bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp
Authors: Jeon S. G. , Baik C. W. , Kim D. H. , Park G. S. , Sato N. , Yokoo K.
Published: July 2002

The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation.
Colored ink dip-pen nanolithography
Authors: Su Ming , Dravid Vinayak P.
Published: July 2002

Colored ink dip-pen nanolithography (DPN) is demonstrated by the direct patterning of organic dyes on substrates to generate optically active and arbitrarily shaped nanostructures with dimensions well below 200 nm in a straightforward manner. The dye nanopatterns are indeed optically active as confirmed by fluorescence emission under external pumping. The efficiency of patterning organic materials on bare and chemically modified Si/SiOx substrates reaffirms that DPN patterning of organic molecules can be done without covalent linkages, and points to importance of noncovalent interactions in DPN. The method can be extended to direct patterning of many colored/colorless organic molecules, and should open many opportunities for miniaturized optical devices and site-specific biological staining.
Laser-focused nanofabrication: Beating of two atomic resonances
Authors: Jurdik E. , Hohlfeld J. , van Kempen H. , Rasing Th. , McClelland J. J.
Published: July 2002

We deposit a laser-collimated chromium beam onto a substrate through a laser standing-wave (SW) tuned above the atomic resonance at either of the two 52Cr transitions 7S3→7P3o at 427.600 nm or 7S3→7P4o at 425.553 nm. In both of these cases, the resulting pattern on the surface consists of nanolines with a period of that of the SW. We extend the range of periods accessible to laser-focused atom deposition by superimposing the structures grown at both these resonances. The resulting beating pattern exhibits a period of 44.46±0.04 μm as determined with a polarizing optical microscope. This structure provides a link between nanoscopic and macroscopic worlds and could potentially become a calibration standard for length metrology.
Bifurcation structures of periodically forced oscillators
Authors: Vance William N. , Ross John
Published: July 2002

A theoretical investigation of bifurcation structures of periodically forced oscillators is presented. In the plane of forcing frequency and amplitude, subharmonic entrainment occurs in v-shaped (Arnol’d) tongues, or entrainment bands, for small forcing amplitudes. These tongues terminate at higher forcing amplitudes. Between these two limits, individual tongues fit together to form a global bifurcation structure. The regime in which the forcing amplitude is much smaller than the amplitude of the limit cycle is first examined. Using the method of multiple time scales, expressions for solutions on the invariant torus, widths of Arnol’d tongues, and Liapunov exponents of periodic orbits are derived. Next, the regime of moderate to large forcing amplitudes is examined through studying a periodically forced Hopf bifurcation. In this case the forcing amplitude and the amplitude of the limit cycle can be of the same order of magnitude. From a study of the normal forms for this case, it is shown how Arnol’d tongues terminate and how complicated bifurcation structures are associated with strong resonances. Aspects of model and experimental chemical systems that show some of the phenomena predicted from the above theoretical results are mentioned.
Barrier fluctuations and stochastic resonance in membrane transport
Authors: Fuliński A.
Published: July 2002

The role of barrier fluctuations in membrane enzymatic processes, in particular in the active transport of ions through cell membranes, is examined. For enzymes embedded in the cell membrane the role of the barrier height (activation energy) is played by the membrane electric potential. This barrier height can be modulated either by internal fluctuations or by external electrical fields, either random or periodic. Existing experimental data on active transport of Na+ and Rb+ in human erythrocytes (catalyzed by Na+–K+–ATPase) can be interpreted as evidence of stochastic resonance between the external ac field and the fluctuations of the membrane potential. The obtained results suggest that the significant part of these fluctuations is supplied by the stimulated action of neighbor voltage-gated ionic channels. This supports the idea that intrinsic noise plays a constructive role in one of most important and most frequent biophysical processs, viz. ion transmission through cell membranes. Means of further experimental verification of this conjecture are proposed.
Hardware and software for a multiparametric concurrent data acquisition system
Authors: Esaulov V. E. , Bartolo R. , Penent F.
Published: July 2002

This paper presents a brief description of the basic characteristics and functioning of a simple hardware/software system for the simultaneous control of several data acquisition channels in atomic collisions experiments. The basic hardware consists of two IBM-PC/AT compatible boards equipped with ADCs, DACs, IO ports, and counters. The software allows simultaneous running of several data acquisition tasks, such as controlling an optical monochromator, an electrostatic energy analyzers and time-of-flight analyzers. The software also allows basic file input/output functions as well as some data processing functions.
A new slow-relaxation phenomenon in semi-insulating GaAs
Authors: Nojima S.
Published: July 2002

A new type of slow-relaxation phenomena is found in low-temperature photoconductivity for undoped semi-insulating GaAs: Irradiation by secondary light subsequent to the primary-light irradiation induces a rapid increase followed by a gradual exponential decrease in photoconductivity. This phenomenon cannot be explained by conventional photoelectric fatigue, though these are similar to each other. A model is proposed to explain this phenomenon, involving a dynamical transition of carriers by primary- and secondary-light irradiation. This model is consistent with the results of annealing experiments for the phenomenon.
Pressure concentration isotherms of thin films of the palladium-hydrogen system as modified by film thickness, hydrogen cycling, and stress
Authors: Lee Ming-Way , Glosser R.
Published: July 2002

We describe the results of a novel adaptation of the volumetric technique to measurement of the pressure concentration isotherms for thin films of the palladium-hydrogen system. The isotherm shapes are comparable to bulk being steep in the alpha and beta phases and flat in the mixed phase region. However, it is noted that the concentration onset of the beta phase is smaller than bulk and drops markedly for thicknesses less than 670 Å. Comparison is made with quartz crystal microbalance results. We find a thickness dependence to the number of absorption-desorption cycles required to obtain reproducible isotherms.
Physical properties of SnOx films
Authors: Croitoru N. , Seidman A. , Yassin K.
Published: July 2002

SnOx films with different values of x were deposited by rf sputtering. Secondary emission yield δ, physical density γ, and electrical resistivity ρ of the films were investigated. Higher values of δ than those of bulk SnO and SnO2 were found. From the experiment it results that δ, γ, and ρ increase with the increase of x. The crossover energy Ec, the primary electron energy for δ=1, decreases with x. Analysis of the experimental data and theory leads to the conclusion that the main factor which determines the maximum secondary electron emission yield δm is the ratio between the escape probability and the work function.
Analysis of polycrystalline silicon diffusion sources by secondary ion mass spectrometry
Authors: Schaber H. , Criegern R. v. , Weitzel I.
Published: July 2002

Polycrystalline silicon diffusion sources have been analyzed using secondary ion mass spectrometry. Polysilicon films were grown by standard low-pressure chemical vapor deposition and doped with As, P, or B by ion implantation. Although dopant segregation at the poly-Si/single-crystal-silicon interface occurred and has been analyzed quantitatively, no diffusion barrier has been observed at this interface. Diffusion profiles in the single-crystal substrate have been measured for diffusion temperatures between 800 and 1000 °C. It is shown by comparison to numerical simulations that these profiles obey standard diffusion theory. Proper boundary conditions to be used for such calculations are deduced for the different dopant species. Furthermore, the saturation concentration of boron in silicon over the temperature range given above has been reliably determined.
Reexamination of the wavelength modulation photoresponse spectroscopies
Authors: Eetemadi S. M. , Braunstein R.
Published: July 2002

Reexamination of the wavelength modulation photoresponse spectroscopies showed that the line shapes obtained by these methods are subject to distortions from several sources of spurious interference spectra. A comparison is made between the wavelength modulation absorption/reflection and the wavelength modulation photoresponse spectroscopies; it is concluded that the former are the most suitable modulation techniques for studies requiring unambiguous line shapes.
Optical reflectance in GaAs/AlGaAs quantum wells
Authors: Pearah P. J. , Klem J. , Henderson T. , Peng C. K. , Morkoç H. , Reynolds D. C. , Litton C. W.
Published: July 2002

Molecular-beam epitaxial GaAs/AlGaAs bulk layers and quantum well heterostructures have been grown and characterized at 3 K using broadband optical reflectance and photoluminescence spectroscopy. Reflectance spectra display sharp, well-defined features due to strong near-band gap excitonic effects that cause the reflectance to deviate by over 50% from the bulk value in some cases. Features due to impurity-bound excitons, free-to-bound transitions, and free excitons have all been identified in quantum well heterostructures. Interband transitions involving the n=1 light hole and higher-lying subbands are much more readily observed in reflectance spectra than in photoluminescence, including ‘‘forbidden’’ Δn≠0 transitions. Additionally, reflectance has been used to probe the interfaces, revealing fine structure due to monolayer and submonolayer deviations in well thickness.
Distributed amplifier using Josephson vortex flow transistors
Authors: McGinnis D. P. , Beyer J. B. , Nordman J. E.
Published: July 2002

A wide-band traveling wave amplifier using vortex flow transistors is proposed. A vortex flow transistor is a long Josephson junction used as a current controlled voltage source. The dual nature of this device to the field effect transistor is exploited. A circuit model of this device is proposed and a distributed amplifier utilizing 50 vortex flow transistors is predicted to have useful gain to 100 GHz.
Optical band gap of indium nitride
Authors: Tansley T. L. , Foley C. P.
Published: July 2002

Room-temperature optical absorption data in the 1.5–2.5-eV range are reported for indium nitride thin films prepared by reactive radio-frequency sputtering. The fundamental absorption edge in high-purity material is located at 1.89±0.01 eV and corresponds to a direct transition at k=0, in agreement with band-structure calculations. A significant Moss-Burstein shift is noted for carrier concentrations in excess of 1019 cm−3 and obeys the empirical relationship EG =1.89+2.1×10−8 n1/3 eV.
Tin-doped GaAs epilayers grown by low-pressure metalorganic chemical vapor deposition using triethylgallium and tetraethyltin
Authors: Lee M. K. , Chang C. Y.
Published: July 2002

A vertical cold-wall low-pressure metalorganic chemical vapor deposition system is used for the growth of Sn-doped n-type GaAs epilayers. Smooth and specular Sn-doped GaAs epilayers can be easily grown. Van der Pauw Hall measurement, and I-V and C-V characteristics show that tetraethyltin is a suitable source for GaAs n-type dopant. Sn surface accumulation has been observed from Auger electron specroscopy (AES) and secondary ion mass spectrometry (SIMS) measurements. From infrared spectroscopy (IR) examination of the deposit on the quartz reactor wall, the decomposition of TEG is incomplete. The results of selective epitaxial growth indicate that the GaAs growth from TEG is controlled by surface kinetics. Tetraethyltin can enhance the growth rate of GaAs and decrease the As/Ga ratio and also EL2 concentration. A EL2 model is proposed.
Erasable laser recording in an organic dye-binder optical disk medium
Authors: Gupta Mool C. , Strome Forrest
Published: July 2002

Erasability in an overcoated organic dye-binder medium has been demonstrated. With thin (∼50 nm) overcoats on such media, a laser pulse forms a pit in the dye-binder layer, while the overcoat forms a dome over the pit. Information is erased by heating the rim material with low laser power which fills the recorded pit. During recording into a thickly (∼300 nm) overcoated recording medium, material flow occurs from the trailing edge towards the leading edge of the mark. Results of modeling, observations of pit morphology, evidence of long-term stability, and measurements of optical disk performance are presented for thinly and thickly overcoated erasable organic dye-binder layers.
Mechanism of laser writing for optical data storage in an overcoated tellurium alloy trilayer
Authors: Holstein W. L. , Begnoche B. C.
Published: July 2002

Mark formation by laser writing in an overcoated thin-film tellurium alloy-based optical storage media with a trilayer design was studied by transmission electron microscopy, scanning electron microscopy, optical microscopy, differential interference contrast optical microscopy, and optical interferometry. Mark formation was observed to occur through coalescence of the relatively uniform amorphous tellurium alloy film into discrete particles. The mark microstructure and, correspondingly, the optical properties of the mark, were dependent on the write laser power. At low power, incomplete breakup of the film occurred. At high power, the film coalesced into spherical particles. Laser writing also caused changes in the organic overcoat layer.
Efficiency of a capacitor-transfer-type discharge excimer laser with automatic preionization
Authors: Miyazaki Kenzo , Hasama Toshifumi , Yamada Kawakatsu , Fukatsu Toru , Eura Takashi , Sato Takuzo
Published: July 2002

Energy transfer aspects in a capacitor-transfer-type discharge excimer laser with automatic preionization (API) have been studied to improve the laser efficiency. Detailed measurements on the discharge and output characteristics of the XeCl laser show that efficient energy transfer from the storage capacitor to the discharge capacitor is essential for improvement in the overall efficiency. The circuit analysis based on the measurements suggests that the API discharge excimer laser could be operated with an electrical efficiency of about 4%. The overall efficiencies of 2.9, 2.8, and 1.3% have been obtained with the XeCl, KrF, and ArF lasers, respectively.
Profile distortions during secondary ion mass spectrometry analyses of resistive layers due to electron stimulated desorption and charging
Authors: McPhail D. S. , Dowsett M. G. , Parker E. H. C.
Published: July 2002

The problem of charge compensation during SIMS depth profiling of resistive-layer structures on insulating substrates is discussed with reference to BF2 and As-implanted silicon-on-sapphire (SOS). Accurate positive ion fluorine profiles (from the BF2 in SOS samples) could not be obtained using electron beam charge compensation, due to an intense electron stimulated desorption (ESD) signal at mass 19. This species is shown to be F+. Evaporation of a gold-surface-edge electrode, 50 nm thick, represents an alternative charge compensation technique, providing a conduction path from crater edge to sample holder that bypasses the insulating substrate. Fluorine profiles can thus be obtained to within a few hundred angstroms of the sapphire. Such an electrode may be of more general use as it simplifies the setting up of electron beam charge compensation, where profiles are to be taken through a conductor and into an insulator, facilitating correct charge compensation at both sides of the interface. Accurate arsenic profiles (from the As in SOS samples) also require careful charge compensation, particularly in quadrupole based machines. Small changes in surface potential can lead to the illusion of dopant pile up (at an interface, for example) as Si2O is swept into the bandpass of the instrument. It is demonstrated that the intercomparison of mass channels, tuned to the same mass but different starting potentials, is an invaluable aid in the detection of such artifacts. The comparison of matrix-channel-ion images obtained at different stages in the profile is also useful and shows that the charging of the crater base does not occur uniformly.
Electric and magnetic flux compression theory for arbitrary large liner velocities
Authors: Wilhelm H. E.
Published: July 2002

Theoretical analyses of the compression of axial (i) magnetic and (ii) electric fluxes by means of cylindrical liners are presented for arbitrary large implosion velocities v<c0. For comparison, quasistatic theories of (i) magnetic and (ii) electric flux compression are given, which are good approximations for nonrelativistic liner speeds v≪c0. For relativistic liner velocities, significant amounts of electromagnetic radiation would be generated in magnetic or electric flux compression. Relativistic liners can eventually be realized by means of relativistic pulses of electrons of high density. During magnetic flux compression, electrical breakdown is prevented through magnetic self-insulation. The experimental field strengths achievable through electric flux compression are limited by electrical breakdown, since the condition for magnetic self-insulation is not satisfied.
Metalloid redistribution in Ni75B15Si10 amorphous alloy observed by scanning Auger microprobe
Authors: Okuyama F. , Fumjimori N. , Sobue S. , Fujimoto S. , Fujimoto Y.
Published: July 2002

The redistribution behavior of metalloid atoms in the amorphous alloy Ni75B15Si10 was studied by means of a scanning Auger microprobe. Si atoms were found to be segregated beneath the surface of samples annealed above 470 K, but B atoms formed no segregated region in the temperature range employed (400–800 K). The periphery of samples annealed around 640 K was rich in Si, and metastable crystals growing along the edge were detected by transmission electron microscopy. It is supposed that Si atoms segregated in the edge area played a role in nucleating the crystals.
Comparison of calculated and measured hysteresis loss in multifilamentary superconducting wire
Authors: Ashkin M. , Wagner G. R.
Published: July 2002

A previously developed theory for a single round filament of type II superconductor is applied to hysteresis losses in multifilamentary composite conductors. The single filament theory was extended for a wider range of time varying field amplitudes. Two contrasting wires were used to test the theory which predicts a universal curve for the loss in all conductors. A very close agreement was obtained in all details between theory and experiment for the wire with widely spaced (∼2.5 μm) large-diameter (15 μm) filaments. The other wire had closely spaced (<1 μm) small-diameter (2 μm) filaments and the shapes of the loss versus field plots for theory and experiment were in excellent agreement for this case. However, the effective filament diameter and superconductor volume fraction λ extracted from fitting the theory and measurements are much larger than the physical diameter and slightly larger than the physical λ, respectively. This is expected due to the proximity effect and possible interfilament contact. This effective diameter is approximately the size of clearly defined filament bundles.
Electronical properties of metal-insulator-semiconductor devices prepared on thermally treated InP in phosphorus overpressure
Authors: Choujaa A. , Chave J. , Blanchet R. , Viktorovitch P.
Published: July 2002

The effect of excess phosphorus vapor during the process of MIS structures on InP is analyzed in detail. It is shown that the density of interface state distribution is considerably modified after in situ thermal precleaning of the substrate in phosphorus overpressure (suppression of the Fermi-level pinning and significant reduction of the density of surface states near midgap). Phosphorus overpressure also provides an efficient protection of the surface during the insulator deposition. Fermi-level pinning in the upper part of the gap is assigned to the uncontrolled native oxide left on the surface after a stay of InP substrate in ambient atmosphere.
Digital image processing of velocity-interferometer data obtained from laser-driven shock experiments
Authors: Fisk G. A. , Mastin G. A. , Sheffield S. A.
Published: July 2002

This paper discusses digital image processing techniques suitable for use with the velocity interferometric records obtained from shock-wave experiments using ORVIS (optically recorded velocity interferometer system). An ORVIS system is capable of measuring shock events with subnanosecond time resolution, the data consisting of fringe motion (proportional to the impacted material velocity) recorded with a streak camera. Two image processing methods are described which permit the determination of accurate velocity-time data from the records. The first, based on global analysis of the records, requires no operator intervention during reduction of the data, but breaks down when records show very rapid acceleration of the target under observation. The second, based on a thinning algorithm, can be used to treat rapid acceleration data and data in which the fringes are less than ideal. It requires operator intervention in some cases. The two techniques are shown to agree well when applied to the same data.
The integro-differential equations predicting transient decay of space-charge currents in media
Authors: Henson Bob L.
Published: July 2002

A pair of coupled, nonlinear integro-differential equations, which exactly describe the transient current produced by the drift and collection of a swarm of space charge in a medium between two electrodes, has been derived for a single charge carrier species using a field-independent mobility model. The equations represent the solution of the mathematical problem involving arbitrary space-charge sizes and distributions coupled with the effects of the inherent time constants of the physical system. Computer-generated numerical solutions, for the special case of the initial charge distributions which correspond to steady-state currents, are reported. The equations under these conditions can be decoupled to form a stiff third-order differential equation. The numerical results indicate a possible scheme for correcting transient current waveforms, which are distorted by space-charge fields, in order to obtain the proper, ideal times of flight needed for true mobility measurements.
Growth-induced optical anisotropy of epitaxial garnet films grown on (110)-oriented substrates
Authors: Kitamura K. , Iyi N. , Kimura S. , Chevrier F. , Devignes J. M. , Le Gall H.
Published: July 2002

Garnet films of nominal composition (Y,Nd)3Ga5O12, were grown on (110) 1°-off Gd3Ga5O12 substrates for investigation of their growth-induced optical anisotropy. Optical birefringence and directions of the electric vectors of polarized rays passing through the films were measured under a polarizing microscope using a Brace–Köhler compensator. The growth-induced anisotropy of these films optically exhibited orthorhombic characteristics with the X, Y, and Z optic elasticity axes coinciding with the [001], [110], and [1̄10] directions, respectively. The crystallographic data obtained by means of single-crystal diffractometry suggested that the cubic crystal system of the garnet film was distorted, though very slightly, to an orthorhombic one with a,b, and c axes that coincided, respectively, with the [1̄10],[001], and [110] of the original cubic cell. In addition, by annealing at 1150 °C, this distortion disappeared and the crystal system reverted to cubic.
Mechanism of damage formation in antireflection coatings
Authors: Yoshida K. , Yabe T. , Yoshida H. , Yamanaka C.
Published: July 2002

Theoretical interpretation of damage formation in coated optical glasses is given and its low damage threshold is found to be due to the energy confinement in a narrow gap between the glass substrate and the coated material. The experiments supporting this mechanism are conducted with noncoated, hard-coated, and porous-coated glasses.
Extended step-by-step analysis in space-charge-limited current: Application to hydrogenated amorphous silicon
Authors: Shimakawa K. , Katsuma Y.
Published: July 2002

A new method for analyzing space-charge-limited currents (SCLC) has been presented. This is based on the step-by-step calculation of the density of state g(E) using Poisson’s equation, which could reduce the relative error in determining g(E) encountered in various analyzing methods. The present method has been applied to deducing g(E) in hydrogenated amorphous silicon: The density of states at the Fermi level g(Ef) has been estimated to be 1×1015 cm−3 eV−1 and g(E) for deep states varies slowly with energy.
Theoretical study of ion assisted chemical reactions on a semiconductor solid. Model: Ar++Cl2/Si(001)
Authors: Park Seung C. , Clary David C.
Published: July 2002

The reaction of Cl2 with a Si solid under Ar+ ion bombardment is investigated theoretically by the classical trajectory method. The etching yield of Si is calculated and is in good agreement with recent experimental results. The main products of the reaction are atomic Si and Cl together with molecular SiCl and SiCl2. This is also consistent with experimental findings. We report calculations of product, energy, and angular distributions. The relevance of these calculations for the dry etching of semiconductors is discussed.
Thermal and structural stability of cosputtered amorphous TaxCu1−x alloy thin films on GaAs
Authors: Oh J. E. , Woollam J. A. , Aylesworth K. D. , Sellmyer D. J. , Pouch J. J.
Published: July 2002

The thermal and chemical stabilities of amorphous-metal diffusion barrier films are of importance in high-temperature semiconductor device applications. The reaction characteristics of the barrier constituents with the surrounding elements as well as the crystallization temperature determine the thermal stability of an amorphous-alloy diffusion barrier. We report that suitable thin films of Ta-Cu have been prepared over a wide range of compositions, by cosputter deposition onto GaAs and fused-quartz substrates. The amorphous nature and crystallization behavior of the films have been monitored by x-ray diffraction and van der Pauw resistivity measurements. Films were found to be amorphous over the range of 55–95 at. % Ta. In addition, Auger electron spectroscopy surveys and depth profiles were used to investigate the various interdiffusion reactions between the amorphous diffusion barrier, polycrystalline Au overlayers, and GaAs substrates. Barriers of Ta93Cu7 are remarkably effective in preventing Au in-diffusion, a 3000-Å layer remaining unpenetrated after an annealing at 700 °C for 20 min. Diffusion of Ga and/or As into amorphous 93 at. % Ta is more rapid than that of Au. Interfacial reactions formed Ta3Au, CuAu, TaAs2, Ga3Cu7, Cu3As, and other unidentified compounds formed above 700 °C.
Reply to ‘‘Comment on ‘Crystallization characteristics of late transition metal-Zr glasses around the composition M9Zr1’ ’’ [J. Appl. Phys. 5
9, 2364 (1986)]
Authors: Altounian Z. , Batalla E. , Strom-Olsen J. O.
Published: July 2002

We demonstrate that the crystallization products of glassy Fe90Zr10 are α-Fe and Fe3Zr. We attribute the apparent observation of Fe2Zr in dynamic temperature x-ray diffraction studies to the formation of FeO.
Vacancy self-diffusion in a screw dislocation in a simple cubic lattice
Authors: Stark J. P.
Published: July 2002

Correlated self-diffusion in a screw dislocation in a simple cubic crystal is treated with a vacancy mechanism. First and second neighbor jumps are considered within the dislocation core and matrix functions are generated which permit the limit of an infinite dislocation length to be examined for the tight binding approximation. The correlation factor f for positive vacancy binding to the dislocation is found in the range of 0.73≥f ≥0.52 as the binding energy increases without bounds. Previous calculations for an edge dislocation showed that the correlation factor was bound by the limits 0.75≥f ≥0. Comparable calculations of the diffusion coefficient suggest that the diffusivity becomes infinitely large in the same limit in a manner similar with what happens in an edge dislocation. Namely, as the binding energy of the vacancy increases without bounds, the number of available vacancies for diffusion increases indefinitely as a result of the length of dislocation acting as a source.
Influence of substrate structure on the growth of hydrogenated amorphous silicon studied by i
n s
i
t
u ellipsometry
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

Using in situ ellipsometry as a probe, the effect of substrate microstructure on the growth habit of high-quality hydrogenated amorphous silicon (a-Si:H) has been studied. An understanding of the growth process is important when combining a-Si:H with other materials in thin-film multilayer devices. The present study concentrates on cases where a-Si:H of different microstructure, microcrystalline Si:H (μc-Si:H), and single-crystal Si are used as substrates. The a-Si:H top film is grown under identical conditions on each substrate material and pseudo-dielectric-function trajectories are collected during growth. These trajectories have been applied to characterize the bulk and interface structure and the evolution of surface roughness layers during growth. For the same deposition conditions, a range of growth patterns is observed, depending on the structure of the substrate.
Effect of a-SiNx:H composition on band bending near the interface of a-Si:H/a-SiNx:H layered structures
Authors: Hiranaka Kouichi , Yoshimura Tetsuzo , Yamaguchi Tadahisa , Yanagisawa Shintaro
Published: July 2002

The effect of band bending near the interface of a-Si:H/a-SiNx:H layered structures has been investigated for various a-SiNx:H compositions by measuring in-plane dark current and photocurrent. The dark current of a-Si:H/a-SiNx:H layered structures increases about four orders of magnitude and the activation energy decreases with a decrease in x of a-SiNx:H. The photocurrent also increases about four orders of magnitude with a decrease in x. This photocurrent enhancement is larger in the shorter wavelength region, and this spectral change agrees with the photocurrent spectral change induced by an increase in gate bias in thin-film transistor structures. From these results it is found that the band bending toward electron accumulation in a-Si:H near the a-Si:H/a-SiNx:H interface increases with a decrease in x of a-SiNx:H, resulting in high photoconductivity.
A new analytical technique of photoluminescence for optimization of organometallic chemical vapor deposition
Authors: Hsu J. K. , Jones S. H. , Lau K. M.
Published: July 2002

An analytical method for quantitative interpretation of GaAs photoluminescence spectra was developed. Because of various transition mechanisms the photoluminescence spectrum of a sample may vary significantly under different measurement conditions. Based on a proposed scheme of transition priorities, spectra taken at various excitation powers were analyzed. Comparing results of undoped GaAs epitaxial layers grown by organometallic chemical vapor deposition under similar conditions but different V/III ratios, an optimum ratio corresponding to a minimum number of shallow impurities was clearly identified. Carbon and zinc were found to be the major shallow acceptors in most samples. At very low V/III ratios, carbon was the most dominant acceptor. The carbon concentration diminishes with an increasing ratio and the amount of zinc becomes more significant.
A novel fabrication technique for a quasicoplanar super-Schottky diode on GaAs
Authors: Ruby R. , Van Duzer T.
Published: July 2002

We report here fabrication of a super-Schottky diode on GaAs using a novel structure. This device takes advantage of the reverse-beveled walls of anisotropically etched GaAs. The reverse-beveled edge acts as a shadow mask to a direct-line evaporation of the superconducting electrodes. The controllable etch rate of the GaAs etching solution (H2O, H2O2, and H2SO4 8:1:1) allows for the definition of a small critical geometry (submicron) in the vertical direction without the need of electron beam lithography, or any other fine lithography system. The small critical geometry between superconducting electrodes is necessary for reduction of the parasitic-substrate resistance.
Electron-optical simulation of rotationally symmetric triode electron guns
Authors: van den Broek M. H. L. M.
Published: July 2002

Methods and approximations underlying the calculation of currents and spot sizes in rotationally symmetric triode electron guns are described. In the beam-forming region, the Poisson equation is solved self-consistently taking into account the initial velocities of the electrons (Langmuir’s law instead of Child’s law). In the remainder of the gun the space-charge force is calculated directly from the solution of the Laplace equation and the position of the trajectories in the beam, which avoids the time-consuming iterative solution of the Poisson equation. The space-charge density and spot profiles are calculated with a fitting technique. The results of the simulation are compared with experimental values obtained for a gun similar to the guns used in modern display tubes. The currents agree within 5% over a range from 0.1 to 4 mA. The 5% intensity spot sizes were measured as a function of the focusing potential and they agree with the calculated spot size within 10%. At the lowest focusing potentials, for which the spot is focused too strongly, the discrepancies are somewhat larger. The spot profiles give a fairly accurate impression of the haze surrounding the spot and the optimum focusing potentials agree within 50 V.
Influence of phosphorus vapor ambient for InGaAsP growth on GaAs substrate
Authors: Ishikawa Joji , Ito Toshio , Shin-ichi Takahashi N. , Kurita Shoichi
Published: July 2002

For visible-light-emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid-phase epitaxy. As the growth temperature is as high as about 780 °C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In-P-Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (λPL=805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x-ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of increasing the flow rate of H2 gas in order to protect the solution for the active layer from phosphorus contamination, the double heterostructure wafers with the high-quality active layer can be obtained reproducibly. Thus, pulsed lasing operation at room temperature has been achieved. The lasing wavelength is 816 nm and the threshold current density is ∼4.6 kA/cm2.
Theoretical analyses of amorphous semiconductor multijunctions
Authors: Chen I.
Published: July 2002

The transport of charge carriers in a multijunction, consisting of alternating thin p- and n-type sublayers of amorphous semiconductor, has been analyzed theoretically. It is shown that the multijunction behaves in the dark like a pn-junction diode, while it has an advantage in reducing range limitation of photogenerated carriers. These properties are realized when the sublayer thickness is of the order of 100 nm for realistic values of doping levels and localized state density.
Discharge time lag with electron-beam injection in a low-pressure gas
Authors: Ando Kiyomi , Oshige Tsuyoshi , Yagura Shinya , Fujita Hiroharu , Harada Tatsuya
Published: July 2002

Discharge time lag is experimentally studied when a single stepped voltage is applied to a gap with a stationary electron-beam injection in a low-pressure gas (0.06–2 mTorr). The time lag is found to be almost independent of the electron-beam density. The beam density does, however, determine a discharge current, which is independent of the applied gap voltage and beam energy. A systematic measurement of the time lag as functions of the gap voltage, beam energy, gas pressure, and gap length is presented. The time becomes extremely short when the beam energy exceeds the ionization energy of the gas. The time lag, when a single pulsed e-beam is injected into the dc gap field, is also studied. The result is essentially the same in spite of pulsed operation.
Si diffusion in GaInAs-AlInAs high-electron-mobility transistor structures
Authors: Brown A. S. , Itoh T. , Wicks G. , Eastman L. F.
Published: July 2002

Secondary-ion-mass spectrometry, Hall-effect measurements, and dc I-V characteristics of 1-μm Ga0.47In0.53As-Al0.48In0.52As high-electron mobility transistor structures indicate that significant diffusion of Si can occur in these layers. The source of the Si is both the intentional Si used for modulation doping of the devices, and Si which is an unintentional impurity in the Fe-doped InP substrates on which the layer is grown. Preannealing and polishing the substrates can lessen the effect.
Determination of minority-carrier diffusion length in a p-silicon wafer by photocurrent generation method
Authors: Sharma S. K. , Singh S. N. , Chakravarty B. C. , Das B. K.
Published: July 2002

A nondestructive method to determine the diffusion length of minority carriers in a p-silicon wafer is outlined. This novel method is based on creating an accumulation layer on one side and an inversion layer on the other side of the wafer by depositing thin semitransparent layers of high (e.g., palladium) and low (e.g., aluminum) workfunction metals, respectively. The wafer acquires a structure akin to p+-p-n+ and is capable of generating a photocurrent when illuminated. The photocurrent Isc (where sc represents short circuit) as a function of the intensity Pin of a monochromatic radiation incident on the accumulation layer (p+) side of the wafer is measured. The diffusion length L is determined from the slope of the Jsc vs Pin curve. The values of L so determined were compared with that determined from the measurement of spectral response by illuminating the wafer from the inversion layer (n+) side and were found to be in excellent agreement.
Effects of Joule heating and transpiration on heat transfer in magnetohydrodynamic boundary layers
Authors: Chuang Hsing
Published: July 2002

A steady two-dimensional magnetohydrodynamic boundary-layer flow on a flat plate with a uniform transpiration through the plate which is kept at a constant temperature is considered. Heat transfer at the plate is found to increase with the Joule heating, the transpiration number, the magnetic interaction number, and the Prandtl number. The temperature profile is substantially altered by transpiration, magnetic interaction, and the Prandtl number.
Simultaneous annealing for implantation activation and spin-on source diffusion into GaInAs: A novel approach for the formation of p
n junctions
Authors: König U. , Kuisl M.
Published: July 2002

A new process—simultaneous implantation and diffusion annealing—has been developed for the formation of pn junctions in compound semiconductors. It combines implantation and diffusion, by using doped SiO2 spin-on films simultaneously as a surface protection during activation of the implants and as a diffusion source. Only a single annealing step is necessary, which is very important for a careful heat treatment of existing semiconductor structures. Examples are presented for GaInAs. The n level formed by Si implantation varies from 1×1017 cm−3 to 6×1018 cm−3, with an increasing dose. The p level is adjusted to about 1×1019 cm−3 by the amount of Zn salt in the spin-on solution. The position of the pn junction is shifted by the annealing step.
Finite-size effects on Raman scattering from GaAs-AlAs superlattices
Authors: Nakayama M. , Kubota K. , Kato H. , Sano N.
Published: July 2002

We have investigated finite-size (total number of periods) effects on Raman scattering by longitudinal acoustic (LA) and longitudinal optic (LO) phonon modes in GaAs-AlAs superlattices. Every superlattice has the same period (10-monolayer GaAs and 10-monolayer AlAs), while the total number of periods ranges from 3 to 100 periods. Even in the superlattice with three periods, folded LA phonon modes are induced by the superlattice period. Raman linewidths of folded LA phonon modes increase as the total number of periods decreases. The Raman linewidth broadening becomes remarkable below 20 periods. The dependence of linewidth broadening on the total number of periods results from the relaxation of the Raman selection rule for phonon wave vectors induced by the finiteness of superlattices. On the other hand, for LO phonon modes the finite size does not affect Raman line shapes; this originates in the confinement of LO phonon modes in individual layers.
Pulsed laser-induced changes in structural and electrical properties of Pb0.8Sn0.2Te thin films
Authors: Dawar A. L. , Jagadish C. , Mathur P. C.
Published: July 2002

Pb0.8Sn0.2Te films, grown by flash evaporation, were irradiated with Nd:YAG laser pulses of various energy densities. Transmission electron microscopy, x-ray diffraction, and electrical studies reveal that the irradiation significantly increases grain size, and the mobility increases by a factor of 5.
Prediction of the electrical conductivity of two-dimensionally misoriented short fiber composites by a percolation model
Authors: Ueda Naoki , Taya Minoru
Published: July 2002

A percolation model combined with Monte Carlo method has been applied to two-dimensionally misoriented short fiber composites with the aim of predicting the effective electrical conductivity of the composite. Then the threshold volume fraction of fiber (VFth) at and above which the composite becomes conductive was computed for several cases of misoriented short fiber composites, i.e., from completely random to reasonably well oriented short fiber composites. It was found in this study that the larger the fiber aspect ratio and the more randomly fibers are oriented, the smaller the value of VFth becomes.
Magnetic properties and anisotropy of CoCr thin films for perpendicular recording (abstract)
Authors: Khan Mahbub R. , Seagle David J. , Fernelius Nils C. , Lee Jae I.
Published: July 2002

The magnetic properties, microstructure, and anisotropy of CoCr thin films have been studied using VSM, x-ray, torque magnetometer, and electron microscopy techniques. These films were grown on a number of different substrates including sapphire, glass, mica, Al, and Ni-P, by rf sputtering, in the thickness range 300 Å–1 μm. The microstructures dominate the magnetic properties of these films and the coercivity Hc continues to increase even up to the grain diameters of 1000 Å. The Δθ50 value for the (0002) x-ray peak reached 2°. For the sapphire the anisotropy field Hk is positive down to a film thickness of 500 Å. Effective anisotropy constants as measured by torque magnetometer increase from 1.31 to 3.16×10+5 erg/cm3 for film thicknesses ranging from 0.1 to 1 μm. We have estimated the magnetocrystalline anisotropy from the measured anisotropy values from the torque magnetometer. In calculating the shape anisotropy, this model accounts for magnetostatically interacting cylindrical columns as opposed to the simple uniform thin-film model. Since there is experimental evidence that Cr segregates towards the grain-boundary walls, a variety of models were used where the diameter of the grains were kept constant while the diameter of the magnetic parts of the grains were gradually reduced. When the magnetic columns are in contact, the shape anisotropy field Hs is 5% lower than the uniform thin film approximation. When the magnetic radius is 80% of the grain radius, then the Hs is 34% lower, but the magnetocrystalline anisotropy constant Ku is 7% higher.
Johnson noise in one- and two-dimensional distributed resistor-capacitor systems
Authors: Pimbley J. M.
Published: July 2002

Johnson noise is often the dominant noise source in microelectronic devices. While the magnitude and frequency dependence of noise within a network of discrete resistors and capacitors is well documented, there appears to be a lack of analogous results for distributed resistor-capacitor systems. This latter model is quite relevant to microelectronic devices since one finds that long resistive conductors are capacitively coupled with varying strength to other elements along the entire conductor length. We solve both the one-and two-dimensional distributed resistor-capacitor systems and find both the autocorrelation function of the potential at any point and the frequency spectrum of the associated mean-square potential fluctuations. We note that the one-dimensional result exhibits an extended ‘‘1/f’’ region in the power spectrum at high frequencies and speculate that all systems with macroscopic behavior governed by a diffusion equation may share this frequency dependence if the diffusivity depends appropriately on spatial frequency. The two-dimensional system solution shows us that Johnson noise within the epitaxial layer of a two-dimensional image sensor will not dominate other imager noise sources.
An open-ended photothermal cell for i
n v
i
v
o measurements
Authors: De Paula M. H. , Carvalho M. A. , Alves L. M. , Aegerter M. A.
Published: July 2002

A new photothermal open-ended cell particularly adapted for in vivo spectroscopic measurements is described. The detector is a transparent LiNbO3 crystal or a crystalline quartz transducer in direct contact with the sample. The cell can be attached to an optical fiber cable for light excitation. The cell has a high signal-to-noise ratio and its frequency variation is proportional to ω−1.16. In vivo and in vitro measurements performed on green leaf and carbon black samples are presented.