bluuebunny/crossref_metadata_2025 huggingface dataset:
Growing Primacy of Human Agency in Adaptation and Change in the Electronic Era
Authors: Bandura Albert
Published: April 2003

The extraordinary advances in electronic technologies and global human interconnectedness present novel adaptational challenges and expanded opportunities for people to shape their social future and national life. The present article analyzes these pervasive transformational changes from an agentic theoretical perspective rooted in the exercise of perceived personal and collective efficacy. By acting on their efficacy beliefs, people ply the enabling functions of electronic systems to promote their education, health, affective well-being, worklife, organizational innovativeness and productivity and to change social conditions that affect their lives. Technology influences, and is influenced by, the sociostructural nature of societies. The codetermining sociostructural factors affect whether electronic technologies and globalization serve as positive forces that benefit all or divisive ones in human lives.
A Common Framework for the Training of Psychologists in Europe
Authors: Lunt Ingrid
Published: April 2003

This paper presents the common framework for the training of psychologists in Europe, developed by a team of 15 members from 12 European countries partially funded by the European Union under its Leonardo da Vinci program. The team worked for over 2 years (1999-2001) through a series of transnational meetings and workshops, using consultation networks both in individual countries and across Europe, conference presentations, and an analysis of existing national education and training routes for psychologists in various European countries. The resulting framework provides a general structure for education and training which meets the requirements of the majority of participating countries.
The Equivalence Framework in Relationship to the Basic Training of Psychologists and Specialization Training: The Nordic Scene
Authors: Jern Stefan , Nieminen Pirkko , Odland Torleiv
Published: April 2003

This paper describes and compares university education and training, the procedures for licensing, and the specialist training systems for professional psychologists in the Nordic countries of Finland, Norway, and Sweden. The inter-Scandinavian and European regulations and agreements affecting mobility are presented. The systems presented are compared to each other, and a discussion follows on the following topics: What is the relationship between generic and specialized training? Will it be possible in the future for these countries to mutually recognize their different specialization educational programs? How specialized should further education be?
Method of increasing spatial resolution of the scanning near-field microwave microscopy
Authors: Kantor R. , Shvets I. V.
Published: April 2003

In this article we propose methods for the measurement of electric intensity of a microwave field above the surface of microwave circuits. Using miniaturized coaxial antennas and a special probe positioning system, we measure both the amplitude and the phase of the induced field above the device under test. We introduce a position/signal difference method to further increase the spatial resolution down to about 30 μm—about one order better than contemporary microwave scanning devices utilizing coaxial antennas. The effect is theoretically analyzed and experimentally verified. The probes are calibrated in a well-defined field standard to allow quantitative characterization of the measured field. Performance of our scanning system utilizing these methods is demonstrated using a PCB finger capacitor.
Electrical and physical characterization of gate oxides on 4H-SiC grown in diluted N2O
Authors: Cheong Kuan Yew , Dimitrijev Sima , Han Jisheng , Harrison H. Barry
Published: April 2003

A systematic electrical and physical characterization of gate oxides on 4H-SiC, grown in diluted N2O at 1300 °C, has been performed. Electrical characterization by the high-frequency C-V technique, conductance technique, and slow trap profiling method reveals that the densities of interface and near-interface traps, and the effective oxide charge for gate oxides grown in 10% N2O are the lowest, compared to gate oxides grown in 100% and 0.5% N2O. These results are supported by physical characterizations using x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and atomic force microscopy. It has been shown that carbon clusters, accumulated at the SiC-SiO2 interface, directly influence the roughness of the interface and the densities of the interface and near-interface traps.
Complete basis set limit studies of conventional and R12 correlation methods: The silicon dicarbide (SiC2) barrier to linearity
Authors: Kenny Joseph P. , Allen Wesley D. , Schaefer Henry F.
Published: April 2003

The problematic SiC2 barrier to linearity is investigated in a benchmark study of one-electron basis set convergence properties of both the conventional and linear R12/A formulations of second-order Møller–Plesset (MP2) perturbation theory. A procedure for computational molecular partial-wave expansions is constructed and applied to the T-shaped and linear forms of SiC2. The largest basis set used [Si(22s17p14d6f5g2h2i1k)/C(19s14p14d6f5g2h2i1k)] included functions of orbital angular momentum as large as l=7 (k), and systematic saturation was performed through l=6 (i). With respect to angular momentum l, correlation energy increments are found to decay in accord with analytical models that suggest (l+1/2)−6 and (l+1/2)−4 functional forms for the R12/A and conventional methods, respectively. A benchmark complete basis set (CBS) limit for the second-order correlation contribution to the SiC2 barrier to linearity, 5.66 kcal mol−1, was determined via MP2-R12/A partial-wave expansions. Conventional MP2 calculations, using both the standard cc-pV6Z and the [Si(22s17p14d6f5g2h2i1k)/C(19s14p14d6f5g2h2i1k)] basis sets, underestimate MP2 correlation energies by at least 3 kcal mol−1, while the barrier is underestimated by at least 0.1 kcal mol−1. Both X−3 cc-pVXZ extrapolations and partial-wave extrapolations greatly improve conventional correlation energies, with the cc-pVXZ extrapolated barrier in error by only 0.07 kcal mol−1. While the absolute accuracy of the conventional partial-wave extrapolations is substantially better than the cc-pVXZ extrapolated values, unbalanced errors result in an overestimation of the barrier by nearly 0.2 kcal mol−1. The CBS-limit MP2 contribution is combined via a focal-point analysis with conventional coupled cluster computations through triple excitations (CCSDT), resulting in an inferred CBS CCSDT barrier of 5.45 kcal mol−1 after accounting for core correlation and relativistic effects. The critical question of post-CCSDT corrections is approached through explicit coupled cluster computations perturbatively accounting for connected quadruple excitations [BD(TQ) and CCSD(2)], as well as shifted [2,1] Padé approximants of MPn series and continued fraction and quadratic Padé approximants of coupled-cluster series. The best available post-CCSDT correction, extracted from BD(TQ)/cc-pVTZ theory, of 0.87 kcal mol−1, results in a final prediction near 6.3 kcal mol−1 for the SiC2 barrier to linearity.
Converting Kohn–Sham eigenenergies into electron binding energies
Authors: Jellinek Julius , Acioli Paulo H.
Published: April 2003

A new accurate scheme for converting the Kohn–Sham eigenenergies into electron binding energies is formulated. The accuracy of the scheme is illustrated in applications to ten atoms and three molecules.
Fundamental vibrational frequencies of small polyatomic molecules from density-functional calculations and vibrational perturbation theory
Authors: Neugebauer Johannes , Hess Bernd A.
Published: April 2003

An extensive study of fundamental frequencies and anharmonic vibrational constants for polyatomic molecules obtained from Becke three parameter Lee–Yang–Parr (B3LYP) and Becke–Perdew (BP86) density functional calculations is presented. These calculations are based on standard perturbation theory, and are compared to correlation-corrected vibrational self-consistent field (CC-VSCF) calculations for the water dimer. The anharmonic corrections obtained from density-functional calculations compare well with experimental values and with results from correlated ab initio methods. While fundamental frequencies from B3LYP calculations are reliable, they are considerably too small for BP86 calculations. Consequently, the good agreement of unscaled harmonic frequencies from BP86 calculations with experimental frequencies is due to an error cancellation effect. This is of importance for the prediction of vibrational spectra for large molecules, because the perturbation theory approach naturally becomes unreliable for very large molecules due to the increasing number of anharmonic resonance effects. These resonances seriously limit the applicability of perturbation theoretical approaches to anharmonic vibrational constants, whereas the computational effort for the calculation of cubic and quartic force constants, is feasible because calculations can be performed very efficiently by a parallelized calculation of harmonic force constants for several structures, which are distorted along the normal coordinates, followed by numerical differentiation.
On the mechanism of adhesion in biological systems
Authors: Persson B. N. J.
Published: April 2003

I study adhesion relevant to biological systems, e.g., flies, crickets and lizards, where the adhesive microstructures consist of arrays of thin fibers. The effective elastic modulus of the fiber arrays can be very small which is of fundamental importance for adhesion on smooth and rough substrates. I study how the adhesion depend on the substrate roughness amplitude and apply the theoretical results to lizards.
Exciton self-trapping and formation of diradical intermediates in 5,7-dodecadiyne-1,12-diol bis[phenyl carbamate] (TCDU) crystals at low temperatures
Authors: Itoh Chihiro , Kondoh Takafumi , Tanimura Katsumi
Published: April 2003

The fundamental crystalline excitation of 5,7-dodecadiyne-1,12-diol bis[phenyl carbamate] (TCDU) single crystals results in emission of two luminescence bands peaked at 4.28 eV and 2.57 eV, both of which show wide widths and significant degree of natural polarization at low temperatures. Measurements of the decay characteristics indicate that the initial state of the 4.28-eV luminescence is singlet, while that of the 2.57-eV band is triplet in nature. Analysis of the temperature dependence of Urbach tail shows that exciton-phonon coupling is strong enough to form self-trapped state of excitons. Therefore, we identify that the 4.28-eV and 2.57-eV luminescence are due to radiative recombination of the self-trapped excitons (STEs) in TCDU crystals. Excitation of the crystal with intense 4.66-eV laser light results in the formation of dimer diradicals, with expense of the concentration of only the triplet STE. The result shows that the triplet STEs is the metastable precursor responsible for the dimer-diradical formation, which initiates the polymerization of this diacetylene crystal.
Exchange-correlation energy and potential as approximate functionals of occupied and virtual Kohn–Sham orbitals: Application to dissociating H2
Authors: Grüning M. , Gritsenko O. V. , Baerends E. J.
Published: April 2003

The standard local density approximation and generalized gradient approximations fail to properly describe the dissociation of an electron pair bond, yielding large errors (on the order of 50 kcal/mol) at long bond distances. To remedy this failure, a self-consistent Kohn–Sham (KS) method is proposed with the exchange-correlation (xc) energy and potential depending on both occupied and virtual KS orbitals. The xc energy functional of Buijse and Baerends [Mol. Phys. 100, 401 (2002); Phys. Rev. Lett. 87, 133004 (2001)] is employed, which, based on an ansatz for the xc-hole amplitude, is able to reproduce the important dynamical and nondynamical effects of Coulomb correlation through the efficient use of virtual orbitals. Self-consistent calculations require the corresponding xc potential to be obtained, to which end the optimized effective potential (OEP) method is used within the common energy denominator approximation for the static orbital Green’s function. The problem of the asymptotic divergence of the xc potential of the OEP when a finite number of virtual orbitals is used is addressed. The self-consistent calculations reproduce very well the entire H2 potential curve, describing correctly the gradual buildup of strong left–right correlation in stretched H2.
Two general methods for grand canonical ensemble simulation of molecules with internal flexibility
Authors: Chempath Shaji , Clark Louis A. , Snurr Randall Q.
Published: April 2003

Two simulation methods are presented for generating a grand canonical ensemble of molecules with internal degrees of freedom. Molecular dynamics integration is used as a Monte Carlo perturbation move in these methods. The integration move helps to explore the intramolecular degrees of freedom with high acceptance ratios. The proofs of the acceptance criteria for both methods are presented. Tests are described to show that the simulation produces results matching an analytical solution for a simple test system. The method is further tested by predicting adsorption isotherms of n-butane in the zeolite silicalite. An example using these algorithms to generate adsorption isotherms of more complex chiral molecules in chiral zeolitelike materials is also presented.
An intermolecular potential model for the simulation of ice and water near the melting point: A six-site model of H2O
Authors: Nada Hiroki , van der Eerden Jan P. J. M.
Published: April 2003

An intermolecular potential model of H2O with six interaction sites is proposed. The model is developed for the simulation of ice and water near the melting point. Parameters in the potential are determined to reproduce the real melting point of ice, and densities of ice and water near the melting point, which are predicted by calculating derivatives of the free energies and volumes of ice and water against potential parameters. Free energy calculations are carried out for several ice structures and water, and the results are compared with those obtained in four- and five-site models, which are currently in use. It is shown that, only in the present six-site model, the proton-disordered hexagonal ice is the stable structure at the melting point, as in real ice. The melting point of the proton-disordered hexagonal ice at 1 atm is estimated to be 271±9 K in the present model, which is in good agreement with the real melting point of 273.15 K. Moreover, results of Monte Carlo simulations of ice and water show that the present six-site model reproduces well the real structural and thermodynamic properties of ice and water near the melting point.
Conductivity of molten sodium chloride and its supercritical vapor in strong dc electric fields
Authors: Petravic Janka , Delhommelle Jérôme
Published: April 2003

We investigate the influence of thermostatting methods on the electrical conductivity and structure of molten and supercritical sodium chloride obtained in nonequilibrium molecular dynamics simulations in strong constant (dc) electric fields. The strong dependence of the results on the type of thermostat employed in simulations becomes apparent only at extremely high fields (>0.5×109 V/m). For this range of fields, quantitative differences of unexpected size can be seen in the melt. In the supercritical fluid, different thermostats predict qualitatively very different behavior and structure. While the kinetic-type thermostats predict increased association of ions in the field, configurational thermostat predicts enhanced dissociation.
Lattice discretization effects on the critical parameters of model nonpolar and polar fluids
Authors: Moghaddam Sarvin , Panagiotopoulos Athanassios Z.
Published: April 2003

The effects of the ratio of particle diameter to lattice spacing, ζ, on critical parameters for both polar and nonpolar fluids have been examined in detail. Nonpolar systems studied have short range Buckingham exponential-6 interactions, while polar systems have long range Coulombic forces treated with Ewald summation. Monte Carlo simulations in the grand canonical ensemble combined with histogram reweighting and mixed field finite size scaling have been used. Both critical temperature and critical density decrease on increasing ζ. The critical temperature scales as 1/ζα where the exponent was obtained as α=(6±2) for the nonpolar and α=(2±0.5) for the polar fluids. The large difference in α values between nonpolar and polar fluids results from a much weaker effect of discretization on the critical parameters of nonpolar fluids.
A novel path sampling method for the calculation of rate constants
Authors: van Erp Titus S. , Moroni Daniele , Bolhuis Peter G.
Published: April 2003

We derive a novel efficient scheme to measure the rate constant of transitions between stable states separated by high free energy barriers in a complex environment within the framework of transition path sampling. The method is based on directly and simultaneously measuring the fluxes through many phase space interfaces and increases the efficiency with at least a factor of 2 with respect to existing transition path sampling rate constant algorithms. The new algorithm is illustrated on the isomerization of a diatomic molecule immersed in a simple fluid.
Amphiphilic lamellar model systems under dilation and compression: Molecular dynamics study
Authors: Guo Hongxia , Kremer Kurt
Published: April 2003

Using an effective simplified continuum model for diblock copolymers, surfactants, and liquid crystals, the response of lamellar systems upon dilation and compression along the layer normal is investigated by large-scale parallelized dissipative particle dynamics like stabilized molecular dynamics simulation. We demonstrate dilation induced long-lived undulations and give clear evidence for introduction or elimination of a layer by the creation and movement of dislocation under higher dilation or compression strain.
Fluctuation effects in block copolymer melts
Authors: Vassiliev O. N. , Matsen M. W.
Published: April 2003

Fluctuation effects in symmetric diblock copolymer melts are quantitatively examined with the first direct comparison between Monte Carlo simulations and mean-field theory where both are performed on the same identical model. The simulations provide the most conclusive evidence to date that fluctuations transform the continuous mean-field order–disorder transition (ODT) into a discontinuous transition. Furthermore, the fluctuations shift the ODT toward high segregation, χN, by a factor of ∼2.7, which is much greater than that suggested by the Fredrickson–Helfand fluctuation theory. For the range of small molecules examined in our study, this shift is nearly independent of molecular weight. In the disordered phase, we find the usual large deviations from mean-field theory, but we find no indication whatsoever that they set in abruptly at some well-defined temperature as previously claimed.
Eckart frames for planar molecules
Authors: Wei Hua
Published: April 2003

Explicit analytic expressions of Eckart frames for planar molecules in Radau, Jacobi and bond coordinates have been presented. The orientation of the frame axis system with respect to the molecular plane at equilibrium is specified by an angle θ1e.
An Eckart-frame kinetic energy operator for tetra-atomic planar molecules
Authors: Wei Hua
Published: April 2003

A closed-form kinetic energy operator (KEO) for tetra-atomic planar molecules in Eckart frame has been expressed explicitly in terms of the internal coordinates with a parameter θ1e which labels a specific Eckart frame. This KEO has zero Coriolis coupling at equilibrium and an expression for the best θ1e has been given that makes zero centrifugal coupling. A method treating the singularities of this KEO has been shown and all matrix elements are finite in the basis presented in this paper.
Shape resonance of H2− anion stabilized in a molecular trap
Authors: Sobczyk Monika , Anusiewicz Iwona , Skurski Piotr
Published: April 2003

The possibility of stabilizing an electronically metastable anion in a molecular trap is studied using ab initio electronic structure methods. The low-energy H2− p-wave Σ2u+ shape resonance state is used as the metastable anion solute, and a pair of inwardly oriented LiCN molecules (NCLi⋯LiCN) is used as a molecular trap. It is found that for the (NCLi⋯LiCN) trap at its local minimum geometry, the B22u state (that corresponds to the Σ2u+ state for the isolated H2−) becomes electronically stable and is the ground state of the system. It is also found that, in this model trap, two other (excited) anionic states are bound (2Ag and B23u). Detailed numerical results are presented for the (NCLi⋯H2⋯LiCN)− species (i.e., the trapped H2−) whose vertical electron detachment energy is 3.429 eV at the CCSD(T) level with the aug-cc-pVDZ basis sets.
The He–CaH (2Σ+) interaction. I. Three-dimensional ab initio potential energy surface
Authors: Groenenboom Gerrit C. , Balakrishnan N.
Published: April 2003

The interaction potential of the He–CaH(2Σ+) van der Waals complex is computed with the partially spin-restricted open-shell single and double excitation coupled cluster method with perturbative triples [RCCSD(T)] for more than 3700 geometries. An accurate fit of the three-dimensional potential is made available for the RCCSD as well as the RCCSD(T) results. Also the CaH diatomic potential is calculated at the RCCSD(T) level and shown to be very accurate by comparison of computed vibrational levels and rotational constants to spectroscopic data. In the accompanying paper the potentials are employed in a study of collisions of He with CaH at cold and ultracold temperatures.
Quantitative analysis of dislocation arrangements induced by electromigration in a passivated Al (0.5 wt % Cu) interconnect
Authors: Barabash R. I. , Ice G. E. , Tamura N. , Valek B. C. , Bravman J. C. , Spolenak R. , Patel J. R.
Published: April 2003

Electromigration during accelerated testing can induce plastic deformation in apparently undamaged Al interconnect lines as recently revealed by white beam scanning x-ray microdiffraction. In the present article, we provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during an in situ electromigration experiment. Laue reflections from individual interconnect grains show pronounced streaking during the early stages of electromigration. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of unpaired randomly distributed dislocations as well as geometrically necessary dislocation boundaries. Approximately half of all unpaired dislocations are grouped within the walls. The misorientation created by each boundary and density of unpaired individual dislocations is determined. The origin of the observed plastic deformation is considered in view of the constraints for dislocation arrangements under the applied electric field during electromigration.
Metal drift induced electrical instability of porous low dielectric constant film
Authors: Fang Kuo-Lung , Tsui Bing-Yue
Published: April 2003

Nano-porous carbon doped oxide (CDO) is one of the potential low dielectric constant (low-k) materials that can achieve a dielectric constant as low as 2.2 and is expected to be suitable for the next generation multilevel interconnection. However, the electrical stability of CDO in contact with metal has not been addressed. In this work, metal ions’ drift into nano-porous CDO is investigated. It is observed that both the Al and Cu ions can be driven into porous CDO film easily by applying electric field or thermal treatment. This results in a severe flat band voltage shift of the metal/CDO/Si capacitor structure. It is hypothesized that the lacking formation of self-limited aluminum oxide between Al and CDO film make Al ions drift into CDO. The adhesion of Al and Cu to CDO is also very poor. A physical model, combining weak dielectric polarization and metal ions drift, was proposed to explain the observed electrical instability. The inconsistent results regarding the Al/porous low-k/Si structure reported in the previous literatures can also be explained with this proposed model. Fortunately, TaN, as a common diffusion barrier material for Cu interconnect structure, is proved to have good adhesion to CDO. Negligible metal ions would drift in CDO during electrical stress. It is concluded that with a suitable diffusion barrier, such as TaN, CDO is still a very promising material for next generation Cu-interconnect technology.
A simple quantum mechanical treatment of scattering in nanoscale transistors
Authors: Venugopal R. , Paulsson M. , Goasguen S. , Datta S. , Lundstrom M. S.
Published: April 2003

We present a computationally efficient, two-dimensional quantum mechanical simulation scheme for modeling dissipative electron transport in thin body, fully depleted, n-channel, silicon-on-insulator transistors. The simulation scheme, which solves the nonequilibrium Green’s function equations self consistently with Poisson’s equation, treats the effect of scattering using a simple approximation inspired by the “Büttiker probes,” often used in mesoscopic physics. It is based on an expansion of the active device Hamiltonian in decoupled mode space. Simulation results are used to highlight quantum effects, discuss the physics of scattering and to relate the quantum mechanical quantities used in our model to experimentally measured low field mobilities. Additionally, quantum boundary conditions are rigorously derived and the effects of strong off-equilibrium transport are examined. This paper shows that our approximate treatment of scattering, is an efficient and useful simulation method for modeling electron transport in nanoscale, silicon-on-insulator transistors.
Comparative experimental study of ionic polymer–metal composites with different backbone ionomers and in various cation forms
Authors: Nemat-Nasser Sia , Wu Yongxian
Published: April 2003

An ionic polymer–metal composite (IPMC) consisting of a thin perfluorinated ionomer (usually, Nafion or Flemion) strip, platinum, and/or gold plated on both faces and neutralized by a certain amount of appropriate cations undergoes large bending motion when, in a hydrated state, a small electric field is applied across its thickness. When the same membrane is suddenly bent, a small voltage of the order of millivolts is produced across its surfaces. Hence IPMCs can serve as soft bending actuators and sensors. This coupled electrical–chemical–mechanical response of IPMCs depends on the structure of the backbone ionic polymer, the morphology and conductivity of the metal electrodes, the nature of the cations, and the level of hydration (or other solvent uptake). We have carried out extensive experimental studies on both Nafion- and Flemion-based IPMCs in various cation forms, seeking to understand the fundamental properties of these composites, to explore the mechanism of their actuation, and finally, to optimize their performance for various potential applications. The results of some of these tests on both Nafion- and Flemion-based IPMCs with alkali-metal or alkyl-ammonium cations are reported here. Compared with Nafion-based IPMCs, Flemion-based IPMCs with fine dendritic gold electrodes have higher ion-exchange capacity, better surface conductivity, higher hydration capacity, and higher longitudinal stiffness. They also display greater bending actuation under the same applied voltage. In addition, they do not display a reverse relaxation under a sustained dc voltage, which is typical of Nafion-based IPMCs in alkali-metal form. Flemion IPMCs thus are promising composites for application as bending actuators.
Determination of the friction coefficient of a Brownian particle by molecular-dynamics simulation
Authors: Ould-Kaddour F. , Levesque D.
Published: April 2003

By using the formula first derived by Kirkwood, the friction coefficient of a solvated Brownian particle is determined from the integration on time of the autocorrelation function of the force that the solvent exerts on this particle. Extensive molecular dynamics simulations show that above a definite size of the studied systems the value of the integral defining the friction coefficient goes to a quasiconstant value (a plateau) when the upper bound on time increases. The minimal value of the system size where the integral exhibits this asymptotic behavior, rises with the Brownian particle size. From the plateau, a reliable estimate of the friction coefficient is obtained.
Dynamic and structural behavior of different rigid nonpolarizable models of water
Authors: Nieto-Draghi Carlos , Bonet Avalos Josep , Rousseau Bernard
Published: April 2003

The local structure and the dynamical behavior of water have been analyzed in two different regimes (the dense isochore of 0.995 g/cm2 and the supercritical isotherm of 673 K) through four rigid nonpolarizable models of water. An important change in the slope of temperature dependence of the self-diffusion coefficient at ρ=0.995 has been observed at T≈450 K, showing two main regions that are related to a change on the activation energy of the process (originated for a change of the structure of the first solvation shell from a tetrahedral to dodecahedral arrangement). The local orientational structure of water has been analyzed through the use of tetrahedral order parameters q. A direct relation between q and D has been observed for all models showing some kind of master curve up to 450 K at the 0.995 g/cm3 isochore. The structure of the system at short and large radial distances has been analyzed through a decomposition of the site–site radial distribution functions in terms of spherical harmonics, and a three-dimensional picture of the total pair distribution function has been reconstructed from this set of spherical harmonic projections.
A density functional approach to chemical reaction equilibria in confined systems: Application to dimerization
Authors: Tripathi Sandeep , Chapman Walter G.
Published: April 2003

The effect of confinement on chemical equilibria is investigated within the framework of a density functional theory for chemical reactions in slit pores in equilibrium with a bulk reservoir. Factors like pore size, temperature, bulk pressure, external field, and capillary condensation are known to have considerable impact on the phase equilibria of a confined system. We analyze the impact of these factors on the composition (hence conversion) of a model reacting system, from a chemical equilibria perspective. Canonical Monte Carlo simulations are performed to compare with the theoretical findings for the spatial distribution of the reactants and products in the pore. Enhanced adsorption leads to significantly higher conversions in reactions occurring in the pore phase than in the bulk phase. The validity of this framework for reacting systems is then further tested on a real system, viz., dimerization of nitric oxide in graphite micropores (size <3 nm). The results obtained are in very good agreement with the reactive Monte Carlo simulations results reported for the same system by Turner, Johnson, and Gubbins [J. Chem. Phys. 114, 1851 (2001)].
Doppler-free high resolution laser spectroscopy of the Na2 C 1Πu state: Perturbation and predissociation
Authors: Kabir Md. Humayun , Shinano Toyoki , Kasahara Shunji
Published: April 2003

High resolution absorption spectra of the C 1Πu←X 1Σg+ transition of the Na232 molecule have been measured in the range 29 680–30 950 cm−1 by exploiting the technique of Doppler-free UV-visible optical–optical double resonance polarization spectroscopy. The molecular constants of the C 1Πu(v=0–10) levels are determined, and the Rydberg–Klein–Rees potential energy curve is calculated. A number of C 1Πu(v=0–9,Je and f ) levels were found to be perturbed. The energy shifts of e and f parity levels of the C 1Πu state were studied and identified as originating from perturbations between the C 1Πu and 3 3Σu+ states. Remarkable line broadenings were observed only in the perturbed region and identified as the lifetime broadening effect originating from indirect (accidental) predissociation through the two diabatic Σ3u+ states.
Infrared spectra and density functional calculations of the copper thiocarbonyls: CuCS, Cu(CS)2, and Cu2CS in solid argon
Authors: Kong Qingyu , Zeng Aihua , Chen Mohua , Zhou Mingfei , Xu Qiang
Published: April 2003

Microwave discharge through CS2 vapor yielded CS which was cocondensed with laser-ablated copper atoms at 12 K in an argon matrix. Binary copper thiocarbonyl complexes: CuCS, Cu(CS)2, and Cu2CS were formed via the reactions of ground state copper atoms or dimers with CS in solid argon. On the basis of isotopic shifts and splittings as well as density functional calculations, absorptions at 1187.2, 1291.3, and 1353.9 cm−1 are assigned to the C–S stretching vibrations of the bent CuCS, linear Cu(CS)2, and end-on bonded Cu2CS molecules, respectively. The calculation results show that these copper thiocarbonyl complexes are more strongly bonded than the corresponding copper carbonyl complexes.
Photoassociation of ultracold K atoms: Observation of high lying levels of the 1g∼1 1Πg molecular state of K2
Authors: Pichler M. , Chen H. M. , Wang H. , Stwalley W. C. , Ross A. J. , Martin F. , Aubert-Frécon M. , Russier-Antoine I.
Published: April 2003

Very high-lying vibrational levels of the 1g∼1 1Πg electronic state of K2 have been observed in a photoassociation experiment using an ion detection scheme. The photoassociation measurements have been treated together with laser induced fluorescence data recorded by Fourier transform spectrometry to construct a pointwise potential curve for this electronic state. Several vibrational levels were observed by both techniques, so the dissocation energy can be deduced without extrapolation, from the sum of binding energies measured in photoassociation and vibrational energies established with respect to the potential minimum (defined by the fluorescence data), giving De=1290.292±0.002 cm−1 (1 standard deviation). The potential curve reproduces over 2000 term values (up to v=138) with a root mean square error of 0.0025 cm−1. Nevertheless, small differences are found between the rotational constants generated from the potential curve and the effective rotational constants deduced from binding energy measurements at very high v. The smoothness of the outermost part of the pointwise potential energy curve has been investigated through fits to a Hund’s case (c) asymptotic model.
Mixed quantum-classical study of energy transfer in a Na+ collision with a peptide
Authors: Wang Ming L. , Zhang J. Z. H.
Published: April 2003

We use a mixed quantum-classical (MQC) approach to study energy transfer to a peptide’s torsional modes through collision with an atomic ion. In this study, the torsional motion of the peptide is treated quantum mechanically while the translational motion of the attacking atomic ion is treated classically. The MQC approach is applied to study the excitations of torsional modes of GLY-ALA dipeptide by colliding the peptide with a sodium ion Na+. In particular, we study the energy transfer to torsional motions around the Cα–C and Cα–N bond and rotation of the CH3 side chain. Calculation shows that the efficiency of energy transfer is strongly dependent on initial orientation of the colliding partners. For the majority of approaching angles, the energy transfer to torsional mode is rather small. However, for certain attacking angles, the torsional mode is strongly excited and the Na+ is found to be trapped near the peptide. The average ratios of energy transfer to torsional motions along Cα–C, Cα–N and the side chain CH3 are about 58%, 27%, and 17%, respectively.
An advanced electric probing system: Measuring DNA derivatives
Authors: Shimotani Kei , Shigematsu Taishi , Manabe Chikara , Watanabe Hiroyuki , Shimizu Masaaki
Published: April 2003

We have developed an advanced electric probing system, which has two probes, with the spatial resolution of ∼1 nm and the detection limit of <1 pA in order to measure electric properties of nanometer-scale samples. This system consists of a conventional AFM system and a piezoactuator system. In electric measurements of samples, two probes must be connected to the sample with keeping an electric isolation between two probes. For a connection of probes with a nanometer-scale sample, the radiuses of curvature of the probes should be smaller than the sample size. Thus, we used carbon nanotube as one of two probes, so that we could measure current–voltage (I–V) curves of the nanometer-scale samples. We have applied our system to measuring I–V curves of a lambda phage DNA (λ-DNA) bundle. The curves showed that the current through the λ-DNA was less than ∼1 pA. In order to increase conductance of DNA molecule with chemical doping, we synthesized DNA-acceptor cross-linked derivatives (DACD). We measured I–V curves of DACD at various distances between two probes with our electric probing system. The results showed that the chemical doping increased the conductance of DNA. Furthermore, we explained the electrical transport mechanism through DACD with hopping model.
Effects of particulate curvature and sizes of charged species on the adsorption of a biocolloid bearing nonuniformly distributed fixed charges
Authors: Kuo Yung-Chih
Published: April 2003

The adsorption of a nonplanar biocolloid on a rigid collector surface is evaluated theoretically. Here, a biocolloid consists of a rigid core and an ion-penetrable membrane carrying nonuniformly distributed fixed charges. Both a biocolloid and a collector are immersed in an electrolyte solution. The simulated results demonstrate that based on constant total amount of fixed charges in the membrane phase, the classical point-charge model overestimates the rate of adsorption. The larger the curvature of a biocolloid, the faster the rate of adsorption, and the adsorption rate calculated for a cylindrical surface is faster than that for a corresponding spherical one. The greater the nonuniformity of the distribution of fixed charges, the longer the time required for biocolloidal adsorption, and the adsorption time evaluated for a nonlinear distribution of fixed charges is longer than that for a corresponding linear one. Thin membrane, high average concentration of fixed charges, low permittivity of dielectric medium and large sizes of cations, anions and fixed charges lead to slow rates of adsorption.
Blinking molecules: Determination of photophysical parameters from the intensity correlation function
Authors: Hegerfeldt Gerhard C. , Seidel Dirk
Published: April 2003

An explicit expression is given for the correlation function of blinking systems, i.e., systems exhibiting light and dark periods in their fluorescence. We show through the example of terrylene in a crystalline host that it is possible to determine by means of this explicit expression photophysical parameters, like Einstein coefficients and the mean light and dark periods. In addition we obtain further parameters like the frequency of the various intensity periods and the probability density of photons scattered off the host crystal. It turns out that this approach is simpler and allows greater accuracy than previous procedures.
An improved 6-31G* basis set for first-row transition metals
Authors: Mitin Alexander V. , Baker Jon , Pulay Peter
Published: April 2003

We propose a modification to the popular 6-31G* basis set, which has recently been extended to cover first-row transition metals [Rassolov et al., J. Chem. Phys. 109, 1223 (1998)]. As demonstrated by a number of calculations, the existing basis performs poorly for many transition metals, particularly those toward the end of the series (Co, Ni, and especially Cu). The reason for this lies primarily with the 3D shell, which lacks a sufficiently diffuse exponent. A reoptimization of the D-shell exponents and coefficients by a two-step procedure, keeping the rest of the basis unchanged, corrects the problem, giving a basis set that performs uniformly well across the entire first-row transition metal series from scandium to copper.
Simulation of blue InGaN quantum-well lasers
Authors: Chang Jih-Yuan , Kuo Yen-Kuang
Published: April 2003

For InGaN laser diodes with emission wavelengths longer than 435 nm, the threshold current density usually increases with the number of InGaN well layers. This phenomenon could be attributed to the dissociation of the high indium content InGaN well layer at a high growth temperature of 750 °C due to a high InGaN dissociation pressure. In this article, the laser performance of the blue InGaN laser diode structures have been numerically investigated with a laser technology integrated program simulation program. The simulation results suggest that the inhomogeneous hole distribution in the quantum wells also plays an important role in the laser performance as a function of the number of InGaN well layers. In addition to the inhomogeneous hole distribution in the quantum wells, the phenomenon and resolution of the electronic current overflow problem in the blue InGaN quantum-well lasers are also investigated.
Fourier-transform infrared and optical emission spectroscopy of CF4/O2/Ar mixtures in an inductively coupled plasma
Authors: Cruden Brett A. , Rao M. V. V. S. , Sharma Surendra P. , Meyyappan M.
Published: April 2003

Characterization of CF4/O2/Ar inductively coupled plasmas by Fourier-transform infrared (FTIR) spectroscopy and optical emission spectroscopy (OES) in a Gaseous Electronics Conference reference cell has been carried out. Characterization was performed at three mixture compositions (80/10/10, 60/20/20, and 40/30/30), powers of 200 and 300 W and pressures between 10 and 50 mTorr. Quantitative estimates of CF4, CO, COF2, and SiF4 etch products are made via FTIR, while the OES combined with actinometry allows for qualitative characterization of conversion of CF4 to atomic C, CF, and C2, and molecular oxygen to atomic oxygen. Qualitative measurements of F density and etch products Si and SiF are also made by OES. Results are explained by a combination of electron-impact dissociation and recombination processes. In the absence of significant capacitive coupling, etch species are believed to be formed primarily by window interactions with atomic F. Rotational temperatures are estimated by both FTIR and analysis of emission spectra. The FTIR technique tends to estimate temperatures several hundred K lower than OES data due to the absorption of colder gas species outside of the plasma.
Hybrid-integrated GaAs/GaAs and InP/GaAs semiconductors through wafer bonding technology: Interface adhesion and mechanical strength
Authors: Shi Frank , MacLaren Scott , Xu Chaofeng , Cheng K. Y. , Hsieh K. C.
Published: April 2003

In this study, the interface adhesion and mechanical strength of wafer bonded GaAs/GaAs and GaAs/InP semiconductors, each of (100) face, were characterized by combining the measurements of interface fracture energy γo and lap shear strength Es. The relations between the interface adhesion and annealing processes for four different types of bonding configurations, i.e., antiphase bonding, in-phase bonding, and twist bonding with 5° and 30° misalignments, were systematically studied. The surface free energy γα-GaAs/oxide (0.11–0.28 J/m2) of amorphous α-GaAs/oxide mixture was estimated based upon the reported surface free energy γc-GaAs (0.63 J/m2) of crystalline [100] GaAs and measured overall interface fracture energy γtotal (0.525 J/m2) of GaAs/GaAs bonded wafers. The micromorphologies of the bonded and debonded wafer interfaces were characterized by atomic force microscopy (AFM) and transmission electron microcopy (TEM). The interface microfailure mechanism of directly bonded GaAs wafers was proposed based on AFM and TEM microstructural analysis.
Equilibrium behavior of sessile drops under surface tension, applied external fields, and material variations
Authors: Shapiro Benjamin , Moon Hyejin , Garrell Robin L. , Kim Chang-Jin “CJ”
Published: April 2003

This article describes the equilibrium shape of a liquid drop under applied fields such as gravity and electrical fields, taking into account material properties such as dielectric constants, resistivities, and surface tension coefficients. The analysis is based on an energy minimization framework. A rigorous and exact link is provided between the energy function corresponding to any given physical phenomena, and the resulting shape and size dependent force term in Young’s equation. In particular, the framework shows that a physical effect, such as capacitive energy storage in the liquid, will lead to 1/R “line-tension”-type terms if and only if the energy of the effect is proportional to the radius of the liquid drop: E∝R. The effect of applied electric fields on shape change is analyzed. It is shown that a dielectric solid and a perfectly conducting liquid are all that is needed to exactly recover the Young–Lippmann equation. A dielectric liquid on a conducting solid gives rise to line tension terms. Finally, a slightly resistive liquid on top of a dielectric, highly resistive solid gives rise to contact angle saturation and accurately matches the experimental data that we observe in our electro-wetting-on-dielectric devices.
Long-ranged solvation forces in a fluid with short-ranged interactions
Authors: Pertsin Alexander J. , Grunze Michael
Published: April 2003

The grand canonical Monte Carlo technique is used to calculate the solvation force and interfacial tension in a simple Lennard-Jones fluid confined between two solid walls. Emphasis is placed on large wall-to-wall separations, where the oscillations of density and solvation force due to layering effects have decayed. Despite the short range of the fluid–fluid and fluid–wall interaction potentials used, the solvation force shows an unsuspectedly long-ranged behavior, remaining quite perceptible up to a separation of 100 molecular diameters. It is also found that the sign of the solvation force at large separations is not uniquely determined by the sign of the interfacial tension: The walls that are “philic” with respect to the constrained fluid may well exhibit both repulsive and attractive solvation forces.
Comparison of three-dimensional photonic crystal slab waveguides with two-dimensional photonic crystal waveguides: Efficient butt coupling into these photonic crystal waveguides
Authors: Moll N. , Bona G.-L.
Published: April 2003

Butt coupling into photonic crystal waveguides is computationally investigated for a three-dimensional photonic crystal slab and a two-dimensional photonic crystal. The photonic crystal slab consists of a silicon-on-insulator substrate with a triangular array of holes, in which the silicon layer is the optical guiding layer. The transmission spectra of the two-dimensional system and the slab system differ significantly. The slab system supports only a small range of frequencies in which a guided mode exists. In this frequency range, the transmission is comparable with that of the two-dimensional system, and its value is around 0.8. For the other frequencies, where for the slab system only resonances exist, the transmission is much lower than that of the two-dimensional system because of losses in the photonic crystal waveguide. Therefore, we conclude that complete three-dimensional computations have to be performed to obtain quantitative results for photonic crystal slab systems.