bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity
Authors: Pritchett P. L. , Strangeway R. J. , Ergun R. E. , Carlson C. W.
Published: December 2002

The properties of the electron‐cyclotron maser radiation produced in the auroral kilometric radiation (AKR) source cavity are investigated by means of two‐dimensional particle‐in‐cell simulations and observations made by the Fast Auroral SnapshoT (FAST) Explorer. The simulations assume a population of primary auroral electrons with a downgoing shell distribution. Driven simulations in a meridional plane with a finite magnetic field gradient demonstrate that the maser radiation builds up very rapidly with decreasing altitude and that bursts of radiation with timescales of the order of 0.5 ms are produced at only 5–6 km below the injection level. Initial value simulations in a longitudinal plane show that the radiation component striking the cavity boundary at normal incidence is damped away via particle absorption and conversion to the Z mode. In contrast, the longitudinally propagating component is able to be amplified along an extended path length. The FAST observations of the electric field in the source region reveal that the polarization in the plane perpendicular to the ambient magnetic field varies between being approximately isotropic to having a substantial (as much as a factor of 100) enhancement of the “along‐track” polarization. No evidence is found that the “across‐track” polarization is ever dominant, and thus the AKR emissions do not form a standing wave structure between the cavity boundaries.
A laboratory study of the heterogeneous uptake and oxidation of sulfur dioxide on mineral dust particles
Authors: Usher C. R. , Al‐Hosney H. , Carlos‐Cuellar S. , Grassian V. H.
Published: December 2002

The heterogeneous uptake and oxidation of SO2 on particle surfaces representative of mineral dusts found in the atmosphere have been investigated. These particles include metal oxides (e.g., hematite, corundum), calcite, and China loess. FT‐IR spectroscopy was used to characterize surface‐bound species following exposure to gaseous SO2. It was found that SO2 irreversibly adsorbs as sulfite (SO32−) and/or bisulfite (HSO3−) on all particle surfaces with the exception of SiO2. The adsorbed species can be oxidized to sulfate and/or bisulfate (SO42− and/or HSO4−) upon exposure to ozone. Knudsen cell reactor studies were done to measure heterogeneous uptake coefficients for SO2. Initial uptake coefficients, calculated using BET surface areas, γBET, are found to be lower than that found for water droplets. As shown here, the γBET value for China loess can be predicted from the reactivity of the single component oxide and carbonate particles along with the average composition of the dust sample, with each component weighted by its natural abundance in the sample.
Ground‐based lidar and radar remote sensing of tropical cirrus clouds at Nauru Island: Cloud statistics and radiative impacts
Authors: Comstock Jennifer M. , Ackerman Thomas P. , Mace Gerald G.
Published: December 2002

Ground‐based active and passive remote sensing instrumentation are combined to derive radiative and macrophysical properties of tropical cirrus clouds. Eight months of cirrus observations at the Department of Energy Atmospheric Radiation Measurement site located on Nauru Island provide independent retrieval of cloud height and visible optical depth using lidar and radar techniques. Comparisons reveal the millimeter cloud radar does not detect 13% of cirrus clouds with a cloud base higher than 15 km that are detected by the lidar. Lidar and radar cloud heights demonstrate good agreement when the cloud lies below 15 km. Radar and lidar retrievals of visible optical depth also compare well for all but the optically thinnest clouds. Cloud occurrence at Nauru as measured by lidar reveal clear‐sky conditions, low clouds, and high clouds occur on average 40%, 16%, and 44% of the time, respectively. Analysis of observed cirrus macrophysical and radiative properties suggests that two different types of cirrus exist in the tropical western Pacific: high, thin, laminar cirrus with cloud base higher than 15 km, and lower, physically thicker, more structured cirrus clouds. Differences in cirrus types are probably linked to their formation mechanisms. Radiosonde profiles of temperature and equivalent potential temperature near the tropical tropopause show a clear transition between neutrally stable and stable air at ∼15 km, which may also explain the presence of two distinct cirrus types. Radiative heating rate and cloud forcing calculations for specific cirrus cases reveal the impact of tropical cirrus clouds on the Earth's radiation budget.
Stability of tropospheric hydroxyl chemistry
Authors: Lelieveld J. , Peters W. , Dentener F. J. , Krol M. C.
Published: December 2002

Tropospheric hydroxyl (OH) is the cleaning agent of the atmosphere, because most oxidation processes are initiated by OH. If the OH chemical system were unstable, runaway growth of oxidants (autocatalytic conditions) or of reduced gases (catastrophic conditions) might occur, especially because the atmospheric composition is changing rapidly. We present simulations with a global chemistry‐transport model, indicating that during the past century, global mean OH has nevertheless remained nearly constant. This constancy is remarkable, because CH4 and CO, the main OH sinks, have increased strongly. We studied the system's sensitivity to perturbations using the OH recycling probability, calculated from primary OH formation and OH recycling. We conclude that the constancy of global mean OH does not imply that regional OH has not changed or that the system is insensitive to perturbations. Over the tropical oceans, where OH concentrations are highest, the system stability is relatively low. During the past century, the OH concentration decreased substantially in the marine troposphere, however, on a global scale, it has been compensated by an increase over the continents associated with strong pollution emissions of nitrogen oxides. Our results suggest that the changing atmospheric composition due to industrialization has been accompanied with a 60% increase in the tropospheric oxidation power (i.e., gross OH production).
Wave packet interferometry for short-time electronic energy transfer: Multidimensional optical spectroscopy in the time domain
Authors: Cina Jeffrey A. , Kilin Dmitri S. , Humble Travis S.
Published: December 2002

We develop a wave packet interferometry description of multidimensional ultrafast electronic spectroscopy for energy-transfer systems. After deriving a general perturbation-theory-based expression for the interference signal quadrilinear in the electric field amplitude of four phase-locked pulses, we analyze its form in terms of the underlying energy-transfer wave packet dynamics in a simplified oriented model complex. We show that a combination of optical-phase cycling and polarization techniques will enable the experimental isolation of complex-valued overlaps between a “target” vibrational wave packet of first order in the energy-transfer coupling J, characterizing the one-pass probability amplitude for electronic energy transfer, and a collection of variable “reference” wave packets prepared independently of the energy-transfer process. With the help of quasiclassical phase-space arguments and analytic expressions for local signal variations, the location and form of peaks in the two-dimensional interferogram are interpreted in terms of the wave packet surface-crossing dynamics accompanying and giving rise to electronic energy transfer.
Crossover from nonadiabatic to adiabatic electron transfer reactions: Multilevel blocking Monte Carlo simulations
Authors: Mühlbacher L. , Egger R.
Published: December 2002

The crossover from nonadiabatic to adiabatic electron transfer has been theoretically studied under a spin-boson model (dissipative two-state system) description. We present numerically exact data for the thermal transfer rate and the time-dependent occupation probabilities in largely unexplored regions of parameter space, using real-time path-integral Monte Carlo simulations. The dynamical sign problem is relieved by employing a variant of the recently proposed multilevel blocking algorithm. We identify the crossover regime between nonadiabatic and adiabatic electron transfer, both in the classical (high-temperature) and the quantum (low-temperature) limit. The electron transfer dynamics displays rich behaviors, including multi-exponential decay and the breakdown of a rate description due to vibrational coherence.
Statistics of transitions in single molecule kinetics
Authors: Gopich Irina V. , Szabo Attila
Published: December 2002

The probability distribution of observing N state-to-state transitions in a finite time t is calculated for an arbitrary kinetic scheme. In the Laplace domain, this probability distribution can be expressed analytically in terms of the (sI−K)−1 where K is the rate matrix. For long times simple expressions are found for the mean and variance of the number of transitions.
Oxygen atom interactions with fused silica surfaces: 1D and 3P state-resolved energy transfer dynamics
Authors: Buntin Steven A. , Litorja Maritoni
Published: December 2002

A laser-based O atom beam source together with state-resolved detection techniques are used to characterize the energy transfer dynamics of ground (3P) and electronically excited (1D) state O atoms interacting with a fused silica surface. Time-of-flight spectra of the incident beam and scattered O atoms are measured, and provide detailed information regarding state-resolved angular and velocity distributions. We find a significant degree of “thermalization” (angular, fine structure state, and velocity distributions) in the scattered O(3P) atoms. The survival probability of O(1D) is determined to be ⩽0.01, and the probability for O(1D) quenching to “super-elastic” O(3P) is 0.05. Given that the measured probability for radiative quenching of 1D is not significant (⩽0.001), these results indicate that the majority of the available energy in the incident O atoms (both 3P and 1D) is transferred to the substrate. The implications of the scattering/energy transfer dynamics with respect to the O atom/fused silica surface interactions are discussed.
Electronic structure and spectroscopic properties of electronic states of VC2, VC2−, and VC2+
Authors: Majumdar D. , Roszak S. , Balasubramanian K.
Published: December 2002

Theoretical studies on the electronic and thermodynamic properties of several electronic states are presented for the VC2 molecule, the VC2− anion, and the VC2+ cation employing state-of-the-art techniques that included up to 12 million configurations. The ground and the low-lying electronic states of these three species have been found to have C2v triangular structures. On the basis of our computed results, we have suggested an assignment of the observed anion photodetachment spectra of VC2− and predicted transitions that were not observed. Our computed electron affinity is in excellent agreement with experiment. The observed thermodynamic properties of reactions involving VC2, VC2−, and VC2+ are corrected using the computed gas phase properties of the molecule and the partition functions. The bent quartet states of VC2 exhibit large dipole moments (8.65−9.3 D).
A comparative study of elastic scattering of low-energy electrons by boron, aluminum and gallium trihalides
Authors: da Costa Romarly F. , Ferreira Luiz G. , Lima Marco A. P. , Bettega Márcio H. F.
Published: December 2002

In this paper we present integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by some metal-halogen molecular compounds, namely, BF3, BCl3, BBr3, BI3, AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, and GaI3. The pseudopotential based calculations were carried out with the Schwinger multichannel method at the static-exchange level of approximation. It is the purpose of this work to make a comparative study of the scattering processes involving aluminum and gallium trihalides with previous results for the boron ones [M. H. F. Bettega, Phys. Rev. A 61, 042703 (2000)]. We find through direct comparison of the elastic cross sections that, at low energies, the scattering processes are mainly dominated by the halogen atoms.
A theoretical prediction on intermolecular monoelectron dihydrogen bond H⋯e⋯H in the cluster anion (FH)2{e}(HF)2
Authors: Hao Xi-Yun , Li Zhi-Ru , Wu Di , Wang Yi , Li Ze-Sheng , Sun Chia-Chung
Published: December 2002

Using the aug-cc-pVDZ basis set supplemented with bond functions (BF), the existences of the systems (FH)2{e}(HF)2 have been studied. It was found to have equilibrium geometry with all frequencies real at the second-order Møller–Plesset perturbation (MP2/aug-cc-pvdz+BF) level. The calculated vertical electron detachment energy is 1.065 eV for (FH)2{e}(HF)2 at the coupled cluster level of theory with single, double, and noniterative triple excitations (CCSD(T)). The result calculated indicated that the stabilities of the system own to forming the monoelectron dihydrogen bond H⋯e⋯H, which comes not only from the static Coulomb interaction but also from the dispersion interaction between the loosely bound (excess) electron and the neutral molecular (cluster’s) hosts. The characteristics of the monoelectron dihydrogen bond H⋯e⋯H of the system have been revealed. The H⋯e⋯H bond length is 2.359 Å for (FH)2{e}(HF)2. Some vibrational modes that display the presence of the bond H⋯e⋯H have been found and a novel secondary interaction, H-bond-excess electron attracting has been discussed.
Stability of ice XII relative to ice V and ice VI at high pressures
Authors: Johari G. P.
Published: December 2002

The Gibbs energy difference between ice XII and ice V and between ice XII and ice VI at high pressures has been estimated in their fully orientationally disordered states from the available data. The Gibbs energy of ice XII is 183 J/mol higher than that of ice V at 0.5 GPa, and therefore ice XII is metastable with respect to ice V. The Gibbs energy of ice XII is 180–475 J/mol higher than that of ice VI at 1.1 GPa and 100 K. This is inconsistent with the recent deduction [T. Loerting, I. Kohl, C. Salzmann, E. Mayer, and A. Hallbrucker, J. Chem. Phys. 116, 3171 (2002)] that ice VI in the range 0.7–1.5 GPa and 158–212 K is metastable with respect to XII, and also with the speculation that proton (or orientationally)-ordered ice XII could have formed in Johari and Whalley’s [J. Chem. Phys. 70, 2094 (1979)] search for orientationally ordered ice VI. An examination of the available dielectric data and Raman spectral features show no indication of ice VI to ice XII transformation at high pressures. Therefore, ice VI, not ice XII, is the stable phase at ≈1 GPa and in the 158–212 K range. Ice polymorphs coexist in a thermoelastic equilibrium when the strain energy increase at the two-phase interface of the crystals growing in the parent phase becomes equal to the Gibbs energy decrease resulting from the growth. Hence a multiplicity of phases may coexist at high pressures.
Development of a simple, self-consistent polarizable model for liquid water
Authors: Yu Haibo , Hansson Tomas , van Gunsteren Wilfred F.
Published: December 2002

The charge-on-spring method is used to develop a rigid, three-site, polarizable water model, a noniterative and a self-consistent version. In this method, the polarizability is taken into account by a variable separation of charges on selected polarizable centers. One of the pair of polarization charges resides on a polarizable center, while the other one is treated as an additional particle attached to the polarizable center by a parabolic restraint potential. The separation is calculated in response to the instantaneous electric field. We parametrized two models which are based on noniterative and self-consistent versions of the method, respectively. We computed several liquid-phase and gas-phase properties and compared with data available from experiment and ab initio calculations. The condensed-phase properties of both models are in reasonable accord with experiment, apart from discrepancies in electrostatic properties consistent with a slightly too large liquid-state dipole.
Instabilities in a spatially correlated autocatalytic chemical system
Authors: Chakrabarti J.
Published: December 2002

We study the stability of a homogeneous state to inhomogeneous density modulations in a chemical system where the constituents undergo diffusion as well as chemical reaction. The system is autocatalytic: One species activates the recation, while the other is an inhibitor. We show that the stability of the homogeneous state is enhanced, if the activator species is spatially correlated due to interparticle repulsion.
Lifetime measurements and quantum-defect theory treatment of the k 3Πu− state of hydrogen molecule
Authors: Kiyoshima T. , Sato S. , Pazyuk E. A. , Stolyarov A. V. , Child M. S.
Published: December 2002

The experimental and theoretical lifetimes for rovibronic k 3Πu− states of H2 and D2 isotopomers have been investigated over a wide range of vibrational v′ and rotational N′ quantum numbers. Lifetimes have been measured by a delayed coincidence method, combined with direct electron-impact excitation of the ground state molecules and single photon counting techniques to detect induced fluorescence to the a 3Σg+ state. Pronounced pressure-dependence of the experimental lifetimes was observed and properly taken into account. The pure radiative lifetimes of the k 3Πu− states were estimated using theoretical transition dipole moments responsible for the visible k 3Πu→a 3Σg+ transition plus infrared emission on the higher-lying Λg3 states belonging to the 3s,d 3Λg complex. Both the predissociative and autoionization decay rates were predicted by the Fermi-Golden rule based on radial coupling matrix elements for the k 3Πu∼c 3Πu and k 3Πu∼X2Σg+(H2+) pairs of interacting states, respectively. The required electronic matrix elements as a function of internuclear distance R were derived in the framework of quantum-defect theory modified to allow explicit consideration of regular radial coupling effects. The relevant quantum-defect functions of all states treated were extracted from published highly accurate Born–Oppenheimer potential curves. Both the total theoretical radiative, predissociative plus autoionization rates and the calculated rovibronic term values agree well with their experimental counterparts. The N′-dependence of the experimental and theoretical lifetimes is found to be negligible for both isotopomers while a pronounced v′-dependence is observed for a H2 isotopomer. The vibrational predissociation is very weak comparing with radiative decay for both isotopomers whereas the autoionization rate is comparable with the radiative ones for the H2 v′⩾4 levels though it is still negligible for the D2 v′⩽6 levels.
Laser spectroscopy of free pentacene molecules (II): Stark effect of the vibrationless S1←S transition
Authors: Heinecke E. , Hartmann D. , Hese A.
Published: December 2002

Laser Stark spectroscopy has been performed for the first time on free pentacene molecules seeded in a highly collimated supersonic argon beam. The Stark effect of the vibrationless S1←S0 transition of pentacene at 18 649 cm−1 was investigated in a static homogeneous electric field up to 81 kV/cm. Within the unresolved rotational structure, an unexpected large quadratic Stark effect was observed. An analysis of the shifts of sub-band heads and characteristic structures was performed by simulating the complete Stark spectrum using second-order perturbation theory. Surprisingly large values for the differences of the molecular polarizability between the electronic ground state X 1A1g and the excited A 1B2u state were found: ΔP̄=1/3(ΔPaa+ΔPbb+ΔPcc)=9.1(3)×102 Å3, ΔPcc=Pcc′−Pcc″=13.7(8)×102 Å3, ΔPxx=−1.4(8)×102 Å3, ΔPyy=15.0(7)×102 Å3 (x=a, y=b, or vice versa). Attributing the in-plane axes uniquely and the determination of the ground state anisotropy was not possible. It is assumed that the large polarizability of the excited state is dominated by contributions of low-frequency vibrational levels. Indications for deviation from second-order perturbation theory are observed.
Unimolecular decay pathways of state-selected CO2+ in the internal energy range of 5.2–6.2 eV: An experimental and theoretical study
Authors: Liu Jianbo , Chen Wenwu , Hochlaf M. , Qian Ximei , Chang Chao , Ng C. Y.
Published: December 2002

The vacuum ultraviolet pulsed field ionization (PFI)-photoelectron (PFI-PE) spectrum of CO2 has been measured in the energy region of 19.0–20.0 eV. The PFI-PE vibrational bands resolved for CO2+(C 2Σg+) are overwhelmingly dominated by the origin band along with weak vibrational bands corresponding to excitations of the ν1+ (symmetric stretching), ν2+ (bending), and ν3+ (antisymmetric stretching) modes. The simulation of the rotational contour resolved in the origin PFI-PE band yields a value of 19.3911±0.0005 eV for the ionization energy of CO2 to form CO2+(C 2Σg+). A PFI-PE peak is found to coincide with each of the 0 K dissociation thresholds for the formation of O+(4S)+CO(X 1Σ+) and CO+(X 2Σ+)+O(3P). This observation is tentatively interpreted to result from the lifetime switching effect, arising from the prompt dissociation of excited CO2 in high-n (n⩾100) Rydberg states prior to PFI. We have also examined the decay pathways for state-selected CO2+ in the internal energy range of 5.2–6.2 eV using the PFI-PE-photoion coincidence scheme. The coincidence TOF data show unambiguously the formation of O+(4S)+CO(X 1Σ+;ν″=0,1) and CO+(X 2Σ+;ν+=0,1)+O(3P). Analysis of the kinetic energy releases of fragment ions suggests that the dissociation of excited CO2+ involved is nonstatistical and proceeds with an impulsive mechanism. Potential energy functions (PEFs) for the CO2+(C 2Σg+) state and the lowest quartet states of CO2+, together with their spin–orbit interactions, have been calculated using the complete active space self-consistent field and internal contracted multireference configuration interaction methods. Based on these PEFs, vibrational levels for CO2+(C 2Σg+) have been also calculated using a variational approach. With the aid of these theoretical calculations, vibrational bands resolved in the PFI-PE spectrum for CO2+(C 2Σg+) have been satisfactorily assigned, yielding a ν3+ value of 2997 cm−1. The theoretical calculation also provides a rationalization that the predissociation for CO2+(C 2Σg+) to form O+(4S)+CO(X 1Σ+) and CO+(X 2Σ+)+O(3P) most likely proceeds via the repulsive a 4Σg− and b 4Πu (or B14 in a bent geometry) states.
Phase transitions in systems small enough to be clusters
Authors: Reguera D. , Bowles R. K. , Djikaev Y. , Reiss H.
Published: December 2002

We analyze peculiarities of phase transitions in small systems. We focus on the formation of a tiny liquid drop in a small N, V, T system, and develop an “extended modified liquid drop” model, which incorporates the effect of the fluctuations relevant for small systems. We compare the predictions for the p−v isotherms and the density profiles with the results of Monte-Carlo simulations of a Lennard-Jones system, and Density Functional Theory.
Collective dynamics of liquid HCl: The density–density and longitudinal current correlations
Authors: Balucani U. , Pasqualini D. , Garberoglio G. , Vallauri R. , Sutmann G.
Published: December 2002

In this work the dynamics of density fluctuations in liquid HCl is investigated by computer simulation experiments, with the main goal of ascertaining the influence of hydrogen bonding in the features of the collective excitations of this molecular fluid. The data analysis shows that in HCl the hydrogen bonding has quite a small relevance on the dynamics, in strong contrast with the findings reported for both HF and water. Within the framework of generalized hydrodynamics we have been able to derive values for otherwise unknown quantities like the ratio of specific heats and the adiabatic sound velocity. An evaluation of the average effective interaction potential between the molecular centers of mass, clarifies the interpretation of the collective dynamical behavior explored in the present investigation.
Semiclassically optimized complex absorbing potentials of polynomial form. I. Pure imaginary case
Authors: Poirier Bill , Carrington Tucker
Published: December 2002

We present an optimal, pure imaginary complex absorbing potential (CAP) of polynomial form, for calculating resonance energies and widths, photodissociation cross sections, rate constants, etc. The optimal CAP is derived by minimizing reflection from, and transmission through, the CAP. Reflection and transmission are computed semiclassically. The optimal CAP is general, and can be used at any energy and with any absorbing region width. It significantly reduces the absorbing region width required to compute resonances of the one-dimensional Hazi–Taylor system. We also clearly discuss different types of reflection, and resolve apparent discrepancies relating to optimal CAPs.
Collisional deexcitation of the excited rare gas atoms in resonant states: The Watanabe–Katsuura theory revisited
Authors: Fukuzawa Hironobu , Murata Makoto , Kiyoto Naoharu , Mukai Tomonori , Fukuchi Yuji , Bahadur Khadka Deba , Ukai Masatoshi , Odagiri Takeshi , Kameta Kosei , Kouchi Noriyuki , Hatano Yoshihiko
Published: December 2002

The cross sections for the collisional deexcitation of neon atoms in the lowest excited P11 state by Ar, Kr, Xe, N2, O2, CO, NO, and CH4, and in the lowest excited P13 state by O2 and CH4 have been measured at a mean collisional energy corresponding to room temperature. Data are also included for collisions of argon atoms in the lowest excited P11 and P13 states by C2H4, cyclo-C3H6, and C3H8, and collisions of krypton atoms in the lowest excited P11 and P13 states by C2H4 and cyclo-C3H6. The measured cross sections, together with those obtained in our previous studies, are compared with the cross sections calculated using the Watanabe–Katsuura theory. An extension of the Watanabe–Katsuura theory to the deexcitation of excited rare gas atoms in collisions with molecular quenchers, not atoms, is examined.
The deposition angle-dependent density of amorphous solid water films
Authors: Dohnálek Z. , Kimmel Greg A. , Ayotte Patrick , Smith R. Scott , Kay Bruce D.
Published: December 2002

The index of refraction and thickness of amorphous solid water (ASW) films are determined using laser optical interferometry. From the film thickness, the density of ASW can be calculated directly since the molecular beam flux and the H2O condensation coefficient are both known. From the index of refraction the ASW density can also be determined using the Lorentz–Lorenz relationship. The densities determined via both methods agree within experimental uncertainty. For films deposited at 22 K using a collimated molecular beam, the index of refraction and density decrease monotonically as the deposition angle is varied from normal to oblique incidence. At normal incidence the films have an index of refraction of 1.285 and are presumed to be fully dense (0.94 g/cm3). At glancing incidence (86°) the film has a refractive index of 1.05 and a density of 0.16 g/cm3, indicating a porosity exceeding 80%. The angle-dependent film density is in semiquantitative agreement with the results of ballistic deposition simulations of ASW film growth.
Two regimes of thermal resistance at a liquid–solid interface
Authors: Xue L. , Keblinski P. , Phillpot S. R. , Choi S. U.-S. , Eastman J. A.
Published: December 2002

Using nonequilibrium molecular dynamics simulations in which a temperature gradient is imposed, we determine the thermal resistance of a model liquid–solid interface. Our simulations reveal that the strength of the bonding between liquid and solid atoms plays a key role in determining interfacial thermal resistance. Moreover, we find that the functional dependence of the thermal resistance on the strength of the liquid–solid interactions exhibits two distinct regimes: (i) exponential dependence for weak bonding (nonwetting liquid) and (ii) power law dependence for strong bonding (wetting liquid). The identification of the two regimes of the Kapitza resistance has profound implications for understanding and designing the thermal properties of nanocomposite materials.
Hyperfine coupling tensors for multi-configurational quasi-degenerate perturbation theory
Authors: Pak Michael V. , Gordon Mark S.
Published: December 2002

Analytic calculation of the hyperfine coupling tensors for multi-configurational quasi-degenerate perturbation theory is developed based on the Lagrange multiplier formalism. Calculation of Lagrange multipliers is not required if the corresponding constraining conditions do not depend explicitly on the magnetic moments of the nuclei. Except for the explicit form of the one-electron perturbation operator, the derivation presented in this work is also applicable to other molecular properties for which the basis functions do not depend on the differentiation variable, and for which the dependence of the Hamiltonian is through a one-electron operator only.
Studies on energy transfer in dendrimer supermolecule using classical random walk model and Eyring model
Authors: Rana Dipankar , Gangopadhyay Gautam
Published: December 2002

We have analyzed the energy transfer process in a dendrimer supermolecule using a classical random walk model and an Eyring model of membrane permeation. Here the energy transfer is considered as a multiple barrier crossing process by thermal hopping on the backbone of a cayley tree. It is shown that the mean residence time and mean first passage time, which involve explicit local escape rates, depend upon the temperature, size of the molecule, core branching, and the nature of the potential energy landscape along the cayley tree architecture. The effect of branching tries to create a uniform distribution of mean residence time over the generations and the distribution depends upon the interplay of funneling and local rates of transitions. The calculation of flux at the steady state from the Eyring model also gives a useful idea about the rate when the dendrimeric system is considered as an open system where the core is absorbing the transported energy like a photosynthetic reaction center and a continuous supply of external energy is maintained at the peripheral nodes. The effect of the above parameters of the system are shown to depend on the steady-state flux that has a qualitative resemblence with the result of the mean first passage time approach.
Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition
Authors: Kim Sang-Woo , Fujita Shizuo , Fujita Shigeo
Published: December 2002

ZnO quantum dots (QDs) were fabricated on SiO2/Si substrates by metalorganic chemical vapor deposition. The densities and sizes of dots were investigated by atomic force microscopy. Photoluminescence at 10 K showed the broad spectra with band tails up to about 3.55 and 3.65 eV for the as-grown and the annealed ZnO QDs, respectively, which were located at the higher energy with respect to the free exciton emission of the ZnO thin film located at about 3.377 eV. These results indicate that the broad emission band results from the quantum size effect, reflecting the dot size inhomogeneity.
Realization of hollow SiO2 micronozzles for electrical measurements on living cells
Authors: Lehnert T. , Gijs M. A. M. , Netzer R. , Bischoff U.
Published: December 2002

We present a microfluidic device for the immobilization and electrical measurements, such as patch-clamp or impedance measurements, on individual living cells. Micron-sized hollow SiO2 nozzles are realized in Si wafers using a deep plasma etching process. The micronozzles are integrated with glass wafers containing microfluidic channels and Ag/AgCl electrodes. Reliable cell positioning on the nozzles via hydrodynamic forces is obtained. Relevant electrical parameters of the system, especially seal resistances between attached cells and the nozzle, are determined.
Millisecond minority carrier lifetimes in n-type multicrystalline silicon
Authors: Cuevas Andres , Kerr Mark J. , Samundsett Christian , Ferrazza Francesca , Coletti Gianluca
Published: December 2002

Exceptionally high minority carrier lifetimes have been measured in n-type multicrystalline silicon (mc-Si) grown by directional solidification and subjected to phosphorus gettering. The highest effective lifetimes, up to 1.6 ms averaged over several grains and 2.8 ms within some of them, were measured for relatively lowly doped, 2–3 Ωcm, wafers. The lifetime was found to decrease for lower resistivities, still reaching 500 μs for 0.9 Ωcm and 100 μs for 0.36 Ωcm. Several important findings are reported here: (i) achievement of carrier lifetimes in the millisecond range for mc-Si, (ii) effectiveness of phosphorus gettering in n-type mc-Si, and (iii) demonstration of good stability under illumination for n-type mc-Si.
Superconducting single-electron transistor coupled to a locally tunable electromagnetic environment
Authors: Lu W. , Rimberg A. J. , Maranowski K. D.
Published: December 2002

We have developed a system consisting of a superconducting single-electron transistor (S-SET) coupled to a two-dimensional electron gas (2DEG), for which the dissipation can be tuned in the immediate vicinity of the S-SET. Such tuning can be performed easily, and provides access to a significant range of environmental impedances. For temperatures above 100 mK, we find qualitative agreement between measured changes in the S-SET conductance versus dissipation and a model incorporating electromagnetic fluctuations in both the S-SET leads and the 2DEG.
Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe
Authors: Frey Heinrich G. , Keilmann Fritz , Kriele Armin , Guckenberger Reinhard
Published: December 2002

We show improvement of the optical and topographical resolution of scanning near-field optical microscopy by introducing a “tip-on-aperture” probe, a metallic tip formed on the aperture of a conventional fiber probe. The tip concentrates the light passing through the aperture. Thus the advantages of aperture and apertureless scanning near-field optical microscopy are combined. Tips are grown by electron beam deposition and then covered with metal. Fluorescent beads are imaged with a resolution down to 25 nm (full width at half maximum) in the optical signal. The near-field appears strongly localized within 5 nm in z direction, thus promising even higher resolution with sharper tips.
Epitaxial growth and dielectric properties of homologous Srm−3Bi4TimO3m+3 (m=3,4,5,6) thin films
Authors: Zhang S. T. , Chen Y. F. , Sun H. P. , Pan X. Q. , Liu Z. G. , Ming N. B.
Published: December 2002

The first four members of Bi-layered Srm−3Bi4TimO3m+3 homologous series with m=3, 4, 5, and 6, i.e., Bi4Ti3O12, SrBi4Ti4O15, Sr2Bi4Ti5O18, and Sr3Bi4Ti6O21, were grown on SrTiO3 (001) single-crystal substrates by pulsed-laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) reveal that the films grew epitaxially with in-plane epitaxial alignment of [11̄0]Srm−3Bi4TimO3m+3‖[010]SrTiO3. HRTEM cross-sectional images show that the films with m=3, 4, and 5 are nearly free of intergrowth, whereas a number of growth defects were observed in the film with m=6. Using an evanescent microwave probe, the room-temperature dielectric constants of these epitaxial films are measured to be 221±13, 205±15, 261±29, and 249±17 for films with m=3, 4, 5, and 6, respectively.
Effect of underlayers of laser-assisted magnetic recording media on high-density recording
Authors: Katayama Hiroyuki , Watanabe Kosuke , Takayama Kazuhisa , Sato Jun-ichi , Miyanishi Shintaro , Kojima Kunio , Ohta Kenji
Published: December 2002

The effect of underlayers of laser-assisted magnetic recording media has been investigated from the view point of high-density magnetic recording. The frequency response of a carrier-to-noise ratio (C/N) was measured in the media with various kinds of underlayers. It was found that they affect the high-frequency recording capability; the C/N at higher frequencies has been drastically improved for an Al-underlayered recording medium and a C/N of 40 dB was obtained at a recording frequency of 45 MHz and a track width of 0.35 μm. These results are explained by the surface morphology of the underlayer and its pinning effect on the domain-wall motion that is considered to work well for recording smaller stable domains.
Influence of LaAlO3 surface topography on rf current distribution in superconducting microwave devices
Authors: Zhuravel A. P. , Ustinov A. V. , Harshavardhan K. S. , Anlage Steven M.
Published: December 2002

A laser scanning microscope with a thermal spot size of about 4 μm is used to measure a quantity proportional to the rf current density in an operating superconducting coplanar waveguide microwave resonator. The twinning of the LaAlO3 substrate produces a meandering of the current at the edges due to irregularities in the wet etching of the YBa2Cu3O7−δ film associated with substrate twin domain blocks, and an (∼20%) enhancement of the rf photoresponse at these locations. These irregularities are candidates for enhanced nonlinear response from the device.
Effect of LaNiO3 interlayer on dielectric properties of (Ba0.5Sr0.5)TiO3 thin films deposited on differently oriented Pt electrodes
Authors: Yoon Ki Hyun , Sohn Ji-Hoon , Lee Byoung Duk , Kang Dong Heon
Published: December 2002

The (Ba0.5Sr0.5)TiO3 (BST) thin films were deposited on the LaNiO3/Pt(111)/Ti/SiO2/Si [LNO/Pt(111)] and LaNiO3/Pt(200)/SiO2/Si [LNO/Pt(200)] substrates by metalorganic deposition process. The BST films directly grown on the Pt(200) and Pt(111) substrates exhibited random orientation. In case of the LNO/Pt(111) substrates, the BST film was also randomly oriented, but the insertion of LNO interlayer on the Pt(200) substrates caused the growth of (100) textured BST films. The dielectric constant of the 350-nm-thick BST films on LNO/Pt(200) was around 400, which was higher than that of the films on LNO/Pt(111) (around 340). This result was attributed to the fact that the polar axis of the (100) oriented film was more tilted away from the normal to the film surface than that of randomly oriented film. Also, the tunabilities of BST films deposited on the LNO/Pt(200) and LNO/Pt(111) substrates were nearly 60% and 51% at the applied electric field of 400 kV/cm, respectively. Improved tunability has been attributed to the (100) texture of the film leading to an enhancement of the in-plane oriented polar axis.
Optical microcavities with subnanometer linewidths based on porous silicon
Authors: Reece P. J. , Lérondel G. , Zheng W. H. , Gal M.
Published: December 2002

We have fabricated a number of high-quality porous silicon optical microcavities operating in the near infrared that exhibit cavity resonances with subnanometer linewidths. This was achieved through the low temperature anodic oxidation of highly doped p-type silicon wafers. We have investigated the optical properties of these microcavities using reflectivity and photoluminescence measurements and compared our results with theoretical predictions. From our analysis, we conclude that, for the low temperature fabrication process, the refractive index difference between adjacent layers of the multilayered structure is maximized while optical losses in the cavity are minimized. Furthermore, by considering the origin of optical losses in these microcavities, we demonstrate that fluctuations in the position of the resonance wavelength and optical absorption play an important role in the realization of high-quality interferometric structures.
Proton tunneling in fatty acid/soap crystals?
Authors: Saitta A. Marco , Klein Michael L.
Published: December 2002

Fatty acids and acid/soap crystals have a bilayer structure, which is held together by hydrogen bonding between head groups. The present ab initio Car–Parrinello molecular dynamics calculations suggest that proton tunneling or sharing along such hydrogen bonds could be the key structural features in the acid/soap crystal but not in the pure acid. This effect seems to be due to sodium cations, which induce a dramatic shortening of the hydrogen bond and its signature should be visible in the experimental vibrational spectra.
Magnetically-modulated refractive index of magnetic fluid films
Authors: Yang S. Y. , Chen Y. F. , Horng H. E. , Hong Chin-Yih , Tse W. S. , Yang H. C.
Published: December 2002

We developed a setup to probe the refractive index of the magnetic fluid films under external magnetic fields. This setup possesses a high resolution of 0.0001 in the measured refractive index. It was found that the refractive index of the magnetic fluid depends linearly on the concentration of the dilute magnetic fluid under zero field. For a given magnetic fluid film, the refractive index increases with the increasing field strength over a critical value, and then becomes saturated as the field reaches around 200 Oe. It is noteworthy that the magnetically modulated refractive index of the magnetic fluid films could have great potential in electro-optical applications.
Determination of the azimuthal orientational spread of GaN films by x-ray diffraction
Authors: Sun Yue Jun , Brandt Oliver , Liu Tian Yu , Trampert Achim , Ploog Klaus H. , Bläsing Jürgen , Krost Alois
Published: December 2002

We present a simple but reliable method to determine the azimuthal orientational spread of imperfect epitaxial layers by x-ray diffraction. This method requires the measurement of ω-scans in skew geometry from reflections with increasing lattice plane inclination φ, and a fit of the data by a geometrical model that considers the simultaneous presence of polar and azimuthal orientational spread within the layer. The values thus obtained for various GaN layers grown on SiC are shown to be in good agreement with those measured directly by φ-scans of the (11̄00) reflection in grazing incidence, and with those deduced from the edge dislocation densities determined by plan-view transmission electron microscopy.
Scattering rings in optically anisotropic porous silicon
Authors: Oton C. J. , Gaburro Z. , Ghulinyan M. , Pancheri L. , Bettotti P. , Negro L. Dal , Pavesi L.
Published: December 2002

We report the observation of strongly anisotropic scattering of laser light at oblique incidence on a (100)-oriented porous silicon layer. The scattered light forms cones tangent to the incident and reflected beams. The conical pattern is caused by scattering on the vertical walls of pores, which are straight along the layer thickness. The light cone defines structured light rings onto a screen normal to the cone axis. We explain the various structures by optical anisotropy of porous silicon. For the sample under analysis, we directly measure from the ring patterns a value of Δn/nord=8% of positive birefringence.
Milliwatt power deep ultraviolet light-emitting diodes over sapphire with emission at 278 nm
Authors: Zhang J. P. , Chitnis A. , Adivarahan V. , Wu S. , Mandavilli V. , Pachipulusu R. , Shatalov M. , Simin G. , Yang J. W. , Khan M. Asif
Published: December 2002

We report on AlGaN multiple-quantum-well (MQW)-based deep ultraviolet light-emitting diodes over sapphire with peak emission at 278 nm. A new buffer layer growth process was used to reduce the number of defects and hence the nonradiative recombination. The improved material quality and carrier confinement resulted in pulsed powers as high as 3 mW at 278 nm and a significantly reduced deep-level-assisted long-wavelength emission.
Low-dose n-type nitrogen implants in 4H-SiC
Authors: Saks N. S. , Ryu S.-H. , Suvorov A. V.
Published: December 2002

Lightly-doped n-type layers have been fabricated in 4H-SiC by low-dose implantation of nitrogen ions and characterized using the Hall effect. Near-bulk electron mobility is achieved in the implanted layers. Activation rates for the implanted nitrogen ions, energies and densities of the two-level nitrogen donor, and compensation are found from fitting the measured Hall free-electron density to a charge neutrality model as a function of temperature. Measured nitrogen activation rates are 55% and 71% for 1300 and 1600 °C anneal temperatures, respectively. Compensation due to unannealed implant damage is 32% and 17% of the implant dose for 1300 and 1600 °C anneal temperatures, respectively.
Field emission from MoO3 nanobelts
Authors: Li Y. B. , Bando Y. , Golberg D. , Kurashima K.
Published: December 2002

Single-crystalline MoO3 nanobelts having an orthorhombic structure were prepared on a Si wafer via heating a Mo foil in air. The nanobelts were 50–300 nm wide and tens of nanometers thick. The nanobelt lengths lie in the [001] direction. Field-emission measurements showed that the threshold field decreased with the anode–sample separation increasing. Typically, a threshold field of 12.9 V/μm was determined at a spacing of 80 μm. The nanobelts exhibited a sharp increase in emission current density near the threshold field and, thus, reached a high current density at a relatively low field. Emission from both sharp corners and edges of the nanobelts is assumed to contribute to the high emission current. The high-current emission paired with high stability indicates that the prepared MoO3 nanobelt films are excellent field emitters.
Giant polarized photoluminescence and photoconductivity in type-II GaAs/GaAsSb multiple quantum wells induced by interface chemical bonds
Authors: Chiu Y. S. , Ya M. H. , Su W. S. , Chen T. T. , Chen Y. F. , Lin H. H.
Published: December 2002

Anisotropic property of type-II GaAs/GaAsSb heterostructures was studied by photoluminescence (PL) and photoconductivity (PC). It was found that the PL and PC spectra exhibit a strong in-plane polarization with respect to 〈011〉 axis with polarization degrees up to 40%. We showed that the polarization does not depend on the excitation intensity as well as temperature, which excludes any extrinsic mechanisms related to the in-plane anisotropy. The observed polarized optical properties of GaAsSb/GaAs multiple quantum wells was attributed to the intrinsic property of the orientation of chemical bonds at heterointerfaces.
Charge injection in individual silicon nanoparticles deposited on a conductive substrate
Authors: Mélin T. , Deresmes D. , Stiévenard D.
Published: December 2002

We report on charge injection in individual silicon nanoparticles deposited on conductive substrates. Charges are injected using a metal-plated atomic force microscope tip, and detected by electric force microscopy (EFM). Due to the screening efficiency of the conductive substrate, up to ∼200 positive or negative charges can be stored at moderate (<10 V) tip–substrate injection voltage in ∼40 nm high nanoparticles, with discharging time constants of a few minutes. We propose an analytical model in the plane-capacitor approximation to estimate the nanoparticle charge from EFM data. It falls in quantitative agreement with numerical calculations using realistic tip/nanoparticle/substrate geometries.
A neutron reflectometry study of the interface between poly(9,9-dioctylfluorene) and poly(methyl methacrylate)
Authors: Higgins A. M. , Jukes P. C. , Martin S. J. , Geoghegan M. , Jones R. A. L. , Cubitt R.
Published: December 2002

Neutron reflectivity was used to study the interface between the semiconducting polymer poly(9,9-dioctylfluorene) (PFO) and the insulating polymer poly(methyl methacrylate) (PMMA). The PFO/PMMA interfacial width was measured in the nematic and crystalline phases of the PFO, both with the PMMA on top of the PFO and vice versa. These interfaces are broad compared to atomic length scales, with measured interfacial widths in the range from 10 to 20 Å. We found that the interfacial width was independent of both the chosen geometry and the thermal processing history. The equilibrium interfacial width only depended on temperature, with the width in the nematic phase of the PFO being broader than in the crystalline regime.