bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-resolved spectroscopy of superconductors using synchrotron infrared pulses (abstract)
Authors: Carr G. L.
Published: July 2002

Infrared synchrotron radiation is a high brightness, pulsed source that enables a variety of novel spectroscopic techniques. One of these is time-resolved, broadband spectroscopy for probing dynamical processes. At the National Synchrotron Light Source (Brookhaven) we have implemented a synchronized laser system for performing pump–probe spectroscopy of superconductors and other materials. In the case of superconductors, we use laser pulses to break Cooper pairs, producing an excess population of quasiparticles. The relaxation (recombination) of this population is then probed with synchrotron infrared pulses, and analyzed in terms of the intrinsic relaxation times for excited quasiparticles and phonons. This presentation will describe the time-resolved technique and results for various metallic and oxide superconductors.
An improved approach for precise in situ measurements of microflows
Authors: Zhang Xuanxiong , He Xujiang , Xu Yuan , Gong Thomas H. , Tay Francis Eng Hock
Published: July 2002

An improved approach for extremely low fluid dosing rate on-line measurements was described. The approach can be employed to conduct in situ calibration of microfluidic devices. It is essentially a standard gravimetric method, with some modifications. The experimental setup included a high precision balance interfaced to a data sampling/processing PC. The continuous dosing rate generated from an electrochemical actuator was measured. A stable dosing rate reached as low as 0.19 μl/min (deionized water), which was lower than the water evaporation rate.
Human cadaverous finger bone images by synchrotron x rays (abstract)
Authors: Lee Kyu-Ho , Suh S. S. , Tsai W. L. , Chung I. H. , Lee H. Y.
Published: July 2002

Using unmonochromotized synchrotron radiation and a simple image detecting system at the 5C1 beam line of PLS in Korea, human cadaverous finger bones of various conditions were visualized with extremely high resolution. Bone images of synchrotron radiation were verified by figures and their characteristics qualified with respect to the calcium content. They were also compared with images and information from other radiological instruments including conventional x-ray, dual energy densitometry and micro-computed tomography. Synchrotron images of older human cadaverous bones in poorer condition showed flat and narrow traveculae with fragmentation, and shift were noted to the right by brightness. These findings seem to be considered as valuable information for the diagnosis of bone related diseases in the clinic.
Design, construction, and measurements of a bender, which provide constant position of the central part of the crystal monocromator during bending process (abstract)
Authors: Artemev A. , Artemiev N. , Busetto E. , Franc F. , Hrdý J. , Mrázek D. , Savoia A.
Published: July 2002

The bender described is a part of the double crystal monochromator for the QUICKEXAFS spectrometer, which is under development for ELETTRA. Technical specification for the bender include the following: constant position of the central point of the crystal during the bending process, the full size of the crystal must be as small as possible in the dynamic bending process, and the bender must be highly vacuum compatible. To satisfy all of these demands we propose a new scheme for a bender of rectangular crystal with four living supports. The bender has two inner wings, which bear two inner crystal supports, and two outer wings, which bear two outer supports. These wings are moved by two cones placed on the same rod. The cones have different profiles. In order to keep the central part of the crystal in a constant position during the bending process these cone profiles are designed and manufactured in a very special way. Measurements of the bender characteristics were made with the help of a test bench. Instead of a Si single crystal we used a bronze plate of the same size, which had very similar elastic constants. The full scattering of the position of the central part of the bronze plate during the bending process is less then 100 μm. The measured profile of the plate bent to about 506 mm was compared with a circle fitted by the least square method. The relative difference between measured and fitted radius appeared to be about 10−5.
Instrumentation for synchrotron based micromachining at the Center for Advanced Microstructures and Devices (abstract)
Authors: Aigeldinger G. , Goettert J. , Desta Y. , Ling Z. L. , Rupp L.
Published: July 2002

The J. Bennett Johnston Sr., Center for Advanced Microstructures and Devices (CAMD) is a synchrotron radiation facility owned by Louisiana State University and operated with financial support from the State of Louisiana (for information how to submit a project proposal go to: http://www.camd.lsu.edu). The centerpiece of CAMD is a 1.3–1.5 GeV electron storage ring. CAMD supports a strong program in x-ray lithography micromachining (XRLM) or LIGA. A total of four beamlines equipped with different scanners is available for exposures. A 2.500 sq. ft class 100 clean room provides basic processing capability for MEMS including optical lithography, thin film deposition, electroplating, and metrology. Three micromachining beamlines are connected to bending magnets. All beamlines are “white light” beamlines, terminated with a beryllium window. The typical source point to scanner distance is 10 m and the horizontal acceptance ranges from 6.5 to 10 mrad. A number of low Z filters can be inserted into the beam adapting the exposure spectrum to the resist thickness. Two beamlines are equipped with commercial scanners from Jenoptik GmbH (for details see Jenoptik’s webpage at www.jo-mikrotechnik.com/) and one beamline with a “vacuum” scanner designed in house. The latest model of Jenoptik’s DEX02 scanner has been installed at CAMD’s XRLM1 beamline in December 2000 and allows advanced exposures using overlay as well as tilt and rotate functions. In addition to these beamlines CAMD has installed a “white light” beamline at its 7 T wiggler source. Preliminary exposure tests in ultrathick samples (1 mm and thicker) have been conducted using an “air scanner.” Currently this beamline is dismantled and will be reinstalled together with a PX beamline. In the article further details of the beamlines and scanners as well as some examples of applications of LIGA microstructures fabricated at CAMD will be discussed.
Spin waves, phase separation, and interphase boundaries in double exchange magnets
Authors: Golosov D. I.
Published: July 2002

We study a classical double exchange magnet with direct antiferromagnetic superexchange coupling, J, between the localized spins. It is shown that the destabilization of the ferromagnetic ground state with increasing J leads to phase separation; the latter always preempts the spin-wave instability (softening of the magnon spectrum). It is also found that the boundaries separating the ferromagnetic and antiferromagnetic areas of the sample tend to be abrupt.
Photothermal device for water dynamics measurement and thermophysical characterization: Application on textile samples
Authors: Duvaut T. , Limare A. , Bachmann J. M.
Published: July 2002

The photopyroelectric method in a noncontact configuration (excitation source: diode laser at 1.94 μm) is capable of yielding information on the water content of a textile sample and on its influence on the thermal properties. A one-dimensional theoretical model was developed assuming the sample thermally homogeneous and taking into account the optical absorption and scattering. The experimental setup designed for this purpose included an excitation source resonant with water absorption, signal and data processing units and cells for conditioning the samples. We optimized the experimental conditions in order to identify the parameters related to the water content in the sample, and to monitor the dynamics of the process. The effective thermal conductivity and the volume specific heat were determined at different moments of time while the sample was taking up water. Two thermal parameters related to the comfort of a fabric were also calculated: the thermal effusivity and the thermal resistance.
Magnetic properties and crystal structures of self-ordered ferromagnetic nanowires by ac electroforming
Authors: Lee K. H. , Lee H. Y. , Jeung W. Y. , Lee W. Y.
Published: July 2002

We have investigated the magnetic properties and crystal structures of α-Fe and Fe21Ni79 nanowire arrays fabricated by ac electroforming into self-ordered nanosized pores in anodic aluminum oxide (AAO). The nanopores were found to have diameters of 5–100 nm and aspect ratios of 300–1000 depending on the anodization conditions. X-ray diffraction patterns provide direct experimental evidence that the α-Fe and Fe21Ni79 nanowires have preferred crystallographic orientations, indicating that those were electroformed in the (221) and (220) orientations, respectively. For the α-Fe (Fe21Ni79) nanowires, coercivity Hc and squareness Mr/Ms were found to be ∼2.02 (∼1.20) kOe and ∼0.9 (∼0.99), respectively. It is observed that the coercivity in Fe21Ni79 nanowires increased up to 1.35 kOe with increasing annealing temperature.
Magnetic properties of a mixed-valence (III/IV) terbium fluoride KTb3F12
Authors: Guillot M. , El-Ghozzi M. , Avignant D. , Andre G. , Bouree F. , Cousson A.
Published: July 2002

The mixed-valence terbium (III/IV) fluoride KTb3F12 crystallizes with the tetragonal symmetry, space group I4/m. Below TN=3.6±0.1 K this compound exhibits an antiferromagnetic collinear structure with k=0 characterized by ferromagnetic chains of edge-sharing Tb4+ polyhedra and an antiferromagnetic order between the nearest chains. The magnetic moments of the Tb4+ ions deduced from neutron diffraction are equal to 6.95(4) μB at 1.4 K and aligned along the c axis. The Tb3+ ions lie in a special position with zero magnetic moments due to a symmetry cancellation effect of the internal molecular field. In other words, Tb3+ ions present a zero time-averaged magnetic moments in the ordered state, whereas TN corresponds to the long-range antiferromagnetic ordering of the moments of the Tb4+ ions. From the thermal variation of the reciprocal magnetic susceptibility a molar Curie constant of 27.97(1) emu K mol−1 has been obtained, in good agreement with the theoretical value of 27.64 expected for two Tb4+ and one Tb3+ free ions. The Tb4+ contribution to the magnetization is approximated by the Langevin function and then the Tb3+ contribution is obtained by subtracting the calculated Tb4+ contribution to the total magnetization.
In situ magnetoresistance measurements during patterning of spin valve devices
Authors: Morecroft D. , Prieto J. L. , Leung C. W. , Burnell G. , Blamire M. G. , Jardine D. B.
Published: July 2002

An in situ magnetoresistance test rig has been designed and built into an argon ion milling rig. The results of these experiments allow direct analysis of the evolution of magnetic and electrical properties of ferromagnetic structures. Arrays of wires of equal mark/space ratio were patterned using photolithography in the 15 nm thick top layer of Ni80Fe20 trilayers with the structure: Ta(3 nm)/Ni80Fe20(6 nm)/Cu(2.2 nm)/Ni80Fe20(15 nm)/Ta(3 nm). The in situ test rig was used to analyze the change in the magnetoresistance response as the anisotropy of the top layer was increased during milling. The results show that it is possible to partially decouple the Ni80Fe20 ferromagnetic layers with large milling depths and a small spin valve response is observed. It is also shown that as the anisotropy of the top layer is further increased by decreasing the width of the wires, the spin valve response is magnified. This spin valve design has considerable potential for high temperature device operation.
Magnetoresistive sensors for string instruments
Authors: Lenssen K.-M. H. , Somers G. H. J. , van Zon J. B. A. D.
Published: July 2002

Pickup elements for string instruments, in particular for electric guitars, represent a new application area for magnetoresistive sensors. Recently we developed a sensor configuration with permanent magnets for this purpose. For the first experiments we used commercial anisotropic magnetoresistance sensors (Philips KMZ10) mounted on small ferrite bias magnets. Recently we equipped an electric guitar with prototypes comprising giant magnetoresistance (GMR) sensors. These prototype MR pickup elements showed several clear advantages compared to the presently commonly used inductive pickup units. They are much less sensitive to disturbing electromagnetic fields (>1000×at 5 kHz), mainly because their active sensor area is several orders of magnitude smaller (a few mm2 instead of cm2). Also the larger freedom in the choice of the permanent magnets (due to the larger sensitivity of the GMR elements) is advantageous: employing smaller magnets reduces the damping and thus significantly improves the sustain, the magnets can be less expensive and more stable magnet materials can be chosen so that aging effects are eliminated.
To which extent is the influence of each electrode of a magnetic tunnel junction separable?
Authors: Montaigne F. , Hehn M. , Schuhl A.
Published: July 2002

Tunnel magnetoresistance is often explained using the Jullière model which predicts a magnetoresistance ratio function of two quantities, named polarization, characteristic of each electrode of the junction. However, the dispersion of experimental data indicates that the polarization is not only related to the band structure of the electrode material but rather to the combination electrode barrier. The parabolic band model shows indeed that all the characteristics of the barrier have to be taken into account for defining the polarization of an electrode. Following the Jullière model, the magnetoresistance of an asymmetric tunnel junction should be entirely defined by the polarizations of each of its electrode. We show theoretically that this approach can be used for dissimilar materials and asymmetric barriers. This approach is still valid when a voltage is applied to the junction but, the evolution of the polarization with the voltage is mainly ruled by the deformation of the barrier (and not only by band-structure effects). However, the domain of validity of the Jullière model and its picture of separated electrodes is limited to resistive enough junctions. For low resistive junctions, it is necessary to consider the tunnel junction as a single entity as shown by our calculations.
On the spectral properties of Hamiltonians without conservation of the particle number
Authors: Sigal I. M. , Soffer A. , Zielinski L.
Published: July 2002

We consider quantum systems with variable but finite number of particles. For such systems we develop geometric and commutator techniques. We use these techniques to find the location of the spectrum, to prove absence of singular continuous spectrum, and identify accumulation points of the discrete spectrum. The fact that the total number of particles is bounded allows us to give relatively elementary proofs of these basic results for an important class of many-body systems with nonconserved number of particles.
Spin-dependent electron transport in ferromagnetic bilayers: Application to three-dimensional spin detectors
Authors: Rougemaille N. , Drouhin H.-J. , Lampel G. , Peretti J. , Lassailly Y. , Schuhl A.
Published: July 2002

A general analysis of spin-polarized electron transmission through ferromagnetic bilayers is presented. We calculate the transmitted current through two consecutive layers with in-plane magnetizations and we investigate the particular case where these magnetizations are orthogonal. We show that it is possible to obtain a three-dimensional spin detector for low-energy electrons which is compact and performant.
Magnetic-field simulation for shielding from high magnetic fields
Authors: Uetake H. , Hirota N. , Ikezoe Y. , Kitazawa K. , Miyoshi K.
Published: July 2002

Magnetic-field simulations have been carried out to attain efficient magnetic shielding from high and static magnetic fields. A stray field created by a 10 T solenoid superconducting magnet with a φ100 mm room-temperature bore was assumed. As a shielding material, plate-, cylindrical-, and the combination of a plate- and framework-shaped irons were selected. To investigate the effect of the iron shield, the shielding factors were evaluated systematically by changing the shape, size, thickness, etc. of the shield emphasizing the area around 2 m apart from the field center in the axial direction. Various simulations led us to conclude that the shielding factor becomes high because of the use of large iron plates and not because of either the thickness or the number of layered plates. Then, the combination of a iron plate and framework was suggested and examined as a way of efficient shielding. On the other hand, when the shield was placed in the radial direction, the larger and the thicker the shield became, the higher the shielding factor. In designing magnetic shields, it is important to consider what to be shielded from and where to be shielded from stray fields. In this respect, an easy method to reduce stray fields in one direction was obtained.
Thermal pole tip protrusion finite element analysis of thin film inductive recording heads
Authors: Yan Wentao
Published: July 2002

In recent low flying height hard disk drives, the head write current causes thermal protrusion of the pole tip region that results in head–disk contact. Finite element analysis is performed in this work to study the temperature and displacement fields in heads during writing. Three-dimensional steady-state thermal-structural analysis of a head in air and over a disk is presented. Complex head geometry is modeled. Velocity slip and temperature jump boundary conditions are used in formulating heat transfer through the air bearing. Moreover, transient analysis of head thermal protrusion is presented. Step direct current is applied. Snapshots of the temperature field as well as temperature and displacement time functions of several locations in the head are exhibited. It is found that head protrusion first occurs at the pole tip, then spreads to the trailing end of the slider. For the head–disk interface studied, it takes 0.6 ms for the head to come in contact with the disk after writing starts.
Preisach modeling of clockwise hysteresis and its application to front propagation problems
Authors: Mayergoyz I. D. , Andrei P.
Published: July 2002

The Preisach model is appropriately modified to describe the clockwise hysteresis with the positive saturation state achieved for some positive input value. It is demonstrated that this type of clockwise hysteresis may naturally appear in front propagation problems such as nonlinear diffusion of electromagnetic fields.
Magnetic intergranular interaction in nanocomposite CoxPt100−x:C thin films
Authors: Powers N. , Yan M. L. , Gao L. , Liou S. H. , Sellmyer D. J.
Published: July 2002

Magnetization reversal and intergranular interactions have been studied in composite CoxPt100−x:C thin films using several magnetic characterization techniques. The intergranular interactions, as determined by ΔM curves, were strongly dependent on the ratio of Co and Pt concentration. For films with high Co content, the intergranular exchange coupling was predominant, while dipolar interactions were exhibited in the film with the equiatomic concentration of Co and Pt. Magnetic intergranular interaction was directly observed using magnetic force microscopy. There is a strong correlation between the value of the ΔM and magnetic correlation length obtained from the magnetic domain images.
Photo thermal patterning on magnetic media
Authors: Wang Li-Ping , Kuo David , Gui Jing
Published: July 2002

A method of creating magnetic patterns on magnetic media has been proposed and demonstrated. The method, named the photo thermal patterning process, adopts photolithography technique to deliver patterns on the medium surface. The patterns are then recorded magnetically to the medium surface by thermomagnetic effects. Magnetic force microscopic (MFM) imaging of the patterns exhibits a high degree of fidelity in pattern replication. Spinstand readback data showed good transition characteristics.
Imprint reduction in a plasma layer preformed with x-ray irradiation
Authors: Nishikino M. , Shiraga H. , Miyanaga N. , Ohnishi N. , Shigemori K. , Fujioka S. , Nakai M. , Nishimura H. , Azechi H. , Mima K. , Takabe H. , Nakai S. , Yamanaka T.
Published: July 2002

Indirect–direct-hybrid irradiation scheme has been proposed for suppressing the initial imprint of the laser irradiation nonuniformities. The target is irradiated by a low intensity x-ray radiation prior to the direct-drive laser pulse. The x-ray irradiation generates a plasma expansion layer on the target surface. The thermal smoothing effect is expected to take place in the preformed plasma when the direct-drive laser pulse comes onto the target, and then, the initial imprint can be significantly reduced. Planar target experiments on the indirect–direct-hybrid irradiation scheme were performed. The preformed plasma profile was measured by using x-ray side-on backlighting method. The reduction of the initial imprint was demonstrated by the indirect–direct-hybrid irradiation scheme on planar target experiments. The imprint is suppressed by a factor of 1.5–7 depending on x-ray preirradiation conditions. Results are in good agreement with the cloudy-day model with parameters derived from one-dimensional simulation.
Shielding from instantaneously and adiabatically applied potential wells in collisionless plasmas
Authors: Reimann A. B. , Fajans J.
Published: July 2002

The response of collisionless plasmas to an applied potential can differ from classic Debye shielding, and when the potential is rapidly applied (“instantaneous shielding”), the shielding can differ from when it is slowly applied (“adiabatic shielding”). Experiments demonstrate that when a test potential well is applied to a one-dimensional pure-electron plasma, instantaneous and adiabatic shielding are similar for small potentials, but that instantaneous shielding is weaker than adiabatic shielding for large potentials. These results have been confirmed with particle-in-cell computer simulations. Simulations also show that the peculiar distribution functions of instantaneously and adiabatically shielded plasmas agree with theoretical predictions.
Impact of head thermal movement to adjacent track encroachment measurement
Authors: Li Zhaohui , Hong Soo-Youl , Lee Hyung Jai
Published: July 2002

The impact of the head thermal movement to adjacent track encroachment (ATE) measurement with spin stand is studied. At head-gimbal assembly (HGA) and head-stack assembly (HSA) levels, the current technique measures the track amplitude reduction after continuously writing the adjacent tracks in the nominal write current and full write gate condition. However, the head thermal movement could result in a big problem for ATE value and stability with the spin stand. From the one-side adjacent track encroachment experiment, head thermal movement is the major reason for quick rising ATE when the adjacent track writing iteration increases. The experimental data also show strong correlation between ATE and adjacent track write gate and write current. Further work shows that the writer trace is the major reason for this thermal movement. However, ATE is much more stable when the write gate total open rate is less than 25%. A technique, which inserts the idle revolutions among adjacent track writing, is proposed to reduce the head thermal movement during ATE test. This methodology has been applied to a spin stand software module for HGA/HSA level ATE measurement.
Bulk nanocomposite permanent magnets produced by crystallization of (Fe,Co)–(Nd,Dy)–B bulk glassy alloy
Authors: Zhang Wei , Inoue Akihisa
Published: July 2002

The glass-forming ability, thermal stability, and magnetic properties have been investigated for an Fe67Co9.4Nd3.1Dy0.5B20 glassy alloy with a large supercooled liquid of 48 K before crystallization prepared by copper mold casting. The glassy phase is formed in a rod form with a diameter of 0.5 mm. The crystallized nanocomposite structure consists of Fe3B, α-Fe, and Nd2Fe14B phases, and the remanence (Br), coercivity (iHc) and maximum energy product (BH)max are 1.19 T, 244 kA/m, and 92.7 kJ/m3, respectively, for the rod of 0.5 mm in diameter annealed at 913 K for 600 s.
Quantum effects on collisional ionizations in semiclassical plasmas
Authors: Kim Chang-Geun , Jung Young-Dae
Published: July 2002

Electron collisional ionization of hydrogenic ions in semiclassical dense high-temperature plasmas is investigated using the effective pseudopotential model taking into account both the quantum-mechanical effects and the plasma screening effects. The impact parameter method is applied to the path of the projectile electron in order to visualize the ionization probability as a function of the impact parameter, thermal de Broglie wavelength, Debye length, and projectile energy. The ionization probability is found to be significantly decreased with increasing quantum-mechanical and plasma screening effects. It is also found that the maximum position of the ionization probability is receded from the target nucleus with increasing quantum and screening effects.
Local contactless measurement of the ordinary and extraordinary Hall effect using near-field microwave microscopy
Authors: Abu-Teir M. , Sakran F. , Golosovsky M. , Davidov D. , Frenkel A.
Published: July 2002

We report a polarization-sensitive scanning microwave microscope based on a bimodal dielectric resonator with a cross-slit aperture. The microscope operates at ∼26 GHz in the reflection mode and has a subwavelength spatial resolution. It allows contactless mapping of the conductivity tensor, including magnetic-field-induced terms such as the Hall effect. We demonstrate local contactless measurement of the ordinary Hall effect in semiconducting wafers and of the extraordinary Hall effect in thin ferromagnetic Ni films. The latter yields out-of-plane magnetization. The microwave measurements are in good agreement with the dc Hall-effect measurements.
Optical properties of the deep Mn acceptor in GaN:Mn
Authors: Korotkov R. Y. , Gregie J. M. , Wessels B. W.
Published: July 2002

The optical and electrical properties of Mn-doped epitaxial GaN were studied. Low-temperature optical absorption measurements indicate the presence of a Mn-related band with a well-resolved fine structure. The zero-phonon line is at 1.418±0.002 eV with a full width at half maximum of 20±1 meV. Two pseudolocal vibrational modes associated with manganese were observed with energies of hv1=20 and hv2=73 meV. Deep-level optical spectroscopy measurements on lightly Mn-doped samples indicate that Mn forms a deep acceptor level at Ev+1.42 eV. Using the vacuum referred binding energy model for transition metals and the measured Mn energy level, the electron affinity of GaN is calculated to be 3.4 eV, which agrees well with experimental values.
Demultiplexer using directly resonant tunneling between point defects and waveguides in a photonic crystal
Authors: Jin Chongjun , Han Shouzhen , Meng Xiaodong , Cheng Bingying , Zhang Daozhong
Published: July 2002

We propose a frequency selective demultiplexer that is realized by the directly resonant tunneling between waveguides and point defects in a two-dimensional photonic crystal. The multiple scattering method is used to simulate the behavior of the demultiplexer. Results show that the demultiplexing efficiency is very high when the point defects are symmetrically arranged at both sides of the central line of the inlet waveguide. The selective frequency is only determined by the defect mode of the corresponding point defect in the photonic crystal and is not affected by the other point defects. A microwave experiment results agree well with the simulation. This structure may be valuable for the design of all-optical integrated circuits.
Whistler wave emission from a modulated electron beam injected in a cylindrical duct with enhanced plasma density
Authors: Kudrin A. V. , Lyakh M. Yu. , Zaboronkova T. M. , Krafft C.
Published: July 2002

A study is made of the electromagnetic radiation from a thin modulated electron beam of finite length injected parallel to an external magnetic field in a magnetic-field-aligned cylindrical density duct immersed in a uniform ambient magnetoplasma. A rigorous solution for the beam-excited field is obtained and the power lost by the beam in the presence of the duct is examined. Although a general theory is developed, attention is focused on ducts with enhanced density and modulation frequencies belonging to the whistler band. Expressions for the time-averaged power emitted from the beam are derived as a function of the beam and duct parameters. A significant difference between the features of whistler wave emission in the presence of a duct and in the case of a homogeneous unbounded plasma is revealed. Estimates of the power emitted in the whistler band are given for representative examples of artificial density ducts in the laboratory and space plasmas. It is shown that the power lost by the beam in the presence of an enhanced-density duct can increase noticeably due to Čerenkov excitation of guided whistler modes.
Transient characteristics of a neon-like x-ray laser at 19.6 nm
Authors: Lu Xin , Li Ying-jun , Zhang Jie
Published: July 2002

A transient Ne-like x-ray laser at 19.6 nm (J=0→1, 3p→3s) is numerically investigated using a hydrodynamic code for a 100 μm thick Ge planar target irradiated by a nanosecond prepulse followed by a subpicosecond or a picosecond main optical laser pulse. Simulations are performed for different main pulse lengths of 50 fs, 500 fs, 5 ps, and 50 ps but with fixed pulse energy. For a drive pulse even as short as 500 fs, the x-ray laser gain still shows quasisteady state behaviors. A real transient nature can only be seen when the x-ray laser is driven by a laser pulse with a duration as short as tens of femtoseconds.
Dipole formation and band alignment at the Si(111)/CuInS2 heterojunction
Authors: Hunger R. , Pettenkofer Chr. , Scheer R.
Published: July 2002

Heterojunctions between Si(111):H faces and molecular beam epitaxy grown CuInS2 thin films were investigated. The interface formation was studied by means of photoelectron spectroscopy and low energy electron diffraction. Initial sulfur exposure of the Si substrate at 750 K leads to a surface dipole of (0.61±0.10) eV. Upon subsequent CuInS2 deposition, an interface dipole of (1.0±0.2) eV is observed. The valence band offsets between Si and CuInS2 films of different [Cu]/[In] ratios were determined and an average valence band offset of (0.08±0.15) eV is obtained. Comparison with model considerations points out that the experimental values of the valence band offset are consistent with the observed interface dipole.
Equilibrium and confinement of bunched annular beams
Authors: Hess Mark , Chen Chiping
Published: July 2002

The azimuthally invariant cold-fluid equilibrium is obtained for a periodic, strongly bunched charged annular beam with an arbitrary radial density profile inside of a perfectly conducting cylinder and an externally applied uniform magnetic field. The self-electric and self-magnetic fields, which are utilized in the equilibrium solution, are computed self-consistently using an electrostatic Green’s function technique and a Lorentz transformation to the longitudinal rest frame of the beam. An upper bound on the maximum value of an effective self-field parameter for the existence of a bunched annular beam equilibrium is obtained. As an application of the bunched annular beam equilibrium theory, it is shown that the Los Alamos National Laboratory relativistic klystron amplifier experiment is operating slightly above the effective self-field parameter limit, and a discussion of why this may be the cause for their observed beam loss and microwave pulse shortening is presented. The existence of bunched annular beam equilibria is also demonstrated for two other high-power microwave (HPM) experiments, the relativistic klystron oscillator experiment at Air Force Research Laboratory and the backward wave oscillator experiment at the University of New Mexico. In general, the results of the equilibrium analysis will be useful in the determination of the stability properties of strongly bunched annular beams in HPM devices.
Probing the nature of the K-rotor in unimolecular reactions: Scalar and vector correlations in the photodissociation of NCNO
Authors: McGivern W. Sean , North Simon W.
Published: July 2002

The photodissociation dynamics of thermal NCNO at 520 and 532 nm have been examined using transient frequency modulation Doppler spectroscopy to measure state-selected CN scalar and vector correlations. Previous work has suggested that the global vibrational and rotational distributions may be described using separate statistical ensembles/phase space theory (SSE/PST). We find that the correlated vibrational and rotational distributions are well described by SSE at 520 nm if the K-rotor is considered inactive. At both wavelengths studied, the correlation between the velocity and the rotational angular momentum vector of the CN product is found to be described by phase space theory with no restriction of the projection of the rotational angular momentum vectors along the relative velocity axis. This is indicative of approximate K-scrambling at the transition state, and a discussion of these results in light of the evolution of the K-quantum number is provided.
Hydrodynamic instability of shells accelerated by direct ion beam heating
Authors: Basko M. M. , Maruhn J. A. , Schlegel T.
Published: July 2002

The Rayleigh–Taylor (RT) instability of planar shells accelerated by direct heating of an underlying absorber layer is analyzed. A specific feature of the problem considered is a fixed in space energy deposition region, which allows the unstable transition layer to develop only gradually as the heated matter is pushed out of the deposition region. The linear growth spectrum ω(k) is investigated by relating a simple analytic estimate for a stationary exponential transition layer with the results of two-dimensional hydrodynamic simulations. For the unperturbed motion, an analytic solution is used which describes a uniform acceleration of the payload driven by a time-dependent uniform heating of the absorber with a fixed spatial extension. It is shown that an enhancement factor of 1.5(h/d), where h is the effective half-thickness of the heated region and d is the in-flight thickness of the payload, can be achieved for the distance-moved-over-thickness ratio as compared to the classical RT case of a strong density jump.
Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic resonance study
Authors: Vyas S. , Hernandez C. J. , Augustine M. P.
Published: July 2002

The nuclear magnetic resonance (NMR) spectra of the I=3/2 monovalent ions Na23, Cl35, K39, and Br79 for NaCl and KBr dissolved into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction between the nuclear spin and the electric field gradient produced by the Pf1 particles. The average electric field gradient and thus the spectral splitting for ions in the void space between magnetically aligned Pf1 particles is modeled using a numerical solution to the Poisson–Boltzmann equation. An NMR titration experiment in a 57 mg/mL Pf1 solution is used to determine the background Na+ ion concentration in solution as 32 mM which compares well with the 31.1 mM negative surface charge on Pf1.
Thermally stimulated photoluminescence in poly(2,5-dioctoxy p-phenylene vinylene)
Authors: Kadashchuk A. , Skryshevski Yu. , Piryatinski Yu. , Vakhnin A. , Emelianova E. V. , Arkhipov V. I. , Bässler H. , Shinar J.
Published: July 2002

Results of thermally stimulated photoluminescence (TSL) measurements in poly(2,5-dioctoxy p-phenylene vinylene) (DOO–PPV) are reported. The obtained results are analyzed in terms of the hopping model of TSL in disordered organic materials. It is shown that the experimentally obtained TSL curve can be fitted on the basis of a double-peak Gaussian density-of-states distribution. The upper peak is associated with intrinsic localized states while the lower one can be ascribed to aggregates. The latter assignment is also supported by measurements of steady-state and time-resolved photoluminescence in DOO–PPV films and solutions. Possible mechanisms of charge carrier photogeneration in DOO–PPV are discussed.
Mechanics of the ion layer gas reaction–A preparation method of nanocrystalline thin layers
Authors: Muffler H. J. , Fischer Ch. H. , Giersig M. , Bär M. , Lux-Steiner M. C.
Published: July 2002

Nanocrystalline CdS thin layers can be prepared using the ion layer gas reaction (ILGAR), a low-cost deposition technique for compound semiconductor thin films. We investigated the layers by optical spectroscopy and transmission electron microscopy, and found that lower CdCl2 precursor concentrations and thicker films favor larger nanoparticles and a lower band gap energy, whereby the concentration effect is more pronounced. The nucleation mechanism of the CdCl2 precursor seems to determine the particle size and the probability of its growth. A minimum CdS particle diameter of 4.7 nm has been extrapolated, which corresponds to an optical band gap energy of 2.83 eV, as a result of quantum confinement. ILGAR enables deposition of nanoparticles of controlled size.
Response to “Comment on ‘The α-relaxation process in simple glass forming liquid m-toluidine. II. The temperature dependence of the mechanical response’ ” [J. Chem. Phys. 116, 7323 (2002)]
Authors: Cutroni M. , Mandanici A.
Published: July 2002

Discrepancies between the mechanical response of m-toluidine obtained from ultrasonic measurements and Brillouin scattering have been observed. The concepts of aging and thermodynamic fictive temperature as well as the differences in the liquid samples investigated are indicated by the authors as relevant features for the comparison.
Time evolution of an ion-ion plasma after the application of a direct current bias voltage
Authors: Midha Vikas , Ramamurthi Badri , Economou Demetre J.
Published: July 2002

A one-dimensional fluid model was developed to investigate the time evolution of a positive ion-negative ion (ion-ion) plasma after the application of a direct current (dc) bias voltage. The ion mass and momentum continuity equations were coupled to the Poisson equation for the electric field. The applied bias is shielded and space charge sheaths are formed within the time scale of ion response (ion plasma frequency). When the ion collision frequency is low compared to the ion plasma frequency, electric field oscillations develop in the bulk due to the ion inertia (overshoot). The net charge density in the sheath, the sheath electric field, and the flux and energy of ions bombarding the electrodes all go through maximum values at a time comparable to the ion plasma frequency. Over long time scales the sheaths are in quasiequilibrium with the bulk plasma. At this time, the ion flux on each electrode is twice the free diffusion flux.
Insulating Van Vleck paramagnets at high magnetic fields (Review)
Authors: Tagirov M. S. , Tayurskiı̆ D. A.
Published: July 2002

Theoretical and experimental results are presented on the magnetic properties of insulating Van Vleck paramagnets at high magnetic fields, where the Zeeman energy of an ion becomes comparable to the characteristic energies of the Stark splittings.
Multiwalled carbon nanotubes with bamboo-like structure and effects of heat treatment
Authors: Katayama Tetsutaroh , Araki Hisashi , Yoshino Katsumi
Published: July 2002

Microstructures of bamboo-like multiwalled carbon nanotubes prepared by pyrolysis of Ni-phthalocyanine are studied by high-resolution transmission electron microscopy. The intershell spacings of graphitic shells in these nanotubes are estimated. From pristine nanotubes with a tube diameter of 40–260 nm, the spacing values of 0.339–0.342 nm are obtained almost independent of their tube diameters. However, after heat treatment at 2800 °C they are reduced to a value equivalent to the interlayer spacing of graphite, and tube walls with a clear polygonal cross section come to be observed. The heat treatment of samples is also a very useful method to prepare metal-free nanotubes. The bamboo-like graphitic shells are interpreted to be determined by a cone-shaped Ni nanoparticle included at the base of the multiwalled carbon nanotube.
Dispersive ionic space charge relaxation in solid polymer electrolytes. I. Experimental system polyethylene oxide
Authors: Wagner Achim , Kliem Herbert
Published: July 2002

As a model system for solid polymer electrolytes thin polyethylene oxide (PEO) films (0.6–30 μm) are prepared as Al–PEO–Al and as Al–PEO–Si structures with blocking electrodes. Dielectric measurements (capacitance and loss angle) are carried out in a frequency range of 3 mHz⩽f⩽1 MHz in atmospheres of different relative humidities (0%–75%) and at different temperatures (293–313 K). The nominal permittivity varies from 4 at high frequencies to up to 150 000 at low frequencies. We find true volume polarization in the high frequency range and a thermally activated space charge relaxation process in the low frequency range. Its time constant exhibits a remarkable dependence on the sample thickness, the relative humidity, the ion concentration, and the temperature. Due to the absorbed dipolar water molecules the activation energy of this process is decreased, leading to higher mobility of the ions. An increase in ion concentration also leads to a lower activation energy. The ions are able to move through the sample to the electrode interfaces and build up ionic space charge. We assume that at the interfaces oxide layers are formed, and these are almost impermeable to these ions. The space charge relaxation process has a broad frequency spectrum. The imaginary part of the nominal permittivity εr″(ω)∝ωβ has a slope of β=−0.8 to 0.7 above the main relaxation frequency. In the time domain, after application of a voltage step a Kohlrausch behavior of the relaxation current is found. In the short time range we find a current of j∝t−0.3 and in the long time range we find j∝t−1.1. A comparison of the frequency and the time domain by Fourier transform shows that the space charge relaxation process is time invariant for small applied voltages. Nonlinear properties that appear at higher voltages are investigated in the frequency domain and in the time domain.
Effect of phase change on shock wave attenuation in GeO2
Authors: Liu C. , Ahrens T. J. , Brar N. S.
Published: July 2002

Stress-wave profiles in vitreous GeO2 induced by planar and spherical projectile impact were measured using piezoresistance gauges in the 4 to 18 GPa shock pressure range. The planar experiments demonstrate the response of vitreous GeO2. This response can be divided into three regimes: (1) An elastic shock regime with ramp 4 GPa Hugoniot elastic limit (HEL) precursor. Shock propagation velocity decreases from an initial longitudinal elastic wave speed of 3.5 to 2.8 km/s at 4 GPa. (2) A transition wave regime where the ramp wave is superimposed on the precursor with an additional amplitude of 0 to 2 GPa followed by a sharp increase in shock pressure achieving peak loading pressures of 8 to 14 GPa. Above 4 GPa the ramp wave velocity decreases to a value below 2.5 km/s (the speed of the bulk wave, at the HEL). (3) A shock wave achieving the final shock state forms when peak pressure is >6 GPa specified by linear shock-particle velocity relation D=0.917+1.71 u (km/s) over the 6–40 GPa range for an initial density of 3.655 g/cm3. The Hugoniots of GeO2 and SiO2, both initially vitreous, are found to be virtually coincident if pressure in SiO2 is calculated by multiplying the GeO2 pressure by the ratio of the initial densities of vitreous GeO2 to fused SiO2. The volume axes are translated by aligning the specific volumes for onset and completion of the four- to six-fold coordination phase change. Although only limited spherical impactor spherically diverging shock experiments were conducted, our present results demonstrate (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. A supported elastic precursor in vitreous GeO2 decays faster with radius than a linear elastic wave; (2) in GeO2 (vitreous) unsupported shock waves decay with peak pressure in a phase transition range (4–15 GPa) with propagation radius (r) as ∝r−3.35.
Electrical isolation of p-type GaAs layers by ion irradiation
Authors: Boudinov H. , Coelho A. V. P. , de Souza J. P.
Published: July 2002

The electrical isolation of p-type GaAs layers doped with acceptor impurities incorporated in the Ga sublattice (Mg) or As sublattice (C) was studied using proton bombardment. It was found that practically the same proton dose is required to reach complete isolation (isolation threshold dose, Dth) in layers doped with either Mg or C of comparable original sheet hole concentration (ps). This result is evidence that the sublattice where the acceptor dopant atoms are incorporated does not play any significant role for the isolation formation process in GaAs. The behavior of the recovery of the conductivity during subsequent thermal annealing was found very similar in Mg and C doped samples irradiated to equal proton doses. In samples irradiated to doses 100 °C, reaches a maximum at ≅200 °C, and then decreases progressively toward the original value. For proton doses ranging from Dth to 5Dth, the isolation is preserved up to the temperature of ≈500 °C. The temperature of ≈700 °C was found to be the upper limit for the thermal stability of the isolation in samples irradiated to doses of 100 Dth.
On simulation methods to compute surface and interfacial free energies of disordered solids
Authors: Grochola Gregory , Russo Salvy P. , Snook Ian K. , Yarovsky Irene
Published: July 2002

We study λ-integration paths, specifically designed for calculating “exact” surface and interfacial free energies of solids at elevated temperatures using molecular dynamics or Monte Carlo simulation methods. We compare various paths with the standard technique of thermodynamic integration by application to the surface free energy for the (100) and (110) faces of alpha iron using embedded atom method (EAM) potentials. We demonstrate which paths are completely reversible at high temperatures and show consistency of results for these paths. The λ-integration paths can be applied with confidence to find equilibrium surface free energies, within the limits of the surface area, intermolecular potentials and other approximations implicit to the simulation methods used.
Study of ferroelectric-thin-film thickness effects on metal-ferroelectric-SiO2–Si transistors
Authors: Lin Yih-Yin , Singh Jasprit
Published: July 2002

This article examines the thickness effects of ferroelectric films on gate tunneling suppression and charge control in metal-ferroelectric-insulator-semiconductor field-effect transistors (MFISFETs). The formalism used is based on a blocking-layer model for the ferroelectric film and a self-consistent solution of the Poisson and Schrödinger equation. We show that with a polar ferroelectric the threshold voltage of the FET can be altered by controlling the ferroelectric film thickness. We also study the thickness dependence of the capacitance–voltage curve and the surface charge density and the effects of ferroelectric hysteresis. The tunneling probability and leakage current calculation in a MFISFET device are provided in this article. Ferroelectrics-based transistors show higher sheet charges and lower tunneling currents than oxide-based devices.