bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of phase morphology on the nature of long-lived charges in semiconductor polymer:fullerene systems
Authors: Dou Fei , Buchaca-Domingo Ester , Sakowicz Maciej , Rezasoltani Elham , McCarthy-Ward Thomas , Heeney Martin , Zhang Xinping , Stingelin Natalie , Silva Carlos
Published: February 2015

We investigate the effect of phase morphology on the nature of charges in semicrystalline polymer:fullerene blends on submillisecond timescale by quasi-steady-state photoinduced absorption spectroscopy.
Thermoset polymers consisting of novolac and melamine derivatives as insulators for organic thin-film transistors
Authors: Ha Jong-Woon , Jang Jae-Ho , Kim Yongnam , Lee Jin-Kyun , Kwak Jeonghun , Hwang Do-Hoon
Published: February 2015

A potential gate dielectric material that can be cured and processed at low temperatures was designed and synthesized via the cross-linking of bisphenol A novolac (Novolac) and hexamethoxymethylmelamine (HMMM) in the presence of a catalytic amount of p-toluenesulfonic acid.
Introducing a new radical trifluoromethylation reagent
Authors: Sato Azusa , Han Jianlin , Ono Taizo , Wzorek Alicja , Aceña José Luis , Soloshonok Vadim A.
Published: February 2015

Radical trifluoromethylations of aromatic molecules have been achieved by using a persistent perfluoroalkyl radical as a precursor of the CF3radical. The process works efficiently in terms of chemical yields to produce mixtures of regioisomeric trifluoromethylated compounds.
Synthesis and indole coupling reactions of azetidine and oxetane sulfinate salts
Authors: Nassoy Anne-Chloé M. A. , Raubo Piotr , Harrity Joseph P. A.
Published: February 2015

Azetidine and oxetane sulfinate salts are easily prepared from commercially available 3-iodoheterocycle precursors in a three-step sequence.
Theoretical investigation of thermodynamic stability and mobility of the intrinsic point defects in Ti3AC2 (A = Si, Al)
Authors: Wang Jiemin , Liu Bin , Wang Jingyang , Zhou Yanchun
Published: February 2015

Interstitial configurations, formation energies, and migration paths of intrinsic point defects of Ti3AC2 (A = Si or Al) were investigated by a first-principles method.
Confined helium on Lagrange meshes
Authors: Baye D. , Dohet-Eraly J.
Published: February 2015

The Lagrange-mesh method has the simplicity of a calculation on a mesh and can have the accuracy of a variational method.
Iridium–bipyridine periodic mesoporous organosilica catalyzed direct C–H borylation using a pinacolborane
Authors: Maegawa Yoshifumi , Inagaki Shinji
Published: February 2015

Iridium complex fixed on periodic mesoporous organosilica containing bipyridine ligands within a framework showed efficient heterogeneous catalysis for direct C–H borylation of arenes and heteroarenes in combination with an inexpensive pinacolborane.
Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins
Authors: Borguet Yannick , Zaragoza Guillermo , Demonceau Albert , Delaude Lionel
Published: February 2015

Second-generation ruthenium–alkylidene complexes featuring the 1,3-di(2-tolyl)benzimidazol-2-ylidene ligand (BTol) are highly efficient catalysts for the synthesis of tetrasubstituted cycloolefinsviaring-closing metathesis (RCM).
A novel synthetic chemistry approach to linkage-specific ubiquitin conjugation
Authors: Morgan Rachel E. , Chudasama Vijay , Moody Paul , Smith Mark E. B. , Caddick Stephen
Published: February 2015

Site-specific ubiquitin cysteine mutants enable an elegant method for the linkage-specific conjugation of ubiquitins through dibromomaleimides and dibromopyrdazinediones.
Largely improved electromechanical properties of thermoplastic polyurethane dielectric elastomer by carbon nanospheres
Authors: Yao Yang , Ning Nanying , Zhang Liqun , Nishi Toshio , Tian Ming
Published: February 2015

Carbon nanospheres (CNS) were used as a new conductive filler to improve the electromechanical properties of a thermoplastic polyurethane (TPU) dielectric elastomer (DE).
Highly flexible transparent conductive graphene/single-walled carbon nanotube nanocomposite films produced by Langmuir–Blodgett assembly
Authors: Yang Tan , Yang Junhe , Shi Lifang , Mäder Edith , Zheng Qingbin
Published: February 2015

Transparent conductive films composed of ultra-large graphene oxide and functionalized single-walled carbon nanotubes are assembled on a flexible poly(ethylene terephthalate) (PET) substrate using the Langmuir–Blodgett technique.
Chemical synthesis of the tumor-associated globo H antigen
Authors: Mandal Satadru S. , Liao Guochao , Guo Zhongwu
Published: February 2015

A convergent synthesis of Globo H antigen based on glycosylation reactions using thioglycoside and trichloroacetimidate glycosyl donors.
Propargyl ether-functionalized poly(m-phenylene): a new precursor for the preparation of polymers with high modulus and high Tg
Authors: Luo Yijie , Sun Jing , Jin Kaikai , Wang Jiajia , Huang Guangsu , Fang Qiang
Published: February 2015

A propargyl ether-functionalized poly(m-phenylene) (PE-PMP) is reported here.
Plasmonic organic solar cell employing Au NP:PEDOT:PSS doped rGO
Authors: Lee Seung Joo , Kim Jae-Yeon , Mohd Yusoff Abd. Rashid bin , Jang Jin
Published: February 2015

We report a comprehensive study of the influence of NPs on organic solar cells by introducing Au NPs into OSCs fabricated using PEDOT:PSS:rGO. The PEDOT:PSS:rGO embedded with Au NPs had better Jsc and PCE values than the control devices.
Physical and chemical studies of tungsten carbide catalysts: effects of Ni promotion and sulphonated carbon
Authors: Rodella Cristiane B. , Barrett Dean H. , Moya Silvia F. , Figueroa Santiago J. A. , Pimenta Maria T. B. , Curvelo Antonio Aprígio S. , Teixeira da Silva Victor
Published: February 2015

Ni promoted tungsten carbides have been shown to be an effective catalyst for cellulose conversion reaction.
Polymer fullerene solution phase behaviour and film formation pathways
Authors: Dattani Rajeev , Cabral João T.
Published: February 2015

We report the phase behaviour of polymer/fullerene/solvent ternary mixtures and its consequence for the morphology of the resulting composite thin films.
Self-assembling dual component nanoparticles with endosomal escape capability
Authors: Wong Adelene S. M. , Mann Sarah K. , Czuba Ewa , Sahut Audrey , Liu Haiyin , Suekama Tiffany C. , Bickerton Tayla , Johnston Angus P. R. , Such Georgina K.
Published: February 2015

This work reports a modular nanoparticle system engineered to undergo disassembly within a biologically relevant pH range. These nanoparticles demonstrate endosomal escape, making them attractive for biomedical applications.
Designing a thiophene-fused DPP unit to build an A–D–A molecule for solution-processed solar cells
Authors: Chen Bing , Yang Yang , Cheng Pei , Chen Xingguo , Zhan Xiaowei , Qin Jingui
Published: February 2015

A thiophene-fused DPP unit has been designed to build a new kind of A–D–A molecule for solution-processed solar cells.
Project-Based Treatments: Evidence From the TBI Population and Suggested Applications for Adults With Dementia
Authors: Mason-Baughman Mary Beth , Beichner Kelsey
Published: February 2015

Project-based treatment will be addressed as a possible technique to utilize with people with dementia. Project-based treatments are designed to facilitate increased engagement for meaningful activities as part of a long-term, collaborative project that culminates in the creation and presentation of a tangible product, such as a care partner training manual or video. Project-based treatments have been successfully implemented with people with traumatic brain injury. Evidence from the traumatic brain injury population will be reviewed and possible applications of project-based treatment for people with dementia will be discussed.
A Longitudinal Posthumous Study of Letter Writing in a Late Elderly Case
Authors: Ball Angel , Neils-Strunjas Jean , Krival Kate
Published: February 2015

This study is a posthumous longitudinal study of consecutive letters written by an elderly woman from age 89 to 93. Findings reveal a consistent linguistic performance during the first 3 years, supporting “normal” status for late elderly writing. She produced clearly written cursive form, intact semantic content, and minimal spelling and stroke errors. A decline in writing was observed in the last 6–9 months of the study and an analysis revealed production of clausal fragmentation, decreasing semantic clarity, and a higher frequency of spelling, semantic, and stroke errors. Analysis of writing samples can be a valuable tool in documenting a change in cognitive status differentiated from normal late aging.
Vibration analysis of an elastically restrained microcantilever beam under electrostatic loading using wavelet‐based finite element method
Authors: Bashmal Salem , Oke Wasiu Adeyemi , Khulief Yehia
Published: February 2015

An electro‐mechanical analysis of a microcantilever beam considering the effect of size dependence and flexible supports is presented. Both static and dynamic analyses are performed to show the coupled effect of flexible support and electrical voltage on the static and dynamic performance of the microcantilever beam. The wavelet‐based finite element method (FEM) is used to derive the elastodynamic model of the microcantilever beam. The energy expressions are derived using couple stress theory, while additional energy terms are introduced to represent the flexible boundaries and fringing fields. Numerical simulations and comparisons with experimental data show the validity of the developed wavelet‐based finite element model and its potential in tackling practical problems in the design and evaluation of micro‐devices.
Preparation and properties of polyaniline–anionic spherical polyelectrolyte brushes nanocomposite
Authors: Su Na , Gu Ping , Zhao Junjie
Published: February 2015

A novel polyaniline–anionic spherical polyelectrolyte brushes (PANI/ASPB) nanocomposite was synthesised by means of chemical oxidative polymerisation. Different characterisation and analytical methods involving scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction and thermo‐gravimetric analysis confirmed that anionic spherical polyelectrolyte brushes served both as a dopant and as a template. While polyaniline (PANI) nanocomposites have a ‘rod‐like’ or fibrillar morphology, the PANI/ASPB nanocomposite displayed a sphere‐like structure. The room temperature electrical conductivity of the PANI/ASPB nanocomposite was 26.3 S/cm, which is higher than that of PANI (7.1 S/cm). In addition, PANI/ASPB nanocomposites possessed enhanced thermal stability and good solubility properties.
Aligning in Practice: From Current Cases to a New Agenda
Authors: Karpovsky Anna , Galliers Robert D
Published: February 2015

Although there is extensive literature on IT/IS-business alignment, we argue that the topic's current research trajectory is limited given the concept's predominantly static focus to date. While the process perspective on alignment is a promising avenue to study the phenomenon's dynamic nature, we still know little about what it is that organizational actors actually do, on a day-to-day basis, to align IS and related concerns with business imperatives. In order to address this lack of understanding regarding the practices of aligning, we argue for research that goes beyond abstract macro analysis of alignment processes to that which considers the actual micro practices of aligning. An analysis of the extant literature on the topic leads to the identification and classification of aligning activities that are being undertaken in practice. We argue that this review and critical appraisal of the IT/business alignment field has the potential for substantive and insightful contributions to our understanding of alignment as it is enacted – in practice. Arising from the review, we discuss important new research themes that are to be addressed if research on alignment is to be demonstrably relevant.
Damping of liquid sloshing by foams
Authors: Sauret A. , Boulogne F. , Cappello J. , Dressaire E. , Stone H. A.
Published: February 2015

When a container is set in motion, the free surface of the liquid starts to oscillate or slosh. Such effects can be observed when a glass of water is handled carelessly and the fluid sloshes or even spills over the rims of the container. However, beer does not slosh as readily as water, which suggests that foam could be used to damp sloshing. In this work, we study experimentally the effect on sloshing of a liquid foam placed on top of a liquid bath. We generate a monodisperse two-dimensional liquid foam in a rectangular container and track the motion of the foam. The influence of the foam on the sloshing dynamics is experimentally characterized: only a few layers of bubbles are sufficient to significantly damp the oscillations. We rationalize our experimental findings with a model that describes the foam contribution to the damping coefficient through viscous dissipation on the walls of the container. Then we extend our study to confined three-dimensional liquid foam and observe that the behavior of 2D and confined 3D systems are very similar. Thus, we conclude that only the bubbles close to the walls have a significant impact on the dissipation of energy. The possibility to damp liquid sloshing using foam is promising in numerous industrial applications such as the transport of liquefied gas in tankers or for propellants in rocket engines.
Valence-bond non-equilibrium solvation model for a twisting monomethine cyanine
Authors: McConnell Sean , McKenzie Ross H. , Olsen Seth
Published: February 2015

We propose and analyze a two-state valence-bond model of non-equilibrium solvation effects on the excited-state twisting reaction of monomethine cyanines. Suppression of this reaction is thought responsible for environment-dependent fluorescence yield enhancement in these dyes. Fluorescence is quenched because twisting is accompanied via the formation of dark twisted intramolecular charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localizations, there are two possible twisting pathways with different charge localizations in the excited state. For parameters corresponding to symmetric monomethines, the model predicts two low-energy twisting channels on the excited-state surface, which leads to a manifold of TICT states. For typical monomethines, twisting on the excited state surface will occur with a small barrier or no barrier. Changes in the solvation configuration can differentially stabilize TICT states in channels corresponding to different bonds, and that the position of a conical intersection between adiabatic states moves in response to solvation to stabilize either one channel or the other. There is a conical intersection seam that grows along the bottom of the excited-state potential with increasing solvent polarity. For monomethine cyanines with modest-sized terminal groups in moderately polar solution, the bottom of the excited-state potential surface is completely spanned by a conical intersection seam.
Low-jitter wide-range integrated time interval/delay generator based on combination of period counting and capacitor charging
Authors: Klepacki K. , Pawłowski M. , Szplet R.
Published: February 2015

We present the design, operation, and test results of a new time interval/delay generator that provides the resolution of 0.3 ps, jitter below 10 ps (rms), and wide delay range of 10 s. The wide range has been achieved by counting periods of a reference clock while the high resolution and low jitter have been obtained through the two-time use of inner interpolation. This interpolation, based on charging of a single capacitor, provides both the precise external trigger synchronization and accurate generation of residual time interval. A combination of both processes virtually eliminates triggering indeterminacy. The jitter between the trigger and output is below 1 ps, which ensures a high performance delay. The generator is integrated in a single application specific integrated circuit chip using a standard cost-effective 0.35 μm CMOS process.
Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)
Authors: Bouhafs C. , Darakchieva V. , Persson I. L. , Tiberj A. , Persson P. O. Å. , Paillet M. , Zahab A.-A. , Landois P. , Juillaguet S. , Schöche S. , Schubert M. , Yakimova R.
Published: February 2015

Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn.
Benzene derivatives adsorbed to the Ag(111) surface: Binding sites and electronic structure
Authors: Miller Daniel P. , Simpson Scott , Tymińska Nina , Zurek Eva
Published: February 2015

Dispersion corrected Density Functional Theory calculations were employed to study the adsorption of benzenes derivatized with functional groups encompassing a large region of the activated/deactivated spectrum to the Ag(111) surface. Benzenes substituted with weak activating or deactivating groups, such as methyl and fluoro, do not have a strong preference for adsorbing to a particular site on the substrate, with the corrugations in the potential energy surface being similar to those of benzene. Strong activating (N(CH3)2) and deactivating (NO2) groups, on the other hand, possess a distinct site preference. The nitrogen in the former prefers to lie above a silver atom (top site), but in the latter a hollow hexagonal-closed-packed (Hhcp) site of the Ag(111) surface is favored instead. Benzenes derivatized with classic activating groups donate electron density from their highest occupied molecular orbital to the surface, and those functionalized with deactivating groups withdraw electron density from the surface into orbitals that are unoccupied in the gas phase. For benzenes functionalized with two substituents, the groups that are strongly activating or deactivating control the site preference and the other groups assume sites that are, to a large degree, dictated by their positions on the benzene ring. The relative stabilities of the ortho, meta, and para positional isomers of disubstituted benzenes can, in some cases, be modified by adsorption to the surface.
Supramolecular order and structural dynamics: A STM study of 2H-tetraphenylporphycene on Cu(111)
Authors: Stark Michael , Träg Johannes , Ditze Stefanie , Brenner Wolfgang , Jux Norbert , Steinrück Hans-Peter , Marbach Hubertus
Published: February 2015

The adsorption of 2H-tetraphenylporphycene (2HTPPc) on Cu(111) was investigated by scanning tunneling microscopy (STM). At medium coverages, supramolecular ordered islands are observed. The individual 2HTPPc molecules appear as two pairs of intense protrusions which are separated by an elongated depression. In the islands, the molecules are organized in rows oriented along one of the close packed Cu(111) substrate rows; the structure is stabilized by T-type interactions of the phenyl substituents of neighboring molecules. Two types of rows are observed, namely, highly ordered rows in which all molecules exhibit the same orientation, and less ordered rows in which the molecules exhibit two perpendicular orientations. Altogether, three different azimuthal orientations of 2HTPPc are observed within one domain, all of them rotated by 15° ± 1° relative to one closed packed Cu direction. The highly ordered rows are always separated by either one or two less ordered rows, with the latter structure being the thermodynamically more stable one. The situation in the islands is highly dynamic, such that molecules in the less ordered rows occasionally change orientation, also complete highly ordered rows can move. The supramolecular order and structural dynamics are discussed on the basis of the specific molecule-substrate and molecule-molecule interactions.
Surface activity of octanoic acid in ethanol-water solutions from molecular simulation and experiment
Authors: Htet April N. , Gil Phwey S. , Lacks Daniel J.
Published: February 2015

The surface activity of a typical surfactant, octanoic acid (OA), in ethanol-water solutions is investigated with a combined experimental and molecular simulation approach. The experiments show that OA reduces the surface tension of ethanol-water solutions at low ethanol concentration, but the effectiveness decreases with increasing ethanol concentration and vanishes for ethanol concentrations above 60%. Molecular dynamics simulations are used to obtain free energy landscapes for OA as a function of the distance from the surface. The free energy driving force pushing OA to the surface decreases with increasing ethanol concentration, and becomes insignificant (i.e., less than kT) for ethanol concentrations above 70%. Thus, the decrease in the effectiveness of OA in reducing the surface tension at higher ethanol concentrations can be attributed to the decrease in the free energy driving force keeping OA at the surface. We expect these results to apply generally to hydrocarbon-based surfactants.
Note: Strain sensitivity comparison between fiber Bragg gratings inscribed on 125 and 80 micron cladding diameter fibers, case study on the solidification monitoring of a photo-curable resin
Authors: Maccioni E. , Morganti M. , Brandi F.
Published: February 2015

The influence of fiber Bragg grating diameter when measuring strain is investigated and quantified. Two fiber Bragg gratings with bare cladding diameter of 125 μm and 80 μm are produced by excimer laser irradiation through a phase mask, and are used to simultaneously monitor the Bragg wavelength shift due to the strain produced by the solidification of a photo-curable resin during light exposure. It is found that the ratio of the measured strains in the two fiber Bragg gratings is close to the inverse ratio of the fiber’s cladding diameter. These results represent a direct simultaneous comparison between 125 μm and 80 μm diameter fiber Bragg grating strain sensors, and demonstrate the feasibility of strain measurements in photo-curable resins using bare 80 μm cladding diameter fiber Bragg gratings with an increased sensitivity and spatial resolution compared with standard 125 μm diameter fiber Bragg gratings.
Accommodation of tin in tetragonal ZrO2
Authors: Bell B. D. C. , Murphy S. T. , Burr P. A. , Grimes R. W. , Wenman M. R.
Published: February 2015

Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The SnZr× defect was shown to be dominant across most oxygen partial pressures, with SnZr″ charge compensated by VO•• occurring at partial pressures below 10−31 atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which SnZr″ is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys.
A continued fraction resummation form of bath relaxation effect in the spin-boson model
Authors: Gong Zhihao , Tang Zhoufei , Mukamel Shaul , Cao Jianshu , Wu Jianlan
Published: February 2015

In the spin-boson model, a continued fraction form is proposed to systematically resum high-order quantum kinetic expansion (QKE) rate kernels, accounting for the bath relaxation effect beyond the second-order perturbation. In particular, the analytical expression of the sixth-order QKE rate kernel is derived for resummation. With higher-order correction terms systematically extracted from higher-order rate kernels, the resummed quantum kinetic expansion approach in the continued fraction form extends the Pade approximation and can fully recover the exact quantum dynamics as the expansion order increases.
Backward-propagating MeV electrons in ultra-intense laser interactions: Standing wave acceleration and coupling to the reflected laser pulse
Authors: Orban Chris , Morrison John T. , Chowdhury Enam A. , Nees John A. , Frische Kyle , Feister Scott , Roquemore W. M.
Published: February 2015

Laser-accelerated electron beams have been created at a kHz repetition rate from the reflection of intense (∼1018 W/cm2), ∼40 fs laser pulses focused on a continuous water-jet in an experiment at the Air Force Research Laboratory. This paper investigates Particle-in-Cell simulations of the laser-target interaction to identify the physical mechanisms of electron acceleration in this experiment. We find that the standing-wave pattern created by the overlap of the incident and reflected laser is particularly important because this standing wave can “inject” electrons into the reflected laser pulse where the electrons are further accelerated. We identify two regimes of standing wave acceleration: a highly relativistic case (a0 ≥ 1), and a moderately relativistic case (a0 ∼ 0.5) which operates over a larger fraction of the laser period. In previous studies, other groups have investigated the highly relativistic case for its usefulness in launching electrons in the forward direction. We extend this by investigating electron acceleration in the specular (back reflection) direction and over a wide range of intensities (1017–1019 W cm−2).
The onset of sub-surface oxidation induced by defects in a chemisorbed oxygen layer
Authors: Li Jonathan , Li Liang , Zhou Guangwen
Published: February 2015

We investigate the onset of internal oxidation of a Cu(110) surface induced by oxygen subsurface adsorption via defects in the Cu(110)–(2 × 1)–O chemisorbed layer. The presence of a boundary formed by merged add-row structure domains due to a mismatch of half unit-cell leads to preferred oxygen adsorption at the subsurface tetrahedral sites. The resulting distorted Cu–O tetrahedra along the domain boundary have comparable bond length and angles to those of the bulk oxide phase of Cu2O. Our results indicate that the presence of defects in the oxygen-chemisorbed adlayer can lead to the internal oxidation via the formation of Cu2O-like tetrahedra in between the topmost and second outermost atomic layers at the oxygen coverage θ = 0.53 and the second and third outermost atomic layers at θ = 0.56. These results show that the internal oxidation of a metal surface can occur in the very beginning of the oxygen chemisorption process enabled by the presence of defects in the oxygen chemisorbed layer.
Effect of interfacial structures on spin dependent tunneling in epitaxial L1-FePt/MgO/FePt perpendicular magnetic tunnel junctions
Authors: Yang G. , Li D. L. , Wang S. G. , Ma Q. L. , Liang S. H. , Wei H. X. , Han X. F. , Hesjedal T. , Ward R. C. C. , Kohn A. , Elkayam A. , Tal N. , Zhang X.-G.
Published: February 2015

Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L10-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.
Reversible suppression of second harmonic generation in dye-doped liquid crystal by light-induced thermal phase transition on sub-micrometer scale
Authors: Zhuo Guan-Yu , Chen Kuan-Chieh , Lai Kai-Wen , Wang Chao-Ran , Chao Chih-Yu , Chu Shi-Wei
Published: February 2015

Optically controllable signals are fundamental to various applications from communication to super-resolution imaging. However, literature on non-fluorescent, nonlinear optical signals that can be reversibly turned on/off on a sub-micrometer scale is scant. In this work, we experimentally demonstrate a scheme for the reversible suppression of second harmonic generation (SHG) based on dye-doped nematic liquid crystal molecules. Under a pump (suppressing SHG) and probe (generating SHG) setup with a tightly focusing microscope and a time-gated detection, outstanding modulation depth (>80%) has been realized. Surprisingly, the mechanism of liquid crystal SHG switch on a sub-micrometer scale was found to be light-induced thermal phase transition as against optical Frederick's transition. Quantitative analysis of the optical nonlinearity χ(2) versus local heating shows an excellent agreement of SHG signal suppression as well as its dependence on the liquid crystal molecular order and phase change. Our work provides an innovative example of applying nonlinear optical properties of soft materials, and can be further optimized for all-optical modulation applications.
Effects of disorder on spin injection and extraction for organic semiconductor spin-valves
Authors: Shi Sha , Liu Feilong , Smith Darryl L. , Ruden P. Paul
Published: February 2015

A device model for tunnel injection and extraction of spin-polarized charge carriers between ferromagnetic contacts and organic semiconductors with disordered molecular states is presented. Transition rates for tunneling are calculated based on a transfer Hamiltonian. Transport in the bulk semiconductor is described by macroscopic device equations. Tunneling predominantly involves organic molecular levels near the metal Fermi energy, and therefore typically in the tail of the band that supports carrier transport in the semiconductor. Disorder-induced broadening of the relevant band plays a critical role for the injection and extraction of charge carriers and for the resulting magneto-resistance of an organic semiconductor spin valve.
Room-temperature amorphous alloy field-effect transistor exhibiting particle and wave electronic transport
Authors: Fukuhara M. , Kawarada H.
Published: February 2015

The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The Id-Vg characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni0.36Nb0.24Zr0.40)90H10 FETs were measured at a gate-drain bias voltage of 0–60 μV in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 μV under nonmagnetic conditions, and a Fano effect with a period of 0.26 mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics.
Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
Authors: Mårsell Erik , Larsen Esben W. , Arnold Cord L. , Xu Hongxing , Mauritsson Johan , Mikkelsen Anders
Published: February 2015

We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.
Pinning of reaction fronts by burning invariant manifolds in extended flows
Authors: Megson P. W. , Najarian M. L. , Lilienthal K. E. , Solomon T. H.
Published: February 2015

We present experiments on the behavior of reaction fronts in extended, vortex-dominated flows in the presence of an imposed wind. We use the ferroin-catalyzed, excitable Belousov-Zhabotinsky chemical reaction, which produces pulse-like reaction fronts. Two time-independent flows are studied: an ordered (square) array of vortices and a spatially disordered flow. The flows are generated with a magnetohydrodynamic forcing technique, with a pattern of magnets underneath the fluid cell. The magnets are mounted on a translation stage which moves with a constant speed Vd under the fluid, resulting in motion of the vortices within the flow. In a reference frame moving with magnets, the flow is equivalent to one with stationary vortices and a uniform wind with speed W = Vd. For a wide range of wind speeds, reaction fronts pin to the vortices (in a co-moving reference frame), propagating neither forward against the wind nor being blown backward. We analyze this pinning phenomenon and the resulting front shapes using a burning invariant manifold (BIM) formalism. The BIMs are one-way barriers to reaction fronts in the advection-reaction-diffusion process. Pinning occurs when several BIMs overlap to form a complete barrier that spans the width of the system. In that case, the shape of the front is determined by the shape of the BIMs. For the ordered array flow, we predict the locations of the BIMs numerically using a simplified model of the velocity field for the ordered vortex array and compare the BIM shapes to the pinned reaction fronts. We also explore transient behavior of the fronts (before reaching their steady state) to highlight the one-way nature of the BIMs.
Effects of Schmid factor and slip nucleation on deformation mechanism in columnar-grained nanotwinned Ag and Cu
Authors: Borovikov Valery , Mendelev Mikhail I. , King Alexander H. , LeSar Richard
Published: February 2015

We report the results of a molecular dynamics study of the effect of texture on the yield and peak stresses in columnar-grained nanotwinned Ag and Cu. The simulations suggest that in pure nanotwinned face-centered cubic metals, the strength is determined primarily by the cooperation or competition between two major factors: the magnitude of the Schmid factors for the available slip systems and the effectiveness of grain boundaries (and their triple-junctions) in generating dislocations. These factors and their relative impact depend on the geometry of the specimen relative to the applied stress, which is typically reflected in the texture of the material in experimental studies. The detailed mechanisms of plastic deformation are discussed for seven specific geometries that represent a range of different textures.
Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics
Authors: Hirai Daigorou , Matsuno Jobu , Takagi Hidenori
Published: February 2015

We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.
Interaction of ultrashort laser pulses and silicon solar cells under short circuit conditions
Authors: Mundus M. , Giesecke J. A. , Fischer P. , Hohl-Ebinger J. , Warta W.
Published: February 2015

Ultrashort pulse lasers are promising tools for numerous measurement purposes. Among other benefits their high peak powers allow for efficient generation of wavelengths in broad spectral ranges and at spectral powers that are orders of magnitude higher than in conventional light sources. Very recently this has been exploited for the establishment of sophisticated measurement facilities for electrical characterization of photovoltaic (PV) devices. As the high peak powers of ultrashort pulses promote nonlinear optical effects they might also give rise to nonlinear interactions with the devices under test that possibly manipulate the measurement outcome. In this paper, we present a comprehensive theoretical and experimental study of the nonlinearities affecting short circuit current (ISC) measurements of silicon (Si) solar cells. We derive a set of coupled differential equations describing the radiation-device interaction and discuss the nonlinearities incorporated in those. By a semi-analytical approach introducing a quasi-steady-state approximation and integrating a Green's function we solve the system of equations and obtain simulated ISC values. We validate the theoretical model by ISC ratios obtained from a double ring resonator setup capable for reproducible generation of various ultrashort pulse trains. Finally, we apply the model to conduct the most prominent comparison of ISC generated by ultrashort pulses versus continuous illumination. We conclude by the important finding that the nonlinearities induced by ultrashort pulses are negligible for the most common ISC measurements. However, we also find that more specialized measurements (e.g., of concentrating PV or Si-multijunction devices as well as highly localized electrical characterizations) will be biased by two-photon-absorption distorting the ISC measurement.
Improved microwave absorption and electromagnetic properties of BaFe12O19-poly(vinylidene fluoride) composites by incorporating reduced graphene oxides
Authors: He Hongcai , Luo Feifei , Qian Neng , Wang Ning
Published: February 2015

Three-phase composites of poly(vinylidene fluoride)-BaFe12O19-reduced graphene oxide (PVDF–BFO-RGO) were synthesized by a facile wet chemical method and hot-pressing approach. The phase structure, topography of the hybrid materials were characterized by X-ray diffraction, scanning electron microscopy, and Raman spectra. Influence of RGO on their electromagnetic properties was investigated. Especially, improved microwave absorption and electromagnetic properties of BaFe12O19–PVDF composites by incorporating RGO were obtained and studied. The PVDF/BFO/RGO sample with m(RGO):m(BFO) = 5:100 shows the best microwave absorption properties with a minimum RL = −32 dB at 11 GHz and with the bandwidth less than −20 dB from 9.6 to 12.8 GHz. The composites were believed to have potential applications as the microwave absorber.
Mechanisms of material removal and mass transport in focused ion beam nanopore formation
Authors: Das Kallol , Freund Jonathan B. , Johnson Harley T.
Published: February 2015

Despite the widespread use of focused ion beam (FIB) processing as a material removal method for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing, the basic material removal mechanisms of FIB processing are not well understood. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms of material removal and rearrangement and describe the role of explosive boiling in forming nanopores. FIB nanopore fabrication is typically understood to occur via sputter erosion. This can be shown to be the case in low flux systems, where individual ion impacts are sufficiently separated in time that they may be considered as independent events. But our detailed MD simulations show that in high flux FIB processing, above a threshold level at which thermal effects become significant, the primary mechanism of material removal changes to a significantly accelerated, thermally dominated process. Under these conditions, the target is heated by the ion beam faster than heat is conducted away by the material, leading quickly to melting, and then continued heating to nearly the material critical temperature. This leads to explosive boiling of the target material with spontaneous bubble formation and coalescence. Mass is rapidly rearranged at the atomistic scale, and material removal occurs orders of magnitude faster than would occur by simple sputtering. While the phenomenology is demonstrated computationally in silicon, it can be expected to occur at lower beam fluxes in other cases where thermal conduction is suppressed due to material properties, geometry, or ambient thermal conditions.
The recombination mechanisms leading to amplified spontaneous emission at the true-green wavelength in CH3NH3PbBr3 perovskites
Authors: Priante D. , Dursun I. , Alias M. S. , Shi D. , Melnikov V. A. , Ng T. K. , Mohammed O. F. , Bakr O. M. , Ooi B. S.
Published: February 2015

We investigated the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material using low-temperature, power-dependent (77 K), and temperature-dependent photoluminescence (PL) measurements. Two bound-excitonic radiative transitions related to grain size inhomogeneity were identified. Both transitions led to PL spectra broadening as a result of concurrent blue and red shifts of these excitonic peaks. The red-shifted bound-excitonic peak dominated at high PL excitation led to a true-green wavelength of 553 nm for CH3NH3PbBr3 powders that are encapsulated in polydimethylsiloxane. Amplified spontaneous emission was eventually achieved for an excitation threshold energy of approximately 350 μJ/cm2. Our results provide a platform for potential extension towards a true-green light-emitting device for solid-state lighting and display applications.
Modeling quasi-static magnetohydrodynamic turbulence with variable energy flux
Authors: Verma Mahendra K. , Reddy K. Sandeep
Published: February 2015

In quasi-static magnetohydrodynamics, experiments and numerical simulations reveal that the energy spectrum is steeper than Kolmogorov’s k−5/3 spectrum. To explain this observation, we construct two variable energy flux based turbulence phenomenologies. Variable energy flux is due to the Joule dissipation, which is active at all scales. In the first phenomenology, which is applicable to small interaction parameters, the energy spectrum is a power law, but with a spectral exponent steeper than −5/3. In the other limit of large interaction parameters, the second phenomenology predicts an exponential energy spectrum and flux. The predictions of the phenomenologies are in good agreement with the numerical results.
Analysis of Nb3Sn surface layers for superconducting radio frequency cavity applications
Authors: Becker Chaoyue , Posen Sam , Groll Nickolas , Cook Russell , Schlepütz Christian M. , Hall Daniel Leslie , Liepe Matthias , Pellin Michael , Zasadzinski John , Proslier Thomas
Published: February 2015

We present an analysis of Nb3Sn surface layers grown on a bulk Niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb3Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperatures (Tc) up to 16.3 K. Scanning transmission electron microscopy performed on cross sections of the sample's surface region shows an ∼2 μm thick Nb3Sn surface layer. The elemental composition map exhibits a Nb:Sn ratio of 3:1 and reveals the presence of buried sub-stoichiometric regions that have a ratio of 5:1. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb3Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low Tc regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb3Sn-coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.
From disk to ring: Aspect ratio control of the magnetoplasmonic response in Au/Co/Au nanostructures fabricated by hole-mask colloidal lithography
Authors: Feng Hua Yu , Luo Feng , Meneses-Rodríguez David , Armelles Gaspar , Cebollada Alfonso
Published: February 2015

Morphology tuning of a series of Au/Co/Au nanostructures which gradually evolve from disk to ring allows controlling their optical and magneto-optical spectral responses in the visible and near infrared ranges. This is achieved by the combined use of hole mask colloidal lithography with off-normal deposition and substrate rotation. The morphological parameters responsible for this control, the disk/ring outer diameter and height, are determined by the off-normal deposition angle and the amount of deposited material, respectively. The single dipolar symmetric resonance mode in nanodisk splits into two characteristics, low (symmetric) and high energy (antisymmetric) ring modes. The ring's high energy mode, determined by the rings' section, is basically independent of the deposition angle, while the low energy symmetric mode is basically controlled by the outer diameter/height aspect ratio for both disk-like and ring structures, and therefore allowing a fine tuning of the wavelength position of this resonance.