bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear properties of lead zirconate–titanate piezoceramics
Authors: Jiang Wenhua , Cao Wenwu
Published: July 2002

Nonlinear properties of lead zirconate-titanate (PZT) piezoceramics are investigated using ultrasonic second harmonic generation technique. When a sinusoidal ultrasonic wave of frequency ω0 is sent into a nonlinear material, the second harmonic wave with frequency 2ω0 is generated. Through measuring the absolute amplitude of the fundamental (ω0) and of the second harmonic (2ω0) waves, the ultrasonic nonlinearity parameter β can be determined, which involves certain combinations of the third-order elastic constants and piezoelectric coefficients. We report the measured nonlinear parameters for four types of doped PZT ceramics, PZT-4, PZT-5A, PZT-5H, and PZT-5H HD, which are widely used in practice. We found that the nonlinear parameter is much more sensitive than the linear parameter in responding to microstructural changes in piezoceramics. It could be used to distinguish unpoled samples from depoled samples, which are undistinguishable in terms of the linear parameters.
Photoluminescence from mesoporous silica: Similarity of properties to porous silicon
Authors: Glinka Yu. D. , Lin S. H. , Hwang L. P. , Chen Y. T.
Published: July 2002

Photoluminescence (PL) from mesoporous silica (MS) with the pore size of ∼6 nm and the thickness of walls among pores of ∼1 nm has been studied at room temperature. The heat pretreatment of MS in air at different temperatures and the variation of the excitation wavelengths allow one to shift the PL peak through the whole visible spectral range. The PL is suggested to originate from nonbridging oxygens (red bands), hydrogen-related species (green bands), and water-carbonyl groups (blue bands). The spectroscopic properties of MS are found to be similar to those of surface-oxidized silicon nanocrystals and porous silicon.
SiGe bulk crystal as a lattice-matched substrate to GaAs for solar cell applications
Authors: Usami N. , Azuma Y. , Ujihara T. , Sazaki G. , Nakajima K. , Yakabe Y. , Kondo T. , Koh S. , Shiraki Y. , Zhang B. , Segawa Y. , Kodama S.
Published: July 2002

SiGe bulk crystal fabricated by a multicomponent zone-melting method was used as a substrate for epitaxial growth of GaAs. Compared with conventional GaAs/Ge heterostructure, the lattice mismatch of GaAs/Si0.022Ge0.978 was confirmed to be reduced by a decrease of the peak separation of (400) x-ray diffraction from the epitaxial GaAs layer and the substrate. Furthermore, the linewidth of the rocking curve of GaAs on SiGe was found to be narrower than that of GaAs on Ge. These results show that SiGe is promising material as an alternative substrate to Ge for realization of exactly lattice-matched GaAs/SiGe solar cells.
Magnetic and electric “dead” layers in (La0.7Sr0.3)MnO3 thin films
Authors: Borges R. P. , Guichard W. , Lunney J. G. , Coey J. M. D. , Ott F.
Published: July 2002

The magnetic, transport, and structural properties of (La0.1Sr0.3)MnO3 films deposited on MgO (001) are reported as a function of thickness and substrate temperature. The substrate temperature is fundamental in determining the structural properties and a deviation from the optimum temperature (680 °C) leads to grain boundaries and an imperfect (001) texture. Films with different thicknesses were deposited at the optimum deposition temperature. Magnetization and resistivity measurements on these films are interpreted in terms of magnetic and electric “dead” layers. The electric dead layer is an insulating layer approximately 4 nm thick while the magnetic dead layer is a region of weakly coupled noncollinear spins approximately 10 nm thick at each interface.
Incorporation of Mg in GaN grown by plasma-assisted molecular beam epitaxy
Authors: Namkoong Gon , Doolittle W. Alan , Brown April S.
Published: July 2002

We describe dramatically decreased Mg incorporation in GaN above a critical Mg flux. Secondary ion mass spectroscopy analysis showed a linear increase in Mg concentration up to a flux equivalent to 8.0×10−10 Torr beam equivalent pressure (BEP) and 1.6×10−9 Torr BEP at 550 and 615 °C respectively, beyond which the Mg incorporation was reduced by factors of 10 for 550 °C, and 2 for 615 °C. In a transition region between this critical flux and higher flux, a time dependent incorporation phenomenon was observed. An increase in the GaN growth rate was also observed in the presence of Mg above the critical flux.
The improved virtual orbital-complete active space configuration interaction method, a “packageable” efficient ab initio many-body method for describing electronically excited states
Authors: Potts Davin M. , Taylor Caroline M. , Chaudhuri Rajat K. , Freed Karl F.
Published: July 2002

We describe a computationally efficient ab initio many-body method that can be used as a “packageable approximation” for computing excited state properties for small to large molecular systems, including those of multiconfigurational character. The method is based on first order multi-reference many-body perturbation theory (MR-MBPT), where the unoccupied valence orbitals are obtained by using an extension of Huzinaga’s improved virtual orbital (IVO) generation technique. Because the method employs a complete active space (CAS) which contains singly, doubly, and higher excited state configurations with respect to the zeroth order ground state configuration, the approach (IVO-CASCI) is capable of providing a more accurate description of the excited states than the widely used packageable configuration interaction with singles (CIS) at a fraction of computational labor. Moreover, unlike the CASSCF approach this IVO-CASCI method does not require iterations and therefore is more computationally efficient and free of the convergence problems that sometimes plague CASSCF calculations with increasing size of the CAS. Excited state energies are compared with energies from the widely used CIS, MCSCF, and CASSCF methods for the C2H+, C2H, CaOH, cyclic-C3H, and porphin molecules. The computed IVO-CASCI transition energies are generally more accurate than the CASSCF. For example, our energies are comparable to CIS energies for CaOH and porphin, while the C2H+, C2H, and C3H IVO-CASCI transition energies are more accurate than the CASSCF and CIS energies.
Ab initio studies of phonons in CaTiO3
Authors: Parlinski K. , Kawazoe Y. , Waseda Y.
Published: July 2002

Using the local-density approximation, and calculating the Hellmann–Feynman forces, the stability of the perovskite-like structures of CaTiO3 have been studied by applying the direct method and deriving the phonon dispersion relations. The cubic Pm3̄m phase shows dispersionless soft phonon branch spreading from R to M points of the cubic Brillouin zone. Low-symmetry phase I4/mcm can be considered as a result of the soft mode condensation at R point. The experimentally observed Pmnb phase is a consequence of the intersection of Imma and P4/mbm space groups, being the result of soft mode condensation at R and M points, respectively. Thus, the Pmnb can be regarded as simultaneous condensations of two soft modes. The phonon dispersion relations of Pmnb suggest that this phase is stable.
Short-range order and strain in SiGeC alloys probed by phonons
Authors: Finkman E. , Meyer F. , Mamor M.
Published: July 2002

We report a detailed study of the dependence of the vibrational modes in rapid thermal chemical vapor deposition grown Si1−x−yGexCy samples on substitutional carbon concentration. The difficulty in incorporating substitutional carbon in these alloys with concentrations higher than a few tenths of an atomic percent is well known. We show that simultaneous analysis of x-ray diffraction, infrared absorption, and Raman scattering measurements can be used to determine the fraction of substitutional carbon from the total carbon content. We claim that the uncertainty in defining this fraction led to the discrepancies between the interpretations of previous studies. The frequency shifts of the C local modes and the Si–Si mode are studied, in addition to the intensity dependence of the former. The evolution of C satellite peaks and their dependence on total C concentration are presented. There is a large frequency change of these modes, indicating a very large local bond distortion induced by the presence of carbon in the lattice. We show that the shifts of the Si–Si mode frequencies due to the Ge and C content are not simply the addition of each contribution separately. The rate at which they shift with changing C concentration depends on the Ge content in the alloy. The probability of creating ordered substitutional C–C pairs, rather than randomly distributed C atoms in the crystal lattice, increases nonlinearly as a function of the carbon content.
Optical harmonic generation in a quasi-phase-matched three-component Fibonacci superlattice LiTaO3
Authors: Chen Y. B. , Zhang C. , Zhu Y. Y. , Zhu S. N. , Wang H. T. , Ming N. B.
Published: July 2002

Optical harmonic generation in a three-component Fibonacci optical superlattice (3CFOS) is studied experimentally. Quasi-phase-matched second-harmonic spectrum and third-harmonic generation have been measured in a LiTaO3 3CFOS. Results show that the structure of the spectrum in a 3CFOS is richer than that in a two-component Fibonacci optical superlattice. The intrinsic self-similarity is shown in its Fourier spectrum.
Lateral AlxGa1−xN power rectifiers with 9.7 kV reverse breakdown voltage
Authors: Zhang A. P. , Johnson J. W. , Ren F. , Han J. , Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Redwing J. M. , Lee K. P. , Pearton S. J.
Published: July 2002

Al x Ga 1−x N  (x=0–0.25) Schottky rectifiers were fabricated in a lateral geometry employing p+-implanted guard rings and rectifying contact overlap onto an SiO2 passivation layer. The reverse breakdown voltage (VB) increased with the spacing between Schottky and ohmic metal contacts, reaching 9700 V for Al0.25Ga0.75N and 6350 V for GaN, respectively, for 100 μm gap spacing. Assuming lateral depletion, these values correspond to breakdown field strengths of ⩽9.67×105 V cm−1, which is roughly a factor of 20 lower than the theoretical maximum in bulk GaN. The figure of merit (VB)2/RON, where RON is the on-state resistance, was in the range 94–268 MW cm−2 for all the devices.
Painlevé–Calogero correspondence revisited
Authors: Takasaki Kanehisa
Published: July 2002

We extend the work of Fuchs, Painlevé and Manin on a Calogero-like expression of the sixth Painlevé equation (the “Painlevé–Calogero correspondence”) to the other five Painlevé equations. The Calogero side of the sixth Painlevé equation is known to be a nonautonomous version of the (rank one) elliptic model of Inozemtsev’s extended Calogero systems. The fifth and fourth Painlevé equations correspond to the hyperbolic and rational models in Inozemtsev’s classification. Those corresponding to the third, second and first are not included therein. We further extend the correspondence to the higher rank models, and obtain a “multi-component” version of the Painlevé equations.
Auger recombination in long-wavelength infrared InNxSb1−x alloys
Authors: Murdin B. N. , Kamal-Saadi M. , Lindsay A. , O’Reilly E. P. , Adams A. R. , Nott G. J. , Crowder J. G. , Pidgeon C. R. , Bradley I. V. , Wells J.-P. R. , Burke T. , Johnson A. D. , Ashley T.
Published: July 2002

Dilute nitrogen alloys of InSb exhibit strong band gap bowing with increasing nitrogen composition, shifting the absorption edge to longer wavelengths. The conduction band dispersion also has an enhanced nonparabolicity, which suppresses Auger recombination. We have measured Auger lifetimes in alloys with 11 and 15 μm absorption edges using a time-resolved pump-probe technique. We find the lifetimes to be longer at room temperature than equivalent band gap Hg1−yCdyTe alloys at the same quasi-Fermi level separation. The results are explained using a modified k⋅p Hamiltonian which explicitly includes interactions between the conduction band and a higher lying nitrogen-related resonant band.
Linear wave dispersion laws in unmagnetized relativistic plasma: Analytical and numerical results
Authors: Bergman Jan , Eliasson Bengt
Published: July 2002

In this paper dispersion laws for electrostatic and electromagnetic waves in a homogeneous and unmagnetized relativistic Vlasov plasma are derived. From the dispersion laws the relativistic plasma frequency, which is temperature dependent is derived. Using the standard technique of successive approximations, simple but powerful approximate relativistic dispersion laws are derived, resembling the electromagnetic dispersion law and the electrostatic Bohm–Gross dispersion law in the nonrelativistic case. The relation between the relativistic plasma frequency ωpe, Debye wave number kD and the thermal velocity vth,e is established. The approximate dispersion laws are compared with numerical solutions of the full dispersion laws. The full dispersion equations are transformed so that they are well suited for numerical evaluation in the temperature range where a fully relativistic treatment is needed.
Direct patterning of self-assembled nanocrystal monolayers by electron beams
Authors: Lin X. M. , Parthasarathy R. , Jaeger H. M.
Published: July 2002

We demonstrate a method for laterally patterning metal nanocrystal monolayers. Extended monolayers are first self-assembled onto a solid substrate. Direct electron-beam exposure is then used to strip the dodecanethiol ligand coating from the nanocrystal cores, enabling the cores to stick to the underlying substrate. During a subsequent washing step in a solvent mixture, nanocrystals from the unexposed regions are removed and floated off, leaving behind the desired pattern.
Large domain wall magnetoresistance up to room temperature in La0.7Sr0.3MnO3 bridges with nanoconstrictions
Authors: Wolfman J. , Haghiri-Gosnet A. M. , Raveau B. , Vieu C. , Cambril E. , Cornette A. , Launois H.
Published: July 2002

To obtain low field magnetoresistance (MR) in manganites, we have introduced a geometrically constrained magnetic domain wall (DW) in La0.7Sr0.3MnO3 micrometric devices. Nanoconstrictions artificially induced using high resolution e-beam lithography are shown to effectively reduce the DW width leading to strongly enhanced DW resistance. Sharp and large resistance switches result from the appearance and annihilation of the DWs. Room temperature sharp resistance switches, with a MR of 16%, are evidenced in a manganite-based device.
Liquid-crystal display of stress fields in ferroelectrics
Authors: Lupascu Doru C. , dos Santos e Lucato Sergio L. , Rödel Jürgen , Kreuzer Markus , Lynch Christopher S.
Published: July 2002

Direct optical images of local surface potentials generated by the process zone of a crack are shown for a thickness-poled ferroelectric ceramic using liquid crystals. The observed potentials can be mapped to stresses within the material revealing the complex shape and time development of the process zone so far not accessible using other techniques.
A swarm of Stokeslets with interfacial tension
Authors: Nitsche Ludwig C. , Schaflinger Uwe
Published: July 2002

A formal analogy between sedimenting drops in Stokes flow and a swarm of Stokeslets [Machu et al., J. Fluid Mech. (in press)] is extended to include interfacial tension. Using a cohesive potential, mean curvature is extended as a meaningful quantity off the interface, allowing the boundary-integral formulation to be rewritten in volumetric form. A prescription for assigning forces to the Stokeslets comprising the swarm incorporates the action of interfacial tension without having to identify a boundary surface. Numerical simulations agree with linear small-deformation theory, and reproduce the spontaneous coalescense of two touching drops.
Pyrolytically grown arrays of highly aligned BxCyNz nanotubes
Authors: Han Wei-Qiang , Cumings John , Zettl Alex
Published: July 2002

A pyrolysis route has been used to synthesize arrays of highly aligned BxCyNz nanotubes in bulk. The structure and composition of the product were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and electron energy-loss spectroscopy. The length and diameter of the nanotubes are quite uniform in a large area of the reaction zone. The sizes of the aligned BxCyNz nanotubes from the whole reaction zone are 10–30 μm in length and 20–140 nm in diameter. The x/z ratio of BxCyNz nanotubes for most nanotubes is about 1:1. The x/y ratio of BxCyNz nanotubes is up to 0.6. Within one nanotube, the x/y ratio is usually heterogeneous. The growth mechanism is also discussed.
Soft x-ray spectromicroscope at the Pohang Light Source
Authors: Lee Min-Kyu , Shin Hyun-Joon
Published: July 2002

A soft x-ray spectromicroscope for scanning transmission x-ray microscopy (STXM) and scanning photoelectron microscopy (SPEM) has been installed at the first undulator-radiation beamline at the Pohang Light Source. The spatial resolution of the spectromicroscope is 0.4 μm in the vertical direction and 0.5 μm in the horizontal direction, with a focused photon flux of 5×107–1×108 photons/s. The operational energy ranges for the STXM and the SPEM are 250–1000 eV and 400–1000 eV, respectively, with spectral resolving power of 1000–3000. The setup details of the spectromicroscope and the SPEM application results of semiconductor devices are presented.
Anisotropy of the flux creep in the motion of vortices along twin-boundary planes in YBa2Cu3O7−x single crystals
Authors: Bondarenko A. V. , Prodan A. A. , Obolenskiı̆ M. A. , Vovk R. V. , Arouri T. R.
Published: July 2002

The anisotropy of the magnetic flux creep in vortex motion parallel to the planes of twin boundaries is investigated experimentally. It is shown that at relatively low magnetic fields the creep velocity is independent of the magnetic field and of the angle α≡∠H,ab. It is found that the differential resistivity ρd≡dE/dJ tends to saturation at large transport currents, where its value is approximately equal to the viscous drag on vortices in the Bardeen–Stephen model. In low magnetic fields oriented near the ab plane of the crystal the trapping of flux lines between CuO superconducting planes is observed.
Combined fluctuating charge and polarizable dipole models: Application to a five-site water potential function
Authors: Stern Harry A. , Rittner F. , Berne B. J. , Friesner Richard A.
Published: July 2002

We present a general formalism for polarizable electrostatics based on fluctuating bond-charge increments and polarizable dipoles and its application to a five-site model for water. The parametrization is based largely on quantum-chemical calculations and should be easily transferable to other molecules. To examine basis-set effects we parametrized two models from two sets of quantum calculations, using the aug-cc-pVTZ and aug-cc-pVQZ basis sets. We computed several gas-phase and condensed-phase properties and compared with experiment or ab initio calculations as available. The models are quite similar and give condensed-phase properties at ambient conditions that are in reasonable accord with experiment, but evince errors consistent with a liquid-state dipole moment that is slightly too large. The model fit to the aug-cc-pVTZ basis set has a smaller liquid-phase dipole moment and thus gives a somewhat better description of liquid water at ambient conditions. This model also performs well away from room temperature, deviating less than 2% from the experimental density from 0 to 100 °C, and showing good agreement with experimental radial distribution functions, although the temperature of maximum density (∼20 °C) is slightly too high and the model somewhat underpredicts the persistence of the hydrogen-bond network at elevated temperatures.
Morphology and thermochromic phase transition of merocyanine J-aggregate monolayers at the air–water and solid–water interfaces
Authors: Kato Noritaka , Saito Kentaro , Serata Toshinori , Aida Hiroaki , Uesu Yoshiaki
Published: July 2002

Thermal changes of the merocyanine dye (MD) monolayer at the air–water interface were investigated under various subphase conditions in order to elucidate the formation mechanism and to control morphological and chromatic properties of two-dimensional MD J-aggregate crystallites (JC) formed in the monolayer. The dissociation temperature (Td) of the JC to the monomer MD was measured for different counterions of MD molecules in the subphase. The JC size was found to be dependent on the subphase temperature; it becomes larger when the JC is formed at a temperature closer to Td. This phenomenon is qualitatively reproduced by the numerical simulation of the Cahn–Hilliard equation. In the case of the MD monolayer on the subphase which contains two kinds of counterions, it exhibits a reversible thermochromic transition between two different JC states. The chromatic change is discrete, and is attributed to the structural phase transition of the JC induced by the mutual recombination of two kinds of counterions to MD molecules. The structural difference between the high and low temperature JC states is examined by the point dipole model. The transition temperature and thermal hysteresis width can be varied by the fraction of 2 counterions. In situ observations using a multipurpose nonlinear optical microscope revealed that the transition is of first order and the nucleation and growth process of the low temperature phase in the high temperature matrix was observed. The JC size of the low temperature phase became much larger through the recrystallization process. For future application of this phenomenon, an airtight cell consisting of two monolayers at the solid–water interface and the subphase was developed. In the cell, the same reversible transition occurs, but with a slow relaxation.
Cooling dynamics of an optically excited molecular probe in solution from femtosecond broadband transient absorption spectroscopy
Authors: Kovalenko S. A. , Schanz R. , Hennig H. , Ernsting N. P.
Published: July 2002

The cooling of p-nitroaniline (PNA), dimethylamino-p-nitroaniline (DPNA) and trans-stilbene (t-stilbene) in solution is studied experimentally and theoretically. Using the pump–supercontinuum probe (PSCP) technique we observed the complete spectral evolution of hot absorption induced by femtosecond optical pumping. In t-stilbene the hot S1 state results from Sn→S1 internal conversion with 50 fs characteristic time. The time constant of intramolecular thermalization or intramolecular vibrational redistribution (IVR) in S1 is estimated as τIVR≪100 fs. In PNA and DPNA the hot ground state is prepared by S1→S0 relaxation with characteristic time 0.3–1.0 ps. The initial molecular temperature is 1300 K for PNA and 860 K for t-stilbene. The subsequent cooling dynamics (vibrational cooling) is deduced from the transient spectra by assuming: (i) a Gaussian shape for the hot absorption band, (ii) a linear dependence of its peak frequency νm and width square Γ2 on molecular temperature T. Within this framework we derive analytic expressions for the differential absorption signal ΔOD(T(t),ν). After calibration with stationary absorption spectra in a low temperature range, the solute temperature T(t) may be evaluated from a transient absorption experiment. For highly polar PNA and DPNA, T(t) is well described by a biexponential decay which reflects local heating effects, while for nonpolar t-stilbene the local heating is negligible and the cooling proceeds monoexponentially. To rationalize this behavior, an analytic model is developed, which considers energy flow from the hot solute to a first solvent shell and then to the bulk solvent. Fastest cooling is found for PNA in water: a time constant of 0.64 ps (68%) corresponds to solute–solvent energy transfer while 2.0 ps (32%) characterizes the cooling of the first shell. In aprotic solvents cooling is slower than in alcohols and slows down further with decreasing solvent polarity. This contrasts with nonpolar t-stilbene which cools down with 8.5 ps both in acetonitrile and cyclohexane. Comparison of the cooling kinetics for PNA in water with those for DPNA in water-acetonitrile mixtures suggests that the solute–solvent energy transfer proceeds mainly through hydrogen bonds.
On-line monitoring of perfluoro compounds in exhaust gases during semiconductor manufacture: Use of Li+ ion attachment mass spectrometry
Authors: Fujii Toshihiro , Nakamura Megumi
Published: July 2002

Li + ion attachment mass spectrometry was used to continuously measure trace amounts of perfluoro compounds (PFCs) and byproducts in exhaust gas during semiconductor manufacture. Effluents were characterized to assess the environmental impact of dry-etching processes and operations. The feasibility of performing real-time measurements of PFCs in exhaust gas at the parts per billion level by direct introduction of the Li+ ion attachment source was demonstrated.
High-detectivity, normal-incidence, mid-infrared (λ∼4 μm)InAs/GaAs quantum-dot detector operating at 150 K
Authors: Stiff A. D. , Krishna S. , Bhattacharya P. , Kennerly S.
Published: July 2002

Normal-incidence InAs/GaAs quantum-dot detectors have been grown, fabricated, and characterized for mid-infrared detection in the temperature range from 78 to 150 K. Due to the presence of an Al0.3Ga0.7As current blocking layer in the heterostructure, the dark current is very low, and at T=100 K, Idark=1.7 pA for Vbias=0.1 V. The peak of the spectral response curve is at λ∼4 μm, with Δλ/λ=0.3 and Vbias=0.1 V. At T=100 K, for Vbias=0.3 V, the peak detectivity, D*, is 3×109 cm Hz1/2/W, and the peak responsivity, Rp, is 2 mA/W with a photoconductive gain of g=18.
Effect of strain on temperature measurements using the fluorescence intensity ratio technique (with Nd3+- and Yb3+-doped silica fibers)
Authors: Wade S. A. , Collins S. F. , Baxter G. W. , Monnom G.
Published: July 2002

The effect of strain upon the fluorescence intensity ratio technique of optical fiber based temperature sensing has been investigated using a series of different Yb3+- and Nd3+-doped optical fibers. Measurements were conducted with each of the doped fibers for temperatures between approximately 10 and 140 °C and for strain values between 50 and 2100 με. Results suggest that the strain-temperature cross sensitivity for the fluorescence intensity ratio method is minimal, with an applied strain of 1000 με inducing temperature errors of less than 0.4 °C.
Evolutionary Monte Carlo for protein folding simulations
Authors: Liang Faming , Wong Wing Hung
Published: July 2002

We demonstrate that evolutionary Monte Carlo (EMC) can be applied successfully to simulations of protein folding on simple lattice models, and to finding the ground state of a protein. In all cases, EMC is faster than the genetic algorithm and the conventional Metropolis Monte Carlo, and in several cases it finds new lower energy states. We also propose one method for the use of secondary structures in protein folding. The numerical results show that it is drastically superior to other methods in finding the ground state of a protein.
Preisach distribution function approach to piezoelectric nonlinearity and hysteresis
Authors: Robert G. , Damjanovic D. , Setter N.
Published: July 2002

The Preisach approach was used to describe the widely observed quadratic field dependence of the direct longitudinal piezoelectric coefficient and its associated hysteresis loop. In this perspective, a four parameters distribution function was put forward and refined experimentally using bias stress variations. It permitted one to fully describe the stress bias dependence of the nonlinear coefficients. Considering the hysteresis loop associated with the proposed distribution function, modeling of the experimental data was made possible by the addition of a viscous term. Moreover, the distribution parameters extracted from the loops were in strict agreement with the values obtained either directly from experiments or from bias stress dependence characterization. This new set of results is considered as a further confirmation of the applicability of the Preisach model to piezoelectricity.
A high-temperature high-pressure optical cell for general-purpose spectrometers designed for supercritical water experiments
Authors: Amita Fujitsugu , Okada Kazuo , Oka Hiroyuki , Kajimoto Okitsugu
Published: July 2002

We have developed a compact size high-temperature high-pressure optical cell that can be mounted on a commercially available general-purpose spectrometer. A small electric furnace heats the high-pressure optical cell while a water-cooled thermal shielding jacket protects the spectrometer. This cooling device works quite effectively to eliminate undesirable heating of spectrometer optics and thus makes it possible to take spectra at temperatures up to 600 °C with an ordinary spectrometer. The optical cell is made of Hastelloy-X and equipped with two optical windows of synthetic sapphire. The length and the diameter of the optical path are 10 and 6 mm, respectively. As the optical cell is combined with a flow system, which allows the quick replacement of the sample solution with the reference water, the reference signal can be taken immediately after the measurement of the sample signal. The developed cell can be operated up to 60 MPa and 600 °C without any special modification to the spectrometer. The NiBr2 absorption spectra were taken under the supercritical water condition to demonstrate the efficiency of the optical cell.
Thermodynamics of computing: Entropy of nonergodic systems
Authors: Ishioka Shunya , Fuchikami Nobuko
Published: July 2002

Landauer discussed the minimum energy necessary for computation and stated that erasure of information is accompanied with kT ln 2/ bit of heat generation. We reconsider this problem on the basis of Clausius’s equation defining the thermodynamic entropy. We show that the erasing process, involving a transition from a nonergodic to an ergodic state, is irreversible and accompanied with k ln 2/bit of entropy generation, while the heat generation occurs in a writing process. The inverse of the erasing process corresponds to spontaneous symmetry breaking from an ergodic to a nonergodic state, which induces a decrease(!) in thermodynamic entropy. Our theory is examined by a simulation of a binary device described by a Langevin equation. We argue that the so-called residual entropy of symmetry broken states, such as in ice, is not a thermodynamic quantity, even if it might be called “information entropy.”
Theoretical study of spin-orbit coupling constants for O2+ (A 2Π3/2,1/2u, v+=0–17 and a 4Π5/2,3/2,1/2,−1/2u, v+=0–25)
Authors: Fedorov D. G. , Gordon M. S. , Song Y. , Ng C. Y.
Published: July 2002

The spin-orbit coupling constants (Av+) for O2+(A 2Πu,v+=0–17) and O2+(a 4Πu,v+=0–25) were computed based on the Pauli–Breit Hamiltonian with one and two electron terms for comparison with experimental measurements. In the present theoretical study, the vibrational wave functions are obtained using the potential energy curve calculated at the multireference configuration interaction (MRCI) level of theory, with single and double excitations from the complete active space self-consistent field (CASSCF) reference wave function. The electronic wave functions and spin-orbit coupling constants are obtained at the CASSCF and restricted MRCI levels. The effect on Av+ for O2+(A 2Πu,v+) and O2+(a 4Πu,v+) due to interactions of the O2+(A 2Πu,v+), O2+(a 4Πu,v+), and O2+(2Σu+) states is examined. The theoretical Av+ predictions for O2+(A 2Πu,v+) are found to be consistent with the experimental finding that O2+(A 2Πu) is an inverted spin-orbit state at low v+ levels and becomes a regular spin-orbit state at higher v+ levels. Good accord between theoretical predictions and experimental results for O2+(A 2Πu,v+=0–12) is observed with discrepancies in the range of 2–10 cm−1. In the case of O2+(a 4Πu,v+), excellent agreement between theoretical ab initio and experimental results is found with a discrepancy of 2–5 cm−1. Our effort to theoretically reproduce experimental fine structure in the Av+ curve for O2+(a 4Πu,v+) based on interstate vibrational interactions has met with limited success.
Spectroscopic ellipsometry study of SrBi2Ta2O9 ferroelectric thin films
Authors: Bahng Jae Ho , Lee Mierie , Park H. L. , Kim Ill Won , Jeong Jung Hyun , Kim Kwang Joo
Published: July 2002

Optical properties of SrBi2Ta2O9 (SBT) ferroelectric thin films were investigated by spectroscopic ellipsometry at room temperature in the 1.5–5.5 eV spectral range. The films were grown on platinized silicon (Pt/Ti/SiO2/Si) with a Bi/Sr ratio (x) range from 1.2 to 2.8 by pulsed-laser deposition. The measured pseudodielectric functions of the samples indicate the band-gap energy of SBT shifts to lower energies as x increases. The optical constants and band-gap energies of the SBT films were determined through multilayer analyses on their pseudodielectric functions. The band-gap energy of SBT is found to shift to lower energies quite linearly with x. The band-gap energy at stoichiometric composition (x=2) is estimated to be 4.1 eV.
Phase transition and acoustic localization in arrays of air bubbles in water
Authors: Ye Zhen , Hsu Haoran
Published: July 2002

Wave localization is a ubiquitous phenomenon. It refers to situations that transmitted waves in scattering media are trapped in space and remain confined in the vicinity of the initial site until dissipated. Here, we report a phase transition from acoustically extended to localized states in arrays of identical air-filled bubbles in water. It is shown that the acoustic localization in such media is coincident with the complete band gap of a corresponding lattice arrangement of the air bubbles. When the localization or the band gap occurs, a collective behavior of the bubbles appears, a unique feature differentiating the localization effect from the residual absorption effect.
Effect of thermal processing on strain relaxation and interdiffusion in Si/SiGe heterostructures studied using Raman spectroscopy
Authors: Koester S. J. , Rim K. , Chu J. O. , Mooney P. M. , Ott J. A. , Hargrove M. A.
Published: July 2002

The effect of thermal annealing on Si/SiGe heterostructures is studied using Raman spectroscopy. The structures consisted of Si on relaxed Si0.8Ge0.2 where the top Si thickness was 20–30 nm. Micro-Raman spectroscopy with 488 nm incident radiation revealed no significant shift in the strained Si peak position with thermal annealing at temperatures up to 1100 °C for 30 s. However, the intensity of the Si peak was systematically reduced with increasing thermal processing, a result which is attributed to interdiffusion at the Si/SiGe interface resulting in an apparent thinning of the Si cap layer.
Electronic transport in Cd–Yb and Y–Mg–Zn quasicrystals
Authors: Pope A. L. , Tritt T. M. , Gagnon R. , Strom-Olsen J.
Published: July 2002

Electronic transport properties of the stable binary Cd5.7Yb quasicrystal and a quasicrystal in the Y–Mg–Zn family is presented. Electrical conductivity in these systems is an order of magnitude higher than other quasicrystals, resulting in larger thermal conductivity values due to enhanced electronic contributions (λE=L0σT). Room temperature Hall measurements provide a charge carrier density of 2.3×1021 and 3.1×1020 cm−3 in Cd5.7Yb and Y–Mg–Zn, respectively, indicating these materials have a higher carrier concentration and are better conductors than other quasicrystalline counterparts. Thermoelectric power in both Cd5.7Yb and Y–Mg–Zn have relatively small magnitudes (16 and 8 μV/K, respectively). Despite many similarities between these two systems, low temperature specific heat reveals a low Debye temperature in Cd5.7Yb(140 K) while the Debye temperature of Y–Mg–Zn and other quasicrystals is at least twice as large. Consequences of the electrical transport in these systems will be discussed.
Nanoicosahedral quasicrystalline phase in Zr–Pd and Zr–Pt binary alloys
Authors: Saida J. , Matsushita M. , Inoue A.
Published: July 2002

It is found that a nanoicosahedral phase in the diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nanoicosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. The slight redistribution of approximately 3 at % is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nanoicosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. It is suggested that the precipitation of nanoicosahedral phase in the Zr70Pd30 alloy takes place by a diffusion-controlled growth mode accompanying an increase in nucleation rate. The activation energy for grain growth is calculated to be 270 kJ mol−1, which implies the growth of icosahedral phase without a long-range atomic redistribution. The icosahedral medium-range order in the diameter range less than ∼2 nm is observed in the high-resolution electron micrographs of the melt-spun Zr70Pd30 and Zr80Pt20 amorphous alloys. It is realized that the icosahedral quasicrystalline phase can grow easily with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nanoicosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys appears to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states.
Solvent effect on the nuclear magnetic shielding: ab initio study by the combined reference interaction site model and electronic structure theories
Authors: Yamazaki Takeshi , Sato Hirofumi , Hirata Fumio
Published: July 2002

A method for calculating the nuclear magnetic shielding constant of atoms in solution is proposed based on the ab initio electronic structure theory combined with the extended reference interaction site model in statistical mechanics for molecular liquids. The method is applied to a water molecule solvated in water, acetone, chloroform, and carbon tetrachloride. The results for solvation effect demonstrate capability to predict the experimental results. The theory provides a tool to investigate the solvent effect on the nuclear magnetic shielding and its temperature dependence from a molecular viewpoint. The theory takes account for the effect of the electrostatic interaction on the electronic structure of solute, but disregards the electron overlap. The effect of intermolecular overlap of the electron on the nuclear magnetic shieldings is examined using a molecular cluster model.
Analog frequency modulation detector for dynamic force microscopy
Authors: Kobayashi Kei , Yamada Hirofumi , Itoh Hiroshi , Horiuchi Toshihisa , Matsushige Kazumi
Published: July 2002

A new analog frequency modulation (FM) detector (demodulator) for dynamic force microscopy (DFM) is presented. The detector is designed for DFM by utilizing the FM detection method where the resonance frequency shift of the force sensor is kept constant to regulate the distance between a tip and a sample surface. The FM detector employs a phase-locked loop (PLL) circuit using a voltage-controlled crystal oscillator (VCXO) so that the thermal drift of the output signal is negligibly reduced. The PLL is used together with a frequency conversion (heterodyne) circuit allowing the FM detector to be used for a wide variety of force sensors with the resonance frequency ranging from 10 kHz to 10 MHz. The minimum detectable frequency shift was as small as 0.1 Hz at the detection bandwidth of 1 kHz. The detector can track a resonance frequency shift as large as 1 kHz. We also present some experimental results including the observations of the Si(111)-7×7 reconstructed surface and fullerene molecules deposited on the surface by DFM using this FM detector.
Evolution of the growth stress, stiffness, and microstructure of alumina thin films during vapor deposition
Authors: Proost Joris , Spaepen Frans
Published: July 2002

The evolution of the growth stress and stiffness of amorphous alumina thin films was studied in situ during electron-beam evaporation on Si and sapphire substrates in the temperature range of 170–400 °C. The curvature of a cantilevered substrate was measured from the spacings between multiple laser reflections. Tensile growth stress developed from the start of deposition. For a deposition rate of 3 Å/s, its magnitude decreased with increasing deposition temperature in the thickness range of 0.1–0.7 μm, from 540±97 MPa at 170 °C to 215±15 MPa at 400 °C. Ex situ analysis by atomic force microscopy (AFM) showed an island growth mode, with average radii at 170 and 400 °C of, respectively, 34±5 and 44±4 nm. For all thicknesses between 0.2 and 0.6 μm, the O/Al ratio was 1.51±0.03 and the density 3.15±0.27 g/cm3. No change in stress was observed during isothermal annealing after deposition. Tensile stress, therefore, cannot be explained by the Nix–Hoffman coalescence mechanism, changes in stoichiometry or density, or microstructural changes such as island growth. A constant biaxial modulus of 197±30 GPa was measured at 400 °C up to a thickness of 1.17 μm when depositing at 3 Å/s. This value was identical to that of films thinner than 0.30 μm deposited at an average rate of 6 Å/s at 400 °C. Above 0.30 μm, the modulus of these films decreased continuously to a value of 50±8 GPa at a final thickness of 2.05 μm. The decrease in modulus is attributed to the presence of open, cylindrical pores with a volume fraction of 27% at the final thickness, determined by adsorption porosimetry. The final average growth stress at 3 and 6 Å/s was, respectively, 171 and 40 MPa; the ratio is similar to that of the biaxial moduli. For films deposited at 6 Å/s, the thickness dependence of the growth stress and biaxial modulus was also similar. A constant ratio of stress to modulus, independent of film thickness, was found at other deposition temperatures as well. This suggests that at a given temperature, a constant strain is generated throughout the growth of amorphous alumina films, up to a thickness of 3 μm. New analytical expressions were derived to quantify the effect of surface roughening on the reflectance signal of a substrate/film/ambient optical system. Using the measured intensity of the laser reflections in the in situ curvature measurement, a constant root-mean-square roughness was found for deposition at 170 °C. At 400 °C, the surface roughness increased linearly with the thickness, in qualitative agreement with ex situ AFM measurements.
Plasmon energy shift in porous silicon measured by x-ray photoelectron spectroscopy
Authors: Mannella N. , Gabetta G. , Parmigiani F.
Published: July 2002

In order to provide experimental support for quantum confinement models describing electronic effects in porous silicon (p-Si), the Si 2s and Si 2p plasmon losses have been studied by x-ray photoelectron spectroscopy. The p-Si plasmon energy was found at a value 0.8÷1.6 eV higher than that of bulk Si (17.4 eV), as measured on the cleaned Si substrate as a reference. The magnitude of these shifts suggests possible quantum confinement effects ascribed to the p-Si nanostructures.
Wrinkling of a compressed elastic film on a viscous layer
Authors: Huang R. , Suo Z.
Published: July 2002

A compressively strained elastic film bonded to a viscous layer can form wrinkles. The present study provides a theoretical model for the wrinkling process. The elastic film is modeled with the nonlinear theory of a thin plate subject to in-plane and out-of-plane loads. The flow of the viscous layer is modeled with the theory of lubrication. The interface between the elastic film and the viscous layer is assumed to be perfect with no slipping or debonding. A set of partial differential equations evolves the deflection and the in-plane displacements as functions of time. A linear stability analysis identifies the critical wave number, below which the elastic film is unstable and the wrinkles can grow. For any fixed wave number less than the critical wave number, the wrinkles reach a kinetically constrained equilibrium configuration, in which the stress is partially relaxed in the elastic film and the viscous layer stops flowing. Numerical simulations reveal rich dynamics of the system with many unstable equilibrium configurations.
Simulation of direct injection scheme for RFQ linac
Authors: Okamura M. , Katayama T. , Jameson R. A. , Takeuchi T. , Hattori T.
Published: July 2002

A new efficient injection method from a laser ion source to a RFQ was proposed and is being tested in RIKEN (The Institute of Physical and Chemical Research, Japan). Laser plasma is induced just before the entrance of the RFQ and is injected directly into the RFQ channel. In order to understand this new scheme, a particle tracking simulation study, which focused on the entrance of the RFQ, has been started with three-dimensional (3D) space charge effect in a realistic 3D electric field map. According to the beam tracking calculation, the predicted currents are smaller than experimentally obtained values. To obtain better accuracy of the simulation, motion of electrons should be described adequately.
Electrical properties of microporous rock as a function of saturation and temperature
Authors: Roberts Jeffery J.
Published: July 2002

We measured the electrical resistivity of densely welded tuff (Topopah Spring tuff) as a function of saturation by water between 23 and 145 °C. Measurements at 23–95 °C were performed at ambient pressure and measurements up to 145 °C were performed at pressures up to 5.5 MPa in an externally heated pressure vessel. Pore and confining pressures were controlled independently, allowing electrical measurements as the sample was subjected to boiling conditions. Resistivity changes associated with liquid water flashing to steam were observed. Incremental increases in resistivity with decreasing pore pressure are attributed to vapor pressure lowering caused by capillary tension in the nanometer-size pores. This result has important implications for models of reservoir engineering, geologic nuclear-waste disposal, and geophysical sensing techniques.
A theory of electrical conductivity of molten salt
Authors: Koishi T. , Kawase S. , Tamaki S.
Published: July 2002

The electrical conductivity of molten salt has been theoretically investigated starting from the linear response theory in view of a microscopic point. The velocity correlation functions in molten salt are expressed in terms of pair potentials and pair distribution functions in detail. Using these functions and generalized Langevin equations for the cation and anion of molten salt, the unified relations among the conductivity coefficients are obtained. In particular, it is shown that the ratio of partial conductivities, σ+/σ−, is equal to the inverse mass ratio, m−/m+. The friction constant of this molten salt is also expressed in terms of the pair potential and pair distribution function, by using the fluctuation dissipation theorem for random fluctuating force. Numerical results for molten alkali halides are presented and they are, more or less, the same order as the experimental results and computational ones.
Nonlinear regime of a multimode Richtmyer–Meshkov instability: A simplified perturbation theory
Authors: Vandenboomgaerde Marc , Gauthier Serge , Mügler Claude
Published: July 2002

In this paper we present a drastic simplification of the perturbation method for the Richtmyer–Meshkov instability developed by Zhang and Sohn [Phys. Fluids 9, 1106 (1997)]. This theory is devoted to the calculus of the growth rate of the perturbation of the interface in the weakly nonlinear stage. In the standard approach, expansions appear to be power series in time. We build accurate approximations by retaining only the terms with the highest power in time. This simplifies and accelerates the solution. High-order expressions are then easily reachable. Furthermore, computations for multimode interfaces become tractable. The accuracy of this approach is checked against two-dimensional numerical simulations. The selection mode process is studied and the phase between modes is shown to be as important as the wave number or the amplitude. Inferences for the intermediate nonlinear regime are also proposed. In particular, a class of homothetic configurations is inferred; its validity is verified with numerical simulations even as vortex structures appear at the interface.