bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy
Authors: Lu Pei-Dong , Wang Feng , Zhao Li-Jun , Li Wen-Xue , Li Xiao-Hong , Dong Jin-Ling , Zhang Yun-Hong , Lu Gao-Qing
Published: September 2008

The NaNO3 droplets with sizes of 1–5μm generated from a nebulizer were deposited on a ZnSe substrate in a Fourier transform infrared attenuated total reflection (FTIR-ATR) chamber. After solidification of the droplets with dry N2 gas passing through the chamber, the solid NaNO3 particles were monitored by in situ FTIR-ATR spectra in cycles of deliquescence and efflorescence processes with varying relative humidities (RHs). With an increase in the RH, a dominant peak at ∼3539cm−1, together with three relatively weak peaks at ∼3400, ∼3272, and ∼3167cm−1, in the O–H stretching band of water was resolved by the high signal-to-noise ratio FTIR-ATR spectra. The dominant peak and the three relatively weak peaks were contributed by the water monomers and the aggregated water molecules adsorbed on the surfaces of solid NaNO3 particles, respectively. When the RH approached ∼72%, slightly lower than the deliquescence RH (74.5%), the band component at ∼3400cm−1 became the main peak, indicating that the water monomers and the aggregated water molecules aggregated to form a thin water layer on the surfaces of solid NaNO3 particles. A splitting of the ν3-NO3− band at 1363 and 1390cm−1 at the RH of ∼72%, instead of the single ν3-NO3− band at 1357cm−1 for the initial solid NaNO3, was observed. We suggested that this reflected a phase transition from the initial solid to a metastable solid phase of NaNO3. The metastable solid phase deliquesced completely in the region from ∼87% to ∼96% RH according to the fact that the ν3-NO3− band showed two overlapping peaks at 1348 and 1405cm−1 similar to those of bulk NaNO3 solutions. In the efflorescence process of the NaNO3 droplets, the ν1-NO3− band presented a continuous blueshift from 1049cm−1 at ∼77% RH to 1055cm−1 at ∼36% RH, indicating the formation of contact ion pairs between Na+ and NO3−. Moreover, in the RH range from ∼53% down to ∼26%, two peaks at 836 and 829cm−1 were observed in the ν2-NO3− band region, demonstrating the coexistence of NaNO3 solid particles and droplets.
Effects of O18 isotopic substitution on the rotational spectra and potential splitting in the OH–OH2 complex: Improved measurements for O16H–O16H2 and O18H–O18H2, new measurements for the mixed isotopic forms, and ab initio calculations of the A2′-A2″ energy separation
Authors: Brauer Carolyn S. , Sedo Galen , Dahlke Erin , Wu Shenghai , Grumstrup Erik M. , Leopold Kenneth R. , Marshall Mark D. , Leung Helen O. , Truhlar Donald G.
Published: September 2008

Rotational spectra have been observed for O16H–O16H2, O16H–O18H2, O18H–O16H2, and O18H–O18H2 with complete resolution of the nuclear magnetic hyperfine structure from the OH and water protons. Transition frequencies have been analyzed for each isotopic form using the model of Marshall and Lester [J. Chem. Phys. 121, 3019 (2004)], which accounts for partial quenching of the OH orbital angular momentum and the decoupling of the electronic spin from the OH molecular axis. The analysis accounts for both the ground (A2′) and first electronically excited (A2″) states of the system, which correspond roughly to occupancy by the odd electron in the py and px orbitals, respectively (where py is in the mirror plane of the complex and px is perpendicular to py and the OH bond axis). The spectroscopic measurements yield a parameter, ρ, which is equal to the vibrationally averaged A2′-A2″ energy separation that would be obtained if spin-orbit coupling and rotation were absent. For the parent species, ρ=−146.560 27(9) cm−1. O18 substitution on the water increases |ρ| by 0.105 29(10) cm−1, while substitution on the OH decreases |ρ| by 0.068 64(11) cm−1. In the OH–OH2 complex, the observed value of ρ implies an energy spacing between the rotationless levels of the A2′ and A2″ states of 203.76 cm−1. Ab initio calculations have been performed with quadratic configuration interaction with single and double excitations (QCISD), as well as multireference configuration interaction (MRCI), both with and without the inclusion of spin-orbit coupling. The MRCI calculations with spin-orbit coupling perform the best, giving a value of 171 cm−1 for the A2′-A2″ energy spacing at the equilibrium geometry. Calculations along the large-amplitude bending coordinates of the OH and OH2 moieties within the complex are presented and are shown to be consistent with a vibrational averaging effect as the main cause of the observed isotopic sensitivity of ρ.
The role of carbon contamination in voltage linearity and leakage current in high-k metal-insulator-metal capacitors
Authors: Miao Bing , Mahapatra Rajat , Wright Nick , Horsfall Alton
Published: September 2008

The effect of carbon contamination on the electrical properties of metal-insulator-metal (MIM) capacitor using HfO2 dielectric has been reported. The HfO2 film with lower carbon contamination shows an overall high performance, such as a higher capacitance density of 5.21 fF/μm2, a lower leakage current of 1.3×10−7 A/cm2 at 1 V, lower-voltage coefficients of capacitance, and better frequency and temperature dispersion properties compared with the capacitor of theHfO2 film with higher carbon contamination. The calculated ac barrier heights by electrode polarization model from capacitance-voltage (C-V) characteristics are 0.58 eV for the HfO2 film with high carbon contamination and 0.95 eV for the HfO2 film with negligible carbon contamination. The dc barrier heights extracted from current-voltage (I-V) characteristics are 0.26 eV for the HfO2 film with high carbon contamination and 1.1 eV for the HfO2 film with negligible carbon contamination. All of these experimental results exhibit that the increase in defect density in HfO2 films generated from carbon impurities results in the degradation of barrier heights and poor performance of the MIM capacitor. It is important to point out that, during the fabrication process of the MIM capacitor, the carbon contamination must be minimized.
Analysis of pentacene field-effect transistor with contact resistance as an element of a Maxwell–Wagner effect system
Authors: Lim Eunju , Manaka Takaaki , Iwamoto Mitsumasa
Published: September 2008

In organic field-effect transistors (OFETs), the carrier injection from the source and drain electrodes depends on the contact resistance. Results of this study show, based on a dielectric physics analysis of a pentacene OFET as a Maxwell–Wagner (MW) effect element with the contact resistance, that the contact resistance leads to an increase in the time required for charge accumulation at the interface. Considering that background, the carrier injection, transport, and accumulation mechanisms were investigated. Capacitance frequency and time-resolved microscopic optical second harmonic generation (SHG) measurements were discussed, taking into account the usefulness of the MW model analysis, and to clarify the effect of contact resistance. Our experimental results corroborate our analysis, based on the carrier mechanism in OFETs, was supported by optical SHG measurements.
The phase transitions, magnetocaloric effect, and magnetoresistance in Co doped Ni–Mn–Sb ferromagnetic shape memory alloys
Authors: Han Z. D. , Wang D. H. , Zhang C. L. , Xuan H. C. , Zhang J. R. , Gu B. X. , Du Y. W.
Published: September 2008

The phase transitions, magnetocaloric effect, and magnetoresistance in Ni50−xCoxMn39Sb11 (x=0–11) ferromagnetic shape memory alloys were investigated. The temperatures of martensitic transformation and magnetic transition in austenitic phase depend strongly on the Co concentration, while the magnetic transition temperature in martensitic phase shows small dependence on alloy composition. For 7≤x≤9, the martensitic transformation is accompanied by a sudden change in magnetization. Large positive magnetic entropy changes and negative magnetoresistance near room temperature, which originate from the magnetic-field-induced transformation from the weak-magnetic high-resistance martensitic phase to the ferromagnetic low-resistance parent phase, are observed in these alloys. Our results indicate the potential application of Ni50−xCoxMn39Sb11 alloys in magnetic refrigeration and magnetic sensors.
Thickness and Nb-doping effects on ferro- and piezoelectric properties of highly a-axis-oriented Nb-doped Pb(Zr0.3Ti0.7)O3 films
Authors: Zhu Zhi-Xiang , Ruangchalermwong C. , Li Jing-Feng
Published: September 2008

Tetragonal Nb-doped Pb(Zr0.3Ti0.7)O3 (PNZT) films with a lead oxide seeding layer were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates by sol-gel processing. The as-grown PNZT films with thicknesses ranging from about 0.08 to 0.78 μm show highly a-axis preferential orientation, and their ferroelectric and piezoelectric properties improved with increasing film thickness. Due to the combined effects of Nb doping and a-axis texturing as well as reduced substrate constraint, a high d33 constant up to 196 pm/V was obtained for PNZT film at 0.78 μm in addition to a large remnant polarization of 69 μC/cm2. This well a-axis-oriented PNZT films on platinized Si with a high piezoresponse are suitable for the fabrication of microelectromechanical devices.
SrTiO
3
on piezoelectric PMN-PT(001) for application of variable strain
Authors: Bilani-Zeneli O. , Rata A. D. , Herklotz A. , Mieth O. , Eng L. M. , Schultz L. , Biegalski M. D. , Christen H. M. , Dörr K.
Published: September 2008

SrTiO 3 (STO) is the most frequently used substrate material for complex oxide films. In this work, STO is explored as a buffer layer on piezoelectric pseudocubic Pb(Mg1/3Nb2/3)0.72Ti0.28O3(001) (PMN-PT) substrates, which serve to reversibly strain thin films. The STO buffer layer reduces the in-plane lattice parameter and allows for a better lattice matching to a broader range of thin film materials. STO films (30 nm) have been grown with epitaxial orientation on PMN-PT with an in-plane lattice parameter close to that of bulk STO. The substrate’s rhombohedral domain structure has been imaged by atomic force microscopy. The related ferroelectric domain structure has been investigated by piezoresponse force microscopy. Within a domain, STO grows with a rather low roughness (rms<0.2 nm). The transfer of the piezoelectric substrate strain to the STO film and its variation with an applied electric field are studied using x-ray diffraction. The strain dependence of the electrical resistance is measured for a ferromagnetic manganite film grown on top of the STO. Both experiments confirm qualitatively that the STO buffer transfers the substrate strain into a functional film deposited on top.
Investigation of nanodefect properties in optical coatings by coupling measured and simulated laser damage statistics
Authors: Gallais Laurent , Capoulade Jérémie , Natoli Jean-Yves , Commandré Mireille
Published: September 2008

We propose a model to link laser damage initiator properties (such as nature, size distribution, and density) to measured laser damage probabilities in optical materials. The model is based on the calculation of light absorption in nanoabsorbers and subsequent heating, coupled to laser damage statistics, and allows to obtain the laser damage probability as a function of laser fluence. Applications to the case of optical coatings irradiated in the nanosecond regime are presented. Laser damage probability curves are measured in hafnia single layer coatings made under different conditions: electron beam deposition and reactive low voltage ion plating. By studying the influence of the laser irradiation parameters (wavelength and beam size) and coating properties on the simulations, we show with our methodology that initiating defects (hafnium inclusions) can be identified. The implications of this approach for physical understanding and metrology applications are discussed.
The impact of water vapor transmission rate on the lifetime of flexible polymer solar cells
Authors: Hauch Jens A. , Schilinsky Pavel , Choulis Stelios A. , Rajoelson Sambatra , Brabec Christoph J.
Published: September 2008

In this paper we perform accelerated lifetime testing on high efficiency flexible poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) solar cells encapsulated with food package quality barrier films with a water vapor transmission rate of 0.2 g/(m2 day) at 65 °C/85% relative humidity. We show that lifetimes exceeding 1250 h, even at high temperature/high humidity conditions, may be reached, proving that organic solar cells are significantly less sensitive against the environmental effects of water and oxygen than previously expected.
Fe
3
C
cluster confined in single-walled carbon nanotubes: A first-principles study
Authors: Yuan Shijun , Wang Xueli , Li Pai , Li Fashen , Yuan Songliu
Published: September 2008

First-principles calculations are performed to investigate Fe3C cluster confined in various single-walled carbon nanotubes (SWCNTs). We study the structures and magnetic and electronic properties of the SWCNT+Fe3C composites. It is found that the templating effect of a SWCNT due to strong Fe-SWCNT interaction determine the most stable configuration of Fe3C cluster, and 6.9 Å is an optimum diameter of SWCNT for combining single Fe3C cluster. The remaining C atom inside carbon nanotube remarkably reduces the Fe magnetic moment; however, the whole SWCNT+Fe3C system still exhibits a high spin polarization. Our results elucidate its potentiality as spintronics devices with controllable structure and properties.
The effect of implanting boron on the optical absorption and electron paramagnetic resonance spectra of silica
Authors: Magruder R. H. , Stesmans A. , Weeks R. A. , Weller R. A.
Published: September 2008

Silica samples (type III, Corning 7940) were implanted with B using multiple energies to produce a layer ∼600 nm thick in which the concentration of B ranged from 0.034 to 2.04 at. %. Optical absorption spectra were measured from 1.8 to 6.5 eV. Electron paramagnetic resonance (EPR) measurements were generally made at ∼20.3 and 33 GHz for sample temperatures ranging from 77 to 100 K. Based on the EPR spectra three types of defects, namely, Eγ′, the E′-type 73 G split doublet (E73′), and the peroxyradical (POR) were identified. No oxygen-associated hole centers (OHCs) nor specific B-associated paramagnetic defects were detected, not even at the largest B concentration of 2.04 at. %. Unlike previous assignments, there was no correlation between the 4.83 eV optical absorption band and the observed PORs. From these results, we infer that in addition to POR, there is at least one additional Si-related state absorbing in the 4.8–4.9 eV range that is likely diamagnetic. The 5.85 eV optical absorption band is found to be due to the Eγ′ and E73′ centers, with, in average, quite similar oscillator strengths inferred as before. Both the optical absorption and the electron spin resonance data can be satisfactorily explained without the need for specific B-associated defect site (s). As no OHCs are detected by ESR, these do not seem to make a detectable contribution to the optical spectra.
Z
-matrix formalism for quantitative noise assessment of covariance nuclear magnetic resonance spectra
Authors: Snyder David A. , Ghosh Arindam , Zhang Fengli , Szyperski Thomas , Brüschweiler Rafael
Published: September 2008

Due to the limited sensitivity of many nuclear magnetic resonance (NMR) applications, careful consideration must be given to the effect of NMR data processing on spectral noise. This work presents analytical relationships as well as simulated and experimental results characterizing the propagation of noise by unsymmetric covariance NMR processing, which concatenates two NMR spectra along a common dimension, resulting in a new spectrum showing spin correlations as cross peaks that are not directly measured in either of the two input spectra. It is shown how the unsymmetric covariance spectrum possesses an inhomogeneous noise distribution across the spectrum with the least amount of noise in regions whose rows and columns do not contain any cross or diagonal peaks and with the largest amount of noise on top of signal peaks. Therefore, methods of noise estimation commonly used in Fourier transform spectroscopy underestimate the amount of uncertainty in unsymmetric covariance spectra. Different data processing procedures, including the Z-matrix formalism, thresholding, and maxima ratio scaling, are described to assess noise contributions and to reduce noise inhomogeneity. In particular, determination of a Z score, which measures the difference in standard deviations of a statistic from its mean, for each spectral point yields a Z matrix, which indicates whether a given peak intensity above a threshold arises from the covariance of signals in the input spectra or whether it is likely to be caused by noise. Application to an unsymmetric covariance spectrum, obtained by concatenating two 2D C13–H1 heteronuclear, single quantum coherence (HSQC) and C13–H1 heteronuclear, multiple bond correlation (HMBC) spectra of a metabolite mixture along their common proton dimension, reveals that for sufficiently sensitive input spectra the reduction in sensitivity due to covariance processing is modest.
Elongation of extreme ultraviolet (at 13.5 nm) emission with time-of-flight controlled discharges and lateral fuel injection
Authors: Hosokai Tomonao , Yokoyama Takuma , Zhidkov Alexei , Sato Hiroto , Hotta Eiki , Horioka Kazuhiko
Published: September 2008

A way toward a quasicontinuous extreme ultraviolet (EUV) radiation source is proposed and explored. Tin and lithium vapor discharges with the lateral laser-ablation injection are experimentally studied as possible efficient sources of quasicontinuous emission of EUV radiation at a wavelength of 13.5 nm. It is shown that the time-of-flight control of optimal plasma parameters by means of varying ablating laser pulse parameters provides a considerable elongation of maximal-power EUV emission with an overall efficiency of 0.1% and with an energy output exceeding 1% of the energy deposited in the discharge plasma. Along with a high average power and a stable position, such an emitter may have its size small enough to be used in the projection lithography.
A dynamic study of the warm-up phase of a high-pressure mercury lamp
Authors: Araoud Z. , Ben Ahmed R. , Bouaoun M. , Ben El Hadj Rhouma M. , Charrada K. , Zissis G.
Published: September 2008

A time-dependent two-dimensional computational fluid model has been adopted to investigate the dynamic behavior of the high-pressure mercury lamp during the last phase of the warm-up period. The model solves the combined momentum, continuity, energy, and electric field equations for the plasma and the energy equation for the wall. Two models have been compared. The first takes convection into account and is called “convection model.” The second, which neglects this term, is termed “convectionless model.” Good agreement between the predictions and experimental data from literature has been obtained. It is found that the convection affects the lamp performance by increasing the mercury losses behind the electrodes and the mercury-evaporation time.
C
N
x
nanotubes with pyridinelike structures: p-type semiconductors and Li storage materials
Authors: Li Y. F. , Zhou Z. , Wang L. B.
Published: September 2008

Using density functional theory (DFT) computations, we investigated pyridinelike structures in a series of single-walled CNx nanotubes and found that tube chirality and diameter play important roles in the formation of pyridinelike structures. Not pyridinelike structures but more NC defects (N atoms substituting for C atoms) should be responsible for the experimentally observed donor states of CNx nanotubes. The adsorption energies of Li at the pyridinelike defect are so large and the energy barrier for lithium penetrating the defect is so low that CNx nanotubes with pyridinelike structures have enhanced capability for lithium storage.
Chlorine interaction with defects on the Au(111) surface: A first-principles theoretical investigation
Authors: Baker Thomas A. , Friend Cynthia M. , Kaxiras Efthimios
Published: September 2008

Chlorine is an important element in promoting oxidation on noble metal surfaces. Here, we report a comprehensive theoretical study of chlorine interaction with defects on the Au(111) surface, using density functional theory calculations and periodic slabs to model the surface. We find that chlorine binds preferentially on steps, vacancies, and gold adatoms. The increase in binding energy per chlorine atom, compared to binding on the flat, defect-free surface, is 0.29 eV when the chlorine atom is on top of a gold adatom, 0.38 eV when it is at the edge of a step, and 0.19 eV when it is next to a single surface vacancy. An extensive study of chlorine interaction with different numbers of surface gold vacancies revealed that chlorine interacts the strongest with three vacancies.
Plume propagation dynamics of complex oxides in oxygen
Authors: Sambri A. , Amoruso S. , Wang X. , Granozio F. Miletto , Bruzzese R.
Published: September 2008

The influence of background gas pressure and deposition temperature on plume propagation dynamics of La0.7Sr0.3MnO3 in oxygen is investigated and discussed. Fast imaging analysis is exploited to obtain a complete set of images of plume emission at the typical oxygen pressures used in pulsed laser deposition of this material, and for deposition temperatures ranging from room temperature up to 900 °C. We have observed that the deposition temperature can induce a remarkable change on both plume emission characteristics, in the early stage of the expansion, and on the velocity of the species impacting the substrate during film growth. The results are interpreted in the frame of a simple model which yields consistent and quantitative agreement with the experimental data. Our findings point to an interesting cross-correlation among important deposition parameters, such as background gas pressure and deposition temperature, also suggesting that the optimization of processing parameters, such as background gas pressure and target-substrate distance, during the growth of complex oxides should be also performed as a function of the deposition temperature.
Micromagnetics of signal propagation in magnetic cellular logic data channels
Authors: E Chunsheng , Rantschler James , Khizroev Sakhrat , Litvinov Dmitri
Published: September 2008

The physics of magnetic signal propagation in one-dimensional antiferromagnetically coupled nanomagnetic arrays is studied using micromagnetic modeling. The results are used to develop the design guidelines such as the criteria for the interelement spacing for efficient operation and the error suppression due to the magnetization misalignment in individual elements in the array. The propagation speed is found to decay significantly as the damping is increased. The external “clocking” field is applied to improve the data channel characteristics. However, premature relaxation of the end elements inhibits the proper operation of longer channels. A proposed solution is a zone-by-zone propagation scheme, which is compatible with the pipelining approach. Simulation results demonstrate a possibility of successful signal propagation at 2 GHz clocking field frequency with no limitation on the length of the channel.
Spatial and temporal studies of laser ablated ZnO plasma
Authors: Joshy N. V. , Saji K. J. , Jayaraj M. K.
Published: September 2008

Gallium doped zinc oxide was ablated using the third harmonics of Nd:YAG laser at various laser fluences and nitrous oxide ambient gas pressures. Optical emission spectroscopic technique was used to determine the plasma parameters. Spatial variation of electron number density (Ne) was determined along the direction normal to the target surface. The electron density obtained was of the order of 1017 cm−3, for the laser fluence in the range of 1.27–6.35 J cm−2. The influence of the substrate temperature on the plasma plume was studied by keeping an Al2O3 (alumina) substrate at a distance of 5 cm distance from the target at various temperatures. The increase in the substrate temperature enhanced the electron number density and intensity of spectral emissions of various species in the plume. The time of flight transients of specific emissions from the plume were recorded. The velocity of neutral gallium decreased from 6.45 to 3.87 km/s at 4 mm distance from the target when the ambient gas pressure was increased from 0.0001 to 0.1 mbar. The velocities of the species increased considerably with an increase in laser fluences. ZnO thin films were deposited on alumina substrates. The plasma plume kinematics were used to corroborate the nature of thin film deposition.
Temperature and TiO2 content effects on the photoluminescence properties of Eu3+ doped TiO2–SiO2 powders
Authors: Zhao Jianguo , Duan Huigao , Ma Ziwei , Wang Tao , Chen Changcheng , Xie Erqing
Published: September 2008

Eu 3 + doped TiO2–SiO2 powders were produced by the sol-gel method. The TiO2 content was changed from low to high content (20–100 mol %) annealing at 900 °C for 1 h, and the 2 mol % Eu3+ doped 60%TiO2–40%SiO2 powders were annealed at different temperatures (600–1000 °C). The structure of the samples was investigated by high resolution transmission electron microscopy, x-ray diffraction, and Raman technique. The photoluminescence (PL) spectra and PL excitation spectra were recorded at room temperature. The results showed that the PL intensity was dependent on the annealing temperatures and TiO2 content, which could be attributed to the cluster formation.
Femtosecond laser blackening of platinum
Authors: Vorobyev A. Y. , Guo Chunlei
Published: September 2008

Using a femtosecond laser processing technique, we produce the black platinum with absorptance of about 95% over a broad wavelength range from ultraviolet to infrared. From scanning electron microscopy and energy dispersive x-ray spectroscopy studies, we find that the enhanced absorption of the black metal is due to a variety of nano- and microscale surface structures. Using a unique calorimetry technique, we perform a shot-to-shot comparison study of the metal absorption change in air and vacuum. Our study shows that the blackening process for platinum is more efficient in vacuum.
Effect of HCl addition on gas-phase and surface reactions during homoepitaxial growth of SiC at low temperatures
Authors: Melnychuk G. , Lin H. D. , Kotamraju S. P. , Koshka Y.
Published: September 2008

A complex influence of HCl addition on gas-phase and surface reactions during the low-temperature halo-carbon homoepitaxial growth of 4H-SiC was investigated. The addition of HCl was employed to reduce the undesirable effects of homogeneous gas-phase nucleation leading to formation of silicon clusters in the gas phase. It was established that dissociation of silicon clusters by HCl is efficient even at untraditionally low homoepitaxial growth temperature below 1300 °C. The information about the spatial distribution of this dissociation process along the gas flow direction was obtained. It was established that the influence of HCl is more complicated than the simple model suggesting that the enhanced dissociation of silicon clusters in the gas phase leads to an additional supply of silicon species for the epitaxial growth. While the growth rate does significantly increase at least for some HCl flow rates, complex changes in the effective silicon-to-carbon ratio in the growth zone of the reactor indicate that the supply of carbon species may also be enhanced at least at low HCl flow rates. This fact supports the hypothesis that the gas-phase clusters may contain a significant amount of carbon in addition to silicon. Also, the magnitude of the growth rate enhancement was found to be less significant than what was expected from the apparent degree of the cluster dissociation. Evidence of a new mechanism for precursors’ depletion are provided. Pronounced changes in the pattern of the polycrystalline deposits at the upstream portion of the hot zone of the reactor were caused by the HCl addition. Premature dissociation of the gas-phase clusters and release of silicon may cause depletion of silicon by vigorous polycrystalline deposition. Depending on the kinetics of the process, the carbon species may also get depleted by the polycrystalline deposition mechanism. This mechanism partially reduces the benefits of the HCl addition unless its influence is minimized.
High brightness extreme ultraviolet (at 13.5 nm) emission from time-of-flight controlled discharges with coaxial fuel injection
Authors: Hosokai Tomonao , Yokoyama Takuma , Zhidkov Alexei , Sato Hiroto , Horioka Kazuhiko , Hotta Eiki
Published: September 2008

Extreme ultraviolet (EUV) emission from discharge produced plasma with the coaxial injection of fuel vapor (tin and lithium) produced by laser ablation is experimentally studied. Multiple plasma pinches preceding a strong and long recombination radiation of EUV are observed in the first half cycle of a sinusoidal discharge current. Due to the time-of-flight control type of the discharge, the shape of pinch radiation pulses is almost identical. With the coaxial injection of time-of-flight controlled discharges, the highest brightness of EUV emission (maximum extracted energy of 244.3 mJ/2π sr per pulse with the emitter size of ∼1×0.3 mm2 in full width at half maximum) is provided with efficiency exceeding 2% of deposited energy into the plasma (or 1% of dissipated energy in the discharge) due to a much better matching with the optimal plasma parameters in the recombination regime and a decrease in the off-duty factor. Stability of emitting plasma of the repetitive pinches is essentially improved with use of a second laser pulse.
Modeling inertial particle acceleration statistics in isotropic turbulence
Authors: Ayyalasomayajula S. , Warhaft Z. , Collins L. R.
Published: September 2008

Our objective is to explain recent Lagrangian acceleration measurements of inertial particles in decaying, nearly isotropic turbulence [Ayyalasomayajula et al., Phys. Rev. Lett. 97, 144507 (2006)]. These experiments showed that as particle inertial effects increased, the variance in the particle acceleration fluctuations was reduced, and the tails of the normalized particle acceleration probability density function (PDF) became systematically attenuated. We model this phenomenon using a base flow that consists of a two-dimensional array of evenly spaced vortices with signs and intensities that vary randomly in time. We simulate a large sample of inertial particles moving through the fluid without disturbing the flow (one-way coupling). Consistent with Bec et al. [J. Fluid Mech. 550, 349 (2006)], we find that our model exhibits preferential concentration or clustering of particles in regions located away from the vortex centers. That is, inertial particles selectively sample the flow field, oversampling regions with high strains and undersampling regions with high vorticities. At low Stokes numbers, this biased “sampling” of the flow is responsible for the reduction in the acceleration variance and partially explains the attenuation of the tails of the acceleration PDF. However, contrary to previous findings, we show that the tails of the PDF are also diminished by “filtering” induced by the attenuated response of the inertial particles to temporal variations in the fluid acceleration: Inertial particles do not respond to fluctuations with frequencies much higher than the inverse of the particle stopping time. We show that larger fluid acceleration events have higher frequencies and hence experience greater filtering by particle inertia. We contrast the vortex model with previous Lagrangian acceleration models by Sawford [Phys. Fluids A 3, 1577 (1991)] and Reynolds [Phys. Fluids 15, L1 (2003)] and show that although these models capture some aspects of the inertial particle behavior, it is necessary to employ a model of the flow with spatial structure to capture the effect of sampling on the inertial particle dynamics.
One-dimensional model for water and aqueous solutions. IV. A study of “hydrophobic interactions”
Authors: Ben-Naim Arieh
Published: September 2008

The solute-solute pair correlation function and the potential of mean force (PMF) between two hard-rod solutes in two solvents are studied in one-dimensional systems. One solvent consists of particles interacting via square well (SW) potential. The second consists of particles interacting via “hydrogen-bond-like” (HB) pair potential. It was found that the first minimum of the solute-solute PMF at infinite dilution in the two solvents grows deeper as we increase the strength of the solvent-solvent interaction. In the SW (but not in the HB) solvent, we found that the range of solute-solute pair correlation is larger at lower temperatures (or at larger εBB∕kBT). The relevance of this finding to the problem of hydrophobic interactions is discussed.
New method for deciphering free energy landscape of three-state proteins
Authors: Li Mai Suan , Gabovich A. M. , Voitenko A. I.
Published: September 2008

We have developed a new simulation method to estimate the distance between the native state and the first transition state and the distance between the intermediate state and the second transition state of a protein which mechanically unfolds via intermediates. Assuming that the end-to-end extension ΔR is a good reaction coordinate to describe the free energy landscape of proteins subjected to an external force, we define the midpoint extension ΔR* between two transition states from either constant force or constant loading rate pulling simulations. In the former case, ΔR* is defined as a middle point between two plateaus in the time-dependent curve of ΔR, while, in the latter one, it is a middle point between two peaks in the force-extension curve. Having determined ΔR*, one can compute times needed to cross two transition state barriers starting from the native state. With the help of the Bell and microscopic kinetic theory, force dependencies of these unfolding times can be used to locate the intermediate state and to extract unfolding barriers. We have applied our method to the titin domain I27 and the fourth domain of Dictyostelium discoideum filamin (DDFLN4) and obtained reasonable agreement with experiments, using the Cα-Go model.
Steric and hyperconjugative contributions to rotation barriers in diboron analogs B2L4 (L=F, OH, NH2, CH3, and H)
Authors: Watts Casey R. , Badenhoop Jay K.
Published: September 2008

The rotational barriers of B2L4 (where L=F, OH, NH2, CH3, and H) were investigated with respect to the hyperconjugation and steric effects at the levels of RHF, MP2, and B3LYP using a basis set of 6-311G(d,p). At all levels of theory, the LBBL dihedral angle of the minimum energy conformation was found to increase with decreasing electronegativity of the atom bonded to boron. The L substituents that possess no lone pairs have greater steric exchange energy, destabilizing the planar conformation relative to the perpendicular. However, the planar conformation of compounds with L substituents having lone pairs on the heavy atom is counterstabilized by conjugative delocalization into the “empty” p-orbitals associated with boron. For B2(NH2)4, neither factor dominates and the optimal geometry is skewed at a dihedral angle of 37.62° (MP2).
Origin of hardness in WB4 and its implications for ReB4, TaB4, MoB4, TcB4, and OsB4
Authors: Wang Mei , Li Yinwei , Cui Tian , Ma Yanming , Zou Guangtian
Published: September 2008

First-principles calculations were performed on the superhard material, WB4 (Vicker hardness exceeding 46GPa), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar B2 dimer along the z-axis and a xy planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (TMB4, TM=Re, Mo, Ta, Os, and Tc) within the WB4 structure are potential superhard materials.
Radio frequency atmospheric pressure glow discharge in α and γ modes between two coaxial electrodes
Authors: Shang Wanli , Wang Dezhen , Zhang Yuantao
Published: September 2008

The discharge in pure helium and the influence of small nitrogen impurities at atmospheric pressure are investigated based on a one-dimensional self-consistent fluid model controlled by a dielectric barrier between two coaxial electrodes. The simulation of the radiofrequency (rf) discharge is based on the one-dimensional continuity equations for electrons, ions, metastable atoms, and molecules, with the much simpler current conservation law replacing the Poisson equation for electric field. Through a computational study of rf atmospheric glow discharges over a wide range of current density, this paper presents evidence of at least two glow discharge modes, namely the α mode and the γ mode. The simulation results show the asymmetry of the discharge set exercises great influence on the discharge mechanisms compared to that with parallel-plane electrodes. It is shown that the particle densities are not uniform in the discharge region but increase gradually from the outer to the inner electrode in both modes. The contrasting dynamic behaviors of the two glow modes are studied. Secondary electron emission strongly influences gas ionization in the γ mode yet matters little in the α mode.
Modulation instability of low-frequency electrostatic ion waves in magnetized electron-positron-ion plasma
Authors: Jehan Nusrat , Salahuddin M. , Saleem H. , Mirza Arshad M.
Published: September 2008

The nonlinear amplitude modulation of low-frequency electrostatic ion waves propagating in collisionless magnetized electron-positron-ion plasma are studied. The Krylov–Bogoliubov–Mitropolsky perturbation method is employed to derive the nonlinear Schrödinger equation. Modulation instability of both ion-acoustic and ion-cyclotronlike modes is examined. We found that the ion-acoustic mode, which propagates below the ion-cyclotron frequency, is stable if the strength of the external magnetic field is small. However, as the strength of the magnetic field increases, this mode becomes modulationally unstable for a range of wave numbers and angles of propagation. This range increases as the strength of the magnetic field and/or positron density increases. For the ion-cyclotronlike mode, which propagates above the ion-cyclotron frequency, a number of stability/instability regions appear in the (kc,θ) plane even for a very small value of the magnetic field. It is found that, for both modes, critical wave number kc separating the stability and instability regions, shifts towards higher values as the density of the positron increases.
Pair annihilation effects on a surface ion cyclotron wave in semibounded electron-positron-ion plasmas
Authors: Jung Young-Dae , Kato Daiji
Published: September 2008

Electron-positron pair annihilation effects on a surface ion cyclotron wave are investigated in magnetized electron-positron-ion plasmas in atmospheres of neutron stars. The dispersion relation of the surface ion cyclotron wave is obtained by the specular reflection boundary condition with the plasma dielectric function. It is shown that the high- and low-frequency modes of the surface ion cyclotron wave could exist in electron-positron-ion plasmas. For the high-frequency mode, the pair annihilation enhances the wave frequency in large wave-number domains. However, the pair annihilation effects are found to be negligible for the low-frequency mode. It is also found that an increase of the electron temperature or a decrease of the positron temperature strongly suppresses the wave frequency. It is shown that an increase of the magnetic field strongly enhances the wave frequency.
Rupture of radially spreading liquid films
Authors: Dhiman Rajeev , Chandra Sanjeev
Published: September 2008

The rupture of thin water films (thickness of ∼100 μm) spreading radially outward on a solid surface was studied experimentally. Circular water films were produced by directing a 1 mm diameter water jet onto a flat horizontal plate for 10 ms. Jet impact velocity was varied from 1.6 to 6.1 m/s, giving Reynolds numbers from 1600 to 6100. Three different plates were used (glass, Plexiglas, and wax) to vary substrate wettability. Both rough and smooth wax surfaces were tested. Water films did not rupture on glass and Plexiglas plates, but holes formed and expanded in films spreading on wax, which had the highest liquid-solid contact angle. Tests in which the spreading film was not supported on a surface, but spread after impact on a pin to simulate a perfectly nonwetting surface, did not show formation of holes. A thermodynamic stability analysis predicted film rupture behavior by showing that films would be stable at very small or very large contact angle but unstable in between. Film rupture was also found to be promoted by increasing surface roughness or decreasing film thickness.
High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents
Authors: Carey M. J. , Smith N. , Maat S. , Childress J. R.
Published: September 2008

It is shown that the maximum stable output of a current-perpendicular to the plane giant magnetoresistance sensor is increased significantly by using a synthetic-ferrimagnet free layer, provided the electron current flows from free layer to reference layer. This free layer allows a larger magnetoresistance ratio for a given free layer magnetic moment, and in addition results in a greater than threefold increase in the critical current, above which spin-torque instability of the free layer occurs. In read heads with net free layer moments equivalent to only 4.5 nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2×108 A/cm2.
Suppression of spin torque noise in current perpendicular to the plane spin-valves by addition of Dy cap layers
Authors: Maat S. , Smith N. , Carey M. J. , Childress J. R.
Published: September 2008

We demonstrate that the addition of Dy capping layers in current perpendicular to the plane giant magnetoresistive spin-valves can increase the critical current density beyond which spin-torque induced instabilities are observed by about a factor of three. While Dy capped samples exhibit nonmagnetic 1/f noise, it is sufficiently small to be unimportant for read head operation at practical data rates.
Investigation of substrate-induced strain effects in La0.7Ca0.15Sr0.15MnO3 thin films using ferroelectric polarization and the converse piezoelectric effect
Authors: Zheng R. K. , Jiang Y. , Wang Y. , Chan H. L. W. , Choy C. L. , Luo H. S.
Published: September 2008

We have fabricated manganite film/ferroelectric crystal heterostructures by growing La0.7Ca0.15Sr0.15MnO3 (LCSMO) films on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-PT) single-crystal substrates. The efficient mechanical coupling at the interface, originated from ferroelectric polarization or the converse piezoelectric effect in the PMN-PT substrate, gives rise to large changes in the strain state, electrical resistance, magnetoresistance, and insulator-to-metal transition temperature (TP) of the film. We interpreted all these changes in terms of substrate-induced strain, which modifies the tetragonal distortion of MnO6 octahedra and the electron-lattice coupling strength in the film. Quantitative relationships between TP and induced strain in the LCSMO film have been established.
Isotype heterojunction between organic crystalline semiconductors
Authors: Wang Haibo , Wang Xiujin , Huang Haichao , Yan Donghang
Published: September 2008

We report the effect of n-n isotype organic heterojunction consisting of copper hexadecafluorophthalocyanine (F16CuPc) and phthalocyanatotin(IV) dichloride (SnCl2Pc). Their interfacial electronic structure was observed by Kelvin probe force microscopy (KPFM), and there is band bending in two materials, resulting in an electron accumulation region in F16CuPc layer and an electron depletion region in SnCl2Pc layer. The forming of organic heterojunction was explained by carriers flowing through the interface due to thermal emission of electrons. Furthermore, the carrier transport behavior parallel and vertical to heterojunction interface was also revealed by their heterojunction field-effect transistor with normally on operation mode and heterojunction diodes with rectifying property.
Electrochemical fabrication of ultralow noise metallic nanowires with hcp crystalline lattice
Authors: Singh Amrita , Sai T. Phanindra , Ghosh Arindam
Published: September 2008

We experimentally demonstrate that low-frequency electrical noise in silver nanowires is heavily suppressed when the crystal structure of the nanowires is hexagonal closed pack (hcp) rather than face centered cubic (fcc). Using a low-potential electrochemical method we have grown single crystalline silver nanowires with hcp crystal structure, in which the noise at room temperature is two to six orders of magnitude lower than that in the conventional fcc nanowires of the same diameter. We suggest that motion of dislocations is probably the primary source of electrical noise in metallic nanowires, which is strongly diminished in hcp crystals.
Charge transport in accumulation layers of organic heterojunctions
Authors: Zhu Feng , Wang Haibo , Song De , Lou Kun , Yan Donghang
Published: September 2008

We studied the charge transport in organic heterojunction films consisting of copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc). The heterojunction effect between CuPc and F16CuPc induced high-density carriers at both sides of heterojunction. The Hall effect was observed at room temperature, which demonstrated the existence of free carriers and their delocalized transport under heterojunction effect. The Hall mobility of 1.2cm2∕Vs for holes and 2.4cm2∕Vs for electrons indicated that the transport capability of the heterojunction films is comparable to single crystals. The transport process was further explained by the multiple trap-and-release model according to the temperature dependence of conduction.
High response organic ultraviolet photodetector based on blend of 4,4′,4″-tri-(2-methylphenyl phenylamino) triphenylaine and tris-(8-hydroxyquinoline) gallium
Authors: Su Zisheng , Li Wenlian , Chu Bei , Li Tianle , Zhu Jianzhuo , Zhang Guang , Yan Fei , Li Xiao , Chen Yiren , Lee Chun-Sing
Published: September 2008

The authors demonstrate high response organic ultraviolet (UV) photodetector (PD) using 4,4′,4″-tri-(2-methylphenyl phenylamino) triphenylaine (m-MTDATA) and tris-(8-hydroxyquinoline) gallium (Gaq3) to act as the electron donor and acceptor, respectively. The m-MTDATA:Gaq3 blend device shows a photocurrent of 405μA∕cm−2 at −8V, corresponding to a response of 338mA∕W under an illumination of 365nm UV light with an intensity of 1.2mW∕cm2. The high response is attributed to the enhanced dissociation of geminate hole-electron pairs in the distributed heterojunction of the blend and suppression of radiative decay. Photophysics of the PD involved is also discussed in terms of the performance and device structures.
Phase diagram of lossy negative index metamaterials
Authors: Wu Rui-xin , Zou Da-yong
Published: September 2008

For lossy metamaterials, there exist the negative index of refraction regimes that may originate from double negative or single negative of the real parts of complex permittivity and permeability. To represent the regimes of negative index, a material quality factor space is proposed. Within the space the different negative index regimes are found located in the different regions. The contour map of the complex index of refraction in the space show that the negative index can be always possible to realize in three ways, and the loss of single negative metamaterials is greater than that of double negative metamaterials.