bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection of the ground state in CsCuCl3 by quantum fluctuations
Authors: Rastelli E. , Tassi A.
Published: July 2002

The Heisenberg triangular antiferromagnet is a model widely studied by analytic low-temperature expansion and Monte Carlo simulation. The classical version of the model is characterized by infinitely many minimum energy configurations even if an in-plane external magnetic field is turned on. This degeneracy is lifted by thermal fluctuations and the same effect is found when quantum fluctuations are accounted for. We find an analogous scenario in the 3D hexagonal model where the intrachain coupling is ferromagnetic and the interchain one is antiferromagnetic. Such a model is suitable to describe some hexagonal ABX3 compounds. We are interested, in particular, in CsCuCl3, where our theoretical results compare favorably with magnetic resonance experimental data and with magnetization measurements as a function of the external magnetic field. The role of quantum and thermal fluctuations in the selection of a particular spin pattern out of the infinitely many configurations that minimize the classical energy of the model is discussed.
A microwave transmission spectrometer
Authors: Waldfried Carlo , Wadewitz Scott , Dewar G.
Published: July 2002

The design and performance of a microwave transmission spectrometer operating in the 12.4–18 GHz frequency range is described. This spectrometer measures the microwave power passing through a magnetic, metallic sample as a function of temperature and applied magnetic field. Significant features of the apparatus are the use of a solid state microwave amplifier as the homodyne receiver’s front end and the inclusion of a calibration signal which is injected into the receiver simultaneously with the signal to be measured. The excellent noise figure (<2 dB) and gain (≳34 dB) of the amplifier yield a receiver sensitivity of ≊10−20 W in a 1 Hz bandwidth. The present microwave source is a dielectric resonant oscillator which generates 100 mW at 16.95 GHz, although the system can also operate with a klystron or microwave sweep oscillator locked to any frequency between 12.4 and 18 GHz. The first use of the system was to measure the transmission through the amorphous ferromagnet Metglas(R) 2605SC (Allied Chemical Corporation). A peak in the transmission was observed at ferromagnetic resonance. This transmission peak was contaminated by a signal going around, not through, the sample which we tentatively identify with surface acoustic waves.
Three component magnetic field measurements using cubic anisotropy in (111) YIG films (abstract)
Authors: Perlov A. Ya. , Voronko A. I. , Vetoshko P. M. , Volkovoy V. B.
Published: July 2002

A magnetization behavior in YIG films with (111) orientation for a saturation in-plane magnetic field, taking into account the fourth (K1) and the sixth (K2) cubic anisotropy constants, is investigated theoretically and experimentally. Dependencies of a magnitude of the saturation field on material parameters were found. Different situations of a static and a rotating saturation magnetic field were considered. Analytical expressions for an induction signal caused by interference of in-plane magnetization homogeneous rotation with an ambient quasistatic magnetic field were obtained. It was shown that there exists a linear harmonic response to the ambient field both tangentially and perpendicularly to the film plane field orientations. Experimental results obtained for different kinds of YIG films were in good agreement with theory. Measured sensitivity was of the order of 10−7 Oe with a dynamic range of 80 dB. This, thereby, enables the design of a three component induction sensor with a high sensitivity and a large dynamic range.
Relaxation dynamics in a reentrant (FeNi)Mn ferromagnet: A percolation analysis
Authors: Li D. , Roshko R. M. , Yang G.
Published: July 2002

Measurements of the low-field thermoremanent relaxation in a reentrant (Fe0.65Ni0.35)1−xMnx ferromagnet with x=0.117 reveal a crossover, in the vicinity of the reentrant transition, from equilibrium dynamics in the ferromagnetic phase to age-dependent, nonequilibrium dynamics in the reentrant phase. Least-squares fits to two mesoscopically exact relaxation functions show that both dynamic regimes can be described within a common theoretical framework of magnon relaxation on a percolation distribution of fixed, finite domains of dynamically correlated spins.
Macroscopic random magnetic anisotropy constant in crystalline DyxY1−xAl2 (x=0.3, 0.4)
Authors: del Moral A. , Ciria M. , Arnaudas J. I. , Abell J. S. , Bi Y. J.
Published: July 2002

Cooling in a weak magnetic field the random magnetic anisotropy (RMA) spin glasses DyxY1−xAl2 (x=0.3, 0.4) induces unidirectional and uniaxial anisotropies, on top of the cubic coherent one. The unidirectional anisotropy constant KRMAu has been determined at 3.8 K, amounting at zero applied field 127 and 255 J/m3 for x=0.3 and 0.4, respectively. The predicted model ratio between KRMAu and the uniaxial constant KRMAa, i.e., KRMAa=2KRMAu, has been confirmed. As by-product the relevant RMA parameter D2/J, where D is the RMA crystal field strength and J, the exchange constant has been determined, as well as separate estimates of D and J.
Fine structure and magnetic properties of Mn- and Co-doped nanocrystalline γ-Fe2O3
Authors: Deng Ming-Cheng , Chin Tsung-Shune , Chen F. R.
Published: July 2002

High resolution TEM (HRTEM), Mössbauer spectroscopy and SQUID magnetometry were utilized to study the fine structure of equiaxed, Mn- and Co-doped γ-Fe2O3 nanocrystals with a particle size of 30–50 nm. The allocation of cation distribution, based on a redox mechanism and known cation site preferences is (Mn2+0.11Fe3+0.89) [Mn4+0.07Mn3+0.16) Co2+0.34Fe3+1.23⧠0.20]O4, in which ⧠ is the vacancy, (⋅⋅) is the A site, and [⋅⋅] is the B site. This leads to an Fe occupancy ratio of B sites to A sites of 1.38, as verified by Mössbauer spectroscopy. The calculated saturation magnetic moment of 2.99μB/MF is very close to the measured 2.84μB/MF. HRTEM micrographs of the air-cooled nanocrystals fits well with the simulated lattice images using the proposed cation distribution (without directional ordering). While the HRTEM micrograph of the core of an annealed nanocrystal are not in good agreement. This is thought to arise from directional ordering inside the annealed particles.
Magnetic properties of fine Ni particles coated with Pd (abstract)
Authors: Yamaguchi Makoto , Otani Yoshichika , Miyajima Hideki
Published: July 2002

Ni-Pd composite fine particle is an ideal system to study surface and interface magnetism because of its large surface area compared with the total volume. In this work, magnetic properties of Ni-Pd composite fine particles were studied in terms of the magnetic proximity effect and the effect of hydrogenation. The composite particle consists of Ni core and Pd shell. Five different particles with different Pd shell thicknesses, 50, 100, 150, 200, and 350 Å, were prepared. The average diameter of the Ni core is about 0.7 μm. The Curie temperatures of all the samples are lying around 630 K and are nearly equal to that of a bulk Ni. Unlike pure Ni, the samples exhibit a relatively large coercive force of a few hundred Oersted in the temperature range from 4.2 to 750 K. The magnetization of the Ni core is found to be somewhat lower than that of pure Ni. An enhanced interface anisotropy due to the Pd coating (∼−1.5×105 J/m3) seems to impede saturation. Before hydrogenation, there appears quite a large thermal hysteresis. On heating, the isofield magnetization exhibits ferromagnetic behavior with a rise of magnetic moment below 30 K, suggesting that there is induced magnetization in the Pd shell. The change in magnetization follows the Curie–Weiss law, which gives a Curie temperature of 22 K. However, the steep rise of magnetization is not observed in the cooling process. After hydrogenation, this ferromagnetic behavior completely vanishes. There is also observed no lattice expansion, but this isovolumetric constraint seems to have little change on the saturation hydrogen loading.
Nuclear magnetic resonance studies on the surface magnetism of vanadium ultrafine particles (abstract)
Authors: Hirayama Yukihiro , Erata Tomoki , Kita Eiji , Tasaki Akira
Published: July 2002

Nuclear magnetic resonance studies were carried out on the ultrafine particles of vanadium prepared by the gas evaporation method for making clear its Curie–Weiss like magnetism, which appeared besides the ordinary Pauli paramagnetism reported already.1 The observed NMR signal was composed of two lines; one of those signals was identified as being from metal vanadium because of its Knight shift, 0.58%, and the other line with less intensity had a 0.7% Knight shift. Since the relative intensity of this low field shifted line was proportional to the inverse diameter of the particle and increased with the decrease of temperature, this line can be identified as being from the surface region of the particles. The spin-lattice relaxation time of the surface region has shown the Corringa’s relaxation, which indicates that the surface electrons show metallic character. The resonance line with a 0.7% Knight shift originated from surface vanadium suggests the existence of the narrow band at its Fermi level and a rather localized character of the surface electrons, and this characteristic surface region increases with lower temperatures. The origin of the observed temperature dependent paramagnetism of vanadium ultrafine particles can be considered as the surface magnetism still having a metallic character.
Physical information in polarized x-ray absorption spectroscopy and x-ray photoemission spectroscopy (invited) (abstract)
Authors: Thole Bernard Theodoor
Published: July 2002

Core level and localized level x-ray absorption spectroscopy and x-ray photoemission spectroscopy contain information that can be extracted in a way independent of the theory used for the valence band. The sum rule method essentially integrates over core hole effects, which average to zero, leaving only one-particle effects. The results present interesting problems for both localized and band structure theory. In particular, more information on orbital moments has already become available, which needs a correct treatment of spin-orbit coupling. On the other hand, the multiplet structure is for a large part due to interactions in the final state and therefore gives only indirect information on the ground state. The interpretation is more complex and theory dependent.
Quantum renormalization of the XY model
Authors: Cuccoli Alessandro , Tognetti Valerio , Verrucchi Paola , Vaia Ruggero
Published: July 2002

The statistical mechanics of the two-dimensional ferromagnetic model with easy-plane anisotropy is approached by the pure-quantum self-consistent harmonic approximation (PQSCHA), that reduces the calculation of thermodynamic averages to effective classical expressions. In the PQSCHA, the quantum corrections to the classical thermodynamics are reduced to suitable (temperature-dependent) renormalizations of the interaction parameters, so that the full role of the nonlinear excitations is preserved. A particular case is the XX0 model (also known as the quantum XY model), which undergoes a Kosterlitz–Thouless phase transition at some finite temperature Tc. Since it is possible to calculate how much the effective exchange interaction is weakened by quantum fluctuations, we can predict, for instance, the corresponding amount of reduction of Tc for any value of the spin. Even in the extreme quantum case of the spin-1/2 model, our result is compatible with the estimates of Tc obtained by other authors.
Monte Carlo calculation of the correlation range for the S=1/2 isotropic Heisenberg ferromagnetic thin film
Authors: Rojdestvenski I. V. , Cottam M. G. , Favorski I. A.
Published: July 2002

The Handscomb Monte Carlo technique is used to investigate the critical properties of S=1/2 isotropic Heisenberg ferromagnetic films with nearest-neighbor interactions. We study a simple-cubic lattice with the number of monolayers L=1,2 as done previously, but we now include the effects of different values for interlayer and intralayer exchange parameters. We calculate numerically the temperature dependences of the correlation range. For the two-monolayer film, for the investigated temperature interval these results confirm our previous conclusions about the two-dimensional type of critical behavior of the system with a renormalized (modified) exchange parameter. Numerical data on the behavior of the surface-surface spin correlation function are also presented.
Parameter template in local magnetic measurements
Authors: Kaczmarek R. , Dautain M. , Defoug S.
Published: July 2002

Surface Kerr-effect hysteresis loops used to determine loop parameters such as coercive field and remanence in the percent of saturation, may be obtained with video detection via uniform illumination but without invoking multiple image summation, averaging and subtraction as previously used to overcome poor signal to noise when investigating weak Kerr-contrast materials. The approach taken here applied to power ferrite surfaces is to calculate for each applied field in the repetitive field excitation cycle, an accurate number representing the average of all pixels over a grain area. The grain under study had 20–50 microns across. Results stabilize after 20 cycles, within a parameter range that may be qualified as the parameter template. For small grains the template values become more important, which seems to be in accord with theories of the Hc fluctuations and the nature of hysteresis losses.
Magnetic behavior of (CuIn)1−xMn2xTe2
Authors: Shand P. M. , Polstra P. A. , Miotkowski I. , Crooker B. C.
Published: July 2002

Magnetic susceptibility measurements have been made on the chalcopyrite diluted magnetic semiconductor (CuIn)1−xMn2xTe2 for concentrations 0.01≤x≤0.101 and temperatures 33 mK≤T≤300 K. Samples with x≳0.05 had similar values of the effective nearest-neighbor exchange constant, with Jeff/kB≊−18.5 K. The strength of Jeff fell sharply in samples with lower x, a characteristic not seen in wide band gap II–VI based alloys. Low-field ac susceptibility measurements showed spin-glass behavior. Analysis of freezing temperature Tf vs x data showed a possible crossover between different modes of exchange, coincident with the sharp drop in Jeff. Preliminary carrier concentration data suggests that the crossover may be driven by increased numbers of free holes in some samples.
Computation of magnetic fields from recording surfaces with multiple tracks
Authors: Burke E. R. , Gomez R. D. , Madabhushi R. , Mayergoyz I. D.
Published: July 2002

Calculations of the magnetic fields emanating from a recorded surface that contains an infinite number of identical tracks are presented. The solutions are obtained by assuming that the magnetization is uniform through the thickness of the film and can be represented by Fourier series in the other two dimensions. Solutions are obtained for both longitudinal and vertical recording. To make these calculations useful Fourier distributions are obtained with arctan transitions that are both representative and easy to use. These magnetic fields are then used to calculate the voltage from an idealized reproduce head. Effects on the output voltage caused by track width, track separation, head registration, and transition lengths can then be calculated. Examples are given and it is shown that the effects can be large, compared to the usual infinite track width calculations, when the track width or the track separation become comparable to the recorded wavelength.
2D vector Preisach models and rotational hysteretic losses
Authors: Mayergoyz I. D.
Published: July 2002

Depending on the physical nature of hysteresis, rotational hysteretic losses in isotropic materials may decrease to zero or even continuously increase with the increase in the magnitude of uniformly rotating magnetic fields. It is shown in the paper that recently developed 2D Preisach models of vector hysteresis accommodate this broad spectrum of behavior of rotational hysteretic losses.
A computer simulation of the microstructure of a particulate dispersion
Authors: Coverdale G. N. , Chantrell R. W. , Hart A. , Parker D.
Published: July 2002

A computational simulation of a dispersion of iron particles undertaken to study the influence of the magnetostatic interactions on the microstructure of a particle ensemble is reported herein. The simulation considers an equilibrium state derived from an initial random state by the force-bias Monte Carlo technique. This method favors particle moves in the direction of the magnetostatic forces. A three dimensional ensemble in zero field and a saturating field are studied. An approach which takes into account the magnetostatic interactions between clusters by allowing Monte Carlo moves of whole clusters has been developed. This approach leads to the formation of extended networks consisting of particles in strongly bound clusters which themselves interact and give rise to an extended network. This is similar to the long-range order observed in practical dispersions. The structure analysis is found to characterize the local order, being especially sensitive to anisotropy in the order produced by an aligning field.
The effect of dc bias fields on the switching speed in magnetic particulate media (abstract)
Authors: Doyle W. D. , He L.
Published: July 2002

New results on the switching speed limit in high coercivity particulate magnetic media have recently been reported using pulse fields with widths t<1 ns. Because the pulse amplitude is presently limited to <950 Oe, switching measurements on media with higher coercivities were carried out in the presence of a dc bias field HB and the switching constant Sw at zero bias field estimated by extrapolating the data at several high bias fields to HB=0. The sensitivity of Sw to HB was significant particularly in barium ferrite so it is prudent to examine this dependency more carefully in a lower coercivity system in which Sw can be measured from 0≤HB≤HCR and HCR is the remanent coercivity. The results (Fig. 1) for a standard γ-Fe2O3 iron oxide tape with HCR=375 Oe show a nearly linear dependence of Sw on HB except for HB/HCR≥0.7 and validate our earlier speculation that switching in barium ferrite particles is significantly slower than in metal particles. The experimental results will be compared to the calculated switching time as a function of HB expected for an appropriate distribution of uniaxial, single domain particles.
Spin-wave chaotic transients
Authors: de Aguiar F. M. , Rezende S. M. , da Silva F. C. S.
Published: July 2002

We report the observation of transient chaotic spin-wave auto-oscillations in X-band pulsed subsidiary-resonance experiments in a YIG sphere. Chaotic transients to a periodic attractor have been observed near a critical microwave power pc∼10 dB relative to the Suhl instability threshold. By an averaging of 100 randomly chosen initial conditions at each power, we estimate a critical exponent γ ∼ 0.57. In addition, we demonstrate that the results can be qualitatively understood within the framework of the standard two-mode model. Numerical simulations yield, for a particular set of parameters, chaotic transients obeying the predicted scaling law with a critical exponent γ ∼ 0.54.
Magnetoelastic interaction in yttrium iron garnet films with magnetic inhomogeneities through the film thickness
Authors: Gulyaev Yu. V. , Temiryazev A. G. , Tikhomirova M. P. , Zil’berman P. E.
Published: July 2002

Experimental study of the spin-wave resonance (SWR) spectrum of a nonuniform yttrium iron garnet (YIG) film has revealed an existence of sharp disturbances inside the spectrum. The experiments were carried out at frequency range 4–12 GHz. The observation has been attributed to excitation of acoustic waves. The interpretation follows from the facts that (1) nonuniformity of magnetic parameters across the thickness of the tested film results in effective excitation of spin waves; and (2) coincidence of phase velocities of the spin waves and the transverse acoustic waves leads to partial power, transforming from the magnetic into the elastic system.
Applications of ferrites and ferromagnets in tuning rf cavities for accelerators
Authors: Hanna S. M.
Published: July 2002

Traditionally ferrites have been used in accelerators for tuning rf cavities and in nonreciprocal devices controlling the power flow in rf accelerating systems. Recently, the development of cavity tuners based on perpendicularly biased ferrites has shown good progress. Yttrium iron garnet (YIG) is gradually replacing the traditional Ni Zn ferrites. The use of conventional parallel-biased Ni Zn ferrites for varying the frequency of accelerating cavities has the disadvantage of high saturation magnetization (4πMs). This precludes practical operation in low magnetic loss regions. Different substitutions have been used with YIG to reduce its 4πMs, making it a practical candidate for perpendicular biasing operating in the saturation region. In addition, YIG is known for its low dielectric and magnetic losses. In this paper we give a short review of development in accelerator cavity tuners based on perpendicularly biased iron garnet ferrites. We use the operation of a 52 MHz stripline-based YIG tuner which we have tested at BNL as an example to demonstrate the advantages of using YIG in cavity tuners. We also discuss magnetic tuning techniques based on magnetostriction of Ni.
Random-exchange to random-field crossover breaking in Mn0.35Zn0.65F2
Authors: Montenegro F. C. , de Jesus J. C. O. , Rosales-Rivera A.
Published: July 2002

The critical phase boundary Tc(H) of Mn0.35Zn0.65F2 has been mapped in a (H,T) phase diagram using dc magnetization measurements. Our data show that Tc(H) is governed by a scaling law TN−Tc(H)∼H2/φ, with φ=3.4±0.2. This value of φ exponent is in clear departure with the universal random-exchange Ising model to random-field Ising model (REIM-RFIM) crossover exponent φ≂1.4, found in weakly diluted samples of MnxZn1−xF2 and FexZn1−xF2. This observation and results from previous birefringence studies for samples of MnxZn1−xF2 with x≥0.4 suggest that a REIM-RFIM crossover breaking occurs somewhere in the interval 0.35<x<0.4.
Anomalous mobility enhancement in heavily carbon-doped GaAs
Authors: Chen H. D. , Feng M. S. , Lin K. C. , Chen P. A. , Wu C. C. , Wu J. W.
Published: July 2002

An anomalous mobility enhancement and metallic-type conductivity were observed in heavily carbon-doped GaAs grown by low-pressure metalorganic chemical vapor deposition. The 77 K mobility was slightly lower than that of 300 K for hole concentration between 1×1018 and 4×1018 cm−3. However, the 77 K mobility was enhanced from p≳4×1018 cm−3, and the 300 K mobility slowly decreased with increasing hole concentration that ranged from 7×1018 to 3×1019 cm−3. As a result, the 77 K mobility was around 50%–60% greater than the 300 K mobility due to the metallic-type conductivity.
X-ray diffraction studies of the epitaxy of a/b-axes oriented YBa2Cu3O7−δ films grown by liquid phase epitaxy
Authors: Sandiumenge F. , Dubs C. , Görnert P. , Galí S.
Published: July 2002

A detailed x-ray diffraction study is reported for a/b-axes oriented YBa2Cu3O7−δ films obtained by the liquid phase epitaxy technique. The films were grown epitaxially in the tetragonal state on (110) NdGaO3 substrates so that [001]film∥ [110]subs and [100]film∥ [001]subs, 90°-[100]/[010] boundaries were almost absent. Below the tetragonal-to-orthorhombic transition temperature, the film undergoes intensive {hh0}-type twinning. The volume of the a-axis oriented material is similar to that of the b-axis oriented fraction and the presence of both orientations is likely to be controlled by {hh0}-type twinning. High temperature diffraction of the substrate indicates that nucleation of YBa2Cu3O7−δ on (110) NdGaO3 takes place on a square two-dimensional lattice and therefore the observed strong in-plane alignment is probably controlled by impurity action and/or surface relaxation rather than simple mismatch effects. The difference between the thermal expansion coefficients of the film and the substrate (αfilm[100], αfilm[010]≳αsubs[001]) is compensated for upon cooling by a slight rotation (ε∼0.12°) of {hh0}-type domain boundaries around the common [001] direction.
Effect of sputter-etching polymer substrates on the magneto-optical properties of ultrathin Co/Pt multilayers
Authors: Hashimoto S.
Published: July 2002

Ultrathin Co/Pt multilayers deposited directly on polymer substrates displayed poorer Kerr hysteresis loops than multilayers deposited on glass substrates. However, sputter-etching the polymer substrates with oxygen gas produced a square Kerr hysteresis loop. Analysis of the liquid-solid contact angle at the substrate surface confirmed that the low surface free energy of the substrate gives rise to poor magneto-optical (MO) properties of the deposited Co/Pt film. The MO properties are improved by etching. This is the result of an increase in the surface free energy, which is probably related to a chemical reaction involving oxygen atoms and not due to a change in the surface morphology. Higher surface free energy or better wetting of the surface made possible by etching probably brings about better nucleation of the deposited atoms in the initial stage of film growth and improves the crystalline quality of film, resulting in an improvement in the MO properties.
Scanning tunneling microscopy of the GaAs(001) surface morphology prepared by migration enhanced epitaxy
Authors: Xue Qikun , Zhou Junming , Hashizume Tomihiro , Sakurai Toshio
Published: July 2002

Employing field ion-scanning tunneling microscopy (FI-STM), we have studied the GaAs(001) surface prepared by the migration enhanced epitaxy (MEE) technique in a wide range of growth temperatures. The STM images clearly show the advantageous effect of enhanced Ga migration of MEE on the surface morphology of the GaAs(001) surface.
Annealing effect on an amorphous Si film deposited on a 7×7 superlattice surface of Si(111) studied with low-energy electron diffraction
Authors: Shigeta Yukichi , Maki Kunisuke
Published: July 2002

The intensity profile of low-energy electron diffraction (LEED) was observed for a Si film grown on a Si(111)–7×7 substrate under low-temperature epitaxial growth conditions. The epitaxial relation for Si(111) holds for each film with its thickness region below a certain value (dC) from the substrate, and an amorphous phase is formed above it. The values of dC were 0.5, 6.5, 17, and 100 nm at substrate temperatures (TS) of 35, 170, 200, and 250 °C, respectively. The annealing effect on the films grown at Ts=35 and 170 °C was studied. The LEED intensity (IS) is proportional to the surface area occupied by the 7×7 and 5×5 superlattices such that (1) IS depends sensitively on the film thickness (d) and TS, and (2) the dependence of IS on the annealing temperature is independent of TS and d. This is discussed from the viewpoint of the change in structural hierarchy formed in the as-grown film due to the annealing.
Thin dielectric waveguide with a phased array of two gratings on its surfaces
Authors: So Daniel W. C. , Seshadri S. R.
Published: July 2002

The deexcitation and the excitation of the transverse electric (perpendicular polarization) and the transverse magnetic (parallel polarization) guided modes in a thin-film planar dielectric waveguide sandwiched between a cover and a substrate (two different dielectrics) are considered. There are two gratings, one on each surface of the film, with the same grating wave number but with different relative amplitudes and phases. The three governing equations are derived by a quasioptical technique, and the reciprocal property and the power conservation requirements are examined. An output coupler with no radiative leakage in the substrate and a practical input coupler with the incident beam in the cover only and with a high input coupling efficiency are designed with a suitable choice of the grating depth ratio and the lateral phase shift. An output coupler can be achieved with no radiative leakage either in the substrate or in the cover by an appropriate choice of film thickness and the grating parameters. This configuration of the output coupler is used in the development of a grating polarizer with the output either in the perpendicular or in the parallel polarization. Selected numerical results are presented to illustrate the important characteristics of the output and the input couplers and the polarizers as well as the sensitivities of the performance of these devices to small changes of the physical parameters about their designed values.
Creation and optimization of vertical cavity phase flip modulators
Authors: Trezza J. A. , Harris J. S.
Published: July 2002

The creation of vertical cavity phase flip modulators is demonstrated, both theoretically and experimentally. These modulators rely on both the ability to make Fabry–Pérot cavities which switch the dominant mirror responsible for reflection and the use of excitons in a manner which allows them to provide large absorption changes with zero parasitic refractive index changes. The current device provides a 180° phase change while only changing reflectivity from 65% to 63% with an applied bias of 13.5 V while using an active region only 5000 Å long. These devices can be placed into dense arrays and should have numerous applications for stackable optical switching and logic, high-efficiency spatial light modulation, and, with appropriate optimization, low-reflectivity-change analog phase modulators.
Hydrogen content in oxygen-doped polysilicon film
Authors: Wang Yunzhen , Huang Bilin
Published: July 2002

In this paper, we use the 4He+—H elastic recoil detection to measure the hydrogen content with depth and to study the hydrogen incorporation with oxygen in semi-insulating polysilicon (SIPOS) film; we also show that the Si—H bond stretching-vibration frequencies from both infrared measurements and calculations of electronegativity, then discuss the behavior and the role of hydrogen in the SIPOS film.
PbSrS lasers prepared by hot wall epitaxy
Authors: Ishida A. , Takashiba H. , Izutu T. , Fujiyasu H. , Böttner H.
Published: July 2002

PbSrS/PbS double-heterostructure and multiple quantum well lasers were prepared by hot wall epitaxy, and the dependence of the properties on the cladding layer band gap and active layer thickness was investigated. Output photon energy of the double-heterostructure laser shifted to the high energy side owing to the strain between PbSrS cladding and the PbS active layers. The shift decreased by increasing the PbS active layer thickness. It was estimated that the lattice mismatch between cladding and the active layers is accommodated by the strain when the PbS active layer thickness is as thin as 0.5 μm.
Carrier densities and electron-hole recombination lifetimes in GaAs-(Ga,Al)As quantum-well photoluminescence
Authors: de Dios-Leyva M. , Oliveira Luiz E.
Published: July 2002

A quantum-mechanical calculation of the carrier densities and electron-hole recombination lifetimes in GaAs-(Ga,Al)As quantum wells is performed, under steady-state optical excitation conditions and in the high-temperature regime. The variables are the continuous-wave (cw) laser intensity, well widths, and acceptor distribution in the well. Radiative recombination of electrons with free holes and holes bound at neutral acceptors are considered. Our calculations for the dependence of the electron density on laser intensity are in quantitative agreement with recent experimental results for multiple asymmetric coupled quantum wells at T=300 K and for intermediate excitation. Also, results for the carrier-density-dependent e-h recombination decay time at T=155 K are in good agreement with recent experimental data in semiconductor quantum wells.
Comment on ‘‘Monte Carlo simulation of electron transport in alternating-current thin-film electroluminescent devices’’ [J. Appl. Phys. 73, 3390 (1993)]
Authors: Brennan Kevin F.
Published: July 2002

In this communication, we present a short discussion in order to correct some apparent misinterpretations of a previous work of ours. We discuss the interpretation of the electron distribution function presented in an earlier work [K. Brennan, J. Appl. Phys. 64, 4024 (1988)].
Secondary-ion mass spectrometry analysis in pseudomorphic GaAs/InGaAs/GaAs heterostructures utilizing a δ-doping superlattice
Authors: Wu C. L. , Hsu W. C. , Shieh H. M.
Published: July 2002

Significant improvement on two-dimensional electron gas (2DEG) concentration and mobility in a δ-doping superlattice GaAs/In0.25Ga0.75As/GaAs pseudomorphic heterostructures prepared by low-pressure metalorganic chemical vapor deposition have been demonstrated and discussed. The secondary-ion mass spectrometry profiles of these δ-doping superlattice structures were studied. The triple and double δ-doping superlattice heterostructures showed extremely high 2DEG concentrations of 8.8 (6.0) and 4.3 (2.5)×1012 cm−2 along with enhanced mobilities of 2710 (6500) and 3916 (18400) cm2/V s at 300 (77) K, respectively. The 2DEG concentrations, to our knowledge, are among the highest for previously reported pseudomorphic heterostructures with similar mobilities.
Observation of miniband transport in GaAs/Al0.33Ga0.67As superlattices
Authors: Hutchinson H. J. , Higgs A. W. , Herbert D. C. , Smith G. W.
Published: July 2002

The low temperature current-voltage characteristics of a strongly coupled, short-period GaAs/Al0.33Ga0.67As superlattice structure have been studied with applied magnetic fields both parallel and perpendicular to the current flow. The complex dependence of the current-voltage characteristics on magnetic field perpendicular to the current flow is consistent with a simple model based on Bloch transport via the lowest miniband. From fits to the data the scattering time and mobility have been estimated as 0.15 ps and 4100 cm2/V s, respectively. Further evidence of negative-differential velocity associated with miniband transport comes from the observation of an extended negative-differential resistance region at room temperature in a structure with 50 superlattice repeats.
Silicon doping from phosphorus spin-on dopant sources in proximity rapid thermal diffusion
Authors: Zagozdzon-Wosik W. , Grabiec P. B. , Lux G.
Published: July 2002

Rapid thermal diffusion (RTD) of phosphorus has been investigated using a spin-on dopant (SOD) deposited on a silicon wafer and placed as a dopant source in proximity to a processed Si wafer. In such a process, the efficiency of doping is affected by the amount of P supplied from the SOD to the processed wafer. Doping in RTD is controlled by the thickness of the SOD and its structure, which depends on low-temperature baking. Experimental results of secondary-ion-mass spectroscopy analyses and sheet resistance indicate that diffusion coefficients of phosphorus in the SOD during RTD are considerably larger than in thermal oxides.
Defect assisted tunneling in GaAs/AlGaAs/GaAs heterostructures
Authors: Magno R. , Spencer M. G.
Published: July 2002

A zero-bias conductance peak has been observed in conductivity versus voltage G(V) measurements at 4 K on GaAs/AlGaAs/GaAs tunnel junctions. The peak was found in junctions prepared from several different molecular-beam-epitaxial growths. The central portions of the barriers were spike doped with Si or Be. The peak fits the functional form G(V)=M ln(AV+B) which is expected for electron tunneling via paramagnetic impurities in the barrier, or for Coulomb correlation effects at defects. Shining white light on the junctions reduced the amplitude of the peak, and the new G(V) was found to persist for at least 15 h. Following exposure to light, the conductivity peak was recovered by warming the sample to room temperature. The G(V) curves measured before and after exposure to light were independent of temperature between 1.3 and 30 K. The reduction in amplitude of the peak in G(V) results in a negative photo conductivity at zero bias. At high enough biases, the conductivity after the exposure to light is larger than before as is expected when the light removes electrons from the barrier by photo ionizing defects or impurities. The photo effect indicates that the peak is associated with transport via defects. The defects may be associated with either the Si or Be which were used to spike dope the central portion of the barriers, or with stoichiometric defects produced by the growth. Tunneling assisted by interactions with paramagnetic defects or Coulomb correlation effects are possible explanations for the origin and photo behavior of the peak in G(V).
Two-dimensional quantum model on photoyield of the p+-SiGe/p-Si heterojunction internal photoemission infrared detector
Authors: Lin Benjamin S. M. , Hwang J.
Published: July 2002

A two-dimensional free-carrier like model has been applied to interpreting the internal photoemission data of the p+-Si0.7Ge0.3/p-Si photodiode. A new analytical photoyield formula concerning photoexcited carriers on heavy and light hole bands has been developed based on energy and momentum conservation. Both transmission coefficient and absorption probability were two primary factors in determining the photoyield spectrum. The light hole band dominated the internal photoemission due to its greater absorption probability and lower threshold energies for photoexcited carriers to transport over the SiGe/p-Si interface. The finite yield was mainly contributed by the light hole band while the roll-off was due to the transmission characteristics of all the two-dimensional photoexcited carriers.
Vortex flow characteristics of high-T
c flux flow transistors
Authors: Miyahara Kazunori , Kubo Shugo , Suzuki Minoru
Published: July 2002

High-Tc superconducting flux flow transistors were fabricated from thin films of coevaporated YBaCuO. The vortex flow characteristics of the devices were experimentally investigated. The flow velocity of a vortex along a channel was measured from the applied magnetic field dependence of the I-V characteristics. It is 3.6–6.9×105 m/s when the bias current is 3–6 mA. This value is of the same order as that of a Josephson vortex flowing along a barrier region in a super-normal-super junction, and more than three orders of magnitude larger than that in type-II metal superconducting thin films.
Surface segregation and growth-mode transitions during the initial stages of Si growth on Ge(001)2×1 by cyclic gas-source molecular beam epitaxy from Si2H6
Authors: Tsu R. , Xiao H. Z. , Kim Y.-W. , Hasan M.-A. , Birnbaum H. K. , Greene J. E. , Lin D.-S. , Chiang T.-C.
Published: July 2002

Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2×1 by cyclic gas-source molecular beam epitaxy from Si2H6 has been investigated using in situ reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy, electron-energy-loss spectroscopy, and scanning tunneling microscopy, combined with post-deposition high-resolution cross-sectional transmission electron microscopy. The layers were deposited using repetitive cycles consisting of saturation Si2H6 dosing at room temperature, followed by annealing for 1 min at 550 °C. Film growth was observed to proceed via a mixed Stranski–Krastanov mode. Single-step-height two-dimensional growth was obtained for nominal Si deposition thicknesses tSi up to ≂1.5 monolayers (ML). However, the upper layer remained essentially pure Ge which segregated to the surface through site exchange with deposited Si as H was desorbed. At higher tSi, the Ge coverage decreased slowly, the surface roughened, and two-dimensional multilayer island growth was observed for tSi up to ≂7.5 ML, where bulk reflections in RHEED patterns provided evidence for the evolution of three-dimensional island formula.
Characterization of the titanium silicon two/Si interface in titanium disilicide films on silicon, formed by deposition of alternate titanium-silicon layers and annealing
Authors: Revva P. , Nassiopoulos A. G. , Travlos A.
Published: July 2002

Interfaces of titanium disilicide films formed on silicon by alternate titanium-silicon electron gun deposition and annealing were characterized by current-voltage measurements on specially prepared Schottky diodes at both room and low temperatures, down to liquid nitrogen. The influence of the bilayer silicon/titanium thickness ratio on the interface properties was examined and the optimum value for good quality Schottky diodes with smooth interfaces and low series resistance was determined. The value of the barrier height derived from the silicide formed by multilayer deposition with the optimum value of the ratio silicon/titanium does not differ significantly from that of the silicide formed by deposition of a single layer and the same applies also to their temperature dependence, although the interfaces of these silicides appear different, deemphasizing so the role of the interface on the Schottky barrier formation. The present results are complimentary to previous measurements by scanning and transmission electron microscopy, x-ray diffraction, and Rutherford backscattering.
Surface impedance of YBa2Cu3O7−x thin film grain boundary Josephson junctions: Evaluation of the I
cR
n product
Authors: Hein M. A. , Strupp M. , Piel H. , Portis A. M. , Gross R.
Published: July 2002

The temperature and the dc magnetic field dependence of the effective surface impedance Zs of epitaxial YBa2Cu3O7−x thin films on [001] tilt SrTiO3 bicrystals with tilt angles of 36.8° and 24° have been investigated at 87 GHz. The effects of the grain boundaries become increasingly important with decreasing characteristic voltage IcRn and increasing unit areal normal resistance RnA. The boundaries can consistently be described with a resistively shunted Josephson transmission line model taking into account the effect of finite film thickness. Thermal or magnetic loading of the junction leads to additional losses, whereas the effective microwave penetration depth exhibits a specific extremal behavior. From the magnetic response of Zs at 4.2 K, the junction lower critical fields as well as the values of IcRn and RnA can be deduced. The data agree well with dc transport measurements.
Time constant measurement in technical superconductors: A theoretical solution of the problem
Authors: Krempasky Ludo , Schmidt Curt
Published: July 2002

Time constant measurements are a useful method for characterizing technical superconductors. The interpretation of measured pickup voltages may, however, lead to misleading results, because the signals are composed of an infinte number of exponentials. The complete theoretical solution is given using a slab model approach. With some modifications, the theory is also valid for superconducting wires. Comparison with experiments shows good agreement.
Modal analysis of second-order mechanical reflections in oblique incidence grooved gratings
Authors: Robinson H. , Hahn Y. , Gau J. N.
Published: July 2002

Reflection effects in oblique incidence grooved gratings in the presence of propagating surface acoustic waves are analyzed. The particle displacements associated with these waves are described by a modal expansion including second-order evanescent and propagating bulk waves. The reflection coefficient and velocity shift are derived to first and second order (in the overlay height) using the boundary condition matching method. It is shown that the same second-order effects predicted for normal incidence groove gratings will exist for oblique incidence groove gratings. In addition, the reflection coefficient and velocity shift behavior are examined as functions of incidence angle and metallization ratio.
Analysis of the detectability of buried inhomogeneities by means of photothermal microscopy
Authors: Seidel U. , Haupt K. , Walther H. G. , Burt J. , Bein B. K.
Published: July 2002

Calculated photothermal contrast functions arising from lateral scanning of buried stripe- and disk-shaped deviations in thermal conductivity k are presented. From the theoretical findings the measuring conditions are derived in terms of the modulation frequency for which optimal photothermal discrimination of subsurface thermal inhomogeneities can be achieved. The theoretical results have been verified experimentally be measuring model samples, in which localized inhomogeneities were embedded.
Exoelectron analysis of amorphous silicon
Authors: Dekhtyar Yu. D. , Vinyarskaya Yu. A.
Published: July 2002

The basic aim of the present article is proposing a new field in the study of structural imperfections in amorphous silicon, particularly in the a-Si:H system. The method is based on registering photothermostimulated exoelectron emission (PTSE). The PTSE method is brought into effect as a near-threshold single-photon photoemission process. Its quantum yield is modulated by change in the density of states created by point defects, such as D centers. It is shown that exoelectron spectroscopy makes it possible to investigate heat- and light-modified changes in the electronic structure of the defects, their annealing, as well as diffusion of atomic particles, such as hydrogen.
Primary origin of dislocation formation in oxygen-implanted silicon substrates
Authors: Yoshino Akira , Sugiyama Mitsuhiro , Morikawa Takenori , Tamegai Haruko , Nishio Naoharu , Tashiro Tsutomu , Okumura Koichiro
Published: July 2002

Experimental results are presented showing the effects of various process parameters on dislocation density in SIMOX (separation by implanted oxygen) substrates. Possible origins of the dislocation formation mechanism in single-, double-, and multiple-implant SIMOX substrates are discussed based on results for samples formed by single and double implant, together with data from Rutherford backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements, and wafer warp measurements. One of the primary origins is considered to be the emission of interstitial silicon atoms into the top silicon layer from the buried-oxide/Si interface through internal oxidation process during oxygen implantation. SIMOX substrates that can be regarded as essentially dislocation free have been successfully made.
Transmission electron microscopy analysis of ‘‘black belt:’’ The masking film of white ribbon of Kooi effect in the local oxidation of silicon process
Authors: Sheng Tan-Tsu , Lu Chih-Yuan , Chang Ruey-Dar , Chiang Song-Tsan
Published: July 2002

The first direct observation of the top view of micromasking film on the Si surface to gate oxidation in the local oxidation of silicon process with transmission electron microscopy (TEM) has been made. The micromasking film looks like an ‘‘eyelash’’ in cross-sectional transmission electron microscopy and like a ‘‘black belt’’ in top view TEM. In addition, direct and sequential TEM observations on the removal of the micromasking film by sacrificial oxidation were presented.