bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental and theoretical study of the electronic spectrum of the HBCl free radical
Authors: Gharaibeh Mohammed A. , Nagarajan Ramya , Clouthier Dennis J. , Tarroni Riccardo
Published: January 2015

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the Ã2A″Π−X̃2A′ band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl3 and H2 or D2 in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground and excited state vibrational energy levels. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a 2Π electronic state at linearity. We have used high level ab initio theory to calculate the ground and excited state potential energy surfaces and have determined the vibronic energy levels variationally. The theory results were used to assign the LIF spectra which involve transitions from the ground state zero-point level to high vibrational levels of the excited state. The correspondence between theory and experiment, including the transition frequencies, upper state band symmetries, and H, B, and Cl isotope shifts, was used to validate the assignments.
A general flux-based analysis for spherical electrocatalytic nanomotors
Authors: Nourhani Amir , Lammert Paul E. , Crespi Vincent H. , Borhan Ali
Published: January 2015

We present a flux-based analysis of the motion of spherical electrocatalytic nanomotors based on an electrokinetic model with general distribution of cation flux over the motor surface. Using the method of matched asymptotic expansions, we find a general expression for the motor velocity to leading order in the Debye length in the limit of weak surface cation flux. The nanomotor velocity is proportional to the first Legendre coefficient of surface cation flux and depends non-linearly on the interfacial potential at the particle surface, inversely on the fluid viscosity and background ion concentration in the electrolyte. The results are consistent with previous experimental observations and numerical calculations. We also provide a scaling analysis that portrays the physical picture of self-electrophoresis at the molecular level based on migration of ions and transfer of their momentum to fluid.
Stability results for multi-layer radial Hele-Shaw and porous media flows
Authors: Gin Craig , Daripa Prabir
Published: January 2015

Motivated by stability problems arising in the context of chemical enhanced oil recovery, we perform linear stability analysis of Hele-Shaw and porous media flows in radial geometry involving an arbitrary number of immiscible fluids. Key stability results obtained and their relevance to the stabilization of fingering instability are discussed. Some of the key results, among many others, are (i) absolute upper bounds on the growth rate in terms of the problem data; (ii) validation of these upper bound results against exact computation for the case of three-layer flows; (iii) stability enhancing injection policies; (iv) asymptotic limits that reduce these radial flow results to similar results for rectilinear flows; and (v) the stabilizing effect of curvature of the interfaces. Multi-layer radial flows have been found to have the following additional distinguishing features in comparison to rectilinear flows: (i) very long waves, some of which can be physically meaningful, are stable; and (ii) eigenvalues can be complex for some waves depending on the problem data, implying that the dispersion curves for one or more waves can contact each other. Similar to the rectilinear case, these results can be useful in providing insight into the interfacial instability transfer mechanism as the problem data are varied. Moreover, these can be useful in devising smart injection policies as well as controlling the complexity of the long-term dynamics when drops of various immiscible fluids intersperse among each other. As an application of the upper bound results, we provide stabilization criteria and design an almost stable multi-layer system by adding many layers of fluid with small positive jumps in viscosity in the direction of the basic flow.
Discontinuity of the exchange-correlation potential and the functional derivative of the noninteracting kinetic energy as the number of electrons crosses integer boundaries in Li, Be, and B
Authors: Morrison Robert C.
Published: January 2015

Accurate densities were determined from configuration interaction wave functions for atoms and ions of Li, Be, and B with up to four electrons. Exchange-correlation potentials, Vxc(r), and functional derivatives of the noninteracting kinetic energy, δK[ρ]/δρ(r), obtained from these densities were used to examine their discontinuities as the number of electrons N increases across integer boundaries for N = 1, N = 2, and N = 3. These numerical results are consistent with conclusions that the discontinuities are characterized by a jump in the chemical potential while the shape of Vxc(r) varies continuously as an integer boundary is crossed. The discontinuity of the Vxc(r) is positive, depends on the ionization potential, electron affinity, and orbital energy differences, and the discontinuity in δK[ρ]/δρ(r) depends on the difference between the energies of the highest occupied and lowest unoccupied orbitals. The noninteracting kinetic energy and the exchange correlation energy have been computed for integer and noninteger values of N between 1 and 4.
Approaching the Shockley-Queisser limit: General assessment of the main limiting mechanisms in photovoltaic cells
Authors: Vossier Alexis , Gualdi Federico , Dollet Alain , Ares Richard , Aimez Vincent
Published: January 2015

In principle, the upper efficiency limit of any solar cell technology can be determined using the detailed-balance limit formalism. However, “real” solar cells show efficiencies which are always below this theoretical value due to several limiting mechanisms. We study the ability of a solar cell architecture to approach its own theoretical limit, using a novel index introduced in this work, and the amplitude with which the different limiting mechanisms affect the cell efficiency is scrutinized as a function of the electronic gap and the illumination level to which the cell is submitted. The implications for future generations of solar cells aiming at an improved conversion of the solar spectrum are also addressed.
Investigation of defect structure of impurity-doped lithium niobate by combining thermodynamic constraints with lattice constant variations
Authors: Koyama Chihiro , Nozawa Jun , Maeda Kensaku , Fujiwara Kozo , Uda Satoshi
Published: January 2015

The defect structures of impurity-doped congruent lithium niobates (c-LN) were determined for impurities with various valences, including divalent, trivalent, and tetravalent impurities, in a concentration range where antisite niobium (NbLi) exists. On the basis of the “Li site vacancy model,” six kinds of defect structures in impurity-doped c-LN are possible. Using thermodynamic constraints, these can be narrowed down to two kinds. The first structure is that in which impurities, vacancies and Nb exist as defects in the Li site and no defects exist in the Nb site (structure A), described as {[LiLi] 1-5x-jy[NbLi]x[MLi]y[VLi]4x+(j-1)y}[NbNb][OO] 3 (V: vacancy, M: impurity, j: valence of impurity, x, y: compositional variable (≠0), Li/Nb = congruent ratio). {[LiLi×] 1-5x-2y[NbLi••••]x[MLi•]y[VLi′]4x+y}[NbNb×][OO×] 3 is an example by the Kröger-Vink notation for divalent M. In the second structure, vacancies and Nb exist as defects in the Li site and impurities exist as defects in the Nb site (structure B), described as {[LiLi] 1-5x-(j-5)y[NbLi]x[VLi]4x+(j-5)y}{[NbNb] 1-y[MNb]y}[OO] 3. {[LiLi×] 1-5x+y[NbLi••••]x[VLi′]4x-y}{[NbNb×] 1-y[MNb′]y}[OO×] 3 is an example for tetravalent M. Since the relationship between impurity concentration and lattice constants for structures A and B differs, the defect structures can be differentiated by analyzing lattice constant variations as a function of impurity concentration. The results show that the defect structure of divalent and trivalent impurity-doped c-LN is structure A and that of tetravalent impurity-doped c-LN is structure B. The NbLi concentration increased with increasing tetravalent impurity concentration. In contrast, the NbLi concentration decreased with increasing divalent and trivalent impurities, leading to suppression of optical damage. The valence of an impurity determines whether the impurity is located in the Li site or Nb site in c-LN, consequently determining whether NbLi decreases or increases when the population of the impurity changes.
Phonon scattering due to van der Waals forces in the lattice thermal conductivity of Bi2Te3 thin films
Authors: Park Kyeong Hyun , Mohamed Mohamed , Aksamija Zlatan , Ravaioli Umberto
Published: January 2015

In this work, we calculate the thermal conductivity of layered bismuth telluride (Bi2Te3) thin films by solving the Boltzmann transport equation in the relaxation-time approximation using full phonon dispersion and compare our results with recently published experimental data and molecular dynamics simulation. The group velocity of each phonon mode is readily extracted from the full phonon dispersion obtained from first-principle density-functional theory calculation and is used along with the phonon frequency to compute the various scattering terms. Our model incorporates the typical interactions impeding thermal transport (e.g., umklapp, isotope, and boundary scatterings) and introduces a new interaction capturing the reduction of phonon transmission through van der Waals interfaces of adjacent Bi2Te3 quintuple layers forming the virtual superlattice thin film. We find that this novel approach extends the empirical Klemens-Callaway relaxation model in such anisotropic materials and recovers the experimental anisotropy while using a minimal set of parameters.
Effect of feature size on dielectric nonlinearity of patterned PbZr0.52Ti0.48O3 films
Authors: Yang J. I. , Polcawich R. G. , Sanchez L. M. , Trolier-McKinstry S.
Published: January 2015

Lead zirconate titanate, PZT (52/48), thin films with a PbTiO3 seed layer were patterned into features of different widths, including various sizes of squares and 100 μm, 50 μm, and 10 μm serpentine designs, using argon ion beam milling. Patterns with different surface area/perimeter ratios were used to study the relative importance of damage produced by the patterning. It was found that as the pattern dimensions decreased, the remanent polarization increased, presumably due to the fact that the dipoles near the feature perimeter are not as severely clamped to the substrate. This investigation is in agreement with a model in which clamping produces deep wells, which do not allow some fraction of the spontaneous polarization to switch at high field. The domain wall mobility at modest electric fields was investigated using the Rayleigh law. Both the reversible, εinit, and irreversible, α, Rayleigh coefficients increased with decreasing serpentine line width for de-aged samples. For measurements made immediately after annealing, εinit of 500 μm square patterns was 1510 ± 13; with decreasing serpentine line width, εinit rose from 1520 ± 10 for the 100 μm serpentine to 1568 ± 23 for the 10 μm serpentine. The irreversible parameter, α, for the square patterns was 39.4 ± 3.2 cm/kV and it increased to 44.1 ± 3.2 cm/kV as the lateral dimension is reduced. However, it was found that as the width of the serpentine features decreased, the aging rate rose. These observations are consistent with a model in which sidewall damage produces shallow wells that lower the Rayleigh constants of aged samples at small fields. These shallow wells can be overcome by the large fields used to measure the remanent polarization and the large unipolar electric fields typically used to drive thin film piezoelectric actuators.
Spin-orbit interaction in multiple quantum wells
Authors: Hao Ya-Fei
Published: January 2015

In this paper, we investigate how the structure of multiple quantum wells affects spin-orbit interactions. To increase the interface-related Rashba spin splitting and the strength of the interface-related Rashba spin-orbit interaction, we designed three kinds of multiple quantum wells. We demonstrate that the structure of the multiple quantum wells strongly affected the interface-related Rashba spin-orbit interaction, increasing the interface-related Rashba spin splitting to up to 26% larger in multiple quantum wells than in a stepped quantum well. We also show that the cubic Dresselhaus spin-orbit interaction similarly influenced the spin relaxation time of multiple quantum wells and that of a stepped quantum well. The increase in the interface-related Rashba spin splitting originates from the relationship between interface-related Rashba spin splitting and electron probability density. Our results suggest that multiple quantum wells can be good candidates for spintronic devices.
Single-color, in situ photolithography marking of individual CdTe/ZnTe quantum dots containing a single Mn2+ ion
Authors: Sawicki K. , Malinowski F. K. , Gałkowski K. , Jakubczyk T. , Kossacki P. , Pacuski W. , Suffczyński J.
Published: January 2015

A simple, single-color method for permanent marking of the position of individual self-assembled semiconductor Quantum Dots (QDs) at cryogenic temperatures is reported. The method combines in situ photolithography with standard micro-photoluminescence spectroscopy. Its utility is proven by a systematic magnetooptical study of a single CdTe/ZnTe QD containing a Mn2+ ion, where a magnetic field of up to 10 T in two orthogonal, Faraday and Voigt, configurations is applied to the same QD. The presented approach can be applied to a wide range of solid state nanoemitters.
Anomalous high photoconductivity in short channel indium-zinc-oxide photo-transistors
Authors: Choi Hyun-Sik , Jeon Sanghun
Published: January 2015

Upon light exposure, an indium-zinc-oxide (IZO) thin-film transistor (TFT) presents higher photoconductivity by several orders of magnitude at the negative gate bias region. Among various device geometrical factors, scaling down the channel length of the photo-transistor results in an anomalous increase in photoconductivity. To probe the origin of this high photoconductivity in short-channel device, we measured transient current, current–voltage, and capacitance–voltage characteristics of IZO–TFTs with various channel lengths and widths before and after illumination. Under the illumination, the equilibrium potential region which lies far from front interface exists only in short-channel devices, forming the un-depleted conducting back channel. This region plays an important role in carrier transport under the illumination, leading to high photoconductivity in short-channel devices. Photon exposure coupled with gate-modulated band bending for short-channel devices leads to the accumulation of Vo++ at the front channel and screening negative gate bias, thereby generating high current flow in the un-depleted back-channel region.
Exciton-exciton scattering in vapor phase ZnO nanoparticles
Authors: Mohanta Antaryami , Kung Patrick , Thareja Raj K.
Published: January 2015

Photoluminescence (PL) properties of suspended ZnO nanoparticles formed in vapor phase due to the condensation of the Nd:YAG laser ablated ZnO plasma species are investigated by varying both ablating and excitation intensity at different time delays with respect to the ablating pulse and at different axial distances from the target surface. Emission due to inelastic exciton-exciton (X-X) scattering is observed and is found to be dependent on the size of the vapor phase ZnO nanoparticles. The PL intensity shows nonlinear behavior with increasing ablating intensity, indicating generation and participation of more excitons in X-X scattering process in lager size ZnO nanoparticles.
Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings
Authors: Castellano F. , Zanotto S. , Li L. H. , Pitanti A. , Tredicucci A. , Linfield E. H. , Davies A. G. , Vitiello M. S.
Published: January 2015

We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0° and 50° was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers.
Dielectric investigations of polycrystalline samarium bismuth ferrite ceramic
Authors: Palaimiene E. , Macutkevic J. , Karpinsky D. V. , Kholkin A. L. , Banys J.
Published: January 2015

Results of broadband dielectric investigations of samarium doped bismuth ferrite ceramics are presented in wide temperature range (20–800 K). At temperatures higher than 400 K, the dielectric properties of samarium bismuth ferrite ceramics are governed by Maxwell-Wagner relaxation and electrical conductivity. The DC conductivity increases and activation energy decreases with samarium concentration. In samarium doped bismuth ferrite, the ferroelectric phase transition temperature decreases with samarium concentration and finally no ferroelectric order is observed at x = 0.2. At lower temperatures, the dielectric properties of ferroelectric samarium doped bismuth ferrite are governed by ferroelectric domains dynamics. Ceramics with x = 0.2 exhibit the relaxor-like behaviour.
Photovoltaic conversion of visible spectrum by GaP capped InP quantum dots grown on Si (100) by metalorganic chemical vapor deposition
Authors: Halder Nripendra N. , Biswas Pranab , Banerji P. , Kundu Souvik , Nagabhushan B. , Sarkar Krishnendu , Chowdhury Sisir , Chaudhuri Arunava
Published: January 2015

Growth of GaP capped strained InP quantum dots was carried out by metal organic chemical vapor deposition technique on Si (100) substrates to explore an alternative material system for photovoltaic conversion. Studies on reflectance spectroscopy show higher absorption of visible photons compared to scattering. Smooth and defect free interface provides low dark current with high rectification ratio. A solar cell made of five periods of quantum dots is found to provide a conversion efficiency of 4.18% with an open circuit voltage and short circuit current density of 0.52 V and 13.64 mA/cm2, respectively, under AM 1.5 solar radiation.
Atomistic simulations of nanowelding of single-crystal and amorphous gold nanowires
Authors: Wu Cheng-Da , Fang Te-Hua , Wu Chung-Chin
Published: January 2015

The mechanism and quality of the welding of single-crystal (SC) and amorphous gold nanowires (NWs) with head-to-head contact are studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. The results are discussed in terms of atomic trajectories, slip vectors, stress, and radial distribution function. Simulation results show that the alignment for the amorphous NWs during welding is easier than that for the SC NWs due to the former's relatively stable geometry. A few dislocations nucleate and propagate on the (111) close-packed plane (slip plane) inside the SC NWs during the welding and stretching processes. During welding, an incomplete jointing area first forms through the interactions of the van der Waals attractive force, and the jointing area increases with increasing extent of contact between the two NWs. A crystallization transition region forms in the jointing area for the welding of SC-amorphous or amorphous-SC NWs. With increasing interference, an amorphous gold NW shortens more than does a SC gold NW due to the former's relatively poor strength. The pressure required for welding decreases with increasing temperature.
Impact of total ionizing dose irradiation on Pt/SrBi2Ta2O9/HfTaO/Si memory capacitors
Authors: Yan S. A. , Zhao W. , Guo H. X. , Xiong Y. , Tang M. H. , Li Z. , Xiao Y. G. , Zhang W. L. , Ding H. , Chen J. W. , Zhou Y. C.
Published: January 2015

In this work, metal-ferroelectric-insulator-semiconductor (MFIS) structure capacitors with SrBi2Ta2O9 (300 nm) as ferroelectric thin film and HfTaO (6 nm, 8 nm, 10 nm, and 12 nm) as insulating buffer layer were proposed and investigated. The prepared capacitors were fabricated and characterized before radiation and then subjected to 60Co gamma irradiation in steps of two dose levels. Significant irradiation-induced degradation of the electrical characteristics was observed. The radiation experimental results indicated that stability and reliability of as-fabricated MFIS capacitors for nonvolatile memory applications could become uncontrollable under strong irradiation dose and/or long irradiation time.
A large displacement, high frequency, underwater microelectromechanical systems actuator
Authors: Hoelzle David J. , Chan Clara K. , Scott Michael B. , Lake Melinda A. , Rowat Amy C.
Published: January 2015

Here, we demonstrate an in situ electrostatic actuator that can operate underwater across a wide range of displacements and frequencies, achieving a displacement of approximately 10 μm at 500 Hz and 1 μm at 5 kHz; this performance surpasses that of existing underwater physical actuators. To attain these large displacements at such high speeds, we optimized critical design parameters using a computationally efficient description of the physics of low quality (Q) factor underwater electrostatic actuators. Our theoretical model accurately predicts actuator motion profiles as well as limits of bandwidth and displacement.
Tunable strong nonlinearity of a micromechanical beam embedded in a dc-superconducting quantum interference device
Authors: Ella Lior , Yuvaraj D. , Suchoi Oren , Shtempluk Oleg , Buks Eyal
Published: January 2015

We present a study of the controllable nonlinear dynamics of a micromechanical beam coupled to a dc-SQUID (superconducting quantum interference device). The coupling between these systems places the modes of the beam in a highly nonlinear potential, whose shape can be altered by varying the bias current and applied flux of the SQUID. We detect the position of the beam by placing it in an optical cavity, which sets free the SQUID to be used solely for actuation. This enables us to probe the previously unexplored full parameter space of this device. We measure the frequency response of the beam and find that it displays a Duffing oscillator behavior which is periodic in the applied magnetic flux. To account for this, we develop a model based on the standard theory for SQUID dynamics. In addition, with the aim of understanding if the device can reach nonlinearity at the single phonon level, we use this model to show that the responsivity of the current circulating in the SQUID to the position of the beam can become divergent, with its magnitude limited only by noise. This suggests a direction for the generation of macroscopically distinguishable superposition states of the beam.
Modification of the structural and magnetic properties of granular FePt films by seed layer conditioning
Authors: Wicht S. , Neu V. , Schultz L. , Mehta V. , Jain S. , Reiner J. , Mosendz O. , Hellwig O. , Weller D. , Rellinghaus B.
Published: January 2015

The steadily increasing amount of digital information necessitates the availability of reliable high capacity magnetic data storage. Here, future hard disk drives with extended areal storage densities beyond 1.0 Tb/in2 are envisioned by using high anisotropy granular and chemically L10-ordered FePt (002) perpendicular media within a heat-assisted magnetic recording scheme. Perpendicular texturing of the [001] easy axes of the individual grains can be achieved by using MgO seed layers. It is therefore investigated, if and how an Ar+ ion irradiation of the MgO seed layer prior to the deposition of the magnetic material influences the MgO surface properties and hereby the FePt [001] texture. Structural investigations reveal a flattening of the seed layer surface accompanied by a change in the morphology of the FePt grains. Moreover, the fraction of small second layer particles and the degree of coalescence of the primarily deposited FePt grains strongly increases. As for the magnetic performance, this results in a reduced coercivity along the magnetic easy axis (out of plane) and in enhanced hard axis (in-plane) remanence values. The irradiation induced changes in the magnetic properties of the granular FePt-C films are traced back to the accordingly modified atomic structure of the FePt-MgO interface region.
Si/Ge hetero-structure nanotube tunnel field effect transistor
Authors: Hanna A. N. , Hussain M. M.
Published: January 2015

We discuss the physics of conventional channel material (silicon/germanium hetero-structure) based transistor topology mainly core/shell (inner/outer) gated nanotube vs. gate-all-around nanowire architecture for tunnel field effect transistor application. We show that nanotube topology can result in higher performance through higher normalized current when compared to nanowire architecture at Vdd = 1 V due to the availability of larger tunneling cross section and lower Shockley-Reed-Hall recombination. Both architectures are able to achieve sub 60 mV/dec performance for more than five orders of magnitude of drain current. This enables the nanotube configuration achieving performance same as the nanowire architecture even when Vdd is scaled down to 0.5 V.
Time-resolved observation of thermally activated rupture of a capillary-condensed water nanobridge
Authors: Bak Wan , Sung Baekman , Kim Jongwoo , Kwon Soyoung , Kim Bongsu , Jhe Wonho
Published: January 2015

The capillary-condensed liquid bridge is one of the most ubiquitous forms of liquid in nature and contributes significantly to adhesion and friction of biological molecules as well as microscopic objects. Despite its important role in nanoscience and technology, the rupture process of the bridge is not well understood and needs more experimental works. Here, we report real-time observation of rupture of a capillary-condensed water nanobridge in ambient condition. During slow and stepwise stretch of the nanobridge, we measured the activation time for rupture, or the latency time required for the bridge breakup. By statistical analysis of the time-resolved distribution of activation time, we show that rupture is a thermally activated stochastic process and follows the Poisson statistics. In particular, from the Arrhenius law that the rupture rate satisfies, we estimate the position-dependent activation energies for the capillary-bridge rupture.
Auger recombination in In(Ga)Sb/InAs quantum dots
Authors: Zabel T. , Reuterskiöld Hedlund C. , Gustafsson O. , Karim A. , Berggren J. , Wang Q. , Ernerheim-Jokumsen C. , Soldemo M. , Weissenrieder J. , Götelid M. , Hammar M.
Published: January 2015

We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170–200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 × 10−28 cm6/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 × 10−27 cm6/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.
Analysis and prediction of aperiodic hydrodynamic oscillatory time series by feed-forward neural networks, fuzzy logic, and a local nonlinear predictor
Authors: Gentili Pier Luigi , Gotoda Hiroshi , Dolnik Milos , Epstein Irving R.
Published: January 2015

Forecasting of aperiodic time series is a compelling challenge for science. In this work, we analyze aperiodic spectrophotometric data, proportional to the concentrations of two forms of a thermoreversible photochromic spiro-oxazine, that are generated when a cuvette containing a solution of the spiro-oxazine undergoes photoreaction and convection due to localized ultraviolet illumination. We construct the phase space for the system using Takens' theorem and we calculate the Lyapunov exponents and the correlation dimensions to ascertain the chaotic character of the time series. Finally, we predict the time series using three distinct methods: a feed-forward neural network, fuzzy logic, and a local nonlinear predictor. We compare the performances of these three methods.
Effects of vacuum-ultraviolet irradiation on copper penetration into low-k dielectrics under bias-temperature stress
Authors: Guo X. , King S. W. , Zheng H. , Xue P. , Nishi Y. , Shohet J. L.
Published: January 2015

The effects of vacuum-ultraviolet (VUV) irradiation on copper penetration into non-porous low-k dielectrics under bias-temperature stress (BTS) were investigated. By employing x-ray photoelectron spectroscopy depth-profile measurements on both as-deposited and VUV-irradiated SiCOH/Cu stacks, it was found that under the same BTS conditions, the diffusion depth of Cu into the VUV-irradiated SiCOH is higher than that of as-deposited SiCOH. On the other hand, under the same temperature-annealing stress (TS) without electric bias, the Cu distribution profiles in the VUV-irradiated SiCOH were same with that for the as-deposited SiCOH. The experiments suggest that in as-deposited SiCOH, the diffused Cu exists primarily in the atomic state, while in VUV-irradiated SiCOH, the diffused Cu is oxidized by the hydroxyl ions (OH−) generated from VUV irradiation and exists in the ionic state. The mechanisms for metal diffusion and ion injection in VUV irradiated low-k dielectrics are discussed.
Ex post manipulation of barriers in InGaAs tunnel injection devices
Authors: Talalaev Vadim G. , Cirlin George E. , Novikov Boris V. , Fuhrmann Bodo , Werner Peter , Tomm Jens W.
Published: January 2015

Ex post manipulation of ∼1.1 μm emitting InGaAs/GaAs-based quantum dot–quantum well tunnel injection light emitting devices is demonstrated experimentally. The devices were operated at elevated forward currents until irreversible alterations were observed. As a result, changes in the steady-state optical spectra (electroluminescence, photoluminescence, and photocurrent), in carrier kinetics, in transport properties, and real structure are found. Except for degradation effects, e.g., of larger quantum dots, also restoration/annealing effects such as increased tunnel barriers are observed. The results furnish evidence for a generic degradation mode of nanostructures. We qualitatively interpret the mechanisms involved on both the nanoscopic and the device scales.
Time-resolved photoluminescence measurements for determining voltage-dependent charge-separation efficiencies of subcells in triple-junction solar cells
Authors: Tex David M. , Ihara Toshiyuki , Akiyama Hidefumi , Imaizumi Mitsuru , Kanemitsu Yoshihiko
Published: January 2015

Conventional external quantum-efficiency measurement of solar cells provides charge-collection efficiency for approximate short-circuit conditions. Because this differs from actual operating voltages, the optimization of high-quality tandem solar cells is especially complicated. Here, we propose a contactless method, which allows for the determination of the voltage dependence of charge-collection efficiency for each subcell independently. By investigating the power dependence of photoluminescence decays, charge-separation and recombination-loss time constants are obtained. The upper limit of the charge-collection efficiencies at the operating points is then obtained by applying the uniform field model. This technique may complement electrical characterization of the voltage dependence of charge collection, since subcells are directly accessible.
Improvement of plasmonic enhancement of quantum dot emission via an intermediate silicon-aluminum oxide interface
Authors: Wing Waylin J. , Sadeghi Seyed M. , Campbell Quinn
Published: January 2015

We studied the emission of quantum dots in the presence of plasmon-metal oxide substrates, which consist of arrays of metallic nanorods embedded in amorphous silicon coated with a nanometer-thin layer of aluminum oxide on the top. We showed that the combined effects of plasmons and the silicon-aluminum oxide interface can lead to significant enhancement of the quantum efficiency of quantum dots. Our results show that such an interface can significantly enhance plasmonic effects of the nanorods via quantum dot-induced exciton-plasmon coupling, leading to partial polarization of the quantum dots' emission.
Thickness modulated MoS2 grown by chemical vapor deposition for transparent and flexible electronic devices
Authors: Park Juhong , Choudhary Nitin , Smith Jesse , Lee Gilsik , Kim Moonkyung , Choi Wonbong
Published: January 2015

Two-dimensional (2D) materials have been a great interest as high-performance transparent and flexible electronics due to their high crystallinity in atomic thickness and their potential for variety applications in electronics and optoelectronics. The present study explored the wafer scale production of MoS2 nanosheets with layer thickness modulation from single to multi-layer by using two-step method of metal deposition and CVD process. The formation of high-quality and layer thickness-modulated MoS2 film was confirmed by Raman spectroscopy, AFM, HRTEM, and photoluminescence analysis. The layer thickness was identified by employing a simple method of optical contrast value. The image contrast in green (G) channel shows the best fit as contrast increases with layer thickness, which can be utilized in identifying the layer thickness of MoS2. The presence of critical thickness of Mo for complete sulphurization, which is due to the diffusion limit of MoS2 transformation, changes the linearity of structural, electrical, and optical properties of MoS2. High optical transparency of >90%, electrical mobility of ∼12.24 cm2 V−1 s−1, and Ion/off of ∼106 characterized within the critical thickness make the MoS2 film suitable for transparent and flexible electronics as compared to conventional amorphous silicon (a-Si) or organic films. The layer thickness modulated large scale MoS2 growth method in conjunction with the layer thickness identification by the nondestructive optical contrast will definitely trigger development of scalable 2D MoS2 films for transparent and flexible electronics.
Designing of spin-filtering devices in zigzag graphene nanoribbons heterojunctions by asymmetric hydrogenation and B-N doping
Authors: Zhang Dan , Long Mengqiu , Zhang Xiaojiao , Ouyang Fangping , Li Mingjun , Xu Hui
Published: January 2015

Using nonequilibrium Green's function in combination with the spin-polarized density functional theory, the spin-dependent transport properties of boron and nitrogen doped zigzag graphene nanoribbons (ZGNRs) heterojunctions with single or double edge-saturated hydrogen have been investigated. Our results show that the perfect spin-filtering effect (100%), rectifying behavior and negative differential resistance can be realized in the ZGNRs-based systems. And the corresponding physical analysis has been given.
Effect of the electron energy distribution on total energy loss with argon in inductively coupled plasmas
Authors: Kim June Young , Kim Young-Cheol , Kim Yu-Sin , Chung Chin-Wook
Published: January 2015

The total energy lost per electron-ion pair lost εT is investigated with the electron energy distribution function (EEDF). The EEDFs are measured at various argon powers in RF inductively coupled plasma, and the EEDFs show a depleted distribution (a discontinuity occurring at the minimum argon excitation threshold energy level) with the bulk temperature and the tail temperature. The total energy loss per electron-ion pair lost εT is calculated from a power balance model with the Maxwellian EEDFs and the depleted EEDFs and then compared with the measured εT from the floating probe. It is concluded that the small population of the depleted high energy electrons dramatically increases the collisional energy loss, and the calculated εT from the depleted EEDFs has a value that is similar to the measured εT.
Magnetotransport in La0.7Sr0.3MnO3/CuCr2O4/Fe3O4 magnetic junctions
Authors: Iwata-Harms Jodi M. , Chopdekar Rajesh V. , Wong Franklin J. , Nelson-Cheeseman Brittany B. , Jenkins Catherine A. , Arenholz Elke , Suzuki Yuri
Published: January 2015

We demonstrate distinct magnetic and resistive switching with junction magnetoresistance up to −6% in magnetic tunnel junctions with a CuCr2O4 barrier. Junction magnetoresistance is inversely related to barrier thickness and reveals a maximum at a finite applied bias that converges to zero bias at low temperatures for all barrier thicknesses. The non-monotonic bias dependence is attributed to a charge gap from the Fe3O4 electrode and possible spin filtering from the spin-split conduction band of the ferrimagnetic CuCr2O4 barrier.
Model for temperature-dependent magnetization of nanocrystalline materials
Authors: Bian Q. , Niewczas M.
Published: January 2015

A magnetization model of nanocrystalline materials incorporating intragrain anisotropies, intergrain interactions, and texture effects has been extended to include the thermal fluctuations. The method relies on the stochastic Landau–Lifshitz–Gilbert theory of magnetization dynamics and permits to study the magnetic properties of nanocrystalline materials at arbitrary temperature below the Currie temperature. The model has been used to determine the intergrain exchange constant and grain boundary anisotropy constant of nanocrystalline Ni at 100 K and 298 K. It is found that the thermal fluctuations suppress the strength of the intergrain exchange coupling and also reduce the grain boundary anisotropy. In comparison with its value at 2 K, the interparticle exchange constant decreases by 16% and 42% and the grain boundary anisotropy constant decreases by 28% and 40% at 100 K and 298 K, respectively. An application of the model to study the grain size-dependent magnetization indicates that when the thermal activation energy is comparable to the free energy of grains, the decrease in the grain size leads to the decrease in the magnetic permeability and saturation magnetization. The mechanism by which the grain size influences the magnetic properties of nc–Ni is discussed.
Generation of fast cumulative water jets by underwater electrical explosion of conical wire arrays
Authors: Shafer D. , Gurovich V. Tz. , Yanuka D. , Zvulun E. , Gleizer S. , Toker G. , Krasik Ya. E.
Published: January 2015

The results of experiments with underwater electrical explosion of conical arrays of copper wires are presented. A pulsed generator producing a 300 kA-amplitude current with a 1.2 μs rise time was used in the explosion of the arrays. As a result of the explosion, fast-moving water jets, with velocities of up to 1200 m/s, were observed being ejected from the surface of the water covering the wire array. The position of the water jets was measured by multiple-exposure fast framing imaging. The apex angle of the array or the thickness of the water layer above the arrays was altered from shot to shot, which changed the resulting velocities and shapes of the emitted jets. A numerical model, based on the models of cumulation and penetration of a jet through material of similar density, is suggested. The velocities of jets obtained by this model agree well with the experimentally observed jet velocities.
Radial InP/InAsP/InP heterostructure nanowires on patterned Si substrates using self-catalyzed growth for vertical-type optical devices
Authors: Kawaguchi Kenichi , Sudo Hisao , Matsuda Manabu , Takemoto Kazuya , Yamamoto Tsuyoshi , Arakawa Yasuhiko
Published: January 2015

Radial InP/InAsP/InP heterostructure nanowires (NWs) on SiO2-mask-pattered Si substrates were reported using self-catalyzed InP NWs. Self-catalyzed growth was performed using low growth temperatures and high group-III flow rates, and vertical InP NWs were formed on the mask openings. The diameter and tapering of the self-catalyzed InP NWs were controlled by the introduction of HCl and H2S gases during the NW growth, and InP NWs that have a straight region with decreased diameter were formed. Radial InP/InAsP/InP quantum wells (QWs) were grown on the sidewall of the vertical InP NWs on Si substrates. Room-temperature photoluminescence of single NWs from the QW was clearly observed, which exhibited the potential of building blocks for vertical-type optical devices on Si substrates.
Formal Institutional Change and Informal Institutional Persistence: The Case of Dutch Provinces Implementing the Spatial Planning Act
Authors: Evers David
Published: January 2015

Conscious attempts to affect planning practice by reforming the statutory planning system are a common form of institutional design. Despite this, the effectiveness of institutional design as a strategy has not been sufficiently addressed in the planning literature. The Dutch case has been monitored thoroughly and provides a good opportunity to assess the extent to which the instruments introduced under the new legislation were used according to the stated intent of lawmakers. As the national level has largely devolved responsibility to provinces, these comprised the objects of study. The empirical evidence covering the 2008–11 period reveals remarkable variation between provinces in applying the law, including applications that run directly counter to the law's objectives. These findings point to the difficulty of institutional design in planning practice, and suggest that lawmakers should rethink their approach to influencing behaviour of planning agents.
The Extent of Visual Space Inferred from Perspective Angles
Authors: Erkelens Casper J.
Published: January 2015

Retinal images are perspective projections of the visual environment. Perspective projections do not explain why we perceive perspective in 3-D space. Analysis of underlying spatial transformations shows that visual space is a perspective transformation of physical space if parallel lines in physical space vanish at finite distance in visual space. Perspective angles, i.e., the angle perceived between parallel lines in physical space, were estimated for rails of a straight railway track. Perspective angles were also estimated from pictures taken from the same point of view. Perspective angles between rails ranged from 27% to 83% of their angular size in the retinal image. Perspective angles prescribe the distance of vanishing points of visual space. All computed distances were shorter than 6 m. The shallow depth of a hypothetical space inferred from perspective angles does not match the depth of visual space, as it is perceived. Incongruity between the perceived shape of a railway line on the one hand and the experienced ratio between width and length of the line on the other hand is huge, but apparently so unobtrusive that it has remained unnoticed. The incompatibility between perspective angles and perceived distances casts doubt on evidence for a curved visual space that has been presented in the literature and was obtained from combining judgments of distances and angles with physical positions.
Poggendorff Rides Again!
Authors: Ekroll Vebjørn , Gilchrist Alan , Koenderink Jan , van Doorn Andrea , Wagemans Johan
Published: January 2015

The Poggendorff illusion is one of the most exhaustively studied illusions. Can it be revived as an interesting problem? Perhaps by moving it to a slightly different domain. Here, we consider the occlusion of a subjectively linear ramp of tonal values. In a simple experiment, we find results closely resembling those of the geometrical Poggendorff. Yet, the “explanations” offered for the latter hardly apply to the former case. Depending upon one's perspective, this may be taken to “revive” the Poggendorff illusion.
Single cell-derived clonal analysis of human glioblastoma links functional and genomic heterogeneity
Authors: Meyer Mona , Reimand Jüri , Lan Xiaoyang , Head Renee , Zhu Xueming , Kushida Michelle , Bayani Jane , Pressey Jessica C. , Lionel Anath C. , Clarke Ian D. , Cusimano Michael , Squire Jeremy A. , Scherer Stephen W. , Bernstein Mark , Woodin Melanie A. , Bader Gary D. , Dirks Peter B.
Published: January 2015

Significance

Glioblastoma is an incurable brain tumor. It is characterized by intratumoral phenotypic and genetic heterogeneity, but the functional significance of this heterogeneity is unclear. We devised an integrated functional and genomic strategy to obtain single cell-derived tumor clones directly from patient tumors to identify mechanisms of aggressive clone behavior and drug resistance. Genomic analysis of single clones identified genes associated with clonal phenotypes. We predict that integration of functional and genomic analysis at a clonal level will be essential for understanding evolution and therapeutic resistance of human cancer, and will lead to the discovery of novel driver mechanisms and clone-specific cancer treatment.
Programmable motion of DNA origami mechanisms
Authors: Marras Alexander E. , Zhou Lifeng , Su Hai-Jun , Castro Carlos E.
Published: January 2015

Significance

Folding DNA into complex 3D shapes (DNA origami) has emerged as a powerful method for the precise design and fabrication of self-assembled nanodevices. Current efforts have focused largely on developing static objects or structures with small movements and/or unspecified motion paths. Here we establish a basis for developing DNA-based nanomachines by creating dynamic mechanisms with well-defined motion. We demonstrate the design of nanoscale 1D, 2D, and 3D motion by integrating concepts from engineering machine design with DNA origami nanotechnology.
Crowd science user contribution patterns and their implications
Authors: Sauermann Henry , Franzoni Chiara
Published: January 2015

Significance

Involving the public in research may provide considerable benefits for the progress of science. However, the sustainability of “crowd science” approaches depends on the degree to which members of the public are interested and provide continued labor inputs. We describe and compare contribution patterns in multiple projects using a range of measures. We show that effort contributions can be significant in magnitude and speed, but we also identify several challenges. In addition, we explore some of the underlying dynamics and mechanisms. As such, we provide quantitative evidence that is useful for scientists who consider adopting crowd science approaches and for scholars studying crowd-based knowledge production. Our results also inform current policy discussions regarding the organization of scientific research.