bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of plasma space potentials and chemical vapor deposition of nanocrystalline diamond films in surface-wave excited low-pressure plasmas
Authors: Kim Jaeho , Katsurai Makoto
Published: January 2007

A dc biasing method, developed in this work, has been investigated for the control of plasma space potentials and the chemical vapor deposition of nanocrystalline diamond (NCD) films in a planar surface-wave excited plasma at gas pressures below 100mTorr. A negative dc voltage was applied to a specially shaped thin metal plate attached below the upper dielectric window with respect to the grounded substrate and discharge chamber, instead of the conventional positive substrate dc biasing method. Plasma parameters were measured using a single-probe and deposited films were evaluated by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The application of the dc bias voltage (0to−150V) enabled the net dc bias current (−0.46–+0.6A) to be varied and plasma space potentials to be decreased over a wide range (34–7V) in the bulk region, resulting in the control of the bombarding ion energy on the grounded substrate. The vertical plasma parameter profiles showed the spatial difference in electron temperature between the local surface-wave region (∼10eV) near the upper dielectric window and the bulk region (below 3eV). It was found that the spatial difference in electron temperature permits the control of net currents and plasma space potentials in the dc biasing method. NCD films were deposited with smooth surfaces (rms=12.4nm), a deposition rate of about 63nm∕h, and a continuous surface coverage on Si substrates maintained at a temperature of about 650°C for hydrogen-based CO–H2 plasmas by biasing with −70V to the metal plate.
Actin polymerization under pressure: A theoretical study
Authors: Artyomov Maxim N. , Freed Karl F.
Published: January 2007

An extended Flory-Huggins-type equilibrium polymerization theory for compressible systems is used to describe experimental data for the unusual pressure and temperature dependence of the equilibrium polymerization of G-actin to F-actin. The calculations provide rich insights into the reaction mechanism and the thermodynamics of actin polymerization at the molecular level. Volume changes associated with individual steps of the mechanism are calculated to be ΔVactiv=(s1*−s1)υ0=+1553ml∕mol for the activation reaction, ΔVdim=(s2−s1*)υ0=−3810ml∕mol for dimerization, and ΔVprop=(sP−s1)υ0=+361ml∕mol for the propagation reaction, where s1υ0, s1*υ0, s2υ0, and sPυ0 are the monomer volumes in the G-actin monomer, the activated G-action, the dimer, and higher polymers, respectively. Comparison with experimental measurements is made, and discrepancies are discussed.
Zero dispersion slow light with low leakage loss in defect Bragg fiber
Authors: Lin Chenxi , Zhang Wei , Huang Yidong , Peng Jiangde
Published: January 2007

By introducing a defect layer into the periodic cladding of Bragg fiber, the core mode and the defect mode may anticross near their cutoff inside band gap. The defect location suppresses and flattens dramatically the group velocity (vg) of coupled core mode and the defect thickness changes gradually its dispersion. Theoretical investigation reveals zero dispersion and zero dispersion slope at various low vg’s can be achieved simultaneously at arbitrary wavelengths. Specially, the proper defect in the sixth bilayer leads to the lowest vg of 0.074 of light speed in vacuum at 1550nm. The optical energy is confined well in the core and the leakage loss is sufficiently low.
Wavelet investigation of La0.5Ca0.5CoO3−δ x-ray absorption data
Authors: Sahnoun M. , Daul C. , Haas O.
Published: January 2007

Morlet wavelet transformation was used to analyze the Co K-edge extended x-ray absorption spectrum of La0.5Ca0.5CoO3−δ. Due to recent success in wavelet analysis of extended x-ray absorption fine structure (EXAFS) data we hoped that the Co–La scattering path could be separated from the Co–Ca scattering path in the EXAFS spectrum of La0.5Ca0.5CoO3−δ. The result showed a certain resolution of the wavelet transformed spectrum in the k space. Using theoretical scattering functions of the individual scattering paths calculated with ab initio multiple scattering codes (FEFF), it was possible to assign some maxima in the wavelet transformation EXAFS spectrum. The Co–La scattering path could be identified, but no additional information about the Co–Ca scattering function was obtained. A detailed analysis of the theoretical Co–La and Co–Ca scattering functions revealed that the two scattering functions overlap considerably in k space and have almost the same frequency. Morlet wavelet transformation of the sum of the two theoretical scattering functions did not allow a satisfactory separation of the two scattering functions. This separation is probably only possible with wavelets, which mimic the fundamental properties of the real scattering function more accurately.
Chemical analysis of HfO2∕Si (100) film systems exposed to NH3 thermal processing
Authors: Lysaght Patrick S. , Barnett Joel , Bersuker Gennadi I. , Woicik Joseph C. , Fischer Daniel A. , Foran Brendan , Tseng Hsing-Huang , Jammy Raj
Published: January 2007

Nitrogen incorporation in HfO2∕SiO2 films utilized as high-k gate dielectric layers in advanced metal-oxide-semiconductor field effect transistors has been investigated. Thin HfO2 blanket films deposited by atomic layer deposition on either SiO2 or NH3 treated Si (100) substrates have been subjected to NH3 and N2 anneal processing. Several high resolution techniques including electron microscopy with electron energy loss spectra, grazing incidence x-ray diffraction, and synchrotron x-ray photoelectron spectroscopy have been utilized to elucidate chemical composition and crystalline structure differences between samples annealed in NH3 and N2 ambients as a function of temperature. Depth profiling of core level binding energy spectra has been obtained by using variable kinetic energy x-ray photoelectron spectroscopy with tunable photon energy. An “interface effect” characterized by a shift of the Si4+ feature to lower binding energy at the HfO2∕SiO2 interface has been detected in the Si 1s spectra; however, no corresponding chemical state change has been observed in the Hf 4f spectra acquired over a broad range of electron take-off angles and surface sensitivities. The Si 2p spectra indicate Si–N bond formation beneath the HfO2 layer in the samples exposed to NH3 anneal. The NH3 anneal ambient is shown to produce a metastable Hf–N bond component corresponding to temperature driven dissociation kinetics. These findings are consistent with elemental profiles across the HfO2∕Si(100) interface determined by electron energy loss spectroscopy measurements. X-ray diffraction measurements on similarly treated films identify the structural changes resulting from N incorporation into the HfO2 films.
Effect of dc bias control on the power absorption in low-pressure, radio-frequency capacitive sheaths
Authors: Gahan D. , Soberón F.
Published: January 2007

Many of today’s processing plasma tools are operated at low pressures to achieve high etch directivity and reduce side erosion on the wafer. At these pressures electron-neutral collisions are rare and the electrons cannot gain energy through the ohmic heating process. Instead, the heating mechanism is attributed to a stochastic process between the electrons and the sheath electric field. Theoretical models of this stochastic process include the hard wall approximation and the pressure heating effect. The former is inconsistent with electron current conservation at the sheath, while the latter shows a difference in power absorption when electron loss to the electrodes is considered. This article examines the effects of electron current on a capacitive sheath by controlling this current with an additional dc bias on the electrode. Experimental and particle-in-cell model results for a low-pressure argon plasma are compared and presented. Results show that the electron power absorption is more effective when the electron current is removed. The model also shows a high harmonic content on the sheath voltage which is attenuated by removing the electron current. These high-frequency harmonics are measured in the experiment with a floating probe, and their correlation with the electron current is in agreement with the model results.
Growth of ternary PbTiOx films in a combination of binary oxide atomic layer depositions
Authors: Watanabe Takayuki , Hoffmann-Eifert Susanne , Mi Shaobo , Jia Chunlin , Waser Rainer , Hwang Cheol Seong
Published: January 2007

Ternary PbTiOx films were deposited at 240°C on Pt-covered Si substrates using a combination of liquid injection atomic layer depositions of binary TiOx and PbO films. Ti(OC3H7)2(C11H19O2)2 [Ti(Oi−Pr)2(DPM)2] and Pb(C11H19O2)2 [Pb(DPM)2] dissolved in ethylcyclohexane and H2O were used as source materials. The deposition rates of Pb and Ti were enhanced in the ternary process compared to their binary processes under comparable deposition conditions. The Pb∕Ti ratio of PbTiOx films saturated with an increase in Ti precursor input, while it continued to increase with an increasing Pb precursor input. The self-regulated growth nature of the Pb–O layer in the binary film growth was lost in the mixed PbTiOx process as a result of interaction with the predeposited Ti–O layer. It was confirmed that for the PbTiOx film to grow on Pt substrates, an initial incubation period is required. Both Pb–O and Ti–O layers shared a common incubation period of up to ten sequences. The incubation period was shortened by increasing the input of Pb precursor. It was independent of the input of the Ti precursor and the order of precursor supply. This variable incubation period was considered as a potential key issue for growing stoichiometric and uniform multicomponent films over three-dimensional (3D) structures. The order of precursor supply affected the effective deposition rate after the incubation period. A sequence starting with a Ti precursor injection showed a higher growth rate than a sequence that started with a Pb precursor supply. A PbTiOx film was deposited on a 3D substrate precoated with an Ir layer to demonstrate the uniformity in film thickness and cation composition. Although the present PbTiOx process does not have an ideal wide-process window in the cation composition, the PbTiOx film showed uniform coverage and the distribution of cation composition over the hole structure was within ±10%.
The effect of low-energy-ion irradiation on photoluminescence of porous silicon
Authors: Zhao N. Q. , Jin Y. , Du X. W. , Fu Y. S.
Published: January 2007

Porous silicon (PS) was irradiated by low-energy (800eV) nitrogen or argon ions. The photoluminescence (PL) properties changed significantly after irradiation, namely, PL was first quenched and then recovered as the postirradiated PS stored in air. X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy results indicate that the Si–N bonds were formed during low-energy-nitrogen-ion irradiation, while Raman scattering spectroscopy suggests the crystal structure of PS did not change during ion irradiation. The PL quenching is due to the defects created by ion irradiation, whereas the PL recovery originates from the oxidation of Si–H back bonds and the formation of radiative recombination centers; the Si–N bonds are helpful to obtain high PL intensity.
Fabrication of H+ implanted channel waveguides in Y3Al5O12:Nd,Tm single crystal buried epitaxial layers for infrared to blue upconversion laser systems
Authors: Szachowicz Marta , Moretti Paul , Joubert Marie-France , Couchaud Maurice , Ferrand Bernard
Published: January 2007

Fabrication and intense infrared to blue upconversion emission of proton-implanted Tm3+, Nd3+:Y3Al5O12 (YAG) channel waveguides are reported for the first time to authors’ knowledge. The single or multiple implanted channels are buried by positive induced index change in stacked planar layers grown by liquid-phase epitaxy on pure YAG substrates. The Nd3+ codoping considerably enhances the IR to blue upconversion emission of Tm3+ ions after excitation in resonance with either Nd3+ or Tm3+ absorption transition around 800nm.
Radiation properties in electron waveguides
Authors: Chen Yupeng , Wu Thomas X.
Published: January 2007

We study the radiation properties in electron waveguide structure with multistep discontinuities and soft wall lateral confinement. Radiation mechanism and conditions are examined by numerical simulation of dispersion relations and transport properties. The study of geometry variations shows its significant impact on the radiation intensity and direction. In particular, the periodic corrugation structure exhibits strong directional radiation. This interesting feature may be useful to design a nanoscale transmitter, a communication device for future nanoscale system.
Singlet-triplet gaps in large multireference systems: Spin-flip-driven alternatives for bioinorganic modeling
Authors: de la Lande Aurélien , Moliner Vicent , Parisel Olivier
Published: January 2007

The proper description of low-spin states of open-shell systems, which are commonly encountered in the field of bioinorganic chemistry, rigorously requires using multireference ab initio methodologies. Such approaches are unfortunately very CPU-time consuming as dynamic correlation effects also have to be taken into account. The broken-symmetry unrestricted (spin-polarized) density functional theory (DFT) technique has been widely employed up to now to bypass that drawback, but despite a number of relative successes in the determination of singlet-triplet gaps, this framework cannot be considered as entirely satisfactory. In this contribution, we investigate some alternative ways relying on the spin-flip time-dependent DFT approach [Y. Shao et al. J. Chem. Phys. 118, 4807 (2003)]. Taking a few well-documented copper-dioxygen adducts as examples, we show that spin-flip (SF)-DFT computed singlet-triplet gaps compare very favorably to either experimental results or large-scale CASMP2 computations. Moreover, it is shown that this approach can be used to optimize geometries at a DFT level including some multireference effects. Finally, a clear-cut added value of the SF-DFT computations is drawn: if pure ab initio data are required, then the electronic excitations revealed by SF-DFT can be considered in designing dramatically reduced zeroth-order variational spaces to be used in subsequent multireference configuration interaction or multireference perturbation treatments.
Geometric constraints in semiclassical initial value representation calculations in Cartesian coordinates: Excited states
Authors: Issack Bilkiss B. , Roy Pierre-Nicholas
Published: January 2007

The authors show that a recently proposed approach [J. Chem. Phys. 123, 084103 (2005)] for the inclusion of geometric constraints in semiclassical initial value representation calculations can be used to obtain excited states of weakly bound complexes. Sample calculations are performed for free and constrained rare gas clusters. The results show that the proposed approach allows the evaluation of excited states with reasonable accuracy when compared to exact basis set calculations.
Coarse-grained simulation of amphiphilic self-assembly
Authors: Michel David J. , Cleaver Douglas J.
Published: January 2007

The authors present a computer simulation study of amphiphilic self-assembly performed using a computationally efficient single-site model based on Gay-Berne [J. Chem. Phys. 74, 3316 (1981)] and Lennard-Jones particles. Molecular dynamics simulations of these systems show that free self-assembly of micellar, bilayer, and inverse micelle arrangements can be readily achieved for a single model parametrization. This self-assembly is predominantly driven by the anisotropy of the amphiphile-solvent interaction, amphiphile-amphiphile dispersive interactions being found to be of secondary importance. While amphiphile concentration is the main determinant of phase stability, molecular parameters such as head group size and interaction strength also have measurable affects on system properties.
Enhanced alignment and orientation of polar molecules by vibrational resonant adiabatic passage
Authors: Yatsenko L. P. , Guérin S. , Amniat-Talab M. , Jauslin H. R.
Published: January 2007

The authors show that polar molecules can be adiabatically aligned and oriented by laser pulses more efficiently when the laser frequencies are vibrationally resonant. The aligned molecules are found in a superposition of vibrational pendular states, each associated with the alignment of the rotor in one vibrational state. The authors construct the dressed potential associated with this mechanism. Values of detunings and field amplitudes are given to optimize the degree of alignment and orientation for the CO molecule.
Pulsed-field ionization spectroscopy of high Rydberg states (n=50–200) of bis(η6-benzene)chromium
Authors: Choi Kyo-Won , Choi Sunyoung , Baek Sun Jong , Kim Sang Kyu
Published: January 2007

The ionization behavior of the high Rydberg states of bis(η6-benzene)chromium in the presence of ac and/or dc fields has been explored. The application of an ac scrambling field at the time of laser excitation lengthens the lifetime of the Rydberg state by almost two orders of magnitude. The lifetime enhancement by the scrambling field is much more effective for n<100 than it is for n>100 Rydberg states. The pulsed-field ionization of Rydberg states of n<100 shows the typical diabatic ionization behavior for low n. The two distinct ionization behaviors observed for the relatively low (n=50–100) and high (n=100–200) Rydberg states suggest that the former originate from the optically accessed nf Rydberg series, whereas the latter are due to np Rydberg series. Based on the understanding of the ionization behavior of bis(η6-benzene)chromium, the accurate ionization potential is deduced to give IP=5.4665±0.0003eV. Optimization of the various electric field conditions greatly enhances the spectral sensitivity of the mass-analyzed threshold ionization (MATI) spectroscopy. The high-resolution MATI spectrum of the title molecule obtained here provides precise cationic vibrational frequencies for many skeletal and benzene ring modes. A number of vibrational modes are newly identified, and the ambiguity regarding to some mode assignments is now clearly resolved through the Frank-Condon analysis based on ab initio calculations.
Phase diagrams of alkali halides using two interaction models: A molecular dynamics and free energy study
Authors: Rodrigues Pedro C. R. , Silva Fernandes Fernando M. S.
Published: January 2007

Phase diagrams for potassium and sodium chlorides are determined by molecular dynamics and free energy calculations. Two rigid-ion interaction models, namely, the Born-Mayer-Huggins (BMH) and Michielsen-Woerlee-Graaf (MWG) effective pair potentials, have been used. The critical and triple point properties are discussed and compared with available experimental and simulation data. The MWG model reproduces the experimental liquid-gas equilibria better than the BMH model, being the accordance very good in the lowest temperature region of the coexistent liquids, particularly for NaCl. However, both models underestimate the critical temperatures of KCl and NaCl. Relatively to the solid-gas equilibria, the models do not reproduce well the experimental data. As for the solid-liquid coexistences either the BMH or the MWG models appear unrealistic.
Two-peak property in asymmetric left-handed metamaterials
Authors: Song J. , Zhao W. , Fu Q. H. , Zhao X. P.
Published: January 2007

The transmission and reflection properties of left-handed metamaterials (LHMs) with the local asymmetry are investigated at the X-band frequency range in free space. Experimental results show that two transmission peaks and two reflection dips are exhibited in the presence of the asymmetric configuration of split ring resonators (SRRs). Furthermore, the position and intensity of the peaks and dips are significantly dependent on the asymmetry between the SRRs and the wires. In addition, the numerical calculations indicate that two left-handed frequency regions can exist if another configuration of the SRRs is introduced into the LHMs, which is in agreement with the experimental results.
Calibration of nonlocal scaling effect parameter for free vibration of carbon nanotubes by molecular dynamics
Authors: Duan W. H. , Wang C. M. , Zhang Y. Y.
Published: January 2007

In this paper, the small scaling parameter e0 of the nonlocal Timoshenko beam theory is calibrated for the free vibration problem of single-walled carbon nanotubes (SWCNTs). The calibration exercise is performed by using vibration frequencies generated from molecular dynamics simulations at room temperature. It was found that the calibrated values of e0 are rather different from published values of e0. Instead of a constant value, the calibrated e0 values vary with respect to length-to-diameter ratios, mode shapes, and boundary conditions of the SWCNTs. In addition, the physical meaning of the scaling parameter is explored. The results show that scaling parameter assists in converting the kinetic energy to the strain energy, thus enabling the kinetic energy to be equal to the strain energy. The calibrated e0 presented herein should be useful for researchers who are using the nonlocal beam theories for analysis of micro and nano beams/rods/tubes.
Stability and debris in high-brightness liquid-metal-jet-anode microfocus x-ray sources
Authors: Otendal M. , Tuohimaa T. , Hertz H. M.
Published: January 2007

We investigate the x-ray spot stability and the debris emission in liquid-metal-jet anode electron-impact x-ray sources operating in the 10–100W microfocus regime. The x-ray spot size is 15–23μm in diameter and the electron-beam power density is up to ∼210kW∕mm2, an order of magnitude higher than for conventional microfocus sources. In the power range of the investigation the source is stable in terms of spot size and position. The debris emission rate increases exponentially with the applied electron-beam power but may be reduced by combining larger and faster target jets with smaller e-beam foci and by mitigation schemes. It is concluded that the investigated factors will not limit the performance and function of liquid-metal-jet-anode electron-impact microfocus sources when operating in this high-brightness regime.
Magnetic properties of polymer bonded soft magnetic particles for various filler fractions
Authors: Anhalt M. , Weidenfeller B.
Published: January 2007

Samples of polypropylene filled with iron powder from 20to85vol% filler content were produced and examined. The permeabilities of the materials versus the magnetic field strength (up to 50kA∕m) were recorded as well as the low field and maximum permeability and the coercivity versus filler fractions were measured and compared with existing mathematical models. Investigations of the permeability as well as of the coercivity of two materials containing 85vol% filler material varying in mean particle size versus frequency (1Hz⩽f⩽2000Hz) and magnetic field strength have been carried out. Results show permeabilities μlow>100 for highest filled materials with low coercivities. Measurement data were compared with theoretical models.
Electrical characterization of metal/pentacene contacts
Authors: Diao Lei , Daniel Frisbie C. , Schroepfer Dominic D. , Paul Ruden P.
Published: January 2007

We report on the results of electrical characterization experiments on metal/pentacene contacts. The metals explored were gold, silver, and platinum. Two kinds of devices were fabricated and tested: symmetric metal/pentacene/metal structures and nonsymmetric metal/pentacene/indium-tin-oxide structures. The rectification ratio of the latter devices was found to depend strongly on the metal and ranged between 2 and 103 for applied voltages of ±1V. Schottky barrier heights were extracted from the reverse current activation energy measurements over the temperature range of ∼240–340K. Numerical device modeling using the experimentally determined Schottky barrier heights yielded results that are consistent with the experimental current-voltage characteristics, and indicated the presence of a non-negligible (trapped) positive space charge in the pentacene films.
Reduction of switching fields of submicrometer sized magnetic tunnel junction with NiFe-based synthetic ferrimagnetic free layer
Authors: Lee Young Min , Ando Yasuo , Miyazaki Terunobu , Kubota Hitoshi
Published: January 2007

We fabricated submicrometer sized magnetic tunnel junctions (MTJs) with soft NiFe-based synthetic ferrimagnet (SynF) free layers. An extremely low switching field of 13Oe was achieved when the stacking structure of the free layer was NiFe(2 nm)/CoFe(0.2 nm)/Ru(0.4 nm)/CoFe(0.2nm)/NiFe(2.1 nm) with 0.4μm cell. The switching field of the SynF structure was almost independent of the cell width. Small magnetic anisotropy of NiFe and enhanced antiferromagnetic coupling strength from insertion of 0.2-nm-thick CoFe were important attributes for the low switching field in the submicrometer sized MTJs.
Structure and photoluminescence of ZnSe nanostructures fabricated by vapor phase growth
Authors: Philipose U. , Sun Ping , Xu Tao , Ruda Harry E. , Yang L. , Kavanagh K. L.
Published: January 2007

The synthesis of ZnSe nanowires is a rapidly expanding research field with numerous applications. Key to realizing the potential of such nanowires is an ability to prepare structurally uniform defect-free material. Microstructure studies on as-grown nanostructures reveal that the structure of these nanowires are highly sensitive to the growth temperature, with higher temperature growth (750°C) resulting mostly in nanoribbons having different morphologies. Planar defects (mainly stacking faults and twins) are found to extend throughout the nanoribbons. At lower growth temperatures (650°C) structurally uniform nanowires are typically found. Photoluminescence (PL) measurements on crystalline nanowires show that the spectrum comprises two characteristic peaks corresponding to strong near band edge emission, and a weaker emission associated with defect states. However, the PL spectra of ZnSe nanoribbons which contain a high density of structural defects are dominated by defect related emission.
Analysis for toggling magnetic random access memories with low writing field using four ferromagnetic layers for free layer stack
Authors: Suzuki T. , Fukumoto Y. , Ishiwata N.
Published: January 2007

We calculate writing characteristics of two kinds of low-current magnetic random access memory (MRAM) devices using a single domain model. A four-layer synthetic antiferromagnet (SAF) has four antiferromagnetically coupled ferromagnetic (FM) layers, and a two-SM-layer-FC SAF has a two-FM-layer SAF with ferromagnetically coupled (FC) two soft magnetic (SM) layers. The threshold field of these free layers can be calculated analytically. The spin flop field of four-FM-layer SAF film is independent of the strength of antiferromagnetic coupling (AFC) between inner films. The saturation field increases with increasing the AFC strength. The spin flop field of the two-SM-layer-FC SAF film decreases, and the saturation field increases with decreasing ferromagnetic coupling strength. However, activation energy analysis demonstrates that both types of films exhibit a decrease in activation energy near the spin flop field. Considering the activation energy decrease during the toggling write sequence and a sufficient writing margin, MRAM with four ferromagnetic layers decreases writing current by 40%.
Oscillation-induced static deflection in scanning force microscopy
Authors: Heim Lars-Oliver , Johannsmann Diethelm
Published: January 2007

Employing an atomic force microscope (AFM) in conjunction with a quartz crystal microbalance, we have investigated how a high-frequency lateral oscillation of the substrate influences the imaging process of the AFM. It was found that the time-averaged deflection of the cantilever (both vertical and lateral) changed when the oscillation of the quartz resonator was turned on. The vertical-tip–substrate distance increased, while the lateral force of sliding decreased at the same time. A mode of imaging based on this effect was demonstrated. The oscillation was periodically interrupted at a rate of 73Hz and the corresponding periodic modulation of the deflection was filtered and amplified using lock-in amplifiers. Slowly scanning the sample and displaying the outputs of the lock-in amplifiers versus x and y produced an image of the oscillation-induced static (OIS) deflection. Various mechanisms by which a lateral oscillation can generate a time-averaged vertical force are discussed. The fact that the vertical OIS deflection scaled linearly with amplitude and, also, that the OIS deflection was stronger on the sloped portions of the sample than on the flat regions, suggests a geometric interpretation. We term the phenomenon “cobble stone effect.” Experiments in liquids showed that the generation of an OIS deflection required immediate contact between the sample and the tip: a search for an OIS deflection in the presence of a liquid-filled gap between the sample and the tip yielded a negative result. Hydrodynamic forces are thereby ruled out as dominating factors.
Study of anisotropic character induced by microscale laser shock peening on a single crystal aluminum
Authors: Chen Hongqiang , Wang Youneng , Kysar Jeffrey W. , Yao Y. Lawrence
Published: January 2007

The beam spot size used in microscale laser shock peening is of the same order as grain size in many materials. Therefore, the deformation is induced in only a few grains so that it is necessary to treat the material as being anisotropic and heterogeneous. In order to investigate the corresponding anisotropic features, different experimental techniques and three-dimensional finite element simulations are employed to characterize and analyze anisotropic responses for single crystal aluminum under single pulse shock peening at individual locations. X-ray microdiffraction techniques based on a synchrotron light source affords micron scale spatial resolution and is used to measure the residual stress spatial distribution along different crystalline directions on the shocked surface. Crystal lattice rotation due to plastic deformation is also measured with electron backscatter diffraction. The result is experimentally quantified and compared with the simulation result obtained from finite element analysis. The influence of crystalline orientation is investigated using single crystal plasticity in finite element analysis. The results of the finite element simulations of a single shock peened indentation are compared with the finite element results for a shocked line of plain strain deformation assumption. The prediction of overall characters of the anisotropic characters associated with microscale laser shock peening will lay the ground work for the practical application of microscale laser shock peening.
Excimer UV-assisted rapid thermal annealing of PbLa(Zr,Ti)O3 thin films by a sol-gel deposition method
Authors: Shannigrahi S. R. , Lim X. , Tay F. E. H.
Published: January 2007

Excimer UV-assisted rapid thermal annealing (UV-RTA) process has been employed to fabricate sol-gel derived ferroelectric Pb0.97La0.03(Zr0.53Ti0.47)O3 (PLZT) thin films on Pt∕Ti∕SiO2∕Si substrates. X-ray diffraction analysis showed that the single phase PLZT thin film can be achieved at a relatively low processing temperature of 580°C. The films appeared to have improved dielectric properties with dielectric constant (ε) and loss (tanδ) values of 3300 and 0.03 at 1kHz, respectively. Comparatively good remnant polarization (Pr) value of 36μCcm−2 and coercive field (Ec) value of 60kVcm−1 along with a good fatigue resistance up to 1010 switching cycles have been observed. This method of fabrication of the Pb-based material with the aid of UV-RTA at a comparatively lower temperature opens the door for their better employability in the Si integrated circuit technology.
Temperature dependence of the Raman-active modes in the nonpolar a-plane GaN film
Authors: Yan Fawang , Gao Haiyong , Zhang Huixiao , Wang Guohong , Yang Fuhua , Yan Jianchang , Wang Junxi , Zeng Yiping , Li Jinmin
Published: January 2007

Temperature dependences of the polarized Raman scattering spectra in the backscattering configuration of the nonpolar a-plane (or [112¯0]-oriented) GaN thin film are analyzed in the range from 100to570K. The nonpolar a-plane GaN film is grown on an r-plane [or (11¯02)-oriented] sapphire substrate by metal organic chemical vapor deposition. The spectral features of the Raman shifts, intensities, and linewidths of the active phonons modes A1(TO), E1(TO), and E2(high) are significantly revealed, and corresponding temperature coefficients are well deduced by the empirical relationships. With increasing the measurement temperature the Raman frequencies are substantially redshifted and the linewidths gradually broaden. The compressive-strain-free temperature for the nonpolar a-plane GaN film is found to be at about 400K. Our studies will lead to a better understanding of the fundamental physical characteristics of the nonpolar GaN film.
An effective route for the fabrication of rare earth-iron-boron thin films having strong c-axis texture and excellent hard magnetic properties
Authors: Tang S. L. , Gibbs M. R. J. , Davies H. A. , Liu Z. W. , Lane S. C. , Mateen N. E.
Published: January 2007

Rare-earth iron-boron (RE-Fe–B) thin films with a c-axis texture were prepared on a Ta (110) buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The microstructure, magnetic structure, and magnetic properties of these films were studied as a function of the deposition temperature. The results show that c-axis texture can be obtained over a wide range of deposition temperatures and that the degree of c-axis orientation improves with deposition temperature. It was established that deposition of a RE-Fe–B thin film to obtain grains with a strong c-axis RE2Fe14B texture, coexisting with an amorphous phase, followed by annealing at higher temperature, is an effective route for obtaining excellent hard magnetic properties. Initial results show that a film, which was deposited at 470°C and annealed at 590°C, had a high perpendicular coercivity of 1.8T, in combination with a large maximum energy product of 238kJ∕m3.
Multiple harmonic plasma emission
Authors: Yi Sumin , Yoon Peter H. , Ryu Chang-Mo
Published: January 2007

A generalized weak turbulence theory for electromagnetic emission at multiple harmonics of the plasma frequency is developed. In the literature, the electromagnetic emission at the plasma frequency and/or its second harmonic has been intensively studied. However, the emission at harmonics higher than the second harmonic is scarcely discussed. In the present paper, the higher harmonic plasma emission is explained by taking the interactions between the transverse mode and electrostatic nonlinear eigenmodes into consideration. The present analysis incorporates electrostatic nonlinear harmonic Langmuir waves into the fully electromagnetic weak turbulence formalism recently reformulated on the basis of the statistical mechanical Klimontovich approach. The wave kinetic equations for the transverse electromagnetic and Langmuir waves interacting with the harmonic Langmuir waves are derived, on the basis of which the emission of electromagnetic waves near multiple harmonics of the plasma frequency is qualitatively discussed.
On the quantum theory of electron transfer: Effect of potential surfaces of the reactants and products
Authors: Banerjee Sumana , Gangopadhyay Gautam
Published: January 2007

In this study the electron transfer theory for the high frequency intramolecular mode and low frequency medium mode has been rederived using different methods. For a single-mode case when the reactant surface is not in a thermal equilibrium but in a thermocoherent state the authors have derived the rate and discussed about the quantum features of the rate. In the limit of very low and very high temperatures the expressions are derived analytically and compared with the case of thermal distribution. Secondly, a Franck-Condon factor for a multimode displaced, distorted, and Duschinsky rotated adiabatic potential surfaces has been derived to obtain the rate. Lastly, a systematic investigation is made to show the temperature dependence on the rate due to displacement, distortion, and Duschinsky rotation of the harmonic potential energy surfaces of the reactant and product manifold.
Nuclear magnetic shielding constants of liquid water: Insights from hybrid quantum mechanics/molecular mechanics models
Authors: Kongsted Jacob , Nielsen Christian B. , Mikkelsen Kurt V. , Christiansen Ove , Ruud Kenneth
Published: January 2007

We present a gauge-origin independent method for the calculation of nuclear magnetic shielding tensors of molecules in a structured and polarizable environment. The method is based on a combination of density functional theory (DFT) or Hartree-Fock wave functions with molecular mechanics. The method is unique in the sense that it includes three important properties that need to be fulfilled in accurate calculations of nuclear magnetic shielding constants: (i) the model includes electron correlation effects, (ii) the model uses gauge-including atomic orbitals to give gauge-origin independent results, and (iii) the effect of the environment is treated self-consistently using a discrete reaction-field methodology. The authors present sample calculations of the isotropic nuclear magnetic shielding constants of liquid water based on a large number of solute-solvent configurations derived from molecular dynamics simulations employing potentials which treat solvent polarization either explicitly or implicitly. For both the O17 and H1 isotropic shielding constants the best predicted results compare fairly well with the experimental data, i.e., they reproduce the experimental solvent shifts to within 4ppm for the O17 shielding and 1ppm for the H1 shielding.
Internal wave transmission in nonuniform flows
Authors: Nault J. T. , Sutherland B. R.
Published: January 2007

We compute transmission coefficients for internal waves propagating in a fluid with continuously varying stratification and background shear. In stationary fluid the transmission is characterized by the ratio of transmitted to incident energy. More generally, transmission across the shear is appropriately characterized by the ratio of transmitted to incident pseudoenergy flux. First, we examine the transmission and reflection of internal waves incident upon a weakly stratified layer in stationary fluid focusing upon the opposing limits of piecewise-linear theory and a heuristic application of Wentzel-Kramers-Brillouin (WKB) theory. We find the WKB prediction is reasonably accurate if the distance of transition from strong to weak stratification is as small as one sixth the vertical wavelength of the transmitted waves. In the limit of infinitesimally small transition distances the prediction of piecewise-linear theory is reproduced. Second, we consider the transmission of internal waves across a shear layer which initially is uniformly stratified. In particular, we show that significant transmission is possible across critical layers if the minimum gradient Richardson number is less than 1∕4. Finally, we show that internal waves can partially transmit across a mixed region that results from the evolution of an unstable shear layer. Transmission across critical layers occurs for waves whose horizontal phase speed matches the background flow speed at levels where the gradient Richardson number is less than 1∕4.
Nanoscale oxidation of Cu(100): Oxide morphology and surface reactivity
Authors: Lampimäki M. , Lahtonen K. , Hirsimäki M. , Valden M.
Published: January 2007

Surface oxidation of Cu(100) in O2 has been investigated in situ by x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy (XAES), and scanning tunneling microscopy (STM) as a function of surface temperature (TS=303–423K) and O2 pressure (pO2=3.7×10−2–213mbars). Morphology of the oxide on the surface and in the near surface layers is characterized by utilizing STM and the inelastic electron background of the XAES O KLL signal. Analysis of the peak shape of the XAES Cu LMM facilitates the quantification of Cu, Cu2O, and CuO surface concentrations. The authors conclude that the surface oxidation of Cu(100) proceeds in three distinct steps: (1) Dissociative adsorption of O2 and the onset of Cu–(2√2×√2)R45°–O (θO=0.5ML) surface reconstruction, (2) initial formation of Cu2O and the appearance of 1.8Å high elongated islands that also adopt the Cu–(2√2×√2)R45°–O structure, and (3) formation of highly corrugated Cu–O islands which together with the surface reconstruction strongly enhance the reactivity of the surface towards further oxide formation. Both Cu2O and CuO formations are enhanced by increased surface temperature, but no pressure dependence can be seen.
Permeation of a hard sphere fluid into a quenched matrix
Authors: Sung Bong June , Yethiraj Arun
Published: January 2007

The permeation of a hard sphere fluid through a model membrane, composed of quenched (in space) hard spheres, is studied using molecular dynamics simulations. The fluid is initially placed outside the porous matrix and their initial intake is investigated and found to be non-Fickian. This non-Fickian behavior can be attributed to the high concentration difference between the fluid in the bulk and in the membrane. Once the system is equilibrated, the authors mark fluid particles that are outside the membrane and investigate their diffusion (color diffusion). Color diffusion is Fickian, and the mass intake and density profiles are well described by a continuum composite medium model with no adjustable parameters, i.e., with self-diffusion coefficients obtained from simulations. The matrix becomes impermeable when there are no percolating paths for the fluid.
Optical behavior of GaAs∕AlGaAs ringlike nanostructures
Authors: AbuWaar Ziad Y. , Mazur Yuriy I. , Lee Jihoon H. , Wang Zhiming M. , Salamo Gregory J.
Published: January 2007

Atomic force microscopy and photoluminescence (PL) measurements were carried out to investigate the role of the morphology of GaAs∕Al0.3Ga0.7As ringlike nanostructures on their optical properties. A small amount of Ga material (less than three monolayers) was used to fabricate single ringlike and double ringlike (DRL) nanostructures using droplet epitaxy technique. The height of the ringlike nanostructures increased with the increase of the Ga material while the corresponding PL emission energy was found to decrease as the ringlike nanostructure height increased. The PL peak energy showed a blueshift with increasing excitation intensity that can be understood as due to state filling while increasing temperature showed that the peak energy of the larger DRL nanostructures redshifts at a lower rate than the small ones due to larger confinement potential and lower energy emissions.
Accurate modeling of sequential decay in clusters over long time scales: Insights from phase space theory
Authors: Calvo F. , Parneix P.
Published: January 2007

A general theoretical framework for describing the thermally induced sequential decay in atomic clusters is presented. The scheme relies on a full treatment of individual dissociation steps based on phase space theory (PST), built into a kinetic Monte Carlo (kMC) procedure. This combined PST/kMC approach allows one to follow the evolution of several statistical properties such as the size, the angular momentum, or the temperature of the cluster over arbitrarily long time scales. Quantitative accuracy is achieved by incorporating anharmonicities of the vibrational densities of states, the rigorous conservation of angular momentum via the effective dissociation potential, and a proper calibration of the rate constants. The approach is tested and validated on selected Lennard-Jones clusters in various situations. Several approximations, including a mean-field rate equation treatment, are critically discussed; possible extensions are presented.
Computation of the amide I band of polypeptides and proteins using a partial Hessian approach
Authors: Besley Nicholas A. , Metcalf Katie A.
Published: January 2007

A partial Hessian approximation for the computation of the amide I band of polypeptides and proteins is introduced. This approximation exploits the nature of the amide I band, which is largely localized on the carbonyl groups of the backbone amide residues. For a set of model peptides, harmonic frequencies computed from the Hessian comprising only derivatives of the energy with respect to the displacement of the carbon, oxygen, and nitrogen atoms of the backbone amide groups introduce mean absolute errors of 15 and 10cm−1 from the full Hessian values at the Hartree-Fock/STO-3G and density functional theory EDF1∕6-31G* levels of theory, respectively. Limiting the partial Hessian to include only derivatives with respect to the displacement of the backbone carbon and oxygen atoms yields corresponding errors of 24 and 22cm−1. Both approximations reproduce the full Hessian band profiles well with only a small shift to lower wave number. Computationally, the partial Hessian approximation is used in the solution of the coupled perturbed Hartree-Fock/Kohn-Sham equations and the evaluation of the second derivatives of the electron repulsion integrals. The resulting computational savings are substantial and grow with the size of the polypeptide. At the HF/STO-3G level, the partial Hessian calculation for a polypeptide comprising five tryptophan residues takes approximately 10%–15% of the time for the full Hessian calculation. Using the partial Hessian method, the amide I bands of the constituent secondary structure elements of the protein agitoxin 2 (PDB code 1AGT) are calculated, and the amide I band of the full protein estimated.
Microstructure, magnetic, and optical properties of sputtered Mn-doped ZnO films with high-temperature ferromagnetism
Authors: Mi W. B. , Bai H. L. , Liu Hui , Sun C. Q.
Published: January 2007

The microstructure, magnetic, and optical properties of Mn-doped ZnO films have been examined. It has been found that Mn doping could improve the growth of ZnO (002) orientation without Mn oxide formation. All the films are ferromagnetic with a Curie temperature of above 350K. The ferromagnetism comes from the ferromagnetic interaction activated by oxygen vacancies between the Mn ions that replace Zn ions, but not from Mn oxide impurities. At an atomic fraction of 2.2% Mn, the average moment per Mn ion reaches a maximum of 0.55μB. With the further increase of Mn atomic fraction, the average moment per Mn ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Mn ions. Meanwhile, the optical band gap value increases from 3.120to3.162eV with the increase of Mn atomic fraction from 0% to 7.5%.
Manometer extension for high pressure measurement: Nuclear quadrupole resonance study of Cu2O with a modified Bridgman anvil cell up to 10 GPa
Authors: Fukazawa H. , Yamatoji N. , Kohori Y. , Terakura C. , Takeshita N. , Tokura Y. , Takagi H.
Published: January 2007

We report C63u nuclear quadrupole resonance (NQR) measurement of Cu2O under pressure up to about 10 GPa at low temperatures. Because the lattice parameter of Cu2O changes with increasing pressure, the electric field gradient at the Cu site also changes correspondingly with pressure. This enables us to use the Cu2O as an in situ manometer for high pressure nuclear magnetic resonance/NQR up to about 9 GPa.