bluuebunny/crossref_metadata_2025 huggingface dataset:
Incoherent microwave-induced resistive states of small Josephson junctions
Authors: Koval Y. , Fistul M. V. , Ustinov A. V.
Published: December 2010

We report an experimental and theoretical study of low-voltage resistive states observed in small tunnel Josephson junctions subject to microwave radiation. The observed features result from Shapiro steps in the current–voltage characteristics and appear when both thermal fluctuations and high frequency dissipation are strong. Without microwave radiation, Josephson junctions have a phase diffusion supercurrent branch characterized by a finite small resistance and hysteretic switching to a higher voltage range under these conditions. When microwave radiation is applied, three different types of resistive states are observed in the current-voltage characteristics. First, a phase diffusion branch steadily evolves and its maximum voltage Vm increases with the microwave power. Another interesting observed feature is a zero-crossing resistive state characterized by a negative resistance. Finally, we find that the low-voltage resistive state can split into numerous hysteretic fine branches resembling incoherent Shapiro-like steps. The appearance of a particular resistive state depends on the interrelations among the Josephson energy EJ, the energy kBT of thermal fluctuations, and the microwave frequency ω. A theoretical analysis based on incoherent multi-photon absorption by a junction biased in the Josephson phase diffusion regime is in good agreement with the experimental observations.
Chiral effects in normal and superconducting carbon nanotube-based nanostructures
Authors: Parafilo A. V. , Krive I. V. , Bogachek E. N. , Landman U. , Shekhter R. I. , Jonson M.
Published: December 2010

The novel phenomenon of chiral tunneling in metallic single-wall carbon nanotubes is considered. It is induced by the interplay of electrostatic and pseudomagnetic effects in electron scattering in chiral nanotubes and is characterized by an oscillatory dependence of the electron transmission probability on the nanotube chiral angle and the strength of the scattering potential. The appearance of a special (Aharonov–Bohm-like) phase in chiral tunneling affects various phase-coherent phenomena in nanostructures. We examine chiral effects in: (i) persistent currents in circular nanotubes, (ii) Josephson currents in nanotube-based SNS junctions, and (iii) resonant electron tunneling through chiral nanotube-based quantum dots.
Detection of bottom ferromagnetic electrode oxidation in magnetic tunnel junctions by magnetometry measurements
Authors: Chen Wei , Nam Dao N. H. , Lu Jiwei , Wolf Stuart A.
Published: December 2010

Surface oxidation of the bottom ferromagnetic (FM) electrode, one of the major detrimental factors to the performance of a magnetic tunnel junction (MTJ), is difficult to avoid during the fabrication process of the MTJ’s tunnel barrier. Since Co rich alloys are commonly used for the FM electrodes in MTJs, overoxidation of the tunnel barrier results in the formation of a CoO antiferromagnetic (AF) interface layer which couples with the bottom FM electrode to form a typical AF/FM exchange bias (EB) system. In this work, surface oxidation of the CoFe and CoFeB bottom electrodes was detected via magnetometry measurements of EB characterizations including the EB field, training effect, uncompensated spin density, and enhanced coercivity. Variations in these parameters were found to be related to the surface oxidation of the bottom electrode, among them the change in coercivity is most sensitive. Annealed samples show evidence for an oxygen migration back to the MgO tunnel barrier by annealing.
Liquid separation by a graphene membrane
Authors: Fileti E. E. , Dalpian G. M. , Rivelino R.
Published: December 2010

The behavior of liquids separated by a single graphene membrane has been studied with extensive molecular dynamics (MD) simulations at ambient conditions. With the help of appropriate empirical potentials, we have exploited two liquid phases forming distinct systems; say XGY, where G stands for graphene and X (Y) represents water (W), benzene (B), or acetonitrile (A). Our MD simulations revealed important changes in the wettability patterns of these liquids near the graphene surface. For instance, WGW exhibits strong density oscillations in a thin interfacial region with thickness of ∼2.4 nm. In the case of BGB and AGA the oscillating-density interfacial region extends beyond ∼3 nm and ∼5 nm, respectively, under ambient conditions. More interestingly, our findings indicate that a liquid at one side of the graphene sheet can affect the degree of wetting on the other side, by means of dispersion interactions through the graphene membrane. These systems can offer a useful framework to understand the structural as well as thermodynamic properties of interfaces by considering a real two-dimensional substrate.
New approach to the synthesis of layered double hydroxides and associated ultrathin nanosheets in de-ionized water by laser ablation
Authors: Hur Tae-Bong , Phuoc Tran X. , Chyu Minking K.
Published: December 2010

This paper introduces a new method to synthesize layered double hydroxides and its ultrathin nanosheets in de-ionized water. By employing pulsed laser ablation, ultrathin layered double hydroxide nanosheets of Zn–Al, Co–Fe, Co–Al, and Mg–Fe were formed with a molecular thickness, corresponding to the thickness of the exfoliated two-dimensional nanosheets. The nanosheets formed directly were well-defined with a hexagonal shape, and were stable without any chemical for preventing agglomeration or formation of three-dimensional lamellar crystals. The nanosheets are assembled layer-by-layer up to the finite thickness on solid surface by the incorporation of carbonate anions from the atmospheric CO2. Observation of the seedlike layered double hydroxide nanosheets as well as the lamellar structures shows a similar structural relationship. Consequently, the laser ablation technique is deemed to have played a critical role in the formation of nanosheets. This suggests that the contamination of the as-synthesized layered double hydroxide colloidal solutions by carbonate is considerably insignificant.
Effect of irregularities in the work function and field emission properties of metals
Authors: de Assis Thiago A. , Andrade R. F. S. , de Castilho C. M. C. , Losada J. C. , Benito Rosa M. , Borondo F.
Published: December 2010

The effect of geometrical irregularities in the work function and emitting properties of metallic surfaces at low potentials is studied. For this purpose, we propose a simplified model consisting of rectangular fractures and a classical formalism for the work function determination. The dependence of the work function with the fractures size is determined by using the electrostatic image potential method. The emission current density properties when an external electric field is applied are also analyzed.
Multilevel resistive switching in Ti/CuxO/Pt memory devices
Authors: Wang Sheng-Yu , Huang Chin-Wen , Lee Dai-Ying , Tseng Tseung-Yuen , Chang Ting-Chang
Published: December 2010

The multilevel resistive switching (RS) behaviors of the Ti/CuxO/Pt device were investigated by controlling the operated parameters of current and voltage bias in this study. We demonstrated that at least five-level memory states for data storage could be determined by controlling the current compliance, the span of voltage sweeping, and the amplitude of voltage pulse imposed on the memory device. During the dc voltage sweeping mode, not only the multilevel ON-states but also the multilevel OFF-states were achieved for the multilevel storage. The RS mechanism of the Ti/CuxO/Pt device is proposed to be related to the formation/rupture of the conducting filaments, arising from the interfacial oxygen ion migration between the Ti top electrode and CuxO films. Moreover, a possible conduction scenario for the multilevel RS behaviors is also suggested. Owing to all the multilevel memory states are distinguishable and possess the nondestructive readout property, it implies that the Ti/CuxO/Pt device has the promising potential for the future multilevel-capability memory cell application.
Improved photoluminescence properties of sol-gel derived Er3+ doped silica films
Authors: Pal Sudipto , Mandal Abhijit , De Goutam , Trave Enrico , Bello Valentina , Mattei Giovanni , Mazzoldi Paolo , Sada Cinzia
Published: December 2010

Silica films (amorphous and crystalline) doped with erbium were fabricated on silica glass substrate and characterized. The inorganic-organic hybrid sol-gel method was used to prepare the films and the Na codoping induced the crystallization of silica film. Photoluminescence (PL) measurements revealed that the Er3+ ions can be excited from the ground state through an energy transfer process mediated by active defective sites in SiO2 film matrix. The annealing temperature and atmospheres have large effects on the local environment of Er3+ and the 1.54 μm PL intensity can be improved significantly by suitable heating treatments. We could correlate Er3+ sensitization effect due to the presence of carbon related species in the films. The PL intensity at nonresonant (476.5 nm) condition can be made as intense as the resonant (488 nm) one, for particular annealing conditions. Noticeable changes in PL emission intensities have not been observed whether the matrix silica film is amorphous or crystalline in nature; however, the defect-related luminescence is almost vanished in case of crystalline silica films.
Anisotropic magnetostatic interactions in arrays of ellipsoidal shaped Ni80Fe20 magnets
Authors: Jain S. , Adeyeye A. O.
Published: December 2010

We have modified the existing “rigid vortex model” to probe magnetostatic interactions in coupled elements of arbitrary shape. We predict that in coupled ellipsoidal magnets, reversal can occur by nucleating either one or two vortex cores, depending on the lattice configuration. When the ellipsoids are arranged along their major axis, the reversal occurs by nucleation of a single vortex core. However, when the ellipsoids are arranged along their minor axis, two vortex cores are nucleated. Our theoretical predictions have been validated experimentally using magnetic force microscopy.
Large reversible magnetocaloric effect due to a rather unstable antiferromagnetic ground state in Er4NiCd
Authors: Hermes Wilfried , Rodewald Ute Ch. , Pöttgen Rainer
Published: December 2010

Er 4 NiCd crystallizes with the Gd4RhIn type structure, space group F4¯3m, a=1333.3 pm. The nickel atoms have trigonal prismatic rare earth coordination. Condensation of the NiEr6 prisms leads to a three-dimensional network which leaves voids that are filled by regular Cd4 tetrahedra. Er4NiCd shows Curie–Weiss behavior above 50 K with TN=5.9 K. At field strength of 4 kOe a metamagnetic step is visible, together with the positive paramagnetic Curie-temperature (7.5 K) indicative for the rather unstable antiferromagnetic ground state. Therefore, a large reversible magnetocaloric effect (MCE) near the ordering temperature occurs and the values of the maximum magnetic-entropy change −ΔSMmax reach 18.3 J kg−1 K−1 for the field change of 5 T with no obvious hysteresis loss around 17 K. The corresponding RCP of 595 J kg−1 is relatively high as compared to other MCE materials in that temperature range. These results indicate that Er4NiCd could be a promising system for magnetic refrigeration at temperatures below liquid H2.
Josephson currents in point contacts between dirty two-band superconductors
Authors: Yerin Y. S. , Omelyanchouk A. N.
Published: December 2010

We develop a microscopic theory of the Josephson effect in point contacts between dirty two-band superconductors. A general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. This formula is used to calculate the current-phase relations and temperature dependence of the critical current in MgB2 superconductors. We also examine the effect of interband scattering on the contact characteristics of dirty superconductors. The correction to the Josephson current owing to interband scattering is found to depend on the phase shift in the bulk superconductors (i.e., the s- or s±-wave symmetry of the order parameters).
Resolving interparticle position and optical forces along the axial direction using optical coherence gating
Authors: Chow T. H. , Lee W. M. , Tan K. M. , Ng B. K. , Sheppard C. J. R.
Published: December 2010

In this paper, we demonstrate the use of coherence gating to resolve particle positions and forces in the axial direction. Through coherence gating, particle displacements and interparticle separations can be resolved with a high signal-to-noise ratio. We achieved both high depth resolvability (10−6m) and weak optical force (10−15 N) measurements in an optical trapping system using a low coherence interferometry system. Trap stiffness as low as 1.46 fN μm−1 was measured. This technique is well-suited for the direct visualization of interparticle optical-mechanical interactions.
Impact of strain on radio frequency characteristics of flexible microwave single-crystalline silicon nanomembrane p-intrinsic-n diodes on plastic substrates
Authors: Qin Guoxuan , Yuan Hao-Chih , Celler George K. , Ma Jianguo , Ma Zhenqiang
Published: December 2010

This letter presents radio frequency (rf) characterization of flexible microwave single-crystalline silicon nanomembrane (SiNM) p-intrinsic-n (PIN) diodes on plastic substrate under various uniaxial mechanical tensile bending strains. The flexible single-crystalline SiNM PIN diode shows significant/negligible performance enhancement on strains under forward/reverse operation modes from dc to 20 GHz. An rf strain equivalent circuit model is developed to analyze the underlying mechanism and reveals unproportional device parameters change with bending strains (∼0.4% tensile strain induces ∼10% change for diode internal and parasitic inductance/resistance). The study provides guidelines of properly designing and using single-crystalline SiNMs diodes for flexible monolithic microwave integrated circuits.
Persistent currents in ballistic normal-metal rings
Authors: Moskalets M.
Published: December 2010

Recent experiments have revived interest in persistent currents in mesoscopic normal-metal rings. We show that in ballistic rings in high magnetic fields, Zeeman splitting leads to periodic current quenching with a period much longer than the period of the persistent current. Simple arguments show that this effect might apply to diffusive rings as well. This paper also discusses fluctuations in the persistent current owing to thermal excitation of high energy levels. If observed, these fluctuations might reveal a coherent state of the electron system at high temperatures when the persistent current is exponentially suppressed.
Phase diagram of a current-carrying superconducting film in the absence of a magnetic field
Authors: Bezuglyi E. V. , Zolochevskii I. V.
Published: December 2010

A phase diagram of the current states of superconducting films is produced on the basis of an experimental study of the resistive transitions induced by the transport current. It is found that a comparatively narrow film of width w<5λ⊥ (λ⊥ is the penetration depth of the magnetic field) never enters a vortex state, but undergoes a direct transition from the purely superconducting state into a resistive state with phase-slip centers as soon as the current exceeds the critical Ginzburg-Landau current IcGL. The Meissner current state of films with intermediate widths 5λ⊥(T)<w<10λ⊥(T) transforms, when I>0.8IcGL, into a vortex resistive state which exists at currents 0.8IcGL<I10λ⊥(T) exists for currents IcAL<UIm, films with widths w>5λ⊥(T) enter a vortex-free resistive state with phase-slip lines.
Exact analytical solution of a classical Josephson tunnel junction problem
Authors: Kuplevakhsky S. V. , Glukhov A. M.
Published: December 2010

We give an exact and complete analytical solution of the classical problem of a Josephson tunnel junction of arbitrary length W∊(0,∞) in the presence of external magnetic fields and transport currents. Contrary to a wide-spread belief, the exact analytical solution unambiguously proves that there is no qualitative difference between so-called “small” (W⪡1) and “large” junctions (W⪢1). Another unexpected physical implication of the exact analytical solution is the existence (in the current-carrying state) of unquantized Josephson vortices carrying fractional flux and located near one of the edges of the junction. We also refine the mathematical definition of critical transport current.
Communication: On the locality of Hydrogen bond networks at hydrophobic interfaces
Authors: Lambeth Bradley P. , Junghans Christoph , Kremer Kurt , Clementi Cecilia , Site Luigi Delle
Published: December 2010

The formation of structured hydrogen bond networks in the solvation shells immediate to hydrophobic solutes is crucial for a large number of water mediated processes. A long lasting debate in this context regards the mutual influence of the hydrophobic solute into the bulk water and the role of the hydrogen bond network of the bulk in supporting the solvation structure around a hydrophobic molecule. In this context we present a molecular dynamics study of the solvation of various hydrophobic molecules where the effect of different regions around the solvent can be analyzed by employing an adaptive resolution method, which can systematically separate local and nonlocal factors in the structure of water around a hydrophobic molecule. A number of hydrophobic solutes of different sizes and two different model potential interactions between the water and the solute are investigated.
Electron-acoustic solitary waves in a nonextensive plasma
Authors: Tribeche Mouloud , Djebarni Lyes
Published: December 2010

The problem of arbitrary amplitude electron-acoustic solitary waves (EASWs) in a plasma having cold fluid electrons, hot nonextensive electrons, and stationary ions is addressed. It is found that the “Maxwellianization” process of the hot nonextensive component does not favor the propagation of the EASWs. In contrast to superthermality, nonextensivity makes the electron-acoustic solitary structure less spiky. Our theoretical analysis brings a possibility to develop more refined theories of nonlinear solitary structures in astrophysical plasmas.
Modulating the electronic structures of graphene by controllable hydrogenation
Authors: Luo Zhiqiang , Shang Jingzhi , Lim Sanhua , Li Dehui , Xiong Qihua , Shen Zexiang , Lin Jianyi , Yu Ting
Published: December 2010

The evolution of electronic structures of hydrogenated graphene with different amount of hydrogen (H) coverage was investigated by ultraviolet photoemission spectroscopy and optical absorption spectroscopy. Raman spectroscopy and x-ray photoelectron spectroscopy were used to monitor and evaluate the H coverage. At low H coverage, the sp3 CH bonds embedded within a sp2 C matrix behave as defects in graphene and depress the delocalized π electron system. At high H coverage, two localized π electron states originating from the sp2 C clusters encircled by the sp3 CH matrix appear in the electronic band structures, and an opening of a band gap has been observed.
Nanowaveguides and couplers based on hybrid plasmonic modes
Authors: Tian Jie , Ma Zhe , Li Qiang , Song Yi , Liu Zhihong , Yang Qing , Zha Chaolin , Åkerman Johan , Tong Limin , Qiu Min
Published: December 2010

Experimental demonstration of silicon nanowires based hybrid plasmonic waveguides and couplers with subwavelength mode confinement at the near infrared wavelength λ=980 nm are presented. By measuring the radiating light from the discontinuities in a nanowire, the estimated propagation length of the hybrid plasmonic waveguide is about 30 μm (corresponding to a propagation loss of ∼0.14 dB/μm). For the coupler, the experimental results show that the hybrid plasmonic modes can be efficiently coupled between two overlapping nanowires only with a 1.9 μm long coupling length.
Effects of flat-topped ion distribution and dust temperature on small amplitude dust-acoustic solitary waves and double layers in dusty plasma
Authors: Alinejad H. , Mamun A. A.
Published: December 2010

The combined effects of the flat-topped ion distribution and dust temperature are incorporated in the study of small but finite amplitude dust-acoustic (DA) solitary waves (SWs) as well double layers (DLs) in an unmagnetized dusty plasma. Due to the flat-trapped ions, our plasma model admits only rarefactive localized structures. It is found that the effects of dust temperature and resonant particles significantly modify the criteria for the existence of DA SWs and DLs, as well as significantly modify their basic properties.
Hybrid ion acceleration with ultrathin composite foils irradiated by high intensity circularly-polarized laser light
Authors: Andreev A. A. , Steinke S. , Schnuerer M. , Henig A. , Nickles P. V. , Platonov K. Y. , Sokollik T. , Sandner W.
Published: December 2010

A complete analytical description of ion acceleration in the laser radiation-pressure regime is presented. The combined effects of hot electron and light-pressure phenomena are used to qualitatively and quantitatively describe most recent experimental results in this regime. An essential part of the developed model is exhibited in the calculation of nonlinear laser light reflection and transmission properties, as well as in the spectral characterization of the laser light after interaction. The validity of the analytical model is supported by recent experimental results and by particle-in-cell simulations.
Intersubband polaritons in a one-dimensional surface plasmon photonic crystal
Authors: Zanotto Simone , Biasiol Giorgio , Degl’Innocenti Riccardo , Sorba Lucia , Tredicucci Alessandro
Published: December 2010

In this work we demonstrate the achievement of light-matter strong coupling regime between an intersubband transition and the photonic bandlike mode supported by a metallic grating. Polaritonic resonances have been identified in the reflectivity spectra at 10° incidence, with a clear anticrossing appearing when the photonic mode is tuned across the transition line. Experimental results are in good agreement with the simulations performed with a scattering-matrix approach. This cavity design can be further optimized and is likely to open the way to a new class of time-resolved measurements, as it allows pump-and-probe measurements to be performed in collinear geometries.
Transient growth in stable linearized Vlasov–Maxwell plasmas
Authors: Podesta J. J.
Published: December 2010

Large amplitude transient growth of kinetic scale perturbations in stable collisionless magnetized plasmas has recently been demonstrated using a linearized Landau fluid model. Initial perturbations with lengthscales of the order of the ion gyroradius were shown to have transient timescales that in some cases were long compared to the ion gyroperiod, Ωit⪢1. Moreover, it was suggested that such perturbations are not rare but instead form a large class within the set of all possible initial conditions. For collisionless plasmas, the Vlasov–Maxwell equations provide a more complete description of kinetic physics and the existence of transient growth of solutions for the linearized Vlasov–Maxwell system is an interesting question. The existence of transient growth of solutions is demonstrated here for a special case of the Vlasov–Maxwell equations, namely, the one dimensional Vlasov–Poisson system. The analysis is different from the standard approach of nonmodal analysis since the initial value problem is described by a Volterra integral equation of the second kind, reflecting the fact that the time evolution of the system depends on the memory of the state from time zero through time t. For the case of a thermal equilibrium plasma, it is shown how initial conditions may be constructed to obtain solutions that grow linearly in time; the duration of this growth is the time required for a thermal electron to traverse the wavelength of the initial perturbation, a timescale that can last for many plasma periods 2π/ωpe, thus demonstrating the existence of transient growth of solutions for the linearized Vlasov–Poisson system. The results suggest that the phenomenon of transient growth may be a common feature of the linearized Vlasov–Maxwell system as well as for Landau fluid models.
Experimental observation of polarized electroluminescence from edge-emission organic light emitting devices
Authors: Ran G. Z. , Jiang D. F. , Kan Q. , Chen H. D.
Published: December 2010

We have observed a strongly polarized edge-emission from an organic light emitting device (OLED) with a silicon anode and a stacked Sm/Au (or Ag) cathode. For the OLED with a Sm/Au cathode, the transverse magnetic (TM) mode is stronger than the transverse electric (TE) mode by a factor of 2, while the polarization ratio of TM:TE is close to 300 for that with a Sm/Ag cathode. The polarization results from the scattering of surface plasmon polaritons at the device boundary. Such a silicon-based OLED is potentially an electrically excited SPP source in plasmonics.
Promotion of hydrogen production using spectrally controlled thermal radiation
Authors: Maegami Yuriko , Iguchi Fumitada , Yugami Hiroo
Published: December 2010

By controlling the thermal radiation spectrum using surface grating technologies, we promote the methane steam reforming to produce hydrogen. We fabricated a two-dimensional surface grating to tune its thermal emittance peak to the vibrational absorption bands of methane and water. We demonstrated that hydrogen production strongly depends on the spectral intensity within the resonant wavelength range, and that the hydrogen production rate is four times greater than that obtained when the spectrally controlled thermal radiation is not tuned to vibrational resonances. The optical excitation of the vibrational energy levels of gas molecules is found to effectively promote hydrogen production.
Capacitive nanoelectromechanical switch based on suspended carbon nanotube array
Authors: Acquaviva D. , Arun A. , Esconjauregui S. , Bouvet D. , Robertson J. , Smajda R. , Magrez A. , Forro L. , Ionescu A. M.
Published: December 2010

We present the fabrication and high frequency characterization of a capacitive nanoelectromechanical system (NEMS) switch using a dense array of horizontally aligned single-wall carbon nanotubes (CNTs). The nanotubes are directly grown onto metal layers with prepatterned catalysts with horizontal alignment in the gas flow direction. Subsequent wetting-induced compaction by isopropanol increases the nanotube density by one order of magnitude. The actuation voltage of 6 V is low for a NEMS device, and corresponds to CNT arrays with an equivalent Young’s modulus of 4.5–8.5 GPa, and resistivity of under 0.0077 Ω⋅cm. The high frequency characterization shows an isolation of −10 dB at 5 GHz.
Photoluminescence and extinction enhancement from ZnO films embedded with Ag nanoparticles
Authors: Liu M. , Qu S. W. , Yu W. W. , Bao S. Y. , Ma C. Y. , Zhang Q. Y. , He J. , Jiang J. C. , Meletis E. I. , Chen C. L.
Published: December 2010

ZnO films embedded with Ag nanoparticles are deposited at 750 °C with a reactive radio-frequency magnetron sputtering. The films are found to have a large enhancement in the intensity of photoluminescence emission and in the extinction of incident light. The enhancement is assigned to be from the interaction between the localized surface plasmons in the Ag nanoparticels and the light. The surface plasmons in the films can be excited in a wide range, from ultraviolet to near infrared wavelength of light.
All-optical switching of diffraction gratings infiltrated with dye-doped liquid crystals
Authors: Lucchetta D. E. , Vita F. , Simoni F.
Published: December 2010

We report the realization and the characterization of an all-optical switching device based on a transmission grating recorded in a polymeric substrate infiltrated with a methyl red-doped liquid crystal. The properties of this highly nonlinear mixture are exploited to modulate the diffraction of the grating by a pump beam when a static electric field is applied. The behavior of the device is in agreement with the existing model for methyl red-doped liquid crystals.
Droplet motion in a microconfined shear flow via a three-dimensional spectral boundary element method
Authors: Khan Mohammad A. , Wang Yechun
Published: December 2010

A 3D spectral boundary element method is employed to compute the dynamics of a single droplet in a microconfined shear flow. Comparisons have been made for the motion of an initially spherical droplet near a single wall and that between two parallel plates. Investigations are conducted for the influences of the capillary number, viscosity ratio, and initial location of the droplet on the droplet deformation, orientation, velocities, as well as the transition between the initial rapid deformation and the subsequent relaxation stage. Computational results for the deformation and velocities are compared with analytical predictions. It is found that the analytical predictions are limited for small deformations, large droplet-wall distances, and near equiviscous droplets.
Rational computational design of optimal catalytic surfaces
Authors: Paul Sujata , Nardelli Marco Buongiorno
Published: December 2010

Using calculations from first-principles based on density functional theory, we introduce an innovative concept for the design of catalysts based on the tuning of the surface properties by progressive layering of thin metal films on an oxide support, where the substrate is substantially exploited as an active design element for the tuning of the reactivity of the metallic surface. We demonstrate this idea by studying the adsorption and activation properties of CO2 on Pd and oxide-supported Pd thin films.
Optical transitions and energy relaxation of hot carriers in Si nanocrystals
Authors: Poddubny A. N. , Prokofiev A. A. , Yassievich I. N.
Published: December 2010

Dynamics of hot carriers confined in Si nanocrystals is studied theoretically using atomistic tight binding approach. Radiative, Auger-like, and phonon-assisted processes are considered. The Auger-like energy exchange between electrons and holes is found to be the fastest process in the system. However, the energy relaxation of hot electron-hole pair is governed by the single optical phonon emission. For a considerable number of states in small nanocrystals, single-phonon processes are ruled out by energy conservation law.
Surface plasmon-coupled emission on metallic film coated with dye-doped polymer nanogratings
Authors: Zhang D. G. , Yuan X.-C. , Teng Jinghua
Published: December 2010

In this letter, we report the experimental results on plasmonic waves excited on a silver film coated with dye-doped poly(methyl methacrylate) nanogratings, which are characterized by leakage radiation microscopy. Various patterns of the surface plasmon-coupled emission are demonstrated with the structured nanogratings. Plasmonic waves of anisotropic wave-numbers and Bragg mirror effect are both observed in this configuration. Mechanism of the experimental results is discussed from the viewpoint of coupling between adjacent stripe loaded surface plasmons. Our work has potential application in the development of plasmon lasers.
Surface polar phonon dominated electron transport in graphene
Authors: Li X. , Barry E. A. , Zavada J. M. , Buongiorno Nardelli M. , Kim K. W.
Published: December 2010

The effects of surface polar phonons on the electronic transport properties of monolayer graphene are studied by using a Monte Carlo simulation. Specifically, the low-field electron mobility and saturation velocity are examined for different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case. While the results show that the low-field mobility can be substantially reduced by the introduction of surface polar phonon scattering, corresponding degradation of the saturation velocity is not observed for all three substrates at room temperature. It is also found that surface polar phonons can influence graphene’s electrical resistivity even at low temperature, leading potentially to inaccurate estimation of the acoustic phonon deformation potential constant.
Electrically induced conducting nanochannels in an amorphous resistive switching niobium oxide film
Authors: Jung Kyooho , Kim Yongmin , Jung Woong , Im Hyunsik , Park Baeho , Hong Jinpyo , Lee Jiyeong , Park Jongku , Lee Jeon-Kook
Published: December 2010

Metallic nanostructures that act as electrical switches between bistable resistance states are created electrically in an insulating amorphous niobium oxide thin film. The physical formation of the metallic nanostructures are probed using in situ focused ion beam scanning electron microscopy equipped with a current-voltage measurement system. While the electroforming process changes the film, dramatically inducing metallic nanochannels across it, significant changes in the film do not occur during repeated resistance switching afterward. A qualitative resistive switching model is proposed taking into account the gradual forming process.
High conductive gate leakage current channels induced by In segregation around screw- and mixed-type threading dislocations in lattice-matched InxAl1−xN/GaN heterostructures
Authors: Song J. , Xu F. J. , Yan X. D. , Lin F. , Huang C. C. , You L. P. , Yu T. J. , Wang X. Q. , Shen B. , Wei K. , Liu X. Y.
Published: December 2010

A correlation between microstructures and high gate leakage current density of Schottky contacts on lattice-matched InxAl1−xN/GaN heterostructures has been investigated by means of current-voltage measurements, conductive atom force microscopy (C-AFM), and transmission electron microscopy (TEM) investigations. It is shown that the reverse-bias gate leakage current density of Ni/Au Schottky contacts on InxAl1−xN/GaN heterostructures is more than two orders of magnitude larger than that on AlxGa1−xN/GaN ones. C-AFM and TEM observations indicate that screw- and mixed-type threading dislocations (S/M-TDs) are efficient leakage current channels in InxAl1−xN barrier and In segregation is formed around S/M-TDs. It is believed that In segregation around S/M-TDs reduces local Schottky barrier height to form conductive channels and leads to high leakage current density of Schottky contacts on InxAl1−xN/GaN heterostructures.
Identification of zinc and oxygen vacancy states in nonpolar ZnO single crystal using polarized photoluminescence
Authors: Liu J. , Zhao Y. , Jiang Y. J. , Lee C. M. , Liu Y. L. , Siu G. G.
Published: December 2010

Polarized photoluminescence spectra of the nonpolar ZnO single crystals annealed at different temperatures in air were investigated, for which the whole emission spectra from visible up to ultraviolet range for zinc and oxygen defects states are taken separately via the parallel and the crossed polarization geometries, respectively. It is also deduced from the spectra that the density of oxygen vacancy defects attains minimum for the sample annealed at 400 °C, and above which both anharmonic effects of ultraviolet emission and enhancement of defect-related deep band emission band due to the increase of oxygen and zinc vacancy defects are observed.
Room-temperature continuous wave operation of distributed feedback quantum cascade lasers with watt-level power output
Authors: Lu Q. Y. , Bai Y. , Bandyopadhyay N. , Slivken S. , Razeghi M.
Published: December 2010

We demonstrate surface-grating distributed feedback quantum cascade lasers (QCLs) with a watt-level power output at 4.75 μm. A device with a 5 mm cavity length exhibits an output power of 1.1 W in room-temperature cw operation. Single-mode operation with a side mode suppression ratio of 30 dB is obtained in the working temperature of 15–105 °C. A double-lobed far field with negligible beam steering is observed. The significance of this demonstration lies in its simplicity and readiness to be applied to standard QCL wafers with the promise of high-power performances.
Simulation study of Hohlraum experiments on SGIII-prototype laser facility
Authors: Huo Wen Yi , Ren Guoli , Lan Ke , Li Xin , Wu Changshu , Li Yongsheng , Zhai Chuanlei , Qiao Xiumei , Meng Xujun , Lai Dongxian , Zheng Wudi , Gu Peijun , Pei Wenbing , Li Sanwei , Yi Rongqing , Song Tianming , Jiang Xiaohua , Yang Dong , Jiang Shaoen , Ding Yongkun
Published: December 2010

The Hohlraum physics experiments performed on the SGIII-prototype laser facility are simulated by using our two-dimensional radiation hydrodynamic code LARED-H, and the influence of laser intensity on the two-dimensional Hohlraum simulations is studied. Both the temporal radiation temperature and the x-ray spectrum from the simulations agree well with the observations, except that the simulated M-band fraction (greater than 2 keV) is obviously smaller than the observation. According to our study, the coupling efficiency from laser to x-ray is around 70% for SGIII-prototype laser facility Hohlraums.
Simulations of multipactor in circular waveguides
Authors: Semenov V. E. , Zharova N. A. , Anderson D. , Lisak M. , Puech J.
Published: December 2010

Detailed numerical simulations have been done to investigate the properties of multipactor breakdown in circular waveguides operating in the propagating fundamental TE11 mode. Main attention has been given to a comparison between the two fundamental cases corresponding to linear and circular polarizations, respectively, of the propagating electromagnetic wave. It is found that circular polarization is considerably more susceptible to multipactor than linear polarization. The reason for this difference is clarified by a comprehensive study of the electron motion in the waveguide.
Full toroidal plasma response to externally applied nonaxisymmetric magnetic fields
Authors: Liu Yueqiang , Kirk A. , Nardon E.
Published: December 2010

The plasma response to resonant magnetic perturbation (RMP) and nonresonant perturbation fields is computed within a linear, full toroidal, single-fluid resistive magnetohydrodynamic framework. The response of resonant harmonics depends sensitively on the plasma resistivity and on the toroidal rotation. The response of nonresonant harmonics is not sensitive to most of the plasma parameters, except the equilibrium pressure. Both midplane and the off midplane odd parity RMP coils trigger a similar field response from the plasma. The RMP fields with different toroidal mode numbers trigger qualitatively similar plasma response. A simple model of the electron diamagnetic flow suggests significant effects both in the pedestal region and beyond.
The effect of ion current density amplification in a diode with passive anode in magnetic self-isolation mode
Authors: Pushkarev Alexander I. , Isakova Yulia I. , Vakhrushev Dmitry V.
Published: December 2010

The results of a study on gigawatt power pulsed ion beam parameters are presented here. The pulsed ion beam is formed by a diode with an explosive-emission potential electrode, in magnetic self-isolation mode [A. I. Pushkarev, J. I. Isakova, M. S. Saltimakov et al., Phys. Plasmas 17, 013104 (2010)]. The ion current density is 20–40 A/cm2, the energy of the ions is 200–250 keV, and the beam composition is of protons and carbon ions. Experiments have been performed on the TEMP-4M accelerator, set in double-pulse formation mode. To measure the beam parameters, we used a time-of-flight diagnosis. It is shown that the carbon ion current density, formed in a planar diode with graphite potential electrode, is five to seven times higher than the values calculated from the Child–Langmuir ratio. A model of ion current density amplification in a diode with magnetic self-isolation is proposed. The motion of electrons in the anode-cathode gap is simulated using the program CST PARTICLE STUDIO.
Electron acoustic solitary waves and double layers with superthermal hot electrons
Authors: Sahu Biswajit
Published: December 2010

The problem of arbitrary amplitude electron acoustic solitary waves (EASWs) are discussed using Sagdeev’s pseudopotential technique for a plasma comprising cold electrons, superthermal hot electrons, and stationary ions. The standard normal-mode analysis is used to study the dispersion relation for linear waves. It is found that the present plasma model supports EASWs having negative potential. The influence of superthermal hot electrons on the present plasma model is investigated for the existence of solitary waves. The investigation shows that the solitary structure ceases to exist when the parameter κ crosses a certain limit. It is also found that the small amplitude double layer solution can exist in such a plasma system in some parametric regions. It is shown that solitary structures and double layers are affected by superthermality, as well as by relevant plasma parameters.
Dynamics of laser self-triggered plasma shutter for shortening laser pulses
Authors: Xia Changquan , Liu Jiansheng , Deng Aihua , Wang Wentao , Wang Cheng , Li Ruxin , Xu Zhizhan
Published: December 2010

The dynamics of a solid foil irradiated by a circularly polarized laser pulse in the normal incidence is investigated by performing particle-in-cell simulations. After sufficiently compressed by the light pressure, the foil becomes transparent, with a part of the incident pulse transmitted through, and then it turns opaque again, blocking the tail of the pulse. It is found that the transparency dynamically depends on the motion of the compressed foil and relies on the incident pulse. Thus, the foil can be used to shorten the incident pulse as a self-triggered shutter.
Stellarator coil design and plasma sensitivity
Authors: Ku Long-Poe , Boozer Allen H.
Published: December 2010

The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first developing a simple direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sensitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, and (3) choose the ratios of the magnitudes of the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) which are either smoother or can be located much farther from the plasma boundary than those of the present design.
Generation of wakefields by whistlers in spin quantum magnetoplasmas
Authors: Misra A. P. , Brodin G. , Marklund M. , Shukla P. K.
Published: December 2010

The excitation of electrostatic wakefields in a magnetized spin quantum plasma by the classical and the spin-induced ponderomotive force (CPF and SPF, respectively) due to whistler waves is reported. The nonlinear dynamics of the whistlers and the wakefields is shown to be governed by a coupled set of nonlinear Schrödinger and driven Boussinesq-like equations. It is found that the quantum force associated with the Bohm potential introduces two characteristic length scales, which lead to the excitation of multiple wakefields in a strongly magnetized dense plasma (with a typical magnetic field strength B0≳109 T and particle density n0≳1036 m−3), where the SPF strongly dominates over the CPF. In other regimes, namely, B0≲108 T and n0≲1035 m−3, where the SPF is comparable to the CPF, a plasma wakefield can also be excited self-consistently with one characteristic length scale. Numerical results reveal that the wakefield amplitude is enhanced by the quantum tunneling effect; however, it is lowered by the external magnetic field. Under appropriate conditions, the wakefields can maintain high coherence over multiple plasma wavelengths and thereby accelerate electrons to extremely high energies. The results could be useful for particle acceleration at short scales, i.e., at nanometer and micrometer scales, in magnetized dense plasmas where the driver is the whistler wave instead of a laser or a particle beam.
Structural basis for active site closure by the poliovirus RNA-dependent RNA polymerase
Authors: Gong Peng , Peersen Olve B.
Published: December 2010

Positive-strand RNA viruses include a large number of human and animal pathogens whose essential RNA-dependent RNA polymerases (RdRPs) share a structurally homologous core with an encircled active site. RdRPs are targets for antiviral drug development, but these efforts are hindered by limited structural information about the RdRP catalytic cycle. To further our understanding of RdRP function, we assembled, purified, and then crystallized poliovirus elongation complexes after multiple rounds of nucleotide incorporation. Here we present structures capturing the active polymerase and its nucleotide triphosphate complexes in four distinct states, leading us to propose a six-state catalytic cycle involving residues that are highly conserved among positive-strand RNA virus RdRPs. The structures indicate that RdRPs use a fully prepositioned templating base for nucleotide recognition and close their active sites for catalysis using a novel structural rearrangement in the palm domain. The data also suggest that translocation by RDRPs may not be directly linked to the conformational changes responsible for active site closure and reopening.
Functional dynamics in the voltage-dependent anion channel
Authors: Villinger Saskia , Briones Rodolfo , Giller Karin , Zachariae Ulrich , Lange Adam , de Groot Bert L. , Griesinger Christian , Becker Stefan , Zweckstetter Markus
Published: December 2010

The voltage-dependent anion channel (VDAC), located in the outer mitochondrial membrane, acts as a gatekeeper for the entry and exit of mitochondrial metabolites. Here we reveal functional dynamics of isoform one of VDAC (VDAC1) by a combination of solution NMR spectroscopy, Gaussian network model analysis, and molecular dynamics simulation. Micro- to millisecond dynamics are significantly increased for the N-terminal six β-strands of VDAC1 in micellar solution, in agreement with increased B-factors observed in the same region in the bicellar crystal structure of VDAC1. Molecular dynamics simulations reveal that a charge on the membrane-facing glutamic acid 73 (E73) accounts for the elevation of N-terminal protein dynamics as well as a thinning of the nearby membrane. Mutation or chemical modification of E73 strongly reduces the micro- to millisecond dynamics in solution. Because E73 is necessary for hexokinase-I-induced VDAC channel closure and inhibition of apoptosis, our results imply that micro- to millisecond dynamics in the N-terminal part of the barrel are essential for VDAC interaction and gating.