bluuebunny/crossref_metadata_2025 huggingface dataset:
Excited state nuclear forces from the Tamm–Dancoff approximation to time-dependent density functional theory within the plane wave basis set framework
Authors: Hutter Jürg
Published: February 2003

An efficient formulation of time-dependent linear response density functional theory for the use within the plane wave basis set framework is presented. The method avoids the transformation of the Kohn–Sham matrix into the canonical basis and references virtual orbitals only through a projection operator. Using a Lagrangian formulation nuclear derivatives of excited state energies within the Tamm–Dancoff approximation are derived. The algorithms were implemented into a pseudo potential/plane wave code and applied to the calculation of adiabatic excitation energies, optimized geometries and vibrational frequencies of three low lying states of formaldehyde. An overall good agreement with other time-dependent density functional calculations, multireference configuration interaction calculations and experimental data was found.
The electron–electron interaction in the Douglas–Kroll–Hess approach to the Dirac–Kohn–Sham problem
Authors: Matveev Alexei , Rösch Notker
Published: February 2003

Incorporation of relativistic effects into all-electron density functional (DF) calculations via scalar relativistic corrections to the kinetic energy and the nuclear attraction energy has become rather common. On the other hand, a self-consistent treatment of the spin–orbit interaction and relativistic corrections to the electron–electron interaction (or both simultaneously) requires substantially more computational effort. We present an extension of the Douglas–Kroll approach to the Dirac–Kohn–Sham problem that accounts for relativistic corrections to the Hartree potential and permits a self-consistent treatment of spin–orbit interaction. To construct computationally efficient approximations, we exploit the electron charge density fitting scheme with an auxiliary basis set. These approximate schemes introduce effects of the relativistic transformation of the Hartree part of the electron–electron interaction, but leave the (smaller) exchange-correlation contributions untransformed. These approximations were implemented in the parallel DF program PARAGAUSS. Quantitative effects of the new relativistic DF procedures were illustrated for the spin-orbit splittings of the Kohn–Sham levels in the Hg atom and the g-tensor shifts of NO2 where we show the value of new scheme. We also studied how properties of the diatomic molecules TlH, PbO, Pb2, and Bi2 change due to the improved treatment of relativistic effects.
Trapped metastable anions in low-energy electron scattering from C20 clusters
Authors: Gianturco F. A. , Lucchese R. R. , Sanna N.
Published: February 2003

Calculations are reported on scattering resonances in low-energy electron collisions with the fullerene carbon cluster C20. The quantum treatment of the scattering process is carried out using a single-center expansion of the total (bound + scattering electronic) wave function and with the electron–molecule interaction represented by a set of adiabatic multipolar effective potential curves. All resonant wave functions with scattering energies less than 20 eV are analyzed. In some of the resonant states the scattered electron density is seen to remain partly trapped inside carbon cage, although in all cases the resonant, continuum orbital density in the anionic state is primarily distributed near the surface of the cluster cage.
Ab initio studies of ClOx reactions. IV. Kinetics and mechanism for the self-reaction of ClO radicals
Authors: Zhu R. S. , Lin M. C.
Published: February 2003

The self-reaction of ClO radicals has been investigated by ab initio molecular orbital and variational transition state theory calculations. Both singlet and triplet potential energy surfaces were predicted by the modified Gaussian-2 method. The reaction was shown to take place mainly over the singlet surface by forming ClOOCl (k1) and ClOClO (k1′). These association processes were found to be strongly pressure dependent and the predicted total rate constants are in good agreement with the experimental data. The predicted second- and third-order rate constants for formation of ClOOCl and ClOClO can be expressed, respectively, in units of cm3 molecule−1 s−1 and cm6 molecule−2 s−1 by k1∞=1.6×10−9T−0.67 exp(−64/T), k1′∞=6.4×10−9T−0.78 exp(−76/T), and k10=8.31×10−20T−4.96 exp(−336/T), k1′0=1.72×10−14T−6.99 exp(−926/T) in the temperature range 180–500 K for N2 as the third body. The observed T, P-dependent data could be best accounted for with the heat of formation of ClOOCl, ΔfH0o(ClOOCl)=29.4±1 kcal/mol. The formation of Cl2+O2 (2), Cl+ClOO (3), and Cl+OClO (4) products have been confirmed, with the predicted pressure-independent rate constants: k2=1.09×10−13T0.66 exp(−1892/T); k3=1.36×10−13T0.77exp(−2168/T); k4=6.26×10−11T0.005 exp(−2896/T), respectively, in units of cm3 molecule−1 s−1, covering the temperature range 200–1500 K. These results are also in reasonable agreement with existing experimental kinetic data.
Polymer dynamics in 3PEG–LiClO4–TiO2 nanocomposite polymer electrolytes
Authors: Karlsson C. , Best A. S. , Swenson J. , Howells W. S. , Börjesson L.
Published: February 2003

The microscopic polymer dynamics in nanocomposite polymer electrolytes has been investigated using quasielastic neutron scattering experiments. Four samples based on the fully amorphous copolymer trihydroxy poly(ethylene oxide-co-propylene oxide) (3PEG) were investigated: 3PEG, 3PEG 1.5 mol/kg LiClO4, 3PEG 1.5 mol/kg LiClO4 10 wt % TiO2, and 3PEG 1.5 mol/kg LiClO4 20 wt % TiO2. In addition to a slow relaxation giving rise to elastic scattering, at least two dynamical processes were observed: a fast, local chain motion and a slower diffusive segmental motion. No changes of the quasielastic peak widths could be observed between the filled or unfilled composites; however, the elastic scattering of the sample was found to increase upon addition of the filler to the polymer electrolyte. The results indicate the presence of a roughly 5-nm-thick immobilized polymer layer (∼5 vol %) around filler particles, while the dynamics of the bulk polymer (∼95 vol %) is not influenced by the filler. The results imply that the ionic conductivity increase observed in the nanocomposite polymer electrolyte cannot be attributed to enhanced polymer dynamics.
Behavior of monocrystalline silicon under cyclic microindentations with a spherical indenter
Authors: Zarudi I. , Zhang L. C. , Swain M. V.
Published: February 2003

This study discusses the behavior of high-pressure phases of monocrystalline silicon when subjected to cyclic indentations with a spherical indenter. It was found that specific phases form in the second and subsequent indentation cycles under low maximum loads. An increase of the maximum indentation load causes changes of subsequent indentation cycles of the phase transformation events to occur earlier on both loading and unloading. The repeated indentations result in the formation of a multiphase structure in the deformed zone, featuring a nonhysteresis behavior. After a critical stage, the properties of the transformed material are stabilized and further indentations can no longer alter the load–displacement curve. It was also found that the greater the maximum load, the faster the occurence of property stabilization.
A high level theoretical investigation of the N2O4→2 NO2 dissociation reaction: Is there a transition state?
Authors: Ornellas Fernando R. , Resende Stella M. , Machado Francisco B. C. , Roberto-Neto Orlando
Published: February 2003

The N2O4→2 NO2 dissociation reaction was investigated at a high level of theory using the couple cluster with all single and double excitations and connected triples [CCSD(T)] and complete active space self-consistent field approaches, and the cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ basis sets. Only at the coupled cluster level a first-order saddle point was found connecting reactant and products. Collectively, structural, vibrational, and thermodynamic data for the three stationary points represent the best theoretical description of this reaction system to date, and are in good agreement with available experimental results. Unimolecular transition state theory rate constants (k∞) were also evaluated at 250, 298.15, and 350 K. At the CCSD(T)/cc-pVTZ level of calculation these results are 0.62×101, 1.90×103, and 1.66×105 s−1, respectively. Known experimental results at 298 K vary from 1.7×105 to 1.0×106 s−1. Including an estimate for basis set superposition error, we predict ΔH2980 for the dissociation reaction to be 12.76 kcal/mol (Expt. 13.1–13.7 kcal/mol).
Protein dynamics in viscous solvents
Authors: Caliskan G. , Kisliuk A. , Tsai A. M. , Soles C. L. , Sokolov A. P.
Published: February 2003

The mechanism of protein stabilization by glassy solvents is not entirely clear, and the stabilizer effective for a given protein is often discovered empirically. We use low frequency Raman spectroscopy as an effective tool to directly evaluate the ability of different solvents to suppress the conformational fluctuations that can lead to both protein activity and denaturation. We demonstrate that while trehalose provides superior suppression at high temperatures, glycerol is more effective at suppressing protein dynamics at low temperatures. These results suggest that viscosity of the solvent is not the only parameter important for biopreservation. It is also shown that glycerol and water enhance the high temperature conformational fluctuations relative to dry lysozyme, which explains the lower melting temperatures Tm in the hydrated protein and protein formulated in glycerol.
Computer simulation studies of electron transfer parameters for cyanoanthracene/N,N-dimethylaniline solutions
Authors: Scherer P. O. J. , Tachiya M.
Published: February 2003

The relevant parameters for photoinduced electron transfer in solutions of 9-cyanoanthracene in N,N′ dimethylaniline solvent are investigated. Using a combined molecular-dynamics–quantum-mechanics approach we calculate the dependence of the transfer matrix element on distance and relative orientation of donor and acceptor. Different contributions to the reorganization energy from intramolecular vibrations, relative motion of donor and acceptor and the rearrangement of the solvent are investigated. We find a rather strong coupling of the optically excited state to ion pair states involving the first solvation layer. Low energy excitations are identified as exciplex states which carry large permanent dipole moments as well as considerable intensities. Coupling of the excited acceptor to solvent molecules outside the first layer is considerably weaker and can be well described by the conventional electron transfer theory.
Bonding interaction, low-lying states and excited charge-transfer states of pyridine–metal clusters: Pyridine–Mn (M=Cu, Ag, Au; n=2–4)
Authors: Wu D. Y. , Hayashi M. , Chang C. H. , Liang K. K. , Lin S. H.
Published: February 2003

The binding interactions between the pyridine and small coinage metal clusters such as copper, silver and gold in different sizes (n=2–4) have been investigated by a density function theory approach. We obtain the binding energies of these pyridine–metal cluster complexes and analyze the nature of the binding interactions in terms of the metal cluster-dependent molecular orbital properties and binding orientations. The calculated binding energies show a good agreement with the experimental values of the pyridine adsorbed on the metal surfaces. We find that the order in the binding energies between pyridine and then metals clusters is Cu–Au>Ag and the interaction between pyridine and the silver is the weakest among these three metals. The donation of the lone-pair electrons on the nitrogen atom of the pyridine molecule is the major contribution to the binding interaction between pyridine and each metal cluster. The back-donation interaction from the metal atoms to the π-type anti-bonding orbital is very weak in all these complexes. The time-dependent density functional theory has also been performed to provide information on the relative energies of the low-lying states of each complex with respect to its ground state. In particular, we have explored the excited charge-transfer states, which play an important role in surface-enhanced Raman scattering processes. Based on the calculated molecular properties, we discuss Raman spectroscopy of pyridine adsorbed on rough metal surfaces.
Experimental demonstration of photonic crystal waveplates
Authors: Solli D. R. , McCormick C. F. , Chiao R. Y. , Hickmann J. M.
Published: February 2003

We have constructed and experimentally tested a microwave half-waveplate using the dispersive birefringent properties of a bulk, two-dimensional, photonic crystal away from its band gap. Our waveplate device exhibited a 200:1 polarization contrast, limited by our experimental resolution. We anticipate that photonic crystal waveplates will have important practical applications in several areas, including integrated photonic circuits.
Landau expansion for the critical point of a polydisperse system
Authors: Rascón C. , Cates M. E.
Published: February 2003

The effect of polydispersity on the phase diagram of a simple binary mixture is to split the binodal curve into cloud and shadow curves that cross at the critical point (which, in general, is not at the maximum of either curve). Recent theories of polydispersity have shown, in favorable cases, how to project the (infinite-dimensional) free energy of the polydisperse system into a low dimensional space of “moment densities.” We address here the issue of how to construct a Landau expansion from the projected free energy. For the simplest case where the excess free energy depends on one moment density ρ1 (this includes Flory–Huggins theory for length-polydisperse chains) we show that the minimal expansion remains quartic in ρ1 but nonetheless has seven independent coefficients, not two. When this expansion is handled correctly all the peculiar qualitative features of the polydisperse phase diagram are recovered, as are the slopes of the cloud and shadow curves, and the curvature of the cloud. However, to correctly predict the curvature of the shadow, certain fifth order terms must be retained. We also consider the phase diagram on the temperature–pressure plane, where the coexistence line broadens into a region. In general, the critical point lies between the point of maximum temperature and the point of maximum pressure on the perimeter of this region. This behavior is again captured by the Landau expansion.
Lateral control of self-assembled island nucleation by focused-ion-beam micropatterning
Authors: Kammler M. , Hull R. , Reuter M. C. , Ross F. M.
Published: February 2003

We demonstrate that the nucleation sites of nanoscale, self-assembled Ge islands on Si(001) can be controlled by patterning the Si surface in situ with a focused ion beam. At low doses of 6000 Ga+ ions per <100 nm spot, the selective growth is achieved without modifying the initial surface topography. At larger doses, topographic effects produced by sputtering and redeposition control the selective nucleation sites. Islands grown on irradiated spots are smaller with higher aspect ratio than islands grown on clean Si(001), suggesting a strong surfactant effect of Ga.
Oxygen adsorption on Au clusters and a rough Au(111) surface: The role of surface flatness, electron confinement, excess electrons, and band gap
Authors: Mills Greg , Gordon Mark S. , Metiu Horia
Published: February 2003

It has been shown recently that while bulk gold is chemically inert, small Au clusters are catalytically active. The reasons for this activity and its dramatic dependence on cluster size are not understood. We use density functional theory to study O2 binding to Au clusters and to a Au(111) surface modified by adsorption of Au clusters on it. We find that O2 does not bind to a flat face of a planar Au cluster, even though it binds well to its edge. Moreover, O2 binds to Au clusters deposited on a Au(111) surface, even though it does not bind to Au(111). This indicates that a band gap is not an essential factor in binding O2, but surface roughness is. Adding electrons to the surface of a Au(111) slab, on which one has deposited a Au cluster, increases the binding energy of O2. However, adding electrons to a flat Au surface has no effect on O2 binding energy. These observations have a simple explanation: in clusters and in the rough surface, the highest occupied molecular orbital (HOMO) is localized and its charge density sticks out in the vacuum. This facilitates charge transfer into the π* orbital of O2, which induces the molecule to bind to gold. A flat face of a cluster or a flat bulk surface tends to delocalize the HOMO, diminishing the ability of the surface to bind O2. The same statements are true for the LUMO orbital, which is occupied by the additional electron given to the system to charge the system negatively.
Magnetism and interface properties of epitaxial Fe films on high-mobility GaAs/Al0.35Ga0.65As(001) two-dimensional electron gas heterostructures
Authors: Cuenya B. Roldan , Doi M. , Keune W. , Hoch S. , Reuter D. , Wieck A. , Schmitte T. , Zabel H.
Published: February 2003

An optimized heterostructure design and an optimized surface sputter-cleaning procedure allow the growth of high-quality epitaxial Fe(001) thin films at Ts<∼50 °C on selectively doped GaAs/Al0.35Ga0.65As heterostructures, while retaining the high quality transport property of the two-dimensional electron gas. Magneto-optic Kerr effect measurements and model calculations indicate a dominant uniaxial in-plane anisotropy (easy axis along [110], hard axis along [1−10]) and small coercivity (∼15 Oe). Interface sensitive Fe57 Mössbauer measurements prove the absence of both magnetic “dead layers” and “half-magnetization” phases (compared to pure Fe), and provide evidence for intermixing within a few monolayers, retaining, however, a metallic Fe state and high Fe magnetic moments at the interface.
Optical nonlinearity resulting from a light-induced structural transition in gallium nanoparticles
Authors: MacDonald K. F. , Fedotov V. A. , Zheludev N. I.
Published: February 2003

We report that a light-induced structural transformation between different phases of gallium provides a mechanism for a strong optical nonlinearity. The nonlinearity has been studied in transient pump-probe experiments on nanoparticle films deposited on the ends of optical fibers. The magnitude and relaxation time of the response show hysteretic dependencies on temperature in the range from 100 to 300 K, are enhanced near the phase transition points and disappear at temperatures above 220 K.
Polaron–excitons and electron–vibrational band shapes in conjugated polymers
Authors: Karabunarliev Stoyan , Bittner Eric R.
Published: February 2003

The neutral excitations in poly(p-phenylenevinylene) are studied in conjunction with the vibronic structure of the lowest optical transitions. Combining the configuration interaction of Wannier-localized electron–hole pairs with an empirical description of electron–phonon coupling, we obtain the potential energy surfaces of monoexcited states and the Condon electron–vibrational spectra in absorption and emission. The S1→S0 luminescence band shape is found compatible with self-localization of S1 within about 10 monomers, driven exclusively by electron–phonon coupling. The singlet and triplet polaron–excitons are exchange–split by about 1 eV and differ substantially in terms of average electron–hole separation.
Toward photonic-crystal metamaterials: Creating magnetic emitters in photonic crystals
Authors: Povinelli M. L. , Johnson Steven G. , Joannopoulos J. D. , Pendry J. B.
Published: February 2003

In this work, we explore the possibility of designing photonic crystals to act as magnetic metamaterials: structures that exhibit magnetic properties despite the nonmagnetic character of their constituents. The building blocks of a magnetic material are microscopic magnetic dipoles, and to create a synthetic analog we employ point-defect modes in a photonic crystal. We begin by identifying a point defect mode in a three-dimensional crystal whose local field pattern resembles an oscillating magnetic moment. By analyzing the far-field pattern of the field radiated from the defect, we prove quantitatively that such modes can be designed with a primarily magnetic character: over 98% of the emitted power goes into magnetic multipole radiation. Unlike the constituents of natural para- and ferromagnetic materials, these synthetic magnetic emitters can be designed to operate without losses even at optical frequencies.
Magnetically modulated optical nanoprobes
Authors: Anker Jeffrey N. , Kopelman Raoul
Published: February 2003

We have developed magnetically modulated optical nanoprobes (MagMOONs) to magnetically modulate the signal from fluorescent probes and thus separate it from autofluorescence, electronic offsets, and other background signals. These micro- and nanosized particles emit fluorescence signals, indicating chemical concentrations, and blink in response to rotating magnetic fields. Demodulating the signal dramatically enhances the probe’s signal to background ratio. The probes and methods promise to improve immunoassays, intracellular chemical sensing, and fundamental biochemical research.
Localized epitaxial growth of α-Al2O3 thin films on Cr2O3 template by sputter deposition at low substrate temperature
Authors: Jin P. , Nakao S. , Wang S. X. , Wang L. M.
Published: February 2003

Low-temperature growth of α-Al2O3 films by sputtering was studied with x-ray diffraction and high-resolution transmission electron microscopy (HRTEM). Pure α-Al2O3 film was formed at 400 °C using Cr2O3 as template, whereas amorphous or θ-Al2O3 was formed without Cr2O3. HRTEM revealed localized epitaxial growth of α-Al2O3 on Cr2O3 with the relationship [011]Al2O3/[011]Cr2O3, suggesting the importance of Cr2O3 as a structural template for the growth of α-Al2O3, in addition to other contributions such as good stoichiometry, low sputter pressure, and low deposition rate under optimized deposition conditions. Successful growth of α-Al2O3 by sputtering at 400 °C or below makes the film widely applicable to even glass substrates.
Demonstration of bottom mirrors for resonant-cavity-enhanced GaAs homojunction far-infrared detectors
Authors: Zhang Y. H. , Luo H. T. , Shen W. Z.
Published: February 2003

A proposal for the bottom mirrors of resonant-cavity-enhanced GaAs homojunction far-infrared (FIR) detectors has been suggested and optimized based on undoped/doped GaAs layers with the Fresnel matrix method. With this kind of bottom mirror, the calculated absorption probability in the detector cavity increases two times over that in the normal detector structure. Comparing optical measurements have been carried out on n-GaAs homojunction FIR detector structures with and without the bottom mirrors, as well as a single optimized bottom mirror structure (without the detector cavity structure). The experimental FIR reflection and transmission results demonstrate well the theoretical design.
Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering
Authors: Carcia P. F. , McLean R. S. , Reilly M. H. , Nunes G.
Published: February 2003

We fabricated ZnO thin-film transistors by rf magnetron sputtering on Si substrates held near room temperature. The best devices had field-effect mobility of more than 2 cm2/V s and an on/off ratio>106. These ZnO films had resistivity ∼105 ohm cm, with high optical transparency (>80% for wavelength >400 nm), and compressive stress <0.5 GPa. The combination of transparency in the visible, excellent transistor characteristics, and low-temperature processing makes ZnO thin-film transistors attractive for flexible electronics on temperature sensitive substrates.
Potential energy functions of the X̃ 2B1, Ã 2B2, B̃ 2A1, and C̃ 2A2 states of Cl2O+ and the X̃ 1A1 state of Cl2O: Franck–Condon simulations of photoelectron bands of Cl2O which include anharmonicity
Authors: Chau Foo-Tim , Dyke John M. , Lee Edmond P. F. , Mok Daniel Kam-Wah
Published: February 2003

Restricted-spin coupled-cluster single and double plus perturbative triple excitations [RCCSD (T)] and/or complete-active-space self-consistent-field multireference internally-contracted configuration interaction (CASSCF/MRCI) potential energy functions of the X̃ 2B1, Ã 2B2, B̃ 2A1, and C̃ 2A2 states of Cl2O+ and the X̃ 1A1 state of Cl2O, with basis sets of up to the augmented-correlation-consistent-polarized-valence-quadruple-zeta quality, have been reported. For each of these states, vibrational wave functions of the symmetric stretching and bending modes have been computed, employing the potential energy function obtained at the highest level of calculation, with Watson’s Hamiltonian and anharmonic vibrational wave functions expressed as linear combinations of harmonic basis functions. The helium I photoelectron spectrum of Cl2O has been simulated with Franck–Condon factors calculated using computed anharmonic vibrational wave functions and allowing for Duschinsky rotation. The adiabatic ionization energies (AIEs) to the four lowest cationic states of Cl2O+ have been evaluated at the RCCSD(T) level with basis sets of up to polarized-valence-quintuple-zeta quality and by various extrapolation techniques to the basis set limit. Revised equilibrium geometrical parameters of the X̃ 2B1 and C̃ 2A2 states of Cl2O+ were obtained from the iterative Franck–Condon analysis procedure, and revised AIEs for the Ã 2B2 and B̃ 2A1 states of Cl2O+ were estimated based on comparison between the simulated and observed photoelectron spectra. It was found that inclusion of anharmonicity in the Franck–Condon factor calculations for each electronic state improves the quality of the simulated spectrum. The computed T1 diagnostics from the RCCSD calculations suggest that the B̃ 2A1 state of Cl2O+, with the ⋯(9a1)1(3b2)2(10a1)0 electronic configuration, possesses multiconfigurational character in the region of r(ClO)=1.87 Å and θ(ClOCl)=125°. CASSCF/MRCI/aug-cc-pVQZ(no g) calculations show an avoided crossing between the B̃ 2A1 state and (2)2A1 state [with the ⋯(9a1)2(3b1)0(10a1)1 electronic configuration], in the region of 1.96>r>1.80 Å and 137.0>θ>132.0°.
3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation
Authors: Williams Benjamin S. , Callebaut Hans , Kumar Sushil , Hu Qing , Reno John L.
Published: February 2003

We report the development of a quantum cascade laser, at λ=87.2 μm, corresponding to 3.44 THz or 14.2 meV photon energy. The GaAs/Al0.15Ga0.85As laser structure utilizes longitudinal-optical (LO) phonon scattering for electron depopulation. Laser action is obtained in pulsed mode at temperatures up to 65 K, and at 50% duty cycle up to 29 K. Operating at 5 K in pulsed mode, the threshold current density is 840 A/cm2, and the peak power is approximately 2.5 mW. Based on the relatively high operating temperatures and duty cycles, we propose that direct LO-phonon-based depopulation is a robust method for achieving quantum cascade lasers at long-wavelength THz frequencies.
Imaging of vortex configurations in thin films by scanning-tunneling microscopy
Authors: van Baarle G. J. C. , Troianovski A. M. , Nishizaki T. , Kes P. H. , Aarts J.
Published: February 2003

We report on imaging of vortices in thin superconducting films using surface passivation with an ultrathin Au layer. This allows investigation of surfaces that oxidize easily, as well as the mounting of samples in air. We studied vortex configurations in a material with weak vortex pinning (a-Mo2.7Ge) and a strongly pinning material (NbN) at 4.2 K in magnetic fields up to 1.4 T. In a-Mo2.7Ge, we observe a well-ordered hexagonal lattice, with local defects beginning to appear around 1.0 T. In NbN, the vortex lattice is fully disordered.
Investigation of interface trap states in TiN/Al2O3/p-Si capacitor by deep level transient spectroscopy
Authors: Jeon In Sang , Park Jaehoo , Eom Dail , Hwang Cheol Seong , Kim Hyeong Joon , Park Chan Jin , Cho Hoon Young , Lee Jong-Ho , Lee Nae-In , Kang Ho-Kyu
Published: February 2003

The minority carrier (electron) capture process and the interface trap density of a TiN/Al2O3/p-Si metal–oxide–semiconductor capacitor were examined by deep level transient spectroscopy (DLTS). It was found that the activation energies of the large peaks detected at higher temperatures with gate bias voltages of 1.8, 1.5, 1.3, and 1.1 V were 0.19, 0.24, 0.29, and 0.37 eV, respectively. These energies were related to the electron-capture process from the conduction band by interface states in the upper half of the Si band gap. The interface state passivation effect of postannealing in a hydrogen ambient was studied from the minority carrier capture process and the usual DLTS signals. The Dit at an energy of 0.35 eV from the valence bandedge decreased from 1×1012 cm−2 eV−1 at the as-fabricated state to 4×1011 cm−2 eV−1 after H2 annealing at 450 °C. It was also found that the Dit at an energy of 0.3 eV from the conduction bandedge decreased to the same amount by the same annealing process.
Thermomigration in Pb–Sn solder joints under joule heating during electric current stressing
Authors: Ye Hua , Basaran Cemal , Hopkins Douglas
Published: February 2003

Electromigration of solder joint under high dc current density is known as a reliability concern for the future high-density flip chip packaging and power packaging. Biased mass diffusion within solder joint from cathode to anode under high dc current density is observed in these experiments. In this letter, the experiments on flip chip solder joints under dc current stressing are conducted and thermomigration due to the thermal gradient in the solder joint caused by joule heating is reported. A three-dimensional coupled electric thermal finite-element (FE) simulation of a realistic flip chip module shows the existence of thermal gradient in the solder joint which is high enough to trigger thermomigration.
Ab initio studies of quasi-one-dimensional pentagon and hexagon ice nanotubes
Authors: Bai J. , Su C.-R. , Parra R. D. , Zeng X. C. , Tanaka H. , Koga K. , Li J.-M.
Published: February 2003

Ab initio plane-wave total-energy calcuation is carried out to study the relative stability of the quasi-one-dimensional (Q1D) pentagon and hexagon ice nanotubes. Electronic structure calculations indicate the two Q1D ice nanotubes have nearly the same band structures and energy bandgap as those of proton-ordered bulk ice Ih. Ab initio molecular-orbital and density-functional theory calculations, as well as three classical potential models of water, are also employed to investigate the relative stability of the pentagon and hexagon water clusters (H2O)30, (H2O)60, and (H2O)120. Clusters of this kind can serve to bridge the gap between the small polygonal water rings and the infinitely long Q1D polygon ice nanotubes. It is found that the polygon water prisms with the size (H2O)120 begin to show the relative energetic behavior of the infinitely long polygon ice nanotubes.
Hydrogen storage capacity of commercially available carbon materials at room temperature
Authors: Kajiura H. , Tsutsui S. , Kadono K. , Kakuta M. , Ata M. , Murakami Y.
Published: February 2003

The hydrogen storage capacity of five types of commercially available carbon materials with different nanostructures was measured at up to 8 MPa at room temperature using an apparatus based on a volumetric method with an error of less than 0.04 wt %/gr. The highest storage capacity of 0.43 wt % was obtained for purified HiPco™ single-walled carbon nanotubes (SWNTs). In the SWNTs, the hydrogen density in pores with a diameter of less than 1 nm was estimated to be a 0.022 g/ml, which corresponds to 31% of the density of liquid hydrogen. Issues in the development of carbon-based hydrogen storage media are discussed.
Formation of crystalline Si nanodots in SiO2 films by electron irradiation
Authors: Du Xi-wen , Takeguchi Masaki , Tanaka Miyoko , Furuya Kazuo
Published: February 2003

Amorphous SiO2 transforms into crystalline Si by 200 kV electron irradiation at ambient temperature. The transformation of amorphous SiO2 to crystalline Si takes place in two steps; the first step involves transformation of amorphous SiO2 into amorphous Si, while the second step is the crystallization of amorphous Si. Valence electron ionization is determined as the key factor for the transformation from SiO2 to amorphous Si; beam heating and knock-on displacement are responsible for the transformation from amorphous Si to crystalline Si. The energy threshold for the crystallization of amorphous Si is determined to be 150.2 kV.
Generation-recombination low-frequency noise signatures in GaAs metal–semiconductor field-effect transistors on laterally oxidized AlAs
Authors: Tzeng S. Y. , Cich M. J. , Zhao R. , Feick H. , Weber E. R.
Published: February 2003

Low-frequency noise characteristics of GaAs-on-insulator metal–semiconductor field-effect transistors, for which the insulating buffer layer was produced by lateral wet-oxidation of AlAs, are studied. Devices with different gate widths were fabricated resulting in different overoxidation times for the AlAs layer. Three characteristic generation-recombination noise signatures are observed depending on the measurement temperature and the gate bias. A generation-recombination noise signature with energy level at Ec−0.69 eV is found to increase with the amount of overoxidation time. This near midgap trap shows an increase in concentration towards the oxide interface, and it is tentatively assigned to an arsenic-antisite-related defect known from previous studies as EB4. A possible mechanism for the formation and the microscopic origin of this defect are discussed.
Bremsstrahlung reduction by dielectric trapping
Authors: Wade J. J. , Hollis D. L.
Published: February 2003

A mathematical model is used to analyze the effects of trapped negative charges in a dielectric absorber on bremsstrahlung production from low to moderate energy electrons. Significant changes in the bremsstrahlung spectra are predicted when the induced field due to trapped electrons is sufficiently large. Experiments with T1-204 and an electron accelerator as electron sources indicate that bremsstrahlung reduction does occur, although the effect is limited by radiation-induced conductivity.
Photoelectric properties of cuprous oxide
Authors: Pollack G. P. , Trivich Dan
Published: February 2003

The effects of transient and steady−state illumination on the electrical properties of single−crystal cuprous oxide have been investigated in the temperature range from 230 to −20 °C. For samples equilibrated well within the region of Cu2O stability, conduction was governed by an acceptor level at 0.4 eV above the valence band as determined from the temperature dependence of the Hall effect. The presence of two minority carrier trapping levels was also established and trapping parameters were determined from an analysis of the transient photoconductivity. The 0.4−eV acceptor level was also found to be present in a sample equilibrated under conditions placing its composition in a region near the CuO−Cu2O phase boundary. For this sample, however, only a single deeper trapping level was observed. A third type of sample, equilibrated under conditions which placed its composition in a region near the Cu−Cu2O phase boundary, was characterized by both a high hole density and a high mobility with an acceptor level energy of 0.16 eV. Also, the presence of two effects, the thermal quenching of the steady−state photoconductivity and its nonlinear dependence on light intensity, were shown to be consistent with the presence of deep traps in this material.
Properties of noncoaxial passing dislocation loops
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2003

Equilibrium configurations of single dislocation loops, as well as those of noncoaxial passing dislocation loops, have been determined by means of numerical techniques and by approximating the loops in terms of piecewise segments. Among other things, it is found that the passing behavior of the loops depends on the relative magnitidues of applied stress, dipole strength, and drag stress, and where the dipole strength is the stress to break the dipole formed by the unlike segments of the two loops and the drag stress is the stress needed to generate a unit length of the dipole. For an applied stress greater than the dipole strength, the dislocaiton loops pass one another and their equilbrium shape is identical to that of a single dislocation loop. The passing behavior of the loops also depends on whether or not the loops are constrained by the presence of other neighboring dislocation loops that are usually present in a real crystal. For applied stresses less than the dipole stress, but greater than or equal to the drag stress, the constrained dislocation loops, in particular, form elongated loops with long screw dipoles. For the cases where the cross slip of screw segments is difficult, the results also show that screw dipoles are much more stable than edge dipoles and arises from the higher dipole strength and lower drag stress for screw dislocations as compard to the corresponding stresses for edge dislocations.
Evaluation of the agglomeration of acicular magnetic oxide particles in polymer substrate using the Maxwell−Wagner effect
Authors: Dasgupta S. , Conner W. P.
Published: February 2003

The measurement of dielectric constant and dielectric loss (based on interfacial polarization or the Maxwell−Wagner effect) provides a method for studying the agglomeration of elongated magnetic particles in a polymer substrate. Some experimental results calculated on the basis of this method are presented. An estimate of a weighted average size and shape spectrum of the dispersed material is possible and can be used as one tool for evaluating the performance quality of the product formed during the several processing steps.
Longitudinal modes in distributed feedback lasers with external reflectors
Authors: Streifer William , Scifres Donald R. , Burnham Robert D.
Published: February 2003

Thresholds and propagation constants for longitudinal modes in distributed feedback lasers with external reflectors are computed. The general case in which the reflectors are located asymmetrically with respect to the grating is treated, and it is shown that depending on reflector spacing and position, modes may have lower thresholds than conventional lasers with identical reflectors. Also computed is the ratio of transmitted power through the right−hand reflector to that transmitted through the left−hand reflector. In general, since the device is asymmetric that ratio differs from unity.
Infrared stress birefringence in KBr, KCl, LiF, and ZnSe
Authors: Chen C. S. , Szczesniak J. P. , Corelli J. C.
Published: February 2003

The application of a variation of intensity method using static stress and polarized light to measure stress birefringence in the infrared wavelength region (∼4−11 μm) is described. We have used this method to measure the stress optic coefficient Cλ for the alkali halide cubic crystals KBr, KCl, LiF, and polycrystalline ZnSe. A detailed discussion of the definition of Cλ in terms of piezo−optic coefficients is given in the paper. Our results indicate that no wavelength dependence is observed for Cλ in the 4−11−μm region for KCl and KBr which have typical measured Cλ values of +3.3 and +3.4 Brewsters, respectively. For LiF at 8 μm we get Cλ=−3.08 Brewsters and for ZnSe we obtain Cλ values of −13.2 Brewsters at 9.4 μm and −13.0 Brewsters at 11 μm.
Aerosol−induced thermal blooming
Authors: Brown Robert T. , Smith David C.
Published: February 2003

Experiments have been carried out to study the nonlinear distortion of a laser beam due to absorption by aerosol particles in the air. A 15−W 10.6−μ beam was passed through a 1.5−m cell containing a carbon aerosol in air at STP, and various measurements of the distorted beam profile were made. The data show that aerosol absorption can lead to severe nonlinear distortion and that, for the regime in which the beam transit time is long compared to the interparticle thermal diffusion time, this distortion is qualitatively similar to that produced by molecular absorption, but has a magnitude somewhat below that predicted by conventional thermal blooming theory.
Effect of target temperature on surface composition changes of Cu−Ni alloys during Ar ion bombardment
Authors: Shimizu Hazime , Ono Masatoshi , Nakayama Katsuya
Published: February 2003

The effect of target temperature on surface composition changes of Cu−Ni alloys during Ar ion bombardment was studied by means of quantitative Auger electron spectroscopy. After sputtering at various temperatures the surface composition changes were analyzed at room temperature. At room temperature, the surface was enriched with Ni. It was found that the sputtering yield ratio of Cu/Ni was 1.9 over a whole range of the composition and that the value was almost coincident with that estimated from pure metals. As the temperature increased, the inclination toward Ni enrichment was enhanced. Though the sputtering yields of pure metals were independent of the temperature, in the alloys the yield ratio increased to 3.5 at 250 °C. However, above 400 °C the yield ratios decreased. The surface composition was mainly determined by the fast diffusion of Cu on the sputter−damaged layers.
Model for surface diffusion in AgBr
Authors: Tan Yen T.
Published: February 2003

The theory of ionic surface space−charge layers is used to interpret tracer diffusion data on thin epitaxial films of AgBr. This leads to the conclusion that the interstitialcy mechanism is the dominant mode of ionic transport in the space−charge region.
Thermal expansion of some diamondlike crystals
Authors: Slack Glen A. , Bartram S. F.
Published: February 2003

The thermal expansion of AlN, cubic BN, and BP has been measured from 77 to 1300 K by x−ray techniques. The derived thermal expansion coefficients are compared with those of diamond, Si, Ge, SiC, GaP, and BeO using the Debye temperature as a scaling parameter. It is apparent that the thermal expansion of Si is the smallest, SiC is intermediate, and all of the others are larger. The thermal expansion of Mo and W is also reviewed in order to determine how well these metals match the thermal expansion of the adamantine or diamondlike crystals.
Electro−optic light modulation in a planar zinc−blende−type crystal waveguide
Authors: Caton William M.
Published: February 2003

Electro−optic modulation of light in an optical single mode slab waveguide of a zinc−blende−type crystal is calculated theoretically. Both linear and quadratic dependence of phase velocity on modulation voltage is found for different crystal orientations. Agreement is found between the theoretical results and previously reported experimental results.
Transient photostimulated charge transfer from a photoconductor to an insulating fluid
Authors: Hartmann George C. , Schmidlin Fred W.
Published: February 2003

An investigation was made of photostimulated transfer of charge from a photoconductor into an insulating fluid. A theoretical description of the dynamics of charge−carrier generation and transport in the photoconductor, carrier accumulation at the photoconductor−fluid interface, and charge exchange into the fluid was developed in which the various physical processes are characterized by rate constants. Measurements of the dependence on electric field, light intensity, sample thickness, and carrier mobility in the fluid were carried out to determine which current−limiting mechanisms are dominant. The results illustrate a method of separately determining the interfacial charge−transfer efficiency and the efficiency of supplying photogenerated carriers to the interface.
Hydrodynamic calculations of surface response in the presence of laser-supported detonation waves
Authors: Nielsen P. E.
Published: February 2003

Numerical calculations of the formation, propagation, and effect on surface response of laser-supported detonation waves have been performed with a cylindrically symmetric two-dimensional Eulerian hydrodynamic computer program. These calculations demonstrate the validity and limits of applicability of blast wave models which have been used to describe such phenomena in the past and are consistent with a large body of experimental data. It is concluded that all these data may be understood within the framework of the model presented.
Deep craters produced by shock focusing in relativistic electron-beam diodes
Authors: Kelly J. G. , Widner M. M.
Published: February 2003

Narrow craters have been produced in aluminum-rod targets mounted in the anode of the Nereus electron-beam accelerator (150 kV, 50 kA, 40 ns). These craters (∼0.025 cm in diameter), which are characteristically deeper than their diameter and which extend into the electrode materials significantly beyond the classical range of the primary electrons in a relativistic electron-beam diode, were generated by a converging shock wave that melted and fractured the material in the region of shock focus. It is suggested that similar craters seen by other experimenters were also produced by the same mechanism.
Thermal and nonthermal switching in a-CdAs2 thin-film sandwich structures: The effect of bias rate
Authors: Thornburg David D.
Published: February 2003

Thin-film devices incorporating a-CdAs2 which display current-controlled negative differential resistance (CNDR) under quasistatic bias conditions are described. By biasing devices with short rapid rise-time pulses, threshold switching is observed to set in at much higher voltages than needed for quasistatic CNDR. The transition region between these extremes has been studied by biasing the devices with an adjustable power ramp whose slope was varied over many orders of magnitude. Under ramp bias, the devices show CNDR with a turnover voltage approaching the quasistatic value for bias times to turnover of 0.1 sec or longer. More rapid bias rates result in CNDR with a strongly increasing turnover voltage with increasing bias rate. Analysis of the temperature of the device during ramp bias indicates that the turnover mechanism is Joule-heat induced for bias times of 0.5 sec or longer, ’’electronic’’ for bias times of 10−3 sec or less, and of mixed origin in between.
Impurity conduction in transmutation-doped germanium during decay of the radioactive products
Authors: Thomas H. C. , Covington Billy
Published: February 2003

Measurements of impurity conduction in transmutation-doped germanium have been made in the temperature range 1.5–6 K during the radioactive decay of the electrically active products. Because the decay constant for the acceptor impurity is different than those for the donor impurities the compensation ratio, as well as the impurity concentration, changes continuously. After initial annealing to heal the damage caused by slow neutron capture, resistivity vs 1/T measurements were made for several samples beginning 11 days after irradiation and continuing until the radioactive decay was essentially complete. For a typical sample the gallium concentration increased from about 1015 to 1016 atoms/cm3 with a corresponding compensation ratio of about 0.5–0.26. Values of resistivity and activation energy determined are in good agreement with previously measured values indicating that effects due to the radioactive decay do not appreciably change the conductivity of the samples in the range 1.5–6.0 K.
Theory of diffraction of guided optical waves by thick holograms
Authors: Kenan Richard P.
Published: February 2003

A theory is developed which describes the diffraction of guided optical beams into the same or other modes of the waveguide structure. Expressions are derived for the coupling constants connecting the incident and diffracted beams. Numerical calculations on a hypothetical waveguide structure indicate that, for holograms written at the intersection of two guided beams, the effects of modal dispersion are weak as long as neither the incident nor the diffracted modes are near cutoff. In the converse case, where one of these beams is near cutoff, strong effects of modal dispersion appear.