bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved optical properties of CuInSe2 thin films prepared by alternate-feeding physical vapor deposition
Authors: Chichibu S. , Shioda T. , Irie T. , Nakanishi H.
Published: July 2002

High optical-quality polycrystalline and epitaxial CuInSe2 thin films were grown by a simultaneous-feeding or alternate-feeding physical vapor deposition method. The existence of the liquid-phase Cu2−xSe during the growth was confirmed in terms of meltback of the substrate. The grown films exhibited predominant near-band-edge photoluminescence peaks from 2 K up to room temperature. A clear free exciton absorption peak was observed and its full width at half maximum decreased with decreasing repetition periods of the metal feeding cycle. This result demonstrates the importance of stabilized CuInSe2 solute and Cu2−xSe solvent concentrations to obtain improved film quality and homogeneity.
Temperature distribution and transport mode in a close-spaced vapor transport reactor for CuInSe2 depositions
Authors: Guenoun K. , Djessas K. , Massé G.
Published: July 2002

The present work is an improvement of a close-spaced vapor transport method to deposit CuInSe2 thin films in a closed vertical reactor. The study concerns two points: (i) the determination of the actual source (Ts) and substrate (Td) temperatures from experimental values measured in accessible points. For that, the equivalent thermal circuit of the reactor was established, and the equations were written to deduce Ts and Td. (ii) The determination of the process governing the mass transfer, from experimental values of the deposition rate measured as a function of Ts and Td. In our experimental conditions, the transport is limited by the reaction kinetics, not by the diffusion.
X-ray diffraction study of intentionally disordered (GaIn)As/Ga(PAs) heterostructures
Authors: Rettig R. , Marschner T. , Stolz W. , Tapfer L.
Published: July 2002

The influence of layer thickness fluctuations and deviation from perfect periodicity on high resolution x-ray diffraction (HR XRD) profiles are investigated experimentally and theoretically for (GaIn)As/Ga(PAs) symmetrically strained multiple quantum well heterostructures. Structural properties are deduced from the experimental HR XRD profiles by comparison with full dynamical XRD simulations. Samples with periodic thickness modulations are systematically studied with respect to periodicity, amplitude of modulation and layer mismatch. The high sensitivity of XRD in the strained (GaIn)As/Ga(PAs) material system allows a quantitative description of the nature (type), amplitude, and period of modulation. The results are experimentally compared to the lattice matched AlAs/GaAs material system. The influence of the modulation function of periodic modulations is studied. We investigate two types of graded structures with layer thickness grading either for one ternary layer (one side grading) or for both ternary layers (double side grading). The effects of grading steepness and layer mismatch are systematically studied. We develop a kinematical model which qualitatively describes specific peak characteristics of XRD patterns of one and double side graded heterostructures and allows the deduction of analytical expressions for specific peak features thus improving the understanding of measured and calculated patterns.
DX centers in Al0.3Ga0.7As/GaAs analyzed by point contact measurements
Authors: Hauke M. , Jakumeit J. , Krafft B. , Nimtz G. , Förster A. , Lüth H.
Published: July 2002

The influence of DX centers on the low-dimensional transport through point contacts in silicon δ-doped Al0.3Ga0.7As/GaAs heterostructures is investigated. The charge state of the DX centers is changed by temperature as well as optical and infrared irradiation. The experimental results reveal that the point contact resistance is strongly influenced by carriers in a quantum well formed at the δ-doping layer. The carriers screen the split gate voltage of the point contact and the point contact resistance is reduced or even suppressed. During irradiation with visible light a part of the electrons ionized from the DX centers remains in the quantum well at the silicon dopants and hinders formation of a point contact. After irradiation a strongly temperature dependent relaxation of these carriers was observed. Infrared radiation with wavelengths up to 11.5 μm reduces the screening effect. Infrared and temperature dependent measurements suggest a logarithmic dependence of the screening effect on the carrier density at the silicon doping layer.
Theory of giant magnetoresistance of magnetic granular films
Authors: Yang Rong , Zhang Wei , Song W. J.
Published: July 2002

Based on an extended effective-medium approach model, we investigate the giant magnetoresistance effect in systems of spherical or cylindrical ferromagnetic granular films, and give an analytical expression for the giant magnetoresistance of these systems. Our result is in agreement with the observed dependence of the giant magnetoresistance on size and volume fraction of the ferromagnetic granules.
Influence of defect inhomogeneities on the Hall mobility and concentration in undoped GaAs
Authors: Kažukauskas V.
Published: July 2002

We report the investigation of the steady-state Hall mobility and carrier concentration behavior depending on extrinsic light excitation intensity, wavelength and temperature in n-type liquid-encapsulated Czochralski (LEC) GaAs crystals. The carrier concentration of the samples measured in the dark ranged from 108 to 3×1011 cm−3, and the Hall mobility showed a pronounced minimum in the concentration region 109–1011 cm−3. The measured dependencies demonstrated peculiarities in this region which could not be explained by a homogeneous semiconductor model. We demonstrate that the observed effects are caused by the complex influence of the deep levels in the band gap and of the defect inhomogeneities related to the cellular structure of dislocations. The effect of inhomogeneities is intensified in the samples from the intermediate concentration region 109–1011 cm−3. It is related to the specific compensation conditions, which take place when the Fermi level appears between the EL2 level and the negative-U double oxygen-related donor level EC−0.43 eV. The influence of nonuniformities can be modified significantly in a nonunique way by changing the excitation conditions. The numerical modeling according to the effective medium theory qualitatively confirms the influence of the mesoscopic inhomogeneities with different effective activation energies associated with the cellular distribution of the EL2 defect and oxygen-related donor EL3. Different activation energies of the cells and their walls may sometimes cause the intensified effect of inhomogeneities with increasing temperature. Nevertheless, the experimental results imply that the observed phenomena are actually more complicated and the appearance of the additional scattering associated with the change of defect structure most probably should be taken into account.
Transmission of polarized infrared radiation through lamellar gratings on a silicon wafer
Authors: Hava S. , Ivri J. , Auslender M.
Published: July 2002

Studies of the zero angle of incidence transmission through lamellar gratings on silicon wafers were performed with polarized radiation in the spectral interval from 1.5 to 14 μm. All measured spectra consist of two parts: an oscillatory part at the wavelengths smaller than the grating period, and a nonoscillatory part at the wavelengths larger than the grating period. In some cases the transmittance in the oscillatory parts can be low, down to 4%, that demonstrates the effect of infrared “color separation.” We found experimentally that for gratings with periods larger than the maximum wavelength, the shape of the spectrum is polarization independent, while for gratings with periods smaller than the maximum wavelength the spectrum is very sensitive to the polarization of the radiation, especially in the nonoscillatory part. These results are consistent with the electromagnetic theory which states that at wavelengths smaller than the typical distance of index variations scalar approximation works, making no difference between the polarization states of radiation, whereas in the opposite case vector treatment is required. We developed a method of smoothing the interference fringes that emerge theoretically due to Fabry–Perot resonances in the substrate, but are not seen in the experiment due to the scattering of radiation by imperfections in the substrate. The method assumes this scattering to cause fluctuations of optical-path phase φo through the substrate. To calculate the apparent transmittance, the fringed one is specially filtered over φo. It is shown that for gratings with large periods the transmission spectra measured in our experimental conditions can be accounted for provided that one adopts a certain contribution of the ± first-order beam. The numerical simulations are in good agreement with experimental results.
Studies of epitaxial Fe0.5Pd0.5 thin films by x-ray diffraction and polarized fluorescence absorption spectroscopy
Authors: Gehanno V. , Revenant-Brizard C. , Marty A. , Gilles B.
Published: July 2002

The long range order as well as the short range order of magnetic Fe0.5Pd0.5 epitaxial thin films was studied. These alloys were elaborated by five methods: codeposition at room temperature, codeposition at room temperature followed by a 700 K annealing, codeposition at 600 K, and alternating deposit of pure Fe and pure Pd atomic layers at room temperature controlled either by the deposition time or by the reflection high energy electron diffraction oscillations. These samples were studied by x-ray diffraction (XRD) and polarized fluorescence extended x-ray absorption fine structure (EXAFS). These (001) oriented thin films have a face-centered tetragonal structure flattened along the growth direction. For each sample, a simulation program based on an inverse Monte Carlo method was used to build an atomic configuration satisfying both the long range order obtained by the XRD study and the directional short range order obtained by the EXAFS study. The best ordered sample (both on a long range and a short range scale) is the one codeposited at 600 K.
1.3 μm Fluorescence quenching in Pr-doped glasses
Authors: Naftaly Mira , Jha Animesh , Jordan Wayne G.
Published: July 2002

Short fluorescence lifetime is the main problem encountered in designing an efficient Pr3+-doped amplifier at 1.3 μm. Lifetimes observed in low phonon energy glasses are far shorter than those indicated by calculations. We examine 1.3 μm fluorescence quenching in Pr3+-doped glasses via concentration and impurity quenching in order to estimate the limits on metastable lifetimes achievable in low-doped, low-impurity glasses. The optimum doping level and the requirements for impurity content are assessed. Three glass hosts are studied in detail; cadmium-halide, gallium-indium-fluoride, and germanium-gallium-sulphide. The prospects for extending the Pr3+ metastable lifetime in these glasses are considered.
Threshold currents of 1.55 μm InGaAs/InGaAsP multiple quantum well laser diodes
Authors: Kakimoto Syoichi , Takagi Kazuhisa , Watanabe Hitoshi , Higuchi Hideo
Published: July 2002

We investigate threshold currents (Ith’s) of 1.55 μm InGaAs/InGaAsP multiple quantum well (MQW) distributed feedback (DFB) laser diodes (LDs) experimentally and theoretically. The measured Ith of the 1.55 μm MQW LD with barriers whose band gap energy corresponds to 1.3 μm (λg=1.3 μm) is 10 mA, which nearly agrees with the calculated value of 8.5 mA. However, the measured Ith of the 1.55 μm MQW LD with barriers (λg=1.15 μm) is 19 mA, which is much larger than the calculated value. We explain this discrepancy by a nonuniform distribution of injected holes among the wells. The separation, ΔEv1, between the first quantized level of hole for the well valence band and the top energy for the barrier valence band prevents a uniform distribution of holes among the wells. The re-evaluated Ith, taking into account ΔEv1, is 18.8 mA which agrees well with the measured one. We also show that 1.55 μm p-type doped MQW DFB LD with barrier (λg=1.15 μm) is 5.4 mA, which is comparable to Ith’s of 1.55 μm strained MQW DFB LDs.
Dose and energy uniformity over inner surface in plasma immersion ion implantation
Authors: Liu A. G. , Wang X. F. , Tang B. Y. , Chu P. K.
Published: July 2002

The absence of the line-of-sight restriction makes plasma immersion ion implantation an excellent interior surface treatment technique. In our experiments, we implanted both the outside and inside surfaces of a set of hollow cylindrical samples with and without a grounded conductive electrode positioned along the center of the bores to evaluate the impact energy as well as dose uniformity along the specimens. Our experimental results show that the use of the coaxial electrode increases the impact energy by 43% and retained dose by 71%. The nonuniformity is 20% to 30% and is worse with larger bore length.
Theoretical study of Auger effect in 1.5 μm quantum-well lasers
Authors: Gilard O. , Lozes-Dupuy F. , Vassilieff G. , Barrau J. , Le Jeune P.
Published: July 2002

A new methodology for the derivation of the Auger recombination rate in quantum wells is presented. An expression of the Auger recombination rate is given, taking into account a realistic valence band structure, the Fermi–Dirac statistics, and the analytic expressions of the transition matrix element for both bound-bound and bound-unbound Auger processes. Using this method, distributions of carriers involved in bound-bound and bound-unbound recombination processes are carried out. The bound-unbound recombination mechanism is identified as a significant contribution to the Auger total current density. Because the transition matrix element is found to be a significantly increasing function of the quantum-well width, our computations show that the Auger effect is expected to be enhanced in narrow wells. Subsequently, strain dependence of the Auger current density is analyzed. It is found that the Auger effect is reduced by strain in some cases but it is equally shown that this is not a general rule as it depends on the valence subband structure. The effect of temperature on Auger events is also investigated. In particular, it is found, that around room temperature, the temperature sensitivity of Auger current density is quite low in good agreement with many experimental data.
Studies of carbon nitride thin films synthesized by KrF excimer laser ablation of graphite in a nitrogen atmosphere
Authors: Lu Y. F. , Ren Z. M. , Song W. D. , Chan D. S. H. , Low T. S. , Gamani K. , Chen G. , Li K.
Published: July 2002

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite in a nitrogen atmosphere. Different excimer laser fluences and pressures of the nitrogen atmosphere were used in order to achieve a nitrogen content as high as possible in the deposited thin films. Fourier transform infrared and x-ray photoelectron spectroscopies were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The N/C ratio 0.42 was obtained at an excimer laser fluence of 0.8 J cm−2 at a repetition rate of 10 Hz under a nitrogen pressure of PN=100 mTorr. A high content of C=N double bond instead of C≡N triple band was indicated in the deposited thin films. Ellipsometry was used to analyze the optical properties of the deposited thin films. The carbon nitride thin films have amorphous-semiconductorlike characteristics with an optical band gap Eopt of 0.42 eV.
Nonreciprocal light channeling in a film by a magnetic nonuniformity akin to a Néel domain wall
Authors: Popkov A. F. , Fehndrich M. , Zhuromskyy O. , Dötsch H.
Published: July 2002

The problem of light propagation along a magneto–optic nonuniformity which is similar to a wide Néel domain wall is analyzed by perturbation theory. The Maxwell equations of the three-dimensional problem are reduced to a system which describes the amplitude evolution of the coupled TM and TE modes in a two-dimensional approximation. Numerical analysis shows a strong nonreciprocal character of light beam propagation: The waveguide supports a localized TM-like mode in one direction and scatters the light beam in the opposite direction. For a garnet film of 1 μm thickness, having a Faraday rotation of 3150 °/cm at a wavelength of 1.3 μm, an isolation of 25 dB is calculated for a propagation length of 1 cm. This waveguide may be used as optical isolator. It may also be applied as a magneto–optical switch or modulator tuned by an external magnetic field.
Metal/Al
2
O
3
multilayers: Interface structure, thermal stability and reflectivities in the soft x-ray regime
Authors: Veldkamp M. , Zabel H. , Schäfers F. , Mertins H.-Ch.
Published: July 2002

We report on a novel type of multilayer mirrors for the soft x-ray regime, namely M/Al2O3 layered stacks with M=V and C. Our investigations indicate that the Al2O3 layers show very low absorption and smooth growth characteristics with a root-mean-square roughness of about 0.2 nm. Therefore, M/Al2O3 multilayers are promising as mirrors for the soft x-ray regime. Here we discuss the interface structure before and after annealing of the multilayers as derived from small angle scattering experiments using a conventional x-ray diffractometer. Our measurements indicate that C/Al2O3 multilayers are stable for at least 1 h at an annealing temperature of 1100 °C. The interface roughness of only 0.3 nm remains nearly constant after annealing. Furthermore, we present simulations and for the first time experimental reflectivities in the soft x-ray regime obtained with synchrotron radiation from the BESSY I storage ring. For C/Al2O3 multilayers without interfacial roughness a normal incidence reflectivity of 61% is expected at the C K edge (E=284 eV). Measurements with synchrotron radiation and with fixed energy corresponding to the C K edge yielded reflectivities of 31% for an incidence angle of 13° and 5.6% for an incidence angle of 52°. In addition, V/Al2O3 multilayers are promising as mirrors within the water window exhibiting theoretical reflectivities of up to 70% without roughness at the V L resonance (E=512 eV). For V/Al2O3 multilayers we have measured a reflectivity of 30% at the V L edge at an incidence angle of 16°.
Noise in Al single electron transistors of stacked design
Authors: Krupenin V. A. , Presnov D. E. , Savvateev M. N. , Scherer H. , Zorin A. B. , Niemeyer J.
Published: July 2002

We have fabricated and examined several Al single electron transistors whose small islands were positioned on top of a counterelectrode and hence did not come into contact with a dielectric substrate. The equivalent charge noise figure of all transistors turned out to be surprisingly low, (2.5–7)×10−5e/Hz at f=10 Hz. Although the lowest detected noise originates mostly from fluctuations of background charge, the noise contribution of the tunnel junction conductances was, on occasion, found to be dominant.
Effect of [111] texture on the perpendicular magnetic anisotropy of Co/Ni multilayers
Authors: Naik V. M. , Hameed S. , Naik R. , Pust L. , Wenger L. E. , Dunifer G. L. , Auner G. W.
Published: July 2002

[111] fcc oriented [Co(2 Å)/Ni(7 Å)]20 multilayers were prepared by molecular beam epitaxy at room temperature on epitaxial Au/Ag buffer layers grown on chemically etched Si(111) surfaces. NH4F etching of Si(111) leads to a smaller spread in the 〈111〉 orientation of the Au/Ag buffer layers and the Co/Ni multilayers as compared to a similar sample prepared on HF-etched Si(111). This results in a stronger perpendicular magnetic anisotropy as determined from the magnetic hysteresis loops. Cross-sectional transmission electron microscopy studies show that the magnetic multilayer film is not flat but has significant waviness at both top and bottom surfaces. The observed waviness originates in part from the waviness already present on the surface of the Au buffer layer and appears to be further enhanced by the difference in the surface free energies of Au and the magnetic elements. A flatter Au/Ag buffer layer is essential to further improve the [111] texture of the [Co/Ni] multilayers.
Barrier thickness dependence of the photoscreening of the piezoelectric field in (111) orientated GaAs–InxGa1−xAs double quantum wells
Authors: Moran M. , Moore K. J. , Dawson P.
Published: July 2002

In this article we present low temperature photoluminescence spectra from a series of (111) orientated GaAs–InxGa1−xAs double quantum well structures with differing barrier thicknesses. We demonstrate an enhancement in the carrier screening of the strain induced internal piezoelectric field by photocreated electrons and holes as the barrier thickness is increased. The enhanced screening arises from an increase in the spatial separation of the electron and hole populations. Additionally, we observed a photoinduced spatial transfer of the second lowest lying heavy hole level. This spatial transfer is a strong function of the electron and hole separation and limits the amount of the optically pumped “blue” shift of the lowest energy intersubband transition.
Optimizing the Q value in three-dimensional metallic photonic band gap crystals
Authors: Leung W. Y. , Tuttle G. , Sigalas M. M. , Biswas R. , Ho K. M. , Soukoulis C. M.
Published: July 2002

A metallic photonic band gap crystal with different defect structures is fabricated. The structure is designed and built to operate in the 8–26 GHz frequency range. Defects with sharp peaks in the transmission are created by removing portions of the metallic rods in a single defect layer. A high quality factor (Q) for the defect state is obtained by larger filling ratios and spatial separations between the unit cells. An optimized value of Q⩾300 is found for three unit cell metallic photonic band gap structure. The experimental observations agree very well with theoretical calculations using the transfer matrix method.
Microscopic analysis of the influence of strain and band-gap offsets on noise characteristics in Si1−xGex/Si heterojunctions
Authors: Martı́n Martinez M. J. , Pardo D. , Velázquez J. E.
Published: July 2002

A detailed study under forward-bias conditions of the physical origin of high frequency noise in p+(Si)-n (Si1−xGex) heterojunctions using ensemble Monte Carlo simulation is reported. Based on the internal magnitudes, we determine how the strained SiGe layer induces different features in the perpendicular transport of a heterojunction as compared with that of a silicon p+n homojunction. The main part of this study focuses on a comparative microscopic analysis of current fluctuations in homojunction and heterojunctions over a wide range of frequencies. A method based on considering a spatial analysis of noise to isolate the contributions of both types of carrier on the Si and Si1−xGex epilayers of the devices is described. The role of electrons and holes in the different regions of the devices and the combined effects of the band discontinuities and strain on noise characteristics in Si1−xGex/Si bipolar heterojunctions is discussed.
Influence of process pressure on the growth of hydrocarbon films under direct dc bias in an electron cyclotron resonance plasma
Authors: Rusli  , Yoon S. F. , Yang H. , Ahn J. , Zhang Q. , Wu Y. S. , New W. L.
Published: July 2002

The effects of pressure on the deposition of hydrogenated amorphous carbon (a-C:H) thin films using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique are reported. In this study, the ions were accelerated under a constant direct dc bias achieved through a screen grid positioned above the substrate. The deposition pressure was varied to study its effects on the plasma environment under the ECR conditions and also on the properties of the films deposited. It was found that changing the process pressure has a very significant effect on the properties of the films deposited. The hardness and the optical gap of the films were noted to increase with pressure. The sp3 content in the films, as deduced from their Raman spectra, was also observed to increase. The results obtained in this study show that the plasma chemistry, in addition to the ion energy, plays a very significant role in determining the properties of the films deposited. The denser plasma created under the ECR condition at higher pressure, accompanied by the presence of a relatively large amount of atomic hydrogen resulting in enhanced plasma etching of the films, is believed to lead to the results observed. Comparisons have also been made between films deposited under rf induced bias and direct dc bias in the ECR-CVD system. The difference in the characteristics observed can be attributed to the narrower ion energy distribution in the case of direct dc bias.
Effects of stress changes after demagnetization on magnetization curves and domain wall motions in a grain-oriented Si–Fe sheet
Authors: Yamamoto Ken-ichi , Sasaki Tadashi , Yamashiro Yasumasa
Published: July 2002

Domain structure observations on a grain-oriented Si–Fe sheet were made to investigate into the magnetization process of demagnetization stress effect, which occurs on the sample to which stress was applied in its demagnetized state. Irreversible 180° wall motions corresponding to the stress effect were observed, and those were due to irreversible motions of neighboring spike domains. It is concluded that the stress effect is related to domain structure and pinning states of the sample.
Effect of surface segregation of sulfur on recrystallization kinetics in 3% Si–Fe alloy strip
Authors: Heo N. H. , Chai K. H. , Na J. G. , Kim J. , Woo J. S.
Published: July 2002

Effects of bulk content of sulfur on sulfur segregation and surface energy induced recrystallization kinetics have been investigated in two alloys containing 6 and 30 ppm sulfur. During final annealing under a high vacuum, the convex profile in sulfur concentration, which is attributed to sulfur segregation and evaporation, corresponded to the trough in magnetic induction, irrespective of bulk sulfur content. During annealing, surface energy induced secondary and tertiary recrystallization were in turn observed. While the grain boundary pinning effect of segregated sulfur was very weak in the alloy containing 6 ppm sulfur, the grain boundaries in the other alloy were strongly pinned by the segregated sulfur. Under the relatively higher sulfur atmosphere appearing in the alloy containing 30 ppm sulfur, the growth rate of {100} grain was absolutely governed by the Zener term related to the segregation concentration of sulfur. Through such a recrystallization process, a complete {110}〈001〉 Goss texture was formed, and magnetic induction higher than 1.9 T was obtained in both alloys after final annealing for 14.4 ks.
Creep deformation of a soft magnetic iron–cobalt alloy
Authors: Fingers R. T. , Coate J. E. , Dowling N. E.
Published: July 2002

The U.S. Air Force is in the process of developing magnetic bearings, as well as an aircraft integrated power unit and an internal starter/generator for main propulsion engines. These developments are the driving force for the new emphasis on the development of high saturation, low loss magnets capable of maintaining structural integrity in high stress and high temperature environments. It is this combination of desired material characteristics that is the motivation of this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hiperco® Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for these applications. Material specimens were subjected to a battery of mechanical tests in order to study and characterize their behaviors. Tensile tests provided stress versus strain behaviors that clearly indicated: a yield point, a heterogeneous deformation described as Lüders elongation, the Portevin–LeChatelier effect at elevated temperatures, and most often a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated three distinct types of behavior. Two types resembled a traditional response with primary, secondary, and tertiary stages; while the third type can be characterized by an abrupt increase in strain rate that acts as a transition from one steady-state behavior to another. The relationships between the tensile and creep responses are discussed. Analyses of the mechanical behavior include double linear regression of empirically modeled data, and constant strain rate testing to bridge the tensile and creep test parameters.
Ferromagnetic behavior of a triplet superconductor
Authors: Knigavko A. , Rosenstein B. , Chen Y. F. , Huang H. L. , Lin M. T.
Published: July 2002

Properties of a type II triplet superconductor with equal spin pairing are investigated using the phenomenological Ginzburg–Landau approach. It is shown that there exist two kinds of fluxons: vortices and magnetic skyrmions. Vector nature of the order parameter allows a direct coupling of the effective spin of the condensate to a magnetic field. This coupling, which is reminiscent to Zeeman interaction in the form, significantly modifies the structure of an isolated vortex, as compared to the usual Abrikosov vortex, and changes the energetics of a vortex lattice. If the coupling is sufficiently strong, then magnetization of the triplet superconductor becomes positive at high magnetic fields. Formation of spontaneous vortex state is also possible.
Phase transition of an S=1 quasi-one-dimensional Heisenberg antiferromagnet in applied magnetic fields
Authors: Honda Z. , Katsumata K.
Published: July 2002

The phase transition of the S=1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6) in an applied magnetic field (H) is studied from the measurement of the heat capacity (Cp). There is no anomaly in Cp below H=4 T (H parallel to the chain) or H=6 T (H perpendicular to the chain). A sharp anomaly in Cp is observed above H=4 T (H parallel to the chain) or H=6 T (H perpendicular to the chain) indicating the occurrence of long-range ordering. The H dependence of the critical temperature is studied and a temperature versus magnetic field phase diagram is constructed.
Aging behavior in Cu–Al–Be shape memory alloy
Authors: Somoza Alberto , Romero Ricardo , Mañosa Lluı́s , Planes Antoni
Published: July 2002

This article reports positron annihilation spectroscopy and calorimetric measurements of the aging behavior in a Cu–Al–Be shape memory alloy. An excess of single vacancies is retained in the alloy as a result of a quench. All vacancies in excess disappear after long aging time, and a migration energy EM=1.0±0.1 eV for this process has been found to be larger than in other Cu-based shape memory alloys. The good correlation found for the concentration of vacancies and the shift in the martensitic transition temperature demonstrates that, in Cu–Al–Be, changes in the transition after a quench are deeply related to the excess of vacancies.
Observation of ballistic carrier propagation in Bi and W by scanning electron microscopy
Authors: Knauth S. , Lenzner J. , Herrnberger H. , Grill W. , Böhm A. , Gröger A. , Heil J. , Primke M. , Wyder P.
Published: July 2002

A scanning electron microscope with cryogenic sample holder has been employed for spatially resolved excitation of carriers. A point contact at a fixed position on the sample surface opposing the area scanned by the electron beam serves as a local current probe. Ballistic propagation and focusing of electron beam excited carriers is observed in single crystalline high purity samples of bismuth and tungsten over distances of typically 100 μm. Signal contributions from diffusive carrier flow as well as ballistic phonons are observed in addition to the ballistic electron signals.
Alternating current field effect on the freezing temperature of relaxor ferroelectrics
Authors: Colla Eugene V. , Gupta Surya M. , Viehland Dwight
Published: July 2002

Alternating current-field effects on the freezing temperature of La-modified lead magnesium niobate–lead titanate crystalline solutions for compositions near to the morphotropic phase boundary have been studied by dielectric spectroscopy. Charge imbalance due to La substitution (0–10 at. %) in [Pb(Mg1/3Nb2/3)O3]0.65(PbTiO3)0.35 was compensated by changing the B-site cation ratio. The frequency dispersion in the dielectric constant was found to increase with increasing La substitution. Relaxor-like dielectric characteristics were induced for La concentrations greater than 5 at. %. It was also found that the dielectric constant maximum (εmax′) increased and the temperature of εmax′ decreased with increasing ac field. In addition, a threshold electric field was observed above which nonlinearities became evident in the dielectric response and the freezing temperature was reduced.
Microstructure characterization of amorphous thin solid films in a fringe-free environment
Authors: Li Tong , Kanicki Jerzy
Published: July 2002

We have comprehensively analyzed the influence of the probe beam’s polarization state and incident angle on the vibrational absorption spectra of thin solid films such as hydrogenated amorphous silicon nitride and hydrogenated amorphous silicon in Fourier transform infrared spectroscopy. This analysis demonstrates the nuisance of interference fringes in distorting the bond structure of thin solid films in conventional vibrational absorption spectra. Based on the spectrum analysis and optical fundamentals, a practical method of recording a vibrational absorption spectrum of a thin solid film in an interference fringe-free environment is proposed. Furthermore, it is also demonstrated that a fringe-free spectrum can be recorded even in an interference-embedded environment if a right light incident angle is chosen. This interference-embedded fringe-free spectrum is only valid for material’s qualitative microstructure assessment but not for direct quantitative analysis. Finally, a comparison between ideal spectra and those fringe-corrected by conventional measures indicates a nontrivial discrepancy. Therefore, only interference-free spectrum exhibits the absolute features of the bond structures, and should be the standard spectrum used for thin solid film microstructure assessment.
Type II and mixed type I–II radiative recombinations in AlInAs–InP heterostructures
Authors: Duez V. , Vanbésien O. , Lippens D. , Vignaud D. , Wallart X. , Mollot F.
Published: July 2002

Spatially indirect radiative recombination processes (type II) are analyzed in InAlAs–InP heterostructures by means of a self-consistent solver for Poisson and Schrödinger equations. The cases of heterostructures at equilibrium (under darkness) and under illumination are specifically considered. Special attention is paid to the interface transition energy variation as a function of the photocreated carrier density and to the exact composition of the interface. This study is supported by photoluminescence experiments carried on InAlAs–InP heterostructures fabricated under different growth conditions. It is shown that the type II recombination energy is very sensitive to the exact composition of the interface: a 3 Å thick interface InAs layer is sufficient to shift the type II transition towards lower energies.
Identification of the nature of platinum related midgap state in silicon by deep level transient spectroscopy
Authors: Rao K. S. R. K. , Rangaiah S. V. Pandu , Reddy P. N. , Reddy B. P. N.
Published: July 2002

In this article, we present the detailed investigations on platinum related midgap state corresponding to Ec−0.52 eV probed by deep level transient spectroscopy. By irradiating the platinum doped samples with high-energy (1.1 MeV) gamma rays, we observed that the concentration of the midgap state increases and follows a square dependence with irradiation dose. However, the concentration of the acceptor corresponding to Ec−0.28 eV remained constant. Furthermore, from the studies on passivation by atomic hydrogen and thermal reactivation, we noticed that the Ec−0.52 eV level reappears in the samples annealed at high temperatures after hydrogenation. The interaction of platinum with various defects and the qualitative arguments based on the law of mass action suggest that the platinum related midgap defect might possibly correspond to the interstitial platinum-divacancy complex (V–Pt–V).
Influence of the domain size on the band gap of ordered (GaIn)P
Authors: Saß Torsten , Pietzonka Ines , Schmidt Heidemarie
Published: July 2002

The domain size and the band-gap energy of ordered epitaxial (GaIn)P layers have been determined by means of transmission electron microscopy and photoluminescence measurements, respectively. With decreasing domain size the symmetry of the ordered layers is reduced from the trigonal space group R3m (CuPtB type) to the monoclinic Pm space group. Pseudopotential band-structure calculations reveal an increase of the band-gap energy of ordered (GaIn)P with diminishing domain size. This would affect the determination of the degree of order by methods, which rely on the band-gap energy of perfectly ordered (GaIn)P. By correlating the theoretical with the experimental band-gap energies we demonstrate that the order parameter η of layers with small domains is higher if the dependence of the band-gap energy on the domain size is considered. Hence, for the determination of the degree of order not only the band-gap energy, but also the domain size have to be taken into account.
Structural and magnetoresistive properties of La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3
Authors: Sun J. R. , Rao G. H. , Gao X. R. , Liang J. K. , Wong H. K. , Shen B. G.
Published: July 2002

Structural, magnetic, and transport properties of ABO3-type La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3 are investigated. Different structure deformation from that in the A-site doping, characterized by the synchronous variation of the lattice constants b with c/√ versus the content of In in the compounds, is observed. The metal–semiconductor transition shows a strong In content dependence. The transition temperature decreases monotonously from 180.7 to 103.4 K as x varies from 0 to 1, with a corresponding maximum resistivity ranging from 2.9 to 410.8 Ω cm. The magnetoresistive properties of the materials are strongly affected by the size mismatch between A- and B-site ions, and a relation similar to that presented by Hwang et al. [Phys. Rev. Lett. 75, 914 (1995)] is observed though controlling of the tolerance factor, is realized by B-site doping.
Laser-assisted removal of particles on silicon wafers
Authors: Vereecke G. , Röhr E. , Heyns M. M.
Published: July 2002

Laser cleaning is one of the new promising dry cleaning techniques considered by semiconductor companies to replace wet cleans in the near future. A dry laser cleaning tool was tested that uses an inert gas jet to remove particles lifted off by the action of a DUV excimer laser. A model was developed to simulate the cleaning process and analyze the influence of experimental parameters on laser cleaning efficiency. The best cleaning efficiencies obtained with 1.0 μm SiO2, ∼0.3 μm Si3N4, and 0.3 μm SiO2 particles deposited on Si wafers were 84±8%, 33±4%, and 12±7%, respectively. This is in qualitative agreement with theoretical calculations showing the existence of a size threshold for the removal of nonabsorbing particles by dry laser cleaning. Among the process parameters tested to optimize the process efficiency, fluence showed the highest influence on removal efficiency, before the number of laser pulses and the laser repetition rate. The use of high fluences was limited by the damaging of the wafer surface, which was not homogeneous on a macroscopic scale. The optimum number of laser pulses per unit area depended on the type of particle. The laser repetition rate had no significant influence on cleaning efficiency and can be used to reduce process time. The influence of capillary condensation on the process was demonstrated by the higher removal efficiency of 0.3 μm SiO2 and Si3N4 particles, 88±6% and 78%, respectively, upon exposure of wafers to air saturated with moisture prior to laser processing. This was attributed to the explosive evaporation of capillary condensed water, similar to the mechanism proposed for liquid assisted laser cleaning.
Chemically reduced lithium niobate single crystals: Processing, properties and improved surface acoustic wave device fabrication and performance
Authors: Bordui P. F. , Jundt D. H. , Standifer E. M. , Norwood R. G. , Sawin R. L. , Galipeau J. D.
Published: July 2002

Lithium niobate single-crystal wafers were chemically reduced using nitrogen/hydrogen atmospheres at a variety of temperatures between 350 and 750 °C. Reduced wafers were measured to have increased optical absorptivity and increased direct current (dc) electrical conductivity as a function of reduction-processing temperature. Absorptivity increases were measured larger than 1000×; conductivity could be increased by more than a factor of 105. Standard 78 MHz surface acoustic wave (SAW) filters were successfully fabricated using reduced wafers, and shown to have increased resistance to spurious pyroelectric charging effects during thermal cycling. The observed increases in optical absorptivity and dc electrical conductivity can also be expected to provide benefits for SAW device fabrication processing.
Wear-induced modifications of amorphous carbon in the presence of magnetic media
Authors: Ramı́rez A. G. , Sinclair R.
Published: July 2002

The effects of wear and annealing on the microstructural features of amorphous carbon thin films were investigated. Amorphous-carbon thin films on hard disks were subjected to wear by full-sized alumina–titanium carbide sliders. The associated microstructural changes were analyzed by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). TEM micrographs and EELS spectra directly showed structural differences between worn and unworn regions, and indicated increased graphitic content. For comparison, unworn amorphous-carbon thin films were annealed and analyzed by near-edge x-ray absorption fine structure spectroscopy. The annealed unworn carbon films also showed structural changes. The microstructural changes at these low temperatures suggest that the metals of the magnetic layers mediate graphitization. This article presents the experiments and proposes a wear mechanism.
Correlation of macromagnetic properties with recording performance measurements in advanced metal particle tape
Authors: Jackson M. , O’Grady K. , Sinclair G.
Published: July 2002

In this work we present measurements of the macromagnetic properties and associated recording performance, for two different metal particle tape samples, which are proposed to be used in a high density helical scan recording system. Data in such a system is recorded along two channels, which are oriented at −14° and +26° to the parallel/machine direction. It is thus important to measure the angular variation in the magnetic properties, in particular along the recording channel directions, and to correlate these measurements with the recording performance. In addition, care should be taken that the properties of the recording channels are similar to avoid any imbalance in the read back signal between the two channels. We show that, when a choice of the “best” media is made, it may be advantageous to perform more detailed macromagnetic measurements within the sample plane. In particular, measurements along the recording channel orientations should be undertaken, as it is found that these will highlight differences between the characteristics of the two channels. We conclude that a more detailed analysis of the magnetic behavior within the sample plane is required to predict any channel imbalance which may arise.
Powder magnetoresistance (invited)
Authors: Coey J. M. D.
Published: July 2002

Magnetoresistance observed in pressed powder compacts of half-metallic ferromagnetic oxides is reviewed. The main, isotropic negative magnetoresistance, which exceeds 50% in CrO2 at low temperature, is due to alignment of the the ferromagnetic moments of contiguous ferromagnetic grains. The effect is related to interparticle tunelling and shows hysteresis similar to that of the bulk magnetization. Spin-dependent Coulomb blocade observed in the smallest particles. There is also, an anisotropic magnetoresistance of up to 1% and a high-field increase in conductivity of order 1%/T in the powder compacts.
Magnetic properties and microstructure of nanocomposite R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd, Pr) magnets
Authors: Chen Zhongmin , Zhang Yong , Ding Yuquan , Hadjipanayis G. C. , Chen Qun , Ma Baomin
Published: July 2002

Nanocomposite R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd, Pr) magnets prepared by crystallizing the as-made R8(Fe,Co,Nb)86B6 amorphous melt-spun ribbons have been studied. The coercivity is found to depend mainly on the grain size of the soft phase which is very sensitive to the sample composition. The average grain size is about 30 nm in R8Fe86B6, but the microstructure is not homogeneous and there are several large α-Fe grains with sizes up to 50–100 nm. The coercivities are 3.3 kOe in Nd8Fe86B6 and 4.9 kOe in Pr8Fe86B6 samples. Nb substitution significantly reduces the grain size of α-Fe and increases the coercivity. The highest coercivities obtained are 5.5 kOe in Nd8(Fe0.97Nb0.03)86B6 and 9.3 kOe in Pr8(Fe0.92Nb0.08)86B6 samples. Co substitution for Fe increases the grain size of both the 2:14:1 phase and α-Fe and dramatically decreases the coercivity. Increasing the B content in Co substituted samples leads to the formation of a more homogeneous and finer microstructure and thus to a partial recovery of the coercivity from 2.3 kOe in Nd8((Fe0.5Co0.5)0.97Nb0.03)86B6 to 4.3 kOe in Nd8((Fe0.5Co0.5)0.97Nb0.03)82B10 and from 2.1 kOe in Pr8((Fe0.5Co0.5)0.94Nb0.06)86B6 to 6.5 kOe in Pr8((Fe0.5Co0.5)0.94Nb0.06)82B10. It is further found that Co substitution improves the temperature dependence of the saturation magnetization.
Growth of ultrafine Co–Mn ferrite and magnetic properties by a sol–gel method
Authors: Kim Chul Sung , Yi Young Suk , Park Key-Taeck , Namgung Hae , Lee Jae-Gwang
Published: July 2002

Ultrafine Co0.9Mn0.1Fe2O4 particles are fabricated by a sol–gel method. Magnetic and structural properties of powders are investigated with x-ray diffraction, vibrating samples magnetometer, and Mössbauer spectroscopy. Co–Mn ferrite powders which were fired at and above 673 K have only a single phase spinel structure and behave ferrimagnetically. Powders annealed at 673 K have a typical spinel structure and the paramagnetic and ferrimagnetic nature, simultaneously. The formation of nanocrystallized particles is confirmed when Co–Mn ferrite is annealed at 623 K. The magnetic behavior of Co–Mn ferrite powders fired at and above 823 K shows that an increase of the annealing temperature yields a decrease of the coercivity and an increase of the saturation magnetization. The maximum coercivity and the saturation magnetization of Co–Mn ferrite powders are 1523 Oe and 66.7 emu/g, respectively. Fe57 Mössbauer spectra of Co–Mn ferrite have been taken at various temperatures from 13 to 850 K. The isomer shifts indicate that the valence states of the Fe ions have a ferric character.
Ferromagnetic metal/semiconductor hybrid structures for magnetoelectronics
Authors: Xu Y. B. , Freeland D. J. , Kernohan E. T. M. , Lee W. Y. , Tselepi M. , Guertler C. M. , Vaz C. A. F. , Bland J. A. C. , Holmes S. N. , Patel N. K. , Ritchie D. A.
Published: July 2002

We report on the following new ferromagnetic metal/semiconductor heterostructure material systems: (1) Fe/InAs(100)-4×2, (2) Fe/InAs(graded)/GaAs(100), and (3) Fe/InAs/AlSb/GaSb/AlSb/InAs/GaAs resonant tunneling diodes. Single crystal Fe films have been stabilized in these structures using molecular beam epitaxy growth, as evidenced by low energy electron diffraction. The magnetic and electrical properties have been studied using in situ (and focused) magneto-optical Kerr effect, alternating gradient field magnetometry, and current–voltage measurements. The results show that Fe/InAs based heterostructures are very promising systems for use in future magnetoelectronic devices as they have well defined magnetic properties as well as favorable electrical properties.