bluuebunny/crossref_metadata_2025 huggingface dataset:
The Transference Numbers of Potassium Acetate in Aqueous Solution
Authors: Le Roy D. J. , Gordon A. R.
Published: January 2005

The transference numbers for aqueous solutions of potassium acetate at 25°C have been determined by the moving boundary method for the concentration range 0.01 N to 0.25 N. Two different types of cell and two different methods of measuring the number of coulombs were employed. Up to 0.16 N the transference numbers can be represented by the Shedlovsky-Longsworth equation within ±0.05 percent, and lead to a transference number for the cation at infinite dilution of 0.6428, in close agreement with that obtained from the limiting ionic mobilities.
Primary Processes in Photodecomposition
Authors: Burton Milton , Rollefson G. K.
Published: January 2005

When energy is absorbed by a molecule at a particular bond by a process of transition to a repulsive energy level or a sufficiently high point on an attractive level, rupture always results within one vibration period. All other photodecomposition processes are properly included under the title of predissociation. Thus, rupture may also result at the locus of absorption as the result of either spontaneous or induced adiabatic transition from an attractive to a repulsive or ``weakly attractive'' level. These are the only mechanisms of predissociation in diatomic molecules. In polyatomic molecules, spontaneous or induced shifts of energy or rearrangements of groups, resulting in decomposition, may also occur. Illustrations of the various processes suggested are cited from the photochemistry of sulfur, iodine, ozone, and the aldehydes. In the case of formaldehyde it has been possible to distinguish potential hypersurfaces and to indicate two different types of predissociation: one in a single hypersurface and the other a spontaneous transition between two hypersurfaces. The method used is extended to other aldehydes. Suggestions are made as to the interpretation of the photochemistry of several other substances and as to several problems which require solution.
The Raman Spectrum of Boron Trifluoride Gas
Authors: Yost Don M. , DeVault Don , Anderson Thomas F. , Lassettre Edwin N.
Published: January 2005

The Raman spectrum of BF3 was photographed using a purified preparation obtained from the thermal decomposition of C6H5N2BF4. Of the lines observed, that with the frequency 888 cm—1 is certainly, and the band at 439–513 cm—1 is probably due to BF3. The Raman frequencies and the infra-red results of Bailey et al. are assigned to the fundamental modes of vibrations.
Kinetics of OH Radicals as Determined by Their Absorption Spectrum III. A Quantitative Test for Free OH; Probabilities of Transition
Authors: Oldenberg O. , Rieke F. F.
Published: January 2005

(1) In order to make the OH absorption bands applicable to a quantitative chemical test for free OH their probability of transition (f value) was measured by the concentration of ``dispersion electrons'' in a known concentration of OH. (2) This concentration of OH is produced by water vapor dissociated at 1473°C, the equilibrium of which was computed. (3) The concentration of the ``dispersion electrons'' was measured by photometry of the absorption lines photographed with high resolving power. (4) The f values of the various absorption lines are given in a table. The most intense lines have f values of the order of magnitude 2×10—4. The accuracy is estimated to be 15 percent, the sensitivity (smallest detectable pressure under the conditions of the present experiment) 0.01 mm. (5) Comparison with other f values leads to the conclusion that the OH absorption band belongs to a half-forbidden transition. The lifetime of the excited state is computed as approximately 4×10—6 sec.
The Absolute Rates of Heterogeneous Reactions I. The General Theory of Adsorption
Authors: Kimball George E.
Published: January 2005

The statistical theory of reaction rates, developed by Eyring for homogeneous reactions, is extended to include heterogeneous reactions. It is shown that rates of adsorption and desorption are governed by the same form of mathematical expression in terms of partition functions of the system as rates of homogeneous reactions, provided only that for the activated state a ``super-partition function,'' formed by adding together the partition functions for all the active spots, is used. The pseudothermodynamical form of the rate constant form is discussed, and illustrated by applications to special cases.
A Determination of the Magnetic Susceptibilities of Certain Inorganic Complex Compounds
Authors: Frazer J. H. , Long N. O.
Published: January 2005

A standard method used in the determination of the gyromagnetic effect has been so modified as to permit the determination of magnetic susceptibilities. Its use is suggested for the determination of the susceptibilities of complex compounds, since it utilizes weak fields, and also requires only a small amount (less than 0.5 g) of the material to be tested. The susceptibilities of some compounds containing NO have been measured.
The Entropy of Acetone and Isopropyl Alcohol from Molecular Data. The Equilibrium in the Dehydrogenation of Isopropyl Alcohol
Authors: Schumann S. C. , Aston John G.
Published: January 2005

The entropy and free energy of acetone and isopropyl alcohol gases have been calculated from the molecular data at several temperatures on the basis of (a) free internal rotation (b) restricted rotation (with the potentials: Acetone, about C–C bond=1000 cal.; isopropyl alcohol, about C–C bond=3400 cal. about C–O=5000 cal.). The values based on restricted internal rotation were made to be consistent with the third law values. They are in better agreement with the ΔS values from the equilibrium data than those assuming free rotation.
Exchange Forces and Electrostatic Forces Between Ions in Solution
Authors: Gurney Ronald W.
Published: January 2005

Though the treatment of ionic dissociation by thermodynamic methods has been fruitful, the mechanism can be better understood by the use of statistical mechanics. For this purpose one needs to know the potential energy of the ions as a function of temperature. The work D required to dissociate a molecule or molecular ion consists of two parts, one part Del due to electrostatic forces, and the other Dnon due to nonelectrostatic forces. As the former varies rapidly with temperature, for each species the value of dD/dT is a guide to the value of Del. It is shown that for acid molecules and molecular ions in aqueous solution the relative values of dD/dT for different types are in the order predicted. Further, the characteristic temperature θ at which the dissociation constant passes through a maximum should depend, not on the value of D, but on the relative magnitudes of Dnon and Del. It is found that the known values of θ fall into line in accordance with this rule. Between two Hg+ ions, or two Te— ions, there will be exchange forces of attraction similar to those which give rise to the molecules Na2 and Br2; thus in aqueous solution the ions (Hg2)++ and (Te2)—— are stable, although for them Del is negative.
Photochemical Studies. XXVII. The Effect of Radiation on Mixtures of Nitrogen Dioxide and Nitrous Oxide and its Relationship to the Photochemical Decomposition of Nitrous Oxide
Authors: Henriques F. C. , Duncan A. B. F. , Noyes W. Albert
Published: January 2005

Oxygen atoms were produced in NO2–N2O mixtures by the photochemical decomposition of NO2 alone. No reaction of these atoms with N2O could be detected. Results of calculations give a minimum activation energy of 14,000 cal. for the reaction O+N2O = 2 NO and a probable maximum activation energy of 24,000 cal. The activation energy of the reaction O+NO2 = NO+O2 is estimated to be 4000 cal. It is concluded that two primary processes are necessary to explain the direct photochemical decomposition of N2O, N2O+hv = N2+O and N2O+hv = NO+N. The latter reaction must be followed by N+N2O = NO+N2 to explain previously determined quantum yields. The energy of activation of this reaction is probably less than 10,000 cal.
On the Interaction of Atoms in Alloys
Authors: Shockley William
Published: January 2005

A generalization of Bethe's theory of superlattices so as to take into account the interactions between atoms which are not nearest neighbors in the lattice is considered. This process will not furnish any great improvement in agreement between theory and experiment because it predicts, in disagreement with experiment, that many properties of binary alloys are symmetrical between the two constituents. It is further shown to be in disagreement with certain fundamental features of the interactions of atoms in alloys.
Shock Waves in Chemical Kinetics: The Use of Reflected Shock Waves
Authors: Johnson Charles D. , Britton Doyle
Published: January 2005

Rate constants for the dissociation of bromine molecules in argon have been measured behind reflected shock waves. The disagreement between these values and those measured behind incident shock waves at the same temperature indicates that between 1500° and 1900°K the temperatures in the reflected shock waves are 35°±5° lower than those calculated from ideal theory. Possible uncertainties in the temperature, even if ideal theory is obeyed, are also discussed.
Influence of Room-Temperature Atmospheric Reaction Products on the Ductility of Sodium Chloride Single Crystals
Authors: Otterson Dumas A.
Published: January 2005

Bend tests were made using sodium chloride single crystals which had previously been exposed to one of several atmospheres at room temperature. Crystals exposed to moist carbon dioxide showed the most consistent brittle behavior while those aged in moist air containing hydrogen chloride showed more ductile behavior. Evidence is given which indicates that hydroxide ion is needed for carbon dioxide to cause embrittlement. Furthermore, room-temperature hydrolysis is shown by experiments in which the increase of alkalinity of finely divided sodium chloride is measured upon long exposure to moist air. These results lead to the proposal of a new mechanism to explain age embrittlement of sodium chloride crystals: sodium chloride crystals containing hydroxide ion react with carbon dioxide to become embrittled. Crystal surfaces initially free from hydroxide can become contaminated with it by reaction with water vapor of the air. Changes in ductility due to physical adsorption of carbon dioxide or hydrogen chloride were not observed.
Infrared Studies of Hydrogen Bonding in Isopropanol and in Mixtures of Isopropanol with Poly (n-Butyl Methacrylate) and with Poly(Propylene Oxide)
Authors: Blanks R. F. , Prausnitz J. M.
Published: January 2005

Infrared spectra have been measured in the 3-μ region for isopropanol in carbon tetrachloride solutions from 0.005 to 1.0M and from 0° to 60°C. Equilibrium constants for cyclic dimer formation were calculated from the spectral data for this temperature range. The enthalpy for cyclic dimer formation is −5.7±0.9 kcal/mole. Infrared spectra have also been measured for three hydrogen-bonding systems with isopropanol as the proton donor over the same temperature range. The proton acceptors were di-isopropyl ether, liquid poly (propylene oxide), and poly (n-butyl methacrylate). Equilibrium constants were determined. The enthalpies of formation for the three complexes are −2.1±0.4, −3.8±0.8, and −2.4±0.5 kcal/mole, respectively.
Symmetry Considerations in the Spectrum of Ruby
Authors: Artman J. O. , Murphy John C.
Published: January 2005

The role of the point symmetry of the Cr3+ ion in the spectral analysis of Cr3+ in Al2O3 is reviewed. Previous energy-level calculations were made on the basis of C3v symmetry with a reflection plane perpendicular to the unique axis. Little change in the gross spectral features is expected if C3 (noninversion center) operators are used. However, as noted by McClure, it is necessary to go to C3(NIC) when calculating electric dipole radiation matrices. For consideration of the axial optical and microwave electric effects it is sufficient to consider C3v(NIC). For the full microwave electric effect tensor, C3(NIC) must be used. The interelations between the electric effects and the optical radiation dipole operators are explored. A substantial contribution to the ruby 4A2 ground-state splitting 2D is expected from the ``odd NIC fields.'' The magnitude of this effect for Cr2O3 is considered.
Spin—Orbit Splitting of the F-Center Band
Authors: Suffczynski Maciej
Published: January 2005

Spin—orbit splitting of the first excited state of the F center is estimated in the simple effective-mass approximation. The splitting due to the outermost s orbitals of the atoms neighboring the vacancy in the crystal is related to the splitting of the p state in the free atom. As an example, spin—orbit splitting of the F center in cesium halides is estimated. It is found to 4-to-6 orders of magnitude too small to account for the structure observed in the F-center absorption band in cesium halides.
``Free Volume'' and the Viscosity of Liquid Water
Authors: Miller A. A.
Published: January 2005

The viscosity of liquid water between −10° and +150°C (Psat=4.7 atm) is expressed by the equation: η=A exp[B/ (T−T0)], in which A = 290 μp, B = 510°, and T0 = 150°K. The true temperature-independent activation energy for viscous flow is E = RB = 1020 cal/mole.

The ``free volume'' representation uses the equation η=A exp(1/f), in which the free-volume fraction, f=vf/vl, increases linearly with temperature above the theoretical zero point, T0. Thus, f=(T−T0)/B. It evolves that f coincides with the volume fraction of unbonded water molecules, as defined by a structural model reported recently by Némethy and Scheraga.

This empirical correlation between the viscosity and the structure of liquid water demonstrates the effects of internal structural rearrangements, which are not directly reflected in changes in the total volume. The implications regarding the effects of temperature and pressure on viscosity and other relaxation processes, particularly in hydrogen-bonded, structured liquids, are discussed.
Nuclear Magnetic Resonance Studies of Electron Transfer between Tris (2,2′-dipyridyl) osmium (II) and (III) Ions, between Bis(cyclopentadienyl)iron(II) and (III) Ions, and between Tris(1,10-phenanthroline)iron(II) and (III) Ions
Authors: Dietrich M. W. , Wahl A. C.
Published: January 2005

Changes in linewidths and positions of the proton NMR absorption peaks for the diamagnetic species on addition of the corresponding paramagnetic species are interpreted as being due to very rapid electron transfer between the two species. On the assumption that the rates of electron transfer are first-order with respect to each reactant, the following lower limits on the rate constants are obtained: Os(dipy)32+−Os(dipy)33+:   k>5×104 mole−1sec−1(6°C and 26°C, D2O,5×10−3 M D+, 0.14 mole Cl−),Fe(C5H5)2−Fe(C5H5)2+:   k>1×105 mole−1sec−1(26°C, CD3COCD3),Fe(phen)32+−Fe(phen)33+:   k>1×105 mole−1sec−1(26°C, D2O,3 F D2SO4).

The reactions could not be studied by the electron spin resonance method because the ESR spectra of the paramagnetic species showed no observable absorption peaks, presumably because the peaks are very broad.
Ground State of the HeH+ Molecule Ion
Authors: Anex Basil G.
Published: January 2005

Configuration interaction calculations have been carried out for the system HeH+ using one-electron basis functions in confocal elliptical coordinates. Four internuclear separations, R=1.00, 1.40, 1.80, and 2.20 bohrs (B) were studied rather intensively. One of these, R=1.40 B, lies very close to the equilibrium R and the energies found in this region represent the lowest thus far reported for HeH+. Self-consistent field calculations were also made and in combination with the configuration interaction results lead to an estimation of correlation energies. The binding energy, the equilibrium internuclear separation, and the first few vibrational energies for the system were also estimated. The center of negative charge, which is closely related to the dipole moment, was studied as a function of R and of the size of the one-electron basis.
Three Sum Rules for Total Optical Absorption Cross Sections
Authors: Gordon R. G.
Published: January 2005

A sum rule is proved for the total optical absorption cross section for a system of interacting polarizable particles, each of which may have a total charge, a dipole moment, and an arbitrary mass distribution. This sum rule may be applied to the measurement of dipole moments of molecules or ions. The total absorption intensity due to an internal transition in a system of interacting asymmetric rotors is calculated. The first moment of the absorption intensity distribution about an internal transition is found for a system of interacting asymmetric rotors. This rule may be used to determine the true internal transition energy from an absorption spectrum.
On the Thermodynamic Properties of Solutions of Polar Polymers. Theory
Authors: Yamakawa Hiromi , Rice Stuart A. , Corneliussen Roger , Kotin Leonard
Published: January 2005

In this paper we present a simple analysis of the thermodynamic properties of solutions of polar polymers. It is found that:

(a) In the dilute solution regime, a cluster analysis identical with that used in the theory of solutions of nonpolar polymers can be developed, but with the thermodynamic parameter z now dependent on the dipole moment, dielectric constant, etc.

(b) In the concentrated solution regime, a continuum theory can be developed based on the assumption of uniform mixing of polymer chains and the use of cavity field and reaction field arguments.

(c) For dilute solutions of a polar polymer in a nonpolar solvent, or a nonpolarizable polar polymer in a polar solvent, the system is equivalent to an ordinary nonpolar polymer-poor solvent system.

(d) It is generally true that the solvent becomes poorer as the dipole moment and/or polarizability of the segment are increased. Also, the solvent becomes better as its dielectric constant increases.

(e) In the case of concentrated solutions of a polar polymer in a nonpolar solvent, the polar contribution to the Flory-Huggins free-energy parameter, χp, decreases with increasing concentration.

(f) In the case of concentrated solutions of a nonpolar polymer in a polar solvent, χp increases with increasing concentration.

(g) The dilute solution theory and concentrated solution theory predict the same functional form for χp in the limit of zero polymer concentration, but the numerical coefficients differ.

(h) The results of extensive digital computer calculations are presented in terms of the predicted concentration dependence of χp with varying properties of both polymer and solvent.

Agreement between theory and experiment is examined in detail in the following paper.
On the Thermodynamic Properties of Solutions of Polar Polymers. A Comparison of Experiment and Theory
Authors: Corneliussen Roger , Rice Stuart A. , Yamakawa Hiromi
Published: January 2005

In this paper we present a comparison of experimental and theoretical studies of the thermodynamic properties of solutions of polar polymers. In particular: (a) A new method of achieving isopiestic equilibruim is described in detail. (b) The excess free energies of solutions of toluene with poly-p-methylstyrene, poly-p-bromostyrene and several copolymers of p-methyl and p-bromostyrene are reported and analyzed. (c) The continuum model of concentrated solutions of polar polymers presented in the preceding paper is shown to be accurate for φ1>0.4, for the polymers studied. (d) The perturbation theory of dilute solutions of polar polymers presented in the preceding paper is shown to predict the proper behavior in the limit of zero polymer concentration. (e) The properties of copolymers with small skeletal concentration of polar subunits is shown to agree with the predictions of the perturbation theory presented in the preceding paper. (f) The fundamental assumption of the continuum theory concerning the relationship between dipolar orientation and chain connectivity is examined and shown to agree with experiment. (g) Deviations between theory and experiment are briefly discussed in terms of the basic assumptions of the model, and methods by which the theory can be improved are described.
Phosphorescence Lifetime Studies in Some Organic Crystals at Low Temperatures
Authors: Olness D. , Sponer H.
Published: January 2005

Triplet-singlet decay curves form naphthalene, phenanthrene, chrysene, durene, and hexamethylbenzene have been studied in the crystalline phase at temperatures of 4°K and higher, and for comparison in rigid glass solutions at 77°K. The decay from true dilute solutions was found to follow an exponential law. At 4°K, the phosphorescence emission from crystals of naphthalene, phenanthrene, and chrysene followed an exponential law, while that from durene and hexamethylbenzene was always nonexponential. Various theories concerning the causes of the nonexponential decay and the change in the general shape of the decay curves with different modes of sample preparation and with temperature are discussed.
Growth of biaxially textured BaxPb1−xTiO3 ferroelectric thin films on amorphous Si3N4
Authors: Brewer Rhett T. , Boyd David A. , El-Naggar Mohamed Y. , Boland Stacey W. , Park Young-Bae , Haile Sossina M. , Goodwin David G. , Atwater Harry A.
Published: January 2005

We prepared highly aligned, biaxially textured BaxPb1−xTiO3 (PBT) on amorphous Si3N4 by using an ion-beam-assisted deposited MgO as a template layer. PBT was deposited on a biaxially textured MgO using sol-gel synthesis, metal-organic chemical-vapor deposition, and molecular beam epitaxy. The biaxial texture of the PBT was inherited from the MgO template. The reflection high-energy electron diffraction (RHEED) and cross-section transmission electron microscopy (TEM) experiments suggest that exposure of the MgO template to atmospheric moisture before PBT heteroepitaxy resulted in a significant narrowing of the PBT in-plane orientation distribution. The microstructures of the biaxially textured PBT films were analyzed by x-ray diffraction, RHEED, and TEM. The dynamic contact mode electrostatic force microscopy polarization hysteresis loops confirmed that these films are ferroelectric.
The crossbar latch: Logic value storage, restoration, and inversion in crossbar circuits
Authors: Kuekes Philip J. , Stewart Duncan R. , Williams R. Stanley
Published: January 2005

Programmable crossbar circuits are one key architecture proposed for integrated nanoscale electronics. Emphasizing practicality of fabrication, many scenarios advocate crossbar circuits based on two-terminal devices. In this case, however, signal restoration and inversion remain critical weaknesses. Restoration is essential before the degraded output of one logic gate can drive the input of a subsequent logic gate. Inversion is required to generate a complete logic family. Here we describe and demonstrate a solution to both problems, the crossbar latch. This device stores a logic value on a signal wire, enabling logic value restoration, and inversion. In combination with resistor/diode logic gates, these operations in principle enable universal computing for crossbar circuits, and potentially, integrated nanoscale electronics.
Raman study of phonons in bismuth triborate BiB3O6 crystal
Authors: Hu Xiaobo , Wang Jiyang , Teng Bing , Loong Chun-Keung , Grimsditch Marcos
Published: January 2005

A Raman-scattering study of the vibrational modes in a BiB3O6 crystal was conducted at room temperature. The numbers of external and internal modes obtained in experiment are consistent with the results of a group theoretical analysis. The Raman lines below ∼300cm−1 and from ∼300to1600cm−1 are assigned to the external modes of the lattice and internal vibrations of the BO3 and BO4 subunits of the BiB3O6 structure, respectively.
Interface and confined optical-phonon modes in wurtzite multi-interface heterostructures
Authors: Lü J. T. , Cao J. C.
Published: January 2005

Interface and confined optical-phonon modes in wurtzite multi-interface heterostructures are studied numerically based on the dielectric continuum model and Loudon’s uniaxial crystal model. The phonon dispersion relation and electrostatic potential are calculated using the transfer matrix method. The anisotropic characteristics of wurtzite phonons are demonstrated. The electron-optical-phonon Fröhlich interaction is studied in a fully numerical manner. The dispersion relation is taken into account in the derivation of Fermi’s golden rule. The method presented here is general and can be easily applied to the design and simulation of optoelectronic devices based on wurtzite multi-interface heterostructures.
Noninvasive monitoring of ion energy drift in an inductively coupled plasma reactor
Authors: Sobolewski Mark A.
Published: January 2005

A noninvasive method for monitoring ion current and ion kinetic energy has been used to monitor drift in an inductively coupled, rf-biased plasma reactor. The technique detects a slow decrease in ion current over time caused by the deposition of a conductive layer on the dielectric window of the inductive source. Accompanying this drift in ion current are changes in ion energy which, depending on conditions, may be large or small, increasing or decreasing. The changes in ion energy are explained by three different kinds of mechanisms: bias voltage effects, sheath impedance effects, and ion transit-time effects. For each mechanism, a simple analysis is given that allows one to estimate the resulting drift in ion energy for a given drift in ion current. The mechanisms of ion energy drift, and the monitoring technique itself, are not limited to the particular experimental conditions of this study; rather, they apply to a wide range of plasmas and reactors. Drifts in ion energy caused by the mechanisms reported here have undoubtedly occurred in many plasma reactors but have gone largely or entirely unnoticed for lack of any reliable method to detect them.
Ferroelectric behaviors and charge carriers in Nd-doped Bi4Ti3O12 thin films
Authors: Gao X. S. , Xue J. M. , Wang J.
Published: January 2005

Nd-doped Bi4Ti3O12 thin films, (Bi3.25Nd0.85)4Ti3O12, of layered perovskite structure were synthesized by rf sputtering, followed by postannealing at 600–700°C. They show enhanced ferroelectricity with rising postannealing temperature in the range of 650–750°C. When annealed at 700°C, a remanent polarization 2Pr of 25.2μC∕cm2 and a coercive field Ec of 87.2kV∕cm were measured at 9V, together with an almost fatigue-free behavior up to 1.4×1010 switching cycles. Their ferroelectric, dielectric, and ac conductivity properties over the temperature range from 25to300°C were studied over the frequency range of 0.1–1MHz. Space-charge relaxation by oxygen vacancies was shown to play an important role in determining the dielectric and conductivity behaviors of Nd-doped Bi4Ti3O12 thin films.
Raman-scattering and structure investigations on porous SiC layers
Authors: Torchynska T. V. , Hernandez A. Vivas , Cano A. Diaz , Jiménez-Sandoval S. , Ostapenko S. , Mynbaeva M.
Published: January 2005

Raman scattering spectroscopy, scanning electron microscopy, and scanning acoustic microscopy were studied on porous SiC layers prepared by different technological routes and subjected to reactive ion treatment. The Raman spectra revealed a number of features specific for nanocrystallite materials, which can be used for characterization and diagnostics of porous SiC layers for technological applications.
Intense switchable fluorescence in light wave coupled electrowetting devices
Authors: Heikenfeld J. , Steckl A. J.
Published: January 2005

Switchable fluorescence has been obtained from light wave coupled (LWC) electrowetting (EW) devices fabricated on an optical waveguide substrate. The LWC device structure contains a polar water component and a nonpolar oil component that compete for placement on a hydrophobic surface under the influence of an applied electric field. The oil film contains organic lumophores that fluoresce intense red (608nm), green (503nm), and blue (433nm) light with ∼90% quantum efficiency when excited by violet light. Violet InGaN light-emitting diodes (LEDs) couple ∼405nm excitation light into the waveguide substrate. EW of the water layer displaces the fluorescent oil film such that it is either optically coupled to, or decoupled from, the underlying waveguide. The output luminance can be modulated from >100cd∕m2to<5cd∕m2 as a dc voltage ranging from 0to−24V is applied to the water layer. Maximum luminance of 15×30 arrays of the devices may exceed ∼500cd∕m2 by simply increasing the output of the InGaN LEDs.
Three-dimensional macroporous silicon photonic crystal with large photonic band gap
Authors: Schilling J. , White J. , Scherer A. , Stupian G. , Hillebrand R. , Gösele U.
Published: January 2005

Three-dimensional photonic crystals based on macroporous silicon are fabricated by photoelectrochemical etching and subsequent focused-ion-beam drilling. Reflection measurements show a high reflection in the range of the stopgap and indicate the spectral position of the complete photonic band gap. The onset of diffraction which might influence the measurement is discussed.
Zeeman splitting in ferromagnetic Schottky barrier contacts based on doped EuS
Authors: Ren Cong , Trbovic Jelena , Xiong Peng , von Molnár Stephan
Published: January 2005

Schottky barrier contacts of nonstoichiometric EuS, a ferromagnetic semiconductor, have been fabricated on Si (100) substrate and the current–voltage (I–V) characteristics are investigated at temperatures 150–5.0K. The electrical transport across such Schottky contacts is found to be dominated by thermionic emission at high temperatures, while at low temperatures and low biases, electron tunneling is dominant. The lower bound estimate of the Schottky barrier heights was obtained by analyzing the high-bias current–voltage characteristics. A decrease in barrier height of 0.26±0.06eV was deduced from the I–V characteristics as the temperature decreases below the ferromagnetic ordering temperature (TC) of the EuS. The variation of the barrier height below TC is the result of a spontaneous Zeeman splitting of the conduction band, and its temperature dependence resembles that of the spontaneous moment in EuS. The results point to the plausibility of using doped EuS as a spin injector and detector.
Reconfigurable magnetologic computing using the spin flop switching of a magnetic random access memory cell
Authors: Ney A. , Harris J. S.
Published: January 2005

Today’s computers rely on dissipative logic gates that are based on transistors. Increasing computational power means increasing the integration density and power dissipation. Among other alternatives, utilization of magnetism is a promising approach. Based on recent developments for improving the technology for magnetic random access memory (MRAM), a concept is proposed of how to utilize forthcoming generations of MRAM chips in the spin flop switching mode as versatile reconfigurable magnetologic gate arrays. A single MRAM cell can be directly operated as either NOT, AND, or NAND gates, and the use of bipolar current makes XOR and XNOR feasible as well. The actual functionality can be pre-programmed at run-time and the output is nonvolatile. Based on the spin flop switching mode, this concept is directly applicable to second-generation MRAMs.
High-efficiency surface-emitting channel drop filters in two-dimensional photonic crystal slabs
Authors: Min Bok-Ki , Kim Jae-Eun , Park Hae Yong
Published: January 2005

We analyze theoretically the output efficiencies of surface-emitting channel drop filters using channel drop tunneling processes in two-dimensional photonic crystal slabs. By using the channel drop tunneling processes, the output efficiencies of the filters can be easily improved to the values much higher than 50%, the maximum output efficiency of surface-emitting channel drop filters using one single-mode cavity, and the output efficiency of 100% is possible theoretically. In order to demonstrate the theoretical results, we present a surface emitting channel drop filter using the channel drop tunneling processes in a two-dimensional photonic crystal slab. The output efficiency of the presented filter is about 94% in good agreement with the theoretical analysis.
Study of the internal structure of individual CdSe quantum rods using electron nanodiffraction
Authors: Yu Zhiheng , Hahn Megan A. , Calcines Joaquin , Krauss Todd D. , Silcox John
Published: January 2005

Electron beam nanodiffraction was used to study the internal structure of colloidal CdSe quantum rods (QRs). Small-angle (2°–3°) rotations between various sections of individual colloidal CdSe QRs were observed indicating imperfection in the QRs. These imperfections may significantly impact the electronic, optical, and mechanical properties of the QRs.
Long-wavelength HgCdTe on silicon negative luminescent devices
Authors: Haigh M. K. , Nash G. R. , Gordon N. T. , Edwards J. , Graham A. , Giess J. , Hails J. E. , Houlton M.
Published: January 2005

We have investigated the negative luminescent properties of a device fabricated from metalorganic vapor phase epitaxy grown HgCdTe on a Si substrate. The peak emission was at 7.2μm, and the intrinsic Auger processes were found to be very well suppressed. The low currents (minimum current density, Jmin, of 0.84A∕cm2 at 295K) needed to drive these devices makes them suitable for a range of device applications.
Chemical reactions at Cu∕ZnS(001) and In∕ZnS(001) heterojunctions: A comparison of photoelectron and SL2,3 x-ray emission spectroscopy
Authors: Zhang L. , Wett D. , Schulze D. , Szargan R. , Nagel M. , Peisert H. , Chassé T.
Published: January 2005

Occurrence and extent of chemical reactions at Cu∕ZnS(001) and In∕ZnS(001) heterojunctions have been investigated by SL2,3 x-ray emission spectroscopy as well as photoelectron spectroscopy. With the formation of metal-sulfur bonds, spectral features originating from shallow metal d core levels (Zn3d, In4d) or valence states (Cu3d)) may appear in the SL2,3 emission spectra. Thus the x-ray emission spectroscopy was employed to detect chemical reactions at the heterojunctions, together with conventional photoelectron spectroscopy. Considerable reactions at the Cu∕ZnS(001) interface are more clearly indicated in the SL emission spectrum than in the Cu2p3∕2 or S2p core level spectra, whereas relatively confined reactions at the In∕ZnS(001) interface can only be probed in the In3d5∕2 core level spectra. The partial densities of states calculated for a reference CuInS2 on the basis of density functional theory agree well with features occurring in its SL2,3 emission spectrum.
High mobility in ZnO thin films deposited on perovskite substrates with a low temperature nucleation layer
Authors: Bellingeri E. , Marré D. , Pallecchi I. , Pellegrino L. , Siri A. S.
Published: January 2005

High electron mobility is measured down to low temperature in epitaxial ZnO thin films deposited on (110) oriented strontium titanate substrates. Electron mobility is evaluated by both magnetoresistance and resistivity-Hall effect data. Values up to 400cm2∕Vs are found below 50 K in epitaxial thin films grown by a two-step method: first a 100-nm-thick ZnO relaxing layer is deposited on the SrTiO3 (110) substrate at relatively low temperature (550–600 °C) and then the deposition temperature is raised up to 800 °C for the growth of a second ZnO layer. Reflection high energy electron diffraction analysis during the deposition, ex situ x-ray diffraction and AFM morphology studies performed separately on each layer reveal that the first layer grows in a quasi-two-dimensional mode while the increased temperature in the second step improves the crystalline quality of the film. The integration of ZnO transparent semiconductor with high-k dielectric perovskite substrates may lead to a wide variety of new electronic∕optoelectronic devices.
Birefringent cadmium–telluride-based metamaterial
Authors: Markham M. L. , Baumberg J. J. , Smith D. C. , Li X. , Gabriel T , Attard G. S. , Nandhakumar I.
Published: January 2005

A CdTe-based optical metamaterial, with large induced optical birefringence (4%), has been produced and its optical properties fully characterized and modeled over the spectral range 1500– 450 nm. This metamaterial, which is related to mesoporous silica, is made using electrochemical deposition in the presence of a lyotropic liquid crystal template. This process produces a stoichiometric CdTe film containing a hexagonal array of ∼4.2nm cylindrical pores with interpore separation ∼6.5nm. A model of the dielectric properties of the films indicates that their birefringence can be entirely attributed to the film’s nanoporosity.
Fabrication and characterization of face-centered-cubic void dots photonic crystals in a solid polymer material
Authors: Zhou Guangyong , Ventura Michael James , Vanner Michael Ross , Gu Min
Published: January 2005

Spherical void dots with a diameter of 1.2–1.8 μm have been generated in a solid polymer material by use of the ultrafast laser driven micro-explosion method. Micron-sized structures with a face-centered cubic lattice stacked in the [100] and [111] directions have been fabricated. Confocal microscopic images show the high uniformity of the fabricated structures. Photonic stopgaps with a suppression rate of approximately 70% as well as the second-order stopgaps have been observed in both directions. It is shown that the dependence of the stopgaps on the illumination angle in the [100] direction is significantly different from that in the [111] direction.
Sb-induced bicrystal ZnO nanobelts
Authors: Zou Kai , Qi Xiao-Ying , Duan Xiao-Feng , Zhou Shao-Min , Zhang Xiao-Hong
Published: January 2005

Zinc oxide bicrystal nanobelts of wurtzite structure were synthesized by simple thermal evaporation of a powder mixture of Zn and Sb2O3. The bicrystal nanobelts were found to have a growth direction of [2¯113], widths of 80–200 nm, and lengths up to several hundreds of micrometers. Energy dispersive x-ray spectroscopy and high angle annular dark field images showed that antimony was rich in the grain boundary of the bicrystal nanobelts. It was discovered that both sides of the bicrystal nanobelts were O-terminated toward the grain boundary. The mechanism of formation of the bicrystal nanobelts was also discussed.
Application of NaYF4:Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response
Authors: Shalav A. , Richards B. S. , Trupke T. , Krämer K. W. , Güdel H. U.
Published: January 2005

Erbium-doped sodium yttrium fluoride (NaYF4:Er3+) up-conversion phosphors were attached to the rear of a bifacial silicon solar cell to enhance its reponsivity in the near-infrared. The incident wavelength and light intensity were varied and the resulting short circuit current of the solar cell was measured. A close match between the spectral features of the external quantum efficiency and the phosphor absorption is consistent with the energy transfer up-conversion process. The peak external quantum efficiency of the silicon solar cell was measured to be (2.5±0.2)% under 5.1 mW laser excitation at 1523 nm, corresponding to an internal quantum efficiency of 3.8%.
Structural transformation and localization during simulated nanoindentation of a noncrystalline metal film
Authors: Shi Yunfeng , Falk Michael L.
Published: January 2005

A simulation study demonstrates that localization can arise as the result of the breakdown of stable quasicrystal-like atomic configurations. Samples produced at elevated quench rates and via more energetic processes contain a lower fraction of such configurations and exhibit significantly less pronounced localization and shorter spacing between bands. In the samples produced by the lowest quench rates, localization is accompanied by the amorphization of material with initially quasicrystal-like medium range order. This result is of particular significance in light of recent experimental evidence of local quasicrystal order in the most stable of the bulk metallic glasses.
A microelectromechanical load sensor for in situ electron and x-ray microscopy tensile testing of nanostructures
Authors: Zhu Yong , Moldovan N. , Espinosa Horacio D.
Published: January 2005

We report on the performance of a microelectromechanical system (MEMS) designed for the in situ electron and x-ray microscopy tensile testing of nanostructures, e.g., carbon nanotubes and nanowires. The device consists of an actuator and a load sensor with a gap in between, across which nanostructures can be placed, nanowelded, and mechanically tested. The load sensor is based on differential capacitance measurements, from which its displacement history is recorded. By determining the sensor stiffness, the load history during the testing is obtained. We calibrated the device and examined its resolution in the context of various applications of interest. The device is the first true MEMS in which the load is electronically measured. It is designed to be placed in scanning and transmission electron microscopes and on x-ray synchrotron stages.
Epitaxial liftoff of ZnSe-based heterostructures using a II-VI release layer
Authors: Balocchi A. , Curran A. , Graham T. C. M. , Bradford C. , Prior K. A. , Warburton R. J.
Published: January 2005

Epitaxial liftoff is a post-growth process by which the active part of a semiconductor heterostructure, the epitaxial layer, is removed from its original substrate and deposited onto a new substrate. This is a well established technique in GaAs-based heterostructures where epitaxial liftoff can be achieved by exploiting the contrast in the etch rates of GaAs and AlAs in hydrofluoric acid. We report here successful epitaxial liftoff of a ZnSe-based heterostructure. We find that a metastable layer of MgS acts as a perfect release layer based on the huge contrast in the etch rates of ZnSe and MgS in hydrochloric acid. Epitaxial liftoff of millimeter-sized ZnSe samples takes a fraction of the time required for GaAs liftoff. Photoluminescence experiments confirm that the liftoff layer has the same optical characteristics as the original wafer material.
Noncontact measurement of high-temperature surface tension and viscosity of bulk metallic glass-forming alloys using the drop oscillation technique
Authors: Mukherjee S. , Johnson W. L. , Rhim W. K.
Published: January 2005

High-temperature surface tension and viscosities for five bulk metallic glass-forming alloys with widely different glass-forming abilities are measured. The measurements are carried out in a high-vacuum electrostatic levitator using the drop oscillation technique. The surface tension follows proportional mathematical addition of pure components’ surface tension except when some of the constituent elements have much lower surface tension. In such cases, there is surface segregation of the low surface tension elements. These alloys are found to have orders of magnitude higher viscosity at their melting points compared to the constituent metals. Among the bulk glass-forming alloys, the better glass former has a higher melting-temperature viscosity, which demonstrates that high-temperature viscosity has a pronounced influence on glass-forming ability. Correlations between surface tension and viscosity are also investigated.
Gain saturation in InP∕GaInP quantum-dot lasers
Authors: Lutti J. , Smowton P. M. , Lewis G. M. , Blood P. , Krysa A. B. , Lin J. C. , Houston P. A. , Ramsay A. J. , Mowbray D. J.
Published: January 2005

We have measured the gain-current and gain-quasi–Fermi level separation characteristics for InP∕AlGaInP quantum-dot-laser structures. Saturation of the gain-current characteristics is apparent even though photoluminescence excitation spectroscopy measurements indicate that the 2D states are energetically distant from the dot states. The gain is reduced from the maximum value by the distribution of carriers in the excited dot states, the states in smaller dots and the 2D states.
Electrically switchable mesoscale Penrose quasicrystal structure
Authors: Gorkhali Suraj P. , Qi Jun , Crawford Gregory P.
Published: January 2005

We present the design, fabrication, and electro-optical properties of a switchable Penrose quasicrystal configuration in holographic polymer dispersed liquid crystal (H-PDLC) materials using a 5-beam hololithography exposure technique. The Penrose quasicrystal structure is confirmed through diffraction patterns and scanning electron microscopy (SEM); both show the expected tenfold symmetry. We also present electro-optic switching parameters of this quasicrystal structure and determine its index modulation to be 3×10−3 using coupled wave theory.
Abnormal contact resistance reduction of bonded copper interconnects in three-dimensional integration during current stressing
Authors: Chen K. N. , Tan C. S. , Fan A. , Reif R.
Published: January 2005

Bonded copper interconnects were stressed with current to measure the specific contact resistance. For bonded copper interconnects without a prebonding HCl clean, the corresponding specific contact resistance did not change while increasing the stress current. However, for some interconnects with the prebonding HCl clean, an abnormal contact resistance reduction was observed during the increase of the stress current. The rise of temperature at the bonding interface area due to Joule heating under high current density may have caused the decrease of contact resistance. This behavior may be one option for quality enhancement in 3D integration at low temperature.
Thermal distributions of surface states causing the current collapse in unpassivated AlGaN∕GaN heterostructure field-effect transistors
Authors: Oh C. S. , Youn C. J. , Yang G. M. , Lim K. Y. , Yang J. W.
Published: January 2005

The dc characteristics of the AlGaN∕GaN heterostructure field-effect transistors were examined at temperatures ranging from 25 to 260 °C under white light illumination. Drain current collapse measured was defined by the difference of drain current between light on and light off at Vgs=1V and Vds=5V. The surface-passivated device showed no drain current collapse, but the unpassivated device showed severe drain current collapse at 25 °C. Drain current and drain current collapse with an increase in temperature reduced, which resulted from the reduction of the electron mobility or saturation velocity and the thermal activation of the trapped electrons, respectively. Eventually, drain current collapse disappeared completely above 250 °C. The behavior of the temperature-dependent drain current collapse showed that the surface states for trapping electrons were continuously distributed with the temperature not having specific energy states.
Effect of damage by 2MeV He ions on the normal and superconducting properties of magnesium diboride
Authors: Gandikota R. , Singh R. K. , Kim J. , Wilkens B. , Newman N. , Rowell J. M. , Pogrebnyakov A. V. , Xi X. X. , Redwing J. M. , Xu S. Y. , Li Q.
Published: January 2005

We have studied the effect of damage induced by 2MeV alpha particles on the critical temperature, Tc, and resistivity, ρ, of MgB2 thin films. This technique allows defects to be controllably introduced into MgB2 in small successive steps. Tc decreases linearly as the intragrain resistivity at 40K increases, while the intergrain connectivity is not changed. Tc is ultimately reduced to less than 7K and we see no evidence for a saturation of Tc at about 20K, contrary to the predictions of the Tc of MgB2 in the dirty limit of interband scattering.