bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural properties of ion-beam-synthesized β-FeSi2 in Si(111)
Authors: Gerthsen D. , Radermacher K. , Dieker Ch. , Mantl S.
Published: July 2002

A continuous buried β-FeSi2 layer was obtained by implantation of 200 keV Fe+ ions into Si(111) wafers at elevated temperature. During the subsequent rapid thermal annealing at 1150 °C for 10-s, a continuous buried layer of the metallic α-FeSi2 phase is formed. During the second annealing step at 800 °C, the α phase is completely transformed into the semiconducting β phase. The epitaxial relationship between the β-FeSi2 and the silicon substrate was investigated by transmission electron microscopy. It was found that the β-FeSi2(010) plane grows parallel to the Si(111) substrate. Two different azimuthal orientations were observed. For the first azimuthal orientation, the β-FeSi2[001] direction is oriented almost parallel to one of the three Si〈110〉 directions lying in the interface. In the second azimuthal orientation, the β-FeSi2[100] direction lies parallel to one of the Si〈110〉 directions in the interface. The lattice parameter mismatch and the growth mechanism must be considered to be the main reasons for the epitaxial relationship of the Si(111)/β-FeSi2/Si(111) heterostructures studied in this investigation. The orientation of the β-phase is likely to be predetermined by the orientation of the α-phase which is formed during the first annealing step. Different orientation relationships were observed for β-FeSi2 prepared by solid phase epitaxy and ion beam synthesis without high-temperature annealing.
Channeling effects for silicon implantation into large-diameter gallium arsenide substrates
Authors: Simonton R. B. , Rosenblatt D. H. , Corcoran E. , Kamenitsa D.
Published: July 2002

Previous investigations have reported substrate tilt and azimuthal (twist) orientations for bare, single-crystal gallium arsenide (GaAs) targets that control channeling-induced device parameter nonuniformities in variable scan angle (electrostatically scanned) ion implanters. However, those results were obtained using 2-in. (50.8 mm) and 3-in. (76.2 mm) diam GaAs substrates. Concern remains over whether the orientations reported will adequately control these nonuniformities when GaAs substrates with greater than 3-in.-diam are implanted. In this study implant profile and pinch-off voltage (Vp) dependence on twist orientation angle with a fixed 10° tilt along 150-mm-diam of bare GaAs targets are measured. Shottky capacitance-voltage measurements are employed to examine channeling-induced variations in Vp and electron concentration profiles for 29Si+ implantation at 100 and 60 keV. It is concluded that 10° tilt is not generally adequate to avoid the effects of planar channeling across the full diameter of bare GaAs wafers ≥100 mm. An analysis employing a stereographic projection, combined with data from this investigation, indicates that, in order to obtain optimum control over implant depth profile variations across large diameter (≥100 mm) GaAs wafers implanted with electrostatic scanning, the use of tilt angles ≳10° (perhaps 12°–15°) may be required.
InGaAs/InP hole intersubband normal incidence quantum well infrared photodetector
Authors: Gunapala S. D. , Levine B. F. , Ritter D. , Hamm R. , Panish M. B.
Published: July 2002

We demonstrate the first In0.53Ga0.47As/InP p-doped quantum well infrared photodetector (QWIP). This detector has the shortest wavelength response, λp=2.7 μm, ever achieved in a QWIP and operates at normal incidence.
Director-configuration diagram for a closed-cylinder nematic liquid crystal
Authors: Liang B.-J. , Chen Shu-Hsia
Published: July 2002

This study reports that the director configuration diagram of a closed cylinder of nematic liquid crystal (CC NLC) with normal orientation at the walls may contain four kinds of stable director configurations. Sample cells were prepared by treating all walls of a closed cylindrical cavity with DMOAP (N,N-dimethyl-N-octadecyl-3- aminopropyltrimethoxysilyl-chloride) and then filling with NLC 5CB. The optical patterns of the CC NLCs were observed between crossed linear polarizers. A theory explaining these observations was developed by calculating the spatial distribution of the nematic director fields. The stable director configurations depend not only on the ratio of the splay and bend Frank elastic constant (K11/K33), but also on the aspect ratio of the cylinder. In general, the occurrence of a transformation between the radial and the hyperbolic type is determined by a critical transformation ratio K11/K33; there is also a critical aspect ratio remarking the transformation between the point and the ring structure. The calculations predict that the characteristic lengths of both the radial and the hyperbolic ring structure are nearly invariant with respect to K11/K33 and the aspect ratio of the cylinder.
Evidence of current-generated spatially periodic space charge in a semiconductor
Authors: Zitter R. N. , Zhang Xuesong
Published: July 2002

The voltage–current characteristics of pure p-type germanium samples at 4.2 K show the features expected from theoretical models which predict that current generates a spatially periodic distribution of space charge, carrier velocity, and potential. The effects are observed at temperatures up to 68 K.
Oscillatory magnetic coupling and magnetoresistance in Co/Re superlattices
Authors: Huai Y. , Cochrane R. W.
Published: July 2002

We have studied the magnetoresistance (MR) properties of sputtered Si/Re 50Å[Co 20 Å/Re x Å]40 superlattices with xRe=3–32 Å. Transverse and longitudinal MR exhibit oscillation of the interlayer coupling as a function of Re layer thickness with a period of ≂12 Å and a maximum transverse MR of ≂1.2% for xRe=5 Å at 4.2 K. The saturation magnetic field Bs and MR magnitude ΔR/R for samples with xRe=5 and 7 Å are nearly constant up to 40 K, above which they decrease approximately linearly with increasing temperature. In addition, the perpendicular MR in magnetic fields up to 1 T changes sign from negative for samples with xRe≤7 Å (strong antiferromagnetic coupling) to positive for those with xRe≥10 Å.
Analysis of the transient spectral density of velocity fluctuations in GaAs and InP
Authors: González Sánchez T. , Velázquez Pérez J. E. , Gutiérrez Conde P. M. , Pardo Collantes D.
Published: July 2002

Using a multiparticle Monte Carlo method, a theoretical analysis of the spectral density of velocity fluctuations in semiconductors has been performed, under both stationary and transient conditions (when the electric field applied to a semiconductor changes). In the case of the transient analysis a general method has been developed and applied to N-type GaAs and InP. The results obtained are interpreted in terms of the microscopic processes occurring during the transient. Significant differences between these materials have been observed. The following results were found: (i) The main source of noise is the presence of carriers in the Γ valley subject to the action of high fields, and the velocity-disorienting effect of the intervalley mechanisms; (ii) the maximum in the spectral density is essentially due to the presence of intervalley mechanisms; (iii) the dominant frequencies in the spectral density are strongly affected by the duration of the free flights; (iv) for long times, the transient spectral density converges on the steady-state one of the final field.
Kinetics of diffusion growth of silicides in silicon–thin-metal-film systems
Authors: Barg A. I. , Bokstein B. S. , Klinger L. M.
Published: July 2002

A kinetic model for diffusional growth of silicides in thin-metal-film–silicon systems is proposed. The time dependence of the growth has been shown to be a function of the morphology of the growing silicide and the controlling diffusion process (diffusion in the film, interface diffusion). If the phase grows only in depth the parabolic dependence of silicide thickness h on time t in most cases follows the relation h≂t0.5. If silicide grows only in width w, then w≂t. In the case of simultaneous change of thickness and width when h/w=const the growth is proportional to t0.33.
Growth-temperature dependence of electrical and luminescent properties of high-quality GaSb grown by liquid-phase epitaxy
Authors: Wu Meng-Chyi , Chen Chyuan-Wei , Chen Chi-Ching
Published: July 2002

The growth-temperature dependence of electrical and photoluminescent properties from high-quality GaSb layers grown by liquid-phase epitaxy has been studied. At the growth temperature of 600 °C, a hole concentration of ∼ 1 × 1017 cm−3 is obtained and the 16 K photoluminescence spectrum is dominated by the line BE2 at 802.9 meV associated with excitons bound to acceptors, and a stronger band-acceptor emission band at 777.8 meV. With reducing the growth temperature, the hole concentration gradually decreases, as does the line BE2 in the photoluminescence spectrum. The GaSb layer conduction converts from p to n with a minimum hole concentration of 2–6 × 1015 cm−3 when the growth temperature is below 450 °C. The line D located at 808.2 meV, due to a donor-bound exciton transition, becomes dominant and the band-acceptor emission becomes very weak at lower growth temperatures. The is the first report on the growth-temperature dependence of the excitonic transitions from high-quality GaSb layers.
Electrical conduction in polyaniline compressed pellets doped with alkylbenzenesulfonic acids
Authors: Kobayashi Atsushi , Xu Xinfei , Ishikawa Hitoshi , Satoh Masaharu , Hasegawa Etsuo
Published: July 2002

Anion dependent processes of the electrical conduction in chemically prepared polyaniline compressed pellets doped with alkylbenzenesulfonate anion of alkyl chain length 1, 8, and 12 have been investigated by the measurement of the temperature dependence of the conductivity. The conductivity of the samples changes with the temperature as T−1/2, which shows the conduction followed a one dimensional variable range hopping process. With the increase of the alkyl chain length of the dopant anion, the conductivity of the heavily doped 50 mol % sample decreases in whole temperature range, but an exponential factor of the variable range hopping remains unchanged. The results concerning the alkyl chain length of the dopant anion have been discussed from the ‘‘quasi-one dimensional’’ variable range hopping mechanism and demonstrated the decrease of the transverse localization length and the interchain transfer integral of electron.
Bolometric response of superconducting YBa2Cu3O7−x microbridges
Authors: Haung C. J. , Chang C. Y. , Tseng T. Y.
Published: July 2002

The optical properties of superconducting bolometers have been presented in YBa2Cu3O7−x epitaxial films irradiated by a light emission diode with an 0.94 μm wavelength. The better response occurring in the resistive transition region has been shown and studied. A thermal fluctuation on the flux creep behavior can be employed to illustrate the nonlinearity optical current-voltage (I-V) characteristics in the low-resistive region. However, a dissipative mechanism of flux flow should be used in explaining the best response that reveals a linear I-V relation. Measurement of the bridges yielded the bolometric responsivity of approximately 77 V/W, by illuminating a 2 Hz dynamic signal with 0.15 mW. The noise equivalent power has been estimated as 3.2×10−10 W Hz−0.5.
Ion mixing enhanced wafer bonding for silicon-on-insulator structures
Authors: Khánh N. Q. , Fried M. , Tóth A. , Gyulai J. , Pécz B.
Published: July 2002

Bonding of a 1360-nm-thick single crystalline silicon membrane onto an oxidized wafer was enhanced by ion mixing using 1250 keV 14N+ ion implantation. The oxidized wafer was covered by a thin, thermally grown oxide (134 nm) and implantation was performed either in random or in channeling directions through the membrane. Ion doses were in the range of 0.5×1016 to 5×1016 atoms/cm2. Implantation was followed by an annealing at 1000 °C for 0.5 h in nitrogen gas to remove the radiation defects. Due to the effect of implantation, the bonding quality was very good in all cases. In addition, results of Rutherford backscattering spectroscopy and transmission electron microscopy showed that using channeled implantation with a dose of 0.5×1016 atoms/cm2, the adherent silicon layer was of high quality (∼1.5×103 dislocations/cm2) and the interface remained sharp.
Role of impurities on diffusion-induced defective states
Authors: Castaldini A. , Cavallini A. , Fraboni B. , Giannotte E.
Published: July 2002

The defective states induced in floating zone Si by the heavy diffusion of dopants have been investigated by means of the electron beam-induced current method. By measuring the minority carrier diffusion length with the first order moment method, and by directly imaging the defects, their electrical activity has been analyzed. The diffused samples have subsequently been dry oxidized, so that the evolution of the electrical and morphological properties of the induced defects could be followed. Two sets of samples, one diffused with B and the other with B and Al, have been investigated in order to study the effects of the presence of Al. Significant improvements in the diffusion length have been observed in samples where Al had been codiffused, thus providing indication for the role played by Al on the electrical activity of bulk defective states.
Activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 alloys
Authors: Chou H. , Chen H. S. , Fang W. C. , Wu M. K.
Published: July 2002

We have measured the activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 at 930 and 900 °C, respectively, by a modified coulometric titration method on the galvanic cell: O_ in liquid alloys/yttria stabilized zirconia/air, Pt. The standard Gibbs formation energy and the diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 alloy for 1/2O2(1 atm)→O_(1 at. %) are determined to be ΔG=−247.4 kJ/g atom, and D=1.52×10−4 cm2/s. The oxygen solubility Cs in the Ag-Yb1Ba2Cu3 alloy is 0.0913 at. %, a factor of 5.5 higher than that in Yb1Ba2Cu3 alloy. The addition of Ag does not alter the growth mechanism and the oxygen diffusion controls the film growth. The growth speed is enhanced as a result of the enhanced oxygen solubility. ΔG and the diffusion coefficient of oxygen in the Tl1Ba2Ca2Cu3 liquid alloy are −257 kJ/g atom and 1.2×10−4 cm2/s, respectively. The oxygen solubility of the Tl1Ba2Ca2Cu3 alloy at 900 °C is found to be very high at ∼5.74 at. %. All thermodynamic data for oxygen in the precursor alloys are consistent with each other but there is a deviation of activity coefficient with composition for the different alloys from the theoretical model.
Amorphization of Nd15Fe77B8 alloy ingots by mechanical grinding
Authors: Harada T. , Kuji T.
Published: July 2002

Amorphous powders of a Nd15Fe77B8 alloy were obtained by mechanical grinding of the alloy ingots. Mechanical grinding of Nd15Fe7B8 alloy ingots reduced the average particle size to 1 μm within the relatively short period of milling times. Extended milling did not yield further reduction in particle size, but resulted in a change in the structures from Nd2Fe14B crystallites to an amorphous structure. It was found that the crystallization of α-iron from amorphous matrix took place in some stage of milling. The amorphous materials were stable up to 820 K at a heating rate of 0.33 K/s. Heat treatment of the amorphous materials above the crystallization temperature resulted in the crystallization of the Nd2Fe14B phase and the resultant materials showed a high coercivity of 11.9 kOe as in the case for the amorphous Nd-Fe-B materials produced by rapid quenching techniques.
Epitaxial growth of PrOx thin films on sapphire by pulsed laser deposition
Authors: Ling S. H. , Au W. S. , Tang Y. S. , Wong H. K.
Published: July 2002

PrOx thin films have been grown epitaxially on r-plane sapphire by pulsed laser deposition. The films have (100) orientation if grown at 800 °C, and twinned (111) at lower substrate temperatures. The lattice constant of the PrOx film can be varied by thermal treatment at different oxygen partial pressures. a axis-oriented YBa2Cu3O7−δ films have been grown epitaxially on (100) Pr6O11 layers.
Two-dimensional damage distribution induced by ion implantation in Si under arbitrarily shaped mask edges: Simulations and cross-sectional transmission electron microscopy observations
Authors: Faye M. M. , Beauvillain J. , Salles Ph. , Laânab L. , Messaoud A. Yahia , Martinez A. , Claverie A.
Published: July 2002

A method is presented to calculate two-dimensional defect distributions induced by ion implantation through openings in a masking layer. It is shown that a realistic description of this model requires depth-dependent lateral standard deviations to describe the dopant and the damage point response functions. Further refinements of the theory include arbitrary shapes for the mask edges and different materials in the masking layer and in the substrate. Cross-sectional electron microscopy observations have been carried out to visualize the two-dimensional extension of amorphous layers created by As implantation in silicon for different mask edge angles. It is shown that the theory fits well the cross-sectional transmission electron microscopy observations. More generally, this study shows that for abrupt mask edges, the lateral extension of the two-dimensional defect profile beneath the mask edge is directly governed by scattering of the ions and of the subsequent recoil atoms and, as a direct consequence, by the lateral standard deviation of the damage point response function. For tapered mask edges, however, the contribution of ions that pass through the mask edge region before damaging the substrate may be very high with respect to scattering effects.
Radiation effects on gate induced drain leakage current in metal oxide semiconductor transistors
Authors: Das N. C. , Nathan V. , Tallon R. , Maier R. J.
Published: July 2002

The gate induced drain leakage current (Idl) of metal oxide semiconductor (MOS) transistors changes significantly when the devices are exposed to ionizing radiation. For n-channel MOS transistors, Idl decreases, whereas for p-channel devices, it increases. The change of leakage current at higher tunneling fields is proportional to the increase of hole trap density in the gate oxide region. The leakage current measurement technique is a useful tool for characterizing radiation effects in MOS transistors because at higher bias it is dependent on increase of oxide charge while independent of interface states. The annealing of trapped charges at the tunnel junction is faster than in the channel region as determined from subthreshold characteristics. The results of the thermal annealing experiment reveal that the drain current in the control region is attributed to interface state assisted tunneling.
Calculations of resonant tunneling levels across arbitrary potential barriers
Authors: Hsu Dongsheng , Hsu Mingzhen , Tan Changhua , Wang Yang Yuan
Published: July 2002

A hybrid method has been presented for calculating the resonant tunneling energy levels in a complex quantum structure. It couples the Airy function and plane wave function methods. And the δ-type potential, which may be at the boundary of two materials, has also been included.
YBa2Cu3O7−δ films: Calculation of the thermal conductivity and phonon mean-free path
Authors: Richardson R. A. , Peacor S. D. , Uher C. , Nori Franco
Published: July 2002

We estimate the phonon mean-free path (mfp) in YBa2Cu3O7−δ by performing a theoretical fitting procedure on bulk single-crystal data. This analysis indicates that the mfps of the phonons that are most responsible for the transport of heat are much longer than would be predicted from kinetic theory. These values are incorporated into a recently proposed treatment of the size effect to provide an estimate of the thermal conductivity of YBa2Cu3O7−δ films.
An optical waveguide with a nonlinear optical susceptibility inversion structure in the thickness direction
Authors: Asai Nobutoshi , Tamada Hitoshi , Fujiwara Ichiro , Seto Jun’etsu
Published: July 2002

A nonlinear optical susceptibility (χ(2)) inversion structure in the thickness direction (NIST) is proposed for an optical waveguiding layer to achieve efficient second-harmonic generation (SHG) in the form of Cerenkov radiation. Using a coupled-mode analysis, it is found that the SHG efficiency of the Langmuir–Blodgett (LB) film waveguide incorporating NIST is several tens of times larger than that of the conventional LB film waveguide. 2-docosylamino-5-nitropyridine (DCANP) was used as the LB film material. High precision is not so strongly required for the inversion position in the waveguiding layer thickness as for the total thickness of the waveguiding layer, if the refractive indices are almost uniform in the layer. A guiding principle is shown for selecting suitable materials for the substrate and the clad to achieve the highest efficiency with Cerenkov angle approaching zero. A waveguide structure was designed using a kind of perfluoropolymer for the clad. Several fabrication methods are proposed for the NIST waveguide. An enhancement of 20–30 times in the efficiency of Cerenkov radiation SHG due to the NIST is also experimentally demonstrated using DCANP-LB film as the waveguiding layer.
Titanium disilicide formation by interdiffusion of titanium/amorphous silicon multilayers: Influence of the bilayer silicon to titanium thickness ratio on the film properties
Authors: Nassiopoulos A. G. , Tambouris D. , Travlos A. , Traverse A. , Aloupogiannis P.
Published: July 2002

Titanium disilicide is formed by thermal annealing of amorphous Si/Ti multilayers, deposited on monocrystalline silicon by alternate electron-gun evaporation of Si and Ti. The bilayer periodicity was equal to 4. The bilayer Si/Ti thickness ratio was varied between 2 and 3 and its influence on the film properties (stoichiometry, surface and interface roughness and resistivity) was studied and compared to the properties of a silicide of the same thickness, formed by annealing of a single deposited Ti layer on monocrystalline silicon. The characterization techniques used are: x-ray-diffraction, Rutherford backscattering, scanning electron microscopy, surface profilometry, and electrical measurements. The reaction rate of deposited Ti with monocrystalline silicon for the formation of TiSi2 is also compared in a special experiment to that of deposited Ti with amorphous Si (α-Si).
Effect of scattering on intrinsic bistability in a resonant tunneling diode
Authors: Hu Yuming , Stapleton Shawn
Published: July 2002

Intrinsic bistability in a resonant tunneling diode has been investigated theoretically using a modified resonant tunneling model. A self-consistent solution including feedback of charges in the quantum well is found through an iterative method, where the stable and unstable solutions can be easily identified. The intrinsic bistability corresponds to the existence of two stable solutions. We find that scattering will reduce the intrinsic bistability or completely eliminate it, even for a large current peak-to-valley ratio (about 19).
Nb-Al-AlOx-Al-Nb tunnel junctions using electron beam evaporation
Authors: Simon W. , Liebemann E. K. , Simon M. , Bucher E.
Published: July 2002

For the first time tunnel junctions are prepared by a selective niobium etching process from Nb-Al-AlOx-Al-Nb sandwiches electron beam evaporated in ultrahigh vacuum. A quality factor of Vm=27 mV at 4.2 K has been obtained by cooling the Nb base electrode before Al deposition. The cooling of the Nb base layer had a considerable influence on the subgap current below 4.2 K. The temperature dependence of the subgap current down to 1.5 K is compared to the BCS prediction.
Band calculation of antiferromagnetic ground state of K2NiF4
Authors: Hatta S. , Kasowski R. V. , Hsu W. Y.
Published: July 2002

The electronic structure of K2NiF4 is calculated with ab initio, full potential and spin polarized pseudofunction energy band method. The bands are flat and have the indirect band gap of 0.7 eV between the occupied valence bands and empty conduction bands. The band gap is strongly influenced by the existence of [NiF6] crystal field and antiferromagnetic exchange interaction. Charge density plots show an anisotropic bonding between Ni and F in the basal plane and along the apical direction. Spin density plots exhibit an antiferromagnetic ordering with large localized moments on the Ni sites. However, a small fluctuation of net spin density is observed at the F sites. The computed optical conductivity is rather unremarkable with very small optically active structure. The salient features of our results are consistent with experimental observations.
Measurements of x-ray emission from photoabsorption-edge transition radiation
Authors: Pincus C. I. , Piestrup M. A. , Boyers D. G. , Li Qiang , Harris J. L. , Maruyama X. K. , Skopik D. M. , Silzer R. M. , Caplan H. S. , Rothbart G. B.
Published: July 2002

This article describes the measurements of x-ray power, spatial, and spectral distributions from transition radiators whose spectra are narrowed by the foil material’s K-shell photoabsorption edge. We used two foil stacks, one composed of 10 foils of 2-μm-thick titanium and the other composed of 18 foils of 2-μm-thick copper. The x-ray flux produced by a foil stack was compared with the flux produced by a single foil of equivalent thickness. The Ross-filter technique was used for measuring the magnitude of the flux within specific energy bands, 1.56–4.96 keV, and 4.96–9.66 keV. The maximum flux from the titanium radiator was 4.8 mW. The maximum flux from the copper radiator was 3.6 mW. In addition both the flux distribution as a function of photon energy and the spatial flux distribution of the titanium radiator were measured. The x-ray emission was measured by pulse height analysis to be between 3.8 and 6 keV. The spatial measurements showed the x rays to be emitted in an annular cone with angular divergence of approximately 5 mrad. These measurements compared well with calculations.
Negative electron affinity silicon heterojunction photocathodes with alkali antimonide intermediate layers
Authors: Guo Tailiang
Published: July 2002

In this paper, some new types of p-Si(100) photocathodes with n-K3Sb, n-Na3Sb, and p-Cs3Sb intermediate layers are fabricated. They are the (Si-K3Sb-Cs)-O-Cs and (Si-Na3Sb-Cs)-O-Cs negative electron affinity heterojunction photocathodes, and the (Si-Cs3Sb-Cs)-O-Cs positive electron affinity photocathode. For cathodes with n-K3Sb, n-Na3Sb, and p-Cs3Sb intermediate layers, the maximum photoemission sensitivities attainable are, respectively, 1050, 950, and 150 μA/lm, and the measured minimum work functions of these cathodes are, respectively, 0.9, 1.0, and 0.85 eV. The photoemission stability of the Si photocathode with an alkali antimonide intermediate layer is better than that of the conventional Si-O-Cs and GaAs-O-Cs cathodes. The stability of the cathode is also related to the states of the cesium and oxygen during the activation process and the light illumination condition.
1/f noise from levels in a linear or planar array. IV. The origin of the Hooge parameter
Authors: Morrison S. Roy
Published: July 2002

In part III under this title, fluctuations in electron trapping at semiconductor dislocations are analyzed. In this contribution these fluctuations of trapped charge are related to mobility fluctuations and reasonable agreement is found with the Hooge [F. N. Hooge, Phys. Lett. A 29, 139 (1969)] expression for 1/f noise. The calculated noise power is found to be proportional to the dislocation density and varies inversely with the doping level ND at high ND. We conclude from the analysis that the calculated frequency span of 1/f noise from dislocations will only be wide if the dislocations are random; for aligned, impurity free dislocations a spectrum similar to generation-recombination noise will be observed. Such behavior is observed experimentally.
Magnetoelastic properties of gadolinium
Authors: Bodriakov V. Yu. , Nikitin S. A. , Tishin A. M.
Published: July 2002

The results of an investigation of the temperature and magnetic field dependencies of the Young’s modulus E and the internal friction Q−1 in the temperature region 4.2–350 K and the magnetic field up to 14 kOe for a single crystal (c axis) and polycrystalline samples of gadolinium are presented. The experiments were carried out by the flexural vibrating-reed method at frequencies ∼1 kHz. Anomalies in temperature dependencies of the Young’s modulus for single crystal and polycrystalline gadolinium in regions of the paramagnetism-ferromagnetism phase transition and spin-reorientation (SR) transition are accompanied by an abrupt increase of the internal friction. In the SR transition range a considerable temperature hysteresis of the internal friction has been observed. This hysteresis is connected with the coexistence of phases having different magnetic ordering. The ΔE effect has been studied in detail.
Model of cavity coupling for beam breakup control
Authors: Colombant D. G. , Lau Y. Y.
Published: July 2002

The coupling of the accelerating cavities to dummy cavities was recently found to reduce beam breakup growth. This article analyzes a more sophisticated model that includes the time delay between coupled cavities and covers the possibilities of wave cutoff and resonance in the coupling path. A dispersion relation is obtained. We show that the peak spatial exponentiation rate of the dominant beam breakup mode is reduced by as much as a factor of 2, and this reduction is insensitive to the coupling path length. Other modes are destabilized, however, but they have lower growth rates, in general.
Optically pumped laser action and photoluminescence in HgCdTe layer grown on (211) CdTe by metalorganic chemical vapor deposition
Authors: Ravid A. , Sher A. , Cinader G. , Zussman A.
Published: July 2002

Photopumped laser action and photoluminescence (PL) in HgCdTe layers grown by metalorganic chemical vapor deposition on (211) oriented CdTe substrates were studied as a function of temperature in the wavelength range 2.5–3.3 μm. Lasing was observed up to 160 K. External quantum efficiency of 5% and single-mirror peak power of 14 mW were measured at 12 K for a 500-μm-long device. The external quantum efficiency was measured for different laser cavity lengths and the results were used to derive the internal efficiency and the laser loss. HgCdTe layers covered with a CdTe cap layer exhibited a lower PL intensity and laser devices with higher threshold.
Optical switching dynamics of the nonlinear Bragg reflector: Comparison of theory and experiment
Authors: Sankey N. D. , Prelewitz D. F. , Brown T. G. , Tiberio R. C.
Published: July 2002

An experimental and numerical study of nonlinear dynamical effects is presented using a corrugated silicon-on-insulator waveguide as a model structure. The advantages of the material used and the fabrication of the grating structures are discussed. The dynamics studied include optical bistability, optical switching at low intensities, and unstable behavior at higher pulse energies. The effects of both the free-carrier decay and lattice heating on the dynamics are assessed.
Theoretical and experimental study of inhomogeneously pumped distributed feedback lasers
Authors: Hansmann S. , Hillmer H. , Janning H. , Burkhard H.
Published: July 2002

We have investigated inhomogeneously pumped index-coupled distributed feedback (DFB) laser structures both theoretically and experimentally. Using a transfer matrix method, an optimized device structure was designed which drastically suppresses the longitudinal sidemodes by concentrating the injection current in the region close to the phase-shift position. In this way, a high yield of monomode lasers together with an easy fabrication technique was achieved without the necessity of end facet antireflection coating. Experimental evidence of the improvement of the single-mode stability is given first by three-section DFB lasers operated by two different injection currents. Second, the proposed three-segment laser pumped with a single drive current was implemented simply by splitting up the contact of a mushroom type 2×λ/8 phase-shifted DFB laser. We observed the theoretically predicted enhanced stability of the Bragg mode with a sidemode suppression ratio of 52 dB and a higher yield of monomode lasers compared with uniformly pumped conventional DFB laser devices.
Floating potential and plasma sheath in vacuum arc plasma
Authors: Radić Nikola , Šantić Branko , Vujnović Vladis
Published: July 2002

Variation of the electric field across the plasma sheath and floating-potential magnitude are calculated at vacuum arc plasma-plane floating surface contact. Due to the nonequilibrium conditions in the cathode-governed vacuum arc plasma, the floating-potential magnitude is smaller and the effective plasma sheath thickness is larger, compared to the values obtained from the expressions valid for the plasma in local thermodynamic equilibrium. The electric-field strength at floating surface is lower accordingly. It is suggested that the electric-field strength is insufficient to bring about the unipolar arc initiation by explosive field-emission mechanism at distances of the order of 1 cm away from the cathode spot(s).
Absorption of the 441.6 nm He-Cd+ laser line in a He-Cd positive column utilized in cataphoretic confinement
Authors: Mizeraczyk J. , Jakob G. , Schmidt E. , Mentel J.
Published: July 2002

The experimental investigation showed that the absorption of the 441.6 nm He-Cd+ laser line by the He-Cd positive column in the cataphoretic confinement sections used in hollow-cathode discharge He-Cd+ lasers is relatively low (∼0.1% per a few-cm-long He-Cd positive column). Such a low absorption should not decrease the 441.6 nm output power of the hollow-cathode discharge He-Cd+ lasers more than a few percent. Estimates show that the Cd*2 molecules may be responsible for this absorption.
Multiple-species ion beams from titanium-hafnium alloy cathodes in vacuum arc plasmas
Authors: Sasaki Jun , Sugiyama Kenji , Yao Xiang , Brown Ian
Published: July 2002

We have studied the ion spectra of the plasma produced by the metal vapor vacuum arc for the case when the cathode material is a solid solution TiHf alloy of variable composition ratio. A vacuum arc ion source was used to generate an intense beam of metal ions and a time-of-flight ion charge-to-mass diagnostic was used to measure the beam ion species and charge state distributions. A range of different cathode compositions was examined, from pure Ti to pure Hf and with five different alloy mixes between these extremes. We find that the ratio of ion currents in the multiple-species ion beam corresponds approximately to the ratio of elements in the cathode, and that the mean charge states of the elemental ion components remain approximately constant as the cathode composition ratio is changed. Multispecies metal ion beams can readily be generated in this way and the ion species characteristics of the beam are predictable.
Solid-state amorphization reaction in polycrystalline Ni and amorphous Si multilayer
Authors: Wang W. H. , Bai H. Y. , Zhang Y. , Chen H. , Wang W. K.
Published: July 2002

Interdiffusion-induced solid-state amorphization reaction (SSAR) in polycrystalline Ni/amorphous Si multilayers has been studied using an in situ x-ray diffraction technique together with transmission electron microscope observations. The amorphization reaction was found to occur both on the Ni/Si interfaces in terms of a planar-layer growth model and along the grain boundaries in the Ni sublayers. Thermodynamic and kinetic interpretations for the SSAR at grain boundaries are presented and an amorphous growth model is also suggested for elucidating the SSAR in polycrystalline Ni/amorphous Si multilayers.
Investigation of lateral straggling of Xe ions in potassium titanyl phosphate
Authors: Wang Ke-Ming , Shi Bo-Rong , Qu Bao-Dong , Wang Zhong-Lie , Liu Xiang-Dong , Liu Yao-Gang , Zhao Qing-Tai
Published: July 2002

150 keV Xe ions were implanted in potassium titanyl phosphate (KTP) at different angles of 0°, 45°, 60°, and 75°. The lateral straggling of Xe ions in KTP was investigated by normal and oblique incidence Rutherford backscattering of 2.1 MeV He ions. The result extracted is compared with the Monte Carlo code TRIM’89. The lateral straggling is seemed to be in a good agreement with TRIM’89 simulation within experimental error.
Size effects on the magnetic properties of fine Fe-Cr particles (abstract)
Authors: Yiping L. , Gong W. , Hadjipanayis G. C. , Sorensen C. M. , Klabunde K. J. , Papaefthymiou V. , Kostikas A. , Simopoulos A.
Published: July 2002

The magnetic and structural properties of Fe100−xCrx ultrafine particles with x=5–20 have been studied as a function of particle size. Particles with sizes in the range of 100–450 Å were prepared by gas evaporation under Ar atmosphere. The particles had a high coercivity with the smaller particles showing a stronger temperature dependence of coercivity than the larger particles. In the smaller x=5 particles the coercivity was about 2500 Oe at 10 K and 100 Oe at room temperature. The temperature coefficient of coercivity of Fe-Cr fine particles was smaller than that of Fe particles.1 Mössbauer spectroscopy was used in the temperature range of 4.2–300 K to better understand the magnetic hysteresis behavior of the particles. The spectra showed the presence of Fe-Cr, α-Fe, and Fe-oxide components in the larger particles, and Fe-Cr and Fe oxide in the smaller particles. The coercivity at low temperature is increased with decreasing particle size and this is attributed to the higher percentage of Fe oxide in the smaller particles. The magnetic and structural properties of protected Fe-Cr particles sandwiched between two Ag films are being studied in an attempt to understand the effect of surface Fe oxide on the magnetic hysteresis behavior of the whole particle.
Spin liquid and exchange frustration
Authors: Rastelli E. , Tassi A.
Published: July 2002

The customary perturbation expansion in 1/S suggests that long-range order could be destroyed by zero-point quantum fluctuations in two-dimensional Heisenberg antiferromagnets when a suitable exchange competition is present. The resulting disordered phase is called ‘‘spin liquid’’ (SL), the existence of which was suggested on the basis of the simple spin-wave approach concerning the square Heisenberg antiferromagnet with nearest- and next-nearest-neighbor exchange interaction (J1-J2 model). However, nonlinear contributions prevent the onset of the SL phase in the J1-J2 model. In spite of this we find that the spin liquid phase reappears in a wider parameter space that allows the existence of helical configurations too. An interesting S dependence of the phase diagram is suggested.
Quantum tunneling of magnetization in single domain particles
Authors: Tejada J. , Balcells Ll. , Linderoth S. , Perzynski R. , Rigau B. , Barbara B. , Bacri J. C.
Published: July 2002

We present a study of the magnetic relaxation of several ferrofluids composed of particles of about 40 Å in diameter (Fe3O4FeC, CoFe2O4). Our key observation is a nonthermal character of the relaxation below 3 K for the CoFe2O4 ferrofluid and below 1 K for the FeC ferrofluid. The crossover temperature from thermal to nonthermal (quantum) regime is in accordance with theoretical suggestions of macroscopic quantum tunneling of magnetization in single domain particles.
Optical fibers for magneto-optic recording heads (abstract)
Authors: Opsasnick Michael N. , Stancil Daniel D.
Published: July 2002

Access times of magneto-optic recording systems is limited by the size and weight of the magneto-optic head. One possible solution to this problem is to use optical fibers for magneto-optic recording heads. Since a polarization preserving fiber is a birefringent waveguide, the output state of polarization of light is dependent upon the orientation of light with respect to the fiber axes, and the length of the optical fiber. However, if the phase relation between the two fiber modes is maintained, the input polarization state can be reconstructed. Unfortunately, the phase relation between the two fiber modes is not maintained under flexure and in the presence of small temperature fluctuations. These phase fluctuations can be removed by common mode rejection using the reciprocal rotated reflection method (RPRR).1,2 Using a single mode polarization preserving fiber at 633 nm, striped domains were statically written and read using the RPRR method. The size of the domains were ∼1.4 μm in width and were spaced at 50 μm intervals. Static readings were taken at 10 μm intervals. A microsope imaging system was incorporated into the experimental setup to visually verify written domains and to ensure accuracy in reading these domains. Measurements were made with and without the RPRR method to demonstrate the effectiveness of the common mode cancellation. Composition of the magneto-optic sample used is RE/TM gadolinium iron terbium cobalt with a Kerr rotation of 84 min and a coercivity of 3500 Oe.
Magnetoresistance measurement in magnetic alloys in ultralow magnetic fields
Authors: Barnard R. D.
Published: July 2002

A method of measuring magnetoresistance (MR) in magnetic alloys is described in which fields comparable with those used in ac susceptibility methods, i.e., <5 G, are employed. To achieve the ultrasensitivity required, the MR voltage is entirely separated from the standing voltage present in zero field. The temperature stability of the standing voltage, crucial by normal methods, now becomes relatively unimportant. The separation of the MR voltage is achieved by using a unidirectional square-wave field which produces a square-wave MR signal which is amplified using a capacitor-transformer system f eeding a lock-in amplifier. An investigation of the response of the input circuit was made and its limitations with respect to frequency and input resistance deduced. Precautions necessary for the successful operation of the apparatus are given together with examples of MR measured on some reentrant FeNi amorphous spin glasses. In these cases MR coefficients as small as 10−6 have been measured with a resolution of 10−8.
Real-time fast-Fourier-transform analysis of M-H hysteresis loops
Authors: Wallace John L.
Published: July 2002

In this work it is demonstrated by experimental evidence and by computer simulation that small changes in the shape of the M-H loops or switching properties of magnetically soft materials may be much more noticeable in the frequency domain than in the time domain. This fact will have practical application in the areas of sensors, transducers, theft-detection systems, and nondestructive testing. Since digital signal processing (DSP) plug-in cards for personal computers have recently become commercially available at reasonable prices with the capability to do fast Fourier transforms (FFT) in milliseconds, an ‘‘M-H looper’’ interfaced to a dedicated DSP workstation that will provide real-time FFT displays has been designed.
A new method to measure magnetization and coercivity using a torque magnetometer (abstract)
Authors: Shin Sung-Chul , Hur Jeen
Published: July 2002

A vibrating sample magnetometer (VSM) is commonly used to measure magnetization and coercivity. In this paper, we present a new method to determine magnetization and coercivity of uniaxial magnetic anisotropic materials using a torque magnetometer. To measure magnetization, a sample is saturated along the uniaxial orientation by applying an external magnetic field and then it is rotated by 90°. Under this arrangement, the torque τ at a low applied field H can be approximately expressed by τ=HM, where M is the magnetization. An accuracy of this approximation depends on the strength of the anisotropy field Hk of a sample. A better result is expected for a higher Hk. For an instance, an inaccuracy of 0.5% is yielded from a linear approximation of this method for a case of H/Hk=0.1. To measure the coercivity, the sample is rotated by (180+δ) degrees after it is saturated along the uniaxial orientation. Under this configuration, the torque is measured with an applied field. Then, the value of the torque becomes from positive to negative with increasing an applied field. Here, the field where the torque is zero is the coercivity of the sample. Our new method was compared with a conventional VSM technique by measuring several Co/Pd multilayers having a uniaxial anisotropy along the growth orientation. A difference of within 2% between two techniques was found in measuring the magnetization and coercivity, except the sample having a low anisotropy field less than about 1 kOe.
Magnetic and structural characteristics of epitaxial FexCo1−x alloy films on ZnSe(001)
Authors: Gutierrez C. J. , Harris V. G. , Krebs J. J. , Elam W. T. , Prinz G. A.
Published: July 2002

Ferromagnetic alloy films of bcc FexCo1−x(001) were epitaxially grown on ZnSe-epilayered GaAs substrates spanning both the thermodynamically allowed bcc regime (0.25<x≤1) and the epitaxy-extended metastable bcc regime (0≤x≤0.25). Conversion-electron extended x-ray absorption fine-structure (EXAFS) and reflection high-energy electron-diffraction (RHEED) measurements verify that metastable bcc FexCo1−x films with 0≤x≤0.25 are stabilized by epitaxy on ZnSe. Additionally, the composition-dependent magnetic properties of these films were characterized by ferromagnetic resonance and vibrating sample magnetometry.
Analysis of magnetic energy stored in superconducting coils with and without ferromagnetic inserts
Authors: Cha Y. S.
Published: July 2002

Inductance and energy of superconducting coils are calculated by (1) a long-solenoid approximation, (2) a finite-element model, and (3) working formulas and tables. The results of the finite-element model compare favorably with those of the working formulas. The long-solenoid approximation overpredicts the energy and inductance compared to the other two methods. The difference decreases with increasing length-to-diameter ratio. Energy stored in a coil with a ferromagnetic insert is calculated by using a long-solenoid approximation and a finite-element model. The analysis shows that the gain in energy ratio is equal to the relative permeability of the insert (which decreases with increasing current or current density). Even though large gains can be achieved at relatively low currents, the energy level itself is too low. The stored energy increases with current, but the gain decreases with increasing current because relative permeability decreases. If a coil with a diameter of 0.3 m and a length of 0.3 m is required to store 10 kJ of energy, the current density must equal 4000 A/cm2. The gain in energy ratio is equal to 2.55 when the insert is used.
Crystallographic study of cobalt treatment on γ-Fe2O3
Authors: Sadamura H. , Yamashita K. , Nagai N.
Published: July 2002

Chemical analysis and x-ray diffraction measurements of samples during the reaction of cobalt treatment were carried out to study the mechanism of reaction. X-ray diffraction, TEM observation, and magnetic measurements of core γ-Fe2O3 and the modified particles were performed to investigate the crystal growth of cobalt ferrite on core γ-Fe2O3 particles. From chemical analysis of Fe2+ and total-iron ions in the reacting suspension and x-ray diffraction measurements of samples during the reaction, it is clear that the lattice constant becomes larger due to the formation of cobalt ferrite on core γ-Fe2O3 without decrement of Fe2+/total-iron ratio. So, cobalt ferrite on core γ-Fe2O3 particles is formed not by the oxidation of added Fe2+ ions, but by the electron transfer from Fe(OH)2 to core material. From x-ray diffraction measurements, I400/I311, I220/I311, and I111/I311 were calculated. While I400/I311 and I220/I311 are almost constant, only I111/I311 increases with increasing the amount of cobalt and ferrous ions added. These results show that cobalt ferrite is preferentially grown on (111) plane which is the close-packed plane of spinel lattice.