bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal structure and magnetic characteristics of alloys based on R-Fe-Si (R=Y, Nd, Gd, Dy, Ho, Er)
Authors: Pourarian F. , Obermyer R. , Zheng Y. , Sankar S. G. , Wallace W. E.
Published: July 2002

Crystal structure and magnetic properties of ternary compounds based on R2Fe14Si2 (off-stoichiometric R2Fe17 type) were investigated. Results of the powder x-ray-diffraction indicated that the compounds examined in this study crystallize in the rhombohedral Th2Zn17-type structure when R is Nd or Gd and in the hexagonal Th2Ni17-type when R is Y, Dy, Ho, or Er. The Curie temperature TC and room-temperature saturation magnetization Ms of R2Fe14Si2 system range from 465 to 572 K and 65 to 150 emu/g, respectively. The behavior of TC is found to follow the root of the de Gennes function and can therefore be ascribed to the strength of the rare-earth–iron exchange interaction. The average magnetic moment of Fe in R2Fe14Si2 is estimated to be approximately 2.0 μB at 77 K. Addition of Si in the binary R-Fe lattice induced a large uniaxial magnetic anisotropy at room temperature in some alloys. Results of M vs T for Er2Fe14Si2 indicate a spin reorientation transition at about 100 and 35 K. Dy2Fe14Si2 and Ho2Fe14Si2 exhibit a remarkable magnetic hardening at low temperatures.
Processing-properties relationships in Fe3O4 thin films (abstract)
Authors: Kim Y. K. , Oliveria M.
Published: July 2002

As part of a fundamental study of interface magnetism in Fe/Fe3O4 multilayer systems, we have examined the magnetic properties of polycrystalline Fe3O4 thin films. Fe3O4 thin films, deposited by reactive evaporation and sputtering, have been previously studied because they serve as a precursor for the formation of γ-Fe2O3. The film thicknesses used in these studies have typically been greater than 100 nm. We have examined the magnetic properties and microstructure of Fe3O4 films with thicknesses less than 100 nm, a regime in which the magnetic properties have been reported to be strongly dependent on thickness.1 The films were deposited by rf sputtering. The processing variables examined include substrate material, substrate temperature, oxygen partial pressure, and film thickness. The microstructural origins of the observed coercivity and anisotropy will be discussed, as well as trends in the saturation behavior.
Electronic transitions of Ho in Pb2Sr2HoCu3O8 observed by inelastic neutron scattering
Authors: Soderholm L. , Loong C.-K. , Xue J. S. , Hammonds J. P. , Greedan J. E. , Maric M.
Published: July 2002

The electronic behavior of the 5I8 Russell Saunders ground multiplet of Ho3+ in Pb2Sr2HoCu3O8 has been investigated using inelastic neutron scattering. We observe ten peaks in the excitation spectra that are associated with crystal field transitions. The peaks are only slightly broader than expected from instrument resolution, indicating that there are no strong interactions between the local Ho f states and the CuO conduction states. Comparing the energies and intensities of the experimental peaks with those expected from modeling convinces us that there are at least three states populated at the temperature of our experiment (15 K), making the assignments of transitions very difficult in the absence of further data.
Magnetic property variation in carbon steel and chrome-molybdenum steel as a function of uniaxial stress noncoaxial with the magnetic field (abstract)
Authors: Sablik M. J. , Kaminski D. A. , Jiles D. C. , Biner S. B.
Published: July 2002

Magnescope1 magnetic measurements were made on carbon steel specimens ranging from 0.1–0.8 wt %C and on chrome-molybdenum steel specimens cut from electric power plant pipes previously in service. The carbon steel specimens were heat-treated using three procedures: (1) spheroidization, (2) quenching, and (3) quench and tempering. The specimens were subjected to uniaxial tension up to 40 ksi. The inspection head was aligned so that the magnetic field was oriented at different angles with respect to the stress axis. Magnetic properties (such as coercivity and maximum differential permeability) were extracted from digitized magnetic hysteresis loop measurements. Magnetic properties were studied as a function of stress at each angle of stress-field orientation. To our knowledge, such a comprehensive study of noncoaxial stress and field effects has never been accomplished before for such a wide variety of steel specimens. Results for the various materials are presented for different orientation angles and compared to numerical results from the noncoaxial magnetomechanical hysteresis model of Sablik et al.2
A new model of magnetostrictive ‘‘jumps’’ in twinned Terfenol-D (abstract)
Authors: Zhao Xue-Gen , Li J. Y. , Jiang W. C. , Li Qiang
Published: July 2002

A new three dimensional model is set up for interpreting the magnetostrictive ‘‘jumps’’ in Terfenol-D compressed along the [112̄] or magnetically heat treated perpendicular to the [112̄]. This model considers the combined effects of magnetic anisotropy, stress, and magnetic field. It assumes no domain interaction and separates the magnetizing process of such Terfenol into three steps: (a) 180° domain wall movements at low applied H; (b) three dimensional domain rotations at high H; (c) non-180° domain wall movements at higher H. The magnetostrictions along the three orthogonal directions of [111], [112̄], and [11̄0] in Terfenol Tb0.3Dy0.7Fe1.9 compressed along the [112̄] are calculated. The ratios of these to the saturated [111] magnetostriction of single crystalline Terfenol are 0, 0, 0 at the end of (a); −4/3, 5/6, 1/2 at the end of (b); −4/3, 4/3, 0 at the near end of (c), respectively. These data are consistent with our measurements and others.1
Quantum fluctuations in easy-plane spin-one ferromagnet
Authors: Pan K. K. , Wang Y. L.
Published: July 2002

The magnetic properties of easy-plane spin-one Heisenberg ferromagnet, H=D∑i(Six)2 −J∑(i,j)Si⋅Sj−h∑iSiz, are investigated using the linked cluster series expansion. The results of the linked cluster series expansion method cover the whole range of temperatures, both magnetically ordered and disordered phases. The order parameter is included in correlations of spin fluctuation and solved self-consistently to high orders. The magnetization as a function of temperature for a given value of easy-plane anisotropy is shown. The observed values of magnetization from the linked cluster series expansion are appreciably depressed from their mean-field approximation values due to the quantum and thermal fluctuations. The effects of the quantum fluctuation on the magnetic ordering in three-dimensional (3D) systems are discussed.
Spontaneous magnetostriction of RCo4B (R=Y and Ce)
Authors: Lindbaum A. , Hong N. M. , Müller H. , Gratz E. , Thuy N. P. , Hien T. D.
Published: July 2002

The spontaneous linear magnetostriction at T=0 K in YCo4B is positive along the a axis (λa=1.1×10−3) and negative along the c axis (λc=−2.1×10−3), although the volume magnetostriction below Tc is negligibly small and below the resolution of the x-ray measurement. In CeCo4B, however, both λa and λc are smaller and below about 130 K, a negative volume magnetostriction of the order of 10−3 is observed. An anomalous increase of the resistivity is also found at the same temperature range. This anomalous behavior is assumed to be related with the Ce magnetism in CeCo4B.
Mössbauer analysis of the microwave desulfurization process of raw coal
Authors: Weng Sihao
Published: July 2002

57Fe Mössbauer spectroscopy was used to study the evolution of pyrite inherent in raw coal during microwave irradiation. The results for phase analyses show that the decomposing reaction of pyrite in coal, caused by microwave heating, FeS2→Fe1−xS→FeS consecutively progresses to the right with increase of irradiation time. The whole process of microwave desulfurization of raw coal consists of the initiation, the promotion, and the saturation stages. Calculated results show that the inorganic desulfurization efficiencies from microwave treatment for irradiation time of 30–100 s are 5%–44%. The relatively higher desulfurization efficiencies are probably relative to the smaller particle size of both the pyrite and coal sample.
Data analysis strategies for the characterization of normal: superconductor point contacts by barrier strength parameter
Authors: Smith Charles W. , Reinertson Randal C. , Dolan P. J.
Published: July 2002

The theoretical description by Blonder, Tinkham, and Klapwijk [Phys. Rev. B 25, 4515 (1982)] of the I-V curves of normal: superconductor point contacts encompasses a broad range of experimental behavior, from the tunnel junction case, on the one hand, to the clean metallic microconstriction limit on the other. The theory characterizes point contacts in terms of a single parameter, the barrier strength. The differential conductance of a point contact, at zero bias, as a function of temperature, offers a direct experimental method by which the barrier strength parameter can be evaluated. In view of the full range of phenomena incorporated by this theory, we suggest several different strategies for the evaluation of the barrier strength parameter from data in the low and intermediate barrier strength regimes and for measurements in the low temperature (near T=0 K) and high temperature (near T=Tc) limits.
Determination of the ferromagnetic coupling across Pd by magneto-atomic engineering
Authors: Bloemen P. J. H. , de Jonge W. J. M. , Donkersloot H. C.
Published: July 2002

The ferromagnetic coupling across Pd interlayers has been determined from hysteresis loop measurements on perpendicular-magnetized multilayers of the type M3/8 Ru/M2/xPd/M1. Here M1, M2, and M3 denote magnetic layers consisting of (strongly ferromagnetically coupled) Co/Pd multilayers with perpendicular magnetic anisotropy: M1=[3Co+4×(4Co+6Pd)], M2=[3Co+4×(4Co+6Pd)+7Co] and M3=[20×(6Pd+4Co)+3Co]. (The layer thicknesses are in Å.) The determination of the ferromagnetic coupling across the Pd interlayer with variable thickness x was enabled by pinning the second magnetic layer M2. This pinning was achieved by the relatively strong antiferromagnetic coupling (by the Ru layer) to the thickest magnetic layer M3. The hysteresis loops displayed a staircase behavior, with two or three steps (levels), depending on the strength of the ferromagnetic coupling. From the fields at which the steps occurred, the ferromagnetic coupling across Pd, as well as the antiferromagnetic coupling across the 8 Å Ru layer, were determined. A monotonic decrease of the former was observed from 0.17 mJ/m2 at 14 Å Pd to ≊0.02 mJ/m2 at 20 Å Pd.
The long-range-order structures of III-V semiconductor alloys
Authors: Ni Jun , Lai Xinchun , Gu Binglin
Published: July 2002

The concentration wave method is used to determine the ordered structures appearing in the epilayers of III-V semiconductor alloys. Based on a two-dimensional planar model, possible ordered structures of zinc-blende structure are deduced. Some experimental features are explained. Phase diagrams of interaction parameters are given.
A theoretical model for the density distribution of mobile ions in the oxide of metal-oxide-semiconductor structures
Authors: Mitra V. , Bentarzi H. , Bouderbala R. , Benfdila A.
Published: July 2002

A theoretical model for the density distribution of the mobile ions in the oxide of a metal-oxide-semiconductor structure is developed. It is based on the concept that at any point in the oxide the equilibrium concentration of these mobile ions is attained when the combined mobilizing forces, namely, thermal diffusion, internal, and external electric fields, become just sufficient to provide necessary activation energy to the ions to surmount the effective potential well. All these forces, acting on a single ion, have been obtained independent of each other and then combined to yield the equilibrium density distribution of the mobile ions. The results of the present model are consistent and in good agreement with earlier experimental results.
Two photon confined-to-continuum intersubband transitions in the semiconductor heterostructures
Authors: Li S. , Khurgin Jacob B.
Published: July 2002

The two-photon transitions from the confined states to the continuum in the semiconductor quantum wells and superlattices are considered theoretically. Both the two-photon absorption coefficient and the third order nonlinear susceptibility related to it are calculated. The results show that the nonlinear index of refraction as large as 10−9 cm2/W can be achieved in the important 10 μm region where the absorption is small, opening a possibility of operating nonlinear optical devices in the far infrared domain.
Formation of metallic, crystalline NiSi2 thin film on amorphous SiO2/Si
Authors: Luo Li , Nastasi M. , Maggiore C. J. , Pinizzotto R. F. , Yang H. , Namavar F.
Published: July 2002

Thin metallic, oriented crystalline NiSi2 films that are suitable for additional epitaxial growth have been formed on amorphous SiO2 layers on Si substrates. The orientation of the Si substrate is maintained in the NiSi2 film as if the SiO2 is not present. This was achieved by combining the separation by implantation of oxygen process and e-beam evaporation techniques. The results are comparable with NiSi2 films formed directly on Si. This technique should, in general, be applicable to other silicides that have been epitaxially grown on Si.
Laser action and photoluminescence in an indium-doped n-type Hg1−xCdxTe (x=0.375) layer grown by liquid phase epitaxy
Authors: Ravid A. , Zussman A.
Published: July 2002

Photoluminescence, carrier lifetime, and laser oscillation in an indium-doped n-type Hg1−xCdxTe (x=0.375) layer grown by liquid phase epitaxy on CdZnTe were studied. A single-line photoluminescence spectrum was observed up to room temperature. The temperature-dependence of the photoluminescence peak energy and linewidth agrees with a model of band-to-band transitions obeying the k-conservation rule. The carrier lifetime derived from the observed photoluminescence intensity agrees with the observed photodecay lifetime in the temperature range 12–200 K. Laser action was observed in the temperature range 12–90 K at λ=3.6 μm. The laser threshold power increased exponentially with temperature, with a characteristic temperature of 17.5 K. The calculated equivalent threshold current density was found to closely follow the observed one, indicating a maximum threshold gain of 150 cm−1. The calculation shows that at low temperature the threshold power is determined by radiative recombination, while above 50 K Auger recombination becomes dominant. The high value of the threshold gain is attributed to the gain guiding mechanism governing this laser device operation. The observed differential quantum efficiency decreased from 15% at 12 K to 4% at 90 K. A possible mechanism giving rise to this decrease in the efficiency is discussed. The spectrum of the laser with a 3-μm-thick active layer exhibited at high pumping power up to three lines, which were attributed to index guided transverse modes. The 9-μm-thick active layer device exhibited a quasisingle mode spectrum most probably due to gain guiding in both the lateral and the transversal directions.
Zinc diffusion in GaSb
Authors: Sundaram V. S. , Gruenbaum P. E.
Published: July 2002

We report here the diffusion behavior of zinc in n-type GaSb in the temperature range of 450–540 °C. The diffusion was carried out in a closed box system using a zinc-gallium source. The diffusion profiles were obtained using secondary ion mass spectrometry. From the diffusion profiles, concentration dependent diffusion coefficients were calculated using Boltzman–Montano analysis. These data have been qualitatively interpreted in terms of the interstitial-substitutional diffusion model originally proposed for zinc diffusion in GaAs. Finally, diffused junction GaSb solar cells were fabricated and their performance evaluated.
Photodissociation of dimethylaluminum hydride on Si(100) at 193 nm studied by x-ray photoelectron spectroscopy
Authors: Ohashi Masafumi , Shogen Satoshi , Kawasaki Masahiro , Hanabusa Mitsugu
Published: July 2002

By irradiation of 193 nm photons on the molecularly adsorbed species of dimethylaluminum hydride on Si(100) at 150 K, the [C]/[Al] atom ratio decreased and the Al2p binding energy was lowered. This change is due to the Al—C bond cleavage by direct photoabsorption of the adsorbed species. Irradiation at 351 nm induces no appreciable dissociation of the adsorbed species. When dimethylaluminum hydride was adsorbed on the Si substrate at room temperature, the 193 nm irradiation induced only a small change in the x-ray photoelectron spectra of the dissociatively adsorbed species. Variation of the photodissociation quantum yield is discussed in terms of dissociative adsorption mechanisms.
Investigation of erbium doping of InGaAsP layers grown by liquid-phase epitaxy
Authors: Wu Meng-Chyi , Chen En-Hsing , Chiu Cheng-Ming
Published: July 2002

Electrical and optical measurements of InGaAsP layers grown by liquid-phase epitaxy with different amounts of Er metal (0–0.60 wt %) added to growth solutions are reported. The presence of Er during growth causes the decrease of electron concentration and the strong suppression of donor-related optical transitions due to the effective removal of donors. The characteristic Er3+ emission lines located in the 1.503–1.542 μm region can only be detected in the 1.3 μm wavelength Er-doped InGaAsP layers. We attribute it to be the formation of a new type of Er3+ center in the InGaAsP host.
Mismatched InGaAs/InP and InAlAs/InP heterostructures with high crystalline quality
Authors: Bennett Brian R. , del Alamo Jesús A.
Published: July 2002

Mismatched epitaxial layers of InxGa1−xAs and InyAl1−yAs were grown on InP by molecular beam epitaxy. Samples were characterized by high-resolution x-ray diffraction to assess layer quality as well as composition and strain. Measurement of epitaxial layer peak width is shown to be a sensitive, nondestructive means to judge the structural quality of a strained heterostructure. We find that for lattice mismatch of ±1% or less, the crystalline quality of epitaxial layers of InGaAs and InAlAs consistently remains high to thicknesses up to 3–9 times the Matthews–Blakeslee [J. Cryst. Growth 27, 118 (1974)] critical layer thickness. The findings are applied to the design and growth of high-performance mismatched InAlAs/InGaAs/InP heterostructure field-effect transistors.
Investigation of mesoscopic structures fabricated by channeled Si++ ion implantation of deep heterostructures
Authors: Hornsey R. I. , Thornton T. J. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

Channeled ions offer a means of patterning a wafer with a two-dimensional electron gas (2DEG) buried deep below the surface. The implantation of 60–140 keV Si++ ions into a 580-nm-deep 2DEG formed at a GaAs/AlGaAs heterojunction has been characterized, with respect to ion energy, dose, and angle of incidence. Transverse electron focusing measurements have been used to investigate the roughness of the implanted boundary, leading to measured values for the specularity coefficient of about 0.5 at 1.7 and 4.2 K. Similar measurements at lower temperatures (120 mK) have shown fine structure in the magnetoresistance, in addition to the classical transverse electron focusing effect. The fine structure is attributed to electron interference effects at, or close to, the boundary. Channeled ion implantation has been used to define an in-plane-gated transistor which, at 300 mK, shows clear evidence of ballistic electron transport.
Simulations of hydrogen deposition processes in a-Si:H film growth
Authors: Biswas R.
Published: July 2002

Molecular dynamics simulations of the deposition of atomic H on both c-Si and a-Si:H substrates are performed to understand the physical processes occurring in the presence of an atomic H flux during growth. The absorption probability, and dynamical behavior of the H are studied as a function of the incident H energy. Both hydrogen absorption and backscattering events are observed. The hydrogen reflection probability has a maximum around 50 eV and decreases at higher incident kinetic energies. In the hydrogen backscattering events a substantial subsurface penetration and energy transfer through collisions are observed. Hydrogen absorption events have been closely analyzed and a surface hydrogen release event was observed during an absorption event.
Predictions for gain in the fission-fragment-excited atomic xenon laser
Authors: Shon Jong W. , Kushner Mark J. , Hebner Gregory A. , Hays Gerald N.
Published: July 2002

The infrared atomic xenon laser (5d→6p) is an attractive candidate for fission fragment excitation, which provides low-power deposition (1–100 W cm−3), long pulse lengths (1–10 ms), and high-energy deposition (100s J ℓ −1). Optical gain at 1.73 and 2.03 μm has recently been measured in a reactor-excited xenon laser yielding values exceeding 0.03–0.05 cm−1 at power depositions of less than 10s W cm−3. Gain was also found to rapidly terminate before the peak of the pump pulse for some experimental conditions. A computer model has been developed to predict gain in fission-fragment-excited xenon lasers and these experiments have been analyzed. It is found that the termination of gain is most likely attributable to gas heating which increases the electron density, leading to electron collision quenching. The specific dependence of gain on pump rate suggests that a reduced rate of recombination of molecular ions with increasing gas temperature is partly responsible for this behavior.
Charging and discharging properties of electron traps created by hot-carrier injections in gate oxide of n-channel metal oxide semiconductor field effect transistor
Authors: Vuillaume Dominique , Bravaix Alain
Published: July 2002

The charging and discharging properties of electron traps created by hot-carrier injections in the thin gate oxide of n-channel metal oxide semiconductor transistors are analyzed by means of the effects that charge state transitions induce on the low-level gate current (lower than 1 pA) of the transistor. This current is measured by a very senstive floating-gate technique [F.H. Gaensslen and J.M. Aitken, IEEE Electron. Device Lett. EDL-1, 231 (1980)]. Two traps with electron capture cross sections of the order of 10−14 and 10−15 cm2 are analyzed which are linked with optical and field-dependent measurements of electron emission properties. Thermal and optical ionization energies of these defects are determined at ≊1.7±0.2 and ≊3.0±0.5 eV, respectively. Comparison with theory suggests that Si dangling bonds or oxygen vacancy in the oxide should be the defects created by hot-carrier injections.
Microwave loss in nonlinear optical polymers
Authors: Mohapatra Sarat K. , Francis Cecil. V. , Hahn Kenneth , Dolfi David W.
Published: July 2002

Microwave loss measurements to 40 GHz are reported for side-chain and cross-linked nonlinear optical polymers. Measurements on poled and unpoled materials are described. In addition, reference structures using SiO2 in place of the polymer material are also measured in order to isolate the material loss from the electrode and package losses. Material loss for poled and unpoled polymers is estimated to be less than the measurement uncertainty (0.25 dB/cm) over the entire frequency range.
High mobility metal-oxide-semiconductor transistor with high temperature annealed thick polycrystalline-silicon films
Authors: Sakakibara Nobuyoshi , Fujino Seiji , Muramoto Hidetoshi , Hattori Tadashi , Goto Keisuke
Published: July 2002

We studied the regrowth of grains in polycrystalline-silicon (poly-Si) films deposited on a SiO2 layer. The poly-Si films were grown at 610 °C, by low pressure chemical vapor deposition, up to a thickness of 1.5 μm. The films were then annealed at 1200 °C in flowing N2 for regrowth of the grain. The as-deposited film has small grains and contains many twin boundaries in the grains. In the 1200 °C annealed sample, the grain size strikingly increases to 2 μm, whereas the density of the twin boundaries decreases. Accordingly, metal-oxide-semiconductor thin film transistors are fabricated using poly-Si films annealed at 1200 °C. The field effect mobility augments to 148 and 96 cm2 V−1 s−1 in the n- and p-channel thin film transistors, respectively.
Ultraviolet absorption and photodissociation of As4
Authors: Killeen K. P.
Published: July 2002

Ultraviolet absorption spectroscopy has been used to measure the photodissociative absorption band of As4 in the spectral range from 190 to 370 nm. The As4 absorption bands are assigned to 1A1→1T1A,B Rydberg transitions with measured cross sections of 7.8±0.5×10−18 cm2 at 256.7 nm and 1.4±0.1×10−17 cm2 at 193.7 nm. Photolysis of As4 is shown to yield a large As2/As4 ratio at modest photon intensities, thus suggesting a viable nonthermal method for generation of arsenic dimers for epitaxy of III-V materials.
Intermixed GaAs/AlGaAs quantum wires and the influence of implantation species on the steepness of the lateral potential
Authors: Prins F. E. , Lehr G. , Fröhlich E. M. , Schweizer H. , Smith G. W.
Published: July 2002

We have studied the influence of the implantation species on the steepness of the lateral potential of GaAs/AlGaAs quantum wires fabricated by the implantation induced intermixing technique. Using Ga as the ion species wires with a very steep lateral potential have been fabricated. The steepness was limited by the lateral straggling of the ions during implantation. For the first time wires have been realized after In and Xe implantation and these results are compared to the steepness achieved by Ga implantation. Although ion straggling is reduced for heavier ions, Xe and In implantations result in more shallow lateral potentials than Ga implantation. This effect is attributed to a more effective intermixing in the low dose region for Xe and In compared to Ga as observed from homogeneously implanted samples. From the point of view of a patterning technique the intermixing dependence on dose can be compared to the resist contrast in lithography.
Magnetic properties of hydrogenated amorphous Fe–Si–B fiber
Authors: Mitra A. , Bhattamishra A. K. , Chattoraj I.
Published: July 2002

Magnetic properties of a hydrogenated amorphous Fe–Si–B fiber have been studied. Hydrogen was charged electrochemically. Saturation magnetization and the switching characteristics of the fiber have been investigated for different charging conditions. Saturation magnetization is found to decrease with the increase of charging time and charging current density. Variation of switching characteristics with the charging conditions is rather complex. Magnetic properties have also been studied during degassing of hydrogen. Hydrogen inside the specimen induces tensile stress due to volume expansion and at the same time modifies Fe–Fe exchange interaction. The magnetic behavior due to hydrogenation and during degassing have been explained by considering the dual role of hydrogen inside the fiber.
Sodium passivation dependence on phosphorus concentration in tetraethylorthosilicate plasma-enhanced chemical vapor deposited phosphosilicate glasses
Authors: Cramer J. Kalpathy , Murarka S. P. , Srikrishnan K. V. , Patrick W.
Published: July 2002

Mobile ions like sodium are known to cause instabilities in metal oxide semiconductor devices. Phosphosilicate glasses (P glasses) have been used as passivating layers to isolate the active devices from such contamination. In this study we have examined the effectiveness of tetraethylorthosilicate plasma-enhanced chemical vapor deposited P glasses, as the barrier to sodium diffusion, as a function of the phosphorus concentration. High-frequency capacitance versus voltage (C-V) measurements, bias-temperature measurements, C-V measurements after etch back, and current versus voltage (I-V) measurements were performed. The results of these C-V and I-V studies on P-glass samples purposely contaminated with sodium and annealed indicate that 2–4 wt % of phosphorus is sufficient to passivate successfully against sodium.
Ion implantation ranges and range straggles in organic polymers and comparison with calculations
Authors: Wilson R. G.
Published: July 2002

More than 40 elements were implanted into PMMA/polymethyl methacrylate/Lucite/AZ111, polypyromellitimide/polyimide/Kapton, and epoxy, at energies up to 0.6 MeV and at fluences from 3×1013 to 1015 cm−2 and were depth profiled using secondary ion mass spectrometry (SIMS). SIMS depth profiling was performed for these combinations using both oxygen and cesium primary ions and positive and negative secondary ions, respectively. Implantation ranges and straggles were determined from the experimental profiles using a Pearson IV computer fitting program, and are compared with the corresponding results of TRIM 91, Lindhard, Scharff, Schio/tt theory, and Implant Sciences Profile Code calculations. The agreement among the three calculations and between the three calculations and the experimental results is discussed. The experimental error is about 25%.
In situ transmission electron microscopy study of dislocation loops induced by P implantation in CdTe single crystals
Authors: Leo G. , Ruault M.-O.
Published: July 2002

We have performed in situ transmission electron microscopy observations during room-temperature 100 keV P ion implantation in CdTe single crystals up to 1015 P/cm2. Beyond a defect-depleted zone whose thickness increases with the total fluence, interstitial loops lying in a {110} plane were observed. At least two Burgers’ vector types (<100≳ and <110≳) were determined. The results are explained in terms of the high interstitial defect mobility.
Phase signal of optical beam deflection from single microparticles: Theory and experiment
Authors: Harada Masaaki , Kitamori Takehiko , Sawada Tsuguo
Published: July 2002

The optical beam deflection (OBD) signal from a single microparticulate sample was theoretically derived for the photothermal response to an intensity-modulated excitation in the transverse experimental configuration. The dependencies of phase signal on the normal and transverse offsets of the probe beam were calculated and then experimentally verified. The OBD phase signal was chosen as a means of inspecting the particle interior, since it contains information about the heat source depth. The results showed that the phase signal was independent of the excitation beam power and that the surface absorbing layer thickness could be estimated from the phase variation using the modulation frequency. The possibility of correcting beam offsets by the phase signal was also considered.
Growth of InGaP by metalorganic molecular beam epitaxy using novel Ga sources
Authors: Abernathy C. R. , Wisk P. W. , Ren F. , Pearton S. J. , Jones A. C. , Rushworth S. A.
Published: July 2002

We have investigated the use of tri-isobutylgallium (TIBG) and tri-isopropylgallium (TIPG) for growth of InGaP on GaAs by metalorganic molecular beam epitaxy. In particular, we have explored the effect of growth temperature on carbon background and lattice constant. The incorporation rate of carbon was found to decrease with increasing temperature while that for Ga was found to increase. Both trends suggest enhanced alkyl-Ga decomposition with increased temperature similar to that observed for growth with triethylgallium (TEG). The variation in composition with growth temperature was, however, reduced for TIBG and TIPG relative to previous reports using TEG. Measured lattice constant varied linearly with TMI flow up to a value of ∼5.675 Å. The band gap was found to vary discontinuously with lattice constant suggesting enhanced ordering in Ga-rich layers. Finally, Sn doping from tetraethyltin was shown to vary linearly with TESn flux provided the combination of low V/III ratios and Ga-rich compositions was avoided.
Composition of porous silicon
Authors: Sabet-Dariani R. , Haneman D. , Hoffman A. , Cohen D. D.
Published: July 2002

Samples of porous Si were prepared from p-type, 10 Ω cm Si under 10 mA cm−2 anodization in aqueous HF (mostly 50%) for 5 min. These showed photoluminescence peaking at 835 nm at 10 K, with full width half maximum of 78 nm, the data showing little change up to 150 K. High-resolution scanning electron microscopy showed column widths of 2–6 nm in the 2-μm-thick films. Hydrogen content was measured by the method of elastic recoil detection, and carbon and oxygen by nuclear reaction analysis. The fluorine content was measured by particle-induced gamma emission as 0.03 at. %. The Si, O, C, and H contents were confirmed by Rutherford backscattering analysis, as approximately Si2.5O1.2C1.3H1.2. The data, particularly the low Si content, are not inconsistent with the presence of complex chemical compounds in the films, although any role they play is not established.
In adatom migration studies by reflection high-energy electron diffraction oscillations on vicinal InAs(001) surfaces
Authors: Toyoshima H. , Shitara T. , Fawcett P. N. , Zhang J. , Neave J. H. , Joyce B. A.
Published: July 2002

The transition from growth by the formation and coalescence of two-dimensional clusters to the growth by step advancement on vicinal InAs(001) surfaces has been examined during molecular-beam epitaxy by the measurements of reflection high-energy electron diffraction oscillations. The growth mode transition is compared with results from vicinal GaAs(001) surfaces and qualitatively analyzed on the basis of the surface migration and attachment kinetics of In adatoms.
Reduction of interface phonon modes using metal-semiconductor heterostructures
Authors: Bhatt A. R. , Kim K. W. , Stroscio M. A. , Iafrate G. J. , Dutta Mitra , Grubin Harold L. , Haque Reza , Zhu X. T.
Published: July 2002

Based on a simplified analysis of perfectly conducting metals, it has been suggested qualitatively that establishing metal-semiconductor interfaces at the heterojunctions of polar semiconductor quantum wells introduces a set of boundary conditions that dramatically reduces or eliminates unwanted carrier energy loss caused by interactions with interface longitudinal-optical (LO) phonon modes. In this article, it is theoretically demonstrated that comparable reductions in LO phonon scattering strengths may be achieved for metal-semiconductor structures with metal having realistic conductivities and Thomas–Fermi screening lengths.
Physical origin of the temperature dependence of chromatic dispersion in fused silica
Authors: Lines M. E.
Published: July 2002

The static and dynamic effects of temperature upon chromatic dispersion in fused silica are analyzed using a Sellmeier representation. By separately calculating the temperature modulation of the Sellmeier parameters induced by thermal expansion on the one hand, and by the dynamic vibrational motion of acoustic and optic phonons on the other, the individual contributions to the total effect have been analyzed. It is shown that all manifestations of chromatic dispersion in the silica optic window possess a temperature modulation which is dominated by a single term—namely the temperature derivative of the Sellmeier valence to conduction band energy gap. In addition, this term itself results overwhelmingly from a single physical process, namely the Debye–Waller-like modulation of one-electron band energies by the thermal activation of acoustic phonons.
Periodic submicrometer dot structures on n-GaAs substrates fabricated by laser-induced surface electromagnetic wave etching
Authors: Kumagai H. , Ezaki M. , Toyoda K. , Obara M.
Published: July 2002

Periodic submicrometer dot structures were fabricated by laser-induced surface electromagnetic wave (SEW) etching of n-GaAs substrates using the holographic exposure system of the frequency-tripled Nd:YAG laser. The shorter and longer diameters were about 310 and 540 nm, respectively. Spatial periods along two perpendicular axes were 370 and 545 nm, respectively. These periods were nearly in agreement with the calculation. The period of SEW grating depended on not only the laser wavelength, but also the number density of the laser-induced quasifree carriers.
Tungsten deposition on GaAs using WF6 and atomic hydrogen
Authors: van Maaren A. J. P. , Sinke W. C.
Published: July 2002

Tungsten was deposited on GaAs employing WF6 as precursor gas. A comparison is made between molecular and atomic hydrogen as reducing agent. Atomic hydrogen is produced in situ by dissociating molecular hydrogen on a hot (2100 °C) filament. Tungsten deposition was not observed only when molecular hydrogen and the substrate were available as reducing agents. Introduction of atomic hydrogen did lead to W deposition on GaAs.
Two-dimensional electrical transport of pentacene thin films doped with iodine
Authors: Minakata Takashi , Ozaki Masaru
Published: July 2002

The logarithmic electrical resistivities of pentacene (PEN) thin films doped with iodine in the direction parallel to the substrate plane fit the T−1/3 dependence well. This indicates that the lateral transport of the film was governed by two-dimensional variable range hopping. In contrast, the logarithmic resistivities of the films perpendicular to the substrate were observed to be almost independent of temperature and to be weakly T−1/2 dependent. This shows that the tunneling mechanism is predominant in perpendicular transport. Two-dimensional conduction of the film was confirmed by these transport properties, which was expected from the intercalated structure of PEN film doped with iodine.
Defect reactions by heat treatment of heavily silicon doped gallium arsenide
Authors: Okada Yasumasa , Fujii Katsushi , Orito Fumio , Muto Shunsuke
Published: July 2002

Silicon is an amphoteric impurity of gallium arsenide that is present in different defect configurations. This work reports on the effects of heat treatment on defect reactions of heavily silicon-doped gallium arsenide crystals. The distribution of segregation, lattice parameter, and electrical properties was studied for several heat treatments. When the crystals were bulk-annealed at between 700 °C and 1000 °C for 20 h, zone-distributed segregation was observed at the area with a silicon concentration of about 1×1019 cm−3 by etching and x-ray topography. Regions observed to have silicon-related segregation exhibited a decrease in lattice parameter when the crystals were annealed below 850 °C for 20 h then quenched. In addition, such regions exhibited little change in lattice parameter when the crystals were annealed above 850 °C. For electrical properties, the largest decrease in carrier concentration and mobility of such regions was observed when the crystals were annealed at 700 °C. This change in the characteristics of such regions seems to be affected not only by heavily doped silicon but also by excess arsenic.
The effectiveness of electron holography, microscopy, and energy-loss spectroscopy in characterizing thin silicon oxide-nitride-oxide structures
Authors: Waytena G. L. , Hren J. , Rez P.
Published: July 2002

High-resolution transmission electron microscopy, electron holography, and high-spatial- resolution (19 Å) computer-controlled parallel electron-energy-loss spectrometry (PEELS) were used to probe the structure of and chemical profile across two thin silicon oxide-nitride-oxide layered structures of nominal widths of 10 Å-50 Å-10 Å and 30 Å-50 Å-30 Å. It was found that the individual layers of the stacked structures could be clearly imaged using electron holography, but not with electron microscopy due to the behavior of the microscope transfer function and the shape of the potential profile of the structure. Holography revealed that the layers of the 10 Å-50 Å-10 Å system were in fact 14 Å-28 Å-18 Å±5 Å, and the oxide layer in contact with the substrate (first oxide layer) was discontinuous. PEELS showed that the second oxide layer contained nitrogen, and the nitride layer had a silicon-to-nitrogen concentration ratio of 1.0±0.1. The 30 Å-50 Å-30 Å system was in fact 30 Å-20 Å-40 Å-15 Å±5 Å. The second oxide layer was SiO1.6±0.2, and nitrogen was found near the film surface which made the structure appear to be four layers. These results show the power of holography in characterizing thin, light-element, amorphous layers and the importance of computer-controlled parallel energy-loss line scans for obtaining analytical information at the highest spatial resolution with minimum dose.
Low-temperature copper etching via reactions with Cl2 and PEt3 under ultrahigh vacuum conditions
Authors: Farkas J. , Chi K.-M. , Hampden-Smith M. J. , Kodas T. T. , Dubois L. H.
Published: July 2002

Reflection–absorption infrared spectroscopy, Auger electron spectroscopy (AES), temperature programmed desorption, and reactive scattering were used to investigate the adsorption and desorption behavior of PEt3 on copper and chlorinated copper surfaces under ultrahigh vacuum conditions. No reaction was observed between PEt3 and clean Cu(100) or between PEt3 and a c(2×2)–Cl overlayer. At temperatures above 320 K, PEt3 reacted rapidly with a heavily chlorinated copper surface (10 000 L exposure of Cl2 at 300 K). Subsequent examination of the substrate by AES showed removal of chlorine and presumably copper. The remaining chlorine corresponded roughly to 0.5 monolayer coverage. This is consistent with reactive scattering, infrared and AES experiments carried out on thin chlorinated layers (8 L Cl2 exposure), where essentially no reaction of PEt3 with the surface was observed. The reaction between PEt3 and a heavily chlorinated Cu(100) surface yields both ClCu(PEt3)2 and Cl2PEt3. These data are consistent with the etching of copper under ultrahigh vacuum conditions at low temperatures by reaction with Cl2 and PEt3 to form CuCl(PEt3)2.
Energy splitting of the EL2 level in Si-implanted GaAs/GaAs by field-effect deep-level transient spectroscopy
Authors: Halder N. C. , Misra V.
Published: July 2002

Field-effect deep-level transient spectroscopy studies have been carried out in molecular-beam-epitaxy-grown GaAs on n+-GaAs implanted with Si. Four electron traps and one weak hole trap have been detected. Thermal-emission rate, capture cross section, and activation energy have been found to be influenced by the applied field; the effect was particularly significant in the case of the EL2 level. The energy versus field plots have shown a general tendency that the applied field modulates the activation energy of the trap states; for example, the Arrhenius plot of a single EL2 level at lower fields (<−3 V/cm) is split up into as many as three at higher fields (≳−4 V/cm). These results have been interpreted in terms of recent theories of electron-phonon interaction on the electron emission from the trap states to the conduction band.
Aging of superconducting Y1Ba2Cu3O7−x structures on silicon
Authors: Copetti C. A. , Schubert J. , Zander W. , Soltner H. , Poppe U. , Buchal Ch.
Published: July 2002

The long-term stability of epitaxial thin film structures of superconducting Y1Ba2Cu3O7−x on silicon wafers (100), using a yttria-stabilized ZrO2(YSZ) buffer, is presented and compared to identical structures on SrTiO3 (100) and yttria-stabilized ZrO2 (100) single crystals. For Y1Ba2Cu3O7−y/YSZ/Si heterostructures, the maximum Y1Ba2Cu3O7−y film thickness is limited to 50 nm; otherwise thermal strain induces microcracks. Thinner films are more stable, but nevertheless show aging over several weeks, which affects critical current density and room-temperature resistivity, but not the critical temperature Tc.
An elementary paradigm for nonequilibrium diffusion
Authors: Lever R. F. , Morehead F. F.
Published: July 2002

Modern semiconductor processes, in which low temperatures, short times, and ion implant or oxidation-induced interstitials may occur, raise the possibility that the mobile species may not be in equilibrium with their immobile parent substitutional dopants. The simplest possible example of nonequilibrium diffusion is analyzed and shown to occur in three stages. In the first, where the diffusion time is short compared with the lifetime of the mobile species, the dopant profile is an error function complement. The second stage, in which the diffusion time is long compared with the lifetime of the mobile species but short compared with that of the parent species, yields an exponential profile. The third stage, for long diffusion times, corresponds to the usual equilibrium assumption, and the measured profile is again a complementary error function.
Observation of activation of Li atoms in ZnSe by photoluminescence
Authors: Zhu Ziqiang , Mori Hiroshi , Yao Takafumi
Published: July 2002

This article reports on the photoluminescence study of activation of a Li dopant in ZnSe films. It has been found that the amphoteric role of the Li dopant is strongly influenced by annealing or substrate temperature. The temperature ranges for efficient activation of Li are estimated to be 430–460 °C in the annealing experiment and 280–350 °C in the thermal diffusion experiment. The correlation of emission intensities between acceptor-bound exciton (I1), donor-bound exciton (I2), and donor-acceptor pair (DAP Q0) is described in detail. As the Li acceptor increases, the emission intensities of both I1 and DAP increase, which leads to the decrease in the emission intensity of I2.
Magnetic forces for type II superconductors in a levitation field
Authors: Torng Terry , Chen Q. Y.
Published: July 2002

A complete loop of hysteretic force has been calculated for hard superconductors in an almost-constant-gradient magnetic suspension system, which consists of a pair of oppositely wound superconducting coils. The dependences of levitation forces on the sample size, critical current density, external field strength, field gradient, and the magnetic history were investigated. Dynamic spring constants as well as magnetic damping coefficients were inferred from minor loop calculations. The minor loops, similar to the Rayleigh loops for ferromagnetic materials, could be described in quadratic terms. The major loops strongly depend on the magnetic passage, a flux-trap effect which is responsible for the subtlety in obtaining reproducible hysteresis loop. The basic physics of levitation and inverse levitation will be quantitatively illustrated.
Numerical calculation of flow orientation effects in the Langmuir–Blodgett deposition process
Authors: Tabe Yuka , Ikegami Keiichi , Sugi Michio
Published: July 2002

The angular distribution function of rodlike particles in Langmuir–Blodgett (LB) films is numerically analyzed. The calculation is based on the integral form of the rotatory diffusion equation and, in contrast with previous analyses, does not assume an instantaneous thermal equilibrium. As each particle keeps memory of the flow history on the water surface, the final distribution function is dependent on the initial conditions of the particle. However, when the initial point is so far from the substrate that the memory of initial point is almost lost, the final distribution function is approximately determined by the dimensionless number C=(ζ′G+τ0)/2kBT, where ζ′ is the rotational friction coefficient, τ0 the Bingham yield value, a the substrate width, and vd the dipping velocity of the substrate. The presence of a meniscus region around the substrate should be taken into account. The streamlines between the water surface and the substrate surface are smoothly connected, while assuming a cylindrical shape for the meniscus. The angular distribution function obtained by this numerical calculation is in good agreement with the experimental results for a mixed LB system of merocyanine dye/fatty acid.
Thermal shock cleavage of silicon (111) thin crystals
Authors: Savage T. S. , Xu P. , Marks L. D.
Published: July 2002

Clean thin samples of silicon (111) have been irradiated by 350–400 ns dye-laser pulses of 590 nm radiation under ultrahigh vacuum (UHV) conditions. Results obtained using a UHV transmission electron microscope on the thermal shock cleavage of these samples are reported. Classic cleavage along {111} planes was observed at relatively low fluences (less than 0.04 J/cm2). The observations on the sample morphology before and after laser irradiation demonstrate that under the conditions that yield to cleavage, there is no long range diffusion of point defects and there is no tendency for the cleavage to occur at pre-existing defects. Although in some cases, cleavages occur at locations that are logically weak, in general, there appears to be no correlation between the cleavage sites and the three-dimensional crystal structure.