bluuebunny/crossref_metadata_2025 huggingface dataset:
Point defect based modeling of low dose silicon implant damage and oxidation effects on phosphorus and boron diffusion in silicon
Authors: Park Heemyong , Law Mark E.
Published: July 2002

Point defect kinetics are important for understanding and modeling dopant diffusion in silicon. This article describes point defect models and compares them with experimental results for intrinsically doped material. Transient dopant diffusion due to low dose silicon implant damage can be modeled with the same parameters as oxidation enhanced diffusion, and therefore provides an additional technique to probe point defect behavior. Parameters are extracted consistently for both experimental conditions and fit to Arrhenius relationships. The theory of dopant-defect pairing is found to be crucial in modeling the implantation damage effects, and the effective binding energies for boron-defect and phosphorus-defect pairs are experimentally determined.
Factors affecting the Cl atom density in a chlorine discharge
Authors: Deshmukh Shashank C. , Economou Demetre J.
Published: July 2002

A mathematical model was developed for the bulk plasma of an electrodeless chlorine discharge sustained in a tubular reactor. The model was used to investigate the factors affecting the Cl atom density in the plasma. Rate coefficients for electron-particle reactions in the Cl2/Cl mixture were obtained by solving the Boltzmann transport equation for the electron-energy distribution function. These rate coefficients were then used in a plasma model to calculate the self-sustaining electric field, electron density, and atomic chlorine density in the plasma. The effect of frequency, power, gas flow rate, neutral density, tube radius, and wall recombination coefficient was examined. For otherwise identical conditions, nearly the same atom density was obtained in 13.56 MHz and 2.45 GHz discharges. It was found that very high degrees of molecular dissociation are possible with only a few W/cm3 in the plasma. Despite the fact that the atom density decreased with increasing feed gas flow rate, the atom flux increased with flow rate. In the parameter range investigated, lower pressures and larger tube radii favored higher atom density in the plasma. The model is useful for optimizing source efficiency and for use as a ‘‘module’’ in multidimensional radical transport and reaction models of remote plasma processing reactors.
Thermal transport properties of single crystal lanthanum aluminate
Authors: Michael Peter C. , Trefny John U. , Yarar Baki
Published: July 2002

The thermal diffusivity and thermal conductivity of single crystal (100) lanthanum aluminate (LaAlO3) have been determined in the temperature range 77–353 K. The thermal diffusivity was measured using a transient heat-pulse technique and the thermal conductivity by a steady state dc technique. The specific heat capacity was calculated from the thermal diffusivity and thermal conductivity data obtained. The temperature dependence of the thermal diffusivity was found to be of the form [T exp(TD/bdT)] and that of the thermal conductivity of the form [T3 exp(TD/bcT)]. Both results are consistent with the expected behavior of the thermal transport, limited by phonon-phonon collision (‘‘Umklapp’’) processes, in high purity dielectric single crystals. The Debye temperature (TD) was calculated as 720±22 K and the parameters bd and bc were found to be 1.4±0.1 and 0.7±0.1, respectively. The average sound velocity was calculated to be (5.4±0.6)×105 cm/s. The phonon mean-free-path at 303 K was found to be (2.2±0.2)×10−7 cm.
Valency and type conversion in CuInSe2 with H2 plasma exposure: A photoemission investigation
Authors: Nelson Art J. , Frigo Sean P. , Rosenberg Richard
Published: July 2002

The effect of H2 plasma exposure on CuInSe2 was studied by synchrotron radiation soft-x-ray photoemission spectroscopy. The low-power H2 plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2 with the plasma exposure being performed at 200 °C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence-band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H2 plasma exposure type converts the CuInSe2 surface to an n-type surface as well as converting the In+3 valency state to an In+1 valency state.
Magnetic properties of sputtered Fe thin films: Processing and thickness dependence
Authors: Kim Y. K. , Oliveria M.
Published: July 2002

The microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200–1000 Å have been investigated. The films were prepared by rf sputtering onto SiO2 substrates. The investigation was prompted by the lack of data on sputtered Fe films in this thickness regime as well as disagreement in the data for evaporated films. In addition to thickness, substrate temperature and deposition pressure were varied to examine their effect on the microstructure. The film microstructure was characterized by x-ray diffraction, transmission electron microscopy, and Auger spectroscopy. The polycrystalline films did not display a strong preferred orientation and had average grain sizes of 60–85 Å. Surface oxide layers formed upon exposure to air ranged from 10 to 80 Å, the thicker oxides formed on films with lower density. Magnetic hysteresis measurements were made with a vibrating sample magnetometer. Below 1000 Å, porosity and surface oxidation result in reductions up to 25% in the saturation magnetization. An anomalous peak in coercivity at film thicknesses of 300–500 Å was observed, which can be explained by the change in domain wall type.
Molecular magnets V(tetracyanoethylene)x⋅y(solvent): Applications to magnetic shielding
Authors: Morin B. G. , Hahm C. , Miller Joel S. , Epstein A. J.
Published: July 2002

The specific advantages and limitations of a new class of polymer based magnets [exemplified by V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene)] for static and low frequency magnetic shielding and inductive applications are evaluated using results of dc superconducting quantum interference device magnetization and ac permeability measurements. Present materials have very low density (ρ∼1 g/cm3), relatively high resistivity (∼104 Ω cm), and low power loss (as low as ∼2 erg cm−3 cycle−1). The highest initial room temperature permeability observed to date (for solvent=CH2Cl2) of μi=13 is modest for practical applications. Flexible processing methods are suggested for optimization of magnetic properties important for shielding applications.
Magnetic study of the diluted magnetic semiconductor Sn1−xMnxTe
Authors: Eggenkamp P. J. T. , Vennix C. W. H. M. , Story T. , Swagten H. J. M. , Swüste C. H. W. , de Jonge W. J. M.
Published: July 2002

New measurements of the magnetic carrier-induced properties of Sn1−xMnxTe for x≤0.10 are presented. The results of these and previously reported measurements for other compositions and carrier concentrations will be compared to model calculations of the low-temperature magnetic state. A magnetic phase diagram will be presented.
Magnetic properties of a new amorphous magnet
Authors: Landee C. P. , Wynn C. M. , Albrecht A. S. , Zhang W. , Vunni G. B. , Parent J. L. , Navas C. , Turnbull M. M.
Published: July 2002

An amorphous phase of Co3BTCA2(H2O)6 has been prepared (BTCA=1,3,5-benzenetri- carboxylate). The static properties (dc susceptibility, hysteresis) of Co3BTCA2(H2O)6 are similar to those of other ‘‘glassy’’ magnetic systems, but the dynamics of Co3BTCA2(H2O)6 (absence of long relaxation times, disappearance of frequency dependence at low temperatures) are unusual. The amorphous phase is characterized by a narrow hysteresis loop at low temperature. For the hysteresis curve at 4.2 K, the coercive field is several hundred Oersted and the remnant magnetization is on the order of 10−2 Msat. The temperature dependence of the dc magnetic susceptibility shows an unusual field dependence below 30 K, with the largest effective moments being obtained in the smallest applied fields. The freezing temperature, Tf, in zero field, as determined by both dc and ac susceptibilities, has been found to be Tf=23 K. The ac susceptibility shows the characteristic spin glass frequency dependence, yet loses all frequency dependence for temperatures below 9 K.
Refractive index of (AlxGa1−x)0.5In0.5P quaternary alloys
Authors: Adachi Sadao , Kato Hirokazu , Moki Akira , Ohtsuka Kouji
Published: July 2002

Refractive-index dispersion in (AlxGa1−x)0.5In0.5P quaternary alloys has been measured at room temperature in the 1.2–2.9 eV photon-energy range by using spectroscopic ellipsometry. The measured data are fitted to the first-order Sellmeier equation. The resulting expression can be used in the design of various waveguiding devices.
Quasipotential and the stability of phase lock in nonhysteretic Josephson junctions
Authors: Kautz R. L.
Published: July 2002

The principle of minimum available noise energy is used to calculate the quasipotential over the state space of a nonhysteretic Josephson junction driven by a rf bias. This potential surface provides an intuitive picture of the dynamics of phase lock and defines a stability parameter, the activation energy for thermally induced phase slippage, which determines the optimum operating conditions for a proposed programmable voltage standard.
A secondary-ion-mass spectrometry study of magnesium diffusion in lithium niobate
Authors: Caccavale F. , Chakraborty P. , Mansour I. , Gianello G. , Mazzoleni M. , Elena M.
Published: July 2002

A detailed study of magnesium indiffusion in lithium niobate (LiNbO3) crystal is presented. The aim of the work was to obtain a comprehensive understanding of the diffusion process as a function of film thickness, temperature, diffusion time, crystal cut-direction. The secondary-ion-mass spectrometry technique was employed to obtain magnesium concentration depth profiles. Our results show that the strongest factor that controls the diffusion process is the temperature. A noticeable increase of the diffusion coefficient is observed with increasing temperature. The diffusion time has a small effect on the diffusion coefficient, but if the former is less than a certain value, the deposited MgO film does not diffuse completely. On the other hand, if it is quite long it will enter into the annealing regime. Diffusion parameters to realize buried waveguides (which reduce the coupling loss between single-mode fibers and diffused waveguides) have also been derived. The present studies could be important in consideration of the synthesis of LiNbO3 optical devices with improved optical qualities.
Dependence of giant magnetoresistance in Co/Cu multilayers on the thickness of the Co layers
Authors: Shukh A. M. , Shin D. H. , Hoffmann H.
Published: July 2002

The dependence of the giant magnetoresistance (GMR) on the thickness of the Co layers in Co/Cu multilayers was investigated experimentally. The thickness of the Cu layer was held constant at tCu=19 Å, which corresponds to the second maximum of the GMR ratio oscillating dependence on tCu. The Co layer thickness was varied from 4.8 to 79.0 Å. High resolution transmission electron microscopy showed the existence of the two-dimensional artificial superstructure with defined periodicity as well as sharp and flat interfaces. From wide angle x-ray diffraction it was concluded that at Co layer thickness below 40 Å the multilayers are polycrystalline with mainly fcc lattice structure and (111) texture. In the case of thicker Co layers indications of hcp Co could be found. The GMR ratio reaches a maximum at Co layer thickness about 11 Å. It was shown that the GMR in sputtered Co/Cu multilayers is due to spin scattering at the interfaces and resistance is strongly influenced by interface scattering.
Effect of submonolayer coverage on magnetic anisotropy of ultrathin cobalt films M/Co/Au(111) with M=Au, Cu, Pd
Authors: Beauvillain P. , Bounouh A. , Chappert C. , Mégy R. , Ould-Mahfoud S. , Renard J. P. , Veillet P. , Weller D. , Corno J.
Published: July 2002

Using in situ polar magneto-optical Kerr-effect measurements, the variation of the Kerr rotation and magnetic anisotropy of a (0001)Co ultrathin film on a (111)Au substrate has been precisely recorded, during the first stages of the growth of an overlayer of metal M=Au, Cu, and Pd. As reported earlier, a drastic increase of the magnetic anisotropy was observed, with a peak around 1 monolayer of overlayer thickness. From a careful study of the variation of the remanent Kerr rotation, it could be shown that only the interface contribution to the anisotropy changes with the overlayer thickness, while the bulk contribution remains mostly constant. The overall behavior can be interpreted in terms of electronic effects in the metal overlayer, acting on the interface anisotropy via band hybridization at the interface.
Structural and microstructural evolution of barium titanate thin films deposited by the sol-gel process
Authors: Kamalasanan M. N. , Kumar N. Deepak , Chandra Subhas
Published: July 2002

Barium titanate thin films were fabricated by the sol-gel technique from two different precursors, one using barium 2-ethyl haxanoate and other using barium hydroxide dissolved in methoxy ethanol as barium source. The films were examined at different curing temperatures using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, optical transmission spectroscopy, and x-ray diffraction. The films prepared from an ethyl hexanoate precursor were found to crystallize around 550 °C into tetragonal polycrystalline form, whereas those prepared from a barium hydroxide precursor were crystallized into cubic form around 600 °C. The films prepared from the ethyl hexanoate precursor showed larger shrinkage during heat treatment and were more porous than those made from the hydroxide precursor. The changes in thickness, refractive index, and band gap of the films annealed at different temperatures were correlated with chemical modifications of the precursor film as well as structural and microstructural changes occurring during the formation of the final barium titanate thin film. FTIR spectroscopy and electron microscopy were used to support these observations.
Hydrogen incorporation into Si-doped InP deposited by gas-source molecular beam epitaxy
Authors: Sidhu L. S. , Zukotynski S. , Kruzelecky R. V. , Thompson D. A.
Published: July 2002

Hydrogen incorporation into Si-doped InP grown by gas-source molecular beam epitaxy was studied. P-H sites were identified by infrared spectroscopy. Proton-implanted reference samples were used to quantify the infrared results. Approximately 0.1 at. % hydrogen was found to be incorporated into InP:Si. Hall measurements indicated that most of the Si atoms were electrically active as donors. Rapid thermal annealing at 600 °C removed most of the bonded hydrogen from the samples. However, this resulted in relatively little change in either the room-temperature free-carrier concentration or Hall mobility.
Strain, dislocations, and critical dimensions of laterally small lattice-mismatched semiconductor layers
Authors: Atkinson A. , Jain S. C. , Harker A. H.
Published: July 2002

A rectangular strained epilayer with its length much larger than its height h and width 2l is considered. The energy change on introducing a 60° dislocation either parallel to the long dimension (longitudinal) or parallel to the short dimension (transverse) into the epilayer is calculated. The effects of free surfaces on the mismatch stress and on the dislocation energy are taken into account approximately. For a given misfit, there is a critical height and critical width such that if the dimensions of the layer exceed their critical values, introduction of a longitudinal misfit dislocation is energetically favored. However we show that a transverse dislocation always sets in before a longitudinal one and as a result, the critical thickness is almost equal to that for a film of infinite extent even when the width is very small. The results are found to be different from an earlier calculation [S. Luryi and E. Suhir, Appl. Phys. Lett. 49, 140 (1986)] and show that the relaxation caused by the free surfaces cannot explain the lower densities of dislocations observed experimentally in such structures.
Superconducting properties of Nb-CuMn multilayers
Authors: Attanasio C. , Maritato L. , Prischepa S. L. , Salvato M. , Engel B. N. , Falco C. M.
Published: July 2002

The superconducting properties of spin-glass superconducting multilayers made of Nb (superconducting) and CuMn (spin glass) have been studied. The superconducting critical temperature Tc of the multilayers was strongly dependent on the thickness of the spin-glass layers. The Radovic et al. theory [Phys. Rev. B 44, 759 (1991)], which foresees a phase difference 0≤φ≤π between neighboring superconducting layers, has given a qualitative description of these experimental data. The parallel and perpendicular critical magnetic-field measurements have shown many interesting effects related to the reduced dimensionality of the samples.
Quantitative imaging of local defects in very thin silicon dioxide films at low bias voltage by true oxide electron-beam-induced current
Authors: Lau W. S. , Chan D. S. H. , Phang J. C. H. , Chow K. W. , Pey K. S. , Lim Y. P. , Sane V. , Cronquist B.
Published: July 2002

A new low-voltage contrast mechanism due to electron-hole pairs generated in the oxide by an electron beam was observed at electric fields lower than 3.5 MV/cm. This is in addition to the tunneling current microscopy (TCM) contrast mechanism observed at electric fields higher than 3.5 MV/cm. The new contrast mechanism is opposite in sign to the TCM contrast mechanism such that the image of a local thinning defect in the oxide is dark at low bias voltage and bright at higher bias voltage. Good contrast can be obtained at electric field as low as 2.4 MV/cm. Applications include large area imaging of oxide defects and quantitative mapping of small oxide thickness variations.
Defect-induced nucleation of sputter-deposited gold on graphite
Authors: Ahn You-Ock , Seidl Milos
Published: July 2002

The early stages of thin film formation are studied on atomic scale by scanning tunneling microscopy imaging. Gold is sputter deposited on a graphite substrate using Cs+ ion bombardment of a gold target at a few keV energy. Stable gold nuclei are formed at defect sites which are produced by the impact of gold atoms with energy larger than 180 eV. This energy is needed to displace a carbon atom from the lattice in a binary collision. Three-dimensional clusters grow by attachment of additional gold atoms to the nuclei. The fraction of gold atoms with energy larger than 180 eV depends on Cs+ ion energy and typically is less than one percent of the incident gold flux. After 1 s of deposition, the average size of the clusters is 10 atoms. Cluster density is 1012 clusters per cm2, and a few percent of the incident flux is condensed in the clusters. These phenomena are a consequence of the weak interaction strength between gold and graphite.
Secondary-ion-mass spectrometry and near-field studies of Ti:LiNbO3 optical waveguides
Authors: Caccavale F. , Chakraborty P. , Quaranta A. , Mansour I. , Gianello G. , Bosso S. , Corsini R. , Mussi G.
Published: July 2002

Secondary-ion-mass spectrometry (SIMS) and near-field (NF) methods have been applied to study Ti:LiNbO3 optical waveguides. Ti concentration as a function of diffusion process parameters has been studied by the SIMS method. The main determining factors that were found to affect the depth-diffusion behavior of titanium in LiNbO3 slab waveguides are the initial thickness of the dopant film and the diffusion temperature. Anisotropy in the diffusion rate for Xand has been applied to the refractive index profile reconstruction for single-mode optical channel waveguides. A sharp change in the index at the air–guide interface has been observed, as expected. The dependence of refractive index change on Ti concentration has been found to be nonlinear, such as quadratic, approximately.
Characterization of photon recycling in thin crystalline GaAs light emitting diodes
Authors: Patkar M. P. , Lundstrom M. S. , Melloch M. R.
Published: July 2002

Gallium arsenide light emitting diodes (LEDs) were fabricated using molecular beam epitaxial films on GaAs substrates and removed by epitaxial lift-off (ELO). Lifted off devices were then mounted on a Si wafer using a Pd/Au/Cr contact layer, which also served as a back surface reflector. Devices were characterized by electrical and optical measurements, and the results for devices on the GaAs substrate were compared to those for ELO devices. ELO LEDs coated with a ZnS/MgF2 antireflection coating exhibited an optical output that was up to six times that of LEDs on GaAs substrates. At the same time, the measured current-voltage characteristics of the ELO devices displayed a lower n=1 current component. ELO LEDs with efficiencies up to 12.5% were realized. We attribute these results to photon recycling enhanced by the back-surface reflector in the ELO LEDs. The luminescence versus current and current versus voltage characteristics of the LEDs were analyzed to obtain the nonradiative minority carrier lifetimes and the photon recycling factors. The results demonstrate that the measured characteristics are well described by photon recycling theory. ELO LEDs may prove useful for characterizing recombination processes in LEDs, and thin-crystalline structures could provide substantial efficiency enhancements for LEDs and solar cells.
Acoustic emission during plastic deformation of crystals: A lattice-dynamics approach
Authors: Trochidis A. , Polyzos B.
Published: July 2002

A lattice-dynamics approach to acoustic emission during plastic deformation of crystals is proposed. First the dynamics of a dislocation interacting with transverse acoustic waves is investigated on the basis of a microscopic Frenkel–Kontorova model in which the rigidity of the substrate is relaxed. It is shown that the interaction can be described by a d’Alembert wave equation for the elastic displacement coupled to a sine-Gordon equation that governs the dislocation dynamics. Within the framework of this model and considering the soliton nature of dislocations, two basic mechanisms of acoustic emission are investigated both analytically and numerically: One is the accelerated motion of dislocations and the other is the annihilation of dislocation kink-antikink pairs during Frank–Read source operation. The results are discussed on the basis of existing experimental data.
Electron-beam-induced crystallization of isolated amorphous regions in Si, Ge, GaP, and GaAs
Authors: Jenc̆ic̆ I. , Bench M. W. , Robertson I. M. , Kirk M. A.
Published: July 2002

An energetic electron beam has been used to stimulate crystallization of spatially isolated amorphous regions in Si, Ge, GaP, and GaAs at 30 and 300 K. In the four materials it was found that crystallization was induced even when the energy of the electron beam was less than that required to create point defects in the crystalline structure. The rate of crystallization depended on the material and on the electron energy. In all materials, the rate decreases as the electron energy increases from 50 keV (the lowest electron energy used), reaching a minimum value at an electron energy slightly below the displacement threshold voltage. Above the displacement threshold, the regrowth rate again increases with increasing electron energy. The possible role of electron-beam heating was studied both theoretically and experimentally. Calculations suggested heating effects were negligible and this was confirmed by in situ ion implantations and electron irradiations performed at 30 K, where subthreshold electrons stimulated crystallization. The subthreshold and low-temperature results are consistent with the model that the crystallization process is dependent on the creation of defects (dangling bonds and kinks) at the crystalline-amorphous (c-a) interface. The crystallization stimulated by the subthreshold electron beams suggests that electronic excitation of the bonds along the c-a interface can induce the amorphous to crystalline transition.
Simulation of the crystallization of thin films by rapid thermal processing
Authors: Pascual R. , Sayer M. , Lo A. , Herbert S. , Rolim L. C. , Townley N.
Published: July 2002

A computer simulation has been performed of phase transformations taking place in thin films under various time–temperature regimes. The conditions used resemble those encountered in the rapid thermal processing of thin films. The effect of heating rate and final temperature have been studied in detail. It is observed that the two parameters can strongly influence the grain size and the grain size distribution within the films. The feasibility of using multiple step rapid thermal processing to optimize thin film microstructure is demonstrated.
Misfit stress-induced compositional instability in hetero-epitaxial compound semiconductor structures
Authors: Chu S. N. G. , Logan R. A. , Tsang W. T.
Published: July 2002

We have calculated the effect of misfit stress on the compositional stability of strained-layer hetero-epitaxial compound semiconductor structures. For uniformly stressed layers, a simple formula is derived for the change in chemical potential of the lattice atoms diffusing across the hetero-interface. An increase in the total chemical potential indicates that interdiffusion of the specific elements is thermodynamically unfavorable and therefore the composition of the structure is stable with respect to the misfit stress-induced interdiffusion of the specific elements. On the other hand, a decrease in the total chemical potential indicates that the interdiffusion will be driven by the misfit stress and the composition of the heterostructure is unstable. Various strain-layer systems of III–V compound semiconductors such as In1−xGaxAsyP1−y/InP, In1−xGaxAsyP1−y/GaAs, (Al1−xGax)yIn1−yP/GaAs, (Al1−xGax)yIn1−yAs/GaAs, In1−xGaxP/GaAs, In1−xGaxSb/InP, etc., are examined and their stability is discussed.
Three-dimensional imaging with a nuclear magnetic resonance force microscope
Authors: Züger O. , Hoen S. T. , Yannoni C. S. , Rugar D.
Published: July 2002

A magnetic resonance force microscope was used to demonstrate three-dimensional nuclear magnetic resonance imaging with micrometer-scale spatial resolution. The sample was mounted on a silicon nitride cantilever that served as a micromechanical force sensor. A nearby magnetic tip generated a field gradient of 22 G/μm. A three-dimensional magnetic resonance force map of the 1H spins in the sample was produced by lateral scanning of the magnetic tip relative to the sample and by varying the rf frequency of the spin excitation. The real-space spin density of the sample was reconstructed from the force map by means of a deconvolution technique. The spatial resolution achieved in the experiment was ∼3 μm in the axial direction.
Band offsets and electronic structure of SiC/SiO2 interfaces
Authors: Afanas’ev V. V. , Bassler M. , Pensl G. , Schulz M. J. , Stein von Kamienski E.
Published: July 2002

The electronic structure of SiC/SiO2 interfaces was studied for different SiC polytypes (3C, 4H, 6H, 15R) using internal photoemission of electrons from the semiconductor into the oxide. The top of the SiC valence band is located 6 eV below the oxide conduction band edge in all the investigated polytypes, while the conduction band offset at the interface depends on the band gap of the particular SiC polytype. In the energy range up to 1.5 eV above the top of the SiC valence band, interface states were found. Their electron spectrum is similar to that of sp2-bonded carbon clusters in diamond-like a-C:H films suggesting the presence of elemental carbon at the SiC/SiO2 interfaces.
Magnetic domain control of thick Fe-M(Zr,Ta)-N films for digital VCR metal in gap heads
Authors: Uchizawa M. , Fujita J. , Kobayashi H. , Tanabe S.
Published: July 2002

Magnetic domain structures of thick and small area (45×45×5 μm3) Fe-M(Zr or Ta)-N films were observed by a scanning Kerr-effect microscope (SKEM). The important factors in controlling the magnetic domains are the magnetostriction and the uniaxial anisotropy. By changing the N content in bcc Fe and the Ar pressure during sputtering, the saturation magnetostriction constant λs and the anisotropy field Hk were controlled in the range of 3×10−6–6×10−6 and 10–130 A/m, respectively. Clear and consecutive changes in the domain structures were observed by varying the film’s λs, Hk, and stress σ, and the observed structures agree qualitatively with the structures predicted by theoretical calculations. The wall structure where Bloch-like rotations and the Neel-like rotations are combined was observed by SKEM. The metal in gap heads using different λs and Hk films were fabricated and the output at 20 MHz was measured. A lower Hk is not necessarily better for obtaining a higher output in high-frequency ranges. The head output depends on the film’s magnetic domain structure, and the structure can be controlled by changing the λs and Hk.
Response of a kinetic Ising system to oscillating external fields: Amplitude and frequency dependence
Authors: Sides S. W. , Ramos R. A. , Rikvold P. A. , Novotny M. A.
Published: July 2002

The S=1/2, nearest-neighbor, kinetic Ising model has been used to model magnetization switching in nanoscale ferromagnets. For this model, earlier work based on the droplet theory of the decay of metastable phases and Monte Carlo simulations has shown the existence of a size dependent spinodal field which separates deterministic and stochastic decay regimes. We extend the above work to study the effects of an oscillating field on the magnetization response of the kinetic Ising model. We compute the power spectral density of the time-dependent magnetization for different values of the amplitude and frequency of the external field, using Monte Carlo simulation data. We also investigate the amplitude and frequency dependence of the probability distributions for the hysteresis loop area and the period-averaged magnetization. The time-dependent response of the system is classified by analyzing the behavior of these quantities within the framework of the distinct deterministic and stochastic decay modes mentioned above.
Imposition of periodic magnetization patterns on high-energy-product magnetic plates
Authors: Leupold H. A. , Tilak A. S. , Potenziani E.
Published: July 2002

Periodically magnetized permanent magnet plates with high-energy products are potentially very useful in high-field structures such as free-electron lasers, electrical machinery, and various mechanical applications such as magnetic bearings, for which they are already being used. A major problem is the lack of field sources with sufficient field amplitude to impose such patterns of magnetization on high-coercivity materials. This paper shows how such high amplitudes can be obtained for several patterns by use of modified sources of the augmented ‘‘magic ring’’ and ‘‘magic sphere’’ types.
Surface structures and electronic states of H2S-treated InP(001)
Authors: Shimomura M. , Naka K. , Sanada N. , Suzuki Y. , Fukuda Y. , Mo/ller P. J.
Published: July 2002

We find two different surface structures, (1×2) and (1×1), for H2S-treated InP(001). They depend upon exposure of H2S at about 350 °C. The coverage of sulfur is estimated to be about a half monolayer and one full monolayer for the (1×2) and (1×1) structures, respectively. The (1×1) structure is reconstructed to the (1×2) structure upon annealing at about 550 °C. It is suggested that sulfur is bonded to only In atoms and substitutes some of the phosphorus atoms below the first layer. Inverse photoemission spectra show strong reduction in intensity of 1.2 eV peak above the Fermi level for a clean InP(001)-(4×2) surface upon adsorption of H2S. This reduction implies a decrease in unoccupied surface states due to dangling bonds of indium dimers on the clean surface. The result of adsorption of oxygen on the (1×2) and (1×1) surfaces indicates significant passivation to oxidation of the surfaces.
Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes
Authors: Bejan Adrian
Published: July 2002

Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics. These simple models are used in the optimization of real (irreversible) devices and processes, subject to finite-size and finite-time constraints. The review traces the development and adoption of the method in several sectors of mainstream thermal engineering and science: cryogenics, heat transfer, education, storage systems, solar power plants, nuclear and fossil power plants, and refrigerators. Emphasis is placed on the fundamental and technological importance of the optimization method and its results, the pedagogical merits of the method, and the chronological development of the field.
Initial growth studies of silicon oxynitrides in a N2O environment
Authors: Tang H. T. , Lennard W. N. , Zhang C. S. , Griffiths K. , Li B. , Feldman L. C. , Green M. L.
Published: July 2002

We have investigated the initial growth of silicon oxynitride films on a clean Si(100) single crystal in a N2O ambient under ultrahigh vacuum conditions using Auger electron spectroscopy and nuclear reaction analysis. Variations in the growth parameters, e.g., exposure, N2O pressure and sample temperature, have been systematically investigated. Nitrogen incorporated in the oxynitride film is distributed in a region close to the film/substrate interface and most nitrogen is incorporated within a film thickness of ∼2.5 nm. These studies find an important application to the semiconductor industry with regard to possible new high quality gate oxide materials.
Photoeffects in WO3/GaAs electrode
Authors: Yoon Ki Hyun , Lee Jeong Won , Cho Yong Soo , Kang Dong Heon
Published: July 2002

Photoeffects of a p-type GaAs coated with WO3 thin film have been investigated as a function of film thickness and photoresponse transients of the WO3/GaAs electrode were studied. Also, these results were compared to those for a single p-type GaAs electrode. The photocurrent of the WO3/GaAs electrode depended on the film thickness of the WO3, showing an optimum photon efficiency for specimens of 800 Å thickness. This is due to the existence of an effective interface state within the band gap which reduces trapping of carriers and facilitates carrier movement. For an 800-Å-thick WO3 thin film deposited p-GaAs photoelectrode, the photogenerated electrons were found to move to an electrolyte at a higher positive onset potential compared with that of single p-type GaAs, which was confirmed as a result of transient behavior. I–V and C–V characteristics of the WO3/GaAs electrode were also compared with those of a single p-type GaAs electrode.
Dielectric response of strained and relaxed Si1−x−yGexCy alloys grown by molecular beam epitaxy on Si(001)
Authors: Lange Rüdiger , Junge Kelly E. , Zollner Stefan , Iyer S. S. , Powell A. P. , Eberl K.
Published: July 2002

Using spectroscopic ellipsometry, we measured the pseudodielectric function of Si1−x−yGexCy alloys (0≤x≤0.48,0≤y≤0.05) grown on Si(001) using molecular beam epitaxy. For pseudomorphically strained layers, the energy shifts of the E1, E1+Δ1, E0′, and E2 transitions are determined by line shape analysis and are due to alloy composition effects, as well as hydrostatic and shear strain. We developed expressions for hydrostatic and shear shift from continuum elasticity theory, using deformation potentials for Si and Ge, for biaxial stress parallel to the (001) growth plane in a diamond or zinc blende-type crystal and applied this to the ternary Si–Ge–C alloy. The energies of E1 and its spin-orbit split partner E1+Δ1 agree fairly well with theory. The E2 transitions in Si1−xGex at around 4.3 eV depend linearly on Ge concentration. In case of relaxed layers, the E1 and E1+Δ1 transitions are inhomogeneously broadened due to the influence of misfit and threading dislocations. For a silicon cap on top of a dislocated, relaxed SiGe layer, we recovered the bulk Si dielectric function.
Investigations of the 147 nm radiative efficiency of Xe surface wave discharges
Authors: Gibson N. D. , Kortshagen U. , Lawler J. E.
Published: July 2002

The radiative efficiency of the 147 nm resonance radiation of Xe excited in a low pressure, high-frequency surface wave sustained plasma has been investigated. The radiative UV power has been obtained from optical absorption spectroscopic measurements of the Xe resonance level population and from Monte Carlo calculations of the effective decay rate of this level. Precise measurements of the rf power absorbed by the plasma enable the determination of the absolute vacuum ultraviolet discharge efficiency for the Xe surface wave discharge. Results show efficiencies up to more than 80(±11)% .
Residual stress behavior of thin plasma-enhanced chemical vapor deposited silicon dioxide films as a function of storage time
Authors: Haque M. S. , Naseem H. A. , Brown W. D.
Published: July 2002

Residual stress in thin silicon dioxide films has been studied as a function of storage time. Films of varying microstructure and impurity content were deposited by plasma-enhanced chemical vapor deposition. Initially, all the films exhibited compressive stress, the magnitude of which was found to increase rapidly with time for the first few hours after deposition. For all the deposited thin films, this increasing compressive stress eventually saturates and then begins to decrease with time. The time at which the transition occurs depends on film thickness and quality, whereas, for relatively thicker films deposited under identical conditions, a saturation in compressive stress after long aging time was observed. No existing model of thin oxide films successfully explains the observed time variation of stress. In this paper, the variation of film stress as a function of storage time and film properties, such as porosity and impurity content, is discussed. Three driving forces, namely, surface reactivity, silanol buildup, and water dipole interaction, each of whose contribution varies depending on film thickness and quality, have been identified as potential mechanisms behind stress change in oxide films. A unified model consisting of these driving forces can explain the time variation of stress behavior in oxide films, irrespective of film quality and thickness.
Direct observation of interface roughness dependence of interfacial magnetism using diffuse x-ray resonant magnetic scattering (abstract)
Authors: MacKay J. F. , Teichert C. , Lagally M. G.
Published: July 2002

Interfacial roughness plays an important role in the magnetoresistance of magnetic multilayers, yet the relationship between roughness and the magnetic properties at interfaces is not well understood. In recent years, x-ray resonant magnetic scattering (XRMS) has been developed to investigate the interaction of polarized x rays and magnetic materials. By combining XRMS in azimuthal transverse scans, the diffuse intensity scattered from the roughness of the boundary between magnetic and nonmagnetic layers can be probed to yield information on the relationship between magnetism and interfacial roughness that cannot be obtained by any other method. Using synchrotron produced circularly polarized x rays tuned to the L2 edge of Co, x-ray diffuse intensity scans for a fixed angle of incidence are made for sputter deposited Co films and Co/Cu/Co sandwiches. For smooth films, the ratio of the XRMS diffuse intensity to the XRMS specular intensity is smaller than the ratio of the average specular intensity to the average diffuse intensity. In addition, the shape of the XRMS diffuse intensity differs from the average diffuse intensity. We conclude that the roughness of the magnetic boundary between magnetic and magnetic layers is less than the interfacial roughness, and that long-wavelength roughness contributes more to magnetic scattering than does short-wavelength roughness. By depositing identical magnetic films on substrates with well characterized laterally correlated roughness, we investigate the effect of the roughness feature size on the XRMS diffuse intensity. We find that for long-wavelength laterally highly correlated roughness, the roughness of the magnetic boundary is the same as the interfacial roughness.
The EL2-like metastable defect and the n- to p-type transition in silicon planar-doped GaAs
Authors: da Silva M. I. N. , de Oliveira A. G. , Ribeiro G. M. , Rubinger R. M. , Corrêa J. A. , Baeta Moreira M. V.
Published: July 2002

Through photo-Hall measurements at temperatures below about 120 K, we have observed the presence of a deep donor defect, with characteristics similar to those of the EL2 center, in planar-doped GaAs samples grown by molecular beam epitaxy at 300 °C. We have shown that this EL2-like center can account for the remarkable photoreleasing of electrons and holes into the conduction and valence bands, respectively. The two different kinds of carriers accumulate in two spatially separated channels, which can secondarily account for the n- to p-type transition we have observed.
Impact neutralization of D− ions in GaAs and InP
Authors: Dargys A. , Kundrotas J. , Čėsna A.
Published: July 2002

Impact neutralization coefficient for the reaction D−+e→D0+2e is reported, where D− and D0 are the negatively charged and neutral donor, respectively, and e is the conduction band electron. The coefficient was calculated using the Boltzmann transport equation and the scaled neutralization cross section of the negatively charged hydrogen atom. At liquid helium and lower temperatures the above reaction for n-GaAs and n-InP doped with shallow donors was found to be characterized by a relatively large impact neutralization coefficient. At weak electric fields, from about 0.2 to 1 V/cm, the neutralization coefficient increases exponentially and at higher fields saturates at the value of about 1.5×10−3 cm3/s for n-GaAs and 9×10−4 cm3/s for n-InP.
Dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures
Authors: Shan W. , Xu S. , Little B. D. , Xie X. C. , Song J. J. , Bulman G. E. , Kong H. S. , Leonard M. T. , Krishnankutty S.
Published: July 2002

We present results of a time-resolved photoluminescence study of the dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures (DHs). The carrier dynamics including generation, diffusion, spontaneous recombination, and nonradiative relaxation were studied by examining the time decay of photoluminescence associated with the spontaneous recombination from the samples. The temporal evolution of the luminescence from the GaN active layers of the DH samples was found to be governed by a carrier–diffusion dominated capture process. The determination of the capture time for the carriers drift and diffusion into the GaN active region, in addition to the effective lifetimes of the spontaneous recombination for carriers in the AlGaN cladding layers and the GaN active region, allows an estimation of the diffusion constants for the minority carriers in the AlxGa1−xN cladding layers of the DHs. Our results yield a diffusion constant of 2.6 cm2/s for Al0.03Ga0.97N and 1.5 cm2/s for Al0.1Ga0.9N at 10 K.
Optical properties of erbium-doped organic polydentate cage complexes
Authors: Slooff L. H. , Polman A. , Oude Wolbers M. P. , van Veggel F. C. J. M. , Reinhoudt D. N. , Hofstraat J. W.
Published: July 2002

The optical properties of different erbium (Er)-doped polydentate hemispherand organic cage complexes are studied, for use in polymer-based planar optical amplifiers. Room temperature photoluminescence at 1.54 μm is observed, due to an intra-4f transition in Er3+. The Er is directly excited into one of the 4f manifolds (at 488 nm), or indirectly (at 287 nm) via the aromatic part of the cage. The luminescence spectrum is 70 nm wide (full width at half maximum), the highest known for any Er-doped material, enabling high gain bandwidth for optical amplification. The absorption cross section at 1.54 μm is 1.1×10−20 cm2, higher than in most other Er-doped materials, which allows the attainment of high gain. Measurements were performed on complexes in KBr tablets, in which the complex is present in the form of small crystallites, or dissolved in the organic solvents dimethylformamide and butanol-OD. In KBr the luminescence lifetime at 1.54 μm is <0.5 μs, possibly due to concentration quenching effects. In butanol-OD solution, the lifetime is 0.8 μs, still well below the radiative lifetime of 4 ms estimated from the measured absorption cross sections. Experiments on the selective deuteration of the near-neighbor C–H bonds around the Er3+-ion indicate that these are not the major quenching sites of the Er3+ luminescence. Temperature dependent luminescence measurements indicate that temperature quenching is very small. It is therefore concluded that an alternative luminescence quenching mechanism takes place, presumably due to the presence of O–H groups on the Er-doped complex (originating either from the synthesis or from the solution). Finally a calculation is made of the gain performance of a planar polymer waveguide amplifier based on these Er complexes, resulting in a threshold pump power of 1.4 mW and a typical gain of 1.7 dB /cm.
Optical absorption study of Si grown in a hydrogen ambient
Authors: Suezawa Masashi
Published: July 2002

We studied optical absorption spectra of Si crystals grown in a hydrogen ambient. Specimens were grown by the floating-zone growth method in a hydrogen ambient of 1 atm. Optical absorption spectra of those specimens were measured at 6 K. Many optical absorption lines were observed in the range of 1900–2200 cm−1. They were observed only when the concentrations of carbon or boron were high. To understand these results, we referred to a report according to which a so-called A-type swirl, an interstitial-type dislocation loop, was observed when impurities of smaller covalent radii than that of Si were doped. Hence, we concluded that the above optical absorption lines were due to localized vibration of hydrogen atoms bound to interstitial Si atoms.
Experimental and theoretical study of a glow discharge at atmospheric pressure controlled by dielectric barrier
Authors: Massines Françoise , Rabehi Ahmed , Decomps Philippe , Gadri Rami Ben , Ségur Pierre , Mayoux Christian
Published: July 2002

The aim of this paper is to confirm the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs, and numerical modeling were used to achieve this task. Experimental observations and numerical simulation are in good agreement. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved, showing the main role played by the electron as well as helium metastable density just before the discharge is turned on.
Modelling of kinetics of creation and passivation of interface traps in metal-oxide-semiconductor transistors during postirradiation annealing
Authors: Ristić Goran S. , Pejović Momčilo M. , Jakšić Aleksandar B.
Published: July 2002

The dependencies of creation–passivation processes of interface traps in irradiated n-channel metal-oxide-semiconductor transistors on the temperature and gate bias during annealing have been investigated. The experimental results, which are explained by the hydrogen–water (H–W) model, show the influence of both the annealing temperature and gate bias on these processes. The modelling of creation–passivation kinetics of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical modelling shows that the H–W model can include the temperature and gate bias dependencies of creation of interface traps, latent interface trap buildup and the decrease of interface trap density.