bluuebunny/crossref_metadata_2025 huggingface dataset:
Exactly solvable models of relativistic δ-sphere interactions in quantum mechanics
Authors: Shabani J. , Vyabandi A.
Published: December 2002

We discuss the quantum Hamiltonian HG̳ describing a δ-sphere interaction introduced in [J. Math. Phys 30, 2275 (1989)] and formally given by HG̳=HD+G̳δ(|x|−R), where HD is the Dirac Hamiltonian and G̳ is a real 4×4 matrix defined by G̳=(0A B0). We obtain a series of new results for this model, in particular the resolvent equation, the spectral properties, the nonrelativistic limit and the various quantities related to the scattering theory. These results are generalized to the case of an asymmetric δ-sphere interaction and a δ-sphere plus Coulomb interaction, respectively.
“Linearizing” an ion cyclotron resonance cell
Authors: Barlow S. E. , Tinkle Mark D.
Published: December 2002

We describe an ion cyclotron resonance (ICR) mass spectrometer that we have built. The design of the instrument was guided in large measure by theoretical consideration; in particular we wished to investigate the effects of improved electrostatic linearity on ICR performance. We found, for instance, that the trap’s performance as a mass spectrometer is essentially independent of the trapping potential. By studying both cyclotron and magnetron modes we were able to characterize both the trap and the magnet. Further, we were able to separate effects of image charge from space charge; this gave us measurements of ion number and ion cloud shape. Finally, we show that the instrument readily provides accurate mass measurements with minimal calibration.
Crossed-beam two-photon readout system for three-dimensional radiation dosimeters
Authors: Song Joon Myong , Cullum Brian M. , Mobley Joel , Bogard James S. , Moscovitch Marko , Phillips Gary W. , Vo-Dinh Tuan
Published: December 2002

Three-dimensional optical random access memory (3D ORAM) materials with enormous capacity and fast access speed have shown a great potential in overcoming limitations of access and storage capacity in current memory devices. As another useful development of this 3D ORAM, we have shown the application of 3D ORAM materials as a practical dosimeter. The local heating of the polymer matrix by the deposited energy of ionizing radiation is thought to contribute to the conversion of the fluorescent photochromic dye to a nonfluorescent form. The two-photon readout system is very useful in tracking the interactions of energy of ionizing radiation deposited in a polymer matrix. However, the polymer fracturing that has occurred during two-photon readout has been an obstacle in utilization of 3D ORAM materials as a dosimeter. In this work, we further evaluated the readout system using a high-energy variable attenuator in order to prevent polymer fracturing due to the strong absorption of the 1064 nm beam by the polymer matrix. Through adjustment of the 1064 nm beam intensity using this attenuator, two-photon excited fluorescence of anthracene-doped 3D ORAM materials could be obtained without polymer fracturing. As a result of this improved procedure, a highly spatially resolved fluorescence image of anthracene-doped 3D ORAM material could be observed with the two-photon readout system.
Design and capabilities of a cluster implantation and deposition apparatus: First results on hillock formation under energetic cluster ion bombardment
Authors: Popok V. N. , Prasalovich S. V. , Samuelsson M. , Campbell E. E. B.
Published: December 2002

A description, advantages, and capabilities of a cluster implantation and deposition apparatus supplied by a pulsed cluster source from gaseous precursors are presented. A number of possible in situ and ex situ experimental methods to study cluster–surface collisions and modified substrate surfaces are discussed. Test experiments on cluster production show formation of Ar, N2, and O2 clusters with size up to 150 atoms for Ar and 60–70 molecules for the other gases. The possibility of cluster mass selection and acceleration up to 25 keV is reported. Nanosize hillock formation was found as a result of cluster–surface collisions with pyrolytic graphite and indium–tin–oxide. It is suggested that the hillocks’ parameters such as size and density per surface area can be controlled by varying the implantation parameters and substrate material and thus provide a promising technique for nanoscale surface modification.
Resonant two-photon ionization spectroscopy of NiC
Authors: Brugh Dale J. , Morse Michael D.
Published: December 2002

A spectroscopic investigation of jet-cooled diatomic NiC has revealed a complex pattern of vibronic levels in the wave number range from 21 700 to 27 000 cm−1. Of the more than 50 vibronic bands observed, 31 have been rotationally resolved and analyzed. All are Ω′=0+←Ω″=0+ transitions, consistent with the calculated Σ+1 ground state of this molecule. Through the observation of vibrational hot bands in the spectra, these measurements have established that ωe″=875.155 cm−1, ωexe=5.38 cm−1, Be=0.640 38(14) cm−1, αe=0.004 44(36) cm−1, and re=1.6273(2) Å for Ni58C12. Several possible electronic band systems are observed, but the identification of these is hampered by extensive perturbations among the excited states. The observation of long-lived vibronic states as far to the blue as 26 951 cm−1 indicates that D0(NiC)⩾3.34 eV, and the ionization energy of NiC has been determined to fall in the range IE(NiC)=8.73±0.39 eV. A discussion of these results, in the context of work on other 3d transition metal carbides is also presented.
Micron-scale buckling of SiO2 on Si
Authors: Serrano Justin R. , Cahill David G.
Published: December 2002

Thermal oxidation of Si produces SiO2 films which are compressively strained after cooling to room temperature. Pulsed laser irradiation of the oxidized surface melts the silicon substrate while maintaining the rigidity of the oxide film. Residual compressive stresses in the film lead to deformation of the film surface through elastic buckling. We study this buckling using atomic force microscopy. For irradiation of diameters smaller than 3 μm, the film buckles through a downward deflection of the center with a magnitude that depends on the oxide thickness—thicker films behave more rigidly and undergo a smaller central deflection. Large area irradiation produces rings of upward and downward deflections with a periodicity that varies with the diameter of the melt. The measured wavelength of the buckling of 0.8 μm for 25 nm films and 1.6 μm for 50 nm films is in good agreement with theory.
Study of the reversal mechanism in longitudinal hard disk media: The role of K2/K1
Authors: Papusoi C. , Abarra E. N. , Suzuki T.
Published: December 2002

The validity of the coherent rotations mechanism of reversal in CoCrPtB longitudinal hard disk media is probed. The proposed method is based on a comparison between the K2/K1 ratios (K1 and K2 being the first and second order anisotropy constants) measured by a hard axis loop method, and that estimated using in-plane isothermal remanent magnetization and dc-demagnetization processes in the hypothesis of coherent reversal. The disagreement between the two values of K2/K1, noticed for all the investigated samples, indicates an incoherent reversal mechanism. The origin of this mechanism is believed to be the grain coupling. The high values of the switching field at π/2 angle between the applied field and the easy axis HSW(ψ=π/2), measured by hard axis loop, can be larger than the writing field. This may explain the experimentally noticed degradation of signal/noise ratio with increasing HSW(ψ=π/2).
Influence of surface anisotropy on magnetoimpedance in wires
Authors: Melo L. G. C. , Ménard D. , Ciureanu P. , Yelon A.
Published: December 2002

The variation of the amplitude of the giant magnetoimpedance maxima for a magnetic cylindrical conductor in the range of 1<f<300 MHz has been investigated. Emphasis is put on the effect of the surface anisotropy, Ks, which was neglected in previous studies. The calculation of the impedance of a perfect anisotropic, nonsaturated wire with a helical magnetic structure also includes exchange-conductivity effects and Landau–Lifshitz damping. The results are compared with experimental data on CoFeSiB amorphous wires. It is found that other factors must also be taken into consideration to describe the data.
Designing reversible measure invariant algorithms with applications to molecular dynamics
Authors: Legoll Frédéric , Monneau Régis
Published: December 2002

A new method for generating measure invariant algorithms is presented. This method is based on a reformulation of the equations of molecular dynamics. These new equations are non-Hamiltonian but have a normal form which guarantees that the invariant measure is the canonical one for the new variables. Furthermore, from this normal form, one can easily build algorithms to integrate these equations. Using a Trotter-type factorization of the classical Liouville propagator, we build (time) reversible measure invariant integrators as successive direct translations. We apply this method to propose new algorithms to generate the Nosé–Hoover chain dynamics and the isothermal-isobaric dynamics. We also give a measure invariant integrator for the generalized Gaussian moment thermostating dynamics recently introduced by Liu and Tuckerman. Finally, we present numerical results which show comparable performances with previously proposed algorithms.
Diffusion of small light particles in a solvent of large massive molecules
Authors: Murarka Rajesh K. , Bhattacharyya Sarika , Bagchi Biman
Published: December 2002

We study the diffusion of small light particles in a solvent which consists of large heavy particles. The intermolecular interactions are chosen to approximately mimic a water–sucrose (or water–polysaccharide) mixture. Both computer simulation and mode coupling theoretical (MCT) calculations have been performed for a solvent-to-solute size ratio 5 and for a large variation of the mass ratio, keeping the mass of the solute fixed. Even in the limit of large mass ratio the solute motion is found to remain surprisingly coupled to the solvent dynamics. Interestingly, at intermediate values of the mass ratio, the self-intermediate scattering function of the solute, Fs(k,t) (where k is the wave number and t is the time), develops a stretching at long time which could be fitted to a stretched exponential function with a k-dependent exponent, β. For very large mass ratio, we find the existence of two stretched exponentials separated by a power law type plateau. The analysis of the trajectory shows the coexistence of both hopping and continuous motions for both the solute and the solvent particles. It is found that for mass ratio 5, the MCT calculations of the self-diffusion underestimates the simulated value by about 20%, which appears to be reasonable because the conventional form of the MCT does not include the hopping mode. However, for larger mass ratio, MCT appears to breakdown more severely. The breakdown of the MCT for large mass ratio can be connected to a similar breakdown near the glass transition.
Low-noise and fast-locking phase-locked loop
Authors: Shahruz S. M.
Published: December 2002

In this article, a phase-locked loop (PLL) is introduced. The proposed PLL, denoted by NPLL, is similar to the standard PLL except that it incorporates a nonlinear element and a low-pass filter in its loop. It is shown that by appropriate choices of these two components, the NPLL outperforms the standard PLL in three respects: (i) it has a large acquisition range, i.e., it can achieve locking in situations where the standard PLL cannot; (ii) it achieves locking fast; and (iii) it has low noise in its output phase. The role of the nonlinear element in enhancing the locking capabilities and noise characteristics of the NPLL is carefully examined. Many tests, results of three of which are reported in this article, show the superior performance of the NPLL.
Hall micromagnetometry on iron electrodes suitable for spin-polarized transport
Authors: Meier G. , Eiselt R. , Halverscheid M.
Published: December 2002

Iron electrodes suitable as injectors and detectors for spin-polarized transport in ferromagnet/semiconductor hybrid devices are investigated by Hall micromagnetometry. The Hall effect generated by the stray field of the iron structures is measured for single electrodes and electrode pairs with the external magnetic field aligned in plane either parallel or perpendicular to their easy axes. The strength of the stray field of the double structure in the sensor area is comparable for both configurations.
Geometric coupling thresholds in a two-dimensional strip
Authors: Borisov D. , Exner P. , Gadyl’shin R.
Published: December 2002

We consider the Laplacian in a strip R×(0,d) with the boundary condition which is Dirichlet except at the segment of a length 2a of one of the boundaries where it is switched to Neumann. This operator is known to have a non-empty and simple discrete spectrum for any a>0. There is a sequence 0<a1<a2<⋯ of critical values at which new eigenvalues emerge from the continuum when the Neumann window expands. We find the asymptotic behavior of these eigenvalues around the thresholds showing that the gap is in the leading order proportional to (a−an)2 with an explicit coefficient expressed in terms of the corresponding threshold-energy resonance eigenfunction.
Damascene process simulation using molecular dynamics
Authors: Ju Shin-Pon , Weng Cheng-I , Hwang Chi-Chuan
Published: December 2002

This article uses a molecular dynamics parallel computing technique to investigate trench filling in the damascene process. The qualitative behavior of the trench filling process for different incident energies and substrate temperatures is described in terms of the filling morphology and the filling characteristics. The significance of the geometric size of the simulation model is evaluated by comparing the coverage percentage results obtained from the current large model with the results presented previously for a small model. Similar filling characteristics are identified for both simulation models. This indicates that the qualitative behavior is independent of the model size. However, a quantitative comparison shows that when the incident energy is small, or when the substrate temperature is high, the geometric dimensions of the model become significant. Finally, the results demonstrate that the nature of the relationship between coverage percentage improvement and incident energy is dependent on the model size.
Charged species dynamics in an inductively coupled Ar/SF6 plasma discharge
Authors: Rauf Shahid , Ventzek Peter L. G. , Abraham Ion C. , Hebner Gregory A. , Woodworth Joseph R.
Published: December 2002

The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a combination of computational modeling and experimental diagnostics has been utilized to understand charged species dynamics in an inductively coupled Ar/SF6 plasma discharge. The model is based on the two-dimensional Hybrid Plasma Equipment Model with a detailed plasma chemical mechanism for Ar/SF6. In the experiments, absolute electron density and total negative ion density have been measured using microwave interferometry and laser photodetachment, respectively. In addition, we have also utilized prior measurements of mass and energy resolved ion fluxes by Goyette et al. [J. Vac. Sci. Technol. A 19, 1294 (2001)]. Computational results show that all SFx+(x=0–5) ions are present in the plasma discharge. Important negative ions include SF6−, SF5−, and F−. Electron and positive ion densities increase with coil power due to enhanced ionization. However, negative ion densities decrease with coil power as the main negative ion precursor, SF6, is lost through neutral dissociation. An increase in SF6 concentration in the Ar/SF6 gas mixture decreases electron density due to enhanced electron loss through (dissociative) attachment, which enhances negative ion densities. RF bias power does not have an appreciable impact on the ion and electron densities for the parameter range of interest. Experiments show that electron density decreases with gas pressure while the total negative ion density increases up to 25 mTorr. This is due to a decrease in electron temperature, which enhances electron loss through (dissociative) attachment. Although the model is able to capture most of the experimentally observed trends, there are discrepancies regarding the impact of gas pressure on electron density and relative flux of large positive ions.
Self-affine and mound roughness effects on the double-layer charge capacitance
Authors: Palasantzas G. , Backx G. M. E. A.
Published: December 2002

In this article, we investigate the influence of self-affine and mound roughness on the charge capacitance of double layers. The influence of self-affine roughness is more significant for small roughness exponents (H<0.5) and/or large roughness ratios w/ξ, as well as small charge and counter charge separations in electrolyte plasma as described by the Debye length λD(<ξ). On the other hand, mound roughness has a more complex influence on the charge capacitance, when the system correlation length ζ is larger than the average mound separation λ. In this case, the charge capacitance oscillates as a function of the parameters λ and ζ before it approaches the Gouy–Chapman [G. Gouy, J. Phys. (Paris) 9, 457 (1910); D. L. Chapman, Philos. Mag. 25, 475 (1913)] asymptotic limit for smooth interfaces. Furthermore, the oscillation magnitude is larger for relatively small Debye lengths λD(<ζ,λ).
Experimental and computational study of the new gaseous molecules OMnF and OMnF2
Authors: Balducci G. , Campodonico M. , Gigli G. , Meloni G. , Cesaro S. Nunziante
Published: December 2002

The new gaseous species OMnF and OMnF2 were identified and studied by high-temperature Knudsen Cell Mass Spectrometry. Their thermochemical atomization energies were derived through the study of several all-gas equilibria in the temperature range 1735–1913 K. FTIR matrix isolation experiments together with ab initio and density functional calculations were performed to determine the molecular parameters, bond distances, and vibrational frequencies of OMnF(g) and OMnF2(g). The results allowed us to evaluate a set of thermal functions for the new species that were used in the evaluation of the equilibrium data. The proposed atomization energies and enthalpies of formation are ΔaH0∘(OMnF,g)=(903±5) kJ mol−1, ΔfH298.15∘(OMnF,g)=(−297±5)kJ mol−1, and ΔaH0∘(OMnF2,g)=(1470±70) kJ mol−1, ΔfH298.15∘(OMnF2,g)=(−789±70)kJ mol−1.
Calculation of the Jahn-Teller effect in benzene cation: Application to spectral analysis
Authors: Applegate Brian E. , Miller Terry A.
Published: December 2002

Ab initio calculations have been performed for the cations of benzene, C6H6, and its fluorinated analogs, C6F6 and C6H3F3. Calculated molecular parameters characterizing the Jahn-Teller potential energy surface (PES) are very consistent with those derived from the spectra of C6F6+ and C6H3F3+. However the calculated Jahn-Teller stabilization energy for the benzene cation is roughly three times greater than that previously reported experimentally. With the aid of the calculated values, a more complete analysis of the available spectral data for C6H6+ and C6D6+ is performed, with an emphasis on the data from ZEKE experiments and IR spectra of the Ar⋅C6H6+, Ne⋅C6H6+, and Ar⋅C6D6+ complexes. The comprehensive analysis reveals Jahn-Teller activity in 3 e2g modes for C6(H/D)6+ and provides values for their vibrational frequencies, linear and quadratic Jahn-Teller coupling constants, as well as quadratic coupling constants for several other degenerate modes. These new molecular parameters are generally in good agreement with the corresponding values derived from the ab initio calculations and produce a total Jahn-Teller stabilization energy in good agreement with the computed value.
The application of a vacuum ultraviolet Fourier transform spectrometer and synchrotron radiation source to measurements of: V. The β(11,0) band of NO
Authors: Rufus J. , Yoshino K. , Thorne A. P. , Murray J. E. , Imajo T. , Ito K. , Matsui T.
Published: December 2002

The β(11,0) band of NO was measured at high resolution (0.06 cm−1) by the vacuum ultraviolet Fourier transform spectrometer from Imperial College, London, using synchrotron radiation at the Photon Factory, KEK, Japan, as a continuum light source. Such resolution facilitates a line by line analysis of the NO β(11,0) band which yields accurate rotational line positions and term values as well as the photoabsorption cross sections. The molecular constants of the B(11) Πr2 level are found to be T0=55 983.203±0.017 cm−1, A=47.977±0.024, Bv=1.010 77±0.000 37 cm−1, Dv=(6.7±0.8)×10−6 cm−1 and AD=0.0438±0.0035 cm−1. The sum of the line strengths for all rotational transitions of the NO β(11,0) band is determined as 3.04×10−16 cm2 cm−1, corresponding to a band oscillator strength of (3.44±0.21)×10−4.
High-temperature phase transitions, dielectric relaxation, and ionic mobility of proustite, Ag3AsS3, and pyrargyrite, Ag3SbS3
Authors: Schönau Kristin A. , Redfern Simon A. T.
Published: December 2002

The nature of phase transitions in natural and synthetic proustite, Ag3AsS3, has been studied in darkness above 300 K and compared with its natural counterpart pyrargyrite, Ag3SbS3. The behavior of proustite is characterized by silver ion mobility within the structure. Proustite and (to a lesser extent) pyrargyrite were investigated as a function of temperature by x-ray and neutron powder diffraction, dielectric spectroscopy, and dynamic mechanical analysis. At 305 K (280 K for pyrargyrite) proustite undergoes a second-order phase transition, exhibiting a positive nonsymmetry breaking spontaneous strain of the unit cell, with thermal expansion along [001] changing from negative to positive. This strain results from the onset of thermally induced hopping of silver ions, as revealed by impedance spectroscopy. It may be described as an almost undamped Debye oscillator, which is not present below Tc (305 K) with an activation energy of 0.42 eV (0.40 eV for pyrargarite). Around 420 K the high-frequency conductivity of proustite begins to increase, accompanied by elastic softening. At this temperature increasing random disorder of silver within possible unoccupied sites in the structure leads to increased electrical conductivity and destabilizes the material. When almost all silver ions are disordered into a so-called “molten sublattice,” a transition to fast ion conduction (at 540 K in proustite and 490 K in pyrargyrite) is reached. The additional component to the thermal expansion disappears and a linear negative spontaneous strain suggests a second-order phase transition. Above the transition silver seems to be maximally disordered, the structure itself is weakened and the sample starts to decompose.
Dispersive one-dimensional (Mo/Si) nanocrystals for single molecular detection systems using x rays
Authors: Okumura Yasuaki , Taniguchi Yoshio , Sasaki Yuji C.
Published: December 2002

To directly observe the behavior of single molecules in real time and space, the x-ray methodology, diffracted x-ray tracking, has been proposed. This system monitors the spots of a diffracted x ray from individual nanocrystals, which are labeled with the individual single molecules. To operate single molecular detection systems with x rays, it is necessary to fabricate dispersive nanocrystals and observe the diffracted spots from the nanocrystals. We succeeded in fabrications of dispersive one-dimensional (Mo/Si) nanocrystals with diameters of approximately 25 nm using reactive ion etching. Furthermore, we monitored well-defined diffracted x-ray spots from Mo/Si nanocrystals (2.5 bilayers: Mo/Si/Mo/Si/Mo, d-space=5.0 nm) in real time (2.0 ms).
Strain distribution of Si thin film grown on multicrystalline-SiGe with microscopic compositional distribution
Authors: Usami Noritaka , Takahashi Tatsuya , Fujiwara Kozo , Ujihara Toru , Sazaki Gen , Murakami Yoshihiro , Nakajima Kazuo
Published: December 2002

We report on growth and characterizations of Si/multicrystalline-SiGe (mc-SiGe) heterostructure as a promising candidate to surpass mc-Si solar cells. Spatial distribution of the status of strain in Si was investigated using microscopic Raman spectroscopy. The strain was found to be strongly influenced by the composition and microstructure of underlying mc-SiGe. Spatial variation of the strain as well as strain relaxation was found to be suppressed by decreasing average Ge composition of underlying SiGe.
Simple fiber optic coupled luminescence cryostat
Authors: Meyer G. D. , Ortiz T. P. , Costello A. L. , Brozik J. A. , Kenney J. W.
Published: December 2002

An easy to fabricate, easy to operate, miniature liquid helium insert cryostat has been designed for variable low-temperature luminescence investigations in the 2.7–77 K region with minimal liquid helium consumption. The cryostat, which can be used inside of a standard liquid helium storage Dewar, is optically coupled both to the luminescence spectrophotometer and to the chosen luminescence excitation source (laser or conventional) by a single 1 mm fused silica fiber optic cable. This extremely simple and compact optical system is designed to give highly reproducible luminescence excitation and collection efficiencies for quantitative luminescence intensity studies. Temperature control in the cryostat is achieved through the dynamic balance of up to three distinct heating/cooling processes: raising or lowering the cryostat with respect to the liquid helium level in the Dewar, heating the cryostat with a small resistance heater, or pumping on the cryostat for sub-4.2 K temperatures. The cryostat can operate effectively throughout the 2.7–77 K range in liquid helium storage Dewars containing less than a liter of liquid helium. The wide range of spectroscopic experiments that this novel optical cryostat design can support is illustrated by a temperature-dependent zero field splitting luminescence lifetime study of Ru(bpy)3Cl2, a temperature-dependent relative luminescence intensity (quantum yield) study of Ru(bpy)3Cl2, and a temperature-dependent luminescence vibronic fine structure study of Ti(Cp)2(NCS)2.
Application of a time-resolved event counting technique in velocity map imaging
Authors: Dinu L. , Eppink A. T. J. B. , Rosca-Pruna F. , Offerhaus H. L. , van der Zande W. J. , Vrakking M. J. J.
Published: December 2002

We illustrate the use of a three-dimensional (x,y,t) charge-coupled-device (CCD) camera detection system in an ion imaging experiment. The time measurement is based on the decay characteristics of the phosphor screen, which is recorded in two successive images by a double exposure CCD camera. The strength of the method is illustrated in a velocity map imaging experiment on iodine molecules that are ionized and dissociated by intense femtosecond laser pulses. Singly and doubly charged iodine fragments are detected and their (x,y) coordinates and arrival time are recorded in an event counting routine. We estimate the time resolution of the system to be 1.3 ns. We show that the fragment velocity distribution derived from the (x,y,t) data is similar and in some conditions more accurate than the distribution obtained by a mathematical inversion of the (x,y) data only. This principle of detection can be used in all situations in which inversion methods are impossible, for example, when the particle distribution does not have an axis of symmetry.
Generation of 600 T by electromagnetic flux compression with improved implosion symmetry
Authors: Matsuda Y. H. , Herlach F. , Ikeda S. , Miura N.
Published: December 2002

We have developed a device for generating ultrahigh magnetic fields by means of electromagnetic flux compression. The device that we call “feed gap compensator” is a flux concentrator that consists of a thick-walled copper cylinder with a number of thin radial slits. This is inserted between the primary coil and the liner; it has resulted in a substantial improvement of the implosion symmetry that is normally disturbed by the feed gap of the primary coil. A maximum field exceeding 600 T can be generated reproducibly by using this device. Because of the improved symmetry of the liner motion, we observed turnaround phenomena not only in the wave form of the magnetic field but also in the photographs of the liner that are taken by a high-speed image converter camera. The final implosion speed and the turnaround radius have been determined by calculating the magnetic flux from a combination of framing camera data and the measured field. It is confirmed that the turnaround field is a function of the implosion speed; this function is given by the particle speed of the shock wave associated with the pressure pulse induced by the magnetic field. Further optimization of the flux compression system is discussed with a view to obtaining higher fields that are suitable for application in experiments.
Quantitative geometry of the Rayleigh wave oscillation ellipse by surface acoustic wave scanning tunneling microscopy
Authors: Voigt P. U. , Koch R.
Published: December 2002

In recent studies it has been demonstrated that the scanning tunneling microscope (STM) after sophisticated modification is a powerful technique to investigate surface acoustic waves (SAWs) with high spatial resolution. Here we apply our ultrahigh vacuum (UHV) SAW–STM to investigate the surface motion induced by a Rayleigh wave on LiNbO3. After establishing the theoretical basis for evaluating SAW–STM images recorded as usual in the constant–current scanning mode we apply the method to quantitatively determine the complete geometry of the atomic oscillation ellipse given by its eccentricity and the amplitude of the transverse displacement. The obtained eccentricity parameter is 36° being in good agreement with the theoretical value of 35.1°. Our investigations show that the dynamic range of our UHV–SAW–STM comprises at least 3 orders of magnitude down to SAW amplitudes as small as 0.001 Å and, furthermore, that the spatial resolution for acoustic measurements lies in the lower nanometer range.
Positive charge distribution in (benzene)1(toleune)2+ and (benzene)2(toluene)1+ studied by photodissociation spectroscopy
Authors: Inokuchi Yoshiya , Ohashi Kazuhiko , Sekiya Hiroshi , Nishi Nobuyuki
Published: December 2002

The positive charge distribution in benzene–toluene heterotrimer ions is investigated by photodissociation spectroscopy in the near-infrared (6000–14 000 cm−1) and infrared (2800–3150 cm−1) regions. The electronic spectra of (benzene)1(toluene)2+ and (benzene)2(toluene)1+ in the near-infrared region display a strong band at 9430 and 8330 cm−1, respectively. These bands are ascribed to the charge resonance band; the positive charge is not localized on a single molecule. The vibrational spectrum of (benzene)1(toluene-d8)2+ shows three distinct bands at 3054, 3084, and 3108 cm−1; these bands are assigned to the CH stretching vibrations of the benzene moiety. The similarity of the spectral features to those of the neutral benzene monomer suggests that the benzene molecule in the (benzene)1(toluene)2+ ion has a neutral character. The positive charge is localized on the toluene dimer unit with a structure written as (toluene)2+⋯(benzene)1. The vibrational spectrum of (benzene)2(toluene)1+ bears a resemblance to that of (benzene)2+. The vibrational spectrum of (benzene-d6)2(toluene)1+ shows dissimilar features to the spectrum of the neutral toluene monomer, suggesting that a certain amount of the positive charge is carried by the toluene moiety. These results are explained by the charge resonance interaction between (benzene)2 and (toluene)1. A simple perturbation theory is applied for determining the positive charge distribution in (benzene)2(toluene)1+. The probability of finding the charge on the (benzene)2 and (toluene)1 moieties is analyzed to be 58% and 42%, respectively.
Benchmark calculations on high-dimensional Henon–Heiles potentials with the multi-configuration time dependent Hartree (MCTDH) method
Authors: Nest M. , Meyer H.-D.
Published: December 2002

We present quantum dynamical simulations on generalized, high-dimensional Henon–Heiles potentials. The calculations can serve as benchmark results for other, approximative methods. Especially, we will give a comparison with semiclassical and Gaussian wave packet Monte Carlo calculations from two other groups. The scaling behavior of the multi-configuration time dependent Hartree method with the dimensionality of the problem is investigated and discussed.
HPO does not follow Walsh’s rules! Improved molecular structures from the spectroscopy of jet-cooled HPO and DPO
Authors: Tackett Brandon S. , Clouthier Dennis J.
Published: December 2002

The Ã 1A″–X̃ 1A′ electronic spectra of jet-cooled HPO and DPO have been studied using the techniques of pulsed discharge jet, laser-induced fluorescence, and wavelength resolved emission spectroscopy. All of the vibrational frequencies in the ground and excited states have been obtained for both isotopomers and vibrational force fields have been determined for both states. Rotational analysis of the high-resolution 000 band spectrum of DPO has yielded the first rotational constants of the deuterated species. By combining the rotational constants of DPO with literature values for the rotational constants of HPO, we have derived reliable structures of HPO in the combining states with estimated equilibrium values of r″(PH)=1.4578(6) Å, r″(PO)=1.4801(1) Å, θ″=104.62(7)°, r′(PH)=1.4671(26) Å, r′(PO)=1.5579(6) Å, and θ′=97.4(4)°. The decrease in the bond angle on n–π* electronic excitation is contrary to predictions based on Walsh diagrams. A quantitative ab initio study shows that the variation of the orbital energies with bond angle differs in the ground and excited states of HPO, and these differences account for the anomalous change in bond angle on electronic excitation.
N coupled nonlinear Schrödinger equations: Special set and applications to N=3
Authors: Hioe F. T.
Published: December 2002

Analytic solutions for a special set of N coupled nonlinear Schrödinger equations characterized by 2N interaction types are presented for N=1–3. They provide an overview of the important role played by nonlinear couplings.
Magnetic and electronic properties of DyNi5−xAlx compounds
Authors: Burzo E. , Chiuzbăian S. G. , Neumann M. , Valeanu M. , Chioncel L. , Creanga I.
Published: December 2002

The DyNi5−xAlx compounds crystallize in CaCu5-type structure for an aluminum content x⩽1.5 and in HoNi2.6Ga2.4 type for x⩾2. The saturation moments per formula unit extrapolated at 0 K, in composition range x<2 are ∼9.2 μB in agreement with x-ray photoelectron spectroscopy studies which show negligible crystal field effects. For x⩾2 a mictomagnetic type contribution to magnetic ordering develops which becomes dominant only for the DyNi2Al3 compound. Band structure calculations on DyNi5−xAlx show that the Dy 5d band is polarized parallel to the 4f moment. For DyNi5 the nickel moments at 2c and 3g sites are antiparallel oriented to that of Dy. The nickel contributions to magnetization decrease when increasing aluminum content and are near nil for x⩾2. Above the Curie points the reciprocal susceptibilities follow linear dependencies. The effective nickel moments decrease from 2.11 μB/atom (x=0) to 0.87 μB/atom (x=2.5). The magnetic behavior of nickel is analyzed in models which take into account the electron correlation effects in d bands.
Investigation of the cobalt distribution in TiO2:Co thin films
Authors: Stampe P. A. , Kennedy R. J. , Xin Yan , Parker J. S.
Published: December 2002

We report a detailed study of the morphology of TiO2:Co films grown on both LaAlO3 (001) and SrTiO3 (001) substrates by pulsed laser deposition. The films are optically transparent and ferromagnetic at room temperature with a magnetic moment of 1.7±0.4 μB/Co. Plan view transmission electron microscope studies show clear evidence of cobalt segregation with the clustering more pronounced for higher cobalt concentrations. Films grown on SrTiO3 substrates show the presence of a thin surface rutile (111) layer, into which the cobalt appears to migrate. These results are supported by x-ray structure determination and resistivity measurements.
Reverse current transport mechanism in shallow junctions containing silicide spikes
Authors: Chi D. Z. , Wang W. D. , Chua S. J. , Ashok S.
Published: December 2002

In this article, a simple physical model describing the current transport mechanism in shallow Si p-n junctions containing silicide spikes is proposed and discussed. It includes analytical calculations of maximum electrical field around a silicide spike tip and tunneling probability of electrons at the silicide/silicon interface. The athermal behavior of the reverse current in shallow junctions containing silicide spikes is explained in terms of electric field enhancement at the sharp spikes and the resulting dominance of electron field-emission across the silicide/silicon Schottky barrier. The model also allows extraction of important parameters of such shallow junctions, such as the average radius of the silicide spikes.
Secondary growth of carbon nanotubules by the fragments of Ni tip
Authors: Park Gyeong-Su , Kim Mi-Young , Baik Hyeon-Seok , Song Se-Ahn , Han In-Taek , Lee Nae-Sung , Han Jae-Hee , Yoo Ji-Beom
Published: December 2002

We report the generation of small Ni particles by the fragmentation of Ni tips during the growth process of vertically aligned carbon nanotubules at 500 °C. A high-voltage transmission electron microscopy study revealed the role of small Ni particles in the secondary growth of carbon nanotubules. The small Ni particles lead to catalytic growth of a large amount of nanobell-like carbon nanotubules ranging from 10 to 20 nm in diameter. Comparison of the Ni tip structure formed at 500 °C with that at 620 °C suggests that only the proper size of Ni particles can lead to the secondary growth of carbon nanotubules. We propose a phenomenological model for the secondary growth of carbon nanotubules.
Electrochromic properties of SnO2-incorporated Ni oxide films grown using a cosputtering system
Authors: Ahn Kwang-Soon , Nah Yoon-Chae , Sung Yung-Eun
Published: December 2002

SnO 2 -incorporated Ni oxide (NiO:SnO2) films were grown by means of a cosputtering system, consisting of two rf sputter guns, and their electrochromic properties were compared with those of a Ni oxide film. The Ni oxide films crystallized with an increased film thickness due to a plasma heating effect, leading to a decreased maximum bleached transmittance and coloration efficiency (CE). However, the NiO:SnO2 films grown by cosputtering showed acceptable maximum bleached transmittance and CE values, which were independent of film thickness. This indicates that SnO2 adatoms generated by the side sputter gun interfere with the movement of Ni oxide adatoms deposited by the main sputter gun, preventing the crystallization of the films. This was verified by x-ray diffraction and scanning electron microscopic data. We propose that the cosputtering technique described herein has the capability of providing good maximum bleached transmittance and CE properties in thick electrochromic films with no degradation due to the plasma heating effect.
Magneto-optics of thin magnetic films composed of Co nanoparticles
Authors: Kalska B. , Paggel J. J. , Fumagalli P. , Hilgendorff M. , Giersig M.
Published: December 2002

The magneto-optic properties of 8, 10, and 12 nm diameter Co particles deposited on Si and Al substrates are investigated at room temperature in the photon-energy range from 0.8 to 4.8 eV using the magneto-optic Kerr effect. The 10 and 12 nm particles give rise to a magneto-optic signal, while the 8 nm particles show virtually no magneto-optic response at room temperature. The spectral features of the polar Kerr rotation depend on particle size and are at variance from those of a reference spectrum of a thick Co film. For the 10 nm particles an aging effect on a time scale of months is observed through the magneto-optic signature. The magneto-optic signal also depends on the arrangement of the particles within the film of nanoparticles. The magnetization of the 10 and 12 nm particle films is analyzed in terms of a Langevin function. From this analysis, the effective magnetic core of the 10 nm particles is estimated as 4.5 nm, while the 12 nm particles appear to show ferromagnetic coupling.
Connectedness percolation in fluids of persistent chains
Authors: Chatterjee Avik P.
Published: December 2002

An integral equation approach to understanding connectedness percolation in macromolecular fluids is extended to investigate semiflexible linear homopolymers. A coarse-grained threadlike approximation is developed for persistent chains. Results are presented for the percolation threshold, and number of intermolecular contacts at the threshold, as functions of the polymer stiffness. A substantial reduction of the percolation threshold is observed, and a dependence of this threshold on the contour length similar to that for rigid rodlike particles is found, even for large ratios of the contour to the persistence lengths provided the latter exceeds the range over which neighboring monomers are viewed as belonging to the same physical cluster. Accounting for chain stiffness leads to pair correlation functions which, at small separations, display features akin to those observed in fluids of rodlike particles, resulting in much lower critical volume fractions than for fully flexible molecules.
Exceptionally high ion-induced electron emission yield from hydrogenated diamond and its decay
Authors: Cheifetz E. , Richter V. , Koenigsfeld N. , Kalish R.
Published: December 2002

Extremely high ion-induced electron emission (IIEE) yields-γ-(exceeding 400) are measured for boron-doped hydrogenated diamond, bombarded with sub-MeV Ar ions. These high values are found to rapidly diminish with an increasing number of ions impinging on the diamond surface, eventually reaching the low values of IIEE (of the order of 5) found for graphite and most materials. This reduction is shown to be caused by two processes: One, which affects a very large area around each ion-impingement point (and thus causes the rapid reduction in γ), may be either due to electron transport limitations caused by point defects introduced by the ion during their slowing down in the diamond or to surface hydrogen loss induced by the outgoing electrons; the second, more gradual loss process, is attributed to local graphitization around each ion track. A material with such a high electron-emission yield as the presently studied B-doped hydrogenated diamond, may find an application in the detection and counting of single ions or molecules, as needed mainly for biological applications.
Sensitivity of a piezoelectric micromechanical displacement detector based on the radio-frequency single-electron transistor
Authors: Zhang Yong , Blencowe Miles P.
Published: December 2002

We investigate the displacement and force sensitivity of a micromechanical detector in which a GaAs cantilever is capacitively coupled to a radio-frequency single-electron transistor (rf-SET). The piezoelectric effect in GaAs is utilized to convert the displacement signal into an electrical signal which is read out using the rf-SET. We analyze the input displacement noise due to the tunneling current shot-noise and back-action displacement noise due to the SET island voltage noise, and show, as an example, that a displacement sensitivity of 1.2×10−3 Å and a force sensitivity of 73×10−18 N in a 6 KHz bandwidth are possible for a detector design with a resonant frequency of 38.4 MHz.
Analytical solution for the current distribution in multistrand superconducting cables
Authors: Bottura L. , Breschi M. , Fabbri M.
Published: December 2002

Current distribution in multistrand superconducting cables can be a major concern for stability in superconducting magnets and for field quality in particle accelerator magnets. In this article, we describe multistrand superconducting cables by means of a distributed parameters circuit model. We derive a system of partial differential equations governing current distribution in the cable and we give the analytical solution of the general system. We then specialize the general solution to the particular case of uniform cable properties. In the particular case of a two-strand cable, we show that the analytical solution presented here is identical to the one already available in the literature. For a cable made of N equal strands we give a closed-form solution that to our knowledge was never presented before. We finally validate the analytical solution by comparison to numerical results in the case of a steplike spatial distribution of the magnetic field over a short Rutherford cable, both in transient and steady-state conditions.
Amorphous silica between confining walls and under shear: A computer simulation study
Authors: Horbach Jürgen , Binder Kurt
Published: December 2002

Molecular dynamics computer simulations are used to investigate a silica melt confined between walls at equilibrium and in a steady-state Poisseuille flow. The walls consist of point particles forming a rigid face-centered cubic lattice and the interaction of the walls with the melt atoms is modeled such that the wall particles have only a weak bonding to those in the melt, i.e., much weaker than the covalent bonding of a Si–O unit. We observe a pronounced layering of the melt near the walls. This layering, as seen in the total density profile, has a very irregular character which can be attributed to a preferred orientational ordering of SiO4 tetrahedra near the wall. On intermediate length scales, the structure of the melt at the walls can be well distinguished from that of the bulk by means of the ring size distribution. Whereas essentially no structural changes occur in the bulk under the influence of the shear fields considered, strong structural rearrangements in the ring size distribution are present at the walls as far as there is a slip motion. For the sheared system, parabolic velocity profiles are found in the bulk region as expected from hydrodynamics and the values for the shear viscosity as extracted from those profiles are in good agreement with those obtained in pure bulk simulations from the appropriate Green–Kubo formula.
Abstraction of atomic hydrogen by atomic deuterium from an amorphous hydrogenated silicon surface
Authors: Agarwal Sumit , Takano Akihiro , van de Sanden M. C. M. , Maroudas Dimitrios , Aydil Eray S.
Published: December 2002

We have studied the interactions of atomic deuterium with hydrogenated amorphous silicon (a-Si:H) surfaces using surface-sensitive infrared spectroscopy. We deconvoluted the effects of the abstraction reaction from insertion and etching reactions and determined the activation energy barrier for abstraction of H by D from a-Si:H surfaces. Both abstraction and insertion are observed in our experiments conducted over times ranging from a few seconds to hundreds of seconds and sequential insertion of D eventually results in the formation of deuterated silane and etching of the film. The abstraction rate is found to be independent of temperature with an essentially zero activation energy barrier (0.011±0.013 eV), consistent with an Eley–Rideal mechanism and in agreement with recent atomistic calculations.