bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear effects in defect production by atomic and molecular ion implantation
Authors: David C. , Varghese Anto C. , Dholakia Manan , Chandra Sharat , Nair K. G. M. , Panigrahi B. K. , Santhana Raman P. , Amirthapandian S. , Amarendra G. , Kennedy John
Published: January 2015

This report deals with studies concerning vacancy related defects created in silicon due to implantation of 200 keV per atom aluminium and its molecular ions up to a plurality of 4. The depth profiles of vacancy defects in samples in their as implanted condition are carried out by Doppler broadening spectroscopy using low energy positron beams. In contrast to studies in the literature reporting a progressive increase in damage with plurality, implantation of aluminium atomic and molecular ions up to Al3, resulted in production of similar concentration of vacancy defects. However, a drastic increase in vacancy defects is observed due to Al4 implantation. The observed behavioural trend with respect to plurality has even translated to the number of vacancies locked in vacancy clusters, as determined through gold labelling experiments. The impact of aluminium atomic and molecular ions simulated using MD showed a monotonic increase in production of vacancy defects for cluster sizes up to 4. The trend in damage production with plurality has been explained on the basis of a defect evolution scheme in which for medium defect concentrations, there is a saturation of the as-implanted damage and an increase for higher defect concentrations.
Hybrid architecture for shallow accumulation mode AlGaAs/GaAs heterostructures with epitaxial gates
Authors: MacLeod S. J. , See A. M. , Hamilton A. R. , Farrer I. , Ritchie D. A. , Ritzmann J. , Ludwig A. , Wieck A. D.
Published: January 2015

Accumulation mode devices with epitaxially grown gates have excellent electrical stability due to the absence of dopant impurities and surface states. We overcome typical fabrication issues associated with epitaxially gated structures (e.g., gate leakage and high contact resistance) by using separate gates to control the electron densities in the Ohmic and Hall bar regions. This hybrid gate architecture opens up a way to make ultrastable nanoscale devices where the separation between the surface gates and the 2D electron gas is small. In this work, we demonstrate that the hybrid devices made from the same wafer have reproducible electrical characteristics, with identical mobility and density traces over a large range of 2D densities. In addition, thermal cycling does not influence the measured electrical characteristics. As a demonstration of concept, we have fabricated a hybrid single-electron transistor on a shallow (50 nm) AlGaAs/GaAs heterostructure that shows clear Coulomb blockade oscillations in the low temperature conductance.
A novel dual-band terahertz metamaterial absorber for a sensor application
Authors: Wang Ben-Xin , Zhai Xiang , Wang Gui-Zhen , Huang Wei-Qing , Wang Ling-Ling
Published: January 2015

We present a new type of dual-band terahertz metamaterial absorber formed by a patterned metallic strip and a dielectric layer on top of a metallic ground plane. It is found that besides a strong absorption in the fundamental resonance, a prominent high-order resonance with near-unity absorption is also unveiled. The origin of the induced dual-band absorption was elucidated. Importantly, the quality factor (Q) and the figure of merit (FOM) of the high-order resonance are 8.4 and 22.7 times larger than that of the fundamental resonance, respectively, which makes the proposed absorber to have significant potential in biological monitoring and sensing. Moreover, we demonstrate a dual-band and insensitive for two orthogonal polarizations terahertz absorber based on a metallic cross and a metallic ground plane separated by a dielectric layer. The Q and FOM of the high-order resonance are still larger than that of the fundamental resonance. The proposed absorbers appear to be very promising for solar cells, detection, and imaging applications.
Demixing and confinement of non-additive hard-sphere mixtures in slit pores
Authors: Almarza N. G. , Martín C. , Lomba E. , Bores C.
Published: January 2015

Using Monte Carlo simulation, we study the influence of geometric confinement on demixing for a series of symmetric non-additive hard spheres mixtures confined in slit pores. We consider both a wide range of positive non-additivities and a series of pore widths, ranging from the pure two dimensional limit to a large pore width where results are close to the bulk three dimensional case. Critical parameters are extracted by means of finite size analysis. As a general trend, we find that for this particular case in which demixing is induced by volume effects, the critical demixing densities (and pressures) increase due to confinement between neutral walls, following the expected behavior for phase equilibria of systems confined by pure repulsive walls: i.e., confinement generally enhances miscibility. However, a non-monotonous dependence of the critical pressure and density with pore size is found for small non-additivities. In this latter case, it turns out that an otherwise stable bulk mixture can be unexpectedly forced to demix by simple geometric confinement when the pore width decreases down to approximately one and a half molecular diameters.
Anisotropic spin dephasing of impurity-bound electron spins in ZnO
Authors: Lee Jieun , Venugopal Aneesh , Sih Vanessa
Published: January 2015

We investigate the electron spin dynamics of n-type c-axis oriented bulk zinc oxide (ZnO) by using time-resolved Kerr rotation and resonant spin amplification measurements. Calculating resonant spin amplification using an anisotropic spin dephasing model reveals that there are two species involved in the spin dynamics, which we attribute to conduction and impurity-bound electron spins, respectively. We find that the impurity-bound electron spin dephasing mechanism is strongly anisotropic due to anisotropic exchange interactions. The identification of the two spin species and their dephasing mechanisms is further supported by the temperature, power, and wavelength dependence of the spin coherence measurements.
The effect of periodic wavy profile on suppressing window multipactor under arbitrary electromagnetic mode
Authors: Chang C. , Liu Y. S. , Verboncoeur J. , Chen C. H. , Guo L. T. , Li S. , Wu X. L.
Published: January 2015

The three-dimensional periodic ripple profile with each unit of rotational symmetric surface is proposed to suppress multipactor for arbitrary electromagnetic mode with any polarization. The field distribution and multipactor electron dynamics on the wavy surface are studied to illustrate the multipactor inhibition mechanism. High power microwave experiment was conducted to demonstrate the effect of wavy surface on significantly improving the window power capacity.
Electrical conductivity of reconstructed Si(111) surface with sodium-doped C60 layers
Authors: Tsukanov D. A. , Ryzhkova M. V. , Borisenko E. A. , Zotov A. V. , Saranin A. A.
Published: January 2015

Electrical conductance of sodium-doped C60 ultra-thin layers (1–6 monolayers) grown on the Na-adsorbed Si(111)√3 × √3-Au surface has been studied in situ by four-point probe technique, combined with low-energy electron diffraction observations. Evidence of conductance channel formation through the C60 ultrathin layer is demonstrated as a result of Na dosing of 3 and 6 monolayers thick C60 layers. The observed changes in surface conductivity can be attributed to the formation of fulleride-like NaC60 and Na2C60 compound layers.
Unique properties of photoluminescence excitation spectra in a Eu-doped GaN epitaxial film
Authors: Nakayama Masaaki , Nakamura Satoshi , Takeuchi Hideo , Koizumi Atsushi , Fujiwara Yasufumi
Published: January 2015

We have investigated the temperature dependence of photoluminescence-excitation (PLE) spectra of Eu3+ emission due to the intra-4f shell transitions in a Eu-doped GaN epitaxial film from the viewpoint of the energy transfer process by carriers and excitons from the host GaN to Eu3+ ions. It was found that the excitonic band of the PLE spectrum disappears in a low temperature region below ∼140 K in spite of the fact that the optical transitions of the A and B excitons are clearly observed in a reflectance spectrum. The excitonic PLE band becomes remarkable with an increase in temperature. This fact indicates that carriers originating from the thermal dissociation of photogenerated excitons contribute to the Eu3+ emission. In other words, excitons play no role in the energy transfer process. Furthermore, the PLE spectrum at room temperature exhibits an oscillatory structure resulting from longitudinal-optical phonon emission in a hot carrier relaxation process.
A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy
Authors: Jäck Berthold , Eltschka Matthias , Assig Maximilian , Hardock Andreas , Etzkorn Markus , Ast Christian R. , Kern Klaus
Published: January 2015

Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 1020 cm−2 s−1 is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.
Nitrogen-doped graphene films from simple photochemical doping for n-type field-effect transistors
Authors: Li Xinyu , Tang Tao , Li Ming , He Xiancong
Published: January 2015

Highly nitrogen-doped GO (NGO) and n-type graphene field effect transistor (FET) have been achieved by simple irradiation of graphene oxide (GO) thin films in NH3 atmosphere. The electrical properties of the NGO film were performed on electric field effect measurements, and it displays an n-type FET behavior with a charge neutral point (Dirac point) located at around −8 V. It is suggested that the amino-like nitrogen (N-A) mainly contributes to the n-type behavior. Furthermore, compared to the GO film irradiated in Ar atmosphere, the NGO film is much more capable to improve the electrical conductivity. It may attribute to nitrogen doping and oxygen reduction, both of which can effectively enhance the electrical conductivity.
Correlation of magnetoelectric coupling in multiferroic BaTiO3-BiFeO3 superlattices with oxygen vacancies and antiphase octahedral rotations
Authors: Lorenz Michael , Wagner Gerald , Lazenka Vera , Schwinkendorf Peter , Modarresi Hiwa , Van Bael Margriet J. , Vantomme André , Temst Kristiaan , Oeckler Oliver , Grundmann Marius
Published: January 2015

Multiferroic (BaTiO3-BiFeO3) × 15 multilayer heterostructures show high magnetoelectric (ME) coefficients αME up to 24 V/cm·Oe at 300 K. This value is much higher than that of a single-phase BiFeO3 reference film (αME = 4.2 V/cm·Oe). We found clear correlation of ME coefficients with increasing oxygen partial pressure during growth. ME coupling is highest for lower density of oxygen vacancy-related defects. Detailed scanning transmission electron microscopy and selected area electron diffraction microstructural investigations at 300 K revealed antiphase rotations of the oxygen octahedra in the BaTiO3 single layers, which are an additional correlated defect structure of the multilayers.
Derivation of effective penetration depth of femtosecond laser pulses in metal from ablation rate dependence on laser fluence, incidence angle, and polarization
Authors: Miyasaka Yasuhiro , Hashida Masaki , Nishii Takaya , Inoue Shunsuke , Sakabe Shuji
Published: January 2015

Ablation rate dependence on laser fluence for copper subjected to oblique femtosecond laser irradiation has been determined experimentally in order to investigate processing induced by oblique irradiation. A difference of ablation rate between p-polarized and s-polarized oblique irradiation is clearly observed. Effective penetration depth is defined to explain the ablation rate dependence instead of using optical penetration depth, which is treated as a key value for determining the ablation rate in conventional theory. The effective penetration depth for copper is presented in simple formulas as a function of laser incidence angle for each polarization.
Extraordinary Hall effect and universal scaling in Fex(ZnO)1–x granular thin films at room temperature
Authors: Li Hao-Bo , Liu Mengyin , Lu Feng , Wang Weichao , Cheng Yahui , Song Shutao , Zhang Yan , Li Zhiqing , He Jie , Liu Hui , Du Xiwen , Zheng Rongkun
Published: January 2015

On the benefit of the concept of the so-called diluted magnetic oxides, Fex(ZnO)1–x (x = 0.50–0.85) granular thin films with different thickness through 2D and 3D percolation region were prepared by ion beam assisted deposition. All samples are ferromagnetic at room-temperature due to the ferromagnetic nature of the Fe-doped ZnO matrix, which is quite different from the superparamagnetic behavior in the insulator-matrix based granular films. Along with decreasing thickness, the Hall coefficient RS is largely enhanced. The maximum RS reaches 4.27 × 10−7 m3/C in ∼2.8 nm Fe0.6(ZnO)0.4 granular film, which is nearly 9 times larger than the RS (4.64 × 10−8 m3/C) of the ∼50 nm Fe0.6(ZnO)0.4 sample. Meanwhile, the RS could maintain in a wide temperature region from 10 K to 300 K and the Hall sensitivity reaches ∼130 V/AT at room-temperature. The scaling exponential of n = 1.7 ± 0.1 in σxy∼σxxn is observed, fitting well with the recent developed universal scaling theory characterized by n = 1.6 in the dirty limit.
Large area strain analysis using scanning transmission electron microscopy across multiple images
Authors: Oni A. A. , Sang X. , Raju S. V. , Dumpala S. , Broderick S. , Kumar A. , Sinnott S. , Saxena S. , Rajan K. , LeBeau J. M.
Published: January 2015

Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase.
High-resolution electrohydrodynamic printing of silver nanoparticle ink via commercial hypodermic needles
Authors: Kim Yeongjun , Jang Shin , Oh Je Hoon
Published: January 2015

The effect of the needle shape on electrohydrodynamic (EHD) printing was investigated by comparing flat outlet needles and hypodermic needles. Line fabrication was performed to confirm the tendency of jetting stability and the printed line width with various driving voltage and stage speed by using Ag nanoparticle ink as a jetting solution on a hydrophobic surface. We verified that the hypodermic needle greatly improves the resolution in EHD printing. The ink slips down the inner wall of the hypodermic needle, and a very small meniscus is generated at the tip of the needle. Due to this phenomenon, high-resolution printing can be accomplished. The narrowest line that was fabricated using a hypodermic needle has a line width of 0.7 μm, and it is smaller than 1% of the needle inner diameter.
Atomistic mechanisms governing structural stability change of zinc antimony thermoelectrics
Authors: Yang Xiaolong , Lin Jianping , Qiao Guanjun , Wang Zhao
Published: January 2015

The structural stability of thermoelectric materials is a subject of growing importance for their energy harvesting applications. Here, we study the microscopic mechanisms governing the structural stability change of zinc antimony at its working temperature, using molecular dynamics combined with experimental measurements of the electrical and thermal conductivity. Our results show that the temperature-dependence of the thermal and electrical transport coefficients is strongly correlated with a structural transition. This is found to be associated with a relaxation process, in which a group of Zn atoms migrates between interstitial sites. This atom migration gradually leads to a stabilizing structural transition of the entire crystal framework, and then results in a more stable crystal structure of β–Zn4Sb3 at high temperature.
Low-cost high-haze films based on ZnO nanorods for light scattering in thin c-Si solar cells
Authors: Strano V. , Smecca E. , Depauw V. , Trompoukis C. , Alberti A. , Reitano R. , Crupi I. , Gordon I. , Mirabella S.
Published: January 2015

Light scattering from ZnO nanorods (NR) is investigated, modeled, and applied to a solar cell. ZnO NR (120–1300 nm long, 280–60 nm large), grown by low-cost chemical bath deposition at 90 °C, exhibit diffused-to-total transmitted light as high as 70% and 30% in the 400 and 1000 nm wavelength range, respectively. Data and scattering simulation show that ZnO NR length plays a crucial role in light diffusion effect. A transparent ZnO NR film grown on glass and placed on top of a 1 μm thick c-Si solar cell is shown to enhance the light-current conversion efficiency for wavelengths longer than 600 nm.
Electron scattering in graphene with adsorbed NaCl nanoparticles
Authors: Drabińska Aneta , Kaźmierczak Piotr , Bożek Rafał , Karpierz Ewelina , Wołoś Agnieszka , Wysmołek Andrzej , Kamińska Maria , Pasternak Iwona , Krajewska Aleksandra , Strupiński Włodek
Published: January 2015

In this work, the results of contactless magnetoconductance and Raman spectroscopy measurements performed for a graphene sample after its immersion in NaCl solution were presented. The properties of the immersed sample were compared with those of a non-immersed reference sample. Atomic force microscopy and electron spin resonance experiments confirmed the deposition of NaCl nanoparticles on the graphene surface. A weak localization signal observed using contactless magnetoconductance showed the reduction of the coherence length after NaCl treatment of graphene. Temperature dependence of the coherence length indicated a change from ballistic to diffusive regime in electron transport after NaCl treatment. The main inelastic scattering process was of the electron-electron type but the major reason for the reduction of the coherence length at low temperatures was additional, temperature independent, inelastic scattering. We associate it with spin flip scattering, caused by NaCl nanoparticles present on the graphene surface. Raman spectroscopy showed an increase in the D and D′ bands intensities for graphene after its immersion in NaCl solution. An analysis of the D, D′, and G bands intensities proved that this additional scattering is related to the decoration of vacancies and grain boundaries with NaCl nanoparticles, as well as generation of new on-site defects as a result of the decoration of the graphene surface with NaCl nanoparticles. The observed energy shifts of 2D and G bands indicated that NaCl deposition on the graphene surface did not change carrier concentration, but reduced compressive biaxial strain in the graphene layer.
Growth mechanisms of plasma-assisted molecular beam epitaxy of green emission InGaN/GaN single quantum wells at high growth temperatures
Authors: Yang W. C. , Wu C. H. , Tseng Y. T. , Chiu S. Y. , Cheng K. Y.
Published: January 2015

The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation.
Structural and magnetic properties of epitaxial delafossite CuFeO2 thin films grown by pulsed laser deposition
Authors: Joshi Toyanath , Senty Tess R. , Trappen Robbyn , Zhou Jinling , Chen Song , Ferrari Piero , Borisov Pavel , Song Xueyan , Holcomb Mikel B. , Bristow Alan D. , Cabrera Alejandro L. , Lederman David
Published: January 2015

Growth of pure phase delafossite CuFeO2 thin films on Al2O3 (00.1) substrates by pulsed laser deposition was systematically investigated as a function of growth temperature and oxygen pressure. X-ray diffraction, transmission electron microscopy, Raman scattering, and x-ray absorption spectroscopy confirmed the existence of the delafossite phase. Infrared reflectivity spectra determined a band edge at 1.15 eV, in agreement with the bulk delafossite data. Magnetization measurements on CuFeO2 films demonstrated a phase transition at TC ≈ 15 ± 1 K, which agrees with the first antiferromagnetic transition at 14 K in the bulk CuFeO2. Low temperature magnetic phase is best described by commensurate, weak ferromagnetic spin ordering along the c-axis.
Highly fluorescent silver nanoclusters in alumina-silica composite optical fiber
Authors: Halder A. , Chattopadhyay R. , Majumder S. , Bysakh S. , Paul M. C. , Das S. , Bhadra S. K. , Unnikrishnan M.
Published: January 2015

An efficient visible fluorescent optical fiber embedded with silver nanoclusters (Ag-NCs) having size ∼1 nm, uniformly distributed in alumina-silica composite core glass, is reported. Fibers are fabricated in a repetitive controlled way through modified chemical vapour deposition process associated with solution doping technique. Fibers are drawn from the transparent preforms by conventional fiber drawing process. Structural characteristics of the doped fibers are studied using transmission electron microscopy and electron probe micro analysis. The oxidation state of Ag within Ag-NCs is investigated by X-ray photo electron spectroscopy. The observed significant fluorescence of the metal clusters in fabricated fibers is correlated with electronic model. The experimentally observed size dependent absorption of the metal clusters in fabricated fibers is explained with the help of reported results calculated by ab-initio density functional theory. These optical fibers may open up an opportunity of realizing tunable wavelength fiber laser without the help of rare earth elements.
A robust platform cooled by superconducting electronic refrigerators
Authors: Nguyen H. Q. , Meschke M. , Pekola J. P.
Published: January 2015

A biased tunnel junction between a superconductor and a normal metal can cool the latter electrode. Based on a recently developed cooler with high power and superior performance, we have integrated it with a dielectric silicon nitride membrane, and cooled phonons from 305 mK down to 200 mK. Without perforation and covered under a thin alumina layer, the membrane is rigorously transformed into a cooling platform that is robust and versatile for multiple practical purposes. We discussed our results and possibilities to further improve the device.
Micromachined piezoelectric ultrasonic transducer with ultra-wide frequency bandwidth
Authors: Wang Tao , Kobayashi Takeshi , Lee Chengkuo
Published: January 2015

An ultrasonic transducer with a wide frequency bandwidth is always preferred for diagnostic ultrasound imaging, because a wide frequency bandwidth can reduce the duration of an ultrasonic pulse and enhance the axial imaging resolution. However, the frequency bandwidth of both conventional ultrasonic transducer and normal piezoelectric micromachined ultrasonic transducer (pMUT) is quite limited. To overcome this limitation, the mode-merging pMUT is presented in this letter. By using the rectangular membrane with large length/width aspect ratio, several resonant modes are excited within a narrow frequency range. When this pMUT works in a largely damped medium, excited modes are merged together and result in an ultra-wide bandwidth. A −6 dB bandwidth of 95% is measured in water for the proposed pMUT without matching layer, which is much broader than that of conventional pMUTs. Benefited from such ultra-wide frequency bandwidth, the pulse duration of 1 μs is achieved at a central frequency of 1.24 MHz. If this ultra-wide bandwidth pMUT is utilized to replace the conventional transducer for diagnostic ultrasound imaging, the axial resolution can be significantly enhanced without compromising imaging depth.
Integrated atomistic chemical imaging and reactive force field molecular dynamic simulations on silicon oxidation
Authors: Dumpala Santoshrupa , Broderick Scott R. , Khalilov Umedjon , Neyts Erik C. , van Duin Adri C. T. , Provine J , Howe Roger T. , Rajan Krishna
Published: January 2015

In this paper, we quantitatively investigate with atom probe tomography, the effect of temperature on the interfacial transition layer suboxide species due to the thermal oxidation of silicon. The chemistry at the interface was measured with atomic scale resolution, and the changes in chemistry and intermixing at the interface were identified on a nanometer scale. We find an increase of suboxide (SiOx) concentration relative to SiO2 and increased oxygen ingress with elevated temperatures. Our experimental findings are in agreement with reactive force field molecular dynamics simulations. This work demonstrates the direct comparison between atom probe derived chemical profiles and atomistic-scale simulations for transitional interfacial layer of suboxides as a function of temperature.
Composition- and pressure-induced ferroelectric to antiferroelectric phase transitions in Sm-doped BiFeO3 system
Authors: Xue Fei , Liang Linyun , Gu Yijia , Takeuchi Ichiro , Kalinin Sergei V. , Chen Long-Qing
Published: January 2015

A three-dimensional phenomenological model is proposed to describe both ferroelectricity and antiferroelectricity based on the Ginzburg-Landau-Devonshire theory. Its application to the multiferroic Sm-doped BiFeO3 system describes the temperature-, pressure-, and composition-induced ferroelectric to antiferroelectric phase transitions. The constructed temperature-composition and temperature-pressure phase diagrams show that compressive hydrostatic pressure and Sm doping have similar effects on the ferroelectric and antiferroelectric phase transitions. It is also indicated from the temperature-pressure phase diagram that the experimentally observed phase of BiFeO3 under the hydrostatic pressure from 3 GPa to 10 GPa is a PbZrO3-like antiferroelectric phase.
Hydrogen assisted growth of high quality epitaxial graphene on the C-face of 4H-SiC
Authors: Cai Tuocheng , Jia Zhenzhao , Yan Baoming , Yu Dapeng , Wu Xiaosong
Published: January 2015

We demonstrate hydrogen assisted growth of high quality epitaxial graphene on the C-face of 4H-SiC. Compared with the conventional thermal decomposition technique, the size of the growth domain by this method is substantially increased and the thickness variation is reduced. Based on the morphology of epitaxial graphene, the role of hydrogen is revealed. It is found that hydrogen acts as a carbon etchant. It suppresses the defect formation and nucleation of graphene. It also improves the kinetics of carbon atoms via hydrocarbon species. These effects lead to increase of the domain size and the structure quality. The consequent capping effect results in smooth surface morphology and suppression of multilayer growth. Our method provides a viable route to fine tune the growth kinetics of epitaxial graphene on SiC.
Analysis of subthreshold slope of fully depleted amorphous In-Ga-Zn-O thin-film transistors
Authors: Kawamura Tetsufumi , Uchiyama Hiroyuki , Saito Shinichi , Wakana Hironori , Mine Toshiyuki , Hatano Mutsuko
Published: January 2015

The behavior of the subthreshold slope (SS) of fully depleted (FD) amorphous In-Ga-Zn-O (a-InGaZnO) thin-film transistors (TFTs), which are n-type accumulation mode metal-oxide-semiconductor transistors, was analyzed. Thermal desorption spectra revealed that annealing was necessary to desorb H2 and H2O from the a-InGaZnO films for the FD mode operation along with small SS. Our experimental results indicated that the SS (a) increases with the increase in the thickness of the a-InGaZnO channel layer, (b) increases with the decrease in the oxygen partial pressure during the sputtering of the a-InGaZnO, (c) increases linearly with the increase in the thickness of the gate insulator, and (d) increases linearly with the increase in the temperature of the TFT. A theoretical equation that explains these results was derived by using the relations between the variations in the voltages applied to the electrodes and variations in the surface potentials derived from the charge conservation law. It was assumed during the derivation of the equation that the potential in the channel layer is the lowest along the back surface in the subthreshold region and most of the current flows there.
Ultra-high Q even eigenmode resonance in terahertz metamaterials
Authors: Al-Naib Ibraheem , Yang Yuping , Dignam Marc M. , Zhang Weili , Singh Ranjan
Published: January 2015

We report the simultaneous excitation of the odd and the even eigenmode resonances in a periodic array of square split-ring resonators, with four resonators per unit cell. When the electric field is parallel to their gaps, only the two well-studied odd eigenmodes are excited. As the resonators are rotated relative to one another, we observe the emergence and excitation of an extremely sharp even eigenmode. In uncoupled split-ring resonators, this even eigenmode is typically radiative in nature with a broad resonance linewidth and low Q-factor. However, in our coupled system, for specific range of rotation angles, our simulations revealed a remarkably high quality factor (Q ∼ 100) for this eigenmode, which has sub-radiant characteristics. This type of quad-supercell metamaterial offers the advantage of enabling access to all the three distinct resonance features of the split-ring resonator, which consists of two odd eigenmodes in addition to the high-Q even eigenmode, which could be exploited for high performance multiband filters and absorbers. The high Q even eigenmode could find applications in designing label free bio-sensors and for studying the enhanced light matter interaction effects.
Thickness-dependent metal-insulator transition in epitaxial SrRuO3 ultrathin films
Authors: Shen Xuan , Qiu Xiangbiao , Su Dong , Zhou Shengqiang , Li Aidong , Wu Di
Published: January 2015

Transport characteristics of ultrathin SrRuO3 films, deposited epitaxially on TiO2-terminated SrTiO3 (001) single-crystal substrates, were studied as a function of film thickness. Evolution from a metallic to an insulating behavior is observed as the film thickness decreases from 20 to 4 unit cells. In films thicker than 4 unit cells, the transport behavior obeys the Drude low temperature conductivity with quantum corrections, which can be attributed to weak localization. Fitting the data with 2-dimensional localization model indicates that electron-phonon collisions are the main inelastic relaxation mechanism. In the film of 4 unit cells in thickness, the transport behavior follows variable range hopping model, indicating a strongly localized state. Magnetoresistance measurements reveal a likely magnetic anisotropy with the magnetic easy axis along the out-of-plane direction.
Temperature dependence of microwave oscillations in magnetic tunnel junctions with a perpendicularly magnetized free layer
Authors: Guo Peng , Feng Jiafeng , Wei Hongxiang , Han Xiufeng , Fang Bin , Zhang Baoshun , Zeng Zhongming
Published: January 2015

We experimentally study the temperature dependence of the spin-transfer-torque-induced microwave oscillations in MgO-based magnetic tunnel junction nanopillars with a perpendicularly magnetized free layer. We demonstrate that the oscillation frequency increases rapidly with decreasing temperature, which is mainly ascribed to the temperature dependence of both the saturation magnetization and the perpendicular magnetic anisotropy. We also find that a strong temperature dependence of the output power while a nonmonotonic temperature dependence of spectral linewidth are maintained for a constant dc bias in measured temperature range. Possible mechanisms leading to the different dependences of oscillation frequency, output power, and linewidth are discussed.
Landau level crossing in a spin-orbit coupled two-dimensional electron gas
Authors: Wu Xing-Jun , Li Ting-Xin , Zhang Chi , Du Rui-Rui
Published: January 2015

We have studied experimentally the Landau level (LL) spectrum of a two-dimensional electron gas (2DEG) in an In0.53Ga0.47As/InP quantum well structure by means of low-temperature magneto-transport coincidence measurement in vector magnetic fields. It is well known that LL crossing occurs in tilted magnetic fields due to a competition between cyclotron energy and Zeeman effect. Remarkably, here we observe an additional type of level-crossing resulting from a competition between Rashba and Zeeman splitting in a small magnetic field, consistent with the theoretical prediction for strongly spin-orbit coupled 2DEG.
Stable and efficient multi-crystalline n+p silicon photocathode for H2 production with pyramid-like surface nanostructure and thin Al2O3 protective layer
Authors: Fan Ronglei , Dong Wen , Fang Liang , Zheng Fengang , Su Xiaodong , Zou Shuai , Huang Jie , Wang Xusheng , Shen Mingrong
Published: January 2015

When a Si photocathode is used in a photoelectrochemical cell for H2 production, an open nanostructure capable of enhanced light absorption, low surface recombination, and being fully protected by thin protective layer is highly desirable. Here, we explored a highly stable and efficient multi-crystalline (mc) n+p silicon photocathode. A pyramid-like surface nanostructure on mc-Si wafer was fulfilled through a two-step metal-catalyzed chemical etching process, and then a n+p junction photocathode protected by a thin Al2O3 layer was constructed. The photocathode exhibits a high stability of continuous photoelectrochemical H2 production for above 100 h after a thin layer of Al2O3 is coated on its surface, and its energy conversion efficiency can be up to 6.8% after Pt loading, due to the lowered surface light reflection, increased surface area and minority carrier life time on the electrode surface.
Electrostatic supersolitons and double layers at the acoustic speed
Authors: Verheest Frank , Hellberg Manfred A.
Published: January 2015

Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.
Modification of modulated plasma plumes for the quasi-phase-matching of high-order harmonics in different spectral ranges
Authors: Ganeev R. A. , Boltaev G. S. , Sobirov B. , Reyimbaev S. , Sherniyozov H. , Usmanov T. , Suzuki M. , Yoneya S. , Kuroda H.
Published: January 2015

We demonstrate the technique allowing the fine tuning of the distance between the laser-produced plasma plumes on the surfaces of different materials, as well as the variation of the sizes of these plumes. The modification of plasma formations is based on the tilting of the multi-slit mask placed between the heating laser beam and target surface, as well as the positioning of this mask in the telescope placed on the path of heating radiation. The modulated plasma plumes with the sizes of single plume ranging between 0.1 and 1 mm were produced on the manganese and silver targets. Modification of the geometrical parameters of plasma plumes proved to be useful for the fine tuning of the quasi-phase-matched high-order harmonics generated in such structures during propagation of the ultrashort laser pulses. We show the enhancement of some groups of harmonics along the plateau range and the tuning of maximally enhanced harmonic by variable modulation of the plasma.
Tuning the structural and magnetocaloric properties of Gd5Si2Ge2 with Nd substitution
Authors: Uthaman Bhagya , Raji G. R. , Thomas Senoy , Suresh K. G. , Varma Manoj Raama
Published: January 2015

Structural and magnetocaloric properties of Nd substituted Gd5−xNdxSi2Ge2 with x = 0.05, 0.1, and 0.2 have been investigated. The composition with x = 0.05 crystallizes in monoclinic Gd5Si2Ge2 structure with P1121/a space group and undergoes a first order phase transition with a Curie temperature of 275 K. With increase in Nd content to x = 0.1, the compound is found to stabilize in orthorhombic Gd5Si4 phase with Pnma space group. The compounds with x = 0.1 and 0.2 undergoes a second order magnetic transition at 300 K and 293 K, respectively. Temperature variation of maximum entropy change for Gd5−xNdxSi2Ge2 alloys with x = 0.05, 0.1, and 0.2 are 7.9, 3.7, and 3.2 J/kg K, respectively, for a field change of 20 kOe, and 12.8, 7.6, and 7.2 J/kg K, respectively, for 50 kOe. A large relative cooling power of 295, 205, and 188 J/kg are obtained for x = 0.05, 0.1, and 0.2, respectively, fulfilling the required criteria for a potential magnetic refrigerant in the room temperature regime.
Achieving high strength and high electrical conductivity in Ag/Cu multilayers
Authors: Wei M. Z. , Xu L. J. , Shi J. , Pan G. J. , Cao Z. H. , Meng X. K.
Published: January 2015

In this work, we investigated the microstructure evolution of Ag/Cu multilayers and its influences on the hardness and electric resistivity with individual layer thickness (h) ranging from 3 to 50 nm. The hardness increases with the decreasing h in the range of 5–20 nm. The barrier to dislocation transmission by stacking faults, twin boundaries, and interfaces leads to hardness enhancement. Simultaneously, in order to get high conductivity, the strong textures in-layers were induced to form for reducing the amount of grain boundaries. The resistivity keeps low even when h decreases to 10 nm. Furthermore, we developed a facile model to evaluate the comprehensive property of Ag/Cu multilayers—the results indicate that the best combination of strength and conductivity occurs when h = 10 nm.
Identification of the interstitial Mn site in ferromagnetic (Ga,Mn)As
Authors: Lima T. A. L. , Wahl U. , Augustyns V. , Silva D. J. , Costa A. , Houben K. , Edmonds K. W. , Gallagher B. L. , Campion R. P. , Van Bael M. J. , da Silva M. R. , Correia J. G. , Araújo J. P. , Temst K. , Vantomme A. , Pereira L. M. C.
Published: January 2015

We determined the lattice location of Mn in ferromagnetic (Ga,Mn)As using the electron emission channeling technique. We show that interstitial Mn occupies the tetrahedral site with As nearest neighbors (TAs) both before and after thermal annealing at 200 °C, whereas the occupancy of the tetrahedral site with Ga nearest neighbors (TGa) is negligible. TAs is therefore the energetically favorable site for interstitial Mn in isolated form as well as when forming complexes with substitutional Mn. These results shed new light on the long standing controversy regarding TAs versus TGa occupancy of interstitial Mn in (Ga,Mn)As.
Effectiveness of clinical supervision of physiotherapists: a survey
Authors: Snowdon David A. , Millard Geraldine , Taylor Nicholas F.
Published: January 2015

Objectives
Limited literature exists on the practice of clinical supervision (CS) of professional physiotherapists despite current Australian safety and quality health standards stating that CS is to be provided to all physiotherapists. The aim of the present study was to evaluate the effectiveness of CS of physiotherapists working in an Australian public health service.

Methods
CS was measured using the allied health-specific 26-item modified Manchester Clinical Supervision Scale (MCSS-26). Subscales of the MCSS-26 were summed for three domain scores (normative, restorative and formative) and a total score was calculated, which was compared with the reported threshold score of 73 for effective supervision. Sixty registered physiotherapists (response rate 92%), working for a large metropolitan public health service, with six different site locations, completed the survey.

Results
The mean (± s.d.) total MCSS-26 score was 71.0 ± 14.3 (95% confidence interval (CI) 67.4–74.6). Hospital site was the only variable that had a significant effect on total MCSS-26 score (P = 0.005); there was no effect for supervisor or supervisee experience, or hospital setting (acute vs subacute). Physiotherapists scored a significantly lower mean percentage MCSS-26 score on the normative domain compared with the restorative domain (mean difference 7.8%; 95% CI 2.9–12.7; P = 0.002) and the formative domain (mean difference 9.6%; 95% CI 6.3–13.0; P < 0.001). Of the two subscales that form the normative domain, ‘finding time’ had a significantly lower mean percentage MCSS-26 score than ‘importance/value of CS’ (mean difference 35.4%; 95% CI 31.3–39.4; P < 0.001).

Conclusions
Within this publicly funded physiotherapy department there was uncertainty about the effectiveness of CS, with more than half the physiotherapists rating their supervision as less than effective, suggesting there is opportunity for improvement in the practice of physiotherapy CS. Physiotherapists scored lowest in the normative domain, indicating that they found it difficult to find time for CS.

What is known about the topic?
Previous research into CS for allied health professionals has shown that, on average, it is effective. However, these results cannot be generalised to specific allied health disciplines. Currently, the effectiveness of CS for physiotherapists is unknown.

What does this paper add?
This study is the first to investigate the effectiveness of CS in a large physiotherapy department of a publicly funded Australian healthcare service.

What are the implications for practitioners?
Requiring all physiotherapists to receive CS may not be useful if supervision is not effective. Finding time for CS appears to be the main barrier to effective CS. Focus should be directed towards developing a framework within which to practice CS that includes protected time for participation in CS.
Demographics and discharge outcomes of dysvascular and non-vascular lower limb amputees at a subacute rehabilitation unit: a 7-year series
Authors: Batten Heather R. , Kuys Suzanne S. , McPhail Steven M. , Varghese Paulose N. , Nitz Jennifer C.
Published: January 2015

Objective To examine personal and social demographics, and rehabilitation discharge outcomes of dysvascular and non-vascular lower limb amputees. Methods In total, 425 lower limb amputation inpatient rehabilitation admissions (335 individuals) from 2005 to 2011 were examined. Admission and discharge descriptive statistics (frequency, percentages) were calculated and compared by aetiology. Results Participants were male (74%), aged 65 years (s.d. 14), born in Australia (72%), had predominantly dysvascular aetiology (80%) and a median length of stay 48 days (interquartile range (IQR): 25–76). Following amputation, 56% received prostheses for mobility, 21% (n = 89) changed residence and 28% (n = 116) required community services. Dysvascular amputees were older (mean 67 years, s.d. 12 vs 54 years, s.d. 16; P < 0.001) and recorded lower functional independence measure – motor scores at admission (z = 3.61, P < 0.001) and discharge (z = 4.52, P < 0.001). More non-vascular amputees worked before amputation (43% vs 11%; P < 0.001), were prescribed a prosthesis by discharge (73% vs 52%; P < 0.001) and had a shorter length of stay (7 days, 95% confidence interval: –3 to 17), although this was not statistically significant. Conclusions Differences exist in social and demographic outcomes between dysvascular and non-vascular lower limb amputees. What is known about the topic? Lower limb amputation occurs due to various aetiologies. What does this paper add? Lower limb amputee rehabilitation over 7 years was investigated, comprising 425 admissions, 80% due to dysvascular aetiology. Personal and social demographics, and discharge outcomes are compared by aetiology. What are the implications for practitioners? Demographic and discharge outcome differences exist between dysvascular and non-vascular lower limb amputees. Twenty-one percent were required to change residence and 28% required additional social supports. Discharge planning should begin as soon as possible to limit time spent waiting for new accommodation or major modifications for current homes. Lower limb amputees are not homogeneous, so care should be taken if extrapolating from combined amputee aetiologies or from one aetiology to another.