bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of mass-selected ion species on structure and properties of diamond-like carbon films
Authors: Tang Z. , Zhang Z. J. , Narumi K. , Xu Y. , Naramoto H. , Nagai S. , Miyashita K.
Published: July 2002

Diamond-like carbon (DLC) films were prepared with mass-selected C+, CH2+, CH3+, and CH4+ ions, and the dependence of film microstructures and properties on ion species was investigated with micro-Raman spectroscopy, optical band gap measurement and atomic force microscopy (AFM). The results indicate that highly sp3 bonded DLC films are achieved using carbon and hydrocarbon ions with ion energy of 100 eV. AFM results exhibit that the surface roughness for these films is very low, which is associated with the formation of a dense diamond-like phase as suggested by the subplantation model. The thermal stability of the films were investigated in the temperature region of 200–800 °C. Raman measurements show that the D peak evolves at much lower temperatures for the film prepared with CH4+ than that for the film prepared with C+ ions during annealing. The results indicate that hydrogen-free carbon films have a much better thermal stability than hydrogenated carbon films.
Exact equation of state for 2-dimensional gravitating system within Tsallis statistical mechanics
Authors: Fa Kwok Sau , Lenzi E. K.
Published: July 2002

We obtain an exact expression for the equation of state for a classical 2-dimensional gravitating system, using Tsallis’s statistical mechanics.
Structural study of supercritical water. III. Rotational dynamics
Authors: Matubayasi Nobuyuki , Nakao Naoko , Nakahara Masaru
Published: July 2002

The rotational dynamics of water in super- and subcritical conditions is investigated by measuring the spin-lattice relaxation time T1 of heavy water (D2O). The experimentally determined T1 is shown to be governed by the quadrupolar relaxation mechanism even in the supercritical conditions and to provide the second-order reorientational correlation time τ2R of the O–D axis of a single water molecule. It is then found that while τ2R decreases rapidly with the temperature on the liquid branch of the saturation curve, it remains on the order of several tens of femtoseconds when the density is varied up to twice the critical at a fixed supercritical temperature of 400 °C. The comparison of τ2R with the angular momentum correlation time shows that the rotational dynamics is not diffusive in supercritical water. The dependence of τ2R on the hydrogen bonding state is also examined in combination with molecular dynamics simulations, and the effect of the hydrogen bonding on the rotational dynamics in supercritical water is found to be weaker than but to be on the same order of magnitude as that in ambient water on the relative scale. Actually, although τ2R is divergent in the limit of zero density, it is observed to increase with the density when the density is above ∼1/3 of the critical.
Residual strain and threading dislocation density in InGaAs layers grown on Si substrates by metalorganic vapor-phase epitaxy
Authors: Takano Y. , Kururi T. , Kuwahara K. , Fuke S.
Published: July 2002

InGaAs layers with In contents between 0.007 and 0.055 have been grown on GaAs epilayers on Si substrates by low-pressure metalorganic vapor-phase epitaxy. The threading dislocation density of the order of 105 cm−2 in the InGaAs layer was achieved by insertion of an InGaAs strained layer combined with thermal cycle annealing. Photoluminescence measurement for layers confirmed that the residual strain was lower in InxGa1−xAs layers with x⩾0.038 than that in GaAs. It is suggested that the tensile strain due to the difference in the thermal expansion coefficient between InGaAs and Si materials was compensated by the compressive strain partly due to the slow strain relaxation by work hardening in InGaAs layers grown on GaAs layers or due to the incomplete strain relaxation in InGaAs layers at the small thickness of 1 μm.
Dynamic visualization of subangstrom high-frequency surface vibrations
Authors: Graebner J. E. , Barber B. P. , Gammel P. L. , Greywall D. S. , Gopani S.
Published: July 2002

An optical scanning interferometer for accurate imaging of high-frequency surface vibrations is described. Vertical-displacement (out-of-plane) resolution of the interferometer is ∼0.003 Å, while lateral resolution is diffraction limited, typically ∼0.5 μm. The high-frequency response is limited by the detector to ∼6 GHz. Both the magnitude and phase are recorded at each point of the scan, so that an accurate measurement of the instantaneous surface shape is obtained. Furthermore, the phase information allows one to make a slow-motion movie of the vibrating surface. Data are presented for three examples in the frequency range 4 MHz–2 GHz.
Observation of multiple nearly monoenergetic electron production by heated pyroelectric crystals in ambient gas
Authors: Brownridge J. D. , Shafroth S. M. , Trott D. W. , Stoner B. R. , Hooke W. M.
Published: July 2002

Multiple production of nearly monoenergetic electrons at a given pyroelectric crystal surface charge density is observed on cooling or heating the crystal in ambient gas. Typically, the +z base of a 5 mm diam×5 mm crystal of LiNbO3 is heated to 100 °C and then let cool to 23 °C in dry N2 at 10−2–10−6 Torr. The electron spectrum consists of a series of peaks equally spaced in energy and having decreasing intensity with order superimposed on a continuously decreasing background. The higher-order peaks and the high-energy continuum are due to two or more electrons hitting the surface barrier detector within its resolving time (∼1 μs).
Effect of competition between Coulomb and dispersion forces on phase transitions in ionic systems
Authors: Ciach A. , Stell G.
Published: July 2002

A restricted primitive model (RPM) for ionic systems in which the Coulomb and hard-core interactions are supplemented with short-range (SR) interactions between all the components, including solvent particles, is introduced and studied within a mean-field approximation. Continuum-space as well as simple-cubic lattice systems are considered. A continuous and a first-order phase transition, separated by a tricritical point (tcp), are found between uniform and charge-ordered phases in all the systems considered. The position of the tcp as well as the slope of the line of the continuous transition depend on both the model and the SR interactions. For weak or vanishing SR interactions, at temperatures lower than the transition temperature, two oppositely charged sublattices are found on the simple-cubic lattice, whereas in the continuum case a lamellar structure consisting of charged layers of alternating sign occurs. For strong SR interactions the structure becomes incommensurate with the lattice in the lattice model. Both on the lattice and in the continuum a transition between uniform ion-poor and ion-rich phases occurs for sufficiently strong SR interactions. This critical point (scp) is not to be confused with the liquid–gas type critical point (cp) that already occurs in the continuum-space version of the RPM in the absence of SR interactions. The density at the scp is significantly higher than the density at the cp. The way this latter critical point is perturbed by the presence of SR interactions is not addressed in the analysis here. The SR interactions influence the charge ordering in such a way that the tcp can be located in the same range of densities as the stable critical point. For strong SR the tcp is located close to the scp, whereas for weak SR it is close to the cp.
Role of the cavity field in nonlinear optical response in the condensed phase
Authors: Munn R. W. , Luo Yi , Macák P. , Ågren H.
Published: July 2002

Comparison between a rigorous molecular crystal treatment of nonlinear optical response and a cavity model approach to third harmonic generation shows that a cavity field should be included at the output frequency. The argument for omitting this cavity field, that there is zero macroscopic field at the output frequency, fails to take proper account of polarization at the output frequency outside the cavity.
Langasite for high-temperature bulk acoustic wave applications
Authors: Fritze H. , Tuller H. L.
Published: July 2002

Langasite (La3Ga5SiO14) and related compounds are promising candidates for high-temperature piezoelectric applications. To determine the stable operation of langasite as a high-temperature bulk acoustic wave (BAW) resonator, we characterized electrical conductivity [σel=1.56×exp(−1.07 eV/kT)S/cm] and oxygen diffusivity [DoxT=5×10−5 exp(−1.45 eV/kT)cm2/s] up to elevated temperatures. Langasite was successfully operated up to 900 °C as a BAW resonator with an average mass sensitivity of about 0.17 μg Hz−1 cm−2. This enables, in principle, high-temperature monitoring of deposition rates and thermogravimetry with high sensitivity.
Second-harmonic generation from silicon nanocrystals embedded in SiO2
Authors: Jiang Y. , Wilson P. T. , Downer M. C. , White C. W. , Withrow S. P.
Published: July 2002

We present observations of optical second-harmonic generation (SHG) from silicon nanocrystals embedded in SiO2. SHG sensitivity to Si/SiO2 interface states, charge on the nanocrystals, and particle density gradients is demonstrated. SHG is proven to be a powerful noncontact nondestructive diagnosis tool for characterization of Si-nanocrystal-based devices and materials.
Near-field images of the AgOx-type super-resolution near-field structure
Authors: Liu Wei-Chih , Wen Cheng-Yen , Chen Kuei-Hsien , Lin Wei Chih , Tsai Din Ping
Published: July 2002

As a promising disk structure for ultrahigh density optical data storage, super-resolution near-field structure of AgOx type has been studied by the tapping-mode tuning-fork near-field scanning optical microscope as well as the transmission electron microscope. This structure presents strong near-field intensity enhancement and nonlinear optical effect, compared with the ordinary material. Numerical calculations confirm that the localized surface plasmon and the nonuniform material structures are the main causes for these unusual characteristics.
X-ray magnetic circular dichroic magnetometry on Ni/Pt multilayers
Authors: Poulopoulos P. , Wilhelm F. , Wende H. , Ceballos G. , Baberschke K. , Benea D. , Ebert H. , Angelakeris M. , Flevaris N. K. , Rogalev A. , Brookes N. B.
Published: July 2002

X-ray magnetic circular dichroism measurements have been performed on Ni/Pt multilayers at a temperature of 10 K. The element specificity and shell selectivity of the technique allows us to probe Ni and Pt magnetic moments and to separate them into their constituent spin (μS) and orbital (μL) magnetic moments. The Ni magnetic moment at the interface is found to be reduced. However, magnetically “dead” Ni layers are unambiguously ruled out. Induced Pt magnetic moments up to about 0.3 μB/atom are reported. The results are compared to ab initio calculations and to previous experiments performed on NiPt alloys. The role of intermixing in the reduction of the Ni magnetic moments is also discussed.
Method for the determination of frequency response and signal to noise ratio for constant-temperature hot-wire anemometers
Authors: Weiss J. , Knauss H. , Wagner S.
Published: July 2002

Determination of the frequency response of constant-temperature hot-wire anemometers is needed for measurements of high frequency turbulent fluctuations or when the bridge cannot be well adjusted because of too short a testing time. A method is proposed to determine the complete transfer function of a constant-temperature anemometer bridge in several milliseconds by means of an electrical test. The frequency response is used to perform postcorrection of the data, which enables the measurement of turbulent quantities at frequencies higher than the cut-off frequency of the system, when the bridge adjustment is not optimum. The technique, which is tested in the free stream of a supersonic wind tunnel at M=2.5, also enables a accurate estimation of the signal to noise ratio.
Ferroelectric properties of alkoxy-derived CaBi4Ti4O15 thin films on Pt-passivated Si
Authors: Kato Kazumi , Suzuki Kazuyuki , Nishizawa Kaori , Miki Takeshi
Published: July 2002

CaBi 4 Ti 4 O 15 (CBTi144) thin films were prepared by spin coating a precursor solution of metal alkoxides. As-deposited thin films began crystallization below 550 °C and reached full crystallinity of a single phase of layered perovskite at 650 °C via rapid thermal annealing in oxygen. The 650 °C annealed CBTi144 thin film showed random orientation on Pt-passivated Si substrate and exhibited P-E hysteresis loops. The remanent polarization (Pr) and coercive electric field (Ec) were 9.4 μC/cm2 and 106 kV/cm, respectively, at 11 V. The dielectric constant and loss factor were 300 and 0.033, respectively, at 100 kHz.
Injection-seeded terahertz-wave parametric oscillator
Authors: Imai Kazuhiro , Kawase Kodo , Shikata Jun-ichi , Minamide Hiroaki , Ito Hiromasa
Published: July 2002

The narrow linewidth operation of a THz-wave parametric oscillator was achieved through the use of narrow linewidth laser injection. THz-wave parametric oscillation, generated by a LiNbO3 crystal pumped with a single longitudinal mode Q-switched Nd:YAG laser, was injection seeded with a continuous-wave Yb:fiber laser. The measured THz-wave linewidth was 200 MHz, which corresponded to the measurement resolution limit.
Relativistic electron beams in conducting solids and dense plasmas: Approximate analytical theory
Authors: Fill Ernst E.
Published: July 2002

The response of a conducting medium to an intense electron beam is investigated. For this purpose Maxwell’s equations in cylindrical geometry are approximately solved analytically. The approximation is valid if the pulse duration of the beam is intermediate between two characteristic relaxation times of the medium, viz. the momentum relaxation time and the magnetic diffusion time. This condition is well satisfied in present experiments which use picosecond or subpicosecond laser pulses to generate the electron beam. The theory allows one to calculate the spatial and temporal profiles of the return current and the radial current induced in the conductor, as well as that of the azimuthal magnetic field of the combined beam and return currents. This application of the theory is illustrated by way of example. The theory is applicable to a solid conductor as well as to a dense high-temperature plasma and may be useful in research relating to the fast-ignitor scheme and for clarifying features of recent experiments with femtosecond laser pulses.
Fabrication of arrays of two-dimensional micropatterns using microspheres as lenses for projection photolithography
Authors: Wu Ming-Hsien , Whitesides George M.
Published: July 2002

This letter demonstrates the use of an array of transparent microspheres in forming repetitive, micrometer-scale patterns in photoresist, starting from masks with centimeter-scale patterns. A transparent microsphere with diameter d>1.5 μm acts as a lens and reduces centimeter-scale images into micrometer-scale images on its image plane. A planar array of microspheres projects the image of an illuminated mask onto a corresponding array of micropatterns on their common image plane. We have prepared arrays of polystyrene microspheres (d=1.5–10 μm) embedded in a transparent membrane to generate repetitive patterns in photoresist, and have transferred the resulting patterns into metal films by liftoff. The optical system of this technique is related to that used in conventional projection photolithography, but differs in that the lens that accomplishes size reduction is positioned within 10 μm of the photoresist. The microspheres generate uniform patterns over an area of ∼2 cm2, using a mask with area ∼25×25 cm2 illuminated with a white light source. This method can generate submicron features either within a micropattern or between neighboring patterns.
Polarization-resolved linewidth-power product of a vertical-cavity semiconductor laser
Authors: Willemsen M. B. , van de Nes A. S. , van Exter M. P. , Woerdman J. P. , Kicherer M. , King R. , Jäger R. , Ebeling K. J.
Published: July 2002

We have studied the linewidth around threshold of the lasing and nonlasing polarization mode (x and y) in a TEM00 oxide-confined vertical-cavity semiconductor laser (VCSEL). We experimentally demonstrate: (i) that the nonlasing mode shows surprising behavior when the lasing mode passes through threshold, and (ii) that the polarization fluctuations in a VCSEL are limited by the same quantum noise that sets its finite Schawlow–Townes linewidth.
Many-particle effects in type II quantum dots
Authors: Müller-Kirsch L. , Heitz R. , Schliwa A. , Stier O. , Bimberg D. , Kirmse H. , Neumann W.
Published: July 2002

Many-particle effects are investigated in the photoluminescence of type II GaSb/GaAs quantum dots (QDs). With increasing excitation density, i.e., exciton occupation, the photoluminescence shows first a blueshift and then saturates developing a plateau region. The peculiar behavior is attributed to Coulomb charging and state filling of the localized holes to dominate the many-particle regime. A high temperature stability makes the GaSb/GaAs QDs suitable for room-temperature devices.
Angular effect in laser removal of spherical silica particles from silicon wafers
Authors: Zheng Y. W. , Lu Y. F. , Song W. D.
Published: July 2002

In this study, laser cleaning efficiencies to remove 2.5 μm particles have been investigated with different incident angles ranging from 0° to 60°. It is found that when the laser light irradiated normally to the substrate surface, the particle could be removed most efficiently. In this direction, the cleaning efficiency was also most sensitive to the light intensity. A sharp drop of cleaning efficiency occurred with a small change of the incident angle. Theoretical calculations based on the Lorentz–Mie theory and an accurate solution of the boundary problem, indicate that the light intensity near the contacting point is sensitive to the incident angle even though the incident light is uniform.
Forces between polystyrene surfaces in water–electrolyte solutions: Long-range attraction of two types?
Authors: Vinogradova Olga I. , Yakubov Gleb E. , Butt Hans-Jürgen
Published: July 2002

A great deal of effort has recently been focused on the experimental studies of the phenomenon of long-ranged attraction between identically charged colloidal (polystyrene) particles immersed in an electrolyte. The theoretical validation suggested the need for revision of the existing and established colloidal theories assuming the observed attraction is of electrostatic origin. We, however, demonstrate that for a number of reasons (first of all hydrophobicity and roughness of particles) the Derjaguin–Landau–Verwey–Overbeek (DLVO) behavior should not be expected for polystyrene surfaces. Indeed, the force measurements with an atomic force microscope-related set-up suggest that even within one pair of the interacting surfaces, attractive interaction of various types can be observed. There is usually a difference between the first approach and the later ones. The first approach is characterized by a short-range jump into a contact. Depending on conditions (electrolyte concentration, previous contacts of surfaces, etc.) there exists a late attraction of two types between polystyrene surfaces. The force of the first type is characterized by an abrupt jump from the maximum of a repulsive force, which is typically of longer-range than on the first approach. This is most likely due to submicroscopic bubbles trapped and/or formed due to previous contacts (and separation) of the surfaces. The attraction of the second type is weak and exponentially decaying.
Infrared technique for measuring thickness of a flowing soap film
Authors: Wu X. L. , Levine R. , Rutgers M. , Kellay H. , Goldburg W. I.
Published: July 2002

In conducting two-dimensional laminar and turbulence experiments, use of a vertical flowing soap film is often a good choice. However, one of the most frequently encountered and yet highly nontrivial problems is to measure the thickness of the film precisely. We propose a solution to this problem based on the strong absorbtion of infrared light by the water molecules in the film. At λ≃3 μm, a thin sheet of water is essentially opaque. The extinction length of 0.9 μm serves as a precise ruler for gauging the film thickness. Although only the time-averaged, single-point measurements are presented, the technique is general and can be used for multipoint measurements to investigate turbulent driven spatiotemporal fluctuations of the film thickness.
Non-Lorentzian zero-phonon holes and new insights on nonphotochemical hole burning: Al-phthalocyanine in hyperquenched glassy water
Authors: Reinot T. , Small G. J.
Published: July 2002

Zero-phonon hole (ZPH) profiles and hole spectra that span about eight decades of burn fluence are reported for Al-phthalocyanine tetrasulphonate in hyperquenched glassy water (HGW) films at 5.0 K. The profiles of unsaturated zero-phonon holes (low burn fluence stage) are more sharply tipped than a Lorentzian. It is shown that the non-Lorentzian behavior is a natural consequence of the interplay between the three distributions that govern the dispersive kinetics of nonphotochemical hole growth. They are denoted by λ, α, and ω, where λ is the tunnel parameter associated with nonphotochemical hole burning (NPHB) and α is the angle between the transition dipole and the laser polarization. The ω distribution stems from off-resonant absorption of the zero-phonon line (ZPL). The single site absorption spectrum used in the calculations included the ZPL and the phonon sideband. The contribution of a distribution of homogeneous ZPL widths to the non-Lorentzian behavior was assessed and found to be negligible compared to that of the above distributions. The burn fluence dependence of the hole spectra, which include the ZPH, phonon sideband, and antihole structures, leads to new insights on the mechanism of NPHB, ones that necessitate modification of the Shu–Small mechanism [L. Shu and G. J. Small, J. Opt. Soc. Am. B 9, 724 (1992)]. Although that mechanism recognizes the importance of coupling between the intrinsic and extrinsic two-level systems (TLSint,TLSext) of the chromophore/glass system and diffusion of excess free volume triggered by optical excitation, it does not adequately account for the effects of multiple excitations of redshifted (relative to the burn frequency ωB) preburn and antihole sites. The results show that multiple excitations ultimately lead to the entire antihole being blueshifted. A “second channel” of hole burning becomes apparent at sufficiently high burn fluences. A model for this channel based on a distribution of extrinsic multilevel systems is proposed.
Influence of isotopic substitution on the conformational dynamics of frozen proteins
Authors: Schlichter J. , Friedrich J. , Parbel M. , Scheer H.
Published: July 2002

The spectral diffusion dynamics was measured over 3 orders of magnitude in time of a myoglobin-type protein with the heme group substituted by Zn-pheophorbid a. After burning a photochemical hole at 4.2 K, the width of the spectral diffusion kernel is well described by a power law in waiting time with an exponent of 0.24. Spectral diffusion broadening is subject to “aging,” viz., to the equilibration time at 4.2 K before hole burning. It decays with a power law in aging time. Deuteration of the solvent has a significant effect on the dynamics of the protein. Spectral diffusion broadening is smaller in the deuterated sample, however, the respective power law is not changed. The aging dynamics, on the other hand, does not seem to be influenced significantly by deuteration. The conclusion is that deuteration influences the fluctuations but not the relaxation. In addition to spectral diffusion, we also measured the recovery dynamics of the hole. It is slowed down tremendously by deuteration, confirming that the photoreaction is based on a light-induced proton transfer.
Electron beam-induced carbon masking for electrodeposition on semiconductor surfaces
Authors: Djenizian T. , Santinacci L. , Schmuki P.
Published: July 2002

Carbon patterns were deposited on Si(100) by electron beam-induced contamination decomposition. The feasibility of using such patterns as a mask for a subsequent electrochemical deposition of Au is studied. We demonstrate that under optimized electrochemical conditions electrodeposition of Au can be blocked selectively by single line carbon deposits in the order of only 1 nm thickness. The lateral resolution of this negative patterning process is in the sub 100 nm range. The principle opens perspectives for high definition patterning of semiconductor surfaces by selective electrodeposition.
Chaos and the limits of predictability for the solar-wind-driven magnetosphere–ionosphere system
Authors: Horton W. , Weigel R. S. , Sprott J. C.
Published: July 2002

The solar-wind-driven magnetosphere–ionosphere exhibits a variety of dynamical states including low-level steady plasma convection, episodic releases of geotail stored plasma energy into the ionospheric known broadly as substorms, and states of continuous strong unloading. The WINDMI model [J. P. Smith et al., J. Geophys. Res. 105, 12 983 (2000)] is a six-dimensional substorm model that uses a set of ordinary differential equations to describe the energy flow through the solar wind–magnetosphere–ionosphere system. This model has six major energy components, with conservation of energy and charge described by the coupling coefficients. The six-dimensional model is investigated by introducing reductions to derive a new minimal three-dimensional model for deterministic chaos. The reduced model is of the class of chaotic equations studied earlier [J. C. Sprott, Am. J. Phys. 68, 758 (2000)]. The bifurcation diagram remains similar, and the limited prediction time, which is in the range of three to five hours, occurs in the chaotic regime for both models. Determining all three Lyapunov exponents for the three-dimensional model allows one to determine the dimension of the chaotic attractor for the system.
Capture cross sections of the acceptor level of iron–boron pairs in p-type silicon by injection-level dependent lifetime measurements
Authors: Macdonald Daniel , Cuevas Andrés , Wong-Leung Jennifer
Published: July 2002

Injection-level dependent recombination lifetime measurements of iron-diffused, boron-doped silicon wafers of different resistivities are used to determine the electron and hole capture cross sections of the acceptor level of iron–boron pairs in silicon. The relative populations of iron–boron pairs and interstitial iron were varied by exposing the samples to different levels of illumination prior to lifetime measurements. The components of the effective lifetime due to interstitial iron and iron–boron pairs were then modeled with Shockley–Read–Hall statistics. By forcing the sum of the modeled iron–boron and interstitial iron concentrations to equal the implanted iron dose, in conjunction with the strong dependence of the shape of the lifetime curves on dopant density, the electron and hole capture cross sections of the acceptor level of iron–boron pairs have been determined as (3±2)×10−14 cm−2 and (2±1)×10−15 cm−2.
Metalorganic chemical vapor deposition of GaN on Si(111): Stress control and application to field-effect transistors
Authors: Marchand H. , Zhao L. , Zhang N. , Moran B. , Coffie R. , Mishra U. K. , Speck J. S. , DenBaars S. P. , Freitas J. A.
Published: July 2002

Two schemes of nucleation and growth of gallium nitride on Si(111) substrates are investigated and the structural and electrical properties of the resulting films are reported. Gallium nitride films grown using a 10–500 nm-thick AlN buffer layer deposited at high temperature (∼1050 °C) are found to be under 260–530 MPa of tensile stress and exhibit cracking, the origin of which is discussed. The threading dislocation density in these films increases with increasing AlN thickness, covering a range of 1.1 to >5.8×109 cm−2. Films grown using a thick, AlN-to-GaN graded buffer layer are found to be under compressive stress and are completely crack free. Heterojunction field effect transistors fabricated on such films result in well-defined saturation and pinch-off behavior with a saturated current of ∼525 mA/mm and a transconductance of ∼100 mS/mm in dc operation.
A theoretical study of spectroscopy and predissociation dynamics in nitrosoalkanes
Authors: Toniolo Alessandro , Persico Maurizio
Published: July 2002

We have computed ab initio transition energies, equilibrium geometries, force constants and potential energy curves for the dissociation of S0, T1, and S1 of two nitrosoalkanes, CH3NO and t-BuNO. A normal coordinate analysis has been performed for the three states, and the harmonic wave function for the C–N bond torsional coordinate has been replaced by hindered rotor eigenfunctions. The n→π* absorption spectra have been simulated by computing the appropriate Franck–Condon factors in order to assign the vibrational sub-bands. The predissociation lifetimes of several vibrational states of S1 have been evaluated by computing nonadiabatic and spin-orbit couplings, which determine the Internal Conversion and Intersystem Crossing rates. For t-BuNO the computed lifetimes (10–160 ns) are in the same range as those measured by Noble et al. [J. Chem. Phys. 85, 5763 (1986)]. The lifetimes of CH3NO, for which no experimental data are available, are longer (50–330 ns). Both the IC to S0 and the ISC to T1 are important.
Effects of temperature on the nonlinear response function for two-dimensional vibrational spectroscopy
Authors: Sung Jaeyoung , Silbey Robert J. , Cho Minhaeng
Published: July 2002

We investigate the effects of temperature on the nonlinear response functions associated with various two-dimensional vibrational spectroscopies. It turns out that the system–bath interaction plays an important role in determining the nature of the temperature-dependencies of the nonlinear response functions and spectra of the two-dimensional vibrational spectroscopy. For a model Hamiltonian, we present exact quantum-mechanical expressions for the nonlinear response functions of two-dimensional vibrational spectroscopies in both the time and frequency domains.
Linear interaction of a cylindrical entropy spot with a shock
Authors: Fabre David , Jacquin Laurent , Sesterhenn Jörn
Published: July 2002

The interaction of a cylindrical element of hot or cold gas (the “entropy spot”) with a shock wave is considered. An exact solution in the limit of weak spot amplitudes is elaborated, using the linear interaction analysis theory and the procedure of decomposition proposed by Ribner (Technical Report No. 1164, NACA, 1953). The method is applied to an entropy spot with a Gaussian profile. Results are presented for a wide range of shock Mach numbers, with a special interest at M1=2. The resulting vorticity field consists of a pair of primary counter-rotating vortices, as well as a pair of secondary vortices of opposite sign and weaker amplitude. An expression for the circulation in half a plane is derived and compared to existing results. The pressure field consists of a cylindrical acoustic wave which propagates away from the transmitted spot and an evanescent nonpropagative field confined behind the shock. For a hot spot, the cylindrical wave is a rarefaction wave on its forward front and a compression wave on its upstream propagating parts, and the nonpropagative field corresponds to a pressure deficit. The structure of the transmitted spot and the shock deformation are also discussed. The linear solution is compared with numerical simulation results for M1=2 and M1=4. The comparison shows qualitative and quantitative agreement when linear as well as nonlinear spot amplitudes are considered. Finally, the method is applied to the case of a constant spot with a tophat profile, and the results are compared to the case of a Gaussian spot. This paper also contains in the Appendix a general formulation of the linear interaction problem for the three kinds of plane waves (entropy, vorticity, and pressure waves) impinging upon a shock.
The accuracy of atomization energies from explicitly correlated coupled-cluster calculations
Authors: Noga Jozef , Valiron Pierre , Klopper Wim
Published: July 2002

The accuracy of atomization energies obtained from explicitly correlated coupled-cluster R12 calculations (CC-R12)—including single and double excitation operators (CCSD-R12) and a posteriori perturbative corrections for triple excitations [CCSD[T]-R12 and CCSD(T)-R12]—is studied for CH2(1A1), NH3, H2O, HF, N2, CO, and F2. The basis-set convergence with functions of high angular momentum is demonstrated. Unlike for conventional calculations, already the spdf saturation on nonhydrogen atoms and spd saturation on hydrogen are sufficient for CC-R12 calculations to provide results accurate to within 1 kJ/mol of the limit of a complete basis. Remaining small uncertainties at the CCSD[T]-R12 or CCSD(T)-R12 levels are attributed to the insufficient convergence within the coupled-cluster hierarchy towards the limit of full configuration interaction. It is shown that near the basis-set limit (as provided by CC-R12 calculations) the CCSD[T] variant of the triples correction gives, on average, results closer to the experimental data than its CCSD(T) counterpart. Approximate error bars are estimated by one single CC-R12 calculation from the difference between the CCSD[T] and CCSD(T) methods and from the second-order electronic cusp correction in standard approximation B.
Measurement of the VIRGO superattenuator performance for seismic noise suppression
Authors: Ballardin G. , Bracci L. , Braccini S. , Bradaschia C. , Casciano C. , Calamai G. , Cavalieri R. , Cecchi R. , Cella G. , Cuoco E. , D’Ambrosio E. , Dattilo V. , Di Virgilio A. , Fabbroni L. , Fidecaro F. , Frasconi F. , Gaddi A. , Gennai A. , Gennaro G. , Giazotto A. , Losurdo G. , Holloway L. , La Penna P. , Lelli F. , Majorana E. , Mazzoni M. , Paoletti F. , Pasotti M. , Pasqualetti A. , Passaquieti R. , Passuello D. , Poggiani R. , Puppo P. , Raffaelli F. , Rapagnani P. , Ricci F. , Ruggi P. , Stanga R. , Taddei R. , Vetrano F. , Vicerè A. , Zhang Z.
Published: July 2002

Below a few tens of hertz interferometric detection of gravitational waves is masked by seismic vibrations of the optical components. In order to isolate the mirrors of the VIRGO interferometer, a sophisticated suspension system, called superattenuator, has been developed. Its working principle is based on a multistage pendulum acting on seismic vibrations as a chain of second order mechanical low-pass filters. A complete superattenuator has been built and tested. This apparatus allows extending the VIRGO detection band down to a few Hz. A detailed description of the attenuation system and its performance are presented in this article.
Ultralow-k dielectrics prepared by plasma-enhanced chemical vapor deposition
Authors: Grill A. , Patel V.
Published: July 2002

Carbon-doped oxide materials (SiCOH films) with ultralow dielectric constants have been prepared by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials. The films have been characterized by Rutherford backscattering and forward recoil elastic scattering analysis, Fourier transform infrared spectroscopy and index of refraction measurements, and measurement of step heights in the films. The electrical properties of the films have been measured on metal–insulator–silicon structures. By proper choice of the precursor and deposition conditions, the dielectric constants of the SiCOH films can be reduced to values below 2.1, demonstrating the extendibility of PECVD-prepared carbon-doped oxides as the interconnect dielectrics for future generation of very large scale integrated chips.
Green luminescent center in undoped zinc oxide films deposited on silicon substrates
Authors: Lin Bixia , Fu Zhuxi , Jia Yunbo
Published: July 2002

The photoluminescence (PL) spectra of the undoped ZnO films deposited on Si substrates by dc reactive sputtering have been studied. There are two emission peaks, centered at 3.18 eV (UV) and 2.38 eV (green). The variation of these peak intensities and that of the I–V properties of the ZnO/Si heterojunctions were investigated at different annealing temperatures and atmospheres. The defect levels in ZnO films were also calculated using the method of full-potential linear muffin-tin orbital. It is concluded that the green emission corresponds to the local level composed by oxide antisite defect OZn rather than oxygen vacancy VO, zinc vacancy VZn, interstitial zinc Zni, and interstitial oxygen Oi.
Lattice sums and their phase diagram implications for the classical Lennard-Jones model
Authors: Stillinger Frank H.
Published: July 2002

High-accuracy lattice sums have been evaluated for the Lennard-Jones 12-6 pair potential, without cutoffs, in the close-packed fcc and hcp lattices. The results confirm the small relative stability of hcp at low pressure, and locate precisely the first-order phase transition at zero temperature to the fcc structure. The reduced pressure pσ3/ε at this transition is approximately 878.476… , with both structures having been compressed to about one-half of their zero-pressure volumes. On account of its lower symmetry compared to fcc, the hcp lattice spontaneously distorts from the ideal close-packed geometry to lower its energy by a tiny amount. For low compressions, this distortion involves expansion within close-packed planes, and shrinkage in the perpendicular stacking direction. However this spontaneous distortion changes sign shortly before reaching the compression required for the hcp–fcc phase transition, vanishing at a volume ratio (compared to zero pressure) of about 0.537.
Beyond Navier–Stokes: Burnett equations for flows in the continuum–transition regime
Authors: Agarwal Ramesh K. , Yun Keon-Young , Balakrishnan Ramesh
Published: July 2002

In hypersonic flows about space vehicles in low earth orbits or flows in microchannels of microelectromechanical devices, the local Knudsen number lies in the continuum–transition regime. Navier–Stokes equations are not adequate to model these flows since they are based on small deviation from local thermodynamic equilibrium. To model these flows, a number of extended hydrodynamics or generalized hydrodynamics models have been proposed over the past fifty years, along with the direct simulation Monte Carlo (DSMC) approach. One of these models is the Burnett equations which are obtained from the Chapman–Enskog expansion of the Boltzmann equation [with Knudsen number (Kn) as a small parameter] to O(Kn2). With the currently available computing power, it has been possible in recent years to numerically solve the Burnett equations. However, attempts at solving the Burnett equations have uncovered many physical and numerical difficulties with the Burnett model. As a result, several improvements to the conventional Burnett equations have been proposed in recent years to address both the physical and numerical issues; two of the most well known are the “augmented Burnett equations” and the “BGK–Burnett equations.” This paper traces the history of the Burnett model and describes some of the recent developments. The relationship between the Burnett equations and the Grad’s 13 moment equations is elucidated by employing the Maxwell–Truesdell–Green iteration. Numerical solutions are provided to assess the accuracy and applicability of Burnett equations for modeling flows in the continuum–transition regime. The important issue of surface boundary conditions is addressed. Computations are compared with the available experimental data, Navier–Stokes calculations, Burnett solutions of other investigators, and DSMC solutions as much as possible.
Shear-Alfvén waves in gyrokinetic plasmas
Authors: Lee W. W. , Lewandowski J. L. V. , Hahm T. S. , Lin Z.
Published: July 2002

It is found that the thermal fluctuation level of the shear-Alfvén waves in a gyrokinetic plasma is dependent on plasma β(≡cs2/vA2), where cs is the ion acoustic speed and vA is the Alfvén velocity. This unique thermodynamic property based on the fluctuation–dissipation theorem is verified in this paper using a new gyrokinetic particle simulation scheme, which splits the particle distribution function into the equilibrium part as well as the adiabatic and nonadiabatic parts. The numerical implication of this property is discussed.
Fabrication of three-dimensional microstructures by soft molding
Authors: Kim Y. S. , Suh K. Y. , Lee Hong H.
Published: July 2002

We have developed soft molding as a method for meso-scale-area fabrication of three-dimensional structures. The soft molding, which is a form of soft lithography, involves placing an elastomeric mold on the surface of a spin-coated polymer film with a slight pressure (<1 N/cm2), allowing the mold to absorb solvent, releasing the pressure, and then letting the mold and the substrate remain undisturbed for a period of time. The three-dimensional structure thus formed is robust in that the pattern fidelity is preserved without any distortion or defects. For the soft molding to be successful, the rate of solvent absorption by the mold should be larger than the rate of solvent evaporation. The method is demonstrated with several three-dimensional structures.
Free volume study of amorphous polymers detected by solid-state C13 NMR linewidth experiments
Authors: Asano Atsushi , Takegoshi K.
Published: July 2002

Temperature dependence of solid-state C13 nuclear magnetic resonance linewidths of six different amorphous polymers was examined around their glass-transition temperatures (Tg) under the conditions of magic-angle spinning and high-power proton dipolar decoupling (DD). The observed temperature dependence was explained by motional averaging over a dispersion of isotropic chemical shifts and an interference between local anisotropic motion and DD. On the assumption that the correlation time of the local anisotropic motion follows the Williams–Landel–Ferry equation, we found that the reference temperature approximately equals Tg+5 K. From this reference temperature, the fractional free volume of amorphous polymers at Tg is estimated to be 4.7%, which is much larger than that obtained from rheological experiments (2.5%). The difference is attributed to differences in the amplitude of motions detected by both measurements.
The effect of conjugation length on triplet energies, electron delocalization and electron–electron correlation in soluble polythiophenes
Authors: Monkman A. P. , Burrows H. D. , Hamblett I. , Navarathnam S. , Svensson M. , Andersson M. R.
Published: July 2002

Triplet energies from a family of polythiophenes in which effective conjugation length is controlled by steric torsion have been measured for the isolated polymer chain regime, i.e., benzene solution. Triplet states are stabilized by some 0.6 eV as effective conjugation length increases up to ca. 6 repeat units, then saturation occurs. This triplet stabilization must occur by electron delocalization and implies that singlet states are stabilized as conjugation length increases by a combination of electron and exciton delocalization.
Four wave mixing spectroscopy for a multilevel system
Authors: Sung Jaeyoung , Silbey Robert J.
Published: July 2002

We present a theory of the four-wave-mixing (FWM) spectroscopy for the multilevel system coupled to the bath with arbitrary time scale, in contrast to most previous work that assumes the fast bath dynamic limit (motionally narrowed limit). Exact quantum mechanical expressions for the relevant nonlinear response tensor and the nonlinear polarization vector are obtained for a model Hamiltonian. Effects of molecular rotation and the polarization directions of the input radiation fields are also fully taken into account. The results show how the cross correlation as well as the autocorrelation functions of the fluctuations in the energy-gaps or transition frequencies between eigenstates contribute to the FWM spectroscopy. The result is applied to three-pulse echo spectroscopy. We examine the results for a variety of model spectral density functions, and recover the results of the previously reported theories as limiting cases.
Guiding center particle simulation of wide-orbit neoclassical transport
Authors: Bergmann A. , Peeters A. G. , Pinches S. D.
Published: July 2002

The neoclassical ion transport in a tokamak plasma with circular cross section is studied with guiding center particle simulations. A Monte Carlo model of pitch-angle scattering which includes momentum conservation is employed. The model includes the whole plasma inside closed flux surfaces, but the focus is on the near-axis transport due to particles with wide orbits which lead to a different heat flux than in the standard theory. Neither of two recent theories of banana regime transport near the axis is confirmed by the simulations, nor do the numerical results for the plateau regime agree with a recent theory of wide-orbit transport in this regime.
Lateral composition modulation in AlAs/InAs and GaAs/InAs short period superlattices structures: The role of surface segregation
Authors: Dorin C. , Mirecki Millunchick J.
Published: July 2002

The effect of In surface segregation on the microstructure of short period superlattices (SPSs) in two different material systems with nominally equivalent lattice misfit, AlAs/InAs and GaAs/InAs, has been investigated and compared. It was found that the quality of the SPSs and the appearance of lateral composition modulation are remarkably different in these two systems. For AlAs/InAs SPSs grown at temperatures of T=500 °C, uniform structures devoid of lateral composition modulation were obtained. Samples grown at T>500 °C exhibit lateral composition modulation. Uniform and homogeneous SPS structures were not obtained in the GaAs/InAs structures over the entire temperature range examined in this study (475 °C⩽T⩽510 °C). Instead, lateral composition modulation with varying degrees of regularity was always observed. It was found that In segregation and roughening determine the microstructure. A kinetic exchange model predicts that at an optimum temperature the SPS layers are more intermixed for the AlAs/InAs SPSs. Thus, the lattice mismatch is lower and the driving force for roughening is reduced, resulting in uniform SPS structures. Growing the structure away from the optimum temperature for smooth growth may induce roughening-driven composition modulation. The GaAs/InAs structures are less intermixed over the temperatures studied, which results in higher mismatch between the individual layers and a higher driving force for roughening and lateral composition modulation.
Fiber optic diagnostic techniques applied to electrical discharge machining sparks
Authors: Pillans B. W. , Evensen M. H. , Taylor H. F. , Eubank P. T. , Ma Lianxi
Published: July 2002

Plasma sparks from an electrical discharge machining (EDM) process were observed using fiber optics positioned in the dielectric oil. Measurement techniques were developed to observe the spark in the extremely noisy environment. Optical data were used along with current pulse wave forms from the EDM machine to study the temporal characteristics of the spark in both the pulse time and the pause time. During the pause time, extinction of the sparks was longer than previously thought—perhaps due to the remaining infrared radiation after the collapse of the spark. Further, an optical pattern was identified that indicated in advance when an arc was being formed instead of a spark. Spectral data of the plasma spark was obtained by using a scanning grating spectrometer in conjunction with crosscorrelation to maximize the signal-to-noise ratio. Average spark temperatures from the spectral data were found to be significantly higher than those previously predicted from energy balances. The results showed a shift in the optical spectra to longer wavelengths during the spark, showing that the spark temperature decreased with time.