bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical emission actinometry and spectral line shapes in rf glow discharges
Authors: Gottscho Richard A. , Donnelly Vincent M.
Published: February 2003

Optical emission actinometry has been used recently as a means for estimating relative concentrations of radicals in rf plasmas. The technique relies upon normalization of the radical emission intensity to that from an inert gas (the actinometer) in order to compensate for changes in the electron density or energy distribution. However, actinometry is a valid measure of ground-state densities only when the excited states are created by electron-impact excitation (e.g., as opposed to chemiluminescent reactions or electron-impact dissociation). When techniques such as laser-induced fluorescence and optical-absorption spectroscopy are available, there is little need to use actinometry. However, there are many instances where these techniques are not yet applicable or practical and the use of actinometry may be desirable. In such instances, a simple means of assessing the validity of an actinometer would be advantageous. We describe the use of emission line shapes for determining the mechanism of excited-state formation and assessing the validity of an actinometer. In CF4/O2/Ar plasmas, both Ar* and F* are created with cold (360±70 K) translational distributions over a range of [F] from 0.4 to 4.0×1014 atoms cm−3. This implies that both species are created by electron-impact excitation and that Ar can be used as an actinometer in determining [F]. In Cl2/Ar plasmas, however, Cl* and Ar* emission line shapes in the sheath show substantial broadening during the cathodic part of the rf cycle, which implies that other excitation mechanisms such as dissociation, attachment, ion impact, and charge exchange are important and that actinometry is not valid under these conditions. But, time-averaged Cl* and Ar* emissions in the discharge center have identical linewidths, so that actinometry can be used to determine Cl atom concentrations.
Physical mechanisms of dc switching in a liquid-crystal bistable boundary layer display
Authors: Thurston R. N. , Cheng Julian , Meyer Robert B. , Boyd Gary D.
Published: February 2003

We discuss two mechanisms proposed to explain dc switching of a bistable liquid-crystal boundary layer display. These are (1) biasing by double layer fields that arise from charge of one sign preferentially adsorbed at the walls, and (2) asymmetry in the transient depletion layer fields which result from a difference in mobility of the positive and negative ions. By a quantitative discussion, we argue that both mechanisms are plausible, but crucial parameters remain unknown. For the double layer mechanism the surface density of adsorbed charge is estimated as 8×10−10 C/cm2 from published measurements of the thickness dependence of the resistivity. For a numerical example of the differential mobility mechanism, we arbitrarily take μ−=3μ+=9×10−6 cm2/V sec. Either mechanism may be made dominant by the choice of material and surface properties. For fast switching, it may prove advantageous to choose interfaces to exploit the double layer mechanism because it begins to act immediately upon application of the voltage, whereas the other mechanism entails a delay before field asymmetry builds up from the differential drifting of the ions. To enhance the double layer effect and obtain fast switching, one should use (1) a thin cell, (2) a highly purified liquid crystal, which keeps the ionic charge density low and the Debye screening length significant in comparison with the cell thickness, and (3) interfaces that strongly absorb ions of one sign so that the double layer field will be strong. On the other hand, fast switching by the differential mobility mechanism calls for a somewhat higher ionic density with ions of one sign rather mobile, and the others relatively sluggish.
A study of the initial growth kinetics of the copper-aluminum thin-film interface reaction by i
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u x-ray diffraction and Rutherford backscattering analysis
Authors: Hamm R. A. , Vandenberg J. M.
Published: February 2003

X-ray diffraction and Rutherford backscattering (RBS) analysis were used independently to investigate the interface reaction of Cu-Al thin-film bilayers during in situ annealing in the temperature range 157–220 °C. The growth kinetics of the θ-CuAl2 phase were measured and were found to follow a diffusion limited process. Using Arrhenius plots, activation energies of 1.21 and 1.24 eV and preexponential factors of 4×10−1 and 9×10−1 cm2 s−1 were obtained from x-ray diffraction and RBS, respectively. X-ray and RBS data are presented and advantages of each method are discussed. It was observed in the in situ x-ray scans that the phase γ2-Cu9Al4 grows simultaneously with θ-CuAl2 from the beginning of the interface reaction. The growth of γ2-Cu9Al4 is also diffusion limited with an activation energy of 1.59 eV and a preexponential factor of 6×102 cm2 s−1 as obtained from x-ray data. The growth of both phases is believed to be largely controlled by volume diffusion. A comparison with previous studies indicated that depending on the annealing treatment, either γ2-Cu9Al4 or β1-Cu3Al grows together with θ-CuAl2 in the initial stage of the interface reaction.
Effect of short-range order on the thermal stability in amorphous Ti-Ni alloys
Authors: Buschow K. H. J.
Published: February 2003

Amorphous Ti1−xNix alloys were prepared by means of melt spinning and studied by means of differential scanning calorimetry. The crystallization temperatures and the activation energies for crystallization were determined over a wide concentration range. The former values were found to vary only slightly with concentration while the latter showed a marked concentration dependence. This difference in behavior is discussed in terms of the occurrence of compositional short-range ordering. It is shown that the activation energy for crystallization is not always a good measure of the thermal stability of amorphous alloys.
Study of the enthalpies of formation and crystallization in the system Zr-Ni
Authors: Henaff M. P. , Colinet C. , Pasturel A. , Buschow K. H. J.
Published: February 2003

The enthalpies of formation were measured in the intermetallic compounds ZrNi5, Zr2Ni7, Zr7Ni10, ZrNi, and Zr2Ni, and the amorphous Zr1−xNix alloys with x=0.25, 0.35, and 0.65 by means of a solution calorimeter based on liquid aluminium. For the amorphous system Zr1−xNix, the concentration dependence of the crystallization enthalpy was studied by means of differential scanning calorimetry on 12 different compositions. The concentration dependence of the formation enthalpy of the crystalline materials was analyzed in terms of Miedema’s model. The enthalpy effects observed in some of the amorphous alloys point to the occurrence of compositional short-range ordering.
Selenium self-diffusion study in the 1-3-62 semiconductor: CuInSe2
Authors: von Bardeleben H. J.
Published: February 2003

In the first self-diffusion study for a member of the 1-3-62 chalcopyrite family we have studied by radioactive tracer analysis the isothermal (T=700 °C) diffusion of 75Se in CuInSe2 as a function of Se and In2Se activities; the diffusion coefficient DSe varied between 2×10−13 cm2 s−1 ( pSe2=0.01 atm) and 1×10−12 cm2 s−1 ( pSe2=0.32 atm). The dependence of the diffusion coefficient on the two component activities D∼p0.5Se2 and D∼p0.0In2Se permits us to assign the diffusing species to Sexi. A simple defect model is established and compared to the literature results of the transport properties of CuInSe2.
Heating silicon dioxide at 950–1050 °C in the presence of an NH3+CF4 plasma
Authors: Morita M. , Ishihara T. , Hirose M.
Published: February 2003

Very thin SiO2 films thermally grown on Si were annealed at a temperature of 950 or 1050 °C in the glow discharge of either an NH3 gas containing 4% CF4 or a pure NH3. From the chemical analysis of annealed films using Auger electron spectroscopy and x-ray photoelectron spectroscopy, it is found that annealing has resulted in the formation of silicon nitride layer on the SiO2 surface and in the incorporation of bonded nitrogen into the SiO2 layer. It is also demonstrated that the surface nitride layer is formed primarily by the deposition of silicon nitride resulting from the reaction of fragments of NH3 with the silicon atoms produced by the plasma etching of the quartz tube wall by atomic hydrogen and fluorine.
Alloy disorder scattering contribution to low-temperature electron mobility in semiconductor quantum well structures
Authors: Ogale S. B. , Madhukar A.
Published: February 2003

We present calculations of the alloy disorder effect on the low-temperature mobility of quasi-two-dimensionally-confined electrons in thin square quantum wells involving a ternary III-V semiconductor alloy as either the barrier layer (e.g., GaAs/AlxGa1−xAs) or the well layer itself (e.g., InxGa1−xAs/InP). It is shown that in the former case the alloy disorder at and near the interface arising due to chemical intermixing gives a significant contribution to the electron scattering. Even for structurally and chemically ideal interfaces, the alloy disorder scattering from the barrier layer is found to be comparable to that calculated previously on the basis of fluctuations in the width of the potential well. For well layers made of a ternary alloy, the alloy disorder scattering in the well is shown to yield a dominant contribution to electron scattering. Results are presented for the low-temperature mobility as a function of areal electron density and well thickness for the lattice matched systems In0.53Ga0.47As/InP and GaAs/AlxGa1−xAs. Specifically, it is estimated that for the In0.53Ga0.47As/InP system, the mobility is limited by the alloy disorder scattering once the ionized donors in the barrier layer are separated by an undoped spacer layer of thickness exceeding about 100 Å. It is also shown that the alloy disorder limited mobility in a quantum well made of an alloy can exceed that in the corresponding bulk alloy. Results are also included for the alloy composition dependence of the mobility. Wherever possible, these results are compared with the available relevant experimental mobility values and the implications discussed.
Hot carrier transient response in bulk III-V compounds
Authors: Moore J. Scott , Das P.
Published: February 2003

A theory of transport of hot carriers in bulk III-V compounds is outlined. Equilibrium calculations are performed which show fair agreement with earlier Monte Carlo calculations and with experiment. Transient response calculations indicate velocity overshoot and it is seen that the mechanism primarily responsible for overshoot in these materials is repopulation, in contrast to the relaxation time mechanism observed in silicon. Calculations are performed for GaAs and other III-V compounds.
Transmission electron microscope studies of crystalline LiNbO3
Authors: Pareja R. , González R. , Chen Y.
Published: February 2003

Transmission electron microscope investigations in both as-grown and hydrogen-reduced LiNbO3 reveal that niobium oxide precipitates can be produced by in situ irradiations in the electron microscope. The precipitation process is produced by a combined effect of ionizing electrons and the thermal heating of the specimens during irradiation. It is proposed that the composition of the precipitates is primarily Nb2O5.
Optical bistability in coupled-cavity semiconductor lasers
Authors: Agrawal Govind P. , Dutta Niloy K.
Published: February 2003

Coupled-cavity semiconductor lasers are shown to exhibit bistability when both sections operate in the above-threshold regime. The hysteresis width can be adjusted by controlling the current in the modulator section. The theoretical model is based on a set of generalized rate equations and shows that the bistable behavior is due to nonlinearities associated with above-threshold gain saturation. Experiments are performed using a cleaved-coupled-cavity InGaAsP laser operating at 1.3 μm. The experimental results are in reasonable agreement with the theory.
Theoretical analysis of a self-sustained discharge pumped XeCl laser
Authors: Hokazono Hirokazu , Midorikawa Katsumi , Obara Minoru , Fujioka Tomoo
Published: February 2003

Theoretical analysis of the discharge characteristics and the output performance of a self-sustained discharge XeCl laser is described. Validity of the theoretical laser model including the excitation circuitry is confirmed by comparing the results with the measured discharge and output performance under lasing conditions. The dischare parameters such as E/P (E is the electrical field strength and P is the operating pressure) and discharge resistivity are theoretically studied for both Ne- and He-based gas mixtures. Our model shows that the electron energy distribution functions of these two mixtures become quite equal at each quasi-steady-state E/P, and that the improved laser output performance with Ne-based gas mixtures is not due to the difference of the electron energy distribution function but due to the good optical extraction caused by the faster ion-ion recombination excimer formation channel. Moreover, the model also predicts that the depletion of HCl molecules is one of the most serious problems in the long optical pulse operation.
Improved quartz crystal microbalance technique
Authors: Benes E.
Published: February 2003

The importance of using the most pertinent mathematical description of the mass load versus frequency relation for quartz crystal thin-film thickness monitors is reviewed. The different usable crystal load ranges of the so-called frequency- and period-measurement techniques in comparison with the Z-Match technique are calculated for most of the commonly used deposition materials. A new thin-film thickness monitoring procedure is described, which takes the influence of the acoustic film properties on the mass load versus frequency slope into consideration without need for the explicit knowledge of the acoustic impedance ratio z of the deposited film and the quartz crystal. It is shown how the effective z value in the composite resonator built by the quartz crystal and the deposited foreign layer can be derived from a measurement of a quasiharmonic overtone resonance frequency in addition to the commonly practiced exclusive measurement of the fundamental resonance frequency. The presently established relation between the mass load or the deposited film thickness and the corresponding resonance frequency of the loaded crystal is enhanced by a more rigorous one-dimensional composite resonator description. The introduced so-called series resonance relation is of significance for the accurate determination of the specific acoustic impedance ratio z of the deposited film and the crystal. Furthermore, the deviations of the frequency spectra of plano-convex shaped crystals from that of the one-dimensional (infinite plate) geometry are investigated and taken into account. The achieved accuracy in the z determination from the first and third quasiharmonic frequencies justifies the applicability of the two-frequency or auto slope accommodation technique introduced in this paper.
Series-field-coil ion beam diode experiment and numerical simulation
Authors: Mendel C. W. , Quintenz J. P. , Zagar D. M. , Johnson P. R. , Anderson R. J. , Widner M. M.
Published: February 2003

An experiment with a series-field-coil intense ion beam diode operating at the 1.6-MV, 0.8-TW level is described. The diode operates in the extraction mode with a 20-cm focal length. The diode design procedure is described together with some of the essential ion diode theory used in this design process. The experiment produced a well-focused ion beam while verifying some of the theoretical assumptions about ion diodes of this type. The experimental results are compared with numerical computer simulations and excellent agreement is obtained.
Elastic wave scattering by a surface-breaking or subsurface planar crack
Authors: Visscher William M.
Published: February 2003

A boundary integral representation of the displacement field is developed and solved for the crack-opening displacement by expressing the latter on the crack surface as an expansion in localized functions, whose parametrization is determined by fitting exactly-known cross sections. Numerical results are presented for scattering of antiplane (SH) waves as a function of frequency from surface-breaking and buried 2D cracks for a variety of crack inclinations and burial depths. The theory and the method apply to the 3D case. Its numerical implementation will be straightforward but tedious.
H− production on poly- and monocrystalline converters in a surface-plasma ion source
Authors: van Bommel P. J. M. , Leung K. N. , Ehlers K. W.
Published: February 2003

Monocrystalline (110) and polycrystalline tungsten and molybdenum converter surfaces have been tested in a surface negative hydrogen-ion source, both with and without cesium added to the plasma. With cesium added to the discharge, no significant difference in H− yield is measured between the four converter surfaces. Energy spectra reveal that the contribution to the total H− yield from the backscattered hydrogen is negligible compared to the ion-impact desorbed H− ions. The converter voltage required for optimum H− production increases with the amount of cesium added to the plasma. The measurements without cesium show roughly equal fractions of backscattered and desorbed H− ions in the self-extracted beam. The presence of oxygen on the surfaces enhances the ion-impact desorbed (sputtered) H− yield with respect to the reflected H− yield. This is attributed to the formation of OH on the surfaces.
The work function of sputter-formed Re-1%Mo
Authors: Gordon R. L.
Published: February 2003

Thermally induced changes in work function and surface composition of a sputter-formed Re-1%Mo alloy have been measured. Segregation of Mo to the alloy surface was accompanied by a decrease in surface work function. The relationship between surface composition and work function change fits the Topping model of dipole layer formation with dipoles being formed by electron transfer from Mo to Re. Values for the dipole moment at zero field and the polarizability of Mo on the surface of Re were found to be (5.27±0.36)×10−30 C m and (74.1±10.1) Å3, respectively. The direction of charge transfer is consistent with published electronegativity values for Mo and Re, but its magnitude of 0.126 electrons per atom was significantly smaller than the charge transfer in the bulk expected upon alloy formation.
Point defects in neutron-irradiated quartz
Authors: Jani M. G. , Halliburton L. E.
Published: February 2003

Point defects formed by irradiation with fast neutrons have been characterized in high-quality synthetic quartz using electron spin resonance and optical absorption techniques. Among the paramagnetic defects generated are the E′1 center, the [AlO4]0 center, and two previously unreported S=1 centers. Production and thermal annealing characteristics of these more prominent defects are described. The two S=1 defects have gc values of 2.0205 and 2.0158 and thermally decay near 250 and 470 °C, respectively. They each consist of a pair of unpaired spins (i.e., holes) separated by approximately 5 Å, and either vacancies or interstitials are a part of their models. These latter two centers, along with the E1 centers, result from direct displacements during the neutron irradiation. An optical absorption band at 210 nm grows at the same rate during irradiation as the E′1 centers and S=1 centers but cannot be definitely assigned to particular defects.
Oxygen vacancy annealing in H+ implanted SiO2
Authors: Devine R. A. B.
Published: February 2003

Isothermal and isochronal annealing studies have been performed on E′1 defects created in amorphous SiO2 by implantation of 80-keV H+ ions. Defect creation is via ionization energy deposition. Annealing data are analyzed using models for thermal detrapping and for bimolecular reactions adapted to allow for a Gaussian activation energy spread. Values from 0.82 to 1.27 eV are obtained with spreads of ∼14%. Physical justification of the energy spread approach is discussed. We conclude that defect annealing proceeds via the same mechanism as for E1 defects produced in SiO2 by Ar+ implantation where elastic displacement processes dominate in defect creation.
Effect of flat-band voltage shift and nonvolatile memory in platinum-diffused metal-oxide-semiconductor devices
Authors: Kato Hideo , Mori Seiichi , Kuwano Hiroshi
Published: February 2003

The properties of Pt-diffused metal-oxide-semiconductor structures are experimentally investigated. The amount of charge at the Si-SiO2 interface introduced by Pt-diffusion is strongly dependent on the diffusion ambient and crystal orientation of the wafers. The devices with (111) orientation in which Pt is diffused in an oxygen ambient (stable mode devices) have a large positive shift of flat-band voltage from that of non-Pt diffused control devices. On the other hand, the devices with (111) orientation fabricated in a nitrogen ambient (memory mode devices) have nonvolatile memory effects with an hysteresis loop, but the shift of flat-band voltage is rarely observed. The distributions of the interface trap densities are evaluated by using the Gray–Brown method. The flat-band voltage shift obtained by applying the stress voltage for the memory mode devices can completely turn back to the initial state by annealing at higher temperature than 330 °C.
Optimization of ion-implanted low noise GaAs metal-semiconductor field effect transistors
Authors: Feng M. , Eu V. K. , Kanber H.
Published: February 2003

This paper presents an investigation of the effects of implantation energy and dose on the noise figure and associated gain of low noise GaAs metal-semiconductor field effect transistors. Our results show that the noise figure and associated gain in these devices decrease as the implantation energy and the implanted dose increase. rf and dc performance of devices fabricated by direct ion implantation into liquid encapsulated Czochralski substrates, metalorganic chemical vapor deposited buffer layers, and AsCl3 buffer layers have been evaluated. The equivalent circuit elements derived from the S parameters are used to interpret the variation of critical device properties as a function of implantation energy, dose, and gate recess depth.
Studies on product layers formed during etching of Si in a SF6 plasma
Authors: Brandt Werner W. , Wagner John J. , Honda Takuya
Published: February 2003

Several types of experiments were performed during and after the etching of Si in a dc discharge to confirm the presence of product layers, to characterize these layers, and to determine how such layers and concomitant changes in near-surface regions affect the rates of release of various species formed. The experiments are (1) depth profiling of Si samples etched in SF6 plasmas, using electron spectroscopy for chemical analysis, (2) mass spectrometric study of the concentrations of various species effusing from the plasma etching cell, with emphasis on the transients arising when the plasma is ignited and extinguished, and their dependence on sample history, and (3) exposure of previously etched samples to a second discharge, supported by Ar or H2, and mass spectrometric analysis of the species released during that process. The results show that layers on the surface undergoing etching, and changes in subsurface regions affect the etching rates; even after the etchant gas has been removed, small amounts of the product SiF4 are released, under various conditions.
A mathematical model for spin coating of polymer resists
Authors: Flack Warren W. , Soong David S. , Bell Alexis T. , Hess Dennis W.
Published: February 2003

The success of lithographic processes in microelectronics fabrication depends on the reproducible generation of desired polymer resist film thickness and profile uniformity. Numerous process variables affect the outcome of spin coating of resists on wafers. A thorough understanding of the intricate interdependence of process parameters is essential to guide future process design and improvement. A mathematical model is derived to elucidate the dominant mechanisms governing film formation. The non-Newtonian character of the resist solution is taken into account, as well as the changes in resist viscosity and solvent diffusivity with changing polymer concentration. Results obtained from this model show that polymer film thickness is controlled by convective radial flow of the resist solution and solvent evaporation. The former process governs film thickness during the early stages of the process, while the latter becomes significant in later stages. The model accurately describes the experimentally observed dependence of film thickness on the variables affecting the spin-coating process.
Substrate orientation dependence of enhanced epitaxial regrowth of silicon
Authors: Ho K. T. , Suni I. , Nicolet M-A.
Published: February 2003

This work extends the study of dopant-enhanced epitaxial regrowth rate of amorphized Si from the 〈100〉 to the 〈110〉 and 〈111〉 orientations of Si. Boron and phosphorus dopants are considered. The annealing temperatures are 500 and 550 °C. Phosphorus enhances the growth rates in all three orientations by a constant factor of 8.1±0.9. Boron produces a higher enhancement factor of 12.2±1.2, except in the case of 〈100〉. Implications of the results on various growth models are considered. The crystalline quality of regrown 〈111〉 layers is improved in the doped samples.
Figures of merit for sputtered superlattices
Authors: Falco Charles M.
Published: February 2003

Two figures of merit for sputtered superlattices (FMSS) are proposed which allow a comparison of the quality of artificial superlattices prepared in different sputtering systems. These FMSS also demonstrate several conditions for optimizing the sputtering parameters which are not widely appreciated.
Magnetic structure of Er6Fe23
Authors: Herbst J. F. , Croat J. J. , van Laar B. , Yelon W. B.
Published: February 2003

Analyses of neutron powder diffraction data for Er6Fe23 at several temperatures are described. We find that the Er and Fe moments are essentially collinear throughout the ordered temperature regime, in contrast to other Er-transition metal systems. Our results are compatible with molecular field theory analyses of the Er6Fe23 magnetization.
Effect of antimony ion implantation on Al-silicon Schottky diode characteristics
Authors: Ashok S. , Baliga B. J.
Published: February 2003

Shallow (≲100 Å) antimony ion implantation on n-type silicon is shown to reduce the effective barrier height on Al Schottky diodes formed on the implanted surface irrespective of postimplant annealing. The mechanisms of barrier reduction are quite different in the two cases. In the postimplant annealed case, the antimony is activated resulting in barrier height reduction due to the surface N+ dopant charge, while in the unannealed case, lattice damage causes barrier height reduction as observed earlier for ion etched silicon surfaces.
Diode quality factor in polycrystalline solar cells
Authors: Sen K. , Tyagi B. P.
Published: February 2003

The increase in diode quality factor with decreasing grain size in polycrystalline conductor (metal or degenerate semiconductor)-insulator-semiconductor (MIS) solar cells is explained as due to (1) an increase in insulator-semiconductor interface charge due to the presence of grain boundaries on the I-S surface, and (2) the voltage drop at the grain boundaries in the polycrystalline base semiconductor.
Tracer study of diffusion and electromigration in thin tin films
Authors: Singh Prabjit , Ohring Milton
Published: February 2003

A comprehensive study of lateral self-diffusion and electromigration in evaporated thin Sn films over the temperature range −50 to 198 °C is reported. Sn119m atoms were deposited over a central portion of thin Sn film stripes and the subsequent diffusional spreading and migration of the tracer distribution were evaluated by a high-resolution autoradiographic technique. Activation energies suggestive of grain boundary transport processes were obtained. At low temperatures the ionic drift velocity in grain boundaries Vb is measured to be VbT/j=3.4×10−2 exp[−(8710±360 cal/mol)/RT] cm3 K/A s, while the low-temperature grain boundary diffusivity Db is given by Db=4.9 exp[−(11 700±840 cal/mol)/RT] cm2/s. At higher temperatures (i.e., >80 °C) transport measurements were conducted employing Sn films of two different grain sizes, and apparent drift velocities and diffusivities were obtained. Application of the Hart model enabled the extraction of grain-size independent values of the grain boundary ionic drift velocity and diffusivity given by VbT/j=3.3×10−2 exp[−(8980 cal/mol)/RT] cm3 K/A s and Db=8.3×10−2 exp[−(9790 cal/mol)/RT] cm2/s. The effective valence Z* in the grain boundaries was calculated over the complete temperature range using the Db and VbT/j values obtained in the present investigation. A rapid rise in Z* at low temperatures, similar to that previously reported in Au films, was observed, suggesting that at low temperatures the Z* in the grain boundaries is greater than in the lattice. Electromigration in Sn is anode directed at all temperatures.
Detection of defect structures in arsenic ion-implanted silicon by fluorine decoration
Authors: Prussin S. , Margolese David I. , Tauber Richard N. , Hewitt William B.
Published: February 2003

A series of {100} and {111} wafers were subjected to a 1×1015 F cm−2 implantation followed by an As implantation covering the range from 2×1014 to 5×1015 As cm−2 at 190 keV. Wayflow and Waycool end stations were used. The former permitted dynamic annealing resulting from a temperature rise during the implantation, the latter suppressed it. The as-implanted structures, i.e., the thicknessess of the buried and surface amorphous layers, were correlated with the implant conditions. Using an ion microprobe mass analyzer, the F distribution was measured in the as-implanted wafers, after a 550 °C regrowth anneal and after a 30 min anneal at 900 °C. Decoration of the residual defects with F permitted us to correlate their presence with implant conditions. This decoration technique was particularly sensitive to defects arising from the presence of buried amorphous layers and to a lesser degree to those generated in single crystal silicon recrystallized by dynamic annealing.
Mechanism of phosphorus pile-up in the Si-SiO2 interface
Authors: Kimura T. , Hirose M. , Osaka Y.
Published: February 2003

Phosphorus pile-up in the polycrystalline Si-SiO2 interface has systematically been studied by using Auger in-depth profiling technique. The extent of pile-up is one order of magnitude less than that in the single crystal Si-SiO2 interface. It was found that the density of pile-up phosphorus atoms saturates in the polycrystalline system when the bulk concentration exceeds 5×1019 cm−3, despite no saturation for the single crystal Si system. This pronounced difference was interpreted in terms of the difference in the strain field present in the interface.
V3Ga wire fabricated by the modified jelly roll technique
Authors: Gubser D. U. , Francavilla T. L. , Pande C. S. , Rath B. B. , McDonald W. K.
Published: February 2003

V3Ga wire has been fabricated by the modified jelly roll technique for the first time. Critical current densities in magnetic fields to 22 T, critical magnetic fields, and superconducting transition temperatures are reported for this wire as a function of reaction temperature for forming the interfacial V3Ga layer. Superconducting properties of the reacted wire are optimized for reaction temperatures between 550–580 °C. With a reaction temperature of 580 °C, the overall (noncopper) current density of the wire is over 104 amp/cm2 at 19 T.
Proton implantation effects in amorphous Fe-Ni-P-B alloys
Authors: Fisher D. G. , Murray R. B. , Swann C. P.
Published: February 2003

This paper reports proton-implantation effects on the magnetic properties of amorphous alloys of Fe-Ni-P-B. Proton irradiation (2.25 MeV) effects as well as electron irradiation (1.25 MeV) effects have been given previously for irradiations at sufficient energy to totally penetrate the amorphous melt-spun ribbon. The Curie temperature is enhanced by a structural relaxation from the as-quenched state. Proton implantation (0.25 MeV) effects are similar except that a composite sample is created; the sample has two Curie temperatures, one characteristic of the as-quenched state and the other characteristic of the irradiation-induced structually relaxed state. The region of enhanced Curie temperature is shown by electrochemical thinning to extend only to the end of range of the 0.25-MeV protons in the materials studied. Relative magnetic permeability measurements in the low-field region indicate an increase in permeability upon either proton irradiation or thermal annealing.
Compensation in n-type GaAs resulting from nitrogen ion implantation
Authors: Duncan W. M. , Matteson S.
Published: February 2003

Nitrogen introduced by ion implantation is shown to strongly compensate n-type GaAs after annealing. From transport measurements, this compensation behavior is found to be due to a deep acceptor center associated with the nitrogen. Ion-implanted nitrogen is found to compensate both silicon-doped and sulfur-doped n-type GaAs. A comparison of silicon plus nitrogen co-implants with silicon plus neon co-implants shows that the observed compensation effect of implanted nitrogen is not due solely to residual ion-implantation-induced lattice damage but rather requires nitrogen to be present. The electrical properties of nitrogen plus silicon co-implanted layers are found to be qualitatively similar to those resulting from oxygen plus silicon co-implantation in GaAs.
D grad ν or grad(Dν)?
Authors: Landsberg P. T.
Published: February 2003

An introduction to the problem in the title of the paper is attempted, D being a diffusion constant for particles of concentration ν. A general formalism and some special results are outlined which seek to show that, provided one proceeds in an appropriate and consistent manner, either formulation is permissible. The main area of application envisaged is to electronic flow in solids. The mathematical results also hold for atomic flow.
Photoluminescence from GaAs-AlxGa1−xAs quantum wells with nonuniform p-type doping profiles
Authors: Miller Robert C.
Published: February 2003

GaAs quantum wells with localized Be doping have been produced from the GaAs-AlxGa1−xAs system using molecular beam epitaxy. Structures with the Be doping concentrated at the heterostructure interface and at the well center have been examined at low temperatures via their photoluminescence and excitation spectra. The energies of the emission peaks due to the recombination of n=1 confined electrons with neutral Be acceptors are dependent upon the position of the Be0 centers in the GaAs quantum well and are consistent with expectations from the theoretical work of Bastard. At 5 K these structures exhibit substantial luminescence attributed to bound excitons on the low-energy side of the n=1 free heavy-hole exciton emission. As the sample temperature is increased; this luminescence decreases and significant changes occur in the confined electron-Be emission spectra.
Correlation of the chemical and electrical properties of AZ1350J photoresist solution
Authors: Gupta Tapan Kumar
Published: February 2003

The dielectric properties of the photoresist AZ1350J in diethyloxalate solution have been measured by a capacitance technique. Measurements of permittivity (Er) at different dilutions are seen to obey the logarithmic law of mixing, while the temperature dependence curve predicts a change in phase of the resist at approximately 66 °C. Polarization measurement of the mixtures shows a relaxation type of orientational polarization and a decreasing value of polarization on UV light irradiation, confirming the structural change in the photoresist.
Thermally stimulated currents driven by temperature gradients. II. The model
Authors: Sworakowski J. , Figueiredo M. T. , Ferreira G. F. Leal , Campos M.
Published: February 2003

A simple model was put forward attempting to qualitatively explain features of currents and voltages observed during heating of dipolar dielectrics, not polarized earlier with external bias. It was assumed that temperature gradients, existing usually during the experiments, act as a driving force giving rise to a dipolar orientation. Analytical solutions for particular cases were given, and results of numerical calculations presented.
Magnetic properties of amorphous thin films produced by ion mixing
Authors: Van Rossum M. , Nicolet M-A. , Wilts C. H.
Published: February 2003

We have produced several magnetic amorphous alloys by ion mixing of thin multilayer films. Our results show that the ion mixing technique is able to produce amorphous films of the various categories (transition metal-metalloid, transition metal pairs) at the composition appropriate for the appearance of magnetic ordering. A comparison of their saturation magnetization with that of related vapor quenched films suggests similar nearest-neighbor coordination in both kinds of samples.
Molecular dynamics study of structural instability of two-dimensional lattices
Authors: Toukan Khaled , Carrion Francisco , Yip Sidney
Published: February 2003

Structural transition of a two-dimensional square lattice with Lennard–Jones (6–12) interaction to a triangular lattice has been studied by a molecular dynamics simulation technique which allows the system to vary in size and shape. The results are consistent with lattice dynamics analysis, and furthermore provide sufficient details to determine the mechanism of transition. The same technique was then used to simulate the onset of melting at constant pressure. It is shown that thermodynamic properties and structural behavior give a consistent picture of the evolution of this thermal instability.
Magnetic field biased superconducting rings containing N Josephson junctions
Authors: Blackburn James A.
Published: February 2003

The equations governing the static and dynamic behavior of a superconducting ring, interrupted by N Josephson junctions and containing initial trapped flux, have been developed. In order to follow the phase and voltage activity at each of the junctions, a numerical simulation of the system has been implemented. This computational model confirmed that, by the application of a suitable bias flux, bundles of flux quanta could be induced to enter or leave the loop. Phase winding was seen to occur only at the weakest of the links, except when the bias was changed impulsively.
Ferroelectric switching characteristics in a copolymer of vinylidene fluoride and trifluorethylene
Authors: Furukawa T. , Date M. , Ohuchi M. , Chiba A.
Published: February 2003

Ferroelectric switching characteristics have been measured in the 65/35-mol % copolymer of vinylidene fluoride and trifluoroethylene by applying a step-function high electric field up to 100 MV/m at temperatures between −80 and 90 °C. The amount of reversed polarization is 160 mC/m2 being independent of applied field and temperature. The switching time τs follows an exponential law with an activation field ranging from 0.8 to 1.8 GV/m. Extrapolation to the infinite field yields a switching time of ∼1 nsec. Observed switching transients were fitted by a function, 1−exp[−(t/τs)n]. It is found that the value of the exponent n becomes as large as 5, reflecting an extremely high rate of polarization change with time t. Such a large exponent leads to a switching model which assumes random nucleation of reversed chain molecules and their subsequent two-dimensional growth with accelerated velocity.
Constant current corona charging of PVF2
Authors: Gross B. , Giacometti J. A. , Ferreira G. F. Leal , Oliveira O. N.
Published: February 2003

Conduction of polyvinylidene fluoride is investigated by the method of constant current corona charging. During poling the surface voltage approaches a constant value, proportional to the current, if this is sufficiently small. When the corona is turned off it decreases to zero. Measurements with single and double electroded samples, for both polarities, give identical results, seeming to indicate conduction due to preexisting charges. Measurements in air of different relative humidity and in argon show that the conductivity depends on the presence of water vapor in the surrounding gas. Results are tentatively analyzed in terms of an equivalent circuit in which the sample is represented by a parallel connection of a capacitor and a resistor.
Computer simulation of a CF4 plasma etching silicon
Authors: Edelson David , Flamm Daniel L.
Published: February 2003

A CF4 plasma etching silicon has been simulated to identify dominant chemical processes and to quantify the effects of various reaction and transport parameters. The model was a one-dimensional plug-flow reactor in which a packet of gas is followed through the plasma and into the afterglow region, allowing the simulation to be performed as an initial value problem in ordinary differential equations. Two temperature zones were used with all known significant reactions incorporated into the chemical mechanism with the best available rate constants. Adjustable parameters were included only for certain sticking coefficients, surface recombination rates, and surface polymerization rates. Appropriate adjustment of these parameters gives satisfactory agreement between the simulations and experimental measurements of downstream gas-phase composition. The model unambiguously shows that fluorine atoms are the main reactive species in the plasma, that gas phase chemistry is clearly dominated by neutral reactions, and that formation of surface polymer has a strong effect on the composition of the gas phase. A full sensitivity analysis of the mechanism reveals that transport processes, surface chemistry, and the formation of fluorocarbon polymer on the walls are among the dominant components of the mechanism, but adequate data for these are unavailable. It is concluded that improvements in the model will require the inclusion of three-dimensional spatial dependencies and better information on surface processes.
Thomson spectrometer analysis of collectively accelerated ions
Authors: Smith John R. , Armstrong Carter M. , Doggett Wesley O.
Published: February 2003

An intense relativistic electron beam (0.5 MeV, 30 kA, 60 ns) was used for the collective acceleration of ions from (1) a localized gas ion source and (2) a localized plasma ion source. The ion energy scaling as a function of ion mass and charge state was found by using a Thomson spectrometer. Peak ion energy depended very weakly on ion mass and was independent of ion charge state. Although the presence of the ion source was necessary for ion acceleration to occur, generally the ion source did not supply the bulk of accelerated ions as many impurity ions were present.
Surface waves in SnTe/Sb superlattices
Authors: Kueny A. , Grimsditch M. , Jin B. Y. , Ketterson J. B. , Hilliard J. E.
Published: February 2003

The surface wave velocity in SnTe/Sb superlattices has been determined using Brillouin scattering. The velocity is independent of modulation wavelength over the range studied but is lower than would be expected if the layers of Sb and SnTe possessed their bulk properties. This is consistent with x-ray data which can be interpreted as evidence of a cubic polymorph of Sb which is unstable in bulk form.
Shock compression and flash heating of graphite/metal mixtures at temperatures up to 3200 K and pressures up to 25 GPa
Authors: Kleiman J. , Heimann R. B. , Hawken D. , Salansky N. M.
Published: February 2003

Different aspects of phase-transition processes in carbon in dynamic conditions were studied. Samples of graphite/metal mixtures have been recovered and analyzed after exposure to the combined action of high temperature and pressure pulses generated by a unique flash-heating hemispherical implosion system. Transmission electron microscopy together with x-ray and electron diffraction examinations proved the existence of diamond, different forms of graphite, and carbynes in the samples. A mechanism of formation of diamond is proposed which relies on a solid-vapor-liquid-solid (SVLS) sequence of phase transformations. The experimental results were found to be in reasonable agreement with the proposed SVLS model. A tetragonally crystallized diamondlike carbon phase ( p-diamond) was identified in the course of the work as well as a new linear carbon polymorph (Carbon-XIV).
Angular scattering distributions by long copper and brass cylinders: Experiment and theory
Authors: Cohen A. , Cohen L. D. , Haracz R. D. , Tomaselli V. , Colosi J. , Moeller K. D.
Published: February 2003

Experimental measurements of electromagnetic radiation scattered by long copper and brass cylinders were performed in the IR spectral range (λ=10.6 μm). The cylinders were oriented essentially normal to the scattering plane. The results of the measurements were compared with the theory for infinite tilted cylinders modified for relatively large refractive indices. The good agreement is presented and discussed.
Resolution beyond the diffraction limit in the acoustic microscope: A nonlinear effect
Authors: Rugar D.
Published: February 2003

By operating the reflection mode scanning acoustic microscope at nonlinear power levels, resolution beyond the linear diffraction limit can be achieved. To demonstrate this effect, imaging experiments were performed in liquid nitrogen, liquid argon, and water at frequencies between 2000 and 2800 MHz. The spatial frequency response of the nonlinear imaging system was found to have a cutoff frequency which is at least 1.4 times higher than the cutoff frequency of the linear system. It is proposed that the resolution improvement is the result of interaction between the transmitted fundamental beam and harmonics. The harmonics are generated in the converging portion of the beam and have focal spots which are significantly smaller than the focal spot of the fundamental beam. The harmonic power reflected by the object influences the detected fundamental power due to nonlinear (parametric) interaction and results in the improved imaging resolution. A simple physical model and a gaussian beam analysis are presented to elucidate energy exchange between the focused fundamental beam and the higher harmonics.
Be-implanted GaAs/GaAlAs double heterostructure stripe geometry lasers grown by metalorganic chemical vapor deposition
Authors: Shtrikman Hadas , Fekete D.
Published: February 2003

Be-implanted double heterostructure stripe geometry GaAs lasers grown by metalorganic chemical vapor deposition are described. Near-field and far-field patterns of the lasers are given. A regrowth process was used in order to introduce the highly conductive GaAs cap layer over the implanted structure.
A model for the saturation of the hydromagnetic Rayleigh–Taylor instability
Authors: Roderick N. F. , Hussey T. W.
Published: February 2003

The saturation of the hydromagnetic Rayleigh–Taylor instability is caused by the reduction of driving current in the bubble region between the spikes formed as the instability develops. For short wavelengths linear magnetic field diffusion provides the necessary smoothing of the magnetic field to reduce the driving force. For wavelengths longer than the magnetic field diffusion length, the current is shorted through material which expands into the bubble region. This initially low density accumulates in the bubble and eventually provides a source of sufficiently high conductivity plasma which reduces the magnetic field penetration to the front of the bubble. Simple analytic models have been developed to verify and and quantify these predictions. These models have been compared with two-dimensional magnetohydrodynamic calculations for imploding plasma shells and give good agreement with these more detailed simulations.