bluuebunny/crossref_metadata_2025 huggingface dataset:
Collision and transport properties of Rg+Cl(2P) and Rg+Cl−(1S) (Rg=Ar, Kr) from ab initio potentials
Authors: Buchachenko A. A. , Krems R. V. , Szczȩśniak M. M. , Xiao Yun-De , Viehland Larry A. , Chałasiński Grzegorz
Published: July 2002

Highly accurate ab initio coupled cluster theory calculations, with single, double and noniterative triple excitations [CCSD(T)], and with the extended basis set augmented by the bond functions, were performed for the interactions of chlorine atom and chloride anion with Ar and Kr. Analytical fits to the ab initio points were shown to provide the consistent and reliable set of multiproperty potentials capable of reproducing all the available experimental data, namely: Total cross sections for Rg+Cl, reduced mobilities and diffusion coefficients for Rg+Cl−, as well as the data of spectroscopic zero electron kinetic energy experiments [see Buchachenko et al., J. Chem. Phys. 114, 9929 (2001), following paper]. The relative accuracy of available interaction potentials is discussed.
Capture rates for collisions of C (3Pj) and Ge (1S) with unsaturated hydrocarbons
Authors: Bettens Ryan P. A. , Collins Michael A.
Published: July 2002

We have calculated the capture rate coefficients for collisions of C (3Pj) and Ge (1S0) with unsaturated hydrocarbons and compared them with the experiments of Husain and co-workers [Clary, Haider, Husain, and Kabir, Astrophys. J. 422, 416 (1994); Husain, Ioannou, and Kabir, Z. Phys. Chemie 203, 213 (1998)]. Our findings indicate (i) that all nine electronic surfaces for the C (3P) reactions must contribute to the observed reaction rate coefficients, (ii) a central multipole approach is inappropriate for calculating the capture rate coefficients involving the larger hydrocarbons, (iii) the trends observed in the measured rate coefficients for the Ge and C reactions can simply be understood in terms of the physical size of the hydrocarbons, and (iv) the electrostatic interaction plays a significant role in the determination of capture rate coefficients for reactions involving C (3P) and highly polar species as well as acetylene.
Repetitive operation of water-filled Blumlein generator
Authors: Katsuki S. , Takano D. , Namihira T. , Akiyama H. , Majima T.
Published: July 2002

A water-filled Blumlein generator was operated at different repetition rates of up to 15 Hz, and its temporal performance was investigated. The Blumlein generator having an impedance of 10 Ω provides a rectangular voltage pulse with an amplitude of 200 kV and a duration of 75 ns into a matched load. The resistance of the water in the line decreases quickly at >10 Hz during a continuous operation for an hour and results in a decrease in the output voltage of the Blumlein line. The generator works with a repetition rate of up to 6 Hz without serious degradation in the voltage, while the averaged power density dissipated in the water is approximately 40 mW/cm3. The increase in the water temperature during operation is only a few degrees. This implies that the resistive heating of the water is not the dominant cause of the decrease in the water resistance.
Nonequilibrium tube length fluctuations of entangled polymers
Authors: Schütz G. M. , Santos J. E.
Published: July 2002

We investigate the nonequilibrium tube length fluctuations during the relaxation of an initially stretched, entangled polymer chain. The time-dependent variance σ2 of the tube length follows in the early-time regime a simple universal power law σ2=At originating in the diffusive motion of the polymer segments. The amplitude A is calculated analytically both from standard reptation theory and from an exactly solvable lattice gas model for reptation and its dependence on the initial and equilibrium tube length, respectively, is discussed. The nonuniversality suggests the measurement of the fluctuations (e.g., using flourescence microscopy) as a test for reptation models.
Nucleation of the crystalline phase of proteins in the presence of semidilute nonadsorbing polymer
Authors: Sear Richard P.
Published: July 2002

Starting from a protein solution which is metastable with respect to the crystalline phase, the effect of adding semidilute nonadsorbing polymer is considered. It is found to increase the chemical potential of the protein by a few tenths of kT, which may be enough to lower the barrier to nucleation of the crystalline phase by enough to allow crystallization. It is also shown that assuming that the polymer induces a pairwise additive attraction leads to qualitatively incorrect results.
Modification of diffusion coefficients in MgO(100) through the chemical properties of implanted ions
Authors: Lu M. , Lupu C. , Lee S. M. , Rabalais J. W.
Published: July 2002

Ti bulk diffusion coefficients have been determined for Ti in single crystal MgO(100) for four types of samples: Ti evaporated onto MgO and Ti evaporated onto MgO that was pre-bombarded with 7 keV Cl+, Ar+, and Cr+, respectively. Diffusion was induced by annealing to 1000 °C following the evaporation or pre-bombardment. Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. A model that includes a depth-dependent bulk diffusion coefficient was used to analyze the observed radiation enhanced diffusion (RED) effects. The bulk diffusion coefficients are of the order of 10−20 m2/s and are enhanced due to the defect structure inflected by the ion pre-bombardment. Different RED effects for the samples pre-bombarded with Cl+, Ar+, and Cr+ were observed despite their very similar ballistic implantation parameters. The diffusion model was extended to include the effects of lattice deformation, requirement of electrical neutrality, and chemical effects such as volatile compound formation. This extended model satisfactorily explains the RED differences observed for Cl+, Ar+, and Cr+ implantation. Our results show that RED is strongly influenced by the chemical properties of implanted ions.
Nanocrystallization of amorphous-Ta40Si14N46 diffusion barrier thin films
Authors: Bicker M. , Pinnow C.-U. , Geyer U. , Schneider S. , Seibt M.
Published: July 2002

The nanocrystallization process in thin amorphous-Ta40Si14N46 films, annealed in the range between 800 and 1000 °C for 1 h, is investigated by high-resolution transmission electron microscopy and high-angle annular dark-field and energy-dispersive x-ray analyses. At 800 °C clusters of about 2 nm in size indicate that compositional inhomogeneities have developed while the film has still remained structurally amorphous. The sample annealed at 900 °C contains a high density of nanograins of TaN measuring about 2 nm as well as amorphous structures measuring 75–100 nm having a high tantalum content. After annealing at 1000 °C, an almost entirely crystalline structure is observed with 4-nm-sized particles of cubic TaN and 15-nm-sized grains of Ta5Si3. Possible mechanisms driving these structural changes are discussed.
High pressure neutron diffraction on fluid propane and a mixture of propane and methane
Authors: Pfleiderer Till , Bertagnolli Helmut , Tödheide Klaus , Soper Alan K.
Published: July 2002

High pressure neutron diffraction data on deuterated propane at four supercritical states and on a mixture of 39.93 mole % deuterated propane and 60.07 mole % deuterated methane at two supercritical states are presented. In the case of propane the density could be varied by a factor larger than 2. The molecular structures of deuterated propane and deuterated methane were determined. The density dependence of the intermolecular structure is used in order to test various united-atoms potential for propane in Monte Carlo simulations. The best agreement with the neutron diffraction data is obtained with the parameters from the AUA4 (anisotropic united-atoms) force field recently proposed.
Laser excitation and dispersed fluorescence spectra of the HCBr Ã–X̃ vibronic transition
Authors: Tsai Tsung-Chuan , Chen Chun-Wei , Chang Bor-Chen
Published: July 2002

We recorded the laser-induced fluorescence (LIF) excitation spectra of several HCBr Ã–X̃ vibronic transitions between 580 nm and 630 nm in a direct current (DC) discharge supersonic free jet expansion. Dispersed fluorescence spectra, following excitation of these HCBr Ã–X̃ vibronic transitions were successfully obtained for the first time. The analysis of the dispersed fluorescence spectra reveals the details of the vibrational structure of the X̃ 1A′ state as well as that of the ã 3A″ state. The vibrational frequencies were determined as 1119 cm−1 (bend), 676 cm−1 (C–Br stretch) for the X̃ 1A′ state and 994 cm−1 (bend), 733 cm−1 (C–Br stretch) for the ã 3A″ state. In addition, based upon the observation of the triplet state levels, the value of the triplet–singlet energy gap (the zero-point level energy gap) could be extracted from the dispersed fluorescence spectra and is to be approximately 2006±8 cm−1 (5.73±0.02 kcal/mol).
Use of metal–oxide–semiconductor capacitors to detect interactions of Hf and Zr gate electrodes with SiO2 and ZrO2
Authors: Misra Veena , Heuss Greg P. , Zhong Huicai
Published: July 2002

Metal–oxide–semiconductor capacitors were used to study the interaction of Hf and Zr gate electrodes on SiO2, ZrSixOy, and ZrO2. A large reduction in the SiO2 equivalent oxide thickness accompanied by an increase in the leakage current was observed with Hf and Zr electrodes when subjected to anneal temperatures as low as 400 °C. The reduction in electrical thickness as observed from the capacitance–voltage measurements was attributed to the combination of (a) physical thinning of the SiO2 and (b) formation of a high-K layer. A severe instability of Zr and Hf electrodes was also observed on ZrSixOy and ZrO2 dielectrics. This behavior of Zr and Hf gates was attributed to high negative enthalpy of oxide formation and high oxygen solubility resulting in the reduction of the gate dielectric and subsequent oxygen diffusion to the gate electrode.
Surface phase diagrams for wetting on heterogenous substrates
Authors: Rascón C. , Parry A. O.
Published: July 2002

We propose a simplified description of fluid adsorption on heterogeneous micropatterned substrates. Using this approach, we are able to rederive results obtained earlier using effective interfacial Hamiltonian methods and predict a number of new examples of surface phase behavior for both singly and periodically striped substrates. In particular, we show that, for a singly striped system, the manner in which the locus of surface unbending phase transitions approaches the prewetting line of the infinite pure system, in the limit of large stripe widths, is nontrivial and sensitive to several characteristic length scales and competing free-energies. For periodic substrates, we investigate finite-size deviations from Cassie’s Law for the wetting temperature of the heterogeneous system when the domain sizes are mesoscopic.
Structure and stability of La2O3/SiO2 layers on Si(001)
Authors: Stemmer S. , Maria J.-P. , Kingon A. I.
Published: July 2002

High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to investigate La2O3/SiO2/Si structures. The La2O3 layers were deposited on thermal SiO2 on silicon, followed by rapid thermal annealing treatments at 600 °C and 800 °C in a nitrogen ambient. After annealing at 600 °C, the oxide layers were amorphous. After an 800 °C treatment, crystallites appeared in the original La2O3 layer, and the total oxide layer thickness increased by 17%, most likely due to the oxygen diffusion and reaction at the Si/SiO2 interface. EELS, using a 0.2 nm probe, showed that rapid thermal annealing at 600 °C did not cause significant La diffusion into the SiO2 layer, whereas some intermixing was observed at 800 °C. We use the observed microstructures to estimate equivalent oxide thicknesses. The results demonstrate that oxygen partial pressures and initial SiO2 thickness need to be carefully controlled to control SiO2 formation at the Si interface and to achieve target equivalent oxide thickness.
All-additive fabrication of inorganic logic elements by liquid embossing
Authors: Bulthaup Colin A. , Wilhelm Eric J. , Hubert Brian N. , Ridley Brent A. , Jacobson Joseph M.
Published: July 2002

We report an all-additive patterning technique, liquid embossing, in which a thin liquid film is embossed by an elastomeric stamp. We show that, for sufficiently thin films, isolated features are produced as the stamp contacts the underlying substrate, and that the liquid remains patterned even after removal of the stamp. Such an approach enables the rapid patterning of inorganic nanocrystal solutions, as capping groups and solvents can volatilize efficiently at the exposed liquid surface. Using this technique, we have fabricated all-printed all-inorganic transistors, photodetectors, and resistors, as well as multilayer structures with sacrificial layers and vias. Such an approach may enable a route to all-printed inorganic semiconductor logic and machines.
Mechanism of electron trapping in Ge-doped SiO2 glass
Authors: Uchino T. , Takahashi M. , Yoko T.
Published: July 2002

We present a possible mechanism of electron trapping in Ge-doped SiO2 glass on the basis of first-principles quantum chemical calculations on clusters of atoms modeling the local structures in the glassy system. The calculations suggest that the so-called “Ge(1) and Ge(2)” centers are distinctly different electron centers rather than GeO4− variants and that an electron trapped at an oxygen vacancy site is a promising candidate for Ge(2).
Effect of saturable response to two-photon absorption on the readout signal level of three-dimensional bit optical data storage in a photochromic polymer
Authors: Gu Min , Amistoso Jose Omar , Toriumi Akiko , Irie Masahiro , Kawata Satoshi
Published: July 2002

We observe a saturable change in the refractive index induced by two-photon absorption in a photochromic polymer, while the erasable nature of the polymer is maintained. As a result, the support region of spatial frequencies of the recorded data bits caused by the refractive index change in the polymer is enlarged. This feature leads to the significant enhancement of the signal level in a reflection confocal microscope readout system for three-dimensional photochromic bit optical data storage.
Evolution of energy and enstrophy containing scales in decaying, two-dimensional turbulence with friction
Authors: Scott Robert B.
Published: July 2002

Decaying, two-dimensional (2D), isotropic, incompressible, turbulence with finite Newtonian (lateral) friction and linear bottom drag is examined analytically. The classical result for inviscid, 2D turbulence of an upscale transfer of energy is shown to be robust to the presence of certain types of friction. It is shown that the energy-weighted mean wave number decreases with time, regardless of the Newtonian viscosity (i.e., for all Reynolds number) or linear bottom drag coefficients. For a given flow state, the time rate of change of the energy-weighted mean wave number is shown to be independent of the bottom friction but to increase with the Newtonian viscosity and the rate of spreading of energy in wave number space. There is an implicit dependence upon bottom friction since the second time derivative of the energy-weighted mean wave number involves a term linear in bottom drag coefficient. The forward transfer of enstrophy, on the other hand, is counter-balanced by the enstrophy decay due to finite Newtonian friction. The enstrophy-weighted mean wavelength decreases for sufficiently large Reynolds number, but increases when the Reynolds number becomes small enough. For a given flow state, the first time derivative of the enstrophy-weighted mean wavelength is independent of bottom friction. However, it implicitly affects the evolution through its influence upon the rate of spreading.
A perturbation analysis of the stability of long liquid bridges between almost circular supporting disks
Authors: Meseguer J. , Perales J. M. , Alexander J. I. D.
Published: July 2002

The stability of an isothermal liquid mass of constant properties (density and surface tension) held by capillary forces between two solid disks placed a distance L apart (the so-called liquid bridge model) is considered. For a weightless liquid bridge that is a right circular cylinder, the well-known Rayleigh stability limit holds, and the liquid column becomes unstable when its length is larger than its circumference. Many perturbations from this ideal configuration have been studied in the past, but the supporting disk shape has always been assumed circular. In this Brief Communication the influence of noncircular supports on stability limits of almost cylindrical liquid bridges is analyzed through an asymptotic analysis. Closed form expressions for the stability limits are presented.
Ultrafast dichroism spectroscopy of anthracene in solution. III. Nonpolar solvation dynamics in benzyl alcohol
Authors: Zhang Yunhan , Berg Mark A.
Published: July 2002

Results on single-wavelength transient hole burning (SW-THB) developed in paper II [J. Chem. Phys. 115, 4223 (2001)] are applied to the dichroism experiments on anthracene in benzyl alcohol reported in paper I [J. Chem. Phys. 115, 4212 (2001)]. The intermediate component of the dichroism decay is assigned to a SW-THB effect caused by nonpolar electronic solvation. The presence of a solvation component in dichroism experiments has not been demonstrated previously. The sparseness of anthracene’s electronic spectrum eliminates vibrational dynamics from the solvation measurement. Because data collection is focused on a single dimension, the viscosity dependence of the nonpolar solvation is determined with greater accuracy than in our previous two-dimensional transient hole-burning studies. The solvation time is obtained as a function of viscosity/temperature from 14.4 to 2.7 cP (1–56 °C). The times show good agreement with a viscoelastic theory of the diffusive component of nonpolar solvation. Combining the results of this paper with those of paper I allows for comparison of solvation and rotation dynamics within a single system. A correlation between the ratio of diffusive solvation and rotation times and the magnitude of the inertial rotation is suggested.
Theoretical prediction of local distortion in an ErO6 cluster: Stabilization of a C4v structure by a rack and pinion effect
Authors: Ishii Masashi , Komukai Yasuo
Published: July 2002

As a possible atomic coordination of erbium dopants surrounded by oxygen, a molecular orbital calculation of an ErO6 cluster can predict a C4v pseudo-octahedral structure with Er distortion of ∼0.1 Å from the octahedral center. It was found that bond alternation by a “rack and pinion effect” can minimize the electron transfer from O2− to Er3+ at this distortion range, resulting in stable ionic bonding; the rotation of an O 2p orbital due to Er 5d translation, similar to rack and pinion motion, forms a new O 2p–Er 5d bond, while a dipole moment induced by symmetrical degradation makes an O 2p–Er 6s bond unstable.
A Monte Carlo simulation of nucleation in amphiphilic solution
Authors: Kusaka Isamu , Oxtoby David W.
Published: July 2002

We study nucleation of amphiphilic molecules in a solvent–amphiphile binary solution by Monte Carlo simulation. The method provides detailed information on the free energetics of micelle formation. Our model, despite its simplicity, captures various aspects of real amphiphilic solutions. For example, the density profiles exhibit typical micelle structure. The free energy surface for micelle formation is in line with recent molecular dynamics simulations. From the free energy surface, we identified the critical micelle concentration (CMC), above which the free energy barrier for micelle formation is at most 6kBT for the model we study.
Comparative tests of conventional and retarding-potential Mott polarimeters
Authors: Petrov V. N. , Galaktionov M. S. , Kamochkin A. S.
Published: July 2002

The performance of a spherical field-free and a conical retarding-potential Mott polarimeter is compared. The stability of the detector signal with respect to a change in the position of the incoming electron beam is studied for two different primary electron beam energies. Shifting the incoming electron beam by 0.6 mm does not change the counting rate in the spherical field-free detector but induces a 7% or 18% change in the conical retarding-potential detector when using 1600 and 500 eV electrons, respectively. This may result in an error of the measured electron spin polarization.
Mechanisms of translational and rotational energy transfer in (N2)n cluster–surface scattering
Authors: Koch Denise M. , Peslherbe Gilles H. , Vach Holger
Published: July 2002

Molecular dynamics simulations were employed to investigate the dynamics of surface-induced (N2)n cluster fragmentation. The calculated translational and rotational state distributions of the monomer products of (N2)n clusters scattered off a hard surface indicate that the translational states follow a single Maxwell–Boltzmann distribution, whereas the rotational state distributions are best represented by a sum of two distinct Boltzmann distributions, in agreement with previous experimental findings obtained with a graphite surface. Analysis of the scattering dynamics provides insight into a molecular-level explanation for the differing behaviors of energy transfer to the translational and rotational modes of the monomer products. Our simulation results indicate that translational excitation of scattered products depends on the instantaneous cluster temperature at which the monomers evaporate. The obtention of two rotational distributions indicates that two rotational excitation mechanisms occur during the scattering event. The first mechanism is related to evaporation during cluster–surface impact of molecules lying at the outskirts of the cluster. The degree of rotational excitation of these molecules is shown to depend both on the degree of cluster heating during impact and on the degree of rotational hindrance imparted on a given molecule prior to evaporation. The second mechanism is related to evaporation of molecules that were caged within the interior of the cluster during surface impact. These molecules evaporate after the molecules lying at the outskirts with a degree of excitation that depends on the stabilized instantaneous cluster temperature.
Successive mechanism of double-proton transfer in formic acid dimer: A classical study
Authors: Ushiyama Hiroshi , Takatsuka Kazuo
Published: July 2002

The dynamics of double-proton transfer reaction in formic acid dimer is investigated by performing ab initio molecular dynamics simulations. From the viewpoint of optimized energetics alone, the synchronous (simultaneous) proton transfer is more favorable than the successive one. However, a full-dimensional classical dynamics shows that there is a certain time lag, about 8 fs in average, between two proton transfers. When a proton undergoes the first transfer, it moves from an oxygen with higher electron density to the counterpart having the lower one. The proton thus needs an energy sufficient enough to break the chemical bond, resulting in a clime of a potential barrier. On the other hand, the second proton moves from the lower electron-density oxygen atom to the higher one. Hence, the second proton is shifted predominantly by the thus-formed electronic field. Not only due to the time lag observed but mainly because of the difference in the mechanism of transfer, therefore, the present double-proton transfer is identified as successive. A detailed study on dynamics shows that the vibrational modes of the O–C–O skeletons dominate the second proton transfer.
A comprehensive thermodynamic theory of the Soret effect in a multicomponent gas, liquid, or solid
Authors: Kempers L. J. T. M.
Published: July 2002

A comprehensive theory for the Soret effect (also called thermal diffusion) is presented which incorporates both the thermodynamic contribution from selective attraction/repulsion and the kinetic contribution from selective collision interaction between the components. The new theory is an extension of a theory presented earlier in which the thermodynamic contribution only was modeled. The single assumption of the theory is that the Soret effect in the steady state is the macroscopic state accomplished by a maximum number of microstates with respect to the ideal gas state. As a result, the Soret effect in a multicomponent mixture can be calculated by using input from an equation-of-state of the mixture and kinetic gas theory without the use of matching parameters. The theory is not limited to systems with a small temperature difference and/or a small concentration difference. The methodology of the new theory can be used to model other cross-effects in irreversible thermodynamics. A test of the theory against the measured Soret effect in 18 mixtures shows agreement within a factor of 2 over four decades. Closer agreement cannot be expected since it appears that the calculation of the Soret effect is extremely sensitive to the accuracy of input from the equation-of-state. The present equations-of-state, even those that are calibrated for use in the chemical and petroleum industry, require modification for the calculation of the Soret effect, because of a higher demand in accuracy. In addition, it is also important to examine which frame of reference (center-of-volume or center-of-mass) applies to a particular measurement or practical application, because the frame of reference determines which mathematical expression for the Soret effect must be used.
Wetting on a geometrically structured substrate
Authors: Bruschi L. , Carlin A. , Mistura G.
Published: July 2002

We have measured the growth of liquid films of Ar and Kr adsorbed on a geometrically structured substrate obtained by machining on a lathe a thin Al disk with a sharp cutting tool. Near liquid–vapor bulk coexistence, the film mass is found to diverge as a power law of the chemical potential difference from saturation with an exponent x=−1.93±0.10, in very good agreement with recent scaling analysis results.
Physical and electrical properties of a Si3N4/Si/GaAs metal–insulator–semiconductor structure
Authors: Chen Zhi , Gong Dawei
Published: July 2002

We simulated capacitance–voltage (C–V) curves of Si3N4/GaAs, Si3N4/Si and also Si3N4/Semi* (virtual semiconductor) metal–insulator–semiconductor (MIS) capacitors and compared them with experimental C–V curves of a Si3N4/Si/GaAs structure. The experimental C–V curves of the Si3N4/Si/GaAs MIS capacitors are not in agreement with the simulated C–V curves of the Si3N4/GaAs and Si3N4/Si MIS capacitors, but are in agreement with those of the Si3N4/Semi* MIS capacitors, where Semi* is a virtual semiconductor with ni=7×1011 cm−3 or EG=0.88 eV. This indicates that the Si3N4/Si/GaAs structure is somewhat like a narrow band gap material with EG=0.88 eV. The comparison yields strong support for our theoretical energy band of the Si3N4/Si/GaAs MIS structure based on quantum well confinement. A depletion mode MIS field-effect-transistor (MISFET) is successfully fabricated with transconductance of 85 mS/mm, and an inversion mode MISFET is fabricated with transconductance of 0.05 mS/mm. The small transconductance for the inversion mode MISFET is ascribed to strong scattering due to confinement of electrons in the Si quantum well.
The visible laser excitation spectrum of YbOH: The Ã 2Π–X̃2Σ+ transition
Authors: Melville Todd C. , Coxon John A.
Published: July 2002

The Ã 2Π–X̃ 2Σ+ electronic transition of YbOH has been analyzed for the first time. Gas-phase YbOH was produced in a Broida-type oven by the reaction of ytterbium metal vapor with H2O2 vapor. Low-resolution spectra recorded with a broadband dye laser were used to examine the vibrational structure of the Ã–X̃ system while high-resolution laser spectroscopy with a single-frequency dye laser was employed to obtain spectra of the 000–000 and 000–100 bands of YbOH174 and the 000–000 band of YbOH172 (where v1 is the Yb–O stretching mode). The rotational analysis of the Ã 2Π–X̃ 2Σ+ transition demonstrates YbOH is a linear molecule, much like the alkaline–earth monohydroxides. Rotational and vibrational parameters are presented and the unusual behavior of the ground state spin-rotation splitting is discussed through a comparison with the isoelectronic molecule YbF.
Cooperative walks in a cubic lattice: Protein folding as a many-body problem
Authors: Fernández Ariel
Published: July 2002

A folding protein shapes conformation-dependent solvent environments to which its own intramolecular interactions are sensitive. This context-dependence of the folding process is represented by correlated self-avoiding walks in a cubic lattice. The correlations are shown to account for the nonadditivity of clustering forces and the possible origin of cooperativity in the folding process. The context sensitivity of the sharpness of the canonical ensemble of maximal compact structures is determined. Such results lead to an investigation of the evolutionary consequences of an exogenous modulation of the context sensitivity for natural proteins: biologically disfunctional structural ambiguity or duality may be brought about by an alteration in the environment associated with protein localization.
Composition, atomic transport, and chemical stability of ZrAlxOy ultrathin films deposited on Si(001)
Authors: Morais J. , da Rosa E. B. O. , Pezzi R. P. , Miotti L. , Baumvol I. J. R.
Published: July 2002

The stability of a ZrAlxOy film sputtered on Si upon thermal annealing in vacuum or in O2 was investigated. X-ray diffraction indicated that the as-deposited film was amorphous and remained so after annealing. Rutherford backscattering, narrow nuclear resonance profiling, and low-energy ion scattering provided the average composition of the film and the depth distributions of different elements. Chemical analysis of these elements was accessed by x-ray photoelectron spectroscopy. Annealing in vacuum produced thickness inhomogeneities and/or transport of very small amounts of Si from the substrate into the overlying film, with formation of Si precipitates. Annealing in O2 led to oxygen exchange throughout the film, as well as Si transport in slightly higher amounts than in vacuum. Differently from the observed upon annealing in vacuum, Si was either incorporated into the Zr,Al–O framework or oxidized in SiO2.
Growth of β-FeSi2 films via noble-gas ion-beam mixing of Fe/Si bilayers
Authors: Milosavljević M. , Dhar S. , Schaaf P. , Bibić N. , Huang Y-L. , Seibt M. , Lieb K. P.
Published: July 2002

A detailed study of the formation of β-FeSi2 films by ion-beam mixing of Fe/Si bilayers with noble gas ions is presented. Fe films of 35–50 nm deposited on Si (100) were irradiated with 80–700 keV Ar, Kr, or Xe ions in a wide temperature interval, from room temperature to 600 °C. The structures were analyzed by Rutherford backscattering spectroscopy, x-ray diffraction, conversion electron Mössbauer spectroscopy, elastic recoil detection analysis, cross-section high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. Already after Xe irradiation at 300 °C the whole Fe layer is transformed to a mixture of Fe3Si, ε-FeSi, and β-FeSi2 phases. At 400–450 °C, a unique, layer by layer growth of β-FeSi2 starting from the surface was found. A full transformation of 35 nm Fe on Si to a 105 nm β-FeSi2 layer was achieved by irradiation with 205 keV Xe to 2×1016 ions/cm2, at a temperature of 600 °C. The fully ion-beam grown layers exhibit a pronounced surface roughness, but a sharp interface to Si. This structure is assigned to a growth of β-FeSi2 grains in a local surrounding of interdiffused silicon. Rapid diffusion of silicon to the surface was observed during all ion irradiations. Single-phase β-FeSi2 layers were also synthesized by vacuum annealing for 2 h at 600 °C of 35 nm Fe/Si bilayers premixed with Xe at 450 °C. In this case, the layers form with a smoother surface topography. It is concluded that ion-beam mixing can be used successfully for growth of β-FeSi2 layers at moderate temperatures, either directly or combined with postirradiation annealing.
In situ investigations of the metal/silicon reaction in Ti/Si thin films capped with TiN: Volumetric analysis of the C49–C54 transformation
Authors: Chenevier B. , Chaix-Pluchery O. , Matko I. , Sénateur J. P. , Madar R. , La Via F.
Published: July 2002

The thermal expansion coefficients associated with the C49 and C54 crystal directions have been determined by in situ x-ray diffraction analysis of Ti film annealing deposited on Si substrates. Evidence of a clear anisotropy in the C49 coefficients has been obtained: the αb is considerably smaller than αa and αc. The volume expansion is larger in C54: this contributes to reduce to 1.6% at the transformation temperature, the observed 2.0% volume difference at 300 K. The magnitude of the volume discontinuity during transformation is an indication for a first-order transition.
Tetra point wetting of liquid K–KCl mixtures: Spectroscopic characterization of mesoscopic wetting and prewetting films
Authors: Staroske Sandro , Freyland Werner , Nattland Detlef
Published: July 2002

The wetting and prewetting transitions at the metal-rich K–KCl melt–sapphire interface have been investigated by spectroscopic ellipsometry in combination with normal incidence reflectivity in the spectral range 0.8⩽ℏω⩽2.2 eV at temperatures up to 730 °C. Along the coexistence curve a salt-rich liquid wetting film is observed which is identified by the spectral features of the liquid state F-center. Unusually thick wetting films are found ranging from 30 nm near 540 °C to 300 nm approaching the monotectic temperature of 751 °C. Their composition has been determined from the absorption coefficients of the F-center band and it corresponds to about 90 mole % salt. At conditions off coexistence and near the prewetting line, similar mesoscopically thick wetting films exist. Crossing the prewetting line towards metal-rich solutions, the optical properties at the interface agree with those of the nearly free electron metal. The high thickness of the prewetting films is qualitatively explainable by charging and double layer formation at the interface. The occurrence of liquid F-center-like states up to 200 K below the monotectic temperature gives evidence of a strong undercooling of the wetting films with respect to the bulk phase. These characteristics of the wetting transition in a metal–molten salt solution can be described by the tetra point wetting scenario for binary fluid mixtures.
The 530 nm system of KRb observed in a pulsed molecular beam: New electric quadrupole transitions (1 1Δ-X 1Σ+)
Authors: Lee Yonghoon , Yun Changhun , Yoon Youngjee , Kim Taeshick , Kim Bongsoo
Published: July 2002

New electronic transitions of KRb are identified near 530 nm by resonance enhanced two photon ionization study in a supersonic molecular beam. The rotational structure shows O, P, Q, R, and S branches. From the high resolution rotational analysis and comparison with the spectra of other alkali diatomic molecules we assign the observed bands to the 1 1Δ-X 1Σ+ transitions of KRb, which are allowed by electric quadrupole radiation. We obtain molecular constants for the upper electronic state of K39Rb85 as ωe=64.624 1(35)cm−1, Te=18 991.011 0(14)cm−1, Be′=0.035 703 9(10)cm−1, and Re=4.204 55(6) Å. Another new electronic transition observed in the same wavelength region is assigned to the 3 3Σ+-X 1Σ+ transition from the comparison with ab initio calculations.
High critical current densities in superconducting MgB2 thin films
Authors: Moon S. H. , Yun J. H. , Lee H. N. , Kye J. I. , Kim H. G. , Chung W. , Oh B.
Published: July 2002

Superconducting MgB2 thin films were prepared on Al2O3(0001) and MgO(100) substrates. Boron thin films were deposited by the electron-beam evaporation followed by postannealing process with magnesium. Proper postannealing conditions were investigated to grow good superconducting MgB2 thin films. The x-ray diffraction patterns showed randomly oriented growth of MgB2 phase in our thin films. The surface morphology was examined by scanning electron microscope and atomic force microscope. Critical current density (JC) measured by transport method was about 107 A/cm2 at 15 K, and superconducting transition temperature (TC) was ∼39 K in the MgB2 thin films on Al2O3.
Pump–probe polarization anisotropy study of doubly degenerate electronic reorientation in silicon naphthalocyanine
Authors: Albrecht Ferro Allison , Jonas David M.
Published: July 2002

Measurements with 26 fs pulses that cover the Q(0–0) band of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) yielded an initial anisotropy of 0.40 that decayed to 0.12 over 200 fs. This contradicts theories predicting anisotropy decay from 7/10 to 1/10. Including ground state bleaching and excited state absorption, anisotropy decay from 2/5 to 1/10 is predicted for degenerate electronic reorientation and dephasing.
On entropies of metal-hydrogen systems
Authors: Manchester F. D.
Published: July 2002

Inconsistencies in the metal-hydrogen (M-H) systems literature relating to the use of the partial configurational entropy for hydrogen absorbed in a metal are examined, and the usefulness for M-H systems of the partial excess entropy is questioned. Treatment of the behavior of M-H systems in terms of chemical solution thermodynamics is considered and it is concluded that this approach does not provide an appropriate representation of the special properties of an M-H system; many of these properties are usefully represented by a lattice gas model. An example is given of combining the configurational entropy of a lattice gas, with a summation of the principal changes to the entropies of the lattice-related and electronic subsystems of the metal lattice, resulting from the absorption of hydrogen. Rough estimates of quantitative values for such contributions are made based on experimental data. This summation of contributions is a practical and conceptually useful method for determining the entropy change produced by the formation of an M-H system.
Abnormal temperature behavior of photoluminescence from self-assembled InAs/AlAs quantum dots
Authors: Ma Zhixun , Pierz Klaus , Hinze Peter
Published: July 2002

We report on the temperature dependence of photoluminescence (PL) from self-assembled InAs/AlAs quantum dots (QDs). In the temperature range of 6–90 K, an abnormal blueshift of the first excited-state emission and an enhancement of the ground-state PL are observed. This is explained by carrier transfer within spatially coupled QDs with a reduced barrier between, which give rise to a small activation energy of about 2 meV. Based on the analysis of the PL intensities, the rapid redshift of the ground- and excited-state emissions with respect to the InAs band gap in the temperature range of 90–283 K is explained by stepwise carrier escape from the QDs via the excited states.
Spectroscopy and calculations of weakly bound gallium complexes with ammonia and monomethylamine
Authors: Li Shenggang , Rothschopf Gretchen K. , Pillai Dinesh , Sohnlein Bradford R. , Wilson Benjamin M. , Yang Dong-Sheng
Published: July 2002

The gallium complexes were produced in pulsed molecular beams and studied with zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Intermolecular vibrational frequencies and adiabatic ionization potentials (IPs) were obtained from ZEKE spectra. Ground electronic states were identified by combining the ZEKE spectra with quantum chemical and Franck–Condon calculations. Ga–NH3 has an IP of 40 135 cm−1 and metal-ligand stretching frequencies of 270 cm−1 (ωs+) in the ion and 161 cm−1 (νs) in the neutral. The IP of Ga–NH2CH3 is 39 330 cm−1, and the vibrational frequencies are 93 cm−1 (νb) for the Ga–N–C bending, 124 cm−1 (ωb+) for the Ga+–N–C bending, and 299 cm−1 (ωs+) for the Ga+–N stretching. The strength of the gallium–methylamine binding is stronger than that of the gallium–ammonia. The ground state of Ga–NH3 is A′2(Cs) and that of Ga+–NH3 is A11(C3v). In contrast, Ga–NH2CH3 has two doublets, A′2 and A″2(Cs), with virtually the same energies, whereas Ga+–NH2CH3 has a A′1(Cs) ground state.
Photofragment translational spectroscopy of 1,2-butadiene at 193 nm
Authors: Robinson Jason C. , Sun Weizhong , Harris Sean A. , Qi Fei , Neumark Daniel M.
Published: July 2002

Photofragment translational spectroscopy has been used to investigate the dissociation dynamics of 1,2-butadiene at 193 nm. Ionization of scattered photoproducts was accomplished using tunable VUV synchrotron radiation at the Advanced Light Source. Two product channels are observed: CH3+C3H3 and C4H5+H. The C3H3 product can be identified as the propargyl radical through measurement of its photoionization efficiency curve, whereas the C4H5 product cannot be identified definitively. The translational energy P(ET) distributions suggest that both channels result from internal conversion to the ground electronic state followed by dissociation. The P(ET) distribution for the C4H5 product is sharply truncated below 7 kcal/mol, indicating spontaneous decomposition of the slowest C4H5 product.
Collision-induced hyper-Rayleigh spectrum of octahedral molecules: The case of SF6
Authors: Bancewicz Tadeusz , Godet Jean-Luc , Maroulis George
Published: July 2002

A theoretical expression giving the collision-induced hyper-Rayleigh (CI HR) spectrum due to pairs of centrosymmetric molecules of octahedral symmetry has been derived. The dipole2-quadrupole hyperpolarizability light scattering mechanism of collision-induced hyperpolarizability ΔβLM is discussed in detail and proposed to explain the CI HR spectrum. Numerically we have applied our analytical formulas to binary CI HR spectrum of sulfur-hexafluoride. We have normalized our SF6 CI HR spectrum to the monomer HR spectrum of CCl4. The spectral contribution due to second hyperpolarizability-permanent hexadecapole HR light scattering mechanism has been estimated and showed to be negligible.
Unipolar ion sheath
Authors: Riemann K.-U. , Tsendin L.
Published: July 2002

In technical applications, the ion sheath in front of a highly negative wall is frequently described by the well known Child–Langmuir law. Due to inaccurate boundary conditions, however, this yields only a rather poor approximation. The collisionless Child–Langmuir law can be substantially improved by accounting for universal initial conditions following from the Bohm criterion. By a simple analytical ansatz the resulting unipolar ion sheath law is generalized to account for (charge exchange) ion collisions in the sheath.
A single Lanczos propagation method for calculating transition amplitudes. III. S-matrix elements with a complex-symmetric Hamiltonian
Authors: Li Shenmin , Li Guohui , Guo Hua
Published: July 2002

The recently proposed single Lanczos propagation method [J. Chem. Phys. 111, 9944 (1999); ibid. 114, 1467 (2001)] is extended to complex–symmetric Hamiltonians. It is shown that the complex–symmetric Lanczos algorithm possesses several useful numerical properties similar to those observed in real-symmetric cases, which enable one to compute multiple transition amplitudes with a single Lanczos propagation. The usefulness of the method is illustrated in calculating the S-matrix elements for the collinear H+H2 reaction.
The energy as a functional of the charge density and the charge-density susceptibility: A simple, exact, nonlocal expression for the electronic energy of a molecule
Authors: Hunt Katharine L. C.
Published: July 2002

Simple, new expressions relate the electronic potential energy 〈V〉 and the total electronic energy E of a molecule to its averaged electron density 〈ρe(r)〉, the nonlocal charge-density susceptibility χe(r,r′;iω), the nuclear positions {RN}, and the nuclear charges {ZN}. The expressions derived in this work are exact nonrelativistically, within the Born–Oppenheimer approximation. The results give a nonlocal form for the electronic energy in density functional theory. The virial theorem for a system with Coulomb forces is used to derive the expectation value of the kinetic energy in terms of the expectation values of the potential energy and the derivatives of the potential energy operator with respect to nuclear coordinates; gradient expansions of the kinetic energy functional are not needed. Exchange and correlation effects on 〈V〉 and E are determined by an integral of the charge-density susceptibility χe(r,r′;iω), over imaginary frequencies. The results for 〈V〉 and E are first derived by use of the fluctuation-dissipation theorem and the symmetry properties of the charge-density susceptibility with respect to a change in the sign of ω. Identical results are derived by integration of χe(r,r′;iω) over imaginary frequencies and use of the closure relation.
Thermally induced Zr incorporation into Si from zirconium silicate thin films
Authors: Quevedo-Lopez M. , El-Bouanani M. , Addepalli S. , Duggan J. L. , Gnade B. E. , Wallace R. M. , Visokay M. R. , Douglas M. , Bevan M. J. , Colombo L.
Published: July 2002

Monochromatic x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and Rutherford backscattering spectrometry are used to study the outdiffusion of Zr from the alternate gate dielectric candidate ZrSixOy thin films deposited on Si(100). We find that Zr incorporation into Si from ZrSixOy appears to occur at annealing temperatures higher than 1000 °C. Incorporation of Zr to depths of up to 23 nm into the silicon substrate is observed. A diffusion coefficient of D0∼2×10−15 cm2/s is estimated from the associated depth profiles.
Temperature-modulated Si(001):As gas-source molecular beam epitaxy: Growth kinetics and As incorporation
Authors: Kim H. , Glass G. , Soares J. A. N. T. , Foo Y. L. , Desjardins P. , Greene J. E.
Published: July 2002

Arsenic doping at concentrations CAs ⪞1018 cm−3 during Si(001) growth from hydride precursors gives rise to strong As surface segregation, low film growth rates RSi, poor electrical activation, and surface roughening. Based upon the results of temperature-programmed desorption studies of Si(001):As surface processes during film deposition, we have investigated the use of temperature-modulated growth including periodic arsenic desorption (10 s at 1000 °C) from the surface segregated layer. Both constant-temperature and temperature-modulated Si(001):As layers were grown at Ts=750 °C, selected as a compromise between maximizing CAs and providing a usable deposition rate, by gas-source molecular beam epitaxy from Si2H6/AsH3 mixtures. For constant-temperature growth, RSi is only 0.08 μm h−1, the fraction of electrically active dopant is 55%, and film surfaces are very rough (rms roughness 〈w〉=110 Å). In sharp contrast, Ts-modulated layers exhibit increases in RSi by 2.5× to 0.20 μm h−1, 100% electrical activity, and atomically smooth surfaces with 〈w〉=2 Å. The results are explained based upon the competition among As surface segregation, desorption, and incorporation rates.
Boron penetration and thermal instability of p+ polycrystalline-Si/ZrO2/SiO2/n-Si metal-oxide-semiconductor structures
Authors: Park Dae-Gyu , Lim Kwan-Yong , Cho Heung-Jae , Kim Joong-Jung , Yang Jun-Mo , Ko Jung-Kyu , Yeo In-Seok , Park Jin Won , de Waard Henk , Tuominen M.
Published: July 2002

We report boron penetration and thermal instability of p+ polycrystalline-Si (poly-Si)/ZrO2 (100 Å)/SiO2 (∼7 Å)/n-Si metal-oxide-semiconductor (MOS) structures. The flatband voltage shift (ΔVFB) of the p+ poly-Si/ZrO2/SiO2/n-Si MOS capacitor as determined by capacitance–voltage measurement was ∼0.18 V, corresponding to a p-type dopant level of 1.1×1012 B ions/cm2 as the activation temperature increased from 800 to 850 °C. Additional ΔVFB of ∼0.24 V was measured after the anneal from 850 to 900 °C. Noticeable boron penetration into the n-type Si channel as observed by secondary ion mass spectroscopy also confirmed the VFB instability with activation annealing above 850 °C. An abnormal decrease of accumulation capacitance was also found after anneal at 900 °C due to an excessive leakage current which was attributed to the formation of ZrSix nodules at the poly-Si/ZrO2 interface. We observed 4–5 orders of magnitude lower leakage current from the small-size capacitors (<50×50 μm2) up to the activation anneal of 850 °C for 30 min, while the formation of interfacial ZrSix nodules at 900 °C cannot be avoidable even at 0.6-μm-wide gate lines.