bluuebunny/crossref_metadata_2025 huggingface dataset:
A multiplexed immunoassay system based upon reciprocating centrifugal microfluidics
Authors: Noroozi Zahra , Kido Horacio , Peytavi Régis , Nakajima-Sasaki Rie , Jasinskas Algimantas , Micic Miodrag , Felgner Philip L. , Madou Marc J.
Published: June 2011

A novel, centrifugal disk-based micro-total analysis system (μTAS) for low cost and high throughput semi-automated immunoassay processing was developed. A key innovation in the disposable immunoassay disk design is in a fluidic structure that enables very efficient micro-mixing based on a reciprocating mechanism in which centrifugal acceleration acting upon a liquid element first generates and stores pneumatic energy that is then released by a reduction of the centrifugal acceleration, resulting in a reversal of direction of flow of the liquid. Through an alternating sequence of high and low centrifugal acceleration, the system reciprocates the flow of liquid within the disk to maximize incubation/hybridization efficiency between antibodies and antigen macromolecules during the incubation/hybridization stage of the assay. The described reciprocating mechanism results in a reduction in processing time and reagent consumption by one order of magnitude.
Reentrant excitation in an analog-digital hybrid circuit model of cardiac tissue
Authors: Mahmud Farhanahani , Shiozawa Naruhiro , Makikawa Masaaki , Nomura Taishin
Published: June 2011

We propose an analog-digital hybrid circuit model of one-dimensional cardiac tissue with hardware implementation that allows us to perform real-time simulations of spatially conducting cardiac action potentials. Each active nodal compartment of the tissue model is designed using analog circuits and a dsPIC microcontroller, by which the time-dependent and time-independent nonlinear current-voltage relationships of six types of ion channel currents employed in the Luo-Rudy phase I (LR-I) model for a single mammalian cardiac ventricular cell can be reproduced quantitatively. Here, we perform real-time simulations of reentrant excitation conduction in a ring-shaped tissue model that includes eighty nodal compartments. In particular, we show that the hybrid tissue model can exhibit real-time dynamics for initiation of reentries induced by uni-directional block, as well as those for phase resetting that leads to annihilation of the reentry in response to impulsive current stimulations at appropriate nodes and timings. The dynamics of the hybrid model are comparable to those of a spatially distributed tissue model with LR-I compartments. Thus, it is conceivable that the hybrid model might be a useful tool for large scale simulations of cardiac tissue dynamics, as an alternative to numerical simulations, leading toward further understanding of the reentrant mechanisms.
Transition from Pauli-paramagnetism to ferromagnetism in CaCu3(Ru4−xMnx)O12 (0 ≤ x ≤ 3) perovskites
Authors: de la Calle C. , Sánchez-Benítez J. , Barbanson F. , Nemes N. , Fernández-Díaz M. T. , Alonso J. A.
Published: June 2011

Regarding the perovskite oxides AA′3B4O12, we have investigated the solid solution CaCu3(Ru4−xMnx)O12 (0 ≤ x ≤ 4), where the two end members present very different properties: Pauli-paramagnetic and metallic for x = 0 versus ferrimagnetic and half-metallic with colossal magnetoresistance for x = 4. We have prepared x = 0, 0.5, 1.0, 1.5, 2.0, and 3.0 members. All of the samples crystallize in the cubic space group Im3− (No. 204). The unit-cell parameter, volume, and bond distances evolve linearly along the series, decreasing as Mn content (x) increases. The x = 2 sample has been selected for use in a neutron diffraction study of both structure and magnetism. Low-temperature neutron powder diffraction data allowed us to probe the microscopic origin of the magnetism. Unlike the ferrimagnetic end-member with x = 4, we have found that the magnetic arrangement for x = 2 is ferromagnetic, with the magnetic moments of Cu and (Mn, Ru) oriented along the same direction. Resistivity and magnetic susceptibility measurements of this series were also analyzed: the introduction of Ru increases the number of charge carriers in the compound, leading to metallic behavior and a drastic decrease of the magnetoresistance. The magnetic ordering temperature, TC, has also been found to increase as Mn content in the compound increases.
Parallel versus antiparallel interfacial exchange coupling in ferromagnet/spin-glasses
Authors: He Lin
Published: June 2011

An outstanding question regarding magnetic systems is which type of interaction, i.e., ferromagnetic or antiferromagnetic, dominates the interfacial exchange coupling. Here we report magnetic properties of a ferromagnet (FM)-spin glasses (SG) system above the freezing temperature TF = 10.3 K of SG. Our experimental results demonstrate that the effective interfacial exchange coupling in FM-SG system could be either parallel or antiparallel depending on the cooling magnetic field. The compensation cooling magnetic field, which leads to zero effective interfacial exchange coupling and in which the effective interfacial exchange coupling changes sign, is determined. This work opens up many avenues toward the study of SG and the interfacial exchange coupling.
A-site ion-size effect on the transport and magnetic properties of Ce doping Pr0.3Ce0.2CaxSr0.5−xMnO3 (0≤x≤0.25)
Authors: Shi L. , Wang Y. , Zhou S. M. , Chu S. N. , Guo Y. Q. , Zhao J. Y.
Published: June 2011

The effects of A-site ion-size 〈rA〉 on the crystal structures, transport and magnetic properties of the perovskite manganese oxide Pr0.3Ce0.2CaxSr0.5-xMnO (0 ≤ x ≤ 0.25) have been investigated. In those compounds, when 0≤x≤0.125, the temperatures (Tmax) of the resistivity maximums below Curie Temperature TC are correlated with the Kondo-like scattering of Ce3+ and the onset of antiferromagnetic ordering of Ce3+ with respect to the Mn-sublattice moments. The decrease of 〈rA〉 causes the anomalous increase of lattice parameters b, c and unit cell volume, the decrease of the differences of TC and Tmax, the weakening of the Kondo-like scattering and magnetic order of Ce3+, and the enhancement of saturation magnetic moment, which give the evidences of the valence enhancing of Ce ions from + 3 toward + 4 with 〈rA〉 decreasing. Although the Ca doping is expected to drive the system toward the antiferromagnetic ground state, the increase of valence of Ce enhances the content of Mn3+ in the system, which drives the system to the ferromagnetic ground state. The changes of ion-size 〈rA〉 and the valence of Ce are co-operating on the transport and magnetic properties of the half-doped manganites.
Photoluminescence, morphology, and structure of hydrothermal ZnO implanted at room temperature with 60 keV Sn+ ions
Authors: Dang Giang T. , Kawaharamura Toshiyuki , Nitta Noriko , Hirao Takashi , Yoshiie Toshimasa , Taniwaki Masafumi
Published: June 2011

Hydrothermal ZnO wafers implanted at room temperature with 60 keV Sn+ ions are examined by means of photoluminescence (PL), atomic force spectroscopy (AFM), and X-ray diffractometry techniques. The PL intensity significantly decreases in the wafers implanted to doses of 4.1 × 1013 ions/cm2 and higher. The AFM measurements indicate that surface roughness variation is not the cause of the significant decrease in PL intensity. Furthermore, the PL deep level (DL) band peak blueshifts after illuminating the implanted samples with the He-Cd laser 325 nm line; meanwhile, the DL band intensity first increases and then decreases with illumination time. These abnormal behaviors of the DL band are discussed.
Interfacial reaction induced phase separation in LaxHfyO films
Authors: Ma J. W. , Lee W. J. , Cho M.-H. , Lee K. M. , Sohn H. C. , Kim C. S. , Cho H. J.
Published: June 2011

Amorphous LaxHfyO films containing La at concentrations (x) of 50 and 20% were prepared by atomic layer deposition on ultrathin SiO2 films (1 nm). We examined the electronic structures and microstructures of the LaxHfyO films by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). Phase separation into La2O3 and HfO2 was observed in the LaxHfyO films subjected to annealing temperatures over 900 °C, although the mixture of La2O3 and HfO2 is thermodynamically stable. The structural changes that occurred as the result of phase separation were dependent on the concentrations of La and Hf in the films. During the annealing treatment, silicate was produced due to interfacial reactions and the interfacial reactions were found to be dependent on the La2O3 content in the LaxHfyO films, which has a significant influence on the phase separation process and resulting film structure.
Thermodynamic and mechanical properties of crystalline CoSb3: A molecular dynamics simulation study
Authors: Yang Xu-qiu , Zhai Peng-cheng , Liu Li-sheng , Zhang Qing-jie
Published: June 2011

Molecular dynamics simulations have been performed to study the fundamental thermodynamic and mechanical properties of single-crystalline skutterudite CoSb3 in the nanometric scale. The several interesting thermodynamic predictions, including linear thermal expansion coefficient, specific heat capacity, thermal conductivity, and temperature dependence of elastic constants, show excellent agreement with data available in the literature. The classic mechanical tests of uniaxial tension and compression are performed respectively at constant temperatures. The CoSb3 single-crystal exhibits nonlinear elastic response during the deformation process and the sustainable stress is very high, demonstrating its outstanding stability. An interesting phenomenon occurs at compression that the stress-strain curve undergoes a transition. The cause of the transition is an atomic reconstruction, which is observed and interpreted on the basis of interatomic interactions. Both of the failure patterns under tension and compression reveal brittleness of the material. The increasing of temperature would result in a linear degradation of the effective Young’s modulus and ultimate strength, but its effect on Poisson’s ratio is negligible. The results provide the groundwork for future studies of service behavior of the skutterudites-based thermoelectric devices.
Impurity states in graphene with intrinsic spin-orbit interaction
Authors: Inglot M. , Dugaev V. K.
Published: June 2011

We consider the problem of electron states related to the strongly localized potential of a single impurity in graphene. Our model simulates the effect of a neutral impurity atom (substituting for the carbon atom) on the energy spectrum of electrons near the Dirac points. The model also can describe the effect of an adatom on the surface of graphene. We take into account the internal spin-orbit interaction, which essentially modifies the structure of electron bands near the Dirac points, leading effectively to an energy gap. This might result in the occurrence of additional impurity states in the vicinity of the energy gap. As a result, the spin-orbit gap in graphene can be experimentally unobservable due to a large number of adsorbed light atoms at the graphene surface, which create the impurity states in the gap.
Time-resolved x-ray excited optical luminescence in InGaN/GaN multiple quantum well structures
Authors: O’Malley S. M. , Revesz P. , Kazimirov A. , Sirenko A. A.
Published: June 2011

Synchrotron-based x-ray radiation has been utilized to measure time-resolved x-ray excited optical luminescence (TR-XEOL) from InGaN/GaN multiple quantum well (MQW) structures. Excess carrier recombination lifetimes were determined for MQWs grown on conventional c-plane as well as on non-polar m-plane substrates. In addition, the simultaneous measurement of XEOL and x-ray fluorescence reveals an interaction between inner-core excitations of Si impurities and bound exciton recombination in doped GaN-based device structures. Furthermore, the TR-XEOL characterization technique were also applied to InGaN/GaN MQWs grown on GaN inverted pyramid structures.
Reactivation of sub-bandgap absorption in chalcogen-hyperdoped silicon
Authors: Newman Bonna K. , Sher Meng-Ju , Mazur Eric , Buonassisi Tonio
Published: June 2011

Silicon doped with nonequilibrium concentrations of chalcogens using a femtosecond laser exhibits near-unity absorption of sub-bandgap photons to wavelengths of at least 2500 nm. Previous studies have shown that sub-bandgap absorptance decreases with thermal annealing up to 1175 K and that the absorption deactivation correlates with chalcogen diffusivity. In this work, we show that sub-bandgap absorptance can be reactivated by annealing at temperatures between 1350 and 1550 K followed by fast cooling (>50 K/s). Our results suggest that the defects responsible for sub-bandgap absorptance are in equilibrium at high temperatures in hyperdoped Si:chalcogen systems.
Heterogeneous critical nucleation on a completely wettable substrate
Authors: Iwamatsu Masao
Published: June 2011

Heterogeneous nucleation of a new bulk phase on a flat substrate can be associated with the surface phase transition called wetting transition. When this bulk heterogeneous nucleation occurs on a completely wettable flat substrate with a zero contact angle, the classical nucleation theory predicts that the free-energy barrier of nucleation vanishes. In fact, there always exists a critical nucleus and a free-energy barrier as the first-order prewetting transition will occur even when the contact angle is zero. Furthermore, the critical nucleus changes its character from the critical nucleus of surface phase transition below bulk coexistence (undersaturation) to the critical nucleus of bulk heterogeneous nucleation above the coexistence (oversaturation) when it crosses the coexistence. Recently, Sear [J. Chem. Phys. 129, 164510 (2008)]10.1063/1.2992160 has shown, by a direct numerical calculation of nucleation rate, that the nucleus does not notice this change when it crosses the coexistence. In our work, the morphology and the work of formation of critical nucleus on a completely wettable substrate are re-examined across the coexistence using the interface-displacement model. Indeed, the morphology and the work of formation changes continuously at the coexistence. Our results support the prediction of Sear and will rekindle the interest on heterogeneous nucleation on a completely wettable substrate.
Low gap superconducting single photon detectors for infrared sensitivity
Authors: Dorenbos S. N. , Forn-Díaz P. , Fuse T. , Verbruggen A. H. , Zijlstra T. , Klapwijk T. M. , Zwiller V.
Published: June 2011

The quantum efficiency of NbN and NbTiN superconducting single photon detectors drops with decreasing photon energy. A lower gap material would enable single photon detection deeper in the infrared. We have fabricated a NbSi detector and compare its characteristics with a NbTiN device. NbSi (TC≃2 K) has a smaller superconducting gap than NbTiN or NbN (TC≃15 K). We measure the detection efficiency for a wavelength range from 1100 to 1900 nm. In this range the NbSi detector shows a 10-fold increase in relative efficiency with respect to the NbTiN detector.
Observation of generalized Wolf shifts in short pulse spectroscopy
Authors: Schoonover R. W. , Lavarello R. , Oelze M. L. , Carney P. S.
Published: June 2011

Experimental observations of recently predicted correlation-dependent, propagation-induced changes in the spectrum and cross-spectra of a cyclostationary field are reported. An acoustic Young’s experiment was conducted in which sources were driven by stationary signals modified by a square wave to make the process cyclostationary. The degree of correlation of the underlying stationary processes were controlled to change the spatial coherence of the sources. The far-zone generalized spectra changed with changing degree of correlation.
Pointing the way to the products? Comparison of the stress tensor and the second-derivative tensor of the electron density
Authors: Guevara-García Alfredo , Echegaray Eleonora , Toro-Labbe Alejandro , Jenkins Samantha , Kirk Steven R. , Ayers Paul W.
Published: June 2011

The eigenvectors of the electronic stress tensor can be used to identify where new bond paths form in a chemical reaction. In cases where the eigenvectors of the stress tensor are not available, the gradient-expansion-approximation suggests using the eigenvalues of the second derivative tensor of the electron density instead; this approximation can be made quantitatively accurate by scaling and shifting the second-derivative tensor, but it has a weaker physical basis and less predictive power for chemical reactivity than the stress tensor. These tools provide an extension of the quantum theory of atoms and molecules from the characterization of molecular electronic structure to the prediction of chemical reactivity.
Nitrogen doping-induced rectifying behavior with large rectifying ratio in graphene nanoribbons device
Authors: Zeng Jing , Chen Ke-Qiu , He Jun , Fan Zhi-Qiang , Zhang Xiao-Jiao
Published: June 2011

By applying nonequilibrium Green’s functions in combination with density-function theory, we investigate the electronic transport properties of armchair graphene nanoribbons devices with one undoped and one nitrogen-doped armchair graphene nanoribbons electrode. For the doped armchair graphene nanoribbons electrode, an N dopant is considered to substitute the center or edge carbon atom. The results show that the electronic transport properties are strongly dependent on the width of the ribbon and the position of the N dopant. The rectifying behavior with large rectifying ratio can be observed and can be modulated by changing the width of the ribbon or the position of the N dopant. A mechanism for the rectifying behavior is suggested.
A coupled cluster approach with excitations up to six orbital pairs: The formulation and test applications for bond breaking processes
Authors: Xu Enhua , Kou Zhuangfei , Li Shuhua
Published: June 2011

The formalism of the coupled cluster (CC) method with excitations up to six orbital pairs (CC6P) and its illustrative applications are presented. By definition, CC6P includes connected excitations from full singles, doubles, triples, and partial quadruples, pentuples, and hextuples. CC6P and its approximate variants (CC6P-4, CC6P-5, and CC6P-6a) have the similar computational cost as the CC singles, doubles, and triples (CCSDT). They have been applied to investigate the potential energy surfaces for bond dissociation processes in four small molecules (F2, H2O, N2, and F2+). In comparison with full configuration interaction results, CC6P and its approximate variants are demonstrated to provide very accurate descriptions for the single-bond breaking process in F2. While for multi-bond breaking processes, these methods provide considerable improvement over CCSDT.
Near-wall dynamics of compressible boundary layers
Authors: Lagha Maher , Kim John , Eldredge Jeff D. , Zhong Xiaolin
Published: June 2011

The coherent structures populating the inner-region of a compressible boundary layer with free-stream Mach number equal to 2.5 are analyzed by means of direct numerical simulations of the Navier–Stokes equations. This study shows similarity with the incompressible case in the sense that turbulence in the near-wall region can be sustained without fluctuations in the outer region, proving the existence of a local cycle within the near-wall region. The dynamics are further simplified by making use of the coherence of the inner region. The wall-normal velocity component in this region is split into two: one coherent part representing vortices spanning all the inner-region, and one incoherent part representing the background turbulence. By damping the latter part, the statistical features of the flow are only slightly influenced, showing that the coherent part is essential in determining the flow characteristics. Flow dynamics and turbulence structures within this coherent part are examined. It is shown that the near-wall region is populated by crescent-shaped vortical structures, which are associated with regions with strong positive Reynolds shear stress production. The structure of the flow associated with these regions shares several features with the so-called internal shear layers.
Exploring the details of the martensite–austenite phase transition of the shape memory Heusler compound Mn2NiGa by hard x-ray photoelectron spectroscopy, magnetic and transport measurements
Authors: Blum Christian G. F. , Ouardi Siham , Fecher Gerhard H. , Balke Benjamin , Kozina Xeniya , Stryganyuk Gregory , Ueda Shigenori , Kobayashi Keisuke , Felser Claudia , Wurmehl Sabine , Büchner Bernd
Published: June 2011

Mn 2 NiGa is reported to be a shape memory material with a martensite–austenite phase transition. Temperature dependent measurements of the transport and magnetic properties reveal the martensitic transition close to room temperature with a thermal hysteresis of about 27 K. The electronic structure of the valence band in both phases was studied by hard x-ray photoelectron spectroscopy. The results clearly indicate that strong changes in the electronic structure appear at the phase transition.
Heat conduction across molecular junctions between nanoparticles
Authors: Merabia Samy , Barrat Jean-Louis , Lewis Laurent J.
Published: June 2011

We investigate the problem of heat conduction across molecular junctions connecting two nanoparticles, both in vacuum and in a liquid environment, using classical molecular dynamics simulations. In vacuum, the well-known result of a length independent conductance is recovered; its precise value, however, is found to depend sensitively on the overlap between the vibrational spectrum of the junction and the density of states of the nanoparticles that act as thermal contacts. In a liquid environment, the conductance is constant up to a crossover length, above which a standard Fourier regime is recovered.
Band alignment at the Cu2ZnSn(SxSe1−x)4/CdS interface
Authors: Haight Richard , Barkhouse Aaron , Gunawan Oki , Shin Byungha , Copel Matt , Hopstaken Marinus , Mitzi David B.
Published: June 2011

Energy band alignments between CdS and Cu2ZnSn(SxSe1−x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.
High temperature (1000 °C) compatible Y–La–Si–O silicate gate dielectric in direct contact with Si with 7.7 Å equivalent oxide thickness
Authors: Dubourdieu C. , Cartier E. , Bruley J. , Hopstaken M. , Frank M. M. , Narayanan V.
Published: June 2011

Yttrium lanthanum silicate was formed in direct contact with silicon after a rapid thermal annealing at 1000 °C in metal-oxide-semiconductor capacitors leading to an equivalent oxide thickness (EOT) of 7.7 Å. This represents one of the lowest EOT value reported for a gate-first process with non Hf-based dielectric. The silicate is formed by interdiffusion of La2O3 and YOx layers and interfacial SiO2 consumption. Yttrium incorporation reduces the leakage current density as well as the large negative flatband voltage (Vfb) shift that is associated with lanthanide-based dielectrics. The Vfb value can be appropriately tuned for n-type field-effect transistor operation by changing the silicate composition.
Superconducting a-WxSi1−x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm
Authors: Baek Burm , Lita Adriana E. , Verma Varun , Nam Sae Woo
Published: June 2011

We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1−x) nanowire. Our device made from a uniform a-WxSi1−x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates.
A high voltage pulsed power supply for capillary discharge waveguide applications
Authors: Abuazoum S. , Wiggins S. M. , Issac R. C. , Welsh G. H. , Vieux G. , Ganciu M. , Jaroszynski D. A.
Published: June 2011

We present an all solid-state, high voltage pulsed power supply for inducing stable plasma formation (density ∼1018 cm−3) in gas-filled capillary discharge waveguides. The pulser (pulse duration of 1 μs) is based on transistor switching and wound transmission line transformer technology. For a capillary of length 40 mm and diameter 265 μm and gas backing pressure of 100 mbar, a fast voltage pulse risetime of 95 ns initiates breakdown at 13 kV along the capillary. A peak current of ∼280 A indicates near complete ionization, and the r.m.s. temporal jitter in the current pulse is only 4 ns. Temporally stable plasma formation is crucial for deploying capillary waveguides as plasma channels in laser-plasma interaction experiments, such as the laser wakefield accelerator.
Morphology control in polycarbazole based bulk heterojunction solar cells and its impact on device performance
Authors: Chu Ta-Ya , Alem Salima , Tsang Sai-Wing , Tse Shing-Chi , Wakim Salem , Lu Jianping , Dennler Gilles , Waller David , Gaudiana Russell , Tao Ye
Published: June 2011

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly[N-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/PC71BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0 cm2.
Hole mobility effect in the efficiency of bilayer heterojunction polymer/C60 photovoltaic cells
Authors: Macedo Andreia G. , Marchiori Cleber F. N. , Grova Isabel R. , Akcelrud Leni , Koehler Marlus , Roman Lucimara S.
Published: June 2011

We report here bilayer heterojunction solar cells fabricated by using poly[9,9′-hexyl-fluorene-alt-bithiophene] (LaPPS43) polymer as active layer. The power conversion efficiency (η) displays a sevenfold increase upon annealing at 200 °C, reaching the value of 2.8%. This result is comparable to the highest η reported so far for bulk heterojunction solar cells using the same polymer. Simulation, absorbance spectra, and current versus voltage results indicate that the π–π stacking in solid state is enhanced after annealing with a reduction in traps and thus reflecting in higher hole mobility.
Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation
Authors: Hernandez-Rueda J. , Savoia A. , Gawelda W. , Solis J. , Mansart B. , Boschetto D. , Siegel J.
Published: June 2011

The transient reflectivity response of phase-change Ge2Sb2Te5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases (amorphous, fcc-, and hcp-crystalline), as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investigated for the fcc-crystalline phase and the laser-crystallized material, revealing strong differences. We find evidence that a considerable fraction of amorphous phase remains in the laser-crystallized material, which features a different phonon frequency, not related to other phases. These results are important for emerging strategies aimed at driving ultrafast phase transitions via coherent phonon excitation for applications in data storage.
Postmetallization annealing effect of TiN-gate Ge metal-oxide-semiconductor capacitor with ultrathin SiO2/GeO2 bilayer passivation
Authors: Nakashima Hiroshi , Iwamura Yoshiaki , Sakamoto Keita , Wang Dong , Hirayama Kana , Yamamoto Keisuke , Yang Haigui
Published: June 2011

The postmetallization annealing (PMA) effect was investigated for a TiN-gate Ge metal-oxide-semiconductor capacitor with an ultrathin SiO2/GeO2 bilayer passivation. PMA at 450 °C led to the incorporation of nitrogen atoms into the gate stack. Consequently, the flat band voltage shifted from −0.79 to +0.23 V, resulting from a decrease in the dipole at the SiO2/GeO2 interface and the accompanying creation of a negative charge. The hysteresis decreased from 98 to 27 mV and the interface state density decreased from 6×1011 to 2.5×1011 cm−2 eV−1, as results of the nitrogen termination of defects at the SiO2/GeO2 interface and/or in the GeO2 interlayer.
Charge-carrier dynamics in hybrid plasmonic organic solar cells with Ag nanoparticles
Authors: Xue Mei , Li Lu , Tremolet de Villers Bertrand J. , Shen Huajun , Zhu Jinfeng , Yu Zhibin , Stieg Adam Z. , Pei Qibing , Schwartz Benjamin J. , Wang Kang L.
Published: June 2011

To understand the effects of Ag nanoparticles (NPs) on the performance of organic solar cells, we examined the properties of hybrid poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric-acid-methyl-ester:Ag NP solar cells using photoinduced charge extraction with a linearly increasing voltage. We find that the addition of Ag NPs into the active layer significantly enhances carrier mobility but decreases the total extracted carrier. Atomic force microscopy shows that the Ag NPs tend to phase segregate from the organic material at high concentrations. This suggests that the enhanced mobility results from carriers traversing Ag NP subnetworks, and that the reduced carrier density results from increased recombination from carriers trapped on the Ag particles.
UV irradiation induced switching of surface charge polarity on pyrene modified Si nanowires
Authors: Zhao Wen-Chao , Wang Hui , Ou Xue-Mei , Lee Chun-Sing , Zhang Xiao-Hong
Published: June 2011

It has been widely recognized that surface charge in nanomaterials can significantly affect their electrical properties. In this letter, we demonstrate that polarity of surface charge on pyrene modified silicon nanowires (SiNWs) can be switched by illumination of UV light. Unlike the reported conversion method via changing the surrounding pH value, switching process reported here takes place in real-time and does not require introduction of any other chemical species. Mechanisms of the surface charge polarity switching and potential applications of such systems were discussed.
Interactions of a Mn atom with halogen atoms and stability of its half-filled 3d-shell
Authors: Pradhan Kalpataru , Gutsev Gennady L. , Weatherford Charles A. , Jena Purusottam
Published: June 2011

Using density functional theory with hybrid exchange-correlation potential, we have calculated the geometrical and electronic structure, relative stability, and electron affinities of MnXn compounds (n = 1–6) formed by a Mn atom and halogen atoms X = F, Cl, and Br. Our objective is to examine the extent to which the Mn–X interactions are similar and to elucidate if/how the half-filled 3d-shell of a Mn atom participates in chemical bonding as the number of halogen atoms increases. While the highest oxidation number of the Mn atom in fluorides is considered to be +4, the maximum number of halogen atoms that can be chemically attached in the MnXn− anions is 6 for X = F, 5 for X = Cl, and 4 for X = Br. The MnCln and MnBrn neutrals are superhalogens for n ≥ 3, while the superhalogen behavior of MnFn begins with n = 4. These results are explained to be due to the way different halogen atoms interact with the 3d electrons of Mn atom.
A flexible organic random laser based on poly(9,9-dioctylfluorene) deposited on a surface corrugated poly-phthalate-carbonate substrate
Authors: Anni M.
Published: June 2011

We report on a flexible coherent random laser based on poly(9,9-dioctylfluorene) (PF8) deposited on a surface corrugated poly-phthalate-carbonate (PPC) substrate. We show that the feedback for lasing is due to a combination between the scattering at the rough PF8–PPC interface and the scattering at the PF8–air interface, due to PF8 thickness fluctuations.
Optical studies on a single GaN nanocolumn containing a single InxGa1−xN quantum disk
Authors: Holmes Mark J. , Park Young S. , Wang Xu , Chan Christopher C. S. , Reid Benjamin P. L. , Kim HeeDae , Taylor Robert A. , Warner Jamie H. , Luo Jun
Published: June 2011

Microphotoluminescence studies were carried out on a single GaN nanocolumn containing a single InGaN quantum disk (QDisk) that had been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system.
Shape transformation of nanoporous GaN by annealing: From buried cavities to nanomembranes
Authors: Yerino Christopher D. , Zhang Yu , Leung Benjamin , Lee Minjoo L. , Hsu Ta-Cheng , Wang Chun-Kai , Peng Wei-Chih , Han J.
Published: June 2011

Gallium nitride is considered a chemically inert, ceramic-like semiconductor with no effective etchants available at room temperature. In this letter, we study the shape transformation of nanoporous GaN prepared by an electrochemical process. It is found that the curvature-driven mass transport process at typical growth temperatures is effective in shaping GaN on both the nanoscale and microscale into useful configurations such as buried cavities or semiconductor-on-air structures. This process of “micromachining” GaN adds flexibilities to epitaxy and device designs. A monocrystalline GaN nanomembrane, extending millimeters in width, is reported as a proof-of-concept demonstration.
Ultrasensitive protein detection in terms of multiphonon resonance Raman scattering in ZnS nanocrystals
Authors: Chu Xueying , Hong Xia , Zou Peng , Men Jing , Liu Yichun
Published: June 2011

Ultrasensitive protein detection was realized using multiphonon Resonance Raman scattering in ZnS nanocrystals. The longitudinal optical phonon line of ZnS and its overtones, which are called multiphonon Raman lines (MRLs), were used as the Raman probe signals. MRLs have a narrow bandwidth, high stability in aqueous solution, and strong resistance to interference from surface variations. Our results show that these features allow for reliable biodetection with good selectivity and high specificity. The detection limit is about 5 fM. This Raman scattering-based methodology will greatly extend the potential applications for ZnS in the biomedical sciences.
Scale-free center-of-mass displacement correlations in polymer melts without topological constraints and momentum conservation: A bond-fluctuation model study
Authors: Wittmer J. P. , Polińska P. , Meyer H. , Farago J. , Johner A. , Baschnagel J. , Cavallo A.
Published: June 2011

By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints, we examine the center-of-mass (COM) dynamics of polymer melts in d = 3 dimensions. Our analysis focuses on the COM displacement correlation function \documentclass[12pt]{minimal}\begin{document}$C_\mathrm{N}(t) \approx \partial _t^2 h_\mathrm{N}(t)/2$\end{document}CN(t)≈∂t2hN(t)/2, measuring the curvature of the COM mean-square displacement hN(t). We demonstrate that CN(t) ≈ −(RN/TN)2(ρ*/ρ) f(x = t/TN) with N being the chain length (16 ⩽ N ⩽ 8192), RN ∼ N1/2 is the typical chain size, TN ∼ N2 is the longest chain relaxation time, ρ is the monomer density, \documentclass[12pt]{minimal}\begin{document}$\rho ^*\approx N/R_\mathrm{N}^d$\end{document}ρ*≈N/RNd is the self-density, and f(x) is a universal function decaying asymptotically as f(x) ∼ x−ω with ω = (d + 2) × α, where α = 1/4 for x ≪ 1 and α = 1/2 for x ≫ 1. We argue that the algebraic decay NCN(t) ∼ −t−5/4 for t ≪ TN results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.
The nature of the defects generated from plasma exposure in pristine and ultraviolet-cured low-k organosilicate glass
Authors: Ren H. , Jiang G. , Antonelli G. A. , Nishi Y. , Shohet J. L.
Published: June 2011

Defects in low-k organosilicate glass produced during air and nitrogen plasma exposure were investigated. The defects, through the measurements of electron-spin resonance and Fourier-transform infrared spectroscopy, were found to be silicon-dangling bonds. Air-plasma exposure increases the defect concentrations by breaking silicon–hydrogen bonds. Nitrogen-plasma exposure as well as free-radical exposure has only a small influence on the bond breaking. It was also shown that ultraviolet curing improves the chemical-damage resistance of the dielectric.
False estimates of stimulated Raman pumping efficiency caused by the optical Stark effect
Authors: Bartlett N. C.-M. , Jankunas J. , Zare R. N.
Published: June 2011

One technique for measuring the fraction of molecules pumped to the excited state in stimulated Raman pumping (SRP) is to record the depletion of molecules in the lower state by resonance enhanced multiphoton ionization (REMPI). The presence of electric fields on the order of 107 V/cm arising from the pulsed SRP laser beams is sufficient to shift the line position of the REMPI transition to such an extent that the estimate of the pumping efficiency is overestimated unless this shift is accounted for.
High mobility top-gate and dual-gate polymer thin-film transistors based on diketopyrrolopyrrole-naphthalene copolymer
Authors: Ha Tae-Jun , Sonar Prashant , Dodabalapur Ananth
Published: June 2011

In this letter, the performance characteristics of top-gate and dual-gate thin-film transistors (TFTs) with active semiconductor layers consisting of diketopyrrolopyrrole-naphthalene copolymer are described. Optimized top-gate TFTs possess mobilities of up to 1 cm2/V s with low contact resistance and reduced hysteresis in air. Dual-gate devices possess higher drive currents as well as improved subthreshold and above threshold characteristics compared to single-gate devices. We also describe the reasons that dual-gate devices result in improved performance. The good stability of this polymer combined with their promising electrical properties make this material a very promising semiconductor for printable electronics.
Electron spin ensemble strongly coupled to a three-dimensional microwave cavity
Authors: Abe Eisuke , Wu Hua , Ardavan Arzhang , Morton John J. L.
Published: June 2011

We demonstrate the strong coupling between an electron spin ensemble and a three-dimensional cavity in a reflection geometry. We also find that an anticrossing in the cavity/spin spectrum can be observed under conditions that the collective coupling strength gc is smaller than the spin linewidth γs or the cavity linewidth. We identify a ratio of gc to γs (gc/γs>0.64) as a condition to observe a splitting in the cavity frequency. Finally, we confirm that gc scales with N, where N is the number of polarized spins.
Nanocrystallization in a shear band: An in situ investigation
Authors: Wilde G. , Rösner H.
Published: June 2011

Preferential nanocrystal formation in shear bands that occurred upon applying a tensile strain on an Al-rich metallic glass has been analyzed in situ in a transmission electron microscope as a function of time after the shear band initiation and as a function of local heating. The results indicate the presence of a transient period before nanocrystal formation sets in, as well as the necessity of thermal activation and further show that nanocrystals developed only within the shear bands. These results support models that explain nanocrystal formation in shear bands based on an increased local mobility.
Experimental demonstration of tunable directional excitation of surface plasmon polaritons with a subwavelength metallic double slit
Authors: Li Xiaowei , Tan Qiaofeng , Bai Benfeng , Jin Guofan
Published: June 2011

We demonstrate experimentally the directional excitation of surface plasmon polaritons (SPPs) on a metal film by a subwavelength double slit under backside illumination, based on the interference of SPPs generated by the two slits. By varying the incident angle, the SPPs can be tunably directed into two opposite propagating directions with a predetermined splitting ratio. Under certain incident angle, unidirectional SPP excitation can be achieved. This compact directional SPP coupler is potentially useful for many on-chip applications. As an example, we show the integration of the double-slit couplers with SPP Bragg mirrors, which can effectively realize selective coupling of SPPs into different ports in an integrated plasmonic chip.
Influence of deep-pits on the device characteristics of metal-organic chemical vapor deposition grown AlGaN/GaN high-electron mobility transistors on silicon substrate
Authors: Selvaraj S. Lawrence , Watanabe Arata , Egawa Takashi
Published: June 2011

We have investigated the regions around deep-pits and their limitations on the performance of metal-organic chemical vapor deposition grown AlGaN/GaN high-electron-mobility transistors (HEMTs) on Si. The device characteristics such as maximum drain current density (IDSmax), threshold voltage (Vth), and three terminal-OFF breakdown (BVOFF) of a HEMT were affected based on the distance of deep-pits from a device active region. The deterioration of HEMT characteristics are significant if the active region is present within 50 μm radius of a deep-pit and becomes insignificant for distance beyond 50 μm. These device characteristics were compared with optical measurements and it was found the region around 50 μm radius of a pit have large dislocations and defects as confirmed by cathodoluminescence. Further, the E2 Raman shift measurements reveal additional stress in the 50 μm region around a pit.
Density fluctuations dispersion relationship for a polymer confined to a nanotube
Authors: Carpenter Joshua H. , Karpusenko Alena , Pan Junhan , Lim Shuang Fang , Riehn Robert
Published: June 2011

DNA confined to rigid nanotubes shows density fluctuations around its stretched equilibrium conformation. We report an experimental investigation of the length-scale dependent dynamics of these density fluctuations. We find that for highly elongated molecules a Rouse description is consistent with observations at sufficiently large length scales. We further find that for strongly fluctuating molecules, or short length scales, such Rouse modes cannot be detected due to strong mixing of fluctuation modes.
Communication: State-to-state differential cross sections for H2O($\tilde B$B̃) photodissociation
Authors: Jiang Bin , Xie Daiqian , Guo Hua
Published: June 2011

Quantum state-to-state differential cross sections, along with the absorption spectrum and product internal state distributions, have been calculated for the photodissociation of H2O in its B band on a new set of ab initio potential energy surfaces in a diabatic representation. The theoretical attributes are in good agreement with the recent experimental data, shedding light on the non-adiabatic dissociation dynamics.
Trapping small mammals for research and management: how many die and why?
Authors: Lemckert F. , Brassil T. , Kavanagh R. , Law B.
Published: June 2011

Trapping programs are an essential part of mammal conservation and management, but trapping carries a risk of death for the study animals. Little information is available on mortality levels and its potential to influence studies. We examined the mortality levels recorded during 68 wildlife surveys within New South Wales, recording mortality rates associated with Elliott aluminium box and wire cage trapping for terrestrial mammals and harp traps for bats. We noted 232 deaths from 13623 small ground mammal captures in box traps, one death from 459 mammal captures in wire cage traps, and 44 deaths from 12,274 bat captures in harp traps. Mortality ranged from 0-13.3%, 0-0.6% and 0-9.1% of captures for box, cage and harp traps, respectively. No deaths were reported for 47% of surveys. Antechinus spp. comprised almost 95% of all trap deaths. Thirteen surveys provided detailed information for small ground mammal trapping, recording 111 deaths from 3651 small mammal captures. Box trap mortality in these surveys ranged from 0-7.5%, deaths being attributed to cold temperatures (generally winter) and multiple captures of individuals. Harp trap mortality stemmed from overheating, overcrowding and predation. Post-capture handling also contributed to mortality. No specific level of trap death can be ?expected? during a study as circumstances vary, but all efforts should be made to minimise the risk of deaths. This study found that mortality above 4% is unusual, resulting mainly from one-off ?extreme? mortality events. Minimising unnecessary recaptures and avoiding weather extremes should reduce mortality of small mammals during trapping studies, but will not prevent all deaths.
Demography of a yellow-footed rock-wallaby Petrogale xanthopus colony in the threatened New South Wales sub-population.
Authors: Sharp A. , Norton M. , Marks A.
Published: June 2011

The remnant New South Wales (NSW) yellow-footed rock-wallaby (Petrogale xanthopus) population underwent a substantial decline between 1985 and 1992 and remained at dangerously low levels until 1995. To determine the processes underlying this decline, a population study was conducted at one colony, between winter 1995 and winter 1998. The colony was observed to remain relatively constant in size, consisting of between 12 or 13 individuals throughout the study. Reproductive rates were found to be relatively high. Both reproduction and pouch young survival were comparable with those reported for other P. xanthopus colonies, while adult survival rates were higher than those noted in other studies. Because population size remained constant during the study and adult survivorship was consistently high, this suggested that juvenile recruitment into the colony was low. Such low levels of recruitment may have had a substantive role in the slow decline of the entire NSW P. xanthopus population. The results of this study suggest that any management actions undertaken in the NSW P. xanthopus population should focus on increasing juvenile survival rates. Further research is required to determine whether juvenile survival is constrained by predation or competition with other herbivores.
Longevity in wild populations of the squirrel glider Petaurus norfolcensis.
Authors: van der Ree R. , Harper M. J. , Crane M.
Published: June 2011

Petaurus norfolcensis were trapped between December 1996 and April 2005 at 3 sites in south-eastern Australia. In 2005 nine individuals marked in previous years were captured. Age estimates at first capture were based on body mass, tooth wear and pouch condition. Most recaptured individual were propertly assigned to the correct age category (>3 years), but the age of 2 were underestimated. This indicates uncertainty in using physical characteristics, chiefly wear of upper incisors, to estimate age in P. norfolcensis.One individual captured in 2005 was over 7 years 9 months old. This compares to captive P. breviceps and P. australis records of 9 years and 16 years respectively.