetone to remove the TiO2 second phase, which was formed in the specimens synthesized in the 2-methoxyethanol solvent at above 100 °C due to H2O evaporation. No TiO2 second phase was formed in the specimens synthesized in acetone, even at 260 °C, due to the low boiling temperature of acetone which evaporated at above 55 °C and suppressed the H2O evaporation by increasing the vapor pressure in the vessel. However, for the BT nanopowders synthesized at 250 °C for 60 h, TiO2 second phase was formed at a Ba/Ti ratio of ≤1.5 and the BT nanopowders were agglomerated at a ratio of ≥3.0. Homogeneous BT nanopowders were obtained at a ratio of 2.0 and they exhibited a high c/a ratio of 1.0082 with a small size of 95.2 nm. Therefore, these nanopowders can be a good candidate for future multi-layer ceramic capacitor.
Electronic Transport of Single-Wall Carbon Nanotubes with Superconducting Contacts
Authors: Shimizu Maki , Akimoto Hikota , Ishibashi Koji
Published: March 2011

The electrical transport properties of an individual single-wall carbon nanotube (SWCNT) with superconducting contacts have been studied below 1 K. Depending on the contact resistance between the SWCNT and the metallic contact, the samples were categorized in two different regimes in this study. In the strong coupling regime with ignored Coulomb blockade effect, the zero-voltage conductance enhancement due to the superconducting proximity effect was observed as well as the multi-Andreev reflection (MAR) processes. In the weaker coupling regime, a signature of the Kondo effect was observed when the contact metals were in the normal state. When they were in the superconducting state, the MAR processes were observed, which appeared to be related to the Kondo effect.
Growth Mechanism of Nonpolar and Semipolar GaN Layers from Sapphire Sidewalls on Various Maskless Patterned Sapphire Substrates
Authors: Okada Narihito , Oshita Hiroyasu , Kurisu Akihiro , Tadatomo Kazuyuki
Published: March 2011

Nonpolar and semipolar GaN layers can be selectively grown from sapphire sidewalls of maskless patterned sapphire substrates (PSSs) by selective-area growth using a low-temperature (LT) GaN buffer layer. Various PSSs, such as a-PSS for m-GaN, r-PSS for (1122) GaN, c-PSS for m-GaN, and m-PSS for a-GaN, were prepared to investigate the growth mechanisms. It was revealed that the growth windows of various PSSs to achieve nonpolar or semipolar GaN grown from only the sapphire sidewall by changing the growth conditions are different. To determine the cause of selective-area growth in each PSS, GaN nucleation after annealing of the LT-GaN buffer layer was investigated by scanning electron microscopy, atomic force microscopy and X-ray diffraction analysis. Consequently, GaN was predominantly grown on a region with higher quality and better crystallo-ordered c-oriented GaN nucleation. When such nucleation of GaN occurs on the sapphire sidewall, it proceeds to grow selectively from the sapphire sidewall, and nonpolar or semipolar GaN can be obtained using maskless PSS.
Control of Structure and Film Thickness Using Spray Layer-by-Layer Method: Application to Double-Layer Anti-Reflection Film
Authors: Kyung Kyu-Hong , Fujimoto Kouji , Shiratori Seimei
Published: March 2011

The recently developed practice of spraying solutions onto a substrate to fabricate thin films via layer-by layer (LBL) method has been further investigated and extended. We successfully fabricated double-layer anti-reflection (AR) thin films with high- and low-refractive-index layers by the spray layer-by-layer (spray-LBL) method. For the deposition of a high-refractive-index layer, layers of poly(diallyldimethylammonium chloride) (PDDA) and titanium(IV) bis(ammoniumlactato) dihydroxide (TALH) were alternatively assembled. The average thickness of (PDDA/TALH) was determined to be 7 nm and the refractive index wasn=1.76 at 550 nm. Poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) layers were assembled on the high-refractive-index layer for the deposition of the low-refractive-index layer. The average thickness of (PAH/PAA) was determined to be 14 nm and the refractive index wasn=1.48 at 550 nm. This AR thin film showed the maximum transmittance (94.5%) and the minimum reflection (0.5%) at approximately 550 nm in wavelength.
Preparation and Thermoelectric Properties of a Chimney-Ladder (Mn1-xFex)Siγ (γ∼1.7) Solid Solution
Authors: Miyazaki Yuzuru , Saito Yoshitsugu , Hayashi Kei , Yubuta Kunio , Kajitani Tsuyoshi
Published: March 2011

A partially Fe-substituted solid solution of a higher manganese silicide, (Mn1-x
Fe
x
)Siγ, has been prepared by means of arc-melting and a subsequent annealing process. According to the linear relationship between x and lattice parameters, the solid solution can be prepared up to x = 0.35. The compounds consist of two tetragonal subsystems of [Mn1-x
Fe
x
] and [Si], with an irrational c-axis ratio γ= c
Mn/c
Si ∼1.7. With increasing x from 0 to 0.35, equivalent to increase electron carriers, the a-axis and c
Mn-axis lengths gradually decrease, while the c
Si-axis length linearly increases. On the basis of a valence electron counting rule, we expected that a transition from p-type to n-type would occur at x = 0.23 ±0.05. This transition is experimentally confirmed at x ∼0.28; the n-type samples are prepared at 0.28 ≤x ≤0.35. The electrical conductivity at room temperature exhibits symmetrical curves versus x for both p- and n-type samples. However, the solubility limit of Fe appears to suppress any further increase in carrier concentration, resulting in poor electrical conductivity for n-type samples. As a consequence, the maximum dimensionless figure-of-merit Z
T = 0.071 at 644 K is obtained for a sample with x = 0.30.
Ultrawide Band Microwave Absorption Properties of Ultrasound Processed CrO2–Paraffin Wax Composites
Authors: Xi Li , Yang Yikai
Published: March 2011

The microwave absorption properties of ultrasound processed CrO2–paraffin wax composites are investigated in the frequency range of 0.1–18 GHz by the coaxial method. By analysis and comparison between ultrasound processed sample and the unprocessed sample, we discovered that the ultrasound treatment will induce a thin insulating Cr2O3shell over the CrO2rods to form a core/shell structure that performs excellent in microwave absorption. An optimum reflection loss of -50.9 dB was found at 5.2 GHz with a matching thickness of 3.4 mm for 70 wt % CrO2–paraffin wax composite. Moreover, the frequency range of which the reflection loss is less than -20 dB spreads from 4.0 to 8.7 GHz with the corresponding absorption thickness ranges from 2.3 to 4.0 mm. The comparison among our result and other reported ones indicates that, in addition to its common applications, the CrO2after certain process may have potential in microwave absorption. More profoundly, the technique of ultrasound process employed in this report may suggest a new method to induce, according to different needs, crystalline phase transition for a various range of metastable chemicals.
Tetragonal Phase Stabilization Caused by Pr Ions in Ba(Ti0.99Mn0.01)O3 with Mixed Phases
Authors: Lu Da-Yong , Liu Qiao-Li , Ogata Tateaki , Sun Xiu-Yun , Wang Xue-Feng
Published: March 2011

The tetragonal phase stability of (Ba1-x
Pr
x
)(Ti0.99Mn0.01)O3 (x = 0, 0.01, 0.02) ceramics prepared using a cold-pressing ceramic technique was investigated by X-ray diffraction (XRD), electron spin resonance (ESR), scanning electron microscopy (SEM), and dielectric measurements. Tetragonal and hexagonal phases coexist at x = 0, but at x = 0.02, the hexagonal phase disappears and the tetragonal phase is completely stabilized by the appearance of Mn2+. Co-doped Pr ions serve as a tetragonal phase stabilizer for Mn-doped BaTiO3.
Surface Treatment of TiO2 Electrode for Dye-Sensitized Solar Cells Using Low-Temperature and Low-Energy Dielectric Barrier Discharge in Air
Authors: Teramoto Yoshiyuki , Shiono Taku , Ono Ryo , Oda Tetsuji
Published: March 2011

A low-temperature and low-energy plasma surface treatment of nanoporous titanium oxide (TiO2) electrode for dye-sensitized solar cells (DSCs) is proposed using pulsed dielectric barrier discharge (DBD) under room air condition. When the treatment time is 10 min with the discharge voltage at 21.5 kV, the short-circuit current and the energy conversion efficiency are increased by 10% by the DBD treatment. The DBD treatment has advantages over previously studied plasma treatments of the TiO2 electrode of DSCs using a plasma jet or a low-pressure O2 plasma: (i) it requires no gas flow and no vacuum equipment, (ii) it is low-temperature treatment causing no damage on glass and plastic substrates, and (iii) it requires only a very low energy consumption. The DBD treatment is simple and cost-effective, having a strong potential for promoting the development of high-performance DSCs.
Temperature Analysis of Copper Wire in a Plasma Annealing System at Atmospheric Pressure
Authors: Tran Dam N. , Nguyen Vinh P. , Sasaki Toru , Kikuchi Takashi , Harada Nobuhiro
Published: March 2011

In this study, the temperature characteristic of the thin copper wire annealed in atmospheric pressure dielectric barrier discharge (APDBD) system is studied. An equivalent circuit model was used to analyze the wire surface temperature in APDBD. The analysis model showed that the ion bombardment on the wire surface was the main factor that determined wire surface temperature. The average temperature of the thin copper wire in APDBD reactor was calculated as a function of reactor diameter, dielectric material type, applied voltage, ion mass, and gas thermal conductivity. It was, however, shown that applied voltage was the most important parameter to elevate the thin wire temperature up to appropriate annealing temperature. Also, reactor length and carrier speed were crucial for controlling annealing temperature.
Dissociation Channels of c-C4F8 to CF2 Radical in Reactive Plasma
Authors: Hayashi Toshio , Ishikawa Kenji , Sekine Makoto , Hori Masaru , Kono Akihiro , Suu Koukou
Published: March 2011

It has been generally assumed that octafluorocyclobutane (c-C4F8) is mainly decomposed to CF2 via C2F4 in etching process plasma. However, the detailed mechanism for the dissociations is yet ambiguous. In this paper we have calculated the probable dissociation pathways by using ab initio molecular orbital method. The results show that c-C4F8 is dissociated via the first triplet excited state T1(3A2), the fourth triplet excited state T4(32E) and the fourth singlet excited state S4(12E). One of the degenerate excited states of T4 and S4 is constituted by antibonding combination of two π bonding orbital of C2F4. T1 state is constituted by antibonding combination of b1u antibonding σ orbital of C2F4. Therefore, in the case of the dissociation via S4 and T4 excited states c-C4F8 may dissociate to two C2F4, and in the case of the dissociation via T1 excited state c-C4F8 may dissociate to four CF2 radicals. It is also found that C3F5
+ ion observed as the main peak in c-C4F8 process plasma is produced by electron collision with the slightly larger energy than the ionization threshold value. The main dissociation path of C2F4 is a vertical electron attachment. However, it is also found that dissociation pathways via 1B2g, 3B1u, and 3B2g excited states are very important and should not be ignored.
Reduction in Number of Sparks Generated in High-Density Plasma Process by Fixing the Wall Potential
Authors: Sato Michio , Ohtake Hiroto , Samukawa Seiji
Published: March 2011

The effect of the existence of floating potential on spark generation during high-density plasma processes was investigated using an electromagnetic sensor and an on-wafer monitoring sensor. It was observed that the marked change in the potential corresponded to the occurrence of sparks. It was also shown that the connection between the shielding wall and the grounded line significantly reduced the number of generated sparks as compared with that in the case of the existence of a floating shielding wall. Accordingly, it was found that the existence of a floating wall is one of the main reasons for spark generation, and that fixing the wall potential is very effective for preventing spark generation.
Resolution, Line-Edge Roughness, Sensitivity Tradeoff, and Quantum Yield of High Photo Acid Generator Resists for Extreme Ultraviolet Lithography
Authors: Higgins Craig D. , Szmanda Charles R. , Antohe Alin , Denbeaux Greg , Georger Jacque , Brainard Robert L.
Published: March 2011

Ultrahigh loadings of photoacid generators (PAGs) in phenolic extreme ultraviolet (EUV) resists have generated the highest known film quantum yields (FQYs). We evaluate the performance of these resists in terms of resolution, line-edge roughness (LER), and sensitivity and collectively evaluate these three parameters (known as RLS) in terms of K
LUP and Z-Parameter figures of merit. An analytical model describing the kinetics of photodecomposition was developed to explain the relationship between film quantum yield and PAG concentration. Resists were prepared using a broad range of concentrations of iodonium (DTBPI-PFBS), sulfonium (TPS-PFBS), and non-ionic (NDI-PFBS) PAGs. The model fits the experimental data (correlation coefficient R
2 = 0.998, 0.994, and 0.995) and compares the rate at which electrons react with PAGs or recombine with holes. Resists prepared with 15–20 wt % of iodonium nonaflate PAG exhibit both high quantum yields and the best RLS performance as determined using both K
LUP and Z-Parameter methodologies. The improvement in RLS performance correlates with the increase in FQY at higher PAG concentrations.
Development of a Neutral Beam Profile Monitor
Authors: Takahashi Goh , Baek Kwang Yun , Kawasaki Naoki , Komatsubara Takeshi K. , Lim Gei-Youb , Maeda Yosuke , Masuda Takahiko , Morii Hideki , Naito Daichi , Nanjo Hajime , Nomura Tadashi , Sasao Noboru , Sato Kazufumi , Shimogawa Tetsushi , Shiomi Kouji , Tajima Yasuhisa , Watanabe Hiroaki , Yamanaka Taku
Published: March 2011

We developed a novel beam profile monitor for measuring the shape of an intense neutral beam for particle physics. This monitor is based on a detector technology of scintillating fibers, photomultiplier tubes, and sampling ADCs. It has an advantage for its simplicity, reliability, flexibility, and versatility. This monitor was installed in the small-diameter neutral beam for the K

L

0 →π0 νν experiment at J-PARC. We report in this article the development and performance of this monitor.
Study on All-Solid-State Chloride Sensor Based on Tin Oxide/Indium Tin Oxide Glass
Authors: Cheng Jui-Fu , Chou Jung-Chuan , Sun Tai-Ping , Hsiung Shen-Kan , Kao Hui-Ling
Published: March 2011

An all-solid-state chloride electrode based on a tin oxide (SnO2)/indium tin oxide (ITO) glass was developed in this study. The sensing membrane of the electrode was prepared by mixing poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), [4,5-dimethy-l-3,6-bis(dodecyloxy)-1,2-phenylene] bis(mercury chloride) (ETH9033), and tridodecylmethyl ammonium chloride (TDDMACl). The mixed solution was mixed with tetrahydrofuran (THF), and then dropped on the sensing window of SnO2/ITO glass. According to the experimental results, the optimal weight ratio were PVC:DOS:ETH9033:TDDMACl=33:66:2:5. At this optimum weight ratio, the sensitivity was 54 mV/dec while the range of linear concentrations of NaCl solutions was between 10-4 and 1 M. The lower detection limit of the sensor reached 8×10-5 M and the response time was less than 1 s. The selectivity coefficient was consistent with the theory of Hofmeister lipophilicity. The lifetime was over 60 days and the repeatability was over 50 times. Moreover, the chloride ion sensor was successfully applied to detecting chloride ions in rinsing solutions for contact lenses, and the experimental results revealed that the correlation coefficient was 0.99.
Molecular Dynamics Approach of Ion Channeling through Peptide Nanotubes
Authors: Sumiya Norihito , Igami Daiki , Takeda Kyozaburo
Published: March 2011

We theoretically study the possibility of ion channeling through peptide nanotubes (PNTs). After designing the minimal peptide nanorings (PNRs) and their aggregated form (peptide nanotubes, PNTs) computationally, we carry out molecular dynamics (MD) calculations for cation channeling. Irrespective of the cation species (Li+, Na+, K+, or Mg2+), the present MD calculations show that cation channeling through PNTs occurs. Furthermore, inter-ring hydrogen bonds (HBs) survive and maintain the tubular form of PNTs during cation channeling. We introduce mobility such that cation channeling can be evaluated quantitatively. As the ion radius of the cation becomes smaller, the effective relaxation time τ (an order of pico sec) becomes larger. Accordingly, mobilities of 10-2–10-3 cm2/(V·s) are calculated. In contrast, when an anion (F-) passes through the PNTs, the inter-ring HBs are broken, thus inducing the breakdown of the peptide backbone. Consequently, H atoms from the broken HBs surround the channeling anion (F-) and halt its motion. For PNTs, cation channeling is preferred, while anion channeling does not occur.
Low Voltage Electrowetting Optical Deflector
Authors: Chen Hsiu-Hsiang , Fu Chien-Chung
Published: March 2011

This paper demonstrates a low-operating-voltage electrowetting optical deflector (EOD) by reducing the interfacial surface tension between the electrolyte and the surrounding ambience. The goal of this study was to explore various approaches to achieving a low operating voltage. First, two kinds of fluoropolymers (Teflon®AF1601 and Cytop®CTL-809M) were utilized to confirm the thickness effect and wettability. Second, three different dielectric layers (SiO2, Si3N4, and Ta2O5) with the same thickness were tested to confirm the dielectric constant effect. Finally, three different surfactants (sodium dodecyl sulfate (SDS), Triton X100, and Triton X15) were used to confirm the interfacial surface tension effect. In this article, we demonstrate that the contact angle of water can change as much as 70° in a dodecane/water/Cytop®/Ta2O5system (containing 1% SDS) with 11 V; furthermore, switchable apex angles of ∼±20° and deflection of a beam passing through the meniscus of EOD are presented.
Crystal Structure of Ditetradecyldimethylammonium–Au(dmit)2 Salt
Authors: Miura Yasuhiro F. , Sugi Michio , Honda Kazumasa
Published: March 2011

The ditetradecyldimethylammonium–Au(dmit)2 [2C14–Au(dmit)2] salt, a molecular system for constructing the highly conductive Langmuir–Blodgett films, crystallizes in the triclinic space group P1 with two salts in the unit cell. The crystal is composed of alternate layers of Au(dmit)2 anions and ditetradecyldimethylammonium cations with pronounced interdigitation of the alkyl chains. The planar Au(dmit)2 anions are dimerized by face-to-face stacks, further forming two different extended columns along the a-axis with short side-by-side contacts by sulfur atoms. Although the two different columns have sulfur contacts, the intercolumn sulfur–sulfur distances are appreciably longer than those inside the columns, suggesting a one-dimensional nature.
Carbon Nanotubes, Semiconductor Nanowires and Graphene for Thin Film Transistor and Circuit Applications
Authors: Pribat Didier , Cojocaru Costel-Sorin
Published: March 2011

In this paper, we briefly review the use of carbon nanotubes and semiconductor nanowires, which represent a new class of nanomaterials actively studied for thin film transistors and electronics applications. Although these nanomaterials are usually synthesised at moderate to high temperatures, they can be transferred to any kind of substrate after growth, paving the way for the fabrication of flexible displays and large area electronics systems on plastic. Over the past few years, the field has progressed well beyond the realisation of elementary devices, since active matrix displays driven by nanowire thin film transistors have been demonstrated, as well as the fabrication of medium scale integrated circuits based on random arrays of carbon nanotubes. Also, graphene, a new nanomaterial has appeared in the landscape; although it is a zero gap semiconductor, it can still be used to make transistors, provided narrow ribbons or bilayers are used. Graphene is also a serious contender for the replacement of oxide-based transparent conducting films.
Minority Carrier Lifetime Measurements by Photoinduced Carrier Microwave Absorption Method
Authors: Sameshima Toshiyuki , Nagao Tomokazu , Yoshidomi Shinya , Kogure Kazuya , Hasumi Masahiko
Published: March 2011

We propose a measurement system for photoinduced minority carrier absorption of 9.35 GHz microwaves using periodically pulsed light illumination at 620 nm. The ratio of average carrier density when light illumination is ON to that when light illumination is OFF, P, was theoretically analyzed for different light pulse widths. The analysis of P resulted in a formula giving the minority carrier lifetime τeff of silicon under continuous light illumination. τeff for holes was experimentally determined using the formula, and its spatial distribution was obtained to be from 1.0 ×10-3 to 1.28 ×10-3 s for n-type silicon substrates with a thickness of 520 µm coated with 100-nm-thick thermally grown SiO2 layers. We also demonstrated that τeff depended on the means of light illumination for a defective sample. Two different τeff values were obtained, 7 ×10-5 and 1.73 ×10-4 s, in the cases of light illumination to the top surface and rear surface, respectively, when the SiO2 layer was etched up to 2 nm at the top surface.
Thickness Dependence of Electrical Properties for High-k SrTa2O6 Thin Films Fabricated by Sol–Gel Method
Authors: Lu Li , Nishida Takashi , Echizen Masahiro , Uchiyama Kiyoshi , Uraoka Yukiharu
Published: March 2011

The interface between SrTa2O6 thin films and Pt electrodes, and defects in SrTa2O6 thin films were investigated through the study of thickness dependence. High dielectric constant of about 109 and low leakage current density of about 10-8 A/cm2 were obtained for the 150 nm SrTa2O6 thin film. These values are comparable with metal organic chemical vapor deposition (MOCVD) derived SrTa2O6 thin films. Space-charge limited current mechanism predominated in the 113 and 150 nm SrTa2O6 thin films. Higher Ti concentration was found in the layer close to the bottom interface of 113 and 150 nm SrTa2O6 thin films. From these results, we suggest a two-layered model for these two thin films. The anomalous dispersion of loss tangent and Poole–Frenkel predominated leakage current was found in 75 nm SrTa2O6 thin film. This may be induced by higher Ti concentration not only in the layer close to the bottom interface, but also in the whole thin film.
Extraction Technique of Trap Densities in Thin Films and at Insulator Interfaces of Thin-Film Transistors
Authors: Kimura Mutsumi
Published: March 2011

We have developed an extraction technique of trap densities in thin films and at insulator interfaces of thin-film transistors (TFTs). These trap densities can be extracted and separated from capacitance–voltage (C–V) and current–voltage (I–V) characteristics by numerically calculating Q = C
V, Poisson equation, carrier density equations, and Gauss's law. The trap densities in the upper and lower halves of the band gap are extracted from n- and p-type TFTs, respectively. The outstanding advantages are intuitive understandability and a simple algorithm. Actual trap densities are extracted for high-temperature polycrystalline silicon (poly-Si) TFTs.