bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the acceptor pattern and substitution position on the properties of N-phenyl-carbazolyl based donor–acceptor–donor molecules
Authors: Song Xuejing , Wang Min , Kong Lingqian , Zhao Jinsheng
Published: March 2017

Four D–A–D type molecules were designed and synthesized, and their specific properties including optical, redox and thermal stabilities were studied in detail. The influence of substitution and the heteroatom effects were also studied.
Polyaniline nanoflowers grown on vibration-isolator-mimetic polyurethane nanofibers for flexible supercapacitors with prolonged cycle life
Authors: Khosrozadeh Ali , Darabi Mohammad Ali , Wang Quan , Xing Malcolm
Published: March 2017

Employing a polyurethane nanofibrous membrane as a cushiony support for the deposition of flower-like polyaniline greatly improves the cycling stability of polyaniline pseudocapacitors.
FRET-guided surging of cyanobacterial photosystems improves and stabilizes current in photosynthetic microbial fuel cell
Authors: Kaushik Sharbani , Sarma Mrinal K. , Goswami Pranab
Published: March 2017

A quantum dot-based nano-biocomposite supports FRET to photosystems, biofilm growth and electron relay on the anode in a cyanobacteria-based fuel cell.
Structures, mobility and electronic properties of point defects in arsenene, antimonene and an antimony arsenide alloy
Authors: Sun Xiaotian , Liu Yunxia , Song Zhigang , Li Yongdan , Wang Weizhou , Lin Haiping , Wang Lu , Li Youyong
Published: March 2017

We investigate the structural stability, mobility and electronic properties of typical point defects in 2D arsenene, antimonene and antimony arsenide.
Anti-hyperglycaemic activity of Moringa oleifera is partly mediated by carbohydrase inhibition and glucose-fibre binding
Authors: Azad Sohel Bin , Ansari Prawej , Azam Shofiul , Hossain Saad Mosharraf , Shahid  Mohammad Ibtida-Bin , Hasan Mahmudul , Hannan J.M.A.
Published: March 2017

Moringa oleifera has potential anti-hyperglycaemic effects that have been reported earlier by different scientific groups using animal models of diabetes. We aimed to explore the possible mechanisms of action of M. oleifera extract through different methods. Primarily, we measured fasting blood glucose and performed glucose tolerance test, in Type 2 diabetic rats. Further, we studied the effects of extracts on pancreatic insulin concentration. Extracts’ effect on carbohydrate breakdown was assayed using α-amylase inhibition assays and assay of six different segments of gastrointestinal (GI) tracts. An in situ intestinal perfusion model and a glucose fibre assay were performed to see the potentiality of M. oleifera on glucose absorption. M. oleifera showed no significant change in insulin secretion in vivo. Additionally, substantial effect of the extract was seen on retarded glucose absorption and in the in situ perfusion study of rat intestinal model. α-amylase action was inhibited by the extract, yet again, these findings were further confirmed via the Six Segment assay, where sucrose digestion was found to be inhibited throughout the length of the GI tract. A combined in vitro, in vivo and in situ tests justified the potential of anti-hyperglycaemic activity of M. oleifera and its tissue level mechanism is also justified.
Correlations between ACE single nucleotide polymorphisms and prognosis of patients with septic shock
Authors: Dou Xin-Man , Cheng Hui-Juan , Meng Ling , Zhou Lin-Lin , Ke Yi-Hong , Liu Li-Ping , Li Yu-Min
Published: March 2017

The aim of the present study is to investigate association between septic shock (SS) and angiotensin I-converting enzyme (ACE) single nucleotide polymorphisms (SNPs). From October 2009 to December 2016, 238 SS patients and 242 healthy individuals were selected for our study. ACE activity was detected, ACE rs4291 and rs4646994 polymorphisms were detected using PCR-restriction fragment length polymorphism (PCR-RFLP). The Kaplan–Meier survival curve was employed to evaluate the association between ACE SNPs and patients’ survival and univariate and multivariate analyses to estimate risk factors for SS. ACE activity in the case group was increased in comparison with the control group. Allele and genotype frequencies of rs4291 and rs4646994 were different between the case and control groups. The TT genotype frequency of the rs4291 polymorphisms and the DD genotype of the rs4646994 polymorphisms of the case group were higher than those in the control group. The AT and TT genotypes indicated a significant elevation of ACE activity than the AA genotype, while a significant decline was found in the DI and II genotypes in comparison with the DI genotype. Patients with TT or DD genotypes had increased fatality rate within 7 and 30 days when compared with those with non-TT or non-DD genotypes. Lower sepsis-related organ failure assessment (SOFA) scores, rs4291, serum ACE and rs4646994 were all considered as risky factors for SS patients. The study demonstrates that TT genotype of rs4291 or DD genotype of rs4646994 may be indicative of a higher risk of SS and a poorer prognosis in SS patients.
Language Development in Children With Cleft Palate With or Without Cleft Lip Adopted From Non–English-Speaking Countries
Authors: Morgan Amy R. , Bellucci Claudia Crilly , Coppersmith Jody , Linde Sebastian B. , Curtis Arthur , Albert Meredith , O'Gara Mary M. , Kapp-Simon Kathleen
Published: March 2017

Purpose

The purpose of this study was to determine whether language skills differed between children with cleft palate or cleft lip and palate (CP±CL) who were adopted into an English-speaking home from a non–English-speaking country (late English exposure [LE]) and children with CP±CL raised from birth in an English-speaking home (early English exposure [EE]).

Method

Children (51 LE, 67 EE), ages 3;0 (years;months) to 9;0, completed the Clinical Evaluation of Language Fundamentals (CELF), Preschool Second Edition or Fourth Edition. Linear regression analysis was used to assess the impact of age of adoption and time in an English-speaking home on language skills, as measured by the CELF-P2 and CELF-4.

Results

Children with CP±CL who were adopted scored less well on all language indices, with mean adjusted differences between LE and EE children ranging from 0.4 to 0.7SDon the CELF index scales. Only 53% of the EE children and 57% of the LE children obtained scores above 90 on all indices. For LE children, younger age at adoption was associated with better language skills.

Conclusion

CP±CL increases risk for language delay, with the highest risk for LE children. LE children with CP±CL should receive language services soon after adoption.
Electron holes in phase space: What they are and why they
matter
Authors: Hutchinson I. H.
Published: March 2017

This is a tutorial and selective review explaining the fundamental concepts and some currently open questions concerning the plasma phenomenon of the electron hole. The widespread occurrence of electron holes in numerical simulations, space-craft observations, and laboratory experiments is illustrated. The elementary underlying theory is developed of a one-dimensional electron hole as a localized potential maximum, self-consistently sustained by a deficit of trapped electron phase-space density. The spatial extent of a hole is typically a few Debye lengths; what determines the minimum and maximum possible lengths is explained, addressing the key aspects of the as yet unsettled dispute between the integral and differential approaches to hole structure. In multiple dimensions, holes tend to form less readily; they generally require a magnetic field and distribution-function anisotropy. The mechanisms by which they break up are explained, noting that this transverse instability is not fully understood. Examples are given of plasma circumstances where holes play an important role, and of recent progress on understanding their holistic kinematics and self-acceleration.
Explosive attractor solutions to a universal cubic delay equation
Authors: Sanz-Orozco D. , Berk H. L.
Published: March 2017

New explosive attractor solutions have been found in a universal cubic delay equation that has been studied in both the plasma and the fluid mechanics literature. Through computational simulations and analytic approximations, it is found that the oscillatory component of the explosive mode amplitude solutions are described through multi-frequency Fourier expansions with respect to a pseudo-time variable. The spectral dependence of these solutions as a function of a system parameter, ϕ, is studied. The mode amplitude that is described in the explosive regime has two main features: a well-known envelope (t0−t)−5/2, with t0 the blow-up time of the amplitude, and a spectrum of discrete oscillations with ever-increasing frequencies, which may give experimental information about the properties of a system's equilibrium.
Are two plasma equilibrium states possible when the emission coefficient exceeds unity?
Authors: Campanell M. D. , Umansky M. V.
Published: March 2017

Two floating sheath solutions with strong electron emission in planar geometry have been proposed, a “space-charge limited” (SCL) sheath and an “inverse” sheath. SCL and inverse models contain different assumptions about conditions outside the sheath (e.g., the velocity of ions entering the sheath). So it is not yet clear whether both sheaths are possible in practice, or only one. Here we treat the global presheath-sheath problem for a plasma produced volumetrically between two planar walls. We show that all equilibrium requirements (a) floating condition, (b) plasma shielding, and (c) presheath force balance, can indeed be satisfied in two different ways when the emission coefficient γ > 1. There is one solution with SCL sheaths and one with inverse sheaths, each with sharply different presheath distributions. As we show for the first time in 1D-1V simulations, a SCL and inverse equilibrium are both possible in plasmas with the same upstream properties (e.g., same N and Te). However, maintaining a true SCL equilibrium requires no ionization or charge exchange collisions in the sheath, or else cold ion accumulation in the SCL's “dip” forces a transition to the inverse. This suggests that only a monotonic inverse type sheath potential should exist at any plasma-facing surface with strong emission, whether be a divertor plate, emissive probe, dust grain, Hall thruster channel wall, sunlit object in space, etc. Nevertheless, SCL sheaths might still be possible if the ions in the dip can escape. Our simulations demonstrate ways in which SCL and inverse regimes might be distinguished experimentally based on large-scale presheath effects, without having to probe inside the sheath.
Influence of probe-sample temperature difference on thermal mapping contrast in scanning thermal microscopy imaging
Authors: Kaźmierczak-Bałata Anna , Juszczyk Justyna , Trefon-Radziejewska Dominika , Bodzenta Jerzy
Published: March 2017

The purpose of this work is to investigate the influence of a temperature difference through a probe-sample contact on thermal contrast in Scanning Thermal Microscopy imaging. A variety of combinations of temperature differences in the probe-sample system were first analyzed based on an electro-thermal finite element model. The numerical analysis included cooling the sample, as well as heating the sample and the probe. Due to the simplicity in the implementation, experimental verification involved modifying the standard imaging technique by heating the sample. Experiments were carried out in the temperature range between 298 K and 328 K. Contrast in thermal mapping was improved for a low probe current with a heated sample.
The effect of pre-existing islands on disruption mitigation in MHD simulations of DIII-D
Authors: Izzo V. A.
Published: March 2017

Locked-modes are the most likely cause of disruptions in ITER, so large islands are expected to be common when the ITER disruption mitigation system is deployed. MHD modeling of disruption mitigation by massive gas injection is carried out for DIII-D plasmas with stationary, pre-existing islands. Results show that the magnetic topology at the q = 2 surface can affect the parallel spreading of injected impurities, and that, in particular, the break-up of large 2/1 islands into smaller 4/2 islands chains can favorably affect mitigation metrics. The direct imposition of a 4/2 mode is found to have similar results to the case in which the 4/2 harmonic grows spontaneously.
Laser-driven plasma photonic crystals for high-power lasers
Authors: Lehmann G. , Spatschek K. H.
Published: March 2017

Laser-driven plasma density gratings in underdense plasma are shown to act as photonic crystals for high power lasers. The gratings are created by counterpropagating laser beams that trap electrons, followed by ballistic ion motion. This leads to strong periodic plasma density modulations with a lifetime on the order of picoseconds. The grating structure is interpreted as a plasma photonic crystal time-dependent property, e.g., the photonic band gap width. In Maxwell–Vlasov and particle-in-cell simulations it is demonstrated that the photonic crystals may act as a frequency filter and mirror for ultra-short high-power laser pulses.
A reduced resistive wall mode kinetic stability model for disruption forecasting
Authors: Berkery J. W. , Sabbagh S. A. , Bell R. E. , Gerhardt S. P. , LeBlanc B. P.
Published: March 2017

Kinetic modification of ideal stability theory from stabilizing resonances of mode-particle interaction has had success in explaining resistive wall mode (RWM) stability limits in tokamaks. With the goal of real-time stability forecasting, a reduced kinetic stability model has been implemented in the new Disruption Event Characterization and Forecasting (DECAF) code, which has been written to analyze disruptions in tokamaks. The reduced model incorporates parameterized models for ideal limits on β, a ratio of plasma pressure to magnetic pressure, which are shown to be in good agreement with DCON code calculations. Increased β between these ideal limits causes a shift in the unstable region of δWK space, where δWK is the change in potential energy due to kinetic effects that is solved for by the reduced model, such that it is possible for plasmas to be unstable at intermediate β but stable at higher β, which is sometimes observed experimentally. Gaussian functions for δWK are defined as functions of E × B frequency and collisionality, with parameters reflecting the experience of the National Spherical Torus Experiment (NSTX). The reduced model was tested on a database of discharges from NSTX and experimentally stable and unstable discharges were separated noticeably on a stability map in E × B frequency, collisionality space. The reduced model failed to predict an unstable RWM in only 15.6% of cases with an experimentally unstable RWM and performed well on predicting stability for experimentally stable discharges as well.
Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod
Authors: Creely A. J. , Howard N. T. , Rodriguez-Fernandez P. , Cao N. , Hubbard A. E. , Hughes J. W. , Rice J. E. , White A. E. , Candy J. , Staebler G. M. , Conway G. D. , Freethy S. J. , Sung C.
Published: March 2017

New validation of global, nonlinear, ion-scale gyrokinetic simulations (GYRO) is carried out for L- and I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and temperature fluctuations. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale (cross-scale coupling) effects [Howard PoP 2016] may be less important in I-mode than in L-mode. New results presented here, however, show that global, nonlinear, ion-scale GYRO simulations are able to match the experimental ion heat flux, but underpredict electron heat flux (at most radii), electron temperature fluctuations, and perturbative thermal diffusivity in both L- and I-mode. Linear addition of electron heat flux from electron scale runs does not resolve this discrepancy. These results indicate that single-scale simulations do not sufficiently describe the I-mode core transport, and that multi-scale (coupled electron- and ion-scale) transport models are needed. A preliminary investigation with multi-scale TGLF, however, was unable to resolve the discrepancy between ion-scale GYRO and experimental electron heat fluxes and perturbative diffusivity, motivating further work with multi-scale GYRO simulations and a more comprehensive study with multi-scale TGLF.
MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations
Authors: King J. R. , Kruger S. E. , Burrell K. H. , Chen X. , Garofalo A. M. , Groebner R. J. , Olofsson K. E. J. , Pankin A. Y. , Snyder P. B.
Published: March 2017

Extended-MHD modeling of DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] quiescent H-mode (QH-mode) discharges with nonlinear NIMROD [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)] simulations saturates into a turbulent state but does not saturate when the steady-state flow inferred from measurements is not included. This is consistent with the experimental observations of the quiescent regime on DIII-D. The simulation with flow develops into a saturated turbulent state where the nϕ=1 and 2 toroidal modes become dominant through an inverse cascade. Each mode in the range of nϕ=1–5 is dominant at a different time. Consistent with experimental observations during QH-mode, the simulated state leads to large particle transport relative to the thermal transport. Analysis shows that the amplitude and phase of the density and temperature perturbations differ resulting in greater fluctuation-induced convective particle transport relative to the convective thermal transport. Comparison to magnetic-coil measurements shows that rotation frequencies differ between the simulation and experiment, which indicates that more sophisticated extended-MHD two-fluid modeling is required.
Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold
Authors: Heidbrink W. W. , Collins C. S. , Podestà M. , Kramer G. J. , Pace D. C. , Petty C. C. , Stagner L. , Van Zeeland M. A. , White R. B. , Zhu Y. B.
Published: March 2017

Experiments on the DIII-D tokamak have identified how multiple simultaneous Alfvén eigenmodes (AEs) lead to overlapping wave-particle resonances and stochastic fast-ion transport in fusion grade plasmas [C. S. Collins et al., Phys. Rev. Lett. 116, 095001 (2016)]. The behavior results in a sudden increase in fast-ion transport at a threshold that is well above the linear stability threshold for Alfvén instability. A novel beam modulation technique [W. W. Heidbrink et al., Nucl. Fusion 56, 112011 (2016)], in conjunction with an array of fast-ion diagnostics, probes the transport by measuring the fast-ion flux in different phase-space volumes. Well above the threshold, simulations that utilize the measured mode amplitudes and structures predict a hollow fast-ion profile that resembles the profile measured by fast-ion Dα spectroscopy; the modelling also successfully reproduces the temporal response of neutral-particle signals to beam modulation. The use of different modulated sources probes the details of phase-space transport by populating different regions in phase space and by altering the amplitude of the AEs. Both effects modulate the phase-space flows.
Improving ICF implosion performance with alternative capsule supports
Authors: Weber C. R. , Casey D. T. , Clark D. S. , Hammel B. A. , MacPhee A. , Milovich J. , Martinez D. , Robey H. F. , Smalyuk V. A. , Stadermann M. , Amendt P. , Bhandarkar S. , Chang B. , Choate C. , Crippen J. , Felker S. J. , Field J. E. , Haan S. W. , Johnson S. , Kroll J. J. , Landen O. L. , Marinak M. , Mcinnis M. , Nikroo A. , Rice N. , Sepke S. M.
Published: March 2017

The thin membrane that holds the capsule in-place in the hohlraum is recognized as one of the most significant contributors to reduced performance in indirect drive inertial confinement fusion (ICF) experiments on the National Ignition Facility. This membrane, known as the “tent,” seeds a perturbation that is amplified by Rayleigh-Taylor and can rupture the capsule. A less damaging capsule support mechanism is under development. Possible alternatives include the micron-scale rods spanning the hohlraum width and supporting either the capsule or stiffening the fill-tube, a larger fill-tube to both fill and support the capsule, or a low-density foam layer that protects the capsule from the tent impact. Experiments are testing these support features to measure their imprint on the capsule. These experiments are revealing unexpected aspects about perturbation development in indirect drive ICF, such as the importance of shadows coming from bright spots in the hohlraum. Two dimensional and 3D models are used to explain these features and assess the impact on implosion performance. Experiments and modeling suggest that the fill-tube supported by a perpendicular rod can mount the capsule without any additional perturbation beyond that of the fill tube.
Compatibility of lithium plasma-facing surfaces with high edge temperatures in the Lithium Tokamak Experiment
Authors: Majeski R. , Bell R. E. , Boyle D. P. , Kaita R. , Kozub T. , LeBlanc B. P. , Lucia M. , Maingi R. , Merino E. , Raitses Y. , Schmitt J. C. , Allain J. P. , Bedoya F. , Bialek J. , Biewer T. M. , Canik J. M. , Buzi L. , Koel B. E. , Patino M. I. , Capece A. M. , Hansen C. , Jarboe T. , Kubota S. , Peebles W. A. , Tritz K.
Published: March 2017

High edge electron temperatures (200 eV or greater) have been measured at the wall-limited plasma boundary in the Lithium Tokamak Experiment (LTX). Flat electron temperature profiles are a long-predicted consequence of low recycling boundary conditions. Plasma density in the outer scrape-off layer is very low, 2–3 × 1017 m−3, consistent with a low recycling metallic lithium boundary. Despite the high edge temperature, the core impurity content is low. Zeff is estimated to be ∼1.2, with a very modest contribution (<0.1) from lithium. Experiments are transient. Gas puffing is used to increase the plasma density. After gas injection stops, the discharge density is allowed to drop, and the edge is pumped by the low recycling lithium wall. An upgrade to LTX–LTX-β, which includes a 35A, 20 kV neutral beam injector (on loan to LTX from Tri-Alpha Energy) to provide core fueling to maintain constant density, as well as auxiliary heating, is underway. LTX-β is briefly described.
A methodology for the rigorous verification of Particle-in-Cell simulations
Authors: Riva Fabio , Beadle Carrie F. , Ricci Paolo
Published: March 2017

A methodology to perform a rigorous verification of Particle-in-Cell (PIC) simulations is presented, both for assessing the correct implementation of the model equations (code verification) and for evaluating the numerical uncertainty affecting the simulation results (solution verification). The proposed code verification methodology is a generalization of the procedure developed for plasma simulation codes based on finite difference schemes that was described by Riva et al. [Phys. Plasmas 21, 062301 (2014)] and consists of an order-of-accuracy test using the method of manufactured solutions. The generalization of the methodology for PIC codes consists of accounting for numerical schemes intrinsically affected by statistical noise and providing a suitable measure of the distance between continuous, analytical distribution functions and finite samples of computational particles. The solution verification consists of quantifying both the statistical and discretization uncertainties. The statistical uncertainty is estimated by repeating the simulation with different pseudorandom number generator seeds. For the discretization uncertainty, the Richardson extrapolation is used to provide an approximation of the analytical solution and the grid convergence index is used as an estimate of the relative discretization uncertainty. The code verification methodology is successfully applied to a PIC code that numerically solves the one-dimensional, electrostatic, collisionless Vlasov–Poisson system. The solution verification methodology is applied to quantify the numerical uncertainty affecting the two-stream instability growth rate, which is numerically evaluated thanks to a PIC simulation.
Monochromatic backlighting of direct-drive cryogenic DT implosions on OMEGA
Authors: Stoeckl C. , Epstein R. , Betti R. , Bittle W. , Delettrez J. A. , Forrest C. J. , Glebov V. Yu. , Goncharov V. N. , Harding D. R. , Igumenshchev I. V. , Jacobs-Perkins D. W. , Janezic R. T. , Kelly J. H. , Kosc T. Z. , McCrory R. L. , Michel D. T. , Mileham C. , McKenty P. W. , Marshall F. J. , Morse S. F. B. , Regan S. P. , Radha P. B. , Rice B. , Sangster T. C. , Shoup M. J. , Shmayda W. T. , Sorce C. , Theobald W. , Ulreich J. , Wittman M. D. , Meyerhofer D. D. , Frenje J. A. , Gatu Johnson M. , Petrasso R. D.
Published: March 2017

Backlighting is a powerful technique to observe the flow of cold and dense material in high-energy-density–plasma experiments. High-performance, direct-drive cryogenic deuterium–tritium (DT) implosions are a challenging backlighting configuration because of the low opacity of the DT shell, the high shell velocity, the small size of the stagnating shell, and the very bright self-emission of the hot core. A crystal imaging system with a Si Heα backlighter at 1.865 keV driven by ∼20-ps short pulses from OMEGA EP was developed to radiograph the OMEGA cryogenic implosions. The high throughput of the crystal imaging system makes it possible to record high-quality images with good photon statistics and a spatial resolution of ∼15 μm at 10% to 90% modulation. This imager has been used to study the evolution of preimposed mass-density perturbations in the ablator, to quantify the perturbations caused by the stalk that is used to mount the target, and to study the mix caused by laser imprint or small-scale debris on the target surface. Because of the very low opacity of DT relative to carbon, even 0.1% of mix of carbon into the DT ice can be reliably inferred from the images. With the current implosion designs, mix is only observed for an adiabat below α = 4.
Recent progress of magnetic reconnection research in the MAST spherical tokamak
Authors: Tanabe H. , Yamada T. , Watanabe T. , Gi K. , Inomoto M. , Imazawa R. , Gryaznevich M. , Michael C. , Crowley B. , Conway N. J. , Scannell R. , Harrison J. , Fitzgerald I. , Meakins A. , Hawkes N. , McClements K. G. , O'Gorman T. , Cheng C. Z. , Ono Y. ,   MAST Team
Published: March 2017

In the last three years, magnetic reconnection research in the MAST spherical tokamak achieved major progress by the use of new 32 chord ion Doppler tomography and 130 channel YAG and 300 channel Ruby Thomson scattering diagnostics. In addition to the previously achieved high power plasma heating during merging, detailed full temperature profile measurements including the diffusion region have been achieved for the first time. 2D imaging measurements of ion and electron temperature profiles have revealed that magnetic reconnection mostly heats ions globally in the downstream region of outflow jet and electrons locally around the X-point. The toroidal field in MAST “over 0.3T” strongly inhibits cross-field thermal transport, and the characteristic peaked electron temperature profile around the X-point is sustained on a millisecond time scale. In contrast, ions are mostly heated in the downstream region of outflow acceleration and around the stagnation point formed by reconnected flux mostly by viscosity dissipation and shock-like compressional damping of the outflow jet. Toroidal confinement also contributes to the characteristic ion temperature profile, forming a ring structure aligned with the closed flux surface. There is an effective confinement of the downstream thermal energy due to a thick layer of reconnected flux. The characteristic structure is sustained for longer than an ion-electron energy relaxation time (∼4 ms), and the energy exchange between ions and electrons contributes to the bulk electron heating in the downstream region. The toroidal guide field mostly contributes to the formation of a localized electron heating structure around the X-point but not to bulk ion heating downstream.
Effects of post-deposition annealing on the structure and magnetization of PLD grown yttrium iron garnet films
Authors: Kumar Ravinder , Hossain Z. , Budhani R. C.
Published: March 2017

We report on the recrystallization of 200 nm thick as-grown Yttrium Iron Garnet ( Y3.4Fe4.6O12) films on the (111) face of gadolinium gallium garnet single crystals by post-deposition annealing. Epitaxial conversion of the as-grown microcrystalline yttrium iron garnet films was seen after annealing at 800 °C for more than 30 min both in ambient oxygen and in air. The as-grown oxygen annealed samples at 800 °C for 60 min crystallize epitaxially and show excellent figure-of-merit for saturation magnetization (MS = 3.3 μB/f.u., comparable to the bulk value) and coercivity (HC ∼ 1.1 Oe). The ambient air annealing at 800 °C with a very slow rate of cooling (2 °C/min) results in a double layer structure with a thicker unstrained epitaxial top layer having the MS and HC of 2.9 μB/f.u. and 0.12 Oe, respectively. The symmetric and asymmetric reciprocal space maps of both the samples reveal a locking of the in-plane lattice of the film to the in-plane lattice of the substrate, indicating a pseudomorphic growth. The residual stress calculated by the  sin2ψ technique is compressive in nature. The lower layer in the air annealed sample is highly strained, whereas the top layer has negligible compressive stress.
Effect of annealing on Raman spectra of monolayer graphene samples gradually disordered by ion irradiation
Authors: Zion E. , Butenko A. , Kaganovskii Yu. , Richter V. , Wolfson L. , Sharoni A. , Kogan E. , Kaveh M. , Shlimak I.
Published: March 2017

Raman scattering spectra (RS) of two series of monolayer graphene samples irradiated with various doses of C+ and Xe+ ions were measured after annealing in a high vacuum and in forming gas (95%Ar + 5%H2). It is shown that annealing below 500 °C leads to a significant decrease in both the D-line, associated with defects, and the 2D-line, associated with the intact lattice structure. This can be explained by annealing-induced enhanced doping. Further annealing in a vacuum up to 1000 °C leads to a significant increase in the 2D-line together with a continuous decrease in the D-line. This gives evidence for the partial removal of the defects and restoration of the damaged lattice. Annealing in forming gas is less effective in this sense. A blue shift of all lines is observed after annealing. It is shown that below 500 °C, unintentional doping is the main origin of the shift. At higher annealing temperatures, the blue shift is mainly due to lattice strain arising because of mismatch between the thermal expansion coefficients of graphene and the substrate. Inhomogeneous distribution of stress and doping across the samples lead to the correlated variation of the height and peak position of RS lines.
Discerning lattice and electronic structures in under- and over-doped multiferroic Aurivillius films
Authors: Meng Dechao , Tao Shi , Huang Haoliang , Wang Jianlin , Yun Yu , Peng Ranran , Fu Zhengping , Zheng Lirong , Chu Shengqi , Chu Wangsheng , Zhai Xiaofang , Brown Gail , Knize Randall , Lu Yalin
Published: March 2017

Aurivillius type multiferroic thin films with controllable doping have not been studied. Here, we achieve accurate doping of (La,Bi)6Fe2−xNixTi3O18 epitaxial films using two-target pulsed laser deposition. An upper doping limit of x ∼ 0.4 for fabricating the single-phase structure is found. In over-doped films, secondary phases appear and the Ni valence is close to 2+. The under-doped films exhibit a single-phase and the measured electronic structure agrees with a stoichiometric phase. The multiferroic properties of the single-phase films with under-doping are probed. Our study reveals the doping limit in the Aurivillius-type multiferroic system and demonstrates the lattice-structure and electronic-structure difference between the under- and over-doped films.
Carrier scattering in high-κ/metal gate stacks
Authors: Zeng Zaiping , Triozon François , Niquet Yann-Michel
Published: March 2017

A significant degradation of the mobility has been repeatedly observed at low inversion density in high-κ/metal gate metal-oxide-semiconductor field-effect transistors. However, the scattering mechanisms responsible for this degradation are still debated. It is often assumed that the mobility is limited by remote charges (RCS) at the interface between SiO2 and HfO2. However, the amount of charges needed to reproduce the experimental mobilities is usually very high (a few 1013 cm−2), and does not seem to be consistent with the measured threshold voltages. Scattering by localized dipoles hardly solves these discrepancies. Here, we investigate the contribution from three alternative mechanisms in a non-equilibrium Green's functions framework: (i) scattering by band offset fluctuations at the SiO2/HfO2 interface, (ii) scattering by dielectric constant fluctuations in SiO2 and HfO2, and (iii) scattering by workfunction fluctuations in a granular metal gate. None of these mechanisms significantly shifts the threshold voltage. We show that mechanisms (i) and (iii) efficiently scatter the carriers at low inversion densities. This reduces the amount of RCS charges needed to reproduce the experimental data. RCS and these mechanisms show different dependences on the thickness of the HfO2 layer, which might help to identify the dominant contributions.
Thermodynamics analysis of diffusion in spark plasma sintering welding Cr3C2 and Ni
Authors: Zhang Fan , Zhang Jinyong , Leng Xiaoxuan , Lei Liwen , Fu Zhengyi
Published: March 2017

Spark plasma sintering (SPS) welding of chromium carbide (Cr3C2) and nickel (Ni) was used to investigate the atomic diffusion caused by bypassing current. It was found that the diffusion coefficient with bypassing current was enhanced by almost 3.57 times over that without bypassing current. Different from the previous researches, the thermodynamics analysis conducted herein showed that the enhancement included a current direction-independent part besides the known current direction-dependent part. A local temperature gradient (LTG) model was proposed to explain the current direction-independent effect. Assuming that the LTG was mainly due to the interfacial electric resistance causing heterogeneous Joule heating, the theoretical results were in good agreement with the experimental results both in the present and previous studies. This new LTG model provides a reasonable physical meaning for the low-temperature advantage of SPS welding and should be useful in a wide range of applications.
Intermixing and thermal oxidation of ZrO2 thin films grown on a-Si, SiN, and SiO2 by metallic and oxidic mode magnetron sputtering
Authors: Coloma Ribera R. , van de Kruijs R. W. E. , Sturm J. M. , Yakshin A. E. , Bijkerk F.
Published: March 2017

The initial growth of DC sputtered ZrO2 on top of a-Si, SiN, and SiO2 layers has been studied by in vacuo high-sensitivity low energy ion scattering for two gas deposition conditions with different oxygen contents (high-O and low-O conditions). This unique surface sensitive technique allowed the determination of surface composition and thicknesses required to close the ZrO2 layer on all three substrates for both conditions. The ZrO2 layer closes similarly on all substrates due to more favorable enthalpies of formation for ZrO2 and ZrSiO4, resulting in passivation of the Si from the substrate. However, this layer closes at about half of the thickness (∼1.7 nm) for low-O conditions due to less oxidative conditions and less energetic particles arriving at the sample, which leads to less intermixing via silicate formation. In contrast, for high-O conditions, there is more ZrSiO4 and/or SiOx formation, giving more intermixing (∼3.4 nm). In vacuo X-ray photoelectron spectroscopy (XPS) measurements revealed similar stoichiometric ZrO2 layers deposited by both conditions and a higher interaction of the ZrO2 layer with the underlying a-Si for high-O conditions. In addition, oxygen diffusion through low-O ZrO2 films on a-Si has been investigated by ex situ angular-resolved XPS of samples annealed in atmospheric oxygen. For temperatures below 400 °C, no additional oxidation of the underlying a-Si was observed. This, together with the amorphous nature and smoothness of these samples, makes ZrO2 a good candidate as an oxidation protective layer on top of a-Si.
An analysis of point defects induced by In, Al, Ni, and Sn dopants in Bridgman-grown CdZnTe detectors and their influence on trapping of charge carriers
Authors: Gul R. , Roy U. N. , James R. B.
Published: March 2017

In this research, we studied point defects induced in Bridgman-grown CdZnTe detectors doped with Indium (In), Aluminium (Al), Nickel (Ni), and Tin (Sn). Point defects associated with different dopants were observed, and these defects were analyzed in detail for their contributions to electron/hole (e/h) trapping. We also explored the correlations between the nature and abundance of the point defects with their influence on the resistivity, electron mobility-lifetime (μτe) product, and electron trapping time. We used current-deep level transient spectroscopy to determine the energy, capture cross-section, and concentration of each trap. Furthermore, we used the data to determine the trapping and de-trapping times for the charge carriers. In In-doped CdZnTe detectors, uncompensated Cd vacancies (VCd−) were identified as a dominant trap. The VCd− were almost compensated in detectors doped with Al, Ni, and Sn, in addition to co-doping with In. Dominant traps related to the dopant were found at Ev + 0.36 eV and Ev + 1.1 eV, Ec + 76 meV and Ev + 0.61 eV, Ev + 36 meV and Ev + 0.86 eV, Ev + 0.52 eV and Ec + 0.83 eV in CZT:In, CZT:In + Al, CZT:In + Ni, and CZT:In + Sn, respectively. Results indicate that the addition of other dopants with In affects the type, nature, concentration (Nt), and capture cross-section (σ) and hence trapping (tt) and de-trapping (tdt) times. The dopant-induced traps, their corresponding concentrations, and charge capture cross-section play an important role in the performance of radiation detectors, especially for devices that rely solely on electron transport.
Laser-induced damage threshold of silicon under combined millisecond and nanosecond laser irradiation
Authors: Lv Xueming , Pan Yunxiang , Jia Zhichao , Li Zewen , Zhang Hongchao , Ni Xiaowu
Published: March 2017

The laser–silicon interaction process was investigated with the superposed radiation of two pulsed Nd:YAG lasers. A pulse duration of 1 millisecond (ms) was superposed by 7 nanosecond (ns) pulses, creating a combined pulse laser (CPL). The time-resolved surface temperature of silicon was measured by an infrared radiation pyrometer. The melting thresholds of silicon were attained for a single ms laser and a CPL by infrared radiometry and time-resolved reflectance. The concept of threshold boundary was proposed, and a fitted curve of threshold boundary was obtained. An axisymmetric model was established for laser heating of silicon. The transient temperature fields were obtained for single ms laser and CPL irradiation using finite element analysis. The numerical results were validated experimentally, and an obvious decrease in melting threshold was found under CPL irradiation. That is attributed to pre-heating by the ms laser and the surface damage caused by the ns laser.
Excitation of surface plasmon polaritons by electron beam with graphene ribbon arrays
Authors: Liu Yong-Qiang , Liu Pu-Kun
Published: March 2017

Graphene has emerged as an alternative material to support surface plasmon polaritons (SPPs) with its excellent properties such as the tight electromagnetic field localization, low dissipative loss, and versatile tunability. Thus, graphene surface plasmon polaritons (GSPs) provide an exciting platform to develop a series of novel devices and systems from the optical band to the terahertz (THz) band. In this paper, theoretical and simulated studies about the excitation of SPPs by an injected electron beam with periodic graphene ribbon arrays deposited on a dielectric medium are presented. The analytical dispersion expression of the GSP mode on the graphene ribbon arrays is obtained by using a modal expansion method along with periodic boundary conditions in the structure. With this result, the dispersion relation, propagation loss, and field pattern of the propagating GSPs for both periodic graphene microribbon arrays and the complete graphene sheet are investigated and analyzed in the THz band. It is shown that the electromagnetic field with a better concentration on the interface can be realized with graphene ribbon arrays compared with the graphene sheet for a given frequency. Besides, the excitation of GSPs by an injected electron beam with graphene ribbon arrays is modeled and implemented by the particle-in-cell simulation based on the finite difference time domain algorithm. GSPs can be excited effectively when the dispersion line of the electron beam and SPPs on the graphene ribbon arrays is matched with each other well. Besides, the dependences of output power on electron beam parameters such as the distance of the electron beam above the graphene ribbon surface and beam voltage are studied and analyzed. Finally, the tunability of graphene conductivity via biased voltage with a ground metal is considered and the tunable excitation of GSPs on the structure with biased drive voltage by the injected electron beam is also realized. The present work can find a lot of potential applications such as low loss plasmonic waveguides, graphene metamaterials, and tunable THz electronic sources.
Command splay-bend switching in an optically-compensated bend cell with polymerized liquid crystal photoalignment layers
Authors: Chang Kai-Han , Zhang Cary , Song Shanshan , Chien Liang-Chy
Published: March 2017

We demonstrate a fast-switching optically compensated bend (OCB) mode with polymerized liquid crystal photoalignment (PAL). The polymerized liquid crystal PAL is achieved by spin coating a mixture of reactive mesogens and a photoinitiator and polymerizing it with ultraviolet (UV) light on top of the PAL material, which is illuminated with linear-polarized ultraviolet light to introduce anisotropy and a pretilt angle for liquid crystal alignment. The experimental results show the dependency of the electro-optical properties of OCB cells on the morphology-modulated surface anchoring of polymerized liquid crystal PAL. Furthermore, the polymerized liquid crystal PAL exhibits superior stability against UV exposure and thermal stress, which makes PAL applicable in spatial light modulator application.
Effect of metal particles in cermets on spectral selectivity
Authors: Gao J. D. , Zhao C. Y. , Wang B. X.
Published: March 2017

Most cermet-based coatings achieve their solar selectivities by the tandem interference effect, which has been widely studied. This study focused on the spectral selectivity achieved by the scattering effect of metal particles in cermet-based coatings. Previous research proved that reasonable solar selectivities can be obtained for cermets in the regime of particles with a radius of the order of 100 nm, but their solar absorptance is low (<90%). In our research, the effect of metal particles on the spectral selectivity of cermets was studied by the Mie theory and Monte Carlo simulation for Cr, Ni, and W particles with radii of 10 nm, 50 nm, 100 nm, and 200 nm, which were embedded in Al2O3 and occupied 5% of the volume fraction. It was found that by arranging different particles in different layers, a very high solar absorptance (95.6%) could be achieved. Since their thermal emittance (∼25% at 600 °C) was higher than that of normal coatings, these coatings are recommended to be used in solar absorbers that have a high concentration factor. Finally, the dependent scattering effect was qualitatively considered by the coupled-dipole approach. With a metal volume fraction of 5%, it was found that the effect of dependent scattering was small and should not change the conclusions made based on independent scattering.
Suppression of gate leakage current in in-situ grown AlN/InAlN/AlN/GaN heterostructures based on the control of internal polarization fields
Authors: Kotani Junji , Yamada Atsushi , Ishiguro Tetsuro , Yamaguchi Hideshi , Nakamura Norikazu
Published: March 2017

This paper investigates the gate leakage characteristics of in-situ AlN capped InAlN/AlN/GaN heterostructures grown by metal-organic vapor phase epitaxy. It was revealed that the leakage characteristics of AlN capped InAlN/AlN/GaN heterostructures are strongly dependent on the growth temperature of the AlN cap. For an AlN capped structure with an AlN growth temperature of 740 °C, the leakage current even increased although there exists a large bandgap material on InAlN/AlN/GaN heterostructures. On the other hand, a large reduction of the gate leakage current by 4–5 orders of magnitudes was achieved with a very low AlN growth temperature of 430 °C. X-ray diffraction analysis of the AlN cap grown at 740 °C indicated that the AlN layer is tensile-strained. In contrast to this result, the amorphous structure was confirmed for the AlN cap grown at 430 °C by transmission electron microscopy. Furthermore, theoretical analysis based on one-dimensional band simulation was carried out, and the large increase in two-dimensional electron gas (2DEG) observed in Hall measurements was well reproduced by taking into account the spontaneous and piezo-electric polarization in the AlN layer grown at 740 °C. For the AlN capped structure grown at 430 °C, it is believed that the reduced polarization field in the AlN cap suppressed the penetration of 2DEG into the InAlN barrier layer, resulting in a small impact on 2DEG mobility and density. We believe that an in-situ grown AlN cap with a very low growth temperature of 430 °C is a promising candidate for high-frequency/high-power GaN-based devices with low gate leakage current.
Interplay between epitaxial strain and low dimensionality effects in a ferrimagnetic oxide
Authors: Popova Elena , Deb Marwan , Bocher Laura , Gloter Alexandre , Stéphan Odile , Warot-Fonrose Bénédicte , Berini Bruno , Dumont Yves , Keller Niels
Published: March 2017

Thin film properties are strongly influenced by strain and low dimensionality effects, especially when the film thickness is about a few unit cells, which corresponds to the thicknesses targeted in most of contemporary studies. In oxides, these effects are responsible for the dramatic modification of the physical properties that sometimes can change the nature of a material. Nevertheless, it is not always possible to distinguish the contribution of the strain to the changes in physical properties from the contribution due to low dimensional effects. In the present study, bismuth iron garnet Bi3Fe5O12 (BIG) is chosen to separate both effects. This material possesses, among other outstanding physical properties, the giant Faraday rotation that allows investigating films with the thickness below a few unit cells. Three series of BIG films of various thicknesses were grown on three isostructural substrates with different lattice parameters: Y3Al5O12(001), Gd3Ga5O12(001), and (GdCa)3(GaMgZr)5O12(001). The structural, magnetic, and magneto-optic properties were studied as a function of film thickness and strain. Furthermore, critical behavior of the BIG films was investigated in the vicinity of the Curie temperature. The obtained results allowed distinguishing between the low dimensional effects and the strain due to the epitaxial growth. While the size reduction is mostly responsible for the decrease of the magnetic characteristics of the films, the strain influences rather the critical thickness below which the material starts to behave as a low dimensional system.