bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission loss predictions for dissipative silencers of arbitrary cross section in the presence of mean flow
Authors: Kirby Ray
Published: July 2003

A numerical technique is developed for the analysis of dissipative silencers of arbitrary, but axially uniform, cross section. Mean gas flow is included in a central airway that is separated from a bulk reacting porous material by a concentric perforate screen. The analysis begins by employing the finite element method to extract the eigenvalues and associated eigenvectors for a silencer of infinite length. Point collocation is then used to match the expanded acoustic pressure and velocity fields in the silencer chamber to those in the inlet and outlet pipes. Transmission loss predictions are compared with experimental measurements taken for two automotive dissipative silencers with elliptical cross sections. Good agreement between prediction and experiment is observed both without mean flow and for a mean flow Mach number of 0.15. It is demonstrated also that the technique presented offers a considerable reduction in the computational expenditure when compared to a three-dimensional finite element analysis.
Representation of the voice onset time (VOT) speech parameter in population responses within primary auditory cortex of the awake monkey
Authors: Steinschneider Mitchell , Fishman Yonatan I. , Arezzo Joseph C.
Published: July 2003

Voice onset time (VOT) signifies the interval between consonant onset and the start of rhythmic vocal-cord vibrations. Differential perception of consonants such as /d/ and /t/ is categorical in American English, with the boundary generally lying at a VOT of 20–40 ms. This study tests whether previously identified response patterns that differentially reflect VOT are maintained in large-scale population activity within primary auditory cortex (A1) of the awake monkey. Multiunit activity and current source density patterns evoked by the syllables /da/ and /ta/ with variable VOTs are examined. Neural representation is determined by the tonotopic organization. Differential response patterns are restricted to lower best-frequency regions. Response peaks time-locked to both consonant and voicing onsets are observed for syllables with a 40- and 60-ms VOT, whereas syllables with a 0- and 20-ms VOT evoke a single response time-locked only to consonant onset. Duration of aspiration noise is represented in higher best-frequency regions. Representation of VOT and aspiration noise in discrete tonotopic areas of A1 suggest that integration of these phonetic cues occurs in secondary areas of auditory cortex. Findings are consistent with the evolving concept that complex stimuli are encoded by synchronized activity in large-scale neuronal ensembles.
Robust time reversal focusing in the ocean
Authors: Kim Seongil , Kuperman W. A. , Hodgkiss W. S. , Song H. C. , Edelmann G. F. , Akal T.
Published: July 2003

Recent time-reversal experiments with high-frequency transmissions (3.5 kHz) show that stable focusing is severely limited by the time-dependent ocean environments. The vertical focal structure displays dynamic variations associated with focal splitting and remerging resulting in large changes in focal intensity. Numerical simulations verify that the intensity variation is linked to the focal shift induced by phase changes in acoustic waves resulting from sound speed fluctuations due to internal waves. A relationship between focal range shift, frequency shift, or channel depth changes is illustrated using waveguide-invariant theory. Based on the analysis of experimental data and numerical simulations, methods for robust time-reversal focusing are developed to extend the period of stable focusing.
Adaptive plasticity of loudness induced by chronic attenuation and enhancement of the acoustic background (L)
Authors: Formby C. , Sherlock L. P. , Gold S. L.
Published: July 2003

Strategies for treating hyperacusis, an anomolous condition of loudness perception, paradoxically seek either to minimize or enhance listeners’ sound exposures. We show that these reciprocal treatment approaches, implemented with similar amounts of background sound attenuation and enhancement, produce diametrically opposite perceptual effects in normal listeners. Specifically, we show after continuous, 2-week earplugging and low-level noise treatments that listeners become more and less sensitive, respectively, to the loudness of sounds. This simple demonstration of adaptive plasticity is consistent with modification of a theoretical gain control process, which is the basis for desensitizing sound therapies used in treating hyperacusis and related sound tolerance problems.
Dichotic speech recognition in noise using reduced spectral cues
Authors: Loizou Philipos C. , Mani Arunvijay , Dorman Michael F.
Published: July 2003

It is generally accepted that the fusion of two speech signals presented dichotically is affected by the relative onset time. This study investigated the hypothesis that spectral resolution might be an additional factor influencing spectral fusion when the spectral information is split and presented dichotically to the two ears. To produce speech with varying degrees of spectral resolution, speech materials embedded in +5 dB S/N speech-shaped noise were processed through 6–12 channels and synthesized as a sum of sine waves. Two different methods of splitting the spectral information were investigated. In the first method, the odd-index channels were presented to one ear and the even-index channels to the other ear. In the second method the lower frequency channels were presented to one ear and the high-frequency channels to the other ear. Results indicated that spectral resolution did affect spectral fusion, and the effect differed across speech materials, with the sentences being affected the most. Sentences, processed through six or eight channels and presented dichotically in the low–high frequency condition were not fused as accurately as when presented monaurally. Sentences presented dichotically in the odd–even frequency condition were identified more accurately than when presented in the low–high condition.
Intraspecific and geographic variation of West Indian manatee (Trichechus manatus spp.) vocalizations (L)
Authors: Nowacek Douglas P. , Casper Brandon M. , Wells Randall S. , Nowacek Stephanie M. , Mann David A.
Published: July 2003

Recordings of manatee (Trichechus manatus spp.) vocalizations were made in Florida and Belize to quantify both intraspecific and geographic variation. Manatee vocalizations were relatively stereotypical in that they were short tonal harmonic complexes with small frequency modulations at the beginning and end. Vocalizations ranged from almost pure tones to broader-band tones that had a raspy quality. The loudest frequency was typically the second or third harmonic, with average received levels of the peak frequency of about 100 dB re 1 μPa. Signal parameters measured from these calls showed the manatees from Belize and Florida have overlapping distributions of sound duration, peak frequency, harmonic spacing, and signal intensity, indicating no obvious distinguishing characteristics between these isolated populations.
Broadband sonar considerations for small underwater vehicle applications
Authors: Benjamin Kim C.
Published: July 2003

As underwater vehicles become more prevalent, so too does the design and integration of compact broadband sonar arrays. Rather than rely on conventional tonpilz technology, where the bandwidth is governed by the width of the transducer’s mechanical resonance, designers must consider other transducer technologies that are better suited to small vehicle packaging constraints. These constraints include operational ruggedness, light weight, conformability, and low cost. This talk advocates the use of 1–3 piezocomposite and discusses the rationale behind such a selection. In going to a wideband material such as a 1–3 piezocomposite, with typical mechanical quality factors (Qm) around 2, the selection of where to place the resonance frequency differs from that of its tonpilz counterpart. For the tonpilz array, the sonar operational bandwidth is totally governed by the resonance response of the array element and is typically limited to approximately its 3-dB or half power points. Relaxor-based ferroelectric materials such as single crystal PMN-PT, which exhibit extremely large electromechanical coupling coefficients, cannot attain 3-dB bandwidths of a decade or more when configured in a tonpilz design. This presentation will discuss a 1–3 piezocomposite-based approach that places mechanical resonance near the upper band edge of an operational bandwidth of 1 decade (10–100 kHz).
Patterns of acoustic variance in native and non-native phonemes: The case of Japanese production of /r/ and /l/
Authors: Sato Momoko , Lotto Andrew J. , Diehl Randy L.
Published: July 2003

Acoustic measures were obtained from productions of word-initial and word-final /r/ and /l/ in different vowel contexts (/i/, /a/, and /u/) by six native English Speakers (ES) and six native Japanese Speakers (JS). JS productions of the Japanese rhotic flap were also obtained in the same vowel contexts. F1, F2, and F3 were measured at vowel midpoint, at utterance onset for word-initial stimuli, and at utterance offset for word-final stimuli. For word-initial /r/-/l/, ES productions were distinguished solely by F3, whereas JS productions varied on both F2 and F3. For the word-final contrast, ES and some JS productions showed structured variation in both F2 and F3, whereas many JS productions showed no consonant-dependent variation in these measures. F2 and F3 measures of the Japanese flap (word-initial only) substantially overlapped the /r/-/l/ distributions for ES and JS. In addition, JS productions of /r/ and /l/ and the flap showed significant effects of context vowel with coarticulatory variations in F2 and F3. In contrast, ES productions showed little context-dependent F3 variance. The results suggest that JS difficulties in producing intelligible English liquids may be due to a mismatch between the acoustic variance that is informative for similar phonemes in the two languages.
Superconductivity in Non-adiabatic Ferromagnetic Alloys
Authors: Palistrant M. E. , Kochorbe F. G.
Published: July 2003

The main equations of the theory of superconductivity in non-adiabatic systems with ferromagnetic arrangement of spins of impurity atoms are derived. The influence of non-adiabaticity on the temperature of superconducting transition TC as well as on the critical concentration of impurity is also studied. The behavior of the temperature of magnetic arrangement of spins Tk as function of concentration of impurity c in the superconducting state for the non-adiabatic systems is investigated as well. The phase diagram (T, c) is built and it is proved that the effects of non-adiabaticity favor a raise in the field with coexistence of superconductivity and ferromagnetism.
Ethylene Adsorption on Clean and Oxygen Covered Flat and Stepped Ag(001)
Authors: Vattuone L. , Savio L. , Rocca M.
Published: July 2003

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final adsorption state depends on the translational and on the internal energy of the gas-phase molecules and on the presence of defects. At low translational energy ethylene either physisorbs or very weakly chemisorbs at flat terrace sites. The physisorption probability is thereby hindered by rotational excitation. A more strongly bound, π bonded, state forms at higher translational energy, the activation barrier being related to the energy needed to form the relevant defect at which chemisorption takes place. A further even more strongly bound state forms only when dosing vibrationally excited molecules from the gas phase.
HTSC Isotope Effect with Soft Lattice Modes
Authors: Nettel Stephen
Published: July 2003

An attempt is made to understand the isotope effects measured by Zhao et al. in LaSrCuO in terms of a previous theory for high Tc superconductors, a theory based on pair coupling by soft lattice modes. In the theory, the lattice elastic energy originating with the ion-electron correlation limits the gap. Here we note that this elastic energy does not depend directly on the ionic masses. However, the mechanical lattice parameters in the neighborhood of a structural phase transition are so sensitive that the free energy of oscillation and, hence, the masses are able to have an influence. Minimization of the free energy of the solid with respect to the lattice deformation leads to an equation of state, as basis for finding the effects of the ionic mass changes. With the measured isotope effects at several values of doping as input to the calculation, we obtain, as output, very plausible results for the Fermi energy, the lattice softening, and the electron-phonon coupling constant.
Dynamics of Spin Squeezing in Coupled Two Mode Bose–Einstein Condensates
Authors: Bhattacherjee Aranyabhuti , Ranjan Vikash , Mohan Man
Published: July 2003

We examine the effect of the phase of the external light fields on the dynamics of spin fluctuations in a coupled two-component Bose–Einstein condensates. We discover that the phase of the coherent coupling between the two components to be an easily tunable experimental parameter that can conveniently manipulate the spin squeezing in our given system.
Extrinsic Semiconductor Character of a Double Strand of DNA: Holstein's Polarons as Donors and Acceptors
Authors: Iguchi Kazumoto
Published: July 2003

We study the electrical conductivity problem of DNA, applying the Holstein's polaron model to a double strand of DNA. We show that the Holstein's polarons act as donors and acceptors in DNA and that the existence of such donors and acceptors provides us the extrinsic semiconductor character of DNA. This character of DNA may explain with a unified point of view almost all the known results recently obtained by experiments in the study of conductivity problems of DNA, which seem so controversial so far.
Crossover Characterization of the Spectral Statistics in Fractal-Based Complexes with Random Magnetic Fields
Authors: Ugajin Ryuichi
Published: July 2003

A crossover distribution specified by two parameters (ω, η) is introduced to describe the transition of spectral statistics from Poissonian to the Gaussian unitary ensemble. During the transition, appropriate values of (ω, η) will move along a route from (0,0) to (1,1) in the (ω, η) plane. This difference between the route of a nerve-cell-like fractal-based complex and that of a nebula-like fractal-based complex elicits different spectral behaviors during the Anderson transition in these fractal-based complexes with random magnetic fields.
Magnetic and Transport Properties Ru1 - xSbxSr2(Sm0.7Ce0.3)2Cu2O10 - δ Compounds
Authors: Yang T. R. , Toma V. , Furdui O. , Ilonca G.
Published: July 2003

We have investigated the effect of the partial substitution of Sb for Ru in Ru 1 - x Sb x Sr 2( Sm 0.7 Ce 0.3)2 Cu 2 O 10 - δ, (Ru:1222) prepared by conventional solid state reaction method, using X-ray diffraction analysis, electrical resistivity and DC-magnetic susceptibility measurements. Sb doping reduces the conductivity of the system and the onset superconducting transition temperature decreases from 42 K for x = 0 to 21 K for x = 0.06. This maybe due to a distortion of RuO6 octahedral, which is responsible of the increase in hole localization. The corresponding magnetic moment in the investigated samples is about 0.1 μB for Ru. Furthermore we discuss the influence of phase composition on superconducting and magnetic order.
Two-Gap Superconductivity in MgB2
Authors: Ghosh Angsula
Published: July 2003

We study the superconductivity in MgB2 using a tight binding model to investigate the doping dependence of the order parameter and the critical temperature. We consider both the anisotropic and the isotropic s-wave pairing to study the coexistence of the two gaps. A good agreement between the existing experiments and our theoretical curves is observed. The temperature dependence of order parameter, specific heat and penetration depth at half filling are also demonstrated and are found to be in accord with the available experimental predictions.
Uniqueness of the Solution to a Difference-Partial Differential Equation for Finance
Authors: Mancini C.
Published: July 2003

In this paper we study a difference partial differential equation, arising from a financial model, whose solution represents the price of a security linked to a dividend-paying stock. The market model consists of a jump-diffusion process modelling the stock evolution and an independent diffusion modelling the stochastic spot interest rate. We establish the desirable property of the uniqueness of solution to the equation and, since the specialized model is complete, we can consistently price any contingent claim.
Convection Systems with Stiff Source Terms
Authors: Lorin E. , Seignole V.
Published: July 2003

The aim of this paper is the numerical treatment of some convection systems with stiff relaxation source-terms. We will first define the notion of stiffness for such systems and will select some prototypical and physical problems. We will introduce a new numerical method in order to solve accurately this type of systems. Numerical comparisons will be performed on the evoked problems.
Gravity-Driven Rapid Shear Flows of Dry Granular Masses in Helically Curved and Twisted Channels
Authors: Pudasaini Shiva P. , Eckart Winfried , Hutter Kolumban
Published: July 2003

In this paper we present a two-dimensional depth-integrated theory for the gravity-driven free surface flow of a granular avalanche over a helicoidal topography which is an important extension of the original Savage & Hutter theory. In contrast to other previous extensions, this local coordinate system is based on a generating curve with curvature and torsion. Its derivation was necessary because real avalanches are often guided by rather strongly curved and twisted corries. The motion of the avalanche follows the helicoidal talweg. The theory that is based on the helicoidal metric and non-orthogonal basis allows relatively easy access to comparisons with laboratory experiments. The emerging theory is believed to be capable of predicting the flow of dense granular materials over moderately curved and twisted channels. The model equations are tested by constructing analytical similarity solutions. The qualitative behaviour of both the traditional theory and its present extension agree well through these similarity solutions.
Two-Scale Regularity for Homogenization Problems with Nonsmooth Fine Scale Geometry
Authors: Matache A.-M. , Melenk J. M.
Published: July 2003

Elliptic problems on unbounded domains with periodic coefficients and geometries are analyzed and two-scale regularity results for the solution are given. These are based on a detailed analysis in weighted Sobolev spaces of the so-called unit-cell problem in which the critical parameters (the period ε, the wave number t, and the differentiation order) enter explicitly.
Parameterizations of 1-Bridge Torus Knots
Authors: Choi Doo Ho , Ko Ki Hyoung
Published: July 2003

A 1-bridge torus knot in a 3-manifold of genus ≤ 1 is a knot drawn on a Heegaard torus with one bridge. We give two types of normal forms to parameterize the family of 1-bridge torus knots that are similar to the Schubert's normal form and the Conway's normal form for 2-bridge knots. For a given Schubert's normal form we give algorithms to determine the number of components and to compute the fundamental group of the complement when the normal form determines a knot. We also give a description of the double branched cover of an ambient 3-manifold branched along a 1-bridge torus knot by using its Conway's normal form and obtain an explicit formula for the first homology of the double cover.
Characterization of Y2-Equivalence for Homology Cylinders
Authors: Massuyeau Gwénaël , Meilhan Jean-Baptiste
Published: July 2003

For Σ a compact connected oriented surface, we consider homology cylinders over Σ: these are homology cobordisms with an extra homological triviality condition. When considered up to Y2-equivalence, which is a surgery equivalence relation arising from the Goussarov-Habiro theory, homology cylinders form an Abelian group.

In this paper, when Σ has one or zero boundary component, we define a surgery map from a certain space of graphs to this group. This map is shown to be an isomorphism, with inverse given by some extensions of the first Johnson homomorphism and Birman-Craggs homomorphisms.
Quandles and Monodromy
Authors: Yetter D. N.
Published: July 2003

We show that a variety of monodromy phenomena arising in geometric topology and algebraic geometry are most conveniently described in terms of homomorphisms from a(n augmented) knot quandle associated with the base to a suitable (augmented) quandle associated with the fiber. We consider the cases of the monodromy of a branched covering, braid monodromy and the monodromy of a Lefschetz fibration. The present paper is an expanded and corrected version of [1].
Relation Between Surface Crystallography and Surface Electron Structure of the Superlattice
Authors: Bartoš I. , Strasser T. , Schattke W.
Published: July 2003

Profound gradual changes of surface state energies were predicted for varying surface terminations of the periodic crystal potential in one-dimensional models.1 This situation can be realized in superlattices with different thicknesses of topmost layers. For the ideally terminated (100) surface of a very thin superlattice (GaAs)2(AlAs)2, the shift of the energy of the surface state over the whole minigap in the lower part of the valence band has been found for different terminations of the topmost layer. In the center of the surface Brillouin zone the surface state shift follows model trends. The changes of the energy distribution of photoemitted electrons as determined from the one-step photoemission calculation2 indicate that experimental observation by the surface-sensitive technique of angle-resolved photoemission should be feasible, and preliminary data indicate this. The results show a straigthforward tuning of surface electron structure by geometrical means.
RF-Sputtered MoS2 Film Morphology and the Imperfection Nucleation Model
Authors: Jakovidis G. , Jamieson I. M. , Singh A.
Published: July 2003

RF-sputtered MoS2 films revealing the characteristics of bulk type II orientation on GaAs are reported for the first time. It is found that RF power and temperature have a pronounced effect on film morphology. Type II bulk-oriented films are obtained with a combination of low RF power and high substrate temperature. The results on GaAs are successfully interpreted within the context of an extension to the imperfection nucleation model of film formation. Films deposited on glass display an unusual morphology consisting of two distinct phases. Such phases may be related to the presence of sodium in the glass that leads to chemical texturing via a sodium thio-molybdate phase.
Boron Segregation on the ${\rm Si}(111)\sqrt{3} \times \sqrt{3}{\rm R}30^\circ$ Surface
Authors: Shi Hongqing , Radny M. W. , Smith P. V.
Published: July 2003

In this paper we report the results of calculations of the energies associated with the segregation of boron on the [Formula: see text] surface. These calculations have been carried out using the plane wave pseudopotential density functional code fhi98md in a periodic slab formalism. The segregation energy is predicted to be -0.77 eV. This prediction is intermediate between the "experimentally determined" values of -0.33 eV and -0.48 eV, and the values of -1.83 eV and -2.10 eV determined from AM1 cluster calculations. Additional information has been obtained by performing ab initio density functional cluster calculations using the Gaussian98 code. These latter results indicate that the AM1 calculations significantly overestimate the segregation energy of boron on the [Formula: see text] surface. They also provide strong support for the fhi98md calculations.
Surface Structure and Transport Properties of YBa2Cu3O7-δ Using La2/3Ca1/3MnO3 as Buffer
Authors: Tan W. S. , Yang L. , Sha H. , Wu X. S. , Gao J. , Jiang S. S.
Published: July 2003

The YBa2Cu3O7-δ (YBCO) ultrathin films were prepared by off-axis rf magnetron sputtering on SrTiO3 (STO) substrate with a 300-Å-thick La2/3Ca1/3MnO3 (LCMO) buffer layer. At low temperature, the magnetism of the LCMO buffer layer seemed to be screened by the epitaxial YBCO layer with a thickness of more than about 125 Å. A remarkable magnetoresistance (MR) ratio was obtained for thinner YBCO cap layer. The superconducting transition temperature, Tc, decreases with decreasing YBCO thickness and disappears at the thickness of less than 85 Å. X-ray diffraction (XRD) was used to characterize the quality of the buffer and epitaxial films. The out-of-plane lattice parameters for both buffer and epitaxial layer varied monotonically. The surface structures of the buffer and the epitaxial YBCO films were characterized by atomic force microscopy (AFM). Interfacial diffusions for cations such as Y, Cu, La, Ca and Sr were deduced from Auger electron spectroscopy (AES). The larger diffusion length was found at the interface between YBCO and LCMO, which may relate to the suppression of superconductivity and magnetoresistance.
Beamline for Surface and Interface Structures at SPring-8
Authors: Sakata O. , Furukawa Y. , Goto S. , Mochizuki T. , Uruga T. , Takeshita K. , Ohashi H. , Ohata T. , Matsushita T. , Takahashi S. , Tajiri H. , Ishikawa T. , Nakamura M. , Ito M. , Sumitani K. , Takahashi T. , Shimura T. , Saito A. , Takahasi M.
Published: July 2003

The main components of a new beamline for surface and interface crystal structure determination at SPring-8 are briefly described. Stages for the beamline monochromator are modified for making an incident X-ray intensity more stable for surface X-ray experiments. Absolute photon flux densities were measured with an incident photon energy. A new ultrahigh vacuum system is introduced with preliminary X-ray measurements from an ordered oxygen on Pt (111) surface.
Crystalline Structure and the Role of Low-Temperature-Deposited AlN and GaN on Sapphire Revealed by X-Ray CTR Scattering and X-Ray Reflectivity Measurements
Authors: Takeda Y. , Tabuchi M. , Amano H. , Akasaki I.
Published: July 2003

Crystalline and morphological quality of low-temperature (LT)-deposited and annealed AlN and GaN thin layers were investigated by X-ray crystal truncation rod (CTR) scattering and X-ray reflectivity measurements and atomic force microscope (AFM) observation. It was revealed that the LT-AlN layer was more uniform in terms of the crystalline structure and the layer thickness than the LT-GaN layer, before and after annealing. It suggests that LT-AlN is more suitable as a buffer layer between sapphire substrate and GaN.
Surface Chemical Behavior of Uranium Metal in Hydrogen Atmosphere Studied by XPS
Authors: Wang Xiaolin , Fu Xiaoguo , Zhao Zhengping
Published: July 2003

The surface chemical behavior of clean uranium metal in a hydrogen atmosphere at 80°C and 120°C has been studied using XPS and thermodynamic calculation. The main product is uranium oxide rather than hydride uranium on the uranium surface after the exposure of uranium to extremely pure hydrogen, and the U4f7/2 binding energy of UH3 has been found to be 378.6 ± 0.1 eV. An elevated temperature (120°C) is beneficial to the formation of UH3 species at the same hydrogen exposures. The depth profile analysis of XPS indicates that the chemical structure of the surface layer was UO2/UH3/U after the exposure of hydrogen reached 1.31 × 10-6 L (1 L = 10-6 Torr·s). Results of thermodynamic calculations are in good agreement with the above conclusions.
Modeling of Boron Adsorption on the (110) Tungsten Surface
Authors: Dorfman Simon , Braga Ronan R. , Mundim Kleber C. , Fuks David
Published: July 2003

We have performed the atomistic simulations of the adhesion process of a boron atom on the tungsten (110) surface on the basis of the generalized simulation annealing formalism. The interatomic potentials used in these simulations were obtained from ab initio total energy calculations on the basis of the recursion procedure. The nonempirical calculations have been carried out in the framework of density functional theory in the coherent potential approximation.
Study of the Interface Characteristic of Be/HR-1 Stainless Steel Following Diffusion Bonding
Authors: Zhang Peng-Cheng , Bai Bin , Yang Jiang-Rong , Zou Jue-Sheng , Zhou Shou-Qi
Published: July 2003

The interface structure of Be/HR-1 stainless steel (SS) joint following diffusion bonding was investigated. Metallurgical observation, electron scanning microscopy, X-ray diffraction and scanning Auger microspectroscopy were performed for basic evaluation of bonded joints. There are intermetallic compounds such as Be11Fe and Be12Cr in the interface region of Be/SS joints, which drastically reduce the mechanical strength of the joints. Cu, Ag and Al barriers can block effective inter-diffusion of Be and HR-1 stainless steel, then forming brittle phases.
A Study of Alkanethiol Film on Au by STM-Induced Luminescence
Authors: Nishitani R. , Tateishi Y. , Arakawa H. , Hisanaga T. , Sasaki H. , Kasuya A. , Sumiyama K.
Published: July 2003

Alkanethiol films on Au(111) surface have been studied by means of STM-induced luminescence in UHV. The spectra of STM-induced luminescence have been recorded at the same time as STM topography measurements with a spectrograph and a CCD detector. The spectrally resolved STM-induced photon map shows a similar contrast to the topography of alkanethiol film which has many etch pit structures created during the monolayer-film formation. The spectra for the etch pit region are compared with those for the top layer of the film. Those spectra shapes are nearly identical except for the difference of the emission intensity. The results indicate that the etch pit is also covered with an alkanethiol film in a similar way to the top layer of the film. The bias-voltage dependence of emission spectra has also been recorded in the range from 2.0 to 2.5 V. The results show that the spectra do not change their shape due to adsorption in this range of bias voltage within the experimental accuracy. The density of states due to adsorption has been discussed.
New Insights into the Generation Mechanism of Quasicrystal by the Surface Reaction Between Ultrafine Particles and Deposited Clusters
Authors: Kido O. , Kaito C. , Saito Y.
Published: July 2003

On heating Mn-deposited Al particles (Mn–Al specimen) at 300°C, diffraction spots due to a Al86Mn14 quasicrystal appeared, in addition to those due to Al6Mn alloy. On heating a specimen of the Al-deposited Mn particles (Al–Mn specimen), Al50Mn50 alloy was formed. Neither the quasicrystal nor Al6Mn phases appeared. The electron microscope images of the Mn–Al specimen showed the existence of void clusters in the Al particles. This indicates that the alloys and the quasicrystals were produced by the diffusion of Al atoms to the Mn clusters. In the case of the Al–Mn specimen, the surface of Mn particles was covered with an Al thin film of uniform thickness. The surface Al layer changed to Al50Mn50 alloy. These results indicate that the diffusion direction of atoms and diffusion rates are different between Mn–Al and Al–Mn systems.
Spontaneous Formation of Air Nanobubbles on Hydrocarbons Deposited on the Au(111)/Water Interface
Authors: Otsuka Ichiro , Yaoita Masashi , Higano Michi , Nagashima Seiichi
Published: July 2003

We have observed surface features on hydrocarbons deposited on Au(111) from the laboratory atmosphere in water and in a sodium chloride aqueous solution, using tapping mode atomic force microscopy (TMAFM). TMAFM images of the Au(111)/water interface reveal that the features are pancake-shaped structures with the range of measured dimensions of 20–150 nm in width and 0.5–20 nm in height, and that many features reappear at almost the same sites immediately after the disruption of the features by contact mode AFM imaging. The results of our TMAFM observations imply that the features are nanosized bubbles as those reported previously, and that dissolved gas nucleates at specific sites of the hydrophobized Au(111) surface at low, temporal gas supersaturations under atmospheric pressure.
Pyrrole (C4H4NH) and Polypyrrole Functionalized Silicon Surfaces Calculated from First Principles
Authors: Schmidt W. G. , Seino K.
Published: July 2003

The functionalization of the Si(001) surface by pyrrole and polypyrrole is investigated by means of first-principles pseudopotential calculations. We find dissociative reactions, leading to the partial fragmentation of the molecule, to be energetically most favored for pyrrole adsorption. The lowest-energy configuration for monolayer coverage is characterized by pyrrole rings bonded to the surface via Si–N linkage. In coexistence with adsorption geometries where both N and C are bonded to the surface, this structure accounts very well for the available experimental data. Chemisorption of pyrrole is found to effectively passivate the Si(001) surface, irrespective of the details of the adsorption geometry. The formation of well-ordered polypyrrole structures on Si(001) may require chemical modifications of the polypyrrole chains in order to account for the lattice mismatch.
Surface Ordering of P-rich InP(001): Hydrogen Stabilization vs Electron Correlation
Authors: Hahn P. H. , Schmidt W. G.
Published: July 2003

The influence of hydrogen on the reconstruction of InP(001) surfaces is studied by first-principles calculations. One-monolayer phosphorus forming oppositely buckled dimers with one hydrogen adsorbed per dimer is energetically favored for a wide range of surface preparation conditions. The electronic structure and STM image calculated for this adsorbate geometry agree well with the experimental findings obtained after annealing of MOVPE-grown InP samples. The Si(001)-like surface ordering as well as the surface band gap of more than 1 eV, supposedly arising from electron correlation effects [Li et al., Phys. Rev. Lett.82, 1879 (1999)], are naturally explained by the hydrogen-stabilized surface structure favored by the total-energy calculations.
Microstructural Study of a Passivation Layer on GaAs: An Application of X-Ray Reflectivity Under Grazing Angles Using a Synchrotron Source
Authors: Crompton K. E. , Finlayson T. R. , Kirchner C. , Seitz M. , Klemradt U.
Published: July 2003

X-ray specular reflectivities of GaAs samples passivated with a thin film of (3-mercaptopropyl)-trimethoxysilane (MPT) have been studied using bending-magnet synchrotron radiation. Various preparation procedures covering etching the GaAs, MPT deposition and its baking have been investigated. An oxide film is always observed between the GaAs and MPT films. The microstructural parameters, such as film thickness, density and interfacial roughness (including the external surface), have been determined from appropriate modeling of the reflectivity. The surface roughness has been compared with a direct measurement using tapping-mode atomic force microscopy. The results are discussed with reference to the potential applications of GaAs as a biosensor.
First-Principles Calculation of the Work Functions for the High-Index Copper Surfaces
Authors: Kim I. G. , Lee B. C. , Lee J. I.
Published: July 2003

We calculated the work functions (WFs) for the high-index copper surfaces, (112), (321), and (413), as well as the low-index surfaces, (111), (100), and (110), using the full-potential linearized augmented plane wave (FLAPW) method within both the local density approximation (LDA) and the generalized gradient approximation (GGA). It is found that the GGA lowers rigidly the WFs about 0.46–0.49 eV from the values obtained by the LDA, for all the surfaces, and the experimental values for low-index surfaces are in between the calculated values by the LDA and GGA. It is also found that the WF does not decrease further, for the surfaces with higher indices than (112). This result is different from that of the recent measurements by the Kelvin probe technique [Appl. Phys. Lett.79, 4337 (2001)], which shows a linear dependence of WF on the atomic packing density. The result of our calculation is consistent with the WF anisotropy model, which was recently applied to tungsten surfaces.
Structure of Vanadium Oxide (V2O3) Grown on Cu3Au(100)
Authors: Niehus Horst , Blum Ralf-Peter , Ahlbehrendt Dirk
Published: July 2003

The epitaxial growth of vanadium oxide (V2O3) has been investigated by scanning tunneling microscopy (STM), low energy ion back-scattering (ISS) and low energy electron diffraction (LEED). Direct evaporation of vanadium onto metal surfaces (Cu, Au or Cu3Au) gives rise to massive surface alloying. The attempt to oxidize the vanadium film by consequent oxygen exposure leads to the formation of rough VO x films of poor quality and mixed valency. A new way of oxide formation has been developed by preoxidation of a Cu3Au substrate, which acts positively in two ways since it prevents completely alloy formation and also forces strong surface wetting of the vanadium oxide. As a result, two-dimensional layer growth of good quality has been achieved. Depending on the preoxygen content at Cu3Au(100), the amount of V deposition and annealing temperature, different epitaxial layers of vanadium oxides can be prepared. In particular, the surface structure of V2O3(0001) was investigated. The surface structure appears completely different from the half layer metal termination at Cr2O3(0001). Specifically, the full vanadium layer stabilized by one third of an oxygen layer located in pseudo bridge positions close to regular oxygen positions of a next layer. Close to defects the full vanadium layer appears also without oxygen stabilization.
Highly Angle-Resolved X-Ray Photoelectron Diffraction from Solid Surfaces
Authors: Tamura K. , Shiraki S. , Ishii H. , Owari M. , Nihei Y.
Published: July 2003

We have carried out the highly angle-resolved X-ray photoelectron diffraction (XPED) measurements by using the input-lens system for restriction of the detection angle. In the input-lens system, high angular resolution and high throughput are accomplished by placing an aperture not on the image plane but on the diffraction plane of electron optics. The aperture sizes (ϕ 4 mm, ϕ 2 mm, ϕ 0.5 mm, ϕ 0.25 mm) correspond to the angular resolutions (± 0.6°, ± 0.3°, ± 0.08°, ± 0.04°) respectively. Highly angle-resolved Ge3d XPED patterns from Ge(111) obtained by the angle-resolving system contain fine structure such as Kikuchi patterns. The fine structure was reproduced by multiple scattering cluster calculations.
Dynamic Behavior of a Silicon Oxide Layer on Silicon Ultrafine Particles
Authors: Kimura Yuki , Ueno Hiroshi , Suzuki Hitoshi , Sato Takeshi , Tanigaki Toshiaki , Kido Osamu , Kaito Chihiro , Saito Yoshio
Published: July 2003

In order to clarify the high-temperature behavior of a silicon oxide layer on the surface of Si ultrafine particles, the oxide layer has been studied using the atomic-resolution high-temperature stage of a transmission electron microscope. The natural oxide layer grown on Si ultrafine particles by exposure to air was an amorphous silicon oxide layer with a thickness of 1.5 nm. This oxide layer started to dissolve into the Si crystal upon heating at 500°C, and was fully dissolved into the Si crystal at 600°C in vacuum. When the specimen was cooled back to room temperature, the silicon oxide layer reappeared on the Si surface. This phenomenon, which can be detected only at high temperatures, is presented in this paper.
Hydrogenation of Nanodiamond Surfaces: Structure and Effects on Crystalline Stability
Authors: Russo S. P. , Barnard A. S. , Snook I. K.
Published: July 2003

Presented are results of our ab initio study of the surface reconstruction and relaxation of (100) surfaces on bulk and nanocrystalline diamond. We have used a density functional theory (DFT) within the generalized-gradient approximation (GGA) via the parallel computer version of the Vienna ab initio simulation package (VASP), to consider dehydrogenated and hydrogenated surfaces. Edges and corners of nanocrystals offer a new challenge in the determination of surface structure. We have applied the methodology for stepped diamond (100) surfaces to this problem, and consider it useful in describing nanodiamond edges and corners to first approximation. Our results also indicate that dimer lengths and atomic layer depths of the C(100)(2 × 1) and C(100)(2 × 1):H nanodiamond surfaces differ slightly from those of bulk diamond. The effects of these differences on crystalline stability are discussed, with the intension of offering a better understanding of the effects of nanodiamond surfaces on the stability of diamondoid nanostructures.
Structural Study of Benzene Adsorbed on Si(001) Surface by Photoelectron Diffraction
Authors: Shimomura M. , Munakata M. , Honma K. , Widstrand S. M. , Johansson L. , Abukawa T. , Kono S.
Published: July 2003

The structure of benzene adsorbed on a Si(001)(2 × 1) surface up to saturation at room temperature (RT) has been studied by C 1s photoelectron diffraction (PED). Experimental C 1s PED patterns were measured for two regimes of photoelectron kinetic energies at ~ 100 eV and ~ 1000 eV. Simulation of PED patterns was made for three possible structural models predicted so far. Comparison of actual PED patterns and R-factor analysis leads to the conclusion that the so-called standard butterfly (SB) configuration of benzene is present and stable at the saturation coverage at RT. The present PED patterns were not very sensitive to geometrical parameters of absorbed benzene except for the bond length between the topmost carbons in the SB configuration.
Iron Surfaces: Pathways to Interfaces
Authors: Spencer Michelle J. S. , Hung Andrew , Snook Ian K. , Yarovsky Irene
Published: July 2003

We have used density functional theory to examine the effects of avalanche in adhesion between Fe(100) surfaces, in registry and out of registry. When the central layers of the two surfaces are constrained the surface layers are attracted towards each other, forming a strained crystal region at intermediate interfacial separations. When the constraints in the z-direction are lifted, the surfaces avalanche together. In addition, when the surfaces are allowed to move sideways, we find that an interface initially out of registry will tend to avalanche towards an interface that is in registry.
The Influence of Surface Orientation and Sample Thickness on the Substitutional Bulk Diffusion Coefficient in Thin Samples
Authors: Plessis J. Du , Russo S. P. , Hoadley J. , Mortimer E. C.
Published: July 2003

Model calculations are presented to show that for thin samples the vacancy formation energy is determined by the concentration of vacancies in the bulk. The equilibrium vacancy concentration is calculated and its effect on the substitutional bulk diffusion coefficient is discussed. It is shown that the diffusion coefficient D exhibits abrupt transitions as a function of temperature but that these transitions occur at temperatures which are independent of the surface orientation. The effects are confined to thin samples and for thicker samples the model predicts the well-established bulk diffusion values independent of surface properties.
Influence of Substrate Miscut on the Island Formation Process in In0.2Ga0.8As/GaAs Multilayers
Authors: Gartstein E. , Mogilyanski D. , Barlam D.
Published: July 2003

LPOMVPE-grown In0.2Ga0.8As/GaAs multilayers on GaAs substrates with miscut values of 0°, 0.3° and 2° around the [100] azimuthal direction were investigated by employing X-ray diffraction techniques complemented by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The step-terrace structure evolving on the interfaces upon deposition strongly depends on the initial substrate morphology. The initiation of island nucleation, and both lateral and vertical ordering are related to the interfacial morphological parameters. Finite element analysis (FEA) is performed to elucidate the interplay between structural and strain relaxation processes.
X-Ray Diffraction Study of the Phase Transition of the ${\rm Si}(111)(\sqrt{3} \times \sqrt{3})\mbox{-Ag}$ Surface
Authors: Takahashi Toshio , Tajiri Hiroo , Sumitani Kazushi , Akimoto Koichi , Sugiyama Hiroshi , Zhang Xiaowei , Kawata Hiroshi
Published: July 2003

The structure of the [Formula: see text] surface was studied at both room temperature and a low temperature of 50 K using grazing incidence X-ray diffraction. At low temperatures diffuse scattering was observed in addition to Bragg reflection. Least squares analyses for Bragg reflections using anisotropic Debye–Waller factors show that the structure at 50 K is consistent with an inequivalent triangle (IET) model, while the structure at room temperature is explained by a honeycomb-chained triangle (HCT) model with strong anisotropic Debye–Waller factors. From the temperature dependence of diffuse scattering, the phase transition temperature Tc and critical exponent β were determined to be about 150 K and 0.27. Some Bragg intensities showed discontinuous changes in their first derivatives at Tc. The results favor a displacive phase transition rather than an order–disorder one.
Focusing Elements and Design Considerations for a Scanning Helium Microscope (SHeM)
Authors: MacLaren D. A. , Holst B. , Riley D. J. , Allison W.
Published: July 2003

We describe recent developments in the fabrication of an atom-optical mirror for focusing thermal helium atoms. A bent silicon crystal is, in principle, capable of high intensity, low aberration helium reflection; manipulation of the mirror's macrostructure minimizes optical aberrations in the device whilst chemical control over the mirror's microstructure ensures high intensity reflection. Incorporation of the atom mirror into a novel Scanning Helium Microscope (SHeM) is outlined, in the context of surface-structural studies. In particular, we refer to the expected operation, contrast mechanisms and resolution of such an instrument.
A Refined Leed Analysis of Water on Ru{0001}: An Experimental Test of the Partial Dissociation Model
Authors: Puisto S. R. , Lerotholi T. J. , Held G. , Menzel D.
Published: July 2003

Despite a number of earlier studies which seemed to confirm molecular adsorption of water on close-packed surfaces of late transition metals, new controversy has arisen over a recent theoretical work by Feibelman, according to which partial dissociation occurs on the Ru{0001} surface leading to a mixed (H2 O + OH + H) superstructure. Here, we present a refined LEED-IV analysis of the [Formula: see text] structure, testing explicitly this new model by Feibelman. Our results favour the model proposed earlier by Held and Menzel assuming intact water molecules with almost coplanar oxygen atoms and out-of-plane hydrogen atoms atop the slightly higher oxygen atoms. The partially dissociated model with an almost identical arrangement of oxygen atoms can, however, not unambiguously be excluded, especially when the single hydrogen atoms are not present in the surface unit cell. In contrast to the earlier LEED-IV analysis, we can, however, clearly exclude a buckled geometry of oxygen atoms.