bluuebunny/crossref_metadata_2025 huggingface dataset:
Bright small molecular white organic light-emitting devices with two emission zones
Authors: Kim C.-H. , Shinar J.
Published: July 2002

Bright multilayer organic light-emitting devices (OLEDs) containing both perylene-doped [4,4′-bis(9-carbazolyl) biphenyl (CBP)] and [4-(dicyano-methylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran (DCM1)-doped tris-(8-hydroxy quinoline) Al (Alq3)] are described. The electroluminescence spectra consist of blue and green bands at 453, 487, and 524 nm due to perylene and a red band at 600 nm due to DCM1, although these two emitting layers are separated by a layer of [2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (Bu-PBD)]. As the thickness of the hole-injecting [N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-1, 1′-biphenyl-4,4′-diamine (NPB)] and perylene:CBP layers increases and that of the DCM1:Alq3 layer decreases the perylene emission intensifies strongly relative to the DCM1 emission. For 350 Å thick NPB, 350 Å thick perylene:CBP, 100 Å Bu-PBD, and 150 Å DCM1:Alq3, the brightness reaches 3750 Cd/m2 at 20 V, the efficiency is 2.4 Cd/A at 19 V, and the (x,y) CIE coordinates are well within the white region. However, as the bias is increased the intensity of the perylene emission increases relative to the DCM1 emission. Both the layer thickness and bias dependence are believed to result from changes in the recombination zone and in the field- and cathode-mirror-induced quenching of DCM1 singlet excitons.
TaC as a diffusion barrier between Si and Cu
Authors: Laurila Tomi , Zeng Kejun , Kivilahti Jorma K. , Molarius Jyrki , Suni Iikka
Published: July 2002

The reaction mechanisms and related microstructures in the Si/TaC/Cu metallization system have been studied experimentally and theoretically by utilizing ternary Si–Ta–C and Ta–C–Cu phase diagrams as well as activity diagrams calculated at 800 °C. With the help of sheet resistance measurements, Rutherford backscattering spectrometry, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the metallization structure with the 70 nm thick TaC barrier layer was observed to fail completely at temperatures above 725 °C because of the formation of large Cu3Si protrusions. However, the formation of amorphous Ta layer containing significant amounts of carbon and oxygen was already observed at the TaC/Cu interface at 600 °C. This layer also constituted an additional barrier layer for Cu diffusion, which occurred only after the crystallization of the amorphous layer. The formation of Ta2O5 was observed at 725 °C with x-ray diffraction, indicating that the oxygen rich amorphous layer had started to crystallize. The formation of SiC and TaSi2 occurred almost simultaneously at 800 °C. The observed reaction structure was consistent with the thermodynamics of the ternary system. The metallization structures with 7 nm and 35 nm TaC barrier layers failed above 550 °C and 650 °C, respectively, similarly because of the formation of Cu3Si. The high formation temperature of TaSi2 and SiC implies high stability of Si/TaC interface, thus making TaC layer a potential candidate to be used as a diffusion barrier for Cu metallization.
The subgrid-scale estimation model applied to large eddy simulations of compressible turbulence
Authors: Dubois Thierry , Domaradzki J. A. , Honein Albert
Published: July 2002

A subgrid-scale estimation procedure investigated previously for incompressible turbulence is extended to compressible flows. In the procedure the primary modeled quantities are the unfiltered velocity and temperature fields appearing in the expressions for the subgrid-scale stress tensor and heat flux. Estimates of the unfiltered fields are obtained from the known resolved fields in two steps. In the deconvolution step an approximate inversion of the filtering operation is performed. Subsequently, the nonlinear terms in the momentum and energy equations for the deconvolved quantities are used to generate a range of subgrid scales on a mesh two times smaller than the mesh employed for a discretization of the resolved quantities. Subgrid-scale stress and heat flux are computed directly from the definitions using estimated fields consisting of the deconvolved part and the nonlinear correction. The procedure has been applied and validated in a priori analyses and actual large eddy simulations of spatially decaying turbulence and shock/turbulence interaction exhibiting a very good agreement with filtered direct numerical simulation results. In all cases comparisons with the results provided by the standard implementation of the dynamic model are also made.
Low threshold 1.2 μm InGaAs quantum well lasers grown under low As/III ratio
Authors: Takeuchi T. , Chang Y.-L. , Tandon A. , Bour D. , Corzine S. , Twist R. , Tan M. , Luan H.-C.
Published: July 2002

We have achieved 160 A/cm2 threshold current density of a 1.21 μm InGaAs/GaAs quantum well (QW) laser grown under a very low As/III ratio. We investigated the As/III ratio dependence on the optical quality of InGaAs QWs grown with arsine and tertiarybutylarsine (TBA). We found that TBA allows us to grow high quality InGaAs QWs under a very low As/III ratio (∼3), while a higher As/III ratio (∼10) with arsine is necessary to obtain the similar quality QWs. This high quality InGaAs QW grown under the low As/III ratio leads to the realization of high quality InGaAsN QW which should be grown under a low As/III ratio and a high N/V ratio.
A study of orientational ordering in a fluid of dipolar Gay–Berne molecules using density-functional theory
Authors: Varga Szabolcs , Szalai István , Liszi János , Jackson George
Published: July 2002

We present a density-functional approach to describe the orientational ordering of nonpolar and dipolar Gay–Berne fluids. The first-order perturbation theory developed by Velasco et al. [J. Chem. Phys. 102, 8107 (1995)] for a Gay–Berne fluid is simplified and tested for molecules with a length to breath ratio of κ=3 and energy anisotropies of κ′=1, 1.25, 2.5, and 5. The theory is found to be in fair agreement with existing simulation data for the location of the isotopic–nematic phase transition, but it overestimates the vapor–liquid critical point of the fluid due to a description of the free energy at the mean-field level. The effect on the phase behavior of including a central longitudinal point dipole within the Gay–Berne molecule is studied using a correct treatment of the long-range dipolar contribution at the level of a second-order virial theory [B. Groh and S. Dietrich, Phys. Rev. E 50, 3814 (1994)]. For a given energy anisotropy of κ′=5 and reduced dipole moment μ*=0.5 we search for a stable ferroelectric nematic phase by changing the length to breath ratio κ. We do not find any evidence of ferroelectric nematic ordering for κ>1.5; the system only exhibits vapor–liquid and isotropic–nematic phase transitions for these values of the aspect ratios. For a slightly elongated and oblate shaped potential (e.g., κ=0.5), regions of stable isotropic–ferroelectric nematic and nematic–ferroelectric nematic phase coexistences are observed. The results of the theory indicate that a ferroelectic nematic fluid phase may be stabilized with respect to the positional ordering in the fluid of oblate dipolar particles. Comparison are made, where appropriate, with the existing results of Monte Carlo simulations for dipolar Gay–Berne fluids (Rull and co-workers, Molec. Phys. 94, 439 (1998); J. Chem. Phys. 109, 9529 (1998)).
Effects of electron–phonon interaction and chemical shift on near-band-edge recombination in GaN
Authors: Germain M. , Kartheuser E. , Gurskii A. L. , Lutsenko E. V. , Marko I. P. , Pavlovskii V. N. , Yablonskii G. P. , Heime K. , Heuken M. , Schineller B.
Published: July 2002

A coherent analysis of the near-band-edge luminescence spectra of undoped and Si-doped GaN layers grown by metalorganic vapor phase epitaxy on a sapphire substrate has been performed with a model including the effect of the charge carrier–longitudinal optical (LO) phonon interaction, based on Fröhlich’s polaron theory. This model allows one to correlate the relative intensities of the phonon sidebands to the position of the zero-phonon line from which ionization energies are obtained. Moreover, central-cell corrections are taken into account using two different models: the quantum defect model and the Lucovsky model [Solid State Comm. 3, 299 (1965)]. The effect of the electron-LO phonon interaction has been included in these models. Comparison between theory and experiment through the Huang-Rhys factor [Proc. Roy Soc. A204, 406 (1950)] allows a precise determination of the impurity binding energies and effective radii, as well as a reliable characterization of the charge carrier–LO phonon interaction.
Nonlinear optical properties of tetrahedral donor–acceptor octupolar molecules: Effective five-state model approach
Authors: Cho Minhaeng , An Sun-Young , Lee Hochan , Ledoux Isabelle , Zyss Joseph
Published: July 2002

Theoretical descriptions of the molecular nonlinear optical properties of tetrahedral donor–acceptor molecules are presented by using a valence-bond and four charge-transfer state model. Based on this five-state model, as the extent of the charge transfer from the peripheral donors (acceptors) to the central acceptor (donor) increases, the first hyperpolarizability monotonically increases. The theoretical predictions are confirmed by carrying out ab initio calculations of the first hyperpolarizabilities of three different series of tetrahedral molecules. The π-electron delocalization effect on the nonlinear optical property is elucidated by making a comparison of the first hyperpolarizability of the tetrahedral molecule with that of fictitious tetrahedrally assembled linear polyynes.
Identification of nanocrystal nucleation and growth in Al85Ni5Y8Co2 metallic glass with quenched-in nuclei
Authors: Wang J. Q. , Zhang H. W. , Gu X. J. , Lu K. , Sommer F. , Mittemeijer E. J.
Published: July 2002

The crystallization kinetics of an Al85Ni5Y8Co2 metallic glass, with quenched-in nuclei and a well-defined glass transition temperature (Tg) upon heating, was monitored by x-ray diffraction, differential scanning calorimetry, in situ electrical resistance measurement, and high-resolution transmission electron microscopy. It was found that the formation and the evolution of the primary Al nanocrystals proceed at largely separated stages. The growth of a few quenched-in nuclei of Al occurs predominantly well below Tg. In the vicinity of Tg (T<Tg), an additional large number of nanoscale Al particles appear, prior to the primary crystallization temperature above Tg. Subsequently, the growth of the Al nanocrystals, both the quenched-in ones and those formed upon heating, dominates the primary crystallization reaction.
Time-resolved x-ray diffraction: Statistical theory and its application to the photo-physics of molecular iodine
Authors: Bratos S. , Mirloup F. , Vuilleumier R. , Wulff M.
Published: July 2002

A theory is proposed to study time-resolved x-ray diffraction on the pico- and subpicosecond time scales. Electromagnetic fields are treated in the frame of Maxwellian electrodynamics, whereas the molecular system is treated by using quantum mechanics. An expression is given for the time-resolved x-ray signal; it involves a three-time correlation function of the Fourier transformed electronic density and of the electric dipole moment of the system. This theory is applied to the study of the recombination of photodissociated iodine molecules in solution. Both geminate and nongeminate recombination are considered. The feasibility of the real time visualization of atomic motions is discussed.
Fabrication of frequency-selective surfaces using microlens projection photolithography
Authors: Wu Ming-Hsien , Paul Kateri E. , Yang Jerry , Whitesides George M.
Published: July 2002

This letter describes the use of microlens projection photolithography (μLPL) for the fabrication of repetitive metallic micropatterns, and the application of these patterns as frequency-selective surfaces. Microlens projection photolithography uses an array of microlenses (diameter d=1–1000 micrometers) to project an array of images of an illuminated mask into photoresist. We converted these arrays into patterns in metals by electron beam evaporation and lift off. This technique can produce arrays over areas >10 cm2 with submicrometer feature sizes in a single exposure. We fabricated arrays of metallic micropatterns on substrates transparent to infrared radiation, and demonstrated that appropriate patterns acted as frequency-selective filters.
Spectroscopic investigation of the different long-lived photoexcitations in a polythiophene
Authors: Rothe Carsten , Hintschich Susanne , Monkman Andy P. , Svensson Mattias , Anderson Mats R.
Published: July 2002

Using time-resolved photoinduced transient absorption and gated emission techniques long-lived excitations of the solid-state conjugated polymer poly(3-methyl-4-octyl-thiophene) (PMOT) have been detected and analyzed at different temperatures. At 15 K phosphorescence and delayed fluorescence resulting from triplet and geminate pair decay, respectively, are observed. A redshifted emission (with respect to the prompt fluorescence) detected at ambient temperatures is assigned to excimer fluorescence. We also observed excitations with extremely long lifetimes of 300 ms at 289 K that we allocate to triplet excimer formation.
Extraordinary transmission of organic photoluminescence through an otherwise opaque metal layer via surface plasmon cross coupling
Authors: Gifford Dawn K. , Hall Dennis G.
Published: July 2002

We report extraordinary transmission of organic photoluminescence through an otherwise opaque, thin metal layer. We observe strong, angularly dependent photoluminescence from silver-coated films of Alq3 deposited on a corrugated substrate. Experimental and theoretical analysis indicates that light passes through the silver layer by cross coupling between surface plasmons on opposite sides of that layer. At narrow angles, the observed photoluminescence intensity is up to 10 times greater than that from a nonsilver-coated, uncorrugated organic film. This suggests an alternate device structure for efficient organic light emitting diodes.
Thickness dependent magnetic and magnetotransport properties of strain-relaxed La0.7Ca0.3MnO3 films
Authors: Ziese M. , Semmelhack H. C. , Han K. H. , Sena S. P. , Blythe H. J.
Published: July 2002

La 0.7 Ca 0.3 MnO 3 films with thicknesses between 2 and 300 nm were fabricated on LaAlO3, SrTiO3, and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates using pulsed laser deposition. After annealing at 950 °C in flowing oxygen, on LaAlO3 and LSAT, strain-relaxed epitaxial films of high quality were obtained. The magnetization, resistivity, and magnetoresistance of the films was studied as a function of thickness. Down to a thickness of about 4 nm no decrease of the saturation magnetization could be detected; the Curie temperature decreases slightly with thickness in agreement with finite size scaling theory. The thickness dependence of the conductance can be understood as a size-effect in thin films; there is no indication of an electrically dead interfacial layer.
Energy transfer in rare gas collisions with hydroxyl- and methyl-terminated self-assembled monolayers
Authors: Shuler Shelby F. , Davis Gwen M. , Morris John R.
Published: July 2002

Gas–surface scattering experiments are used to probe the dynamics of energy transfer and thermalization in collisions of 80 kJ/mol Ar with self-assembled monolayers composed of SH–(CH2)11–CH3 and SH–(CH2)11–OH alkanethiols on gold. We find that the extent of thermalization and the fractional energy transferred to the surface during the collision are significantly greater for the CH3-terminated surface than for the OH-terminated surface. Since the two monolayers are similar in structure, packing density, and mass, the differences in scattering dynamics are likely due to a combination of factors that may include differences in the available energy modes between the two terminal groups and the hydrogen-bonding nature of the OH-terminated alkanethiol self-assembled monolayer.
A theory of quantum diffusion localization
Authors: Chirikov Boris V.
Published: July 2002

The quantum localization of chaotically diffusive classical motion is reviewed, using the kicked rotator as a simple but instructive example. The specific quantum steady state, which results from statistical relaxation in the discrete spectrum, is described in some detail. A new phenomenological theory of quantum dynamical relaxation is presented and compared with the previously existing theory.
‘‘Dynamical confinement’’ in neural networks and cell cycle
Authors: Demongeot J. , Benaouda D. , Jézéquel C.
Published: July 2002

In this paper randomization of well-known former mathematical models is proposed (i.e., the Hopfield model for neural networks and the Hahn model for the cell cycle) in order to facilitate the study of their asymptotic behavior: in fact, we replace the determination of the stability basins for attractors and boundaries by the study of a unique (or a small number of) invariant measure(s), whose distribution function maxima (or, respectively, percentile contour lines) correspond to the location of the attractors (or, respectively, boundaries of their stability basins). We give the name of ‘‘confinement’’ to this localization of the mass of the invariant measure(s). We intend to show here that the study of the confinement is in certain cases easier than the study of underlying attractors, in particular if these last are numerous and possess small stability basins (for example, for the first time we calculate the invariant measure in the random Hopfield model in a case for which the deterministic version exhibits many attractors, and in a case of phase transition).
Noise controlled spiral growth in excitable media
Authors: Jung Peter , Mayer-Kress Gottfried
Published: July 2002

We consider a two-dimensional pulse-coupled array of noisy threshold elements with a long-range interaction. For tight coupling, we observe the formation of spatio-temporal excitation waves, such as target and spiral waves. For weak coupling, we find noise sustained spiral growth, where the noise level controls the scale of the spiral.
Chaotic dynamics of charged particles in the field of two monochromatic waves in a magnetized plasma
Authors: Benkadda S. , Sen A. , Shklyar D. R.
Published: July 2002

We study the dynamics of charged particles in the presence of two electrostatic waves propagating obliquely to an ambient magnetic field. The presence of a second wave makes the problem a two-dimensional and time-dependent one with a complicated phase space behavior. We derive a set of difference equations (maps) for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics. For the general case of oblique propagation, we observe synergistic effects leading to the lowering of the stochasticity threshold and the concomitant reduction in electric field amplitudes for particle heating applications. These results can be understood in terms of the resonance structures associated with the two waves and we obtain approximate analytic expressions for the thresholds. For the degenerate case of ω1=nΩ,ω2=mΩ (where ω1,ω2 are the frequencies of the two waves, Ω is the cyclotron frequency and n,m are integers) and strictly perpendicular propagation, the problem simplifies to a one-and-one-half-dimensional one. We observe the presence of stochastic webs in this situation.
Spatial organization, predictability, and determinism in ventricular fibrillation
Authors: Bayly P. V. , KenKnight B. H. , Rogers J. M. , Johnson E. E. , Ideker R. E. , Smith W. M.
Published: July 2002

The degree of spatial organization of ventricular fibrillation (VF) is a fundamental dynamical property of the arrhythmia and may determine the success of proposed therapeutic approaches. Spatial organization is closely related to the dimension of VF, and hence to its predictability and controllability. We have explored several techniques to quantify spatial organization during VF, to predict patterns of activity, and to see how spatial organization and predictability change as the arrhythmia progresses. Epicardial electrograms recorded from pig hearts using rectangular arrays of unipolar extracellular electrodes (1 mm spacing) were analyzed. The correlation length of VF, the number of Karhunen-Loève modes required to approximate data during VF, the number, size and recurrence of wavefronts, and the mean square error of epicardial potential fields predicted 0.256 seconds into the future were all estimated. The ability of regularly-timed pacing stimuli to capture areas of fibrillating myocardium during VF was confirmed by a significant increase in local spatial organization. Results indicate that VF is neither “low-dimensional chaos” (dimension <5) nor “random” behavior (dimension=∞), but is a high-dimensional response with a degree of spatial coherence that changes as the arrhythmia progresses.
A note on solid-state reaction kinetics: The formation of silicides from thin films of metallic alloys
Authors: d’Heurle F. M.
Published: July 2002

The overall kinetics of silicide formation from metal-silicon reactions, like those of most solid state reactions, result from the interactions of specific kinetic effects and thermodynamic terms. The decrease in reaction rate which is observed when Ni-Cr alloys substituted for pure Ni cannot be explained by changes in the thermodynamic driving force. Some alternative suggestions are proposed.
Deep-level transient spectroscopy studies of minority carrier traps in neutron-irradiated silicon
Authors: Tokuda Y. , Usami A.
Published: July 2002

Measurements of minority carrier traps produced in silicon by neutron irradiation at room temperature were performed using deep-level transient spectroscopy (DLTS), and these results were compared with those in 2-MeV electron-irradiated silicon. One electron trap (Ec−0.29 eV) and one hole trap (Ev+0.43 eV) were observed in neutron-irradiated p- and n-type silicon, respectively, which were also observed in the 2-MeV electron case. Furthermore, it was found that the isochronal annealing behavior of these minority carrier traps between the neutron and the 2-MeV electron case coincided with each other. The present results about minority carrier traps and previously reported ones about majority carrier traps indicated that the neutron damage was similar to the electron damage as far as the DLTS measurements are concerned.
Crystal and magnetic structure of Pr2Fe14B and Dy2Fe14B
Authors: Herbst J. F. , Yelon W. B.
Published: July 2002

Rietveld analyses of neutron powder diffraction data on Pr2Fe14B and Dy2Fe14B are reported. Both phases form the Nd2Fe14B tetragonal crystal structure (P42/mnm). At 77 and 293 K our analyses indicate that all magnetic moments in each compound are collinear with the c axis. The rare-earth moments in Pr2Fe14B are parallel to the Fe moments (ferromagnetic) and are antiparallel in Dy2Fe14B (ferrimagnetic).
An application of a statistical model for the calculation of the logarithmic mean excitation energy of molecules: Molecular hydrogen
Authors: Kamaratos Efstathios
Published: July 2002

A statistical model, the local plasma approximation, is considered for the calculation of the logarithmic mean excitation energy for stopping power of chemically bound particles by taking into consideration chemical bonding. This statistical model is applied to molecular hydrogen and leads to results that suggest a value for the logarithmic mean excitation energy of molecular hydrogen that is larger than the accepted experimental and theoretical values.
Measurement of kinetic parameters relevant to the operation of an electron-beam initiated atomic iodine laser
Authors: Ramirez Jorge E. , Bera Ranajit K. , Hanrahan Robert J.
Published: July 2002

Parameters relevant to the operation of an electron-beam initiated atomic iodine laser, which would lase on the transition 5 2P1/2 (I*)→5 2P3/2 (I), have been measured by pulse radiolysis. Kinetic data for the parent compound quenching of I* were obtained by variation of the parent compound pressure at constant buffer gas pressure and observing I* decay rates versus time. Deactivation rates for perfluoroalkyl iodides were found to be much lower than for the corresponding alkyl iodides. Values obtained (in cm3 molec−1 s−1) are as follows: CH3I, (2.0±0.1)×10−13; C2H5I, (5.0±0.3)×10−13; CF3I, (8.8±0.3)×10−16; C2F5I, (9.7±1.0)×10−15; n-C3F7I, (2.5±0.2)×10−15; i-C3F7I, (1.7±0.1)×10−15; n-C4F9I, (1.8±0.1)×10−14. The extent of population inversion was investigated by measuring initial excited state and ground state atomic iodine concentrations, which gives the branching ratio [I*]/[I]. Values obtained are as follows: CH3I, 2.7; CF3I, 3.8; C2F5I, 2.7; i-C3F7I, 3.2; n-C4F9I, 1.8. Comparing both branching ratios and lifetimes, it is seen that CF3I is the most promising candidate for an electron beam initiated atomic iodine laser.
Effects of thermal annealing on semi-insulating undoped GaAs grown by the liquid-encapsulated Czochralski technique
Authors: Chin A. K. , Camlibel I. , Caruso R. , Young M. S. S. , Von Neida A. R.
Published: July 2002

Recently, a number of studies have reported a correlation between variations in threshold voltage of field effect transistors and the nonuniformity of the luminescence efficiency of semi-insulating GaAs crystals grown by the liquid-encapsulated Czochralski technique. The changes in luminescence efficiency and subsequently the variations in threshold voltages were dramatically reduced by postgrowth annealing of the GaAs crystals under a variety of conditions. In this study, we employ the technique of spatially resolved cathodoluminescence (CL) to carefully examine the changes in luminescence efficiency due to postgrowth annealing. In agreement with previous work, we find that the CL variations are greatly reduced from a factor of ∼2 to ∼5% by thermal annealing at 800 °C for 30 h or at 1200 °C for 6 h followed by slow cooling. The latter thermal treatment is the same as that experienced by crystals during growth by the horizontal gradient freeze (HGF) technique. The extremely uniform luminescence efficiency of HGF crystals is thus believed to be a result of the thermal treatment during growth. Using evacuated sealed ampoule annealing in the temperature range of 550–650 °C, we show for the first time that improvements in CL uniformity are a result of a diffusion process which involves an As vacancy. Due to the dependence on As loss, values of the diffusivity (D) depend on the surface conditions. Values of D=9×106 exp(−2.6 eV/kT) cm2/s and D=1×107 exp(−2.5 eV/kT) cm2/s are obtained for polished and as-cut surfaces, respectively.
Auger electron spectroscopy study of alloy formation on MIS solar-cell metal surfaces
Authors: Pandelišev Kiril A. , Wang Edward Y.
Published: July 2002

The alloy formation on MIS solar cell metal surfaces due to the drive-out diffusion have been studied here. Au and Ag were used as metal electrodes, SnO2 as an interfacial layer, and GaAs as a substrate. These microscopic reactions at the interface and at the front metal surface are related to the performance and the stability of the GaAs, MS, and MIS solar cells.
In-depth profiling of sputter-induced space-charge compensation in p-silicon Schottky barriers
Authors: Hellings G. J. A. , Straayer A. , Kipperman A. H. M.
Published: July 2002

The dc sputtering of gold on p-type silicon introduces sputter (damage) effects, which can be divided into surface effects and space-charge region effects. The space-charge region effects are investigated by capacitance profiling in combination with anodic oxide stripping of thin layers of silicon. In this way, it is possible to obtain a complete profile of sputter-induced electrically active states, not only at the end of the space-charge region, but up to the surface of the silicon. It is observed that donorlike states are capable of almost fully compensating the acceptor states over distances of one micrometer typically. Possible explanations for the origin of these states in terms of field-enhanced diffusion of species activated during the sputter process are discussed.
Observation of a doping-dependent orientation effect of the depletion of silicon self-interstitials during oxidation
Authors: Tan T. Y. , Yang K. H. , Schneider C. P.
Published: July 2002

We conducted an experiment to study the growth kintetics of the oxidation-induced stacking faults (OSF) of n- and p-type (100) and (111) Si wafers with resistivities of 0.8–15 Ω cm. The OSF size data are as expected for the p-type (100) and (111) wafers as well as for the n-type (100) wafers. For the n-type (111) 0.8–2 Ω cm wafers, however, no OSF were generated at a temperature higher than ∼1100 °C and those grown at 1050 °C are considerably smaller than expected. This indicates that in the n-type (111) wafers there exists a mechanism that depletes Si self-interstitials, in addition to the normal mechanism of interstitial injection. Obviously, the effect is dependent on orientation as well as on doping. The same kind of effect was found before via diffusion studies, which, however, did not appear as doping dependent. We propose that this discrepancy is apparently due to the fact that, in one diffusion experiment, p+ (111) materials (Ga implanted to a concentration exceeding 1020 cm−3) were oxidized.
Elastic properties of a computer-simulated polycrystalline aggregate of a single component
Authors: Middya T. R. , Basu A. N. , Sengupta S.
Published: July 2002

A simple procedure involving sound velocities in component crystallites has been developed to calculate the effective elastic properties of a hypothetical aggregate which is macroscopically homogeneous but has fluctuations on a microscopic scale, with the underlying assumption that the sound wave can distinguish between the different crystallites oriented at random. For comparison we have also employed the effective medium theory based on a static deformation scheme to calculate the effective elastic properties of the same hypothetical aggregate. Both the procedures use the identical set of input data. Although the assumptions on which the above dynamic and static methods are based are entirely different the results obtained from them for seventeen different aggregates are remarkably close to each other and also to experiments done on polycrystalline specimens using ultrasonic velocities. Finally, a critical discussion of the results and their consequences is presented.
Thermal reaction of gold metallization on InP
Authors: Wada Osamu
Published: July 2002

The thermal reaction of evaporated Au films with InP substrate has been studied using scanning electron microscopy, secondary ion mass and Auger electron spectroscopy, and x-ray diffraction techniques in the temperature range 345–460 °C. Below 450 °C, In and P out-diffusion with In being the faster diffusing species, as well as Au in-diffusion have been found to take place to form Au2P3 and Au3In phases at the Au-InP interface and in the outer region of the Au layer, respectively. The kinetics of P penetration into Au and Au penetration into InP have been determined to be controlled by diffusion kinetics with an activation energy of 2.31 eV. At the temperature above 450 °C, only AuIn2 phase has been found to form within the original InP bulk leaving a planar surface and facets on the {111} P planes. Microstructures, in-depth composition profiles and binary phases observed in the present experiment have been correlated in terms of Au-InP solid state interaction at various temperatures. Based on the result of this study, methods of obtaining Au-based contacts to InP with high stability have been discussed. The use of thin metallization has been found to be effective to restrict the Au-semiconductor reaction. This has been applied to the p contact of InGaAsP/InP light emitting diode and its improved stability has been confirmed under current stress experiments.
Monte Carlo simulation of a thin film of uniform thickness deposition in a stationary system
Authors: Peixoto Luciano T.
Published: July 2002

We have used the Monte Carlo method to simulate the process of thin-film deposition in a stationary vacuum system. By supposing a stationary tube of appropriate dimensions interposed between the source and the substrate it was possible to simulate the deposition of films that have high uniformities over large substrate areas. Our results basically corroborate the experimental ones found with a tube of approximately the same dimensions and may be useful in the search of relative values of the tube parameters which optimize the performance of the system.
Scattering of lateral waves by buried or submerged objects. I. The incident lateral-wave field
Authors: King Ronold W. P.
Published: July 2002

The components of the lateral-wave field generated by vertical and horizontal antennas near the plane interface between air and earth (soil, water, etc.) are determined at points near the surface in air and at all points in the earth. This is the field incident on and scattered from inhomogeneities and objects in the earth.
Epitaxial (100) silicon films grown at low temperatures in an electron-beam evaporator
Authors: Milosavljević M. , Jeynes C. , Wilson I. H.
Published: July 2002

Epitaxial silicon films were grown on (100) silicon wafers at temperatures between 650 and 700 °C without the need of special cleaning procedures. Deposition rates were from 30 to 80 nm/min. The structure of films was analyzed by Rutherford backscattering, transmission electron microscopy, and secondary ion mass spectroscopy. The films were doped by ion implantation. Electrical activity, Hall mobility, and sheet resistivity of the doped layers were measured. Both structural and electrical characterization yielded results indistinguishable from good-quality bulk wafers.
Sputtering of chlorinated silicon surfaces studied by secondary ion mass spectrometry and ion scattering spectroscopy
Authors: Barish E. L. , Vitkavage D. J. , Mayer T. M.
Published: July 2002

We have studied the sputtering of chlorinated Si surfaces by 1-keV Ne+ impact using secondary ion mass spectrometry and low-energy ion scattering spectroscopy. Under steady-state conditions of submonolayer Cl coverage, SiCl+x ions (x=0–3) are all observed with identical coverage dependence. Cross sections for removal of Cl from Si are independent of initial coverage in the submonolayer regime. Sputter cross sections increase from 0.5×10−15 cm2 at normal incidence to a maximum of 22×10−15 cm2 at ∼70° angle of incidence. Secondary ion yields are shown to be markedly dependent on the presence of recoil-implanted Cl in the substrate. The details of Cl sputtering and Si removal processes in ion-assisted etching suggest a major role for recoil implantation of Cl into the Si lattice in formation and removal of SiClx products in etching reactions.
Probability density function of the potential energy due to random impurities in semiconductors
Authors: Scribner Dean A. , Leopold Lutz
Published: July 2002

We have calculated the probability density function of the potential energy for the case of heavily doped uncompensated semiconductors due to randomly located ionized impurities. The approach combines both analytical and numerical techniques to form a piecewise approximation of P(E) and can be used in conjunction with all types of screening potentials. We obtained a measure of the quality of our results by comparing the moments of our approximated function for P(E) with those moments obtained directly from the known generating function. The agreement between the two sets of moments is extremely good for lower and higher order moments which demonstrates the high accuracy of our piecewise approximation for P(E). Our result turns out to be non-Gaussian with a peak that is higher than and shifted in comparison to, the results of previous Gaussian approximations based on lower order moments only.
Electromagnetic wave propagation in a planar helix with a metal shield
Authors: Sinha M. P. , Jha R. K. , Basu B. N. , Prasad R. K.
Published: July 2002

Dispersion properties of the electromagnetic (em) waves propagating through a planar helix are investigated. A dispersion relation is obtained which includes influence of the outer metal shield on the em wave propagation. It is shown that the phase velocity of em waves reduces as the metal shield is brought closer to the planar helix.
Mean speed measurement of Ni and Pd molecular beams
Authors: Yamamoto Shigehiko , Habu Tooru
Published: July 2002

The mean speed of Ni and Pd molecular beams effused from a nonequilibrium source has been measured by means of a phase-sensitive detection technique and is compared with the statistical mean speed. The mean speeds are determined to be 65,000 and 52,000 cm/s for Ni (1450 °C) and Pd (1320 °C), respectively. The ratio of the mean speed with respect to the statistical mean speed varies from 0.9 to 1.1, and from 0.92 to 1.18 for Ni and Pd, respectively, for the modulation frequency range 300–1200 Hz.
Ferrofluid studies of recorded data and defect identification in small high-performance rigid discs
Authors: Weiss R. D. , Schifter J. , Borduz L. , Raj K.
Published: July 2002

In this work, a newly developed ferrofluid was used for studying recorded data patterns on high-performance rigid discs where densities exceed 10 000 frpi. It has been found that ferrofluids must exhibit certain properties to be useful in this application. Fluid properties such as particle size distribution, concentration and stability are described as they relate to optical (microscopic) resolution of the magnetic pattern. The application of this new water based ferrofluid for single-bit defect detection is also discussed in conjunction with a novel method which was developed for this use.
Magnetic filtration of submicroscopic particles through a packed bed of spheres
Authors: Arajs Sigurds , Moyer C. A. , Aidun R. , Matijevic’ E.
Published: July 2002

A small-scale experimental facility for studying the magnetic filtration of submicroscopic particles through a bed of packed spheres is described. The experimental parameters are the particle size and concentration, solution pH, flow rate, magnetic field, filter characteristics, and time. Some results for aqueous solutions containing submicron α-Fe2O3 spherical particles are presented, and discussed from the viewpoint of recent theoretical studies.
Collective acceleration of laser-produced ions
Authors: Cremer J. T. , Destler W. W.
Published: July 2002

The collective acceleration of heavy ions (C, Al, Fe) from a laser produced plasma to energies in excess of 10 MeV/amu has been observed experimentally. In the experiments, an intense relativistic electron beam (1.2 MeV, 30 kA, 30 ns) is injected through an anode aperture into a downstream drift region. Ions to be accelerated are produced by firing a Q-switched ruby laser (0.3–15 J, 15 ns) at a target material located immediately downstream of the anode aperture. Accelerated ion energies are measured by time of flight, range-energy, and Thomson spectrometer techniques.
Determination of variable magnetic anisotropy in sputtered Ni-Fe films using hysteresis loops (abstract)
Authors: Baral Debasis
Published: July 2002

Hysteresis loops from Ni-Fe films are known to take shapes that do not always resemble hard or easy axis loops. Distortions in the loops have earlier been related to the deposition conditions and thicknesses of the films. In this work a new experimental approach was developed to understand the nature of distortions in M-H loops. Ni-Fe films with 80 wt. % Ni were sputter deposited under different conditions to obtain varying amounts of easy [111] and hard [200] axis textures (producing variable magnetic anisotropy) in the film. After x-ray characterization, in-plane hysteresis loops from these films were plotted, digitized, and stored. The digitization of the loop was done to perform mathematical operations on different sets of loops. It was found that a distorted loop can be viewed as an algebraic sum of loops obtained from different crystallographic orientations of the magnetic alloy. This technique was also used to quantify the volume fractions of easy and hard axis orientations present in the film. In this work, it has been shown that observed distortions in M-H loops are due to the presence of easy and hard axis orientations in the plane of the film and can be empirically related to the preparation condition or thickness of the film.
Primary textures of a high-permeability silicon steel cold rolled with interpass aging
Authors: Flowers J. W. , Wright W. S.
Published: July 2002

Primary surface textures and magnetic properties were determined on specimens of a high-permeability grain-oriented silicon steel processed with and without interpass aging treatments of 5 min at 175 °C during cold rolling. The steel contained AlN and MnS as primary grain growth inhibitors. The main primary texture changes associated with the use of interpass aging were significant decreases in the amounts of material with orientations near {111}〈112̄〉 and {554}〈225̄〉 and smaller increases in the amounts of material with orientations near {110}〈001〉 and {100}〈UVW〉. Interpass aging improved the core loss and permeability, in agreement with prior work.
Modeling of the ferromagnetic hysteresis in textured and strained steel
Authors: Szpunar J. A. , Szpunar B.
Published: July 2002

The mean field model has been used to analyze the hysteresis loops in textured and strained steel. We observe an increase of the pinning constant with plastic deformation and a strong variation of the pinning parameter in various directions in Fe-Si steel. The interpretation of changes of the pinning parameter is related to the dislocation density for deformed specimens. It has also been demonstrated that in textured Fe-Si steel the changes in the mean value of magnetocrystalline energy follow closely the observed changes of the pinning parameter.
Bloch line memory: Dams for stripe domain confinement
Authors: Klein D. , Engemann J.
Published: July 2002

In the Bloch line memory, stripe domains are used as storage loops for vertical Bloch lines (VBL). In this paper we report on a technological solution for locally stabilizing these domains and also for setting a one-dimensional potential for VBL propagation by means of ion-milled grooves and dams. The changes in shape of the garnet film have been studied both theoretically and experimentally. The interaction of magnetic domains with topographic shaping of magnetostrictive (111) films are examined in detail in the case of a single groove. Stabilization margins are found to be related to the geometric data of topographic shaping, to the crystallographic orientation of the grooving edges, and to the magnetoelastic properties of the garnet film. Qualitative agreement with the prediction of the theoretical considerations is obtained from measurements on as grown (YSmLuCa)3(GeFe)5O12-garnet films with a periodical arrangement of grooves and dams, carried out by bias-field pulses margins with up to 130 Oe (tp=1 μs) without sweeping the domains from the region of the grooves to the dams.
The trapping of deuterium in argon-implanted nickel
Authors: Frank R. C. , Rehn L. E. , Baldo P.
Published: July 2002

Argon ions with energy 250 keV were implanted at fluences of 2×1016 cm−2 at temperatures of 500, 250, and 21 °C, in a specimen of relatively pure polycrystalline nickel. Deuterium was introduced into the surface and implanted regions by making the specimen the negative electrode of an electrolytic cell containing 1-N pure deuterated sulfuric acid. Deuterium trapped in the vacancy complexes of the implanted regions was analyzed as a function of temperature using the 2H(3He,1H)4He nuclear reaction during an isochronal annealing process. The results indicate that the types of traps and trap densities found in the regions implanted at 21 and 250 °C were essentially identical while the trap density found in the region implanted at 500 °C was approximately 40% of that found in the other regions. Math model comparison with the experimental results suggests the existence of at least two types of traps in each region. Trap binding enthalpies used in the math model to fit the experimental data were slightly higher for the region implanted with argon at 500 °C than for the regions implanted at the lower temperatures. TEM studies revealed the presence of small voids in the region implanted at 500 °C as well as dislocation loops similar to those found in the regions implanted at the lower temperatures.
NbN formation on carbon fibers with a duo magnetron sputtering system
Authors: Ohshima S. , Dietrich M. , Linker G.
Published: July 2002

Superconducting NbN was produced on commercial carbon fibers and sapphire substrates by dc reactive magnetron sputtering. Uniform coating was achieved by spreading 9000 filaments into a strip located between two planar magnetrons facing each other. The conditions for B1 phase formation and homogeneous coating have been studied. Over a rather wide range of total pressures, pAr+pN2, the highest superconducting transition temperature was found for a nitrogen partial pressure pN2 of about 0.05 Pa. In addition, tensile or compressive strains were produced in the NbN film on the carbon fiber as a function of bias. The NbN grain size was controlled in the range between 10 and 25 nm. Without a bias, the usual (111) preferential orientation of the grains was observed in the NbN film on the carbon fiber. The intensity ratio I200/I111 could be controlled between 0.74 and 0.4. Under an increased bias, the lattice parameter grew from about 0.4385 to about 0.4395 nm. This behavior may be due to a variety of reasons. The superconducting critical currents jc in a self-magnetic field are about 105 A/cm2 for NbN on carbon fibers (C-NbN) and about 2×106 for NbN on sapphire (S-NbN). Various microstructures and, to some extent, also mechanical defects are thought to be responsible for this difference. At 13 T, the corresponding jc values are 2×104 and 105 A/cm2 for NbN films of 1-μm thickness. The extrapolated Bc2 (4K) values for C-NbN are about 30–35 T, for S-NbN about 25 T. The nucleation conditions for NbN depended strongly on the substrate; this was found to be true for the existence of the B1 phase with respect to gas composition, microstructure, and deposition rate. The analysis of the composition of the films, which was performed by Rutherford backscattering and scanning Auger depth profiling, revealed uniform compositions with approximately 1-at. % carbon and approximately 0.1-at. % oxygen contaminations.
The size of particles coagulating in a changing environment
Authors: Simons S.
Published: July 2002

A calculation is given for the mean size of particles coagulating in an expanding gaseous medium. It is shown that depending on the rate of expansion and the detailed coagulation mechanism, the particle size may become infinite after a finite or infinite time, or may remain finite after an infinite time. Possible applications are indicated and illustrated numerically.
Effects of substrate polishing on double-heterostructure AlyGa1−yAs-AlxGa1−xAs lasers grown by molecular beam expitaxy
Authors: Caldwell P. J. , Laidig W. D. , Lin Y. F. , Peng C. K. , Magee T. J. , Leung C.
Published: July 2002

Data are presented indicating that remnant damage retained beneath the surface of GaAs substrates as a result of polishing has an adverse effect on the performance of semiconductor laser diodes. Deep subsurface damage, observed on the etched/polished substrates provided by the crystal manufacturer, can be removed with an extended etch using a bromine-methanol solution or with a noncontact polishing process developed at ARACOR. Data are shown for laser structures with both GaAs and AlxGa1−xAs active layers, grown by molecular beam epitaxy on substrates prepared to compare the effects of the three polishing techniques. Laser structures grown on substrates prepared by bromine-methanol and noncontact polishing show lower threshold current densities and a marked increase in device uniformity.