bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of barrier hydrogenation in NbN-based Josephson junctions
Authors: Cukauskas E. J. , Carter W. L.
Published: July 2002

NbN/Si/Nb tunnel junctions with hydrogenated amorphous silicon barriers were investigated for several hydrogen concentrations used during barrier deposition. Junctions with critical current densities exceeding 2 kA/cm2 were fabricated using the selective niobium anodization process junction isolation technique. The penetration depth of the NbN-base electrode material was determined to be 200 nm from the critical current magnetic field modulation period. Some junctions had figure of merit, Vm, values exceeding 40 mV which degraded with reduced junction size. Hydrogen doping of the silicon barrier produced little degradation in Vm for up to 50% of hydrogen in the argon-hydrogen sputter gas mixture. The barrier height, as determined by the Simmons model, increased with increasing hydrogen concentrations in the sputter gas, which is attributed to a decrease in the dangling bond density. Barrier heights of 40 to 350 mV were observed.
A model for laser marking of thin organic data storage layers by short intense pulses
Authors: Hill Davide A. , Soong David S.
Published: July 2002

A mathematical model is developed to describe the pit formation process in thin (∼0.1 μm) organic layers induced by short (<100 ns), intense laser pulses. The basic premise is an ablation-driven viscous flow, in which the reactive pressure gradient due to polymer decomposition causes fluid motion. Contrary to the case of thick layers (∼1 μm) and long (∼500 ns), weak pulses, here surface tension gradients are shown to be too small to promote material flow in the short time span of laser exposure. The derived closed-form expressions for temperature profile and pit contour allow expedient calculation of threshold energies and prediction of functional relationships among imposed (e.g., pulse energy and width) and measured (e.g., pit width) system variables. Model predictions compare favorably with experimental observations of such interrelations.
Effect of deposition conditions on the nucleation and growth of glow-discharge a-Si:H
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

I n situ ellipsometry experiments have been used to study the initial nucleation and growth of glow-discharge hydrogenated amorphous silicon (a-Si:H) deposited on c-Si substrates under different conditions. The substrate temperature (Ts), dc bias, and silane concentration in both hydrogen and inert gas diluents were varied. In the first ∼30–60 Å of film growth, deviations of the in situ ellipsometry data from models assuming thickness independent dielectric functions are observed for a-Si:H prepared under conditions that lead to a low density of electronic defects. The form of the deviations in the in situ data appear to be consistent with the development and convergence of densely packed clusters with a lateral extent of ∼20–30 Å, not with a well-dispersed distribution. The deviations disappear for Ts less than ∼200 °C and for flow ratios less than 1:20 (SiH4):(diluent). The low Ts effect is attributed to the lack of development of the initial growth microstructure caused by (1) the low mobility and desorption rate of surface radicals and/or (2) the low average coordination number due to ineffective hydrogen elimination. The low SiH4:diluent ratio effect is attributed to the lack of effective convergence of the initial growth microstructure since film formation may be limited, not by hydrogen elimination and surface reaction, but by radical flux arriving at the surface. The effect of deposition parameters on the bulk bonding density, surface roughness, and the interface structure is also presented. At very low SiH4:diluent ratios, it has been instructive to consider the damage mechanisms induced by the pure diluent plasmas.
Reaction of microparticles by the diffusion of reactive gases through porous shells
Authors: Rubel Glenn O.
Published: July 2002

A new experimental technique, single-particle electrodynamic balance (SPEB), was used to study the heterogeneous reaction between single acid droplets and basic gases. Experiments with phosphoric acid droplets and ammonia gas show that the droplet reaction dynamics are sequentially controlled by surface-phase, gas-phase diffusion-controlled, and porous-shell diffusion-controlled reactions. Gas-phase diffusion-controlled reactions terminate when ammonium phosphate crystallizes at the droplet surface, and porous-shell diffusion-controlled reactions become rate limiting. We derive a semiempirical model to describe the porous-shell diffusion-controlled reaction of acid droplets with surface layers of crystallized solids. The model is parametrized with an effective porous-shell diffusion coefficient to describe the transport of reactive gases through the porous shell. The model is compared to reaction data obtained from the SPEB for the reaction of phosphoric acid droplets layered with shells of ammonium phosphate. The characteristic pore radius of the porous shell is determined as a function of reaction condition.
Surface roughness evolution on glow discharge a-Si:H
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

I n situ ellipsometry has been used to probe the evolution of surface roughness over a wide range of film thickness during the growth of glow discharge hydrogenated amorphous silicon (a-Si:H). For a-Si:H prepared with pure SiH4, a <5-Å increase in the thickness of the roughness layer is observed during the growth of a ∼4-μm-thick film. In contrast, for a-Si:H prepared with SiH4 highly diluted in Ar, a gradual increase in the roughness layer of ∼100 Å is detected over the same film thickness range. The differences are consistent with recent proposals of different growth mechanisms for the two gas conditions.
Effect of a perturbed acoustic-phonon distribution on hot-electron transport: A Monte Carlo analysis
Authors: Bordone Paolo , Jacoboni Carlo , Lugli Paolo , Reggiani Lino , Kocevar Peter
Published: July 2002

A Monte Carlo simulation code has been developed to study the effect of phonon perturbations in hot-electron transport in semiconductors. The modifications of carrier drift velocity and mean energy induced by the perturbed acoustic-phonon distribution are studied at low temperatures in p-Ge. Under appropriate conditions, current saturation is obtained as a result of the steady-state phonon perturbation. The Monte Carlo analysis has been complemented and compared with an analytical approach based on a heated and displaced Maxwellian distribution for the electron gas.
Theoretical analysis of the x-ray initiation of a high-pressure argon discharge for laser applications
Authors: Bretagne J. , Louvet Y.
Published: July 2002

A theoretical analysis of x-ray initiation in a high-pressure discharge using a Boltzmann approach is presented. For a given power of x rays injected in the discharge, we have studied the influence of the x-ray spectrum on the degradation times of photoelectrons and on the resulting electron distribution function and electron densities. This approach appears to be of interest for the optimization purpose of the initiation of high-pressure glow discharges.
Resonance radiation trapping effects in copper and manganese lasers
Authors: Srigouri K. , Ramaprabhu S. , Prasada Rao T. A.
Published: July 2002

Resonance radiation trapping effects in copper and manganese pure metals and their halides as laser materials have been investigated using Holstein’s theory of resonance radiation trapping. Theoretical calculations have been performed for determining the laser-starting and optimum temperatures, and dissociation levels in the metal halides. The results are found to be in excellent agreement with the reported experimental values. A detailed discussion of the results has been presented.
Slow-relaxation phenomena in photoconductivity for semi-insulating GaAs. II. Distribution among samples
Authors: Nojima S. , Asahi H. , Ikoma T.
Published: July 2002

Photoelectric fatigue and spike photoconductivity (SPC) are systematically studied in twenty-three pieces of undoped semi-insulating liquid-encapsulated Czochralski GaAs crystal (six ingots, four suppliers). Distributions among samples for photosensitivity, SPC-decay time constant, SPC spectrum, and oscillatory behavior are discussed. Through these studies, the metastable state X* (some kind of excited state of the main deep center X present in GaAs) is found to be classified into two states X*a and X*f , according to whether the electronic transition X*→X due to irradiation with the photon energy near 0.80 eV is allowed or forbidden, respectively. State X*a is responsible for the SPC phenomenon, while both states X*a and X*f are responsible for photoelectric fatigue. Moreover, the concentration of state X*a is estimated to be about 10−3 times that of state X*. These results suggest that there exist various configurations of metastable states.
Photocapacitance characteristics of amorphous-silicon Schottky diode sensor arrays and their changes due to the Staebler–Wronski effect
Authors: Hanrieder Wolfgang , Mader Gerhard , Meixner Hans
Published: July 2002

The capacitance measurements on a-Si:H Schottky diodes reported in the literature refer to large-area (some 10-mm2) specimens and were carried out in the dark at frequencies typically around 10 Hz. The main interest in these publications is the determination of the density of states in the band gap. For linear photodetector array applications, however, interest centers around the voltage and frequency characteristics of the capacitance of small-area back-to-back Schottky diodes under illumination and at frequencies typically around 1 kHz. But photoinduced changes in the capacitance are also of significance with a view to possible read-out circuits and their long-term stability. The capacitance was therefore measured over the frequency range 0.2–20 kHz and over the voltage range −5 to +5 V. Whereas the dark capacitance exhibited no changes due to photoinduced degradation, significant differences between degraded and nondegraded states were observed in the voltage and frequency characteristics of the photocapacitance. During degradation under high bias voltage (−5 V), the maximum of the capacitance shifted from −0.1 to +0.4 V indium tin oxide bias voltage and the capacitance showed a distinct increase. The photoinduced changes observed for the photocapacitance characteristics could be minimized by ensuring that the elements adjacent to the sensor were at equipotential with the sensor. Full reversibility of the photoinduced changes due to thermal annealing could be verified. The changes of the C-V and C-ω characteristics can be explained by the occurence of the well-known Staebler–Wronski effect.
Distribution of the electrostatic potential barrier in the n-p, amorphous-crystalline silicon heterojunction
Authors: Rubinelli F. A. , Battioni M. R. , Buitrago R. H.
Published: July 2002

The built-in potential, the distribution of the potential barrier between both semiconductors, the depletion widths, and the electric field at the interface have been evaluated in an n-amorphous/p-crystalline silicon heterojunction. V-shaped and U-shaped distributions have been adopted to approximate the density of states in the gap of amorphous silicon. Flat Fermi levels were assumed across both depletion regions. The results were compared to those of crystalline silicon homojunctions with identical doping levels.
Periodic Si-CoSi2 eutectic structures
Authors: Ditchek Brian M.
Published: July 2002

Submicron periodicity Si-CoSi2 structures were fabricated by the directional solidification of eutectic thin films. The films, grown on oxidized Si wafers by laser recrystallization, were prepared without the ablation and cracking previously encountered. Using growth rates of up to 17 cm/s yielded lamellar periods as small as 60 nm. Defects in the lamellar structure were investigated as a function of growth rate, the shape of the solid–liquid interface, and thermal aging.
Interfacial interactions between (HgCd)Te and Ti, an ultrareactive metal
Authors: Davis G. D. , Beck W. A. , Mo Y. W. , Kilday D. , Margaritondo G.
Published: July 2002

The interfacial interactions between (HgCd)Te and Ti, an ultrareactive metal, have been examined using photoelectron spectroscopy with synchrotron radiation. Deposition of small quantities of Ti, which form tellurides that are thermodynamically more stable than HgTe or CdTe, causes a loss of both Hg and Cd from the interface. The rate of Hg depletion is greater than that of Cd and is greater than the rate of Hg depletion yet observed for any other overlayer metal. This greater Hg loss is attributed to the increased disruption of the semiconductor surface region caused by the loss of Cd. Unlike the cases of Al and In, but similar to that of Cr, no additional band bending is observing during the early stages of metal deposition.
Influence of metal-insulator junction on surface flashover in vacuum
Authors: Pillai A. Sivathanu , Hackam Reuben
Published: July 2002

The influence of the metal-dielectric junction on the electric field distribution along the solid insulator-vacuum interface is analyzed in detail in two widely used electrode-insulator geometries: (1) a cylindrical solid insulator with metal inserts at both ends and (2) a cylindrical solid insulator placed in recessed electrodes at both ends. The effects of the length of the metal inserts and the angle ψ between the solid insulator and the recessed electrode on the electric field and the flashover voltage have been theoretically investigated and experimentally validated. The permittivity of the solid insulator materials used is varied from 2.1 to 100. The surface flashover voltages of Macor glass ceramic and Teflon are measured in vacuum (<10−8 Torr) in different electrode-insulator contact geometries using dc, ac (60 Hz), and 1.2/50-μs lightning impulse. The measurements show good qualitative agreement with the behavior predicted from the computation.
Silicided shallow junction formation by ion implantation of impurity ions into silicide layers and subsequent drive-in
Authors: Kwong D. L. , Ku Y. H. , Lee S. K. , Louis E. , Alvi N. S. , Chu P.
Published: July 2002

We have developed a technique for the fabrication of shallow, silicided n+−p and p+−n junctions with good electrical characteristics. The technique utilizes the ion implantation of dopants into silicide layers previously formed by ion-beam mixing with Si ions and low-temperature annealing, and the subsequent drive-in of implanted dopants into the Si substrate to form shallow junctions. This technique can be applied to the fabrication of metal-oxide-semiconductor field-effect transistor in a self-aligned fashion and can have a significant impact on complementary metal-oxide-semiconductor devices.
The influence of HCl on the oxidation-enhanced diffusion of boron and arsenic in silicon
Authors: Subrahmanyan Ravi , Massoud Hisham Z. , Fair Richard B.
Published: July 2002

The influence of HCl on the oxidation-enhanced diffusion of boron and arsenic in silicon has been studied. Experimental data at 1000, 1100, and 1150 °C were obtained using secondary ion mass spectrometry (SIMS). A previously proposed empirical model was used in analyzing the impurity profiles, and the parameters of this model were determined by matching the computer simulations of dopant diffusion with the SIMS profiles. The dependence of the model parameters on temperature and HCl concentration is discussed.
Microphone detection of the predissociation of iodine in a supersonic beam
Authors: McMillan K. , Bevan J. W. , Fry E. S.
Published: July 2002

Use of a condenser microphone as a detector in laser–molecular beam studies of excited state molecular dynamics is demonstrated through the observation of predissociation in iodine seeded in a supersonic helium beam. Resultant beam loss with the absorption of cw dye laser radiation in individual rotational lines of the 127I2B 3Π+0u−X 1Σ+g (25,0) transition is measured by the on-axis microphone and shows partially resolved hyperfine structure.
Role of oxygen in defect-related breakdown in thin SiO2 films on Si (100)
Authors: Hofmann K. , Rubloff G. W. , Young D. R.
Published: July 2002

The influence of annealing in vacuum and in controlled low-pressure oxygen ambient on breakdown characteristics of thin (∼500 Å) SiO2 films on Si (100) has been studied under ultrahigh vacuum conditions for temperatures 750–900 °C and controlled O2 partial pressures in the range 10−6–5×10−2 Torr. Dark current-voltage measurements on Al-gate capacitors show that vacuum annealing causes low-field self-healing breakdown by the formation of local defects in the oxide. This degradation of breakdown characteristics is suppressed by the presence of sufficient O2 in the annealing ambient, such that the O2 partial pressure must exceed the SiO equilibrium partial pressure by a factor of ∼100×. This behavior suggests that low-field breakdown is a consequence of oxide decomposition (Si+SiO2→2SiO↑) at defects in the oxide, which is suppressed by reoxidation of the volatile SiO reaction product.
Magnetism and the observation of NMR lines in hexagonal Al4Mn and icosahedral Al-Mn alloys
Authors: Bennett L. H. , Rubinstein M. , Xiao Gang , Chien C. L.
Published: July 2002

Previous measurements of the magnetic susceptibility and the intensity of the 55Mn NMR line in a number of periodic and quasiperiodic (i.e., icosahedral) Al-Mn and Al-Mn-Si alloys suggested some correlation, in that the 55Mn line intensity decreases as the magnetic susceptibility increases. This correlation had led to the tentative conclusion that the reduction of the 55Mn line intensity is due to the magnetism, and that the ‘‘magnetic’’ Mn atoms are not seen in the NMR. We have found that the above correlation breaks down in a very substantial way for hexagonal Al4Mn which (i) shows a small magnetic susceptibility, and (ii) no observable 55Mn line. Thus the reduction in intensity in the 55Mn NMR line in the icosahedral phase is not necessarily due to its magnetism but may have its origin in another line broadening mechanism.
Critical behavior of amorphous (Fe1−xMx)90Zr10 alloys with M=Co, Ni, and 0<x<0.04
Authors: Winschuh K. , Rosenberg M.
Published: July 2002

From the critical behavior of the magnetic inhomogeneous (Fe1−xMx)90Zr10 amorphous alloys, where M=Co and Ni, the critical exponents α, β, γ, and δ are derived. Their values are rather large, strongly deviating from the theoretical ones in the case of an ordered 3D-Heisenberg spin system. This behavior is probably due to the magnetically inhomogeneous character of these alloys, as evidenced especially in previous Mössbauer and magnetic studies.
Magnetic properties of Fe/Nd multilayer films
Authors: Sellmyer D. J. , Zhao Z. R. , Shan Z. S. , Nafis S.
Published: July 2002

Measurements are reported on the relationship between magnetic properties and microstructure in thin amorphous and crystalline Fe/Nd multilayer films. The samples, denoted by (XÅFe/YÅNd)≡(X/Y), were prepared in a multiple-gun sputtering chamber with a microprocessor-controlled rotating table. For X and Y values less than about 20 Å an amorphous compositionally modulated structure is obtained, with magnetic properties characterized by speromagnetic ordering associated with strong Nd random anisotropy. The net magnetization in general lies in the plane of the film. The temperature and composition dependence of the coercivity, magnetization, and transition temperatures are discussed.
Magnetism in icosahedral structures (invited)
Authors: McHenry M. E. , O’Handley R. C. , Dmowski W. , Egami T.
Published: July 2002

We examine the consequences for magnetism of icosahedral site symmetry and of long-range icosahedral ordering as found in quasicrystals. Enhanced magnetic moments and Curie temperatures can result from icosahedral site symmetry. Exceptionally low magnetic anisotropy, unusual domain walls, and extremely soft magnetic behavior are predicted for long-range icosahedrally ordered magnets. Preliminary magnetic data on rapidly solidified, metastable icosahedral magnetic phases based on Co-Er(-Si) and Co-Nb(-B) are reviewed and discussed in terms of their chemical short-range order.
Spin waves in the uniaxial spin glass system Fe1−xMgxCl2
Authors: Wong Po-zen , Yoshizawa H. , Shapiro S. M.
Published: July 2002

We report an inelastic neutron scattering study of the uniaxial dilute antiferromagnets Fe1−xMgxCl2, for x=0.3, 0.45, and 0.6. The first two samples have long-range antiferromagnetic (AF) order. Their spin-wave peaks are broadened by the exchange fluctuations. The x=0.6 sample orders like an Ising spin glass with a very short AF correlation length (ξ≊10 Å). For wavelength λ≲ξ, spin wave peaks are similar to the dilute antiferromagnets, but for λ≳2ξ, the peak sharpens up and becomes resolution limited at the zone center. We give a simple explanation for this behavior.
Nonintegrability and quantum spin chains
Authors: Müller G. , Bonner J. C. , Parkinson J. B.
Published: July 2002

This study concerns the concept of nonintegrability in quantum many-body systems, which is related to the important and unresolved problem of quantum chaos. Our findings strongly indicate that nonintegrability affects the reliability of many approximation techniques which have proved to be successful in the study of integrable models. This report is based on finite-size studies of the low-lying spectral excitations of both integrable and nonintegrable 1D quantum spin models. In integrable cases, the characteristic excitation pattern of the infinite system is apparent even in relatively short chains. This is generally not the case in nonintegrable systems where we observe several classes of excitations with qualitatively different character. In some situations, the nature of the lowest-lying excitations actually changes with increasing system size, which makes finite-size studies very vulnerable to misleading conclusions if care is not taken.
Influence of linear and nonlinear excitations in the ferromagnetic S=1/2 chain system [C6H11NH3]CuBr3 (CHAB)
Authors: Kopinga K. , de Gronckel H. A. M. , de Vries G. C. , Frikkee E. , Kakurai K. , Steiner M.
Published: July 2002

The magnetic properties of the title compound have been studied by measurements of the nuclear spin-lattice relaxation time T1, the uniform magnetization M, and by quasielastic and inelastic neutron scattering. The field and temperature dependence of T1 and the wave-number dependence of the magnon excitation energy can be satisfactorily described by linear spin-wave theory. A good description of M, however, requires a contribution from kink solitons. The available evidence suggests that, in contrast to the linear excitations, the nonlinear excitations in CHAB for B∥c can be described very well by a classical model, which is consistent with the interpretation of earlier heat-capacity measurements.
Study of SmTM7.3 microstructure by a simplified method and its correlation to properties
Authors: Tsai D. S. , Ho K. S. , Chin T. S. , Chang Y. H. , Tsai W. T.
Published: July 2002

By using a newly developed potentiostatic etching technique, the microstructural evolution of an SmTM7.3 (TM=Co/Fe/Cu/Zr) alloy during different stages of heat treatment has been easily and successfully observed under a conventional scanning electron microscope (SEM). Specimens up to several centimeters were examined, with their features being statistically measured. It is found that the cell structure has been well developed with a median size of 110 nm after aging 2 h at 1123 K, while the intrinsic coercivity (iHc) was as low as 2 kOe. The cell size grows slowly during subsequent heat treatment to a median size of 220 nm after the whole treatment. For aging at 1123 K for 4 h, iHc value is around 4 kOe, and the platelet phase appears. After aging at 1123 K for 8 h, a large zonal phase and grain boundary phase are visible. It is thus believed that the zonal phase appears after aging for a time period between 4 and 8 h, corresponding to the iHc of 600 kA/m (7.5 kOe). No new microconstituent appears after the isothermal aging for more than 8 h, however growth proceeds. After the whole heat treatment cycle, iHc is much greater than 2400 kA/m (30 kOe), with the zonal phase ranging in size from 300 to 900 nm (in width, averaged 400 nm), 1 to 5 μm in length (averaged 3.6 μm), and 1 to 6 μm in separation (averaged 3.5 μm). The zonal and the grain boundary phases are thus concluded to be the dominating structure for the extremely high coercivity of this alloy. A model is proposed to explain the etching sequence of the microconstituents during the potentiostatic etching, and is successful to explain the resultant microstructure.
Correlation of electrical transport and magnetism in amorphous Mn-B alloys
Authors: Bryden W. A. , Morgan J. S. , Kistenmacher T. J. , Moorjani K.
Published: July 2002

X-ray scattering, magnetism, and electrical transport studies on amorphous thin films of MnxB100−x alloys with x=52 and 48 are reported. Each alloy exhibits a low-field (5 G) static susceptibility peak (10 K, x=52; 16 K, x=48) associated with a spin-glass transition. Isothermal magnetization data (6 K) are analyzed within the random anisotropy model of Chudnovsky, Saslow, and Serota. The magnetization isotherm for the x=52 alloy is dominated at high fields (>24 kG) by field-induced moments, while for x=48 a term (αH−1/2) arising from a ferromagnet with a wandering axis prevails to the highest field strength (44 kG). Initially the electrical resistance for these Mn-B alloys decreases monotonically with decreasing temperature, reaching a minimum (Tm) at 22 K (x=52) and 45 K (x=48). For T>Tm, a quadratic form can be effectively employed, with a negative T2 coefficient and a positive linear coefficient. The rise in resistivity for T<Tm conforms to a −(T)1/2 law and is interpreted in terms of a disorder-induced localization transition in a correlated electron gas. Both alloys display only weakly field-dependent (to 10 kG) magnetoresistance.
Magnetic transitions and scaling in anisotropic rare-earth glasses
Authors: Lee K. M. , O’Shea M. J. , Sellmyer D. J.
Published: July 2002

We report studies of the magnetic critical behavior as a function of anisotropy strength in rare-earth-rich glasses. Anisotropy is induced in Gd-Co by alloying with Tb. The system studied is Gd65−xTbxCo35 and the random magnetic anisotropy (RMA) strength may be increased by increasing x. The x=0 alloy of this series has been shown to exhibit standard critical behavior expected for a second-order phase transition. With increasing x we find deviations from this behavior due to the presence of RMA. We present detailed results for the alloy with composition x=50 at. % and show that for large enough magnetic fields the system continues to show standard ferromagnetic scaling but for low enough fields the system crosses over to a behavior describable by nonlinear scaling similar to that found in spin-glass systems.
Coercivity and its role in thermomagnetic recording
Authors: Mansuripur M.
Published: July 2002

A model is proposed for the mechanism of magnetization reversal in thin films of amorphous rare-earth–transition-metal alloys. The model exhibits the observed features of the magnetization reversal process, coercivity and the processes of thermomagnetic recording and erasure.
Isotope separation during diffusion along an edge dislocation in a simple cubic crystal
Authors: Clark Gary , Stark J. P.
Published: July 2002

During diffusion in crystalline lattices, isotope separation is well known to be proportional to the correlation factor. In a recently published analysis of vacancy-based transport along an edge dislocation in a simple cubic system, the expression for the diffusion coefficient takes on a much more complicated form than is found in the lattice, and it is uncertain whether the isotope separation factor is indeed proportional to the correlation factor. This effect is studied analytically and numerically, and shown to equal the correlation factor for diffusion along the dislocation. In addition, the isotope separation factor for electromigration is also determined to be proportional to the correlation factor for diffusion.
Correlation between dislocation effects on carrier concentration and growth conditions for molecular-beam epitaxially grown GaAs
Authors: Shinohara Masanori
Published: July 2002

The correlation between dislocation effects on carrier concentration and such growth conditions as growth temperature and As4/Ga flux ratio is investigated for Si-implanted and Si-doped molecular-beam epitaxially grown GaAs. Small Hall devices with a 40×40-μm2 measurement area are used to determine the carrier concentration. Then, the relationship between the carrier concentration and the dislocations surrounding these devices is studied. It is found that an increase in carrier concentration due to the dislocations appears in the Si-implanted epilayer grown at low temperatures and at low As4/Ga flux ratios. On the other hand, it is not affected by the dislocations in the Si-doped epilayers. Furthermore, all epilayers, which have observable dislocation effects, include the 0.8-eV photoluminescence deep level. Finally, the reason for the carrier-concentration increase is proposed.
Microstructural characterization of nitrogen-implanted silicon-on-insulator
Authors: Chang P.-H. , Slawinski C. , Mao B.-Y. , Lam H. W.
Published: July 2002

The effects of implant dose and postimplant annealing treatment on the microstructure of nitrogen-implanted silicon-on-insulator were studied by cross-sectional transmission electron microscopy techniques. In the lower dose case (0.75×1018/cm2) an amorphous silicon layer forms after implantation. Annealing at 1200 °C or higher results in a buried polycrystalline α-Si3N4 layer containing many randomly oriented silicon particles. Higher dose implantation results in an amorphous silicon-nitride layer. A porous layer also forms in the middle of the amorphous layer if the implant dose is 1.2×1018/cm2 or higher. The crystallization of the amorphous layer in the higher dose cases is shown to happen in two steps. In the first step nucleation and growth of α-Si3N4 grains occur in the amorphous nitride region to form a spherulitic polycrystalline structure. The second step is the cellular growth of the spherulitic nitride grains into the crystalline silicon regions. Silicon particles are trapped at the cell walls as the cellular reaction advances. These particles are conglomerated and sphereodized but retain the same orientation as the substrate silicon at higher temperatures. The quality of the top silicon film is excellent after annealing at 1200 °C or higher, irrespective of the implant dose.
Magnetic birefringence of a ferromagnetic linear chain CuCl2⋅TMSO
Authors: Lamas A. C. , Landee C. P.
Published: July 2002

Copper chloride monoTMSO has previously been shown to be an example of a spin-1/2 linear chain with Heisenberg ferromagnetic exchange (J/k≊39 K). Motivated by the proportionality between the temperature derivative of the linear magnetic birefringence (TDLMB) and the magnetic specific heat, we have determined the birefringence of the title compound along the 010 and 100 faces between 3.1 and 260 K. The data along the 010 face show no evidence of magnetic behavior. They could be fit to a Debye function with a θD of 123 K. Along the 100 face, a sharp spike was seen at 3.42 K, indicating the transition to long-range magnetic order. The data for the 100 face could not be fit to a Debye function alone but were successfully modeled as a sum of a lattice contribution (θD ≊244 K) and a ferromagnetic contribution with an exchange constant J/k between 30 and 60 K. The data was insensitive to the magnitude of J.
Magnetostriction of the rapidly quenched Co80Nb8B12 alloy: Dependence on quenching rate, structural relaxation, and temperature
Authors: Madurga V. , Barandiarán J. M. , Vázquez M. , Nielsen O. V. , Hernando A.
Published: July 2002

Ribbons of nominal composition Co80Nb8B12 have been prepared by the single roller quenching method using different wheel velocities ranging from 26 to 42 ms−1. X-ray diffraction patterns for ribbons prepared at low velocities show crystalline peaks but characteristic for the amorphous state for samples prepared at velocities above 36 ms−1. Room-temperature values of the magnetostriction constant λs depend on the quenching rate and changes from 4×10−7 to −1×10−6 as the wheel speed increases. Zero magnetostriction samples are obtained at about 34 ms−1. Thermal treatments change the values of the magnetostriction in the same way as a decrease in the quenching rate does. A dependence of the magnetostriction constant on the applied stress has been found. This dependence, fully reversible, is observed at room temperature.
Electron-density distribution in a laser tube with a hyperboloid of revolution boundary
Authors: Kanoussis Demetrios P. , Demas Nicholas G. , Ventrice Carl A.
Published: July 2002

The electron-density distribution is determined in a laser tube that is formed by a hyperboloid of revolution and spherical end surfaces. Calculations are made assuming different symmetrical optical resonator configurations ranging from near-planar to near-confocal. The tube geometry is specified in terms of the optical resonator parameters: resonator length L, mirror radius of curvature, R, and optical spot size at the mirror surface. The active medium is assumed to be a low-temperature, weakly ionized plasma. Schottky boundary conditions are assumed and the electron temperature is taken to be independent of position. The particle-diffusion equation is solved using oblate spheroidal coordinates. The oblate spheroidal angular dependence (which in the cylindrical limit corresponds to the variation perpendicular to the axis of the cylinder) of the density is found to be that of a zero-order Bessel function. The oblate spheroidal radial dependence (which in the cylindrical limit corresponds to the axial dependence) is obtained by means of numerical methods. Radial density profiles are calculated, assuming L=1.0 m, for various R/L ratios. The position Zp of the peak radial density is found to depend on the R/L ratio; as R/L decreases Zp is observed to move towards the end walls of the tube.
Fe reactions with β-SiC
Authors: Geib K. M. , Wilmsen C. W. , Mahan J. E. , Bost M. C.
Published: July 2002

The reaction between β-SiC and a layer of sputter deposited Fe has been investigated by Auger profiling. The samples were vacuum annealed in the analysis chamber up to 800 °C. After a 610 °C anneal an interfacial layer of iron carbide appeared, probably the result of a reaction between the Fe and an adsorbed layer of hydrocarbons. This interfacial layer appears to prevent a reaction with the substrate until the temperature is raised to 800 °C. At this temperature a rapid and violent reaction occurs.
Phase transitions in Heisenberg antiferromagnets on triangular and layered-triangular lattices (invited)
Authors: Kawamura H.
Published: July 2002

Recent results on phase transitions of classical Heisenberg antiferromagnets on the (d=2)-dimensional triangular and the (d=3)-dimensional layered-triangular lattices are summarized. In the ground states, the spins are ordered into a ‘‘120° structure’’ in which the frustration is partially resolved by mutual spin canting. A symmetry argument shows that the order-parameter space associated with the ground state has a quite different topology from those of corresponding nonfrustrated systems being isomorphic to the three-dimensional rotational group SO(3) or the projective space P3. Homotopy analysis establishes that the system sustains a topologically stable vortex characterized by a two-valued topological quantum number: a Z2 vortex. A Monte Carlo study of the d=2 model suggests the occurrence of a novel type of topological phase transition driven by the dissociation of the Z2 vortices. For the corresponding d=3 model Monte Carlo indicates the occurrence of a single continuous transition; by use of finite-size scaling theory, the exponents are estimated to be α≂0.4, β≂0.25, γ≂1.1, and ν≂0.53. These values differ considerably from those for the standard nonfrustrated systems, strongly suggesting a phase transition belonging to a new universality class. Corresponding renormalization-group ε expansions have been carried out to O(ε2). In leading orders a frustration-dominated fixed point exists only for n-component spins with n>3 but for finite ε the corresponding fixed point might continue down to n=3 and ε=1. Several other systems exhibiting an SO(3)-like symmetry, including the superfluid A phase of helium 3 and certain helical or canted magnets, should belong to the same universality class. Possible consequences for experiments are discussed.
Low-pressure etching of GaAs with multipolar plasma confinement
Authors: Mantei T. D. , Jbara J. J.
Published: July 2002

Anisotropic etching of GaAs with 100–400 eV ion radiation energies is reported in a low-pressure, magnetically confined multipolar plasma. Etch rates ∼0.5 μm/min and excellent surface texture are obtained in SiCl4, CFCl3, and CF2Cl2 at pressures of 0.5–2.0 mTorr. Schottky barrier measurements show low substrate damage for ion energies ≤200 eV, increasing sharply for higher energies. Survey spectra using x-ray photoelectron spectroscopy show that chlorine surface contamination also increases with ion radiation energy.
Ceramic coatings produced by means of a gas tunnel-type plasma jet
Authors: Arata Yoshiaki , Kobayashi Akira , Habara Yasuhiro
Published: July 2002

A gas tunnel-type plasma jet has a higher temperature than any other plasma jets; a high-power stabilized plasma beam can be easily obtained. Moreover, it is possible to inject various materials from the center electrode toward the center of this plasma beam. These properties of the gas tunnel-type plasma jet apparatus are of great advantage to the application to the thermal spraying of high melting point materials such as ceramics. The fundamental characteristics of this new type of plasma spraying apparatus were determined through experimentation, and a variety of ceramic coatings produced using this apparatus were studied. Since this system is very effective in heating and melting sprayed powder, high-quality ceramic coatings can be easily produced even at a small power using argon as the working gas. At 30 kW or more, the Vickers hardness of the various ceramic coatings is 30% greater than that produced with a conventional-type plasma spraying apparatus. For example, a Vickers hardness value of 1200 has been achieved for Al2O3 coatings.
Metalorganic growth of HgTe and CdTe at low temperatures using diallyltelluride
Authors: Korenstein R. , Hoke W. E. , Lemonias P. J. , Higa K. T. , Harris D. C.
Published: July 2002

Both HgTe and CdTe films have been grown by metalorganic chemical vapor deposition using a novel tellurium source, diallyltelluride. This compound is found to be less stable than previously examined organotellurium compounds and permits film growth at lower substrate temperatures. This reduced stability is consistent with the presence of double bonds in diallyltelluride compared to single bonds present in alkyl tellurides. Specular HgTe films have been grown at temperatures as low as 180 °C and x-ray analysis indicates that this material is of good crystalline quality.
Impedance characteristics of an rf parallel plate discharge and the validity of a simple circuit model
Authors: Bletzinger P. , Flemming Mark J.
Published: July 2002

Measurements of the electrical characteristics of a parallel plate rf discharge at pressures from 0.1 to 10 Torr in argon and at frequencies from 7.1 to 20 MHz are reported. The discharge impedance reaches a minimum for all frequencies at a pressure of about 1 Torr and the impedance decreases with increasing frequencies. The phase variation over the pressure range is as high as 40°. With added attaching gas, the impedance increases and the minimum occurs at lower pressures. A simple equivalent circuit with a capacitance representing the electrode sheaths can model the measured impedance behavior at pressures up to 1 Torr when the capacitance is made proportional to pressure, analogous to the sheath characteristics. At higher pressures, a good fit can be achieved by making the resistance, which represents the power losses in the discharge volume, a function of pressure. Derived sheath dimensions correlate with observed variations versus pressure and frequency. The fact that at the lower pressures the resistive part of the impedance is independent of pressure and that the resistance no longer properly represents the voltage drop across the discharge volume indicates that collisional losses in the volume no longer dominate the power deposition. The ‘‘wave-riding’’ mechanism is suggested as the dominant process in this pressure range. Its frequency characteristic correlates well with the frequency characteristic of the measured impedance.
Simultaneous formation of TiN and TiSi2 by lamp annealing in NH3 ambient and its application to diffusion barriers
Authors: Okamoto Tatsuo , Shimizu Masahiro , Ohsaki Akihiko , Mashiko Youji , Tsukamoto Katsuhiro , Matsukawa Takayuki , Nagao Shigeo
Published: July 2002

The dependence of TiN/TiSi2 bilayer formation on Si by lamp annealing of Ti upon annealing temperature, ambients, and impurity in Si was investigated. In NH3 ambient, nitridation ratio on undoped Si at 680 and 800 °C is 40% and 25%, respectively. When annealing is performed in N2, the nitridation ratio of Ti is only about 25% at both 680 and 800 °C. The above dependence of nitridation ratio on annealing ambient is due to the difference in decomposition energy of gas molecules. The nitridation ratio increases on arsenic-implanted Si because of a retardation effect of the arsenic on the silicidation reaction. The bilayer formation process was applied to the AlSi contact metallization on the n+ diffused layer. From measurements on electrical characteristics of the AlSi/TiN/TiSi2/n+ Si contact system, the following results were obtained: (1) Contact resisitivity is 3.5–5.3×10−7 Ω cm2. (2) The TiN/TiSi2 contact electrode is thermally stable against Al. In particular, when the bilayer is formed in NH3 at comparatively lower temperature, its thermal stability is still further improved. This is due to the formation of the thicker surface TiN layer.
Noncontact doping level determination in GaAs using photoreflectance spectroscopy
Authors: Peters L. , Phaneuf L. , Kapitan L. W. , Theis W. M.
Published: July 2002

Shifts of the band edge in GaAs layers as measured by photoreflectance (PR) spectroscopy have been accurately calibrated to the N-type doping level (Nd). Samples produced by controlled Si-doping experiments using ion implantation of GaAs substrates and GaAs doped with Si to known levels during growth by molecular-beam expitaxy have been investigated with this technique. A measurable change in the location of the band gap (E) determined from PR directly correlates with the maximum N-type doping level as determined via C-V for both types of samples with a change of band gap δE/δNd=5.8±0.5×10−20 eV cm3 for 1×1016 cm−3 ≤Nd≤8×1017 cm−3. Correlations were also made to sheet carrier concentration (Hall measurements). This method is shown to be fast, accurate, and easily applicable to uniformity studies and a viable alternative to either C-V or Hall measurements for nondestructive determination of Nd.
Anomalous threshold current and time delays in index-guided AlxGa1−xAs-GaAs quantum-well lasers
Authors: Jackson G. S. , Hall D. C. , Holonyak N. , Hsieh K. C. , Epler J. E. , Paoli T. L.
Published: July 2002

Anomalous threshold current (Ith) variation with temperature and with pulse length, and large delays (up to 6 μs) between excitation and the turn-on of stimulated emission are observed in index-guided AlxGa1−xAs-GaAs quantum-well heterostructure (QWH) lasers. These effects are found in laser diodes incorporating ‘‘spike’’ doping layers (δ-Mg and δ-Se) within the QWH active region and that are fabricated via laser-assisted Si impurity-induced layer disordering. The introduction of contaminants during the localized melting and regrowth of the laser-induced layer disordering, and the effect of these impurities (or defects) with the active region ‘‘spike’’ doping create traps. The traps cause Ith to increase (not decrease) at lower temperature and at shorter current pulses, and cause time delay in turn-on of the operation.
Envelope function description of double-heterojunction quantum wells
Authors: Anwar A. F. M. , Khondker A. N.
Published: July 2002

An envelope function model is used to investigate properties of the two-dimensional electron gas (2DEG) confined in a double-heterojunction quantum well formed by the AlGaAs/InGaAs/GaAs system. This type of well has been used in the pseudomorphic modulation-doped field-effect transistor (MODFET). The position of the Fermi level and the average distance of the carriers in the well have been calculated as a function of the 2DEG concentration ns. Results presented in this paper may be used to model the I-V and C-V characteristics of pseudomorphic MODFETs. Furthermore, these results confirm a better containment property of carriers in this type of well compared to that formed at the AlGaAs/GaAs system.
Two-dimensional spatially selective spin inversion and spin-echo refocusing with a single nuclear magnetic resonance pulse
Authors: Bottomley Paul A. , Hardy Christopher J.
Published: July 2002

A new class of nuclear magnetic resonance (NMR) pulses that provides simultaneous spatially selective inversion of nuclear spins in two dimensions following a single pulse application is described and demonstrated. The two-dimensional selective pulses consist of a single square- or amplitude-modulated π rf pulse applied in the presence of an amplitude-modulated magnetic field gradient that reorients through the two dimensions during the rf pulse. For example, square and Gaussian rf pulses produce sharply peaked sombrero-, egg-carton-, and stalagmite-shaped profiles of spin inversion in the xz plane when applied in the presence of a gradient that rotates or describes a figure eight in the xz plane. The theoretical profiles, computed by numerical integration of the Bloch equation, are in good agreement with experimental results obtained by incorporating the pulses into a conventional NMR imaging sequence. The pulses are directly applicable to restricted field-of-view high-resolution imaging for the amelioration of aliasing signal artifacts, and when combined with one-dimensional localized phosphorus (31P) chemical shift spectroscopy techniques that employ surface detection coils, should permit complete three-dimensionally localized 31P NMR spectroscopy. The π pulses provide similar two-dimensional spatial selectivity of the transverse nuclear magnetization when used for refocusing Hahn spin echoes.
A perturbation calculation of the quality factor of the piezoelectric thin film on semiconductor composite resonator resulting from radiation into the wafer
Authors: Shick D. V. , Tiersten H. F.
Published: July 2002

In a variational analysis of the vibrations of the piezoelectric thin film on semiconductor composite resonator it was shown that the quality factor (Q) due to radiation into the semiconductor wafer is a sharply varying function of the ratio of the thickness of the resonator to that of the film if trapping is not present, but not if trapping is present. The treatment is very cumbersome to use and is restricted to the case of strip electrodes and diaphragms. In this work a perturbation procedure for the calculation of the Q due to radiation into the wafer is presented, which is considerably less cumbersome to use than the earlier treatment and is not restricted to the case of strip electrodes and diaphragms. The resonant mode of interest is determined from an equation for transversely varying thickness modes in composite resonators and simple approximate but accurate conditions at the edges of the diaphragm, from which the radiation into the wafer is obtained using a variational approximation procedure. The resonant mode and resulting radiation field are employed in a perturbation integral to calculate the Q. For the case of strip electrodes and diaphragms the calculated results are shown to be in good agreement with the earlier more cumbersome calculations. In addition the perturbation calculations are performed for the case of rectangular electrodes and diaphragms.