bluuebunny/crossref_metadata_2025 huggingface dataset:
Element specific magnetic hysteresis curves of Fe/Cu/Co multilayers (invited) (abstract)
Authors: Idzerda Y. U. , Lin H.-J. , Ho G. , Meigs G. , Chaiken A. , Prinz G. A. , Chen C. T.
Published: July 2002

We report the first results employing a new technique for studying heteromagnetic multilayers by element specific magnetic hysteresis measurements. Dramatically different Fe and Co hysteresis curves of Fe/Cu/Co trilayers were obtained by recording the soft x-ray magnetic dichroism1 at their respective L3 absorption edges as a function of the applied magnetic field. The complicated conventional hysteresis curves, obtained by a vibrating sample magnetometer, were resolved into linear combinations of the two individual elemental hysteresis curves, thus determining the average atomic magnetic moments of each element within the multilayer structure (Fe is 2.0±0.08 μB and Co is 1.1±0.04 μB). Furthermore, fine hysteresis features associated with one element, imperceptible in the conventional curves, were also observed, and demonstrate a new and powerful means for studying heteromagnetic multilayer systems.
Magnetization and static structure factor behavior in a first-order helix-fan phase transition
Authors: Rastelli E. , Sedazzari S. , Tassi A.
Published: July 2002

The behavior of noncollinear spin patterns when an external magnetic field is applied in the plane of the spins can be successfully studied by analytic approaches for helix configurations commensurated with the underlying lattice. Here we study the magnetization and static structure factor as a function of temperature and field for a planar square lattice with exchange coupling up to third neighbor. It has been limited to spin–spin couplings that stabilize a helix characterized by a spin–spin turn angle Q=2π/5 and Q=4π/5 in a zero magnetic field. Analytic calculations in harmonic approximation and Monte Carlo simulations are performed on finite size samples. At low temperature, the static structure factor for Q=2π/5 shows an abrupt transfer of weight from the satellite peak at the helix wave vector to the central peak for a critical field, which is weakly temperature dependent. Above a critical temperature the evolution of the low field helix configuration into the fan configuration occurs in a continuous way. Even richer is the phenomenology found when Q=4π/5, since a spin-flop phase intervenes for intermediate fields, yielding two first-order phase transitions between distorted helix–spin-flop, and spin-flop–fan phases.
Relaxation of magnetization in Cd1−xMnxTe diluted magnetic semiconductors under illumination
Authors: Smith M. , Dissanayake A. , Jiang H. X. , Li L. X.
Published: July 2002

Relaxation of thermoremanent magnetization (TRM) of Cd1−xMnxTe diluted magnetic semiconductors (DMS) in the spin-glass state have been studied under light illumination. The relaxation of TRM can be described well by a power law decay, M(t)=M(t0)t−α (t≳t0, t0∼2 s). The variations of the decay parameter α with the illumination light intensity has been measured and a relation which indicates that α is proportional to the photogenerated carrier concentration n has been observed.
Method for determining both magnetostriction and elastic modulus by ferromagnetic resonance
Authors: McMichael R. D.
Published: July 2002

The magnetostriction constant λs includes a combination of both elastic constants cij and magnetoelastic coupling constants Bi. To provide information on both cij and Bi, a method for measurement of both λs and the elastic modulus Y of thin films has been developed using ferromagnetic resonance (FMR). As in prior FMR schemes for measuring λs, a strain is produced in the film by bending the substrate, and the resulting anisotropy field is measured. However, by using a triangular polymer beam as a substrate, three important advantages are obtained (i) the triangular beam shape has uniform strain along its surface, (ii) the polymer material supports large strains (≳10−3) without breaking, and (iii) the low elastic modulus of the beam allows measurement of the sample elastic modulus through variation of the sample aspect ratio. Measurements on Ni foils yield values of λs and Y which fall within the scatter of literature data.
Hysteretic and other relationships between technical magnetostriction and magnetization
Authors: Garshelis I. J.
Published: July 2002

The appearance of functional relationships between magnetostrictive strain, ε=Δl/l, and magnetization, M, is critically examined. Correlations between ε and M are found to derive entirely from the dependence of each on the orientation of the spin vector relative to a common measurement direction. In single uniaxial domains, or in equivalent bulk bodies, with isotropic magnetostrictions λs, the simple ε∝M2 relationship arises from the closely related trigonometric functions involved in their respective measurements. To be hysteretic it is shown that it is at least necessary for λs to be anisotropic in a single domain or for there to be two or more domains distinguished by their orientations or other factors affecting their switching fields. It is concluded from this study that ε has no direct dependence on M nor are there physical sources in their hysteretic relationships that are not already manifest in M vs H.
Modeling the effects of stress on magnetization in ferromagnetic materials (abstract)
Authors: Jiles D. C.
Published: July 2002

In previous papers, it has been shown how stress affects the magnetic properties of materials. Although a model theory has been developed for the case of changing H field under constant stress, so far no attempts have been made to quantitatively model the effects of changing stress under constant field. The main principle in this case is the approach of the magnetization to the anhysteretic. The anhysteretic is itself stress dependent, and therefore presents a moving target for the bulk magnetization. The displacement of the bulk magnetization in isotropic media is determined by the elastic energy supplied ΔW=(1/E)(Δσ)2, where E is the elastic modulus, and Δσ the change in stress. The displacement of the magnetization D=Man(H,σ)−M(H,σ) decays with W according to dD/dW=−ξD, where ξ is the decay coefficient. Solving this equation gives,Man(H,σ)−M(H,σ)=[(Man(H, σ)−M(H,σ0)]exp[(−ξ/E)(Δσ)2], which can be rewritten in terms of the change in magnetization with stress ΔM(H,σ,σ0) the magnetomechanical effect,ΔM(H,σ,σ0)=[Man(H,σ)−M(H, σ)]{1−exp[(−ξ/E)(Δσ)2]}. The stress dependent anhysteretic Man(H,σ) can then be determined from the unstressed anhysteretic through the addition of the extra effective field term Hσ: Hσ=(3/2)(σ/μ0)(dλ/dM) so that Man(H,σ)=Man(H + Hσ). Through the use of the last three equations it is possible to describe the changes in magnetization of the material arising from changing stress.
Mössbauer investigation of the magnetic hyperfine field distribution in Fe(100)/Ag(100) structures
Authors: Schurer P. J. , Celinski Z. , Heinrich B.
Published: July 2002

A monolayer of 57Fe is used as a probe layer in Ag/9Fe(001)/10Ag(001) structures grown by the molecular beam epitaxy technique. Different Fe sites can be resolved in the spectrum. From the analysis of the isomer shift values, 57Fe deposited at the Fe/Ag interface can be distinguished from 57Fe atoms that are deposited one or more atomic layers removed from the interface. The variation of the magnetic hyperfine field Hhf with distance from the Fe/Ag interface agrees qualitatively with values calculated previously.
Nonlinear statics and dynamics of highly anisotropic magnets
Authors: Ostrovskii V. S.
Published: July 2002

It is shown that an adequate description of static and dynamic properties of highly anisotropic magnets in circumstances, where the violation of their initial symmetry induced by external fields or dynamic perturbations is not small, can be achieved by making use of the generalized coherent states. A complete set of equations governing coupled dipole and quadrupole degrees of freedom is presented for a system of spins S=1. The solutions obtained for uni- and biaxial ferromagnets and antiferromagnets make it apparent that the strong anisotropy qualitatively affects the behavior of such systems in external magnetic fields; in particular, it can change the nature of phase transition and give rise to the new ones. The complete set of equations makes it possible to derive solutions, corresponding to crucially new nonlinear objects such as domain walls, vortices, etc. whose treatment cannot be approached from the classical theory.
Frequency dependence of hysteresis curves in conducting magnetic materials (abstract)
Authors: Jiles D. C.
Published: July 2002

An extension of the differential equation for hysteresis has been developed, which takes into account the effects of eddy currents on the hysteresis curves in electrically conducting media. In the derivation presented, it is assumed that the frequency of the applied field is low enough (or the thickness of the material medium small enough) that the skin effect can be ignored. In this case, the DC hysteresis equation is extended by the addition of a term depending on (i) the rate of change of magnetization with time, (ii) the resistivity of the material, and (iii) the shape of the specimen. In the limit, as the frequency of the exciting field tends to zero, the frequency-dependent hysteresis curve approaches the DC curve.
Exchange stiffness of Ca-doped YIG
Authors: Avgin I. , Huber D. L.
Published: July 2002

An effective medium theory for the zero-temperature exchange stiffness of uncompensated Ca-doped YIG is presented. The theory is based on the assumption that the effect of the Ca impurities is to produce strong, random ferromagnetic interactions between spins on the a and d sublattices. In the simplest version of the theory, a fraction, x, of the ad exchange integrals are large and positive, x being related to the Ca concentration. The stiffness is calculated as function of x for arbitrary perturbed ad exchange integral, Jxad. For Jxad≳(1/5)‖8Jaa+3Jdd‖, with Jaa and Jdd denoting the aa and dd exchange integrals, respectively, there is a critical concentration, Xc, such that when x≳Xc, the stiffness is complex. It is suggested that Xc delineates the region where there are significant departures from colinearity in the ground state of the Fe spins. Extension of the theory to a model where the Ca doping is assumed to generate Fe4+ ions on the tetrahedral sites is discussed. Possible experimental tests of the theory are mentioned.
Electron wave-packet response of above-all-band-edges semiconductor quantum resonant structures
Authors: Walker D. B. , Glytsis E. N. , Gaylord T. K.
Published: July 2002

The time-dependent behavior of above-all-band-edges resonant propagating structures is presented. The results obtained are compared to those for the extensively studied double-barrier resonant tunneling structure for reference. It was found that for structures with the same resonant energies and resonance widths, the time-dependent characteristics are very similar. The structures were compared using two analytic approaches. The first is based on linear systems theory and the second on a finite-differences approach. It was found that for both structures, the quasibound state builds up at a rate determined by the parameters of the incident packet and decays with a time constant which corresponds to the lifetime.
Raman study of the time evolution of the facet temperature of coated AlGaAs single-quantum-well lasers
Authors: Altendorf E. H. , Tang W. C. , Rosen H. J.
Published: July 2002

Facet temperature and output power of coated AlGaAs single-quantum-well lasers were examined as a function of operating time. In contrast to previous results on uncoated lasers, which show a linear rise of facet temperature with time, these measurements on coated lasers show an initial rapid rise and then a substantial slowing of the temperature rise rate. Qualitatively similar behavior is observed in both the temperature rise and power degradation rates. Facet temperature measurements as a function of drive current at time zero show no observable discontinuity at threshold; however, formation of a kink at threshold is observed soon after stressing the lasers at constant current, suggesting a large role of photon heating in the facet degradation process.
Influence of H2O atmosphere on the photoluminescence of HF-passivated porous silicon
Authors: Dittrich Th. , Timoshenko V. Yu.
Published: July 2002

The influence of H2O atmosphere on the photoluminescence (PL) of HF-passivated porous silicon (PS) is investigated in situ for samples oxidized in air during different times. The PL intensity is found to be strongly enhanced by H2O atmosphere up to exposure times of about 50 h and to decrease for longer exposure. The PL enhancement is strongest in the red region of the PL spectra. It is suggested that H2O atmosphere generates surface traps on the PS involved in the visible light emission.
Master equation approach to anhysteresis of noninteracting particles
Authors: Klik Ivo , Chang Ching-Ray , Lee J.
Published: July 2002

Hysteresis in an array of thermally relaxing, aligned, noninteracting uniaxial particles driven by a periodic applied field with an attenuating amplitude and a dc bias is studied. The asymptotic state reached after the ac component attenuated to zero has the characteristics of anhysteretic magnetization. The convergence of the solution is studied, the anhysteresis curve is shown to lie below the curve of the equilibrium magnetization, a heuristic formula for the initial anhysteretic susceptibility is proposed, and the effects of interparticle interactions is discussed.
Charge trapped in biased double-barrier heterostructures
Authors: Rosa Armin , Puri Ashok , Murphy Joseph E. , Odagaki Takashi
Published: July 2002

The behavior of an electron cloud moving in a closed quantum double-barrier heterostructure is reexamined. The charge trapped in the double barrier acts as a nonlinear potential in the time-dependent Schrödinger equation and it is verified that it shows chaotic characteristics. The effect of changing the initial mean kinetic energy of the incident electron wave packet is examined. In order to understand the charge buildup in the biased quantum structures, an electric field is applied to the double-barrier structure with nonlinearity. The results demonstrate that the external field affects the charge buildup and its nonlinear behavior in the well. At resonance, the external field is found to have a marginal effect on the chaotic properties of the system. However, the nonresonant fields lead to an increase in the average charge buildup in the structure, and suggest an increase in the chaotic properties of the system compared to the resonant case. It is concluded that the resonance energy level in a chaotic, nonlinear system gets broadened and, as a function of the nonlinearity parameter α, multiple tunneling states are possible.
Dielectric response induced by intersubband transitions in quantum wells: Transmission ellipsometry studies at Brewster angle
Authors: Ozanyan K. B. , Hunderi O. , Fimland B. O.
Published: July 2002

The potential of infrared transmission spectroscopic ellipsometry is demonstrated for the case of intersubband transitions between the first and second upper-lying conduction-band states in a quantum well. Using the substrate-ambient interface as a Brewster polarizer, multiple reflections in the sample are modeled to occur only at a bare substrate-ambient interface. The ellipsometrically measured polarization ratio is related to the transfer-matrix elements of the overlayer by treating the latter as an effective medium uniaxial layer, grown on top of an isotropic substrate. The above approach is applied for a 60 period n-GaAs/Al0.3Ga0.7As (88 Å/130 Å) quantum-well stack, grown on a semi-insulating GaAs substrate. The experimentally extracted dielectric response of the overlayer to the propagating extraordinary beam is compared to the spectrum, calculated using a Lorentzian oscillator, centered at 1045 cm−1 with broadening of 100 cm−1, as expected from the engineered potential.
Numerical simulation of a coupled-quantum-well resonant tunneling transistor
Authors: Taniyama H. , Tomizawa M. , Yoshii A.
Published: July 2002

The quantum distributed model of the resonant tunneling transistor is improved based on a generalized S-matrix method. As a result, a model of the base current and the collector current is formulated in a consistent way and incoherent tunnelings are also considered. This model is used to study the coupled-quantum-well resonant tunneling transistor, and it is found that the resonance in the collector current disappears because of the spatial dependence of the resonance in the collector current when there is large internal resistance or a large scattering rate. It is also found that inclusion of the hole current is important in calculating the device characteristics of the resonant tunneling transistor.
Inverse delta doping for improvement of solar cells
Authors: Böer K. W. , Piprek J.
Published: July 2002

Delta doping with deep-level centers results in a marked decrease of open-circuit voltage and fill factor of photodiodes and solar cells when the doped layer is located near the crossover of electron and hole densities. The omission of recombination centers in a thin layer (inverse delta doping) at this position consequently causes an increase of the open-circuit voltage. The difficulty of improving the open-circuit voltage in actual high-efficient solar cells may have its origin in the inadvertent creation of donor-acceptor pairs caused by cross doping and consequent compensation. Such pairs are known to act as efficient recombination centers. The insertion of a thin, undoped interlayer is proposed to separate donors and acceptors and thereby reduce the density of close pairs.
Low temperature synthesis of Al-AlN composites from a nanostructure made by controlled magneto-ball milling of Al in ammonia
Authors: Calka A. , Nikolov J. I. , Wantenaar G. H. J.
Published: July 2002

The formation of an AlN compound in ball milled Al powder in ammonia was studied. In this work a magneto-ball milling device with controlled ball movement was used. The end milling product was an Al based nanostructure. This product can be transformed into an AlN-Al nanocomposite upon heating below the melting point of Al. It was found that the level of unreacted Al is dependent on milling time. The maximum amount of AlN was 88.28 wt %. The structure of as-milled and annealed samples was investigated using x-ray diffractometry and transmission electron microscopy. Differential thermal analysis was performed on as-milled samples.
Effect of stress sign and film thickness on interface nucleation of misfit dislocations in strained multilayers
Authors: Park Hyo-Hoon , Yoo Ji Beom , Oh Dae Kon , Kim Jeong Soo , Lee Jeong Yong
Published: July 2002

The strain relaxation mechanism via the homogeneous nucleation of misfit dislocations from the heterointerface in coherently strained layers has been investigated with transmission electron microscopy. It is identified that the dislocations nucleated from the interface are displayed in the form of 90° partial, 30° partial, and 60° perfect dislocations, depending on stress sign and thickness of the strained layer. The tendency is interpreted in terms of the strain relaxation efficiency which is given by the ratio of relieved strain energy to dislocation line energy.
Improved x-ray switched XeCl laser
Authors: van Goor F. A. , Trentelman M. , Timmermans J. C. M. , Witteman W. J.
Published: July 2002

The performance of a discharge excited XeCl laser has been studied using three different excitation circuits; spiker-sustainer excitation with a ferrite saturable inductor as the main switch; x-ray switching with a fast rise time x-ray preionization pulse, and x-ray triggering with a saturable inductor and a peaking capacitor added to the circuit. This circuit can improve the performance of the x-ray switched XeCl laser considerably.
Elastic properties of breakaway glass and liquid by Brillouin scattering up to 170 °C
Authors: Askarpour V. , Manghnani M. H.
Published: July 2002

The compressional VP wave velocity, refractive index n, and acoustic attenuation coefficient Γ of breakaway glass and liquid have been measured by high-resolution Brillouin spectroscopy up to 170 °C in platelet and backscattering geometries. A marked break in the compressional wave velocity-temperature relationship is observed at the glass transition temperature of 52 °C consistent with the glass transition temperature observed in ultrasonic experiments on the same sample. The temperature dependence of the compressional wave velocity determined by Brillouin scattering and ultrasonic interferometry are compared.
Microwave and millimeter wave generation using nonlinear optical mixing in asymmetric quantum wells
Authors: Qu Xiaohua H. , Ruda Harry
Published: July 2002

The possibility of microwave and millimeter wave generation using nonlinear difference-frequency mixing of optical lasers in an asymmetric quantum well (QW) is examined. In principle, this method imposes no limit on the frequency of generated microwave signals. It is shown that these structures are particularly suitable for enhancing the susceptibility of difference-frequency generation, χ(2)(Ω;ω1,−ω2); this originates from the ability to tune the fundamental photon energies ℏω1 and ℏω2 to valence-conduction subband transitions, while ℏΩ is tuned to intervalence and interconduction subband transitions. Under such conditions, the existence of a broad resonant enhancement region of χ(2), which is closely associated with the QW band structure is demonstrated. Enhancements of χ(2)xzx and χ(2)zxx exceeding 10 and 104 times over the bulk values are predicted, respectively.
Laser-induced chemical vapor deposition of titanium diboride
Authors: Elders J. , Voorst J. D. W. v.
Published: July 2002

The CO2 laser-induced chemical vapor deposition process of titanium diboride (TiB2) is described. The TiB2 was deposited on mullite, alumina, and thermally oxidized silicon by a hydrogen reduction of titanium tetrachloride (TiCl4) and boron trichloride (BCl3). The process resulted in a reaction-limited regime, a heat-diffusion limited regime, and a mass-diffusion limited regime. The hydrogen concentration has a large influence on the growth rate, nucleation rate, and morphology of the coatings. The photothermal deposition process is photolytically enhanced by the 193 nm beam of an ArF excimer laser which dissociates TiCl4. However, the 193 nm beam enhances the nucleation rate and crystal-growth rate to a different extent. The nucleation rate increases with increasing atomic hydrogen concentration, as is illustrated by experiments performed with a separate atomic hydrogen source (i.e., hot filament-enhanced chemical vapor deposition).
Growth of silicon thin films on erbium silicide by solid phase epitaxy
Authors: Veuillen J.-Y. , d’Anterroches C. , Tan T. A. Nguyen
Published: July 2002

A study of the growth of thin (20–30 Å) silicon overlayers on erbium silicide films epitaxially grown on Si(111), using the solid phase epitaxy technique under ultrahigh vacuum conditions was made. The silicon overlayers were characterized in situ by photoemission spectroscopy and low-energy electron diffraction for each annealing temperature. The structure of the films was analyzed (ex situ) by means of high resolution transmission microscopy. The Si overlayers are found to be essentially continuous and epitaxial after annealing at 600 °C. Electron microscopy reveals that defects are present in both the silicide and in the silicon films. The stability of thin silicon films has also been investigated.
Crystal-field levels of Tm3+ in gadolinium gallium garnet
Authors: Lupei A. , Lupei V. , Grecu S. , Tiseanu C. , Boulon G.
Published: July 2002

The absorption and emission spectra of Tm3+ ions in gadolinium gallium garnet is reported in order to identify the Stark levels involved in pumped and laser emission processes of this system. The analysis of the laser-excited luminescence from Tm3+ multiplets 1D2, 1G4, 3H4 to the ground manifold 3H6 confirms the assignments of Stark levels, corresponding to D2 symmetry, obtained from absorption and provides additional information. Due to the complex multisite structure, the site-selective excitation and emission data have been also used. A parametrized crystal-field calculation, including nine parameters for D2 symmetry, fits the energy-level diagram satisfactorily.
Third-order stiffness constants of textured hexagonal crystallite aggregates with an orthotropic macroscopic symmetry
Authors: Dai Ji-Dong
Published: July 2002

Voigt-type averaging is carried out to obtain the effective second- and third-order elastic stiffness constants of textured hexagonal (6/mmm, 6̄m2 or 6mm point group) crystallite aggregates with orthotropic macroscopic symmetry. The second-order constants agree with previously reported results. The third-order constants are presented in a compact formula. The formula relates the effective third-order stiffness constants to the crystallite orientation distribution coefficients (CODCs) and the single-crystal third-order stiffness constants. If any two of these three sets of parameters are known, information of the third set can be inferred. The sensitivity of the effective third-order stiffness constants to changes of the CODCs is also given.
Near-infrared spectral characteristics of Ge-doped cultured quartz crystals
Authors: Bahadur Harish
Published: July 2002

Ge-doped cultured quartz crystals have been investigated for their near-infrared absorption bands at low temperatures (∼77 K) in the 3100–3700 cm−1 region. The crystals studied were grown slowly, quickly, and also at high pressure. The Ge levels varied from 1000 to 3000 ppm. In addition to the conventional growth defect bands, a new band at 3481 cm−1 has been found to exist in all Ge-doped quartz. Another band at 3656 cm−1 is produced when the Ge levels are very high (∼3000 ppm). This band is better resolved in slow-grown material. Quickly-grown crystals exhibited an additional band at 3507 cm−1.
Light scattering by liquid crystals in columnar micropores
Authors: Saito M. , Nakamura S. , Miyagi M.
Published: July 2002

The optical transmittances of anodic alumina films which contain nematic liquid crystals in columnar pores were studied. Since liquid crystals are enclosed in narrow pores of ∼2000 Å diameter, light scattering occurs not only by the refractive index mismatch between the liquid crystals and alumina but also by the prominent distribution of the refractive index inside the liquid crystals. The transmittance changes reversibly with an electric field and temperature.
Simulation of dynamic ion-beam mixing
Authors: Seidl A. , Takai M.
Published: July 2002

Dynamic ion-beam mixing (i.e., simultaneous ion irradiation and layer deposition), allowing better control of intermixing and stoichiometry than conventional mixing methods, has been simulated by a Monte Carlo method. Reasonable agreement between simulation and measurements for the systems TiNSi and TiNFe was achieved.
Observation of lattice relaxation at the GaAsP/GaAs interface beyond the critical thickness by transmission electron microscopy
Authors: Soga Tetsuo , Inoue Jiro , Jimbo Takashi , Umeno Masayoshi
Published: July 2002

The lattice relaxation at the GaAs1−xPx/GaAs interface is observed using thickness fringe images in transmission electron microscopy. The bending of the equal thickness fringes observed near the interface is explained, assuming that crystal planes are inclined near the interface and that the inclination has a maximum at the interface. The magnitudes of inclination and the thickness of the strained region are estimated for various phosphorous composition and the GaAsP thickness. The lattice relaxation mechanisms for GaAsP on GaAs is described. It is indicated from the thickness fringe observation that the lattice relaxation occurs gradually beyond the critical thickness.
Thermal diffuse scattering in polycrystalline materials with a texture
Authors: Wu C. H. , Houska C. R. , Rao Satish
Published: July 2002

A simplified method of calculating thermal diffuse scattering (TDS) for materials at or above their Debye characteristic temperature is presented. This method is based upon the properties of the lattice Green’s function and eliminates the need of solving the equations of lattice dynamics. This simplifies the calculation procedure. The general scheme of evaluating the diffuse scattering for polycrystalline materials with a texture is discussed. A sample calculation of the TDS from a polycrystalline material with a fiber texture is given using the simplified procedure just presented.
Planar 1.3 and 1.55 μm InGaAs(P)/InP electroabsorption waveguide modulators using oxygen ion mixing and the photoelastic effect
Authors: Pappert S. A. , Xia W. , Jiang X. S. , Guan Z. F. , Zhu B. , Liu Q. Z. , Yu L. S. , Clawson A. R. , Yu P. K. L. , Lau S. S.
Published: July 2002

Efficient 1.3 and 1.55 μm InP-based electroabsorption waveguide modulators with planar device structures have been demonstrated. Elevated temperature oxygen ion implantation and/or the photoelastic effect induced by W metal stressor stripes deposited on the semiconductor surface have been used to produce these self-aligned planar guided-wave devices. The oxygen ion mixing process has been used to simultaneously achieve compositional disordering and electrical isolation of superlattice material while the photoelastic effect has been used to improve the lateral mode confinement. A 1.3 μm Franz–Keldysh modulator with a ≳10 dB extinction ratio at 2 V and a 1.55 μm device with a ≳10 dB extinction ratio at 7 V are reported. These single growth step planar processing techniques have also been used to fabricate relatively low-loss (<4 dB/cm) double heterostructure InGaAs(P)/InP single-mode optical waveguides which demonstrate their usefulness in developing InP-based photonic integrated circuits.
Carbon incorporation in InP grown by metalorganic chemical vapor deposition and application to InP/InGaAs heterojunction bipolar transistors
Authors: Stockman S. A. , Fresina M. T. , Hartmann Q. J. , Hanson A. W. , Gardner N. F. , Baker J. E. , Stillman G. E.
Published: July 2002

The incorporation of residual carbon has been studied for InP grown at low temperatures using TMIn and PH3 by low-pressure metalorganic chemical vapor deposition. n-type conduction is observed with electron concentrations as high as 1×1018 cm−3, and the electrical activation efficiency is 5%–15%. Carbon incorporation is found to be highly dependent on substrate temperature, suggesting that the rate-limiting step is desorption of CHy (0≤y≤3) from the surface during growth. Hydrogen is also incorporated in the layers during growth. The electron mobilities are lower for C-doped InP than for Si-doped InP. InP/InGaAs heterojunction bipolar transistors with C as the p-type base dopant and either Si or C as the n-type emitter dopant have been fabricated and compared. Devices with a carbon-doped base and emitter showed degraded performance, likely as a result of deep levels incorporated during growth of the emitter.
Reflection of light ions from heavy element targets
Authors: Luo Zhengming , Wu Wengfeng , Hou Qing
Published: July 2002

An improved bipartition theory for light-ion transport is presented. The improved theory allows the use of accurate but more complex nuclear scattering cross sections and stopping powers in the Boltzmann transport equation, instead of the power function approximation of the nuclear scattering cross sections and the stopping powers used in earlier bipartion theory [Z.-M. Luo and S.-M. Wang, Phys. Rev. B 36, 1885 (1987)]. Furthermore, the theory is extended to treat the transport for obliquely incident ions. By the improved bipartition theory, the particle reflection coefficients and energy reflection coefficients, as well as energy distribution of reflected ions for cases of H, D, and He ions incident on C, Ni, Fe, Cu, W, and Au, have been calculated. The comparison of the present calculation results with available experimental data and the Monte Carlo data shows that the improved bipartition model for light ions is useful.
Selective band-gap blueshifting of InGaAsP/InGaAs(P) quantum wells by thermal intermixing with phosphorus pressure and dielectric capping
Authors: Francis C. , Julien F. H. , Emery J.-Y. , Simes R. , Goldstein L.
Published: July 2002

Group V interdiffusion of strained and unstrained InGaAsP/InGaAs(P) quantum wells induced by thermal anneals at 650 °C with phosphorus gas pressure using photoluminescence spectroscopy and x-ray diffraction measurements have been investigated. The blueshift of the annealed quantum well photoluminescence peak exhibits large variations with the phosphorus pressure, with a minimum around 0.1 atm. Samples capped with a SiO2 layer only exhibit minor blueshifts, thus demonstrating the possibility of spatially selective control of the intermixing. A differential blueshift as large as 80 meV is presently obtained between capped and uncapped areas. The interdiffusion of the quantum well interfaces is shown to be dependent on the layer strain.
Adhesion of electrolessly deposited Ni(P) layers on alumina ceramic. II. Interface characterization
Authors: Severin J. W. , Hokke R. , van der Wel H. , de With G.
Published: July 2002

The interface microstructure and interface chemistry of electrolessly deposited Ni(P) on alumina ceramics is studied in order to obtain insight into the influence of molecular interactions upon the adhesion. Detailed static secondary-ion-mass spectrometry, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy (TEM) analyses have been carried out with samples with various roughnesses, of which the mechanical analyses are described in the companion article. TEM cross-section micrographs showed a close contact between the two phases on a nanometer scale for all sample types. In addition, a 1–2-nm-thick interfacial layer was observed. This layer consists of nucleation material and compounds from the metallization solution. Fracture surface analyses showed that fracture takes place through this layer, which is therefore considered to be the weak boundary layer in this system. The presence of this weak boundary layer explains the importance of substrate surface roughness and mechanical interlocking for the fracture energy.
Multiple twinning in GaAs epitaxial layers grown on Si(001) and Si(111)
Authors: Neethling J. H. , Alberts V.
Published: July 2002

Multiple twinning in GaAs epitaxial layers grown on Si by metalorganic vapor phase epitaxy has been studied by transmission electron microscopy. The primary and multiple twin reflections in the diffraction patterns were indexed in terms of matrix indices for the electron beam parallel to the 〈001〉, 〈110〉, and 〈111〉 directions in GaAs.
First-principles mesoscopic dynamics in heterogeneous materials
Authors: Pantelides Sokrates T.
Published: July 2002

A systematic link between microscopic and macroscopic theories of matter has been lacking in the case of heterogeneous materials (polycrystals, composites, etc.). The properties of such materials are largely determined by their collective microstructure, which defines several intermediate or mesoscopic length scales. A microscopic description is presented and the principles of statistical mechanics are used to derive a set of mesoscopic field dynamical equations that describe microstructure evolution under external stresses, temperature gradients, or electric current. The macroscopic dynamical equations of continuum mechanics are recovered. The cross-coupled phenomena of elastic deformations and inelastic diffusive and slip processes are present, setting the stage for a first-principles theory of dislocation dynamics and plasticity.
Optical second harmonic generation of oblique incident light in transmission in potassium dihydrogen phosphate crystal
Authors: Bhanthumnavin V. , Lee Chi H.
Published: July 2002

The intensity of the transmitted inhomogeneous and homogeneous second harmonic light generated from potassium dihydrogen phosphate (KDP) crystals immersed in an optically denser fluid 1-bromonaphthalene have been observed as a function of incident angle θi of the fundamental beam of a mode locked neodymium glass laser. The laser pulses have the polarization in [11̄0] direction with respect to the KDP crystallographic axes. The transmitted second harmonic generation in the neighborhood of critical angle of incidence is performed. The phase matching of second harmonic generation in transmission is demonstrated. Furthermore, we observed that no transmitted inhomogeneous and homogeneous second harmonic light at normal incident angle when the nonlinear polarization PNLS (2w) lies in the direction [001] along the crystal face normal. The experimental result agrees well with the Bloembergen and Pershan theory.
Determination of the complex refractive index of individual quantum wells from distributed reflectance
Authors: Hickernell Robert K. , Christensen David H. , Pellegrino Joseph G. , Wang Jin , Leburton Jean-Pierre
Published: July 2002

We investigate the measurement of the complex refractive index of individual quantum wells by reflectance spectroscopy. Placing the wells at half-wavelength spacing to cause resonant feedback produces an order-of-magnitude increase in measurement sensitivity over that of nonresonant structures. Quantum well dispersive and absorptive effects on reflectance can be differentiated in certain spectral regions. Experimental data confirm a theoretical model of refractive index and absorption for quantum wells of GaAs in Al0.2Ga0.8As in the region of the well band gap.
Halogenation of diamond (100) and (111) surfaces by atomic beams
Authors: Freedman Andrew
Published: July 2002

Diamond (100) and (111) surfaces have been exposed to beams of atomic and molecular fluorine and chlorine in an ultrahigh-vacuum environment. X-ray photoelectron spectroscopy, low-energy electron diffraction, and thermal desorption techniques have been used to elucidate the chemistry involved. F atoms add to both the diamond (100)-(1×1) and (111)-(2×1) surfaces to form a carbon-monofluoride species which reaches a saturation level of approximately three-quarters of a monolayer at 300 K. In other aspects of their behavior, the diamond surfaces differ. On the (111) surface, the rate of fluorine atom uptake is, to first order, proportional to the open site concentration. Adsorption produces a dimming of the half-order electron-diffraction spots, suggesting the breaking of surface π-bonded chains to form regions of the bulk 1×1 reconstruction. The (100) surface uptake rate, though, is second order with respect to open site concentration and no electron-diffraction pattern is observed. This difference in behavior between the two surfaces is ascribed to the difference in bonding geometry, leading to severe steric hindrance to ordered adsorption on the (100) surface. The thermal desorption data show fluorine desorption over a wide temperature range (500–1200 K) on both surfaces indicating binding sites with a range of energies.

Limited mass spectrometric data indicates that atomic fluorine is the major desorption product. These results imply that atomic fluorine will act in a fashion similar to hydrogen atoms in that they will break surface dimer bonds, desorb from the surface at an appropriate temperature without etching diamond, and abstract any surface hydrogen in deposition systems utilizing halocarbon species. The much larger chlorine atoms weakly chemisorb on the diamond (100) surface, producing a saturation coverage of less than half a monolayer at 300 K. The adlayer neither shows a distinct C-Cl peak in the x-ray photoelectron spectra nor exhibits any electron-diffraction pattern. In addition, thermal desorption studies indicate that the concentration of chlorine atoms monotonically decreases to virtually zero as the substrate is heated from 223 to 423 K. A small residual chlorine concentration remains up to 600 K, presumably due to binding at defect sites. This behavior implies that atomic chlorine will exhibit a less significant role in the surface chemistry of diamond deposition systems.
Single-frequency admittance spectroscopy measurement of band offset in a Si/Si1−xGex/Si quantum well
Authors: Lu Fang , Jiang Jiayu , Sun Henghui , Gong Dawei , Wang Xun
Published: July 2002

A single-frequency admittance spectroscopy technique is presented to determine the band discontinuity of the Si/Si1−xGex/Si single quantum well. The accuracy of determining the activation energy for thermionic emission of holes over the Si barrier is improved as compared with the multiple-frequency admittance spectroscopy measurement. To derive the band offset from the activation energy, the Fermi energy with respect to the band edge is calculated more exactly by solving the Poisson equation which accounts for the carrier transfer at the heterointerface. The accuracy of this technique is verified by the reconstruction of the temperature dependence of capacitance and conductance by the computer simulation.
Effects of an electric field on exciton recombination in three-step asymmetric coupled quantum wells
Authors: Brandt O. , Kanamoto K. , Tokuda Y. , Abe Y. , Wada Y. , Tsukada N.
Published: July 2002

The radiative transitions of (100)- and (311)A-oriented three-step asymmetric coupled quantum wells in an electric field are studied by photoluminescence. Four distinct transitions are observed in the spectra which exhibit remarkably complex energy shifts with the applied field. It is shown that these transitions originate from the two pairs of spatially direct and indirect heavy-hole excitons in the three-step quantum well and that their electric-field dependence is dominated by the conversion of the direct into the indirect excitons and vice versa. Furthermore, we discuss the effects of the nonconventional crystal orientation and show that substantial modifications of the basic electro-optical properties can be achieved from internal piezoelectric fields incorporated within the structure.
Microstructure of oxidized layers formed by the low-temperature ultraviolet-assisted dry oxidation of strained Si0.8Ge0.2 layers on Si
Authors: Craciun V. , Boyd I. W. , Reader A. H. , Kersten W. J. , Hakkens F. J. G. , Oosting P. H. , Vandenhoudt D. E. W.
Published: July 2002

Ultraviolet-assisted low-temperature (550 °C) dry oxidation of Si0.8Ge0.2 strained layers on (100)Si has been studied. The oxidation rate of this material was found to be a factor of 2 greater than that of pure Si oxidation under identical irradiation conditions. Initially, the structure of the oxidized material consists of a SiO2 layer on top of a strained Si1−xGex layer with a Ge concentration significantly higher (x≳0.2) than the initial value. Increasing the oxidation time produces more SiO2 and a Si1−xGex layer further enriched with Ge. However, the oxidation rate is reduced and some of the Ge becomes trapped inside the growing SiO2 layer. For a prolonged irradiation time (≳5 h) SiGe oxidation still continues, unlike the case for pure Si, while the Ge trapped inside the SiO2 forms isolated microcrystalline regions.
Recovery of recombination lifetime by pouring de-ionized water onto a rotating plasma-damaged wafer
Authors: Itsumi Manabu , Aoyama Shinji
Published: July 2002

Pouring de-ionized water onto a rotating wafer increases the recombination lifetime reduced by with plasma-induced damage, and this increase is greatest in the central region of the wafer. This recovery is observed with p-type Si and n-type Si substrates and with dry oxides and wet oxides. Electrostatic measurements reveal that the water induces negative charges on a wafer and that the amount of charge increases with increasing rotation speed. Capacitance-voltage analysis indicates that negative charge builds up in the oxides and that interface states are generated at the Si-SiO2 interface. A model is proposed in which electrons produced through the friction between the water and the SiO2 surface play an important role in the recovery of the recombination lifetime.
Magnetic and magnetorestrictive properties of Sm1−xDyxFe2 compounds and its Mössbauer effect studies
Authors: Guo Hui-Qun , Yang Hong-ying , Gong Hua-yang , Yang Lin-yuan , Shen Bao-gen , Li Ru-qi
Published: July 2002

Measurements of x-ray diffraction, magnetization, magnetostriction, and Mössbauer effect were performed on a series of Sm1−xDyxFe2 samples (x=0, 0.1, 0.15, 0.25, 0.45, and 0.65). It is shown that the system retains the cubic MgCu2 structure over the whole range and the lattice constant decreases linearly with increasing x. Results of Mössbauer effect study at room temperature show that for a small amount of Dy substitution for Sm, x<0.15, easy axes of the magnetization keep in the [111] direction. For x≳0.15, the direction of easy axes rotates gradually from [111] for x=0, and 0.1 to [100] for x=0.45 and 0.65. The concentration dependence of the saturation magnetization exhibits a minimum at x=0.30 for 1.5 K and at x=0.45 for room temperature, reflecting the occurrence of the compensation of magnetic moments at various Sm/Dy ratios. For x=0.45 and 0.65, the pinning phenomenon of narrow domain walls was observed at low temperature. The magnetostriction was found to decrease with the increase in the Dy content, as a result of the compensation of λ111 in Sm1−xDyxFe2.
Giant magnetoresistance and its dependence on processing conditions in magnetic granular alloys
Authors: Wang Jian-Qing , Price Edward , Xiao Gang
Published: July 2002

We have studied giant magnetoresistance (GMR) effect and its dependence on processing conditions in Fe-Ag and Co-Ag alloys made by magnetron sputtering. The effect of elevated substrate temperature on GMR has been investigated and compared with the results of post-deposition annealing. As a unique feature, in situ annealing yields a second GMR peak at high deposition temperatures, which is associated with a substantially reduced saturation field for GMR. Deposition rate was found to be another crucial parameter in affecting GMR, whereas little effect was observed in varying the sputtering gas pressure.
Novel magnetoresistance behavior in single trilayer spin valves
Authors: Patel M. , Fujimoto T. , Gu E. , Daboo C. , Bland J. A. C.
Published: July 2002

Single trilayer spin valves consisting of uncapped FeNi(60 Å)/Cu(60 Å)/Co(40 Å) have been grown using ultrahigh vacuum (UHV) electron beam evaporation methods. Room temperature magnetoresistance (MR) measurements exhibit well defined plateaux corresponding to the full antiparallel alignment of the FeNi and Co magnetizations. This sharp switching behavior and precisely defined antiferrimagnetic state is in contrast with the corresponding behavior reported for FeNi/Cu/Co multilayers.
Dependence of contact resistance on metal electronegativity for B-doped diamond films
Authors: Kawaguchi Goro , Nakanishi Jiro , Otsuki A. , Oku T. , Murakami Masanori
Published: July 2002

The contact resistance (Rc) measurements and microstructural analysis at the metal/diamond interfaces were carried out by depositing a variety of metals on the polycrystalline B-doped diamonds which were prepared by microwave plasma chemical-vapor deposition. The Rc values, which were measured by the transmission line method, were found to be dependent on the electronegativities of the metals, and the lower Rc values were obtained for the metals with higher electronegativity. The Rc values of the Ti and Mo contacts decreased upon annealing at elevated temperatures, and the TiC and Mo2C compounds were observed at the metal/diamond interfaces by cross-sectional transmission electron microscopy and x-ray diffraction. The reduction of the Rc values is believed to be due to creation of crystal defects induced by formation of the carbides. The present experiment suggests that the electronegativities of the metals would provide guidance to select Schottky and ohmic contact materials of future diamond semiconductor devices. However, we have a concern in use of semiconductive polycrystalline diamond films as their substrates.