bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Structure of the First Row Hydrides
Authors: King G. W.
Published: January 2005

Stehn's formulae for the energies of the first row hydrides, BH to FH, in terms of Heitler-London exchange integrals have been applied to more recent data. The empirically derived values for the integrals are now smooth functions of the atomic number, Z. They are also considered as functions of the internuclear distance, re, and taken in conjunction with data on BeH, and with the facts that re and the force-constant, k, are smooth functions of Z, but invariant to electronic excitation, the results show that it is 2s2—1s exchange that predominates in fixing the internuclear distance and force-constant. On the contrary, the dissociation energies cannot be expected to be smoothly dependent on Z, re or k. The heat of dissociation of NH is calculated by Stehn's formulae, after interpolating one exchange integral.
Fractionation of the Lithium and Potassium Isotopes by Chemical Exchange with Zeolites
Authors: Taylor Thomas Ivan , Urey Harold C.
Published: January 2005

A study has been made of the fractionation of the lithium isotopes by electrolysis and of the lithium, potassium, and nitrogen isotopes by chemical exchange with zeolites. The fractionation factor obtained by a ``batch'' electrolysis of lithium chloride solution was 1.039. The normal abundance ratio of the lithium and potassium isotopes was determined and found to be 11.71±0.14 for Li7 : Li6 and 14.10±0.09 for K39 : K41. The fractionation factor for the lithium isotopes in exchange with sodium zeolite was found to be 1.022. A partial separation of the lithium, potassium and nitrogen isotopes has been effected using long columns filled with zeolites. Both an increase and a decrease of about 25 percent from the normal abundance ratio has been obtained for the lithium isotopes and a change of about 10 percent for the potassium and nitrogen isotopes. Some of the factors involved in the mechanism of the process are discussed.
Interpretation of the Properties of Zinc Sulphide Phosphors
Authors: Seitz Frederick
Published: January 2005

The properties of pure and copper activated zinc sulfide phosphors are described, and an attempt is made to interpret these properties following the plan of a previous paper on alkali halide phosphors activated by thallium. It is pointed out, as has been done by previous workers, that the combination of photoconductivity and bimolecular decay law of phosphorescence implies that an ionization process accompanies the excitation of zinc sulfide phosphors. By applying the ideas of the quantum theory of solids, it is shown that this ionization process does not correspond to the freeing of an electron from the Zn++ or S—— ions of the lattice. It is concluded that the pure ZnS phosphor probably contains neutral interstitial zinc atoms, and that these are responsible for the luminescence and photoconductivity. By analogous reasoning, it is concluded that the copper activated phosphor contains interstitial copper atoms. The relative stability of interstitial copper atoms and substitutional copper ions is discussed in terms of the Schottky-Wagner theory of deviations from stochiometrical proportions. It is concluded that the interstitial copper atoms probably are in a metastable condition.
The Energy and Entropy of Activation of the Reaction Between Nitric Oxide and Chlorine
Authors: Welinsky Irving , Taylor H. Austin
Published: January 2005

Following a discussion of the concept of entropy of activation and methods for its calculation, it is shown that the energy of activation of the formation of nitrosyl chloride from nitric oxide and chlorine is temperature dependent and permits an evaluation of the entropy of activation. A critical analysis is made of previous work.
On Communal Entropy and the Theory of Fusion
Authors: Rice O. K.
Published: January 2005

The concept of ``communal'' entropy, introduced by Hirschfelder, Stevenson and Eyring, is further discussed in this paper. It appears from both theoretical and empirical considerations that the entropy of fusion of simple solids is not primarily concerned with the excitation of communal entropy. A discussion is given of the nature of communal entropy and its manner of excitation.
The Role of Free Radicals in Elementary Organic Reactions
Authors: Rice F. O. , Teller E.
Published: January 2005

The primary reactions between radicals and organic molecules are discussed from the point of view of a principle which states that there shall be least change in atomic position and least change in electronic configuration during an elementary reaction. We have concluded that alkyl radicals will attack most easily exposed positive atoms, i.e., in organic molecules, the hydrogen atoms. The attack on exposed negative atoms such as N, O or Cl is less probable whereas a completely shielded carbon atom should certainly not be attacked in the primary step. A doubly or triply bonded carbon atom can, however, react with a radical. These statements are discussed from the experimental point of view, together with the question as to when it is necessary to assume that organic reactions proceed through radical chains.
The Electrostatic Influence of Substituents on the Dissociation Constants of Organic Acids. I
Authors: Kirkwood J. G. , Westheimer F. H.
Published: January 2005

Bjerrum's theory of the influence of substituents on dissociation constants has been extended and amplified. The molecules and ions entering into the ionization equilibria are treated as cavities of low dielectric constant, rather than as structureless regions of the same dielectric constant as the solvent. The theory gives better results than the simple Bjerrum formulation, especially for the short chain dicarboxylic acids, and in the fact that it permits a satisfactory treatment of the influence of dipolar substituents on dissociation constants.
The Electrostatic Influence of Substituents on the Dissociation Constants of Organic Acids. II
Authors: Westheimer F. H. , Kirkwood J. G.
Published: January 2005

The theory of the influence of substituents on dissociation constants presented in an earlier article of the same title is extended to acids ellipsoidal in shape. Bjerrum's formula is obtained in the limiting case of unit eccentricity of the elliptical section of a prolate ellipsoid of revolution. The influence of dipolar as well as ionic substituents can satisfactorily be treated.
Vibration Spectra and Molecular Structure IV. The Infra-Red Absorption Spectra of the Double and Single Molecules of Formic Acid
Authors: Bonner Lyman G. , Hofstadter Robert
Published: January 2005

In the present study the absorption spectrum of formic acid vapor between 1 and 15.5μ has been investigated under a variety of temperature conditions. The spectrum at room temperature gives essentially the absorption of the double molecules alone, while that at 140°C gives the absorption of the single molecules. The results are interpreted in terms of the hydrogen bonding existing in the double molecule. In addition an attempt to prepare and investigate pure formic acid-d is reported.
Vibration Spectra and Molecular Structure VI. Infra-Red Absorption Spectrum of Heavy Formic Acid
Authors: Hofstadter Robert
Published: January 2005

The infra-red absorption spectra between 1 and 15.5μ of the monomer and dimer of HCOOD have been found with a rocksalt prism spectrometer. The position of the vibration characteristic of the ``deuterium bond'' in HCOOD has been determined and permits an approximate calculation of the shorter OD distance in the dimer ring. As in CH3COOD the distance is found to be 1.07A.
Raman Spectrum and Fluorescence of Dioxane
Authors: Hunter Hugh W.
Published: January 2005

A. The Raman spectrum of dioxane is shown to include eleven lines, some of which have been reported by one or both of two previous investigators. B. Dioxane, when irradiated by the ultraviolet light from a mercury arc, gives scattered light whose spectrum shows a broad continuous band in the visible region. Intensity of the scattered band diminishes rapidly with increasing temperature of the dioxane. Shortened time exposures bring out two maxima at about 5800A and 4500A. A similar phenomenon has been observed in work on cyclohexane.
An Infra-Red Study of Several Liquid Crystals
Authors: Taschek Richard , Williams Dudley
Published: January 2005

The near infra-red spectra of three liquid crystals have been studied in the isotropic and anisotropic phases, and several band shifts have been observed. A detailed study of the transmission as a function of temperature was made at various wave-lengths. Pronounced changes in transmission were observed at melting and clearing points, the magnitude of the changes being greater at short wave-lengths. Rapid variations in transmission occurred in the mesophase. A qualitative explanation of the observed changes is given in terms of Ornstein's theory of scattering. The application of infra-red methods to the study of changes of state is discussed.
The Infra-Red Absorption Spectra of CH3OD and CH2DOD
Authors: Barker E. F. , Bosschieter G.
Published: January 2005

The infra-red absorption spectra of CH3OD and CH2DOD between 2.5μ and 24μ have been examined with a KBr prism spectrometer, and with appropriate gratings. The observed bands represent all of the fundamental vibrations except the one of lowest frequency which is associated with torsional vibrations about the C–O bond. Since these molecules depart only slightly from axial symmetry, the bands, with the exception of three due to the hydroxyl radical, correspond in position and appearance to those of the methyl halides. The rotational structure for the 10μ band (v5) of CH3OD has been resolved, and partial resolution is obtained in some other bands. The band v5 in CH2DOD has two components arising probably from two forms of the molecule in which the hydroxyl D atom occupies different valleys of the threefold potential. The deformation vibration (v7) is single for CH3OD but has four components in CH2DOD, indicating a separation of levels which for the former molecule are degenerate. A comparison of the frequencies obtained with gaseous and liquid samples indicates large displacements of the bands arising from the hydroxyl valence and deformation vibrations, the former toward greater wave-lengths in the liquid, and the latter toward smaller wave-lengths.
Crystal Field Splitting in CaF2:Nd3+
Authors: Kiss Zoltan J.
Published: January 2005

The crystal field split levels of the 4I9/2 and 4I11/2 states of CaF2:Nd3+ were determined from the fluorescence and absorption spectra. The data are compared to an energy-level calculation for the case of a weak cubic field containing fourth- and sixth-order terms. Both the absorption and fluorescence spectra were found to be strongly concentration dependent at relatively low concentrations (0.01 mole %).
Recombination of Oxygen Atoms in the Presence of Inert Gases
Authors: Morgan J. E. , Schiff H. I.
Published: January 2005

The recombination of oxygen atoms has been studied in an O2-free system containing a known initial atom concentration. The value of the rate constant for the reaction O+O+N2→O2+N2was found to be 2.8×10−33 cm6 molecule−2 sec−1. Failure to remove condensable products from the gas stream resulted in a 40% increase in the recombination rate. The efficiencies of other third bodies relative to N2 are: Ar, ≤0.3; He, 0.3; N2O, 1.4; CO2, 3.0; SF6, 3.0. The presence of vibrationally excited N2 did not affect the recombination rate. The wall recombination coefficient γ was found to be 1.65×10−5. Comparison of these results with high-temperature shock-tube results indicates that the temperature coefficient of the recombination is small.
Microwave Spectrum of Tertiary Butyl Chloride. A Comparison of Tertiary Butyl Structures
Authors: Lide David R. , Jen May
Published: January 2005

The rotational constants of (C12H3)3C12Cl35, (C12H3)3C12Cl37, (C12H3)3C13Cl35, (C12H3)3C13Cl37, and (C13H3) (C12H3)2C12Cl35 have been measured. The rs structure of the t-butyl chloride skeleton calculated from these constants is: r(CCl) = 1.803±0.002 Å, r(CC) = 1.530±0.002 Å,∠CCC=110.9°±0.1°. The quadrupole coupling constant for Cl35 is −66.9±1.5 Mc. The structures of a number of t-butyl compounds are compared. The t-butyl group is practically unaffected by substitution, while the CX bond in (CH3)3CX is systematically longer than in CH3X molecules. Conventional concepts of valence theory do not provide a satisfying explanation for this behavior.
Influence of Electric and Magnetic Fields on the Dielectric Constant and Loss of the Liquid Crystal Anisaldazine
Authors: Carr Edward F.
Published: January 2005

The real and imaginary parts of the complex dielectric constant of the normal liquid phase of anisaldazine were measured at a temperature of 185°C for a frequency range from 900 Mc to 24 kMc. A plot of the complex dielectric constant in the complex plane satisfies the requirements for the Cole—Cole representation reasonably well. The temperature dependence of the dielectric loss at frequencies 6, 15, and 24 kMc indicates that any changes in the dielectric loss for a random orientation are very small as anisaldazine passes from its anisotropic to normal liquid phase. This implies that a plot of the complex dielectric constant in the complex plane for the anisotropic phase would probably satisfy the requirements for a Cole—Cole plot. Measurements of the dielectric loss in the presence of an external electrostatic field show that an ordering exists with the long axes of the molecules parallel to the external electric field.
An Approach to the Internal Rotation Problem
Authors: Karplus Martin , Parr Robert G.
Published: January 2005

A method is described for a direct calculation of the barrier to internal rotation in ethane and ethanelike molecules. The approach suggested should identify the physical origin of the barrier, provided a satisfactory account would be forthcoming from exact Hartree—Fock calculations of the energies of the staggered and eclipsed forms in the Born—Oppenheimer approximation.

A simple model is considered in which the electronic distribution is taken to be cylindrically symmetric about the central bond. It is demonstrated that this model predicts energy differences between staggered and eclipsed forms, composed solely of nuclear—nuclear repulsion energy, that are consistently about 5/3 of the experimental energy barriers. A slight expansion of the wavefunction in the eclipsed configuration is shown to be required by the virial theorem, but this does not appreciably change the predicted magnitude of the barrier.

It is proposed that the model can be refined by a calculation of the electronic energies of the actual staggered and eclipsed forms of ethane relative to that for the cylindrical distribution. By means of second-order Hartree—Fock perturbation theory, it is shown that the energy differences are a simple sum of contributions from the nine occupied molecular orbitals. The individual contributions can be calculated by the solution of certain differential equations or their variational equivalent. To simplify the treatment further, an approximate set of uncoupled differential equations is suggested for finding the perturbed functions from estimates for the charge densities of the cylindrical-model molecular orbitals.
Theoretical Study of Isoelectronic Molecules: Nitrogen and Acetylene
Authors: Gilson Bruce R. , Arents John
Published: January 2005

C2H2 is treated as an N2 molecule perturbed by a transfer of charge from the N nuclei to the positions of the H nuclei in C2H2. CH is similarly treated as a perturbed N atom. First-order perturbation calculations, based on published wavefunctions and empirical energies for N2 and N, give energies for C2H2 and CH that are, respectively, 7.4% above the best calculated value for C2H2 and 11.7% above the empirical value for CH. The electronic perturbation energy per electron is greater in the molecule than in the atom by about 0.2 a.u. for all orbital types.
Temperature Dependence of the Al Nuclear Quadrupole Interaction in Ruby
Authors: Veigele Wm. J. , Bevan A. W. , Tanttila Wm. H.
Published: January 2005

The temperature dependence of the Al nuclear quadrupole coupling constant v in a 0.05% Cr3+ ruby has been measured in the range of 89° to 657°K. Results are consistent with earlier measurements to 4.2°K, but are of greater accuracy. The coefficient (1/vR) (dv/dT) = +5.187×10−5 (°C)−1 was calculated from the experimental data, indicating an increase in v with an increase in T. This temperature dependence is discussed in terms of a possible negative dependence of v on pressure.
Electron Spin Resonance in a Gamma-Irradiated Single Crystal of Mercaptosuccinic Acid
Authors: Hahn Yu Hak , Rexroad H. N.
Published: January 2005

The four most intense resonances in the ESR spectrum of a γ-irradiated single crystal of mercaptosuccinic acid are each shown to be due to the same free radical which has four different orientations in the crystal. By analysis of the anisotropy in the spectroscopic splitting factor the principal values of the g tensor were found to be 2.003, 2.026, and 2.054. It is believed that the free radical HOOC–CH2–HCS–COOH is responsible for the observed resonance. The model of Kurita and Gordy in which the electron spin density is concentrated in a nonbonding 3p orbital of the sulfur atom successfully accounts for the basic features of the anisotropy of the g tensor.
Dielectric Friction on a Rotating Dipole
Authors: Zwanzig Robert
Published: January 2005

The frictional torque on a slowly rotating dipole due to dielectric loss in the surrounding medium is calculated using continuum electrodynamics. In typical cases, this dielectric friction can account for 10% to 20% of the total frictional torque on the dipole.
Theory of Field Desorption
Authors: Gomer Robert , Swanson Lynn W.
Published: January 2005

The theory of field desorption proposed previously has been extended by a more detailed quantum-mechanical calculation of the rate constants of desorption for various cases, including an attempt to evaluate matrix elements for the electronic transition when the latter is slow. A simple, generalized model of chemisorption on metals is presented and used in these calculations. It is found that two-electron transitions lead to somewhat smaller rate constants than one-electron transitions, but that the effect is not very large. In general, a one-dimensional theory leads to rate constants with essentially normal pre-exponential terms, except under conditions where adsorbate tunneling becomes important. A tentative explanation for the compensation effect, i.e., decreases in pre-exponential term with decreasing activation energy observed experimentally in a number of different cases, is given in terms of changes of reaction path with temperature.
Steady-State Unimolecular Processes in Multilevel Systems
Authors: Hoare Michael
Published: January 2005

The problem of reaction efficiencies in steady-state multilevel systems is analyzed using a matrix formulation. Several special cases are treated with particular attention to the existence of a low-pressure anomaly. The results apply equally well to the calculation of unimolecular reaction efficiencies, fluorescence yields and the analogous quantities in any process involving competitive pressure-dependent transitions between two subsets of states.
Vacuum Ultraviolet Absorption Spectrum of Dimethyl Ether
Authors: Hernandez G. J.
Published: January 2005

The vacuum ultraviolet spectrum of dimethyl ether has been reinvestigated and extended to higher frequencies. Rydberg series are found to converge to a first ionization potential at 80 330 cm−1 (9.96 eV). Analysis of the vibronic structure indicates only a slight change in the vibrational frequencies of the excited electronic states from those of the ground state.
Magnetic Susceptibilities of Molten Bi–BiI3 Solutions
Authors: Topol L. E. , Ransom L. D.
Published: January 2005

Magnetic susceptibility measurements were made with a Gouy balance on molten Bi–BiI3 solutions at 450°–600°C over the entire composition range. The susceptibilities were diamagnetic throughout and were found to become less diamagnetic as temperature increased. This temperature dependence varied with concentration of bismuth and was greatest in the 30–70 mole % Bi solutions. The molar susceptibility as a function of mole fraction of bismuth showed slight deviations from simple additivity in a diamagnetic direction in the salt-rich region and larger deviations from additivity in a paramagnetic direction in the metal-rich melts. This magnetic behavior is discussed in terms of possible chemical species as well as the free-electron model.
Electronic Conduction in Bi–BiI3 Melts. A Theoretical Model
Authors: Raleigh Douglas O.
Published: January 2005

Experimental electrical conductivity data for the liquid Bi–BiI3 system are analyzed in terms of predominant conduction in the salt-rich region by an electronic ``jumping'' or exchange process between the mono- and tervalent states of bismuth. Calculations of the jump frequency from the conductivity data show the expected dependence on temperature and average distance between exchange sites. Results of the calculations are used to evaluate the average energy barrier height for the exchange process and the enthalpy of symmetrization of the ionic atmospheres about the exchange sites, as required by the Franck-Condon principle. The latter is found to be independent of the average distance between exchange sites.
Neutron Inelastic Scattering Studies of Globular Compounds
Authors: Becka L. N.
Published: January 2005

The use of neutron inelastic scattering measurements to determine the nature of the solid-state transitions in globular compounds is proposed and exemplified. Patterns were taken of the high- and low-temperature phases of solid cyclohexane, 2–2-dimethylbutane, and 1–4-diazo-bicyclo-(2.2.2)-octane. The first two have broad inelastic scattering peaks in the low-temperature phase. In the high-temperature phase these peaks disappear and the elastic peak broadens markedly. These changes are attributed to ``quasi-free-rotation'' of the molecules. Inelastic peaks do not appear in 1–4-diazo-bicyclo-(2.2.2)-octane, and the elastic peak does not broaden appreciably in the high-temperature phase. Self-diffusion coefficients Ds=4.5×10−5 cm2/sec for cyclohexane and Ds=8.6×10−5 cm2/sec for 2–2-dimethylbutane were determined from the patterns of the liquids at 300°K using the ``small motions'' approximation. These values are larger than those obtained from NMR measurements, presumably as a result of irreversible rotation of the molecules.
Revised Tables for Ion-Exchange Kinetics
Authors: Helfferich F.
Published: January 2005

Revised numerical solutions of the differential equation for exchange of ions of equal valence and different mobilities are presented for finite slabs and spherical particles under simple initial and boundary conditions. The solutions also apply to sorption and desorption with a particular concentration dependence of the diffusion coefficient. The relations with solutions given by others for semi-infinite media are discussed.
Collisional Transition Probabilities for Vibrational Deactivation of Chemically Activated sec-Butyl Radicals. The Rare Gases
Authors: Kohlmaier G. H. , Rabinovitch B. S.
Published: January 2005

Vibrationally excited sec-butyl radicals, having a narrow range of energies above 40 kcal mole−1, were produced in a heat bath of cis-butene-2-rare-gas mixtures by H addition to cis-butene-2. He, Ne, Ar, and Kr were used. Two competing reactions of the chemically activated radicals, decomposition by C–C rupture with critical energy of 33 kcal mole−1 and collisional stabilization, were studied as a function of pressure. Apparent rate constants for decomposition ka were obtained at three temperatures over a range of bath pressures by analysis of the decomposition and stabilization products. Strong and weak multistep collisional deactivation processes, corresponding to transfer of all or only part of the initial excess vibration energy (≥7 kcal mole−1) of the radicals, were considered. Multistep models of various step sizes (ΔE) give a family of calculated curves of ka as a function of p, each of which turns up from a quasi-constant value at higher pressures to higher values at low pressures. Comparison with the low-pressure experimental ``turnup'' yielded information on ΔE, independent of the assumed collision cross section. Comparison of relative rates in the higher-pressure region gave minimum estimates of ΔE or, alternatively, conventional ``efficiency'' factors, βmin; these conclusions are somewhat dependent on the assumed cross section.

Values of ΔE from the lower-pressure turnup data bunch at 2.5–3.5 kcal mole−1 on an assumed stepladder model of transition probabilities. Such a model corresponds only formally to harmonic oscillator restrictions, and encompasses the characteristics of models in which small steps are less probable than large ones. Values of 〈ΔE〉exp for an exponential weighting of transition probabilities group at 1.2–1.8 kcal mole−1; this distribution describes the characteristics of models in which small steps are more probable than large ones and seems to be the preferred description of the rare-gas behavior here. He and Ne appear to transfer less energy than Kr and Ar. ΔE for cis-butene itself was confirmed to be ≥9 kcal, as derived in a previous study of deactivation of sec-butyl-d1 radicals by Harrington, Rabinovitch, and Hoare; and by contrast, the stepladder model is more appropriate here.

From the higher-pressure data, values of βmin which varied from 0.16 for He at 100°C to 0.62 for Kr at −78°C were found. The efficiencies increase with increasing atomic weight of the rare gas and with decreasing bath temperature.

Energy transfer between rare-gas atoms and butyl radicals is thus surprisingly efficient, with relatively large amounts of energy transferred per collision (〈ΔE〉>kT). The findings provide further detailed evidence concerning the inapplicability of the Landau-Teller theory and related models to polyatomic molecules at high vibrational energies (cf. Herzfeld and Litovitz). The possible role of rotational degrees of freedom is considered.
Effective Intermolecular Pair Potentials in Nonpolar Media
Authors: Kestner Neil R. , Sinanoğlu Oktay
Published: January 2005

Using third-order perturbation theory, effective London dispersion forces between two molecules in a medium are evaluated. The reduction in the pair interaction is calculated for spherical and polymeric bodies at various separations. For nearest neighbors in pure liquids, pair potentials decrease by 1.8% in helium, and 32% in carbon tetrachloride. The contribution to the total energy of the liquid is one-third of this. The dispersion forces between lateral base pairs in a single DNA double helix decrease by about 28% due to third- and fourth-order perturbations involving the four neighboring bases of each pair. Solvent effects cause an additional decrease of 14% (in water) to 18% (in formamide). The guanine-cytosine and adenine-thymine pairs change similarly. In general between segments of any two typical linear polymer chains (ionization potential of 10 V), dispersion forces decrease between 17% and 22% in water. In the theoretical sections, operator and diagrammatic techniques are presented which simplify the calculation of higher-order effects. We also show that dispersion forces do not decrease as the square of the high-frequency dielectric constant of the solvent, since this does not include the attractive many-body correlations which reduce the effect of the medium on the pair potential.
Microscopic steady streaming eddies created around short cylinders in a channel: Flow visualization and Stokes layer scaling
Authors: Lutz Barry R. , Chen Jian , Schwartz Daniel T.
Published: January 2005

Microscale steady streaming eddies created using low-intensity fluid oscillations offer appealing options for controlling fluids in microfluidic systems. We describe the three-dimensional (3D) steady streaming flow formed in a small channel containing single fixed cylinders when the channel fluid is oscillated at low intensity. Experiments include three cylinder sizes (length 1.5mm; radii a=125, 250, and 500μm) within identical channels (height 2h=1.5mm; width 4mm) over a range of oscillation frequencies (40⩽ω⩽1000Hz). The size of key flow features is measured from steady particle pathline images recorded within three flow symmetry planes. The resulting 3D streaming exhibits two distinct recirculating flows that are governed by the Stokes layer thickness δAC and geometric length scales. Four symmetric recirculating eddies are created adjacent to the cylinder far from channel walls, and their size is governed by δAC∕a as described by steady streaming theory for a 2D geometry. The cylinder/wall boundary layer junction drives a 3D recirculating flow with size that is directly proportional to δAC∕h and is not affected by a threefold variation of the cylinder radius. The flow images and scaling describe an organized 3D steady streaming flow that may be tuned to control fluid and its contents in microfluidic devices.
Neutron diffraction and ferromagnetic resonance studies on plasma-sprayed MnZn ferrite films
Authors: Yan Q. Y. , Gambino R. J. , Sampath S. , Huang Q.
Published: January 2005

The magnetic properties of MnZn ferrites are affected by the plasma spray process. It is found that improvements can be made by annealing the ferrite films at 500°C–800°C. The annealing induced magnetic property changes are studied by neutron diffraction and ferromagnetic resonance techniques. The increase of the saturation magnetization is attributed to the cation ordering within the spinel lattice, which increases the magnetic moment per ferrite formula. The refinements on the neutron diffraction data suggest that the redistribution of the cation during annealing neither starts from a fully disordered state nor ends to a fully ordered state. The decrease of the coercivity is analyzed with the domain wall pinning model. The measurements on the magnetostriction and residual stress indicate that coercive mechanisms arising from the magnetoelastic energy term are not dominant in these ferrite films. The decrease of the coercivity for annealed ferrite films is mainly attributed to the decrease of the effective anisotropic field, which may result from the homogenization of the film composition and the reduction of the microstructural discontinuity (e.g., cracks, voids, and splat boundaries).
Volume magnetostriction and structure of copper mold-cast polycrystalline Fe–Ga alloys
Authors: Bormio-Nunes C. , Tirelli M. A. , Sato Turtelli R. , Grössinger R. , Müller H. , Wiesinger G. , Sassik H. , Reissner M.
Published: January 2005

The effect of the volume expansion on the total linear magnetostriction of Fe85Ga15, Fe80Ga20, and Fe71Ga29 mold-cast bulk alloys was investigated by measuring the change in length with applied field longitudinal and perpendicular to the temperature gradient during solidification. In the magnetically saturated state, due to the contribution of the volume expansion, the saturation magnetostriction for all three alloys was about 66 % of the total linear magnetostriction. The magnetostriction is strongly dependent on the direction of the temperature gradient, being larger in this direction. The substitution of Fe by Ga atoms increases the lattice constant and causes a change to the A2 crystal structure, which was confirmed by Mössbauer spectroscopy. The thermal-expansion coefficient increases with Ga content at temperatures between 4.2 and 150K.
Giant dielectric permittivity of electron-doped manganite thin films, Ca1−xLaxMnO3 (0⩽x⩽0.03)
Authors: Cohn J. L. , Peterca M. , Neumeier J. J.
Published: January 2005

A giant low-frequency, in-plane dielectric constant, ϵ∼106, for epitaxial thin films of Ca1−xLaxMnO3 (x⩽0.03) was observed over a broad temperature range, 4K⩽T⩽300K. This phenomenon is attributed to an internal barrier-layer capacitor (IBLC) structure, with Schottky contacts between semiconducting grains. The room-temperature ϵ increases substantially with electron (La) doping, consistent with a simple model for IBLCs. The measured values of ϵ exceed those of conventional two-phase IBLC materials based on (Ba,Sr)TiO3 as well as on recently discovered CaCu3Ti4O12 and (Li,Ti)-doped NiO.
Recombination activity of Σ3 boundaries in boron-doped multicrystalline silicon: Influence of iron contamination
Authors: Chen Jun , Yang Deren , Xi Zhenqiang , Sekiguchi Takashi
Published: January 2005

The impact of the boundary plane and impurity contamination on the recombination activity of Σ3 boundaries in multicrystalline silicon (mc-Si) was studied by means of electron-beam-induced current (EBIC) technique. In the as-grown contamination-free mc-Si, the EBIC contrast of different Σ3 boundaries was in the order of Σ3{111}<Σ3{110}<Σ3{112}. This order may be attributed to the difference in the defect density of the Σ3 boundaries due to the effect of the boundary plane. But the maximum EBIC contrast did not exceed 2% at 300K, suggesting that the Σ3 boundaries are originally electrically inactive and the boundary plane has no significant effect on their recombination activity. When contaminated with Fe at 900°C, the EBIC contrasts of the Σ3{110} and Σ3{112} increased at 300K, whereas that of the Σ3{111} was still weak (<3%). This variation in the EBIC contrast may be related to the effect of boron and it is also indicated that the Σ3{111} has the weakest gettering ability. When contaminated with Fe at 1100°C, the EBIC contrasts of all the Σ3 boundaries continued to increase and bright-denuded zones developed around the boundaries. The Σ3 boundaries in the 1100°C air-cooled mc-Si showed stronger EBIC contrasts and broader denuded zones than those in the 1100°C quenched one. This phenomenon was explained in terms of the precipitation of Fe. The precipitation of Fe at grain boundaries (GBs) was affected by both the GB type and cooling rate, that is, Fe is easier to form precipitates onto the Σ3{110} and Σ3{112} boundaries during slow cooling.
Suppression of oxygen diffusion by thin Al2O3 films grown on SrTiO3 studied using a monoenergetic positron beam
Authors: Uedono A. , Kiyohara M. , Yasui N. , Yamabe K.
Published: January 2005

The annealing behaviors of oxygen vacancies introduced by the epitaxial growth of thin SrTiO3 and Al2O3 films on SrTiO3 substrates were studied by using a monoenergetic positron beam. The films were grown by molecular-beam epitaxy without using an oxidant. The Doppler broadening spectra of the annihilation radiation were measured as a function of the incident positron energy for samples fabricated under various growth conditions. The line-shape parameter S, corresponding to the annihilation of positrons in the substrate, was increased by the film growth, suggesting diffusion of oxygen from the substrate into the film and a resultant introduction of vacancies (mainly oxygen vacancies). A clear correlation between the value of S and the substrate conductivity was obtained. From isochronal annealing experiments, the Al2O3 thin film was found to suppress the penetration of oxygen from the atmosphere for annealing temperatures below 600°C. Degradation of the film’s oxygen blocking property occurred due to the annealing at 700°C, and this was attributed to the oxidation of the Al2O3 by the atmosphere and the resultant introduction of vacancy-type defects.
Convenient optical pressure gauge for multimegabar pressures calibrated to 300GPa
Authors: Sun Liling , Ruoff Arthur L. , Stupian Gary
Published: January 2005

The accurate measurement of pressure by a straightforward and inexpensive optical procedure has been needed in the multimegabar region since static pressures over 216GPa, 361GPa, 420GPa and 560GPa were obtained in the diamond anvil cell. Here, a simple optical pressure gauge based on the Raman shift of the diamond at the center of a diamond tip at the diamond–sample interface is calibrated against a primary gauge (Pt isotherm at 300K from shock data) to 300GPa, thus enabling researchers who do not have a synchrotron to conveniently measure pressure with an optical scale from 50to300GPa.
Near-field second-harmonic imaging of magnetic domains
Authors: Dickson W. , Takahashi S. , McHugh D. , Atkinson R. , Pollard R. , Zayats A. V.
Published: January 2005

The principles and mechanisms of scanning near-field microscopy of second-harmonic generation from ferromagnetic films have been investigated. Magnetic domain image formation in near-field second-harmonic microscopy is discussed and the role of the probe tip is considered. It is shown that magnetic contrast can be achieved in the second-harmonic intensity measurements in both the transverse and longitudinal magnetization configurations for both polarizations of the fundamental light. This is related to the electromagnetic near-field properties in the vicinity of the probe tip and the electromagnetic interaction between a tip and a surface. The capabilities of this imaging approach have been illustrated using magnetic domain structures in thin Co and Ni films. The near-field second-harmonic distributions obtained with p-polarized excitation light are strongly correlated to the topography of the films. At the same time, the images obtained with s-polarized excitation light are much less sensitive to the topography.
Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO3 as a template layer
Authors: Pradhan A. K. , Mohanty S. , Zhang Kai , Dadson J. B. , Jackson E. M. , Hunter D. , Rakhimov R. R. , Loutts G. B. , Zhang Jun , Sellmyer D. J.
Published: January 2005

We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature.
Reshaping of a second-harmonic curve in periodically poled Ti:LiNbO3 channel waveguide by a local-temperature-control technique
Authors: Lee Yeung Lak , Noh Young-Chul , Jung Changsoo , Yu Tae Jun , Yu Bong-Ahn , Lee Jongmin , Ko Do-Kyeong , Oh Kyunghwan
Published: January 2005

We have demonstrated reshaping and bandwidth control of a second-harmonic (SH) curve in a periodically poled Ti:LiNbO3 (Ti:PPLN) waveguide (Λ=16.6μm) by using a local-temperature-control technique. With this technique, we have achieved several useful shapes of the SH curve such as an almost ideal sinc function, and double and multipeaks in a 74-mm-long Ti:PPLN waveguide, which has a prechirped SH curve at room temperature. More than 60% improvement of SH conversion efficiency and a 5nm broadening of SH phase-matching bandwidth were achieved.
Optical probing of sample heating in scanning near-field experiments with apertured probes
Authors: Latini G. , Downes A. , Fenwick O. , Ambrosio A. , Allegrini M. , Daniel C. , Silva C. , Gucciardi P. G. , Patanè S. , Daik R. , Feast W. J. , Cacialli F.
Published: January 2005

We have used the inherent thermochromism of conjugated polymers to investigate substrate heating effects in scanning near-field experiments with metal-coated “apertured” probes. Chemically etched and pulled fibers were used to provide near-field excitation of fully converted films of poly(p-phenylene vinylene), PPV, and of poly(4,4′-diphenylene diphenylvinylene). We detect no significant blueshift of the photoluminescence spectra generated with near-field excitation, in comparison to those collected with far-field excitation. We conclude that polymer heating in the region contributing to the luminescence is less than 40K. We also demonstrate that thermolithography of the PPV precursor is not significant by comparing UV (325nm) and red (670nm) illumination.
Terahertz emission from (100) InAs surfaces at high excitation fluences
Authors: Reid M. , Fedosejevs R.
Published: January 2005

The radiated terahertz field from (100) InAs surfaces under excitation at fluences of millijoules per centimeter squared has been studied in detail in order to identify the main generation mechanism. We find that the terahertz emission depends strongly on pump polarization, and that the predominant emission mechanism appears to be the surface nonlinear optical response of the InAs crystal. A saturation fluence of 29±4μJ∕cm2 is found for the emission.
Magneto-optical nanoparticle-doped silica-titania planar waveguides
Authors: Royer F. , Jamon D. , Rousseau J. J. , Roux H. , Zins D. , Cabuil V.
Published: January 2005

This letter describes how composite material, made of maghemite (γ-Fe2O3) nanoparticles embedded in a silica∕titania matrix, can be used to develop new magneto-optical planar waveguides. Thin film samples are coated on Pyrex™ substrates from a magnetic particles doped sol-gel preparation. M-lines spectroscopy measurements performed on these samples show that an out of plane magnetic field applied during the gelation induces a decrease of the planar waveguide phase mismatch. Free space measurements evidence the Faraday rotation of the films up to 25°∕cm at 633 nm. Improvements and leads of further works are proposed in term of magneto-optical waveguide applications.
Ultrahigh piezoelectric response perpendicular to special cleavage plane in BaTiO3 single crystals
Authors: Chu R. , Xu Z. , Li G. , Zeng H. , Yu H. , Luo H. , Yin Q.
Published: January 2005

We report on the ultrahigh piezoelectric response perpendicular to some special cleavage plane in BaTiO3 single crystals. An extremely high value of piezoelectric coefficient d33 value over 2000pC∕N was obtained after being poled perpendicular to special plane (270) in BaTiO3 crystal, which is more than 20 times higher than those poled along spontaneous polarization direction ⟨001⟩ (d33⟨001⟩=87pC∕N). A large strain of 0.6% was obtained at a very low electric field.
Mutual promotion effect of crystal growth in TiN∕SiC nanomultilayers
Authors: Lao Jijun , Shao Nan , Mei Fanghua , Li Geyang , Gu Mingyuan
Published: January 2005

The mutual promotion effect of crystal growth in TiN∕SiC nanomultilayers is described in this letter. TiN, SiC single layers and a series of TiN∕SiC multilayers with different thickness of SiC and TiN layers were prepared using magnetron sputtering. Microstructure analysis shows that TiN and SiC single layers exist as nanocrystal and amorphous, respectively. However, in the alternately deposited nanomultilayers of TiN and SiC, due to the influence of crystal structure of TiN layer, SiC layer forms a B1-cubic phase when its thickness is less than 0.6nm. At the same time, the formation of SiC crystal promotes the growth of TiN layer and greatly improves its integrity when the thickness of the TiN layer is less than 4.3nm. Due to this effect, TiN∕SiC multilayers form a coherent epitaxial grown superlattice within a certain thickness range of TiN and SiC layers. Correspondingly, the multilayers show a superhardness effect which presents an anomalous enhancement of hardness and elastic modulus. The highest hardness of TiN∕SiC nanomultilayers reaches 60GPa.
How does the nickel nanowire melt?
Authors: Hui Li , Pederiva F. , Wang B. L. , Wang J. L. , Wang G. H.
Published: January 2005

In this letter, the melting behavior of nickel nanowire is reported. The curves of the atomic volume, internal energy, and the local cluster are used to monitor the phase transition. We show that upon heating the nanowires undergo a coexistence of crystal and liquid units in the melting process of the nanowire. The thermal stability of nickel nanowires is dependent on the structures and size of the nanowire. The melting is not only due to the single atom’s diffusion, but also the diffusion of the local clusters.
Generation of periodic microrelief in tensioned polymeric substrates with hard coating and their physical properties
Authors: Belyaev Victor , Misnik Victor , Trofimov Sergei , Volynsky Alexander , Konovalov Victor , Muravskii Anatoly
Published: January 2005

The effect of formation of a periodic surface microrelief upon tension of polymeric substrates with thin hard coatings under specified conditions (the processing temperature below the glassing temperature, elongation up to 250%, elongation rate <5mm∕min) is described. The microrelief period ranges from 0.5μm up to hundreds of micrometers, its height up to 1μm. Methods are proposed to measure low values of the optical path length in media Δn∼λ and azimuthal anchoring energy of a liquid crystal on microreliefed surfaces.
Blue-violet InGaN laser diodes grown on bulk GaN substrates by plasma-assisted molecular-beam epitaxy
Authors: Skierbiszewski C. , Wasilewski Z. R. , Siekacz M. , Feduniewicz A. , Perlin P. , Wisniewski P. , Borysiuk J. , Grzegory I. , Leszczynski M. , Suski T. , Porowski S.
Published: January 2005

We report on the InGaN multiquantum laser diodes (LDs) made by rf plasma-assisted molecular beam epitaxy (PAMBE). The laser operation at 408nm is demonstrated at room temperature with pulsed current injections using 50ns pulses at 0.25% duty cycle. The threshold current density and voltage for the LDs with cleaved uncoated mirrors are 12kA∕cm2 (900mA) and 9V, respectively. High output power of 0.83W is obtained during pulse operation at 3.6A and 9.6V bias with the slope efficiency of 0.35W∕A. The laser structures are deposited on the high-pressure-grown low dislocation bulk GaN substrates taking full advantage of the adlayer enhanced lateral diffusion channel for adatoms below the dynamic metallic cover. Our devices compare very favorably to the early laser diodes fabricated using the metalorganic vapor phase epitaxy technique, providing evidence that the relatively low growth temperatures used in this process pose no intrinsic limitations on the quality of the blue optoelectronic components that can be fabricated using PAMBE.
Surface morphology control of strained InAs∕GaAs(331)A films: From nanowires to island-pit pairs
Authors: Gong Z. , Niu Z. C. , Fang Z. D. , Miao Z. H. , Feng S. L.
Published: January 2005

We have studied the effect of molecular beam epitaxy growth conditions on the surface morphology of strained InAs∕GaAs(331)A films. Our results reveal that InAs nanowires aligned along the [11¯0] direction are formed under As-rich conditions, which is explained by the effect of anisotropic buffer layer surface roughing. Under In-rich conditions, however, the surface morphology of the InAs layers is characterized by a feature of island-pit pairs. In this case, cooperative nucleation of islands and pits can lower the activation barrier for domain growth. These results suggest that the surface morphology of strained InAs layers is highly controllable.
A pump-power-controlled luminescent switcher
Authors: Jaque D. , García Solé J. , Macalik L. , Hanuza J. , Majchrowski A.
Published: January 2005

A spectral switcher based on the Yb3+-doped Nd3BWO9 crystal has been demonstrated. This system switches its main luminescence peak from 980nm (the characteristic luminescence of Yb3+ ions) to 1060nm (the characteristic luminescence of Nd3+ ions) as the 808nm pump intensity is increased from 0.4 up to 0.8kW∕cm2. The operation mechanism is based on the interplay between the Nd3+↔Yb3+ energy transfer processes and on the strong pump-induced thermal loading. The operation principles described in this letter allow for the tailoring of promising luminescent switchers operating at any desired spectral range by choosing the suitable sensitized host emitting crystal.
Crystal sensor for microscopy applications
Authors: Peng Zhiqiang , West Paul
Published: January 2005

We report a force sensor based on a quartz crystal that is used for measuring nanoscale topographic images. The crystal is a length-extensional mode oscillator with a resonant frequency of about 650 kHz. Compared to 33 kHz tuning forks, such crystal sensors have a much higher resonance frequency, which allows for high force sensitivity and a fast response time. The crystal sensor is operated in the shear-force mode, with the probes vibrating parallel to the sample surface. The tip-sample interaction during operation is estimated to be less than 300 pN.