bluuebunny/crossref_metadata_2025 huggingface dataset:
Explicitly correlated second-order Møller–Plesset methods with auxiliary basis sets
Authors: Klopper Wim , Samson Claire C. M.
Published: July 2002

In explicitly correlated Møller–Plesset (MP2-R12) methods, the first-order wave function is expanded not only in terms of products of one-electron functions—that is, orbitals—but also in terms of two-electron functions that depend linearly on the interelectronic coordinates rij. With these functions, three- and four-electron integrals occur, but these integrals can be avoided by inserting a resolution of the identity (RI) in terms of the one-electron basis. In previous work, only one single basis was used for both the electronic wave function and the RI approximation. In the present work, a new computational approach is developed that uses an auxiliary basis set to represent the RI. This auxiliary basis makes it possible to employ standard basis sets in explicitly correlated MP2-R12 calculations.
Resistivity of a composite conducting polymer as a function of temperature, pressure, and environment: Applications as a pressure and gas concentration transducer
Authors: Lundberg B. , Sundqvist B.
Published: July 2002

The resistivity of a commercial carbon-filled composite conducting polymer (ET-Semicon■) has been measured as a function of temperature between 80 and 400 K and under pressure up to 1.5 GPa (15 kbar). Large changes in resistivity were observed. The resistivity was also very sensitive to the presence of certain solvents and hydrocarbons. The results are explained as percolation effects caused by changes in volume due to pressure, thermal expansion, or dissolved solvents. The material studied is found to have a wide range of potential applications for pressure measurements and as a transducer for gas or liquid concentration.
Scattering of radiation off random density irregularities in a laser-produced plasma
Authors: Dragila R.
Published: July 2002

The effect of scattering laser radiation penetrating to the critical region off random density irregularities present in the underdense region of a laser-produced plasma is investigated. Two approaches are used to clarify the effect and the result is applied to the problem of plasma density profile modification by the ponderomotive force.
Preparation of c-axis oriented PbTiO3 thin films and their crystallographic, dielectric, and pyroelectric properties
Authors: Iijima Kenji , Tomita Yoshihiro , Takayama Ryoichi , Ueda Ichiro
Published: July 2002

Highly c-axis oriented and epitaxial PbTiO3 thin films were grown on MgO single crystals and epitaxial Pt film substrates by the rf-magnetron sputtering method. The films with a 98% c-axis orientation rate were obtained under low deposition rate (<20 Å/min) and low gas pressure (∼1 Pa) using a PbO-rich target. Phase transition of the PbTiO3 thin film was studied by high-temperature x-ray diffraction. It was found that the c-axis of the tetragonal phase was parallel to the substrate just below Tc and the c-axis becomes perpendicular to the substrate with lowering of temperature. These films show high resistivity (∼1010/Ω cm). It was found that significant pyroelectric currents are detected on all specimens without poling treatment. The polarization directions of the films are the same in all specimens. One of these films had a low relative dielectric constant of 97 and a high pyroelectric coefficient of 2.5×10−8 C/cm2 K without poling treatment. These films will be suitable for applications such as pyroelectric infrared detector and piezoelectric transducer.
Effects of grain size, hardness, and stress on the magnetic hysteresis loops of ferromagnetic steels
Authors: Kwun H. , Burkhardt G. L.
Published: July 2002

Effects of grain size, hardness, and stress on the magnetic hysteresis loops of AISI 410 stainless steel and SAE 4340 steel specimens were investigated experimentally. It was observed that both hardness and stress significantly influenced the hysteresis loops, while the grain size had a minimal effect. For each material, the mechanically harder specimen was more difficult to magnetize. Upon application of uniaxial stress, the magnetic induction increased under tension and decreased under compression, with the sides of the hysteresis loops becoming inclined more toward the vertical axis under tension and the horizontal axis under compression. For each material, the effects of stress on the hysteresis loops were greater for the mechanically softer specimen and exhibited an inverse relationship to the hardness. The effects of stress were not dependent on grain size.
The influence of oxygen and other impurities on the crystallization of NiZr2 and related metallic glasses
Authors: Altounian Z. , Batalla E. , Strom-Olsen J. O. , Walter J. L.
Published: July 2002

The role of oxygen and other impurities on the crystallization characteristics of Ni-Zr glasses near the composition NiZr2, as well as for FeZr2, CoZr2, and NiHf2, has been investigated. For NiZr2 glasses with 1 at. % oxygen, the first crystallization product is the metastable E93 structure with a =1.227 nm instead of the equilibrium C16 structure. A similar effect is found for samples containing ≳3 at. % B. For FeZr2, CoZr2, and NiHf2 the first crystallization product is also E93 structure, even with very small levels of oxygen (≤0.2 at. %). The formation of the E93 structure is always accompanied by an increase in the electrical resistivity, an increase which transmission electron microscopy shows is intrinsic to the phase and unrelated to crystallite size. For Ni36.5Zr63.5 and Ni42Zr58 the crystallization is also accompanied by an increase in electrical resistance and the evolution of a crystal structure similar to the E93 structure in the size of the unit cell and packing fraction but with a different space group. We propose that the formation of these structures is triggered by atomic size nuclei of ZrO2, (or ZrB2) quenched in from the melt.
An equivalent network for resistance and temperature coefficient of resistance versus temperature and composition of thick resistive films
Authors: Kusy A.
Published: July 2002

Two types of elementary resistances in thick resistive films have been considered: (i) constriction resistance RC determined by the bulk properties of conducting material and by the geometry of constriction, and (ii) barrier resistance RB determined by the parameters of a thermally activated type of tunneling process and by the geometry of the metal-insulator-metal unit. On this basis a resistance network composed of a large number of the two types of resistances has been defined. The network has been considered as being equivalent to thick resistive film (TRF) from the point of view of the resistance and temperature coefficient of resistance (TCR). The parameters of this network have been evaluated by the computer-aided approximation of the experimental data found for RuO2-based TRFs. On the basis of the equations derived for the network as well as the results of the approximation process, it can be concluded that the small values of the network TCR result from the superposition of the TCR of the conducting component βC and of the temperature coefficient of barrier resistance αB. In this superposition βC is attenuated (by 1–2 orders of magnitude), while αB is attenuated by only few percentages. The network has been found to be strongly barrier dominated.
Multiply stripped ion generation in the metal vapor vacuum arc
Authors: Brown I. G. , Feinberg B. , Galvin J. E.
Published: July 2002

We consider the charge state distribution of ions produced in the metal vapor vacuum arc plasma discharge. A new kind of high current metal ion source in which the ion beam is extracted from a metal vapor vacuum arc plasma has been used to obtain the spectra of multiply charged ions produced within the cathode spots. The cathode materials used and the species reported on here are: C, Mg, Al, Si, Ti, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, In, Sn, Gd, Ho, Ta, W, Pt, Au, Pb, Th, and U; the arc current was 200 A for all measurements. Charge state spectra were measured using a time-of-flight method. In this paper we report on the measured charge state distributions and arc voltages and compare the distributions with the predictions of a theory in which ionization occurs in the cathode spots via stepwise ionization by electron impact.
Measurements of empty cell gap for liquid-crystal displays using interferometric methods
Authors: Yang K. H.
Published: July 2002

In order to determine the empty cell gap of a liquid-crystal (LC) cell to better than 1% accuracy, the empty LC cell has been modeled as an optical medium consisting of seven layers with an air gap representing the true cell gap in the middle layer. The given index of refraction and thickness for each layer, optical reflections as a function of wavelength ranging from 500 to 650 nm have been calculated. To simulate the experimental measurement, the apparent cell gaps were deduced from reflection peaks and compared with the true cell gaps in the region of 5–10 μm. It was found that the difference between the apparent and true cell gaps was larger than 0.66 μm using a 0.1-μm polyimide as an aligning layer coated on top of the transparent indium-tin-oxide electrode of 0.04 μm in thickness. This modeling is applicable to three interferometric methods commonly used for the measurement of an empty cell gap.
Operating characteristics and comparison of photopyroelectric and piezoelectric sensors for trace hydrogen gas detection. II. Piezoelectric quartz-crystal microbalance sensor
Authors: Christofides Constantinos , Mandelis Andreas
Published: July 2002

A 6-MHz piezoelectric quartz-crystal microbalance coated with palladium electrodes has been used under STP gas flow-through conditions to detect hydrogen adsorption at low concentrations (<5% in nitrogen) where anomalous behavior has been observed due to interferences from other ambient or impurity gases (mainly O2). A systematic study showed that a concentration of 0.4% hydrogen produced no frequency shift in the sensor due to counterbalancing effects from other gases. Thus sensor sensitivity limits were established at 0.5% hydrogen, which is ca.∼200 times lower than the photopyroelectric (P2E) sensor (part I). The hydrogen selectivity of the piezoelectric sensor was found to be inferior to that of the P2E device.
Preisach modeling of magnetostrictive hysteresis
Authors: Adly A. A. , Mayergoyz I. D. , Bergqvist A.
Published: July 2002

Preisach-type models are suggested for the description of strain hysteresis of magnetostrictive materials. It is pointed out that the strain hysteresis has some peculiar properties in comparison with magnetic hysteresis. These peculiarities of strain hysteresis are discussed in detail along with the identification problem for these models.
A one-dimensional, self-consistent numerical solution of Schrödinger and Poisson equations
Authors: Serra A. M. Cruz , Santos H. Abreu
Published: July 2002

A self-consistent, one-dimensional, numerical solution of Schrödinger and Poisson equations has been obtained. To solve Schrödinger equation, instead of the conventional finite difference approach, we start by dividing the space in intervals of constant potential energy, in which the solution type is well known. Next we match the wave functions and their first derivatives, divided by the effective mass on each side of the potential steps. This approach is very efficient on finding the eigenvalues in structures with large regions of almost constant potential energy such as quantum well structures or heterojunctions. Validation is presented by comparing the exact solution of Schrödinger equation for a triangular well with that obtained by our method. Poisson equation is solved considering the deep (DX) and shallow centers assuming a donor with one ground state and two excited states. Applications to isotype n-GaAs/AlxGa1−xAs graded heterojunctions show that the density of the two-dimensional electron gas (2DEG) is almost independent of graduality when this is smaller than about 200 Å and that DX centers may lower the 2DEG concentration by as much as 20%.
Metal-dopant-compound formation in TiSi2 and TaSi2: Impact on dopant diffusion and contact resistance
Authors: Probst V. , Schaber H. , Mitwalsky A. , Kabza H. , Hoffmann B. , Maex K. , Van den hove L.
Published: July 2002

The refractory metal disilicides TiSi2 and TaSi2 were investigated for their usefulness as dopant diffusion sources. During furnace annealing and rapid thermal processing, strong decomposition reactions occur between the dopants D (B or As) and the respective silicide (MSi2) to form MxDy compounds. With the help of special sample preparation methods and various analytical techniques, the compound phases TiB2, TiAs, TaB2, and TaAs were unambiguously detected. The fraction of freely diffusing B in TaSi2 is determined to be below 5% of the total dose; by far, the major part of the dopant is bound within the TaB2 phase detected. Careful sample preparation and analysis of secondary-ion-mass spectrometry profiles is necessary to avoid artifacts caused by these compound particles. The MxDy-compound formation has detrimental consequences: The solubility of arsenic and even more of boron in TiSi2 and TaSi2 is limited to rather low-concentration levels (e.g., B in TaSi2: 4 × 1018 B/cm3 < CB(900 °C) < 1.6 × 1019 B/cm3) and the outdiffusion into poly- or monocrystalline silicon is strongly retarded. Also, the low interface dopant concentrations achievable result in unacceptably high values of contact resistance. The observations on metal-dopant- (M-D-) compound formation are demonstrated to agree well with the predictions from thermodynamic calculations on the respective M-Si-D system. The effects on junction formation are compared to the case of WSi2 and CoSi2, which, from a parallel study, are known not to form compounds. In all cases these comparisons support our statements on the tremendous impact of M-D-compound formation, because much improved data on diffusion and junction formation were obtained for CoSi2 and WSi2. The same holds for a comparison on contact resistances for silicide diffused junctions, which was performed for TiSi2 and CoSi2.
Ablation of polymethyl methacrylate films by pulsed (ns) ultraviolet and infrared (9.17 μm) lasers: A comparative study by ultrafast imaging
Authors: Srinivasan R.
Published: July 2002

Ablation of the surface of a polymethyl methacrylate film by single pulses of 193 or 248 nm laser radiation (∼20 ns) or 9.17 μm laser radiation (∼170 ns) was studied by photographing the emergence of the plume by a pulse (≤1 ns; 596 nm) of visible laser light. The dynamics of the blast wave was similar in the ultraviolet (UV) and in the infrared (IR) but the composition of the product mixture was entirely different. Essentially the only product that IR laser pulses gave was a volatile refractive vapor which is presumed to be the monomer, methyl methacrylate (MMA). UV (248 nm) laser pulses gave gaseous products with very little MMA and a large fraction of solid polymer as has been documented in the literature. Examination of the solid material in the plume at high magnification showed that it was structured in the early phase (≤3 μs) of its emergence from the surface but at longer times melted and formed liquid drops in the region above the surface of the polymer. UV (193 nm) laser pulses yielded gaseous products which included MMA. The solid material in the plume did not show any sign of melting. Gas production at the surface as well as in the first few micrometers below the surface appears to be an important factor in the dynamics of the plume in UV ablation. The relevance of photochemical and photothermal mechanisms in laser ablation is discussed in the light of the chemistry of the products seen in this study.
Deformation of an electrorheological chain under flow
Authors: Chen Tian-jie , Zhang Xuesong , Zitter R. N. , Tao R.
Published: July 2002

The simplest of all structures in an electrorheological fluid is a single chain of dielectric particles. The shape of a chain deformed by flow in a square tube is observed and is found to be reasonably consistent with a model of chain force based on point-dipole nearest-neighbor interactions.
Red to blue up-conversion emission of Tm3+ ions in Yb3+-doped glass ceramic
Authors: Xu Wu , Denis J. P. , Özen G. , Kermaoui A. , Pellé F. , Blanzat B.
Published: July 2002

A detailed study of the spectroscopic properties of PbF2+GeO2+WO3 glass ceramics doped with Tm3+ and codoped with Tm3+ and Yb3+ ions upon 680 nm dye laser light excitation has been made. The absorption, up-conversion emission, excitation, and time-resolved spectra were measured as a function of TmF3 and YbF3 concentrations at room temperature. An enhancement of blue emission centered at 478 nm in the codoped sample was observed. The optium concentrations of TmF3 and YbF3 for this blue emission are about 0.2 and 15 mol %, respectively. It is suggested that the results are due to energy transfer between Yb3+ and Tm3+ ions. Measured oscillator strengths and radiative rates for several transitions are compared with calculated values using the Judd–Ofelt theory with reasonable agreement between theory and experiments for sample doped with Tm3+ ions.
Photoinduced hysteresis changes and optical storage in (Pb,La)(Zr,Ti)O3 thin films and ceramics
Authors: Dimos D. , Warren W. L. , Sinclair M. B. , Tuttle B. A. , Schwartz R. W.
Published: July 2002

Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 thin films and bulk ceramics are shown to exhibit two distinct, but related types of photoinduced changes in their hysteresis behavior: (1) a photoinduced suppression of the switchable polarization and (2) a photoinduced voltage shift. Both effects give rise to stable and reproducible hysteresis changes and, thus, either could be the basis of an optical memory. Both phenomena can be explained by trapping of photogenerated charge at domain boundaries to minimize internal depolarizing fields. The space-charge field that causes the voltage-shift effect is primarily due to the migration and subsequent trapping of electrons. However, the thickness dependence of the voltage shift implies that the trapped charge is not confined to the interface. The voltage-shift kinetics exhibit a stretched-exponential dependence, whereas the polarization-suppression effect follows an exponential time dependence. However, both effects exhibit similar relaxation times. In addition, the relaxation time for the voltage-shift effect decreases with increasing light intensity according to a power-law relationship, τ∝I−n, where 0.67<n<0.75.
Microstructural properties of silicon powder produced in a low pressure silane discharge
Authors: Dutta Joydeep , Bacsa Wolfgang , Hollenstein Ch.
Published: July 2002

Silicon powders produced in a low pressure silane plasma show varying structural properties depending on the location of collection of the powders in the reactor. This is revealed by high resolution transmission electron microscopy, infrared and Raman spectroscopy. The particulates are found to consist either of heterogeneously distributed amorphous and crystalline phases or of nanoscale particles with amorphous and molecular like spectral features as found from the Raman spectroscopic studies. Infrared spectra show clustered silicon-hydrogen phases and the presence of oxidized phases in the powder, upon exposure to atmosphere. Phonon confinement effects due to the nanometer size and expansive strain is observed in the vibrational Raman spectra. The average particle size estimated from the observed phonon quantum confinement corresponds with the particle sizes observed by high resolution electron microscopy if strain contributions are included. Annealing at temperatures as low as 300 °C leads to Raman vibrational band similar to crystalline silicon.
Identification of plasma-sheath resonances in a parallel-plate plasma reactor
Authors: Annaratone B. M. , Ku V. P. T. , Allen J. E.
Published: July 2002

A new, unexpected resonance has been observed in radio frequency, parallel plate plasma reactors. It has been explained using a linear model by analogy with the series resonance of probes. This discovery may be used in different ways; as a diagnostic, to measure the plasma density with high accuracy and, possibly, in improving the plasma performance in the low-pressure range.
High-pressure arcs as vacuum-atmosphere interface and plasma lens for nonvacuum electron beam welding machines, electron beam melting, and nonvacuum ion material modification
Authors: Hershcovitch Ady
Published: July 2002

Atmospheric pressure plasmas can be used to provide a vacuum-atmosphere interface as an alternative to differential pumping. Vacuum-atmosphere interface utilizing a cascade arc discharge was successfully demonstrated and a 175 keV electron beam was successfully propagated from vacuum through such a plasma interface and out into atmospheric pressure. Included in the article are a theoretical framework, experimental results, and possible applications for this novel interface.
Substrate effects on the structure of epitaxial PbTiO3 thin films prepared on MgO, LaAlO3, and SrTiO3 by metalorganic chemical-vapor deposition
Authors: Foster C. M. , Li Z. , Buckett M. , Miller D. , Baldo P. M. , Rehn L. E. , Bai G. R. , Guo D. , You H. , Merkle K. L.
Published: July 2002

Epitaxial PbTiO3 films were prepared by metalorganic chemical-vapor deposition on MgO(001)-, SrTiO3(001)-, and LaAlO3(001)-oriented substrates. Four-circle x-ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single-crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c-axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo-cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°-domain (a-axis) structures with a critical thickness hc for domain formation below the detection level of our experiments (hc≥100 Å). Together, these structural defects result in a low RBS channeling yield reduction. In contrast, films grown on SrTiO3(001) substrates showed no tilting of the c-axis grains and a minimum RBS channeling yield of as low as ∼3%. In addition, we observed that below a critical film thickness of hc∼1500 Å, 90° domain formation was completely suppressed resulting in a nearly perfect single-crystal structure.

The refractive indices and optical birefringence of the films were measured as a function of wavelength using the film-prism coupling method. Both the ordinary and extraordinary refractive indices for films grown on MgO(001) and LaAlO3(001) were higher than that of single-crystal PbTiO3; however, the optical birefringence of films grown on MgO(001) was reduced from that of the bulk. For films grown on SrTiO3(001), the ordinary refractive index was very close to that of single-crystal PbTiO3. We correlate the refractive index values and the reduced birefringence to the degree of residual strain and the volume fraction of 90° domains in the samples, respectively.
The vibrating sample magnetometer: Experiences of a volunteer (invited)
Authors: Foner S.
Published: July 2002

On its 40th anniversary, I describe how the vibrating sample magnetometer (VSM) was developed and, later, how the very low frequency VSM, a flux-integration device, was developed. The important features of the moving sample technique, detection coil symmetry, calibration, sensitivity, and image effects are discussed briefly. Some VSM adaptations discussed include operation at 3He and dilution refrigerator temperatures, at high hydrostatic pressures, in superconducting, high-power water-cooled and hybrid magnets, for very low frequency ac susceptibility, and with SQUID detectors.
Growth of nanometer-size metallic particles on CaF2(111)
Authors: Heim K. R. , Coyle S. T. , Hembree G. G. , Venables J. A. , Scheinfein M. R.
Published: July 2002

Fe, Co, and Ag particles grown on various CaF2 substrates have been studied using ultrahigh vacuum scanning electron microscopy with nanometer resolution. Fe and Co show a very high nucleation density which is remarkably independent of deposition temperature in the range 20<T<300 °C, on both bulk CaF2(111), and on thin CaF2(111) films grown on Si(111). This feature is characteristic of nucleation at defect sites with a high trapping energy. An atomistic nucleation model has been extended to cover this case. The comparison with experiment requires adsorption, pair binding, and defect trapping energies all to be around 1 eV. The trapping sites occupy 1% of the surface, and are thought to be chemical (F-vacancy, oxide, or hydroxide) in nature. In contrast, the growth of Ag on the same substrates shows a more usual nucleation and growth pattern, though the growth of Ag on Fe islands shows interesting features which are discussed. A self-similar coalescence model is tested using the data obtained. The agreement is excellent for Ag, while Co and Fe show the expected deviations due to limited surface diffusion around the islands.
Influence of sample thickness on the performance of photostrictive ceramics
Authors: Poosanaas P. , Dogan A. , Thakoor S. , Uchino K.
Published: July 2002

Ferroelectric materials with high photovoltaic properties are of interest for new optical devices such as photostrictive ceramic actuators. However, fabrication of these devices requires development of materials exhibiting high photovoltage and photocurrent. In pursuit of these high performance photostrictive materials, the present research examines the influence of illumination intensity, degree of polarization, and sample thickness on the photostrictive response of WO3 doped lanthanum-modified lead zirconate titanate (Pb, La)(Zr, Ti)O3 ceramics prepared by oxide mixing process. A model for calculating the optimum sample thickness for maximum photostrictive response is proposed. This model agrees well with experimental results, and should be useful in designing photostrictive devices.
Characterization of charge trapping in insulating films by a scanning electron microscope
Authors: Bigarré J. , Hourquebie P.
Published: July 2002

An electrostatic model has been developed to describe the mirror image formation in the scanning electron microscope mirror method and to calculate the trapping ability by using a semi-infinite sample. However, some results have shown that it is not possible to use this simple model in the case of film insulators. Thus, in this article, we propose an analysis of the electrostatic potential, including image charge effects, to calculate the trapping ability of films. The theoretical expression of the mirror curves is compared to experimental results on polymer films having a minimum thickness of 35 μm.
Growth temperature dependence of GaS thin films on GaAs(001) surface
Authors: Islam A. B. M. O. , Tambo T. , Tatsuyama C.
Published: July 2002

The growth of GaS films on GaAs(001) surfaces by using thermal evaporation of layered-compound GaS has been investigated by Auger electron spectroscopy, low-energy electron-loss spectroscopy (LEELS), x-ray photoemission spectroscopy (XPS), and atomic force microscopy (AFM) as a function of deposition temperature. The LEELS spectrum of the films grown at lower temperatures (⩽400 °C) resembles that of a GaS single crystal, whereas that of the films grown at 450 °C reveals that GaAs surface was terminated by Ga2S3 layer. XPS spectra suggest that after annealing at 500 °C, S atoms moved from As atoms to Ga atoms to form stable Ga–S bonds at the interface and As–S bonds are observed to be less stable. The band discontinuity at the GaS/GaAs(001) interface estimated by XPS showed the straddling-type I band alignment. Surface morphology of the films studied by AFM reveals the layer-by-layer initial growth of GaS.
Nd
2
O
3
doped low silica calcium aluminosilicate glasses: Thermomechanical properties
Authors: Baesso M. L. , Bento A. C. , Duarte A. R. , Neto A. M. , Miranda L. C. M. , Sampaio J. A. , Catunda T. , Gama S. , Gandra F. C. G.
Published: July 2002

The effects of Nd2O3 doping on the thermal and mechanical properties of vacuum melted, low silica, calcium aluminosilicate glasses are presented. For the doped glasses, the vitrification limit was found to correspond to a maximum load of 5 wt % Nd2O3. The influence of the rare earth doping on the thermal diffusivity, thermal conductivity, and Vickers hardness was such that all these physical parameters decreased by roughly the same amount, namely 8%, between the undoped and the 5 wt % doped sample. The dependence of these parameters, as a function of the Nd2O3 doping, strongly supports the idea that the Nd3+ act as network modifiers.
Application of the three omega thermal conductivity measurement method to a film on a substrate of finite thickness
Authors: Kim Jung Hun , Feldman Albert , Novotny Donald
Published: July 2002

The three omega thermal conductivity measurement method is analyzed for the case of one or more thin films on a substrate of finite thickness. The analysis is used to obtain the thermal conductivities of SiO2 films on Si substrates and of a chemical vapor deposition (CVD) diamond plate. For the case of the SiO2 films on a Si, we find an apparent thickness dependence of the thermal conductivity of the SiO2 films. However, the data can also be explained by a thickness-independent thermal conductivity and an interfacial thermal resistance. For the case of the CVD diamond plate, the fit of the theory to the experimental data is significantly improved if we assume that an interface layer separates the heater from the diamond plate.
III–nitrides: Growth, characterization, and properties
Authors: Jain S. C. , Willander M. , Narayan J. , Overstraeten R. Van
Published: July 2002

During the last few years the developments in the field of III–nitrides have been spectacular. High quality epitaxial layers can now be grown by MOVPE. Recently good quality epilayers have also been grown by MBE. Considerable work has been done on dislocations, strain, and critical thickness of GaN grown on different substrates. Splitting of valence band by crystal field and by spin-orbit interaction has been calculated and measured. The measured values agree with the calculated values. Effects of strain on the splitting of the valence band and on the optical properties have been studied in detail. Values of band offsets at the heterointerface between several pairs of different nitrides have been determined. Extensive work has been done on the optical and electrical properties. Near band-edge spectra have been measured over a wide range of temperatures. Free and bound exciton peaks have been resolved. Valence band structure has been determined using the PL spectra and compared with the theoretically calculated spectra. Strain and its effect on the optical properties of the III–nitride layers have been studied both theoretically and experimentally. Both n and p conductivity have been achieved. InGaN quantum wells with GaN and AlGaN barriers and cladding layers have been investigated. PL of the quantum wells is affected by confinement effects, band filling, quantum confined Stark effect, and strain. This work has led to the fabrication of advanced optoelectronic and electronic devices. The light-emitting decodes emitting in the blue and green regions of the spectrum have been commercialized. The work leading to these developments is reviewed in this article. The device processing methods and actual devices are not discussed.
Efficient light emitting diodes by photon recycling and their application in pixelless infrared imaging devices
Authors: Dupont E. , Chiu S.
Published: July 2002

The success of the pixelless imaging concept using a quantum well infrared photodetector integrated with a light emitting diode (QWIP–LED) depends critically on the extent of spatial lateral spreading of both photocurrent generated in the QWIP and near infrared (NIR) photons emitted by the LED as they escape from the device layers. According to the photon recycling model proposed by Schnitzer et al. [Appl. Phys. Lett. 62, 131 (1993)] there appears to be a trade-off between a high LED external quantum efficiency and a small photon lateral spread, the former being a necessary condition for achieving high detector sensitivity. This lateral spreading due to multireflections and reincarnations of the NIR photons could potentially degrade the image quality or resolution of the device. By adapting Schnitzer’s model to the QWIP–LED structure, we have identified device parameters that could potentially influence the NIR photon lateral spread and the LED external efficiency. In addition, we have developed a simple sequential model to estimate the crosstalk between the incoming far infrared image and the up-converted NIR image. We have found that the thickness of the LED is an important parameter that needs to be optimized in order to maximize the external efficiency and to minimize the crosstalk. A 6000-Å-thick LED active layer should give a resolution of ∼30 μm and an external efficiency of ∼10%.
Large magnetostrictive response of Terfenol-D resin composites (invited)
Authors: Duenas T. A. , Carman G. P.
Published: July 2002

In this article we present results for magnetostrictive composites containing between 10% and 50% Terfenol-D (Tb0.3Dy0.7Fe2) in a nonmetallic binder. The composite consists of aligned Terfenol-D particles representative of a [1-3] fiber composite. For this study we measure the modulus of elasticity and other pertinent magnetostrictive properties. The measured stiffness values fall between the upper and lower bounds predicted by a rule of mixtures approximation. The magnetostriction for the composites rival that of the monolithic at comparable magnetic field levels. A mechanically unloaded 20% volume fraction composite produces 900 ppm and a 30% volume fraction composite preloaded with 8 MPa produces 1000 ppm. Contrary to the belief that the greater the magnetostrictive particulate volume, the greater magnetostrictive properties—this study shows that there is an optimal balance of epoxy and magnetostrictive material that will maximize magnetostriction for a mechanically unloaded specimen. For the matrix chosen in this study, the optimal volume fraction is near 20%.
Porosity and specific surface for interpenetrable-sphere models of two-phase random media
Authors: Rikvold Per Arne , Stell George
Published: July 2002

We derive and numerically evaluate expressions for the porosity (matrix volume fraction) φ and the specific surface (interface area per unit volume) s for two specific models of a random two-phase medium in which the medium is considered as a suspension of interpenetrable spheres of radius R, embedded in a uniform matrix. The models and quantities considered have applications to a wide range of problems concerning transport, mechanical, and chemical properties of composite media. Both models contain a continuously variable hardness parameter ε, such that for ε=1 they reduce to mutually impenetrable spheres, and for ε=0 they reduce to fully penetrable spheres. The first of these models, the permeable-sphere model, has been defined only in the context of the Percus–Yevick approximation, which yields for it a unique pair distribution function g2(r1, r2). To find the associated gn(r1,...,rn) for n≳2, which are needed to evaluate φ and s we use the generalized superposition approximation. The second model, the concentric-shell model, can be fully defined without recourse to any particular approximation and proves to be isomorphic to the picture described by the scaled-particle theory of Reiss, Frisch, and Lebowitz. In this case we evaluate φ and s in the scaled-particle approximation introduced by those authors to implement the scaled-particle theory. For both models, we present numerical plots of φ vs dimensionless density, and of s vs φ. We also briefly discuss the relations between the results obtained in the two cases. Finally, we consider generalizations of φ and s that define the volume and surface available to a particle of finite size, rather than a point.
Quasistatic processes as step equilibrations
Authors: Nulton J. , Salamon P. , Andresen B. , Anmin Qi
Published: July 2002

The proportionality between the square of the distance traversed as measured in thermodynamic length and the minimum associated dissipation of a process is established in a new context independent of dynamical laws. A quasistatic thermodynamic process consisting of K steps, each equilibrating with an appropriate reservoir, is optimized with respect to the position of the steps and the allocation of the total time τ for the process among the steps. It is found that the steps should be of equal thermodynamic length. For large K the bounds based on thermodynamic length are recovered.
Universal amplitude ratios and the interfacial tension near consolute points of binary liquid mixtures
Authors: Chaar Hector , Moldover Michael R. , Schmidt James W.
Published: July 2002

The densities of the coexisting phases and the capillary length have been measured to obtain the interfacial tension (σ) near the consolute temperatures Tc of the three binary liquid mixtures: triethylamine+water, triethylamine+heavy water, and methanol+cyclohexane. Our data are combined with data from the literature to test predictions for three temperature-independent ‘‘universal’’ ratios: U+1=σ(ξ+)2/(kBTc) and Y(±)=σ(αt2C±s/kB) −2/3/(kBT0). [Here ξ+ is the correlation length, C±s is the singular part of the heat capacity per unit volume, α=0.11 is the exponent characterizing the specific heat divergence, and t≡(T−Tc)/Tc]. Near Tc, the new experimental values of Y(+) range from 5.5–5.8 in agreement with the value 5.6 obtained by Moldover [Phys. Rev. 31, 1022 (1985)] in a review of earlier experiments. However, the experimental values of Y(+) are inconsistent with either the value Y(+)=4.4±0.4 obtained from a recent simulation of the simple-cubic Ising model or the value Y(+)=2.6–3.0 obtained from a one-loop renormalization group calculation. The experimental values Y(−)=3.7 and U+1 =0.39 are also much larger than both the Ising model and the renormalization group values. It is unlikely that the inconsistency between the experimental and the theoretical ratios Y(±) and U+1 can be explained by systematic errors in the measurements of σ, because diverse techniques for measuring σ have yielded consistent results for a wide variety of fluid systems. A table of the relevant amplitudes for 16 fluid systems is included.
A scaled fundamental equation for the thermodynamic properties of carbon dioxide in the critical region
Authors: Albright P. C. , Edwards T. J. , Chen Z. Y. , Sengers J. V.
Published: July 2002

A scaled fundamental equation is presented for the thermodynamic properties of carbon dioxide in the critical region. The equation is constructed by combining earlier experimental pressure data of Michels and co-workers with new specific heat data obtained by one of the authors and represents the thermodynamic properties of carbon dioxide in the critical region at temperatures from 301.15 to 323 K and at densities from 290 to 595 kg/m3.
Impulsive stimulated light scattering. I. General theory
Authors: Yan Yong-Xin , Nelson Keith A.
Published: July 2002

Theoretical analysis of the time-resolved impulsive stimulated light scattering (ISS) method is presented. A general theoretical framework is developed to describe ISS experiments on any type of material mode which is active in light scattering and conforms to linear response theory. ISS experiments permit time-resolved observation of material motion through the dielectric response function Gεε(q,t). In the simplest case of ideal time and wave vector resolution, ISS signal gives ‖Gεε(q,t)‖2 directly. Various consequences of limited t and q resolution are discussed in detail. ISS experiments on acoustic and optic phonons, Debye relaxational modes, and some combinations of modes are treated explicitly. A detailed comparison of time-domain impulsive stimulated scattering and frequency-domain spontaneous light-scattering spectroscopy is presented in the companion paper.
Analytic energy derivatives in many-body methods. I. First derivatives
Authors: Salter E. A. , Trucks Gary W. , Bartlett Rodney J.
Published: July 2002

The theory of analytic energy derivatives is developed for the coupled cluster (CC) model using diagrammatic techniques. Explicit expressions for the derivative energy and response density for the full coupled-cluster singles, doubles and triples (CCSDT) model are presented. Analytic derivatives for the finite-order MBPT models through MBPT(4) and the recently proposed ‘‘quadratic’’ CI models are derived as special cases of the theory. First derivatives of the energy correspond to first-order response properties and molecular gradients; the analytic expressions for the derivative energy are given in terms of the response (or ‘‘relaxed’’) density for efficient evaluation. The theory of analytic second derivatives of the CC/MBPT energy is presented in part II.
Computer simulation of diffusion-controlled reactions in dispersions of spherical sinks
Authors: Zheng Li Hua , Chiew Yee C.
Published: July 2002

The diffusion-controlled reaction rate of dispersions of overlapping (fully penetrable) and nonoverlapping static sinks are determined through computer simulations. The diffusive or random-walk motions of the solutes are simulated in continuum space based on the first passage time probability distribution. This method yields accurate results for the reduced diffusion-controlled reaction rate k/ks where ks represents the dilute concentration Smoluchowski limit. Values of k/ks over a wide range of sink concentrations are obtained. These ‘‘exact’’ data are compared with a number of approximate theories. The merits and the regimes of validity of these theories are determined.
Line broadening, line shifting, and line coupling effects on N2–H2O stimulated Raman spectra
Authors: Bonamy J. , Robert D. , Hartmann J. M. , Gonze M. L. , Saint-Loup R. , Berger H.
Published: July 2002

In order to understand the influence of H2O on the stimulated Raman Q-branch spectra of nitrogen in combusting media, an exhaustive theoretical and experimental study has been carried out. Starting from a semiclassical model, particularly convenient at high temperature, the Q-line broadening and shifting coefficients have been calculated over a wide temperature range and for a large number of lines. Stimulated Raman Spectra (SRS) measurements have allowed us to test these calculated line broadening coefficients and thus establish the high accuracy of semiclassical values. The theoretical broadening coefficients have been inverted to deduce state-to-state rotational relaxation rates by using two types of fitting laws. A partial test of the resulting Q-branch profiles has been realized at moderate pressures leading to a discrimination between these two laws. Furthermore, the effect of rotational energy transfers on collisionally narrowed profiles at higher densities has been simulated and compared with the pure N2 case.
Pressure dependence of the solubility of nitrogen, argon, krypton, and xenon in water
Authors: Kennan Richard P. , Pollack Gerald L.
Published: July 2002

Measurements are reported for the pressure dependence of the Ostwald L and mole-fraction x2 solubilities for nitrogen, argon, krypton, and xenon in water at 25.0 °C. The approximate pressure ranges were: N2, 44–116 atm; Ar, 22–101 atm; Kr, 33–81 atm; and Xe, 5–48 atm. Our experimental technique is a modified Van Slyke method which allows the simultaneous determination of L, x2, and partial molar volume v2 of the solute gas in the solvent. For N2, Ar, and Kr we observe deviations from Henry’s Law, f2=kHx2 which vary linearly with pressure. For example, the measured values of Henry’s constant range from kH (25 °C, 44.6 atm)=90 269 atm to kH (25 °C, 115.8 atm)=100 340 atm for N2 in water. Extrapolation of the data to low pressure yields results for L and x2 which agree with literature values. For Xe we observe a sharp increase in Henry’s constant at pressures above 20 atm. The measured partial molar volume also changes sharply from 47 to ∼125 cm3/mol. This is attributed to the observed onset of ice-like clathrates at pressures above 20 atm. The solubility data are analyzed in terms of the Kirkwood–Buff solution theory, and the role of hydrophobic interactions is discussed. For the Kr–water system, we compare the experimental results to recent computer simulations. We also use statistical mechanics arguments to introduce a new solubility parameter which is useful in understanding high-pressure measurements. We conclude by discussing extensions of this work to other gas–liquid systems.
Born–Oppenheimer dynamics using density-functional theory: Equilibrium and fragmentation of small sodium clusters
Authors: Barnett R. N. , Landman Uzi , Nitzan Abraham , Rajagopal Gunaretnam
Published: July 2002

The properties of small neutral and positively charged sodium clusters and the fragmentation dynamics of Na++4 are investigated using a simulation technique which combines classical molecular dynamics on the electronic Born–Oppenheimer ground-state potential surface with electronic structure calculations via the local spin-density functional method. Results for the optimal energies and structures of Nan and Na+n (n≤4) are in quantitative agreement with previous studies and experimental data. Fission of Na++4 on its ground state Born–Oppenheimer potential-energy surface, following sudden ionization of selected configurations of an Na+4 (or Na4) cluster, whose vibrational energy content corresponds to 300 K, is found to occur on a picosecond time scale. The preferred fission channel is found to be Na+3+Na+, with an interfragment relative translational kinetic energy of ∼2 eV, and a vibrationally excited Na+3. The dynamics of the fragmentation process is analyzed.
First principles computation of thermochemical properties beyond the harmonic approximation. I. Method and application to the water molecule and its isotopomers
Authors: Martin J. M. L. , François J. P. , Gijbels R.
Published: July 2002

The anharmonic potential energy surface of water has been computed ab initio using an augmented coupled cluster method and various basis sets. Whereas the Pople 6–311 G family is manifestly unsatisfactory, Huzinaga–Dunning basis sets perform quite well. The [5s4p2d1f,3s2p] surface reproduces harmonic frequencies and anharmonicity constants to better than about 2 and 1 cm−1, respectively. For quantitative agreement with experiment, both f functions on oxygen and inclusion of core correlation seem to be prerequisite. Comparison with various experimentally derived force fields reveals that the ab initio force field is of comparable quality. From the best computed force field, a set of spectroscopic constants has been derived for all important isotopomers of water. Using a hybrid analytic/direct summation method recently developed by the present authors, the thermodynamic functions gef(T), hcf(T), S0, and Cp are computed including exact account of anharmonicity and rovibrational coupling, and very good analytical approximations to centrifugal distortion and quantum rotation effects. The computed functions substantially revise previous literature results at high temperatures. Differences between thermodynamic functions from various computed force fields are an order of magnitude smaller than these errors. Thermodynamic tables in JANAF style from 100 to 3000 K, as well as a full set of rovibrational spectroscopic constants, are presented. It is concluded that obtaining force fields of near-spectroscopic accuracy, and thermodynamic tables of very high accuracy, is presently feasible for small polyatomic molecules.