bluuebunny/crossref_metadata_2025 huggingface dataset:
The bending vibrational levels of the acetylene cation: A case study of the Renner-Teller effect in a molecule with two degenerate bending vibrations
Authors: Tang Sheunn-Jiun , Chou Yung-Ching , Lin Jim Jr-Min , Hsu Yen-Chu
Published: October 2006

Forty three vibronic levels of C2H2+, X̃Πu2, with υ4=0–6, υ5=0–3, and K=0–4, lying at energies of 0–3520cm−1 above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+1′ two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the ÃAu1, 4ν3 (K=1–2), 5ν3 (K=1), ν2+4ν3 (K=0), and 47206cm−1 (K=1) levels of C2H2. Seven of the trans-bending levels of C2H2+ (υ4=0–3, K=0–2) had been reported previously by Pratt et al. [J. Chem. Phys. 99, 6233 (1993)]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with υ4+υ5⩽2, except for the unobserved upper Πu2 component of the 2ν4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21cm−1. The vibronic coupling parameter ε5 (about whose magnitude there has been controversy) was determined to be −0.02737. For the higher vibronic levels, an additional parameter, r45, was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the υ4+υ5=3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with υ4+υ5⩽5, an rms deviation of 0.34cm−1 was obtained using 20 parameters. An interesting finding is that Hund’s spin-coupling cases (a) and (b) both occur in the Σu components of the ν4+2ν5 combination level. The ionization potential of C2H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91953.77±0.09cm−1 (3σ).
Nonadiabatic effects in the H+D2 reaction
Authors: Lu Rui-Feng , Chu Tian-Shu , Zhang Yan , Han Ke-Li , Varandas António J. C. , Zhang John Z. H.
Published: October 2006

The state-to-state dynamics of the H+D2 reaction is studied by the reactant-product decoupling method using the double many-body expansion potential energy surface. Two approaches are compared: one uses only the lowest adiabatic sheet while the other employs both coupled diabatic sheets. Rotational distributions for the reaction H+D2 (υ=0,j=0)→HD(υ′=3,j′)+D are obtained at eight different collision energies between 1.49 and 1.85eV; no significant difference are found between the two approaches. Initial state-selected total reaction probabilities and integral cross sections are also given for energies ranging from 0.25 up to 2.0eV with extremely small differences being observed between the two sets of results, thus showing that the nonadiabatic effects in the title reaction are negligible at least for small energies below 2.0eV.
Rotationally resolved reactive scattering: Imaging detailed Cl+C2H6 reaction dynamics
Authors: Huang Cunshun , Li Wen , Suits Arthur G.
Published: October 2006

The hydrogen atom abstraction reaction of Cl (P3∕22) with ethane has been studied using the crossed molecular beam technique with dc slice imaging at collision energies from 3.2to10.4kcal∕mol. The products HCl (v,J) (v=0, J=0–5) were state-selectively detected using 2+1 resonance enhanced multiphoton ionization. The images were used to obtain the center-of-mass frame product angular distributions and translational energy release distributions. Two general features were found in all probed HCl quantum states at 6.7kcal∕mol collision energy, and these features have distinct translational energy release and angular distributions, as described for HCl (v=0, J=2) in a recent preliminary report [Li et al., J. Chem. Phys. 124, 011102 (2006)]. The results for HCl (v=0,J=2) at four collision energies were also compared to investigate the energy-dependent dynamics. We discuss the reaction in terms of a variety of models of polyatomic reaction dynamics. The dynamics of this well studied system are more complicated than can be accounted for by a single mechanism, and the results call for further theoretical and experimental investigations.
Mechanism and control of the F+H2 reaction at low and ultralow collision energies
Authors: Aldegunde J. , Alvariño J. M. , de Miranda M. P. , Sáez Rábanos V. , Aoiz F. J.
Published: October 2006

This article uses theoretical methods to study the dependence on stereodynamical factors of the mechanism and reactivity of the F+H2 reaction at low and ultralow collision energies. The impact of polarization of the H2 reactant on total and state-to-state integral and differential cross sections is analyzed. This leads to detailed pictures of the reaction mechanism in the cold and ultracold regimes, accounting, in particular, for distinctions associated with the various product states and scattering angles. The extent to which selection of reactant polarization allows for external control of the reactivity and reaction mechanism is assessed. This reveals that even the simplest of reactant polarization schemes allows for fine, product state-selective control of differential and (for reactions involving more than a single, zero orbital angular momentum partial wave) integral cross sections.
Probing the electronic structure of UO+ with high-resolution photoelectron spectroscopy
Authors: Goncharov Vasiliy , Kaledin Leonid A. , Heaven Michael C.
Published: October 2006

The pulsed field ionization–zero kinetic energy photoelectron technique has been used to observe the low-lying energy levels of UO+. Rotationally resolved spectra were recorded for the ground state and the first nine electronically excited states. Extensive vibrational progressions were characterized. Ω+ assignments were unambiguously determined from the first rotational lines identified in each vibronic band. Term energies, vibrational frequencies, and anharmonicity constants for low-lying energy levels of UO+ are reported. In addition, accurate values for the ionization energies for UO [48643.8(2)cm−1] and U [49957.6(2)cm−1] were determined. The pattern of low-lying electronic states for UO+ indicates that they originate from the U3+(5f3)O2− configuration, where the uranium ion-centered interactions between the 5f electrons are significantly stronger than interactions with the intramolecular electric field. The latter lifts the degeneracy of U3+ ion-core states, but the atomic angular momentum quantum numbers remain reasonably well defined.
Collision-free photochemistry of methylazide: Observation of unimolecular decomposition of singlet methylnitrene
Authors: Larson Christopher , Ji Yuanyuan , Samartzis Petros , Wodtke Alec M. , Lee Shih-Huang , Lin Jim Jr-Min , Chaudhuri Chanchal , Ching Tao-Tsung
Published: October 2006

Methylazide photolysis at 248nm has been investigated by ionizing photofragments with synchrotron radiation in a photofragmentation translational spectroscopy study. CH3N and N2 were the only observed primary products. The translational energy release suggests a simple bond rupture mechanism forming singlet methylnitrene, C1H3N, and N2. Thus, these experiments reveal the unimolecular decomposition of this highly unstable species. We explain our observations through a mechanism which is initiated by the isomerization of C1H3N to a highly internally excited methanimine H2CNH isomer, which decomposes by 1,1-H2 elimination forming HNC+H2 as well as sequential H-atom loss (N–H followed by C–H bond cleavage), to form HCN. No evidence for dynamics on the triplet manifold of surfaces is found.
A nine-electrode probe for simultaneous measurement of all terms in the ideal radial Ohm’s law
Authors: Si Jiahe , Wang Zhehui
Published: October 2006

A Nine-Electrode Probe (NEP) has been developed for simultaneous measurement of all terms in the ideal Ohm’s law E+U×B=0 in the radial (r̂) direction in cylindrical geometry, where E is the electric field, U is the plasma flow velocity, and B is the magnetic field. The probe consists of two pairs of directional Langmuir probes (“Mach” probes) to measure the axial (ẑ) and azimuthal (θ̂) plasma flows, two pairs of floating Langmuir probes at different radial positions to measure the radial electric field, and two B-dot coils to measure the axial and azimuthal magnetic field. The measurement is performed in the Flowing Magnetized Plasma (FMP) experiment. Two flow patterns are identified in the FMP experiment by the NEP. The peak-to-peak values of radial electric field fluctuation is 1.5–4 times of the mean values. Comparisons of  ∣U×B∣r and Er show that Er+ ∣U×B∣r is not zero within some periods of discharge. This deviation suggests non-ideal effects in Ohm’s law can not be neglected.
Modeling of electrochemomechanical response of ionic polymer-metal composites with various solvents
Authors: Nemat-Nasser Sia , Zamani Shahram
Published: October 2006

Ionic polymer-metal composites (IPMCs) consist of a perfluorinated ionomer membrane (usually Nafion® or Flemion®) plated on both faces with a noble metal such as gold or platinum and neutralized with the necessary amount of counterions that balance the electrical charge of anions that are covalently fixed to the backbone ionomer. IPMCs are electroactive materials with potential applications as soft actuators and sensors. Their electrical-chemical-mechanical response is dependent on the cations used, the nature and the amount of solvent uptake, the morphology of the electrodes, the composition of the backbone ionomer, the geometry and boundary conditions of the composite element, and the magnitude and spatial and temporal variations of the applied potential. Our most recent experimental results show that solvents can have profound effects on the nature of the IPMCs’ actuation. For example, we have discovered experimentally that Nafion-based IPMCs in Li+-form show very small back relaxation when hydrated, but extensive back relaxation with all other solvents that we have considered. On the other hand, the same membrane in the K+-form has extensive back relaxation when solvated with water, ethylene glycol, or glycerol, but none with 18-Crown-6. In the present paper, we seek to model the IPMCs’ actuation and compare results with the experimental data. The modeling rests on the observation that a sudden application of a step potential (dc) of several volts (1–3V) alters the distribution of cations within the ionomer, forcing cations out of the clusters near the anode and additional cations into the clusters near the cathode. The clusters within a thin boundary layer near the anode are thus depleted of their cations, while cations accumulate in the clusters near the cathode boundary layer. We first seek to determine the spatial and temporal variations of the cation distribution across the thickness of the IPMC for various cations and solvents, using an implicit finite difference numerical solution of the basic field equations, and compare the results with those of approximate analytical estimates. Based on this information, we then calculate the changes in the osmotic, electrostatic, and elastic forces that tend to expand or contract the clusters in the anode and cathode boundary layers. Finally, we calculate the amount of solvent out of or into the clusters that produces the bending motion of the cantilever. Comparing the model results with those of experimental measurement, we have arrived at remarkably good agreements. Indeed, our nanoscale-based model correctly predicts the unexpected influence of solvents on the actuation of IPMCs.
A simple and continuous polycrystalline silicon thin-film transistor model for SPICE implementation
Authors: Pappas I. , Hatzopoulos A. T. , Tassis D. H. , Arpatzanis N. , Siskos S. , Dimitriadis C. A. , Kamarinos G.
Published: October 2006

A simple current-voltage model for polycrystalline silicon thin-film transistors (polysilicon TFTs) is proposed, including the sixth-order polynomial function coefficients fitted to the effective mobility versus gate voltage data, the channel length modulation, and impact ionization effects. The model possesses continuity of current in the transfer characteristics from weak to strong inversion and in the output characteristics throughout the linear and saturation regions of operation. The model parameters are used as input parameters in AIM-SPICE circuit simulator for device modeling. The model has been applied in a number of long and short channel TFTs, and the statistical distributions of the model parameters have been derived which are useful for checking the functionality of TFTs circuits with AIM-SPICE.
Recovery of a chemical vapor deposited diamond detection system from strong pulses of laser produced x rays
Authors: Dauffy L. S. , Koch J. A. , Izumi N. , Tommasini R.
Published: October 2006

We are planning an experiment that will study the response of a chemical vapor deposited (CVD) diamond detector to a strong x-ray pulse followed by a second weaker pulse arriving 50–300ns later, with a contrast in amplitude of about 1000. These tests will be performed at the LLNL Jupiter laser facility and are intended to produce charge carrier densities similar to those expected during a DT implosion at the National Ignition Facility, where a large 14.1MeV neutron pulse is followed by a weak downscattered neutron signal produced by slower 6–10MeV neutrons. The areal density ρR is proportional to the number of downscattered neutrons. The challenge of measuring ρR resides consequently in the effects of the first strong pulse on the weaker later pulse, which may include the saturation of the diamond wafer, saturation of the oscilloscope, or saturation of the associated power and data acquisition electronics. We are presenting the preparation of a double pulse experiment that will use a system of three polycrystalline CVD diamond detectors irradiated by 8.6keV x rays produced by two laser beams incident on a zinc target.
Influence of ion induced amorphicity on the diffusion of gold into silicon
Authors: Ehrhardt J. , Klimmer A. , Eisenmenger J. , Müller Th. , Boyen H.-G. , Ziemann P. , Biskupek J. , Kaiser U.
Published: October 2006

It is experimentally demonstrated that, after ion irradiating 60nm thick Au films on Si substrates with 230keV Ar+ ions, annealing conditions can be found leading to strong diffusional contrasts between bombarded and unbombarded areas. While Au readily diffuses into the bombarded part of the sample at 310°C, its diffusion is still completely blocked under identical conditions in the unbombarded parts. Clear evidence is provided that this diffusional contrast is due to bombardment induced amorphization of the underlying Si substrate. The amorphous Silicon (a-Si), however, has to extend right to the Au∕Si interface, since any intermediate crystalline layer will suppress the diffusional contrast. An example for this latter situation is realized by performing the ion bombardment prior to the evaporation of the top Au layer leading to a still crystalline Si surface layer, which is found to act as a barrier against Au diffusion at 310°C. In accordance with the idea that a-Si, independent of its specific preparation, causes the observed Au diffusion enhancement, the effect is also found for a-Si prepared by evaporation at ambient temperature. In that case an even higher Au diffusion coefficient is obtained than for Si amorphized by ion bombardment pointing to subtle structural differences between both types of amorphous Si.
Growth and thermal properties of SrWO4 single crystal
Authors: Fan J. D. , Zhang H. J. , Wang J. Y. , Jiang M. H. , Boughton R. I. , Ran D. G. , Sun S. Q. , Xia H. R.
Published: October 2006

A strontium tungstate (SrWO4) single crystal with dimensions of Φ 25×40mm2 has been grown by the Czochralski method using an iridium crucible. X-ray powder diffraction results show that as grown the SrWO4 crystal belongs to the tetragonal system in the scheelite structure. The effective segregation coefficients of elemental W and Sr in the crystal growth are measured by x-ray fluorescence, and the respective values are close to 1. The thermal properties of the SrWO4 crystal were systemically studied by measuring the thermal expansion, specific heat, and thermal diffusion coefficient. These results show that the crystal possesses a large anisotropic thermal expansion with thermal-expansion coefficients αa=8.61×10−6∕K, αb=8.74×10−6∕K, αc=18.78×10−6∕K over the temperature range of 303.15–773.15K. The measured value of the specific heat is 0.30–0.34Jg−1K−1 when the temperature is increased from 323.15to1073.15K. The thermal diffusion coefficient was measured over the temperature range of 303.15–543.15K. The thermal conductivities of the SrWO4 crystal along the [100] and [001] directions are calculated to be 3.1326Wm−1K−1 and 2.9477Wm−1K−1, respectively, at 303.15K. Then the thermal properties of some other Raman crystals were compared with these data, and the thermal focal lengths for these crystals were also estimated.
Electromagnetic simulation of terahertz frequency range filters for genetic sensing
Authors: Tiang C. K. , Cunningham J. , Wood C. , Hunter I. C. , Davies A. G.
Published: October 2006

We report on a numerical study of the sensitivity of electrical terahertz (THz) frequency range passive filters under conditions of dielectric loading. We investigate band-pass filters, ring resonators, and band-stop filters, all of which have been proposed as devices capable of measuring the hybridization state of overlaid DNA films, thereby acting as genetic sensors. The transmission characteristics of these filters are examined when loaded with samples of different relative permittivities and thicknesses, and these results are discussed in the context of recent experimental works. A comparative analysis of the three filter types is performed, and conclusions are drawn on the suitability of the various filters for the analysis of DNA films during genetic testing and other dielectric materials.
Local field intensity enhancements on gold semicontinuous films investigated with an aperture nearfield optical microscope in collection mode
Authors: Buil S. , Aubineau J. , Laverdant J. , Quélin X.
Published: October 2006

Optical properties of gold semicontinuous films near the percolation threshold are studied using a scanning nearfield optical microscope (SNOM) operated in a collection/transmission mode. Local field intensity enhancements due to localized surface-plasmon-polaritons are accurately observed. An intensity renormalization procedure adapted to this SNOM configuration is proposed to estimate the distribution of the enhancements. This distribution is studied for different incident wavelengths and polarizations. A statistical treatment is applied in order to obtain the probability density function of the field intensity enhancements. This function is found to decay exponentially in a wavelength dependent way.
Strain enhanced p-type metal oxide semiconductor field effect transistors
Authors: Belford R. E. , Guo B. P. , Xu Q. , Sood S. , Thrift A. A. , Teren A. , Acosta A. , Bosworth L. A. , Zell J. S.
Published: October 2006

Results are reported for Si p-channel metal oxide semiconductor field effect transistors (pMOSFETs) subjected to a combination of tensile and compressive strains in different directions. This combination strain is reported and discussed. Results are reported for both partially depleted and bulk architectures. The maximum increase in effective mobility μeff attained in bulk pMOSFETs was 120.19% and the corresponding increase in saturation current Isat was 120.08% for 1.6% strain. Partially depleted devices were strained up to 2.2%, giving an increase in effective mobility μeff of 138.40% and increase in saturation current Isat of 147.74%. Tensile stress was applied orthogonal to the carrier transport direction (transverse) and compressive stress was induced along the channel, resulting in unprecedented increases in both output and effective mobility. Our straining technique involves thinning die and wafer sections of commercially fabricated devices until they are ultrathin (<10μm); stress is then applied mechanically. Measurements were performed on devices “as fabricated” and also after thinning and layer transfer. Stress was applied at predefined values and characterization was carried out. The “strain and characterization” sequence was repeated until the applied stress exceeded the elastic region.
Optical anisotropy induced by pyramidal defects in Mg-doped AlGaN∕GaN superlattices
Authors: Chang H. J. , Sheu Y. M. , Chen Y. F. , Wu C. T. , Chen C. H.
Published: October 2006

Structural and optical properties of Mg-doped AlGaN∕GaN superlattices have been investigated by photoluminescence, scanning electron microscopy, cathodoluminescence (CL), and transmission electron microscopy (TEM). We found that the edge blue-band emission shows a strong optical anisotropy. Through the combination of the CL and TEM images, we clearly establish that the underlying microstructure responsible for the blue luminescence in Mg-doped AlGaN∕GaN arises from the pyramidal defects. The observed optical anisotropy is due to the well aligned pyramidal structure. Our result provides one of the model systems to demonstrate the correlation between optical transition and structural defect in a solid.
Magneto-optical properties for bulk Cd0.63−yMn0.37HgyTe single crystals
Authors: Hwang Younghun , Kim Hyekyeong , Cho Sunglae , Um Youngho , Park Hyoyeol , Jeen Gwangsoo
Published: October 2006

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd1−x−yMnxHgyTe (x∼0.37) single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of y⩽0.07. The band gap energy increases with increasing y (⩽0.03), while decreases with increasing y (⩾0.03). An anomalous behavior was also observed in the magnetic susceptibility and electrical resistivity. Faraday rotation as a function of photon energy with various Hg compositions for CdMnHgTe in the temperature range of 10–300K has been measured. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant becomes larger since the effect of the sp-d exchange interaction is enhanced as the temperature is lowered. At 10K, the Verdet constants of the Faraday rotation for the samples with y=0, 0.01, 0.03, 0.05, and 0.07 were observed to be −1.09, −2.57, −3.94, −0.97, and −0.87deg∕Gcm at 613nm, respectively. The Verdet constant showed a maximum for the sample with y=0.03, and the value is approximately four times larger than that of the Cd0.63Mn0.37Te crystal. The Verdet constant has a maximum around Hg compositions with y∼0.03, and this result agrees well with the behavior of the magnetic susceptibility. This result reflects that Hg ion mediates and enhances the spin-spin interaction between Mn2+ ions with increasing Hg composition up to y∼0.03.
Stability of heterodyne terahertz receivers
Authors: Kooi J. W. , Baselmans J. J. A. , Baryshev A. , Schieder R. , Hajenius M. , Gao J. R. , Klapwijk T. M. , Voronov B. , Gol’tsman G.
Published: October 2006

In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies.
The complex ray theory of photodeflection signal formation: Comparison with the ray theory and the experimental results
Authors: Kobylińska Dorota Korte , Bukowski Roman J. , Burak Bogusław , Bodzenta Jerzy , Kochowski Stanisław
Published: October 2006

A theoretical study of Gaussian probe beam interaction with thermal waves on the basis of the complex geometrical optics equations is presented. This method of describing probe beam propagation in a nonhomogeneous medium, called the complex ray theory, takes into account the influence of the thermal wave on both amplitude and phase of electric field in the probe Gaussian beam. A comparison between the complex ray theory and previously proposed theories is made. Adequate experimental data confirming the correctness of the presented theory are also given. The least-squares procedure was used in multiparameter fitting the theoretical results to the experimental data and some parameters of the experimental setup were determined. It is proven that the complex ray theory allows correct quantitative interpretation of the data obtained in photodeflection experiments.
Dynamics of ion bombardment-induced modifications of Si(001) at the radio-frequency-biased electrode in low-pressure oxygen plasmas: In situ spectroscopic ellipsometry and Monte Carlo study
Authors: Amassian A. , Svec M. , Desjardins P. , Martinu L.
Published: October 2006

Low-pressure O2 plasma exposures were performed on c-Si(001) at a radio frequency (rf)-powered electrode in the presence of substrate self-biasing (VB) from VB=−60to−600V, in order to evaluate ion-surface interactions at the growth surface under ion bombardment conditions suitable for the fabrication of high quality optical coatings. The plasma-surface interactions were monitored in situ using real-time spectroscopic ellipsometry (RTSE), which reveals time- and ion-fluence-resolved information about depth-dependent modifications, such as damage and oxidation below the c-Si substrate surface. RTSE analysis indicates almost immediate damage formation (⪡1s) to a depth of a few nanometers below the surface after exposure to a low oxygen ion fluence (∼5×1014Ocm−2). Oxide growth is detected at intermediate fluence (∼1015–1016Ocm−2) and is attributed to O subplantation (shallow implantation); it forms near the surface of the target on top of an O-deficient interfacial damage layer (DL). Both layers experience a self-limiting growth behavior at high fluence (>1017cm−2) as oxide and DL thicknesses reach bias-dependent steady-state values, determined by the maximum ion penetration depth, which increases from ∼3.6to9.5nm for VB=−60to−600V. The in situ experimental study was complemented by Monte Carlo TRIDYN simulations based on the binary collision approximation, which were modified to calculate dynamic changes in the composition of a target exposed to a broad-energy ion source (rf plasma source) at high fluence. Simulation results are found to agree exceptionally well with experiment. In addition, they reveal that the 1.2–3.5-nm-thick DL formed in the steady-state regime is a result of (1) damage formation due to the presence of a small number of high energy O+ ions in the plasma environment, capable of penetrating and damaging up to 3nm deeper than the majority ion population (O2+), and (2) because of important surface motion resulting from oxidation-induced swelling (at low fluence) and sputtering-induced recession (at high fluence). Surface motion in general is found to inhibit oxygen incorporation at high depth in the substrate, thus forming the O-deficient DL. We discuss the implications of these findings on optical coatings deposition and propose a growth mechanism for coatings subjected to intense ion bombardment.
Direct structural evidences of Mn dilution in Ge
Authors: Ottaviano L. , Passacantando M. , Verna A. , Gunnella R. , Principi E. , Di Cicco A. , Impellizzeri G. , Priolo F.
Published: October 2006

X-ray diffraction, transmission electron microscopy, extended x-ray absorption fine structure spectroscopy, and x-ray photoemission spectroscopy have been used to study the structural properties of MnxGe1−x ion implanted alloys (x≃0.04) at 240 and 270°C substrate temperatures. Between 40% and 50% of the Mn atoms are found to occupy substitutional sites. No interstitial Mn atoms are found. The Mn–Ge coordination distance is 2.50(2)Å. Moreover, in the subsurface implanted layer [up to 32(2)nm depth] all the Mn atoms are effectively diluted in the Ge matrix, reaching a peak doping concentration of 7±1%.
Sound radiation from a turbulent boundary layer
Authors: Hu Zhiwei , Morfey Christopher L. , Sandham Neil D.
Published: October 2006

Sound radiation due to fluctuating viscous wall shear stresses in a plane turbulent boundary layer is investigated by a two-stage procedure using direct numerical simulation (DNS) databases for incompressible turbulent Poiseuille flow in a plane channel, at Reynolds numbers up to Reτ=1440. The power spectral density of radiated pressure and spectra of sound power per unit wall area are calculated in the low Mach number limit by substituting source terms obtained from DNS into a Ffowcs Williams–Hawkings wave equation and using a half-space Green function. The same DNS data are used to predict the spectrum of turbulent boundary layer noise measured in a diffuser downstream of a fully developed channel flow [Greshilov and Mironov, Sov. Phys. Acoust. 29, 275 (1983)]. The measured spectrum is ∼15dB higher at low frequencies, but converges with the prediction at high frequencies.
Structural characteristics of methylsilsesquioxane based porous low-k thin films fabricated with increasing cross-linked particle porogen loading
Authors: Lee Hae-Jeong , Soles Christopher L. , Liu Da-Wei , Bauer Barry J. , Lin Eric K. , Wu Wen-Li , Gallagher Michael
Published: October 2006

Methylsilsesquioxane (MSQ) based porous low-k dielectric films are characterized by x-ray porosimetry (XRP) to determine their pore size distribution, average density, wall density, and porosity. By varying the porogen content from 1% to 30% by mass, the porosity changes from 12% to 34% by volume, indicating that the base MSQ matrix material contains approximately 10% by volume inherent microporosity. The wall density of this matrix material is measured to be 1.33–1.35g∕cm3, independent of porosity. The average pore radii determined from the XRP adsorption isotherms increase from 6to27Å with increased porogen loadings. Small angle neutron scattering measurements confirm these XRP average pore radii for the films with porogen loading higher than 10% by mass.
Effect of low-pressure plasma discharge conditions on the thickness and roughness of ultrathin films of amorphous carbon
Authors: Wan D. , Komvopoulos K.
Published: October 2006

Thin films of amorphous carbon (a-C) were synthesized on smooth silicon substrates under different conditions of low-pressure radio-frequency discharge in pure Ar atmospheres. Transmission electron microscope and atomic force microscope studies provided insight into the dependence of the film thickness and roughness on the plasma discharge conditions. Cross-section thickness measurements revealed a linear relationship between film thickness and sputtered atom number density (defined as the total number of atoms sputtered off from a unit area of the target surface during film growth). Relatively rough films were produced in the absence of energetic Ar+ ion bombardment, especially under plasma conditions conducive to high film growth rates. Increasingly smoother a-C films were deposited with the increase of the Ar+ ion kinetic energy up to ∼200eV. However, much rougher films were produced for Ar+ ion kinetic energy higher than 200eV due to the significantly higher resputtering rate and intense irradiation that resulted in excessive surface damage.
Magnetotransport study on the defect levels of delta-doped In0.22Ga0.78As∕GaAs quantum wells
Authors: Lo Ikai , Lian J. R. , Wang H. Y. , Gau M. H. , Tsai J. K. , Chiang Jih-Chen , Li Y. J. , Hsu W. C.
Published: October 2006

We have studied the electronic properties of delta-doped In0.22Ga0.78As∕GaAs quantum wells (QWs) by van der Pauw Hall measurements and Shubnikov–de Haas measurements. From the temperature-dependent van der Pauw Hall measurements, we observed two kinds of donors, which have binding energies of 104±7 and 9.6±0.1meV. After inserting In0.1Ga0.9As layers between the In0.22Ga0.78As and GaAs layers, a single donor with binding energy of 50±2meV was observed. The carrier concentration determined by SdH measurements did not change after the QWs were illuminated at low temperature, which indicates that these deep donors could not produce a persistent photoconductivity in delta-doped In0.22Ga0.78As∕GaAs QWs.
Size dependence of optical properties and internal structure of plasma grown carbonaceous nanoparticles studied by in situ Rayleigh-Mie scattering ellipsometry
Authors: Hong Suk-Ho , Winter Jörg
Published: October 2006

We have analyzed the growth process of a-C:H nanoparticles in Ar–C2H2 and Ar–CH4 plasmas by means of in situ Rayleigh-Mie scattering ellipsometry. Complex refractive index (m=n−ki), mean particle radius (r), and particle size distribution (σ) of a-C:H nanoparticles are carefully determined and compared with those of a-C:H thin films deposited at similar conditions. It is found that, in both plasmas, small particles (r<25nm) have graphitelike properties whereas large particles have polymerlike characteristics. These results indicate that the particles have internal structures of a hard core and soft mantles on it. The size distribution of the nanoparticles in both Ar–CH4 and Ar–C2H2 plasmas is essentially monodisperse with a narrow Gaussian size distribution. A systematic comparison between the growth and atomic structure models for a-C:H materials and criteria for interstellar dust (ISD) grains known from astrophysical observations is made. Significant agreement is found in a wide range of radii, supporting earlier findings that plasma-polymerized a-C:H nanoparticles might be a good candidate as an ISD analog.
Improvement of magnetic particle stability upon annealing in an exchange-biased nanogranular system
Authors: Normile P. S. , De Toro J. A. , Andrés J. P. , González J. A. , Muñoz T. , Muñiz P. , Barbero A. J. , Riveiro J. M.
Published: October 2006

A nanogranular Co–CoO∕Ag system (with core-shell∕matrix structure), synthesized by reactive cosputtering, has been subjected to thermal treatments at progressively higher temperatures. The exchange-bias onset temperature increases in close correlation with the average superparamagnetic blocking temperature of the magnetic particles. This behavior, together with the nonmonotonic evolution of the exchange-bias field, is explained in terms of two structural relaxation processes previously characterized in simple Co∕Ag granular alloys: (i) segregation of Co solute atoms from the Ag-rich matrix, and (ii) particle coarsening.
A nonlinear constitutive model of magneto-thermo-mechanical coupling for giant magnetostrictive materials
Authors: Zheng Xiao Jing , Sun Le
Published: October 2006

The magnetostrictive strain-applied field curve typical of giant magnetostrictive materials is nonlinear and it is affected notably by prestress and temperature. A constitutive model to describe these properties is suggested in this paper. The model considered here is built on the Gibbs free energy function G(σij,Mk,T). Thermodynamic relations are used to obtain the constitutive expressions. Results based on the model show that the nonlinear property of magnetostrictive strain, the magnetization, and Young’s modulus under different prestress and temperature are in excellent agreement with experimental data. Moreover, the proposed model is convenient to be used in engineering applications since the parameters referred to the model can all be easily determined by experiments.
Nonintegrability of the three-body problems for the classical helium atom
Authors: Stuchi T. J. , López-Castillo A. , Almeida M. A.
Published: October 2006

We give a proof of the nonintegrability of an important three-body problem in atomic physics. We consider the classical model for the helium atom in full dimension, thus completing our previous proof for the frozen planetary approximation. To our knowledge there is not any such a proof in the literature. We apply a theorem due to Morales-Ruiz and Ramis: if a Hamiltonian system, derived from a homogeneous potential is integrable, then all integrability factors, related to the Hessian of the homogeneous potentials, satisfy certain conditions related to the degree of homogeneity. In the helium atom case, these coefficients should all be discrete. We exhibit a set of nondiscrete values determined analytically. This implies the nonintegrability of the helium atom without any computer aid. We also extend this theorem to various two-electron atoms. In the case of strange helium atoms we provide a computer aided proof of nonintegrability.
Strain fields around high-energy ion tracks in α-quartz
Authors: Follstaedt D. M. , Norman A. K. , Doyle B. L. , McDaniel F. D.
Published: October 2006

Transmission electron microscopy has been used to image the tracks of high-energy Au+26197 (374MeV) and I+18127 (241MeV) ions incident in a nonchanneling direction through a prethinned specimen of hexagonal α-quartz (SiO2). These ions have high electronic stopping powers in quartz, 24 and 19keV∕nm, respectively, which are sufficient to produce a disordered latent track. When the tracks are imaged with diffraction contrast using several different reciprocal lattice vectors, they exhibit a radial strain extending outward from their disordered centerline approximately 16nm into the crystalline surroundings. The images are consistent with a radial strain field with cylindrical symmetry around the amorphous track, like that found in models developed to account for the lateral expansion of amorphous SiO2 films produced by irradiation with high-energy ions. These findings provide an experimental basis for increased confidence in such modeling.
In
As
∕
In
Ga
As
P
sidewall quantum dots on shallow-patterned InP (311)A
Authors: Zhou D. , Nötzel R. , van Otten F. W. M. , van Veldhoven P. J. , Eijkemans T. J.
Published: October 2006

Highly strained InAs quantum dots (QDs) embedded in InGaAsP are formed at the fast-growing [01−1] mesa sidewall on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent dashlike QDs in the planar areas to the larger sidewall QDs resulting in well-distinguishable emission around 80K. The large high-energy shift of the PL from the sidewall QDs as a function of excitation power density is ascribed to the screening of the internal piezoelectric field. The linear polarization of the PL from the sidewall QDs is reversed compared to that of the quantum dashes in the planar areas due to the more symmetric shape and possible nonuniform strain in the sidewall QDs.
Buckling characteristics of SiGe layers on viscous oxide
Authors: Yu C.-Y. , Lee C.-J. , Lee C.-Y. , Lee J.-T. , Liao M. H. , Liu C. W.
Published: October 2006

Buckled SiGe films on viscous oxide with different Ge content are studied by wafer bonding and smart-cut process. Compressively strained SiGe layers on the viscous oxide were relaxed to form the buckled state after thermal treatment. Two-dimensional buckling on blanket films is observed. A higher Ge concentration results in a smaller buckling amplitude and a smaller buckling period. Both buckling amplitude and period increase as oxidation time is increased. A small SiGe film (mesa) area can inhibit buckling. Semiempirical analysis gives the critical area size, below which no buckling is observed in the equilibrium states. The critical area size decreases with increasing Ge concentration and decreasing thickness of SiGe films.
Transient dynamics and structure of optimal excitations in thermocapillary spreading: Precursor film model
Authors: Davis Jeffrey M. , Kataoka Dawn E. , Troian Sandra M.
Published: October 2006

Linearized modal stability theory has shown that the thermocapillary spreading of a liquid film on a homogeneous, completely wetting surface can produce a rivulet instability at the advancing front due to formation of a capillary ridge. Mechanisms that drain fluid from the ridge can stabilize the flow against rivulet formation. Numerical predictions from this analysis for the film speed, shape, and most unstable wavelength agree remarkably well with experimental measurements even though the linearized disturbance operator is non-normal, which allows transient growth of perturbations. Our previous studies using a more generalized nonmodal stability analysis for contact lines models describing partially wetting liquids (i.e., either boundary slip or van der Waals interactions) have shown that the transient amplification is not sufficient to affect the predictions of eigenvalue analysis. In this work we complete examination of the various contact line models by studying the influence of an infinite and flat precursor film, which is the most commonly employed contact line model for completely wetting films. The maximum amplification of arbitrary disturbances and the optimal initial excitations that elicit the maximum growth over a specified time, which quantify the sensitivity of the film to perturbations of different structure, are presented. While the modal results for the three different contact line models are essentially indistinguishable, the transient dynamics and maximum possible amplification differ, which suggests different transient dynamics for completely and partially wetting films. These differences are explained by the structure of the computed optimal excitations, which provides further basis for understanding the agreement between experiment and predictions of conventional modal analysis.
Mean excitation energies for the stopping power of atoms and molecules evaluated from oscillator-strength spectra
Authors: Kamakura Sachie , Sakamoto Naoki , Ogawa Hidemi , Tsuchida Hidetsugu , Inokuti Mitio
Published: October 2006

The mean excitation energy for the stopping power of matter, usually expressed by symbol I, is the only nontrivial material property in Bethe’s [Ann. Phys. 5, 325 (1930)] asymptotic stopping-power formula. It is therefore a crucial input for the evaluation of stopping power for swift charged particles. To calculate the I value of a material from its definition, it is necessary to know the oscillator-strength spectrum of the material in question over the entire range of the excitation energy. We evaluate the mean excitation energies of 32 atoms and molecules from the oscillator-strength spectra that were published by Berkowitz in 2002 [Atomic and Molecular Photoabsorption: Absolute Total Cross Sections (Academic, San Diego, 2002)]. We find that most of the present I values are consistent with those given in the literature. The I values of NO2, O3, and C60 in particular are evaluated in the present work. For buckminsterfullerene C60, an estimation of the I value is made also using the local-plasma approximation, in an attempt at understanding differences in the I values of carbon in a free atom, a C60 molecule, and graphite. Systematic trends of I values obtained in the present calculation are discussed, in the context of the Thomas-Fermi model.
Layer thickness effect on the magnetoresistance of a current-perpendicular-to-plane spin valve
Authors: Tan S. G. , Jalil M. B. A. , Bala Kumar S. , Han G. C. , Zheng Y. K.
Published: October 2006

We performed a theoretical study and analysis of the effect of modifying the layer thicknesses of a current-perpendicular-to-plane (CPP) spin valve multilayer on its magnetoresistance (MR) ratio. An increase in the ferromagnetic (FM) layer thickness results in (i) an increase in the spin-dependent component of its total resistance, thereby resulting in higher MR, but also leads to (ii) greater spin relaxation in that layer and (iii) an anomalous MR effect in the high resistance regime, both of which suppress the MR ratio. The interplay of these effects results in a complex MR dependence on FM thickness, instead of the simple monotonic MR increase predicted by the two-current model. It also explains the existence of an optimum FM thickness for maximum MR ratio, as evidenced by experimental data. Finally, we consider the MR dependence on the strength and spin selectivity of interfacial resistances, which can either arise naturally or be engineered in the spin valve structure. The study of the combined effects of the FM layer thickness and resistivity, the MR suppression in the high resistive limit, and the competitive spin-dependent scattering in the bulk and at the interfaces is essential for optimizing the structure and material of a practical CPP spin valve to achieve the maximum MR ratio.
Inverse modeling of a workpiece temperature and melting depth during microthermal machining by scanning thermal microscope
Authors: Hsu Jung-Chang , Fang Te-Hua , Chang Win-Jin
Published: October 2006

In this study, a general methodology for estimating the temperature of the upper surface of the workpiece and the melting depth during microthermal machining using scanning thermal microscopy has been proposed. First the probe in the processing system was considered as an inverse heat conduction problem with an unknown workpiece temperature. Once the temperature of the upper surface of the workpiece was estimated, then the workpiece was also regarded as another inverse heat transfer problem due to an unknown melting depth in the boundary condition. The conjugate gradient method was used to solve the inverse problems. In addition, this methodology herein can also be applied to solve other transient heat conduction problems, which involve latent heat transfer and form a solid and liquid phase such as laser processing, solidification in continuous casting process, and transient recording system on phase-change material using atomic force microscopy.
Response of a Zr-based bulk amorphous alloy to shock wave compression
Authors: Turneaure Stefan J. , Winey J. M. , Gupta Y. M.
Published: October 2006

Plane shock wave experiments were performed on bulk amorphous alloy (BAA) samples having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. Peak compressive stresses ranged from 4to16.4GPa. Piezoelectric pins and a velocity interferometer were used to measure elastic shock speeds and particle velocity histories, respectively. The elastic Hugoniot curve was determined and the Hugoniot elastic limit (HEL) was measured to be approximately 7.0GPa, a value significantly higher than expected from quasistatic uniaxial stress data. Impact loading beyond the HEL results in a distinct two wave structure due to elastic-plastic deformation. Our data also show clear evidence for strength loss under shock loading above the HEL. Unlike most metals, the present data show distinct elastic response during unloading. We present a continuum model to describe the deformation response of the BAA to shock loading. Simulations using this time-dependent, strain-softening strength model were able to successfully match the measured wave profiles. The calculated profiles indicate that the characteristic time for stress relaxation is very small (few nanoseconds) and confirm that a significant loss of strength occurs as the plastic wave propagates through the material. When the material is shocked to a peak stress of 16.4GPa, our model indicates that the yield stress in the shocked state is reduced by at least 0.7GPa from its value of 2.7GPa at the HEL.