bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo study of electron-beam penetration and backscattering in multi-walled carbon nanotube materials: The effect of different scattering models
Authors: Kyriakou Ioanna , Emfietzoglou Dimitris , Nojeh Alireza , Moscovitch Marko
Published: February 2013

A systematic study of electron-beam penetration and backscattering in multi-walled carbon nanotube (MWCNT) materials for beam energies of ∼0.3 to 30 keV is presented based on event-by-event Monte Carlo simulation of electron trajectories using state-of-the-art scattering cross sections. The importance of different analytic approximations for computing the elastic and inelastic electron-scattering cross sections for MWCNTs is emphasized. We offer a simple parameterization for the total and differential elastic-scattering Mott cross section, using appropriate modifications to the Browning formula and the Thomas-Fermi screening parameter. A discrete-energy-loss approach to inelastic scattering based on dielectric theory is adopted using different descriptions of the differential cross section. The sensitivity of electron penetration and backscattering parameters to the underlying scattering models is examined. Our simulations confirm the recent experimental backscattering data on MWCNT forests and, in particular, the steep increase of the backscattering yield at sub-keV energies as well as the sidewalls escape effect at high-beam energies.
Seiberg-Witten equations and non-commutative spectral curves in Liouville theory
Authors: Chekhov Leonid , Eynard Bertrand , Ribault Sylvain
Published: February 2013

We propose that there exist generalized Seiberg-Witten equations in the Liouville conformal field theory, which allow the computation of correlation functions from the resolution of certain Ward identities. These identities involve a multivalued spin one chiral field, which is built from the energy-momentum tensor. We solve the Ward identities perturbatively in an expansion around the heavy asymptotic limit, and check that the first two terms of the Liouville three-point function agree with the known result of Dorn, Otto, Zamolodchikov, and Zamolodchikov. We argue that such calculations can be interpreted in terms of the geometry of non-commutative spectral curves.
An energy-efficient readout circuit for resonant sensors based on ring-down measurement
Authors: Zeng Z. , Pertijs M. A. P. , Karabacak D. M.
Published: February 2013

This paper presents an energy-efficient readout circuit for resonant sensors that operates based on a transient measurement method. The resonant sensor is driven at a frequency close to its resonance frequency by an excitation source that can be intermittently disconnected, causing the sensor to oscillate at its resonance frequency with exponentially decaying amplitude. By counting the zero crossings of this ring-down response, the interface circuit can detect the resonance frequency. In contrast with oscillator-based readout, the presented readout circuit is readily able to detect quality factor (Q) of the resonator from the envelope of the ring-down response, and can be used even in the presence of large parasitic capacitors. A prototype of the readout circuit has been integrated in 0.35 μm CMOS technology, and consumes only 36 μA from a 3.3 V supply during a measurement time of 2 ms. The resonance frequency and quality factor of a micro-machined SiN resonator obtained using this prototype are in good agreement with results obtained using impedance analysis. Furthermore, a clear transient response is observed to ethanol flow using the presented readout, demonstrating the use of this technique in sensing applications.
$\mathcal {CPT}$
CPT
-conserved effective mass Hamiltonians through first and higher order charge operator $\mathcal {C}$C in a supersymmetric framework
Authors: Bagchi B. , Banerjee A. , Ganguly A.
Published: February 2013

This paper examines the features of a generalized position-dependent mass Hamiltonian Hm in a supersymmetric framework in which the constraints of pseudo-Hermiticity and \documentclass[12pt]{minimal}\begin{document}$\mathcal {CPT}$\end{document}CPT are naturally embedded. Different representations of the charge operator are considered that lead to new mass-deformed superpotentials \documentclass[12pt]{minimal}\begin{document}$\mathcal {W}_{m}(x)$\end{document}Wm(x) which are inherently \documentclass[12pt]{minimal}\begin{document}${\mathcal {PT}}$\end{document}PT-symmetric. The qualitative spectral behavior of Hm is studied and several interesting consequences are noted.
Non-polar p-type Zn0.94Mn0.05Na0.01O texture: Growth mechanism and codoping effect
Authors: Zhang L. Q. , Lu B. , Lu Y. H. , Ye Z. Z. , Lu J. G. , Pan X. H. , Huang J. Y.
Published: February 2013

The microstructure and crystal orientations of polycrystalline films crucially affect the properties and performance of the films. Controlling preferred orientations (PO) and related film morphology are necessary to obtain the desirable properties. In this paper, we demonstrate a rational and effective route toward the realization of non-polar p-type ZnO thin film with surface texture on quartz substrate through Mn-Na codoping. It is uncovered experimentally and theoretically that mono-doping of Mn creates opportunity to realize PO from polar (c-axis) to non-polar ((101¯0), (101¯1), and (112¯0)) changing. With Mn-Na codoping, an acute modulation of the growth behavior and electrical conductivity of the film have been revealed, leading to weak p-type non-polar Zn0.94Mn0.05Na0.01O (ZMNO) texture. The dominant mechanism for the non-polar self-texture in the current paper is deliberately elucidated as resulting from the interplane surface diffusion with the cooperative effect of impurity dopants. The ZMNO films exhibit p-type conduction with hole concentration of 9.51 × 1015–1.86 × 1017 cm−3 and enhanced room temperature (RT) ferromagnetism possessing a saturation magnetization (Ms) of 1.52 μB/Mn. The results have potential applications in development of non-polar optoelectronic devices such as lighting emitting diodes (LEDs).
Sudden switchover between the polyamorphic phase separation and the glass-to-liquid transition in glassy LiCl aqueous solutions
Authors: Suzuki Yoshiharu , Mishima Osamu
Published: February 2013

Lithium chloride aqueous solutions (LiClaq solutions) below 10 mol.% are vitrified by cooling from room temperature to 77 K at 0.3 GPa. We examine the solvent state of the glassy sample and its transformation by heating at 1 atm using low-temperature differential scanning calorimetry and Raman spectroscopy. This experimental study suggests strongly that the solvent state of the glassy LiClaq solution closely relates to the state of high-density amorphous ice. Moreover, we reconfirm that the separation into the low-density amorphous ice and the glassy highly concentrated LiClaq solution occurs in the glassy dilute LiClaq solution at ∼130 K, not the glass-to-liquid transition which is commonly observed in the glassy LiClaq solution above ∼10 mol.%. In order to interpret the sudden switchover between the glass-to-liquid transition and the phase separation at ∼10 mol.%, we propose a state diagram of LiClaq solution which connects with a polyamorphic state diagram of pure water and discuss a possibility that the electric field induces a polyamorphic transition of water.
On the structures and bonding in boron-gold alloy clusters: B6Aun− and B6Aun (n = 1−3)
Authors: Chen Qiang , Zhai Hua-Jin , Li Si-Dian , Wang Lai-Sheng
Published: February 2013

Photoelectron spectroscopy and density-functional theory are combined to investigate the electronic and structural properties of a series of B−Au alloy clusters: B6Aun− and B6Aun (n = 1−3). Rich spectral features are observed for each species, and vibrational structures are resolved for numerous detachment transitions of B6Au− and B6Au2−. Electron affinities of B6Aun (n = 1−3) are evaluated to be 2.70 ± 0.03, 2.91 ± 0.02, and 3.21 ± 0.05 eV, respectively. Global structural searches are performed for both the anions and their neutrals. The calculated electronic binding energies are compared with experimental measurements to establish the anion global-minimum structures and their corresponding neutral states. The ground-state structures of these clusters are shown to be planar or quasi-planar with an elongated B6 core, to which the first and second Au atoms are bonded terminally and the third Au in a bridging position. All three anion clusters are π antiaromatic. Natural bond orbital analyses show that the B−Au bonding is highly covalent, providing new examples for the Au/H analogy in Au alloy clusters.
A method to remove odd harmonic interferences in square wave reference digital lock-in amplifier
Authors: Li Gang , Zhang Shengzhao , Zhou Mei , Li Yongcheng , Lin Ling
Published: February 2013

Digital lock-in amplifier using square wave reference is much easier to be implemented compared to digital lock-in amplifier using sinusoidal wave reference. However, because of the odd harmonics containing in the square wave reference, the interferences at the odd harmonics of the reference cannot be removed with conventional algorithm. A new square wave digital lock-in algorithm is presented in this paper. It cannot only be capable of removing the interferences of the odd harmonics in the signal, but also can detect the amplitudes and the phases of the interferences. The real and imaginary parts of the frequency component of interest and those of the odd harmonic interferences are calculated simultaneously. The results of simulation experiments show the feasibility of the proposed algorithm. The algorithm is computationally efficient and thus suitable for weak signal detection implemented in the general microprocessor.
Systematic expansion in the order parameter for replica theory of the dynamical glass transition
Authors: Jacquin Hugo , Zamponi Francesco
Published: February 2013

It has been shown recently that predictions from mode-coupling theory for the glass transition of hard-spheres become increasingly bad when dimensionality increases, whereas replica theory predicts a correct scaling. Nevertheless if one focuses on the regime around the dynamical transition in three dimensions, mode-coupling results are far more convincing than replica theory predictions. It seems thus necessary to reconcile the two theoretic approaches in order to obtain a theory that interpolates between low-dimensional, mode-coupling results, and “mean-field” results from replica theory. Even though quantitative results for the dynamical transition issued from replica theory are not accurate in low dimensions, two different approximation schemes—small cage expansion and replicated hyper-netted-chain (RHNC)—provide the correct qualitative picture for the transition, namely, a discontinuous jump of a static order parameter from zero to a finite value. The purpose of this work is to develop a systematic expansion around the RHNC result in powers of the static order parameter, and to calculate the first correction in this expansion. Interestingly, this correction involves the static three-body correlations of the liquid. More importantly, we separately demonstrate that higher order terms in the expansion are quantitatively relevant at the transition, and that the usual mode-coupling kernel, involving two-body direct correlation functions of the liquid, cannot be recovered from static computations.
The toluene-Ar complex: S and S1 van der Waals modes, changes to methyl rotation, and torsion-van der Waals vibration coupling
Authors: Gascooke Jason R. , Lawrance Warren D.
Published: February 2013

The methyl rotor and van der Waals vibrational levels in the S1 and S0 states of toluene-Ar have been investigated by the technique of two-dimensional laser induced fluorescence (2D-LIF). The S0 van der Waals and methyl rotor levels are reported for the first time, while improved S1 values are presented. The correlations seen in the 2D-LIF images between the S0 and S1 states lead to a reassignment of key features in the S1 ← S0 excitation spectrum. This reassignment reveals that there are significant changes in the methyl rotor levels in the complex compared with those in bare toluene, particularly at low m. The observed rotor energies are explained by the introduction of a three-fold, V3, term in the torsion potential (this term is zero in toluene) and a reduction in the height of the six-fold, V6, barriers in S0 and S1 from their values in bare toluene. The V3 term is larger in magnitude than the V6 term in both S0 and S1. The constants determined are |V3(S1)| = 33.4 ± 1.0 cm−1, |V3(S0)| = 20.0 ± 1.0 cm−1, V6(S1) = −10.7 ± 1.0 cm−1, and V6(S0) = −1.7 ± 1.0 cm−1. The methyl rotor is also found to couple with van der Waals vibration; specifically, the m″ = 2 rotor state couples with the combination level involving one quantum of the long axis bend and m″ = 1. The coupling constant is determined to be 1.9 cm−1, which is small compared with the values typically reported for torsion-vibration coupling involving ring modes.
Spin-polarized state quantum filter used to measure spin-polarized state relaxation time and g-factor
Authors: Makarov Vladimir I. , Khmelinskii Igor
Published: February 2013

A novel method for measurement of g-factor and spin-lattice relaxation time of spin-polarized states in nano-layers of different chemical nature was developed. This method is based on usage of spin-polarized state quantum filter, which was created and tested earlier [V. I. Makarov et al., J Appl. Phys. 110, 063717 (2011) and V. I. Makarov et al., J Appl. Phys. 112, 084310 (2012). The spin state parameters were measured in nanolayers of different materials (Fe, Au, and Si) in function of such experimental parameters as the layer thickness and temperature. The phenomenological model developed earlier for steady-state conditions was presently extended to include time dependence and successfully used in the data analysis. Qualitative models were proposed that explain the observed dependences, forming the basis for future theoretical developments.
Evolution of nickel silicide intrusions in silicon nanowires during thermal cycling
Authors: Katsman Alex , Beregovsky Michael , Yaish Yuval E.
Published: February 2013

Thermally activated axial intrusion of nickel silicides into a silicon nanowire (NW) from pre-patterned Ni reservoirs is used in formation of nickel silicide/silicon contacts in SiNW field effect transistors. This intrusion consists usually of different nickel silicides which grow simultaneously during thermal annealing. Repeated annealing is often accompanied by local thickening and tapering of the NW, up to full disintegration of the silicide segment adjacent to Si. In the present work this process was investigated for SiNWs of various diameters in between 30 and 60 nm with pre-patterned Ni electrodes after a series of rapid thermal cycles including heating, holding at different temperatures of 400-440 °C for 5-15 s and cooling to room temperature. Kinetics of the nickel silicides axial growth was analyzed in the framework of diffusion model. This model is taking into account simultaneous formation of different nickel silicide phases and balance between transition of Ni atoms from the Ni reservoir to the NW surface, diffusion transport of these Ni atoms to the interfaces between different silicides and silicide/Si interface, and corresponding reactions of the nickel silicides' formation. Additional flux of atoms caused by the NW curvature gradients due to different radii of different silicide phases was taken into account. For a certain set of parameters thickening of the nickel-rich silicide intrusion and tapering of the monosilicide part of intrusion were obtained.
Unconfined slumping of a granular mass on a slope
Authors: Maeno Fukashi , Hogg Andrew J. , Sparks R. Stephen J. , Matson Gary P.
Published: February 2013

This study investigates the gravitationally driven dynamics of dense granular materials, released from rest and allowed to flow down a slope until they stop moving. Laboratory experiments were performed in which a measured volume of material was released from rest in a cylindrical tube and spread across an unconfined rigid plane inclined at angles less than the angle of repose. Upon release, the particles initially spread outward radially. However, up-slope motion is rapidly suppressed while down-slope motion is promoted, which leads to an approximately ellipsoidally shaped deposit once the flow has been fully arrested. The flows were modeled under the shallow layer approximation and integrated numerically to capture the motion from initiation to final arrest. In modeling, two types of Coulomb-type friction models were employed. One had a constant friction coefficient, and another had a friction coefficient that depends upon the dimensionless inertial number of the motion. When the initial aspect ratio of a granular mass is small and the slope angle is low (<5°), the model with a constant friction coefficient can capture the shape of the deposit. However, when the slope angle is increased, the friction model that is dependent on inertial number becomes more important. For granular columns of initially high aspect ratios, the shallow water model fails to reproduce some aspects of the experimental observations. Finally, the dependence of the shape and depth of the deposit upon dimensionless parameters that characterize the system is examined under the constant friction coefficient model, demonstrating that the deduced scaling arguments are borne out by the numerical simulations and laboratory data.
Dimensionality and heat transport in Si-Ge superlattices
Authors: Savić Ivana , Donadio Davide , Gygi François , Galli Giulia
Published: February 2013

We investigated how dimensionality affects heat transport in Si-Ge superlattices (SLs) by computing the thermal conductivity of planar superlattices and arrays of Ge nanowires (NWs) and nanodots embedded in Si. We studied superlattices with ∼10 nm periods using a fully atomistic Monte Carlo solution of the Boltzmann transport equation in the relaxation time approximation. We found that for periods larger than 4 nm, the room temperature cross-plane conductivity of planar superlattices with equally thick Si and Ge layers is larger than that of their nanowire and dot counterparts of similar sizes (up to 100%), while the trend is reversed below 4 nm.
Strong correlation of atomic thermal motion in the first coordination shell of a Cu-Zr metallic glass
Authors: Zhang Y. , Mattern N. , Eckert J.
Published: February 2013

We demonstrate a strong correlation of atomic thermal motions in the first coordination shell of Cu50Zr50 metallic glass using molecular dynamics simulations, which explains directly the small thermal expansion coefficient calculated by the first maxima of pair correlation functions. The vibrational anisotropy in the glass is found to be even higher than in crystalline copper. The parallel-perpendicular anisotropy gradually decreases upon heating. The anisotropy in Zr–Zr is the strongest bonds among all the interatomic bonds, which is also very stable near the glass transition at 700 K. Structurally, the anisotropy can be correlated to Cu-centered (0 2 8 1) clusters.
Guest host interaction and low energy host structure dynamics in tin clathrates
Authors: Christensen Sebastian , Bjerg Lasse , Kaltzoglou Andreas , Juranyi Fanni , Fässler Thomas , Unruh Tobias , Christensen Mogens
Published: February 2013

The two binary clathrates with vacancies (□) Rb8Sn44□2 and Cs8Sn44□2 have been examined using powder inelastic neutron scattering (INS). Rattling energies of Rb and Cs are found to be similar by both experiment and calculations, ℏωCs/ℏωRb|Exp.=0.98(1) and ℏωCs/ℏωRb|Calc.=1.0, despite the significant mass difference: mCs/mRb=1.6, which shows that guest-host interaction is non-negligible for the studied system. For Rb8Sn44□2, a low energy phonon mode is observed at ≈3.5 meV, below the phonon mode which in the literature is attributed to the guest atom. The 3.5 meV mode is interpreted to have significant spectral weight of Sn host atoms based on temperature dependence and comparison with published theoretical phonon calculations. The record of low thermal conductivity of the tin clathrates can be attributed to the host structure dynamics rather than the guest atom rattling.
Fabrication of high-aspect-ratio double-slot photonic crystal waveguide in InP heterostructure by inductively coupled plasma etching using ultra-low pressure
Authors: Cui Kaiyu , Li Yongzhuo , Feng Xue , Huang Yidong , Zhang Wei
Published: February 2013

Double-slot photonic crystal waveguide (PCW) in InP heterostructure is fabricated by inductively coupled plasma (ICP) etching. Due to using an ultra-low pressure of 0.05 Pa, etch depths up to 3.5 μm for holes with diameter of 200 nm and 1.8 μm for slots of ∼40 nm are achieved, which indicate a record-high aspect-ratio, i.e. 45, for such narrow slots in InP heterostructure. Moreover, etching quality is evaluated based on both the transmission performance and the linewidth of micro-photoluminescence (μ-PL). In our measurement, a structure-dependent transmission-dip about 17 dB is obtained from a 17-μm-long W3 PCW, and a PL widening as small as 19 nm compared to the corresponding wafer is observed. These promising experimental results evidence the high etching quality realized in this work and confirm the feasibility of etching small-feature-size patterns by ICP technology for InP based devices in future mono-/hetero-integrated photonic circuits.
Cross-plane thermal properties of transition metal dichalcogenides
Authors: Muratore C. , Varshney V. , Gengler J. J. , Hu J. J. , Bultman J. E. , Smith T. M. , Shamberger P. J. , Qiu B. , Ruan X. , Roy A. K. , Voevodin A. A.
Published: February 2013

In this work, we explore the thermal properties of hexagonal transition metal dichalcogenide compounds with different average atomic masses but equivalent microstructures. Thermal conductivity values of sputtered thin films were compared to bulk crystals. The comparison revealed a >10 fold reduction in thin film thermal conductivity. Structural analysis of the films revealed a turbostratic structure with domain sizes on the order of 5–10 nm. Estimates of phonon scattering lengths at domain boundaries based on computationally derived group velocities were consistent with the observed film microstructure, and accounted for the reduction in thermal conductivity compared to values for bulk crystals.
Structure, magnetic, and electronic properties of hydrogenated two-dimensional diamond films
Authors: Li Jia , Li Hongdong , Wang Zhigang , Zou Guangtian
Published: February 2013

In this paper, we study the effects of semi-hydrogenation (SH) and full-hydrogenation (FH) on the structural evolution and properties of two-dimensional (2D) diamond nanofilms by first-principles calculations. Both the hydrogenation processes play an important role in stabilizing the 2D diamond structures. For the FH cases, the direct bandgaps are localized in the region of 2.54–3.55 eV and decreased following an inverse law with layer number (n). For the SH cases, a ferrimagnetism characteristic is presented determining by the unpaired electrons on the un-hydrogenated side, and the spin-related bandgaps are in an infrared region of 0.74–1.17 eV, which are strongly dependent on n. As a result, the hydrogenation is favorable for tuning the electronic and magnetic properties of 2D diamond nanofilms to achieve high performance diamond-based nanodevices.
Development of a cold-neutron imaging detector based on thick gaseous electron multiplier
Authors: Cortesi M. , Zboray R. , Kaestner A. , Prasser H.-M.
Published: February 2013

We present the results of our recent studies on a cold-neutron imaging detector prototype based on THick Gaseous Electron Multiplier (THGEM). The detector consists of a thin Boron layer, for neutron-to-charged particle conversion, coupled to two THGEM electrodes in cascade for charge amplification and a position-sensitive charge-readout anode. The detector operates in Ne/(5%)CF4, at atmospheric pressure, in a stable condition at a gain of around 104. Due to the geometrical structure of the detector elements (THGEM geometry and charge read-out anode), the image of detector active area shows a large inhomogeneity, corrected using a dedicated flat-filed correction algorithm. The prototype provides a detection efficiency of 5% and an effective spatial resolution of the order of 1.3 mm.
Demonstration of glass transition temperature shift in thin supported polystyrene films by internal reference method
Authors: Efremov Mikhail Yu. , Thode Christopher , Nealey Paul F.
Published: February 2013

An internal reference method is used for the first time to clearly demonstrate the glass transition temperature (Tg) depression effect in 5 nm thick polystyrene films spin-cast on silicon wafers. Initially flat films exhibit depressed Tg at approximately 85 °C. Temperature-induced dewetting on hexamethyldisilazane-treated silicon substrates leads to formation of discontinuous films with average effective thickness of 15–30 nm. Dewetted films demonstrate Tg close to the bulk value (≈ 100 °C) and are used as internal references. Data both for continuous and discontinuous films are obtained in the same experimental run for the same sample, which allows direct comparison between datasets. Phase-modulated ellipsometry in vacuum is used to monitor glass transition. Both traditional linear temperature scan method and a novel temperature modulated technique have been employed in the measurements.
A high sensitivity fiber optic macro-bend based gas flow rate transducer for low flow rates: Theory, working principle, and static calibration
Authors: Schena Emiliano , Saccomandi Paola , Silvestri Sergio
Published: February 2013

A novel fiber optic macro-bend based gas flowmeter for low flow rates is presented. Theoretical analysis of the sensor working principle, design, and static calibration were performed. The measuring system consists of: an optical fiber, a light emitting diode (LED), a Quadrant position sensitive Detector (QD), and an analog electronic circuit for signal processing. The fiber tip undergoes a deflection in the flow, acting like a cantilever. The consequent displacement of light spot center is monitored by the QD generating four unbalanced photocurrents which are function of fiber tip position. The analog electronic circuit processes the photocurrents providing voltage signal proportional to light spot position. A circular target was placed on the fiber in order to increase the sensing surface. Sensor, tested in the measurement range up to 10 l min−1, shows a discrimination threshold of 2 l min−1, extremely low fluid dynamic resistance (0.17 Pa min l−1), and high sensitivity, also at low flow rates (i.e., 33 mV min l−1 up to 4 l min−1 and 98 mV min l−1 from 4 l min−1 up to 10 l min−1). Experimental results agree with the theoretical predictions. The high sensitivity, along with the reduced dimension and negligible pressure drop, makes the proposed transducer suitable for medical applications in neonatal ventilation.
Photoluminescence study of Y2O3:Er3+-Eu3+-Yb3+ phosphor for lighting and sensing applications
Authors: Kumar Rai Vineet , Pandey Anurag , Dey Riya
Published: February 2013

The Er3+, Eu3+, and Yb3+ codoped Y2O3 phosphors have been synthesized by combustion synthesis process. For the structural information, the XRD analysis of the developed phosphor has been done. The frequency upconversion (UC) emissions in the codoped Y2O3 phosphor on excitation with 980 nm diode laser in the visible region have been performed and explained on the basis of excited state absorption and energy transfer process. The mechanism responsible in UC emissions was observed to involve two photon absorption and efficiency of the UC luminescence is significantly enhanced by introducing the Yb3+ ions. The tunability in colour of emitted radiation has been visualized by chromaticity diagram on increasing power of excitation source. The temperature sensing behaviour of developed phosphor material has been investigated using fluorescence intensity ratio technique.
Electron-spin-resonance of Gd3+ ions in Y1−xGdxBaCo2O5 (x = 0.01, 0.25, and 1)
Authors: Fang Jun , Wu Na , Tong Wei , Ling Langsheng , Zhang Lei , Xi Chuanying , Pi Li , Sun Yuping , Zhang Yuheng
Published: February 2013

While charge-ordering transition is well established in the oxygen-deficient layered cobaltite YBaCo2O5, there has been no evidence for the transition in the analogous compound GdBaCo2O5 either from neutron diffraction or from magnetic susceptibility experiments. In this paper, we present comparative studies on the electron spin resonance (ESR) of Gd3+ ions in Y1−xGdxBaCo2O5 (x = 0.01, 0.25, and 1) polycrystalline samples. Magnetic susceptibility was also performed for comparison with the ESR results. It was found that charge-ordering transition for Y0.75Gd0.25BaCo2O5 revealed by the susceptibility is also manifested in the characters of the ESR data. The similar temperature-evolution of the ESR parameters for GdBaCo2O5 provides a support for the existence of charge-ordering transition, although no characteristic of the transition is evidenced from susceptibility experiments, which can be understood as being hidden by dominant paramagnetism of Gd3+ ions in this compound. We have interpreted the temperature variation of ESR parameters in terms of electron localization associated with Co2+/Co3+ charge ordering.
Physical limitations in ferromagnetic inductively coupled plasma sources
Authors: Bliokh Yury P. , Felsteiner J. , Slutsker Ya. Z.
Published: February 2013

The ferromagnetic inductively coupled plasma (FICP) source, which is a version of the common inductively coupled plasma sources, has a number of well known advantages such as high efficiency, high level of ionization, low minimal gas pressure, very low required driver frequency, and even a possibility to be driven by single current pulses. We present an experimental study of such a FICP source which showed that above a certain value of the driving pulsed power the properties of this device changed rather drastically. Namely, the plasma became non-stationary and non-uniform contrary to the stationary and uniform plasmas typical for this kind of plasma sources. In this case, the plasma appeared as a narrow dense spike which was short compared to the driving pulse. The local plasma density could exceed the neutral atoms density by a few orders of magnitude. When that happened, the afterglow plasma decay time after the end of the pulse was long compared to an ordinary case with no plasma spike. Experiments were performed with various gases and in a wide range of pressures which enabled us to understand the physical mechanism and derive the parameters responsible for such plasma behavior. A qualitative model of this phenomenon is discussed.
Improving the performance of inorganic-organic hybrid photovoltaic devices by uniform ordering of ZnO nanorods and near-atmospheric pressure nitrogen plasma treatment
Authors: Oh Seungjun , Nagata Takahiro , Volk János , Wakayama Yutaka
Published: February 2013

We investigated the performance of hybrid photovoltaic devices composed of ZnO and poly(3-hexylthiophene) (P3HT). The uniform ordering of ZnO nanorods (NRs) and nitrogen plasma treatment at near-atmospheric pressure offer advantages in modifying the ZnO NR surface. Uniform ordering of the ZnO NRs promoted the effective infiltration of P3HT, increasing the donor–acceptor interface area, which is directly related to short-circuit current density (JSC). Near-atmospheric pressure treatment compensated carriers to form a highly resistant interlayer at the ZnO surface, which reduced carrier recombination and, as a result, increased the open circuit voltage (VOC). Combining these two approaches achieved five-fold increase in JSC compared to that of the planar heterojunction, while the VOC was increased up to 0.71 V.
Residual stress and dislocations density in silicon ribbons grown via optical zone melting
Authors: Augusto A. , Pera D. , Choi H. J. , Bellanger P. , Brito M. C. , Maia Alves J. , Vallêra A. M. , Buonassisi T. , Serra J. M.
Published: February 2013

We investigate the relationships between growth rate, time-temperature profile, residual stress, dislocation density, and electrical performance of silicon ribbons grown via optical zone melting. The time-temperature profiles of ribbons grown at different velocities were investigated using direct measurements and computational fluid dynamics (CFD) modeling. Residual stresses up to 20 MPa were measured using infrared birefringence imaging. The effect of crystallization speed on dislocation density and residual stress is discussed from the context of thermal stresses during growth. More broadly, we demonstrate the usefulness of combining spatially resolved stress and microstructure measurements with CFD simulations toward optimizing kerfless silicon wafer quality.
Cross-correlation detection and analysis for California's electricity market based on analogous multifractal analysis
Authors: Wang Fang , Liao Gui-ping , Li Jian-hui , Zou Rui-biao , Shi Wen
Published: February 2013

A novel method, which we called the analogous multifractal cross-correlation analysis, is proposed in this paper to study the multifractal behavior in the power-law cross-correlation between price and load in California electricity market. In addition, a statistic ρAMF−XA, which we call the analogous multifractal cross-correlation coefficient, is defined to test whether the cross-correlation between two given signals is genuine or not. Our analysis finds that both the price and load time series in California electricity market express multifractal nature. While, as indicated by the ρAMF−XA statistical test, there is a huge difference in the cross-correlation behavior between the years 1999 and 2000 in California electricity markets.
Influence of back contact roughness on light trapping and plasmonic losses of randomly textured amorphous silicon thin film solar cells
Authors: Palanchoke U. , Jovanov V. , Kurz H. , Dewan R. , Magnus P. , Stiebig H. , Knipp D.
Published: February 2013

The influence of nanotextured metallic back contacts on light trapping and plasmonic losses of amorphous silicon solar cells was investigated. The optical losses of the back contact are determined by the texture of the metallic back contact and the dielectric constant of the interlayer between the solar cell and the metal back contact. The investigations show that the optical losses are highest if nano features are present at the back contact, while the texture of the front contact which propagates through the layer stack exhibits only a minor effect on the optical losses.
Influence of interfacial properties on thermal transport at gold:silicon contacts
Authors: Duda J. C. , Yang C.-Y. P. , Foley B. M. , Cheaito R. , Medlin D. L. , Jones R. E. , Hopkins P. E.
Published: February 2013

We measure the Kapitza conductances at Au:Si contacts from 100 to 296 K via time-domain thermoreflectance. Contacts are fabricated by evaporating Au films onto Si substrates. Prior to Au deposition, the Si substrates receive pretreatments in order to modify interfacial properties, i.e., bonding and structural disorder. Through the inclusion of a Ti adhesion layer and the removal of the native oxide, Kapitza conductance can be enhanced by a factor of four at 296 K. Furthermore, interfacial roughness is found to have a negligible effect, which we attribute to the already low conductances of poorly bonded Au:Si contacts.
Strain rate dependent mechanical properties in single crystal nickel nanowires
Authors: Peng Cheng , Zhong Yuan , Lu Yang , Narayanan Sankar , Zhu Ting , Lou Jun
Published: February 2013

We measure the strain rate dependence of 0.2% offset yield stress in single-crystal nickel nanowires with diameters ranging from 80 to 300 nm. In situ tensile experiments with strain rates from 10−4 s−1 to 10−2 s−1 were conducted, and the small activation volume (∼10b3, where b is the Burgers vector length) and high strain-rate sensitivity (∼0.1) were obtained. These results agreed with atomistic simulations. Our work provides insights into the strength-limiting and rate-controlling mechanism of plasticity at the nanoscale.
Interface charge engineering at atomic layer deposited dielectric/III-nitride interfaces
Authors: Hung Ting-Hsiang , Krishnamoorthy Sriram , Esposto Michele , Neelim Nath Digbijoy , Sung Park Pil , Rajan Siddharth
Published: February 2013

Interface charges at atomic layer deposited Al2O3/III-nitride interfaces were investigated for III-nitride layers of different polarity. A large positive sheet charge density is induced at the Al2O3/III-nitride interface on all the orientations of GaN and Ga-polar AlGaN, and this sheet charge can be significantly altered using post-metallization anneals. It is proposed that the charges are caused by interfacial defects that can be passivated and neutralized through a H2 based anneal. Tailoring of the interface charge density described here can be used to improve critical device characteristics such as gate leakage and electron transport, and for lateral electrostatic engineering.
Measurement of frequency gaps and waveguiding in phononic plates with periodic stepped cylinders using pulsed laser generated ultrasound
Authors: Hsu Jin-Chen , Wu Tsung-Tsong , Hsu Hua-Shien
Published: February 2013

In this paper, we theoretically and experimentally study phononic band gaps and waveguiding for plate-mode acoustic waves in a square array of stepped cylinders coated on an aluminum thin plate. We show that the stepped cylinders shaped with a small segment of reduced diameter can change the phonon resonance frequencies and result in tailorable band gaps. We demonstrate the band-gap and waveguiding effects in the phononic plate utilizing finite-element method numerical calculations and pulse laser ultrasonic measurements. Experimental results agree well with the numerical predictions. The phononic band gaps, slow resonant acoustic waves, and waveguiding in the lower frequency range are experimentally observed. The results enable enhanced control over phononic metamaterial, which has applications in low-frequency guiding and isolation of acoustic waves, acoustic absorbers, and nondestructive evaluation.
Identifying local characteristic lengths governing sound wave properties in solid foams
Authors: Tan Hoang Minh , Perrot Camille
Published: February 2013

Identifying microscopic geometric properties and fluid flow through opened-cell and partially closed-cell solid structures is a challenge for material science, in particular, for the design of porous media used as sound absorbers in building and transportation industries. We revisit recent literature data to identify the local characteristic lengths dominating the transport properties and sound absorbing behavior of polyurethane foam samples by performing numerical homogenization simulations. To determine the characteristic sizes of the model, we need porosity and permeability measurements in conjunction with ligament lengths estimates from available scanning electron microscope images. We demonstrate that this description of the porous material, consistent with the critical path picture following from the percolation arguments, is widely applicable. This is an important step towards tuning sound proofing properties of complex materials.
Thermoelectric properties of intermetallic semiconducting RuIn3 and metallic IrIn3
Authors: Haldolaarachchige N. , Phelan W. A. , Xiong Y. M. , Jin R. , Chan J. Y. , Stadler S. , Young D. P.
Published: February 2013

Low temperature (<400 K) thermoelectric properties of semiconducting RuIn3 and metallic IrIn3 are reported. RuIn3 is a narrow band gap semiconductor with a large n-type Seebeck coefficient at room temperature (S(290K)≈−400μV/K), but the thermoelectric figure of merit (ZT(290K)≈0.007) is small because of high electrical resistivity and thermal conductivity (κ(290 K) ∼ 2.0 W/m K). IrIn3 is a metal (n(290K)≈1021cm−3) with low thermopower at room temperature (S(290K)≈−20μV/K). Iridium substitution on the ruthenium site has a dramatic effect on transport properties, which leads to a large improvement in the power factor (S2ρ(390K)∼−207μWm K2) and corresponding figure of merit (ZT(380 K) = 0.053), improving the efficiency of the material by almost an order of magnitude.
Extrinsic and intrinsic photoresponse in monodisperse carbon nanotube thin film transistors
Authors: Sczygelski Erik , Sangwan Vinod K. , Wu Chung-Chiang , Arnold Heather N. , Everaerts Ken , Marks Tobin J. , Hersam Mark C. , Lauhon Lincoln J.
Published: February 2013

Spectroscopic, time-resolved scanning photocurrent microscopy is shown to distinguish the intrinsic photoresponse of monodisperse semiconducting (99%) single-walled carbon nanotubes (SWCNTs) from the extrinsic photoresponse of the substrate. A persistent positive photocurrent induced by near-infrared excitation is attributed to the generation of free carriers by inter-band excitation in SWCNTs. For shorter excitation wavelengths, absorption by the Si substrate generates two types of photocurrent: a transient positive photoresponse, identified as a displacement current, and a persistent negative photocurrent that arises from photogating of the SWCNT thin film.
Ambient condition laser writing of graphene structures on polycrystalline SiC thin film deposited on Si wafer
Authors: Yue Naili , Zhang Yong , Tsu Raphael
Published: February 2013

We report laser induced local conversion of polycrystalline SiC thin-films grown on Si wafers into multi-layer graphene, a process compatible with the Si based microelectronic technologies. The conversion can be achieved using a 532 nm CW laser with as little as 10 mW power, yielding ∼1 μm graphene discs without any mask. The conversion conditions are found to vary with the crystallinity of the film. More interestingly, the internal structure of the graphene disc, probed by Raman imaging, can be tuned with varying the film and illumination parameters, resembling either the fundamental or doughnut mode of a laser beam.
High resolution imaging and optical control of Bose-Einstein condensates in an atom chip magnetic trap
Authors: Salim Evan A. , Caliga Seth C. , Pfeiffer Jonathan B. , Anderson Dana Z.
Published: February 2013

A high-resolution projection and imaging system for ultracold atoms is implemented using a compound silicon and glass atom chip. The atom chip is metalized to enable magnetic trapping while glass regions enable high numerical aperture optical access to atoms residing in the magnetic trap about 100 μm below the chip surface. The atom chip serves as a wall of the vacuum system, which enables the use of commercial microscope components for projection and imaging. Holographically generated light patterns are used to optically slice a cigar-shaped magnetic trap into separate regions; this has been used to simultaneously generate up to four Bose-condensates. Using fluorescence techniques, we have demonstrated in-trap imaging resolution down to 2.5 μm.
Label-free molecular detection with capped carbon nanotubes
Authors: Koleini Mohammad , Colombi Ciacchi Lucio
Published: February 2013

We present a theoretical proof-of-principle analysis of a device composed of mutually faced capped carbon nanotubes for the selective detection of hardly distinguishable gas molecules in binary mixtures (methanol/formaldehyde and H2O/H2S). Selectivity arises, on one side, from I–V responses of the sensor in the presence of different gases trapped between the nanotube caps. On the other side, the different dipole moments and polarizabilities of the molecules lead to different population probabilities in the sensing region, acting as a highly selective electrostatic trapping device. The selectivity can be tuned by the bias voltage and by the gap distance between the nanotubes.
Intrinsic electronic switching time in ultrathin epitaxial vanadium dioxide thin film
Authors: Kar Ayan , Shukla Nikhil , Freeman Eugene , Paik Hanjong , Liu Huichu , Engel-Herbert Roman , Bhardwaja S. S. N. , Schlom Darrell G. , Datta Suman
Published: February 2013

This letter investigates the intrinsic electronic switching time associated with the insulator-to-metal phase transition in epitaxial single crystal vanadium dioxide (VO2) thin films using impedance spectroscopy and ac conductivity measurements. The existence of insulating and metallic phase coexistence, intrinsic to the epitaxial (001) oriented VO2 thin film grown on a (001) rutile TiO2 substrate, results in a finite capacitance being associated with the VO2 films in their insulating phase that limits the electronic switching speed. Insights into the switching characteristics and their correlation to the transport mechanism in the light of phase coexistence are obtained by performing a detailed scaling study on VO2 two-terminal devices.
Temporal dynamics and impact of event interactions in cyber-social populations
Authors: Zhang Yi-Qing , Li Xiang
Published: February 2013

The advance of information technologies provides powerful measures to digitize social interactions and facilitate quantitative investigations. To explore large-scale indoor interactions of a social population, we analyze 18 715 users' Wi-Fi access logs recorded in a Chinese university campus during 3 months, and define event interaction (EI) to characterize the concurrent interactions of multiple users inferred by their geographic coincidences—co-locating in the same small region at the same time. We propose three rules to construct a transmission graph, which depicts the topological and temporal features of event interactions. The vertex dynamics of transmission graph tells that the active durations of EIs fall into the truncated power-law distributions, which is independent on the number of involved individuals. The edge dynamics of transmission graph reports that the transmission durations present a truncated power-law pattern independent on the daily and weekly periodicities. Besides, in the aggregated transmission graph, low-degree vertices previously neglected in the aggregated static networks may participate in the large-degree EIs, which is verified by three data sets covering different sizes of social populations with various rendezvouses. This work highlights the temporal significance of event interactions in cyber-social populations.
Communication: Simplified two-beam rotational CARS signal generation demonstrated in 1D
Authors: Bohlin Alexis , Patterson Brian D. , Kliewer Christopher J.
Published: February 2013

We explore a novel phase matching scheme for gas-phase rotational coherent anti-Stokes Raman spectroscopy (CARS). The scheme significantly simplifies the employment of the technique in general. Two laser beams, one broadband and one narrowband, are crossed at arbitrary angle and the generated rotational CARS signal, copropagating with the probe beam, is isolated using a polarization gating technique. The effect of phase-vector mismatch for various experimental implementations was measured experimentally and compared to calculations. The spatial resolution of the current technique is improved by more than an order of magnitude over standard gas-phase CARS experimental arrangements, providing an interaction length of less than 50 μm when desired. Both the pump and Stokes photons originate from the broadband pulse, and are therefore automatically overlapped temporally and spatially. Significantly improved signal levels are achieved because of both the ease of alignment and the higher pulse energy available to the pump and Stokes fields. We demonstrate the technique for single-laser-shot 1D rotational CARS signal generation over approximately a 1 cm field in a flame.