bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement in electrical insulating properties of 10-nm-thick Al2O3 film grown on Al/TiN/Si substrate by remote plasma annealing at low temperatures
Authors: Kim Jihoon , Song Jaewon , Kwon Ohsung , Kim Sungkeun , Hwang Cheol Seong , Park Sang-Hee’Ko , Yun Sun Jin , Jeong Jaehack , Hyun Kwang Soo
Published: July 2002

The electrical conduction properties of 10-nm-thick atomic-layer deposited Al2O3 thin films with Al bottom and Pt top electrodes were characterized for use in field emission display. The as-deposited films, grown at 300 °C, exhibited such a high electrical leakage that their electrical properties could not be measured. However, post-treatment at 300 °C under a remote O2 or H2O plasma for 30 min improved the insulating properties of the Al2O3 films. However, the electrical conduction mechanism, particularly in the high field (>4 MV/cm) was not Fowler–Nordheim (F–N) tunneling but was influenced by space charge limited conduction implying that there were many traps inside the dielectric film or the electrode interfaces. Postannealing of the top electrode at 300 °C in an oxygen atmosphere resulted in a F–N conduction mechanism by removing the interfacial traps. The calculated barrier height at the Al/Al2O3 interface from the F–N fitting of the current density versus voltage curves using the electron effective mass (m*) of 0.5 m0 was approximately 2.0 eV.
Scanning magnetoresistance microscopy with a magnetoresistive sensor cantilever
Authors: Nakamura Motonori , Kimura Michiya , Sueoka Kazuhisa , Mukasa Koichi
Published: July 2002

In this work, a cantilever with a magnetoresistive (MR) sensor is fabricated for scanning magnetoresistance microscope, in order to realize the simultaneous imaging of surface topography and stray magnetic field distribution. A constant current flowing through a meander-patterned metal wire produces a defined magnetic field, and the wire is used as a sample to demonstrate the simultaneous imaging and to reveal the field sensitivity of the cantilever. A MR image has been successfully obtained with lateral spatial resolution of a few μm and a field sensitivity (Hmin≈1.7 Oe) at room temperature.
Effects of poling on the switching properties of SrBi2Ta2O9 films
Authors: Lu Xiaomei , Zhu Jinsong , Zhang Xuesong , Liu Zhiguo , Wang Yening , Chen Xiaobing
Published: July 2002

The effect of poling on the switching properties of SrBi2Ta2O9 films was investigated via the technique of switching current testing. The samples with 660 nm thickness were poled under dc voltage ranging from 1 to 8.25 V, and for different duration from 1 to 80 min. After poling, both the net-switched charge and switching time first jumped to higher values, then decreased with the elapse of time. The decreases were separated into two regimes, a fast and slow regime. The change of net-switched charge and switching time with poling voltage and poling time showed nonmonotonic behavior. These results were explained by the change of domain kinetics and the redistribution of charge carriers under both the applied and depolarization field.
Na
0.5
K
0.5
NbO
3
thin films for voltage controlled acoustoelectric device applications
Authors: Cho Choong-Rae , Katardjiev Ilia , Grishin Michael , Grishin Alex
Published: July 2002

Perovskite Na0.5K0.5NbO3 (NKN) thin films have been prepared on Y+36° cut single crystal quartz substrates using the pulsed laser ablation technique. X-ray diffraction θ–2θ and ω-scan data demonstrate almost perfectly c-axis oriented film textures with narrow mosaic broadening. Radio frequency dielectric spectroscopy showed that the films possess relatively high dielectric permittivities, low dielectric losses, and low frequency dispersions. Capacitance–voltage (C–V) measurements for a 2 μm slot NKN/quartz interdigital capacitor yield 23.1% tunability by applying 40 V bias at 1 MHz, while C–V hysteresis indicates polarization reversal. The considerable voltage tunability with superior crystallinity in piezoelectric NKN films on quartz substrates suggests their potential use for novel voltage tunable acoustoelectric devices.
A general framework for discrete variable representation basis sets
Authors: Littlejohn Robert G. , Cargo Matthew , Carrington Tucker , Mitchell Kevin A. , Poirier Bill
Published: July 2002

A framework for discrete variable representation (DVR) basis sets is developed that is suitable for multidimensional generalizations. Those generalizations will be presented in future publications. The new axiomatization of the DVR construction places projection operators in a central role and integrates semiclassical and phase space concepts into the basic framework. Rates of convergence of basis set expansions are emphasized, and it is shown that the DVR method gives exponential convergence, assuming conditions of analyticity and boundary conditions are met. A discussion of nonorthogonal generalizations of DVR functions is presented, in which it is shown that projected δ-functions and interpolating functions form a biorthogonal basis. It is also shown that one of the generalized DVR proposals due to Szalay [J. Chem. Phys. 105, 6940 (1996)] gives exponential convergence.
Effects of V and Si additions on the coercivity and microstructure of nanocomposite Fe3B/Nd2Fe14B magnets
Authors: Xiong X. Y. , Hono K. , Hirosawa S. , Kanekiyo H.
Published: July 2002

The microstructure and the temperature dependence of the coercivity of nanocomposite Fe3B/Nd2Fe14B magnets with compositions of Nd4.5Fe77B18.5, Nd4.5Fe74B18.5V3 and Nd4.5Fe73B18.5V3Si1 (at. %) have been studied to understand the role of microalloyed elements of vanadium and silicon in improving hard magnetic properties. The results show that the increase in coercivity by adding vanadium and silicon is mainly caused by the increase in the mass fraction of the hard magnetic phase rather than by the decrease in the grain size. Vanadium atoms partition into the soft magnetic phase with a concentration of about 5 at. %, while silicon atoms partition into the hard magnetic phase with a concentration of about 2 at. %. The partitioning of vanadium and silicon causes the Curie temperatures of the both hard and soft magnetic phases to increase. This increase in the Curie temperature, combined with refinement of the microstructure in these nanocomposite magnets, contributes to the enhancement of the exchange coupling, which leads to an increase in the maximum energy product.
Writing of high-density patterned perpendicular media with a conventional longitudinal recording head
Authors: Albrecht M. , Moser A. , Rettner C. T. , Anders S. , Thomson T. , Terris B. D.
Published: July 2002

We have fabricated arrays of magnetic islands in perpendicular CoCrPt media with ∼100 nm lateral dimension using a focused ion beam. A quasistatic write/read tester was used to study aspects of the recording physics of these patterned media. We present results on the variation of the readback signal as the phase of the written square wave changes with respect to the patterned array as a function of island size and write current. Using an analytic near-field expression for head field we are able to model how the observed dependence between phase shift and readback signal as a function of write current arises. This analysis allows us to gain an insight into the role of the island switching field distribution and the write head magnetic field gradient in the patterned media writing process.
Absolute emission current density of O− from 12CaO⋅7Al2O3 crystal
Authors: Li Q. X. , Hayashi K. , Nishioka M. , Kashiwagi H. , Hirano M. , Torimoto Y. , Hosono H. , Sadakata M.
Published: July 2002

Strong and high purity O− negative ion emission has been observed from a synthesized crystal 12CaO⋅7Al2O3 surface. A μA/cm2-level O− emission from this material has been achieved at the surface temperature of 800 °C and the extraction field over 1000 V/cm, which is about three orders of magnitude higher than the current density emitted from the Y2O3-stabilized ZrO2 electrolyte surface. The strong emissivity of this material, as well as easy and economical fabrication, may provide a useful tool to generate the O− negative ion, which is expected to be one of the most important radicals for chemical syntheses and material modifications.
Magneto-thermal shape memory effect in Ni–Mn–Ga
Authors: Glavatska N. , Glavatsky I. , Mogilny G. , Gavriljuk V.
Published: July 2002

A way to produce shape memory in Ni–Mn–Ga alloys is proposed based on the combined action of the magnetic field and heating. A sample is magnetized under applied magnetic field, which results in the magnetic-field-induced strain caused by the reorientation of martensitic domains so that the tetragonal axis c (axis of easy magnetization) is oriented in direction of the applied field. Thereafter the field is switched off and the sample is heated above the Curie temperature and cooled to the start temperature of the experiment, which leads to the full recovery of the size and structure existing before the action of magnetic field. This effect is explained based on the data of x-ray diffraction studies.
Low-energy ion-induced tensile stress of self-assembled alkanethiol monolayers
Authors: Itakura A. N. , Berger R. , Narushima T. , Kitajima M.
Published: July 2002

Monolayers of alkanethiols on gold have been exposed to low energy Ar ion. A micromechanical cantilever sensor technique was used to determine in situ the influence of the ion dose on the surface stress in the monolayers. In contrast to compressive surface stress during self-assembled monolayer growth, a strong tensile surface stress of about −0.7 N/m was found when the sensor is exposed to Ar ions. This value is 3–4 times larger than the compressive surface stress. We attribute this stress to a reaction between the alkyl chains in the molecules of the alkanethiol monolayer.
Phosphorus-doped silicon nanowires studied by near edge x-ray absorption fine structure spectroscopy
Authors: Tang Y. H. , Sham T. K. , Jürgensen A. , Hu Y. F. , Lee C. S. , Lee S. T.
Published: July 2002

The electronic structure and chemical bonding of heavily phosphorus-doped silicon nanowires have been investigated by near edge x-ray absorption fine structure spectroscopy using total electron yield and x-ray fluorescence yield. The results show that the wires are encapsulated within a silicon oxide layer and that the core of the nanowires was crystalline silicon doped with phosphorus. Phosphorus is found to be inside the core of the Si wire as well as at the silicon oxide–core silicon wire interface but not on the surface of the as-prepared nanowire.
Evidence for braggoriton excitations in opal photonic crystals infiltrated with highly polarizable dyes
Authors: Eradat N. , Sivachenko A. Y. , Raikh M. E. , Vardeny Z. V. , Zakhidov A. A. , Baughman R. H.
Published: July 2002

We studied angle-dependent reflectivity spectra of opal photonic crystals infiltrated with cyanine dye aggregates, which are highly polarizable media with very large Rabi frequency. We show that, at resonance condition between the exciton-polariton of the dye aggregate and the Bragg gap, the Bragg stop band decomposes into two reflectivity bands with a semitransparent spectral range in between, that is due to propagation of braggoritons inside the gap.
Effective laser ultrasonic detection with biased GaAs photoelectromotive force detectors
Authors: Castillo J. , Rodriguez P. , Aguirre A. , Stepanov S. , Mansurova S.
Published: July 2002

Improvement of the sensitivity of laser-induced ultrasonic detection by GaAs adaptive photoelectromotive force (photo-EMF) devices under external dc bias is reported. The gain in responsivity of the detector about 7× in ≈10 MHz frequency band was observed under application of an external dc field ≈50 V/mm at λ=633 nm. Detailed experiments show that this growth is paid by proportional shift of maximum of the photo-EMF response to lower spatial frequencies and by appearance of a relatively broad resonance pick located at modulation frequencies lower than the cutoff frequency of the unbiased GaAs photo-EMF detector. These results are consistently interpreted using a theoretical model of the photo-EMF effect in bipolar photoconductor with large lifetime of one type of the photocarriers.
Substrate nanoprotrusions and their effect on field electron emission from amorphous-diamond films
Authors: Chen Jian , Deng S. Z. , Chen Jun , Xu N. S. , Huq S. E.
Published: July 2002

Geometrical field-enhancement structures at the surface of a substrate have been expected to effectively lower fields required to inject electrons from the substrate into amorphous-diamond (a-D) films. Two techniques have been developed to create a high density of nanoprotrusions on substrate surfaces: (a) on silicon (Si) substrates using our patented chemical-etching technique, and (b) on aluminum (Al) film by following a special deposition procedure. The density of nanoprotrusions can be as high as 108/cm2, and the mean roughness of the substrates is 2–30 nm. From a-D emitters, substrate surfaces with such nanoprotrusions can lower the field for emission. The results are discussed in light of several existing theoretical models.
Dislocation-free formation of relaxed SiGe-on-insulator layers
Authors: Tezuka T. , Sugiyama N. , Takagi S. , Kawakubo T.
Published: July 2002

We demonstrate the fabrication of dislocation-free strain-relaxed SiGe-on-insulator (SGOI) layers as virtual substrates for strained Si-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) by forming SiGe-mesa structures and successive oxidation. A pseudomorphic Si0.9Ge0.1 layer on a SOI layer was etched to form mesa structures. After the oxidation of the mesas, thin (<100 nm) Si0.85Ge0.15 mesa structures were formed on the buried oxide layer. It was found that the mesas with a diameter smaller than 3 μm were almost completely relaxed after oxidation at 1200 °C, without generating any threading dislocations and crosshatch patterns, which generally exist in the relaxed SiGe layers on bulk Si substrates. The formation of SGOI mesas before oxidation has the potential to provide ideal SGOI virtual substrates for strained SOI MOSFETs.
Low-etch-pit-density GaN substrates by regrowth on free-standing GaN films
Authors: Tsai Chiung-Chi , Chang Chen-Shiung , Chen Tsung-Yu
Published: July 2002

In this study, GaN substrates with low-density etch pits were obtained by regrowth on free-standing GaN films (two steps) by hydride vapor-phase epitaxy (HVPE). The etch-pit density was lower than 4×104 cm−2 by atomic-force microscopy. The density is significantly lower than that of the HVPE-grown (one-step) GaN films (HVPE GaN), using sapphire as a substrate. The optical and electrical properties of the two-step HVPE-grown GaN substrates are superior to those of HVPE GaN. Temperature-dependent photoluminescence measurements reveal that thermal quenching behavior of the 2.9 eV band is possibly attributed to a shallow acceptor level at about 118±5 meV above the valence band.
Nondiffracting periodically space-variant polarization beams with subwavelength gratings
Authors: Bomzon Ze’ev , Niv Avi , Biener Gabriel , Kleiner Vladimir , Hasman Erez
Published: July 2002

A class of propagation-invariant vector fields with uniform intensity and periodically space-varying polarization is presented. The beams were formed using computer-generated space-variant subwavelength gratings. A theoretical analysis as well as experimental results using gratings designed for CO2 laser radiation at a wavelength of 10.6 μm is discussed.
Reliable extraction of the energy distribution of Si/SiO2 interface traps in ultrathin metal–oxide–semiconductor structures
Authors: Khosru Quazi Deen Mohd , Nakajima Anri , Yoshimoto Takashi , Yokoyama Shin
Published: July 2002

A simple and effective method for the extraction of interface trap distribution in ultrathin metal–oxide–semiconductor (MOS) structures is presented. By a critical analysis of bipolar-pulse-induced currents through MOS capacitors, a technique is developed to determine the energy distribution of the interface traps without requiring the knowledge of surface potential and doping profile in the semiconductor. The proposed technique can be efficiently used to probe electrical stress, hot-carrier, and radiation-induced interfacial degradations in ultrathin MOS structures.
Ab initio calculations of the dissociative attachment resonance energies for an octafluorocyclopentene molecule with comparisons to electron attachment mass spectrometric measurements
Authors: Nakamura Toshihiro , Tachibana Kunihide
Published: July 2002

Dissociative electron attachment to an octafluorocyclopentene (c-C5F8) molecule has been investigated by means of ab initio molecular orbital calculations. Because of the antibonding character of the virtual valence orbitals, the temporary anions dissociate, producing neutral and negative radical fragments in reactive plasma. In order to identify the valence of virtual orbitals associated with the dissociative electron attachment in the calculation with the diffuse basis set, we examined the spatial distribution and antibonding characteristics of the virtual molecular orbitals. This theoretical approach reproduced experimental resonance energies of the dissociative electron attachment, which display rich resonance energy spectra as observed by electron attachment mass spectrometry.
High efficiency nonvolatile ferromagnet/superconductor switch
Authors: Nadgorny B. , Mazin I. I.
Published: July 2002

A composite magnetosuperconducting switch is proposed. The device, which is based on Andreev reflection at the superconductor/ferromagnet contact, combines high efficiency with nonvolatility. The low-impedance state of the device corresponds to the normal state of the superconductor, whereas the high-impedance state corresponds to the superconducting state. The proposed device does not require high-quality Andreev contacts; on the contrary, interface scattering significantly increases the efficiency of the device. Up to 1000%–2500% efficiency can be achieved with the existing ferromagnetic materials. The device can be used as a basic element for nonvolatile logic and memory.
Dynamics of crystallization and phase transition in La0.5Sr0.5CoO3 thin films
Authors: Chang Hauyee , Chen C. L. , Garrett T. , Chen X. H. , Xiang X.-D. , Chu C. W. , Zhang Q. Y. , Dong C.
Published: July 2002

Dynamics of crystallization and phase transitions were investigated in La0.5Sr0.5CoO3 films with four-probe resistance electrical measurements and x-ray diffraction. Nucleation of crystalline phases from the amorphous phase of La0.5Sr0.5CoO3 was found to start at a temperature of 325 °C. It is very interesting to note that the crystallization completes within a very narrow temperature range of 390–420 °C, and recrystallization occurs at 560 °C. In addition, electron–phonon, electron–grain boundary, and electron–defect interactions, as well as oxygen contents were found to be important factors in various temperature regions during the resistance measurement. The metallic phase La0.5Sr0.5CoO3 films can only be obtained if the films were directly heated to higher than 750 °C. The sequence and knowledge of phase transitions observed for La0.5Sr0.5CoO3 are expected to be ubiquitous for perovskite oxide compounds in general.
Enhancement of mechanical and superconducting properties of MgB2
Authors: Rhyee Jong-Soo , Kim C. A. , Cho B. K. , Kim Jin-Tae
Published: July 2002

We demonstrate the higher mechanical strength and density and superconducting properties of MgB2 compounds by controlling the initial mixing ratio of Mg and B in a Ta tube. It is found that the extra Mg as a starting element in a sealed Ta tube establishes a good environment for the formation of MgB2 with a large grain size of 9–16 μm diam, rather than existing as an impurity. As a result, MgB2, which was synthesized from mixing a ratio of Mg:B=1.3:2, shows much higher mechanical strength and density. In addition, electrical and superconducting properties are also enhanced for application, which indicates a more effective interconnection between grains. The critical current density is increased almost by two times compared with the compound, synthesized from the stoichiometric starting elements, which is important for the application of MgB2.
Modification of laser energy deposition in a gas of deuterium clusters
Authors: Symes D. R. , Comley A. J. , Tisch J. W. G. , Smith R. A.
Published: July 2002

The modification of energy deposition by a 70 fs laser pulse focused to an intensity of 1017 W cm−2 in a medium of deuterium clusters with mean atomic density of 1019 cm−3 has been investigated using short-pulse interferometry. A low-power (<1015 W cm−2) beam propagating transverse to the heating beam was used to destroy clusters in the low-density wings of the medium prior to the arrival of the main heating pulse. Images of the plasma channels produced by the heating beam show that the transverse beam can strongly modify the spatial deposition of laser energy. Using this effect, we have demonstrated a 15-fold enhancement of energy coupling to the densest regions of the cluster medium.
Local control of dynamic nuclear polarization in quantum Hall devices
Authors: Machida Tomoki , Yamazaki Tomoyuki , Komiyama Susumu
Published: July 2002

We manipulate and detect local nuclear spin polarization in integer quantum Hall (IQH) systems using micrometal strips fabricated on top of Al0.3Ga0.7As/GaAs Hall bar devices. The radio-frequency (rf) magnetic fields generated by transmitting rf electrical currents through the micrometal strips causes nuclear magnetic resonance in a limited region along IQH edge channels, and resulting changes in the nuclear spin polarization are detected via Hall resistance of the devices.
Optical emission investigation of laser-produced MgB2 plume expanding in an Ar buffer gas
Authors: Amoruso S. , Bruzzese R. , Spinelli N. , Velotta R. , Wang X. , Ferdeghini C.
Published: July 2002

Optical emission spectroscopy is used to study the dynamics of the plasma generated by pulsed-laser irradiation of a MgB2 target, both in a vacuum and at different Ar buffer gas pressures. The analysis of the time-resolved emission of selected species shows that the Ar background gas strongly influences the plasma dynamics. Above a fixed pressure, plasma propagation into Ar leads to the formation of blast waves causing both a considerable increase of the fraction of excited Mg atoms and a simultaneous reduction of their kinetic flux energy. These results can be particularly useful for optimizing MgB2 thin-film deposition processes.
Reversible changes in the lattice site structure for In implanted into GaN
Authors: Lorenz K. , Ruske F. , Vianden R.
Published: July 2002

The perturbed angular correlation method was employed to study the lattice environment of In implanted into GaN. It was found, after annealing the implantation induced damage, that 65% of the implanted atoms were situated in regular undisturbed Ga lattice sites. The remaining fraction showed an unusual behavior insofar as its lattice surroundings changed reversibly from undisturbed at temperatures above 600 K to strongly disturbed at low temperatures.
Effects of rapid thermal annealing on the optical properties of 1.3 μm InGaAlAs multiquantum wells grown by digital-alloy molecular-beam epitaxy
Authors: Dong Song Jin , Su Yu Jae , Min Kim Jong , Ju Bae Seong , Tak Lee Yong
Published: July 2002

We investigated the effect of rapid thermal annealing (RTA) on the optical properties of digital-alloy 1.3 μm InGaAlAs multiquantum-well structure grown by molecular-beam epitaxy at RTA temperature (TRTA) in the range of 400 °C–675 °C. Photoluminescence (PL) peak intensity taken at room temperature rose drastically at TRTA above 625 °C, which increased up to ∼500 times larger at TRTA of 650 °C and RTA time of 60 s than that of as-grown sample without any significant shift of PL peak wavelength. This extraordinary increase of PL peak intensity at TRTA⩾625 °C is attributed to the curing of nonradiative centers mainly in InAlAs grown at a lower temperature than its congruent temperature, and partially at the heterointerfaces between InGaAs/InAlAs short-period superlattices.
Collective transport in locally asymmetric periodic structures
Authors: Derényi I. , Tegzes P. , Vicsek T.
Published: July 2002

In this paper we give an overview of the cooperative effects in fluctuation driven transport arising from the interaction of a large number of particles. (i) First, we study a model with finite-sized, overdamped Brownian particles interacting via hard-core repulsion. Computer simulations and theoretical calculations reveal a number of novel cooperative transport phenomena in this system, including the reversal of direction of the net current as the particle density is increased, and a very strong and complex dependence of the average velocity on both the size and the average distance of the particles. (ii) Next, we consider the cooperation of a collection of motors rigidly attached to a backbone. This system possesses dynamical phase transition allowing spontaneous directed motion even if the system is spatially symmetric. (iii) Finally, we report on an experimental investigation exploring the horizontal transport of granular particles in a vertically vibrated system whose base has a sawtooth-shaped profile. The resulting material flow exhibits complex collective behavior, both as a function of the number of layers of particles and the driving frequency; in particular, under certain conditions, increasing the layer thickness leads to a reversal of the current, while the onset of transport as a function of frequency occurs gradually in a manner reminiscent of a phase transition.
Measurement of spatial correlation functions using image processing techniques
Authors: Berryman James G.
Published: July 2002

A procedure for using digital image processing techniques to measure the spatial correlation functions of composite heterogeneous materials is presented. Methods for eliminating undesirable biases and warping in digitized photographs are discussed. Fourier transform methods and array processor techniques for calculating the spatial correlation functions are treated. By introducing a minimal set of lattice-commensurate triangles, a method of sorting and storing the values of three-point correlation functions in a compact one-dimensional array is developed. Examples are presented at each stage of the analysis using synthetic photographs of cross sections of a model random material (the penetrable sphere model) for which the analytical form of the spatial correlations functions is known. Although results depend somewhat on magnification and on relative volume fraction, it is found that photographs digitized with 512×512 pixels generally have sufficiently good statistics for most practical purposes. To illustrate the use of the correlation functions, bounds on conductivity for the penetrable sphere model are calculated with a general numerical scheme developed for treating the singular three-dimensional integrals which must be evaluated.
Didymium-Fe-B sintered permanent magnets
Authors: Okada M. , Sugimoto S. , Ishizaka C. , Tanaka T. , Homma M.
Published: July 2002

Present works describe the developments the low cost R-Fe-B sintered permanent magnets. Three different didymiums are chosen for the low cost mixtures of rare-earth elements. The studied alloy compositions are Fe-(32.5–34.5)wt. %R-(1–1.6)wt. %B, where R elements are didymium (Nd-10wt. %Pr), 5Ce-didymium (Nd-15%Pr-5%Ce), and 40 Ce-didymium (Nd-10%Pr-40%Ce). The specimens were prepared by the conventional powder metallurgical techniques. The best magnetic properties obtained in this studies are Br=13.2 kG, iHc=10.2 kOe, and (BH)max=40 MGOe with the Fe-33.5% (5Ce-didymium)-1%B alloy. Temperature dependence of iHc of this alloy is almost comparable to that of the Nd-Fe-B alloys.
Phase transition and compression of LiNbO3 under static high pressure
Authors: da Jornada J. A. H. , Block S. , Mauer F. A. , Piermarini G. J.
Published: July 2002

Lattice parameters of LiNbO3 were measured at room temperature over the pressure range 0–35 GPa by x-ray diffraction using the diamond anvil cell. In the region below 13 GPa (where a hydrostatic pressure was maintained) the pressure dependence of the volume can be well described by the Birch–Murnaghan equation of state, yielding B0=134±3 GPa for the zero-pressure bulk modulus and B′0 =2.9±0.5 for its pressure derivative. A phase transformation was detected at 30±3 GPa both by x-ray diffraction and by optical observation of the change from a transparent to an opaque state. The pattern of the high-pressure phase was tentatively indexed on the basis of a cubic cell with a=6.78 Å.
Slip effect for thin liquid film on a rotating disk
Authors: Yanagisawa Masahiro
Published: July 2002

A flow for thin liquid films on rotating disks has been theoretically and experimentally studied. Liquid depletion behavior during a spin-coating process is calculated by solving the Navier–Stokes equation, taking into account interface slip between liquid and disk. Excellent agreement is seen between the model prediction and experimental data. According to observed depletion behavior on thin liquid films for various spin-coating parameters, half life falls off at the inverse square of rotational speed, and increases when viscosity increases, although the increasing rate falls off. The interface slip, represented as an external friction coefficient, is thermodynamically explained by the different (Δrc) in critical surface tension (rc) values between the liquid and the disk, which will be proportional to the solubility parameter. An infinite external friction coefficient, representing nonslip flow, may be given, when Δrc is zero. Spin-off experiments for liquids of various rc values, prepared by differing surface treatments, support this consideration.
Growth of CdTe on GaAs by hot-wall epitaxy and its stress relaxation
Authors: Tatsuoka H. , Kuwabara H. , Fujiyasu H. , Nakanishi Y.
Published: July 2002

CdTe(100) layers of the thickness range from 0.7 to 15 μm were grown on GaAs(100) substrates by hot-wall epitaxy. The crystallinity of the layer was examined by reflection high-energy electron diffraction, x-ray rocking curve, and photoluminescence. The lattice relaxation were investigated by x-ray analysis and optical reflectance spectra. CdTe layers with thickness up to 15 μm were under compressive biaxial stress. In addition to the split exciton lines (n=1), the emission from excited states (n=2) was observed.
Structure of the Fe-doped high-temperature superconductors Y1Ba2Cu3Oy and Bi2Sr2Ca1Cu2Oy
Authors: Bremert O. , Michaelsen C. , Krebs H. U.
Published: July 2002

The high-temperature superconductors YBa2(Cu1−xFex)3Oy and Bi2Sr2Ca1(Cu1−xFex)2Oy have been examined by resistivity measurements, x-ray diffraction, and Mössbauer experiments in order to understand the influence of Fe on the structure of the perovskites. The concentration dependence of the Fe substitution and the results of the annealing experiments are consistent with the following model which explains the observed structural changes with Fe composition in YBa2Cu3Oy. For low Fe content, the Fe atoms mainly substitute on the Cu(I) sites leading only to a slight decrease of Tc, but to an attraction of more oxygen ions, which are introduced into the (001) plane. The Fe ions with five- or sixfold coordination act like local symmetry points inducing the formation of short orthogonal chains crossing at the Fe ions. This leads to the orthorhombic-to-tetragonal transition at an Fe concentration of 2.3%. For higher Fe content, Tc more rapidly decreases, probably due to a partial substitution of Fe also on the Cu(II) sites of the perovskite until the superconductivity vanishes near 16% Fe. The three occuring Mössbauer doublets are assigned to different (four-, five-, and sixfold) oxygen environments of the Fe ions. Similar environments occur in Bi2Sr2Ca1Cu2Oy with 20% Fe, although it is known that no Cu-O chains exist in this structure.
Effects of oxygen impurities in W films on W/GaAs Schottky-barrier contacts
Authors: Kuriyama Youichi , Ohfuji Shin-ichi
Published: July 2002

Schottky-barrier characteristics and chemical reactions of contacts between oxygen-contained W films and GaAs substrates annealed up to 800 °C have been investigated. Phase transformation from β-W to α-W of the oxygen-contained W films (3 at. % oxygen), sputter deposited in Ar and O2 gas mixture, is observed at temperatures around 650 °C. Electrical degradation of the contacts, especially in capacitance-voltage (C-V) characteristics, is found after annealing above 650 °C. Oxygen accumulation at the W/GaAs interfacial region and Ga and As atom diffusion into the W films are found by secondary-ion mass spectrometry during annealing. Formation of a Ga2O3 layer at the interfacial region is also detected by x-ray photoemission spectroscopy and transmission electron microscopy. These results suggest that Ga2O3-layer formation is related to the electrical degradation. The C-V characteristics can possibly be explained by series capacitance of an interfacial oxide layer and a depletion layer together with an assumption of nonuniform carrier distribution in the GaAs substrate.
Electron states in mesa-etched one-dimensional quantum well wires
Authors: Snider G. L. , Tan I.-H. , Hu E. L.
Published: July 2002

Two-dimensional, self-consistent solutions of the Schrödinger and Poisson equations are used to find the electron states in GaAs/AlGaAs quantum well wires. Both deep and shallow mesa structures are simulated. Our results show that while these structures are capable of providing the single occupied subband and wide energy separations needed for a true quantum wire, the process tolerances allowed are very small, on the order of 200 Å of width variation. Cutoff widths calculated are 1000 Å for the shallow mesa and 2100 Å for the deep mesa. The agreement with experimental results is good for the shallow mesa, but poor for the deep mesa. This suggests additional process-induced sidewall depletion mechanisms contributing to the cutoff of the deep mesa structures.
Growth-induced shallow acceptor defect and related luminescence effects in molecular beam epitaxial GaAs
Authors: Szafranek I. , Plano M. A. , McCollum M. J. , Stockman S. A. , Jackson S. L. , Cheng K. Y. , Stillman G. E.
Published: July 2002

We report a study of a defect responsible for the ‘‘g’’ bound exciton line at 1.5112 eV that is frequently detected in photoluminescence spectra of GaAs grown by molecular beam epitaxy (MBE). A direct correlation has been observed between this line and a transition at 1.4946 eV, which is shown to result from a conduction band-to-acceptor recombination involving a shallow, unidentified acceptorlike defect that is labeled ‘‘A.’’ The activation energy of the defect is 24.8±0.2 meV, about 1.7 meV lower than that of CAs acceptor. Upon hydrogenation the defect is passivated more extensively than any known shallow acceptor species in GaAs. This result is analyzed in terms of a passivation model, from which it can be inferred that the A defect is not due to a simple substitutional Group II impurity on a Ga site. Incorporation of the A defect strongly affects the luminescence properties of the material. An almost complete quenching of the donor-bound exciton lines, profound changes in the line shape and relative intensity of the free exciton recombination, and appearance of a sharp transition of unknown origin at 1.5138 eV were observed with increasing defect concentration. Apparently ‘‘donorless’’ low temperature exciton recombination spectra are reported for defect-rich p-type MBE GaAs layers with donor concentrations as high as 7×1014 cm−3 and compensation ratios of ∼0.3. The dependence of the defect incorporation on MBE growth parameters is discussed. The feasibility of MBE growth of high purity, nearly shallow defect-free p-type GaAs layers at marginally As-stabilized surface conditions over an about 1–5 μm/h range of deposition rates is demonstrated.
On the photoemission from quantum-confined Kane-type semiconductors
Authors: Ghatak K. P. , Mondal M.
Published: July 2002

An attempt is made to investigate the photoemission from ultrathin films, quantum wires and quantum dots of degenerate Kane-type semiconductors, respectively, on the basis of a newly derived dispersion relation of the conduction electrons allowing all types of anisotropies of the band parameters within the framework of k⋅p formalism. It is found, taking n-Cd3As2 as an example, that the photoemission increases with increasing photon energy in a ladderlike manner and also exhibits oscillatory dependences with changing electron concentration and film thickness, respectively, for all types of quantum confinement. The photoemitted current density is greatest for quantum dots and least for ultrathin films in all the cases. In addition, the well-known results for bulk specimens of parabolic semiconductors have also been obtained from the generalized expressions under certain limiting conditions.
Stress, strain, and microstructure of sputter-deposited Mo thin films
Authors: Vink T. J. , Somers M. A. J. , Daams J. L. C. , Dirks A. G.
Published: July 2002

Mo thin films were deposited on glass substrates using direct-current (dc) planar magnetron sputtering. Mechanical determination of the internal stresses, using the bending-beam technique, yielded typical compressive-to-tensile stress transition curves with increasing working-gas pressure. The microstructure of the compressively stressed films consists of tightly packed columns, whereas in the tensily stressed films the development of a void network structure surrounding the columnar grains is observed. At elevated working-gas pressures the onset of microcolumns is observed in the initial stage of film growth. Determination of lattice strains by x-ray diffraction (XRD), utilizing the sin2 ψ method, encounters more difficulties than the more straightforward stress determination by the bending-beam method. Here special attention is focused on deviations from linear dependence of dψ with sin2 ψ along with asymmetry of XRD line profiles that results from stress-depth profiles as well as lateral stress distributions in the tensily stressed films. These anomalies and the discrepancy between bending-beam stresses and XRD lattice strains, observed for high working-gas pressures, can be interpreted in terms of microstructural features revealed by cross-sectional transmission electron microscopy.
Dynamic tortuosity and bulk modulus in air-saturated porous media
Authors: Champoux Yvan , Allard Jean-F.
Published: July 2002

In this paper, the concept of characteristic length introduced in the definition of the dynamic tortuosity by Johnson, Koplik, and Dashen [J. Fluid Mech. 176, 379 (1987)] is extended to express the frequency dependence of the bulk modulus of the saturating fluid at high frequencies. A general phenomenological frequency dependence for this dynamic bulk modulus is obtained using the expression for the dynamic tortuosity. The theoretical predictions for dynamic tortuosity and bulk modulus are compared with experimental results obtained from acoustic measurements on a rigid-frame porous material saturated with air.
Polymer behavior under plasma etching:  Influence of physical properties on kinetics and durability
Authors: Joubert O. , Paniez P. , Pons M. , Pelletier J.
Published: July 2002

The influence of the physical properties of polymers on their plasma behavior has been investigated under O2 and Ar plasma treatments. The glass transition temperature (Tg) has been found to be an important parameter. A steplike increase in the etch kinetics in O2 plasmas has been correlated to the change in the heat capacity of the polymer occurring above Tg whatever the molecular weight of the polymer. Furthermore, above Tg, changes in the viscoelastic properties induce bulk polymer degradation if chain crosslinking cannot be achieved before or during plasma etching.
Electro-optic response of polymer dispersed liquid-crystal films
Authors: Jain S. C. , Rout D. K.
Published: July 2002

The electro-optic response of polymer dispersed liquid-crystal (PDLC) films is reported as a function of frequency and amplitude of the applied voltage and size of the LC droplets. We found that the threshold voltage is minimum and sharpest at frequencies near a few kHz. Visual and optical response studies show that there are two types of PDLC films; type I, which exhibit large partial optical memory, and type II, which quickly regain their original levels of transmittance after switching off relatively small driving voltage. It was observed that both types of PDLC films, in general, exhibit a two-step decay involving fast and slow components. However, the order in which the two components appear as the voltage is increased is different for the two types of PDLC films. Observations under the polarizing microscope show that the LC droplets in the two types of PDLC films undergo different transformations as the applied voltage is changed.
Characteristics of pyrophosphoric acid proton-exchanged waveguides in LiNbO3
Authors: Yamamoto K. , Taniuchi T.
Published: July 2002

The characteristics of proton-exchanged LiNbO3 waveguides fabricated using pyrophosphoric acid process are reported. Using this process, high index change waveguides with step profile have been realized. Low-loss (0.7 dB/cm) channel waveguides have been also obtained by pyrophosphoric acid process. The loss is much lower than that given by conventional benzoic acid process. We show that the reason for low-loss waveguide fabrication is due to the uniform proton-exchange formed by this process, compared with the benzoic acid process.
Energy distribution of negative O− and OH− ions emitted from YBaCuO and iron garnet targets by dc and rf magnetron sputtering
Authors: Krumme Jens-Peter , Hack Ron A. A. , Raaijmakers Ivo J. M. M.
Published: July 2002

Energy-dispersive mass spectrometry has been used to analyze the energy distribution of O− and OH− species ejected from YBaCuO and iron-garnet targets by Ar+, Kr+, and Xe+ bombardment in H2- and in O2-doped dc and rf magnetron plasmas at 0.05–4.2 Pa pressure. The orifice of the plasma monitor was at 70 mm from the erosion groove underneath the plasma ring. The energy spectra of O− and OH− ions are found to exhibit two major peaks: a sharp one at typically 20 eV termed A and a sharp (dc case) or broad (rf case) peak termed B at higher energies. Peak-A ions may be formed near the edge of the cathode sheath by electron attachment to sputtered neutral oxygen atoms accelerated in the remaining potential gradient of the sheath. Peak-B ions are shown to be accelerated from the target surface to kinetic energies given by the potential gradient across the cathode sheath. In the case of rf magnetron plasmas the total flux of O− and OH− ions associated with the peak B steeply increases with pressure up to ∼0.6 Pa for argon, ∼0.4 Pa for krypton, and ∼0.3 Pa for xenon, concomitant with a shift of the mean particle energy from ≳100 eV at 0.1 Pa to <35 eV at these characteristic pressures. This behavior may be explained by charge-exchange collisions within the rf sheath. At pressures beyond this maximum the total flux of negative ions declines due to electron detachment in regions remote from the plasma which may be caused by collisions with noble-gas atoms and Maxwellian electrons, and by charge transfer to positive noble-gas ions. At pressures beyond several Pa elastic scattering is the dominant loss mechanism of energetic atomic oxygen species. Doping of the noble-gas plasma at the vol % level by oxygen or hydrogen causes severe changes of the O− and OH− yield resulting from a change in the density of oxygen vacancies in the target surface. For argon, krypton, and xenon the yield of O− ions is ≳20 times higher with the YBaCuO target, as compared to the iron-garnet target, due to the larger electronegativity of the BaO bond. From these data optimum conditions for magnetron sputtering of YBaCuO films are derived, as summarized in the conclusions.
Bounds for field fluctuations in two-phase materials
Authors: Axell Jörgen
Published: July 2002

In this paper we obtain lower and upper bounds on the field fluctuations in two-phase, isotropic, statistically homogeneous materials. The bounds are optimal in two dimensions, since they are attained by certain geometries, and in three dimensions two of the four bounds are optimal. The other two are believed to be good, and may be optimal. The bounds improve on earlier work by Beran [J. Math. Phys. 21, 2583 (1980)].
Optical tuning by angular constraint of the electron gas in a cylindrical quantum well
Authors: Huang Danhong , Gumbs Godfrey
Published: July 2002

The dielectric response of an electron gas in a cylindrical quantum well is calculated when the electron motion in the angular direction is restricted. The dielectric response is shown to depend in a nontrivial way on the angle of restriction β thereby making it possible to tune the optical response to external electromagnetic radiation. The resonant absorption wavelength can be adjusted by changing β over a wide range which might be used in optoelectronic detectors.
Radiation damage in SiO2/Si induced by low-energy electrons via plasmon excitation
Authors: Yunogami Takashi , Mizutani Tatsumi
Published: July 2002

We have found definite evidence which proves that radiation damage in SiO2/Si induced by low-energy electrons is caused by plasmon excitation in SiO2. The SiO2/Si sample was irradiated by accelerated thermoelectrons, and the flat-band voltage shift, ΔVFB, of the sample was measured by the C-V method. The effective charge generation yield, Rf, in SiO2/Si was evaluated from the ΔVFB and the electron dose. The effective positive charges were measured in p-type SiO2/Si, and the effective negative charges were measured in n-type SiO2/Si. This is because interface states behave like positive charges in p-type SiO2/Si and negative charges in n-type SiO2/Si. The Rf in p-type SiO2/Si oscillated as a function of the incident electron energy of 5–150 eV with several clear peaks. These peaks correspond to the quantum energy of a bulk plasmon or a surface plasmon. Both plasmons decay into electron-hole pairs. The holes that escape from recombination with the electrons are trapped at the SiO2/Si interface and cause effective positive charges. The Rf was maximum when the SiO2 thickness was 20 nm, independent of the incident electron energy. This is because the plasmon region extends to about 20 nm in SiO2, and the hole-trapping efficiency is expected to be maximum at a SiO2 thickness of 20 nm.
A fundamental mode, high-power, large-orbit gyrotron using a rectangular interaction region
Authors: Radack D. J. , Ramaswamy K. , Destler W. W. , Rodgers J.
Published: July 2002

This paper reports on experimental and theoretical studies of a fundamental mode, large-orbit gyrotron oscillator designed to produce high-power radiation in the rectangular TE10 mode at about 650 MHz. A basic linear theory for design and operation is presented and experiments confirm its applicability. Results of initial experiments have demonstrated 40±4.2 MW of microwave radiation in pulses equivalent in duration to the electron beam, corresponding to an efficiency of about 16%. In some cases, much greater power levels of 100±20 MW were observed at the expected frequency but in pulses of very short duration. In both cases, the observed frequency and mode pattern were consistent with operation in the fundamental mode. Experiments also demonstrated that the observed radiation was linearly polarized, as expected.
Transport critical-current properties of Bi2Sr2CaCu2Ox/Ag tapes
Authors: Jain Kiran , Tripathi R. B. , Das B. K.
Published: July 2002

High-transport critical-current density Jc is essential for major bulk applications of the high-Tc superconductors. The critical temperature Tc of the 2212 Ag sheathed tapes was found to increase by quenching the samples, but the transport critical-current density Jc for a slow-cooled sample was higher at low temperature.  Jc as well as its temperature dependence was found to be influenced by the heat treatments, i.e., whether the sample was quenched or slow cooled after the sintering heat treatment. The zero-field Jc was found to be quadratic in 1-T/Tc for the slow-cooled sample, while a linear dependence was observed for the quenched sample. These results are explained in terms of the weak-link structure.