bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of water and alcohols on photoluminescence of porous silicon
Authors: Balagurov L. A. , Leiferov B. M. , Petrova E. A. , Orlov A. F. , Panasenko E. M.
Published: July 2002

The measurements of luminescence spectra were performed on series of porous silicon (PS) samples, obtained in wide range of anodic etching regimes. Photoluminescence (PL) spectra contain two closely spaced luminescence bands. The energy difference between them ∼0.15–0.2 eV depends very slightly on their spectral position. The ratio of the intensities of the two PL bands is monotonously changing with the changes in sample porosity. Thus, in very porous samples only the short-wavelength band is usually observed, while in slightly porous samples only the long-wavelength band is observed. Interaction of PS samples with water at first produces a small decrease of PL band intensities, and then a new band in the range of 0.7 μm appears, which is presumably related to an oxide layer at the surface of PS nanocrystallites. After treating PS in alcohols, the initial band intensity drops and the long-wavelength band disappears completely in less than 1 min. It is discovered that the presence of water contained in the ethanol (even at a content of ∼1%), leads to emergence of a new intensive PL band in the range of 0.7 μm. In very porous samples or after washing or storage of as-anodized PS in water or alcohols, the long-wavelength band is rarely observed experimentally because its intensity is very small.
The change of magnetic properties in nanocrystalline Fe88Zr7B4Cu1 alloy by cooling rate
Authors: Kim K. S. , Ström V. , Wittborn J. , Rao K. V. , Kim K. Y. , Noh T. H. , Yu S. C.
Published: July 2002

We have investigated the effect of cooling rate, followed immediately after the isothermal annealing, on the magnetic properties of melt-spun Fe88Zr7B4Cu1 alloy. As the cooling rate is increased, the effective permeability, 2×104, improved by 50% on annealing at around 650 °C. The remanence ratio is also found to concomitantly decrease with the increasing cooling rate. The increase of permeability and decrease of remanence ratio are consistent with the expected suppression of the induced magnetic anisotropy. From an analysis of the transmission electron microscopy micrographs, and the x-ray diffraction spectral intensities, we find that the volume fraction of the amorphous matrix to that of the nanocrystallized magnetic entities to be about 20%, at which the permeability has the maximum value for this system. Scanning electron microscopy and antiferromagnetic investigations show a much smoother surface morphology with a finer grain distribution in the rapidly quenched sample.
Magnetostriction and anisotropy of twin-free single-crystals Tb0.5Dy0.5(Fe0.9Mn0.1)2
Authors: Wang Jinghua , Wu Guangheng , Zhao Xuegen , Jia Kechang , Zhan Wenshan
Published: July 2002

A study of the effects of substituting a small amount of Mn for Fe in the Terfenol-D system is presented. The twin-free and 〈111〉-oriented single-crystal rods of Tb0.5Dy0.5(Fe0.9Mn0.1)2 were prepared by Czochralski method. The magnetization, lattice constant, Curie temperature, and magnetostriction were examined. From the experimental results, it is possible to determine the effect of Mn substitution on magnetic anisotropy and magnetostriction. Because of Mn substituting for Fe, magnetic moment values of Tb0.5Dy0.5(Fe0.9Mn0.1)2 show two inflections and the easy magnetization directions also show changes from 1.5 to 300 K at an applied field of 1000 Oe. It strongly suggests that Mn substitution remarkably influences magnetocrystalline anisotropy of Tb0.5Dy0.5(Fe0.9Mn0.1)2. Its saturation magnetostrictions are 1.48×10−3 and 1.67×10−3, maximum d33 values are 1 and 1.5 under compressive stress of 0 and 12 MPa, respectively. These magnetostrictive properties are clearly better than those measured from the 〈112〉-oriented twinned samples. This is the first time that the experimental data measured from the single-crystalline samples on the magnetic properties of Tb0.5Dy0.5(Fe0.9Mn0.1)2 are reported.
High-temperature phase transformations of iron anhydrous ammonia system realized by ball milling at room temperature
Authors: Chen Y. , Williams J. S. , Wang G. M.
Published: July 2002

α-Fe powder has been ball milled at room temperature in an anhydrous ammonia atmosphere for various times. The composition and structure of milled powders was investigated using x-ray diffraction spectroscopy, Mössbauer spectroscopy, combustion elemental analysis, and thermal analysis. A high temperature reaction sequence was observed during milling in the nitrogen composition range from 3.75 to 5.56 wt %. The nitriding reaction sequence has been established as a function of milling time. An increase of nitrogen in the powder with an increase of milling time produces a progression to iron nitride phases richer in nitrogen. A distinct similarity is found between nitriding reaction processes during high-energy ball milling and nitrogen ion implantation into iron. Additionally, an inverse (dissociation) reaction sequence is observed during thermal treatments of ball-milled iron powders.
Calculation of nonlinear effective elastic constants of polycrystalline materials
Authors: Kiewel H. , Fritsche L. , Reinert T.
Published: July 2002

We determine nonlinear effective elastic constants of polycrystalline materials within the framework of a recently developed method by Kiewel and Fritsche. This method is based on simulating the real system by a cluster of 100–500 crystallites. For simplicity we confine ourselves to macroscopically isotropic materials. The grains are assumed to have the shape of Wigner–Seitz cells of a body-centered-cubic lattice. This type of cluster is topologically similar to the microstructure of a real polycrystal. Therefore, it may be expected to reliably describe the nonlinear effective moduli of the respective materials.
Magnetic and Mössbauer studies of hot-pressed MnZnNi ferrites (abstract)
Authors: Babbar V. K. , Puri R. K.
Published: July 2002

Hot-pressed MnZn ferrites are extensively used for magnetic recording applications. The present work investigates the magnetic properties of MnZnNi ferrites by using the Mössbauer spectroscopy and taking bulk magnetic measurements. Ferrites of the composition Mn0.6Zn0.4−xNixFe2O4 (0≤x≤0.4) have been prepared by uniaxial hot pressing technique. The final sintering was performed at 1250 °C for 3 h under a pressure of 35 MPa. The samples exhibit high density (porosity <0.1%) nearly uniform grain size (average grain size=0.01 mm approx.), and large Vickers’ hardness (650 approx.). The variations of initial permeability, saturation magnetization, Curie temperature, and coercive field are studied by changing Ni2+ content. The initial permeability increases slightly for x≤0.05, attains a maximum value of 5660, and decreases continuously for x≳0.05. The saturation magnetization increases for x≤0.25 and decreases for x≳0.25. The maximum saturation magnetization obtained for x=0.25 is 4825 G. The Curie temperature increases markedly from 431 to 682 K with increasing Ni2+ content. The coercive field decreases slightly for x≤0.05, becomes as low as 0.09 Oe, and increases almost linearly thereafter.

The results are explained on the basis of sublattice magnetizations, stren of AB exchange interactions and change in magnetocrystalline anisotropy constant. The Mössbauer studies reveal the well-defined hyperfine spectra for Ni2+-substituted samples. The isomer shift remains almost unaffected by Ni2+ substitution, while the quadrupole splitting is observed to be negligible for all the samples. The hyperfine field decreases continuously as x increases from 0 to 0.4. The occupancy ratio of Fe3+ ions on octahedral to tetrahedral sites yields a cation distribution which conforms with the bulk magnetic measurements. The MnZnNi ferrite compositions with x ranging from 0.05 to 0.10 exhibit properties which make them suitable materials for recording head applications.
Modeling effects of temperature annealing on giant magnetoresistive response in discontinuous multilayer NiFe/Ag films
Authors: Oti J. O. , Kim Y. K.
Published: July 2002

The giant magnetoresistive (GMR) behaviors of discontinuous double-layer giant magnetoresistive films with different microstructure arising from different annealing conditions, are calculated using a numerical micromagnetic model. The effect of magnetic grain growths in the perpendicular and lateral directions in the magnetic layers, and the formation and growth of grain clusters were studied. The GMR responses of the films are analyzed in terms of magnetostatic interactions between the magnetic layers and the microstructural geometric effects on the transport properties of the samples.
Modeling of dynamic ferroelectric hysteresis loops in purified Rb2ZnCl4
Authors: Hauke T. , Müller V. , Beige H. , Fousek J.
Published: July 2002

Dynamic hysteresis loops were recorded in the ferroelectric lock-in phase of purified Rb2ZnCl4 crystals at a temperature T=188 K which is 5 K below the incommensurate–commensurate phase transition. The hysteresis loops observed in the frequency range 50 Hz<f<5 kHz can quantitatively be described by a model that treats a sideways shift of planar, nearly regular arranged domain walls as the only mechanism of polarization reversal in Rb2ZnCl4. Due to defect interaction, the velocity v of the domain wall depends nonlinearly on the effective force F acting on it and a scaling behavior v∼(F−Fc)θ with θ=1.45 is observed.
Voltage-tuning in multi-color quantum well infrared photodetector stacks
Authors: Lenchyshyn L. C. , Liu H. C. , Buchanan M. , Wasilewski Z. R.
Published: July 2002

A systematic study of stacked quantum well infrared photodetectors is undertaken to improve the understanding of the voltage-tunable multi-color spectral response. The multi-color capability is achieved by sequentially growing conventional one color detectors, separated by conducting layers. The behavior of the stacked devices is proven to correspond to the individual detectors simply acting in series with each other. The dc resistance, photocurrent and dynamic resistance characteristics of the individual detectors are examined and correlated with the voltage-tuning in the stack.
Resonance splitting in discrete planar arrays of Josephson junctions
Authors: Duwel A. E. , Trías E. , Orlando T. P. , van der Zant Herre S. J. , Watanabe Shinya , Strogatz Steven H.
Published: July 2002

We have measured and modeled the dynamics of inductively coupled discrete arrays of niobium Josephson junctions. We see splitting of the Eck step in the current-voltage characteristic. Numerical simulations reproduce this splitting and are used to find an approximate solution for the junction phases at resonance. Using the technique of harmonic balance, we find an analytic expression for the resonance frequencies and the voltages that match this splitting. We can also predict the amplitude of these oscillations. The analytical results describe both the experiments and simulations well.
The magnetoresistance and microstructure of Fe–xCr–10Co alloy thin films
Authors: Chang H. C. , Chang Y. H. , Ger C. H. , Yao S. Y.
Published: July 2002

Large negative magnetoresistance (MR) is observed in Fe–xCr–10Co (x=10,20,30,40,50,- 60,70, and 80 wt %) ternary heterogeneous alloy films prepared by the IBS (ion beam sputter) deposition process. All the as-deposited films consisted of the α phase alone. After aging treatment, the α phase is decomposited into two phases: the α1 (Fe–Co rich phase) and α2 (Cr rich phase). In the granular alloy, the GMR effect is obtained by virtue of the interface scattering between α1 and α2. After isothermal aging at 400 °C for 1 h, the largest MR of −27% appears around the Cr content of 60 wt % at 77 K and 14 kOe. The MR ratio of Fe–50Cr–10Co and Fe–70Cr–10Co is −12% and −20%, respectively, at the same condition. The MR ratio is also obviously effected by the Cr (or Fe) content in the alloy system.
Mechanisms of molecular beam epitaxial growth of (001) HgTe
Authors: Oehling S. , Ehinger M. , Spahn W. , Waag A. , Becker C. R. , Landwehr G.
Published: July 2002

We report on an investigation of the growth mechanisms of HgTe using a combination of reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). The experiments were carried out on untilted (001) CdTe substrates. Growth rates were determined from RHEED intensity oscillations of the (00) specular spot reflection. The amplitude of these oscillations decrease with increasing substrate temperature. Above 178 °C no RHEED oscillations could be measured. Upon reducing the sample temperature below 178 °C these oscillations could again be observed. This cyclic behavior could be induced several times for each sample, indicating a reversible change in the growth mechanism. In order to correlate the surface structure with RHEED observations, several samples have been investigated with STM. Thus, it could be confirmed that a temperature dependent transition occurs during the MBE growth of HgTe from the island growth mode below the critical temperature of 178 °C to a step flow mode above this temperature.
Experimental approach to the mechanism of the negative bias enhanced nucleation of diamond on Si via hot filament chemical vapor deposition
Authors: Chen Qijin , Lin Zhangda
Published: July 2002

The mechanism of the negative bias enhanced nucleation of diamond on silicon has been studied by a set of experiments using hot filament chemical vapor deposition. Nucleation enhancement was achieved for experimental configurations either with or without the application of a negative bias to the mirror-polished Si substrates. The obtained nucleation density ranged from 108 to 1010 cm−2. The as-deposited films were characterized by scanning electron microscopy and Raman spectroscopy. Our results demonstrate that the electron emission from the diamond coating the substrate holder, which is speculated to greatly increase the concentration of atomic hydrogen and dissociated hydrogen radicals on/near the substrate surface is responsible for the nucleation enhancement during the bias pretreatment.
Effective capture rates of carriers in amorphous hydrogenated silicon
Authors: Kounavis P. , Mataras D. , Rapakoulias D.
Published: July 2002

The effective capture rates of electrons and holes by the defects of undoped a-Si:H are measured using a technique based on the optical bias dependence of the modulated photocurrent. The evolution of the phase shift and modulated photocurrent spectra with the optical bias intensity is used to study the capture coefficient of the defects at different trap depths in the energy gap. The modulated photocurrent spectra are recorded using uniformly, or strongly absorbed light in order to obtain information about the trapping and recombination processes in the surface, the interface, and the bulk of the films. The calculated capture rates of carriers are studied in a series of a-Si:H films and information about the defect structure is obtained. It is found that the effective capture rates of the carriers by the defects are not constant in the studied films and may vary by up to two orders of magnitude from sample to sample. Finally, the importance of the atomic environment and the local strains of the defects of a-Si:H for the capture process of the carriers is discussed.
Dielectric properties of Ta2O5–SiO2 polycrystalline ceramics
Authors: Cava R. J. , Krajewski J. J. , Peck W. F. , Roberts G. L.
Published: July 2002

The dielectric properties of (Ta2O5)1−x(SiO2)x polycrystalline ceramics for 0.0≤x≤0.20 are reported. Measurements were made at 1 MHz and temperature between −40 and +100 °C. The dielectric properties are not very sensitive to SiO2 content. A moderate enhancement of the dielectric constant is found, from −30 for pure Ta2O5 to ∼45 at x≂0.10. The temperature coefficient of dielectric constant in the vicinity of room temperature decreases from ∼200 ppm/°C for Ta2O5 to ∼75 ppm/°C for x=0.14.
Structure and electrical properties of CdNiTe nanostructured thin films
Authors: Alvarez-Fregoso O. , Mendoza-Alvarez J. G. , Zelaya-Angel O. , Morales F.
Published: July 2002

CdNiTe nanostructured thin films were prepared by radio frequency sputtering from a target of CdTe and nickel compressed powders. The structural and electrical film properties were studied as a function of the atomic nickel concentration in the films (x=0.05, 0.10, and 0.15). X-ray diffraction patterns showed a cubic CdTe parent structure with a (111) preferential orientation. The microcrystalline grain size in the films showed a systematic decrease with the increase of Ni content, starting with grain sizes of around 35 nm for x=0.05, down to an average of 26 nm for x=0.15. From scanning electron microscopy micrographs, a fine granular morphology with a random distribution of grain sizes in the films was observed. The film electrical resistivity was measured as a function of the temperature in the range T: 26–473 K. The temperature dependence of the dark resistivity over this wide temperature range showed a clear deviation from a simple thermally activated carrier transport mechanism.
Simple measurement of 300 K electron capture cross section for EL2 in GaAs
Authors: Look D. C. , Fang Z.-Q.
Published: July 2002

A simple experiment involving only the measurement of dark current Idark and 1.1 μm photocurrent IPC in semi-insulating (SI) GaAs allows an accurate determination of the electron capture cross section σn for the important defect EL2 in GaAs. For 45 SI GaAs samples, from 12 different boules, grown by three different techniques, we find that IPC/Idark=1.96±0.05 at 300 K. This relationship gives σn=1.4±0.4×10−16 cm2, which is compared to previously estimated values.
Structures of Al/Si(100) surfaces as determined by scanning tunneling microscopy
Authors: Zhu Changxin , Misawa Shunji , Tsukahara Sonoko
Published: July 2002

The structures of Al/Si(100) surfaces with coverages below 0.5 monolayer have been determined using scanning tunneling microscopy (STM). Through careful STM measurements, Al dimers are atomically resolved, where the Al dimer bond is intuitively demonstrated to be parallel to the Si dimer bond. The atomic arrangements at the ends of Al dimer rows have been discussed on the basis of the interpretation of dual-bias STM images. Two possible structures at the end of an Al dimer row are a single atom termination and a dimer termination, depending on whether the Al dimer row ends at a surface defect, respectively.
CoSi2 heteroepitaxy on patterned Si(100) substrates
Authors: Karpenko O. P. , Yalisove S. M.
Published: July 2002

The influence of starting surface topography on the nucleation and growth of epitaxial silicide layers was investigated. CoSi2 layers were grown via the template technique on one-dimensionally patterned Si(100) substrates. These substrates contained mesa stripes, running parallel to Si[011], and exhibited either a number of Si {hkl} facets, or ‘‘smoothly varying’’ sinusoidal profiles. Conventional plan view and high resolution cross section transmission electron microscopy showed that the orientation and morphology of the CoSi2 grains depend on the angle (θ) between the CoSi2/Si interface normal and Si(100). CoSi2(100) grains nucleated on mesa tops and trench bottoms, where θ<5°, and formed atomically sharp interfaces. CoSi2(110) and CoSi2(221) grains nucleated along sidewalls of the mesa structures, in regions where 5°<θ<11° and θ≳5°, respectively. CoSi2(110) grains formed highly stepped interfaces with the substrate which were punctuated by step bunches at the grain boundary/substrate triple points. CoSi2(221) grains formed rough interfaces with the substrate which were punctuated by facets and B-type silicide/substrate interfaces along Si{111} planes. Analysis of these data suggests that nucleation of CoSi2(110) grains is associated with the presence of double height steps and step bunches with small surface misorientation, and that nucleation of CoSi2(221) grains is associated with Si{111} facets, Si{311} facets, and step bunches with larger surface misorientation.
Field emission properties of diode devices based on amorphic diamond-Si heterojunctions
Authors: Wang W. N. , Fox N. A. , Richardson D. , Lynch G. M. , Steeds J. W.
Published: July 2002

Microscopic and macroscopic field emission properties of amorphic diamond films on n- and p-type silicon substrates were studied by combined scanning tunneling microscopy/spectroscopy and integral field emission I–V measurements. Microscopic scanning tunneling spectroscopy showed that amorphic diamond films on n-Si have lower threshold voltage and higher emission current than amorphic diamond films on p-Si. The observed rectification characteristics suggest that amorphic diamond on n-Si is an ideal forward-biased p-n junction cold cathode emitter; however, there is no significant difference between these two structures by integral field emission I–V measurements. Conversion of the smooth amorphic diamond film into porous sp3/sp2 composites with sharp features under electric fields higher than 50 V/μm, followed by preferred electron emission from the porous composite sites of high transconductance, was believed to be the cause.
Magnetic exchange coupling in (Dy,Tb)FeCo magneto-optical recording films
Authors: Hwang Wein-Kuen , Shieh Han-Ping D.
Published: July 2002

The required bias field of a sperimagnetic film is governed by a finite exchange coupling coefficient (λ) mainly determined by the subnetwork coupling. From the study of a series of (Dy,Tb)FeCo films at compensation composition, it is found that λ is mainly determined by the concentration of the rare earth components. Moreover, the exchange integral between rare earth and transition metal subnetworks can be derived from λ so that the number of uncertain parameters for mean field modeling is reduced. Accordingly, the bias field required for magneto-optical recording is mainly proportional to λ that can be obtained quantitatively from either measurement and/or mean field modeling.
Breakup and grain growth in thin-film array
Authors: Vilenkin A. J. , Kris R. , Brokman A.
Published: July 2002

The problem of the morphological evolution in a polycrystalline thin film during annealing is examined by considering a periodic array in a 2D film. The combined motion of the surface moving by diffusion, and the grain boundary, which moves due to its curvature, is presented as a self-consistent problem. The analysis of this problem leads to two distinct kinetics, namely, (a) film breakup: when the grain size is larger than the film thickness, the surface relaxation is primarily a result of its interaction with a single grain boundary, the groove grows until the film breaks up; and (b) grain growth: when the two adjacent grooves interact before breakup happens, grain growth occurs by means of grain annihilation. Asymptotic analysis of the final stage of grain annihilation reveals the dependence of the groove velocity on the two interface energetic. Numerical analysis of boundary/surface motion demonstrates the morphological evolution with time, and establishes the conditions of transition between the two different regions.
Spatial structure in mode population induced by coherent pumping in a ballistic quantum channel
Authors: Tageman Ola , Gorelik L. Y. , Shekter R. I. , Jonson M.
Published: July 2002

We predict a spatially varying mode population to appear in a ballistic quantum channel formed in the two-dimensional electron gas of a gated GaAs/AlGaAs heterostructure due to pumping by a THz field. If a resonant coupling between two modes is suddenly switched on at the entrance, Rabi oscillations in the mode population will arise. We propose to use an array of gates in order to simulate a moving quantum point contact for detecting mode population oscillations since they discriminate between different modes. By consecutively activating them we expect to see both photovoltaic effects and photoconductive effects that can easily be distinguished from noise.
Electroabsorption in ordered and disordered GaInP
Authors: Schmiedel G. , Kiesel P. , Döhler G. H. , Greger E. , Gulden K. H. , Schweizer H. P. , Moser M.
Published: July 2002

We have investigated the electroabsorption due to the Franz–Keldysh effect in GaInP/AlGaInP p-i-n double heterostructures grown by metalorganic vapor phase epitaxy. The simultaneous evaluation of transmission and photocurrent measurements allowed an accurate determination of the field dependent absorption coefficient of ordered and disordered GaInP alloys. For ordered and disordered material, similar changes of the absorption coefficient as high as 4000 cm−1 have been observed for field changes of ΔE=250 kV/cm. Thermally disordered samples, however, showed a degradation of the electrical and optical properties.
Sharp optical emissions from Cu-rich, polycrystalline CuInSe2 thin films
Authors: Schön J. H. , Alberts V. , Bucher E.
Published: July 2002

Optical properties of Cu-rich CuInSe2 thin films prepared by the selenization of Cu/In/Cu alloys in a H2Se atmosphere have been studied by photoluminescence (PL) spectroscopy. PL spectra of as-grown samples were dominated by transitions due to intrinsic defect levels, which are ascribed to VIn (24 meV), CuIn (75 meV), and Cui (53 meV). After chemical etching (10% KCN), emission lines attributed to free and bound excitonic emissions and their LO phonon replica became visible. Accurate analysis of the peak positions revealed values of 4.3 meV, 1.0441 eV, and 28.7 meV for the binding energy of the free exciton, the band gap, and the value for the LO phonon, respectively.
Comparison of the thermal stability of Si0.603Ge0.397/Si and Si0.597Ge0.391C0.012/Si superlattice structures
Authors: Zaumseil P. , Fischer G. G. , Brunner K. , Eberl K.
Published: July 2002

The annealing behavior of pseudomorphic Si0.603Ge0.397/Si and Si0.597Ge0.391C0.012/Si superlattice structures was studied in the temperature range between 750 °C and 900 °C. Carbon incorporation of 1.2% changes the thermal stability of SiGe structures significantly. It suppresses plastic relaxation due to an effective dislocation pinning. No relaxation of the SiGeC sample was observed during annealing up to 875 °C for 3 h. For comparison the SiGe sample relaxed at 800 °C. Carbon strongly increases the interdiffusion of Ge and Si. The activation energy of this diffusion process for a Ge content of 40% decreases from about 4.8 eV for the pure SiGe to about 2.0 eV with an additional C content of 1.2% assuming a neglectable diffusion of the carbon. This leads to a distinct modification of the Ge profile in the investigated temperature range.
Kerr-effect based magneto-optic imaging with sub-100 nm resolution (abstract)
Authors: Durkan C. , Lodder C. , Shvets I. V.
Published: July 2002

Magneto-optic imaging based on Faraday rotation with lateral resolution of about 60 nm was successfully demonstrated recently using scanning near-field optical microscopy.1 Magnetic contrast based on the Kerr effect with similar resolution still remains a challenge. Due to numerous applications of the Kerr effect this problem is of significant technical and scientific interest. Demonstration of such a contrast based on Kerr effect obtained using near-field optics is the subject of the present work. We have developed a reflection-mode scanning near-field optical microscope (SNOM) that is routinely capable of imaging with 30–50 nm resolution. It is based on a metal coated fiber probe with the light of a diode laser (λ=635 nm) coupled into it. Distance between the scanning probe and the sample is maintained constant at 5–10 nm using a shear force based feedback. Light reflected from the sample is collected with an elliptic mirror and a photomultiplier. We have studied the dependence of polarization of light reflected from the various nonmagnetic metal and dielectric surfaces upon the distance between the probe and the surface. Mechanisms responsible for the change in polarization of the reflected light are analyzed. Finally a periodic array of domains was written in a Co/Pt multilayer film using optical thermomagnetic recording. The domains were imaged using a magnetic force microscopy technique that indicated that the size of the domain was about 400 nm. The domains were then imaged using our reflection-mode SNOM. Features of domains smaller than 100 nm in size are clearly resolved. Values of conventional polar Kerr rotation are compared with ones detected using the SNOM.
Magnetic structure and electronic transport in permalloy
Authors: Nicholson D. M. C. , Butler W. H. , Shelton W. A. , Wang Yang , Zhang X.-G. , Stocks G. M. , MacLaren J. M.
Published: July 2002

Permalloy (Ni0.8Fe0.2) is an important alloy for magnetic devices. We present calculations of the electronic and magnetic structure of permalloy and of an interdiffused interface between permalloy and copper. We also present the results of calculations of the transport properties of permalloy. We find that the magnetic moments in permalloy are collinear, however, there may be noncollinear moments near an interface between permalloy and copper. We find that the calculated electrical conductivity is very sensitive to the details of the electronic and magnetic structure, however calculations which include relativistic effects yield a value for the conductivity that is in reasonable agreement with experiment.
Magnetic properties enhancement of nanocomposite Nd9.5Fe81.5B9 melt–spun ribbons by La and Cr substitutions
Authors: Chang W. C. , Wu S. H. , Ma B. M. , Bounds C. O.
Published: July 2002

The phase transformation and magnetic properties of nanocomposite (Nd0.95La0.05)9.5(Fe1−xCrx)81.5B9, where x=0, 0.033, 0.067, and 0.1, melt–spun ribbons have been studied. For Cr-free ribbons (i.e, x=0,) a slight substitution of La for Nd decreases the crystallization temperature of the over-quenched ribbons. Moreover, the (Nd, La)3Fe62B14 and (Nd, La)2Fe23B3 phases were found to coexist with (Nd, La)2Fe14B/Fe3B/α-Fe phases in the crystallized (Nd0.95La0.05)9.5Fe81.5B9 ribbons. The crystallization temperatures of (Nd0.95La0.05)9.5Fe1−xCrx)81.5B9 were found to increase with Cr concentration. The intrinsic coercivity of (Nd0.95La0.05)9.5(Fe1−xCrx)81.5B9 increased from 6.2 kOe for x=0 to 10.7 kOe for x=0.1: Transmission electron microscopy-energy dispersion analytical x-ray analyses indicated that the increase in intrinsic coercivity may be associated with the increase in Cr concentration around grain boundaries. A sample with Br=8.3 kG, H0=9.1 kOe,i and (BH)max=12.5 MGOe was obtained on (Nd0.95La0.05)9.5(Fe0.967Cr0.033)81.5B9 after appropriate thermal treatment.
Polarization anisotropies in the electric-field-dependent diffraction efficiency in Azo dye doped photoconducting electro-optic polymer
Authors: Nishida Fumito , Tomita Yasuo
Published: July 2002

The steady-state and transient behavior of the photoconducting electro-optic polymer, PVK:TNF:DR1:ECz, was analyzed with various writing and reading beam polarization configurations to elucidate the contribution of various effects including the photoisomerization process on the diffraction phenomenon at the wavelength of 632.8 nm. The effect of the applied field on the diffraction efficiencies was observed to be strongly dependent on the polarization states of the writing and reading beams. It was found that the electro-optic contribution dominated the diffraction phenomenon for the p-polarized writing and reading beams while the molecular reorientation effect dominated for the s-polarized writing and reading beams and when the writing beams are cross polarized. The diffraction grating formed via the photoisomerization process was confirmed to be refractive index grating instead of an absorption grating.
Observation of ion waves in two-dimensional particle simulation of field-assisted plasma expansion
Authors: Patel Kartik
Published: July 2002

We report the results of two-dimensional particle simulations (computer experiments) of finite plasma expansion between biased plane parallel electrodes. We show that the simulation produces results consistent with the existing one-dimensional analytical model. While the plasma expansion on the low-potential side is space-charge limited, on the opposite side it is due to ambipolar diffusion. The time-dependent simulated ion current to the electrode exhibits a modulation which has not been experimentally observed. This is identified to be a consequence of the oscillation in sheath front ion density which occurs because of the ion acoustic waves generated during the expansion. This modulation, which is greater at lower ion temperatures and nonuniform with respect to the electrode surface, can be used to estimate the transient number density in the plasma. Modifications to conventional experimental detection circuits which could help in the detection of these waves are presented.
Effect of extremely fine Y2BaCuO5 precipitates on the critical current density of melt-processed YBa2Cu3Ox
Authors: Sengupta S. , Shi Donglu , Luo J. S. , Buzdin A. , Gorin V. , Todt V. R. , Varanasi C. , McGinn P. J.
Published: July 2002

Based on previously developed melt processing methods, Y2BaCuO5 (211) precipitates with various size were obtained in YBa2Cu3Ox (123). In particular, a wide distribution of 211 size from 100 Å to 10 μm has been found to exist in the matrix of 123, and strongly effected the critical current density, Jc. An enhancement of Jc was always found to be associated with the presence of extremely fine 211 precipitates. The flux pinning by these precipitates can be understood by considering the interaction of flux lines with cavities. It was found that although the flux lines are strongly pinned by cavities, the effectiveness decreases with the increasing number of flux lines trapped by them.
Optical and structural characterization of InAs/GaSb superlattices
Authors: Su Y. K. , Lin C. L. , Chen S. M. , Chang J. R. , Jaw D. H.
Published: July 2002

InAs/GaSb superlattices sandwiched between conventional InAs layers were grown by low pressure metal organic chemical vapor deposition. Period and roughness of the superlattices were examined by field emission transmission electron microscopy. Room temperature infrared absorption spectra for InAs/GaSb superlattices were obtained by Fourier-transform infrared spectroscopy. The effects of varying the doping levels and thicknesses of the InAs sandwiching layers on the absorption spectra of InAs/GaSb superlattices were studied. It was found that by choice of suitable doping levels and cap/buffer thicknesses, the resulting fermi level equalization (as in normal homo or heterojunctions) thereby allowed the setting or “pinning” of the superlattice Fermi level to any desired value within the range made available by the original bulk material characteristics in conjunction with the doping conditions. When the thicknesses of the InAs sandwiching layers became less than 1 μm, the sandwiching effect and the intersubband transition decreased dramatically. The structure of the interfaces inside the superlattice was also studied. Energy dispersive spectroscopy was used to estimate interdiffusion conditions within the superlattice. The effects of different periods and purge gases on the absorption spectra were also studied.
Advancing metal–oxide–semiconductor theory: Steady-state nonequilibrium conditions
Authors: Passlack M. , Hong M. , Schubert E. F. , Zydzik G. J. , Mannaerts J. P. , Hobson W. S. , Harris T. D.
Published: July 2002

This article investigates steady-state nonequilibrium conditions in metal–oxide–semiconductor (MOS) capacitors. Steady-state nonequilibrium conditions are of significant interest due to the advent of wide-gap semiconductors in the arena of MOS (or metal–insulator–semiconductor) devices and due to the scaling of oxide thickness in Si technology. Two major classes of steady-state nonequilibrium conditions were studied both experimentally and theoretically: (i) steady-state deep depletion and (ii) steady-state low level optical generation. It is found that the identification and subsequent understanding of steady-state nonequilibrium conditions is of significant importance for correct interpretation of electrical measurements such as capacitance–voltage and conductance–voltage measurements. Basic implications of steady-state nonequilibrium conditions were derived for both MOS capacitors with low interfaces state density Dit and for oxide semiconductor interfaces with a pinned Fermi level. Further, a photoluminescence power spectroscopy technique is investigated as a complementary tool for direct-gap semiconductors to study Dit and to monitor the interface quality during device fabrication.
High-density crystalline quantum dots in blue emitting porous silicon
Authors: Chen Qianwang , Li X.-J. , Zhou G. E. , Zhu Jingsheng , Zhang Shuyuan , Jia Y. B. , Zhang Yuheng
Published: July 2002

We report on the results of small angle x-ray scattering and high resolution electron micrograph studies which reveal the structure of hydrothermally prepared porous silicon that emits blue light under photoexcitation. Our results constitute direct evidence that blue photoluminescence porous silicon includes high density silicon quantum dots. We show that these quantum dots are isolatedly dispersed in each amorphous SiO2 linear column standing freely on the silicon substrate. The size of individual quantum dots is about 2 nm.
The role of hydrogen and iron in silicon nitridation by ball milling
Authors: Li Z. L. , Williams J. S. , Calka A.
Published: July 2002

We have studied in detail the α-Si3N4 formation during ball milling of Si in NH3 and N2 environments and subsequent annealing. α-Si3N4 can be formed upon annealing after Si is milled in NH3, but no such phase is found for milling in N2. This difference is attributed to the role of H in embrittlement of the powder particles and to the subsequent introduction of Fe contamination into the Si powder. Our studies also show that the presence of Fe greatly enhances the nitridation reaction of as-milled Si powder. Fe silicide phases can be found after milling in NH3 and annealing, and the extent of silicide depends on the N content in the powder. In favorable cases, Fe can be removed from the α-Si3N4 powder by an acid leach.
Samarium-doped thin films of the Matlockite structure: Design, luminescence, and hole-burning experiments
Authors: Monnier A. , Schnieper M. , Jaaniso R. , Bill H.
Published: July 2002

The growth of thin films made from Samarium-doped alkaline earth fluoro halides (AEFH) of composition SrxCa1−xFCl:Sm2+ (0⩽x⩽1) is presented and the possibilities are studied to increase significantly the inhomogeneous width of the Sm2+ optical zero phonon transitions. The best films were obtained when grown with a molecular beam deposition (MBD) method involving two separate molecular beams: one for the alkaline earth fluoride, the other one for the alkaline earth halide (Cl or Br). The results demonstrate that the double beam MBD technique employed is able to produce pure and mixed Matlockite films with targeted composition. The results of mainly optical studies of the samarium f–f transitions and of other complementary techniques are used to assess the composition and homogeneity of the films. With the aid of a model the composition dependence of the positions of specific optical f–f emission lines is established. Their inhomogeneous linewidth is compared with that of corresponding emission lines obtained from bulk samples of the same chemical composition. The linewidths of the films are only slightly larger (∼1.5–2 times). Thus, the film morphology cannot be exploited to increase substantially the inhomogeneous broadening of the luminescence lines. A novel approach to increase this broadening was devised, theoretically modeled and successfully tested by using multilayered sandwich-type thin films in conjunction with interdiffusion. Films with cation disorder of composition SrxCa1−xFCl (x=0.5 /0/ 0.5/ 0/..) were grown. The D15→F07 Sm2+ emission linewidth is thereby increased to 70 cm−1 full width half maximum. A width of 100 cm−1 may be obtained within the composition range x=0, x=1. This represents an enhancement by a factor of 3–5 in comparison with the largest values obtained in appropriate mixed bulk AEFH of constant composition. A factor >50 is gained in comparison with pure bulk AEFH hosts. The room temperature (RT) homogeneous linewidths, on the other hand, are similar to those found in bulk mixed crystals of constant composition. The intrafilm host cation diffusion during film growth of the sandwich structures was further studied. A diffusion constant of 2⋅10−19 m2 s−1 for the Sr and Ca ions was deduced from this observation. These films are among the most promising materials for optical mass data storage through RT hole burning.
Characterization of metallic impurities in Si using a recombination-lifetime correlation method
Authors: Itsumi Manabu , Sato Yoshiyuki , Imai Kazuo , Yabumoto Norikuni
Published: July 2002

Correlation between p-type and n-type Si recombination lifetimes enables us to roughly but rapidly predict the isolation of iron, copper, and stainless-steel components. We examine this correlation method in detail and show that the ratio of p-type Si and n-type Si lifetimes is not 1:1 but 0.67:1 for iron and 1:0.67 for copper. Some kind of precipitates may be responsible for these ratios. The advantages of the correlation method are quantitatively demonstrated for wafer cleaning, furnace processes, and plasma etching processes.
Surface state density distribution of semiconducting diamond films measured from the Al/CaF2/i-diamond metal-insulator-semiconductor diodes and transistors
Authors: Yun Young , Maki Tetsuro , Kobayashi Takeshi
Published: July 2002

Diamond metal-insulator-semiconductor diodes and field-effect transistors (MISFETs) have been prepared using CaF2 gate insulator and nondoped (in some cases, boron was doped) diamond homoepitaxial films. The resultant capacitance-voltage (C-V) curves and drain current-drain voltage (ID−VD) curves strongly depended on the amount of oxygen contamination of diamond surface. From analyses of C-V and ID−VD curves, it was found that the oxygen contamination induced the surface states with two distribution peaks locating very near the valence band edge and at the energy of ∼1 eV from the valence band edge. Although fluorination of oxygen-terminated diamond surface proceeded to a certain extent during CaF2 deposition at the elevated temperatures in vacuum, it still allowed surface state formation of about ∼1014/cm2 eV near the valence band edge due to uncompleted exchange of oxygen by fluorine atoms and easy penetration of residual oxygen in the chamber through the CaF2 insulator at elevated temperatures. Reduced-oxygen process by diamond surface passivation with hydrogen (hydrogenation) and room temperature deposition of CaF2 greatly improved the surface stability, and consequently, the surface state density near the valence band edge was reduced to ∼1012/cm2 eV. In this manner, the effective hole mobility of ∼10 cm2/V s was obtained from the diamond MISFET, which can be well compared with the surface Hall mobility of 35 cm2/V s.
Recovery of time-dependent dielectric breakdown lifetime of thin oxide films by thermal annealing
Authors: Furukawa Taisuke , Yuuki Akimasa , Ono Kouichi
Published: July 2002

Electrical properties of thin silicon dioxide films have been investigated for samples that suffered from the Fowler–Nordheim (F–N) stress and subsequent annealing. The time-dependent dielectric breakdown (TDDB) lifetime for samples after annealing >400 °C was found to be longer than that without anneal; about 60% of the amount of damage responsible for the lifetime was annealed out at a temperature of typically 800 °C for 30 min. On the other hand, capacitance–voltage (C–V) measurements indicated that trapped charges were almost annealed out even at a temperature of 300 °C for 30 min. Moreover, the reinjection of F–N current showed that the trapping sites of holes and electrons which are electrically neutral remained after the annealing of trapped charges at temperatures >300 °C. It follows that the recovery of TDDB lifetime presently observed through annealing at temperatures >400 °C was caused by the anneal of neutral trapping sites created by F–N stresses.
Double relaxation oscillation superconducting quantum interference devices with gradiometric layout
Authors: van Duuren M. J. , Brons G. C. S. , Adelerhof D. J. , Flokstra J. , Rogalla H.
Published: July 2002

Double relaxation oscillation superconducting quantum interference devices (DROSs) with a gradiometric signal SQUID and either a reference SQUID or a reference junction will be presented in this article. The devices are user friendly, particularly those with a reference junction. Because of the large flux-to-voltage transfer of ∂V/∂Φ=0.7–1 mV/Φ0, the devices can be operated in a flux locked loop based on direct voltage readout without loss of sensitivity. The typical white flux noise of the DROSs amounts to √SΦ=5–6μΦ0/√Hz, which corresponds to an energy resolution ε=SΦ/2Lsq≃200 h. Coupled to an external planar first-order gradiometer, a white magnetic field sensitivity of √SB<2 fT/√Hz was measured inside a magnetically shielded room.
Electro-absorptive properties of interdiffused InGaAsP/InP quantum wells
Authors: Li E. Herbert , Choy Wallace C. H.
Published: July 2002

The effects of Group III and Group V interdiffusions with a varied as-grown well width and P concentration in the quaternary InGaAsP quantum well material have been theoretically studied. Interesting features of multiple mini-well profiles, generated by interdiffusion induced compressive and tensile strains, have been obtained and varying envelope overlapping of the electron-hole wave functions has been observed. The results show that the interdiffusion of the Group III elements with a well width of 10 nm offers a wide adjustability of the operation wavelength, enhances Stark shift, and reduces absorption loss, although they bear the shortcomings of low electro-absorption and contrast ratio. Several methods are proposed here to recover the contrast ratio with a maximum improvement of 66%. For the Group V interdiffusion of a 10-nm-wide as-grown well, a low absorption loss and a large Stark shift will result, while that of a narrowed well can widen the band-edge wavelength adjustability with a large electro-absorption. These results are important for the development of electro-absorptive InGaAsP/InP diffused quantum well modulators.
Microstructural evolution of Al-Cu thin-film conducting lines during post-pattern annealing
Authors: Kang S. H. , Morris J. W.
Published: July 2002

This work reports a statistical analysis of the evolution of polygranular segment lengths during high-temperature annealing of Al(Cu) thin-film interconnects with quasi-bamboo microstructures. To create samples of Al(Cu) lines that could be imaged by transmission electron microscopy without breaking or thinning, the lines were deposited on electron-transparent silicon nitride films (the “silicon nitride window” technique). The microstructures of the lines were studied as a function of annealing time and temperature. In particular, the distribution of polygranular segment lengths was measured. The results show that the longer polyglranular segments are preferentially eliminated during post-pattern annealing. As a consequence, the segment-length distribution narrows monotonically during annealing, and changes in shape. The preferential loss of the longest polygranular segments leads to a dramatic increase in resistance to electromigration failure.
Intrinsic Josephson effect devices of TI-2212 thin films
Authors: Yan S. I. , Fang L. , Si M. S. , Wang J.
Published: July 2002

Intrinsic Josephson effect devices from Tl2Ba2CaCu2O8 (Tl-2212) thin films were investigated. The device was produced by epitaxially growing a Tl-2212 thin film on a LaAlO3 substrate with the surface cut at a small angle to the LaAlO3(001) plane, and by patterning a microbridge in the proper direction. The I–V characteristics of the microbridges exhibit large hysteresis at low temperatures, and the temperature dependence of the critical current Ic(T) is in good agreement with the theoretical Ambegaokar–Baratoff relation for superconductor–insulator–superconductor (SIS) junctions. The I–V curves also show multibranches for longer microbridges.