bluuebunny/crossref_metadata_2025 huggingface dataset:
Optically mediated spatial localization of collective modes of two coupled cantilevers for high sensitivity optomechanical transducer
Authors: Fu Hao , Mao Tian-hua , Li Yong , Ding Jiang-fang , Li Jia-dong , Cao Gengyu
Published: July 2014

We demonstrate an optomechanical transducer based on two coupled cantilevers, where the spatially delocalized collective modes are optically optimized for highly sensitive detection. We show that the local densities of the collective modes on the cantilevers can be mediated effectively by optically tuning the intrinsic resonance of one cantilever. Taking the advantage of adiabatically mediating the spatial localization of collective mode, the environmental fluctuation proof measurement can be achieved by transferring the phononic information of one cantilever's motion to another free-standing low-loss cantilever. Further, theoretical analysis reveals that the transduction efficiency can also be enhanced by this optomechancial strategy.
Stress enhanced diffusion of krypton ions in polycrystalline titanium
Authors: Nsengiyumva S. , Raji A. T. , Rivière J. P. , Britton D. T. , Härting M.
Published: July 2014

An experimental investigation on the mutual influence of pre-existing residual stress and point defect following ion implantation is presented. The study has been carried out using polycrystalline titanium samples energetically implanted with krypton ions at different fluences. Ion beam analysis was used to determine the concentration profile of the injected krypton ions, while synchrotron X-ray diffraction has been used for stress determination. Ion beam analysis and synchrotron X-ray diffraction stress profile measurements of the implanted titanium samples show a clear evidence of stress-enhanced diffusion of krypton ions in titanium. It is further observed that for the titanium samples implanted at low fluence, ion implantation modifies the pre-existing residual stress through the introduction of point and open volume defects. The stress fields resulting from the ion implantation act to drift the krypton inclusions towards the surface of titanium.
Dominant thermal boundary resistance in multi-walled carbon nanotube bundles fabricated at low temperature
Authors: Vollebregt Sten , Banerjee Sourish , Chiaramonti Ann N. , Tichelaar Frans D. , Beenakker Kees , Ishihara Ryoichi
Published: July 2014

While carbon nanotubes (CNT) have been suggested as thermal management material for integrated circuits, the thermal properties, and, especially, the thermal boundary resistance (TBR) of as-grown CNT fabricated at low temperature have hardly been investigated. Here, the thermal resistance of CNT vias, with different bundle lengths and diameters fabricated at 500 °C using chemical vapour deposition, are investigated using the 3ω-method. It was found that the thermal resistance hardly changes with length except for the smallest bundle diameter of 2 μm, indicating that the TBR (109–1010 K/W per tube) dominates the thermal conduction. This is in contrast to the electrical resistance and temperature coefficient of resistance, both of which clearly increase with length. From the slope of the thermal resistance versus length of the 2 μm wide bundles, the thermal conductivity of the CNT was estimated to be 1.4–2.8 W/mK. This low thermal conductivity is attributed to the low quality of the samples as determined by Raman spectroscopy.
Coupled Dzyaloshinskii walls and their current-induced dynamics by the spin Hall effect
Authors: Martínez Eduardo , Alejos Óscar.
Published: July 2014

The nucleation of domain walls in ultrathin ferromagnetic/heavy-metal bilayers is studied by means of micromagnetic simulations. In the presence of interfacial Dzyaloshinskii-Moriya interaction, the nucleated walls naturally adopt a homochiral configuration with internal magnetization pointing antiparallely. The interaction between these walls was analyzed and described in terms of a classical dipolar force between the magnetic moments of the walls, which couples their dynamics. Additionally, the current-induced motion of two homochiral walls in the presence of longitudinal fields was also studied by means of a simple one-dimensional model and micromagnetic modeling, considering both one free-defect strip and another one with random edge roughness. It is evidenced that in the presence of pinning due to edge roughness, the in-plane longitudinal field introduces an asymmetry in the current-induced depinning, in agreement with recent experimental results.
A two-in-one superhydrophobic and anti-reflective nanodevice in the grey cicada Cicada orni (Hemiptera)
Authors: Dellieu Louis , Sarrazin Michaël , Simonis Priscilla , Deparis Olivier , Vigneron Jean Pol
Published: July 2014

Two separated levels of functionality are identified in the nanostructure which covers the wings of the grey cicada Cicada orni (Hemiptera). The upper level is responsible for superhydrophobic character of the wing, while the lower level enhances its anti-reflective behavior. Extensive wetting experiments with various chemical species and optical measurements were performed in order to assess the bi-functionality. Scanning electron microscopy imaging was used to identify the nanostructure morphology. Numerical optical simulations and analytical wetting models were used to prove the roles of both levels of the nanostructure. In addition, the complex refractive index of the chitinous material of the wing was determined from measurements.
Nonlinear coupling of left and right handed circularly polarized dispersive Alfvén wave
Authors: Sharma R. P. , Sharma Swati , Gaur Nidhi
Published: July 2014

The nonlinear phenomena are of prominent interests in understanding the particle acceleration and transportation in the interplanetary space. The ponderomotive nonlinearity causing the filamentation of the parallel propagating circularly polarized dispersive Alfvén wave having a finite frequency may be one of the mechanisms that contribute to the heating of the plasmas. The contribution will be different of the left (L) handed mode, the right (R) handed mode, and the mix mode. The contribution also depends upon the finite frequency of the circularly polarized waves. In the present paper, we have investigated the effect of the nonlinear coupling of the L and R circularly polarized dispersive Alfvén wave on the localized structures formation and the respective power spectra. The dynamical equations are derived in the presence of the ponderomotive nonlinearity of the L and R pumps and then studied semi-analytically as well as numerically. The ponderomotive nonlinearity accounts for the nonlinear coupling between both the modes. In the presence of the adiabatic response of the density fluctuations, the nonlinear dynamical equations satisfy the modified nonlinear Schrödinger equation. The equations thus obtained are solved in solar wind regime to study the coupling effect on localization and the power spectra. The effect of coupling is also studied on Faraday rotation and ellipticity of the wave caused due to the difference in the localization of the left and the right modes with the distance of propagation.
Self-field effects on instability of wave modes in a two-stream free-electron laser with an axial magnetic field
Authors: Mohsenpour Taghi , Rezaee Rami Omme Kolsoum
Published: July 2014

Free electron lasers (FEL) play major roles in the Raman Regime, due to the charge and current densities of the beam self-field. The method of perturbation has been applied to study the influence of self-electric and self-magnetic fields. A dispersion relation for two-stream free electron lasers with a helical wiggler and an axial magnetic field has been found. This dispersion relation is solved numerically to investigate the influence of self-fields on the FEL coupling and the two-stream instability. It was found that self-fields can produce very large effects on the FEL coupling, but they have almost negligible effects on two-stream instability.
Quasimonoenergetic collimated electron beams from a laser wakefield acceleration in low density pure nitrogen
Authors: Tao Mengze , Hafz Nasr A. M. , Li Song , Mirzaie Mohammad , Elsied Ahmed M. M. , Ge Xulei , Liu Feng , Sokollik Thomas , Chen Liming , Sheng Zhengming , Zhang Jie
Published: July 2014

A laser wakefield acceleration (LWFA) experiment is performed using 30 TW, 30 fs, and 800 nm laser pulses, focused onto pure nitrogen plasma having relatively low densities in the range of 0.8×1018 cm−3 to 2.7×1018 cm−3. Electron beams having a low divergence of ∼3  mrad (full-width at half-maximum) and quasi-monoenergetic peak energies of ∼105  MeV are achieved over 4-mm interaction length. The total electron beam charge reached to 2 nC, however, only 1%–2% of this (tens of pC) had energies >35 MeV. We tried different conditions to optimize the electron beam acceleration; our experiment verifies that lower nitrogen plasma densities are generating electron beams with high quality in terms of divergence, charge, pointing stability, and maximum energy. In addition, if LWFA is to be widely used as a basis for compact particle accelerators in the future, therefore, from the economic and safety points of view we propose the use of nitrogen gas rather than helium or hydrogen.
Surface electromagnetic wave equations in a warm magnetized quantum plasma
Authors: Li Chunhua , Wu Zhengwei , Yang Weihong , Chu Paul K.
Published: July 2014

Based on the single-fluid plasma model, a theoretical investigation of surface electromagnetic waves in a warm quantum magnetized inhomogeneous plasma is presented. The surface electromagnetic waves are assumed to propagate on the plane between a vacuum and a warm quantum magnetized plasma. The quantum magnetohydrodynamic model includes quantum diffraction effect (Bohm potential), and quantum statistical pressure is used to derive the new dispersion relation of surface electromagnetic waves. And the general dispersion relation is analyzed in some special cases of interest. It is shown that surface plasma oscillations can be propagated due to quantum effects, and the propagation velocity is enhanced. Furthermore, the external magnetic field has a significant effect on surface wave's dispersion equation. Our work should be of a useful tool for investigating the physical characteristic of surface waves and physical properties of the bounded quantum plasmas.
Effect of graphene on photoluminescence properties of graphene/GeSi quantum dot hybrid structures
Authors: Chen Y. L. , Ma Y. J. , Chen D. D. , Wang W. Q. , Ding K. , Wu Q. , Fan Y. L. , Yang X. J. , Zhong Z. Y. , Xu F. , Jiang Z. M.
Published: July 2014

Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488 nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325 nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures.
Statistical charge distribution over dust particles in a non-Maxwellian Lorentzian plasma
Authors: Mishra S. K. , Misra Shikha
Published: July 2014

On the basis of statistical mechanics and charging kinetics, the charge distribution over uniform size spherical dust particles in a non-Maxwellian Lorentzian plasma is investigated. Two specific situations, viz., (i) the plasma in thermal equilibrium and (ii) non-equilibrium state where the plasma is dark (no emission) or irradiated by laser light (including photoemission) are taken into account. The formulation includes the population balance equation for the charged particles along with number and energy balance of the complex plasma constituents. The departure of the results for the Lorentzian plasma, from that in case of Maxwellian plasma, is graphically illustrated and discussed; it is shown that the charge distribution tends to results corresponding to Maxwellian plasma for large spectral index. The charge distribution predicts the opposite charging of the dust particles in certain cases.
Reconnection properties in collisionless plasma with open boundary conditions
Authors: Sun H. E. , Ma Z. W. , Huang J.
Published: July 2014

Collisionless magnetic reconnection in a Harris current sheet with different initial thicknesses is investigated using a 212-D Darwin particle-in-cell simulation with the magnetosonic open boundary condition. It is found that the thicknesses of the ion dissipation region and the reconnection current sheet, when the reconnection rate Er reaches its first peak, are independent of the initial thickness of the current sheet; while the peak reconnection rate depends on it. The peak reconnection rate increases with decrease of the current sheet thickness as Er∼a−1/2, where a is the initial current sheet half-thickness.
An improved suppression method of the transverse-electromagnetic mode leakage with two reflectors in the triaxial klystron amplifier
Authors: Qi Zumin , Zhang Jun , Zhong Huihuang , Zhang Qiang , Zhu Danni
Published: July 2014

Suppression of the transverse-electromagnetic (TEM) mode leakage is crucial in the design of a triaxial klystron amplifier with high gain, because a small microwave leakage from the buncher or the output cavity could overwhelm the input signal with low power. In this paper, a specially designed reflector is proposed to suppress the TEM mode leakage, whose axial electric field is approximately zero at the beam radial position. Theoretical analysis indicates that the reflector introduces little influence on the normal modulation of the beam while keeping a high reflection coefficient. By using two such reflectors with different eigen frequencies located in front of the buncher cavity and the output cavity, respectively, an improved triaxial klystron amplifier is presented. The simulation results show that the reflectors substantially decrease the TEM mode leakage power and achieve very good isolation among the cavities. The improved triaxial klystron amplifier can operate normally with 10's kW microwave injection without self-oscillations.
Anomalous confined electron states in graphene superlattices
Authors: Anh Le H. , Chien Nguyen D. , Nam Do V.
Published: July 2014

We show that periodic scalar potentials can induce the localization of some electronic states in graphene. Particularly, localized states are found at energies outside the potential variation range and embedded in the continuum spectrum of delocalized ones. The picture of the connection of wave functions with typical symmetries defined in relevant-edge nanoribbons is employed to explain the formation of the electronic structure and to characterize/classify eigen-states in graphene superlattices.
Controlling the number of graphene sheets exfoliated from graphite by designed normal loading and frictional motion
Authors: Lee Seungjun , Lu Wei
Published: July 2014

We use molecular dynamics to study the exfoliation of patterned nanometer-sized graphite under various normal loading conditions for friction-induced exfoliation. Using highly ordered pyrolytic graphite (HOPG) as well as both amorphous and crystalline SiO2 substrate as example systems, we show that the exfoliation process is attributed to the corrugation of the HOPG surface and the atomistic roughness of the substrate when they contact under normal loading. The critical normal strain, at which the exfoliation occurs, is higher on a crystalline substrate than on an amorphous substrate. This effect is related to the atomistic flatness and stiffness of the crystalline surface. We observe that an increase of the van der Waals interaction between the graphite and the substrate results in a decrease of the critical normal strain for exfoliation. We find that the magnitude of the normal strain can effectively control the number of exfoliated graphene layers. This mechanism suggests a promising approach of applying designed normal loading while sliding to pattern controlled number of graphene layers or other two-dimensional materials on a substrate surface.
Energy minimization mechanisms of semi-coherent interfaces
Authors: Shao Shuai , Wang J. , Misra Amit
Published: July 2014

In this article, we discussed energy minimization mechanisms of semi-coherent interfaces based on atomistic simulations and dislocation theory. For example, of {111} interfaces between two face centered cubic (FCC) crystals, interface comprises of two stable structures (normal FCC stacking structure and intrinsic stacking fault structure), misfit dislocations, and misfit dislocation intersections or nodes (corresponding to the high energy stacking fault (HESF) structure). According to atomistic simulations of four interfaces, we found that (1) greater spacing between misfit dislocations and/or larger slopes of generalized stacking fault energy at the stable interface structures leads to a narrower dislocation core and a higher state of coherency in the stable interfaces; (2) the HESF region is relaxed by the relative rotation and dilation/compression of the two crystals at the node. The crystal rotation is responsible for the spiral feature at the vicinity of a node and the dilation/compression is responsible for the creation of the free volume at a node; (3) the spiral feature is gradually frail and the free volume decreases with decreasing misfit dislocation spacing, which corresponds to an increase in lattice mismatch and/or a decrease in lattice rotation. Finally, the analysis method and energy minimization mechanisms explored in FCC {111} semi-coherent interfaces are also applicable for other semi-coherent interfaces.
Thermal conductance imaging of graphene contacts
Authors: Yang Jia , Ziade Elbara , Maragliano Carlo , Crowder Robert , Wang Xuanye , Stefancich Marco , Chiesa Matteo , Swan Anna K. , Schmidt Aaron J.
Published: July 2014

Suspended graphene has the highest measured thermal conductivity of any material at room temperature. However, when graphene is supported by a substrate or encased between two materials, basal-plane heat transfer is suppressed by phonon interactions at the interfaces. We have used frequency domain thermoreflectance to create thermal conductance maps of graphene contacts, obtaining simultaneous measurements of the basal-plane thermal conductivity and cross-plane thermal boundary conductance for 1–7 graphitic layers encased between titanium and silicon dioxide. We find that the basal-plane thermal conductivity is similar to that of graphene supported on silicon dioxide. Our results have implications for heat transfer in two-dimensional material systems, and are relevant for applications such as graphene transistors and other nanoelectronic devices.
Structural and ambient/sub-ambient temperature magnetic properties of Er-substituted cobalt-ferrites synthesized by sol-gel assisted auto-combustion method
Authors: Prathapani Sateesh , Jayaraman Tanjore V. , Varaprasadarao Eswara K. , Das Dibakar
Published: July 2014

Er-substituted cobalt-ferrites CoFe2−xErxO4 (0 ≤ x ≤ 0.04) were synthesized by sol-gel assisted auto-combustion method. The precursor powders were calcined at 673–873 K for 4 h, subsequently pressed into pellets and sintered at 1273 K for 4 h. X-ray diffraction (XRD) confirmed the presence of the spinel phase for all the compositions and, additional orthoferrite phase for higher compositions (x = 0.03 and 0.04). The XRD spectra and the Transmission Electron Microscopy micrographs indicate that the nanocrystalline particulates of the Er-substituted cobalt ferrites have crystallite size of ∼120–200 nm. The magnetization curves show an increase in saturation magnetization (MS) and coercivity (HC) for Er-substituted cobalt-ferrites at sub-ambient temperatures. MS for CoFe2O4, CoFe0.99Er0.01O4, CoFe0.98Er0.02O4, and CoFe0.97Er0.03O4 peak at 89.7 Am2/kg, 89.3 Am2/kg, 88.8 Am2/kg, and 87.1 Am2/kg, respectively, at a sub-ambient temperature of ∼150 K. HC substantially increases with decrease in temperature for all the compositions, while it peaks at x = 0.01−0.02 at all temperatures. The combination of Er content—x ∼ 0.02 and the temperature—∼5 K provides the maximum HC ∼ 984 kA/m. Er-substituted cobalt-ferrites have higher cubic anisotropy constant, K1, compared to pure cobalt-ferrite at ambient/sub-ambient temperatures. K1 gradually increases for all compositions in the temperature decreasing from 300 to 100 K. While K1 peaks at ∼150 K for pure cobalt-ferrite, it peaks at ∼50 K for CoFe0.99Er0.01O4, CoFe0.98Er0.02O4, and CoFe0.96Er0.04O4. The MS (∼88.7 Am2/kg), at 5 K, for Er substituted cobalt-ferrite is close to the highest values reported for Sm and Gd substituted cobalt-ferrites. The MS (∼83.5 Am2/kg) at 300 K for Er-substituted cobalt-ferrite is the highest among the lanthanide series element substituted cobalt-ferrites. The HC (at 5 K) for Er substituted cobalt-ferrite is close to the highest values observed for La, Ce, Nd, Sm, and Gd substituted cobalt-ferrites.
Multi-metastable states induced by the optical pump-probe process in terahertz quantum cascade lasers
Authors: Wang F. , Guo X. G. , Wang C. , Cao J. C.
Published: July 2014

The optical pump-probe process in terahertz quantum cascade lasers is studied theoretically by using the open system simulation method. The emitter injection is considered and the charge neutrality in the active region is broken. We find that nonequilibrium oscillations may appear in the recovery processes. In particular, the formation of different equilibrium values of the population change after the periodic pulse pumping is observed clearly. Here, the phenomenon of multi-metastable states stems from the electron regulation by the emitter injection. Finally, we discuss the important impacts of the equilibrium stabilization time and obtain an in-depth understanding of the emitter injection.
Elastic anisotropy and shear-induced atomistic deformation of tetragonal silicon carbon nitride
Authors: Yan Haiyan , Zhang Meiguang , Zhao Yaru , Wei Qun , Zhou Xinchun
Published: July 2014

First-principles calculations are employed to provide a fundamental understanding of the structural features, elastic anisotropy, shear-induced atomistic deformation behaviors, and its electronic origin of the recently proposed superhard t-SiCN. According to the dependences of the elastic modulus on different crystal directions, the t-SiCN exhibits a well-pronounced elastic anisotropy which may impose certain limitations and restrictions on its applications. The further mechanical calculations demonstrated that t-SiCN shows lower elastic moduli and ideal shear strength than those of typical hard substances of TiN and TiC, suggesting that it cannot be intrinsically superhard as claimed in the recent works. We find that the failure modes of t-SiCN at the atomic level during shear deformation can be attributed to the breaking of C-C bonds through the bonding evolution and electronic localization analyses.
Nanoscale monoclinic domains in epitaxial SrRuO3 thin films deposited by pulsed laser deposition
Authors: Ghica C. , Negrea R. F. , Nistor L. C. , Chirila C. F. , Pintilie L.
Published: July 2014

In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO3 layers used as bottom electrodes in multiferroic coatings onto SrTiO3 substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO3 thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO3 orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO3 bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (−4% ÷ −5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO6 octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO3 structure.
Optical gas sensing responses in transparent conducting oxides with large free carrier density
Authors: Ohodnicki P. R. , Andio M. , Wang C.
Published: July 2014

Inherent advantages of optical-based sensing devices motivate a need for materials with useful optical responses that can be utilized as thin film functional sensor layers. Transparent conducting metal oxides with large electrical conductivities as typified by Al-doped ZnO (AZO) display attractive properties for high temperature optical gas sensing through strong optical transduction of responses conventionally monitored through changes in measured electrical resistivity. An enhanced optical sensing response in the near-infrared and ultraviolet/visible wavelength ranges is demonstrated experimentally and linked with characteristic modifications to the dielectric constant due to a relatively high concentration of free charge carriers. The impact of light scattering on the magnitude and wavelength dependence of the sensing response is also discussed highlighting the potential for tuning the optical sensing response by controlling the surface roughness of a continuous film or the average particle size of a nanoparticle-based film. The physics underpinning the optical sensing response for AZO films on planar substrates yields significant insight into the measured sensing response for optical fiber-based evanescent wave absorption spectroscopy sensors employing an AZO sensing layer. The physics of optical gas sensing discussed here provides a pathway towards development of sensing materials for extreme temperature optical gas sensing applications. As one example, preliminary results are presented for a Nb-doped TiO2 film with sufficient stability and relatively large sensing responses at sensing temperatures greater than 500 °C.
Photoluminescence studies on self-organized 1.55-μm InAs/InGaAsP/InP quantum dots under hydrostatic pressure
Authors: Zhou P. Y. , Dou X. M. , Wu X. F. , Ding K. , Luo S. , Yang T. , Zhu H. J. , Jiang D. S. , Sun B. Q.
Published: July 2014

We report an experimental study on the optical properties of the self-organized 1.55-μm InAs/InGaAsP/InP quantum dots (QDs) under hydrostatic pressure up to 9.5 GPa at 10 K. The obtained pressure coefficients of emissions from InGaAsP to InAs QDs are 92 meV/GPa and 76 meV/GPa, respectively. Their photoluminescence intensities are found to decrease significantly with increasing pressure due to the pressure-induced Γ-X mixing of InGaAsP at about 8.5 GPa. The lifetime of excitonic emission from QDs decreases from about 1.15 at zero pressure to about 1.05 ns at 7.41 GPa. The wavelength of QD emission was tuned from 1.55 to 0.9 μm by applying a pressure of 8 GPa, displaying the feasibility for indirectly characterizing the individual InAs/InGaAsP/InP QDs of 1.55-μm emission (at zero pressure) under high-pressure using silicon avalanche photodiode.
Complex dielectric constant of various biomolecules as a function of wavelength using surface plasmon resonance
Authors: Paliwal Ayushi , Tomar Monika , Gupta Vinay
Published: July 2014

Present study focuses on determination of complex dielectric constant of biomolecules as function of frequency by means of surface plasmon resonance (SPR) technique without losing their biofunctionality. Surface plasmon modes have been excited in Kretschmann configuration at interface of ZnO-Au thin films. Various biomolecules (glucose oxidase, cholesterol oxidase, urease, and uricase) have been immobilized successfully on surface of ZnO thin film by electrostatic interaction. SPR reflectance curves for all biomolecules were recorded separately at different wavelengths (407–635 nm). Complex dielectric constant was determined by fitting the experimental SPR data with Fresnel's equations. Dielectric constant of all biomolecules shows frequency dispersion and attributed to ionic polarization.
Enhancement of photoacoustic emission from self-supported plasmonic multilayers
Authors: Namura Kyoko , Nakajima Kaoru , Kimura Kenji , Suzuki Motofumi
Published: July 2014

In this paper, we demonstrate remarkable photoacoustic emission from self-supported Au nanoparticle/dielectric/Ag mirror structures. They were prepared by depositing thin films on both sides of a 50-nm-thick silicon nitride membrane. The photoacoustic emission generated by the self-supported sample is more than 2 orders of magnitude larger than that of a similar structure supported by a Si wafer at a laser modulation frequency of 1 kHz. In this frequency region, the thermal diffusion length becomes much greater than the thickness of the multilayers, so that the photoacoustic amplitude is determined mainly by the thermal conductivity of the substrate. Therefore, the large enhancement of the photoacoustic emission can be understood in terms of the reduced thermal conductivity of the substrate.
Silicon carbide photonic crystal cavities with integrated color centers
Authors: Calusine Greg , Politi Alberto , Awschalom David D.
Published: July 2014

The recent discovery of color centers with optically addressable spin states in 3C silicon carbide (SiC) similar to the negatively charged nitrogen vacancy center in diamond has the potential to enable the integration of defect qubits into established wafer scale device architectures for quantum information and sensing applications. Here, we demonstrate the design, fabrication, and characterization of photonic crystal cavities in 3C SiC films with incorporated ensembles of color centers and quality factor (Q) to mode volume ratios similar to those achieved in diamond. Simulations show that optimized H1 and L3 structures exhibit Q's as high as 45 000 and mode volumes of approximately (λ/n)3. We utilize the internal color centers as a source of broadband excitation to characterize fabricated structures with resonances tuned to the color center zero phonon line and observe Q's in the range of 900–1500 with narrowband photoluminescence collection enhanced by up to a factor of 10. By comparing the Q factors observed for different geometries with finite-difference time-domain simulations, we find evidence that nonvertical sidewalls are likely the dominant source of discrepancies between our simulated and measured Q factors. These results indicate that defect qubits in 3C SiC thin films show clear promise as a simple, scalable platform for interfacing defect qubits with photonic, optoelectronic, and optomechanical devices.
Hydrogenation of the CuPL center in silicon
Authors: Yarykin Nikolai , Weber Jörg
Published: July 2014

The CuPL center, a complex of four copper atoms in silicon with the zero-phonon photoluminescence line at 1014 meV and the donor level at 0.1 eV above the top of the valence band, is studied in the process of hydrogenation at 380 K. Complexes of a substitutional copper atom (Cus) with one and two hydrogen atoms are observed to form in the hydrogenated region at the expense of CuPL, while no isolated Cus atoms are detected. Our results indicate that the addition of a single hydrogen atom induces the dissociation of all interstitial Cu atoms which decorate the Cus core of the CuPL center.
Synchronization in node of complex networks consist of complex chaotic system
Authors: Wei Qiang , Xie Cheng-jun , Liu Hong-jun , Li Yan-hui
Published: July 2014

A new synchronization method is investigated for node of complex networks consists of complex chaotic system. When complex networks realize synchronization, different component of complex state variable synchronize up to different scaling complex function by a designed complex feedback controller. This paper change synchronization scaling function from real field to complex field for synchronization in node of complex networks with complex chaotic system. Synchronization in constant delay and time-varying coupling delay complex networks are investigated, respectively. Numerical simulations are provided to show the effectiveness of the proposed method.
Proton conduction in biopolymer exopolysaccharide succinoglycan
Authors: Kweon Jin Jung , Lee Kyu Won , Kim Hyojung , Lee Cheol Eui , Jung Seunho , Kwon Chanho
Published: July 2014

Protonic currents play a vital role in electrical signalling in living systems. It has been suggested that succinoglycan plays a specific role in alfalfa root nodule development, presumably acting as the signaling molecules. In this regard, charge transport and proton dynamics in the biopolymer exopolysaccharide succinoglycan have been studied by means of electrical measurements and nuclear magnetic resonance (NMR) spectroscopy. In particular, a dielectric dispersion in the system has revealed that the electrical conduction is protonic rather electronic. Besides, our laboratory- and rotating-frame 1H NMR measurements have elucidated the nature of the protonic conduction, activation of the protonic motion being associated with a glass transition.
X-ray excited ZnS:Cu,Co afterglow nanoparticles for photodynamic activation
Authors: Ma Lun , Zou Xiaoju , Bui Brian , Chen Wei , Song Kwang Hyun , Solberg Timothy
Published: July 2014

Copper and cobalt co-doped ZnS (ZnS:Cu,Co) afterglow nanoparticles were conjugated to photosensitizer tetrabromorhodamine-123 (TBrRh123) and efficient energy transfer from the nanoparticles to TBrRh123 was observed. In addition to their X-ray excited luminescence, the ZnS:Cu,Co nanoparticles also show long lasting afterglow, which continuously serve as a light source for photodynamic therapy (PDT) activation. Compared to TBrRh123 or ZnS:Cu,Co alone, the ZnS:Cu,Co-TBrRh123 conjugates show low dark toxicity but high X-ray induced toxicity to human prostate cancer cells. The results indicate that the ZnS:Cu,Co afterglow nanoparticles have a good potential for PDT activation.
A novel metamaterial filter with stable passband performance based on frequency selective surface
Authors: Fang C. Y. , Gao J. S. , Liu Hai
Published: July 2014

In this paper, a novel metamaterial filter based on frequency selective surface (FSS) is proposed. Using the mode matching method, we theoretically studied the transmission performance of the structure. Results show that, by rotating its neighboring elements 90 degree, the novel filter has a better stability to angle of incidence than traditional structures for TE and TM polarization. As the incident angles vary from 0 to 50 degrees, the metamaterial filter exhibits a transmittance higher than 0.98 and the center frequency slightly shifts downward (from 10 GHz to 0.96 GHz) for TE polarization. For TM polarization, a transmittance of 0.98 is achieved and the center frequency retains 0.96 GHz with the varying of the incident angles. Furthermore, an experimental prototype fabricated was tested in a microwave chamber, and the measured results show good agreement with the simulated ones.
Parallel vacuum arc discharge with microhollow array dielectric and anode
Authors: Feng Jinghua , Zhou Lin , Fu Yuecheng , Zhang Jianhua , Xu Rongkun , Chen Faxin , Li Linbo , Meng Shijian
Published: July 2014

An electrode configuration with microhollow array dielectric and anode was developed to obtain parallel vacuum arc discharge. Compared with the conventional electrodes, more than 10 parallel microhollow discharges were ignited for the new configuration, which increased the discharge area significantly and made the cathode eroded more uniformly. The vacuum discharge channel number could be increased effectively by decreasing the distances between holes or increasing the arc current. Experimental results revealed that plasmas ejected from the adjacent hollow and the relatively high arc voltage were two key factors leading to the parallel discharge. The characteristics of plasmas in the microhollow were investigated as well. The spectral line intensity and electron density of plasmas in microhollow increased obviously with the decease of the microhollow diameter.
An unusual route to polarization reversal in ferroelectric ultrathin nanowires
Authors: Herchig R. , Chang Ch.-M. , Mani B. K. , Ponomareva I.
Published: July 2014

Ferroelectric nanowires are promising candidates for miniaturized ferroelectric devices. Some potential nanoscale applications of the nanowires, such as ultra high density ferroelectric memory, utilize their reversible polarization. To meet the ever increasing demand for low energy consumption, it is extremely desirable to reduce the operational fields associated with polarization reversal. In this Letter, we use first-principles-based simulations to explore an unusual route to polarization reversal that utilizes a combination of relatively low bias field and THz pulsed radiation. Such an approach allows for lower operational fields and may lead to other potential applications such as THz radiation sensing and remote switches.
Enhancement of hole injection and electroluminescence by ordered Ag nanodot array on indium tin oxide anode in organic light emitting diode
Authors: Jung Mi , Mo Yoon Dang , Kim Miyoung , Kim Chulki , Lee Taikjin , Hun Kim Jae , Lee Seok , Lim Si-Hyung , Woo Deokha
Published: July 2014

We report the enhancement of hole injection and electroluminescence (EL) in an organic light emitting diode (OLED) with an ordered Ag nanodot array on indium-tin-oxide (ITO) anode. Until now, most researches have focused on the improved performance of OLEDs by plasmonic effects of metal nanoparticles due to the difficulty in fabricating metal nanodot arrays. A well-ordered Ag nanodot array is fabricated on the ITO anode of OLED using the nanoporous alumina as an evaporation mask. The OLED device with Ag nanodot arrays on the ITO anode shows higher current density and EL enhancement than the one without any nano-structure. These results suggest that the Ag nanodot array with the plasmonic effect has potential as one of attractive approaches to enhance the hole injection and EL in the application of the OLEDs.
Time evolution studies of laser induced chemical changes in InAs nanowire using Raman spectroscopy
Authors: Pal Suparna , Aggarwal R. , Kumari Gupta Vandna , Ingale Alka
Published: July 2014

We report the study of time evolution of chemical changes on the surface of an InAs nanowire (NW) on laser irradiation in different power density regime, using Raman spectroscopy for a time span of 8–16 min. Mixture of metastable oxides like InAsO4, As2O3 are formed upon oxidation, which are reflected as sharp Raman peaks at ∼240–254 and 180–200 cm−1. Evidence of removal of arsenic layer by layer is also observed at higher power density. Position controlled laser induced chemical modification on a nanometer scale, without changing the core of the NW, can be useful for NW based device fabrication.
A probability model for the strength of carbon nanotubes
Authors: Xu X. Frank , Jie Yuxin , Beyerlein Irene J.
Published: July 2014

A longstanding controversy exists on the form of the probability distribution for the strength of carbon nanotubes: is it Weibull, lognormal, or something else? We present a theory for CNT strength through integration of weakest link scaling, flaw statistics, and brittle fracture. The probability distribution that arises exhibits multiple regimes, each of which takes the form of a Weibull distribution. Our model not only gives a possible resolution to the debate but provides a way to attain reliable estimates of CNT strength for materials design from practical-sized (non-asymptotic) data sets of CNT strength. Last, the model offers an explanation for the severe underestimation of CNT strength from strength tests of CNT bundles.
Carbon doping induced peculiar transport properties of boron nitride nanoribbons p-n junctions
Authors: Liu N. , Gao G. Y. , Zhu S. C. , Ni Y. , Wang S. L. , Liu J. B. , Yao K. L.
Published: July 2014

By applying nonequilibrium Green's function combined with density functional theory, we investigate the electronic transport properties of carbon-doped p-n nanojunction based on hexagonal boron nitride armchair nanoribbons. The calculated I-V curves show that both the center and edge doping systems present obvious negative differential resistance (NDR) behavior and excellent rectifying effect. At low positive bias, the edge doping systems possess better NDR performance with larger peak-to-valley ratio (∼105), while at negative bias, the obtained peak-to-valley ratio for both of the edge and center doping systems can reach the order of 107. Meanwhile, center doping systems present better rectifying performance than the edge doping ones, and giant rectification ratio up to 106 can be obtained in a wide bias range. These outstanding transport properties are explained by the evolution of the transmission spectra and band structures with applied bias, together with molecular projected self-consistent Hamiltonian eigenvalues and eigenstates.
Effects of symmetry and spin configuration on spin-dependent transport properties of iron-phthalocyanine-based devices
Authors: Cui Li-Ling , Yang Bing-Chu , Li Xin-Mei , Cao Can , Long Meng-Qiu
Published: July 2014

Spin-dependent transport properties of nanodevices constructed by iron-phthalocyanine (FePc) molecule sandwiched between two zigzag graphene nanoribbon electrodes are studied using first-principles quantum transport calculations. The effects of the symmetry and spin configuration of electrodes have been taken into account. It is found that large magnetoresistance, large spin polarization, dual spin-filtering, and negative differential resistance (NDR) can coexist in these devices. Our results show that 5Z-FePc system presents well conductive ability in both parallel (P) and anti-parallel (AP) configurations. For 6Z-FePc-P system, spin filtering effect and large spin polarization can be found. A dual spin filtering and NDR can also be shown in 6Z-FePc-AP. Our studies indicate that the dual spin filtering effect depends on the orbitals symmetry of the energy bands and spin mismatching of the electrodes. And all the effects would open up possibilities for their applications in spin-valve, spin-filter as well as effective spin diode devices.
Impact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface
Authors: Horsley K. , Beal R. J. , Wilks R. G. , Blum M. , Häming M. , Hanks D. A. , Weir M. G. , Hofmann T. , Weinhardt L. , Bär M. , Potter B. G. , Heske C.
Published: July 2014

To enable an understanding and optimization of the optoelectronic behavior of CdTe-ZnO nanocomposites, the morphological and chemical properties of annealed CdTe/ZnO interface structures were studied. For that purpose, CdTe layers of varying thickness (4–24 nm) were sputter-deposited on 100 nm-thick ZnO films on surface-oxidized Si(100) substrates. The morphological and chemical effects of annealing at 525 °C were investigated using X-ray Photoelectron Spectroscopy (XPS), X-ray-excited Auger electron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. We find a decrease of the Cd and Te surface concentration after annealing, parallel to an increase in Zn and O signals. While the as-deposited film surfaces show small grains (100 nm diameter) of CdTe on the ZnO surface, annealing induces a significant growth of these grains and separation into islands (with diameters as large as 1 μm). The compositional change at the surface is more pronounced for Cd than for Te, as evidenced using component peak fitting of the Cd and Te 3d XPS peaks. The modified Auger parameters of Cd and Te are also calculated to further elucidate the local chemical environment before and after annealing. Together, these results suggest the formation of tellurium and cadmium oxide species at the CdTe/ZnO interface upon annealing, which can create a barrier for charge carrier transport, and might allow for a deliberate modification of interface properties with suitably chosen thermal treatment parameters.
Terahertz radiation induced chaotic electron transport in semiconductor superlattices with a tilted magnetic field
Authors: Wang C. , Wang F. , Cao J. C.
Published: July 2014

Chaotic electron transport in semiconductor superlattice induced by terahertz electric field that is superimposed on a dc electric field along the superlattice axis are studied using the semiclassical motion equations including the effect of dissipation. A magnetic field that is tilted relative to the superlattice axis is also applied to the system. Numerical simulation shows that electrons in superlattice miniband exhibit complicate nonlinear oscillating modes with the influence of terahertz radiation. Transitions between frequency-locking and chaos via pattern forming bifurcations are observed with the varying of terahertz amplitude. It is found that the chaotic regions gradually contract as the dissipation increases. We attribute the appearance of complicate nonlinear oscillation in superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode relative to Bloch oscillation and cyclotron oscillation.
Superconducting nanowire single photon detectors fabricated from an amorphous Mo0.75Ge0.25 thin film
Authors: Verma V. B. , Lita A. E. , Vissers M. R. , Marsili F. , Pappas D. P. , Mirin R. P. , Nam S. W.
Published: July 2014

We present the characteristics of superconducting nanowire single photon detectors (SNSPDs) fabricated from amorphous Mo0.75Ge0.25 thin-films. Fabricated devices show a saturation of the internal detection efficiency at temperatures below 1 K, with system dark count rates below 500 cps. Operation in a closed-cycle cryocooler at 2.5 K is possible with system detection efficiencies exceeding 20% for SNSPDs which have not been optimized for high detection efficiency. Jitter is observed to vary between 69 ps at 250 mK and 187 ps at 2.5 K using room temperature amplifiers.
Double Dirac cones in phononic crystals
Authors: Li Yan , Wu Ying , Mei Jun
Published: July 2014

A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.