bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab initio study of the interlayer magnetic couplings in Fe/Pd(001) superlattices and of the polarization induced in the Fe and Pd layers
Authors: Stoeffler D. , Ounadjela K. , Sticht J. , Gautier F.
Published: July 2002

In this paper we present a theoretical study of the magnetic properties of FemPdn(001) superlattices, (m and n being the number of Fe and Pd atomic layers). Our attention is mostly focused on the determination of both the interlayer magnetic couplings and the magnetic moments distributions as a function of the Fe layer’s and Pd spacer’s thicknesses. We use an ab initio LSDA method (ASW) to determine self-consistently the electronic structure, the magnetic moment distributions, and the total energies for the considered systems. For studying the role of the Pd spacer’s structure, we consider two model structures for the Pd spacers (i) a fct structure for which the Pd atoms keep their bulk atomic volume, and (ii) a fcc structure for which the Pd atomic volume is expanded. For the first structure, the magnetic polarization in the palladium spacer is limited mostly to the Fe–Pd interfaces, and the couplings are similar to the ones obtained for nonmagnetic spacers. On the contrary, for the second atomic structure, the whole Pd spacer is polarized with a moment of about 0.15μB/atom for n≤14, and the couplings are ferromagnetic in a large range of Pd thicknesses. We present a detailed study of FemPd1 and Fe3Pdn superlattices to determine both the couplings and the polarization induced in the Fe and Pd layers.
Induced spin polarization on Fe/nonmagnetic metal interfaces
Authors: Pérez-Díaz J. L. , Muñoz M. C.
Published: July 2002

We have investigated the Fe/Au, Ag, Pt, and Al(001) single interfaces by means of an empirical tight-binding Hamiltonian within the Green’s function matching formalism. The method is exact and describes equally interface states and bulk resonances. The evolution of the layer density of states indicates a rearrangement of the electronic density at the interface in form of spin polarization of the nonmagnetic layers. The induced magnetic moments in the nonmagnetic layers are only appreciable in Pt and Al, while variations of the interface Fe magnetization are predicted for all the systems.
Exchange coupling between ferromagnetic layers: Effect of quantum well states (abstract)
Authors: Cullen James R. , Hathaway Kristi B.
Published: July 2002

It is a well-established experimental result that the exchange coupling between ferromagnetic metals Fe, Co, or Ni is an oscillatory function of the thickness of the paramagnetic spacer. Theories of this coupling are almost in complete unanimity in attributing the observed periodicity to the properties of the Fermi surface of the paramagnetic spacer. Little has been done, and no consensus reached, as to the origin of the strength of the coupling. A realistic assessment of this quantity requires the use of an itinerant picture of the ferromagnetic constituent. From a recent study based on this picture, it became clear that the ratio of the spin-split band gap to the Fermi energy is important in establishing not only the strength of the coupling, but the phase of the oscillations in the nonasymptotic spacer thickness regime. Here we extend the work, which was limited to cases in which the minority-spin band of the ferromagnet was energy matched to the paramagnetic band, to cases in which the match is to that of the majority-spin band. In the latter arrangement, electrons of one spin are trapped in a well whose width equals the thickness of the spacer. We calculated the spin-flip current, and hence, the torque, exerted by one ferromagnet on the other as the magnetization direction of the former is rotated with respect to that of the latter. As in the earlier case, the torque leads to higher-order (in the cosine of the angle between the magnetizations of the ferromagnets) coupling as well as the usual linear coupling. The bound states produced by the quantum well structure are most important when the band splitting in the ferromagnet is large. The new features produced by these states will be discussed; in particular, their effects on the coupling strength and the phase shift will be discussed.
The three-dimensional Fourier series method for the calculation of stress and strain: Application to strained-layer structures
Authors: Faux David A. , Gill Jonathan
Published: July 2002

The theory of the Fourier series method for calculating stresses and strains in a rectangular prism of homogeneous, isotropic material is presented. Boundary conditions consists of normal stresses at the surfaces, with the shear stress at all surfaces assumed to be zero. The theory is applied to the case of a single isolated strained layer. The stress relaxation, strain relaxation, and displacements are calculated in the region where the strained layer meets the free surface. It is confirmed that the component of the stress relaxation normal to the surface decays as 1/r within the strained layer, where r is the distance from the free surface.
Quantitative measurement of the vibrational amplitude and phase in photorefractive time-average interferometry: A comparison with electronic speckle pattern interferometry
Authors: Rohleder Henrik , Petersen Paul M. , Marrakchi A.
Published: July 2002

Time-average interferometry is dealt with using four-wave mixing in photorefractive Bi12SiO20. By introducing a proper sinusoidal phase shift in the forward pump beam it is possible to measure the amplitude and phase everywhere on a vibrating object. Quantitative measurements of the phase and amplitude of the vibrating structure are demonstrated in photorefractive time average interferometry. The photorefractive interferometer is compared with the performance of a commercial electronic speckle pattern interferometer (ESPI). It is shown that the dynamic photorefractive holographic interferometer improves the image quality considerably and is able to extend the measurable range for the acoustic vibration amplitude and frequency compared to what is obtainable with the ESPI equipment.
Electrical characterization of Hg1−xCdxTe (0.126≤x≤0.58) grown by organometallic vapor phase epitaxy
Authors: Hahn S. R. , Parsons J. D. , Ellsworth J. A. , Vydyanath H. R.
Published: July 2002

Epilayers of Hg1−xCdxTe (mercury cadmium telluride: MCT) were grown at 300 °C, under atmospheric pressure, in a cold wall annular reactant inlet inverted-vertical reactor chamber. As-grown MCT surfaces (0.126≤x≤0.58) were specular and free of visible stacking faults. Their growth rate and composition were linear functions of the dimethylcadmium flow rate (QCd), for QCd≤0.031 sccm. As-grown epilayers exhibited n-type characteristics at x≤0.40 and p-type characteristics at x=0.580. The mobility (μ) in Hg annealed layers, which were n-type as-grown, decreased by a factor of 3, on average. This reduction in μ, after Hg annealing, is ascribed to the presence of acceptor impurities, such as copper, which propagate into the epilayers during growth process. Hall measurements as a function of temperature, performed on a Hg0.792Cd0.208Te layer, gave a minimum concentration of 1.8×1015 cm−3 and a maximum mobility of 3.8×104 cm2/V s, at approximately 180 K.
Coherent properties of electron emission from a single heterobarrier
Authors: Gault M. , Matsuura H. , Furuya K. , Mawby P.
Published: July 2002

The energy spectrum of emitted electrons from a single barrier is analyzed taking into account the quantized levels of an accumulation layer. A self-consistent model is developed which solves Poisson’s equation, the continuity equation, Schrödinger’s equation, and the heat equation. The relationship between the population of the quantized levels, the energy relaxation time, and the tunneling probability is formulated. The energy spectrum consists of components from three- and two-dimensional electrons. A new emitter structure is proposed which effectively removes the three-dimensional current component providing a highly effective method of producing electrons with a very narrow energy spread in the direction of propagation.
Dielectric and piezoelectric properties of lead zirconate titanate doped with chromium oxide
Authors: Katiyar V. K. , Srivastava S. L. , Singh Janardan
Published: July 2002

Vector impedance measurements of radial modes of thin disks (diameter 13 mm and thickness 1 mm) of Pb(Zr0.515Ti0.485)O3 doped with Cr2O3 have been carried out using an impedance analyzer. Piezoelectric equivalent circuit parameters R, L, Ca in series, and Cb in parallel have been measured by simulating ‖Z‖ and θ plots. Piezoelectric parameters for the first four radial modes have been obtained and it is found they peak at about 0.32 mol % of Cr2O3. The piezoelectric coupling coefficient Kp has been correlated with the dielectric constant. The dielectric quality factor Qe and mechanical quality factor Qm have been measured and (Qe/Qm)<1. ac conductivity follows a frequency power law with exponent p<1, suggesting that the hopping mechanism may be responsible for the dielectric loss.
Selective adsorption of HBO2 and Sb on a Si surface partially covered with ultrathin oxide
Authors: Murakami Eiichi , Kujirai Hiroshi , Kimura Shin’ichiro
Published: July 2002

Solid dopant sources for Si (HBO2 and Sb) are shown to be selectively adsorbed on a Si surface partially covered with ultrathin (<1 nm) SiO2, by using a conventional Si molecular-beam-epitaxy system and wet chemical treatment. The selective adsorption ratio on a clean Si (100) surface relative to on the thin oxide is about 30 for HBO2 at 700 °C and about 150 for Sb at RT as observed by Auger electron spectroscopy and secondary-ion-mass spectroscopy. In addition, it is suggested that hydrogen termination of a (100) Si surface reduces dopant adsorption: <1/500 at RT and 350 °C for Sb. By combining ultrathin oxide mask formation and sublimation, selective doping of B is demonstrated. For Sb, a hydrogen mask seems to be better than a thin oxide mask for lower sublimation temperature (<600 °C).
A dynamic z-pinch as a source of intense extreme ultraviolet radiation
Authors: Mehling A. , Böss T. , Metzner J. , Langhoff H.
Published: July 2002

In order to heat gases with a dynamic z-pinch a simple apparatus was developed which operates with current pulses of up to 80 kA. Energy of about 10 J/pulse is deposited in the gas. During the pinch the plasma cylinder is compressed from an initial radius of 7.6 mm to 650 μm. Experiments with gases of low atomic number Z yield strong fluorescence in the vacuum and extreme ultraviolet region due to the production of highly ionized species. With acetylene C2H2 an ion concentration of 5×1017 cm−3 (dominated by hydrogen-like carbon ions) was achieved.
Formation by ball milling and recrystallization of Y-Ba-Cu-O nanocrystalline phases
Authors: Simoneau M. , L’Espérance G. , Schulz R.
Published: July 2002

The structural transformations occurring during high-energy mechanical milling and subsequent annealing of YBa2Cu3O7−δ samples have been studied. A high initial oxygen content favors the formation of a metastable (Y0.33Ba0.66)CuO3−x disordered cubic phase. The cubic phase decomposes into a nanocrystalline mixture of Y2BaCuO5 and an yttrium deficient amorphous phase upon further milling. The crystallization enthalpy of the amorphous phase was estimated to be approximately 72.2 kJ/mol with a corresponding activation energy of 800±80 kJ/mol. Upon heating the nanocrystalline cubic phase transforms to the high-oxygen tetra X (O6.77) nonsuperconducting phase. Under oxygen, this last phase is stable up to 930 °C where it transforms to the tetra II low-oxygen (O<6.4) structure which reverts to the ortho I superconducting phase after adequate cooling. A structural model is proposed in which the formation of coherent domain boundaries and the unusually short c axis associated with the tetra X phase are related to the reordering of the Y-Ba sublattice of the metastable cubic phase. The relative stability of the cubic and tetra X phases as a function of the initial oxygen content before milling indicates that the oxygen concentration may be higher at the domain boundaries.
Reaction kinetics in the Ti/SiO2 system and Ti thickness dependence on reaction rate
Authors: Russell S. W. , Strane J. W. , Mayer J. W. , Wang S. Q.
Published: July 2002

The reaction kinetics of Ti films on SiO2 were investigated using Rutherford backscattering spectrometry, x-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. Consistent with earlier studies, the reaction results in the formation of a TiOw/Ti5Si3/SiO2 stack at temperatures in the range 700–820 °C. As the silicide layer grows, the concentration of O in TiOw increases, with the reaction ceasing at w∼1.2. In addition, the reaction rate depends on the initial Ti thickness, as thicker Ti films possess faster reaction rates. Applying current diffusion-controlled kinetic growth models, we find nominal agreement with our data at each thickness and predict activation energies in the range 3.0–3.4 eV. However, such a model is unable to account for either the Ti thickness dependence or the slowing and eventual cessation of silicide formation as the oxide composition approaches its limiting value. We implement a model which takes into account the reduction in the thermodynamic driving force for Ti5Si3 formation due to the incorporation of oxygen into the overlying Ti. This model predicts a silicide growth relationship of the form kt= (1/2)x2+ax2f∑∞n=3(1/n)(x/xf)n, with k independent of Ti thickness and given by k=k0 exp(−ΔE/kBT). The final Ti5Si3 thickness, xf, is determined by the initial Ti thickness, the stoichiometries of each phase formed and the final oxide composition. This model yields a more accurate fit to our data than if we assume parabolic growth since it predicts the eventual cessation of the reaction as x approaches xf. We find ΔE=2.9±0.1 eV. Our model also seems to explain the dependence on initial Ti thickness.
A method for predicting the reflection and refraction of spherical waves across a planar interface
Authors: Furlong J. R. , Westbury Catherine F. , Phillips E. A.
Published: July 2002

An approximate method is presented to find the magnitude of the reflected and refracted waves that result when a spherical wave encounters a planar interface separating two elastic solids. This method relies on: a multipole field solution for spherical waves to describe the compressional and shear waves that emerge from the interface upon reflection and refraction, virtual sources to locate the reflected and refracted wave origins above and below the interface, and a discrete, ray-based approach to solve the complex system of equations that result from the boundary conditions imposed. In addition to the elastic constants, the reflection and refraction coefficients are found to depend on the boundary conditions at the interface, the wavefront curvature, and source frequency. The dependence of reflection coefficients on boundary conditions is significant and has important implications for brittle materials subjected to impulsive (shock) loading, such as a turbine blade containment structure or ballistic ceramic armor. It is shown that a good impedance match between two solids is not sufficient to prevent fragmentation due to a reflected wave. Shear coupling of the interface is necessary to minimize damage. The Matrix Algebra for Reflective/Refractive Systems computer program has been developed to solve the resulting system of equations and illustrate these results.
Effects of lanthanum modification on the antiferroelectric-ferroelectric stability of high zirconium-content lead zirconate titanate
Authors: Dai Xunhu , Viehland Dwight
Published: July 2002

Lanthanum-modified lead zirconate titanate specimens with between 0 and 9 at.% lanthanum and a Zr/Ti ratio of 95/5, Pb1−xLax(Zr0.95Ti0.05)1−x/4O3 (PLZT 100x/95/5), have been investigated using dielectric spectroscopy, Sawyer–Tower polarization, and dilatometric measurements. La modification was found to suppress the stability of the ferroelectric state, changing the phase stability and phase sequence observed on cooling. PLZT 0/95/5 was found to be ferroelectric from room temperature to the Curie point; however, an antiferroelectric state was found to be stabilized as the long-range ferroelectric state was disrupted by La substitution on the Pb sites. With increasing La content (≳3 at.%), a multicell cubic (MCC) state was found to be stable near the temperature of the dielectric maximum. This MCC phase region was characterized by a dielectric plateau in the Curie temperature range and by the lack of any macroscopic symmetry changes. It is suggested that competition between long-range ferroelectric and short-range antiferroelectric couplings is responsible for the MCC state, changes in the relative phase stability, and subsequent changes in the macroscopic properties with increasing La content.
(NH4)2Sx-treated InP(001) studied by high-resolution x-ray photoelectron spectroscopy
Authors: Fukuda Y. , Suzuki Y. , Sanada N. , Sasaki S. , Ohsawa T.
Published: July 2002

The chemical state of sulfur on (NH4)2Sx-treated InP(001) surfaces has been studied by high-resolution x-ray photoelectron spectroscopy. We find three kinds of chemical states of sulfur (S2p3/2 lines at 161.2, 162.0, and 163.4 eV) on the sample treated at RT. It is suggested that they correspond to sulfur in phosphorus sites (in the second layer of the InP(001) surface), to sulfur bonded to indium on the first layer, and to elemental sulfur on sulfide, respectively. One (S2p3/2=162.0 eV) of them becomes predominant with long-time exposure to atmosphere at RT. Upon annealing the sample at 400 °C, the 163.4 eV line disappears, while the lines at 162.0 and 161.2 eV remain on the surface. A model of the treated surface is presented.
Solid Kr moderator for producing slow positrons
Authors: Mills A. P. , Voris S. S. , Andrew Tamara S.
Published: July 2002

We find that proper annealing of a solid Kr positron moderator results in a fast positron to slow positron conversion efficiency 90% as good as that of solid Ne. Our results are in agreement with Grund, Maier, and Seeger [Mater. Sci. Forum 105–110, 1879 (1992)] except that our absolute efficiencies (≊0.2%) are higher presumably due to the better vacuum conditions of our experiment. Since the Kr does not have to be cooled below 10 K, the moderator can be made using an inexpensive refrigerator and is suitable for a large surface area intense positron source.
Pyroelectrical investigation of the dipole orientation in nonlinear optical polymers during and after photoinduced poling
Authors: Bauer-Gogonea S. , Bauer S. , Wirges W. , Gerhard-Multhaupt R.
Published: July 2002

Several of the chromophore molecules considered for use in nonlinear optical polymers exhibit photoisomerization. This photoinduced transformation from one isomer to another changes the shape of the dipolar molecule and thus often enhances its mobility within a polymer matrix. Consequently, the molecular dipoles can sometimes be oriented by means of an electric field even well below the glass transition temperature of a nonlinear optical polymer if photoisomerization can be exploited. This effect forms the basis of photoinduced poling which was investigated in detail and also used for the preparation of poling patterns with inverted dipole orientations along the thickness direction of a polymer film. By means of pyroelectrical measurements, the photoinduced poling process was examined in situ and the resulting nonuniform dipole orientation profiles were probed. From the combination of pyroelectrical thermal analysis and thermally stimulated depolarization, a complete description of the relaxation behavior in polymer samples after photoinduced poling was obtained.
The use of graded InGaAs layers and patterned substrates to remove threading dislocations from GaAs on Si
Authors: Knall J. , Romano L. T. , Biegelsen D. K. , Bringans R. D. , Chui H. C. , Harris J. S. , Treat D. W. , Bour D. P.
Published: July 2002

We have investigated threading dislocation (TD) removal from GaAs films on Si by introduction of additional InGaAs graded strain layers in combination with growth on patterned substrates. The substrate patterns consisted of mesas with 10–34 μm widths. The mesa sidewalls were either overhanging (concave), leading to free sidewalls for the film on the mesas, or outward sloping (convex) sidewalls with {111} orientation. The dislocation structure was studied using transmission electron microscopy. It was found that the graded strained layers led to a reduction of dislocation density by a factor of ∼5 in films grown both on mesas with concave sidewalls and on unpatterned substrates. This reduction was due to dislocation reactions leading to annihilation of TDs. For films with graded strained layers on mesas with convex sidewalls, an additional factor of ∼3 reduction in TD density was observed in the part of the film that was grown on top of the mesas. In this case all mobile TDs (TDs associated with 60° misfit dislocations, i.e., TDs that could glide to relieve misfit stress) were removed from the film on top of the mesas to the regions above the sidewalls and only TDs associated with 90° misfit dislocations remained. We suggest that this is due to pinning of the TDs associated with 60° misfit dislocations at the mesa edges and we have presented an explanation for this pinning in terms of the stress conditions at the {111} oriented mesa edges. In addition, this leads us to suggest that in order to obtain minimum TD density it is imperative to prevent formation of 90° misfit dislocation during lattice mismatched heteroepitaxial growth.
Growth of voids in porous ductile materials at high strain rate
Authors: Wang Ze-Ping
Published: July 2002

A hollow-sphere model, with temperature-dependent viscoplastic material response, is developed to investigate the inertial and thermal effects on dynamic growth of voids in ductile materials. Theoretical analysis indicates that the inertial effect (kinetic energy of void growth) mainly dominates the behavior of the void growth in temperature-dependent and high-strain-rate cases. Otherwise, the viscoplastic effect dominates and the inertial effect can be neglected. The rate of the dynamic growth of voids increases when the thermal effect is considered. An expression of the threshold stress for the void growth is obtained, which depends on the initial porosity, the porosity, the yield strength, the density of surface energy of voids, the initial temperature, and the melting temperature.
Interface properties of thin oxides grown on strained GexSi1−x layer
Authors: Nayak D. K. , Park J. S. , Woo J. C. S. , Wang K. L. , Ivanov I. C.
Published: July 2002

The electrical and chemical properties of the interfaces of thin oxides grown on strained GexSi1−x layers are analyzed in detail using capacitance-voltage measurements and Auger electron spectroscopy. It is found that the electrical properties (interface states and fixed oxide charges) of the interface depend on various parameters such as oxidation temperature, oxidation time, Ge distribution near the interface, and Ge distribution in the entire epilayer. The Ge distribution at the interface can be described using concentration-dependent diffusivity of Ge in the epilayer. The electrical properties are improved with the increase in oxidation temperature, but for a given oxidation temperature, the quality of the interface degrades with the increase in oxidation time. At a very high oxidation temperature the Ge distribution in the entire epilayer is altered due to the high diffusivity of Ge.
Photocarrier generation site in a layered photoreceptor based on azo pigment: Effect of wet-coated formations
Authors: Niimi Tatsuya , Umeda Minoru
Published: July 2002

The structures of interfaces between a carrier generation layer (CGL) and a carrier transport layer (CTL) which are considered to be a photocarrier generation site in a layered photoreceptor have been analyzed. It was found that the thickness of the CGL, which consists of the fluorenone-based bisazo pigment (CGM) and binder resin, was expanded about 1.5 times after the CTL was deposited by a wet-coating process. A substantial amount of the carrier transport material (CTM) had penetrated preferentially into the CGL from the CTL to the binder resin, remaining as the CTL dried out. The photocarrier generation site in such a layered photoreceptor is found not to be a planar CGL/CTL interface but a three-dimensional CGM/CTM interface spread out over the bulk of the CGL. The CTM:CGM ratio in the CGL of the layered photoreceptor is estimated to be 0.8–0.95:1 in weight. It is also considered that the number of the photocarrier generation sites originated by the CTMs in the CGL was close to the number needed to saturate the rising function of charge carrier quantum yield ΦET with rising CTM/CGM in the nominal CGL.
First and second harmonics of the laser response to current modulation
Authors: Grinberg A. A.
Published: July 2002

The nonsteady-state generalization of the laser current-voltage and power characteristic model is obtained and used to derive the small-signal systems of equations for first- and second-order laser distortion to current modulation. The model takes into account the heating of the electron-hole gas in the active region and intrinsic leakage current associated with escape of the particles through the heterojunctions. The intrinsic diode capacitances and general form impedance are included in the small-signal equations. The quantitative analysis of the laser response to the current modulation is carried out on the specific example of the 1.3 μm laser based on an InGaAsP compound. A dependence of the light first and second harmonics on the thickness of the cladding layer (due to change of the leakage current) is demonstrated. It is shown that for thicknesses larger than several microns the influence of the leakage is negligible. It is found that modulation of the electron-hole gas temperature (due to heating effect) dramatically increases the second harmonic just in the range of frequencies (<500 MHz) important for laser applications in the transmission of the analog video signals in cable television systems.
Mechanism governing the formation and the magnitude of the induced magnetic anisotropy K
u in amorphous Co-Zr-M (M=Zr, Nb, Ti) and Co-Zr-Pt thin films
Authors: Naili M , Suran G.
Published: July 2002

Amorphous Co95−xZr5Mx (M=Zr, Nb, Ti) and (Co91−x Ptx)Zr9 thin films have been prepared by rf sputtering and the deposition was performed in a dc magnetic field. The variations of Ku studied as a function of the concentration are reported. The experiments revealed that Ku cannot be explained by a pseudodipolar mechanism. A new model is proposed where it is assumed that Ku is the sum of two contributions Kau+Ksu where Kau and Ksu are the induced anisotropies related to the local anisotropy of the octahedral-icosahedral and trigonal-type clusters, respectively. In Pt-submitted films, a supplementary contribution to Ku is observed due to the pseudodipolar ordering, related to the induced moment developed by Pt.
Optical waveguide isolator based on nonreciprocal radiation
Authors: Shintaku Toshihiro , Uno Takehiko
Published: July 2002

A new waveguide isolator which has a simple structure is proposed and experimentally demonstrated. The isolator operates on the basis of nonreciprocal guided-radiation mode conversion in a channel magneto-optic waveguide. The isolator was realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. 13.3 dB isolation was obtained at a wavelength near 1.55 μm.
Interlayer exchange coupling versus ferromagnetic layer thickness in asymmetric Co/Ru/Co trilayer films
Authors: Zhou L. , Zhang Z. , Wigen P. E. , Ounadjela K.
Published: July 2002

A dependence of the interlayer exchange coupling coefficient A12 on the Co layer thickness has been observed in asymmetric Co(32 Å)/Ru(tRu)/Co(t2) trilayer structures for several series within which tRu is a constant. As a function of the second Co layer thickness, the amplitude of A12 varies significantly but the sign of A12 does not change within each series. In both parallel and antiparallel coupled structures, the variation length Δt2 between the maximum and the minimum coupling strength is rather large (about 10 Å) and consistent from series to series.
Shallow junctions formed by BF+2 implantation into thin CoSi films and rapid thermal annealing
Authors: Juang M. H. , Lin C. T. , Cheng H. C.
Published: July 2002

Effects of rapid thermal annealing (RTA) on the shallow p+n junctions formed by BF+2 implantation into thin CoSi films on Si substrates are discussed, with comparison to the implantation into thin Co films. Excellent junctions can be achieved via conventional furnace annealing (CFA) for both the samples prepared by implanting dopant through metal (ITM) and metal silicides (ITS) films. For the RTA process, however, the junction formation for ITS was hindered, with the diodes made by ITM being much better than those by ITS due to a deeper as-implanted profile. Although the problem of knock-on Co induced by heavy dopant implant present in making n+p junctions by ITM can be largely reduced by using ITS, ITS is inferior for forming p+n junctions by RTA.
Role of liquid droplet surface diffusion in the vapor-liquid-solid whisker growth mechanism
Authors: Wang Hongyu , Fischman Gary S.
Published: July 2002

A careful examination of the dissolution/diffusion through liquid/precipitation steps of the well-accepted vapor-liquid-solid whisker growth mechanism has been conducted. Various diffusional processes involved in the whisker growth, such as solid surface diffusion, liquid surface diffusion, and bulk liquid diffusion, have been evaluated. It is noted that the diffusion along liquid alloy droplet surfaces, driven by both a concentration gradient and surface energy decrease, should not be ignored. Mass transport rate calculations using a simplified one-dimensional model show that the surface diffusion becomes more important with decreasing whisker diameter, decreasing solubility of growth species in the liquid phase, and increasing ratio of surface diffusion coefficient to bulk liquid diffusion coefficient. The diffusion along the liquid alloy droplet surface may play a major role in the growth of compound whiskers. Inclusion of the liquid droplet surface diffusion in the vapor-liquid-solid mechanism is proposed.
Propagation loss of magnetostatic waves in single and multilayered waveguides
Authors: Chakrabarti S. , Maiti C. K. , Bhattacharya D.
Published: July 2002

Davidenko’s method [Doklady Akad. Nauk, S.S.S.R. (N.S.) 88, 601 (1953)] is applied for determining the propagation losses of magnetostatic waves in single- and double-layered waveguiding structures. The phase and attenuation constants are directly obtained by solving coupled first-order ordinary differential equations in a dummy variable. Thus, iteration procedures are not necessary. The propagation losses for homogeneous single yittrium-iron-garnet YIG film structure have been calculated for three principal modes of magnetostatic waves. In the case of a double-layered structure, the dependence of propagation losses on the separation between the films and the effect of linewidth of the films in inhomogeneous waveguides have been investigated for magnetostatic surface wave propagation.
Hysteretic behavior of the transport critical current density in a bent Bi-Pb-Sr-Ca-Cu-O silver sheathed tape
Authors: Lee W. D. , Horng L. , Yang T. J. , Chiou Bi-Shiou
Published: July 2002

The hysteretic behavior of transport critical current density of a flexible Bi-based tape with bending strain has been investigated. After zero field cooling (ZFC), the experimental data obtained at 77 K under field cycling in the range of applied field from 0 to 1000 G to 0, indicate that the hysteretic ΔJc(H,ε), which is defined as the difference between the transport critical current Jc(H,ε) in an increasing field and decreasing field H, do not vary when bending strain ε is smaller than a critical bending strain εb, and then decreased gradually with increasing bending strain, but the normalized ΔJc(H,ε)/Jc(H,ε) values are unaffected by the bending strain up to 0.8%. Furthermore, the family of curves of Jc(H,ε)/Jc(0,ε) are independent of bending strain and can be described by an empirical expression, which is analogous to formulae exploited in the generalized critical state model.
Low-frequency noise in high-T
c rf superconducting quantum interference devices made by oxygen-ion irradiation
Authors: Tinchev S. S.
Published: July 2002

It has been found that the high-Tc rf superconducting quantum interference devices (SQUIDs) with oxygen-ion-irradiated weak links show white noise spectrum down to frequencies of about 0.2 Hz. The observed noise at lower frequencies is Lorentzian with a characteristic time constant of about 30 s. In contrast, in SQUIDs fabricated from pre-irradiated and thermal annealed films, the measured noise power scaled as 1/ f. This fact is explained as a result of defect generation in YBa2Cu3O7. The study can provide a new insight into the microscopic origin of the 1/ f noise in high-Tc SQUIDs, because the observed 1/ f noise in the high-Tc SQUID is caused by introduced defects.
Origin of giant thermopower in YBa2Cu3O7−x films
Authors: Palti Alexander , Svetchnikov Vasili , Pan Vladimir , Snarskii Andrei
Published: July 2002

A simple explanation of the origin of unusually large voltage signals observed on high-Tc superconducting thin films of composition YBa2Cu3O7−x (with c axis tilted away from the film surface normal) has been given. The phenomenon is suggested to be due to an anisotropy in the Seebeck coefficient. This treatment leads to an expression which captures the essential results of the experiments.
Theoretical study of electron transport in gallium nitride
Authors: Mansour N. S. , Kim K. W. , Littlejohn M. A.
Published: July 2002

This paper describes characteristic electron transport properties for GaN in bulk and quantum well structures. First, ensemble Monte Carlo calculations of steady-state electron drift velocity in bulk GaN are presented as a function of applied electric field for different lattice temperatures. At 300 K, the calculated peak steady-state drift velocity is 2.8×107 cm/s and the threshold field is 160 kV/cm. It is found that the peak steady-state electron drift velocity decreases only slightly by about 20% as the temperature increases from 300 to 600 K while the threshold field increases slightly by about 20%. Therefore, in addition to its high temperature stability, GaN has a low temperature coefficient making it ideal for high temperature applications. For electron transport in heterostructures, quantum mechanical calculations of the electron capture rate in GaN-based quantum wells as a function of well thickness are also presented. An oscillatory behavior of the electron capture rate as a function of quantum well thickness is observed. It is found that the electron capture time oscillates between 2 and 30 ps, which is about an order of magnitude greater than capture times in GaAs quantum wells. The amplitude of oscillations decreased as the well thickness increased. These results suggest that electron transport and carrier collection in GaN are efficient processes for improved electronic and optoelectronic devices.
Optical second-harmonic generation as a probe of the temperature dependence of the distribution of sites in a poly(methyl methacrylate) polymer doped with disperse red 1 azo dye
Authors: Ghebremichael F. , Kuzyk M. G.
Published: July 2002

We have applied electric-field-induced optical second-harmonic generation to measure the distribution of chromophore sites in a dye-doped polymer [disperse red 1 in poly (methyl methacrylate)] in terms of the standard α and β parameter, that is, the decay rate and the breadth parameter. These parameters have been measured from 100 to 430 K and are modeled with a smooth function over that temperature range. Over a narrow region of temperature where second-harmonic data from other groups exist, we find that our temperature dependence of β is in excellent agreement with these other experiments. In principle, our method can be applied to any glassy polymer to characterize the temperature dependence of the distribution of nonlinear-optical dye sites.
Simulation of influence of particles on photoresist films for lithography
Authors: Kamoshida Mototaka , Inui Hirotomo , Ohta Toshiyuki , Kasama Kunihiko
Published: July 2002

The influence of the particles existing on photoresist films, the sizes of which are comparable or smaller than the exposure light wavelength, on the developed cross-sectional pattern is investigated by using the two-dimensional waveguide model. Then, the smallest sizes of particles capable of causing pattern shorts are obtained as a function of the device design rule, taking into account the calculation results using a three-dimensional Fresnel diffraction approximation. The simulated results show good agreement with the actual critical sizes on the starting material silicon wafers at the 0.5, 0.35, and 0.25 μm design rule periods.
Degradation mechanism of the nonspiking ohmic contacts formed by solid-phase regrowth process on n-GaAs
Authors: Wang L. C.
Published: July 2002

The thermal stability of the Ge/Pd and the Pd-In-Ge ohmic contacts on n-GaAs formed by the solid-phase regrowth process has been investigated. It was found that degradation of these contacts at elevated temperatures cannot be rationalized by a single degradation process. The degradation at different temperatures can be best described by two processes: (a) a diffusion-controlled process and (b) a reaction-controlled process. The experimental results show that the thermal stability of the contacts can be improved by SiNx capping layers when the reaction-controlled process is the most significant process; however, SiNx capping layers cannot improve their thermal stability if the diffusion-controlled process is the dominant degradation process at elevated temperatures.
Kinetics of compositional disordering of AlGaAs/GaAs quantum wells induced by low-temperature grown GaAs
Authors: Tsang J. S. , Lee C. P. , Lee S. H. , Tsai K. L. , Chen H. R.
Published: July 2002

Compositional disordering of GaAs/AlGaAs quantum wells due to the presence of low-temperature grown GaAs (by molecular beam epitaxy) was studied. Ga vacancy enhanced interdiffusion was found to be the mechanism underlying the observed intermixing. Diffusion equations were solved numerically to obtain the band profile after intermixing. The transition energies in the quantum wells under various annealing conditions were solved and agree very well with the observed photoluminescence emission peaks. The diffusivity of Ga vacancies and that of induced Al-Ga interdiffusion were obtained. The vacancy induced interdiffusion diffusivity was found to have an activation energy of 4.08 eV, which is smaller than the activation energy of interdiffusion diffusivity of normal temperature grown GaAs/AlGaAs heterostructures. This is a clear indication of enhanced interdiffusion due to the presence of low-temperature grown GaAs.
SnTe-doping of GaAs grown by atomic layer molecular beam epitaxy
Authors: Kuball M. , Cardona M. , Mazuelas A. , Ploog K. H. , Pérez-Camacho J. J. , Silveira J. P. , Briones F.
Published: July 2002

Using x-ray diffraction and ellipsometry we have studied the incorporation process of SnTe in GaAs for n-type doping. Combining these two techniques allows us to decide whether SnTe is incorporated pairwise, as has been proposed in the literature. We found SnTe doping to change the E1 and E1+Δ1 critical point parameters in a way similar to that previously reported for n-type Si-doped GaAs. X-ray diffraction and Hall measurements show that the free carrier concentration is more than 1/2 of the [Sn]+[Te] concentration. We thus conclude that a large proportion of SnTe is incorporated as independent Sn and Te dopant atoms.
Process dependence of the SiO2/Si(100) interface structure
Authors: Lu Z. H. , Tay S. P. , Miller T. , Chiang T.-C.
Published: July 2002

Synchrotron radiation photoemission spectroscopy has been used to study thermal SiO2/Si(100) interfaces. Oxides were grown at 700 °C and were then post-annealed at higher temperatures. Various Si oxidation states Si+x (x represents the oxidation state) at the interface were detected from Si 2p core level measurements. The results show that the amount of both Si+3 and Si+2 increases while that of Si+1 remains constant as a function of anneal temperature. It is also found that the peak width of the substrate Si 2p increases with increasing anneal temperature. This is attributed to the disordering of substrate Si atoms adjacent to the interface. The above results are interpreted in terms of anneal-induced structural relaxation to reduce the long-range strain on both sides of the interface.
Energy deposition in the cathode layer of transient high pressure glows derived from interferograms of the emanating pressure wave
Authors: Schröder G. , Haferkamp J. , Bötticher W.
Published: July 2002

The large electric fields in the cathode sheath of high pressure glow discharges lead to localized energy deposition in the gas, which drives a gas dynamic pressure wave into the region where the transient high pressure glow is homogeneous. For a range of parameters typical for discharge pumped XeCl-lasers the gas density profiles of these waves have been measured interferometrically with high spatial resolution (20 μm). From comparisons with gas dynamic model calculations the amplitude and the spatial profile of the initial temperature distribution resulting from the energy deposition during the formation of the cathode sheath have been determined. These data can be used to verify assumptions to be made in future improvements of self consistent discharge models of the cathode sheath formation.
Structural transformations and strain relaxation mechanisms of In0.6Ga0.4As islands grown by molecular beam epitaxy on GaAs(001) substrates
Authors: Tillmann K. , Gerthsen D. , Pfundstein P. , Förster A. , Urban K.
Published: July 2002

The shape transformations and the mechanism of misfit strain relaxation of In0.6Ga0.4As islands grown at different temperatures on GaAs(001) substrates have been investigated. Layers with a constant nominal thickness of 12 monolayers were deposited by molecular beam epitaxy on nominal singular and on vicinal substrates. The specimens were characterized by scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. It is shown that an increase of the growth temperature yields a shape transition from rounded islands to elongated cigar-like structures. The lattice-parameter mismatch in the circular islands is relaxed by misfit dislocations at lower growth temperatures. Indium desorption effectively reduces the mismatch at higher growth temperatures and therefore yields the nucleation of coherent islands. In spite of this structural transformation an Arrhenius-like behaviour of the island densities is observed with an activation energy which depends on the substrate tilt.
Dislocation reduction in HgCdTe on GaAs by thermal annealing
Authors: Sasaki Tokuhito , Oda Naoki
Published: July 2002

The effect of dislocation reduction in HgCdTe epilayers grown on GaAs substrates by molecular-beam epitaxy has been studied by thermal annealing in a Hg atmosphere. It is found that dislocation movement in the HgCdTe epilayer is activated when the annealing temperature is higher than 250 °C. This behavior is analyzed by a simple model that was applied to dislocation reduction in GaAs layers on Si. The model is based on the dislocation movement under thermal stress. Thermal cycle annealing was also carried out. From the experiments and the model analysis, it is suggested that a relation between the dislocation reduction and total annealing time is almost independent of the annealing temperature. Furthermore, the activation energy of dislocation movement in the HgCdTe epilayer is estimated to be about 1 eV, which is almost the same value as Hg vacancy formation energy. It is, therefore, likely that dislocations in the HgCdTe epilayer interact with Hg vacancies, so that the dislocation annihilation and reemission take place.
Role of phase boundaries in growth kinetics of new phase inclusions in annealed ion bombarded solids
Authors: Barabanenkov M. Yu.
Published: July 2002

Solids subjected to the bombardment by energetic reactive ions are considered as a nonhomogeneous solid solution with new phase inclusions. The inclusions are formed at the irradiation stage and function at the elevated temperature as a spatially distributed sink for the solute. An analytical ‘‘diffusion-sink’’ model is generalized to describe the decay of the solid solution when the new phase growth is controlled by interface kinetics. The theoretical prediction is compared with experimentally determined growth of silicon dioxide precipitates in the annealed silicon bombarded by relatively low doses of oxygen. The ‘‘asymmetry’’ of oxygen atom absorption rate at the dioxide/silicon interface is discussed. Also it is shown that the supersaturation of silicon interstitials will not slow down the intrinsic silicon oxidation at high temperature (1100 °C). A formula is derived for the critical concentration of self-interstitials in the silicon matrix for the case when dioxide creation is restricted by the blockade of the additional interstitials.
Characteristics of thermal stresses in Al(Cu) fine lines. II. Passivated line structures
Authors: Yeo I.-S. , Anderson S. G. H. , Ho P. S. , Hu C. K.
Published: July 2002

The effects of oxide confinement on the thermal stress and yield behavior of passivated Al(Cu) line structures have been studied as a function of linewidth to submicron dimensions using a bending-beam technique. Principal stresses in the passivated line structures were deduced based on a micromechanical analysis of the curvatures of periodic line structures with lines oriented parallel and perpendicular to the beam direction. Results from the passivated Al(Cu) lines show that with decreasing linewidth, the magnitude of the principal stress components become higher until the line aspect ratio approaching one, then decreased. This behavior is consistent with theoretical predictions by analytical methods and finite element analyses. The stress behavior of the oxide passivation has also been deduced and its magnitude depended on the oxide morphology at the sidewall of the lines. Our result indicates a high level of stress in the sidewall which may cause crack formation during thermal cycling.
Effect of growth rate on step structure and ordering in GaInP
Authors: Su L. C. , Stringfellow G. B.
Published: July 2002

Ga0.5In0.5P layers grown by organometallic vapor-phase epitaxy on GaAs substrates misoriented by angles of 3°, 6°, and 9° from (001) toward the [1̄10] direction in the lattice have been studied using atomic force microscopy. The [110] steps are found to bunch in places to produce supersteps ranging in height from a few monolayers to as large as 30–70 Å. The supersteps, consisting of a (11n) facet adjacent to an (001) facet, are separated by an apparently vicinal surface. Both the height of the largest supersteps and the value of n depend on the growth conditions. The (001) facet length depends only slightly on misorientation angle and declines as (growth rate)−1/2, consistent with a diffusion limitation of the facet size. The distance between supersteps increases rapidly with decreasing growth rate and increasing substrate misorientation. A comparison of the superstep spacing and the distance between antiphase boundaries in the Cu–Pt-ordered structure formed during growth indicates a one-to-one correspondence. This leads to the hypothesis that the supersteps lead to loss of phase in the ordered structure during growth.