bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic Transition Probabilities for Forbidden Lines of the Iron Group Elements: (A Critical Data Compilation for Selected Lines)
Authors: Smith M. W. , Wiese W. L.
Published: June 2010

Atomic transition probabilities for about 750 forbidden spectral lines for elements of the iron group, specifically V, Cr, Mn, Fe, Co, and Ni, have been critically evaluated and compiled using all available literature sources. The selection of the spectra and elements has been made primarily according to their astrophysical importance. The data are presented in separate tables for each element and stage of ionization, and for each ion the data are arranged according to multiplets. For each line within a multiplet the transition probability for spontaneous emission is listed along with the standard spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the upper and lower states. In addition, the estimated accuracy and the source are indicated. In short introductions which precede the individual tables for the ions the main justifications for the choice of the adopted data and for the accuracy rating are discussed. A general introduction contains a detailed discussion of the critical factors entering into the calculations. It also includes detailed comparisons of calculated data with astrophysical observations and a few laboratory results, which serve as a valuable indication for the validity of the estimated accuracies.
Microwave Spectra of Molecules of Astrophysical Interest: IV. Hydrogen Sulfide
Authors: Helminger Paul , DeLucia Frank C. , Kirchhoff William H.
Published: June 2010

The available data on the microwave spectrum of hydrogen sulfide are critically reviewed for information applicable to radio astronomy. Molecular data such as rotational constants, centrifugal distortion constants, hyperfine coupling parameters, and dipole moments are tabulated. A detailed centrifugal distortion calculation has been carried out for the most abundant isotopic form of this molecule, H232S, as well as for HD32S. Transitions have been predicted and tabulated for the frequency range 1 MHz to 1000 GHz for H232S and 1 MHz to 700 GHz for HD32S. All predicted transitions include 95 percent confidence limits; estimated error limits have been reported for all measured transitions. Observed transitions of H232S and H234S are also listed.
Tables of Molecular Vibrational Frequencies: Part 7
Authors: Shimanouchi T.
Published: June 2010

The compilations of fundamental vibrational frequencies of molecules previously published in the NSRDS-NBS publication series and in this journal are here extended to 50 additional molecules. Selected values of the fundamental vibrational frequencies are given for each molecule, together with observed infrared and Raman spectral data and citations to the original literature. The selection of vibrational fundamentals has been based on careful studies of the spectral data and comprehensive normal-coordinate analyses. An estimate of the accuracy of the selected values is included. The tables provide a convenient source of information for those who require vibrational energy levels and related properties in molecular spectroscopy, thermodynamics, analytical chemistry, and other fields of physics and chemistry.
Energy Levels of Neutral Helium (4He I)
Authors: Martin W. C.
Published: June 2010

This compilation of all identified levels is based on the most accurate available observations. It includes 48 levels above the He II 12S limit (two-electron excitation).
Survey of Photochemical and Rate Data for Twenty-eight Reactions of Interest in Atmospheric Chemistry
Authors: Braun W. , Brown R. L. , Garvin D. , Herron J. T. , Huie R. E. , Kurylo M. J. , Laufer A. H. , McKinley J. D. , Okabe H. , Scheer M. D. , Tsang W. , Stedman D. H.
Published: June 2010

Photochemical and rate data have been evaluated for 28 gas phase reactions of interest for the chemistry of the stratosphere. The results are presented on data sheets, one per reaction. For each reaction, the available data are summarized. Where possible there is given a preferred value for the rate constant or, for the photochemical reactions, preferred values for primary quantum yields and optical absorption coefficients.
Compilation of the Static Dielectric Constant of Inorganic Solids
Authors: Young K. F. , Frederikse H. P. R.
Published: June 2010

This compilation contains values of the static dielectric constant of more than 300 inorganic solids. The temperature and frequency of the measurements are listed and the magnitude of the loss tangent is indicated if known. For ninety materials — including most ferroelectrics and antiferroelectrics and several oxides and halides — additional information is presented in the form of graphs depicting the temperature dependence of the dielectric constant. In a few cases the frequency and pressure dependences are also shown. The basic principles and formulas pertinent to the field of dielectrics are reviewed in a short introduction. This part also mentions several measuring techniques and indicates the criteria used for data selection.
Ideal Gas Thermodynamic Properties of Ethane and Propane
Authors: Chao J. , Wilhoit R. C. , Zwolinski B. J.
Published: June 2010

The thermodynamic properties (Cpo, So, Ho−H0o, (Ho−H0o)/T,−(Go−H0o)/T, ΔHfo, ΔGfo and log Kf) for ethane and propane in the ideal gaseous state in the temperature range from 0 to 1500 K and at 1 atm were calculated by statistical thermodynamic methods based on a rigid-rotor harmonic-oscillator model. The internal rotation contributions to thermodynamic functions were evaluated by using a partition function formed by summation of internal rotation energy levels. The calculated heat capacities and entropies compare favorably with available experimental data.
Rate Constants for the Reactions of Atomic Oxygen (O 3P) with Organic Compounds in the Gas Phase
Authors: Herron John T. , Huie Robert E.
Published: June 2010

Rate constants for the reactions of atomic oxygen (O 3P) with organic compounds in the gas phase are compiled and critically evaluated. Data are given here as originally reported in the literature for a total of 107 organic reactants. From a critical evaluation of the data, recommended values for rate constants are given over specified temperature intervals, and where possible at 298 K and 1000 K. Estimated error limits are assigned to all recommended values.
First Spectra of Neon, Argon, and Xenon 136 in the 1.2–4.0 μm Region
Authors: Humphreys Curtis J.
Published: June 2010

Descriptions of the first spectra of neon, argon, and xenon 136, comprising calculated wavelengths, calculated wave numbers, relative intensities, and classifications, are presented. The calculated values are derived from currently best established energy levels, obtained mostly from interferometric observations and adopted as standards by the International Astronomical Union. All listed lines have actually been observed. This paper makes available a compilation of all results previously presented in fragmentary or relatively inaccessible reports with intensities normalized to as nearly a uniform scale as the various observations permit.
The Viscosity and Thermal Conductivity Coefficients of Dilute Argon, Krypton, and Xenon
Authors: Hanley H. J. M.
Published: June 2010

The viscosity and thermal conductivity coefficients of dilute argon, krypton, and xenon are reviewed and tables of recommended values presented. The tables were generated using the appropriate kinetic theory expressions with the m-6–8 potential. The temperature range covers from about one-half critical temperature to 2000 K for each gas. A general estimate of the accuracy is one percent increasing to one and three-quarters percent for temperatures above 1000 K.
Ideal Gas Thermodynamic Properties of Eight Chloro- and Fluoromethanes
Authors: Rodgers A. S. , Chao J. , Wilhoit R. C. , Zwolinski B. J.
Published: June 2010

The structural data, vibrational assignments, enthalpies of vaporization and formation for chloromethane, dichloromethane, trichloromethane, tetrachloromethane, fluoromethane, difluoromethane, trifluoromethane, and tetrafluoromethane were critically reviewed. Based on the selected best values, the thermodynamic properties for each of these eight chloro- and fluoromethanes were calculated by statistical thermodynamic methods using the rigid-rotor harmonic-oscillator approximations. The derived entropies and heat capacities are compared with the available third law entropies and vapor heat capacities. The calculated values of Cpo, So, and ΔHfo at 298.15 and 700 K are compared with those reported in the other major compilations.
Critical Analysis of Heat—Capacity Data and Evaluation of Thermodynamic Properties of Ruthenium, Rhodium, Palladium, Iridium, and Platinum from 0 to 300K. A Survey of the Literature Data on Osmium.
Authors: Furukawa George T. , Reilly Martin L. , Gallagher John S.
Published: June 2010

The literature sources of heat-capacity data on ruthenium, rhodium, palladium, osmium, iridium, and platinum have been compiled and the data critically analyzed. Except for osmium where data are lacking, best values of thermodynamic properties have been evaluated between 0 and 300 K from the analyses. The literature values of heat capacity, the electronic coefficient of heat capacity (γ), and the zero K limiting Debye characteristic temperature (θD(0)) are compared. The sources of data are tabulated chronologically along with the temperature range of measurements, purity of sample, and the pertinent experimental procedures used. A bibliography of the references is listed.
Microwave Spectra of Molecules of Astrophysical Interest VII. Carbon Monoxide, Carbon Monosulfide, and Silicon Monoxide
Authors: Lovas Frank J. , Krupenie Paul H.
Published: June 2010

The available data on the microwave spectra of carbon monoxide, carbon monosulfide, and silicon monoxide are critically reviewed for information applicable to radio astronomy. Molecular data such as rotational constants, centrifugal distortion parameters, dipole moments, hyperfine coupling constants, and structure are tabulated. Observed rotational transitions are presented for all measured isotopic forms of these molecules. All of the available data has been analyzed in order to predict all rotational transitions of these molecules up to 300 GHz. Error limits have been taken from the original literature for each measured transition frequency. All predicted transition frequencies are given with estimated uncertainties which represent the 90 percent confidence limit.
JANAF Thermochemical Tables, 1974 Supplement
Authors: Chase M. W. , Curnutt J. L. , Hu A. T. , Prophet H. , Syverud A. N. , Walker L. C.
Published: June 2010

The thermodynamic tabulations previously published as NSRDS-NBS-37 are extended by 154 new and revised tables. The JANAF Thermochemical Tables cover the thermodynamic properties over a wide temperature range with single phase tables for the crystal, liquid, and ideal gas state. The properties given are heat capacity, entropy, Gibbs energy function, enthalpy, enthalpy of formation, Gibbs energy of formation, and the logarithm of the equilibrium constant for formation of each compound from the elements in their standard reference states. Each tabulation lists all pertinent input data and contains a critical evaluation of the literature upon which these values are based. Literature references are given.
High Temperature Properties and Decomposition of Inorganic Salts, Part 4. Oxy-Salts of the Halogens
Authors: Stern Kurt H.
Published: June 2010

The literature dealing with the high-temperature behavior of inorganic oxygen-containing salts of chlorine, bromine and iodine has been critically reviewed. Values of (GTo−H298o)/T of the reactants and products of the decomposition reactions were calculated and have been tabulated from 298 K up to as high a temperature as possible. Equilibrium constants and partial pressures were tabulated. Auxiliary data on phase transitions and densities have also been included. Qualitative information about the thermal decomposition of the salts is reviewed.
Diffusion in Copper and Copper Alloys, Part II. Copper-Silver and Copper-Gold Systems
Authors: Butrymowicz Daniel B. , Manning John R. , Read Michael E.
Published: June 2010

A survey, comparison, and critical analysis is presented of data compiled from the scientific literature concerning diffusion in copper-silver and copper-gold systems. Here the term ``copper alloy system'' is interpreted in the broadest sense. For example, the review of diffusion in the Cu-M system reports all diffusion situations which involve both copper and element M, including diffusion of Cu in M or in any binary, ternary, or multicomponent alloy containing M: diffusion of M in Cu or in any alloy containing Cu; and diffusion of any element in any alloy containing both Cu and M. Topics include volume diffusion, surface diffusion, grain boundary diffusion, tracer diffusion, alloy interdiffusion, electromigration, thermomigration, strain enhanced diffusion, and diffusion in molten metals. An extensive bibliography is presented along with figures, tabular presentation of data and discussion of results.
Reference Wavelengths From Atomic Spectra in the Range 15 Å to 25000 Å
Authors: Kaufman Victor , Edlén Bengt
Published: June 2010

This is a compilation of atomic lines with accurately known wavelengths covering the range from 15 Å to 25000 Å. The tables are a fairly complete record of available spectrum lines that meet the requirements for useful references with regard to wavelength accuracy and intensity. In general, wavelength uncertainties range from 0.0001 Å to 0.002 Å. Section 1, λ > 2000 Å, gives λair and λvac for 3341 lines belonging to thirteen different spectra of ten elements. Section 2, λ < 2000 Å, contains 2091 lines belonging to 59 different spectra of 28 elements. The lines of section 2 are listed both by spectrum (i.e. element and ionization stage) and in a finding list arranged in order of decreasing wavelength. Detailed explanations of the data and the sources used for the compilation are included.
The Viscosity and Thermal Conductivity Coefficients for Dense Gaseous and Liquid Argon, Krypton, Xenon, Nitrogen, and Oxygen
Authors: Hanley H. J. M. , McCarty R. D. , Haynes W. M.
Published: June 2010

Data for the viscosity and thermal conductivity coefficients of argon, nitrogen, and oxygen have been critically evaluated. A functional form to represent the data has been proposed. The function is basically the same for both coefficients. The critical point enhancement in the thermal conductivity coefficient is included. Transport properties of krypton and xenon are calculated by means of the principle of corresponding states. Tables of values are presented in the range from about the triple point temperature to 500 K for pressures up to 100 MPa. Care has been taken to ensure that the calculated values are consistent with reliable equation-of-state data and also with dilute gas transport coefficients previously determined. The uncertainties of the tabulated coefficients are discussed in the text. The correlation further serves to clarify the state of the art concerning transport data and experiment and to emphasize gaps in data coverage.
General hypothesis governing the growth of single-crystal nanowires
Authors: Mohammad S. Noor
Published: June 2010

The growth and growth rates of single-crystal nanowires by vapor phase mechanisms have been studied. A hypothesis has been proposed, which lays down foundation for the nanowire growth. It redefines the basic concepts of droplets from seeds and describes the fundamental basis of the adhesive properties of droplets. A set of droplet characteristics has been defined, a model in the framework of the hypothesis has been developed, and theoretical calculations have been performed. Experiments have also been carried out. Close correspondences between the theoretical and the experimental results lend support for the hypothesis and the model. Additional experimental evidences quantify the validity of the hypothesis. The calculated results resolve conflicts and controversies. They address the roles of catalysts in the growth of single-crystal nanowires. They shed light on the basic differences in the growth of thin and thick nanowires. They elucidate possible relationship between eutectic temperature and activation energy in the vapor-liquid-solid growth. They provide ground rules that govern the relative supplies of constituent vapor species for the growth of compound semiconductor nanowires. They explain how the same alloyed droplet (e.g., Au/Ga) is activated differently under the influence of different nonmetal elements of different nanowires (for example, As of GaAs, P of GaP, and N of GaN). They demonstrate, for example, that the nanowire growth may be achieved by means that creates thermodynamic imbalance and nanopores inside the seeds at temperatures far below the seed’s melting temperature. Alloying in the vapor-solid-liquid mechanism is one such means where growth of even thick nanowires (radius of rD≥50 nm) is possible at temperatures far below the eutectic temperature. The hypothesis, is called the simple, novel, and malleable (SNM) hypothesis. This hypothesis, together with the model, appears to have solved the basic origin of the nanowire growth. It demonstrates that various vapor phase mechanisms are essentially different forms of one and only one mechanism. They differ only to the extent that different techniques are employed in different mechanisms to create molten/semimolten seeds for nanowire growths.
Surface and interface states of gallium-polar versus nitrogen-polar GaN: Impact of thin organic semiconductor overlayers
Authors: Kim Hyunjin , Guan Ze-Lei , Sun Qian , Kahn Antoine , Han Jung , Nurmikko Arto
Published: June 2010

Using ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy, we have investigated the electronic properties of interfaces between copper phthalocyanine (CuPc) films and gallium-polar (Ga-polar) and nitrogen-polar (N-polar) GaN surfaces, respectively. Prior to the deposition of CuPc films, the clean Ga-polar and N-polar surfaces exhibited about 0.6 and 0.13 eV upward band bendings, respectively, showing the influence of electronic states on the surface termination and growth direction. With the deposition of ultrathin layers of CuPc, no additional band bending or charge displacement was observed for the Ga-polar heterointerface. In contrast, the N-polar interface exhibited an additional 0.54 eV band bending upon deposition of only a CuPc monolayer, attributed to a partial electron displacement from GaN to CuPc. The difference between the two cases is interpreted in terms of the difference between the electron affinity of the N-polar and Ga-polar GaN surfaces. With potential device use in mind, GaN/CuPc hybrid photodetector devices were fabricated and their photocurrent responses were investigated for possible applications as photosensors.
Phase diagrams, dielectric response, and piezoelectric properties of epitaxial ultrathin (001) lead zirconate titanate films under anisotropic misfit strains
Authors: Qiu Q. Y. , Alpay S. P. , Nagarajan V.
Published: June 2010

We develop a nonlinear thermodynamic model to predict the phase stability of ultrathin epitaxial (001)-oriented ferroelectric PbZr1−xTixO3 (PZT) films with x=1.0, 0.9, 0.8, and 0.7 on substrates which induce anisotropic in-plane strains. The theoretical formalism incorporates the relaxation by misfit dislocations at the film deposition temperature, the possibility of formation of ferroelectric polydomain structures, and the effect of the internal electric field that is generated due to incomplete charge screening at the film-electrode interfaces and the termination of the ferroelectric layer. This analysis allows the development of misfit strain phase diagrams that provide the regions of stability of monodomain and polydomain structures at a given temperature, film thickness, and composition. It is shown that the range of stability for rotational monodomain phase is markedly increased in comparison to the same ferroelectric films on isotropic substrates. Furthermore, the model finds a strong similarity between ultrathin PbTiO3 and relatively thicker PZT films in terms of phase stability. The combinations of the in-plane misfit strains that yield a phase transition sequence that results in a polarization rotation from the c-phase (polarization parallel to the [001] direction in the film) to the r-phase, and eventually to an in-plane polarization parallel to the [110] direction (the aa-phase) is determined to be the path with the most attractive dielectric and piezoelectric coefficients resulting in enhancements of 10 to 100 times in the dielectric permittivity and piezoresponse compared to bulk tetragonal ferroelectrics of the same PZT composition.
Singular perturbations with boundary conditions and the Casimir effect in the half space
Authors: Albeverio S. , Cognola G. , Spreafico M. , Zerbini S.
Published: June 2010

We study the self-adjoint extensions of a class of nonmaximal multiplication operators with boundary conditions. We show that these extensions correspond to singular rank 1 perturbations (in the sense of Albeverio and Kurasov [Singular Perturbations of Differential Operaters (Cambridge University Press, Cambridge, 2000)]) of the Laplace operator, namely, the formal Laplacian with a singular delta potential, on the half space. This construction is the appropriate setting to describe the Casimir effect related to a massless scalar field in the flat space-time with an infinite conducting plate and in the presence of a pointlike “impurity.” We use the relative zeta determinant (as defined in the works of Müller [“Relative zeta functions, relative determinants and scattering theory,” Commun. Math. Phys. 192, 309 (1998)] and Spreafico and Zerbini [“Finite temperature quantum field theory on noncompact domains and application to delta interactions,” Rep. Math. Phys. 63, 163 (2009)]) in order to regularize the partition function of this model. We study the analytic extension of the associated relative zeta function, and we present explicit results for the partition function and for the Casimir force.
Molecular simulation on interfacial structure and gettering efficiency of direct silicon bonded (110)/(100) substrates
Authors: Kariyazaki Hiroaki , Aoki Tatsuhiko , Izunome Koji , Sueoka Koji
Published: June 2010

Direct silicon bonded (DSB) substrates with (110)/(100) hybrid orientation technology are attracting considerable attention as a promising technology for high performance bulk complementary metal-oxide semiconductor technology. We have investigated the structure and the gettering efficiency of the (110)/(100) interface parallelling each ⟨110⟩ direction (DSB interface) by molecular dynamics (MD) and first-principles calculation. In MD calculations, initial calculation cells of 15 atomic-configurations with coincidence-site lattices were prepared. It was found that (i) the calculated DSB interface was stable independent of the initial atomic-configurations and (ii) the interfacial structures were essentially the same among the calculated models. Moreover, the calculated interfacial structure corresponds to the reported TEM observation. The first-principles calculation showed that Si atoms in the DSB interface formed covalent bonding. The dangling bonds in Si (110) and (100) surfaces disappeared due to restructuring in the DSB interface. Furthermore, the DSB interface, which exists just below the device active region, was found to be an efficient gettering site for Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Hf atoms.
A model for the dependence of the electrical conductance with the applied stress in insulating-conducting composites
Authors: Negri R. Martín , Rodriguez Silvio D. , Bernik Delia L. , Molina Fernando V. , Pilosof Ana , Perez Oscar
Published: June 2010

A model for the dependence of the electrical conductance, G, with the strain induced by external mechanical stress in conducting particles-polymer composites is presented. The model assumes that the percolation probability between neighboring particles must depart from a scale-invariant behavior but saturate at moderated-high strains, reaching percolation path’s saturation, with sigmoid dependence. This dependence is obtained by proposing a dynamic picture where contacts or bonds between neighboring particles are created but also destructed when a stress is applied and relatively moderated or high strains, ε, are produced in the composite. The electrical conductance of prepared graphite-polydimethylsiloxane composites were measured as function of the applied pressure and fitted by the presented model. The elastic response to the uniaxial compression was studied using a texture analyzer. The possibility of nonuniversal effects in the conduction critical exponent, t, was taken into account. It is concluded that the saturation of the response in the G versus ε plots cannot be assigned to nonuniversal behavior of the exponent t, or to saturation of the elastic response. On the other hand, the presented model accounts for all the main experimental features observed in these systems and for previously reported data of elastomer composites. The simulated behavior of the piezoresistivity coefficient is also in qualitative agreement with previous reports.
Investigation of the 420 nm differential reflectometry peak for 2,4,6 trinitrotoluene by computational chemistry
Authors: Fuller-Tedeschi Anna M. , Hummel Rolf
Published: June 2010

It has been found that 2,4,6 trinitrotoluene (TNT) displays a 420 nm peak in differential reflection spectrometry spectra. Differential reflection spectrometry uses UV and visible light to measure the photon energy absorbed by electrons when they move to a higher energy state. This particular optical feature for TNT has been previously reported by the authors. The physical origin of the described feature is investigated using computational chemistry. Through this molecular modeling, circumstances where the 420 nm feature may occur have been isolated. In addition, the participating molecular orbitals have been suggested from these calculations as in the nitro groups and the ring carbon bonded to this group.
Magnetoexcitons in electron-hole bilayer nanotubes made of rolled-up type-II band aligned quantum wells
Authors: Bagheri Mehran
Published: June 2010

A new Aharonov–Bohm (AB) system based on spatially separated electron-hole bilayer nanotubes made of rolled-up type-II band aligned AlAs/GaAs quantum wells for observation of the so-called excitonic AB-effect is theoretically investigated. Our results explain how the AB oscillations are manifested in both the spectrum and optical intensity of the exciton through angular momentum transitions from zero to successive nonzero values and persistent fluctuations, respectively. We attribute the former regular transitions and later undamped oscillations to the radial and axial charge separation appeared in the electron-hole Coulomb attraction, respectively. The impact of the magnetic field on the binding energy, magnetization, and energy-shift in the magnetoexciton is examined as well. Such study lead to the proposal that electron-hole bilayer nanotubes of type-II could be utilized as magneto-optical switching devices based on the AB-effect which may have potential applications in quantum information systems.
Nanostructural evolution during emission of CsI-coated carbon fiber cathodes
Authors: Drummy Lawrence F. , Apt Scott , Shiffler Don , Golby Ken , LaCour Matt , Maruyama Benji , Vaia Richard A.
Published: June 2010

Carbon-based nanofiber and microfiber cathodes exhibit very low voltages for the onset of electron emission, and thus provide exciting opportunities for applications ranging from high power microwave sources to field emission displays. CsI coatings have been experimentally shown to lower the work function for emission from the fiber tips, although little is known about the microstructure of the fibers themselves in their as-received state, after coating with CsI, or after being subjected to high voltage cycling. Longitudinal cross sections of the original, unused CsI-coated fibers produced by focused ion beam lift-out revealed a nanostructured graphitic core surrounded by an amorphous carbon shell with submicron sized islands of crystalline CsI on the outer surface. Aberration-corrected high resolution electron microscopy (HREM) of the fiber core achieved 0.10 nm resolution, with the graphite (200) clearly visible in digital fast Fourier transformations of the 2–4 nm highly ordered graphitic domains. As the cathode fibers are cycled at high voltage, HREM demonstrates that the graphitic ordering of the core increases with the number of cycles, however the structure and thickness of the amorphous carbon layer remains unchanged. These results are consistent with micro-Raman measurements of the fiber disordered/graphitic (D/G) band ratios. After high voltage cycling, a uniform ∼100 nm film at the fiber tip was evident in both bright field transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (STEM). Low-dose electron diffraction techniques confirmed the amorphous nature of this film, and STEM with elemental mapping via x-ray energy dispersive spectroscopy indicates this layer is composed of CsIO. The oxidative evolution of tip composition and morphology due to impurities in the chamber, along with increased graphitization of the fiber core, contributes to changes in emission behavior with cycling.
Time-resolved x-ray microdiffraction studies of phase transformations during rapidly propagating reactions in Al/Ni and Zr/Ni multilayer foils
Authors: Trenkle J. C. , Koerner L. J. , Tate M. W. , Walker Noël , Gruner S. M. , Weihs T. P. , Hufnagel T. C.
Published: June 2010

We showed how intermetallic formation reactions can be studied under rapid heating (106–107 K s−1) using x-ray microdiffraction with temporal resolution on microsecond time scales. Rapid heating was achieved by initiating an exothermic reaction in multilayer foils comprising alternating nanoscale layers of elemental metals. The reaction occurred in a front ∼100 μm wide which propagated across the foil at ∼1–10 m s−1. By using synchrotron x-rays focused to a small spot (60 μm diameter) and a fast pixel-array detector, we were able to track the evolution of phases in the reaction front during the initial heating transient, which occurred in approximately 1 ms, through cooling over a period of hundreds of milliseconds. In Al/Ni multilayer foils, the first phases to form were an Al-rich liquid and the cubic intermetallic AlNi (which likely formed by nucleation from the liquid). In foils of overall composition AlNi, this is the stable intermetallic and the only phase to form. In foils of composition Al3Ni2, during cooling we observed a peritectic reaction between AlNi and the remaining liquid to form Al3Ni2, which is the stable phase at room temperature and the final product of the reaction. This is in contrast to the sequence of phases under slow heating, where we observed formation of nonequilibrium Al9N2 first and do not observe formation of a liquid phase or the AlNi intermetallic. We also observed formation of an amorphous phase (along with crystalline ZrNi) during rapid heating of Zr/Ni multilayers, but in this system the temperature of the reaction front never reached the lowest liquidus temperature on the Zr–Ni phase diagram. This implies that the amorphous phase we observed was not a liquid arising from melting of a crystalline phase. We suggest instead that a Zr-rich amorphous solid formed due to solid-state interdiffusion, which then transformed to a supercooled liquid when the temperature exceeded the glass transition temperature. Formation of the supercooled liquid presumably facilitated continued rapid intermixing, which may be necessary to sustain a self-propagating reaction front in this system.
Metastability around the insulator-metal transition in La0.2Pr0.5Ca0.3MnO3
Authors: Chatterjee S. , Giri S. , Majumdar S.
Published: June 2010

The magnetic and magnetotransport properties of the doped manganite with nominal composition La0.2Pr0.5Ca0.3MnO3 are studied around the first order insulator-metal transition. The region across the first order transition is found to be highly metastable with the coexisting metallic and insulating phases. The sample shows anomalous transport and magnetic behaviors, which is related to the field-induced arrested state in the region of phase separation. A large magnetoresistance is also present in the sample at the lowest temperature of measurements (well below the first order transition), which is possibly connected to the effect of electron tunneling through grain boundaries.
Multiconfiguration time-dependent Hartree approach to study the OH+H2 reaction
Authors: Bhattacharya Sayak , Panda Aditya N. , Meyer Hans-Dieter
Published: June 2010

Full dimensional quantum scattering calculations have been carried out for the OH+H2→H2O+H reaction on the Walch–Dunning–Schatz–Elgersma and Yang–Zhang–Collins–Lee surfaces employing an exact form of the kinetic energy operator. The multiconfiguration time-dependent Hartree (MCTDH) method has been used to perform the wave packet propagations. The MCTDH method uses relatively little memory and its numerical effort scales much more slowly with the dimensionality of the system compared to conventional propagation methods. The reaction probabilities and cross sections obtained on both the surfaces using the MCTDH method are in good agreement with the previous theoretical results. However, the cross sections on the two surfaces differ significantly as a function of the translational energy of the reagents. The difference in barrier heights for the two surfaces along with the transition state structures account for the different reaction probabilities obtained over the entire energy range considered.
Effective band gap narrowing of anatase TiO2 by strain along a soft crystal direction
Authors: Yin Wan-Jian , Chen Shiyou , Yang Ji-Hui , Gong Xin-Gao , Yan Yanfa , Wei Su-Huai
Published: June 2010

Due to its large band gap (3.2 eV), TiO2 cannot absorb sun light effectively. To reduce its band gap, various approaches have been attempted; most of them are using doping to modify its band structure. Using first-principles band structure calculations, we show that unlike the rutile phases, the band gap of TiO2 in the anatase phase can be effectively reduced by applying stress along a soft direction. We propose that this approach of tuning the band gap by applying stress along soft direction of a layered semiconductor is general and should be applicable to other anisotropic materials.
Rotational dynamics of trehalose in aqueous solutions studied by depolarized light scattering
Authors: Gallina M. E. , Comez L. , Morresi A. , Paolantoni M. , Perticaroli S. , Sassi P. , Fioretto D.
Published: June 2010

High resolution depolarized light scattering spectra, extended from 0.5 to 2×104 GHz by the combined used of a dispersive and an interferometric setup, give evidence of separated solute and solvent dynamics in diluted trehalose aqueous solutions. The slow relaxation process, located in the gigahertz frequency region, is analyzed as a function of temperature and concentration and assigned to the rotational diffusion of the sugar molecule. The results are discussed in comparison with the data obtained on glucose solutions and they are used to clarify the molecular origin of some among the several relaxation processes reported in literature for oligosaccharides solutions. The concentration dependence of relaxation time and of shear viscosity are also discussed, suggesting that the main effect of carbohydrate molecules on the structural relaxation of diluted aqueous solutions is the perturbation induced on the dynamics of the first hydration shell of each solute molecule.
Nonproportional scintillation response of NaI:Tl to low energy x-ray photons and electrons
Authors: Khodyuk I. V. , Rodnyi P. A. , Dorenbos P.
Published: June 2010

Nonproportional response of the scintillation yield of NaI:Tl was measured using highly monochromatic synchrotron irradiation ranging from 9–100 keV. Special attention is paid to the x-ray escape peaks. They provide us additional information about photon response in the range 0.9–12 keV. A rapid variation in the photon response curve is observed near the iodine K-electron binding energy. A dense sampling of data is performed around this energy and that data are used to apply a method, which we call K-dip spectroscopy. This method allows us to derive the electron response curve of NaI:Tl down to energies as low as 30 eV. A comparison of our data with data of others employing different methods is made. Advantages, limitations, and peculiarities of presented techniques and methods are discussed.
Molecular dynamical simulation of the behavior of early precipitated stage in aging process in dilute Cu–Cr alloy
Authors: Feng J. , Xiao B. , Liu L. , Chen J. , Du Y. , Zhou R.
Published: June 2010

The aging behaviors of Cu–Cr alloys in the early stage at different temperatures are investigated by molecular dynamics simulations. First principles potentials are used for the interactions between Cu and Cr atoms. The initial behavior of precipitation is characterized by transmission electron microscope and electron energy disperse spectroscopy. The results showed that Cu–Cr supersaturated solid solution is thermodynamically unstable. The mean-square displacements of the atoms are used to describe the diffusivity. At room temperature, the atoms only show harmonic vibrations near the equilibrium positions. The mutual diffusion at 873 K is different from the unidirectional diffusion in low temperatures. The calculation shows that aging process is accelerated with increasing temperature, which is not only due to the lower diffusion activation energy of Cr at higher temperature, but also because Cu atoms are also participated in the aging process. When “aging” at 1073 K, the precipitation of Cr element is dissolved again into Cu matrix, which is an “over-aging” state of Cu–Cr alloy at high temperature.
Mode characteristics of metallically coated square microcavity connected with an output waveguide
Authors: Che Kai-Jun , Huang Yong-Zhen
Published: June 2010

Mode characteristics of a square microcavity with an output waveguide on the middle of one side, laterally confined by an insulating layer SiO2 and a p-electrode metal Au, are investigated by two-dimensional finite-difference time-domain technique. The mode quality (Q) factors versus the width of the output waveguide are calculated for Fabry–Pérot type and whispering-gallery type modes in the square cavity. Mode coupling between the confined modes in the square cavity and the guided modes in the output waveguide determines the mode Q factors, which is greatly influenced by the symmetry behaviors of the modes. Fabry–Pérot type modes can also have high Q factors due to the high reflectivity of the Au layer for the vertical incident mode light rays. For the square cavity with side length 4 μm and refractive index 3.2, the mode Q factors of the Fabry–Pérot type modes can reach 104 at the mode wavelength of 1.5 μm as the output waveguide width is 0.4 μm.
Combined standard uncertainty in direct emissivity measurements
Authors: del Campo Leire , Pérez-Sáez Raúl B. , González-Fernández Luis , Tello Manuel J.
Published: June 2010

In order to design a device to carry out direct emissivity measurements, a key point is the analysis of all the uncertainty components that give rise to the combined standard uncertainty. This will permit to choose the most appropriate measurement method to minimize the uncertainty, and also to identify the sources of the largest errors. If the experimental device is already in use, the complete uncertainty characterization, in addition to the emissivity uncertainty calculation, will permit the improvement of the device capabilities. Thus, a guideline to the experimentalists working in this subject is provided. In this work, a complete study of the uncertainty components in direct emissivity determination is carried out. First of all, the emissivity measurement method and the uncertainty estimation methodology are introduced. After that, the influence of the uncertainties of each of the magnitudes used to obtain the emissivity is analyzed theoretically. The most important error sources depending on the measuring parameters have been identified. Finally, as a practical example, the error sources on a low emissivity sample are experimentally studied. In this case, it has been found that, at intermediate temperatures and short wavelength, the emissivity uncertainty is determined by the uncertainty in the sample temperature, whereas at long wavelength, the factor determining the emissivity uncertainty is the temperature uncertainty of the surroundings.
Hydrodynamic trap for single particles and cells
Authors: Tanyeri Melikhan , Johnson-Chavarria Eric M. , Schroeder Charles M.
Published: June 2010

Trapping and manipulation of microscale and nanoscale particles is demonstrated using the sole action of hydrodynamic forces. We developed an automated particle trap based on a stagnation point flow generated in a microfluidic device. The hydrodynamic trap enables confinement and manipulation of single particles in low viscosity (1–10 cP) aqueous solution. Using this method, we trapped microscale and nanoscale particles (100 nm–15 μm) for long time scales (minutes to hours). We demonstrate particle confinement to within 1 μm of the trap center, corresponding to a trap stiffness of ∼10−5–10−4 pN/nm.
Electrical characterization of 4H–SiC avalanche photodiodes containing threading edge and screw dislocations
Authors: Berechman R. A. , Skowronski M. , Soloviev S. , Sandvik P.
Published: June 2010

The reverse voltage current characteristics and electroluminescence of small area 4H–SiC avalanche photodiodes were investigated and correlated with the presence of threading screw and edge dislocations. Localized electroluminescence was observed at threading dislocations at voltages close to breakdown whereas diodes without any extended defects exhibited uniform light emission in the active area. Diodes containing either edge or screw dislocations were found to have excess leakage currents and breakdown prematurely compared to diodes without dislocations.
Identification of the deep level defects in AlN single crystals by electron paramagnetic resonance
Authors: Soltamov V. A. , Ilyin I. V. , Soltamova A. A. , Mokhov E. N. , Baranov P. G.
Published: June 2010

Electron paramagnetic resonance (EPR) at 9.4 and 35 GHz were studied on two types of AlN single crystals, grown by a sublimation sandwich method. These investigations revealed the presence of transition metals impurities in the first sample: Fe2+ (S=2) and some paramagnetic centers with S=3/2, we suggest Cr3+ or Ni3+ as the possible candidates. The EPR spectra of Fe2+ were observed up to the room temperature. After sample illumination at 5 K with light (wavelength shorter 700 nm) strong EPR signal with a g factor of shallow donors (SDs) and slightly anisotropic linewidth appears. This light-induced EPR signal, once excited at low temperature, still persists after switching off the light and is about constant up to 30 K then it drops quickly. SDs show a negative correlation energy U and oxygen in the N position (ON) is the most probable model. EPR spectra of deep-donor center which was assumed to be the nitrogen vacancy VN have been observed in the second sample. The x-ray irradiation leads to considerable enhancement of deep donor’s (VN) signals intensity. The annealing resulted in recombination thermoluminescence and the deep donor (VN) energy level was estimated to be about 0.5 eV. The models of shallow (ON) and deep (VN) donor centers were supported by comprehensive hyperfine structure analysis.
Temperature dependence of single-asperity friction for a diamond on diamondlike carbon interface
Authors: Dunckle C. G. , Altfeder I. B. , Voevodin A. A. , Jones J. , Krim J. , Taborek P.
Published: June 2010

A variable temperature, ultrahigh vacuum atomic force microscope (AFM) was used to characterize interfacial friction for a single-asperity diamond contact on a diamondlike carbon (DLC) substrate over a nominal substrate temperature range of 90 to 275 K. Calibrated friction force measurements were obtained by analyzing lateral force hysteresis loops as a function of normal force. For sufficiently large normal forces, the lateral force was proportional to the normal force, and a friction coefficient μ could be identified. μ varied approximately linearly with substrate temperature, with μ=0.28 at T=90 K and μ=0.38 at 275 K. These results are compared to other recent variable temperature AFM friction measurements and to theoretical calculations based on the Tomlinson model. This comparison is obscured by large, experimentally uncontrolled temperature differences between the tip and the substrate which inevitably exist in conventional, variable temperature AFMs. A thermal model which can be used to quantitatively estimate these temperature differences is presented.
Structural and room-temperature ferromagnetic properties of Fe-doped CuO nanocrystals
Authors: Li Youxia , Xu Mei , Pan Liqing , Zhang Yaping , Guo Zhengang , Bi Chong
Published: June 2010

Fe-doped CuO (Cu1−xFexO) nanocrystals (NCs) (x=0, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) are prepared by using the urea nitrate combustion method. X-ray diffraction (XRD) analysis confirmed the monoclinic structure of CuO. Single-phase structure is obtained for the 0%–20% Fe-doped CuO, whereas for the 25% and 30% Fe-doped CuO material, secondary phase, α-Fe2O3, is presented. Rietveld refinements of XRD data revealed that with an increase in Fe doping level, there is a monotonic increase in cation vacancies in the Fe-doped samples. X-ray photoelectron spectroscopy measurements on the Cu0.98Fe0.02O sample revealed that the Cu2+ sites are partly substituted by Fe3+ ions. The microstructure is investigated by high-resolution transmission electron microscopy. The magnetic hysteresis loops and the temperature dependence of magnetization of the samples indicated that the samples are mictomagnetic of ferromagnetic domains originated from ferromagnetic coupling between the doping Fe ions in Cu1−xFexO NCs randomly distributed in the antiferromagnetic CuO matrix. The Curie temperature of the ferromagnetic phase is higher than 400 K for all Fe-doped CuO samples. The ferromagnetic behavior of the samples is discussed.
Terahertz radiation from coherent antiferromagnetic magnons excited by femtosecond laser pulses
Authors: Nishitani Junichi , Kozuki Kohei , Nagashima Takeshi , Hangyo Masanori
Published: June 2010

We report on the observation of terahertz (THz) radiation emitted from antiferromagnetic (AFM) single-crystal nickel oxide irradiated with femtosecond laser pulses. Periodic oscillations observed in the THz waveforms are assigned to the radiation from coherent AFM magnons excited by the laser pulses. Impulsive stimulated Raman scattering process is a possible mechanism of the coherent AFM magnon excitation by the laser pulses. The excited magnons in NiO generate THz waves by magnetic dipole radiation, which is the inverse process of AFM resonance absorption of THz waves.
Ferroelectric Q-phase in a NaNbO3 epitaxial thin film
Authors: Yuzyuk Yu. I. , Shakhovoy R. A. , Raevskaya S. I. , Raevski I. P. , El Marssi M. , Karkut M. G. , Simon P.
Published: June 2010

Epitaxial NaNbO3 thin films have been grown by pulsed laser deposition on cubic (00l) MgO substrate with epitaxial (La0.5Sr0.5)CoO3 buffer layer. Micro-Raman spectroscopy studies revealed that the ferroelectric Q phase (Pmc21, Z=4) is stable in a 250-nm-thick film in contrast to the antiferroelectric phase P (Pbma, Z=8) known to exist in the bulk single crystals and ceramics of undoped stoichiometric NaNbO3. Temperature-dependent Raman spectra indicate that the Q phase is stable over a wide temperature range (at least from 80 to 600 K), while the low-temperature ferroelectric rhombohedral phase N, typical for NaNbO3 single crystals, is not observed.