bluuebunny/crossref_metadata_2025 huggingface dataset:
Basic Study on Acoustic Communication Using Direct-Sequence Spread Spectrum for Underwater Acoustic Positioning
Authors: Watanabe Yoshitaka , Ochi Hiroshi , Shimura Takuya
Published: July 2005

Supershort baseline (SSBL) underwater acoustic positioning is commonly utilized in estimating the positions of transponders, observation devices and submersibles. The new SSBL system in which a sea surface station and a sea bottom station communicate using the spectrum spread (SS) technique was studied with simulation. An M-sequence was adopted as pseudonoise (PN) code and PN code length was set for 15, 31, 63 and 127. Random noise and Doppler shift were considered as distortions. It became clear that the system becomes useless due to Doppler shift exponentially, and that under the condition with a large Doppler shift, the system is not available if the PN code length is longer than 31, that if the relative velocity between the transmitter and the receiver is less than 5 m/s, the system has the highest performance with a PN code length of 31 and that in case of a PN code length of 15 the system is stable under the same condition.
Estimation of Correlation of Acoustic Reciprocal Transmissions Using Central Equatorial Pacific Tomography Data
Authors: Wang Yong , Hachiya Hiroyuki , Nakamura Toshiaki , Fujimori Hidetoshi
Published: July 2005

Ocean acoustic tomography (OAT) is a powerful approach for observation of mesoscale ocean fluctuations. A precise estimation of travel time is essential for measuring ocean current using OAT. Generally, a reciprocal propagation sound waveforms that are transmitted at the same time are similar mutually, and it is considered that their correlation is high. However, we found that reciprocal sound waveforms sometimes become different in the continuous estimation of travel time difference. In this paper, we present the estimation results of the correlation between the reciprocal transmissions. The correlation coefficient of signals depends on the signal-to-noise (SN) ratio of the signals. We propose an estimation method for the correlation of the reciprocal signals without the effect of SN ratio. Using the method, we estimate the variation of the correlation of reciprocal propagated sound transmissions for a distance of 500 km. A low correlation between the reciprocal propagated sound waveforms occurs at a certain rate. These phenomena seem to occur at a short periodical time.
Distribution of Hydrate Saturation Ratios in Artificial Methane Hydrate Sediments Measured by High-Speed X-Ray Computerized Tomography
Authors: Sato Mitsutaka , Takeya Satoshi , Nagao Jiro , Jin Shigeki , Kamata Yasushi , Minagawa Hideki , Ebinuma Takao , Narita Hideo
Published: July 2005

A high-speed X-ray computerized tomography (CT) system was developed for measuring the texture of methane hydrate sediment. The system enabled time dependent nondestructive observations of the hydrate sediment in a volume of φ100×100 mm3 within 40 s. The spatial variation of mass density and the volume fraction of an artificial methane hydrate sediment that is either ice or hydrate, hereafter referred to as the hydrate saturation ratio within methane hydrate sediments, were measured using the X-ray CT system. The three-dimensional (3D) distribution change of density and hydrate saturation caused by the hydrate dissociation were also visualized on the basis of the measured gray scale values of the CT images taken before and after their dissociation. The technique allows us observations of the dissociation process of methane hydrate sediment under experimental conditions which are the same as conditions in the natural environment, and will allow the simulation of methane gas production from wells in both oceanic and permafrost areas.
Azimuth Dependence of Solar Radiation on Inclined Surfaces III
Authors: Shibata Noboru
Published: July 2005

In general, the daily variation pattern of global solar radiation on an inclined surface is estimated by assuming the symmetrical daily variation of global solar radiation. The author carried out an experiment to examine the azimuth dependence of solar radiation on an inclined surface. In the experiment, the amount of solar radiation was found to be greater on a westward-facing surface than on an eastward-facing surface throughout the year.
Morphology Control of Oxadiazole Compounds by Introduction of Amine Moieties
Authors: Mochizuki Hiroyuki , Hasui Takahiro , Ikeda Tomiki
Published: July 2005

Three oxadiazole derivatives with an amine and an alkyl tail were designed and synthesized as novel photo- and electro-active materials: 2-(4'-propylbiphenyl-4-yl)-5-(4-N,N-dimethylaminophenyl-4-yl)-1,3,4,-oxadiazole (3-OXD-Me), 2-(4'-heptybiphenyl-4-yl)-5-(4-N,N-dimethylaminophenyl-4-yl)-1,3,4,-oxadiazole (7-OXD-Me), 2-(4'-heptylbiphenyl-4-yl)-5-(4-N,N-diphenylaminophenyl)-1,3,4,-oxadiazole (7-OXD-Ph). It was found that the length of an alkyl tail and the structure of an amine strongly affect the phase structure of the oxadiazole derivatives; 3-OXD-Me showed a crystalline phase, 7-OXD-Me showed a liquid-crystalline (LC; nematic) phase and 7-OXD-Ph exhibited a glassy amorphous state. All the compounds emitted strong blue fluorescence: the maximum wavelengths of emission were 420–436 nm with high quantum yields (0.81–0.91). Furthermore, polarized photoluminescence was observed in 7-OXD-Me in a nematic phase, and the order parameter estimated by the polarized emission was 0.18. These compounds, therefore, are potential multifunctional materials for photo- and electro-active devices.
Structural Analysis of Bis(1,2-benzoquinonedioximato)platinum(II) Polymorphs Formed Epitaxially on Alkali Halides
Authors: Yoshida Kaname , Yaji Toyonari , Koshino Masanori , Isoda Seiji
Published: July 2005

We analyzed the crystal structures of bis(1,2-benzoquinonedioximato)platinum(II), (Pt(bqd)2), thin films fabricated by vacuum deposition on the (001) surfaces of NaCl, KCl, KBr and KI substrates at room temperature. Pt(bqd)2 thin films exhibited some polymorphs. These structures and crystallographic orientations were studied by transmission electron microscopy (TEM). On NaCl, KCl and KBr, Pt(bqd)2 grows in the β-form; unit cell dimensions are a=2.57 nm, b=0.66 nm and c=0.37 nm. The β-polymorph transforms into the ordinary orthorhombic α-form by heating at different rates depending on the substrate. The instability of the β-form was influenced by lattice-matching between the β-form and substrate used. On KI, Pt(bqd)2 grows as the polymorphic tetragonal form (γ-form: a=1.42 nm and c=0.656 nm). From the result of high-resolution TEM observations, many defects or domain boundaries in this film were observed, which are related to the structural change during the growth.
Characteristic Features of Molecular Structure and Packing of Organopolysilanes with Asymmetric Side Chains
Authors: Furukawa Shoji , Ohta Hidetaka
Published: July 2005

The molecular structure and packing of poly(methyl ethyl silane), [(CH3)Si(C2H5)]
n
, and poly(methyl n-propyl silane), [(CH3)Si(C3H7)]
n
, have been examined by the X-ray diffraction method. For poly(methyl ethyl silane), several configurations are possible for the arrangement of the C2H5 group, whereas the C3H7 groups stretch along one equivalent direction for poly(methyl n-propyl silane). In both cases, the molecular structure and packing are mostly determined by the intramolecular steric hindrance and van der Waals interaction between side chains, which is the same as that of polysilanes with symmetric side chains.
Preparation of Carbon Films by Hot-Filament-Assisted Sputtering for Field Emission Cathode
Authors: Abe Katsuya , Maezawa Yosuke , Hayashibe Rinpei , Yamakami Tomohiko , Nakao Masato , Kamimura Kiichi
Published: July 2005

Carbon thin films on a silicon substrate were prepared by DC magnetron sputtering method with a tungsten hot filament. In order to investigate the effects of the hot filament on film properties, the carbon thin films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and electron emission measurements. The tungsten atoms were evaporated from the hot filament and incorporated in the carbon film. The field emission measurement showed that the incorporation of tungsten was effective in reducing the turn-on voltage. The value of the turn-on voltage was 3.0 V/µm for the sample prepared with a tungsten filament heated at the temperature of 2000°C. The intentional insertion of a tungsten layer between the carbon film and the substrate was effective in obtaining a carbon film with a low turn-on voltage for the field emission.
Preparation of Carbazole Polymer Thin Films Chemically Bound to Substrate Surface by Physical Vapor Deposition Combined with Self-Assembled Monolayer
Authors: Katsuki Kiyoi , Bekku Hiroshi , Kawakami Akira , Locklin Jason , Patton Derek , Tanaka Kuniaki , Advincula Rigoberto , Usui Hiroaki
Published: July 2005

Vinyl polymer thin films having carbazole units were prepared by a new method combining physical vapor deposition and self-assembled monolayer (SAM) techniques. 3-(N-carbazolyl)propyl acrylate monomer was evaporated onto a gold substrate that had a VAZO 56 (DuPont) initiator attached as a SAM. The VAZO initiator was activated by irradiating ultraviolet light after depositing the monomer. Although the polymerization reaction can proceed even without the surface initiator, the SAM was effective in improving the surface smoothness, thermal stability, and film-substrate adhesion as a consequence of the formation of covalent chemical bonds between the film and the substrate. Thermal activation of the initiator was examined for the deposition polymerization of 9-H-carbazole-9-ethylmethacryrate. Substrate heating during the evaporation was not effective for accumulating thin films. On the other hand, performing postdeposition annealing on the film after deposition at room temperature resulted in the formation of a polymer thin film chemically bound to the substrate.
Interface Structures between Polymer Substrates and Fluorescent Dye-Doped Polymer Layers Formed by Vaporization in Vacuum
Authors: Mizokuro Toshiko , Mochizuki Hiroyuki , Mo Xiaoliang , Tanigaki Nobutaka , Hiraga Takashi
Published: July 2005

We have developed a simple vacuum process, termed the “vapor transportation method,” to dope low-molecular-weight molecules into polymer molds by vaporization of the molecules in a vacuum. In this study, we fabricated interfacial structures with a concentration gradient, between polystyrene (PS) substrates and dye-doped PS regions. PS was used to prepare cylindrical molds and molds surrounded by quartz cells. Fluorescent dyes, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)4H-pyran (DCM), were doped into the cylindrical molds and into the molds surrounded by quartz cells from 110 to 160°C. To confirm the DCM doping of PS, UV-vis and fluorescent spectra were measured. To confirm the interfacial structures of the doped dyes, the dye-doped PS molds were examined by optical microscopy, transmission Fourier transform infrared (FT-IR) microscopy, and microspectrophotometry. The intensity profiles of DCM fluorescence from the DCM-doped molds surrounded by quartz cells by microspectrophotometry, show that, as doping temperature increases, interfacial structures had an increase in concentration gradient, in agreement with the results from optical microscopy and transmission FT-IR microscopy.
Interface Control between Pentacene Film and Si(001) by Chemisorbed Buffer Monolayer
Authors: Wakatsuchi Masayuki , Kato Hiroyuki S. , Yamada Taro , Kawai Maki
Published: July 2005

Pentacene films were fabricated by molecular beam deposition on two silicon (Si) substrates. One of the substrates was Si(001) with a chemisorbed 1,4-cyclohexadiene surfactant buffer and the other was Si(001) with a SiO2 oxide layer. The 1,4-cyclohexadiene buffered surface was characterized by high-resolution electron energy loss spectroscopy (HREELS). 1,4-cyclohexadiene molecules were adsorbed on the clean Si(001) (2×1) substrate forming Si-C covalent bonds at 300 K and a well-ordered (2×1) structure was preserved even after adsorption of the molecules. The chemisorbed 1,4-cyclohexadiene layer is thermally stable at approximately room temperature. The morphology and crystallinity of the pentacene films were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis, respectively. The AFM images showed larger grains exceeding 1 µm for the pentacene film deposited on the Si(001) substrate with 1,4-cyclohexadiene buffer, whereas the small grains of 200 nm on average were observed for the film on Si(001) with SiO2 under the same deposition rate and substrate temperature.
Intrinsic Electronic Transport through Alkanedithiol Self-Assembled Monolayer
Authors: Lee Takhee , Wang Wenyong , Reed Mark A.
Published: July 2005

Electronic transport through an alkanedithiol self-assembled monolayer (SAM) is investigated using a nanometer scale device. Temperature-independent current-voltage characteristics are observed, indicating tunneling is the main conduction mechanism. The measured current-voltage characteristics are analyzed with a metal-insulator-metal tunneling model. The inelastic electron tunneling spectroscopy (IETS) study on the octanedithiol device clearly shows the vibrational signatures of molecules. The pronounced IETS peaks correspond to vibrational modes perpendicular to the junction interface, which include the stretching modes of Au-S (at 33 mV) and C-C (at 133 mV), and wagging mode of CH2 (at 158 mV). Intrinsic linewidths are determined as 1.69 (upper limit), 3.73±0.98, and 13.5±2.4 meV for Au-S, C-C streching modes, and CH2 wagging mode, respectively. The observed peak intensities and peak widths are in good agreement with theoretical predictions.
Electronic Transport through Aromatic Thiol Monolayer Assembled in the Nano Via-Hole Electrode
Authors: Lee Changjin , Kang Yongku , Seo Kyungja , Shin Youn Mi , Kim Jae-Ho , Choi Sung-wook , Kim Jinhee , Soh Hei Mi , Lee Hoyoung , Kim Dohyun , Song Chung Kun
Published: July 2005

Nano via-hole devices were fabricated by the e-beam patterning of holes on a SiNxinsulating layer and used as electronic test platforms for the characterization of the electrical properties of molecules. Conditions of RIE were controlled to produce bowl-shaped nano size via-holes such that the diameter of the bottom opening was less than approximately 50 nm when the top diameter was 100 nm. After forming a self-assembled monolayer on the bottom electrode inside the via-hole, a top metal electrode was deposited to produce an MIM type device. When dodecanethiol was used, the fabricated device showed a current density of 1.3×103A/cm2at 1.0 V, which was in the same order of magnitude as the previously reported value. When aromatic thiols were used, most devices showed diode-like behaviors with a higher current density than the dodecanethiol, and a few showed NDR-like characteristics.
Polarization Gratings in Photocrosslinkable Polymer Liquid Crystals Prepared Using Two-Step Ultraviolet Exposure
Authors: Emoto Akira , Ono Hiroshi , Kawatsuki Nobuhiro , Uchida Emi
Published: July 2005

We produced polarization gratings in photocrosslinkable polymer liquid crystal using a two-step ultraviolet exposure method, which causes the molecular reorientation to be modulated periodically in the orthogonal direction corresponding to the direction of linearly polarized ultraviolet light. A theoretical description of the fabricated polarization gratings is given by Jones matrix calculations. The calculated diffraction efficiency using a rectangular function to represent the shape of the grating profile differed from the experimental results in higher-order diffraction. We then applied a trapezoidal function to the same calculation. The difference between the experimental results and the calculated results was explained by considering the effect of scattering on the measured values. Furthermore, from using the trapezoidal function, the area of the molecular alignment transition was estimated to be approximately 3 µm.
Effect of Ultraviolet Light Irradiation on Structure and Electrochemical Properties of Iron Surface
Authors: Nanjo Hiroshi , Deng Huihua , Oconer Irmin S. , Ishikawa Ikuo , Suzuki Toshishige M.
Published: July 2005

The effect of ultraviolet light (UV) irradiation (254 nm, 0.8 mW/cm2) on air-formed oxide films and passivated films on iron was investigated by electrochemical methods and scanning tunneling microscopy (STM), in particular with respect to surface micro/nanostructures and the surface protective property. An as-deposited film appeared uniformly flat after UV irradiation for 2–4 h, which is associated with a decrease in current density. UV irradiation for 1–4 h assisted N-dodecylhydroxamic acid (DHA) molecules to strongly bond to the air-formed oxide film. UV irradiation for 1 h led to the formation of a flat terrace of atomic resolution on a surface passivated at 800 mV for 15 min. However, it was difficult to observe a terrace wider than 3 nm on the passive film irradiated for 4 h.
Study on Relationship between Electroluminescence Properties and Molecular Weight Distribution of Poly(9,9'-dioctylfluorene) Using Photoluminescence
Authors: Fujishima Daisuke , Mori Tatsuo , Mizutani Teruyoshi , Yamamoto Takakazu , Kitamura Naoyuki
Published: July 2005

Polyfluorenes (PFs) have attracted attention as conjugated polymer materials that can be promising as polymer-based emissive displays. PFs have a blue emission, a high photoluminescence (PL) quantum yield and thermal and chemical stabilities. The highly efficient blue emission from the PF structure is attractive for a display consisting of polymer light-emitting diodes (LEDs). We synthesized 10 kinds of poly(9,9'-dioctylfluorene) (PDOF) of different molecular weight distributions and studied their PL and electroluminescence properties. Moreover, we also studied their fluorescent lifetime. As a result, we found that optimum molecular weight of PF-based LEDs is about 105. From this result, it is thought that it is important to control the molecular weight of PDOF for PF-based LEDs.
Analysis for Electron Concentrations in n-Diamond/III–Nitride Heterostructure and Phosphorus δ-Doped Structure in Diamond
Authors: Koide Yasuo
Published: July 2005

In order to explore the possibility of controlling electron concentrations in phosphorus (P)-doped n-diamond, the electron distributions and energy band diagrams of n-diamond/cBN and n-diamond/AlN heterostructures and a P δ-doped structure are calculated by self-consistently solving Poisson and Schrödinger equations. Although the electron concentration is on the order of 1011 cm-3 at room temperature for uniformly-doped n-diamond with a donor concentration of 5×1018 cm-3 and a compensation ratio of 1%, a modulation doping technique provides an activation efficiency larger than 15% in both the heterostructures and an electron concentration larger than 1017 cm-3 at room temperature. On the other hand, a δ-doping technique does not increase activation efficiency since the electrons have a large Debye-tailing length and the compensation significantly reduces the electron concentration activated thermally.
Energy Release and It's Mechanism in Metal/Insulator/Metal Structures with Langmuire-Blodgett Films
Authors: Hino Koji , Kushida Masahito , Hino Taro
Published: July 2005

Energy release and its mechanism in metal/insulator/metal (MIM) structures are reported. Langmuire-Blodgett (LB) films of polyimide (PI), 2-pentadecyl-7,7',8,8'-tetracyanoquinodimethane (C12-TCNQ) and a mixture of C12-TCNQ and Bis(ethyleneditio)tetrathiafulvalene (BEDT-TTF) are used. The thickness of the LB films is approximately 100 Å, in other words very thin. In a previous study, energy was observed to be released from the structure of Al/PI/Au for approximately three years. The energy release from the structures of Al/C12-TCNQ/Al, Al/C12-TCNQ and BEDT-TTF/Au is the same as that from the structure of Al/PI/Au. One factor in the mechanism of energy release is considered to be the difference in work function between Al and Au, or the polarization of C12-TCNQ LB films. An other factor considered is the diffusion of electrons in LB films. The difference in work function is the cause of energy release in an Al/PI/Au structure, the polarization in an Al/C12-TCNQ/Al structure, and both in an Al/mixture/Au structure. A decrease in the temperature of the MIM structure was ascertained with the energy release. That is, thermal energy was considered to be transduced to electrical energy in the MIM structure. Furthermore, it is shown that the force of electron diffusion is stronger than the binding force between the positive and negative charges. It is clarified that neither a chemical reaction nor contact potential is the cause of energy release.
Time Dependence of Optical Properties of Vacuum-Evaporated Poly(di-methyl silane) Thin Films
Authors: Ohta Hidetaka , Takamoto Tomoki , Yasuda Takashi , Furukawa Shoji
Published: July 2005

In this paper, we show an interesting change in the optical properties of poly(di-methyl silane) thin films prepared by vacuum evaporation. We have found that the strength of the optical absorption peak at ∼300 nm is changed depending on the substrate temperature during the deposition. The strength of the optical absorption peak at ∼300 nm decreases with increasing time when the thin film is prepared at a high substrate temperature. On the other hand, the peak does not appear when the thin film is prepared at a low substrate temperature. However, in the latter case, the optical absorption peak appears at ∼300 nm with time. Moreover, the change of the optical absorption strength of the specimen held in a vacuum desiccator is different from that of the specimen held in atmosphere. It is considered that the decrease of the optical absorption strength at ∼300 nm is due to the decrease of the molecular weight of polysilanes, and the increase is due to the structural relaxation of polysilane chains.
Current-Voltage Characteristics of Pentacene Films: Effect of UV/Ozone Treatment on Au Electrodes
Authors: Suzue Yuuma , Manaka Takaaki , Iwamoto Mitsumasa
Published: July 2005

In relation to a metal/organic interface, the effect of an ozone treatment on the electrical properties of a metal surface was investigated by surface potential and current-voltage (I-V) measurements. With a UV/ozone treatment on a gold (Au) surface, the surface potential formed across a vacuum-evaporated pentacene film (100 nm thickness) on a Au substrate varied from -200 mV to 350 mV. The variation in the surface potential is possibly a result of a change in the apparent work function of the Au surface. The results obtained by photoemission spectroscopy support the deepening of the Fermi level of the Au surface with the UV/ozone treatment. The I-V characteristics of a [Au (top)/pentacene/Au (bottom)] structure showed that the rectifying property reverses with the UV/ozone treatment of the bottom Au electrode. These results are discussed based on the potential barrier at the Au/pentacene interface due to the space charge.
Optical Properties of 4-Octyl-4'-Cyanobiphenyl Liquid-Crystalline Free-Standing Films
Authors: Matsuhashi Nobuaki , Okumoto Yoshitaka , Kimura Munehiro , Akahane Tadashi
Published: July 2005

The optical properties of 4-octyl-4'-cyanobiphenyl (8CB) liquid-crystalline free-standing films (FSFs) were studied. The theoretical characteristics of the smectic A (SmA) phase FSF were determined using the analytical method. The incidence angle dependence of the phase difference for 100 8CB-FSFs was measured by transmission ellipsometry using a photoelastic modulator (PEM). The number of layers could clearly be separated from 2 to 9 layers. As a result of the least-squares fitting in all the films, the same anisotropies of the refractive indices n
||
=1.665 and n
⊥=1.523 were obtained, and the layer spacing became approximately 2.3 nm.
Determination of Director Profile of Twisted Nematic Liquid Crystal Cell with Tilted Surface Alignment by Renormalized Transmission Ellipsometry
Authors: Tanaka Norihiko , Kimura Munehiro , Akahane Tadashi
Published: July 2005

Applying renormalized transmission ellipsometry (RTE), the evaluation of a director profile in the case of a twisted nematic cell with a relatively high pretilt angle was performed. To determine the director profile, we proposed a novel technique for determining four cell parameters, namely, the cell gap d, the pretilt angle θp, the twist angle of the director alignment φt, and the angle between the axis of the polarizer and the entrance liquid crystal director φi. To date, several methods of measuring the average tilt angle of a twisted nematic (TN) cell have been proposed, but our method of simultaneously determining the four cell parameters is considered to be quite effective in the evaluation of liquid crystal displays.
Phosphorescence Decay Process of Ir(ppy)3 : Temperature Dependence of Decay Time
Authors: Tsuboi Taiju , Aljaroudi Nadeer
Published: July 2005

Theoretical calculation has been undertaken on the photoluminescence (PL) lifetime of fac tris(2-phenylpyridine) iridium (Ir(ppy)3) doped in polymethyl methacrylate (PMMA) and 4,4'-N,N'-dicarbazole-biphenyl (CBP), and its temperature dependence at 0–300 K. The emitting triplet state consists of three zero-field splitting substates. Taking into account one-phonon non-radiative transitions among these substates, the rate equations for the populations of these substates are solved numerically and three PL lifetimes are derived. The long PL lifetime increases considerably with decreasing temperature from 300 to 0 K, while the two short lifetimes increase very little. A good agreement has been obtained for the temperature dependence between the calculated long lifetime and the observed one for Ir(ppy)3 in PMMA and CBP. Temperature dependence of PL intensity has been also calculated under the three-substate model. The result is consistent with the observed temperature-independence of intensity.
Correlation between Inner Electric Field and Photocurrent of Zn-Phthalocyanine Schottky-Barrier Cells
Authors: Hiromitsu Ichiro , Kinugawa Genki
Published: July 2005

An electroabsorption (EA) study is carried out at an electric-field modulation frequency ωm/(2π) of 1 Hz for two types of typical organic Schottky-barrier cell, namely, Au/Zn-phthalocyanine (ZnPc)/Al and Au/ZnPc/In/Al, in order to elucidate the role of the inner electric field in photocurrent (I
photo) generation. From the bias dependence of the 1F- and 2F-EA intensities measured at the frequencies of ωm and 2ωm, respectively, it is shown that the inner electric field E
0 as well as the modulation electric field E
m is quenched in the ZnPc layer with a forward bias larger than ∼1 V. For Au/ZnPc/Al, a good correlation is observed between E
0 and I
photo, which indicates that I
photo is generated by E
0. For Au/ZnPc/In/Al, on the other hand, no correlation is observed between E
0 and I
photo. An interpretation of the latter is that I
photo is caused by an increase in charge-injection probability at the ZnPc/In interface as a result of the trapping of photogenerated charges in the interface region. For both systems, the depletion layer is detected by capacitance-voltage measurement at 0.2 Hz.
Use of Trapezoid Pulse Voltage in Study of Transient Response of Organic Light-Emitting Diodes
Authors: Wei Bin , Furukawa Kenji , Ichikawa Musubu , Koyama Toshiki , Taniguchi Yoshio
Published: July 2005

We investigated the transient electroluminescence (EL) and transient current (TC) of organic light-emitting diodes under a trapezoid electric pulse at a repetition rate of 1 kHz by changing the transient time of the pulse from ∼ ns to ∼ µs. Our data shows that the change in the transient time of the pulse not only affects the delay time and rise time of transient EL, but also changes the temporal evolution of TC. In addition, we studied the charge accumulation in the interfacial layer of organic films with different heterostructures, particularly the EL spike from a pulsed device with 1,4-Bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene as a light-emitting layer at switch-off. The dynamic behavior of TC was further analyzed by computational approaches.
Preparations and Evaluations of C60 Thin Films for Organic Field-Effect Transistors
Authors: Iwata Nobuyuki , Kinjo Akane , Okuyama Hiroki , Yamamoto Hiroshi
Published: July 2005

Fullerene C60 thin films were grown on a mica top-gate-type substrate and on a CaF2∥Si(111) bottom-gate-type substrate with the aim of fabricating high-performance organic field-effect transistors (FETs). It is expected that single-crystal C60 thin films with a large grain have a high mobility as n-type materials because of the lack of a potential barrier at the grain boundaries for conducting electrons. On both substrates, oriented C60 films were obtained. In particular, on the mica substrate, the highly oriented films had grains larger than 1×1 µm and a two-dimensionally flat surface with 60 and 120 deg facets. The step height was 0.8 nm, consistent with that of an h
c
p bulk structure. The highly oriented films were grown at the substrate temperature at which the C60 molecules at the tips of spiral grains re-evaporated. The obtained single-crystal C60 thin films with large grains are promising for high-performance organic FETs.
Sprayed Organic Electrophosphorescent Devices with Small Organic Molecules
Authors: Echigo Tadahiro , Naka Shigeki , Okada Hiroyuki , Onnagawa Hiroyoshi
Published: July 2005

Sprayed organic electrophosphorescent devices with small organic molecules have been investigated. By heating the entire spray system, i.e., a spray gun and a glass substrate, a high device performance without leakage current has been realized. Using the green electrophosphorescent molecule fac tris(2-phenyl-pyridine)iridium Ir(ppy)3 as a doped material, device performance with a maximum luminance of 18,400 cd/m2, a maximum luminous power efficiency of 20.9 lm/W, and a maximum quantum efficiency of 16.9% could be obtained. By mixing blue and red electrophosphorescent molecules of iridium(III) bis(2-(4,6-difluorophenyl) pyridinato-N,C2') picolinate (FIrpic) and iridium(III) bis(2-(2'-benzothienyl) pyridinato-N,C3') (acetylacetonate) (Btp2Ir(acac)), white emission with Commission Internationale d'Eclairage chromaticity coordinates of (0.33, 0.34) is also achieved.
Dye Doping of Poly( p-phenylenevinylene)s by Vapor Transportation for Photovoltaic Application
Authors: Tanigaki Nobutaka , Mochizuki Hiroyuki , Mo Xiaoliang , Mizokuro Toshiko , Hiraga Takashi , Taima Tetsuya , Yase Kiyoshi
Published: July 2005

Poly( p-phenylenevinylene) (PPV) was doped with a perylene dye using the vapor transportation method under vacuum. The used dye was N,N'-bis(2,6-dimethylphenyl)-3,4,9,10-perylenetetracarboxylic diimide (DMP-PTCDI). The concentration of the dye in PPV was estimated by infrared (IR) spectroscopy as a function of doping conditions, such as temperature and time. The concentration was estimated to be typically 1–5 wt%. The dye-doped PPV was used for a photovoltaic device, which was a simple Schottky-type device with an aluminum electrode. The device using dye-doped PPV had a photocurrent response at a wavelength longer than that of a nondoped PPV device, which was caused from the absorption of the dye.
Field Emission from Carbon-Nanotube-Dispersed Conducting Polymer Thin Film and Its Application to Photovoltaic Devices
Authors: Itoh Eiji , Suzuki Issei , Miyairi Keiichi
Published: July 2005

We investigated the field emission properties of single-wall carbon-nanotube (CNT)-dispersed conducting polymer thin film prepared by spin coating and electrophoresis. A p-type conducting polymer such as poly(3-octylthiophene) (P3OT) or poly(2-methoxy, 5-(2'-ethyl-hexyloxy)-p-phenylenevinylene) (MEHPPV) doped with CNTs is an excellent field emitter. The field emission was successfully reproduced by an electrophoretic technique and the turn-on fields of CNT-dispersed P3OT films were 4–6 V/µm. Moreover, the field emission properties were markedly improved by post-field treatment on a thermally oxidized Si wafer, and a low turn-on field of 1.6 V/µm was successfully obtained probably due to the improved vertical orientation of CNTs. New devices having both photovoltaic and field emission properties were also demonstrated. We also investigated the photovoltaic properties of the devices composed of ITO/TiO2/CNT-MEHPPV composite/Au structure. The open-circuit voltage V
OC and short-circuit current density I
SC of the device without CNTs were 0.6 V and 0.4 mA/cm2, respectively, under 100 mW/cm2 white light illumination. Although V
OC and I
SC were not considerably improved, a marked increase in current density, more than a factor of 1000 at -1 V, was obtained for the device with a CNT-dispersed MEH-PPV layer. Such an increase in current density was obtained only in negative biasing on the Au top electrode and we attributed this increase to the field emission of electrons from CNTs into the TiO2 layer.
The Influence of Interfacial Charge Exchange Phenomena at the Insulator-Semiconductor Interface on the Electrical Properties of Poly(3-hexylthiophene) Based Field Effect Transistors
Authors: Itoh E. , Torres I. , Taylor D. M.
Published: July 2005

Polymer field effect transistors (FET) based on regio-regular poly(3-hexylthiophene) (P3HT) spin-coated onto a gate insulator formed from polyimide (PI) or polysilsesquioxane (PSQ) layers have been prepared and their electrical characteristics examined. The large threshold voltage, +25 V, obtained in PI-based FETs, which contrasts with the small threshold voltage of ∼0 V in PSQ-based devices, has been discussed in terms of charge exchange at the insulator/semiconductor interface. A combination of capacitance measurement as a function of biasing voltage or measured frequency and conventional surface potential measurements reveals a high density of electron trapping states, ∼1012 cm-2, at the PI/semiconductor interface. However, the high threshold voltage in the PI-FETs only partly explains the higher drain currents observed in these devices compared with the PSQ devices. A second factor is the higher hole mobility in PI-FETs (0.005–0.01 cm2/Vs) which is about 3 times greater than in the PSQ devices (0.002–0.004 cm2/Vs). We attribute this to differences in the microscopic structure of the insulator surface. Although the mobility of hole prepared on PSQ is at the low end of the range previously reported for P3HT-based FETs, the ON:OFF ratios (>104) and low threshold voltage (∼0 V) reported here are comparable to those of the FETs prepared on a SiO2 gate insulator. The subthreshold current behaviour suggests that interface states are active in both device types but the density is much lower in the PSQ devices.
Interface Characteristics between Au Electrode and Pentacene Layer in Organic Thin-film Transistors
Authors: Park Jaehoon , Kang Sung In , Jang Sun Pil , Choi Jong Sun
Published: July 2005

In order to investigate interfacial characteristics between top-Au and pentacene layers, devices with the structure of bottom-Au/pentacene/top-Au were fabricated on glass substrates at various deposition rates of top-Au of about 1.0, 3.0 and 15.0 Å/s. It was observed that electrical characteristics could be improved by increasing the deposition rate of top-Au, and the highest electrical conductivity value, 1.5×10-6 S/cm, was obtained for the device with top-Au deposited at 15.0 Å/s. Auger electron spectroscopy (AES) results showed that the atomic content of Au is substantially increased with the deposition rate of top-Au, but there is no marked difference in the depth profile of Au atoms regardless of the deposition rate of top-Au. Likewise, field-emission scanning electron microscopy (FE-SEM) images did not reveal structural defects that might cause short circuit. We also fabricated top-contact organic thin-film transistors (OTFTs) at various deposition rates of the Au layer for source/drain electrodes. As a result, the performance of the OTFTs can be modified by the deposition rate of Au. These results will be discussed.
Organic Thin-Film Transistors Based on Vapor-Deposition Polymerized Gate Insulators
Authors: Pyo S. W. , Lee D. H. , Koo J. R. , Kim J. H. , Shim J. H. , Kim Y. K.
Published: July 2005

In this study, we demonstrated that organic thin-film transistors (OTFTs) can be fabricated by using organic gate insulators using a vapor deposition polymerization (VDP) process. We found that electrical output characteristics in our organic thin-film transistors using a staggered-inverted top-contact structure show a saturated slope in the saturation region and a subthreshold nonlinearity in the triode region. The field-effect mobility, threshold voltage, and on-off current ratio of OTFTs using 4,4'-oxydiphthalic anhydride[ODPA]-4,4'-oxydianiline[ODA] and 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride[6FDA]-[ODA] as gate insulators with a thickness of 0.45 µm were about 0.13–0.5 cm2/Vs, -7 V, and 104, respectively. To form polyimide as a gate insulator, the VDP process was also introduced instead of a spin-coating process, in which a polyimide film was codeposited by the high-vacuum thermal evaporation of ODPA and ODA, 6FDA and ODA, and cured at 150°C for 1 h followed by 200°C for 1 h after codeposition. To explain the differences in the electrical characteristics caused by the insulators, the morphology of pentacene on the polyimide from ODPA-ODA was compared with that from 6FDA-ODA, respectively.
Polymer Solar Cell Prepared by a Novel Vacuum Spray Method
Authors: Mo Xiaoliang , Mizokuro Toshiko , Mochizuki Hiroyuki , Tanigaki Nobutaka , Hiraga Takashi
Published: July 2005

The vacuum spray method was demonstrated to be a novel method for polymer solar cell fabrication. Semiconductor polymers such as poly[2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly(3-dodecylthiophene-2,5-diyl) (PDDT) were chosen as donors in the polymer solar cells, and C60 was used as the acceptor. The polymer layer in the polymer solar cells was prepared by the vacuum spray method. Gold (Au) was used as the electrode material. A significant photovoltaic phenomenon was observed.
Synthesis of Polyethylene/Montmorillonite Nanocomposites by In-situ Intercalative Polymerization
Authors: Zhang Fan , Li Sanxi , Karaki Tomoaki , Adachi Masatoshi
Published: July 2005

Ziegler-Natta catalysts were intercalated into the galleries between the silicate layers of modified organic montmorillonite (OMMT) and then polyethylene/montmorillonite (PE/MMT) nanocomposites were prepared via in-situ intercalative polymerization of ethylene. Characterization studies were carried out on MMT, OMMT and PE/MMT by various techniques. They indicated that the space between MMT layers in OMMT was broadened from 1.26 nm to 3.53 nm and the MMT layers were homogeneously dispersed in the PE matrix of PE/MMT. Compared with pure PE, the thermal and mechanical properties of PE/MMT were improved to different extents.
Growth and Electrochemical Properties of Single-Crystalline V2O5 Nanorod Arrays
Authors: Takahashi Katsunori , Limmer Steven J. , Wang Ying , Cao Guozhong
Published: July 2005

Growth and electrochemical properties of single-crystalline vanadium pentoxide (V2O5) nanorod arrays were investigated. Vanadium pentoxide nanorod arrays were grown by electrochemical deposition, surface condensation induced by a pH change and sol electrophoretic deposition. Uniformly sized vanadium oxide nanorods with a length of about 10 µm and diameters of 100 or 200 nm were grown over a large area with near-unidirectional alignment. Transmission electron microscopy (TEM) micrographs and electron diffraction patterns of V2O5 nanorods clearly show the single-crystalline nature of nanorods fabricated via all three growth routes with a growth direction of [010]. The growth mechanisms of single-crystal V2O5 nanorods have been discussed. Electrochemical analysis revealed that nanorod array electrodes possess significantly improved storage capacity and charge/discharge rate with approximately 5 times higher applicable current density than those of sol-gel derived films. Furthermore, for a given current density, the nanorod array electrode can intercalate up to 3.5 times higher concentration of Li+ intercalation. The relationships between electrochemical property, nano- and microstructure, and growth mechanisms have been discussed.
Unbalanced Magnetron Sputtering Using Cylindrical Target for Low-Temperature Optical Coating
Authors: Wang Cheng-Shih , Sasaki Kimihiro , Yonezawa Yasuto , Hata Tomonobu
Published: July 2005

A new optical coating technology was developed for the first time using unbalanced magnetron sputtering combined with a cylindrical target. A significant reduction of ignition and glow discharge voltages were observed by adding magnets to carry out the unbalanced magnetron sputtering. A high deposition rate of 30 nm/min was realized for TiO2 film preparation; this rate was approximately 3 times larger than that obtained by conventional magnetron sputtering. Moreover, deposition power efficiency twice as large as that obtained by conventional magnetron sputtering was realized. A fine-grain structure was observed and a large refraction index of 2.65 was obtained.
Improvement in Crystallinity of ZnO Films Prepared by rf Magnetron Sputtering with Grid Electrode
Authors: Yasui Kanji , Phuong Nguyen Viet , Kuroki Yuichirou , Takata Masasuke , Akahane Tadashi
Published: July 2005

ZnO films were prepared on Si and quartz substrates by rf magnetron sputtering with a mesh grid electrode. The influence of a negative grid bias on the crystallinity and optical property of ZnO films was investigated. At an appropriate dc grid bias, ZnO films with good crystallinity were grown from room temperature to 300°C. The number of stacking faults, which were observed in the X-ray diffraction spectra of the films deposited without the grid electrode, decreased in the films deposited with the grid electrode. All ZnO films showed a high transmittance in the visible region.
Synthesis of ZnO Nanorods by Laser Ablation of ZnO and Zn Targets in He and O2 Background Gas
Authors: Okada Tatsuo , Kawashima Kou , Nakata Yoshiki , Ning Xu
Published: July 2005

This paper describes the synthesis of nanostructured ZnO crystals by nanoparticle-assisted pulsed-laser deposition (NAPLD), in which nanoparticles formed in the gas phase by the condensation of the ablated species are transported onto the substrate. The influence of the synthesis conditions on the morphologies of the formed ZnO crystals was investigated in detail. ZnO nanorods with a hexagonal- and pyramidal top surface were obtained under limited growth conditions. The most critical process parameter for the growth of ZnO nanorods was gas pressure, whose process window was in the range from 1.0 to 5 Torr.
Preparation of (Pb,Sr)TiO3 Films by Sol-Gel Technique
Authors: Fujii Tadashi , Adachi Masatoshi
Published: July 2005

Ferroelectric (Pb,Sr)TiO3 (PST) thin films with a perovskite structure were prepared by the sol-gel technique. PST precursor solutions were prepared from lead (II) acetate, titanium tetraisopropoxide, and strontium acetate hemihydrate with solvents of acetic acid and 2-methoxyethanol. The PST film fabricated on an Ir/SiO2/Si substrate with a perovskite structure exhibited a ferroelectric hysteresis curve. The Pb/Sr ratio of the PST films could be controlled, however the Ti composition was larger than the stoichiometric value. It is important to obtain stoichiometric PST films for device applications, such as ferroelectric random access memories and piezoelectric filters.
Preparation of SrAl2O4:Eu,Dy Phosphor Thin Films on Organic Substrates by Pulsed Ion-Beam Evaporation
Authors: Honda Naoya , Suzuki Tsuneo , Yunogami Takashi , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2005

Thin films of SrAl2O4:Eu,Dy were successfully deposited on polyethylene substrates at room temperature by pulsed ion-beam evaporation. From X-ray diffraction analysis results, the thin films were found to consist of a crystallized SrAl2O4:Eu,Dy phase. In the measurements of the photoluminescence properties of the thin films, broad peaks at 520 nm, which were characteristic of SrAl2O4:Eu,Dy phosphor, were observed. From the observation by scanning electron microscopy, the thin films were prepared on polyethylene substrates. From various observations, crystallized SrAl2O4:Eu,Dy phosphor thin films on polyethylene substrates were successfully obtained by IBE without damaging the substrates. These results suggest the possibility of IBE to deposit crystallized oxide thin films on various low-melting point substrates.
Annealing Effect on Enlargement of Grain Size in Nanocrystalline Silicon Films Deposited by Silicon Evaporation with Oxygen and Argon Radicals
Authors: Nakamura Kazuhiro , Hirata Makoto , Yokota Katsuhiro
Published: July 2005

Nanocrystalline silicon films were deposited by silicon evaporation in an ultrahigh vacuum with oxygen and argon radicals. The oxygen ratios (O2/(O2+Ar)) in the source gases for the deposition of silicon films were 100, 50, 20 and 5%. The deposited films were annealed at temperatures between 900 and 1100°C for 30 min in oxygen ambient. The films were characterized by X-ray diffractometry (XRD). The grain size of the nanocrystalline silicon was determined using the full-width at half maximum (FWHM) of XRD spectra. The grain size in the films became larger with increasing annealing temperature regardless of the oxygen ratio in the source gases. The enlargement of the grain size was caused by the crystallization of the amorphous silicon region in the deposited films during the annealing process. On the other hand, the grain size became smaller with increasing oxygen ratio in the source gases when compared at the same annealing temperature. It can be concluded that the large amount of oxygen atoms or radicals incorporated in the deposited films suppressed the enlargement of the grain size during annealing.
Optical Characterization of Heavily Sn-Doped GaAs1-xSbx Epilayers Grown by Molecular Beam Epitaxy on (001) GaAs Substrates
Authors: Nishino Fumio , Takei Tatsuya , Kato Ariyuki , Jinbo Yoshio , Uchitomi Naotaka
Published: July 2005

We have optically investigated ternary GaAs1-x
Sb
x
(x<0.58) epilayers and Sn-doped GaAs1-x
Sb
x
(x=0.10–0.14) epilayers grown by molecular beam epitaxy on GaAs (001) substrates. Sn-doped GaAsSb layers were grown as a function of Sn Knudsen-cell temperature, and then characterized by low-temperature photoluminescence (PL) measurements and Hall effect measurements. The Sn-doped GaAsSb films grown at a K-cell temperature of 670°C changed from exhibiting p-type conduction to exhibiting n-type conduction, and showed a maximum PL intensity and a maximum electron mobility of 1900 cm2/V s. The PL intensities obtained for Sn-doped GaAsSb films showed a relatively good correlation with the variations in Hall mobility.
1D-TlInSe2: Band Structure, Dielectric Function and Nanorods
Authors: Mamedov Nazim , Wakita Kazuki , Akita Seiji , Nakayama Yoshikazu
Published: July 2005

Linear combination of atomic orbitals (LCAO) analysis of the electronic band states has been completed for one-dimensional (1D) TlInSe2 having rod-like ground state shape of bulky crystal. The total scenario of the occurrence of the band states from the atomic states has been established. According to this scenario, in dipole approximation the optical transitions at band gap (point T of Brillouin zone) are either entirely forbidden or allowed for T2-T10 transitions in e⊥c configuration provided that either initial or terminate state has T2 symmetry and both are Se-like. As a whole, the obtained results on the electronic spectrum, including dielectric function, are applicable to all obtained 1D-TlInSe2 nanorods which were as thin as 30–50 nm in cross-section, and apparently preserved tetragonal crystal structure of bulky material. The thermal instabilities developing already in bulky samples of 1D-TlInSe2 are considered to be an ultimate source of the nanoparticles emerging in plenty during nanorods preparation. The nanoplates of a chemically similar but 2D material, TlInS2, are demonstrated for comparison to show the absence of nanoparticles in that case. A possibility of nanoparticle preparation using laser excited coherent phonon trains in the nanorods of 1D-TlInSe2 is figured out.