bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction
Authors: Tamura Hiroyuki , Martinazzo Rocco , Ruckenbauer Matthias , Burghardt Irene
Published: September 2012

Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011)10.1021/jp203174e], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs.
Dynamics of two-dimensional monolayer water confined in hydrophobic and charged environments
Authors: Kumar Pradeep , Han Sungho
Published: September 2012

We perform molecular dynamics simulations to study the effect of charged surfaces on the intermediate and long time dynamics of water in nanoconfinements. Here, we use the transferable interaction potential with five points (TIP5P) model of a water molecule confined in both hydrophobic and charged surfaces. For a single molecular layer of water between the surfaces, we find that the temperature dependence of the lateral diffusion constant of water up to very high temperatures remains Arrhenius with a high activation energy. In case of charged surfaces, however, the dynamics of water in the intermediate time regime is drastically modified presumably due to the transient coupling of dipoles of water molecules with electric field fluctuations induced by charges on the confining surfaces. Specifically, the lateral mean square displacements display a distinct super-diffusive behavior at intermediate time scale, defined as the time scale between ballistic and diffusive regimes. This change in the intermediate time-scale dynamics in the charged confinement leads to the enhancement of long-time dynamics as reflected in increasing diffusion constant. We introduce a simple model for a possible explanation of the super-diffusive behavior and find it to be in good agreement with our simulation results. Furthermore, we find that confinement and the surface polarity enhance the low frequency vibration in confinement compared to bulk water. By introducing a new effective length scale of coupling between translational and orientational motions, we find that the length scale increases with the increasing strength of the surface polarity. Further, we calculate the correlation between the diffusion constant and the excess entropy and find a disordering effect of polar surfaces on the structure of water. Finally, we find that the empirical relation between the diffusion constant and the excess entropy holds for a monolayer of water in nanoconfinement.
Imaging spectroscopy diagnosis of internal electron temperature and density distributions of plasma cloud surrounding hydrogen pellet in the Large Helical Device
Authors: Motojima G. , Sakamoto R. , Goto M. , Matsuyama A. , Mishra J. S. , Yamada H.
Published: September 2012

To investigate the behavior of hydrogen pellet ablation, a novel method of high-speed imaging spectroscopy has been used in the Large Helical Device (LHD) for identifying the internal distribution of the electron density and temperature of the plasma cloud surrounding the pellet. This spectroscopic system consists of a five-branch fiberscope and a fast camera, with each objective lens having a different narrow-band optical filter for the hydrogen Balmer lines and the background continuum radiation. The electron density and temperature in the plasma cloud are obtained, with a spatial resolution of about 6 mm and a temporal resolution of 5 × 10−5 s, from the intensity ratio measured through these filters. To verify the imaging, the average electron density and temperature also have been measured from the total emission by using a photodiode, showing that both density and temperature increase with time during the pellet ablation. The electron density distribution ranging from 1022 to \documentclass[12pt]{minimal}\begin{document}$10^{24}\ \rm {m^{-3}}$\end{document}1024m−3 and the temperature distribution around 1 eV have been observed via imaging. The electron density and temperature of a 0.1 m plasma cloud are distributed along the magnetic field lines and a significant electron pressure forms in the plasma cloud for typical experimental conditions of the LHD.
Fundamental limits on the digital phase measurement method based on cross-correlation analysis
Authors: Liang Yu-Rong , Duan Hui-Zong , Yeh Hsien-Chi , Luo Jun
Published: September 2012

Ultra-precision phase measurement is a key technology for state-of-the-art laser interferometry. In this paper we present a fully digital phase measurement method based on cross-correlation analysis, and analyze the measurement errors caused by sampling quantization, intrinsic white noise and non-integral-cycle sampling. The last error source results in a cyclic error that has not been reported ever. We used a high-performance data acquisition system to carry out the cross-correlation-based phase measurement, and obtained a noise level of 1.2 × 10−6 rad/Hz1/2@1 Hz. Moreover, the cyclic phase error of about 10−2 rad/Hz1/2, caused by non-integral-cycle sampling, had been observed. In order to demonstrate the application of this precision phase measurement method, an ultra-precision heterodyne laser interferometer, consisting of digital phase measurement system and ultra-stable optical bench, was constructed for displacement measurement. The experimental results showed that a measurement resolution of 63 pm had been achieved.
Spintronic oscillator based on magnetic field feedback
Authors: Dixit D. , Konishi K. , Tomy C. V. , Suzuki Y. , Tulapurkar A. A.
Published: September 2012

We present a circuit design of a spintronic oscillator based on a magnetic tunnel junction (MTJ). In this design, a dc current is passed through a magnetic tunnel junction which is connected to a “feed-back” wire below it. Any fluctuation in the magnetization direction of the free layer of MTJ, drives a fluctuating current through the feed-back wire, which exerts a magnetic field on the free layer. This in turn can amplify the magnetization fluctuations. If the dc current passing through the MTJ is more than a critical value, periodic precessional states of the magnetization are possible.
Spin gating electrical current
Authors: Ciccarelli C. , Zârbo L. P. , Irvine A. C. , Campion R. P. , Gallagher B. L. , Wunderlich J. , Jungwirth T. , Ferguson A. J.
Published: September 2012

The level of the chemical potential is a fundamental parameter of the electronic structure of a physical system, which consequently plays an important role in defining the properties of active electrical devices. We directly measure the chemical potential shift in the relativistic band structure of the ferromagnetic semiconductor (Ga,Mn)As, controlled by changes in its magnetic order parameter. Our device comprises a non-magnetic aluminum single electron channel capacitively coupled to the (Ga,Mn)As gate electrode. The chemical potential shifts of the gate are directly read out from the shifts in the Coulomb blockade oscillations of the single electron transistor. The experiments introduce a concept of spin gating electrical current. In our spin transistor spin manipulation is completely removed from the electrical current carrying channel.
Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method
Authors: Hamila Radhia , Saidi Faouzi , Maaref Hassen , Rodriguez Philippe , Auvray Laurent
Published: September 2012

In this paper, we report the obtention of quaternary (B)InGaAs/GaAs alloys grown by metal organic vapour phase epitaxy has been studied using high resolution x ray diffraction (HRXRD) and photoluminescence (PL) measurements. HRXRD has been achieved to determine the indium fraction (35%) incorporated into BGaAs, which shows that the strain effects have been reduced compared to the InGaAs one. Through further careful inspection, boron-indium gallium arsenic (BInGaAs) epilayer exhibits several PL peak emissions. They are associated to the exciton bond induced by the boron isoelectronic and cluster defect states. In contrast, for the BInGaAs single quantum well (SQW), we have a band to band transition mainly influenced by the confinement of electron-hole pairs in the BInGaAs well. However, the PL of BInGaAs SQW temperature-dependence has shown a localization effect due to the conduction-band modulation induced by the boron clustering in the structure. At high PL temperature, we have a band to band transition of electron-hole pairs in the BInGaAs well.
Switching of nanosized filaments in NiO by conductive atomic force microscopy
Authors: Nardi F. , Deleruyelle D. , Spiga S. , Muller C. , Bouteille B. , Ielmini D.
Published: September 2012

Resistive switching in binary metal oxides consists of conductivity changes originating from the electrical creation/dissolution of conductive filaments (CFs) at nanoscale. The investigation of CF local properties can only be achieved through physical and electrical studies at the scale of 10 nm or less, that is, the characteristic size of CFs. This work reports on the direct manipulation of individual CFs formed through insulating NiO films by conductive atomic force microscopy (CAFM) and the comparison between forming/reset processes induced by CAFM and those observed in large-area devices with the same NiO film. The switching variability due to local defects, such as grain boundaries and dislocations, is directly evidenced by CAFM during electroforming process. Our results also indicate that the forming voltage under CAFM can be significantly smaller than the one observed in large-area devices, thus providing evidence for the electric-field enhancement underneath the CAFM tip. Filament deactivation, or reset, at extremely low currents close to 100 nA is demonstrated and described in terms of electrode-limited CF. These results suggest that device engineering and CF size limitation may allow for a significant reduction of forming voltage and reset current in resistive switching random-access memory switching.
Nonadiabatic theory of strong-field atomic effects under elliptical polarization
Authors: Wang Xu , Eberly J. H.
Published: September 2012

Elliptically polarized laser fields provide a new channel for access to strong-field processes that are either suppressed or not present under linear polarization. Quantum theory is mostly unavailable for their analysis, and we report here results of a systematic study based on a classical ensemble theory with solution of the relevant ab inito time-dependent Newton equations for selected model atoms. The study's approach is necessarily nonadiabatic, as it follows individual electron trajectories leading to single, double, and triple ionizations. Of particular interest are new results bearing on open questions concerning experimental reports of unexplained species dependences as well as double-electron release times that are badly matched by a conventional adiabatic quantum tunneling theory. We also report the first analysis of electron trajectories for sequential and non-sequential triple ionization.
Self-diffusion and activity coefficients of ions in charged disordered media
Authors: Jardat Marie , Hribar-Lee Barbara , Dahirel Vincent , Vlachy Vojko
Published: September 2012

Self-diffusion and single ion activity coefficients of ions of size symmetric electrolytes were studied in the presence of a collection of charged obstacles (called matrix) within a “soft” version of the primitive model of electrolyte solutions. The matrix subsystem possesses a net charge, depending on the concentration and charge of obstacles. The Brownian dynamics method was used to calculate the self-diffusion coefficients of mobile species. The replica Ornstein–Zernike theory for the partly quenched systems was used to calculate the individual activity coefficients of mobile ionic species. The results reflect the competition between attractive (obstacle–counterion, co-ion–counterion), and repulsive (obstacle–co-ion) interactions in these model systems. For the simplest possible system of symmetric monovalent ions the latter effect wins: Co-ions are excluded from the area around obstacles, and this slows down their diffusion compared to that of counterions. Introduction of divalent charges into the system changes this result when the concentration of obstacles is low. We compare these results to those obtained for the corresponding fully annealed systems, i.e., where all the species are mobile. In most cases the self-diffusion and activity coefficients of counterions and co-ions in the presence of charged obstacles follow the trends of the fully annealed solution, which are dictated by the composition of the mixture. In few situations, however, the presence of charged obstacles modifies these trends. Our study allows us to clearly identify the effects due to obstacles, and to separate them from those arising from the composition of the solution. In the case of charge and size symmetric systems, the results for the individual activity coefficients fully support the hypothesis of the “electrostatic excluded volume”. Thermodynamic and dynamic results are consistent in explaining the behavior of the systems studied.
Flow structures of Jupiter's Great Red Spot extracted by using optical flow method
Authors: Liu Tianshu , Wang Bo , Choi David S.
Published: September 2012

The flow structures of Jupiter's Great Red Spot (GRS) are studied based on a high-resolution velocity field extracted from the Galileo 1996 cloud images of the GRS by using the physics-based optical flow method. The mean transverse velocity profile across the anti-cyclonic near-elliptical collar of the GRS is obtained. The flow structures in the relatively quiescent inner region enclosed by the high-speed collar are revealed at a coarse-grained level. The cyclonic source node in the inner region is identified that is directly associated with the observed cyclonic rotation near the center of the GRS, and its significance in the maintenance of the GRS is explored by using a topological constraint.
Single charge detection in capacitively coupled integrated single electron transistors based on single-walled carbon nanotubes
Authors: Zhou Xin , Ishibashi Koji
Published: September 2012

Single charge detection is demonstrated in the capacitively coupled integrated single electron transistors (SETs) in single-walled carbon nanotubes (SWCNTs) quantum dots. Two SETs are fabricated based on two different SWCNTs aligned in parallel, by taking advantage of the aligned growth of SWCNTs and subsequent transfer-printed techniques. In order to make both two SETs be capacitively coupled, a metal finger is fabricated on the top of them. The charge sensing is proved by the response of a detector current in one SWCNT-SET when the number of electrons in the other SWCNT-SET is changed by sweeping the corresponding gate voltages. In this integrated device, shifts of Coulomb oscillation peaks due to the single electron event are also observed.
Hydrogen passivation of polycrystalline silicon thin films
Authors: Scheller L.-P. , Weizman M. , Simon P. , Fehr M. , Nickel N. H.
Published: September 2012

The influence of post-hydrogenation on the electrical and optical properties of solid phase crystallized polycrystalline silicon (poly-Si) was examined. The passivation of grain-boundary defects was measured as a function of the passivation time. The silicon dangling-bond concentration decreases with increasing passivation time due to the formation of Si-H complexes. In addition, large H-stabilized platelet-like clusters are generated. The influence of H on the electrical properties was investigated using temperature dependent conductivity and Hall-effect measurements. For poly-Si on Corning glass, the dark conductivity decreases upon hydrogenation, while it increases when the samples are fabricated on silicon-nitride covered Borofloat glass. Hall-effect measurements reveal that for poly-Si on Corning glass the hole concentration and the mobility decrease upon post-hydrogenation, while a pronounced increase is observed for poly-Si on silicon-nitride covered Borofloat glass. This indicates the formation of localized states in the band gap, which is supported by sub band-gap absorption measurments. The results are discussed in terms of hydrogen-induced defect passivation and generation mechanisms.
Analysis of the physical contributions to magnetic couplings in broken symmetry density functional theory approach
Authors: Coulaud Esther , Guihéry Nathalie , Malrieu Jean-Paul , Hagebaum-Reignier Denis , Siri Didier , Ferré Nicolas
Published: September 2012

We present a new and simple scheme that aims to decompose into its main physical contributions the magnetic exchange interaction between two unpaired electrons. It is based on the popular broken-symmetry density functional theory (DFT) approach and relies on the frozen orbital capabilities of the local self-consistent field method. Accordingly, the magnetic exchange interaction energy can be separated into three main contributions: the direct exchange between magnetic orbitals, the spin polarization of the core orbitals, and the relaxation of the magnetic orbitals (kinetic exchange). This decomposition scheme is applied to a series of binuclear inorganic magnetic compounds both ferromagnetic and antiferromagnetic. The direct exchange is determined from the restricted DFT description. On the one hand, starting from the restricted orbital set and relaxing only the magnetic orbitals provides the kinetic exchange contribution and an estimate of the t and U parameters of the generalized Anderson mechanism. On the other hand, relaxing the core orbitals only introduces the spin polarization contribution. The decomposition leads to almost additive contributions. The effect of the amount of Hartree-Fock exchange on the different contributions is analyzed.
Propagation of thermal waves across a wedge
Authors: Salazar Agustín , Mendioroz Arantza
Published: September 2012

Photothermal techniques have been widely developed to study the thermal properties and to detect buried defects of samples with flat parallel surfaces. In the last years, there has been a growing interest in the application of photothermal techniques to samples with non-flat surfaces, as is the case of rods, tubes, and balls. The aim of the present work is to study the propagation of thermal waves across wedge samples. We have considered plane illumination (launching plane thermal waves) as well as Gaussian illumination (producing spherical thermal waves). We focus on the behavior of the front and rear surface temperatures, which is recorded using lock-in infrared thermography. This work is aimed at expanding the use of photothermal techniques for the quantitative characterization of wedge samples, as is the case of gear, blades, screws, and other hardware tools.
Polarizability of supported metal nanoparticles: Mehler-Fock approach
Authors: Jung Jesper , Pedersen Thomas G.
Published: September 2012

Using toroidal coordinates and the Mehler-Fock transform, we present an analysis of the polarizability of a complex structure allowing for the study of arbitrarily truncated metal spheres including a dielectric substrate. Our analysis is based on an electrostatic approach, i.e., we are in the quasi-static limit, where we solve the Laplace equation for the potential. The derived method is used to analyze the behavior of localized surface plasmon resonances of truncated metal nanospheres including substrate effects. The method is fast, simple, easy to implement, and useful for analysis of experimental work on supported metal nanoparticles, e.g., within the area of plasmonic photovoltaics.
Leaky mode analysis of luminescent thin films: The case of ZnO on sapphire
Authors: Aad Roy , Divay Laurent , Bruyant Aurelien , Blaize Sylvain , Couteau Christophe , Rogers David J. , Lerondel Gilles
Published: September 2012

Zinc oxide (ZnO) epitaxial thin films grown on c-sapphire substrates by pulsed laser deposition were investigated using angle and polarization-resolved photoluminescence spectroscopy. Side-emission spectra differed significantly from surface-emission spectra in exhibiting dominant, narrow, polarization-resolved peaks. These spectral features were attributed to leaky substrate modes in the layers. Observations were first verified using transmission calculations with non-adjustable parameters, which took into account the dispersion, the anisotropy of the ZnO refractive index, and the dependence on film thickness. Results were consistent with Fabry-Perot-like interference being the origin of the distinctive ZnO luminescence observed at grazing incidence angles. A second analysis, based on the source terms method, was used in order to retrieve the bulk emission properties, including the wavelength-dependent quantum yield and the emission anisotropy. While ZnO thin films were considered here, this analysis method can be extended to any luminescent thin film of similar geometry, demonstrating the potential of leaky mode analysis for probing passive and active material properties.
Crystal growth behaviour in Au-ZnO nanocomposite under different annealing environments and photoswitchability
Authors: Mishra Y. K. , Chakravadhanula V. S. K. , Hrkac V. , Jebril S. , Agarwal D. C. , Mohapatra S. , Avasthi D. K. , Kienle L. , Adelung R.
Published: September 2012

The growth of gold nanoparticles and ZnO nanorods in atom beam co-sputtered Au-ZnO nanocomposite (NC) system by annealing at two different ambient conditions is demonstrated in this work. Annealing in a furnace at 600 °C (air environment) confirmed the formation of ZnO nanorods surrounded with Au nanoparticles. In-situ annealing inside a transmission electron microscope (TEM) led to the formation of gold nanocrystals with different polygonal shapes. TEM micrographs were obtained in real time at intermediate temperatures of 300 °C, 420 °C, and 600 °C under vacuum. The growth mechanisms of Au nanocrystals and ZnO nanorods are discussed in the framework of Au-Zn eutectic and Zn-melting temperatures in vacuum and air, respectively. Current-voltage responses of Au-ZnO NC nanorods in dark as well as under light illumination have been investigated and photoswitching in Au-ZnO NC system is reported. The photoswitching has been discussed in terms of Au-ZnO band-diagram.
Periodic dripping dynamics in a co-flowing liquid-liquid system
Authors: Cramer Carsten , Studer Simon , Windhab Erich J. , Fischer Peter
Published: September 2012

Periodic dripping into air (the “leaky faucet” phenomenon) is now known and understood in detail, while the same problem for fluids dispersed into a second co-flowing immiscible liquid has received far less attention. Depending on the excitation mode of the fluid phases, distinctive oscillations in the dispersed fluid column lead to the formation of droplet groups. In this work, the impact of the velocity of the continuous phase, volume flow rate of the disperse phase, superimposed pressure oscillations of the dispersed phase, and the viscosity of the disperse phase on the drop formation dynamics in liquid-liquid systems is investigated. It is shown that different dripping modes correlate with certain flow conditions and that viscous damping controlled by the disperse fluid viscosity plays an important role in abating the flow-induced sequencing of drop detachment. A Capillary-number–Ohnesorge-number phase diagram is proposed to summarize the experimental results and to generalize periodic dripping dynamics in co-flowing liquid-liquid systems.
HP-sequence design for lattice proteins—An exact enumeration study on diamond as well as square lattice
Authors: Narasimhan S. L. , Rajarajan A. K. , Vardharaj L.
Published: September 2012

We present an exact enumeration algorithm for identifying the native configuration—a maximally compact self-avoiding walk configuration that is also the minimum energy configuration for a given set of contact-energy schemes; the process is implicitly sequence-dependent. In particular, we show that the 25-step native configuration on a diamond lattice consists of two sheet-like structures and is the same for all the contact-energy schemes, {(−1, 0, 0); (−7, −3, 0); (−7, −3, −1); (−7, −3, 1)}; on a square lattice also, the 24-step native configuration is independent of the energy schemes considered. However, the designing sequence for the diamond lattice walk depends on the energy schemes used whereas that for the square lattice walk does not. We have calculated the temperature-dependent specific heat for these designed sequences and the four energy schemes using the exact density of states. These data show that the energy scheme (−7, −3, −1) is preferable to the other three for both diamond and square lattice because the associated sequences give rise to a sharp low-temperature peak. We have also presented data for shorter (23-, 21-, and 17-step) walks on a diamond lattice to show that this algorithm helps identify a unique minimum energy configuration by suitably taking care of the ground-state degeneracy. Interestingly, all these shorter target configurations also show sheet-like secondary structures.
The importance of bendability in the percolation behavior of carbon nanotube and graphene-polymer composites
Authors: Balberg I.
Published: September 2012

The very low percolation thresholds in carbon nanotube and graphene polymer composites are of great recent interest. The values of these thresholds are basically determined by the extreme aspect ratios of the carbon particles. However, examining the many data in the literature we found that, surprisingly, for the corresponding composites the exclusion of the particles positions, due to their “hard cores,” is very small. We propose that this is associated primarily with the bending of these carbon particles within the actual composites.
Optical properties of multi-stacked InGaAs/GaNAs quantum dot solar cell fabricated on GaAs (311)B substrate
Authors: Shoji Yasushi , Akimoto Katsuhiro , Okada Yoshitaka
Published: September 2012

Quantum dot solar cells (QDSCs) comprised of 10 stacked pairs of strain-compensated InGaAs/GaNAs QD structure have been fabricated by atomic hydrogen-assisted molecular beam epitaxy. A homogeneous and high-density QD array structure with improved in-plane ordering and total density of ∼1012 cm−2 has been achieved on GaAs (311)B grown at 460 °C after stacking. The external quantum efficiency (EQE) of InGaAs/GaNAs QDSC increases in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. The short-circuit current density measured for QDSC is 17.2 mA/cm2 compared to 14.8 mA/cm2 of GaAs reference cell. Further, an increase in EQE due to photocurrent production by 2-step photon absorption has been observed at room temperature though it is still small at around 0.1%.
Spectroscopic investigation of nitrogen doped graphene
Authors: Podila R. , Chacón-Torres J. , Spear J. T. , Pichler T. , Ayala P. , Rao A. M.
Published: September 2012

Current research efforts are aimed at controlling the electronic properties via doping graphene. Previously, dopant-induced changes in the Fermi velocity were observed to result in an effectively downshifted Raman peak below the G′-band for n-doped carbon nanotubes. However, in the case of N-doped graphene, we find that several Raman features vary depending upon both dopant concentration and its bonding environment. For instance, only pyridinic/pyrrolic dopants were observed to result in intense D/D′-bands with a concomitant downshift in the G′-band. Here, we correlate x-ray photoelectron measurements with Raman spectra to elucidate effects of dopant bonding configuration on vibrational properties of graphene.
Probing into hybrid organic-molecule and InAs quantum-dots nanosystem with multistacked dots-in-a-well units
Authors: Chen Miaoxiang , Kobashi Kazufumi
Published: September 2012

Hybridizing air-stable organic-molecules with advanced III-V semiconductor quantum-dots (QDs) structures can be utilized to create a new generation of biochemical sensing devices. In order to enhance their optical performances, the active regions in these QDs structures commonly consist of multistacked dots-in-a-well (DWELL) units. The effects of grafted molecules on the performances of the QDs structures with multistacked DWELLs, however, still remain unclear. Here, we show the significant improvements in the optical properties of InAs QDs in a hybrid nanosystem obtained by grafting biocompatible diazonium salt compound (amine donor) atop InAs QDs structure. Since its interface between the QDs structure and molecular monolayer retains an uncontaminated and non-oxidized condition, the nanosystem is an ideal platform to study the intrinsic properties of charge-carrier transport inside the system. Because of the complexity of the energy-levels in the QDs structure due to the existing surface QDs and DWELLs, selective excitation wavelengths (400, 633, and 885 nm, respectively) with different photo-energies are used to exactly analyze the complete charging mechanism in these QDs. A clear view of charge-carrier transfer inside the nanosystem is revealed by employing photoluminescence technique under selective-wavelength excitations. The present work provides new quantitative evidences for exploiting inorganic QDs applications in complex biological systems.
Bubble nucleation on nano- to micro-size cavities and posts: An experimental validation of classical theory
Authors: Witharana S. , Phillips B. , Strobel S. , Kim H. D. , McKrell T. , Chang J.-B. , Buongiorno J. , Berggren K. K. , Chen L. , Ding Y.
Published: September 2012

Recently reported data suggest that bubble nucleation on surfaces with nano-sized features (cavities and posts) may occur close to the thermodynamic saturation temperature. However, according to the traditional theory of heterogeneous bubble nucleation, such low nucleation temperatures are possible only for surfaces with micro-scale cavities. Motivated by this apparent contradiction, we have used infrared thermometry to measure the nucleation temperature of water on custom-fabricated nano- to micro-scale cavities (from 90 nm to 4.5 μm in diameter) and posts (from 60 nm to 5 μm in diameter), machined on ultra-smooth and clean silicon wafers using electron beam lithography. Our cavity data are in agreement with the predictions of the Young-Laplace equation, thus re-affirming the correctness of the classic view of heterogeneous bubble nucleation, at least for the water-silicon system investigated here. The data also suggest that individual posts of any size have an insignificant effect on bubble nucleation, as expected from theory.
Role of shear-thinning on the dynamics of rinsing flow by an impinging jet
Authors: Walker Travis W. , Hsu Tienyi T. , Frank Curtis W. , Fuller Gerald G.
Published: September 2012

Using a jet of one fluid to ablate a second liquid that coats a planar substrate produces a variety of interesting flow structures. These rinsing flows can create alternating layers of jet and coating fluids, creating difficulties in imaging the resulting radial hydraulic jumps for qualitative and quantitative data extraction. This study is an extension of the work done by Hsu et al. [“Role of fluid elasticity on the dynamics of rinsing flow by an impinging jet,” Phys. Fluids. 23, 033101 (2011)10.1063/1.3567215] and presents a method to reveal the positions of the free surfaces in rinsing flows as well as exploring the role of shear thinning in this flow process. Following the previous work, we used an impinging jet of water to rinse coating fluids of varying rheologies to understand the flow structures during the transient growth of the resulting hydraulic jumps, observing rheological dependencies on the jump magnitude and velocity and overall topography. While many instabilities have been shown to arise during rinsing flows, the flow profile strongly depends on the local viscosity ratio of the jet fluid to the coating fluid. Four classes of test liquids, each having approximately equal low-shear viscosities, have been chosen for this study: a Newtonian solution, a shear-thinning and elastic polymer solution, a Boger fluid (an elastic fluid with constant shear viscosity), and a shear-thinning but inelastic colloid suspension. The shear-thinning of the coating liquid is shown to affect the overall velocity of the radial growth and the geometry of the hydraulic jumps associated with both liquids. To confirm that the local shear viscosity controls many of the observed phenomena, experiments on Newtonian fluids having various shear viscosities are also presented.
Electronic structure, optical and magnetic properties of Co2FeGe Heusler alloy films
Authors: Uvarov N. V. , Kudryavtsev Y. V. , Kravets A. F. , Vovk A. Ya. , Borges R. P. , Godinho M. , Korenivski V.
Published: September 2012

Optical properties of ferromagnetic half-metallic full-Heusler Co2FeGe alloy are investigated experimentally and theoretically. Co2FeGe thin films were obtained by DC magnetron sputtering and show the saturation magnetization at T = 10 K of m≈5.6μB/f.u., close to the value predicted by the Slater-Pauling rule. First-principles calculations of the electronic structure and the dielectric tensor are performed using the full-potential linearized-augmented-plane-wave method in the generalized gradient approximation (GGA) and GGA + U approximation. The measured interband optical conductivity spectrum for the alloy exhibits a strong absorption band in the 1–4 eV energy range with pronounced fine structure, which agrees well with the calculated half-metallic spectrum of the system, suggesting a near perfect spin-polarization in the material.
X-ray backlight measurement of preformed plasma by kJ-class petawatt LFEX laser
Authors: Ohira Shinji , Fujioka Shinsuke , Sunahara Atsushi , Johzaki Tomoyuki , Nagatomo Hideo , Matsuo Satoshi , Morio Noboru , Kawanaka Jyunji , Nakata Yoshiki , Miyanaga Noriaki , Shiraga Hiroyuki , Nishimura Hiroaki , Azechi Hiroshi
Published: September 2012

Foot and pedestal pulses that precede the main pulse from a high-intensity laser greatly affect laser–plasma interactions. Especially in fast ignition schemes, preceding pulses generate a plasma prior to irradiation by the main pulse. This results in a too energetic and divergent electron beam being generated in the preformed plasma, which reduces the energy coupling efficiency from the heating laser to the dense fuel core. A preformed plasma with a density scale length of 40–60 μm was observed by a time- and space-resolved x-ray backlight technique using the LFEX laser system at the Institute of Laser Engineering, Osaka University. Preceding pulses (i.e., the foot and pedestal) of the LFEX were characterized by comparing observations with calculations results obtained using a two-dimension (2D) radiation-hydrodynamic simulation code. In a separate experiment, the 2D code was benchmarked with the experimentally observed hydrodynamic behavior of a gold plasma produced by a nanosecond laser pulse that mimicked foot and pedestal pulses (intensity: 1 ×1011−1×1012W/cm2). The preceding pulses were estimated to have an intensity of 1 ×1012−1013W/cm2, a duration of 2.0 ns, and a spot diameter at the target of 200–600 μm by comparing the measured hydrodynamics of the preformed plasma with that calculated by the 2D hydrodynamic simulation code.
Chemical and structural investigations of the interactions of Cu with MnSiO3 diffusion barrier layers
Authors: Casey Patrick , Bogan Justin , McCoy Anthony , Lozano Juan G. , Nellist Peter D. , Hughes Greg
Published: September 2012

X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermodynamic stability of Cu layers deposited onto Mn silicate (MnSiO3) barrier layers formed on SiO2 surfaces. Using a fully in situ growth and analysis experimental procedure, it has been shown that ∼1 nm Cu layers do not chemically react with ultra thin (∼2.6 nm) MnSiO3 surfaces following 400 °C annealing, with no evidence for the growth of Cu oxide species, which are known to act as an intermediate step in the Cu diffusion process into silica based dielectrics. The effectiveness of MnSiO3 as a barrier to Cu diffusion following high temperature annealing was also investigated, with electron energy loss spectroscopy suggesting that a ∼2.6 nm MnSiO3 layer prevents Cu diffusion at 400 °C. The chemical composition of a barrier layer formed following the deposition of a partially oxidised Mn (MnOx)/Cu alloy was also investigated using XPS in order to determine if the presence of Cu at the Mn/SiO2 interface during MnSiO3 growth inherently changes the chemical composition of the barrier layer. In contrast to previous publications, it has been shown that Mn oxide species do not form in the barrier region during thermal annealing, with Cu appearing to be chemically inert in the presence of Mn and SiO2.
First principles determination of the NH2/ND2($\skew4\tilde A, \skew3\tilde X$Ã,X̃) branching ratios for photodissociation of NH3/ND3 via full-dimensional quantum dynamics based on a new quasi-diabatic representation of coupled ab initio potential energy surfaces
Authors: Ma Jianyi , Zhu Xiaolei , Guo Hua , Yarkony David R.
Published: September 2012

The A-band photodissociation of ammonia is an archetypical and long studied example of non-adiabatic dynamics in a polyatomic system. Due to a well-known conical intersection seam, electronically excited NH3 can produce either the ground ($\tilde X^2 B_1 $X̃2B1) state or the excited ($\tilde A^2 A_1 $Ã2A1) state of the NH2 fragment. In this work, the non-adiabatic dynamics is investigated using a six-dimensional wave packet method and an improved version of a newly developed diabatic Hamiltonian based on high quality ab initio data. The $\tilde A^2 A_1 /\tilde X^2 B_1 $Ã2A1/X̃2B1 branching ratios are in excellent agreement with experimental estimates, thus validating the non-adiabatically coupled Hamiltonian.
Note: On the power spectrum of undulations of simulated bilayers
Authors: Stecki J.
Published: September 2012

The best finite Fourier series for a smooth surface h(x, y), closest to the positions of heads of amphiphiles in the least-square sense, agrees fully with the Fourier coefficients obtained by a direct summation over raw data points. Both methods produce structure factors S(q) containing all necessary features: small-q divergence, a minimum, the raise to the ubiquitous nearest-neighbor peak near q = 2π/(coll.diameter) and further peaks. The Laurent series is also discussed.
Wave packet calculations on nonadiabatic effects for the O(3P)+HF(1Σ+) reaction under hyperthermal conditions
Authors: Gómez-Carrasco S. , Bulut N. , Bañares L. , Roncero O.
Published: September 2012

We present wave packet calculations of total and state-to-state reaction probabilities and integral cross sections for the nonadiabatic dynamics of the O(3P)+HF → F(2P)+OH(2Π) reaction at hyperthermal collision energies ranging from 1.2 to 2.4 eV. The validity of the centrifugal sudden approximation is discussed for the title reaction and a comprehensive investigation of the influence of nonadiabatic effects on the dynamics of this reactive system at high (hyperthermal) collision energies is presented. In general, nonadiabatic effects are negligible for averaged observables, such as total reaction probabilities and integral cross sections, but they are clearly observed in detailed observables such as rotationally state-resolved reaction probabilities. A critical discussion of nonadiabatic effects on the dynamics of the title reaction is carried out by comparing with the reverse reaction and the characteristics of the adiabatic and diabatic potential energy surfaces involved.
Design and implementation of an integral wall-mounted quartz crystal microbalance for atomic layer deposition
Authors: Riha Shannon C. , Libera Joseph A. , Elam Jeffrey W. , Martinson Alex B. F.
Published: September 2012

Quartz crystal microbalance (QCM) measurements have played a vital role in understanding and expediting new atomic layer deposition (ALD) processes; however, significant barriers remain to their routine use and accurate execution. In order to turn this exclusively in situ technique into a routine characterization method, an integral QCM fixture was developed. This new design is easily implemented on a variety of chemical vapor deposition (CVD) tools, allows rapid sample exchange, prevents backside deposition, and minimizes both the footprint and flow disturbance. Unlike previous QCM designs, the fast thermal equilibration enables tasks such as temperature-dependent studies and ex situ sample exchange, further highlighting the utility of this QCM design for day-to-day use. Finally, the in situ mapping of thin film growth rates across the ALD reactor was demonstrated in a popular commercial tool operating in both continuous and quasi-static ALD modes.
First measurements of laser-accelerated proton induced luminescence
Authors: Floquet V. , Ceccotti T. , Dobosz Dufrénoy S. , Bonnaud G. , Gremillet L. , Monot P. , Martin Ph.
Published: September 2012

We present our first results about laser-accelerated proton induced luminescence in solids. In the first part, we describe the optimization of the proton source as a function of the target thickness as well as the laser pulse duration and energy. Due to the ultra high contrast ratio of our laser beam, we succeeded in using targets ranging from the micron scale down to nanometers thickness. The two optimal thicknesses we put in evidence are in good agreement with numerical simulations. Laser pulse duration shows a small influence on proton maximum energy, whereas the latter turns out to vary almost linearly as a function of laser energy. Thanks to this optimisation work, we have been able to acquire images of the proton energy deposition in a solid scintillator.
Origin of enhanced water adsorption at $\langle 1\bar{1}0\rangle$⟨11¯⟩ step edge on rutile TiO2(110) surface
Authors: Hong Feng , Ni Yu Heng , Xu Wen Juan , Yan Yanfa
Published: September 2012

Water adsorption behavior at \documentclass[12pt]{minimal}\begin{document}$\langle 1\bar{1}0\rangle$\end{document}⟨11¯0⟩ and ⟨001⟩ step edges on rutile TiO2 (110) surface has been investigated using density-functional theory calculations. We find that the \documentclass[12pt]{minimal}\begin{document}$\langle 1\bar{1}0\rangle$\end{document}⟨11¯0⟩ edge exhibits significantly enhanced water adsorption, especially dissociative adsorption, as compared to the pristine (110) surface and ⟨001⟩ step edge. The origin for the enhanced water adsorption is found to be due to the existence of fourfold coordinated Ti atoms (Ti4c) at the \documentclass[12pt]{minimal}\begin{document}$\langle 1\bar{1}0\rangle$\end{document}⟨11¯0⟩ step edge, which lead to charge transfer to adsorbates more easily than fivefold coordinated Ti atoms on the (110) surface and ⟨001⟩ step edge. Furthermore, due to the local configuration of the dissociative mode, the charge transfer occurs more easily from Ti4c to the hydroxyl group 1π orbital, which considerably increases the adsorbate-substrate interaction. As a result, the \documentclass[12pt]{minimal}\begin{document}$\langle 1\bar{1}0\rangle$\end{document}⟨11¯0⟩ step edge favors dissociative water adsorption, making it more reactive to water than the (110) surface and ⟨001⟩ edge.
Delamination of strained multilayered nanowires
Authors: Colin Jérôme , Cimetière Alain , Grilhé Jean
Published: September 2012

The mechanical stability of a strained multilayered nanowire has been investigated qualitatively from an energy variation calculation. Depending on the strain and Dupré energy of the interfaces, it is found that the layers may delaminate. The expression of the critical radius of the coherent zone below which the layers may delaminate has been determined, and a stability diagram is presented for the nanowire.
Effect of ion-to-electron mass ratio on the evolution of ion beam driven instability in particle-in-cell simulations
Authors: Hong Jinhy , Lee Ensang , Min Kyoungwook , Parks George K.
Published: September 2012

In particle-in-cell (PIC) simulation studies of ion-ion two-stream instability, a reduced ion-to-electron mass ratio is often employed to save computation time. It is tacitly assumed that electrons do not play a significant role in the evolution of the instability as the ion-ion interactions are regarded to occur on time scales much slower than the response time of electrons. However, as the effect of such a reduced mass ratio has never been closely examined, we have studied the evolution of the ion beam driven instability using a one-dimensional electrostatic PIC code by rescaling the simulation parameters according to the ion-electron mass ratio. We made a reference simulation run with a mass ratio of 100 first and compared the results to the simulation results using the real mass ratio with parameters rescaled from those of the reduced mass ratio. External electric fields were applied in these simulations, which accelerated the electrons and excited an ion acoustic type instability, forming electron phase space holes. Merging of the electron holes affected the ion dynamics significantly when the reduced mass ratio was used, while the interplay between the electron and ion dynamics became different depending on the rescaling methods in the case of the real mass ratio. Another simulation test with much enhanced external electric field results in similar mass ratio dependence. The present simulation results clearly show that the reduced mass ratio should be used cautiously in PIC simulations as the electron dynamics can modify the ion instabilities significantly by affecting the ion motions.
Robust low resistivity p-type ZnO:Na films after ultraviolet illumination: The elimination of grain boundaries
Authors: Lin S. S.
Published: September 2012

We propose negatively charged oxygen species at grain boundaries may be detrimental to the p-type behavior. After ultraviolet illumination to release oxygen species, the p-type behavior of moderately Na-doped ZnO films is strengthened in the subsequent several minutes. A robust p-type film with a hole mobility of 7.9 cm2/Vs, a hole concentration of 2.1 × 1017 cm−3, and a film resistivity of 3.8 Ωcm has been reproducibly achieved. Transformation from n-type to p-type conduction is observed for the lightly Na-doped ZnO after ultraviolet illumination. We believe that single crystalline p-type ZnO films are indispensable for ZnO light-emitting diodes.