bluuebunny/crossref_metadata_2025 huggingface dataset:
Localized chemical switching of the charge state of nitrogen-vacancy luminescence centers in diamond
Authors: Shanley Toby W. , Martin Aiden A. , Aharonovich Igor , Toth Milos
Published: August 2014

We present a direct-write chemical technique for controlling the charge state of near-surface nitrogen vacancy centers (NVs) in diamond by surface fluorination. Fluorination of H-terminated diamond is realized by electron beam stimulated desorption of H2O in the presence of NF3 and verified with environmental photoyield spectroscopy (EPYS) and photoluminescence (PL) spectroscopy. PL spectra of shallow NVs in H- and F-terminated nanodiamonds show the expected dependence of the NV charge state on their energetic position with respect to the Fermi-level. EPYS reveals a corresponding difference between the ionization potential of H- and F-terminated diamond. The electron beam fluorination process is highly localized and can be used to fluorinate H-terminated diamond, and to increase the population of negatively charged NV centers.
Investigating high speed phenomena in laser plasma interactions using dilation x-ray imager (invited)
Authors: Nagel S. R. , Hilsabeck T. J. , Bell P. M. , Bradley D. K. , Ayers M. J. , Piston K. , Felker B. , Kilkenny J. D. , Chung T. , Sammuli B. , Hares J. D. , Dymoke-Bradshaw A. K. L.
Published: August 2014

The DIlation X-ray Imager (DIXI) is a new, high-speed x-ray framing camera at the National Ignition Facility (NIF) sensitive to x-rays in the range of ≈2–17 keV. DIXI uses the pulse-dilation technique to achieve a temporal resolution of less than 10 ps, a ≈10× improvement over conventional framing cameras currently employed on the NIF (≈100 ps resolution), and otherwise only attainable with 1D streaked imaging. The pulse-dilation technique utilizes a voltage ramp to impart a velocity gradient on the signal-bearing electrons. The temporal response, spatial resolution, and x-ray sensitivity of DIXI are characterized with a short x-ray impulse generated using the COMET laser facility at Lawrence Livermore National Laboratory. At the NIF a pinhole array at 10 cm from target chamber center (tcc) projects images onto the photocathode situated outside the NIF chamber wall with a magnification of ≈64×. DIXI will provide important capabilities for warm-dense-matter physics, high-energy-density science, and inertial confinement fusion, adding important capabilities to temporally resolve hot-spot formation, x-ray emission, fuel motion, and mix levels in the hot-spot at neutron yields of up to 1017. We present characterization data as well as first results on electron-transport phenomena in buried-layer foil experiments.
Rotational analysis of the $3_0^1 $31 band of the $\tilde A{}^6\Sigma ^ + \leftarrow \tilde X{}^6\Sigma ^ + $Ã6Σ+←X̃6Σ+ system of CrCCH
Authors: Brugh Dale J. , Morse Michael D.
Published: August 2014

The spectrum of chromium acetylide, CrCCH, has been investigated in the near-infrared region (10 500–14 500 cm−1) and an intense band system is observed. The $3_0^1 $301 band of this system has been investigated at high resolution (0.025 cm−1) and this system is identified as the $\tilde A{}^{\rm 6}{\rm \Sigma }^ + \leftarrow \tilde X{}^{\rm 6}{\rm \Sigma }^ + $Ã6Σ+←X̃6Σ+ system, analogous to the near IR spectra of the CrH, CrF, and CrCl molecules. Among the many unidentified lines, we have assigned 341 lines belonging to 43 of the 54 allowed branches. Using combination differences, the rotational constants of the ground state have been determined. Computational results on the ground state are also reported, along with a comparison to other monoligated monovalent chromium compounds.
Ferroelectric domain triggers the charge modulation in semiconductors (invited)
Authors: Morozovska Anna N. , Eliseev Eugene A. , Ievlev Anton V. , Varenyk Olexander V. , Pusenkova Anastasiia S. , Chu Ying-Hao , Shur Vladimir Ya. , Strikha Maksym V. , Kalinin Sergei V.
Published: August 2014

We consider a typical heterostructure “domain patterned ferroelectric film—ultra-thin dielectric layer—semiconductor,” where the semiconductor can be an electrolyte, paraelectric or multi-layered graphene. Unexpectedly, we have found that the space charge modulation profile and amplitude in the semiconductor, that screens the spontaneous polarization of a 180-deg domain structure of ferroelectric, depends on the domain structure period, dielectric layer thickness and semiconductor screening radius in a rather non-trivial nonlinear way. Multiple size effects appearance and manifestation are defined by the relationship between these three parameters. In addition, we show that the concept of effective gap can be introduced in a simple way only for a single-domain limit. Obtained analytical results open the way for understanding of current-AFM maps of contaminated ferroelectric surfaces in ambient atmosphere as well as explore the possibilities of conductivity control in ultra-thin semiconductor layers.
Nonlinear space charge dynamics in mixed ionic-electronic conductors: Resistive switching and ferroelectric-like hysteresis of electromechanical response
Authors: Morozovska Anna N. , Eliseev Eugene A. , Varenyk Olexandr V. , Kim Yunseok , Strelcov Evgheni , Tselev Alexander , Morozovsky Nicholas V. , Kalinin Sergei V.
Published: August 2014

We performed self-consistent modelling of nonlinear electrotransport and electromechanical response of thin films of mixed ionic-electronic conductors (MIEC) allowing for steric effects of mobile charged defects (ions, protons, or vacancies), electron degeneration, and Vegard stresses. We establish correlations between the features of the nonlinear space-charge dynamics, current-voltage, and bending-voltage curves for different types of the film electrodes. A pronounced ferroelectric-like hysteresis of the bending-voltage loops and current maxima on the double hysteresis current-voltage loops appear for the electron-transport electrodes. The double hysteresis loop with pronounced humps indicates a memristor-type resistive switching. The switching occurs due to the strong nonlinear coupling between the electronic and ionic subsystems. A sharp meta-stable maximum of the electron density appears near one open electrode and moves to another one during the periodic change of applied voltage. Our results can explain the nonlinear nature and correlation of electrical and mechanical memory effects in thin MIEC films. The analytical expression proving that the electrically induced bending of MIEC films can be detected by interferometric methods is derived.
Sequential injection of domain walls into ferroelectrics at different bias voltages: Paving the way for “domain wall memristors”
Authors: Whyte J. R. , McQuaid R. G. P. , Ashcroft C. M. , Einsle J. F. , Canalias C. , Gruverman A. , Gregg J. M.
Published: August 2014

Simple meso-scale capacitor structures have been made by incorporating thin (∼300 nm) single crystal lamellae of KTiOPO4 (KTP) between two coplanar Pt electrodes. The influence that either patterned protrusions in the electrodes or focused ion beam milled holes in the KTP have on the nucleation of reverse domains during switching was mapped using piezoresponse force microscopy imaging. The objective was to assess whether or not variations in the magnitude of field enhancement at localised “hot-spots,” caused by such patterning, could be used to both control the exact locations and bias voltages at which nucleation events occurred. It was found that both the patterning of electrodes and the milling of various hole geometries into the KTP could allow controlled sequential injection of domain wall pairs at different bias voltages; this capability could have implications for the design and operation of domain wall electronic devices, such as memristors, in the future.
Electrochemical strain microscopy of silica glasses
Authors: Proksch R.
Published: August 2014

Piezoresponse Force Microscopy and Electrochemical Strain Microscopy (ESM) are two related techniques that have had considerable success in nano-scale probing of functional material properties. Both measure the strain of the sample in response to a localized electric field beneath a sharp conductive tip. In this work, a collection of commercially available glass samples were measured with a variety of Si cantilevers coated with different conductive metals. In some cases, these glasses showed significant hysteresis loops, similar in appearance to those measured on ferroelectric materials with spontaneous permanent electric dipoles. The magnitude of the electrochemical strain and hysteresis correlated well with the molar percentage of sodium in the glass material, with high sodium (soda-lime) glass showing large hysteresis and fused silica (pure SiO2) showing essentially no hysteresis. The “elephant-ear” shape of the hysteresis loops correlated well with it originating from relaxation behavior—an interpretation verified by observing the temperature dependent relaxation of the ESM response. Cation mobility in a disordered glass should have a low diffusion constant. To evaluate this diffusion constant, the temperature of the glass was varied between room temperature to ∼200 °C. Vanishing hysteresis as the temperature increased was associated with a decrease in the relaxation time of the electrochemical response. The hysteretic behavior changed drastically in this temperature range, consistent with bound surface water playing a large role in the relaxation. This demonstrates the ability of ESM to differentiate cationic concentrations in a range of silica glasses. In addition, since glass is a common sample substrate for, this provides some clear guidance for avoiding unwanted substrate crosstalk effects in piezoresponse and electrochemical strain response measurements.
The effects of domain wall thickness on the nanoscale piezoresponse of ferroelectric domains
Authors: Chen L. Q. , Pan K. , Liu Y. Y.
Published: August 2014

The effects of domain wall thickness on the nanoscale piezoresponse of ferroelectric domains, including typical 180°, uncharged 90°, and charged 90° domains, are investigated via treating the domain wall as a piezoelectric medium, which possesses distinct piezoelectric coefficients from the adjacent domains. It is found that increasing the domain thickness can result in enhanced lateral piezoresponse force microscopy response of uncharged 90° domains and vertical piezoresponse force microscopy (VPFM) response of charged 90° domains, while it would reduce VPFM response of uncharged 90° domains. Good agreements with experiments are observed. The different enhancement behaviors maybe result from the distinction of average polarization orientation of those domain walls. These insights point to a new pathway to enhance nanoscale piezoresponse in ferroelectric materials.
Piezoelectricity and ferroelectricity of cellular polypropylene electrets films characterized by piezoresponse force microscopy
Authors: Miao Hongchen , Sun Yao , Zhou Xilong , Li Yingwei , Li Faxin
Published: August 2014

Cellular electrets polymer is a new ferroelectret material exhibiting large piezoelectricity and has attracted considerable attentions in researches and industries. Property characterization is very important for this material and current investigations are mostly on macroscopic properties. In this work, we conduct nanoscale piezoelectric and ferroelectric characterizations of cellular polypropylene (PP) films using piezoresponse force microscopy (PFM). First, both the single-frequency PFM and dual-frequency resonance-tracking PFM testings were conducted on the cellular PP film. The localized piezoelectric constant d33 is estimated to be 7–11pC/N by correcting the resonance magnification with quality factor and it is about one order lower than the macroscopic value. Next, using the switching spectroscopy PFM (SS-PFM), we studied polarization switching behavior of the cellular PP films. Results show that it exhibits the typical ferroelectric-like phase hysteresis loops and butterfly-shaped amplitude loops, which is similar to that of a poly(vinylidene fluoride) (PVDF) ferroelectric polymer film. However, both the phase and amplitude loops of the PP film are intensively asymmetric, which is thought to be caused by the nonzero remnant polarization after poling. Then, the D-E hysteresis loops of both the cellular PP film and PVDF film were measured by using the same wave form as that used in the SS-PFM, and the results show significant differences. Finally, we suggest that the ferroelectric-like behavior of cellular electrets films should be distinguished from that of typical ferroelectrics, both macroscopically and microscopically.
Piezoelectricity in collagen type II fibrils measured by scanning probe microscopy
Authors: Denning D. , Kilpatrick J. I. , Hsu T. , Habelitz S. , Fertala A. , Rodriguez B. J.
Published: August 2014

The converse piezoelectric effect in collagen type II fibrils, the main collagen constituent in cartilage, was investigated using piezoresponse force microscopy. The fibrils exhibited shear piezoelectric behavior similar to that previously reported in collagen type I fibrils and followed the same cantilever-fibril angle dependence present for type I. A uniform polarization directed from the amine to carboxyl termini, as seen for collagen type I, was observed in all type II fibrils studied. The shear piezoelectric coefficient, d15, however, for type II was roughly 28–32% of the value measured for type I fibrils. Possible explanations for the reduced piezoelectric coefficient of type II collagen are provided.
P(VDF-TrFE) nanorod assemblies with anisotropic piezoelectric properties investigated by piezoelectric response microscopy
Authors: Chen Xiaosui , Wang Yunli , Cai Kai , Bai Yang , Bo Shuhui , Guo Dong
Published: August 2014

Highly ordered assemblies of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) nanorods with anisotropic piezoelectric response were fabricated on different substrates by using a template-free self-organization method. The significant difference in vertical and lateral piezoelectric responses of the nanorods in piezoresponse force microscopy (PFM) revealed that their molecular dipoles were preferentially oriented parallel to the substrate plane. In addition, dipole orientation distribution map in the nanorods was derived by analyzing the vertical and lateral PFM amplitude and phase images. Infrared reflection spectra further showed that the macromolecular backbones were oriented perpendicularly relative to the substrate. A flat-on lamellar structure and a confined crystallization of dewetted melt phase nanorod formation mechanism were proposed. The highly anisotropic piezoelectric response of the assemblies of nanorods may be promising for nanoscale devices for application in energy harvesting, etc. More importantly, the results demonstrated that self organization could be used for fabricating P(VDF-TrFE) nanostructures by controlling the surface energy of the substrates.
Piezoelectricity and ferroelectricity in biomaterials: Molecular modeling and piezoresponse force microscopy measurements
Authors: Bystrov V. S. , Seyedhosseini E. , Kopyl S. , Bdikin I. K. , Kholkin A. L.
Published: August 2014

Piezoelectricity is one of the important functional properties inherent to many biomaterials. It stems from the non-centrosymmetric crystal structure of most biopolymers including proteins, polysaccharides, and lipids. Understanding the relationship between the generated electric field and applied mechanical stress has become the main motivation to studying piezoelectricity in biological systems and artificial biomaterials at the nanoscale. In this work, we present a review of the piezoelectric and ferroelectric properties of several molecular systems and nanomaterials revealed by Piezoresponse Force Microscopy (PFM) and compare the results with molecular modeling and computer simulations. Experimentally observed by PFM and calculated dielectric, piezoelectric, and ferroelectric properties of these materials are analyzed in the context of their possible role in functionality of biological systems.
Some well-posedness and general stability results in Timoshenko systems with infinite memory and distributed time delay
Authors: Guesmia Aissa
Published: August 2014

In this paper, we consider a Timoshenko system in one-dimensional bounded domain with infinite memory and distributed time delay both acting on the equation of the rotation angle. Without any restriction on the speeds of wave propagation and under appropriate assumptions on the infinite memory and distributed time delay convolution kernels, we prove, first, the well-posedness and, second, the stability of the system, where we present some decay estimates depending on the equal-speed propagation case and the opposite one. The obtained decay rates depend on the growths of the memory and delay kernels at infinity. In the nonequal-speed case, the decay rate depends also on the regularity of initial data. Our stability results show that the only dissipation resulting from the infinite memory guarantees the asymptotic stability of the system regardless to the speeds of wave propagation and in spite of the presence of a distributed time delay. Applications of our approach to specific coupled Timoshenko-heat and Timoshenko-wave systems as well as the discrete time delay case are also presented.
Algebro-geometric solutions for the complex Sharma-Tasso-Olver hierarchy
Authors: Yue Chao , Xia Tiecheng
Published: August 2014

This paper is dedicated to provide theta function representation of algebro-geometric solutions and related crucial quantities for the complex Sharma-Tasso-Olver (CSTO) hierarchy. Our main tools include the polynomial recursive formalism to derive the CSTO hierarchy, the hyper-elliptic curve with finite number of genus, the Baker-Akhiezer functions, the meromorphic function, the Dubrovin-type equations for auxiliary divisors, and the associated trace formulas. By use of these tools, the explicit representations of the Baker-Ahhiezer functions, the meromorphic function, and the algebro-geometric solutions are obtained for the entire CSTO hierarchy.
Multifunctionalities driven by ferroic domains
Authors: Yang J. C. , Huang Y. L. , He Q. , Chu Y. H.
Published: August 2014

Considerable attention has been paid to ferroic systems in pursuit of advanced applications in past decades. Most recently, the emergence and development of multiferroics, which exhibit the coexistence of different ferroic natures, has offered a new route to create functionalities in the system. In this manuscript, we step from domain engineering to explore a roadmap for discovering intriguing phenomena and multifunctionalities driven by periodic domain patters. As-grown periodic domains, offering exotic order parameters, periodic local perturbations and the capability of tailoring local spin, charge, orbital and lattice degrees of freedom, are introduced as modeling templates for fundamental studies and novel applications. We discuss related significant findings on ferroic domain, nanoscopic domain walls, and conjunct heterostructures based on the well-organized domain patterns, and end with future prospects and challenges in the field.
Reflective all-fiber current sensor based on magnetic fluids
Authors: Li Lin , Han Qun , Liu Tiegen , Chen Yaofei , Zhang Rongxiang
Published: August 2014

A reflective all-fiber current sensor based on magnetic fluid (MF) is reported. The MF is used as the cladding of a piece of no-core fiber which is spliced between two sections of singlemode fiber to form a singlemode-multimode–singlemode structure. An intensity based interrogation scheme with a superluminescent diode as the light source and the dual-balanced detection method is used in the sensing system. The influence of the direction of the magnetic field on the sensitivity of the sensor is also experimentally investigated and analyzed.
Design of charge exchange recombination spectroscopy for the joint Texas experimental tokamak
Authors: Chi Y. , Zhuang G. , Cheng Z. F. , Hou S. Y. , Cheng C. , Li Z. , Wang J. R. , Wang Z. J.
Published: August 2014

The old diagnostic neutral beam injector first operated at the University of Texas at Austin is ready for rejoining the joint Texas experimental tokamak (J-TEXT). A new set of high voltage power supplies has been equipped and there is no limitation for beam modulation or beam pulse duration henceforth. Based on the spectra of fully striped impurity ions induced by the diagnostic beam the design work for toroidal charge exchange recombination spectroscopy (CXRS) system is presented. The 529 nm carbon VI (n = 8 − 7 transition) line seems to be the best choice for ion temperature and plasma rotation measurements and the considered hardware is listed. The design work of the toroidal CXRS system is guided by essential simulation of expected spectral results under the J-TEXT tokamak operation conditions.
Continuous and holomorphic functions with values in closed operators
Authors: Dereziński Jan , Wrochna Michał
Published: August 2014

We systematically derive general properties of continuous and holomorphic functions with values in closed operators, allowing in particular for operators with empty resolvent set. We provide criteria for a given operator-valued function to be continuous or holomorphic. This includes sufficient conditions for the sum and product of operator-valued holomorphic functions to be holomorphic. Using graphs of operators, operator-valued functions are identified with functions with values in subspaces of a Banach space. A special role is thus played by projections onto closed subspaces of a Banach space, which depend holomorphically on a parameter.
Resonances in photoabsorption: Predissociation line shapes in the 3pπD $^1\Pi _u^+ \leftarrow X^1\Sigma _g^+$Πu+1←X1Σg+ system in H2
Authors: Mezei J. Zs. , Schneider I. F. , Glass-Maujean M. , Jungen Ch.
Published: August 2014

The predissociation of the \documentclass[12pt]{minimal}\begin{document}$3p\pi D^1\Pi _u^+,v\ge 3,N=1$\end{document}3pπD1Πu+,v≥3,N=1, N = 2, and N = 3 levels of diatomic hydrogen is calculated by ab initio multichannel quantum defect theory combined with a R-matrix type approach that accounts for interfering predissociation and autoionization. The theory yields absorption line widths and shapes that are in good agreement with those observed in the high-resolution synchrotron vacuum-ultraviolet absorption spectra obtained by Dickenson et al. [J. Chem. Phys. 133, 144317 (2010)] at the DESIRS beamline of the SOLEIL synchrotron. The theory predicts further that many of the D state resonances with v ⩾ 6 exhibit a complex fine structure which cannot be modeled by the Fano profile formula and which has not yet been observed experimentally.
Quantum probabilities as Dempster-Shafer probabilities in the lattice of subspaces
Authors: Vourdas A.
Published: August 2014

The orthocomplemented modular lattice of subspaces ${\cal L}[H(d)]$L[H(d)], of a quantum system with d-dimensional Hilbert space H(d), is considered. A generalized additivity relation which holds for Kolmogorov probabilities is violated by quantum probabilities in the full lattice ${\cal L}[H(d)]$L[H(d)] (it is only valid within the Boolean subalgebras of ${\cal L}[H(d)]$L[H(d)]). This suggests the use of more general (than Kolmogorov) probability theories, and here the Dempster-Shafer probability theory is adopted. An operator ${\mathfrak {D}}(H_1, H_2)$D(H1,H2), which quantifies deviations from Kolmogorov probability theory is introduced, and it is shown to be intimately related to the commutator of the projectors ${\mathfrak {P}}(H_1), {\mathfrak {P}}(H_2)$P(H1),P(H2), to the subspaces H1, H2. As an application, it is shown that the proof of the inequalities of Clauser, Horne, Shimony, and Holt for a system of two spin 1/2 particles is valid for Kolmogorov probabilities, but it is not valid for Dempster-Shafer probabilities. The violation of these inequalities in experiments supports the interpretation of quantum probabilities as Dempster-Shafer probabilities.
Thomson scattering measurements from asymmetric interpenetrating plasma flows
Authors: Ross J. S. , Moody J. D. , Fiuza F. , Ryutov D. , Divol L. , Huntington C. M. , Park H.-S.
Published: August 2014

Imaging Thomson scattering measurements of collective ion-acoustic fluctuations have been utilized to determine ion temperature and density from laser produced counter-streaming asymmetric flows. Two foils are heated with 8 laser beams each, 500 J per beam, at the Omega Laser facility. Measurements are made 4 mm from the foil surface using a 60 J 2ω probe laser with a 200 ps pulse length. Measuring the electron density and temperature from the electron-plasma fluctuations constrains the fit of the multi-ion species, asymmetric flows theoretical form factor for the ion feature such that the ion temperatures, ion densities, and flow velocities for each plasma flow are determined.
Tomographic inversion techniques incorporating physical constraints for line integrated spectroscopy in stellarators and tokamaks
Authors: Pablant N. A. , Bell R. E. , Bitter M. , Delgado-Aparicio L. , Hill K. W. , Lazerson S. , Morita S.
Published: August 2014

Accurate tomographic inversion is important for diagnostic systems on stellarators and tokamaks which rely on measurements of line integrated emission spectra. A tomographic inversion technique based on spline optimization with enforcement of constraints is described that can produce unique and physically relevant inversions even in situations with noisy or incomplete input data. This inversion technique is routinely used in the analysis of data from the x-ray imaging crystal spectrometer (XICS) installed at the Large Helical Device. The XICS diagnostic records a 1D image of line integrated emission spectra from impurities in the plasma. Through the use of Doppler spectroscopy and tomographic inversion, XICS can provide profile measurements of the local emissivity, temperature, and plasma flow. Tomographic inversion requires the assumption that these measured quantities are flux surface functions, and that a known plasma equilibrium reconstruction is available. In the case of low signal levels or partial spatial coverage of the plasma cross-section, standard inversion techniques utilizing matrix inversion and linear-regularization often cannot produce unique and physically relevant solutions. The addition of physical constraints, such as parameter ranges, derivative directions, and boundary conditions, allow for unique solutions to be reliably found. The constrained inversion technique described here utilizes a modified Levenberg-Marquardt optimization scheme, which introduces a condition avoidance mechanism by selective reduction of search directions. The constrained inversion technique also allows for the addition of more complicated parameter dependencies, for example, geometrical dependence of the emissivity due to asymmetries in the plasma density arising from fast rotation. The accuracy of this constrained inversion technique is discussed, with an emphasis on its applicability to systems with limited plasma coverage.
An experimental investigation of the flow dynamics of streamwise vortices of various strengths interacting with a supersonic jet
Authors: Heeb N. , Gutmark E. , Kailasanath K.
Published: August 2014

The results of an experimental study involving the introduction of streamwise vorticity into a supersonic jet are presented. Both streamwise and cross stream PIV measurements of a baseline jet and three vortex generator configurations of varied penetration were acquired in the overexpanded, ideally expanded, and underexpanded regimes. Streamwise vortex pairs were shown to persist no further than two diameters downstream independent of initial magnitude. Integration of the modulus of streamwise vorticity was shown to better correlate with secondary flow field modifications than maximum values. Reductions in shock cell spacing and downstream turbulence, and increases in initial spread rate and upstream integrated turbulence were correlated with increases in streamwise vorticity for all operating conditions. Streamwise vorticity was shown to achieve opposite effects on shock strength in the over/under expanded regimes due to introduction of secondary shock structures in the underexpanded case. Additionally, limited effect on potential core length was quantified.
Bilayer registry in a multicomponent asymmetric membrane: Dependence on lipid composition and chain length
Authors: Polley Anirban , Mayor Satyajit , Rao Madan
Published: August 2014

A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component asymmetric lipid bilayer comprising an unsaturated palmitoyl-oleoyl-phosphatidyl-choline, a saturated sphingomyelin, and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (lo)-liquid disordered (ld) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed ld phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the lo domains across the two leaflets, resulting in bilayer registry. This transbilayer correlation depends sensitively upon the chain length of the participating lipids and possibly other features of lipid chemistry, such as degree of saturation. We find that the lo domains in the upper leaflet can induce phase segregation in the lower leaflet, when the latter is nominally in the mixed (ld) phase.
High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun
Authors: Fu Feichao , Liu Shengguang , Zhu Pengfei , Xiang Dao , Zhang Jie , Cao Jianming
Published: August 2014

A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences.
Lateral critical Casimir force in 2D Ising strip with inhomogeneous walls
Authors: Nowakowski Piotr , Napiórkowski Marek
Published: August 2014

We analyze the lateral critical Casimir force acting between two planar, chemically inhomogeneous walls confining an infinite 2D Ising strip of width M. The inhomogeneity of each of the walls has size N1; they are shifted by the distance L along the strip. Using the exact diagonalization of the transfer matrix, we calculate the lateral critical Casimir force and discuss its properties, in particular its scaling close to the 2D bulk critical point, as a function of temperature, surface magnetic field, and the geometric parameters M, N1, L. We determine the magnetization profiles which display the formation of the bridge joining the inhomogeneities on the walls and establish the relation between the characteristic properties of the lateral Casimir force and magnetization morphologies. We check numerically that breaking of the bridge is related to the inflection point of the lateral force.
Simulation of electric double layers around charged colloids in aqueous solution of variable permittivity
Authors: Fahrenberger Florian , Xu Zhenli , Holm Christian
Published: August 2014

The ion distribution around charged colloids in solution has been investigated intensely during the last decade. However, few theoretical approaches have included the influence of variation in the dielectric permittivity within the system, let alone in the surrounding solvent. In this article, we introduce two relatively new methods that can solve the Poisson equation for systems with varying permittivity. The harmonic interpolation method approximately solves the Green's function in terms of a spherical harmonics series, and thus provides analytical ion-ion potentials for the Hamiltonian of charged systems. The Maxwell equations molecular dynamics algorithm features a local approach to electrostatics, allowing for arbitrary local changes of the dielectric constant. We show that the results of both methods are in very good agreement. We also found that the renormalized charge of the colloid, and with it the effective far field interaction, significantly changes if the dielectric properties within the vicinity of the colloid are changed.
A non-destructive method for measuring the mechanical properties of ultrathin films prepared by atomic layer deposition
Authors: Zhang Qinglin , Xiao Xingcheng , Cheng Yang-Tse , Verbrugge Mark W.
Published: August 2014

The mechanical properties of ultrathin films synthesized by atomic layer deposition (ALD) are critical for the liability of their coated devices. However, it has been a challenge to reliably measure critical properties of ALD films due to the influence from the substrate. In this work, we use the laser acoustic wave (LAW) technique, a non-destructive method, to measure the elastic properties of ultrathin Al2O3 films by ALD. The measured properties are consistent with previous work using other approaches. The LAW method can be easily applied to measure the mechanical properties of various ALD thin films for multiple applications.
Multi-dimensional instability of obliquely propagating ion acoustic solitary waves in electron-positron-ion superthermal magnetoplasmas
Authors: EL-Shamy E. F.
Published: August 2014

The solitary structures of multi–dimensional ion-acoustic solitary waves (IASWs) have been considered in magnetoplasmas consisting of electron-positron-ion with high-energy (superthermal) electrons and positrons are investigated. Using a reductive perturbation method, a nonlinear Zakharov-Kuznetsov equation is derived. The multi-dimensional instability of obliquely propagating (with respect to the external magnetic field) IASWs has been studied by the small-k (long wavelength plane wave) expansion perturbation method. The instability condition and the growth rate of the instability have been derived. It is shown that the instability criterion and their growth rate depend on the parameter measuring the superthermality, the ion gyrofrequency, the unperturbed positrons-to-ions density ratio, the direction cosine, and the ion-to-electron temperature ratio. Clearly, the study of our model under consideration is helpful for explaining the propagation and the instability of IASWs in space observations of magnetoplasmas with superthermal electrons and positrons.
Van der Waals epitaxial growth of topological insulator Bi2−xSbxTe3−ySey ultrathin nanoplate on electrically insulating fluorophlogopite mica
Authors: Tu Ngoc Han , Tanabe Yoichi , Huynh Khuong Kim , Sato Yohei , Oguro Hidetoshi , Heguri Satoshi , Tsuda Kenji , Terauchi Masami , Watanabe Kazuo , Tanigaki Katsumi
Published: August 2014

We report the growth of high quality Bi2−xSbxTe3−ySey ultrathin nanoplates (BSTS-NPs) on an electrically insulating fluorophlogopite mica substrate using a catalyst-free vapor solid method. Under an optimized pressure and suitable Ar gas flow rate, we control the thickness, the size, and the composition of the BSTS-NPs. Raman spectra showing systematic change indicate that the thicknesses and compositions of the BSTS-NPs are indeed accurately controlled. Electrical transport demonstrates a robust Dirac cone carrier transport in the BSTS-NPs. Since the BSTS-NPs provide superior dominant surface transport of the tunable Dirac cone surface states with negligible contribution of the conduction of the bulk states, the BSTS-NPs provide an ideal platform to explore intrinsic physical phenomena as well as technological applications of 3-dimensional topological insulators in the future.
Fine tunable red-green upconversion luminescence from glass ceramic containing 5%Er3+:NaYF4 nanocrystals under excitation of two near infrared femtosecond lasers
Authors: Shang Xiaoying , Chen Ping , Cheng Wenjing , Zhou Kan , Ma Jing , Feng Donghai , Zhang Shian , Sun Zhenrong , Qiu Jianrong , Jia Tianqing
Published: August 2014

In this paper, we report fine tunable red-green upconversion luminescence of glass ceramic containing 5%Er3+: NaYF4 nanocrystals excited simultaneously by two near infrared femtosecond lasers. When the glass ceramic was irradiated by 800 nm femtosecond laser, weak red emission centered at 670 nm was detected. Bright red light was observed when the fs laser wavelength was tuned to 1490 nm. However, when excited by the two fs lasers simultaneously, the sample emitted bright green light centered at 550 nm, while the red light kept the same intensity. The dependences of the red and the green light intensities on the two pump lasers are much different, which enables us to manipulate the color emission by adjusting the two pump laser intensities, respectively. We present a theoretical model of Er3+ ions interacting with two fs laser fields, and explain well the experimental results.
Recovery of Biot's transition frequency of air-saturated poroelastic media using vibroacoustic spectroscopy
Authors: Ogam Erick , Fellah Z. E. A.
Published: August 2014

The transition frequency marks the passage from low-frequency viscosity dominated flow to high-frequency inertia dominated one in porous media. It was one of the principal characteristics predicted by Biot's theory. The transition frequency has been a theoretical concept for which only theoretical expressions have been developed in recent years. A vibroacoustic spectroscopy experimental method to recover the characteristic frequency (fC) and for gaining insight into the frequency response of fluid-saturated porous materials has been developed. Long thin air-saturated porous rods solicited mechanically are employed for the experiment. Changes in the fluid flow profile with excitation frequency results in relative motion between the skeleton and the saturating-fluid. This enhances the frictional viscous forces, which, in turn, increases damping of the skeletal motion. These transitions are signaled by observable cues in the acquired laser-vibrometry spectrum of the rods' longitudinal vibration mode patterns. The resonance peaks exhibit sudden attenuation (increase in damping) and are interrupted at the transition frequencies evoking a change of propagation medium. These patterns are compared with those of two plains, single phase material (viscoelastic) rods whose modes stand out as regularly spaced moderately damped peaks.
Recharging behavior of nitrogen-centers in ZnO
Authors: Philipps Jan M. , Stehr Jan E. , Buyanova Irina , Tarun Marianne C. , McCluskey Matthew D. , Meyer Bruno K. , Hofmann Detlev M.
Published: August 2014

Electron Paramagnetic Resonance was used to study N2-centers in ZnO, which show a 5-line spectrum described by the hyperfine interaction of two nitrogen nuclei (nuclear spin I = 1, 99.6% abundance). The recharging of this center exhibits two steps, a weak onset at about 1.4 eV and a strongly increasing signal for photon energies above 1.9 eV. The latter energy coincides with the recharging energy of NO centers (substitutional nitrogen atoms on oxygen sites). The results indicate that the N2-centers are deep level defects and therefore not suitable to cause significant hole-conductivity at room temperature.
Semiconductor-to-metal transition of Bi2Se3 under high pressure
Authors: Zhang Junkai , Han Yonghao , Liu Cailong , Zhang Xin , Ke Feng , Peng Gang , Ma Yanmei , Ma Yanzhang , Gao Chunxiao
Published: August 2014

Pressure-induced electrical transport properties of Bi2Se3, including Hall coefficient, carrier concentration, mobility, and electrical resistivity, have been investigated under pressure up to 29.8 GPa by in situ Hall-effect measurements. The results indicate that the structural and electronic phase transitions of Bi2Se3 induce discontinuous changes in these electrical parameters. The significant anomaly in Hall coefficient at 5 GPa reveals an electronic topological transition deriving from the topological change of the band extremum (Van Hove singularity). Additionally, electrical resistivity measurements under variable temperatures show that the insulating state of Bi2Se3 becomes increasingly stable with an increase of pressure below 9.7 GPa. But above 9.7 GPa, Bi2Se3 enters into a fully metallic state. As the metallization occurs, the topological property of Bi2Se3 disappears.
Room temperature multiferroicity in orthorhombic LuFeO3
Authors: Chowdhury Ujjal , Goswami Sudipta , Bhattacharya Dipten , Ghosh Jiten , Basu Soumen , Neogi Samya
Published: August 2014

From the measurement of dielectric, ferroelectric, and magnetic properties, we observe simultaneous ferroelectric and magnetic transitions around ∼600 K in orthorhombic LuFeO3. We also observe suppression of the remanent polarization by ∼95% under a magnetic field of ∼15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO3 is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.
Low-density plasma formation in aqueous biological media using sub-nanosecond laser pulses
Authors: Genc Suzanne L. , Ma Huan , Venugopalan Vasan
Published: August 2014

We demonstrate the formation of low- and high-density plasmas in aqueous media using sub-nanosecond laser pulses delivered at low numerical aperture (NA = 0.25). We observe two distinct regimes of plasma formation in deionized water, phosphate buffered saline, Minimum Essential Medium (MEM), and MEM supplemented with phenol red. Optical breakdown is first initiated in a low-energy regime and characterized by bubble formation without plasma luminescence with threshold pulse energies in the range of Ep ≈ 4–5 μJ, depending on media formulation. The onset of this regime occurs over a very narrow interval of pulse energies and produces small bubbles (Rmax = 2–20 μm) due to a tiny conversion (η < 0.01%) of laser energy to bubble energy EB. The lack of visible plasma luminescence, sharp energy onset, and low bubble energy conversion are all hallmarks of low-density plasma (LDP) formation. At higher pulse energies (Ep = 11–20 μJ), the process transitions to a second regime characterized by plasma luminescence and large bubble formation. Bubbles formed in this regime are 1–2 orders of magnitude larger in size (Rmax≳100 μm) due to a roughly two-order-of-magnitude increase in bubble energy conversion (η ≳ 3%). These characteristics are consistent with high-density plasma formation produced by avalanche ionization and thermal runaway. Additionally, we show that supplementation of MEM with fetal bovine serum (FBS) limits optical breakdown to this high-energy regime. The ability to produce LDPs using sub-nanosecond pulses focused at low NA in a variety of cell culture media formulations without FBS can provide for cellular manipulation at high throughput with precision approaching that of femtosecond pulses delivered at high NA.
Identification of critical stacking faults in thin-film CdTe solar cells
Authors: Yoo Su-Hyun , Butler Keith T. , Soon Aloysius , Abbas Ali , Walls John M. , Walsh Aron
Published: August 2014

Cadmium telluride (CdTe) is a p-type semiconductor used in thin-film solar cells. To achieve high light-to-electricity conversion, annealing in the presence of CdCl2 is essential, but the underlying mechanism is still under debate. Recent evidence suggests that a reduction in the high density of stacking faults in the CdTe grains is a key process that occurs during the chemical treatment. A range of stacking faults, including intrinsic, extrinsic, and twin boundary, are computationally investigated to identify the extended defects that limit performance. The low-energy faults are found to be electrically benign, while a number of higher energy faults, consistent with atomic-resolution micrographs, are predicted to be hole traps with fluctuations in the local electrostatic potential. It is expected that stacking faults will also be important for other thin-film photovoltaic technologies.
Trifluoromethylation of graphene
Authors: Zhou Lin , Zhou Lushan , Wang Xi , Yu Jingwen , Yang Mingmei , Wang Jianbo , Peng Hailin , Liu Zhongfan
Published: August 2014

We demonstrate trifluoromethylation of graphene by copper-catalyzed free radical reaction. The covalent addition of CF3 to graphene, which changes the carbon atom hybridization from sp2 to sp3, and modifies graphene in a homogeneous and nondestructive manner, was verified with Raman spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy reveals that CF3 groups are grafted to the basal plane of graphene, with about 4 at. % CF3 coverage. After trifluoromethylation, the average resistance increases by nearly one order of magnitude, and an energy gap of about 98 meV appears. The noninvasive and mild reaction to synthesize trifluoromethylated graphene paves the way for graphene's applications in electronics and biomedical areas.
Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering
Authors: Bathula Sivaiah , Gahtori Bhasker , Jayasimhadri M. , Tripathy S. K. , Tyagi Kriti , Srivastava A. K. , Dhar Ajay
Published: August 2014

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si80Ge20 alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si80Ge20 alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.
Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes
Authors: Mehnke Frank , Kuhn Christian , Guttmann Martin , Reich Christoph , Kolbe Tim , Kueller Viola , Knauer Arne , Lapeyrade Mickael , Einfeldt Sven , Rass Jens , Wernicke Tim , Weyers Markus , Kneissl Michael
Published: August 2014

The design and Mg-doping profile of AlN/Al0.7Ga0.3N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm2.