bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier injection in semiconductors with position-dependent band structure: Electron-beam-induced current at heterojunctions
Authors: Munnix S. , Bimberg D.
Published: July 2002

We present simulations of external carrier injection in semiconductors with position-dependent band structure by numerical solution of the current transport equations across the device. As a model case, we examine electron-beam-induced current at heterojunctions. Our treatment is applicable to an arbitrary position-dependent band structure, and any form of external generation, and allows for an external bias applied to the device. The quality of ohmic contacts is taken account of by realistic boundary conditions. For excitation by an electron beam at a GaAs/AlGaAs n-N isotype heterojunction, we present band profiles, as well as linescans, of electron-beam-induced current and voltage. The influence of external generation rate, interface grading, and contact quality is investigated. The latter is shown to be important in epitaxial layers which are only a few minority-carrier diffusion lengths thick. The saturation behavior of the signal with increasing injection level is studied as a function of device parameters, and the applicability of such measurements to the determination of band offsets is critically discussed.
An optimal endoreversible three-heat-source refrigerator
Authors: Yan Z. , Chen J.
Published: July 2002

An endoreversible three-heat-source refrigerator only affected by thermal resistance, like a reversible three-heat-source refrigerator, may be treated as a combined cycle of a two-heat-source engine driving a two-heat-source refrigerator. The theory of finite time thermodynamics in two-heat-source cycles is then used to analyze it and derive its basic optimum relation. Thus, the fundamental effect of thermal resistance on the optimal performance of a three-heat-source refrigerator is expounded. The conclusions obtained here are more realistic than those of classical thermodynamics. They provide some new theoretical bases for further exploitation of the three-heat-source refrigeration apparatus that applies to ‘‘cheap’’ heat sources, such as solar energy, geothermal energy, waste heat, and so on.
A real time ellipsometry study of the growth of amorphous silicon on transparent conducting oxides
Authors: Kumar Satyendra , Drevillon B.
Published: July 2002

I n situ fast kinetic ellipsometry is used to investigate the early stage of the growth of hydrogenated amorphous silicon (a-Si:H) on tin-doped indium oxide (ITO), tin oxide (TO), and zinc oxide substrates. Transparent conducting oxide (TCO) substrates obtained from various sources and deposited by different techniques are studied. A wide range of deposition parameters of a-Si:H films is considered. For a comparison with growth of amorphous silicon from silane, the ellipsometry data on pure hydrogen plasma degradation of TCO surfaces are also presented. In case of ITO and TO films, a two-step deposition is observed: the first step is dominated by the reduction of TCO and formation of metallic In or Sn (≊10 s time scale) and the second step is the subsequent growth of a-Si:H on the reduced substrates. In contrast, ZnO does not show any reduction. The substrate temperature during a-Si:H deposition is found to have the most important influence on the chemical reduction of the substrates. Variations of other deposition parameters like rf power, total gas pressure, ion bombardment, and p- or n-type doping do not lead to a reduction-free deposition on ITO and TO films. The substrate surface roughness plays an important role during the long-term growth of a-Si:H. In particular, a memory of surface roughness of the TCO substrates is retained in the growing a-Si:H films. The technological consequences of this study are outlined.
Near-band gap optical behavior of sputter deposited α- and α+β-ZrO2 films
Authors: Kwok Chee-Kin , Aita Carolyn Rubin
Published: July 2002

The functional dependence of the optical absorption coefficient on photon energy in the 4.9–6.5 eV range was determined for α- and α+β-ZrO2 films grown by reactive sputter deposition on fused silica. Two allowed direct interband transitions in α-ZrO2 were identified, with energies equal to 5.20 and 5.79 eV. Modification of these transitions in α+β-ZrO2 is reported.
Selected-area deposition of diamond films
Authors: Inoue Takayoshi , Tachibana Hiroyuki , Kumagai Kazuo , Miyata Koichi , Nishimura Kozo , Kobashi Koji , Nakaue Akimitsu
Published: July 2002

Selected-area deposition of diamond film has been accomplished on Si substrates prepared by two different methods: reactive-ion etching (RIE) and amorphous-Si masking (ASM). In the RIE method, a Si substrate polished by a diamond paste was patterned with a photoresist mask, and the unprotected areas were etched by RIE, followed by a complete removal of the photoresist films. The diamond deposition was done by electron-assisted chemical-vapor deposition (CVD), and diamond films grew only in the areas once covered with the photoresist films and not etched by RIE. In the ASM method, a polished Si substrate was also photolithographically masked with photoresist, followed by a uniform deposition of a hydrogenated amorphous silicon (a-Si:H) film. The photoresist film was then lifted off together with the overlay of deposited a-Si:H, leaving the polished Si surface patterned with an a-Si:H mask. In this case, the diamond deposition was done by microwave plasma CVD, and diamond films grew only in the areas not covered with a-Si:H. In both cases, well-defined diamond patterns with line/space dimensions of a few micrometers were formed on the substrates.
Acoustic quality factor of aluminum alloys from 50 mK to 300 K
Authors: Duffy William
Published: July 2002

Measurements of the acoustic quality factor (reciprocal internal friction) of commercial aluminum alloys 2090, 5056, and 6061 in a torsional vibrational mode at a frequency of 1 kHz in the temperature range from 50 mK to 300 K are reported. The temperature dependence of the mode frequency, which is a measure of the shear modulus of the material, is also given. The quality factor (Q) of all alloys exhibited the highest values at the lowest measurement temperature. A heat-treated sample of the 5056 alloy gave the highest Q of 6.5×107 at 53 mK. Maximum Q values of 8.9×106 in 2090 and 6.5×106 in 6061 were observed. Internal friction mechanisms which may explain the measured Q values are discussed. The results provide support for the planned construction and operation of very sensitive 50-mK aluminum-alloy bar gravity-wave detectors.
The thermal conductivity of isotopically enriched polycrystalline diamond films
Authors: Anthony T. R. , Fleischer J. L. , Olson J. R. , Cahill David G.
Published: July 2002

The thermal conductivity of a chemically vapor deposited (CVD) diamond film containing 0.07% 13C was measured as a function of temperature by ac and dc techniques and compared to CVD diamond with a natural isotopic abundance of 1.07% 13C. Unlike the single-crystal case where a large isotope enhancement effect has been reported, no increase in the thermal conductivity was observed in isotopically enriched CVD diamond films. The absence of an isotope effect in CVD diamond films indicates that a phonon scattering mechanism other than isotope scattering dominates in CVD diamond.
Ternary NiFeX as soft biasing film in a magnetoresistive sensor
Authors: Chen Mao-Min , Gharsallah Neila , Gorman Grace L. , Latimer Jacquie
Published: July 2002

The properties of NiFeX ternary films (X being Al, Au, Nb, Pd, Pt, Si, and Zr) have been studied for soft-film biasing of the magnetoresistive (MR) trilayer sensor. In general, the addition of the element X into the NiFe alloy film decreases the saturation magnetization Bs and magnetoresistance coefficient of the film, while increasing the film’s electrical resistivity ρ. One of the desirable properties of a soft film for biasing is high sheet resistance for minimum current flow. A figure of merit Bsρ that takes into account both the rate of increase in Bs and the rate of decrease in ρ when adding X element was derived to compare the effectiveness of various X elements in reducing the current shunting through the soft-film layer. Using this criterion, NiFeNb and NiFeZr emerge as good soft-film materials having a maximum sheet resistance relative to the MR layer. Other critical properties such as magnetoresistance coefficient, magnetostriction, coercivity, and anisotropy field were also examined and are discussed in this paper.
Measurement of Si atom density in radio-frequency silane plasma using ultraviolet absorption spectroscopy
Authors: Sakakibara Masafumi , Hiramatsu Mineo , Goto Toshio
Published: July 2002

The Si atom densities at two ground levels (3p23P2 and 3p21D2) were measured in the on-off modulated radio-frequency discharge silane plasma generated in a plasma-enhanced chemical vapor deposition chamber equipped with a parallel-plate electrode through absorption spectroscopy using an ultraviolet hollow cathode lamp, and were investigated as functions of the SiH4 concentration in SiH4/Ar, the input power, and the total pressure in detail. The Si atom density at the 3p21D2 level was measured first here and found to attain to the same order as that at the 3p23P2 level. The SiH4 concentration dependence of the Si atom densities at two ground levels was different from that at two excited levels (3p4s3P2 and 3p4s1P1). These results were used to discuss the generation and removal processes of the Si atom.
Energetics of self-diffusion in GaAs
Authors: Wager J. F.
Published: July 2002

Atomistic thermodynamic calculations are performed in order to examine the energetics of self-diffusion in GaAs. An energetic assessment of the activation enthalpy of the saddle-point configuration of various modes of vacancy self-diffusion indicates second-nearest-neighbor hopping to be the energetically most favorable mechanism if vacancies are available in equilibrium concentrations. An assessment of the activation entropy indicates that normal diffusion prefactors of magnitude D0≂10−5–10−1 s, cm2 s−1 are consistent with vacancy self-diffusion by second-nearest-neighbor hopping. It is proposed that self-diffusion experiments characterized by prefactors and activation energies of large magnitude, e.g., D0≂107–108 cm2 s−1 and Ea ≊ 6 eV, involve processes in which surface vacancy generation is inhibited and self-diffusion is mediated by Frenkel pair generation.
Artificial dielectric properties of microscopic metallized filaments in composites
Authors: Stockton W. , Lodge J. , Rachford F. , Orman M. , Falco F. , Schoen P.
Published: July 2002

Measurements have been made of the dielectric response of distributions of metallized fibers aligned in epoxy matrices for different loading fractions and fiber lengths. These have been shown to be in reasonable agreement with a simple independent particle theory. Use of the theory allows classification of fiber dielectric behavior by fiber conductivity and a characteristic length. Some aggregation of the fibers has been observed, even at relatively low loading densities. Computer simulation suggests enhanced dielectric constants of the composites for a moderate range of separations where the fibers are offset about 75% of their lengths with respect to each other and are closer than about 10 radii. This effect may be significant for aligned fibers which tend to aggregate in the magnetic field with separations and offsets within this range. The resulting composites are rugged and easily machined, and with less than 5% fiber weight loading have large, highly anisotropic dielectric constants of 60 or more at microwave frequencies in the X band. In conjunction with their (predicted) broadband performance characteristics such media should prove useful for a variety of applications.
Selective resputtering of bismuth in sputtered Bi-Sr-Ca-Cu-O films
Authors: Grace J. M. , McDonald D. B. , Reiten M. T. , Olson J. , Kampwirth R. T. , Gray K. E.
Published: July 2002

We present studies using a dc magnetron in an on-axis configuration to sputter Bi-Sr-Ca-Cu-O films from a composite target. These studies show that bismuth can be preferentially resputtered. The influence of ozone, molecular oxygen, and total pressure on the resputtering of bismuth is investigated and discussed. Ozone, in low concentrations, can dramatically affect the degree of resputtering. By comparing the effects of molecular oxygen and ozone, some insight is gained regarding the possible mechanisms of negative ion formation in the magnetron environment. Based on our results we suggest that molecular oxygen can bring about resputtering primarily by forming O+2, which collides with the target to produce energetic negative oxygen ions. In contrast, ozone may form negative ions by electron impact in the dark space above the target, giving rise to lower-energy negative ions, which can traverse the plasma unneutralized and can be stopped with an applied bias on the sample block. With no added oxidant, negative oxygen ions from the target oxygen may dominate the background resputtering. Similarity is found between our results and those for similar studies on Y-Ba-Cu-O by other workers. Bismuth in Bi-Sr-Ca-Cu-O behaves as barium in Y-Ba-Cu-O with regards to preferential resputtering; furthermore, the response of strontium, calcium, and copper to oxygen in sputtered Bi-Sr-Ca-Cu-O is similar to what is observed for copper in Y-Ba-Cu-O.
Interface microstructure of titanium thin-film/silicon single-crystal substrate correlated with electrical barrier heights
Authors: Ogawa Shin-ichi , Kouzaki Takashi , Yoshida Takehito , Sinclair Robert
Published: July 2002

The titanium (Ti)/single-crystal silicon (Si) interface has been examined by cross-section high-resolution transmission electron microscopy (HRTEM) combined for the first time with 2-nm-diam probe, energy-dispersive spectrometry. HRTEM shows that thin Ti-Si alloy formation always occurs at the interfaces, even in the as-deposited state. The thickness of the reacted alloy depends on the crystallinity of the Si surface, but does not depend on impurities or doping level. Crystallization of the Ti-Si alloy depends on the annealing temperature; it remains in the amorphous phase after annealing at temperatures lower than 430 °C, and the C49 TiSi2 crystal phase was observed as the first crystalline phase after annealing at 460–625 °C. The composition of the Ti-Si alloy at the Si interface is close to TiSi2, and it remains amorphous with variable composition across the alloy. It seems that the electrical barrier height is determined by the degree of crystallinity of TiSi2 at the Si interface. The barrier height for TiSi2/p-type Si interface decreases from 0.73 to 0.57 eV, accompanied by the crystallization of TiSi2 at around 460 °C.
Growth kinetics of ultrathin SiO2 films fabricated by rapid thermal oxidation of Si substrates in N2O
Authors: Ting W. , Hwang H. , Lee J. , Kwong D. L.
Published: July 2002

Growth kinetics of ultrathin SiO2 films formed by rapid thermal oxidizing Si substrates in N2O has been studied in this communication. Results show that the linear-parabolic law still can be applied to the oxidation of Si in N2O and the interfacial nitrogen-rich layers in these films result in oxide growth in the parabolic regime by impeding oxidant diffusion to the SiO2/Si interface even for ultrathin oxides. The parabolic rate constant B exhibits an activation energy of 1.42 eV, which is the activation energy for oxidant diffusion in the interfacial nitrogen-rich layer.
Influence of the applied tensile stress on the magnetic properties of current annealed amorphous wires
Authors: González J. , Blanco J. M. , Vázquez M. , Barandiarán J. M. , Rivero G. , Hernando A.
Published: July 2002

The dependence of the magnetic parameters as switching field H*, coercive field Hc and reduced remanence mr, on applied tensile stress σa has been studied in current annealed amorphous wires. The switching field increases as σ 1/2a in fully relaxed samples, while in both ‘‘as-quenched’’ and partially relaxed samples the σ 1/2a law holds only at high values of σa. The coercive field increases with σa in a way similar to H* and mr increases up to the saturation value. This behavior can be explained by taking into account the different magnetic regions that have been proposed for these wires.
Plasma chemistry in silane/germane and disilane/germane mixtures
Authors: Doyle J. R. , Doughty D. A. , Gallagher Alan
Published: July 2002

A detailed kinetic study of silane-germane glow discharges is presented. Stable gas decomposition and production rates have been measured using mass spectrometry and a kinetic model for the plasma chemistry is developed. It is found that germane depletes about four times faster than silane, nearly independently of their relative fractions. Germane is found to be much more reactive than silane with silylene, germalyn, and atomic hydrogen, and the silylene-germane reaction leads in large part to film rather than stable gases. The spatial characteristics of the discharge are studied using optical emission and fiber deposition profiles. From these it is deduced that the present, low-power discharge operates in a ‘‘hybrid’’ α-γ regime, and that ion effects are important near the electrodes.
Charge distribution in Teflon FEP (fluoroethylenepropylene) negatively corona-charged to high potentials
Authors: Sessler G. M. , Alquié C. , Lewiner J.
Published: July 2002

The charge distribution in negatively corona-charged Teflon FEP (fluoroethylenepropylene) films was investigated with the laser-induced pressure-pulse method. The 12.7- and 25.4-μm samples were charged to potentials up to −2500 and −4500 V, respectively, and thereafter stored at room temperature. Measurements of the charge distribution were taken at time intervals ranging from 1 min to several days after charging. The results indicate that the corona charge is initially trapped at the surface of the samples. A negative bulk charge which is nonuniformly distributed over the entire volume with a density of ∼1013 e/cm3 is found for samples kept at the highest voltages for periods of the order of hours. Within the resolution of the method, a spatial broadening of the surface-charge layer is not observed. These findings suggest that in highly surface-charged samples shallow-trapped holes in the bulk of the material, which compensate deeply trapped electrons, drift to the charged surface and thus cause the observed net-negative charge in the bulk.
A study of case II diffusion of a fluorinated hydrocarbon in poly(styrene) by resonance nuclear reaction analysis
Authors: Umezawa Kenji , Gibson Walter M. , Welch John T. , Araki Koichi , Barros Glaucione , Frisch Harry L.
Published: July 2002

The diffusion of a fluorinated hydrocarbon into glassy poly(styrene) (PS) was studied by using resonance nuclear reaction analysis. It was found that; (1) the activation energy derived from measured diffusion coefficients is in good agreement with the value calculated from measured induction times, (2) the diffusion coefficient depends on molecular weight of PS, reflecting the dependence of the mobility on the polymer chain matrix, (3) the mathematical foundation of Lasky and Kramer provides a framework to obtain swelling kinetics from the experimental diffusion measurements.
k dependence of the impact ionization transition rate in bulk InAs, GaAs, and Ge
Authors: Wang Yang , Brennan Kevin F.
Published: July 2002

We present calculations of the k dependence of the impact ionization transition rate along the principal directions within the first Brillouin zone of bulk GaAs, Ge, and InAs. The calculations are performed using realistic energy-band structures determined using the k⋅p method. The impact ionization transition rate is determined from a two-body screened Coulomb interaction assuming energy and momentum conservation. The transition rate within the first two conduction bands of GaAs and Ge is calculated along with the rate within the first conduction band in InAs. It is found that the impact ionization transition rate depends strongly on the initiating electron k vector; the rate is greatest in all three materials at small values of k, i.e., within the gamma valley. This result implies that the k dependence of the ionization transition rate is important. The results also indicate that the rate is greatest for incident electrons at small k vector independent of whether the material is direct or indirect or of wide or narrow energy band gap. Nevertheless, the total impact ionization rate may prove to be relatively k independent since the total rate depends additionally on the nature of the nonequilibrium distribution function.
Brillouin scattering study of surface acoustic waves in crystalline GaP
Authors: Zuk J. , Kiefte H. , Clouter M. J.
Published: July 2002

Surface acoustic modes in GaP crystals have been observed and identified using the technique of high-contrast Brillouin spectroscopy. Surface acoustic wave velocities were determined for (100) GaP in different directions of wave propagation. The values of the velocities are: 3250 m/s in the [010] direction and 3467 m/s in the [011] direction on the (100) GaP surface. These results are discussed and compared with theoretical calculations and with similar measurements in GaAs and Si.
Photoluminescence study of rapid thermal annealing from nitrogen-implanted In0.32Ga0.68P
Authors: Chen Chyuan-Wei , Wu Meng-Chyi
Published: July 2002

Photoluminescence studies were performed to evaluate the results of rapid thermal annealing of nitrogen-implanted In0.32Ga0.68P layers, which were grown on GaAs0.61P0.39 substrates by a supercooling liquid-phase-epitaxial method. When the annealing temperature used is between 600 and 840 °C with 30 s duration, the N isoelectronic trap can be activated with an activation energy of 0.48 eV which is necessary to place N atoms into P sites. The 9 K photoluminescence spectrum is dominated by the sharp near-band-gap peak EgΓ and the broad N-related band Nx. The N level is located ∼110 meV below the Γ-band minimum for the In0.32Ga0.68P alloy. By selecting different annealing temperatures and times, the optimum annealing condition to obtain the strongest emission intensity of the band Nx is at T=800 °C and 30 s duration.
Thermal diffusivity and thermal conductivity of Chromel, Alumel, and Constantan in the range 100–450 K
Authors: Sundqvist Bertil
Published: July 2002

Data are presented for the thermal diffusivity and the thermal conductivity of commercially available Chromel, Alumel, and Constantan alloys, and the specific heat capacity of Alumel, over the temperature range 100 to 450 K. Over this range, the thermal conductivity of all materials increases by more than 50%; room-temperature values are 17, 29, and 23 W m−1 K−1, respectively. The thermal conductivity data are discussed in terms of simple theory.
A dipole-exchange theory for Brillouin light scattering from ferromagnetic thin films
Authors: Rojdestvenski I. V. , Cottam M. G. , Slavin A. N.
Published: July 2002

A dipole-exchange theory is presented for Brillouin light scattering from the surface and bulk spin-wave modes propagating in perpendicularly magnetized films with general asymmetric pinning at the surfaces. The approach is based on a spin-wave theory with mixed exchange boundary conditions and a Green’s-function (linear-response) formalism for light scattering from magnetic films. The influence of dipole-dipole hybridization of the spin-wave dispersion branches on the calculated light-scattering intensities is taken into account, and the dependence of the Brillouin spectra on the pinning conditions investigated. Applications of the theory to Fe thin films are discussed.
Interference effects in pump-probe spectroscopy of thin films
Authors: Moon J. A. , Tauc J.
Published: July 2002

A method of obtaining the complex change in dielectric constant Δε from values of the photoinduced change in reflection ΔR/R and transmission ΔT/T measured via pump-probe spectroscopy is presented. By solving Maxwell’s equations perturbatively in the small Δε limit, we show that the nonuniformity of the pump absorption profile must be taken into account in order to obtain an accurate measurement of Δε. A method for removing artifacts due to thin-film interference fringes is also presented. The results are applied to picosecond photomodulation studies of amorphous hydrogenated semiconductor films.
Antiferromagnetism of Ni(SCN)2
Authors: DeFotis G. C. , Dell K. D. , Krovich D. J. , Brubaker W. W.
Published: July 2002

The magnetic behavior of Ni(SCN)2 has been studied at low temperatures for the first time. A Curie–Weiss fit, χM=C/(T−θ), to the susceptibility between 100 and 300 K yields g=2.13±0.01 (S=1) and θ=39.8±1.4 K. Systematic curvature in χ−1 vs T is evident, however. Despite the large positive θ Ni(SCN)2 appears to order antiferromagnetically at Tc=52±1 K, slightly below a maximum in χ(T) at T(χmax)=57.2±0.5 K, with χmax=0.0331±0.0003 emu/mol. The ratio Tc/T(χmax)=0.91±0.02 does not suggest lower magnetic dimensionality. Magnetization isotherms are linear to 16 kG; some features suggesting lower temperature transitions occur. Well above Tc the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[Ŝz2−S(S+1)/3] and E[Ŝx2−Ŝy2] spin Hamiltonian terms, with exchange incorporated in a mean field approximation. An extraordinarily large ‖D/k‖≊119 K seems to emerge, a result which is very provisional lacking single crystal data. A mean field analysis of Tc and θ yields ferromagnetic intrachain exchange J1/k=8.6±0.5 K and antiferromagnetic interchain exchange J2/k=−0.76±0.4 K. It seems more likely that D is negative, but even if it is positive the exchange interaction is large enough to induce magnetic order at finite Tc in light of theories relating Tc, J, and D.
Endoreversible thermal cycle with a nonlinear heat transfer law
Authors: Angulo-Brown F. , Páez-Hernández R.
Published: July 2002

We calculate the efficiency of an endoreversible Carnot-type cycle in the maximum power regime by using a nonlinear heat transfer law (the so-called Dulong and Petit’s law of cooling). The results obtained from this model compare well (around 99% in some cases) with observed efficiencies for several power plants. The considered law of cooling includes conductive- convective and radiative contributions to the heat exchange between the working fluid and its surroundings. Our calculations improve considerably those obtained by means of a linear heat transfer law for the same power sources. We also analyze a nuclear power plant using an ecological optimization criterion for finite-time heat engines.
Demagnetized-state dependence of Henkel plots. II. Domain wall motion
Authors: McMichael R. D. , Vajda Ferenc , Della Torre Edward
Published: July 2002

The interpretation of various magnetization curves through Henkel plots and Δm plots has become popular in recent years for characterization of interactions in hysteresis. To investigate this approach, we have calculated Henkel plots using a hysteresis model based on independently moving domain walls. A variety of demagnetized states produced by ac, dc+, and dc− demagnetization methods as well as microscopically and randomly demagnetized states are used to calculate mr(H). The resulting collection of Henkel plots contains examples of both ‘‘positive’’ and ‘‘negative’’ deviations from the Wohlfarth relation which depend on the demagnetization method. Also, the Henkel plot calculated for the ac demagnetized state deviates from the square-root law previously calculated for domain wall pinning using a classical Preisach model.
Scaling aspects of domain wall dynamics and Barkhausen effect in ferromagnetic materials
Authors: Bertotti G. , Durin G. , Magni A.
Published: July 2002

It is shown through theoretical considerations on stochastic domain wall motion in a perturbed medium with quenched-in disorder that the Barkhausen signal v, as well as the size Δx and duration Δu of Barkhausen jumps follow scaling distributions of the form v−α, Δx−β, Δu−γ, where α=1−c, β=3/2−c/2, γ=2−c, and c is proportional to the magnetization rate. In order to test these predictions, Barkhausen effect experiments were performed on polycrystalline SiFe alloys. Preliminary experiments to determine both the absolute value and the c dependence of the measured exponents are in agreement with the theoretical predictions.
Space charge migration in discharging current measurement
Authors: Nagashima H. N. , Faria R. M.
Published: July 2002

A consistent model is developed for explaining an anomalous peak in the discharging current in step-voltage measurements in dielectric materials. It is based on the migration of space charge across the bulk of a short-circuited sample under the action of the internal electric field. The space charge is injected by one of the electrodes during the charging process, and remains trapped close to one of the sample surfaces at surface traps whose capturing time is very short. When applied to a paraelectric poly(vinylidene fluoride/trifluoroethylene) copolymer, which presents a prominent peak in the discharging current, the model permits carrier mobilities and the detrapping time to be obtained. It was also experimentally observed that the current peak depends on the polarization field and on the relative humidity of the environment.
Electroluminescence from radiative decay of surface plasmons in aluminum-insulator-indium tin oxide structures
Authors: Canet P. , Laurent C.
Published: July 2002

Electroluminescence was observed in sandwich structures composed of a thick layer of plasma-deposited hydrogenated carbon and two statistically rough aluminum and indium tin oxide (ITO) electrodes. An indication of the presence of surface plasmons in the emission process is proved by the temperature dependence of the emission efficiency and of the light spectra. Visible light from surface plasmon decay at the ITO surface is due to the formation of a metal-enriched layer at the very surface of the ITO film that occurs during the early phase of hydrogenated carbon deposition. The light output was dominated by the radiative decay of surface plasmons excited at the outer metal-glass interface of a semi-transparent aluminum electrode. Each interface behaved like a probe, sensitive to the low or high energy tail of the electron energy distribution function.
Point defects in high purity silica induced by high-dose gamma irradiation
Authors: Sakurai Yuryo , Nagasawa Kaya , Nishikawa Hiroyuki , Ohki Yoshimichi
Published: July 2002

The defects induced by high-dose (10 MGy) gamma irradiation (60Co) are studied in various types of high-purity silica glasses [including synthetic crystal (α-quartz)]. While the defects induced by gamma irradiation of up to 1 MGy have been reported to be generated through the bond breaking of manufacturing-method-dependent point defect sites (precursors), such precursor dependency disappears or at least weakens in the defects induced by 10 MGy gamma irradiation. Electron spin resonance, optical absorption, and luminescence investigations suggest that at high-dose irradiation the defects are created mainly by radiolysis or bond breaking, and associated oxygen diffusion occurred at silicon–oxygen bonds other than at point defect sites. Crystalline α-quartz shows much higher radiation resistivity than amorphous silica glasses, suggesting that strained silicon–oxygen bonds are the breaking sites.
Growth and shrinkage of surface stacking faults in float-zone and Czochralski silicon
Authors: Dammann M. , Baltes H. , Strecker N. , Thiemann U.
Published: July 2002

A model for the growth and shrinkage of stacking faults in silicon is presented. It accounts for interstitial traps and a nonuniform concentration of intrinsic point defects. The complete system of balance equations of intrinsic point defects is solved numerically to simulate the kinetics of stacking faults during oxidation under the assumption that float-zone silicon contains less interstitial traps than Czochralski silicon. Investigation of the influence of different interstitial trap concentrations on the growth and shrinkage of surface stacking faults shows that the kinetics of surface stacking faults is not strongly affected by the presence of interstitial traps. Surface stacking faults are expected to grow in float-zone and Czochralski silicon in a similar way.
Linewidth calculations of Si11+ and Mg9+ resonance lines and application to photoresonant x-ray laser pumping
Authors: Fill E. E. , Schöning T.
Published: July 2002

The linewidths of the 2p-3d line of lithium-like silicon (Si11+) and of the 2s-3p, 2p-3d, 2s-4p, 2p-4d, 2s-5p, 2p-5d lines of lithium-like magnesium (Mg9+) have been calculated in a range of electron densities and temperatures typical of laser-produced plasmas. The implications of these results for the realization of photoresonantly pumped soft x-ray lasers are discussed.
Reduction of defects in laser-induced crystallized and amorphized silicon films using plasma hydrogenation
Authors: Sameshima T. , Sekiya M. , Hara M. , Sano N. , Kohno A.
Published: July 2002

Plasma hydrogenation of laser-crystallized and -amorphized films was investigated. The hydrogen concentration was determined to be 1.5 at. % using a method of laser-induced hydrogen effusion for 20-nm-thick crystallized films which were hydrogenated at 250 °C for 30 s. The defect density was reduced from 1×1017 to 4×1016 cm−3. The hydrogen concentration was 2.5 at. % for amorphized films of 12 nm-thickness. This low hydrogen concentration resulted in a low optical band-gap energy of 1.7 eV for amorphized films, while the width of the Urbach tail was 0.06±0.005 eV, which is close to that of hydrogenated amorphous silicon (a-Si:H) films fabricated using radio-frequency glow discharge (rf GD). The defect density of the laser-amorphized silicon films was reduced from 2×1020 to 4×1015 cm−3 eV−1 comparable to a-Si:H films fabricated by rf GD.
Ferromagnetism and growth of Ru monolayers on C(0001) substrates
Authors: Steierl G. , Pfandzelter R. , Rau C.
Published: July 2002

The magnetic and growth properties of Ru monolayers on C(0001) are studied using spin-polarized secondary electron emission and Auger electron spectroscopy (AES). Using AES, we find that the initial growth of Ru on C(0001) occurs laterally until the first monolayer is completed. One monolayer-thin Ru film shows ferromagnetic order below a surface Curie temperature of approximately 250 K. The in-plane magnetization saturates in small applied fields of a few tenths of an Oe. This is the first observation of spontaneous, long-ranged, two-dimensional ferromagnetic order in an ultrathin film composed of a 4d transition metal.
Fabrication of multipolar magnetic field sources
Authors: Leupold H. A. , McLane G. F.
Published: July 2002

The emergence of high-energy-product permanent magnets has made possible the generation of extraordinarily high magnetic fields in the internal working spaces of relatively small structures. The widespread use of such structures has been hampered by the variety and complexity of their magnetic components and the concomitant difficulty and expense of manufacture. This paper describes approaches to fabrication and assembly that should significantly ease both fabricational and economic problems. Examples of these approaches are given for the production of cylindrical multipolar sources (magic rings, quadrupolar electron beam guides) and spherical dipolar sources (magic spheres).
Orientation control of (Ca,Sr)CuO2 thin films
Authors: Nagai Satoshi , Tanaka Hideaki , Fujimura Norifumi , Ito Taichiro
Published: July 2002

Control of the orientation of (Ca,Sr)CuO2 films with (001) and (101) texture on glass substrates, and (110) and (101) texture on (001) MgO substrates was obtained by changing the sputtering conditions. Although (110) and (101) films on (001) MgO substrates were epitaxial, they showed a double positioning and fourfold rotation symmetry structure. Calculations using the cohesive energy between the film and the MgO single crystal substrate were used to confirm the epitaxial relationships between the film and the MgO substrate. The reason for the change in the texture of the films as a function of the substrate is also discussed.
Simulation of electronic properties and capacitance of quantum dots
Authors: Macucci M. , Hess Karl , Iafrate G. J.
Published: July 2002

The chemical potential and the capacitance of a 2D circular model quantum dot have been investigated for GaAs, InSb, and Si material parameters, covering a range from a few nanometers to micrometer dimensions. The Schrödinger equation has been solved self-consistently, with the inclusion of many-body effects, using a local density approximation as well as the optimized Krieger-Li-Iafrate exchange potential. Gate structures are included by use of the method of images. We have focused on quantum deviations from classical electrostatic capacitive behavior and found such deviations to be significant even for the material parameters of silicon for feature sizes smaller than 30 nm. The most striking features of quantum dot capacitance are signatures of the dot symmetry analogous to the orbital grouping in atoms: we find structure in the dot capacitance arising from quantum effects in correspondence with the filling of each group of energy-degenerate orbitals. We also cover the influence of a magnetic field perpendicular to the dot plane and we report some results for the chemical potential vs magnetic field and electron number, assuming an effective g-factor corresponding to the one of bulk gallium arsenide.
Kelvin probe force microscopy for potential distribution measurement of semiconductor devices
Authors: Vatel Olivier , Tanimoto Masafumi
Published: July 2002

This paper demonstrates that Kelvin probe force microscopy (KFM) is applicable to the characterization of semiconductor devices. The optimum operating conditions for KFM measurements are determined experimentally. Low potential deviation of less than several mV and high topographic resolution sufficient to display monolayer-height steps were obtained at tip-sample distances ranging from 40 to 60 nm. Potential distributions were measured on thin InGaAs resistors using KFM. The steep potential drops observed at the contact edges attributable to the contact resistance are verified by measuring the contact resistance using the transfer length method and the results of previously reported scanning tunneling potentiometry. The KFM results accurately explain the electrical properties of the metal/semiconductor interface.
Convenient determination of concentration and energy in deep-level transient spectroscopy
Authors: Look D. C. , Fang Z.-Q. , Sizelove J. R.
Published: July 2002

For defects or impurities with deep energy levels, such as the commonly observed EL2, EL3, and EL6 in GaAs, it is very important to take account of the so-called λ effect in order to deduce the correct concentrations of these centers when using capacitance techniques. By measuring capacitance at several forward bias voltages for a given reverse bias voltage it is possible to determine concentration NT and energy ET without requiring the usual emission rate analysis. Convenient formulas for NT and ET are given, although only NT can be determined with a high degree of precision. The results for an n-type horizontal Bridgman wafer (n≂2.8×1016 cm−3) are: NEL2=(1.14±0.02)×1016 cm−3, EEL2(377 K)=0.71±0.06 eV; NEL6=(8.0±0.5)×1015 cm−3, EEL6(167 K)=0.42±0.09 eV.
Vanadium related near-band-edge absorption bands in three SiC polytypes
Authors: Jenny J. R. , Skowronski M. , Mitchel W. C. , Hobgood H. M. , Glass R. C. , Augustine G. , Hopkins R. H.
Published: July 2002

Low-temperature optical absorption experiments have been performed on a variety of n-type, p-type, and high-resistivity silicon carbide samples, including the polytypes: 4H, 6H, and 15R. These experiments reveal a set of absorption band close to the band edge with a fine structure depending upon the polytype. Each sample exhibits a spectrum with the number of lines corresponding to the number of inequivalent substitutional lattice sites contained in the polytype. A correlation of these lines with the neutral vanadium 2E→2T2 intracenter transition indicates that the initial state for the near-band-gap absorption lines is the 2E state of the 3d1 configuration of vanadium. The near-band-edge absorption lines were interpreted as due to an exciton bound to a vanadium donor with an electron occupying an atomic-like d state. The position of the vanadium acceptor level was estimated to be, at most, 250 meV from the conduction band for the cubic site in 6H SiC.
Variation in stress with background pressure in sputtered Mo/Si multilayer films
Authors: Windt D. L. , Brown W. L. , Volkert C. A. , Waskiewicz W. K.
Published: July 2002

We have measured the stress in Mo/Si multilayer films deposited by magnetron sputtering, using the wafer-curvature technique, and find a strong dependence on background pressure. We find that for multilayers containing 40 bilayers of ∼4.3 nm Si layers and ∼2.6 nm Mo layers, the stress increases from approximately −280 MPa (compressive) to −450 MPa as the background pressure in the deposition chamber (i.e., measured just prior to deposition) decreases from 1.0×10−5 to 6.0×10−8 Torr. For multilayers of the same period but with thicker Mo layers, the dependence on background pressure is even stronger. X-ray (λ=0.154 nm) diffraction measurements reveal only a slight increase in interfacial roughness for films deposited at high background pressure, but no evidence was found for any differences in the microstructure of the polycrystalline Mo layers that comprise these structures. The peak soft x-ray (λ=13 nm) reflectance, which is sensitive to interfacial roughness at longer spatial wavelengths, also shows no correlation with background pressure or stress. Atomic concentrations of incorporated oxygen and carbon, measured with Auger electron spectroscopy, were found to be less than ∼0.5 at. % for all samples. However, the average hydrogen concentration, as determined from forward-recoil-scattering measurements made using a 2.6 MeV He beam, was found to increase linearly with background pressure. We discuss possible mechanisms for the observed dependence of film stress on background pressure, including gas incorporation and the affect of residual gas atoms on adatom mobility.
Gold clusters precipitation at the interface between Ni(Au) silicides and (111) silicon
Authors: Mangelinck D. , Correia A. , Gas P. , Grob A. , Pichaud B.
Published: July 2002

The solid-state reaction between a nickel (7 at. % gold) film and a silicon substrate at temperature lower than the gold-silicon eutectic temperature (370 °C) is examined by transmission and scanning electron microscopy and by Rutherford backscattering spectrometry. Epitaxial NiSi and preferentially oriented Ni2Si are present and gold precipitation occurs at the inner interface. This gold precipitation leads to a peculiar backscattering spectrum which is analyzed taking into account morphological information. The driving forces leading to gold redistribution are interpreted in terms of surface energies and chemical interactions with silicon.
Role of sulfur vacancies on the electrical characteristics of sputtered films of ZnS
Authors: Tsakonas C. , Thomas C. B.
Published: July 2002

Films of zinc sulfide (ZnS) have been grown on silicon (Si) substrates by sputtering in argon and either sulfur-enriched or deficient-gaseous environments. The density of electron traps at the ZnS/Si heterojunction is invariant with gas. However the photoluminescent intensity increases for films grown in argon enriched with hydrogen sulfide (Ar:H2S) compared with those grown in argon. Furthermore the density of sulfur vacancies is reduced by the presence of H2S, particularly compared with films grown in a mixture of argon and hydrogen (Ar:H). In these latter films sulfur vacancies increase the electrical conductivity by approximately three orders of magnitude. It is expected, therefore, that the high field condition essential for hot-electron production in thin film electroluminescent devices is optimized in films with a reduced sulfur vacancy content, i.e., grown in Ar:H2S.
Partial vaporization model for pulsed mid-infrared laser ablation of water
Authors: Jansen E. Duco , van Leeuwen Ton G. , Motamedi Massoud , Borst Cornelius , Welch Ashley J.
Published: July 2002

Previous studies have shown that during pulsed infrared laser ablation of tissue, rapidly expanding and collapsing water vapor bubbles are formed. These bubbles are held responsible for inducing collateral mechanical tissue damage. In this study, a theoretical analysis predicting the volume of vaporized water is correlated with measured bubble volumes in water. Laser induced bubble formation was documented using a time-resolved flash photography setup. Evidence for a novel ablation model (partial vaporization) is presented in the form of a picture of small bubblets that form at the very beginning of the vaporization process. The dimensions of the rapidly expanding and collapsing bubble (diameter up to 2.5 mm) induced by Q-switched (500 ns) holmium (2.12 μm) laser pulses, delivered in water via 200, 320, or 400 μm fibers have been measured. The volume of the bubble increases with increasing pulse energy. The partial vaporization theory agreed well with the experimental data. It is concluded that the partial vaporization model may be useful in developing laser delivery strategies that lead to a reduction in bubble volume and hence may lead to reduction in laser-induced mechanical damage to adjacent tissue.
Interaction of copper with cavities in silicon
Authors: Myers S. M. , Follstaedt D. M.
Published: July 2002

Copper in Si was shown to be strongly bound at cavities formed by He ion implantation and annealing. Evolution of this system during heating was observed by Rutherford backscattering spectrometry and transmission electron microscopy. Results were mathematically modeled to characterize quantitatively the binding of Cu in the cavities and, for comparison, in precipitates of the equilibrium silicide, η-Cu3Si. Binding of Cu to cavities occurred by chemisorption on the walls, and the binding energy was determined to be 2.2±0.2 eV relative to solution in Si. The heat of solution from the silicide was found to be 1.7 eV, consistent with the published phase diagram. These findings suggest the use of cavities for metal-impurity gettering in Si devices. Hydrogen in solution in equilibrium with external H2 gas displaced Cu atoms from cavity walls, a mechanistically illuminating effect that is also of practical concern for gettering applications.
GMR properties of spin valves using multilayered Co90Fe10 for free magnetic layer
Authors: Nishioka Koichi , Iseki Takayuki , Fujiwara Hideo , Parker Martin R.
Published: July 2002

To achieve higher GMR ratios in spin valves, Co90Fe10 films were used as the free and the pinned layer. A single layer of CoFe 100 Å and a multilayer of CoFe 18 Å/(Cu 8 Å/CoFe 18 Å)5 were used as the free layer. Although the single layer CoFe showed large coercivities of 58 Oe along the easy axis and 40 Oe along the hard axis, the multilayer CoFe 18 Å/(Cu 8 Å/CoFe 18 Å)5 showed smaller coercivities of 10 Oe along the easy axis and 1.5 Oe along the hard axis on a 100 Å thick Ta underlayer. The anisotropy field of the multilayer was 20 Oe. The film structures of the free layer were evaluated and it was found that the multilayer had higher oriented (111) texture than the single layer. The reason why the multilayer had higher oriented (111) texture was that the Cu layers between CoFe layers helped to have highly oriented (111) texture. To reduce the anisotropy field, the film was annealed in a magnetic field perpendicular to the initial easy axis at several temperatures. As the result, the anisotropy field was reduced to 3 Oe and the coercivity was 4 Oe after annealing at 140 °C. The GMR ratio of the spin valve of Ta 100 Å/CoFe 18 Å/(Cu 8 Å/CoFe 18 Å)4/Cu 24 Å/CoFe 30 Å/FeMn 150 Å/Ta 50 Å was 7% after the annealing.