bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined experimental/theoretical investigation of the He+ICl interactions. I. Rovibronic spectrum of He⋯ICl complexes in the ICl B–X, 3–0 region
Authors: McCoy Anne B. , Darr Joshua P. , Boucher David S. , Winter Paul R. , Bradke Matthew D. , Loomis Richard A.
Published: February 2004

Transitions of two different stereoisomers of the He⋯ICl(X,v″=0) weakly bound complex, one with a T-shaped orientation and another that is most likely linear, have been observed in laser-induced fluorescence experiments performed in the ICl B–X region [Bradke and Loomis, J. Chem. Phys. 118, 7233 (2003)]. Here we present experimental and theoretical results aimed at confirming the previous assignments and at gaining additional insights into the He+ICl interactions. High resolution action spectra were recorded in the same region to identify those features that could be attributed to transitions of the He⋯I35Cl(X,v″=0) isomers and not to higher-order complexes, Hen⋯I35Cl, where n⩾2, or I37Cl containing species. Calculations of the rovibronic spectra of the He⋯I35Cl complexes in the ICl B–X, 2–0 and 3–0 regions were performed using an ab initio potential energy surface for the He+ICl(X,v″=0) ground state [Prosmiti et al., J. Chem. Phys. 117, 7017 (2002)] and two different pairwise additive potentials for the He+ICl(B,v′=2,3) excited states [Waterland et al., J. Chem. Phys. 89, 7277 (1988); Gray and Wozny, J. Chem. Phys. 94, 2817 (1991)]. The rotation-vibration energies and wave functions for the He⋯I35Cl complexes were obtained for all bound states with total angular momentum J<10 using both of these potentials. Electronic spectra were generated using these results, assuming that the transition moment lies along the ICl bond and is not perturbed by the presence of the helium atom. The calculations qualitatively reproduce the He⋯I35Cl action spectrum and strongly support the previous assignments. The calculations also indicate that some of the spectral congestion observed near the linear band may be attributed to transitions of the linear isomer to multiple intermolecular levels in the excited state. Coriolis coupling strongly mixes He⋯ICl(B,v′) states with rotational excitation, making simulations and assignments of the linear band observed in the experimental spectrum difficult.
Determination of fluid–solid transitions in model protein solutions using the histogram reweighting method and expanded ensemble simulations
Authors: Chang Jaeeon , Lenhoff Abraham M. , Sandler Stanley I.
Published: February 2004

Protein crystallization conditions are usually identified by empirical screening methods because of the complexity of the process, such as the existence of nonequilibrium phases and the different crystal forms that may result from changes in solution conditions. Here the crystallization of a model protein is studied using computer simulation. The model consists of spheres that have both an isotropic interaction of short range and anisotropic interactions between patch–antipatch pairs. The free energy of a protein crystal is calculated using expanded ensemble simulations of the Einstein crystal, and NpT–Monte Carlo simulations with histogram reweighting are used to determine the fluid–solid coexistence. The histogram reweighting method is also used to trace out the complete coexistence curve, including multiple crystal phases, with varying reduced temperature, which corresponds to changing solution conditions. At a patch–antipatch interaction strength five times that of the isotropic interaction, the protein molecules form a stable simple cubic structure near room temperature, whereas an orientationally disordered face-centered-cubic structure is favored at higher temperatures. The anisotropic attractions also lead to a weak first-order transition between orientationally disordered and ordered face-centered-cubic structures at low temperature, although this transition is metastable. A complete phase diagram, including a fluid phase, three solid phases, and two triple points, is found for the six-patch protein model. A 12-patch protein model, consistent with the face-centered-cubic structure, leads to greater thermodynamic stability of the ordered phase. Metastable liquid–liquid phase equilibria for isotropic models with varying attraction tails are also predicted from Gibbs ensemble simulations.
The structure of the phenol-nitrogen cluster: A joint experimental and ab initio study
Authors: Schmitt Michael , Ratzer Christian , Meerts W. Leo
Published: February 2004

The rotationally resolved LIF spectra of four different isotopomers of the phenol-nitrogen cluster have been measured to elucidate the structural parameters of the cluster in ground and electronically excited (S1) state. The fit of the rotational constants has been performed by a genetic algorithm and by an assigned fit to the line frequencies. The results of both methods are compared. The intermolecular structures are fit to the inertial parameters and are compared to the results of ab initio calculations for both states. This fit was performed under the restriction that the geometry of the monomer moieties do not change upon complexation. Of the remaining five intermolecular parameters two dihedral angles were fixed due to the planarity of the complex, which was inferred from the inertial defects of all isotopomers. The distance of the nearest nitrogen atom to the hydrogen atom of the phenolic hydroxy group is found to decrease upon electronic excitation of the chromophore considerably more than predicted from ab initio calculations. This deviation between theory and experiment can be traced back to the absence of electron–electron correlation in the performed complete active space self-consistent field calculations. The shortening of the OH⋯NN “hydrogen” bond upon electronic excitation is in agreement with the increased dipole moment of phenol in the S1-state.
Mode dependent vibrational autoionization of Rydberg states of NO2. II. Comparing the symmetric stretching and bending vibrations
Authors: Bell Patrice , Aguirre F. , Grant E. R. , Pratt S. T.
Published: February 2004

Triple-resonance excitation and high-resolution photoelectron spectroscopy are combined to characterize the mode selectivity of vibrational autoionization of the high Rydberg states of NO2. Photoelectron spectra and vibrational branching fractions are reported for autoionizing Rydberg states converging to the NO2+ X 1Σg+(110) state, that is, with one quantum in the symmetric stretch, ν1, and one quantum in the bending vibration, ν2. These results indicate that autoionization proceeds most efficiently through the loss of one quantum from the symmetric stretch rather than from the bending vibration. The implications of this result are discussed in terms of the autoionization mechanism.
Intermolecular electron transfer between coumarin dyes and aromatic amines in Triton-X-100 micellar solutions: Evidence for Marcus inverted region
Authors: Kumbhakar Manoj , Nath Sukhendu , Mukherjee Tulsi , Pal Haridas
Published: February 2004

Photoinduced electron transfer (ET) between coumarin dyes and aromatic amines has been investigated in Triton-X-100 micellar solutions and the results have been compared with those observed earlier in homogeneous medium. Significant static quenching of the coumarin fluorescence due to the presence of high concentration of amines around the coumarin fluorophore in the micelles has been observed in steady-state fluorescence studies. Time-resolved studies with nanosecond resolutions mostly show the dynamic part of the quenching for the excited coumarin dyes by the amine quenchers. A correlation of the quenching rate constants, estimated from the time-resolved measurements, with the free energy changes (ΔG0) of the ET reactions shows the typical bell shaped curve as predicted by Marcus outer-sphere ET theory. The inversion in the ET rates for the present systems occurs at an exergonicity (−ΔG0) of ∼0.7–0.8 eV, which is unusually low considering the polarity of the Palisade layer of the micelles where the reactants reside. Present results have been rationalized on the basis of the two dimensional ET model assuming that the solvent relaxation in micellar media is much slower than the rate of the ET process. Detailed analysis of the experimental data shows that the diffusional model of the bimolecular quenching kinetics is not applicable for the ET reactions in the micellar solutions. In the present systems, the reactions can be better visualized as equivalent to intramolecular electron transfer processes, with statistical distribution of the donors and acceptors in the micelles. A low electron coupling (Vel) parameter is estimated from the correlation of the experimentally observed and the theoretically calculated ET rates, which indicates that the average donor–acceptor separation in the micellar ET reactions is substantially larger than for the donor–acceptor contact distance. Comparison of the Vel values in the micellar solution and in the donor–acceptor close contact suggests that there is an intervention of a surfactant chain between the interacting donor and acceptor in the micellar ET reaction.
Comment on “Analysis of some integrals arising in the atomic four-electron problem” [J. Chem. Phys. 99, 3622 (1993)]
Authors: Harris Frank E. , Frolov Alexei M. , Smith Vedene H.
Published: February 2004

A paper by F. W. King, “Analysis of some integrals arising in the atomic four-electron problem” [J. Chem. Phys. 99, 3622 (1993)], contains expressions which it is shown can be further simplified to an extent making the formulation significantly more efficient. Two errors in one of the equations are also identified.
Reply to “Comment on ‘Analysis of some integrals arising in the atomic four-electron problem’ ” [J. Chem Phys. 99, 3622 (1993)]
Authors: King Frederick W.
Published: February 2004

A reply to the points raised in the comment of Harris, Frolov, and Smith is given.
Wetting of nanopatterned surfaces: The hexagonal disk surface
Authors: Schneemilch M. , Quirke N. , Henderson J. R.
Published: February 2004

Metropolis Monte Carlo simulations are used to investigate the wetting of chemically nanopatterned surfaces, for the case of hexagonal disk patterns where liquid wishes to wet high-energy circular patches but not wet the background surface. We calculate the density profiles of saturated liquid adsorbed on a variety of such substrates, spanning the nanoscale to atomic scale patterns. In addition, statistical mechanical sum rules are used to obtain interfacial order parameters and interfacial free energies. We observe that Cassie’s law is typically obeyed, together with an associated breakdown of the mechanical interpretation of Young’s equation, for pattern wavelengths greater than 15 molecular diameters. Here, the adsorbed fluid exists as an array of hemi-drops. At about half this wavelength, the breakdown of Cassie’s law lies within realistic energy scales and is associated with the unbending of the outer surface of adsorbed films. For atomic scale patterns, the usual interpretation of Young’s equation is restored for films thicker than one monolayer. At high chemical contrast, when the monolayer in contact with high-energy regions would prefer to be crystalline, we observe a variety of exotic interfacial phenomena that may have technological significance.
Statistical mechanics of bilayer membrane with a fixed projected area
Authors: Farago Oded , Pincus Philip
Published: February 2004

The equilibrium and fluctuation methods for determining the surface tension, σ, and bending modulus, κ, of a bilayer membrane with a fixed projected area are discussed. In the fluctuation method the elastic coefficients σ and κ are measured from the amplitude of thermal fluctuations of the planar membrane, while in the equilibrium method the free energy required to deform the membrane is considered. The latter approach is used to derive new expressions for σ and κ (as well as for the saddle-splay modulus), which relate them to the pair-interactions between the amphiphiles forming the membrane. We use linear response theory to argue that the two routes lead to similar values for σ and κ. This argument is confirmed by Monte Carlo simulations of a model membrane whose elastic coefficients are calculated using both methods.
Local quasi-equilibrium description of slow relaxation systems
Authors: Santamarı́a-Holek I. , Pérez-Madrid A. , Rubı́ J. M.
Published: February 2004

We present a dynamical description of slow relaxation processes based on the extension of Onsager’s fluctuation theory to systems in local quasi-equilibrium. A non-Markovian Fokker–Planck equation for the conditional probability density is derived, and from it we obtain the relaxation equation for the moments. We show that the fluctuation-dissipation theorem can be formulated in terms of the temperature of the system at local quasi-equilibrium which is related to that of the bath by means of a scaling factor revealing lack of thermal equilibrium. Our theory may be applied to a wide variety of systems undergoing slow relaxation. We discuss in particular slow dynamics in glassy systems and Brownian motion in a granular gas.
Discrete and heterogeneous rotational dynamics of single membrane probe dyes in gel phase supported lipid bilayer
Authors: Stevens Benjamin C. , Ha Taekjip
Published: February 2004

In order to probe the local dynamics of lipid bilayers in the gel phase, we measured the rotational time trajectories of a membrane probe, diI(3), in supported bilayers of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) using single molecule fluorescence polarization imaging. diI(3) has two hydrocarbon tails that mimic phospholipid tails and has its transition dipole moment lying mostly on the plane of the membrane; hence it is an excellent probe for rotational dynamics in membranes. Above the transition temperature, the probes are laterally mobile and do not display polarized emission. In the gel phase below the transition temperature, lateral mobility is severely reduced and the emission becomes polarized with its polarization direction changing in the milliseconds time scale. Molecule by molecule analysis of the rotational time scales revealed significant heterogeneities among molecules, much larger than would be due to statistical noise. Control experiments using small unilamellar vesicles suggest that the heterogeneities are not caused by surface interactions and are intrinsic to the gel phase membrane. The rotational dynamics is strongly temperature dependent and the thermally activated state for the rotational motion has a large entropic barrier (>30kB), indicating that relatively large local disorder is required for the rotational motion to occur. Rotational hopping between discrete angles has been observed at the lowest temperatures (∼10 °C). Our results suggest that the gel phase membrane is not uniform at the microscopic level but is highly dynamic with the rigidity of local environments constantly changing.
The Enskog-type theory of the velocity autocorrelations in the two-dimensional nematic of hard needles
Authors: Chrzanowska Agnieszka
Published: February 2004

As it was shown from molecular dynamics of two-dimensional hard needles [Phys. Rev. E 66, 012201 (2002)], the uniaxial velocity autocorrelation function (VACF) of this system exhibits a two time scale character. This corresponds to the symmetry of the particles. In this paper we provide a theory of the Enskog type that corroborates the idea that the VACF can be successfully described as a sum of two single decays. From the comparison between molecular dynamics and theoretical results, we show that the Enskog approach is a satisfactory kinetic theory, which functions as well in the nematic as in the isotropic phase. Different properties of VACFs have been investigated, in particular, the dependence on the orientational order, temperature, and particles’ inertness.
Theory of particle segregation in rimming flows of suspensions containing neutrally buoyant particles
Authors: Jin Bo , Acrivos Andreas
Published: February 2004

It has recently been reported that an initially uniform suspension of neutrally buoyant particles within a partially filled horizontal rotating cylinder can, under certain conditions, segregate into bands of particles separated by regions of low particle concentration or even particle-free liquid [M. Tirumkudulu, A. Mileo, and A. Acrivos, Phys. Fluids 12, 1615 (2000)]. An explanation for this phenomenon is proposed on the basis of a model of rimming flows with an axially varying viscosity plus the experimental observation that, when the liquid contains a recirculating region (puddle), the particles segregate radially by migrating out of the puddle into the unidirectional circumferential flow. A linear stability analysis for dilute suspensions shows that such a particle distribution is unstable to axial perturbations with the surface tension being responsible for the selection of the wavelength of the most rapidly amplified disturbance. The calculated and measured spacings between the bands are in good agreement. In addition, since, in the absence of a puddle, the particle concentration appears to remain uniform throughout the cross section of the film, no axial particle segregation is predicted to occur nor has it ever been seen experimentally, even when an axial viscosity variation is imposed on the flow by cooling a preselected portion of the cylinder.
Singularity method for oblate and prolate spheroids in Stokes and linearized oscillatory flow
Authors: Shatz Lisa F.
Published: February 2004

This paper applies the singularity method to obtain analytic solutions for oblate spheroids in Stokes flow, and to obtain numerical results for prolate and oblate spheroids undergoing oscillatory translation, and oscillatory rotation. To apply the method to oblate spheroids, singularities are placed along an imaginary focal length. A novel method is used to determine the hydrodynamic torque by deriving Green’s functions for torque for the unsteady rotlet, stresslet, and potential quadrupole. The results agree with analytic solutions for high and low frequencies, the results of previous studies, and results calculated using the boundary element method.
Motion of a vortex sheet on a sphere with pole vortices
Authors: Sakajo Takashi
Published: February 2004

We consider the motion of a vortex sheet on the surface of a unit sphere in the presence of point vortices fixed on north and south poles. Analytic and numerical research revealed that a vortex sheet in two-dimensional space has the following three properties. First, the vortex sheet is linearly unstable due to Kelvin–Helmholtz instability. Second, the curvature of the vortex sheet diverges in finite time. Last, the vortex sheet evolves into a rolling-up doubly branched spiral, when the equation of motion is regularized by the vortex method. The purpose of this paper is to investigate how the curvature of the sphere and the presence of the pole vortices affect these three properties mathematically and numerically. We show that some low spectra of disturbance become linearly stable due to the pole vortices and thus the singularity formation tends to be delayed. On the other hand, however, the vortex sheet, which is regularized by the vortex method, acquires complex structure of many rolling-up spirals.
Sensitivity of the scale partition for variational multiscale large-eddy simulation of channel flow
Authors: Holmen Jens , Hughes Thomas J. R. , Oberai Assad A. , Wells Garth N.
Published: February 2004

The variational multiscale method has been shown to perform well for large-eddy simulation (LES) of turbulent flows. The method relies upon a partition of the resolved velocity field into large- and small-scale components. The subgrid model then acts only on the small scales of motion, unlike conventional LES models which act on all scales of motion. For homogeneous isotropic turbulence and turbulent channel flows, the multiscale model can outperform conventional LES formulations. An issue in the multiscale method for LES is choice of scale partition and sensitivity of the computed results to it. This is the topic of this investigation. The multiscale formulation for channel flows is briefly reviewed. Then, through the definition of an error measure relative to direct numerical simulation (DNS) results, the sensitivity of the method to the partition between large- and small-scale motions is examined. The error in channel flow simulations, relative to DNS results, is computed for various partitions between large- and small-scale spaces, and conclusions drawn from the results.
Experimental study of a supersonic jet-mixing layer interaction
Authors: Collin E. , Barre S. , Bonnet J. P.
Published: February 2004

An experimental study is performed to analyze the interaction between a control jet (CJ) and a moderately supersonic main jet. Flow visualizations and laser Doppler velocimetry methods are used. A strong instability of the CJ has been identified. The dynamic of this instability corresponds to that of the local mixing layer. Two stability scenarios are proposed, one corresponding to the local Kelvin–Helmholtz instability of the main jet, the other linked to a local absolute instability of the interaction. The impact on the turbulent quantities is analyzed. It is shown that a strong modification of the Reynolds stress is manifest but that this extends only a small distance from the interaction.
On the universality of large-scale turbulence
Authors: Branover H. , Eidelman A. , Golbraikh E. , Gordienko S. , Moiseev S.
Published: February 2004

Large-scale three-dimensional turbulence is a challenge to researchers, being one of the most complicated aspects of turbulence studies. The universal large scales behavior connected with the inverse energy cascade in two-dimensional turbulence has been known for about 35 years and studied experimentally and numerically. We have revealed the universality of three-dimensional large-scale turbulence properties experimentally and described it theoretically. A rigorous solution of this problem in the presence of an energy source gives scaling exponents −4/3 for velocity correlations and 1/3 for energy spectra of the large-scale turbulence. Such spectra are also observed in atmospheric air flows under different conditions—stable, convective, in cirrus clouds. The revealed physical phenomenon is important for the development of turbulence theory complementing the results obtained for its smaller scales.
Modeling of Si self-diffusion in SiO2: Effect of the Si/SiO2 interface including time-dependent diffusivity
Authors: Uematsu Masashi , Kageshima Hiroyuki , Takahashi Yasuo , Fukatsu Shigeto , Itoh Kohei M. , Shiraishi Kenji , Gösele Ulrich
Published: February 2004

Self-diffusion of Si in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si/SiO2 interface and diffusing into SiO2 to enhance the self-diffusion. Based on the model, a recent self-diffusion experiment of ion-implanted Si30 in SiO2, which showed increasing self-diffusivity with decreasing distance between the Si30 diffusers and Si/SiO2 interface [Fukatsu et al., Appl. Phys. Lett. 83, 3897 (2003)], was simulated, and the simulated results fit the experimental profiles. Furthermore, the simulation predicts that the self-diffusivity would increase for a longer annealing time because more SiO molecules should be arriving from the interface. Such time-dependent diffusivity was indeed found in our follow-up experiments, and the profiles were also fitted by the simulation using a single set of parameters.
Parametric study on optical properties of digital-alloy In(Ga1−zAlz)As/InP grown by molecular-beam epitaxy
Authors: Song J. D. , Heo D. C. , Han I. K. , Kim J. M. , Lee Y. T. , Park S.-H.
Published: February 2004

Optical properties of digital-alloy InGaAlAs grown by molecular-beam epitaxy were parametrically investigated by 10-K-photoluminescence (PL) study on (In0.53Ga0.47As)n/(In0.52Al0.48As)n short-period superlattices (SPSs) in the range of n=1–5 monolayers. Two different peaks are resolved in PL spectra, and the higher energy peak (H) results from an excitonic transition while the lower energy peak (L) is related to a phonon-assisted transition. The H peak energies decrease monotonously as n increases, and it is in good agreement with the band-gap calculation with transfer matrix methods. It is found that two monolayer-period length (n=2) is the optimum one, where the PL intensity is largest and the ratio of L peak to H peak intensity is lowest. The various compositions (z) of digital-alloy In(Ga1−zAlz)As are prepared and their optical properties are investigated for z=0.2, 0.4, 0.6, and 0.8. The linewidths of 9-K-PL spectra for various z values are within the range of 10–15 meV, which are comparable to the best analog-alloy InGaAlAs.
Scaling law for the compositional dependence of Raman frequencies in SnGe and GeSi alloys
Authors: Li S. F. , Bauer M. R. , Menéndez J. , Kouvetakis J.
Published: February 2004

The compositional dependence of the Ge–Ge Raman mode in SnGe alloys has been measured in samples grown on Si substrates using a chemical vapor deposition technique. The experimental result, Δω(s)=(−68±5)s (where s is the Sn concentration), is in very good agreement with a theoretical prediction from a simple model with parameters adjusted to the compositional dependence of Raman frequencies in GeSi alloys.
Reversing granular flow on a vibratory conveyor
Authors: Grochowski R. , Walzel P. , Rouijaa M. , Kruelle C. A. , Rehberg I.
Published: February 2004

Experimental results are presented for the transport properties of granular materials on a vibratory conveyor. For circular oscillations of the shaking trough nonmonotonous dependence of the transport velocity on the normalized acceleration Γ is observed. Two maxima are separated by a regime where the granular flow is much slower and, in a certain driving range, even reverses its direction. Similar behavior is found for a single solid body with a low coefficient of restitution, whereas an individual glass bead of 1 mm diameter is propagated in the same direction for all accelerations.
Third-order optical nonlinearity originating from room-temperature exciton in layered compounds LaCuOS and LaCuOSe
Authors: Kamioka Hayato , Hiramatsu Hidenori , Ohta Hiromichi , Hirano Masahiro , Ueda Kazushige , Kamiya Toshio , Hosono Hideo
Published: February 2004

We have studied the third-order optical nonlinearity (χ(3)) of epitaxial thin films of layered compounds LaCuOS and LaCuOSe at room temperature by a spectrally resolved degenerative four-wave mixing technique with femtosecond time resolution. The χ(3) values in both films are sharply resonant to optical absorption bands in the ultraviolet (UV) light region due to room-temperature exciton. The peak values are evaluated to be as large as 2–4×10−9 esu with a fast time response of 250–300 fs. These findings indicate that LaCuOS and LaCuOSe are promising materials for emerging optical nonlinear devices that operate in the UV light region compatible for GaN-based lasers.
Fabrication of ordered array of nanowires of La0.67Ca0.33MnO3 (x=0.33) in alumina templates with enhanced ferromagnetic transition temperature
Authors: Shankar K. Shantha , Kar Sohini , Raychaudhuri A. K. , Subbanna G. N.
Published: February 2004

We report fabrication of array of crystalline nanowires (average diameter of 65 nm) of colossal magnetoresistive oxide La0.67Ca0.33MnO3 (LCMO, x=0.33) within anodized alumina templates by filling the pores with a sol that allows formation of LCMO phase at the relatively low temperature of 600 °C. The crystalline nanowires with correct stoichiometry stabilize in the orthorhombic phase at room temperature. The nanowires are ferromagnetic at room temperature and exhibit enhanced ferromagnetic transition temperature well in excess of 300 K, which is substantially higher than that of single crystalline LCMO. This enhancement we attribute to the size induced lattice contraction in the nanowires.
ULTRAFAST LASER-INDUCED STRESS WAVES IN SOLIDS
Authors: Jones E. D.
Published: February 2004

Shock wave and impulse measurements produced by a single 2–3 psec laser pulse are presented for aluminum. A simple model describing this phenomenon is discussed.
RELATIVE RAMAN CROSS SECTION FOR N2, O2, CO, CO2, SO2, AND H2S
Authors: Fouche D. G. , Chang R. K.
Published: February 2004

The relative Raman cross sections of gases which are of interest in atmospheric pollutant studies have been measured at 5145 Å. These relative cross sections compared to that of N2 are as follows: O2 (1.2), CO (0.91), CO2 (1.5), SO2 (5.5), and H2S (6.6). The Raman cross section of N2 compared to that of benzene has also been measured. Using the absolute cross section of benzene determined by Skinner and Nilsen, the measured Raman cross section of N2 is σN2 = (2.6 ± 1) × 10−31 cm2/sr at 5145 Å.
RAMAN SCATTERING FROM LONGITUDINAL ACOUSTICAL VIBRATIONS OF SINGLE CRYSTALS OF POLYETHYLENE
Authors: Peticolas W. L. , Hibler G. W. , Lippert J. L. , Peterlin A. , Olf H.
Published: February 2004

Raman scattering from the longitudinal-acoustical vibration of single crystals of polyethylene has been observed using an argon laser and an iodine filter. The frequencies observed are in the range 10–40 cm−1 and are inversely proportional to the thickness of the single crystals which varied between 90 and 250 Å.
EXTENDED WAVELENGTH TUNING OF Pb1−xSnx Te LASERS
Authors: Norton P. , Chia P. , Braggins T. , Levinstein H.
Published: February 2004

The strong temperature dependence of the bandgap of Pb1−xSnx Te has made it possible to wavelength-tune a diode laser made from this material by changing the operating temperature. This method permits the tuning of these devices over regions larger than 5000 GHz in the vicinity of 10 μ, making them promising tools for the detection of trace amounts of air pollution gases such as SO2 and N2O.
PYROELECTRICITY AND OPTICAL SECOND HARMONIC GENERATION IN POLYVINYLIDENE FLUORIDE FILMS
Authors: Bergman J. G. , McFee J. H. , Crane G. R.
Published: February 2004

Oriented films of polyvinylidene fluoride [(CH2CF2)n], a polar polymer possessing symmetry mm2, can be made significantly pyroelectric and optically nonlinear by poling in an electric field. A pyroelectric coefficient (dP/dT = 2.4 ± 0.7 nC/cm2°C) comparable to that of single-crystal LiNbO3 is observed. The nonlinear optical coefficients d33, d32, and d31 of polyvinylidene fluoride (PVF2) are measured relative to d11 of crystalline quartz [d33 (PVF2)≃2d31 (PVF2) ≃d11(SiO2); d32(PVF2)≃0]. The poled films have specific advantages for pyroelectric detection of electromagnetic radiation and for optical parametric devices.
CHOLESTERIC LIQUID CRYSTALS FOR OPTICAL APPLICATIONS
Authors: Kahn Frederic J.
Published: February 2004

The optical and thermal properties of mixtures of MBBA and COC are reported on as an example of cholesteric liquid crystals incorporating molecules which are not cholesterol derivatives. These materials exhibit relatively broad optical bandwidths, efficient polarizing characteristics, extremely weak temperature dependences, and high structural order properties which should be useful in optical devices.
METAL-DEPENDENT INTERFACE STATES IN THIN MOS STRUCTURES
Authors: Kar Samares , Dahlke Walter E.
Published: February 2004

Admittance measurements of MOS structures with oxide layers 20 to 40 Å thick have been made to determine interface-state distributions for various metal contacts. These distributions for Au, Cr, Cu, and Mg, exhibiting comparatively sharp characteristic peaks, increase rapidly with decreasing oxide thickness and sample annealing, thus indicating a strong influence of metal diffusion through the oxide on interface-state formation.
Measurements of Second-Harmonic Generation and the Variations in the Free and Clamped Values of the Dielectric Constants and Electro-Optic Coefficients in Barium Sodium Niobate
Authors: Nash F. R. , Turner E. H. , Bridenbaugh P. M. , Dziedzic J. M.
Published: February 2004

This work is primarily concerned with the measurements of some of the properties of crystals of barium sodium niobate (BSN) which are significantly related to the degree of alignment of the ferroelectric domains. We point out that many of the previous measurements of the low-frequency half-wave voltage (HWV) might have been in error because of imperfect alignment (poling). The variations observed in these HWV measurements can be related, in principle, to a connection between the low-frequency resistivity in different regions of the crystal and the degree of poling in those regions. For instances in which we observed variations in the free HWV we could demonstrate that such effects were not related to stoichiometric (compositional) variations within crystals, or from one crystal to another. In fact stoichiometric variations appeared to play no role in determining the outcome of our measurements of the low- and high-frequency electro-optic (EO) coefficients and dielectric constants. We present values for the low-frequency HWV and high-frequency principal axis EO coefficients in a perfectly poled sample and give a detailed discussion of the second-harmonic generation (SHG) tests which were used to establish the single-domain quality. Our measurements of the free dielectric constant ε3T showed only a slight relationship to the degree of poling. The high-frequency value was critically related to poling; this can be explained by the size and nature of the domains present in unpoled samples. The significant fact is that imperfect poling is connected with resistive and dielectric variations. With the application of an electric field, such variations cause unknown field distributions to exist in the poled and unpoled regions of a crystal. Thus, even when optical propagation occurs in a completely poled region, EO measurements can be quite inaccurate. From our SHG measurements we have deduced a parameter which is very useful in evaluating crystal quality for parametric oscillation (PO) and we have obtained corroboration of the value of this parameter from our parametric fluorescence (PF) measurements. In the Appendix we examine the SHG power, the HWV, and their relationship in a multidomain crystal.
Transient Conductivity of Silicon
Authors: Baicker J. A. , Fang P. H.
Published: February 2004

Theoretical studies are made on the transient conductivity behavior of silicon containing (a) one set of monovalent traps, (b) two sets of monovalent traps, and (c) one set of divalent traps. By comparing with experimental results from both p- and n-type silicon, it is found that the observed transient structure is caused by many sets of traps rather than by a small number of multivalent traps. These sets may be either monovalent or multivalent. The method of analysis provided some internal consistency checks: The trap concentrations and energy levels did not change with sample temperature, with the exception of a low-temperature effect attributed to the onset of recombination at the traps. In p-type material, which was subjected to a high-temperature bake, changes are produced which closely resembled the damage due to electron bombardment: The lifetime was reduced and a set of traps was produced at an energy level which was the same as a set of traps seen after electron irradiation.
Analysis of Bulk Negative Differential Mobility Element in a Circuit Containing Reactive Elements
Authors: Solomon P. R. , Shaw M. P. , Grubin H. L.
Published: February 2004

The time and space evolution of the electric field in an inhomogeneous bulk negative differential mobility (NDM) element with a high n0l product, and the response of the surrounding lumped-element circuit, is theoretically investigated. We consider a circuit in which an NDM element of low-field resistance R0 and intrinsic capacitance C0 is in parallel with a parasitic capacitor Cp and in series with a load resistor, inductor L, and a battery. Exact numerical and approximate analytic solutions are obtained and discussed in terms of a damping parameter A [=(LC)1/2/R0C, where C=C0+Cp] and the ratio C0/C. Various oscillatory modes can all occur in the same NDM element for appropriate values of the circuit parameters. The dominant mode of circuit-controlled oscillation in a series L-parallel C circuit is the quenched multiple-dipole relaxation mode. LSA relaxation oscillations occur only for a narrow range of circuit parameters and LSA sinusoidal oscillations are excluded because of domain domination, even for NDM elements with small doping fluctuations. This produces an upper frequency limit for circuit control which must be considered in addition to that imposed by finite intervalley relaxation times.
Approximate Photocount Statistics
Authors: Mandel L.
Published: February 2004

Attention is drawn to the fact that the approximation formula of Bédard, Chang, and Mandel for photoelectric counting yields different probabilities for different spectral distributions, and not just one function as implied in a recent paper of Lachs.
Correlation of electronic surface properties and surface structure on cleaved silicon surfaces
Authors: Bäuerle F. , Mönch W. , Henzler M.
Published: February 2004

The clean, cleaved Si (111) surface exhibits a 2×1 LEED structure which converts to the Si (111)-7 structure upon anneal at elevated temperatures. The conversion temperature was determined to be 370°C. Measurements taken at room temperature indicate that, after passing through a maximum, the surface conductivity decreases with increasing annealing temperature up to the conversion temperature. For higher annealing temperatures the surface conductivity increases again as the Si (111)-7 structure develops. The correlation of LEED pattern with the change of surface conductivity demonstrates that the surface states at the clean Si (111) surface are strongly dependent on surface atomic arrangement with respect to superstructure and domain boundaries.
The 5×20 surface structure of gold
Authors: Gro/nlund F. , Nielsen P. E. Ho/jlund
Published: February 2004

A precision RHEED investigation of the so-called Au (100) (5×20) surface structure has shown that its basic unit is in reality a primitive hexagonal cell, or a similar cell rotated 90° with respect to the first. The cell is repeated by translation in two dimensions, and coincidence occurs in one basic. Au repeat direction only. The designation 5×20, which implies coincidence in two directions, is therefore inappropriate and misleading.
A new representation of the strain field associated with the cube-edge dislocation in a model of a α-iron
Authors: Gehlen P. C. , Hirth J. P. , Hoagland R. G. , Kanninen M. F.
Published: February 2004

The displacement field around an edge dislocation core is examined in an attempt to quantitatively modify the linear elastic Volterra solution. The approach derives from a computer simulation to obtain the equilibrium atomic positions in a dislocated bcc crystallite using Johnson's potential to model α-iron. Unlike many previous calculations of this nature which employ rigid boundary conditions throughout the relaxation, the elastic media bounding the crystallite is here allowed to adjust in response to atomic readjustments within the crystallite. The procedure used to achieve flexible boundaries and its application to this problem is discussed in detail. This scheme permits linear elastic displacements at distances relatively far from the dislocation center. The difference between the computed strain field and the Volterra prescription results from nonlinear effects in the core, and is found to correspond to a net expansion of 0.25b2 per unit dislocation length. This is in accord with findings of experimental studies relating lattice parameters to dislocation densities. The details of this residual field are fairly well described in terms of an elliptical line source expansion center located approximately two Burgers vectors below the tip of the extra half-plane. Thus, these results, while obtained for model material, suggest that an edge dislocation may be characterized by the sum of two linear elastic fields; the Volterra field and an elliptical expansion field. It is found that this result is not explainable by third-order perturbation theories. Finally, we note that the addition of an elliptical dilatation field should have a number of important applications to dislocation theory and specific examples are outlined.
Comparison of theoretical and experimental values of the capacitance of diffused junctions
Authors: Van Overstraeten R. , Nuyts W.
Published: February 2004

Using computer calculations, the exact values of the C−3-vs-U intercept with the U axis are calculated for diffused junctions. These theoretical intercepts are 0.125 V lower than the classical values obtained from Shockley's theory. This difference is due to three factors: the variation of the diffusion voltage, the nonzero electric field at the boundaries of the depletion region, and the contribution of electrons and holes. The exact values also disagree with the experimental results. It is shown that this discrepancy depends on the diffusion parameters and that it may be caused by two effects: irregularities in the diffusion profile around the metallurgical junction and incomplete ionization of impurities.
Light scattering from isotropic polymeric solids
Authors: Stevens J. R. , Bowell I. C. , Hunt J. L.
Published: February 2004

A theory is presented for the scattering of light in an isotropic solid from thermally excited sound waves (Brillouin) and stationary random strains. This theory predicts the intensity, polarization, and spectral distribution of the scattered light as a function of the incident and scattered directions in the solid. From the prediction of the intensity for light polarized perpendicular to the scattering plane the ratio of the central component of the scattered intensity to the longitudinal Brillouin doublet intensity is obtained. Experimental results for PEMA are quoted which support the prediction of the theory for this ratio. The theory permits the separation of the scattered intensity, due to dust particles and similar inclusions, from the central component.
Small-angle x-ray scattering from amorphous polyethylene terephthalate
Authors: Harget Paul J. , Siegmann Arnon
Published: February 2004

Small-angle x-ray scattering from amorphous polyethylene terephthelate (PET) has been detected. It is very weak, more than an order of magnitude less intense than is usually obtained from partially crystallized specimens. It is also of a continuous nature with the absence of any distinct interference peak. Based on the assumption of spherical particles, the diameters are in the range of 30–40 Å. This is somewhat smaller in size than is seen in electron microscopy, but reasonable since it is more a measure of the actual electron density fluctuation and not physical size. The scattering is sensitive to thermal treatment below the glass transition temperature and also depends on the source of the amorphous PET, e.g., films or fibers. When these data are combined with other analyses, parameters such as size, number density, and electron density of the particles can be segregated. The effects of the state of the amorphous material on subsequent crystallization is also presented and discussed.
Solid-state polymerization of diacetylenes
Authors: Baughman R. H.
Published: February 2004

Differences in the solid-state reactivity of two substituted diacetylenes with identical lattice symmetry (P21/c) are described in terms of the molecular rotational and translational motion necessary for 1,4-addition polymerization. The structural relationship between monomer and polymer has been investigated in detail for the solid-state polymerization of 2,4-hexadiynediol. For the thermal, uv, or γ-ray-induced polymerization of this monomer the same crystallographic relationship was found between the polymer chain direction and the monomer lattice. Mutually reacting monomer molecules are related by a unit-cell translation along the a/c diagonal, which is perpendicular to the unique axis of this monoclinic crystal. X-ray diffraction determination of unit-cell parameters for γ-ray-irradiated samples of differing conversion have confirmed that the polymer enters the monomer lattice as a solid solution and verify the mentioned polymerization mechanism. When these irradiated samples were thermally annealed, phase separation occurred, producing discrete monomer and amorphous polymer phases. Despite the instability of the partially polymerized 2,4-hexadiynediol lattice, ir measurements reveal no free hydroxyl hydrogens either before or after phase separation. Neighboring monomer molecules are indirectly hydrogen bonded together in the c-axis direction, but no hydrogen bonding exists between mutually reacting monomer molecules in disagreement with a previously suggested model for lattice-controlled diacetylene polymerizations. During the polymerization of 2,4-hexadiynediol the center-to-center separation of mutually reacting molecules must change by − 0.44 Å and the conjugated molecular rods must rotate by an angle of at least 28°. This large required molecular rotation suggests that the activation energy for rotation contributes significantly to the activation energy for polymerization. The high entropy of fusion (17.0±1.2 eu) measured for this compound is consistent with low solid-state rotational mobility. No solid-state phase transitions were observed calorimetrically for 2,4-hexadiynediol from − 100°C to the melting point (114.5±0.3°C). The low solid-state reactivity observed for diphenyldiacetylene is reasonable in light of the much larger translation and rotation necessary for 1,4-addition polymerization, respectively, − 1.14 Å and 37.5°. No ethanol insoluble polymer was obtained for γ-ray radiation dosages which resulted in high monomer-to-polymer conversions for 2,4-hexadiynediol. No measurable difference was observed in the melting behavior of γ-ray-irradiated and nonirradiated samples of this high entropy of fusion compound (14.1±0.7 eu).
Interfacial parametric electrohydrodynamics of insulating dielectric liquids
Authors: Jones Thomas B.
Published: February 2004

When a high-intensity electric field with a strong gradient, periodic in time, is imposed tangentially at the interface of an insulating dielectric fluid, parametric surface instability may result. Under typical conditions this instability grows to a certain amplitude, where nonlinear effects become dominant, resulting in a steady-state standing-wave pattern. In the linear small-amplitude limit, the surface dynamics are described by the Mathieu equation. The wavelength observed in the nonlinear amplitude-limited state is successfully correlated with the linear theory by determining the ``most unstable wavelength'', that is, the wavelength with the maximum growth rate for given conditions of applied electric field strength and frequency.
Axial yield strengths and phase-transition stresses for 〈100〉, 〈110〉, and 〈111〉 germanium
Authors: Gust W. H. , Royce E. B.
Published: February 2004

The dynamic compressive yield strengths and compression characteristics under uniaxial shock-wave loading have been determined for three axes of crystalline germanium. At less than about 250 kbar, shocks propagated along the three axes exhibited three wave structures that were taken to be related to the Hugoniot elastic limits (HEL's) and to polymorphic phase transitions. Values obtained for HEL's and the stresses required to initiate the phase transition along each axis were 58, 48, 47, and 117, 119, 125 kbar, respectively, for the 〈100〉, 〈110〉, and 〈111〉 axes.