bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Superstructures Fluctuating in the Quasi-One-Dimensional Organic Conductor β-(BEDT-TTF) 2PF 6 Observed by Scanning Tunneling Microscopy
Authors: Masahiko Ishida Masahiko Ishida , Kenji Hata Kenji Hata , Takehiko Mori Takehiko Mori , Keiichi Nakamoto Keiichi Nakamoto , Masashi Iwatsuki Masashi Iwatsuki , Ryozo Yoshizaki Ryozo Yoshizaki , Hidemi Shigekawa Hidemi Shigekawa
Published: October 2002

Two types of surface structures were observed at ∼280 K by scanning tunneling microscopy on a crystal surface of β-(BEDT-TTF)2PF6. One is a structure which corresponds to the expected crystal structure determined by X-ray diffraction measurement, and the other is a modulated structure with two-fold periodicity perpendicular to the one-dimensional conductive axis. Fluctuation between these two types of structures in the same area was observed by scanning tunneling microscopy, with a surface defect used as a positional marker. Occurrence of a double tip effect was considered but concluded not to be responsible for the observed change.
Photo-Induced Structural Transformation on the Surface of Azobenzene Crystals
Authors: Nakayama Keisuke , Jiang Lei , Iyoda Tomokazu , Hashimoto Kazuhito , Fujishima Akira
Published: October 2002

Atomic force microscopy (AFM) was used to investigate the surface structure and photo-induced surface morphological changes in azobenzene crystals. In large-scale images, a layered structure was observed. The thickness of the layer was 1.8±0.2 nm, corresponding to bilayers of azobenzene molecules. Molecular resolution images revealed that the molecular arrangement on the surface of the layers was a (001) face, with intermolecular distances of a=1.32±0.02 nm and b=0.62±0.02 nm. By irradiating the crystal surface with UV or visible light, structural transformations were observed, which are considered to be the trans-cis photoisomerization of surface azobenzene molecules.
Heat-Induced Phase Separation of Self-Assembled Monolayers of a Fluorocarbon-Hydrocarbon Asymmetric Disulfide on a Au(111) Surface
Authors: Ishida Takao , Yamamoto Shin-ichi , Motomatsu Makoto , Mizutani Wataru , Tokumoto Hiroshi , Hokari Hirofumi , Azehara Hiroaki , Fujihira Masamichi , Kojima Isao
Published: October 2002

Heat-induced phase separation of fluorocarbon-hydrocarbon self-assembled monolayers (SAMs) on a Au(111) surface was studied by scanning tunneling microscopy (STM), atomic force microscopy (AFM) and friction force microscopy (FFM). Phase-separated domains were depressed by 0.3 nm with a lateral dimension of 20–200 nm. The friction forces on the higher parts were smaller than those on the lower domains. The higher parts were assigned to the hydrocarbon chains, because the fluorocarbon chains should have a larger friction force acting on them than the hydrocarbon chains against the silicon nitride tip. Phase separation suggests cleavaging of the S–S bonds of disulfides in the SAMs. XPS measurements clearly showed an increase in the isolated Au–S binding species, suggesting the existence of the thiolate (monomer).
Energy-Dependent Effective Mass Approximation in One-Dimensional Quantum Dots
Authors: Norihiko Nishiguchi Norihiko Nishiguchi , Kanji Yoh Kanji Yoh
Published: October 2002

We extend the effective mass approximation by taking into account the energy dependence of the effective mass. The effective Hamiltonian with an energy-dependent effective mass is applied to one-dimensional quantum dots. The eigenvalues of the effective Hamiltonian agree well with the energy levels of confined states in the dots, even in the energy region where the usual effective mass approximation is not useful. The energy dependence of the effective mass, which is common to any size of quantum dot, is derived from the nonparabolic conduction band of bulk materials.
Orientation and Characteristic Movement of Yeast Cells Induced by Homogeneous Electric Field
Authors: Minoru Suga Minoru Suga , Toyomasa Hatakeyama Toyomasa Hatakeyama , Masaharu Isobe Masaharu Isobe
Published: October 2002

A cylindrical yeast cell ( Schizosaccharomyces pombe ) oriented itself parallel or perpendicular to an alternating homogeneous electric field, depending upon the applied frequency. The turnover frequency was about 65 MHz for the living cells in a non-electrolyte solution but about 1.5 MHz for the dead cells in an electric field. Further, the lower the cell activity due to the refrigeration effect, the lower the turnover frequency was. Similar phenomena were observed for budding yeast cells ( Saccharomyces cerevisiae ). Therefore, these phenomena can be used to investigate the cell activity in the solution. We also found a second turnover frequency of about 15 MHz for the dead cylindrical cells. Moreover, when two living cylindrical cells were placed in contact with each other, they exhibited characteristic movement at applied frequencies near the first turnover frequency.
Can Ohmic Spikes Define Quantum Systems?
Authors: Taylor Richard P. , Newbury Richard , Sachrajda Andrew S. , Feng Yan , Coleridge Peter T. , McCaffrey John P. , Davies Michael , Bird Jonathon P.
Published: October 2002

We investigate a system defined by an array of metallic spikes which extend down from an annealed Ni–Au–Ge metallisation deposited on the surface of an AlGaAs/GaAs heterostructure. For the case where the spikes penetrate the two dimensional gas (2DEG), we show that electrons injected from the spikes into the 2DEG maintain phase coherence at low temperatures, resulting in quantum interference processes determined by the spike distribution. A unique device which induces a topological transition from a Corbino disc to a Hall bar is employed to explore this novel phenomenon. We discuss refinements to the spiking process which will facilitate the incorporation of these metallic spikes into nanostructure designs.
Phase Breaking of Coherent Electron Waves in Dot Array Systems
Authors: Ochiai Yuichi , Widjaja A. Wahju , Sasaki Nobuyuki , Yamamoto Kazunuki , Bird Jonathan P. , Ishibashi Kohji , Aoyagi Yoshinobu , Sugano Takuo , Ferry David K.
Published: October 2002

Low temperature magneto-conductance has been studied in ballistic dot arrays using corrugation splitgates. We have obseved many peaks at low fields superimposed upon the large negative magneto-resistance in double sided corrugation wires. These peaks can be considered to arise from three different phase breaking phenomena for coherent electron waves in ballistic quantum dots: weak localization in the quasi-ballistic regime, periodic oscillations due to coherent interferences and electron focusing of collimated electron waves. The three phenomena have been discussed in terms of their phase breaking behavior in dot arrays.
Transport Properties of a Triangular Electron Billiard
Authors: Omling P. , Linke H. , Lindelof L. Christensson
Published: October 2002

The transport properties of triangular electron billiards are investigated. By comparison of experimental data with simulations, maxima of the magnetoresistance are related to classical electron orbits. In order to qualitatively understand why specific electron trajectories give rise to commensurability effects, we analyse the stability of the trajectories using chaos theory. Numerical calculations of the Liapunov exponent of different trajectories show that relatively stable electron trajectories lead to commensurability effects, while more unstable trajectories are less important for the magnetoresistance. Further, we investigated the influence of the geometry of the electron billiard on the symmetry of electric conduction. We find that the triangular billiard has non-symmetric contributions to the conductance that are not present in mirror-symmetric billiards. The dependences on voltage, temperature and magnetic field indicate that this nonlinearity is associated with quantum-interference effects.
Normal-Super-Normal Junction Fabricated in a Split-Gate Wire
Authors: Aoki Nobuyuki , Kikutani Tomoyuki , Oki Akio , Hon Chulun , Hidenobu Hori Hidenobu Hori , Syoji Yamada Syoji Yamada
Published: October 2002

The fabrication and low temperature transport properties of a new class of quantum structures which have a buried superconductor dot in a split-gate wire are described. To create such a structure, we employed a combined scanning electron microscope (SEM)/scanning tunneling microscope (STM) and performed a two-step fabrication process using a tip-induced field and thermal evaporation. We chose indium as a superconductor material and the dot size at the two dimensional electron gas (2DEG) plane was about 100 nm. Such a structure is expected to form a normal (2DEG)-super (In dot)-normal (2DEG) double tunneling junction when the wire is properly squeezed. In transport experiments at 0.3 K, different conductance step behavior and different nonlinear current-voltage characteristics were observed in the systems with and without an In dot.
Fabrication and Electrical Characteristics of Single Electron Tunneling Devices Based on Si Quantum Dots Prepared by Plasma Processing
Authors: Amit Dutta Amit Dutta , Masao Kimura Masao Kimura , Yoshiaki Honda Yoshiaki Honda , Masanori Otobe Masanori Otobe , Akira Itoh Akira Itoh , Shunri Oda Shunri Oda
Published: October 2002

This paper presents results on the fabrication of single electron tunneling devices using silicon nanocrystals. We prepare silicon nanocrystals of uniform particle size by very-high-frequency plasma processing and deposit them on a poly-silicon electrode structure having a very small inter-electrode separation of 26–70 nm. Current-voltage (I–V) characteristics show Coulomb blockade and Coulomb staircase at 77 K. For very narrow electrode separation, Coulomb staircase appears in I-V characteristics even at room temperature.
Atomic-Layer Surface Reaction of SiH4 on Ge(100)
Authors: Watanabe Takeshi , Sakuraba Masao , Takashi Matsuura Takashi Matsuura , Junichi Murota Junichi Murota
Published: October 2002

The single atomic layer growth process of Si on a Ge(100) surface using SiH4 has been investigated by ultraclean cold-wall low-pressure chemical vapor deposition (CVD). Self-limiting reaction of SiH4 on the Ge surface was found at 260° C and the reaction step can be explained by Langmuir-type kinetics. The saturated surface concentration of Si atoms depends on the preheating conditions. A single atomic layer was found for preheating at 350° C in Ar and at 260° C in H2. However, in the case of preheating in H2 at 350° C, the Si atom concentration hardly reached that of a single atomic layer. Reflection high-energy electron diffraction (RHEED) and Fourier-transform infrared reflection adsorption spectroscopy (FTIR/RAS) observations showed that a H-terminated dimer structure was formed on the Ge(100) surface after preheating in H2 at 350° C. The density of the SiH4 reaction sites on the H-terminated surface with the dimer structure is considered to be lower than that of the H-terminated unreconstructed surface and the H-free surface.
Atomic Force Microscope Nanolithography on SiO 2/Semiconductor Surfaces
Authors: Adrian Avramescu Adrian Avramescu , Katsuhiro Uesugi Katsuhiro Uesugi , Ikuo Suemune Ikuo Suemune
Published: October 2002

We report on the fabrication of a nanometer-scale SiO2 mask on a semiconductor surface using an atomic force microscope (AFM). Layers of SiO2 5–35 nm thick sputtered on GaAs substrates are covered with very thin polymethyl methacrylate (PMMA) films by spin-coating. The AFM tips were used mechanically to modify the polymer layers. Lines with 18-nm width and holes with 20-nm diameter were successfully patterned on the PMMA films. These patterns were transferred into the SiO2 layers by wet etching in buffered HF. Linewidths as small as 40 nm have been obtained. Arrays of lines and holes with 200 nm periodicity were successfully fabricated.
Atomic Force Microscope Nanofabrication of InAs/AlGaSb Heterostructures
Authors: Sasa Shigehiko , Ikeda Takatoshi , Chiaki Dohno Chiaki Dohno , Masataka Inoue Masataka Inoue
Published: October 2002

We employ an atomic force microscope (AFM) for the fabrication of InAs/Al(Ga)Sb nanostructures. In order to make nanoscale modifications in the two-dimensional electron gas (2DEG) system, we apply an AFM oxidation process for GaSb, for the first time. We found that the oxidation of GaSb occurs for tip voltages over 7–8 V and that the oxidized GaSb region can be selectively removed by immersion in water for 10 min. We successfully fabricate a lateral periodic structure on the GaSb cap layer using AFM oxidation with a 0.3 µ m spacing. The induced increase in the 2DEG concentration is as high as 80% due to the surface modification. The magnetotransport measurement also implies structural modification of the 2DEG system.
Formation of High-Density Quantum Dot Arrays by Molecular Beam Epitaxy
Authors: Kawabe Mitsuo , Chun Yong Jin , Sigeru Nakajima Sigeru Nakajima , Kouichi Akahane Kouichi Akahane
Published: October 2002

Surface modification by atomic hydrogen homogenizes the distribution and reduces the size of self-organized quantum dots (QDs) grown by molecular beam epitaxy (MBE) and also improves their photoluminescence intensity. Quantum dot arrays of InGaAs are obtained on GaAs(311)B by conventional MBE. The size and the density are approximately 30 nm and 7×1010/ cm2. The ordered structure of QDs shows strong dependence on the In content, and the arrays of the QDs begin to become disordered as the In content increases to more than 0.6. The formation of the dot array is induced by wavy surface instability. The dot array on GaAs(311)B is metastable and disordered upon thermal annealing.
Formation of Two-Dimensional Arrays of InP-Based InGaAs Quantum Dots on Patterned Substrates by Selective Molecular Beam Epitaxy
Authors: Fujikura Hajime , Araki Moriaki , Hanada Yuuki , Michio Kihara Michio Kihara , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

Two-dimensional (2D) arrays of InP-based In0.53Ga0.47As quantum dots are successfully formed using two different approaches of selective molecular beam epitaxial (MBE) growth. One is to introduce modulations into wire-arrays by growing wires on intentionally mis-oriented mesa-stripes based on our recent study on the effect of mis-orientation on the wire growth. The other is to carry out selective MBE growth on a 2D array of <100>-oriented square-mesa pedestals. Both types of InGaAs dot arrays show fairly strong photoluminescence (PL) and cathodoluminescence (CL) emissions, indicating the reasonably good crystal quality of the dots. Both approaches are found to be useful for constructing highly integrated networks of single electron devices.
Control of InAs Self-Assembled Islands on GaAs Vicinal Surfaces by Annealing in Gas-Source Molecular Beam Epitaxy
Authors: Hong-Wen Ren Hong-Wen Ren , Kenichi Nishi Kenichi Nishi , Shigeo Sugou Shigeo Sugou , Mitsuru Sugisaki Mitsuru Sugisaki , Yasuaki Masumoto Yasuaki Masumoto
Published: October 2002

Growth of InAs/GaAs self-assembled quantum dots (SADs) on GaAs vicinal surfaces was studied by gas source molecular beam epitaxy. Low island density was obtained after 1.8 monolayer InAs supply by increasing the annealing time at the growth temperature. The remaining three-dimensional islands kept the “lens-shape" with the height of about 11.8 nm but the average diameter increased by a few percent around 40 nm. 77 K photo-luminescence of the SADs with increasing growth interruption time before being capped by GaAs showed red-shift of the distinct peaks from the sub-band levels of the quantum dots which agrees to the slight increase of their lateral sizes. Large reduction of the dot density was obtained by 80 s growth interruption.
Single-Electron-Tunneling Effect in Nanoscale Granular Microbridges
Authors: Nobuyuki Yoshikawa Nobuyuki Yoshikawa , Hideki Kimijima Hideki Kimijima , Norihiro Miura Norihiro Miura , Masanori Sugahara Masanori Sugahara
Published: October 2002

The single-electron-tunneling (SET) effect in a nanoscale granular microbridge, which consists of a two-dimensional array of small intergrain tunnel junctions, was investigated. We observed the Coulomb blockade effect and the periodic electrical field effect in the microbridges. These results coincide well with results of numerical calculations based on a model of a two-dimensional SET junction array. We showed that electron conduction properties of the microbridges are quasi-zero-dimensional, because the size of the charge soliton is larger than the dimensions of the microbridges. The details of the current-voltage characteristics were considered as an aspect of the Kosterlitz-Thouless (KT) transition, which is a peculiar phase transition in a two dimensional system. The electron conduction properties are extremely affected by the existence of a fixed background charge.
A Single Electron Neuron Device
Authors: Masaharu Kirihara Masaharu Kirihara , Kenji Taniguchi Kenji Taniguchi
Published: October 2002

A neuron device utilizing the single electron tunneling (SET) effect is described. The device consists of four parts: synaptic weight circuits, a multiplier, an adder, and a nonlinear activation function circuit. The synaptic weight memory is designed with only two turnstiles, and the multiplier and the nonlinear activation function are realized with the use of single electron inverter circuits. The total SET transistor count of a neuron with n inputs is only 6n+2, which is an advantage over a neuron consisting of conventional complementary metal-oxide semiconductor (CMOS) transistors from the viewpoint of occupation area and consumption power. Due to the smallness of the SET neuron, large systems of artificial neural networks could be realized with the use of these devices.
Simulations of Relaxation Processes for Non-Equilibrium Electron Distributions in Two-Dimensional Tunnel Junction Arrays
Authors: Tabe Michiharu , Asahi Noboru , Amemiya Yoshihito , Yoichi Terao Yoichi Terao
Published: October 2002

Relaxation processes for non-equilibrium electron distributions in two-dimensional ultrasmall tunnel junction arrays (2D-TJAs) have been studied using a Monte Carlo simulation. Many electrons initially placed in the central island diffuse outward due to single-electron tunneling. When we focus on the number of electrons in square shells dividing the 2D-TJA, the number of electrons strongly fluctuates in time to form electron bunching peaks, and the peaks are propagated to outer shells as a wave. This result indicates a self-organization of electrons in non-equilibrium TJAs, suggesting the possibility of applications based on a new algorithm.
Co/Pt Disks with a Simplified Structure
Authors: Tyan Yuan-Sheng , Hatwar Tukaram K. , Farruggia Giuseppe , Victora Randal H. , Michael W. Culver Michael W. Culver , Charles F. Brucker Charles F. Brucker
Published: October 2002

Potentially low cost Co/Pt multilayer disks were fabricated using a simplified disk structure. Ultrathin seed layers of dielectrics were used to enhance the coercivity and squareness of the Kerr hysteresis loop. Both Co/Pt superlattices and the dielectrics were deposited under low vacuum. The total cycle time consisting of loading the PC substrate into the vacuum chamber, pumping the sputtering chamber to a base pressure, and deposition of the ITO seed layer and the Co/Pt multilayer was reduced to less than ten seconds. Cyclability and recording performance of the conventional media is retained.
Device Performance and Reliability of P-Channel Metal-Oxide-Semiconductor Field Effect Transistors with Chemical-Vapor-Deposited Gate Oxides
Authors: Kwong Jinho Ahn
Published: October 2002

This paper reports the performance and reliability of p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) with ultrathin (65 Å) low pressure chemical-vapor-deposited (LPCVD) gate oxides annealed in N2 ambient as compared to those with thermal gate oxides of identical thickness. It is shown that MOSFETs with CVD gate oxides exhibit better initial performance (transconductance, current drivability, and effective hole mobility) and enhanced reliability (transconductance degradation, threshold voltage shift, enhancement in gate-induced drain leakage, and hot-electron-induced punchthrough) than the MOSFETs with thermal gate oxides. Furthermore, significantly improved time-dependent dielectric breakdown characteristic of CVD gate oxide has been demonstrated. Strainless CVD SiO2 after proper post-deposition annealing and the substrate-independent film formation mechanism are speculated to result in the improvements in performance and reliability of CVD oxide devices.
Metalorganic Chemical Vapor Deposition Study Using Tertiarybutylphosphine and Tertiarybutylarsine for InAlGaP Light-Emitting Diode Fabrication
Authors: Mashita Masao , Ishikawa Hironori , Toshihide Izumiya Toshihide Izumiya , Yoshiko Someya Hiraoka Yoshiko Someya Hiraoka
Published: October 2002

We have investigated the possibility of using tertiarybutylphosphine (TBP) for metalorganic chemical vapor deposition (MOCVD) of Al-containing materials through InAlGaP light-emitting diode (LED) fabrication. It has been shown that a marked decrease in the performance of InAlGaP LEDs results from Zn diffusion into the active layer. The diffusion of Zn in the In0.5(Al0.7Ga0.3)0.5P cladding layer can be enhanced by increasing interstitial group-III, I
I
I
I
. According to our growth model, an intrinsic disadvantage of TBP is that it decomposes at a temperature much lower than the substrate temperature and produces less-active phosphorus molecules ( P4). Since the vapor pressure of P4 is extremely high, it leads to lower effective V/III ratios on the growth surface and generation of I
I
I
I
. In order to increase the effective V/III ratio, we have proposed new organic phosphorus sources that are expected to provide a large number of PH

x

(x=0–2) radicals on the surface.
Ge:Ga Far-infrared Photoconductor with a Low Ga Concentration of 1×1014cm-3
Authors: Mikio Fujiwara Mikio Fujiwara , Norihisa Hiromoto Norihisa Hiromoto
Published: October 2002

Germanium doped with gallium (Ge:Ga) far-infrared photoconductors with a Ga concentration of 1×1014 cm-3 are fabricated for use in sensors for detecting extremely weak radiation, such as for astronomical observations by a space-borne cooled telescope. The performance of the photoconductor at low temperatures and under low background photon influxes to simulate operation in a space environment was evaluated. The responsivity of the new Ge:Ga photoconductor is approximately double that of the previous Ge:Ga photoconductors with a Ga concentration of 2×1014 cm-3 which was developed for astronomical observations using the Infrared Telescope in Space (IRTS) satellite. This increase in responsivity, which is proportional to the product of hole mobility, hole lifetime, and quantum efficiency, is interpreted as being due to the enlargement of both hole mobility and hole lifetime and also because of almost equal quantum efficiency due to the utilization of a metal cavity in which the photoconductor is mounted. The new photoconductor has a slow transient response to a step change in photon influx similar to that in the previous photoconductors, but its magnitude is larger than that of the previous ones. We found good agreement between the time constants estimated from curve-fitting to the response to a step change in photon influx and the transient time constants derived by analytical considerations based on the two-region model of the Ge:Ga photoconductor with ion-implanted ohmic contacts.
Tunneling Current through Si Donor Level in GaAs/AlAs Single-Barrier Diodes
Authors: Hiroyuki Fukuyama Hiroyuki Fukuyama , Takao Waho Takao Waho , Masafumi Yamamoto Masafumi Yamamoto
Published: October 2002

The tunneling current in Si planar-doped GaAs/AlAs single-barrier diodes is studied. First, we determine the effects of growth interruption and doped Si impurities on the tunneling current. We observe excess current for a sample with Si doping during growth interruption (Si planar doping) in the AlAs barrier, while we do not observe it for a sample which was subjected only to growth interruption. This result shows that the excess current is not caused by impurities incorporated from the background during growth interruption but by the intentional doping of Si impurities. We then examine the dependence of the excess current on Si concentration. The excess current increases as the Si concentration increases. This result provides further evidence that Si impurities introduce paths for the flow of the excess current. In the conductance–voltage characteristics, we observe a peak corresponding to the excess current. This peak suggests that the excess current flows through zero-dimensional states. Finally, we discuss the Si donor levels as possible origins of the excess current. The shallow donor level is probably responsible for the excess current.
Characterization of Polycrystalline Silicon Thin Film Transistors Fabricated by Ultrahigh-Vacuum Chemical Vapor Deposition and Chemical Mechanical Polishing
Authors: Lin Hsiao-Yi , Chang Chun-Yen , Lei Tan Fu , Cheng Juing-Yi , Chen Hua-Chou Tseng
Published: October 2002

A high performance top-gate thin film transistor (TFT) has been fabricated using an as-deposited polycrystalline silicon (poly-Si) film by ultrahigh-vacuum chemical vapor deposition (UHV/CVD) followed by chemical mechanical polishing (CMP). In this process, due to the ultraclean environment and very low-pressure deposition of UHV/CVD, high-quality poly-Si films can be obtained and no long-term or post-recrystallization in channel films is needed. Maximum field effect mobilities of 58 cm2/V·s and 98 cm2/V·s for p- and n-channel TFTs, respectively, an ON/OFF current ratio of 1.1×107 for both p- and n-channels, and threshold voltages of -0.54 V for p-channel and 0.36 V for n-channel devices, respectively, are achieved. Finally, an analytical model of poly-Si TFTs was used to simulate the gate-voltage-dependent activation energy on the threshold and above the threshold regions and showed good agreement.
A Novel Bistable Double-Barrier Resonant Tunnel Diode by Charging Effect of InAs Dots
Authors: Nakano Takaya , Takayuki Nakagawa Takayuki Nakagawa , Kanji Yoh Kanji Yoh
Published: October 2002

We report on a novel bistable current voltage characteristics of GaAs/AlGaAs double-barrier resonant tunnel diodes (DBRTDs) with self-assembled InAs dots buried in the GaAs cathode layer. The memory effect was observed at room temperature and is likely to be caused by the charging and discharging of InAs dots, where the discharging takes place through tunneling via resonance states in the adjacent quantum well.
Crystal Structure and Superconductivity of (Hg0.5Pb0.5)Sr2(Sr1-xLax)Cu2Oz
Authors: Kandyel Elsayed , Taniguchi Takashi , Kamiyama Takashi , Asano Hajime , Ikeda Hiroshi , El-Kersh Mokhtar , Abou-Sekkina Morsy
Published: October 2002

An Hg-based superconducting cuprate (Hg0.5Pb0.5)Sr2(Sr1-
x

La

x

)Cu2O

z

has been synthesized. X-ray diffraction patterns indicate that the 1212-compound exists only in a narrow composition range of 0.45≤x≤0.55. Rietveld refinement based on the space group P4/mmm gives tetragonal lattice parameters of a=3.869(7) and c=12.14(2) Å and a chemical composition of (Pb0.50Hg0.28Cu0.22)(Sr0.85La0.15)2(Sr0.44La0.56)Cu2O6.56 for the compound of x=0.55. Electrical resistivity measurements show that the sample with x=0.55 becomes superconducting after annealing in O2 with onset T
c of 97 K.
Rate Equation Analysis of a Microcavity Laser with a Finite Number of Molecules in the Mode Volume
Authors: Shun Morimura Shun Morimura , Kikuo Ujihara Kikuo Ujihara
Published: October 2002

The number of molecules in the mode volume is introduced into the rate equations of a microcavity laser, and the resultant equations are analyzed. It is predicted that the laser does not oscillate and the output power is saturated unless the product of the number of molecules in the mode volume and the spontaneous emission coupling ratio exceeds a certain constant. The step height in a log-log plot of the input-output characteristics is not necessarily equal to the logarithm of the reciprocal spontaneous emission coupling ratio.
Efficient First Stokes Generation Using a Brillouin Resonator Coupled with a Raman Half Resonator
Authors: Chang Do Il , Jae Yong Lee Jae Yong Lee , Hong Jin Kong Hong Jin Kong
Published: October 2002

We report an efficient Raman laser system which utilizes stimulated Brillouin scattering as a dual-cavity resonator mirror for fundamental and Raman waves. A Raman laser at the eye-safe wavelength of 1.54 µ m is generated in high pressure CH4 gas from a passively Q-switched Nd:YAG laser. Employing a meniscus lens with an optimized reflectance of 10% at the fundamental wavelength, a maximum Raman energy of 33 mJ with a residual fundamental energy of 20 mJ has been obtained, where the pressure of CH4 gas is 800 psi.
Masking Problem in the Fabrication of Optical Waveguide Structures in Glass by Double Ion Exchange
Authors: Blagoy Pantchev Blagoy Pantchev , Parvaheh Danesh Parvaheh Danesh
Published: October 2002

Different metal and dielectric films are studied as masking films for the fabrication of optical waveguide structures in glass substrates by double ion exchange. The metal (Al, Ti, and Pt) films with thickness 0.5–1.0 µ m and inorganic dielectric films ( SiO2, Si3N4, and Al3O3) with thickness 0.2–0.5 µ m have piercing defect densities higher than 2×102 cm-2 and are not suitable for masks. For the first time polyimide and high temperature silicon varnish films are proposed for masks, as no pinholes or other piercing defects are found in them. The advantage of the polyimide films is demonstrated by the preparation of thin film homogeneous refracting waveguide lenses free of any highly scattering centers.
Photoluminescence Excitation and Photoacoustic Spectra for Ceramic Al2-xCrxO3 ( 0.002 \Leq x \Leq0.05)
Authors: Taro Toyoda Taro Toyoda , Takashi Obikawa Takashi Obikawa
Published: October 2002

Photoluminescence excitation (PLE) spectroscopy is applied together with photoacoustic (PA) spectroscopy to study the radiative processes of ceramic Al2-
x

Cr

x

O3 (0.002≦
x
≦0.05). The maxima which correspond to the U-band and Y-band can be observed in both PLE and PA spectra. The intensity ratio for the PLE spectra at the Y-band versus the U-band, F(Y-band)/F(U-band), increases and that for the PA spectra, S(Y-band)/S(U-band), decreases with increasing mole fraction x, indicating an increase of nonradiative characteristics of the U-band with increasing mole fraction x.
Viscosity Measurement in Nematic/Lamellar Phase Transition of Lyotropic Liquid Crystal
Authors: Seung Hee Lee Seung Hee Lee
Published: October 2002

Viscosity of the binary perfluorosurfactant/water systems: i) Ammonium perfluoro-octanoate ( NH4PFO)+water and ii) Cesium perfluoro-octanoate (CsPFO)+water, has been measured using a simple capillary method. Both systems clearly show discontinuity in viscosity for high concentrations of surfactant (≥45 wt%) as the temperature decreases from the isotropic to the nematic phase transition temperature, and a collapse in the viscosity at the nematic to lamellar phase transition temperature for all concentrations, thus allowing us to determine the phase transition temperature which is consistent with that obtained by optical microscopic study. The reversal in activation energy, i.e., a higher activation energy in the nematic phase than in the isotropic phase is observed as the concentration of the surfactants decreases. The polymer effect on the viscosity of lyotropic liquid crystals is also discussed.
Thermal Transport of Metallic PrBa2Cu4O8 Compound Prepared by High-Oxygen-Pressure Method
Authors: Matsukawa Michiaki , Iwasaki Kimiaki , Noto Koshichi , Yamada Yuh , Horii Shigeru
Published: October 2002

The thermal conductivity (κ) and thermoelectric power (S) of the PrBa2Cu4O8 compound have been studied as a function of temperature. The κ value of the metallic PrBa2Cu4O8 compound remains nearly constant down to ∼50 K while that of the semiconducting PrBa2Cu3O7-
x

compound shows a monotonical decrease over a wide temperature range. The S(T) value of the PrBa2Cu4O8 sample decreases rapidly below 150 K and then reaches a small value of ∼1 µ V/K. These behaviors in κ(T) and S(T) for the metallic PrBa2Cu4O8 compound are qualitatively different from those for the semiconducting PrBa2Cu3O7-
x

compound, which is probably related to the charge carrier conduction along the double CuO chains. These experimental results of κ and S support a dimensional crossover of electronic transport from a 1-dimensional conduction along the CuO chain to a quasi-2 dimensional one, which results in a bandlike conduction not only along the CuO chain but also between the CuO chains.
Degradation of n+/p Junction Characteristics by Aluminum Contamination
Authors: Itoga Toshihiko , Kojima Hisao , Atsushi Hiraiwa Atsushi Hiraiwa , Makoto Ohkura Makoto Ohkura
Published: October 2002

This paper discusses the effects of Al contamination on n+/p junction characteristics. The Al contamination occurs during ion implantation and the level can be as high as one tenth of the implanted dose. The Al contamination leads to an increase in the n+/p junction leakage current and a decrease in breakdown voltage. This is due to the increase of SiO2/Si interface state density and fixed negative charge in SiO2 film. The contaminating Al is segregated in the SiO2 film and remains very close to the oxide surface even in nm-order SiO2 (less than 10 nm), and the influence of Al becomes greater as SiO2 thickness decreases. Since Al is, and will continue to be, the most widely used material for process equipment, Al contamination control might become one of the key issues in achieving highly reliable future giga-scale ULSIs.
Observation of Molecular Alignment of 3-n-Octadecylthiophene by Scanning Tunneling Microscope
Authors: Tsutomu Fukunaga Tsutomu Fukunaga , Kazuyuki Harada Kazuyuki Harada , Wataru Takashima Wataru Takashima , Keiichi Kaneto Keiichi Kaneto
Published: October 2002

The molecular alignment of an alkylthiophene, 3-n-octadecylthiophene, on highly oriented pyrolytic graphite has been studied by scanning tunneling microscopy (STM). Lateral stripes with a period of 0.42 nm and vertical stripes with one of 5.0 nm are observed and assigned to molecular alignments of alkyl chains and thiophene rings connected by “head to head", respectively. An STM image of N-n-octadecylpyrrole is also presented.
Measurement of Terrace Width Distribution on an Si(110) Surface Using High-Temperature Scanning Tunneling Microscopy
Authors: Yamamoto Youiti , Sueyoshi Takashi , Tomoshige Sato Tomoshige Sato , Masashi Iwatsuki Masashi Iwatsuki
Published: October 2002

High-temperature scanning tunneling microscopy is used to study the statistical distribution of terrace width on an Si(110) surface at 720° C. It is confirmed that the terrace width is fitted by the Gaussian distribution, standard deviations (σ) of which are proportional to the mean terrace width. It is considered that the step-step interaction potential energy is A
x
-2 (x: normal distance to the step edge and A: proportionality constant). As the mean value of the main peak is 19.27 nm and the step height 0.19 nm, it is confirmed that the surface is oriented within 1° from the (110) surface.
Particle-in-Cell Simulation of Expansions of Dense Plasma Sources for X-Ray Laser Systems
Authors: Kenichi Nanbu Kenichi Nanbu , Vladimir V. Serikov Vladimir V. Serikov
Published: October 2002

A numerical model based on the particle-in-cell (PIC) simulation method is applied to C5+high density plasma expansions. Spherical, cylindrical, and planar expansions are simulated and compared for two cases of initial conditions. In the first, a compact plasma cloud of 22 nm in diameter (width) with the ion densityni0= 1029m-3and the ion and electron temperatureskTi0=kTe0= 10 keV is modeled, while in the second an inflated cloud of 20 µm diameter (width) withni0= 1025m-3andkTi0=kTe0= 100 eV is considered. The expansion wave-front is shown to have a double layer structure which rapidly decays with time. The electrons that are diffused beyond the plasma core, are divided into two groups; runaway electrons and captured ones. The split of temperatures which are based on different components of the particle velocity, demonstrate nonequilibrium nature of expansion. The density and temperatures drop rapidly all over the cloud volume during the compact plasma expansion. In the inflated cloud, there exists a core where the plasma density remains unchanged, while the temperature is gradually decreasing. The geometry dependence of the expanding plasma characteristics is also discussed.
Sensing of Decomposition Products in SF 6 by Use of a Corner Cube Prism Coated with a Dye Film as an Optical Sensor Head
Authors: Marenori Kawamura Marenori Kawamura , Koichi Ishii Koichi Ishii , Susumu Sato Susumu Sato
Published: October 2002

A very sensitive optical sensing method for detecting a small quantity of gaseous decomposition products generated by an electric discharge in SF6 was developed. A sensor head is prepared using a corner cube prism of which three total reflection planes are coated with a thin film of methyl orange dye deposited by a vacuum evaporation method. The methyl orange dye is a color reaction reagent for detection of SF6 gas decomposition products such as HF gas, which is generated due to discharge induced in a glass container filled with SF6 gas. The sensor head connected to a halogen lamp through an optical fiber is placed in the container. This optical sensing method can be used to detect in real time problems or failure occurring in gas-insulated equipment.
Observation of Magnetic Head Fields Using Distorted Transmission Electron Microscopy Images
Authors: Suzuki Hiroshi , Shinada Hiroyuki , Yusuke Yajima Yusuke Yajima , Katsuhiro Kuroda Katsuhiro Kuroda
Published: October 2002

We have observed magnetic fields generated from a thin film magnetic head using transmission electron microscopy (TEM) images. The image in which the shadow of the head appears together with the projected pattern of a reference film is acquired with the use of appropriate defocus. From the pattern distortion in the image, both strong and weak components of the head field can be detected. Furthermore, this method makes it possible to quantitatively analyze, with high spatial resolution, the magnetic field strength which depends on distance from the air bearing surface of the head.
Effects of Ekman Layer on Flows and Temperature of Viscoelastic Fluid in a Rotating Frame
Authors: Sasipalli V. S. Rao , Sasipalli G. Shankar , Raju G. Krishnam , Koichi Harada Koichi Harada
Published: October 2002

An experimental analysis of the hydrodynamic flow of a fluid and the temperature distribution in a porous medium is presented. The experiment has been carried out using viscoelastic fluid in a rotating channel, bounded by two impermeable infinite plates at a constant temperature, under the action of a uniform pressure gradient in the direction of the flow. The primary and secondary flow velocities, the temperature distribution and heat transfer in terms of the Nusselt number of the fluid are studied in the model due to the effects of the Ekman layer on the fluid for various values of the viscoelastic parameter (V
e) in the channel height h=-1 to +1.
Negative Hydrogen Ions Produced by Electron Temperature Control in an RF Plasma
Authors: Satoru Iizuka Satoru Iizuka , Kohgi Kato Kohgi Kato , Akira Takahashi Akira Takahashi , Koji Nakagomi Koji Nakagomi , Noriyoshi Sato Noriyoshi Sato
Published: October 2002

The formation of negative hydrogen ions is investigated in a pure hydrogen RF plasma using a grid-method for electron temperature control. Using the grid method we produce both high and low electron temperature plasmas in the separated regions in the chamber, in which the electron temperature in the downstream region is controlled by the grid potential. The production rate of negative ions depends strongly on the grid potential. We observe efficient negative hydrogen ion production in the downstream region when the grid is negatively biased in the hydrogen pressure range of 2–5 mTorr.
Inductively-Coupled-Plasma-Assisted Planar Magnetron Discharge for Enhanced Ionization of Sputtered Atoms
Authors: Setsuhara Yuichi , Kamai Masayoshi , Musil Shoji Miyake
Published: October 2002

The effects of combining an RF inductively coupled plasma (ICP) with a conventional planar magnetron sputtering discharge have been investigated. The planar magnetron discharge is assisted by the ICP, which is sustained by a helical RF coil immersed in the plasma. Use of the technique significantly enhances the plasma density and the sputtering discharge current. Optical emission measurements of Al ions and neutral lines indicate marked enhancement of ionization of the sputtered atoms after they pass through the dense ICP region.
Doppler-Shifted Laser-Induced Fluorescence Diagnostics of an Ultrahigh-Frequency Discharge Plasma
Authors: Toshiki Nakano Toshiki Nakano , Seiji Samukawa Seiji Samukawa
Published: October 2002

Ultrahigh-frequency (UHF) discharge plasma, as well as electron cyclotron resonance (ECR) plasma and inductively coupled plasma (ICP), is diagnosed in a series of measurements of metastable ion (Ar+, Cl+) and neutral (Ne) temperatures by Doppler-shifted laser-induced fluorescence. Cl+ temperature is found to be lower in UHF plasma and ICP than in ECR plasma. In UHF plasma, the ion temperature weakly depends on both pressure and power, suggesting that plasma uniformity is insensitive to these external parameters. Magnetic multipole confinement enables the production of a stable UHF plasma even at pressures below 0.13 Pa where the plasma cannot be produced without the confinement. In this pressure region, Cl+ temperature is decreased to ≈0.1 eV.
Dual Wavelength Optical Head for 0.6 mm and 1.2 mm Substrate Thicknesses
Authors: Katayama Ryuichi , Yuichi Komatsu Yuichi Komatsu , Yuzo Ono Yuzo Ono
Published: October 2002

A dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses, containing 635 nm and 785 nm laser diodes, has been developed. Holographic optical element (HOE) type optics and variable magnification type optics are described. For both types of optics, high light power efficiency is obtained, which is suitable for random access memory (RAM) applications. Moreover, the use of 785 nm light makes it possible to read compact disc-recordable (CD-R). A readout operation for a quadruple density CD and a conventional CD has been successfully demonstrated.
Electron Attachment Mass Spectrometry for the Detection of Electronegative Species in a Plasma
Authors: Stoffels Winfred Willem , Eva Stoffels Eva Stoffels , Kunihide Tachibana Kunihide Tachibana
Published: October 2002

Electron attachment mass spectrometry (EAMS) has been implemented to detect electronegative species in a low pressure 13.56 MHz discharge. For this purpose a source of low energy electrons has been used in combination with a quadrupole mass spectrometer (QMS) and the signal of the negative ions, resulting from electron attachment to neutrals has been recorded as a function of the electron energy. Chemically active fluorocarbon gases like CF4 and CHF3 have been studied. EAMS provides much insight into chemistry in the plasma, especially into mechanisms of negative ion formation. It enables the detection of electronegative species, formed from the parent gas under plasma conditions, based on their different attachment cross sections. Moreover, the effective negative ion formation cross section in a plasma, taking into account the chemical conversion of the feed gas, can be determined. In fluorocarbon plasmas various species are formed, like C2F6 and C3F8 in a CF4 plasma and CF4 and C2F6 in a CHF3 plasma, which significantly influence the negative ion production mechanisms under discharge conditions. Because the active neutrals produced in the plasma have typically both a larger attachment cross section and a lower attachment energy threshold, negative ion formation is dominated by the plasma species and not by the parent gas.
Effects of Dilution Gases on Si Atoms and SiHx
+ (x = 0–3) Ions in Electron Cyclotron Resonance SiH4 Plasmas
Authors: Yasuo Yamamoto Yasuo Yamamoto , Shinji Suganuma Shinji Suganuma , Masafumi Ito Masafumi Ito , Masaru Hori Masaru Hori , Toshio Goto Toshio Goto
Published: October 2002

The behavior of Si atoms and SiH
x

+ (x=0–3) ions in electron cyclotron resonance (ECR) SiH4/Ar and SiH4/H2 plasmas was investigated by ultraviolet absorption spectroscopy and quadrupole mass spectrometry as a function of microwave power, pressure and SiH4 flow rate ratio. The behavior of ions in SiH4/H2 plasmas is different from that in SiH4/Ar plasmas. This behavior is discussed from the generation and loss of each species. Moreover, the effects of Si atoms and ions on film formation are discussed based on these results.
Digital Video Disk/Compact Disk (DVD/CD)-Compatible Pickup Head with Dual Lens Rotating Actuator
Authors: Takahashi Naomasa , Sato Hiroharu , Nagai Hideaki Osawa Koichi , Isobe Hisao , Kasuga Ikuo
Published: October 2002

Recently, a high-density optical disk system (DVD) which has about 7 times higher recording density than the conventional CD has been proposed and many manufacturers have announced plans to market DVD players in 1996. The DVD is also expected to be used as a large-capacity peripheral memory for personal computers and it is assumed that a DVD drive will be compatible with conventional CDs, i.e., the DVD-ROM drive will be able to read CD-ROMs, as well as DVD-ROMs. We have developed a DVD/CD-compatible pickup head which permits reading of data from both DVDs and CDs by means of exchanging objective lenses. These two types of lenses are set on a common table, where two sets of flat coils are situated in order to exchange lenses. Experimental data show that our dual lens actuator head satisfies our preliminary design targets and performs as well as a single lens actuator.
Optical Emission Diagnostic of Laser-Induced Plasma during CNX Film Deposition
Authors: Aldea Eugen , Caricato Anna Paola , Dinescu Gheorghe , Luches Armando , Perrone Alessio
Published: October 2002

To investigate the characteristics of the plasma plume created by reactive laser ablation (RLA) of graphite, optical emission spectra (OES) of the ablated species were recorded for different distances from the target, for various laser fluences and for several N2 pressures. The spectra were dominated by the molecular bands of C2 and CN radical: C2 Swan and CN violet spectral systems. From the molecular band intensities the rotational and vibrational temperatures of CN radicals were derived though there is not a significant dependence of the temperature with fluence, a strong increase of intensity can be observed with the increase of the laser fluence.
Computer-Aided Design of Microwave Plasma Sources: Potential and Applications
Authors: Walter Marko , Korzec Dariusz , Michael Hütten Michael Hütten , Jürgen Engemann Jürgen Engemann
Published: October 2002

The electrical behavior of SLAN (slot antenna) plasma sources is analysed with the Maxwell equations finite integration algorithm (MAFIA). The influence of the source components and their dimensions on resonance frequencies and power coupling of all eigenmodes up to 3 GHz is studied. Resonances close to the excitation frequency may adversely influence the power absorption in the source. By shifting the frequencies of these resonances the source performance can be optimized. As an example the azimuthal plasma homogeneity of a SLAN microwave plasma source is improved by a proper design. To be more realistic the plasma has been introduced into the simulation as a lossy dielectric. Although this is a crude approach, the results yield useful insights into the local power absorption.