bluuebunny/crossref_metadata_2025 huggingface dataset:
The origin of the blue luminescence in ZnSe at room temperature
Authors: Zheng JiaZhen , Allen J. W.
Published: July 2002

It is shown that the blue luminescence band appearing at room temperature in ZnSe is seen in metalorganic chemical vapor deposition (MOCVD) epilayers with carrier concentration 1×1018 cm−3. The photon energy at the emission peak is the same in this material as in material with much lower carrier concentration. Properties of the blue band are surveyed to discriminate between different possible assignments. It is concluded that Shirakawa and Kukimoto [J. Appl. Phys. 51, 2014 (1980)] were correct in assigning it to a transition between a free hole and an electron bound to a donor. However, not all donors contribute. There is a cutoff energy within the spread of donor levels above which there is negligible contribution to the emission. It is suggested that the cutoff corresponds to a localization edge of the same nature as the mobility edge.
Propagation of waves in magnetoelastic media
Authors: Gourakishwar Oinam
Published: July 2002

Wave propagation phenomena in two magnetoelastic, initially stressed, conducting, homogeneous, and isotropic media are discussed. The coefficients of reflection and refraction are obtained in cases of the incident P wave and incident shear wave incident obliquely at a plane interface between two welded, magnetoelastic media. Energy relations in both cases are also derived. Total internal reflection for an incident shear-horizontal (SH) wave is analyzed. The equation of caustic for the SH wave is obtained. The velocities of the SH waves in both media are calculated. Analysis of the results are carried out by drawing graphs between the initial pressure and critical angle and the initial pressure and velocity of the SH wave. The equation of caustic is also analyzed by determining the values of distances of the points on the caustic for different values of the angles of incidence. Taking the initial stress and magnetic field to zero the results obtained are in compliance with those results in elastic homogeneous isotropic media.
A new GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling diode and its tunneling mechanism
Authors: Yang L. , Chen J. F. , Cho A. Y.
Published: July 2002

We propose and demonstrate a new GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling diode with a peak-current density as high as 7.6 kA/cm2 and a peak-to-valley current ratio of 5. In this device, the electrons in the InAs conduction band can resonantly tunnel through the AlSb/GaSb/AlSb double barrier into the GaSb valence band. By narrowing the GaSb well width from 65 to 30 Å, a drastic reduction of the tunneling current was found experimentally. This reduction is interpreted as evidences of the effect of the interband resonant tunneling process and the role of the light hole in the GaSb valence band. In addition, compared with the InAs/AlSb/GaSb/AlSb/InAs tunneling structure, a twice larger peak current density was obtained in the proposed structure which is attributed to a larger density of states of the GaSb light hole valence band compared with that of the InAs conduction band.
Negative capacitance at metal-semiconductor interfaces
Authors: Wu X. , Yang E. S. , Evans H. L.
Published: July 2002

A negative capacitance effect has been observed in metal-semiconductor contacts. This phenomenon is explained by considering the loss of interface charge at occupied states below Fermi level due to impact ionization. A modified Shockley–Read treatment is proposed to interpret the experimental observations. In particular, a two-energy-level simplified model is presented to simulate the capacitance spectrum. The results are in good agreement with the experimental data.
Metal buffer layers and Y-Ba-Cu-O thin films on Pt and stainless steel using pulsed laser deposition
Authors: Russo R. E. , Reade R. P. , McMillan J. M. , Olsen B. L.
Published: July 2002

A versatile pulsed laser deposition chamber was employed for fabricating metal buffer layers and superconducting YBaCuO thin films on metallic substrates. Ag buffer layers were found to improve the resistive transition behavior for superconducting films on Pt and stainless steel. As-deposited YBaCuO films with Tc (R=0) at 84 K were produced on stainless steel using in situ laser-deposited Ag buffer layers. The critical current density was measured to be approximately 103 A/cm2 at 67 K.
Growth and characterization of undoped and in situ doped Si1−xGex on patterned oxide Si substrates by very low pressure chemical vapor deposition at 700 and 625 °C
Authors: Tsai Curtis , Jang Syun-Ming , Tsai Julie , Reif Rafael
Published: July 2002

Results of strained layer Si1−xGex heteroepitaxy on patterned oxide silicon substrates using a very low pressure chemical vapor deposition reactor are presented. Patterned oxide wafers were in situ cleaned at 700 °C using an Ar/H2 plasma. Undoped Si1−xGex strained layers at 625 and 700 °C along with in situ doped p and n-type Si1−xGex strained layers at 625 °C were deposited using SiH4, GeH4, B2H6, and AsH3 with H2 as a carrier gas. Alternating layers of Si1−xGex and Si were formed by switching the inlet gases. Scanning electron microscope showed a smooth surface morphology for Si1−xGex strained layers deposited with GeH4/SiH4 gas ratios <7.5%. Cross-sectional transmission electron microscope revealed a sharp transition between the Si1−xGex and Si layers with dislocation densities below the detection limit of 105 cm−2. Defect etching confirmed the low defect density at the surface. For epitaxial windows smaller than 50×50 μm, no defects were observed. Germanium solid mole fraction, boron and arsenic chemical dopant concentrations, and interfacial carbon and oxygen contamination were measured by secondary ion mass spectrometry. Undoped, B2H6, and AsH3 in situ doped Si1−xGex strain layers with germanium content up to 23% were demonstrated. The Ge incorporation was controlled by the GeH4/SiH4 gas ratio and the Si1−xGex growth rate decreased with increasing Ge solid mole fraction. The addition of B2H6 did not affect the Si1−xGex growth rate and modulation of the boron chemical incorporation was possible by controlling the B2H6 gas concentration. On the other hand, AsH3 severely degraded the Si1−xGex growth rate and varying the AsH3 gas concentration did not change the arsenic chemical incorporation. Lastly, selective AsH3 doped Si1−xGex heteroepi
Surface states studies in semiconductors by photothermal deflection spectroscopy
Authors: Zammit U. , Gasparrini F. , Marinelli M. , Pizzoferrato R. , Scudieri F. , Martellucci S.
Published: July 2002

A method based on the analysis of both the amplitude and phase of the photothermal deflection spectroscopy signal which enables one to locate surface states on the front or rear surface of semiconductor wafers and to measure their absorption. The procedure also allows the determination of the sample thermal conductivity.
Electric-field dependence of observables in finite parabolic quantum wells
Authors: Herling G. H. , Rustgi M. L.
Published: July 2002

The electric-field dependence of eigenvalues, eigenfunctions, electron-hole overlap integrals, and dipole moments in several finite parabolic quantum wells are calculated with the shooting method and compared with corresponding results for a square well. The results are more strongly field dependent for parabolic wells with a fixed-volume integral than those for the square well. Reasons for this behavior are discussed.
The effects of He addition on the performance of the fission-fragment excited Ar/Xe atomic xenon laser
Authors: Alford William J. , Hays Gerald N. , Ohwa Mieko , Kushner Mark J.
Published: July 2002

The intrinsic power efficiency of the atomic xenon laser depends upon the electron density because of the mixing of the laser levels by electron collisions while the electron density in high-pressure particle-beam excited plasmas increases with increasing gas temperature. Therefore, in order to reduce the amount of electron collisional mixing when operating at high-energy loadings (≳100’s J/1-atm) mixtures having a high-heat capacity are required. In particle-beam excited Ar/Xe mixtures, which typically yield the highest intrinsic laser efficiencies, increasing the gas pressure to increase the heat capacity is not always practical due to the high-stopping power of the gas mixture. For this reason we have experimentally and theoretically investigated adding He to Ar/Xe mixtures in studies of a fission-fragment excited atomic xenon laser. Adding He increases the heat capacity without appreciably perturbing the favorable kinetics resulting in efficient operation of the laser in Ar/Xe mixtures. We find that when adding He to Ar/Xe mixtures the dominant laser transition switches from 1.73 to 2.03 μm without significantly decreasing the efficiency. The laser pulse length also increases, an effect attributed to a lowering of both the electron temperature and gas temperatures.
In situ spectroellipsometry study of the nucleation and growth of microcrystalline silicon
Authors: Fang M. , Drévillon B.
Published: July 2002

A detailed in situ spectroellipsometry analysis of the nucleation and growth of μc-Si films deposited on c-Si substrate is presented. The deposition is analyzed up to a final thickness of 0.43 μm. In order to perform a precise analysis, various real-time trajectories recorded at different photon energies are studied. New insights into the growth mechanisms are obtained. The growth of μc-Si is described as an evolution of a dense material and microstructures. The dense phase consists of microcrystallites embedded in an amorphous tissue. The nucleation-coalescence mechanism of μc-Si is compatible with a columnar microstructural development during the early stage of the growth. Then a multilayer model is used to describe the formation of a surface roughness. The free surface of μc-Si is rough at a 100–200-Å scale. This surface roughness strongly increases as a function of the deposited thickness. The various stages of the growth of μc-Si and a-Si:H are systematically compared. The growth of a-Si:H displays a more uniform behavior.
Variation of the mobility and the two-dimensional electron gas concentration with indium composition in δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures
Authors: Hsu W. C. , Chen C. M. , Lin W.
Published: July 2002

The electron mobility and the two-dimensional electron gas (2DEG) concentration in different indium compositions (0.1<x<0.6) δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures grown by low-pressure metalorganic chemical vapor deposition are studied. The electron mobilities of a δ-doped GaAs layer are comparable to those of previous reports. Furthermore, the maximum mobility (5500 and 33 000 cm2/V s at 300 and 77 K, respectively) of the proposed pseudomorphic structure appears at x=0.37. Taking into account of strain and quantum effects, the variation trends of calculated 2DEG concentrations are in good agreement with the experimental results.
Permanent magnets composed of high temperature superconductors
Authors: Weinstein Roy , Chen In-Gann , Liu Jay , Lau Kwong
Published: July 2002

A study of persistent, trapped magnetic field has been pursued with high-temperature superconducting (HTS) materials. The main effort is to study the feasibility of utilization of HTS to fabricate magnets for various devices. The trapped field, when not in saturation, is proportional to the applied field. Thus, it should be possible to replicate complicated field configurations with melt-textured YBa2Cu3O7 (MT-Y123) material, bypassing the need for HTS wires. Presently, materials have been developed from which magnets of 1.5 T, at 77 K, can be fabricated. Much higher field is available at lower operating temperature. Stability of a few percent per year is readily attainable. Results of studies on prototype motors and minimagnets are reported.
Unified theory of the backscattering of electromagnetic missiles by a perfectly conducting target
Authors: Wen Geyi , Ruan Chengli , Lin Weigan
Published: July 2002

It has been shown recently that when an electromagnetic (EM) missile with an energy decreasing as r−ε is incident upon a perfectly conducting plate the reflected energy will decrease as r−ε with the same exponent as the incident EM missile. It has also been shown that when the same EM missile is incident upon a perfectly conducting sphere the rate of the reflected energy decay will be proportional to r−(2+ε). In this paper we present a generalized study of the backscattering of EM missile by a perfectly conducting target of arbitrary shape. Utilizing the tangent-plane approximation, we find that the rate of energy decay of the backscattered field of an EM missile whose energy decreases as r−ε is proportional to r−εR1R2/(R1+2r)(R2+2r), where R1 and R2 are the two principal radii of curvature of the surface at the specular point.
Electron cyclotron resonance plasma etching of photoresist at cryogenic temperatures
Authors: Varhue Walter , Burroughs Jeffrey , Mlynko Walter
Published: July 2002

An electron cyclotron resonance oxygen plasma discharge was used to anisotropically etch photoresist at a low substrate temperature (−100 °C). The results of using a lower temperature are seen in a reduction in lateral etch rate, with concomitant improvement in anisotropy. Langmuir probe and flux analysis at the substrate with a quadropole mass spectrometer was used to characterize the plasma stream as a function of the operating conditions. The plasma stream flux was composed of approximately 10 times as many reactive oxygen neutrals as O2+ ions. Etch rate was found to be strongly affected by the ion power density impinging on the substrate. Four mechanisms were identified that may contribute to lateral etching. Lateral etching was observed to decrease by the combined application of rf substrate bias and low substrate temperature.
Effects of Sb on phase transformations of amorphous TiSi2 thin films
Authors: Li X.-H. , Carlsson J. R. A. , Gong S. F. , Hentzell H. T. G.
Published: July 2002

Co-deposited amorphous TiSi2 thin films with various Sb concentrations were prepared in order to study the effects of Sb on TiSi2 phase transformations. The crystallization behavior of the films was investigated by in situ annealing in a transmission electron microscope. The phase transformation from C49 TiSi2 to C54 TiSi2 in the films was examined with x-ray diffraction. It was observed that incorporation of Sb resulted in a higher crystallization temperature of the amorphous TiSi2 film and a lower crystal growth rate. The activation energies for the crystal growth during the crystallization were determined to be 1.37, 1.62, 1.63, and 1.87 eV (±0.07 eV) for the films with 0, 0.3, 1.3, and 2.5 at. % Sb, respectively. For the C49→C54 transformation, it was, however, observed that the activation energy decreased when the Sb content increased. These indicate that the Sb incorporation in TiSi2 retards the crystallization of the amorphous TiSi2 film, but enhances the transformation from C49 TiSi2 to C54 TiSi2.
GaAs surface reconstruction obtained using a dry process
Authors: Choquette Kent D. , Hong M. , Luftman H. S. , Chu S. N. G. , Mannaerts J. P. , Wetzel R. C. , Freund R. S.
Published: July 2002

We report attaining Ga-terminated (4×2) surface reconstruction on virgin GaAs substrates using a completely dry process at temperatures below the oxide sublimation temperature and without group V overpressure. The native oxides are removed with an electron cyclotron resonance hydrogen plasma treatment, followed by annealing at 500 °C in ultrahigh vacuum, which yields a reconstructed surface suitable for epitaxial overgrowth. Characterization by secondary ion mass spectroscopy and transmission electron microscopy reveals the complete removal of O, reduced C, and high structural order at the epilayer/substrate interface when this preparation method is used before molecular beam epitaxy. Annealing the substrate at a lower temperature yields a nonreconstructed surface possessing significant impurity concentrations, and leads to dislocation defects at the epilayer/substrate interface.
Intrinsic carrier concentration and minority-carrier mobility of silicon from 77 to 300 K
Authors: Sproul A. B. , Green M. A.
Published: July 2002

A considerable improvement in the accuracy of the measurement of the intrinsic carrier concentration in silicon near room temperature has recently been reported. This was achieved by the accurate analysis of minority-carrier current flow in specially fabricated p-n junction devices. In this paper this technique has been extended to measurements down to 77 K. A further improvement of the technique has been the simultaneous measurement of the minority-carrier electron mobility utilizing open-circuit voltage decay measurements.
Crystallographic orientation of textured CoCrTa/Cr sputtered thin film media for longitudinal recording
Authors: Nolan T. P. , Sinclair R. , Ranjan R. , Yamashita T.
Published: July 2002

We have studied the influence of deposition conditions on the structure and properties of Co84Cr14Ta2 alloy magnetic thin films and Cr underlayers sputtered onto circumferentially textured and smooth polished NiP/Al substrates. Suitable processing conditions provide in-plane magnetic anisotropy in the textured media, with enhanced coercivity (Hc) and coercivity squareness (S*) in the circumferential direction and reduced Hc and S* in the radial direction. The crystallography in these films was studied by transmission electron microscopy (TEM) to address the origin of the observed magnetic anisotropy. The CoCrTa alloy grains are found to grow semicoherently on the chromium underlayer, resulting in vertical <200≳ Cr and <112̄0≳ CoCrTa axes. This requires an in-plane orientation of the CoCrTa c axis, which is observed to be nearly random by high-resolution TEM. Microdiffraction shows apparent preferred c-axis alignment locally at texture lines, but this observation is primarily attributable to asymmetric tilting of the vertical growth direction caused by the substrate topography. The <112̄0≳ growth axis appears to be perpendicular to the local grooved surface, not the bulk surface, requiring a local c-axis out-of-plane tilt near the grooves. The anisotropic surface topography induces a corresponding anisotropy in the out-of-plane component of the magnetically easy c axis in the CoCrTa alloy, which we suggest has implications on the bulk magnetic anisotropy in such films.
Analysis of a diode with a ferroelectric cathode
Authors: Schachter L. , Ivers J. D. , Nation J. A. , Kerslick G. S.
Published: July 2002

It has been shown experimentally that electron current densities of more than 30 A/cm2 can be achieved from a cathode made of ferroelectric ceramic, when applying a field of order 0.1 MV/m. This current exceeds the Child–Langmuir current by two orders of magnitude. The current in the diode varies linearly with the applied voltage, provided that the latter is positive. In this theoretical study we show that the ferroelectric material plays a crucial role in the emission process. When a voltage is applied to the ferroelectric, the internal polarization field varies and the amount of screening charge required decreases. As a result, the electrons distribution near the cathode changes, forming a cloud which fills part of the diode gap. If now a positive voltage is applied to the anode, electrons are readily transferred through the diode gap. The qualitative and quantitative results of the theory are in good accordance with the experiment.
Ferroelectric bismuth titanate films by hot wall metalorganic chemical vapor deposition
Authors: Si Jie , Desu Seshu B.
Published: July 2002

Ferroelectric bismuth titanate thin films were successfully deposited on Si, sapphire disks, and Pt/Ti/SiO2/Si substrates by hot wall metalorganic chemical vapor deposition. Triphenyl bismuth [Bi(C6H5)3] and titanium ethoxide [Ti(C2H5O)4] were used as the precursors. The deposition rates were in the range of 3.9–12.5 nm/min. The Bi/Ti ratio was easily controlled by precursor temperature, carrier gas flow rate, and deposition temperature. As-deposited films were pure Bi4Ti3O12 phase. The films were specular and showed uniform and fine grain size. Optical constants as a function of wavelength were calculated from the film transmission characteristics in the ultraviolet-visible-near infrared (UV-VIS-NIR) region. The 550 °C annealed film showed a spontaneous polarization of 26.5 μC/cm2 and a coercive field of 244.3 kV/cm.
The effects of silicon and beryllium on the interdiffusion of GaAs/ AlxGa1−xAs and InxGa1−xAs/GaAs quantum well structures
Authors: Gillin W. P. , Bradley I. V. , Howard L. K. , Gwilliam R. , Homewood K. P.
Published: July 2002

The effects of silicon and beryllium at doping levels of up to 1019 cm−3 on the interdiffusion of GaAs/AlxGa1−xAs and InxGa1−xAs/GaAs quantum wells after annealing have been studied using photoluminescence. It was found that for beryllium concentrations up to 2.5 ×1019 cm−3 and for silicon doping concentrations up to 1018 cm−3, no change in the interdiffusion coefficients could be measured. For a silicon doping concentration of 6×1018 cm−3 a dramatic degradation of the material quality was observed following annealing at 750 °C for 15 s. This resulted in the luminescence from the well disappearing and the appearance of deep level luminescence related to donor-gallium vacancy complexes and arsenic antisite defects. From these results we suggest that the position of the Fermi level plays no role in the intermixing of III-V heterostructures and that most of the enhanced intermixing observed in silicon-doped GaAs/AlxGa1−xAs structures is related to silicon relocation at very high doping levels.
Crystallographic anisotropy in thin film magnetic recording media analyzed with x-ray diffraction
Authors: Kataoka H. , Bain J. A. , Brennan S. , Clemens B. M.
Published: July 2002

The crystallographic anisotropy of CoCr alloy films deposited on a Cr underlayer was investigated with grazing incidence x-ray scattering (GIXS). The effect of circumferential mechanical texturing of the NiP substrate (producing microgrooves through polishing) was explored. The Co was found to grow heteroepitaxially on the Cr underlayer with the Co(112̄0) growth planes parallel to the Cr(001) growth planes. We observe no significant differences in Co lattice parameter in the circumferential and radial directions, although we do see variations in crystallographic texture between these two directions. From GIXS peak intensities, we observe that there is a greater population of crystallites with their c axis pointed along the grooves. This analysis was done after allowing for the effect of the varying local surface normal due to the substrate grooves. The ratio of the coercivities in the two directions scales with the ratios of the c-axis population densities. Two simple quantitative models of the magnetic properties of the aggregate have been constructed: strongly coupled grains and uncoupled grains. The predictions of these models are compared to the observed properties.
Antipolarity domain nucleation and growth during heat treatment of proton-exchanged LiTaO3
Authors: Nakamura Kiyoshi , Hosoya Masahiko , Tourlog Ailie
Published: July 2002

Ferroelectric local domain inversion occurs in LiTaO3 crystals by proton exchange followed by heat treatment at temperatures just below the Curie point, thereby yielding an inversion layer at the −c surface. This article reports the domain inversion phenomenon in LiTaO3 plates and the experiments performed to clarify the mechanism. Measurements of dielectric constant and electrical conductivity near the Curie temperature suggest that the pyroelectric fields induced during the cooling down period are not likely to be the main cause of the domain inversion. This experimental result is reinforced by measurements of the piezoelectric response during heat treatment, which shows that the antipolarity domain nucleates at the initial stage of heat treatment and grows gradually.
Inverse problem for the nonexponential deep level transient spectroscopy analysis in semiconductor materials with strong disorder: Theoretical and computational aspects
Authors: Batovski D. A. , Hardalov Ch. M.
Published: July 2002

A new method for nonexponential deep level transient spectroscopy (DLTS) theoretical analysis is proposed. This method is based on the numerical solving of the inverse problem for the theoretical model via regularization algorithms. It is shown that it is possible to obtain the shape of the deep level energy spectrum from the noisy DLTS spectra in systems with strong disorder.
Microstructural origin of in-plane magnetic anisotropy in magnetron in-line sputtered CoPtCr thin-film disks
Authors: Kim Myong R. , Guruswamy Sivaraman , Johnson Kenneth E.
Published: July 2002

The microstructural origin of magnetic anisotropy in a magnetron in-line sputter-deposited CoPtCr/Cr magnetic thin-film disk was examined by mapping magnetic properties and microstructure. The film coercivity (Hc), remanence-thickness product (Mrδ), and coercivity squareness (S*) were determined as a function of radial (r) and angular (θ) co-ordinates using a transfer curve magnetometer. The observed variations in Hc, Mrδ, and S* across the disk were 85 Oe, 0.15 emu/cm2, and 0.03, respectively. The angular variation in magnetic properties showed a sinusoidal pattern with the maxima corresponding to the regions where the tracks were parallel (θ=270°) to the pallet movement direction. High-resolution scanning transmission electron microscopy showed subtle differences in the Co-alloy grain morphology and crystallographic orientation between θ=270° and θ=360° locations. The grains were equiaxed in general except for a small fraction of grains elongated in the direction of pallet movement. Lattice images clearly showed that about 45% of the Co-alloy grains had in-plane c axes and a preferred alignment of the c axes along the texture groove. A greater preference for the c axes to lie along the texture line was observed for the θ=270° location. A coherency stress-based model is proposed to explain the preferred c-axis alignment. While the crystalline anisotropy appears to be the main factor responsible for the magnetic anisotropy, both crystalline and shape anisotropies contribute to the magnetic anisotropy variations.
Observation of charge behavior in multiply low-density polyethylene
Authors: Li Ying , Takada Tatsuo , Miyata Hiroyuki , Niwa Toshio
Published: July 2002

Effects of interfaces such as metal/polymer interfaces and polymer/polymer interfaces on the space-charge distribution in multiply low-density polyethylene have been investigated using a pulsed electroacoustic method. It has been found that the heterocharge was dominant in an artificial interface existing in a polyethylene sample. The time dependence of the heterocharge distribution in the interface on applied voltages and polarity was studied. From these charge distributions, the modified electrical field was calculated based on Poisson’s equation. The calculated result indicated that the actual field was stronger than the applied uniform field at the artificial interface. A new data display method for a three- or two-dimensional plot is employed to display all measurement data on one plot in which the space charge becomes visible so that the results can be easily and conveniently understood.
Loss characteristics of potassium and silver double-ion-exchanged glass waveguides
Authors: Wang W. J. , Honkanen S. , Najafi S. I. , Tervonen A.
Published: July 2002

Loss characteristics of potassium and silver double-ion-exchanged glass waveguides are studied. Low propagation losses (less than 0.25 dB/cm) at 1.296 μm wavelength are measured, although aluminum as a mask and inexpensive multipurpose glass as a substrate are used in the fabrication process. The losses are compared to the losses of waveguides made by one-step aluminum masked silver ion exchange and by silver ion exchange with ionic masking (dielectric mask). The reasons for the loss reduction in double-ion-exchanged waveguides compared to one-step silver ion-exchanged waveguides are discussed.
The Talbot effect (a self-imaging phenomenon) in holography
Authors: Maripov A. , Ismanov Y.
Published: July 2002

The Talbot effect in holography has been studied. The study has shown that in monochromatic illumination of a bleached off-axis hologram of a periodic grating, self-images of the grating are reconstructed in the real image region. These self-images of the reconstructed grating appear not only in the rays of the ±1st orders but also in the zeroth diffraction order.
A novel scanning electron microscope method for the investigation of charge trapping in insulators
Authors: Gong H. , Ong C. K.
Published: July 2002

A new technique using a copper detector in a scanning electron microscope is introduced for the investigation of charging in insulators, and pure single-crystalline α-quartz samples are studied. The curve of charging rate varying with time is obtained, and the total charge trapped in the sample is accurately determined. Furthermore, the effects of electron-beam energy and current on charging are also examined. Our results suggest that electron-radiation-induced defects in the sample play major roles in the charge trapping. Details of the experimental setup are given.
Positive ion current to a spherical electrode in a negative ion plasma
Authors: Amin Ali , Kim Hyun-Soo , Yi Seungjun , Cooney Jamie L. , Lonngren Karl E.
Published: July 2002

Critical parameters for the development of the plasma-source ion implantation process are the ion implantation current and the sheath expansion characteristics. Recently, Xia and Chan [J. Appl. Phys. 73, 3651 (1993)] have investigated these parameters for small spherical electrodes inserted in a two component positive ion-electron plasma. This investigation is extended to a plasma that consists of three components: positive ions, negative ions, and electrons.
Optical and electronic properties modifications in Pd-Ni multilayers
Authors: Logothetidis S. , Flevaris N. K.
Published: July 2002

The optical and electronic properties of compositionally modulated Pdm-Nin multilayers (CMMs), for modulation period up to 20 monolayers, have been studied by conventional and synchrotron radiation ellipsometry. A broad structure around 4.6 eV was found to depend strongly on the composition modulation period (m+n) whereas the plasma energy depended on both Pd-layer thickness m and modulation period. In higher energies (about 7 eV) additional features were observed to occur in the dielectric function spectra of Pd-Ni CMMs depending on the layer thicknesses. These effects are discussed in terms of the coherency strains and influence of the layer thickness on the electronic structure.
Layered structure of luminescent porous silicon
Authors: Ambrazevičius G. , Zaicevas G. , Jasutis V. , Leščinskas D. , Lideikis T. , Šimkienė I. , Gulbinaitė D.
Published: July 2002

The structural and optical properties of anodized p-Si were investigated using a combination of transmission and scanning electron microscopy, photoluminescence, Raman scattering, and infrared transmission spectroscopy. The results obtained show clear evidence of the existence of three layers, exhibiting different luminescent and structural properties. The upper porous film displaying bright red-yellow luminescence, consists of small unoriented Si microcrystals and contains a substantial amount of oxygen and hydrogen. A range of Si-O-H compounds is suggested to be responsible for the light emission from the surface porous film. The lower porous silicon layer has ordered microcrystalline structure and produces weak, hardly reproducible and unstable green luminescence. Its origin is to be revealed. It is suggested that the presence of ethanol in the electrolyte is the main cause of the formation of the layered structure of porous silicon.
Physical and electrical investigation of ohmic contacts to AlGaAs/GaAs heterostructures
Authors: Taylor R. P. , Coleridge P. T. , Davies M. , Feng Y. , McCaffrey J. P. , Marshall P. A.
Published: July 2002

The mechanism by which Ni-Au-Ge metallizations establish electrical contact to the two-dimensional electron gas (2DEG) in modulation-doped AlGaAs/GaAs heterostructures is investigated. Transmission electron microscopy was used to examine samples after electrical characterization by magnetoresistance measurements at cryogenic temperatures. We present a picture in which a 2DEG of reduced electron density exists under the deposited metallization. The success of the contacting procedure is described in terms of the magnitude of this density and the size, areal density, and penetration depth of a series of metallic spikes which establish the electrical link to the 2DEG. We suggest that the electrical behavior is not dominated by the current injection process at the spike/2DEG interface but is instead dictated by scattering from the array of antidots formed by the spikes and by a dependence of the 2DEG density on the size of the metallic pad. The implications of this picture for future nanostructure devices, featuring patterned ohmic metallization smaller than a micron, are discussed and preliminary results are reported.
Size effects on switching field of isolated and interactive arrays of nanoscale single-domain Ni bars fabricated using electron-beam nanolithography
Authors: Wei Mark S. , Chou Stephen Y.
Published: July 2002

Isolated nanoscale Ni bars with a length of 1 μm, a width from 15 to 300 nm, and interactive bar arrays with a spacing from 200 to 600 nm were fabricated using electron-beam lithography and were studied using magnetic force microscopy. The study showed that the virgin magnetic state of bars with a width smaller than 150 nm was single domain and otherwise multidomain. It also showed that the switching field of isolated bars initially increases with decreasing bar width, then reaches a maximum switching field of 740 Oe at a width of 55 nm, and afterwards decreases with further bar width reduction. Furthermore, it was found that the switching field of the interactive bars decreases almost linearly with reduction of the spacing between the bars.
Some specific features of fine Fe and Fe-Ni particles
Authors: Baldokhin Yu. V. , Kolotyrkin P. Ya. , Petrov Yu. I. , Shafranovsky E. A.
Published: July 2002

By comparing results of Mössbauer spectroscopy and x-ray diffraction investigations of ultrafine Fe and Fe-Ni particles, a formerly stated supposition on the existence of two spin states of the fcc phase in pure iron and Fe-Ni alloys has been verified. Some structural peculiarities of particles under study have been observed also. For the pure bcc-Fe particles with an average diameter of 30 and 50 nm the existence of two hyperfine fields (H1=330 kOe, H2=360 kOe) at room temperature has been found. It is supposed that H2 in the bcc phase could be considered as a remnant of a high spin state of the fcc-Fe phase at high temperature. Particles of Fe-Ni(30.3 wt %), Fe-Ni(35 wt %), and Fe-Ni(52 wt %) alloys with an average diameter ranging from 5 to 15 nm were studied also. Particles of Fe-Ni (30.3 wt %) and Fe-Ni(35 wt %) alloys with diameter of 5–8 nm had the bcc structure. A mixture of the bcc and fcc phases appeared with an increase of the particle size. At the same time only the fcc structure remained for the largest particles. The observed size structural dependences and the existence of the stable bcc phase in small particles can be explained by the martensite fcc-bcc transition.
Magnetic viscosity, fluctuation fields, and activation energies (invited)
Authors: Street R. , Brown S. D.
Published: July 2002

Time dependence of magnetization in ferromagnetic materials was first described towards the end of the 19th century. Subsequently, two types of mechanisms responsible for time dependent behavior were identified and became known as ‘‘diffusion’’ and ‘‘fluctuation’’ after-effect or viscosity. The former depends on thermally induced motion of impurity atoms. The latter is a consequence of thermal activation of irreversible domain processes such as domain-wall motion and the nucleation of domains of reverse magnetization. Fluctuation viscosity affects, to a greater or smaller extent, all magnetic materials subject to hysteresis. In the late 1940s descriptions of magnetic viscosity in terms of fluctuation fields (Néel) and activation energy distributions (Street and Woolley) were developed. The two approaches will be described. An analysis of the time dependent phenomena exhibited by magneto-optical films will be presented as a simple example of the application of activation energy modeling.
Structure of Ba(Y+31/2Ta+51/2)O3 and its dielectric properties in the range 102–1014 Hz, 20–600 K
Authors: Zurmühlen R. , Colla E. , Dube D. C. , Petzelt J. , Reaney I. , Bell A. , Setter N.
Published: July 2002

The goal of this work was to understand the correlation between microscopic material parameters and the dielectric function of candidate materials for applications in the microwave frequency range. The structure and dielectric properties of Ba2+(Y3+1/2Ta5+1/2)O3 (BYT), a typical representative of the Ba(B3+1/2B5+1/2)O3 complex perovskite family, has been investigated from 102 to 1014 Hz and from 20 to 600 K. At Tc=253±1 K, BYT undergoes an equitranslational improper ferroelastic, second-order phase transition, characterized by the tilting of the oxygen octahedra. The space group symmetry changes from Fm3̄m, in the high temperature phase, to I4/m below Tc. The existence of an intermediate temperature region (Tc−40<T<Tc) has been observed, where the compound exhibits structural and dielectric properties different from those in the well-defined high (T≳Tc) and low (T<Tc−40 K) temperature phases. Infrared reflectivity (1012–1014 Hz) and submillimeter transmission (1011–3×1012 Hz) measurements yield dielectric losses which are believed to be mainly of intrinsic origin (one- and two-phonon absorption). Comparing a theory of two-phonon difference absorption processes, due to thermally activated polar branches, with the loss measured at 400–1400 GHz, the intrinsic loss can be extrapolated to lower frequencies. At 10 GHz the extrapolated value is about 1/4 of the loss actually measured in a BYT resonator. Nonpolar phonons, including the soft branch, which have not been considered for the extrapolation procedure, are partially responsible. The temperature dependencies indicate the soft branch to be of considerable importance for intrinsic losses. Oxygen vacancies can be excluded as an extrinsic loss source, as sintering and annealing in N2, air, and O2 had no measurable influence on the loss at 10 GHz.
Micromagnetic modeling of magnetic anisotropy in textured thin-film media
Authors: Zhao Yang , Bertram H. Neal
Published: July 2002

Existing micromagnetic models, based on single domain grains that individually follow coherent rotation during reversal, have been utilized to study the effect of various texture-induced microstructures on the hysteretic behavior of Co-alloy thin films with circumferentially textured substrates. The roles of preferential orientation of Co c axes, grain elongation, and segregation, as well as possible short-range intergranular coupling, have been examined in an effort to understand the origins of widely observed magnetic anisotropy in these media. Preferential c-axis distribution along the track direction yields reasonable remanences and coercivities for both circumferential and radial loops, but the observed loop closure remains unaccounted for by c-axis distribution alone. Closely packed arrays of elongated grains maintain relative isotropy in terms of magnetostatic interactions, while voids along texture lines contribute to the magnetostatic anisotropy of the film. The limitations of the model are also discussed.
Consistent quantitative model for the spatial extent of point defect interactions in silicon
Authors: Agarwal Anuradha M. , Dunham Scott T.
Published: July 2002

The silicon point defect properties which control the spatial extent of their interactions (e.g., interstitial diffusivity) have been calculated by many researchers. However, large discrepancies exist in the reported values of these parameters, and it is essential to have a consistent set of parameters for use in process simulation. To meet this need, we present here a model which includes important interactions which have been ignored in previous analyses, specifically bulk recombination of interstitials with vacancies and segregation of interstitials to surface oxide films. We assess the effectiveness of the model in predicting the spatial extent of point defect interactions by comparing simulation results with a wide range of experimental data. Although this same experimental data previously gave large differences in calculated parameter values, we obtain a single set of model parameters which can account for the full range of data in a consistent manner.
Plasma remediation of perchloroethylene in humid gas streams
Authors: Gentile Ann C. , Kushner Mark J.
Published: July 2002

Perchloroethylene (PCE) is one of a class of industrial solvents for which alternate disposal strategies are being investigated. Among these strategies is plasma remediation. In this paper we report on a computational study of the plasma remediation of PCE using repetitively pulsed dielectric barrier discharges. We discuss the dominant reaction pathways in the remediation of PCE and show that remediation is significantly improved in humid gas mixtures. Although plasma remediation does not totally oxidize PCE to the desired end-products (CO2 and HCl), the dominant end-products are more easily treated than PCE and can be disposed of using conventional methods.
Breakdown, steady-state, and decay regimes in pulsed oxygen helicon diffusion plasmas
Authors: Charles C. , Boswell R. W.
Published: July 2002

Continuous and pulsed oxygen plasmas have been created in a helicon diffusion reactor used for the deposition of silicon dioxide films. An energy selective mass spectrometer and a Langmuir probe attached to the wall of the silica-covered aluminum diffusion chamber below the source have been used to characterize the plasma [ion energy distribution function (IEDF), plasma potential, floating potential, plasma density]. The ion flux can be significantly modified by pulsing the discharge. In the continuous case, the IEDF of the O+2 ions escaping from the plasma to the sidewalls of the chamber consists of a single peak at an energy corresponding to the plasma potential in the chamber (≊32 V). In the pulsed case, the IEDF exhibits two additional peaks at high (≊60 eV) and low (≊15 eV) energy as a result of different states of the plasma during the pulse period: three regimes corresponding to the plasma breakdown, steady state, and decay have been observed and characterized. The time decay of the fundamental mode of diffusion in the post-discharge was measured and calculated (about 1 ms). The breakdown regime is highly dependent on the state of the plasma at the end of the post-discharge.
Photoelastic waveguides and the controlled introduction of strain in III-V semiconductors by means of thin film technology
Authors: Liu Q. Z. , Deng F. , Yu L. S. , Guan Z. F. , Pappert S. A. , Yu P. K. L. , Lau S. S. , Redwing J. M. , Kuech T. F.
Published: July 2002

We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have fabricated low-loss (∼1 dB/cm at 1.52 μm wavelength) photoelastic waveguides in GaAs/AlGaAs heterostructures, and explored the interrelationship between the photoelastic waveguide characteristics and the stress.
Can normal-incidence absorption be realized with n-doped (001)-grown direct-gap quantum wells?
Authors: Yan Voon L. C. Lew , Willatzen M. , Ram-Mohan L. R.
Published: July 2002

Recent experiments suggest that normal incidence (TE) absorption due to inter-conduction subband transitions in quantum wells is just as strong as in-plane absorption (TM). However, a theoretical estimate based on a simplified k⋅p model predicts otherwise. We present here explicit numerical calculations based on a more elaborate microscopic model to confirm that TE absorption of III-V quantum wells is usually negligible. Hence, a new interpretation of the above-mentioned experiments is necessary. On the other hand, HgTe quantum wells are predicted to have a TE absorption coefficient comparable to the TM absorption of GaAs quantum wells.
Enhanced magnetoresistance in as-deposited oxygen-deficient La0.6Pb0.4MnO3−y thin films
Authors: Satyalakshmi K. M. , Manoharan S. Sundar , Hegde M. S. , Prasad V. , Subramanyam S. V.
Published: July 2002

The La0.6Pb0.4MnO3(LPMO) thin films were in situ deposited at different oxygen partial pressure and at a substrate temperature of 630 °C by pulsed laser deposition. The films grown at lower oxygen partial pressures showed an increase in lattice parameter and resistivity and a decrease in the insulator–metal transition temperature as compared to the stoichiometric LPMO thin film grown at 400 mTorr. Further, these oxygen-deficient thin films showed over 70% giant magnetoresistance (GMR) near the insulator–metal transition temperature against the 40% GMR in the case of stoichiometric thin films.
Current pulses in dc glow discharges in electronegative gas mixtures
Authors: Pérès Irène , Pitchford L. C.
Published: July 2002

Regular oscillations in the current are predicted in low-pressure, planar discharges under certain conditions in electronegative gas mixtures in which the attachment rate coefficient is large at low values of E/P, the ratio of the electric-field strength to the gas pressure. The frequency of the oscillations is about 10 kHz, and depending on the conditions of pressure, gap spacing, and applied voltage, the current wave form varies from a near-sinusoidal shape to regularly repeating and well-separated spikes with a peak current density on the order of or less than 1 mA/cm2. The instability which gives rise to these oscillations is due to attachment, and the oscillations result from alternate phases of space charge buildup and decay. Thus, the current oscillations predicted here in planar discharges are analogous to Trichel pulses, periodic current spikes which are observed in negative point-plane corona discharges in electronegative gases.