bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity of molten Pd40Ni40P20
Authors: Tsang K. H. , Lee S. K. , Kui H. W.
Published: July 2002

The viscosity of molten Pd40Ni40P20 was measured from 980 to 1160 K by capillary flow method. At temperatures below its liquidus ∼1030 K, the measurement was carried out with the molten specimen immersed in anhydrous boron oxide flux in order to inhibit the formation of small crystallites. In the presence of crystallites, the viscosity values were scattered and also were considerably larger than those of crystallite free liquid. The viscosity of crystallite free molten Pd40Ni40P20 can be described by the following Vogel–Fulcher equation: ln η=−4.072+1310.1/(T−551). The curve here cannot be joined to those viscosity data of Volkert and Spaepen [Mater. Sci. and Eng. 97, 449 (1988)] of the same system near the glass transition temperature by a single Vogel–Fulcher equation of constant parameters. Earlier, Polk and Turnbull [D. E. Polk and D. Turnbull, Acta Metall. 20, 493 (1972)] determined the viscosity of molten Au77Ge13.6Si9.4 also by the capillary method. Their results were compared with the current work and it was found that the principle of corresponding states apparently holds here and the reduced temperature is defined as T/Tg.
Observation of liquid-solid phase transitions using a shear horizontal acoustic plate mode sensor
Authors: Hoummady M. , Bastien F.
Published: July 2002

We present a method for characterizing liquid-solid phase transitions by using an acoustic shear horizontal (SH) plate mode sensor. The sensor consists of a Y-cut quartz plate provided with suitable interdigital transducers on the lower surface. To study the temporal evolution of a phase transition, the liquid is deposited in a thin layer on the upper surface and the SH mode attenuation is observed as a function of time during a programed temperature change. With this sensor the theoretical time resolution is about 1 μs. Experimental results are presented for the liquid-solid transition for deionized water, tap water, and 90%/10% mixture of tap water and ethanol, measured with an instrument time resolution of 50 ms.
LiNbO3 thin-film optical waveguide grown by liquid phase epitaxy and its application to second-harmonic generation
Authors: Tamada Hitoshi , Yamada Atsuo , Saitoh Masaki
Published: July 2002

LiNbO3 thin-film optical waveguides with high crystallinity and good surface morphology have been grown on 5 mol % MgO-doped Z-plate LiNbO3 substrates by liquid-phase epitaxy using Li2O-V2O5 flux. A small lattice mismatch less than 4×10−3 Å in the X axis, a small linewidth of 11s in an x-ray rocking curve, and a perfect mirror surface are realized by choosing a melt composition. Ordinary refractive index no at a wavelength of 0.6328 μm is unchanged (2.287) with melts of different compositions, but extraordinary refractive index ne can be changed from 2.205 to 2.192 or less by increasing Li2O in the melt with V2O5 fixed at 40 mol %. The optical absorption loss at a wavelength of 0.5145 μm caused by V incorporated from the flux is significantly reduced from 25 to 1.6 dB/cm by O3 annealing for 1 h at 600 °C. Efficient second-harmonic generation of TE0(1.064 μm) →TM0(0.532 μm) for a single-poled film is observed by a temperature-tuning method. The mechanism of self poling and domain inversion which were revealed by the present research is discussed.
A novel experimental procedure for removing ambiguity from the interpretation of neutron and x-ray reflectivity measurements: ‘‘Speckle holography’’
Authors: Sivia D. S. , Hamilton W. A. , Smith G. S. , Rieker T. P. , Pynn R.
Published: July 2002

The analysis of neutron or x-ray reflectivity data to obtain density profiles close to surfaces is akin to the notorious phaseless Fourier problem, well known in many fields such as crystallography. It is a difficult problem because a highly nonlinear transform relates the density profile to the data; this results in the existence of several very different solutions, which are also hard to find. A novel experimental procedure is presented, the analogue of astronomical speckle holography, which is designed to eliminate the ambiguity problems inherent in traditional reflectivity measurements. The theoretical basis of this procedure is explained, and it is illustrated with a simple example using both simulated and real experimental data.
Magnetic properties of RTiCo11 compounds with the ThMn12 structure
Authors: Ohashi K. , Ido H. , Konno K. , Yoneda Y.
Published: July 2002

Magnetic properties of RTiCo11 (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) compounds with the ThMn12 structure were investigated in the temperature range from 4.2 to 1400 K. The Curie temperatures of this series exceed 1000 K and the Co atomic moments were found to take the values ranging from 0.99 to 1.80 μB, which depend on R. The easy magnetization direction of RTiCo11 was found to be axial(c∥) for R except being planar for R=Sm and Er. This result suggests that the R sublattice with a positive Stevens factor demonstrates planar anisotropy. The Co sublattice anisotropy constant was estimated to be K1 = 7.5 × 106 erg/cc at room temperature from measurements on YTiCo11. By subtracting K1 of YTiCo11 from K1 of DyTiCo11, the anisotropy constant of the Dy sublattice was obtained to be 5.7×106 erg/cc. Spin reorientation was also observed in RTiCo11 with R=Pr, Nd and Dy, which are considered to be an axial to planar one with increasing temperature.
Electrical properties of polycrystalline chalcopyrite AgInS2 films
Authors: Hattori K. , Akamatsu K. , Kamegashira N.
Published: July 2002

Polycrystalline chalcopyrite AgInS2 films 2.0–3.5 μm thick have been formed on glass substrates. Resistivities, carrier concentrations, and Hall mobilities are measured at room temperature. These quantities are shown to be changed greatly by annealing under maximum S pressure for 1 h at different temperatures. Resistivities of 1–104 Ω cm and carrier concentrations of 2×1015–3×1020 cm−3 are obtained in n-type films. In p-type films, resistivities are found to be higher than 1×104 Ω cm, and carrier concentrations are less than 3×1015 cm−3. The effects of vacancies and interstitials of Ag, In, and S atoms are discussed to explain the observed changes in the electrical properties of the films. Owing to various structural imperfections, Hall mobilities are found to be less than 2 cm2/V s in both n- and p-type films. Au-p-type AgInS2 Schottky diodes have been fabricated. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics are measured at room temperature. The ideality factor is evaluated as about 1.63. In the frequency range 10−4–1 MHz, large frequency dispersion is observed in the C–V curves, and explained in terms of the response of deep defect levels.
Thresholds of impact ionization in semiconductors
Authors: Bude J. , Hess K.
Published: July 2002

Using a first-principles approach to the ionization rate, we re-examine some of the prejudices concerning impact ionization and offer a new view of the role of thresholds. We also discuss trends of ionization coefficients related to the energy band structure for silicon and a number of III-V compounds.
Optothermal evaluation of oil film thickness on water
Authors: Krapez J. C. , Cielo P.
Published: July 2002

A thermally stimulated spectroscopic approach is described for remote thickness evaluation of a crude oil film on water, with possible applications to airborne monitoring of oil spills. The oil-water medium is irradiated by a laser pulse which is partially absorbed within the oil film. The corresponding temperature rise of the different material components is probed by two infrared detectors operating over different spectral bands, and a correlation is established between a combination of the detector outputs and the oil film thickness in the range below 1 mm. Computations and experimental results are presented for different wavelengths of excitation and detection.
Isothermal ramped field-desorption of water from metal surfaces
Authors: Stintz A. , Panitz J. A.
Published: July 2002

It is shown that water vapor deposited onto metal surfaces between 80 and 130 K can be isothermally desorbed by applying a ramped electric field. At a ramp rate of ∼1 MV/cm/s the desorption field strength for physisorbed layers of amorphous ice on tungsten and iridium surfaces is ∼80 MV/cm. As the ice layers desorb in the presence of the high electric field, positive ions are formed which are detected. During this process, the ice exhibits properties of an electrical conductor or a semiconductor.
Nonequilibrium solidification in undercooled melts of the alloy Ag-39.9 at. % Cu
Authors: Walder S. , Ryder P. L.
Published: July 2002

Melts of the eutectic alloy Ag-39.9 at. %Cu were cooled below the liquidus temperature by the glass flux method. The solidification behavior was followed by measuring the temperature change (recalescence), and the resulting microstructures were investigated by optical and electron microscopy. Up to a certain critical undercooling ΔT*≊76 K, the recalescence rate is less than 100 K s−1, and a feathery, lamellar microstructure is formed, with typically one or two growth centers. When the undercooling exceeds ΔT*, a sudden increase in the recalescence rate (up to 104 K s−1) is observed, and the microstructure consists of a dendritic, irregular two-phase component surrounded by a lamellar eutectic. The critical undercooling temperature coincides with the temperature (T0) at which the Gibbs free energies of the liquid and the supersaturated Ag-Cu solid solution are equal. The critical behavior is therefore thought to be due to the formation of this metastable phase. A model is proposed to explain the observed behavior and microstructures.
Energy transfer in Tm:Eu codoped fluorozirconate fiber
Authors: Tohmon Genji , Sato Hisanao , Ohya Jun , Fujita Toshihiro
Published: July 2002

Excited state absorption-induced up conversion at 452 and 480 nm in Tm:Eu:ZBLAN fiber was observed for a single pump laser source at 650 nm. Compared to Tm:ZBLAN fiber, codoping with Eu3+ increases the 452 nm emission while the 480 nm emission is reduced. The effective lifetime of the terminal 3H4 level of the 452 nm transition in Tm3+ is shortened by energy transfer to the 7F6 level in Eu3+. This energy transfer scheme is useful in discriminating radiative transitions.
Characterization of the performance of 1–3 type piezocomposites for low-frequency applications
Authors: Zhang Q. M. , Cao Wenwu , Wang H. , Cross L. E.
Published: July 2002

In general, the piezoelectric ceramic and polymer in a 1–3 type composite will have different deformations when subjected to an external field. How each component deforms, to a large extent, determines the performance of the composite. Based on the force equilibrium condition, an elastic model is introduced to analyze the strain profiles of these composites, and the theoretical results are in quantitative agreement with the strain profiles measured on several composites using a double beam ultradilatometer. The results obtained provide quantitative information on how various parameters in a composite affect the performance of the composite. Furthermore, a scheme is proposed for evaluating the strain profile of a 1–3 type composite under a hydrostatic pressure using a double beam dilatometer.
The growth of highly mismatched InxGa1−xAs (0.28≤x≤1) on GaAs by molecular-beam epitaxy
Authors: Chang Shou-Zen , Chang Tien-Chih , Lee Si-Chen
Published: July 2002

The material quality of InxGa1−xAs epilayers with 0.28≤x≤1 grown on a highly mismatched GaAs substrate and the initial growth mechanisms have been studied in detail. Cross-sectional transmission electron microscopy and double-crystal x-ray diffraction analysis of the InxGa1−xAs (x≥0.28) layers indicate that although three-dimensional island growth was found in all cases, their dislocation generation mechanisms are quite different. To study the strain relaxation process in the initial growth stage and its effects on the generation of the dislocations, 15-monolayer-thick InxGa1−xAs was grown on the GaAs. It was found that for the x=0.5 case, the thin InGaAs layer formed many small-size coherent islands; while for x=1, they changed to lower-density and much larger size relaxed islands. This shows that the growth of the highly mismatched InxGa1−xAs/GaAs heterojunction (x≥0.28) is a kinetically limited strain relaxation process. The large lattice mismatch (7.16%) between InAs and GaAs favors the early relaxation of InAs islands before they coalesce; this explains why the material quality of the InAs epilayer is better than that of InxGa1−xAs with x=0.28, 0.5, and 0.75 in spite of its larger lattice mismatch.
A comparison between different numerical methods used to solve Poisson’s and Schroedinger’s equations in semiconductor heterostructures
Authors: Abou-Elnour Ali , Schuenemann Klaus
Published: July 2002

A comparison between different numerical methods which are used to solve Poisson’s and Schroedinger’s equations in semiconductor heterostructures is presented. Considering Schroedinger’s equation, both the Rayleigh–Ritz method and the finite difference method are examined. The accuracy and the computational speed are investigated as a function of both the mesh size and the number of Rayleigh–Ritz functions and the numerical results are compared with analytical solutions for special cases. To solve Poisson’s equation, direct and iterative methods are implemented and the advantages and limitations of each method are discussed. The previous methods are used to solve Poisson’s and Schroedinger’s equations self-consistently in typical heterostructures to obtain the wave functions, the carrier distribution, and the subband energies.
Characteristics of a distributed Bragg reflector for the visible-light spectral region using InGaAlP and GaAs: Comparison of transparent- and loss-type structures
Authors: Sugawara H. , Itaya K. , Hatakoshi G.
Published: July 2002

Distributed Bragg reflectors (DBRs) for the visible-light spectral region constructed by InAlP/InGaAlP pairs and InAlP/GaAs pairs, grown by metalorganic chemical-vapor deposition, have been investigated with the point of comparing optical and structural properties. In the case of the InAlP/InGaAlP stacked type, a reflectivity above 80% has been realized; however, the bandwidth decreased by shortening the peak wavelength. The reflection spectrum of the InAlP/GaAs DBR showed a wide-band characteristic and provided a relatively high reflectivity to the green region in spite of the absorption loss of the GaAs layers. These results were in good agreement with theoretical calculations considering the absorption loss and refractive index of individual stacked layers. These DBRs have also been confirmed to have good uniformity and periodicity through cross-sectional transmission electron microscopy and x-ray rocking curve analysis. Good electrical conductivity through these DBRs has been obtained for the n-type structure.
Nonlinear optical materials based on MBe2BO3F2 (M=Na,K)
Authors: Mei Linfeng , Wang Yebin , Chen Chuangtian , Wu Bochuang
Published: July 2002

MBe2BO3F2 (M=Na,K) have been discovered to be nonlinear optical (NLO) materials for UV applications. They have relatively large NLO coefficients: deff is about 2.5 times as large as that of KH2PO4 (λ=1079 nm, Nd:YAP laser), the UV cutoff wavelengths are as short as 155 nm, and they have a moderate birefringence of nearly 0.10. Their structures are characterized by an infinite sheet which is formed by six-membered rings [Be2BO6F2] with Be-O and B-O edges in common. Such structures are favorable for good NLO properties. These NLO properties make MBe2BO3F2 promising candidates for vacuum UV NLO materials.
Neutron-diffraction and Mössbauer effect study of the preferential silicon site occupation and magnetic structure of Nd2Fe14−xSixB
Authors: Marasinghe G. K. , Pringle O. A. , Long Gary J. , James W. J. , Xie D. , Li J. , Yelon W. B. , Grandjean F.
Published: July 2002

A neutron-diffraction study of Nd2Fe14−xSixB has shown that silicon preferentially occupies the 4c site in the transition-metal sublattice in Nd2Fe14B. Silicon also exhibits a moderate preference for the 8j1 site, is almost excluded from the 16k2 site, and avoids the 16k1, 8j2, and 4e sites. The silicon site occupancy is correlated with a preference for a silicon atom to have rare-earth atoms in its coordination environment. The Mössbauer spectra of Nd2Fe14−xSixB have been fit with a model which takes into account the distribution of near-neighbor environments of an iron atom due to the presence of silicon. These fits show that the substitution of silicon in the near-neighbor environment of an iron atom primarily influences the long-range contributions to the hyperfine field experienced by the iron. The mechanism for the increase in the Curie temperature when silicon is added to Nd2Fe14B-type magnets is more subtle than previously believed, but can be explained by the relative decrease in the proportion of short iron-iron bonds when silicon is substituted for iron.
Mass and energy analysis of gaseous species in NF3 plasma during silicon reactive ion etching
Authors: Konuma M. , Bauser E.
Published: July 2002

Neutral molecules and positive ions, extracted directly from the reaction zone during reactive ion etching of silicon in NF3 plasma, have been identified by quadrupole mass spectrometry. The main etching end products are SiF4 molecules and SiF+3 ions. Reactive species that contribute to the etching are atomic F radicals and F+2 molecular ions. Most of the positive ions in the plasma hold NF+2 ions and this facilitates etching of negatively biased Si by bombardment. Likewise, the kinetic energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain range of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3 pressure of 6.7 Pa, the characteristic mean ion energy of 4 eV at an rf power of 10 W increases to 20 eV by increasing the rf power to 90 W.
Magnetic anomalies in single crystal Fe3O4 thin films
Authors: Margulies D. T. , Parker F. T. , Berkowitz A. E.
Published: July 2002

Fe3O4 thin films were reactively sputtered onto 〈100〉 and 〈110〉 MgO substrates. X-ray diffraction data indicate single crystal Fe3O4 films under a tensile stress. Magnetization data show good agreement with bulk Fe3O4 for Ms, but also show the presence of a large anisotropy component manifest in the lack of saturation in fields up to 70 kOe. Conversion electron Mössbauer spectroscopy data taken at zero field also show good agreement with bulk Fe3O4 for the values of the hyperfine fields and isomer shifts of the two Fe3O4 sites, indicate good stoichiometry, but indicate the presence of a large anisotropy component randomizing the moments. In-plane torque measurements on 〈100〉 oriented Fe3O4 are consistent with bulk Fe3O4 magnetocrystalline anisotropy. However, in-plane torque measurements on 〈110〉 oriented Fe3O4 show the presence of a uniaxial anisotropy superimposed on the crystalline terms. This anisotropy, modeled as being due to the stress induced by epitaxy, changes the easy axis from the 〈111〉 directions to the 〈110〉 directions in the (110) plane. Since the directional dependence of the crystal and stress anisotropy are measurable the ‘‘large anisotropy’’ component is considered to be random.
A new structure of torque sensors using thin pickup head—Use of mutual coupling modulation
Authors: Sasada I. , Koga F.
Published: July 2002

A new structure is proposed for the magnetoelastic torque sensors using a pair of figure-eight coils as a pickup. Mutual coupling between two figure-eight coils is used as a measure of torque applied to a shaft. The mutual coupling is governed by torque-induced anisotropic permeability at the surface of the shaft. Basic characteristics of the torque sensor are examined using a tempered steel shaft of 25 mm in diameter and a pair of 25-turn figure-eight coils. Sensitivity was 16 μV/N m and hysteresis was 1.3% at the coil excitation condition of 60 kHz, 0.8 A (RMS). Exciting power needed to reduce hysteresis is much smaller with this structure than with previous methods using self-inductance as a measure of torque.
Remanent magnetization in the diluted Ising antiferromagnet Fe0.6Zn0.4F2
Authors: Djurberg C. , Mattsson J. , Nordblad P.
Published: July 2002

The field, H≤5 T, and temperature, T≥2 K, dependence of the remanent magnetization μ of the diluted Ising antiferromagnet Fe0.6Zn0.4F2 has been investigated utilizing a superconducting quantum interference device magnetometer. The results at low temperatures, where there is no growth of random field domains after the field removal, are analyzed according to μ=AHx(T ln t/t0)−Ψ+B, where the two terms are domain wall and volume contributions to the remanent magnetization, respectively. It is found that Ψ decreases continuously with decreasing temperature, and reaches a value of ≊0.15 at 3 K. The field exponent x is found to decrease with increasing temperature, attaining values between 2 and 3. The results show a more complex behavior of the low-temperature remanent magnetization than a model proposed by Nattermann and Vilfan which predicts constant values of the exponents: Ψ≊0.4 and x≊2.
The lattice strains in a specimen (hexagonal system) compressed nonhydrostatically in an opposed anvil high pressure setup
Authors: Singh Anil K. , Balasingh C.
Published: July 2002

A general expression has been derived for the lattice strain which corresponds to the measurement by x-ray diffraction method on a specimen (hexagonal system) compressed nonhydrostatically in an opposed anvil high pressure setup. The expressions relevant to the different diffraction geometries used in high pressure experiments with opposed anvils emerge as the special cases of this equation. The effect of the deviatoric stress component on the lattice parameters derived from the interplanar spacings measured at high pressure is discussed.
Depletion layer width in undoped a-Si:H Schottky barrier revealed by reverse bias photocurrent
Authors: Maeda Keiji , Chiyoda Wataru , Umezu Ikurou , Kuroe Atsushi
Published: July 2002

Reverse bias photocurrent of undoped a-Si:H Schottky barrier was investigated under excitation with uniformly absorbed light. Dependence of the photocurrent on the applied voltage V gives unambiguous dependence of the depletion layer width W on voltage V, which cannot be obtained by conventional capacitance-voltage measurements for undoped a-Si:H. There are two voltage ranges giving parabolic dependence of W with different apparent ionized donor densities due to a spatial variation of the space-charge density. These observations are considered to be characteristic of semiconductors with major deep gap states of large energy width. The experimental results were analyzed using a simple model of energy distribution of the gap state density by dividing the depletion layer into two. In one of these deep depletion occurs. The variation of the apparent W-V relation observed upon lowering the exciting photon energy was analyzed to be related to a decrease in the absorption coefficient with the applied voltage due to an emptying of the initial states of the gap state absorption. Results of the analysis are consistent with the electron-spin density observed in the same undoped a-Si:H.
Silicon roughness induced by plasma etching
Authors: Pétri Richard , Brault Pascal , Vatel Olivier , Henry Daniel , André Elie , Dumas Philippe , Salvan Franck
Published: July 2002

A parametric study of single-crystal silicon roughness induced by an SF6 plasma has been carried out by means of atomic force microscopy. An helicon source (also called resonant inductive plasma etcher) has been used to study the relation between plasma parameters and subsequent surface damage. The surface damage has been examined in terms of height roughness analysis and in terms of spatial (lateral) extent of the surface roughness. The central result is that roughness scales with the ratio of the ion flux over the reactive neutral flux (J+/JF), showing the combined role of both ionic and neutral species. At low ion flux, the neutrals smooth the surface, while at higher ion flux, they propagate the ion-induced defects, allowing the roughness to be enhanced. Influences of other parameters such as exposure duration, ion energy, or substrate temperature have also been quantified. It is shown that the roughness growth is well described by an empirical law: rms∝(1/√E)(J+/JF)ηtβ, with η≊0.45 and β≊1 (rms is the root mean square of the roughness). In other respects, we analyze the data with a Fourier transform analysis. The main advantage is to minimize noise and to separate the magnitude of the roughness, the lateral correlation length on which the roughness is growing, and the behavior of short and long range roughness. The results are identical to the rms analysis, especially, the above scaling law. The time evolution of the lateral correlation length follows a scaling law (which is not accessible by means of the rms) leading to a fractal dimension of 2.67. Also is observed a variation of the short range roughness as a function of the substrate bias voltage. Consequence for further scaling down of integrated circuits is called to mind.
Production of semi-insulating layers in n-doped InP by Fe implantation
Authors: Carnera A. , Gasparotto A. , Tromby M. , Caldironi M. , Pellegrino S. , Vidimari F. , Bocchi C. , Frigeri C.
Published: July 2002

A detailed study of Fe implantation and damage annealing in indium phosphide is presented. The technological goal was to obtain thermally stable semi-insulating layers in n-type InP. Different characterization techniques were employed, including structural (x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy), chemical (secondary ions mass spectrometry), and electrical (current-voltage) measurements. Both undoped and n-type (Sn) doped substrates were implanted with Fe doses ranging from 5×1011 to 2.2×1014 cm−2 and annealed at a temperature of 650 °C. The high doses used to compensate n+ doping caused amorphization of the material. The reordering process of the amorphous layers and its influence on the Fe redistribution properties were studied in detail. The activation of the implanted Fe atoms after annealing was derived. Although the recovery process of the amorphized layer appears to be rather complex, our results show that good crystal quality and full compensation can be reached also for n+ doped substrates, leading to resistivity values above 2×107 Ω cm, even starting from an initial doping level as high as 1.4×1018 cm−3.
Control of ordering in Ga0.5In0.5P using growth temperature
Authors: Su L. C. , Ho I. H. , Stringfellow G. B.
Published: July 2002

The kinetic processes leading to ordering in Ga0.52In0.48P have been studied by observing the effects of substrate misorientation (0°–9°), growth rate (0.1–0.5 μm/h), and substrate temperature (570–670 °C) during growth. The ordered structure and degree of ordering are determined using transmission electron microscopy and photoluminescence (PL) spectroscopy. Low growth rates were used for samples with misorientations of 0°–9° toward the [1̄10] lattice direction to elucidate the ordering mechanism; however, due to the long times required to grow layers thick enough for PL characterization (≊1 μm), at a temperature of 670 °C the samples became less ordered with increasing misorientation angle. This was attributed to a disordering annealing process occurring during growth which leads to disorder. In order to reduce the rate of this annealing process, the growth temperature was reduced from 670 to 570 °C. At this temperature, a growth rate of 0.5 μm/h produces material with an increasing degree of order as the angle of substrate misorientation is increased from 0° to 9°. This shows that the kinetics of the ordering process are assisted by an increasing density of [110] steps on the surface.
B-site order and infrared reflectivity in A(B′B″)O3 complex perovskite ceramics
Authors: Reaney I. M. , Petzelt J. , Voitsekhovskii V. V. , Chu F. , Setter N.
Published: July 2002

Complex perovskite A(B′B″)O3 ceramics with various degrees of B-site order have been structurally and spectroscopically characterized by means of x-ray diffraction, transmission electron microscopy, and infrared reflectivity. In Ba(Fe1/2Nb1/2)O3 and Pb(Fe1/2Nb1/2)O3, no order could be detected whereas Pb(In1/2Nb1/2)O3, Pb(Mg1/3Nb2/3)O3, and Pb(Sc1/2Ta1/2)O3 (unannealed) all exhibited weak reflections associated with small ordered regions Pb(Sc1/2Ta1/2)O3 was also prepared by appropriate heat treatment in the fully ordered form and exhibited strong maxima arising from the ordered superlattice in both electron and x-ray diffraction. The infrared reflectivity (30–4000 cm−1) revealed correlation between the degree of ordering and appearance of the extra mode in the 260–320 cm−1 range assigned to B′–B″ vibrations. Despite an apparently low volume fraction of ‘‘ordered material’’ in ‘‘partially ordered’’ samples of Pb(Sc1/2Ta1/2)O3, the extra mode was observable. It is suggested that infrared spectroscopy is sensitive to short-range ordering down to the nm range which is proposed to exist in between the small regions of order.
Theoretical analysis of the spin-density distributions in Y2Fe17N3 and Y2Fe17C3
Authors: Ching W. Y. , Huang Ming-Zhu , Zhong Xue-Fu
Published: July 2002

The electronic structures and spin-density distributions in Y2Fe17N3 and Y2Fe17C3 are calculated using the self-consistent spin-polarized orthogonalized-linear-combination-of-atomic-orbitals method. The N or C atoms are assumed to occupy the (9e) sites in the rhombohedral structure. The Fe (18f) and N or C at the (9e) site form covalent bonds which result in a very nonspherically symmetric spin-density distribution. The calculation shows a reduced moment for the Fe (18f) sites due to doping. However, the moments at other sites are increased due to lattice expansion. There are some differences in the spin-density distribution between N and C at the (9e) site. By comparing with the results of calculation on the pure Y2Fe17 at different volumes, changes in moment enhancement and density of states at the Fermi level due to lattice expansion alone and that due to the chemical effect of introducing N or C are separated.
Photoconductive spectroscopy of diamond grown by chemical vapor deposition
Authors: Allers L. , Collins A. T.
Published: July 2002

The photoconductivity of diamonds grown by chemical vapor deposition has been studied in the near infrared and visible spectral regions. The dominant photoconductive response has a threshold at approximately 1.5 eV. There is additional sharp structure in the region extending 165 meV to higher energy from the threshold, where 165 meV is the energy of the longitudinal optical (LO) phonon in diamond. It has also been found that there are minima in the photoconductivity spectrum at energies which are multiples of the energy of the LO phonon from the threshold energy. These minima have been associated with the decay of carriers to the bottom of the band by rapid emission of LO phonons. The optical absorption spectra of these diamonds show previously undocumented, sharp lines between 1.3 and 1.5 eV. These features are due to absorption to excited states of the same defect which is giving rise to the photoconductivity threshold at 1.5 eV. The sharp structure in the one-phonon region of the photoconductivity spectrum has been associated with capture to these excited states by the emission of LO phonons. Similar structure in the same region of the absorption spectrum has been attributed to Fano resonances—interference effects caused by the interaction of bound states with a continuum of states
Influence of discharge production conditions, gas pressure, current intensity and voltage type, on SF6 dissociation under point–plane corona discharges
Authors: Belarbi A. , Pradayrol C. , Casanovas J. , Casanovas A. M.
Published: July 2002

The study of the formation of Sulfur Hexafluoride (SF6) dissociation products under point to plane corona discharges was carried out at PSF6=300 kPa using different discharges production conditions (50 Hz ac voltage, dc negative polarity voltage, mean discharge current intensity Ī varying between 2 and 45 μA for dc negative polarity voltage), for two plane electrode materials (aluminum and stainless steel), and moisture levels (200 and 2000 ppmv H2O). The stable gaseous by-products formed (SO2F2, SOF4, SOF2, and S2F10) were assayed by gas-phase chromatography. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions whatever the SF6 pressure (100–300 kPa), discharges intensity (Ī) and voltage type studied. An effect of the increase of SF6 pressure up to 300 kPa was mainly observed for S2F10 and corresponds to a greater formation of this compound with PSF6. The influence of the mean discharge current intensity on SF6 by-product formation carried out for a transported charge of 1 C showed that for Ī≤10 μA, the effect varies according to the compound considered and depends on the water content of the SF6 and/or on the plane electrode material, whereas for Ī≳10 μA, the levels of the four compound studied hardly vary with the current. Comparison of results obtained under ac and dc voltage for a cumulated charge of between 0.5 and 11 C showed that (SO2F2+SOF4) and SOF2 were formed in larger quantities with ac than with dc, unlike S2F10 for which the opposite effect was observed.
Sm2Fe17 interstitial magnets (invited)
Authors: Müller K.-H. , Cao Lei , Dempsey N. M. , Wendhausen P. A. P.
Published: July 2002

Various processing routes for making permanent magnets based on interstitially modified Sm2Fe17 have been recently developed. Zn bonding of coarse grained Sm2Fe17N3 gives coercivities μ0JHc as high as 2.2 T. Effective methods to prepare highly coercive Sm2Fe17N3 powders for polymer bonding are mechanical alloying and rapid quenching. With the very simple method of additional milling of coarse grained nitrided powders we achieved μ0JHc≊1.5 T. A coercivity up to 3.5 T has been achieved by a modified HDDR procedure, reducing the particle size of the starting material by milling prior to the hydrogenation–disproportionation–desorption–recombination (HDDR) treatment. This is attributed to a better control of two critical parameters, namely grain size and the amount of unrecombined α-Fe accompanying the intermediate TbCu7 structure-type phase. Resin bonded HDDR-Sm2Fe17N3 magnets show an unexpected high initial susceptibility. This may be due to a strong magnetic interaction of the grains. To develop coercivity in Sm2Fe17Cy≳1 obtained by gas–solid reactions of Sm2Fe17 the same methods as those applied to Sm2Fe17N3 can be successfully used. Fully dense magnets with a coercivity up to 1.5 T were made from the interstitially as well as substitutionally modified compound Sm2Fe15Ga2C2 by hot pressing of highly coercive powders.
Giant nonlinear magneto-optical Kerr effects from Fe interfaces (invited)
Authors: Rasing Th. , Koerkamp M. Groot , Koopmans B. , Berg H. v.d.
Published: July 2002

Second harmonic generation from magnetic materials is shown to lead to a nonlinear magneto-optical Kerr effect that can be orders of magnitude larger than its linear equivalent. The origin of this effect can be found in the differences between the linear and nonlinear solutions of the optical wave equations and in the symmetry properties of the corresponding optical tensors. Applications for the study of magnetic surfaces, thin films, and multilayers will be discussed.
Growth twins in nanocrystalline SnO2 thin films by high-resolution transmission electron microscopy
Authors: Zheng J. G. , Pan Xiaoqing , Schweizer M. , Zhou F. , Weimar U. , Göpel W. , Rühle M.
Published: July 2002

Growth twins in nanocrystalline SnO2 thin films with grain size 5–50 nm have been investigated by high-resolution transmission electron microscopy. They show the {101}〈101〉 geometry, metal atom mirror symmetry, and slight distortion of oxygen atoms. Multiple twins and step twin boundaries with a density about 1015 m−2 were frequently observed in the films. It appears there are tin interstitials at step twin boundaries and, hence, electronic donors associated with the interstitials.
Band-gap engineering in CdS/Cu(In,Ga)Se2 solar cells
Authors: Topič Marko , Smole Franc , Furlan Jože
Published: July 2002

Using a numerical device simulation program, the band-gap engineering in CdS/Cu(In,Ga)Se2 solar cells is examined. The device physics of different design concepts is analysed. Normal band-gap grading improves performance, especially due to the additional quasi-electric field, and the analysis showed that the best results are achieved if the grading extends from the highest band-gap value at the back up to the space charge region. The double grading concept does not yield further improvement, because the front grading—even if located in the space charge region—repels the minority carriers (electrons) away from the CdS interface, and consequently, the fill factor drops significantly. Notch structures in the base also exhibit lower performance than the uniform band-gap base due to the lower open-circuit voltage and poorer fill factor. Therefore, the best results are achieved by a normal grading in a Cu(In,Ga)Se2 base from the edge of the space charge region to the back contact.
Micromechanics of randomly oriented ellipsoidal inclusion composites. Part II: Elastic moduli
Authors: Luo Jie , Stevens R.
Published: July 2002

The elastic moduli of composites containing randomly oriented ellipsoidal inclusions are derived, calculated from the average stress and the average strain in the matrix and the inclusions, obtained using a modified Eshelby model. The quantitative expressions for the elastic moduli of the composite are obtained in relation to the volume fraction, the shape, and the elastic moduli of the inclusions. Specific cases are discussed: First, the elastic moduli of the materials containing randomly oriented penny-shaped microcracks are derived and compared with those obtained by Budiansky and O’Connell [Int. J. Solids Struct. 12, 81 (1976)] and Nemat-Nasser and Hori. The general expressions for the elastic moduli of multiphase inclusion composites and the effect of porosity or in the form of isolated voids on the elastic moduli of homogeneous materials and inclusion containing composites are derived. Experimental results have been employed to compare the predictions with engineering materials.
Properties of niobium–titanium superconducting wires with Nb artificial pinning centers
Authors: Heussner R. W. , Nunes C. Bormio , Lee P. J. , Larbalestier D. C. , Jablonski P. D.
Published: July 2002

Artificial pinning center (APC) Nb 47 wt % Ti composite wires containing 24 vol % Nb pins were characterized as the wire diameter was reduced. As the nominal pin diameter dp was reduced from 165 to 15 nm, the nominally round pins transformed into ribbons with a relatively wide distribution in thickness, as compared to the α-Ti ribbons in optimized, conventionally processed Nb 47 wt % Ti. The maximum in the bulk flux pinning force Fp of 25 GN/m3 (4.2 K, 2.5 T) occurred at dp=40 nm, for which the measured Nb ribbon thickness ranged from 1 to 16 nm. This Fp value was about one third higher than that found in the best conventional Nb 47 wt % Ti. The upper critical magnetic field Hc2, measured by magnetization, decreased from 10.3 to 9 T as the Nb pins became proximity-effect coupled to the matrix. To better compare APC and conventional wires, we measured the properties of the best APC wire at a reduced temperature so that its Hc2 was the same as Hc2(4.2 K) for Nb 47 wt % Ti. The peak value of Fp was then 36 GN/m3 at 3 T, almost twice the maximum value yet reported for conventional Nb–Ti (∼19 GN/m3 at 5 T). In spite of the pinning force curve remaining sharply peaked at lower fields, the equalized 5 T critical current density was 4600 A/mm2, some 25% higher than the best values of conventional Nb–Ti. These properties demonstrate the strong potential of APC composites.
SiC formation at the interface of polyimide Langmuir–Blodgett film and silicon
Authors: Ji Mingrong , Zhu Jingsheng , Ma Maosheng , Wu Jianxin , Liu Xianming , Jin Bangkun , Yang Beifang , He Pingsheng , Ruan Yaozhong
Published: July 2002

X-ray photoelectron spectroscopy has been used to explore the process of the interaction between the polyimide film made by the Langmuir–Blodgett method and the substrate Si(111). It is evident that the process includes three stages: The polymer degrades below temperature of about 500 °C resulting in some hydrocarbon species on the surface; at higher temperatures the residual hydrocarbons convert to some state of elemental carbon and then diffuse into the substrate to form ‘‘C–Si alloy’’ which is regarded as a precursor of SiC formation; SiC starts to form at about 700 °C and grows at higher temperatures.
The fluorescence of Nd3+ in lead borate and bismuth borate glasses with large stimulated emission cross section
Authors: Saisudha M. B. , Koteswara Rao K. S. R. , Bhat H. L. , Ramakrishna J.
Published: July 2002

The stimulated emission cross section σp for the 1060 nm transition of Nd3+ in lead borate and bismuth borate glasses has been determined from fluorescence measurements. The compositional dependence of σp, which has been evaluated using radiative transition probability, refractive index of the host glass, effective fluorescence linewidth, and position of the band, with PbO/Bi2O3 content is investigated. The σp values of the 1060 nm band of Nd3+ for lead borate and bismuth borate glasses are found to be in the range 2.6–5.7×10−20 cm2 at 298 K and 3.0–6.3×10−20 cm2 at 4.2 K. The σp values are comparatively large suggesting the possible utilization of these materials in laser applications.
Origin of internal field and visualization of 180° domains in congruent LiTaO3 crystals
Authors: Gopalan Venkatraman , Gupta Mool C.
Published: July 2002

We have observed a strong correlation between the internal fields and the infrared absorption spectra of OH− ions in congruent LiTaO3 crystals. After reversal of the direction of polarization (Ps) of the crystal by an electric field at room temperature, (a) the internal field is antiparallel to Ps, (b) the relative intensities of the infrared absorption bands of OH− ions (at ∼3462, ∼3476, and ∼3490 cm−1) change, and (c) the 180° domain walls are visible under a light microscope. Annealing the domain-reversed crystal at 200 °C or above and cooling back to 25 °C has the following effects: (a) The internal field realigns parallel to Ps. (b) The shape of the OH− spectrum returns to the shape observed before domain reversal. The time–temperature dependence of the shape of the infrared absorption spectrum of OH− ions also shows the same characteristics as that of the realignment process for the internal field. (c) The optical domain wall contrast becomes extremely weak. Infrared absorption studies suggest that domain inversion as well as the heating of LiTaO3 crystal induce structural changes that are similar in nature. It is proposed that the origin of internal fields lies in OH− ions and/or nonstoichiometric point defects in the LiTaO3 crystals. We also explain the optical 180° domain wall contrast based on internal fields.
New Fick’s law for self-diffusion in liquids
Authors: Yang Fuqian , Li James C. M.
Published: July 2002

While the same atomic mechanism is usually assumed in both viscous flow and diffusion in a liquid, viscous flow is found much faster (by many orders of magnitude) in all situations studied where the mass transfer is caused by pressure gradients. A detailed study shows that Fick’s law must be modified for self-diffusion in liquids.
Glow dynamics in a semiconductor-gas discharge image converter
Authors: Portsel L. M. , Astrov Yu. A. , Reimann I. , Purwins H.-G.
Published: July 2002

Transient phenomena which accompany the breakdown of gas in a semiconductor-gas discharge (SGD) system with 100 μm interelectrode distance have been studied experimentally and with numerical calculations. This system serves as the basis for an image converter operating in the infrared (IR) spectral region. The experiments are done for a cryogenic discharge in helium at a temperature close to that of liquid nitrogen. Depending on specific experimental conditions, oscillatory or aperiodic modes approaching to the steady-state current are observed after breakdown has been induced by a step-like voltage pulse. Numerical calculations of transient phenomena were performed for experimental conditions within the framework of the Townsend model, taking into account direct ionization, Penning ionization and secondary emission of electrons from the cathode. The main features of discharge kinetics obtained are in accordance with experimental data. At the same time, with the steady-state discharge current density varying from j= 1×10−4 A/cm2 to 7×10−2 A/cm2, inconsistencies between experimental and theoretical results are observed. A possible reason for this discrepancy is related to the complex process of secondary ionization at the cathode under the conditions of a cryogenic discharge and to the dependence of the secondary electron emission factor on current density, that has been neglected in constructing the model. The results obtained are considered from the viewpoint of the response time of gas-discharge IR image converters.
High performance glow discharge a-Si1−xGex:H of large x
Authors: Wickboldt Paul , Pang Dawen , Paul William , Chen Joseph H. , Zhong Fan , Chen Chih-Chiang , Cohen J. David , Williamson D. L.
Published: July 2002

Radio frequency glow discharge chemical vapor deposition has been used to deposit thin films of a-Si1−xGex:H which possess optoelectronic properties that are greatly improved over any yet reported in the range of x⩾0.6. These films were deposited on the cathode (cathodic deposition) of an rf discharge. Their properties are assessed using a large variety of measurements and by comparison to the properties of alloys conventionally prepared on the anode (anodic deposition). Steady state photoconductivity measurements yield a quantum-efficiency-mobility-lifetime product, ημτ, of (1–3)×10−7 cm2 V−1 for 1.00⩾x⩾0.75 and (6–10)×10−8 cm2 V−1 for 0.75⩾x⩾0.50, and photocarrier grating measurements yield ambipolar diffusion lengths several times greater than previously obtained for alloys of large x. It is confirmed that the improvements in phototransport are not due to a shift in the Fermi level. In fact, results of recent measurements on lightly doped samples strongly suggest that for these cathodic alloys neither photocarrier is dominant [(μτ)e≈(μτ)h]. The improvements are attributed in large part to the reduction of long range structural heterogeneity observed in x-ray scattering and electron microscopy, and partly to the reduction in midgap state density. In spite of the superior properties, an assessment of the data of the cathodic alloys suggests that alloying introduces mechanisms detrimental to transport which are not present in a-Si:H or a-Ge:H. The Urbach tail width is 42±2 meV for cathodic a-Ge:H and 45±2 meV for cathodic a-Si1−xGex:H and is constant with x. From differences in the band edges and tails we infer that the atomic bond ordering is different between the cathodic and anodic alloys. For a given composition the cathodic alloys have roughly an order of magnitude lower midgap state density than do the anodic alloys, and both midgap densities increase exponentially with x, consistent with defect creation models from which the lower midgap density can be attributed to a larger band gap and decreased valence band tail width. A photoluminescence peak is observed with an intensity roughly an order of magnitude greater than for the anodic alloys, and a significantly different peak energy. Section VII E provides an overview of the results and conclusions. The improved properties of these alloys have significant implications for current and future device applications.