bluuebunny/crossref_metadata_2025 huggingface dataset:
A screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator
Authors: Chu Xiangcheng , Wang Jiawei , Yuan Songmei , Li Longtu , Cui Hongchao
Published: June 2014

A novel screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator, with an assembly comprised a threaded shaft, is presented. The bolt-clamped Langevin vibrator consists of 4 chips of PZT ceramics and generates more energy with a certain input power. The threads of the stator multiply the linear force and position resolution, and the threaded rod is rotated directly to achieve linear movement without additional mechanical conversion. The actuator was designed and optimized using the Finite Element Method (FEM), and a prototype was fabricated. At 300 Vp-p, the maximum thrust force, velocity, and efficiency were approximately 4.2 N, 9.5 mm s−1, and 5.6%, respectively.
Trapped energetic electron driven modes with second stable regime in tokamak plasmas
Authors: He Hongda , Dong J. Q. , Zhao K. , He Zhixiong , Zheng G. Y. , Lu Gaimin , Hao G. Z. , Tao Xie , Wang L. F.
Published: June 2014

Features of fishbone-like trapped energetic electrons driven modes (TEEMs), which are a particular manifestation of the fishbone gap modes, are investigated taking into account model radial profile and the pitch angle distribution of the energetic electrons (EEs). The TEEMs are found unstable only when the beta values of EEs βh (=pressure of the energetic electrons/pressure of magnetic field) are higher than certain critical values which are proportional to perturbed energy δŴc of background plasma and much lower than that for traditional fishbone modes. In addition, TEEMs become stable again and enter a second stable regime when βh values are higher than second critical values. Furthermore, the modes can only be excited in plasmas which are stable for MHD instabilities. The real frequency and growth rate of the modes are approximately linear and parabolic functions of βh, respectively. The real frequency is very low but not zero in the vicinity of lower beta region, whereas it is comparable to the toroidal precession frequency of the EEs in higher critical beta region. The numerical results show that the second stable regime is easy to form when q = 1 flux surface is close to the magnetic axis. Suitable density gradient of EEs and magnetic shear are other two necessary conditions for excitation of the TEEMs.
Growth of ring ripple in a collisionless plasma in relativistic-ponderomotive regime and its effect on stimulated Raman backscattering process
Authors: Rawat Priyanka , Gauniyal Rakhi , Purohit Gunjan
Published: June 2014

A theoretical and numerical study has been made of the propagation of a ring rippled laser beam in collisionless plasma with dominant relativistic ponderomotive nonlinearity and its effect on the excitation of electron plasma wave and stimulated Raman backscattering process. The growth of ring ripple, riding on an intense Gaussian laser beam in plasma has also been studied. A paraxial-ray and WKB approximation has been invoked to understand the nature of propagation of the ring rippled Gaussian laser beam in plasma, electron plasma wave and back reflectivity under the influence of both nonlinearities. The growth rate and focusing of a ring rippled beam is found to be considerably affected by the power of the main beam and the phase angle between the electric vectors of the main beam and the ring ripple. It has also been observed that the focusing is released by the coupling of relativistic and ponderomotive nonlinearities, which significantly affected the dynamics of the excitation of electron plasma wave and back reflectivity of stimulated Raman scattering (SRS). Due to the strong coupling between ring rippled laser beam and the excited electron plasma wave, back reflectivity of SRS is enhanced. It has been observed from the computational results that the effect of the increased intensity leads to suppression of SRS back reflectivity. The results have been presented for established laser and plasma parameters.
Self-generated magnetic fields in direct-drive implosion experiments
Authors: Igumenshchev I. V. , Zylstra A. B. , Li C. K. , Nilson P. M. , Goncharov V. N. , Petrasso R. D.
Published: June 2014

Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA Laser Facility were investigated employing radiography with ∼10- to 60-MeV protons. The experiment used plastic-shell targets with imposed surface defects (glue spots, wires, and mount stalks), which enhance self-generated fields. The fields were measured during the 1-ns laser drive with an on-target intensity ∼1015 W/cm2. Proton radiographs show multiple ring-like structures produced by electric fields ∼107 V/cm and fine structures from surface defects, indicating self-generated fields up to ∼3 MG. These electric and magnetic fields show good agreement with two-dimensional magnetohydrodynamic simulations when the latter include the ∇Te × ∇ne source, Nernst convection, and anisotropic resistivity. The simulations predict that self-generated fields affect heat fluxes in the conduction zone and, through this, affect the growth of local perturbations.
Stranski-Krastanow islanding initiated on the stochastic rough surfaces of the epitaxially strained thin films
Authors: Tarik Ogurtani Omer , Celik Aytac , Emre Oren Ersin
Published: June 2014

Quantum dots (QD) have discrete energy spectrum, which can be adjusted over a wide range by tuning composition, density, size, lattice strain, and morphology. These features make quantum dots attractive for the design and fabrication of novel electronic, magnetic and photonic devices and other functional materials used in cutting-edge applications. The formation of QD on epitaxially strained thin film surfaces, known as Stranski-Krastanow (SK) islands, has attracted great attention due to their unique electronic properties. Here, we present a systematic dynamical simulation study for the spontaneous evolution of the SK islands on the stochastically rough surfaces (nucleationless growth). During the development of SK islands through the mass accumulation at randomly selected regions of the film via surface drift-diffusion (induced by the capillary and mismatch stresses) with and/or without growth, one also observes the formation of an extremely thin wetting layer having a thickness of a few Angstroms. Above a certain threshold level of the mismatch strain and/or the size of the patch, the formation of multiple islands separated by shallow wetting layers is also observed as metastable states such as doublets even multiplets. These islands are converted into a distinct SK islands after long annealing times by coalescence through the long range surface diffusion. Extensive computer simulation studies demonstrated that after an initial transient regime, there is a strong quadratic relationship between the height of the SK singlet and the intensity of the lattice mismatch strain (in a wide range of stresses up to 8.5 GPa for germanium thin crystalline films), with the exception at those critical points where the morphological (shape change with necking) transition takes place.
Exact analytic solutions of the Schrödinger equations for some modified q-deformed potentials
Authors: Sebawe Abdalla M. , Eleuch H.
Published: June 2014

In this paper, we introduce the exact solution for the wave function in the presence of potential energy, consisting of combination between q-deformed hyperbolic and exponential function with different argument. The functions we have used in the present communication can be regarded as a generalization of the Arai q-deformed function (modified q-deformed Morse potential). In this context, we have restricted our discussion for some particular cases of the q-deformed hyperbolic functions. This is due to the difficulty for dealing with most of the arguments included in the potential functions. For the most particular cases, the energy eigenfunctions are obtained, and the behavior is also discussed. It has been shown that the wave functions are sensitive to the variation in the value of q-deformed parameter as well as the strength of the potential parameter λ. Furthermore, the energy eigenvalues are also considered for some particular cases where the argument of the exponential function plays a strong role effecting its value.
Theory to carrier recombination in organic disordered semiconductors
Authors: Hofacker A. , Oelerich J. O. , Nenashev A. V. , Gebhard F. , Baranovskii S. D.
Published: June 2014

A theoretical description for recombination kinetics of charge carriers in a disordered system with a broad energy distribution of localized states (DOS) is suggested. This kinetics is governed by the exchange of carriers between transport states and traps. Concentration transients in systems with Gaussian DOS, typical for organic semiconductors, appear much steeper than those obtained for systems with exponential DOS. This difference in recombination kinetics is caused by the difference in thermalization kinetics for these two types of the DOS functions. The comparison of the recombination transients for mobile and trapped carriers in exponential and Gaussian DOS might help to distinguish between these two possible shapes of the DOS using experimental data for transient photoconductivity and photoabsorption.
Rapid misfit dislocation characterization in heteroepitaxial III-V/Si thin films by electron channeling contrast imaging
Authors: Carnevale Santino D. , Deitz Julia I. , Carlin John A. , Picard Yoosuf N. , De Graef Marc , Ringel Steven A. , Grassman Tyler J.
Published: June 2014

Electron channeling contrast imaging (ECCI) is used to characterize misfit dislocations in heteroepitaxial layers of GaP grown on Si(100) substrates. Electron channeling patterns serve as a guide to tilt and rotate sample orientation so that imaging can occur under specific diffraction conditions. This leads to the selective contrast of misfit dislocations depending on imaging conditions, confirmed by dynamical simulations, similar to using standard invisibility criteria in transmission electron microscopy (TEM). The onset and evolution of misfit dislocations in GaP films with varying thicknesses (30 to 250 nm) are studied. This application simultaneously reveals interesting information about misfit dislocations in GaP/Si layers and demonstrates a specific measurement for which ECCI is preferable versus traditional plan-view TEM.
Visible light stimulating dual-wavelength emission and O vacancy involved energy transfer behavior in luminescence for coaxial nanocable arrays
Authors: Yang Lei , Dong Jiazhang , Jiang Zhongcheng , Pan Anlian , Zhuang Xiujuan
Published: June 2014

We report a strategy to investigate O vacancy (VO) involved energy transfer and dual-wavelength yellow emission in coaxial nanocable. By electric field deposition and subsequent sol-gel template approach, ZnO:Tb/Y2O3:Eu coaxial nanocable arrays are synthesized. After visible light excitation, system is promoted to O vacancy charge transfer state of VO(0/+). In the following cross relaxation, energy transfer from VO to the excitation energy level of Tb3+ in ZnO:Tb core area. While in Y2O3:Eu shell area, energy transfer to the excitation energy level of Eu3+. Subsequently, dual-wavelength emission is observed. By constructing nanocable with dual-wavelength emission, yellow luminescence is obtained. Adjust doping concentration of Eu3+ or Tb3+ in the range of 0.01–0.05, chromaticity coordinates of ZnO:Tb/Y2O3:Eu nanocable stably stays at yellow region in color space except ZnO:Tb0.01/Y2O3:Eu0.01. As Vo states act as media in energy transfer process in nanocablers, visible light can stimulate dual-wavelength emissions. Yellow luminescent nanocable arrays will have great applications in light-emitting diode luminescence.
Surface nanostructuring by ion-induced localized plasma expansion in zinc oxide
Authors: El-Said A. S. , Moslem W. M. , Djebli M.
Published: June 2014

Creation of hillock-like nanostructures on the surface of zinc oxide single crystals by irradiation with slow highly charged ions is reported. At constant kinetic energy, the nanostructures were only observed after irradiation with ions of potential energies above a threshold between 19.1 keV and 23.3 keV. The size of the nanostructures increases as a function of potential energy. A plasma expansion approach is used to explain the nanostructures creation. The calculations showed that the surface nanostructures became taller with the increase of ionic temperature. The influence of charged cluster formation and the relevance of their polarity are discussed.
Practical realization of DB metasurface
Authors: Zaluški Davor , Hrabar Silvio , Muha Damir
Published: June 2014

In this Letter, experimental realization of recently proposed DB metasurface is presented. A compact DB unit cell is proposed and its operating principle is tested both numerically and experimentally. Practical realization of a single layer DB metasurface, composed of 16 DB unit cells, is presented. Prototyped DB metasurface was measured in a waveguide environment and obtained experimental results support theoretically predicted DB properties.
Quasi-Moseley's law for strong narrow bandwidth soft x-ray sources containing higher charge-state ions
Authors: Ohashi Hayato , Higashiguchi Takeshi , Suzuki Yuhei , Arai Goki , Otani Yukitoshi , Yatagai Toyohiko , Li Bowen , Dunne Padraig , O'Sullivan Gerry , Jiang Weihua , Endo Akira , Sakaue Hiroyuki A. , Kato Daiji , Murakami Izumi , Tamura Naoki , Sudo Shigeru , Koike Fumihiro , Suzuki Chihiro
Published: June 2014

Bright narrow band emission observed in optically thin plasmas of high-Z elements in the extreme ultraviolet spectral region follows a quasi-Moseley's law. The peak wavelength can be expressed as λ=(21.86±12.09)×R∞−1×(Z−(23.23±2.87))−(1.52±0.12), where R∞ is the Rydberg constant. The wavelength varies from 13.5 nm to 4.0 nm as the atomic number, Z, increases from Z = 50 to Z = 83. The range of emission wavelengths available from hot optically thin plasmas permits the development of bright laboratory-scale sources for applications including x-ray microscopy and x-ray absorption fine structure determination.
GaAs-based high temperature electrically pumped polariton laser
Authors: Baten Md Zunaid , Bhattacharya Pallab , Frost Thomas , Deshpande Saniya , Das Ayan , Lubyshev Dimitri , Fastenau Joel M. , Liu Amy W. K.
Published: June 2014

Strong coupling effects and polariton lasing are observed at 155 K with an edge-emitting GaAs-based microcavity diode with a single Al0.31Ga0.69As/Al0.41Ga0.59As quantum well as the emitter. The threshold for polariton lasing is observed at 90 A/cm2, accompanied by a reduction of the emission linewidth to 0.85 meV and a blueshift of the emission wavelength by 0.89 meV. Polariton lasing is confirmed by the observation of a polariton population redistribution in momentum space and spatial coherence. Conventional photon lasing is recorded in the same device at higher pump powers.
Characterisation and analysis of flow over two side by side cylinders for different gaps at low Reynolds number: A numerical approach
Authors: Supradeepan K. , Roy Arnab
Published: June 2014

Numerical simulations were performed for two-dimensional viscous incompressible flow past two stationary side by side circular cylinders at Reynolds number (Re) 100 by varying centre to centre distance between the cylinders from 1.1 to 8 times the diameter (D) of a cylinder. The incompressible Navier-Stokes equations were solved using a finite volume method. Five different flow regimes were observed in the flow as the distance between the cylinders was increased systematically. An attempt has been made to characterise the different flow regimes using different numerical tools like Proper Orthogonal Decomposition (POD), λ2 criterion, instantaneous streamwise normal stress produced due to periodic variation of flow, frequency spectrum analysis and phase diagrams. All these tools confirm the clear existence of five different regimes in the flow when the gap between the cylinders is varied over the above stated range.
Cavity polaritons in an organic single-crystalline rubrene microcavity
Authors: Tsuchimoto Yuta , Nagai Hikaru , Amano Masamitsu , Bando Kazuki , Kondo Hisao
Published: June 2014

We fabricated a single-crystalline rubrene microcavity using a simple solution technique and observed cavity polaritons in the microcavity at room temperature (RT). Large Rabi splitting energies were obtained from dispersion of the cavity polaritons. Furthermore, photoluminescence from the cavity polaritons was observed at RT. The findings will be of importance for the application of cavity polaritons.
Magnetism in grain-boundary phase of a NdFeB sintered magnet studied by spin-polarized scanning electron microscopy
Authors: Kohashi Teruo , Motai Kumi , Nishiuchi Takeshi , Hirosawa Satoshi
Published: June 2014

The magnetism in the grain-boundary phase of a NdFeB sintered magnet was measured by spin-polarized scanning electron microscopy (spin SEM). A sample magnet was fractured in the ultra-high-vacuum chamber to avoid oxidation, and its magnetizations in the exposed grain-boundary phase on the fracture surface were evaluated through the spin polarization of secondary electrons. Spin-SEM images were taken as the fracture surface was milled gradually by argon ions, and the magnetization in the grain-boundary phase was quantitatively obtained separately from that of the Nd2Fe14B phase. The obtained magnetization shows that the grain-boundary phase of this magnet has substantial magnetization, which was confirmed to be ferromagnetic.
Investigation of the temperature-dependence of ferromagnetic resonance and spin waves in Co2FeAl0.5Si0.5
Authors: Loong Li Ming , Kwon Jae Hyun , Deorani Praveen , Tung Yu Chris Nga , Hirohata Atsufumi , Yang Hyunsoo
Published: June 2014

Co2FeAl0.5Si0.5 (CFAS) is a Heusler compound that is of interest for spintronics applications, due to its high spin polarization and relatively low Gilbert damping constant. In this study, the behavior of ferromagnetic resonance as a function of temperature was investigated in CFAS, yielding a decreasing trend of damping constant as the temperature was increased from 13 to 300 K. Furthermore, we studied spin waves in CFAS using both frequency domain and time domain techniques, obtaining group velocities and attenuation lengths as high as 26 km/s and 23.3 μm, respectively, at room temperature.
Breakdown mechanisms and reverse current-voltage characteristics of organic bulk heterojunction solar cells and photodetectors
Authors: Li Kejia , Li Lijun , Khlyabich Petr P. , Burkhart Beate , Sun Wenlu , Lu Zhiwen , Thompson Barry C. , Campbell Joe C.
Published: June 2014

We investigate the reverse current-voltage characteristics and breakdown mechanisms of organic bulk heterojunction solar cells and photodetectors. Dark current and photo current measurements at different temperatures indicate that tunneling is the dominant mechanism at high reverse voltage. A band-to-band tunneling model that accommodates either Gaussian or exponential-parabolic density of states distributions is developed and used for simulations. At high reverse bias, the model explains the observed breakdown, which differs from the bias independent dark current behavior predicted by the Onsager-Braun model. At low reverse voltage, the incorporation of shunt resistance in the model provides good agreement between the measured reverse bias characteristics and simulations.
Understanding the amorphous-to-microcrystalline silicon transition in SiF4/H2/Ar gas mixtures
Authors: Dornstetter Jean-Christophe , Bruneau Bastien , Bulkin Pavel , Johnson Erik V. , Roca i Cabarrocas Pere
Published: June 2014

We report on the growth of microcrystalline silicon films from the dissociation of SiF4/H2/Ar gas mixtures. For this growth chemistry, the formation of HF molecules provides a clear signature of the amorphous to microcrystalline growth transition. Depositing films from silicon tetrafluoride requires the removal of F produced by SiF4 dissociation, and this removal is promoted by the addition of H2 which strongly reacts with F to form HF molecules. At low H2 flow rates, the films grow amorphous as all the available hydrogen is consumed to form HF. Above a critical flow rate, corresponding to the full removal of F, microcrystalline films are produced as there is an excess of atomic hydrogen in the plasma. A simple yet accurate phenomenological model is proposed to explain the SiF4/H2 plasma chemistry in accordance with experimental data. This model provides some rules of thumb to achieve high deposition rates for microcrystalline silicon, namely, that increased RF power must be balanced by an increased H2 flow rate.
Inelastic electron tunneling spectroscopy of local “spin accumulation” devices
Authors: Tinkey Holly N. , Li Pengke , Appelbaum Ian
Published: June 2014

We investigate the origin of purported “spin accumulation” signals observed in local “three-terminal” (3T) measurements of ferromagnet/insulator/n-Si tunnel junctions using inelastic electron tunneling spectroscopy (IETS). Voltage bias and magnetic field dependences of the IET spectra were found to account for the dominant contribution to 3T magnetoresistance, thus indicating that it arises from inelastic tunneling through impurities and defects at junction interfaces and within the barrier, rather than from spin accumulation due to pure elastic tunneling into bulk Si as has been previously assumed.
Study on lower hybrid current drive efficiency at high density towards long-pulse regimes in Experimental Advanced Superconducting Tokamak
Authors: Li M. H. , Ding B. J. , Zhang J. Z. , Gan K. F. , Wang H. Q. , Peysson Y. , Decker J. , Zhang L. , Wei W. , Li Y. C. , Wu Z. G. , Ma W. D. , Jia H. , Chen M. , Yang Y. , Feng J. Q. , Wang M. , Xu H. D. , Shan J. F. , Liu F. K. ,   EAST Team
Published: June 2014

Significant progress on both L- and H-mode long-pulse discharges has been made recently in Experimental Advanced Superconducting Tokamak (EAST) with lower hybrid current drive (LHCD) [J. Li et al., Nature Phys. 9, 817 (2013) And B. N. Wan et al., Nucl. Fusion 53, 104006 (2013).]. In this paper, LHCD experiments at high density in L-mode plasmas have been investigated in order to explore possible methods of improving current drive (CD) efficiency, thus to extend the operational space in long-pulse and high performance plasma regime. It is observed that the normalized bremsstrahlung emission falls much more steeply than 1/ne_av (line-averaged density) above ne_av = 2.2 × 1019 m−3 indicating anomalous loss of CD efficiency. A large broadening of the operating line frequency (f = 2.45 GHz), measured by a radio frequency (RF) probe located outside the EAST vacuum vessel, is generally observed during high density cases, which is found to be one of the physical mechanisms resulting in the unfavorable CD efficiency. Collisional absorption of lower hybrid wave in the scrape off layer (SOL) may be another cause, but this assertion needs more experimental evidence and numerical analysis. It is found that plasmas with strong lithiation can improve CD efficiency largely, which should be benefited from the changes of edge parameters. In addition, several possible methods are proposed to recover good efficiency in future experiments for EAST.
First-principles calculation on β-SiC(111)/α-WC(0001) interface
Authors: Jin Na , Yang Yanqing , Li Jian , Luo Xian , Huang Bin , Sun Qing , Guo Pengfei
Published: June 2014

The α-WC(0001) surface and β-SiC(111)/α-WC(0001) interface were studied by first-principles calculation based on density functional theory. It is demonstrated that the α-WC(0001) surface models with more than nine atom-layers exhibit bulk-like interior, wherein the surface relaxations localized within the top three layers are well converged. Twenty-four specific geometry models of SiC/WC interface structures with different terminations and stacking sites were chosen. The calculated work of adhesion and interface energy suggest that the most stable interface structure has the C-C bonding across the interface, yielding the largest work of adhesion and the lowest interface energy. Moreover, the top-site stacking sequence is preferable for the C/C-terminated interface. The effects of the interface on the electronic structures of the C/C-terminated interfaces are mainly localized within the first and second layers of the interface. Calculations of the work of adhesion and interface energy provide theoretical evidence that the mechanical failure may initiate at the interface or in SiC but not in WC.
In situ growth and coalescence of He-filled bi-dimensional defects in Si by H supply
Authors: Vallet M. , Barbot J. F. , Oliviero E. , Donnelly S. E. , Hinks J. A. , Beaufort M. F.
Published: June 2014

In this work, ion implantations with in situ transmission electron microscopy observations followed by different rates of temperature ramp were performed in (001)-Si to follow the evolution of He-plates under the influence of hydrogen. The JANNUS and MIAMI facilities were used to study the first stages of growth as well as the interactions between co-planar plates. Results showed that under a limited amount of H, the growth of He-plates resulting from a subcritical stress-corrosion mechanism can be fully described by the kinetic model of Johnson-Mehl-Avrami-Kolmogorov with effective activation energy of 0.9 eV. Elastic calculations showed that the sudden and non-isotropic coalescence of close He-plates occurs when the out-of-plane tensile stress between them is close to the yield strength of silicon. After hydrogen absorption, surface minimization of final structure occurs.
Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates
Authors: McDaniel Martin D. , Posadas Agham , Ngo Thong Q. , Karako Christine M. , Bruley John , Frank Martin M. , Narayanan Vijay , Demkov Alexander A. , Ekerdt John G.
Published: June 2014

Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5–25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1−xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (∼225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ∼2.0 × 10−2 Ω cm for 20-nm-thick La:STO (x ∼ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.
On the electrical and interface properties of nanostructured CdTe Schottky diodes electrodeposited from an ionic liquid medium
Authors: Chauhan Khushbu R. , Mukhopadhyay Indrajit
Published: June 2014

A simple and cost effective method to fabricate nearly ideal Schottky diode out of p-CdTe semiconductor is discussed. The efficient re-use of ionic liquid for the deposition of nano-microstructures of CdTe is also disclosed. The I–V characteristic of the diode configured as Cu:FTO:p-CdTe:Cu showed the rectifying nature with a small forward voltage (0.8 V) and a rectification ratio of 6 × 103 at 4.8 V. Theoretical model suggests the diffusion controlled carrier transport process with an ideality factor of 1.1 up to a small forward voltage range whereas the thermionic transport with generation recombination dominates at higher voltages. The interface properties of p-CdTe and FTO were studied by impedance spectroscopy under varied bias conditions to electrically represent the diode.
Origin of the current discretization in deep reset states of an Al2O3/Cu-based conductive-bridging memory, and impact on state level and variability
Authors: Belmonte A. , Degraeve R. , Fantini A. , Kim W. , Houssa M. , Jurczak M. , Goux L.
Published: June 2014

In this paper, we develop a Quantum-Point-Contact (QPC) model describing the state conduction in a W/Al2O3/TiW/Cu Conductive-Bridging Memory cell (CBRAM). The model allows describing both the voltage- and the temperature-dependence of the conduction. For deep current levels, a resistance component is added in series to the point-contact constriction to account for electron scattering in the residual filament. The fitting of single-particle perturbation also allowed to estimate the number and effective size of the conduction-controlling particles in the QPC constriction. The results clearly point to smaller particles for CBRAM (Cu particles) as compared to oxide-based resistive RAM involving oxygen-vacancy defects, which is discussed as a possible origin of deeper reset level obtained in CBRAM. We also evidence a beneficial impact of this smaller particle size on lower Random-Telegraph-Noise amplitude measured on CBRAM devices.
Transverse magnetic surface plasmons and complete absorption supported by doped graphene in Otto configuration
Authors: Ramos-Mendieta F. , Hernández-López J. A. , Palomino-Ovando M.
Published: June 2014

High sensitivity of the Attenuated Total Reflectance technique for exciting transverse magnetic surface plasmons in free-standing doped graphene is reported; complete agreement with the electromagnetic dispersion relation is numerically demonstrated in the terahertz regime. By reducing the air gap between prism and graphene in the Otto configuration we found that the surface plasmon excitation is weakened, but interference effects arise producing perfect absorption. At 5 THz two dips of zero-reflection were found, one of them with residual plasmonic contribution. Consequently, the reflection can be suppressed by changing the separation between prism and graphene; it is not needed to modify the graphene doping level. Conditions for destructive interference leading to complete absorption are presented and a particular behavior of the evanescent magnetic fields just at perfect absorption is reported
Low temperature thin film transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels
Authors: Bolat S. , Ozgit-Akgun C. , Tekcan B. , Biyikli N. , Okyay A. K.
Published: June 2014

We report GaN thin film transistors (TFT) with a thermal budget below 250 °C. GaN thin films are grown at 200 °C by hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD). HCPA-ALD-based GaN thin films are found to have a polycrystalline wurtzite structure with an average crystallite size of 9.3 nm. TFTs with bottom gate configuration are fabricated with HCPA-ALD grown GaN channel layers. Fabricated TFTs exhibit n-type field effect characteristics. N-channel GaN TFTs demonstrated on-to-off ratios (ION/IOFF) of 103 and sub-threshold swing of 3.3 V/decade. The entire TFT device fabrication process temperature is below 250 °C, which is the lowest process temperature reported for GaN based transistors, so far.
Comparison of electrostatic and localized plasmon induced light enhancement in hybrid InGaN/GaN quantum wells
Authors: Lin Jie , Llopis Antonio , Krokhin Arkadii , Pereira Sergio , Watson Ian M. , Neogi Arup
Published: June 2014

The light enhancement phenomena in InGaN/GaN multi-quantum wells (MQWs) infiltrated with metal nanoparticles (NPs) are studied using resonant and off-resonant localized plasmon interactions. The emission and recombination characteristics of carriers in InGaN/GaN MQW structures with inverted hexagonal pits (IHPs) are modified distinctly depending on the nature of their interaction with the metal NPs and with the pumping and emitted photons. It is observed that the emission intensity of light is significantly enhanced when the emission energy is off-resonant to the localized plasmon frequency of the metal nanoparticles. This results in enhanced emission from MQW due to Au nanoparticles and from IHPs due to Ag nanoparticles. At resonant-plasmon frequency of the Ag NPs, the emission from MQWs is quenched due to the re-absorption of the emitted photons, or due to the drift carriers from c-plane MQWs towards the NPs because of the Coulomb forces induced by the image charge effect.
Measurements of liquid surface fluctuations using a self-mixing solid-state laser
Authors: Sudo S. , Otsuka K.
Published: June 2014

We propose a highly sensitive method for measurements of liquid surface fluctuations with nanometer-order displacement using a self-mixing laser Doppler velocimeter (LDV) comprising a laser-diode-pumped thin-slice solid-state laser and a simple photodiode. In this measurement system, the scattered light from the liquid surface is reinjected into the solid-state laser, and then the laser output from the solid-state laser is modulated by this reinjected laser light. The time dependence of the displacement of liquid surface fluctuations can be obtained from the analysis of the modulated laser output. We describe various measuring methods and the optical system of the self-mixing LDV for real-time measurements of liquid surface fluctuations. Real-time measurement of liquid surface fluctuations can be performed with high amplitude and frequency resolutions by the analysis of the modulated laser output.
Robust topological surface states of Bi2Se3 thin films on amorphous SiO2/Si substrate and a large ambipolar gating effect
Authors: Bansal Namrata , Koirala Nikesh , Brahlek Matthew , Han Myung-Geun , Zhu Yimei , Cao Yue , Waugh Justin , Dessau Daniel S. , Oh Seongshik
Published: June 2014

The recent emergence of topological insulators (TI) has spurred intensive efforts to grow TI thin films on various substrates. However, little is known about how robust the topological surface states (TSS) are against disorders and other detrimental effects originating from the substrates. Here, we report the observation of a well-defined TSS on Bi2Se3 films grown on amorphous SiO2 (a-SiO2) substrates and a large gating effect on these films using the underneath doped-Si substrate as the back gate. The films on a-SiO2 were composed of c-axis ordered but random in-plane domains. However, despite the in-plane randomness induced by the amorphous substrate, the transport properties of these films were superior to those of similar films grown on single-crystalline Si(111) substrates, which are structurally better matched but chemically reactive with the films. This work sheds light on the importance of chemical compatibility, compared to lattice matching, for the growth of TI thin films, and also demonstrates that the technologically important and gatable a-SiO2/Si substrate is a promising platform for TI films.
Enhanced electro-mechanical actuation strain in polyaniline nanorods/silicone rubber nanodielectric elastomer films
Authors: Wang Dongrui , Zhang Ling , Zhang Liang , Zha Jun-Wei , Yu Haizhu , Hu Sheng , Dang Zhi-Min
Published: June 2014

Nanodielectric elastomer films consisting of a silicone rubber as the matrix and conductive polyaniline nanorods (PANI-NR) as the filler were fabricated and their electro-mechanical actuation performance was investigated. The nanodielectric elastomers displayed a typical insulator-to-conductor transition as the content of PANI-NR increased. The percolation threshold was observed to show a relatively low value of 5.2 vol. %, which should be mainly ascribed to the one-dimensional structure of the nanorods. As the concentration of PANI-NR approached to the percolation threshold, the electro-mechanical actuation strain of the elastomer films was significantly enhanced. The actuation coefficient of nanodielectric elastomer films with only 4.0 vol. % PANI-NR loading was about 5 times higher than that of pure silicone rubber matrix.
Optical spacing effect in organic photovoltaic cells incorporating a dilute acceptor layer
Authors: Menke S. Matthew , Lindsay Christopher D. , Holmes Russell J.
Published: June 2014

The addition of spacing layers in organic photovoltaic cells (OPVs) can enhance light absorption by optimizing the spatial distribution of the incident optical field in the multilayer structure. We explore the optical spacing effect in OPVs achieved using a diluted electron acceptor layer of C60. While optical spacing is often realized by optimizing buffer layer thickness, we find that optical spacing via dilution leads to cells with similar or enhanced photocurrent. This is observed despite a smaller quantity of absorbing molecules, suggesting a more efficient use of absorbed photons. In fact, dilution is found to concentrate optical absorption near the electron donor-acceptor interface, resulting in a marked increase in the exciton diffusion efficiency. Contrasting the use of changes in thickness to engineer optical absorption, the use of dilution does not significantly alter the overall thickness of the OPV. Optical spacing via dilution is shown to be a viable alternative to more traditional optical spacing techniques and may be especially useful in the continued optimization of next-generation, tandem OPVs where it is important to minimize competition for optical absorption between individual sub-cells.
Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures
Authors: Hajłasz M. , Donkers J. J. T. M. , Sque S. J. , Heil S. B. S. , Gravesteijn D. J. , Rietveld F. J. R. , Schmitz J.
Published: June 2014

For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact is thought to come from reactions between the contact metals and the AlGaN/GaN. As a consequence, conventional extraction of the specific contact resistance and transfer length leads to erroneous results. In this Letter, the sheet resistance under gold-free Ti/Al-based Ohmic contacts to AlGaN/GaN heterostructures on Si substrates has been investigated by means of electrical measurements, transmission electron microscopy, and technology computer-aided design simulations. It was found to be significantly lower than that outside of the contact area; temperature-dependent electrical characterization showed that it exhibits semiconductor-like behavior. The increase in conduction is attributed to n-type activity of nitrogen vacancies in the AlGaN. They are thought to form during rapid thermal annealing of the metal stack when Ti extracts nitrogen from the underlying semiconductor. The high n-type doping in the region between the metal and the 2-dimensional electron gas pulls the conduction band towards the Fermi level and enhances horizontal electron transport in the AlGaN. Using this improved understanding of the properties of the material underneath the contact, accurate values of transfer length and specific contact resistance have been extracted.
A hydrogen peroxide electrochemical sensor based on silver nanoparticles decorated three-dimensional graphene
Authors: Zhan Beibei , Liu Changbing , Shi Huaxia , Li Chen , Wang Lianhui , Huang Wei , Dong Xiaochen
Published: June 2014

A facile strategy has been developed to synthesize sliver nanoparticles (Ag NPs) decorated three-dimensional graphene (3DG) through hydrothermal process. The AgNPs-3DG composites are directly fabricated into a free standing sensing electrode for electrochemical detection of hydrogen peroxide (H2O2) in phosphate buffered solutions. Various techniques equipments including scanning electron microscopy, X-ray diffraction, and Raman spectroscopy are used to characterize the morphology and structure of the as-prepared composite. The electrochemical experiments reveal the AgNPs-3DG based biosensor exhibits fast amperometric sensing, low detection limitation, wide linear responding range, and perfect selectivity for non-enzyme H2O2 detection, indicating the well synergistic effect of Ag NPs high electrocatalytic activity and 3DG high conductivity and large surface area.
Study on the hydrotreatment of C9 aromatics over supported multi-metal catalysts on γ-Al2O3
Authors: Li Dan , Zhang Honghua , Usman Muhammad , Li Zengxi , Han Lijun , Li Chunshan , Zhang Suojiang
Published: June 2014

With the dramatic increasing of economy, the conflict between the lack of petroleum resource and sharply increasing demand for gasoline and diesel has restricted the continuous development of economy and energy of our world. The catalytic conversion of C9 aromatics into clean fuel was studied in our laboratory using hydrotreating catalysts which were prepared by new synthesis technologies that combine vacuum-impregnation and temperature-programmed calcinations. Characterization results indicate that these catalysts have a high surface area, and the activity sites dispersed well on the supporter. Hydrogenation performance of reaction conditions was carried out in two-stage fixed beds. Products of gasoline (<180 °C) and diesel (180–360 °C) fractions were separated from intermediate products via distillation, and the analysis results demonstrate that S/N content, density, and viscosity decreased. However, the H/C molar ratio increased. The main reactions of isomerization, disproportionation, and dealkylation occurred during the conversion of C9 aromatics and the activity order accorded the mechanism of carbenium ion reaction. This study indicates that C9 aromatics could be considerably upgraded through catalytic hydroprocessing to high-quality fuel in the presence of high-performance catalysts and appropriate reaction conditions. Thus, they are promising catalytic technologies and materials. Furthermore, the products could substitute gasoline and diesel partly.
Exact soliton solutions of the generalized Gross-Pitaevskii equation based on expansion method
Authors: Wang Ying , Zhou Yu
Published: June 2014

We give a more generalized treatment of the 1D generalized Gross-Pitaevskii equation (GGPE) with variable term coefficients. External harmonic trapping potential is fully considered and the nonlinear interaction term is of arbitrary polytropic index of superfluid wave function. We also eliminate the interdependence between variable coefficients of the equation terms avoiding the restrictions that occur in some other works. The exact soliton solutions of the GGPE are obtained through the delicate combined utilization of modified lens-type transformation and F-expansion method with dominant features like soliton type properties highlighted.
Optimization of excess Bi doping to enhance ferroic orders of spin casted BiFeO3 thin film
Authors: Gupta Surbhi , Tomar Monika , Gupta Vinay , James A. R. , Pal Madhuparna , Guo Ruyan , Bhalla Amar
Published: June 2014

Multiferroic Bismuth Ferrite (BiFeO3) thin films with varying excess bismuth (Bi) concentration were grown by chemical solution deposition technique. Room temperature multiferroic properties (ferromagnetism, ferroelectricity, and piezoelectricity) of the deposited BiFeO3 thin films have been studied. High resolution X-ray diffraction and Raman spectroscopy studies reveal that the dominant phases formed in the prepared samples change continuously from a mixture of BiFeO3 and Fe2O3 to pure BiFeO3 phase and, subsequently, to a mixture of BiFeO3 and Bi2O3 with increase in the concentration of excess Bi from 0% to 15%. BiFeO3 thin films having low content (0% and 2%) of excess Bi showed the traces of ferromagnetic phase (γ-Fe2O3). Deterioration in ferroic properties of BiFeO3 thin films is also observed when prepared with higher content (15%) of excess Bi. Single-phased BiFeO3 thin film prepared with 5% excess Bi concentration exhibited the soft ferromagnetic hysteresis loops and ferroelectric characteristics with remnant polarization 4.2 μC/cm2 and saturation magnetization 11.66 emu/g. The switching of fine spontaneous domains with applied dc bias has been observed using piezoresponse force microscopy in BiFeO3 thin films having 5% excess Bi. The results are important to identify optimum excess Bi concentration needed for the formation of single phase BiFeO3 thin films exhibiting the improved multiferroic properties.
Enhanced half-metallicity in the zigzag graphene nanoribbons by adsorption of the zigzag hydrogen fluoride molecular chains
Authors: Gong Xue , Zhang Jialing , Xu Bo. , Xia Yidong , Yin Jiang , Liu Zhiguo
Published: June 2014

A comprehensive theoretical study of the half-metallicity in the zigzag graphene nanoribbons (ZGNRs) by adsorption of the zigzag hydrogen fluoride chains was presented. The ZGNR by adsorption of the hydrogen fluoride chains could be half-metallic when a critical length of the hydrogen fluoride chain is achieved on the ZGNR at low temperature. It was found that the strong dipole moments of the hydrogen fluoride chains act as the constant electric field. Our results suggest a huge possibility in spintronics device applications for achieving half-metallicity in the ZGNRs without the excessively high external electric fields.
Studies of the Structure, Amidicity, and Reactivity of N-Chlorohydroxamic Esters and N-Chloro-β,β-dialkylhydrazides: Anomeric Amides with Low Resonance Energies
Authors: Glover Stephen A. , Rosser Adam A. , Spence Robert M.
Published: June 2014

Density functional calculations have been carried out to determine the properties of the title anomeric amides. At the B3LYP/6-31G(d) level, N-chloro-N-methoxyacetamide 8a is computed to be strongly pyramidal at nitrogen with a long amide bond that is untwisted. N-Chloro-N-dimethylaminoacetamide 9a is completely planar, but its amide bond is still much longer than that in N,N-dimethylacetamide 4. This is a steric, rather than a resonance, effect. COSNAR and a trans-amidation method calculate low resonance energies for both model amides, which is attributed to the combined electronegativity of the heteroatoms at the amide nitrogen and the strong anomeric effect when there is a chlorine substituent on nitrogen. When M06 and ωB97X-D dispersion-corrected density functional methods are used with the expanded 6-311++G(d,p) basis set, the resonance energies of 8a (–34 kJ mol–1) and 9a (–49 kJ mol–1) are in line with the gross electronegativity of the substituent atoms. Unlike other anomeric amides, 8a and 9a are not predicted to undergo HERON reactivity.