bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetophotoluminescence of neutral acceptor states in InSb
Authors: Stotz J. A. H. , Thewalt M. L. W.
Published: July 2002

Magnetophotoluminescence experiments on n-type bulk indium antimonide crystals have been performed using a cryogenically cooled interferometer. Both donor–acceptor-pair and free electron-to-neutral acceptor recombination transitions have been observed for four distinct acceptor species. Despite the small difference in the cadmium and germanium binding energies, the high-resolution photoluminescence experiments presented were able to resolve the two acceptors. Acceptor binding energies for Cd, 72.3 cm−1 (8.96 meV), and Ge, 69.0 cm−1 (8.55 meV), are consistent with previously published results. Two unknown acceptors having binding energies of 99.6 cm−1 (12.35 meV) and 161.9 cm−1 (20.07 meV) are also discussed.
Approach to measure thermal efficiency of bolometer sensors
Authors: Mei T. , Neuzil P. , Karunasiri G. , Zeng W.
Published: July 2002

Evaluation of thermal efficiency is of great importance for verifying the design optimization of microbolometer-based sensors. In this work, a measurement technique has been developed to determine the thermal efficiency of a microbolometer without using structural and material parameters. The microbolometer thermal efficiency is obtained by measuring the responsivity under infrared illumination and responsivity for unity thermal efficiency using the self-heating effect. The thermal efficiency of a metal–film microbolometer sensor was determined using this technique to demonstrate its viability.
Electron-phonon resonance in InAs/GaSb type-II laser heterostructures
Authors: Kisin M. V. , Stroscio M. A. , Belenky G. , Luryi S.
Published: July 2002

The rate of interband electron transitions assisted by LO-phonon emission is studied in an InAs/GaSb double quantum well heterostructure, which models the active region of a type-II intersubband cascade laser. The main peak of the electron-phonon resonance corresponds to electron transitions from the lowest electron-like subband to the top of the highest light-hole-like subband that is displaced from the center of the Brillouin zone due to the asymmetry of the InAs/GaSb double quantum well heterostructure.
Low temperature growth of InGaAs layers on misoriented GaAs substrates by metalorganic vapor phase epitaxy
Authors: Takano Y. , Kobayashi K. , Iwahori H. , Kuroyanagi N. , Kuwahara K. , Fuke S. , Shirakata S.
Published: July 2002

InGaAs layers with In composition of 0.57 were grown with metalorganic vapor phase epitaxy (MOVPE) using graded buffer layers on exactly oriented and misoriented GaAs(100) substrates. No mirror-like surface was obtained at growth temperatures between 570 °C and 630 °C. A mirror-like surface was achieved at a growth temperature of 450 °C. The threading dislocation density in the layer grown at 450 °C on the GaAs substrate misoriented toward (111)A was determined to be 1×107 cm−2 using transmission electron microscopy. Photoluminescence results also confirmed that the density of recombination centers in layers grown at 450 °C was low. Low temperature growth with MOVPE was found to be effective in InGaAs layers on GaAs substrates with high In composition above 0.4.
High pressure effects on the luminescent properties and structure of coumarin 153
Authors: Li Hong , Zhong Bo , He Liming , Yang Guoqiang , Li Yi , Wu Shikang , Liu Jing
Published: July 2002

The absorption and emission spectra of coumarin 153 (C153) at high pressure have been detected up to 7.0 GPa. Because of the strong electron-withdrawing group at 7 site in the coumarin, the fluorescence spectrum of the title compound exhibits one band emission at ambient pressure from its charge transfer (CT) state. At higher pressure, the decreased distance of the crystal face, as proved by in situ x-ray diffraction measurement, and the increased interactions between the molecules enhance the energy gap between the local excited (LE) state and the CT state. Two-band emissions of C153, from LE and CT, respectively, have been observed.
Arithmetic of 1/f noise in a phase locked loop
Authors: Planat M. , Henry E.
Published: July 2002

Frequency countings close to a phase locked zone in an electronic receiver show a 1/f power spectral density. The noise scaling versus the frequency deviation and the open loop gain are found from Adler’s model of the phase locked loop. This fully agrees with experiments performed at 5 MHz on a receiver with a Schottky diode mixer and a low pass filter. The 1/f amplitude and frequency noise due to the whole set of (sub)harmonics is explained from a nonlinear mapping, with a coupling coefficient related to the structure of prime numbers.
Room-temperature 1.54-μm electroluminescence from the Au/nanometer (SiO2:Er/Si/SiO2:Er)/n+-Si structure
Authors: Chen Y. , Ran G. Z. , Dai L. , Zhang B. R. , Qin G. G. , Ma Z. C. , Zong W. H.
Published: July 2002

The (SiO2:Er/Si/SiO2:Er) nanometer sandwich structure, in which the thickness of the Si layer between the two SiO2:Er barriers was varied from 1.0 to 4.0 nm with an interval of 0.2 nm, was deposited on both n+-Si and p-Si substrates using the magnetron sputtering technique. Electroluminescence (EL) from the Au/(SiO2:Er/Si/SiO2:Er) nanometer sandwich /n+-Si diodes under reverse biases has been observed. The EL spectrum of each diode can be fitted by three Gaussian bands with peak energies of 0.757 eV (1.64 μm), 0.806 eV (1.54 μm), and 0.860 eV (1.44 μm), and full widths at half maximum of 0.052 eV, 0.045 eV, and 0.055 eV, respectively. The marked effect of the nanometer Si layer with suitable thickness on enhancing the EL from the Er3+ in the SiO2 layers has been demonstrated. Among the diodes with Si layers having various thicknesses, the intensities of the 1.64-, 1.54-, and 1.44-μm bands of the diode with a 1.6-nm Si layer attain maxima which are 22, 8, and 7 times larger than those of the control diode without any Si layer, respectively.
Percolation behavior in the Raman spectra of ZnBeTe alloy
Authors: Pagès O. , Tite T. , Bormann D. , Maksimov O. , Tamargo M. C.
Published: July 2002

Zone-center longitudinal (LO) and transverse (TO) optical phonons of Zn1−xBexTe epilayers are identified by Raman spectroscopy. On top of the expected BeTe- and ZnTe-like modes, which obey the modified-random-element-isodisplacement model, we observe an extra BeTe-like (TO, LO) doublet at intermediate x values. It has the same atypical characteristics as its BeSe-like counterpart in ZnBeSe alloy. Its activation validates our percolative picture for multimode description in Be–chalcogenide alloys that open the attractive class of mixed crystals with a sharp contrast in the bond stiffness. Also, the local modes of Be in ZnTe and of Zn in BeTe are identified at 411 cm−1 and 195 cm−1, respectively.
Few-electron filling effect in laterally coupled spherical InAs/GaAs quantum-dot system
Authors: Dai Zhen-Hong , Zhang Li-De , Sun Jin-Zuo , Li Zuo-Hong , Huang Shi-Yong
Published: July 2002

Artificial molecules, i.e., systems of excess electrons confined in multiple semiconductor InAs/GaAs quantum dots, are studied with the unrestricted Hartree–Fock–Roothaan method. We focus our attention on calculating the chemical potential for two laterally coupled spherical quantum dots. The confinement potential in each quantum dot of the molecule is assumed in a form of three-dimensional spherical finite potential well of radius R and depth V0. The chemical potential is found to depend strongly on the proportionality of the radii of the two quantum dots. This method can be extended to study large quantum-dot arrays.
Surface-force measurement with a laser-trapped microprobe in solution
Authors: Ota Taisuke , Sugiura Tadao , Kawata Satoshi
Published: July 2002

Surface force between a micron-sized polystyrene and dielectric substrate in solution has been analyzed by measuring the displacement of the laser-trapped probe. The amount of displacement is measured by detecting the intensity of light scattering at the probe illuminated by evanescent field. The sensitivity of 27 fN and the range of 5.2 pN have been achieved in the experiment with various concentrations of electrolyte trisaminomethane. The distribution of the surface force of 3-aminopropyltriethoxysilane coated on the glass substrate was also detected.
Smectic ordering in confined liquid crystal films: A depth study
Authors: Martı́nez-Miranda L. J.
Published: July 2002

Grazing incidence x-ray scattering was used to study the structure of films of a room temperature smectic-C* mixture, deposited on glass substrates, that consisted of gratings with a 9 μm period. There is evidence for the presence of two regions of confinement as function of film thickness. The first region, of thickness ranging from 1 to 5 μm, is dominated by the size and depth effects of the individual grating grooves. The second region, of thickness ranging between 5 and 20 μm, is dominated by the cooperative alignment effect of all the grooves in the grating and the grating density. Finally, the structural evolution has been studied as a function of depth in the film for samples between 1 and 20 μm by changing the incidence angle. We find that for films between 10 and 20 μm this structural evolution is equal to the structural evolution observed as a function of film thickness.
Folded pendulum tiltmeter
Authors: Wu Shuchao , Fan Shuhua , Luo Jun , Hsu Houtse
Published: July 2002

The application of the folded pendulum (FP) as a tiltmeter is proposed and some features of it have been studied both theoretically and experimentally. First, FP could have a quite low resonance frequency due to its mechanical structure. The period of our prototype FP is 6.2 s and the amplification factor is about 100. Second, FP is not sensitive to the environmental temperature variation but seriously affected by the temperature gradient. The experiment with a temperature gradient modulation shows that the static equilibrium position of the FP will change by 2.5 μrad if the temperature difference between the horizontal platform and the base of the FP is 0.1 °C. With a prototype FP, we have observed obvious tilt tides, and the calibration result shows that the resolution of the FP is about 1.2 nrad.
Magnetization reversal probed by spin-polarized tunneling
Authors: Jo Moon-Ho , Mathur N. D. , Blamire M. G.
Published: July 2002

We report magnetic reversal processes in the magnetic tunnel junction (MTJ) based on a half metallic manganite, La0.7Ca0.3MnO3 by comprehensive spin-polarized tunneling (SPT) measurements. The large tunnel magnetoresistance up to 77% of (Rap−Rp)/Rap in the present MTJ is highly sensitive to the local magnetization fluctuation in the ferromagnetic electrodes and thus enables us to establish an instantaneous one-to-one correlation between the magnetization reversal and the SPT with the two-dimensional SPT measurements. We have found the systematic angular variations of the SPT features in the resistance-field curves, and based on the observed angular dependences, we propose a crucial role of the edge-domain pinning and the resultant multi-domain breakup for the magnetization reversal.
All solution-chemistry approach for YBa2Cu3O7−δ-coated conductors
Authors: Siegal M. P. , Clem P. G. , Dawley J. T. , Ong R. J. , Rodriguez M. A. , Overmyer D. L.
Published: July 2002

A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K)=1.3 MA/cm2.
Polarization effects of a europium complex in stretched polyethylene
Authors: Srdanov V. I. , Robinson M. R. , Bartl M. H. , Bu X. , Bazan G. C.
Published: July 2002

Polarization effects in photoluminescence spectra of Eu3+ ions in tris(dinaphthoylmethane) (monophenanthroline)europium(III) complex [abbreviated hereafter as Eu(dnm)3phen] dispersed in stretched polyethylene (PE) reveal quasi-uniaxial alignment of the molecular complex, not present in the unstretched PE. The ligand field structure of D50−F72 transition in the Eu(dnm)3phen single crystal differs from that of a single molecule in stretched PE, indicating rearrangement of the organic ligands upon stretching.
Subpicosecond transmission change in semiconductor–embedded photonic crystal slab: Toward ultrafast optical switching
Authors: Shimizu Makoto , Ishihara Teruya
Published: July 2002

We have measured the subpicosecond photoinduced transmission change of the photonic crystal slab, in which inorganic–organic layered perovskite semiconductor is embedded for large optical nonlinearity. It is observed that sharp transmission dips shift to the blue during the irradiation of the pump pulse. This result is explained in terms of the change of the polariton dispersion relation due to the excitonic optical Stark effect. Possible application for ultrafast optical switching is discussed.
Short-time thermoelastic contributions to picosecond-time scale reflectivity measurements of metals
Authors: Richardson C. J. K. , Spicer J. B.
Published: July 2002

The thermoelastic transients observed in aluminum during the first few picoseconds after absorption of a subpicosecond duration laser pulse are described through numerical simulations using a nonlinear, two-temperature parabolic model of thermal stresses. Comparisons between these simulations and experimental measurements obtained from a single-crystal aluminum sample and polycrystalline aluminum films on silicon illustrate that the thermal and elastic transients must both be considered at all times in order for the physical properties that are interpreted from the experimental measurements to be consistent with those obtained from other measurements made at various time scales.
Measurements of InGaAs metal–semiconductor–metal photodetectors under high-illumination conditions
Authors: Aliberti K. , Wraback M. , Stead M. , Newman P. , Shen H.
Published: July 2002

We report on temporal response measurements of InGaAs metal–semiconductor–metal photodetectors (MSM–PDs) under high-illumination conditions. The peak current efficiency of the MSM–PDs decreases as optical pulse energy increases due to space-charge-screening effects. The screening effect begins to occur at an optical pulse energy as low as 1.0 pJ, as predicted by a recent two-dimensional model. The fall time and full width at half maximum of the impulse response increase as the optical pulse energy increases and decrease as the bias voltage increases. For optical pulse energies between 1.0 and 100 pJ, the rise time displays a U-shaped behavior as the bias voltage increases. This may be associated with the shape of the electron velocity-field characteristic in conjunction with the screening of the dark field by optical generated carriers.
Wavelength stabilization of semiconductor lasers with a tunable photodetector
Authors: Colace Lorenzo , Masini Gianlorenzo , Assanto Gaetano
Published: July 2002

We introduce an approach to stabilizing the wavelength of a semiconductor laser employing a voltage-tunable photodetector. The latter provides a bipolar error signal driving a feedback loop for the laser retuning. We demonstrate wavelength stabilization within ±25 pm in the 1.55 μm window. Performances, system compactness, and integrability make the approach quite appealing for use in dense wavelength division multiplexing networks.
Resonant terahertz radiation from Tl2Ba2CaCu2O8+δ thin films by ultrafast optical pulse excitation
Authors: Tominari Yukihiro , Kiwa Toshihiko , Murakami Hironaru , Tonouchi Masayoshi , Wald Hagen , Seidel Paul , Schneidewind Henrik
Published: July 2002

We have observed the free-space radiation of the resonant terahertz wave from c-axis oriented Tl2Ba2CaCu2O8+δ thin films by femtosecond optical pulse excitation under a radial magnetic field of about 100 Oe nearly parallel to the c axis of the thin film. The observed wave form showed clear oscillations up to 80 K. The frequency was shifted from ∼620 GHz at 24 K to ∼300 GHz at 80 K, corresponding to an increase in c-axis penetration depth, λc, from ∼26 μm to ∼53 μm, and disappeared above TC as expected for the Josephson plasma resonance.
Resonant tunneling through metal (Ag–Ti)/insulator (MgO) triple barrier structures
Authors: Kado T.
Published: July 2002

Resonant tunneling through metal (Ag–Ti)/insulator (MgO) triple barrier structures has been demonstrated. The multilayers with the triple barrier structures were epitaxially grown on MgO (001) substrates under 473 K by the electron beam evaporation method. For the measurement of current–voltage characteristics, the mesa-isolated diodes were fabricated by photolithography. The observed current peaks in the current–voltage characteristics of the diodes could be explained as the resonant tunneling current.
Comparison of magnetic- and chemical-boundary roughness in magnetic films and multilayers
Authors: Kelly J. J. , Barnes B. M. , Flack F. , Lagally D. P. , Savage D. E. , Friesen M. , Lagally M. G.
Published: July 2002

Diffuse x-ray resonant magnetic scattering, atomic-force microscopy, and magnetic hysteresis measurements are used to explore the relationship between the roughness and magnetic properties of interfaces between magnetic and nonmagnetic thin films. Bare Co films and Co films capped with magnetic and nonmagnetic thin films are investigated to elucidate why and under what circumstances the magnetic boundary differs from the chemical boundary. Competing models to explain why the magnetic boundary appears smoother than the chemical boundary are explored.
Separation of optical anisotropies by angular dependent reflection anisotropy spectroscopy
Authors: Macdonald B. F. , Cole R. J.
Published: July 2002

Double rubbing of polymer films, which finds applications in modern liquid crystal devices, has been investigated using reflection anisotropy spectroscopy (RAS) and atomic force microscopy. A method of gauging the relative strength of rubbing in two different directions, based upon the dependence of observed RAS signals on the sample azimuthal angle, has been found. Angular dependent measurements are shown to be a useful extension of the standard technique by allowing angular dependent sources of optical anisotropy to be separated experimentally.
Spectral method for the simultaneous determination of uncorrelated and correlated amplitude and timing jitter
Authors: Gross Michael C. , Hanna Marc , Patel Ketan M. , Ralph Stephen E.
Published: July 2002

We present a technique for simultaneous determination of the uncorrelated and correlated timing and amplitude jitter of a pulse train from its radio-frequency spectrum. First, we present a robust analysis that separately identifies both correlated and uncorrelated jitter. Second, we show that all four noise components can be uniquely determined by combining the traditional integrating calculation with a nonintegrating computation. We present simulation results that confirm the accuracy of this technique.
Nonlinear photonic band-gap structure with extremely high efficiency for third-harmonic generation
Authors: Shi B. , Wang X.
Published: July 2002

A method of tailoring the electromagnetic states in photonic band-gap structures was used in designing a dielectric structure optimized for third-harmonic generation. The structure we considered was a stack of several kinds of χ(2) nonlinear bilayers approximately 10 μm in length. In the theoretical analysis and numerical experiment, a conversion efficiency enhancement of more than 14 orders of magnitude, as compared with that in a normal conventional setup of two crystals, was found. The possibility of efficient third-harmonic generation in a single structure of χ(2) materials and the phenomenal enhancement of the conversion efficiency show that the electromagnetic state control in photonic band-gap structures offers great potential in nonlinear optics.
Fabrication and properties of low-temperature (⩽600 °C) processed n-type nanocrystalline SiC/p-type crystalline Si heterojunction diodes
Authors: Kerdiles S. , Berthelot A. , Rizk R. , Pichon L.
Published: July 2002

Silicon carbide layers were grown on Si at 600 °C by magnetron sputtering in a pure hydrogen plasma. The transmission-electron-microscopic observations reveal a high crystallization degree and the formation of SiC nanocrystals of ∼5 nm average size. The nanocrystalline SiC was used to fabricate SiC/Si heterojunction diodes which show good performance with a rectification ratio of ∼104 at ±2 V and low leakage current. The behavior of this latter with temperature suggests that it is due to thermal emissions amplified by a Poole–Frenkel effect.
Integrated optical interferometric detection method for micromachined capacitive acoustic transducers
Authors: Hall Neal A. , Degertekin F. Levent
Published: July 2002

An integrated optical interferometric detection method for micromachined capacitive acoustic transducers is reported. The back electrode of the capacitive transducer on a transparent substrate is shaped as an optical diffraction grating and the displacement of the transducer membrane is determined with interferometric resolution by measuring the intensity of the reflected diffraction orders. By applying voltage to deflect the membrane electrostatically, the detection sensitivity is kept at the optimum level and transmission signals are generated. Initial experiments on devices microfabricated on quartz substrates show a minimum detectable displacement of 2×10−4 Å/√Hz around 250 kHz and low frequency detection capability for microphone applications. Ultrasonic pulse-echo experiments in air at 750 kHz are also demonstrated using both a HeNe laser and a 850 nm vertical cavity surface emitting laser as the light source.
High hole mobility (1300 cm2/V s) at room temperature in hydrogen-terminated (001) diamond
Authors: Kasu Makoto , Kobayashi Naoki
Published: July 2002

We have obtained high hole mobility of 1300 cm2/V s at room temperature in a hydrogen-terminated homoepitaxial diamond (001) layer grown at 766 °C and with the thickness of 6.5 μm. Above room temperature, the hole sheet density increased proportionally as the homoepitaxial-layer thickness increased. We discuss the mechanism for the high hole mobility near room temperature assuming parallel conduction in the homoepitaxial layer and on (or near) the surface.
Comparing leakage currents and dark count rates in Geiger-mode avalanche photodiodes
Authors: Jackson J. C. , Hurley P. K. , Lane B. , Mathewson A. , Morrison A. P.
Published: July 2002

This letter presents an experimental study of dark count rates and leakage current in Geiger-mode avalanche photodiodes (GM APD). Experimental results from circular diodes over a range of areas (20–500 μm diam), exhibit leakage current levels orders of magnitude higher than anticipated from dark count rates. Measurements of the area and peripheral components of the leakage current indicate that the majority of the current in reverse bias does not enter the high-field region of the diode, and therefore, does not contribute to the dark count rate. Extraction of the area leakage current term from large-area devices (500 μm) corresponds well with the measured dark count rates on smaller devices (20 μm). Finally, the work indicates how dark count measurements represent 10−18 A levels of leakage current detection in GM APDs.
Suppression of phase segregation during molecular-beam epitaxial growth of GaMnN using nitrogen–hydrogen plasma
Authors: Cui Y. , Li L.
Published: July 2002

Epitaxial growth of GaMnN by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy using nitrogen–hydrogen plasma was studied by reflection high-energy electron diffraction, scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The electron diffraction pattern changed from streaky to spotty when hydrogen was added to the nitrogen plasma, indicating that the effective group V/III ratio was increased. Films grown with nitrogen plasma are phase segregated into GaN and manganese nitrides. In contrast, when nitrogen–hydrogen plasma was used, the films are single phase Ga1−xMnxN, and x can be as high as 0.06. These results indicate that phase segregation can be suppressed by adding hydrogen to the nitrogen plasma during growth.
Anomalous isothermal charging and discharging currents in polytetrafluoroethylene
Authors: Neagu Eugen R. , Marat-Mendes Jose N.
Published: July 2002

Transient charging and discharging currents in polytetrafluoroethylene have been investigated at various temperatures and field strengths in a vacuum. Anomalous charging and discharging currents have been identified. At low electric fields, the anomalous discharging current is almost the mirror image of the anomalous charging current. Three characteristic zones have been identified that can provide information about dielectric polarization, bulk conduction, electrode effects, and diffusion. The mobility at 140 °C and 16 MV m−1 was determined to be 5.4×10−16 m2 V−1 s−1.
Improvement of hole injection in phenyl-substituted electroluminescent devices by reduction of oxygen deficiency near the indium tin oxide surface
Authors: Low Beeling , Zhu Furong , Zhang Keran , Chua Soojin
Published: July 2002

We report the use of an in situ four-point probe method to investigate the relation between oxygen plasma treatment on indium tin oxide (ITO) and the variation in its sheet resistance. Analyses on the ITO surface composition made with time-of-flight secondary ion mass spectroscopy probe a dual-layer parallel resistor model for oxygen plasma-treated ITO anodes. We have shown that the increase in the ITO sheet resistance can be attributed to the reduction of oxygen deficiency near the surface. The improvement in carrier injection in phenyl-substituted poly(p-phenylenevinylene)-based light-emitting diodes correlates directly with a layer of low conductivity, several nanometers thick. This was induced on the ITO surface and serves as an efficient hole injecting anode.
Preliminary investigations of infrared Er-related photoluminescence in ion-implanted In0.07Ga0.93N
Authors: Correia M. R. , Pereira S. , Cavaco A. , Pereira E. , Alves E.
Published: July 2002

We report the observation of the 1.54 μm emission from optically excited Er3+ in an ion-implanted In0.07Ga0.93N layer epitaxially strained grown by metalorganic chemical vapor deposition. The Er was implanted at 150 keV with a dose of 1×1015 Er+ cm−2 at room temperature. After annealing the sample at 400 °C during 30 min in a vacuum, the intraionic 4I13/2→4I15/2 transition was observed. Photoluminescence studies were carried out in the temperature range from 70–250 K under below band gap excitation. The dominant line emission at 1.5353 μm revealed complex temperature dependence. Two activation energies of 33±4 meV and 189±86 meV were calculated.
Probing confined interfacial excitations in buried layers by Brillouin light scattering
Authors: Zhang X. , Sooryakumar R.
Published: July 2002

Brillouin light scattering from silicon oxynitride films grown on GaAs reveals an excitation at frequencies lying below that of the Rayleigh surface wave. The mode, identified as a localized interfacial excitation, arises from the presence of a soft, thin transition layer between the film and substrate. The results are discussed in the framework of a Green’s function formalism that reproduces the experimental features and illustrates the nature of the mode and its difference from Stoneley excitations that exist in special cases for an abrupt interface separating two semi-infinite solid media. Observations of this low-frequency excitation offer a previously unexplored approach to characterize, nondestructively, the elastic properties of buried interfaces.
Spin-filter diode based on ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures
Authors: Guo Yong , Chen Xin-Yi , Zhai Feng , Gu Bing-Lin , Kawazoe Yoshiyuki
Published: July 2002

We propose and demonstrate a spin-filter diode based on semimagnetic semiconductor ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures. It is found that the degree of spin polarization greatly depends on the electric field direction and its magnitude. There is significant difference of the spin polarization between under forward bias and under reverse bias. It is also found that the spin polarization will reverse under relatively small magnetic field, which is originated from resonant enhancement effect for spin-up electrons tunneling through effective steplike potential of the corresponding structure.
Measurement of electronic stopping power of swift heavy ions using high-resolution time-of-flight spectrometer
Authors: Zhang Y. , Possnert G. , Weber W. J.
Published: July 2002

Using only time of flight data to determine energy loss, an analysis procedure has been developed to improve the precision of simultaneously measuring electronic stopping powers of swift heavy ions from a continuous energy spectrum provided by a typical elastic recoil detection analysis geometry. This procedure eliminates the well-known calibration problem of Si detectors when used with heavy ions. Consequently, the stopping powers and the energy dependence are determined with higher precision. This approach is demonstrated by measuring the stopping powers of Be, C, Si, and Br in amorphous C over a continuous range of energies. The results exhibit good agreement with limited existing data but indicate some deviations from the predicted theoretical values.
Structural behavior of Zr52Ti5Cu18Ni15Al10 bulk metallic glass at high temperatures
Authors: Mattern Norbert , Eckert Jürgen , Kühn Uta , Hermann Helmut , Sakowski Jan , Herms Gerhard , Neuefeind Jörg
Published: July 2002

The structural behavior of the Zr52Ti5Cu18Ni15Al10 bulk glass-forming alloy has been investigated in situ by means of high-temperature x-ray synchrotron diffraction. The dependence of the structure factor of the glass can be well described with a Debye–Waller factor and a Debye temperature θ=412 K. At the glass transition, the structure factor significantly decreases due to additional thermal excitations. The extrapolation of the structure factor of the supercooled liquid to temperatures above the liquidus curve is in agreement with experimentally determined values of the melt. The short-range order of the glass, of the supercooled liquid state, and of the equilibrium melt at T=1193 K, is found to be quite similar. The formation of complex chemically ordered clusters in the melt is proposed to be essential for the high-glass-forming ability of this alloy.
Study of magnetic properties and Mössbauer effect of Pr-Fe and melt-spun Pr-Fe-B alloys
Authors: Rotenberg L. R. K. , Oliveira R. F. , Rechenberg H. R. , Missell F. P.
Published: July 2002

We prepared samples of the intermetallic compound Pr2Fe17 that were free of segregated Fe and measured the Mössbauer spectra as a function of temperature, obtaining TC=301±2 K. Mössbauer spectra from samples of annealed Pr2Fel4B powder show considerable complexity. Melt-spun ribbons of Prl5Fe79B6, magnetized to 20 kOe, showed an intrinsic coercive field Hci=14.5 kOe at room temperature. Mössbauer spectra of melt-spun material show slight differences with respect to those from annealed ingots. The origin of these differences is not yet clear.
A model for high-field transport in alloys: Application to In0.53Ga0.47As
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

We propose a new model for alloy scattering in semiconductor alloys in which the alloy scattering potential is allowed to have an energy dependence which is calculated from the band structures of the components. At low electric fields this model reduces to the conventional model based on electronegativity differences of the components. At high fields where the electron distribution function is shifted to higher electron energies, our model leads to reduced alloy scattering. This in turn leads to a reduction in the threshold fields and an increase in peak velocities. This model is applied to In0.53Ga0.47As and the results thus obtained are compared with the available experimental data.
Characteristics of submicron patterns fabricated by gallium focused-ion-beam sputtering
Authors: Morimoto H. , Sasaki Y. , Watakabe Y. , Kato T.
Published: July 2002

Cross sections of the patterns fabricated in (100) GaAs by 100-keV gallium focused ion beam have been studied using a scanning electron microscope (SEM). The probe size of the ion beam is 0.1–0.15 μm at the current of 100 pA. The etched depth becomes saturated at the high dose region (about 5.0×10−6 C/cm) because of the redeposition effect. The pattern profile becomes asymmetric if it is made up of several adjacent lines perpendicular to the beam scanning direction due to the redeposition effect and the increase of sputtering yield for each scan, which is caused by the change of ion beam incident angle. These effects can be eliminated by the use of multiwriting method.
Performance characteristics of sealed-off CO2 laser with La1−xSrx CoO3 oxide cathode
Authors: Iehisa N. , Fukaya K. , Matsuo K. , Horiuchi N. , Karube N.
Published: July 2002

The sealed-off CO2 laser with La1−xSrxCoO3 oxide cathode was found to improve laser performances in both output power and operating life. The maximum output power from 120-cm discharge length was 62 W and the life defined by the power decrease by 10% was 3500 h at this power level. The power enhancement of this laser is due to the combined effects of catalytic activity and O2 emissivity of the oxide cathode, while the life improvement is due to the combined effects of its chemical inertness, O2 emissivity, and low sputtering rate.
Phase-change optical recording in TeSeSb alloys
Authors: van der Poel C. J. , Gravesteijn D. J. , Rippens W. G. V. M. , Stockx H. T. L. P. , van Uijen C. M. J.
Published: July 2002

Some characteristics of reversible phase-change optical data storage in TeSeSb alloys are given. High signal-to-noise ratios are reached at low recording energies. Upon passage of an oblong scanning laser spot, erasure occurs by growth from the crystalline surroundings of the amorphous effects at growth velocities of up to 5 cm/s. Isothermal transformation appears to be dominated by phase separation and diffusion processes. The tradeoff between long-term stability and erasure time varies with alloy composition and, for some alloys, attractive properties with respect to data retention and erasure times are found.
Annealing of plasma silicon oxynitride films
Authors: Denisse C. M. M. , Troost K. Z. , Habraken F. H. P. M. , van der Weg W. F. , Hendriks M.
Published: July 2002

The anneal behavior of plasma-enhanced chemical vapor deposited silicon oxynitride films has been studied using Fourier transform infrared absorption spectroscopy, nuclear reaction analysis, and electron-spin resonance. The anneal temperature range was 500–1000 °C. It is observed that the oxynitrides which contain only N–H bonds are thermally stable in the temperature range under study. The layers which also contain Si–H bonds are considerably less thermally stable. Abundant hydrogen effusion from these layers is observed at temperatures as low as 600 °C, accompanied by cracking and shrinkage of the films. It is suggested that the coexistence of both Si–H and N–H bonds offers the possibility for cross linking and that consequently the decomposition temperature of both types of bonds is lowered. Evidence for the occurrence of cross linking is found in the infrared difference spectra. Consistently, the silicon unpaired electron density does not increase upon annealing. The Si–H and N–H bands effectively shift towards higher wave numbers upon annealing at higher temperatures. This is ascribed to the inhomogeneity in bond strength, which in turn is related to a variation in electronegativity of the surrounding groups.
Structural changes produced in silicon by intense 1-μm ps pulses
Authors: Smirl Arthur L. , Boyd Ian W. , Boggess Thomas F. , Moss Steven C. , van Driel Henry M.
Published: July 2002

The numerous bulk and surface structural changes observed in c-Si following melting with 1-μm pulses that range from 4 to 260 ps in duration and fluences from about 0.6 to 2.8 J cm−2 are examined by Nomarski and transmission electron microscope techniques. For melting pulse widths 30 ps or longer, recrystallization from the melt was observed. By contrast, for the shorter pulses (∼7 ps), the steep temperature gradients that accompany the onset of two-photon absorption associated with pulses of this width produce an undercooled melt. Under these conditions, the resolidification velocities are evidently too high to allow epitaxial regrowth from the crystalline substrate and, for the first time, regions of amorphous and large- and fine-grain polycrystalline silicon are observed to form directly on a crystalline underlayer. In addition, alternate stripes of amorphous and crystalline material are produced by these short pulses. These are associated with localized melting, demonstrating that uniform surface melting is not always required before a spatial modulation of the absorbed surface energy can occur.
The chemical oxygen-iodine laser: Comparison of a theoretical model with experimental results
Authors: Churassy Serge , Bacis Roger , Bouvier Annie J. , Mery Claire Pierre dit , Erba Bernard , Bachar Jehuda , Rosenwaks Salman
Published: July 2002

The experimental performance of a small-scale chemical oxygen-iodine laser is compared to a theoretical model. Measuring the consumption of O2 (1Δg) in the region of the flame indicates that less than five molecules of O2 (1Δg) are required to dissociate one I2 molecule. It is shown that the hyperfine relaxation rates in the iodine atom increase both the laser threshold and the active transverse length of the cavity.
Nuclear reaction analysis of shallow B and BF2 implants in Si
Authors: Ridgway M. C. , Scanlon P. J. , Whitton J. L.
Published: July 2002

Impurity diffusion induced by rapid thermal annealing has been investigated for low-energy 11B and 49BF2 implants in Si. Samples were annealed with an oxide cap in an AG Associates Heatpulse system. Depth profiles were determined with nuclear reaction analysis. This technique is sensitive to impurities at or near the surface and can reveal impurity diffusion to near-surface regions not usually detectable with secondary ion mass spectrometry. Significant B diffusion to the SiO2/Si interface was observed for a 1050 °C/20-s anneal of 10-keV 11B implanted in crystalline and preamorphized Si. B interfacial concentrations were comparable to peak concentrations in unannealed samples. Diffusion of B and F to the SiO2/Si interface and impurity gettering by ion straggling damage was observed for a 1050 °C/20-s anneal of 45-keV 49BF2 implanted in crystalline Si. Impurity segregation at the SiO2/Si interface was minimal for a 1050 °C/20-s anneal of 45-keV 49BF2 implanted in preamorphized Si, although a loss of F was apparent.
Fracture testing of silicon microelements i
n s
i
t
u in a scanning electron microscope
Authors: Johansson Stefan , Schweitz Jan-Åke , Tenerz Lars , Tirén Jonas
Published: July 2002

Fracture testing of silicon cantilever beams (thicknesses 10–20 μm) was performed in situ in a scanning electron microscope by means of an equipment specially designed for this purpose. Beams of various sizes and orientations (〈011〉 and 〈001〉) were manufactured in Si (100) wafers by two different micromachining procedures. The beams were tested by simple bending to fracture, and a number of fundamental fracture parameters were determined from an analytical model of elastic fracture. To verify its validity, the model was utilized to evaluate an experimental E modulus, which was found to agree well with previous results. Fracture limits, fracture strains, and initiating flaw sizes were determined. The maximum fracture limit was very high; about 10 GPa. The strengths of different beams scattered from this value down to practically zero strength, with an average close to 4 GPa. The corresponding fracture strains and initiating flaw sizes were 6% and 3 nm, respectively (maximum strength), and 2% and 17 nm (average strength). Finally, a simple fractography study was performed on the fractured beams.
A time domain analysis of the charge pumping current
Authors: Ghibaudo Gerard , Saks Nelson S.
Published: July 2002

A general time domain analysis of the recombination currents involved in the charge pumping phenomenon occurring in a metal-oxide-semiconductor structure is presented. This analysis not only allows a better understanding of the physical origin of the charge pumping current, but also furnishes quantitative information about the charge pumping current intensity versus the frequency, shape, and amplitude of the applied gate voltage signal. A comparison between our numerical simulations and analytical models available in the literature is also conducted. In particular, the range of applicability of the Groeseneken formula is studied both for trapezoidal and triangular time dependence of the gate voltage.
A novel method for determining the gap-state profile and its application to amorphous Si1−xGex:H films
Authors: Matsuura Hideharu
Published: July 2002

A novel technique has been proposed for determining the density-of-state (DOS) distribution in the energy gap of highly resistive amorphous semiconductors, using amorphous/crystalline heterojunction structures. The technique has been tested and applied to undoped hydrogenated amorphous silicon (a-Si:H) films and silicon-germanium (a-Si1−xGex:H ) alloy films, covering the optical gap (E0) range of 1.3–1.7 eV. For undoped a-Si:H with E0=1.7 eV, the peak of the midgap DOS distribution has been located at 0.84 eV below the conduction-band mobility edge, EC, with a value of 2×1015 cm−3 eV−1. For undoped a-Si1−xGex:H (E0=1.44 eV), the same has been obtained at 0.70 eV below EC, with a magnitude of 7×1016 cm−3 eV−1. Those midgap DOS have been found to be correlated with singly occupied dangling bonds, representative of a homogeneous bulk property of the material, unaffected by interface states.
Early stages of channel formation in a short-gap breakdown
Authors: Novak J. P. , Bartnikas R.
Published: July 2002

A description and analysis of the solution of a two-dimensional model for a HV breakdown of a short gap is presented. The model consists of the electron, ion, and excited-atom conservation and Poisson equations and is applied to a plane-parallel gap with an electrode separation of 0.48 mm in helium gas at atmospheric pressure and a temperature of 293 K subjected to an electrical field of 10 kV cm−1. Two-dimensional plots of the charged and excited-particle densities and electric field components are presented and discussed. It is shown that in the first, diffusion-controlled, stage density profiles are close to a Gaussian distribution with an effective radius increasing in time. The subsequent stage is controlled by the space-charge field, causing prominent constriction of the electron density channel. In consequence, a high ionization near the discharge axis results in a virtual narrowing of the ion and excited-atom profiles as well, and the forming conductive chanel exhibits a tendency towards constriction. Calculations were conducted up to a maximum time of t=1139 ns, when maximum electron, ion, and excited-atom densities reached values of 3.1×1010, 3.7×1011, and 2.5×1012 cm−3. Among the ionization processes the direct and Penning interactions are dominant, accounting at average for approximately 70% and 30% of the total at time t=1139 ns; ionization frequencies are substantially affected by space-charge field and vary considerably in time and space near the end of calculations.
High-energy cast Pr-Fe-B magnets
Authors: Shimoda T. , Akioka K. , Kobayashi O. , Yamagami T.
Published: July 2002

A new process has been developed to produce high-energy bulk Pr-Fe-B magnets directly from the melt without the handling of magnetic powder or powderlike ribbons. The process mainly consists of only three steps—casting/hot pressing/annealing—and minimizes the oxygen contamination of magnets. A typical composition of cast alloy is Pr17 Fe76.5 B5 Cu1.5 . Using this type of alloy, a magnetic alignment is easily introduced by hot pressing. Copper plays two important roles: high coercivity and excellent magnetic alignment are achieved simultaneously by the addition of copper. Magnetic properties of hot-pressed Pr17 Fe76.5 B5 Cu1.5 magnets are as follows: Br=12.5 kG, i Hc =10.0 kOe, and (BH)max =36.2 MGOe. The cast alloy of this composition also has an i Hc of 7.4 kOe and a (BH)max of 8.8 MGOe after annealing at 1000 °C for 24 h. The steep rise in the initial magnetization curve indicates a type of nucleation-controlled coercivity mechanism.
Hydrogen desorption from crystalline silicon and its modification due to the presence of dislocations
Authors: Kisielowski-Kemmerich C. , Beyer W.
Published: July 2002

Hydrogen effusion spectra of oxidized Si samples are investigated and characteristic activation energies associated with the rupture of hydrogen bonds are estimated. Dislocation-enhanced solubility of hydrogen is found in deformed crystals and macroscopic diffusion depth (mm) can be realized. Hydrogenation is performed by exposure of the crystals to H2 gas at 800 °C. Beside the desorption of hydrogen bound close to the Si surface, the rupture of hydrogen-hydrogen bonds of molecules stored in deformed crystals is observed. The storage of the H2 molecules requires the presence of dislocations or deformation-induced point defects, and the H:H binding energy ranges from 2.7 to 3.8 eV. Most likely this energy variation comes from different local strain around dislocations. Atomic hydrogen is found to dominate the effusion kinetics.
Raman study of amorphous to microcrystalline phase transition in cw laser annealed a-Si:H films
Authors: Mavi H. S. , Shukla A. K. , Abbi S. C. , Jain K. P.
Published: July 2002

The dynamic behavior of continuous wave (cw) laser-induced crystallization in the a-Si:H film on a quartz substrate is studied by light scattering. Microcrystals of dimensions less than 30 Å could be grown in a stable state and it is demonstrated that the surface-to-volume correction is essential for estimating the frequency of the crystallinelike mode. It is suggested that bulk-induced crystallization may be responsible for the formation of very small crystallites.
Surface magneto-optical Kerr effect for ultrathin Ni-Fe bilayers
Authors: Zhong Q.-M. , Arrott A. S. , Heinrich B. , Celinski Z.
Published: July 2002

Surface magneto-optical Kerr effect is used to measure magnetic hysteresis loops for Ni-Fe bilayers previously studied by ferromagnetic resonance [Phys. Rev. 38, 12879 (1988)]. The approach to saturation in the [11] direction confirms the existence of enhanced fourfold in-plane magnetic anisotropy, attributed to the effect of arrays of misfit dislocations arising during the epitaxial growth of bcc Ni overlayers on ultrathin layers of bcc (001)Fe. The [11] magnetization curves for 10 monolayers (ML) of Ni on 7 ML of Fe shows a breaking of symmetry between positive and negative fields. This is ascribed to spin configurations frozen during growth.