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Stimulated Brillouin scattering (SBS) has complex dependence on the plasma electron temperature via the Landau damping, particle trapping, and consequent nonlinear frequency shift. It is found from our numerical simulation that the SBS reflectivity in its saturation stage tends to increase with the plasma electron temperature within a certain range, although the linear growth rate of SBS normally reduces with the increasing electron temperature. This is because the phase velocity of an ion acoustic wave (IAW) increases with the electron temperature, which tends to reduce the Landau damping of the IAWs and hence reduce ion trapping. In the nonlinear saturation stage, ion trapping will modify the ion distribution function and induce a negative frequency shift in the IAW. This nonlinear frequency shift will break the three-wave coupling, thereby causing saturation of the SBS. With further increase in the electron temperature, however, electron trapping will dominate over ion trapping, which induces a positive frequency shift in the IAW and can lead to the SBS saturation as well. As a result, the SBS reflectivity first increases and then decreases with increase in the electron temperature. At around the peak of the SBS reflectivity, the positive frequency shift of IAW induced by electron trapping roughly offsets the negative frequency shift induced by ion trapping. [ABSTRACT FROM AUTHOR]

The generation of ultrashort high-power light sources in the mid-infrared (mid-IR) to terahertz (THz) range is of interest for applications in a number of fields, from fundamental research to biology and medicine. Besides conventional laser technology, photon deceleration in plasma wakes provides an alternative approach to the generation of ultrashort mid-IR or THz pulses. Here, we present a photon deceleration scheme for the efficient generation of ultrashort mid-IR or THz pulses by using an intense driver laser pulse with a relatively short wavelength and a signal laser pulse with a relatively long wavelength. The signal pulse trails the driver pulse with an appropriate time delay such that it sits at the front of the second wake bubble that is driven by the driver pulse. Owing to its relatively long wavelength, the signal pulse will be subjected to a large gradient of the refractive index in the plasma wake bubble. Consequently, the photon deceleration in the plasma wake becomes faster and more efficient for signal pulses with longer wavelengths. This greatly enhances the capacity and efficiency of photon deceleration in the generation of ultrashort high-power light sources in the long-wavelength IR and THz spectral ranges. [ABSTRACT FROM AUTHOR]

Broadband lasers have been proposed as future drivers of inertial confined fusion (ICF) to enhance the laser–target coupling efficiency via the mitigation of various parametric instabilities. The physical mechanisms involved have been explored recently, but are not yet fully understood. Here, stimulated Raman scattering (SRS) as one of the key parametric instabilities is investigated theoretically and numerically for a broadband laser propagating in homogeneous plasma in multidimensional geometry. The linear SRS growth rate is derived as a function of scattering angles for two monochromatic laser beams with a fixed frequency difference δω. If δω/ω0 ∼ 1%, with ω0 the laser frequency, these two laser beams may be decoupled in stimulating backward SRS while remaining coupled for sideward SRS at the laser intensities typical for ICF. Consequently, side-scattering may dominate over backward SRS for two-color laser light. This finding of SRS transition from backward to sideward SRS is then generalized for a broadband laser with a few-percent bandwidth. Particle-in-cell simulations demonstrate that with increasing laser bandwidth, the sideward SRS gradually becomes dominant over the backward SRS. Since sideward SRS is very efficient in producing harmful hot electrons, attention needs to be paid on this effect if ultra-broadband lasers are considered as next-generation ICF drivers. [ABSTRACT FROM AUTHOR]

Electromagnetic emission via linear mode conversion from electron plasma waves (EPWs) excited by stimulated Raman scattering (SRS) of an incident laser pulse in inhomogeneous plasma is investigated theoretically and numerically. It is found that the mode conversion can occur naturally in underdense plasma region below the quarter critical density provided that EPWs are generated due to the development of backward SRS when the laser pulse is incident at certain angle with the plasma density gradient. The produced radiation may cover a broad frequency range up to half of the incident laser frequency. The dependence of the radiation conversion efficiency on the laser intensity, incident angle, laser pulse duration, plasma density scale length, and initial electron temperature is analyzed based on one-dimensional particle-in-cell simulation. In two-dimensional geometry, due to the development of sideward SRS, it is found that the mode conversion to occur even at normal incidence of the laser pulse. The radiation frequency, bandwidth, duration, and amplitude can be well controlled by the laser and plasma parameters, suggesting that it may provide a new source of tunable broadband radiation as well as a diagnosis of the development of SRS. [ABSTRACT FROM AUTHOR]

Simulations of the movement of the excited neutral atoms were performed with random sampling and the ponderomotive model. The modeling parameters were setup according to the experiment of laser acceleration of neutral helium [Nature 431(7268), 1261 (2009)]. A comparison between the simulation results and the experiment measurements is made in detail, and the characteristics of the final distribution of the Rydberg neutral atoms are analyzed. Two important factors that determine the final distribution of Rydberg neutral atoms, namely, the ponderomotive force and the original distribution of the Rydberg atoms corresponding to the distribution of the laser intensity, are discussed. [ABSTRACT FROM AUTHOR]

Pages 2 and 4: Our sample points are distributed in a space scale that should be HT ht , not HT ht . Page 3: The relationship should be HT ht but not HT ht ("2" should be outside of HT ht ), so we conversely calculated that the laser pulse length adopted in our simulation should be HT ht , not HT ht . Erratum: "Distribution of Rydberg atoms acceleration by a laser pulse" [J. Appl. Phys. [Extracted from the article]

Nominal stoichiometric NaxCo2O4 (x?=?1.0, 1.2, 1.4, 1.6, 1.8, and 2.0) polycrystals were synthesized by a solid-state reaction method. They were further pressed into pellets by the spark plasma sintering. The crystal structure and morphology of NaxCo2O4 samples were characterized by X-ray diffraction and scanning electron microscopy measurements. Good crystallinity and layered structures were observed for all the samples. Positron annihilation measurements were performed for NaxCo2O4 as a function of Na content. Two lifetime components are resolved. τ1 is attributed mainly to positron annihilation in the O-Co-O layers and shifts to Na layers only in the H3 phase. The second lifetime τ2 is due to positron annihilation in vacancy clusters which may exist in the Na layers or grain boundary region. The size of vacancy clusters grow larger but their concentration decreases with increasing Na content in the range of 1.0?1. The thermal conductivity κ, on the other hand, shows systematic decrease with increasing Na content. This suggests that the increasing spacing of O-Co-O layer could effectively reduce the thermal conductivity of NaxCo2O4. [ABSTRACT FROM AUTHOR]

Wurtzite GaN films grown by hydride vapor phase epitaxy were implanted with 280 keV C+ ions to a dose of 6×1016cm-2. Vacancy-type defects in C+-implanted GaN were probed using a slow positron beam. The increase of Doppler broadening S parameter to a high value of 1.08-1.09 after implantation indicates introduction of very large vacancy clusters. Post-implantation annealing at temperatures up to 800 °C makes these vacancy clusters to agglomerate into microvoids. The vacancy clusters or microvoids show high thermal stability, and they are only partially removed after annealing up to 1000 °C. The other measurements such as X-ray diffraction, Raman scattering and Photoluminescence all indicate severe damage and even disordered structure induced by C+-implantation. The disordered lattice shows a partial recovery after annealing above 800 °C. Amorphous regions are observed by high resolution transmission electron microscopy measurement, which directly confirms that amorphization is induced by C+-implantation. The disordered GaN lattice is possibly due to special feature of carbon impurities, which enhance the damage buildup during implantation. [ABSTRACT FROM AUTHOR]

Microstructure of unfilled and Ba-filled CoSb3 has been studied by positron lifetime measurements together with theoretical calculation. Positron trapping in intrinsic voids is observed in the CoSb3, which contributes a positron lifetime of 263 6 2 ps. After filling Ba atoms with content up to x=0.4, the positron lifetime shows continuous increase. By comparing the experimental results with calculation following the phase diagram of BaxCo4Sb12 with x in the range of 0-0.5, it is found that when the Ba content is lower than 0.16, the filling of Ba atoms is in a phase of solid solution. At x=0.2, γ phase is formed, which is mixed with solid solution. At x>0.25, transition from γ phase to a mixture of γ and α phases is confirmed. [ABSTRACT FROM AUTHOR]

Sunlight-like lasers that have a continuous broad frequency spectrum, random phase spectrum, and random polarization are formulated theoretically. With a sunlight-like laser beam consisting of a sequence of temporal speckles, the resonant three-wave coupling that underlies parametric instabilities in laser–plasma interactions can be greatly degraded owing to the limited duration of each speckle and the frequency shift between two adjacent speckles. The wave coupling can be further weakened by the random polarization of such beams. Numerical simulations demonstrate that the intensity threshold of stimulated Raman scattering in homogeneous plasmas can be doubled by using a sunlight-like laser beam with a relative bandwidth of ∼1% as compared with a monochromatic laser beam. Consequently, the hot-electron generation harmful to inertial confinement fusion can be effectively controlled by using sunlight-like laser drivers. Such drivers may be realized in the next generation of broadband lasers by combining two or more broadband beams with independent phase spectra or by applying polarization smoothing to a single broadband beam. [ABSTRACT FROM AUTHOR]

With the development of laser communication, remote sensing imaging, and other technologies, an inertial reference unit (IRU) plays an essential part in the line-of-sight (LOS) stabilization system used for acquiring, pointing, and tracking targets. The IRU provides a stable reference beam to realize accurate LOS pointing under external disturbances. Compared with the frame style IRU, the platform style IRU (PIRU) can achieve a higher bandwidth and better precision. However, mechanical resonance is introduced by a flexure hinge inevitably in the PIRU, which affects the performance of the LOS stabilization system. In this paper, an open-loop dynamic model of PIRU is established. Identification experiments are carried out with results indicating a 28.7 dB resonance peak at 27.07 Hz in the x axis and a 30.3 dB resonance peak at 26.59 Hz in the y axis. An asymmetric notch filter is used to suppress the resonance peak to achieve a higher control bandwidth. A fitness function is designed to represent the effect of resonance suppression. A particle swarm optimization algorithm is used to search for an optimal solution of the fitness function to obtain the parameters of the asymmetric notch filter. Experimental results show that the resonance peak is reduced by 97.88% and the system bandwidth reaches 159.31 Hz. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) was utilized to measure the valence band offset (ΔEV) of the TiZnSnO (TZTO)/Si heterojunction. TZTO films were deposited on Si (100) substrates using magnetron sputtering at room temperature. By using the Zn 2p3/2 and Sn 3d5/2 energy levels as references, the value of ΔEV was calculated to be 2.69 ± 0.1 eV. Combining with the experimental optical energy band gap of 3.98 eV for TZTO extracted from the UV-vis transmittance spectrum, the conduction band offset (ΔEC) was deduced to be 0.17 ± 0.1 eV at the interface. Hence, the energy band alignment of the heterojunction was determined accurately, showing a type-I form. This will be beneficial for the design and application of TZTO/Si hybrid devices. [ABSTRACT FROM AUTHOR]

Load-displacement responses and ultimate strength of polyhedral graphite particles (PGPs) undergoing in situ nano-compression at ambient temperature have been studied. The dynamic responses of PGPs to uniaxial loads exhibit a typical nonlinear elastic behavior for graphitic nanomaterials. Based on the analysis of stress-strain relationship, the intrinsic strength is slightly larger than actual ultimate strength, indicating the mechanical properties influenced by the initial defects in PGPs. For a given case, compressive Young's modulus E and third-order elastic modulus D achieve to 12.8GPa and –13.9GPa, respectively. Weibull probability analysis confirmed its broad range of structural defects inside PGPs and mechanical properties are sensitive to initial defects. The values of ultimate strength of tested PGPs with diameter of 150-400 nm fall within 2-4.5 GPa, which are in the range between shear elastic modulus C44 of turbo-g (minimum) and C44 of hex-g (maximum) in the literature. The deformation and failure mechanisms are discussed and rationalized in terms of structural factors and elastic moduli of perfect graphite crystals. [ABSTRACT FROM AUTHOR]

The plasma density grating induced by intersecting intense laser pulses can be utilized as optical compressors, polarizers, waveplates, and photonic crystals for the manipulation of ultra-high-power laser pulses. However, the formation and evolution of plasma density grating are still not fully understood as linear models are adopted to describe them usually. In this paper, two theoretical models are presented to study the formation process of plasma density grating in the nonlinear stages. In the first model, an implicit analytical solution based on the fluid equations is presented, while in the second model, a particle-mesh method is adopted. It is found that both models can describe the plasma density grating formation at different stages, well beyond the linear growth stage. More importantly, the second model can reproduce the phenomenon of ion "wave-breaking" of plasma density grating, which eventually induces the saturation and collapse of plasma density grating. Using the second model, the saturation time and maximum achievable peak density of plasma density grating are obtained as functions of laser intensity and plasma density, which can be applied to estimate the lifetime and capability of plasma density grating in experiments. The results from these two newly developed models are verified using particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

We propose a specifically designed structure to fabricate thin-film transistors using amorphous indium-gallium-zinc-oxide (a-IGZO) films as the active channel layers. The I-shaped gate electrode is employed to define the channel width, reducing overlaps between the gate and source/drain electrodes. The devices with such a structure exhibit acceptable electrical performance and stability after annealing treatment. The XPS data show that the as-deposited a-IGZO film has not a very dense structure that may induce shallow traps. A shallow trap model is proposed to explain the large threshold voltage shifts of the as-deposited device. Annealing treatment can eliminate these shallow traps and improve the device stability. [ABSTRACT FROM AUTHOR]

Considering electro-osmotic flow in axisymmetric microducts is of both fundamental interest and practical significance. In this paper, an axisymmetric lattice Boltzmann model which solves the complete nonlinear Poisson-Boltzmann equation is presented to obtain the electric potential distribution in the electrolytes, and another axisymmetric lattice Boltzmann model is employed to solve the velocity field. First, the lattice Boltzmann model is validated by the electric potential distribution in the electrolyte with analytical solutions and finite volume method. Second, velocity distributions in circular tubes at various conditions are discussed. Then, we extend the lattice Boltzmann model for steady and pulsating electro-osmotic flow through annular microducts and the influences of inner to outer radius ratio, inner to outer zeta potential ratio and oscillating frequency are investigated. In addition, a numerical study of electro-osmotic flow in circular and annular microducts considering the non-Newtonian fluid behavior is also conducted for the first time. The results show that the microannular electro-osmotic flow exhibits much difference from the planar flow and the non-Newtonian rheology has significant effect on the flow behavior as well. [ABSTRACT FROM AUTHOR]

We have verified that extraordinary transmission of long-wavelength light through extremely narrow slits in a thick metal film can be achieved by hybrid surface-plasmon and Fabry–Pérot modes. Transmittance of these ultranarrow slits, which have width and thickness of 0.56 μm and 100 μm, respectively, for a terahertz light with wavelength of 225 μm can be 2.1×108 times higher than that predicted by using classic theory. Furthermore, the corresponding ratio between transmission wavelength and slit width can be up to 400, which is over 60 times larger than that the conventional grating-based surface-plasmon modes can provide. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are employed to investigate the melting behavior and thermal stability of magnesium oxide clusters (MgO)n (n=18, 21, and 24). The rocksalt and hexagonal tube structures are two dominant low-energy structural motifs for small (MgO)n clusters and it results in the magic sizes n=3k (k is an integer). For n=6, 9, 12, and 15, the rocksalt and hexagonal tube structures have the same topological geometry, but for n≥18, the two isomers are separated by high energy barriers. The simulations show a one-step melting process for the rocksalt structures of (MgO)18,24 (no perfect rocksalt structure exists for n=21). The melting transition occurs sharply between 1800 and 1950 K for n=24 but gradually from 1400 to 2450 K for n=18. The relative root-mean-square bond length fluctuation reveals a premelting stage from about 700 K to the melting transition for the hexagonal tube structures of all the three clusters. The short-time averages of kinetic energy and a visual molecular dynamics package are used to monitor the structures along the trajectories. The low-energy isomers are identified by the quenching technique and the isomerization processes are traced. The results show that there exists a family of isomers which are only 0.1–0.4 eV higher in energy than the corresponding hexagonal tube structures and separated by low energy barriers. The premelting stage is caused by the isomerizations among these structures. The melting characteristics demonstrated in the simulations are clarified in terms of the energies of the isomers and the energy barriers separating them. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to study the modal characteristics of a second-order concentric-circular metal grating surface-emitting distributed-feedback (DFB) laser operating at terahertz regime. A series of high-order diffracted fields, which can be expressed as a Floquet–Bloch expansion of Hankel functions, is assumed to be generated from the concentric-circular metal grating. The resonant frequencies and transverse profiles of all the diffracted fields can be deduced from the related eigenequations established through the boundary conditions of the interfaces of the metal-dielectric-metal waveguide. The results show that the interference of the diffracted cylindrical waves can form two types of resonant modes, namely, quasisymmetric and quasiantisymmetric modes. Surface radiation is excited mainly by the influence of quasisymmetric modes, which exhibit constructive interference with the grating geometry. Furthermore, the resultant intensities of the diffracted waves decay exponentially from the center of the circular grating, indicating that the proposed grating geometry has the potential to realize surface terahertz radiation with excellent beam quality. The influence of grating duty cycle on the resonant conditions and transverse distributions of the diffracted fields are also investigated. [ABSTRACT FROM AUTHOR]

Backward terahertz radiation can be produced by a high-intensity laser normally incident upon an underdense plasma. It is found that terahertz radiation is generated by electrons refluxing along the bubble shell. These shell electrons have similar dynamic trajectories and emit similar backward radiations to vacuum. This scheme has been proved through electron dynamic calculations and by using an ionic sphere model. In addition, the bubble shape is found to influence the radiation frequency, and this scheme can be implemented in both uniform and up-ramp density gradient plasma targets. The terahertz radiation may be used for diagnosing the electron bubble shape in the interaction between an intense laser and plasma. All the results are presented via 2.5 dimensional particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Focuses on a study that developed a pulsed-gas jet with interesting properties. Characteristics of the jet; Laser used in the experiment; Experimental arrangement used to study the radiation produced.

In this paper, we studied the characteristics of radiation emitted by electrons accelerated in a laser-plasma interaction by using the Lienard-Wiechert field. In the interaction of a laser pulse with a underdense plasma, electrons are accelerated by two mechanisms: direct laser acceleration (DLA) and laser wakefield acceleration (LWFA). At the beginning of the process, the DLA electrons emit most of the radiation, and the DLA electrons emit a much higher peak photon energy than the LWFA electrons. As the laser-plasma interaction progresses, the LWFA electrons become the major radiation emitter; however, even at this stage, the contribution from DLA electrons is significant, especially to the peak photon energy. [ABSTRACT FROM AUTHOR]

The electromagnetic field in the electron "bubble" regime for ultra-intense laser wakefield acceleration was solved using the d'Alembert equations. Ignoring the residual electrons, we assume an ellipsoidal bubble forms under ideal conditions, with bubble velocity equal to the speed of light in vacuum. The general solution for bubble shape and electromagnetic field were obtained. The results were confirmed in 2.5D PIC (particle-in-cell) simulations. Moreover, slopes for the longitudinal electric field of larger than 0.5 were found in these simulations. With spherical bubbles, this slope is always smaller than or equal to 0.5. This behavior validates the ellipsoid assumption. [ABSTRACT FROM AUTHOR]

It is well known that if electrons are externally injected into a density upramp, then their dephasing lengths will be extended greatly, and thus these electrons will gain more energy. However, we find that a density upramp can also be used to control the beam's collimation and the emittance that occurs by self-injection in the gradient. When electrons self-inject into the wakefield in a density gradient, an electron filtering mechanism is found to occur in the injection process. Electrons with high transverse velocities are scattered and only electrons with high longitudinal to transverse velocity ratios can be candidate electrons for self-injection. This causes the trapped electrons to be more highly collimated. In addition, the injection occurs near the axis, which causes the accelerated electron beam to have reduced emittance. An ultra-collimated electron beam with an angle spread of ~1 and emittance of ~0.01 mmmrad is generated by a 2.5-dimensional particle-in-cell (2.5-D PIC) simulation. [ABSTRACT FROM AUTHOR]

The bubble structure generated by laser-plasma interactions changes in size depending on the local plasma density. The self-injection electrons' position with respect to wakefield can be controlled by tailoring the longitudinal plasma density. A regime to enhance the energy of the wakefield accelerated electrons and to improve the beam quality is proposed and achieved using layered plas-mas with increasing densities. Both the wakefield size and the electron bunch duration are signifi-cantly contracted in this regime. The electrons remain in the strong acceleration phase of the wakefield, while their energy spread decreases because of their tight spatial distribution. An elec-tron beam of 0.5 GeV with less than 1% energy spread is obtained through 2.5D particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

The effect of bubble shape in laser-plasma electron acceleration was investigated. We showed the general existence of an ellipsoid bubble. The electromagnetic field in this bubble and its dependence on bubble shape were determined through theory. The electron-trapping cross-section for different bubble aspect ratios was studied in detail. When the shape of the bubble was close to spherical, the trapping cross-section reached to the maximum. When the bubble deviated from a spherical shape, the cross-section decreased until electron injection no longer occurred. These results were confirmed by particle-in-cell simulation. [ABSTRACT FROM AUTHOR]

Proton acceleration is investigated by 2.5-dimensional particle-in-cell simulations in an interaction of an ultra intense laser with a near-critical-density plasma. It was found that multi acceleration mechanisms contribute together to a 1.67 GeV collimated proton beam generation. The W-BOA (breakout afterburner based on electrons accelerated by a wakefield) acceleration mechanism plays an important role for the proton energy enhancement in the area far from the target. The stable and continuous acceleration maintains for a long distance and period at least several pico-seconds. Furthermore, the energy scalings are also discussed about the target density and the laser intensity. [ABSTRACT FROM AUTHOR]

The mechanism of Coulomb explosion induced by the interactions of ultra-intense laser pulses with near-critical density plasmas was investigated using 2.5D particle-in-cell simulations. While the Coulomb explosion occurred continuously during pulse propagation inside the plasma, a large quantity of charge was generated and acquired in the backward direction. The accelerated ion beam had a peak energy of several tens of MeV, and the maximum energy was over hundreds MeV. A theoretical model has been proposed to estimate the total acquired charge quantity, the maximum ion energy, and their dependence on the initial plasma density. [ABSTRACT FROM AUTHOR]

Direct laser acceleration (DLA) of electron by an ultra intense and short-pulsed laser interacting with under-dense plasma is investigated based on 2.5-dimensional particle-in-cell simulation. A high-density electron beam is generated by the laser longitudinal ponderomotive force. Although the total number of DLA electrons is significantly smaller than the number of electrons trapped in the bubble, the total charge of high-energy DLA electrons (E>800MeV) reaches 67 pC/μm. It is found that the electron beam occurs in a two-stage acceleration, i.e., accelerated in vacuum by the laser directly soon after a DLA process in plasma. The beam is accelerated violently with effective acceleration gradient in 100 GeV/cm. The energy spectrum of electrons presents a Maxwellian distribution with the highest energy of about 3.1 GeV. The dependence of maximum electron energy and electric quantity with laser intensity, laser width, pulse duration, and initial plasma density are also studied. [ABSTRACT FROM AUTHOR]

The third CH stretching vibration overtone (4νCH) of the acetylene molecule has been a prototype for intra-molecular dynamics studies. Using a sensitive cavity ring-down spectrometer calibrated with precise atomic transitions, the absolute line frequencies of 50 lines of this band have been determined with sub-MHz accuracy, or relatively 2 × 10-9. The accuracy is also confirmed by the combination differences between the transitions sharing the same upper level. The improved accuracy, two orders of magnitude better than previous studies, allows us to reveal finer ro-vibrational couplings. Fitting of the rotational energies indicates that the J-dependent interactions take place after J > 7. The precise line positions present useful confinements to the models of the intra-molecular interactions of the acetylene molecule. [ABSTRACT FROM AUTHOR]

Self-formed plasma channels induced by ultra-intense and ultra-short laser pulses have been investigated with 2.5-dimensional particle-in-cell simulations. A criterion of channel formation under the highly relativistic regime is proposed and tested by simulation results. Good matches between criterion predictions and simulations are found in most cases, but small deviations occur when the plasma density is very low or near critical. The possibility of generating a channel by a femtosecond pulsed laser is also discussed. [ABSTRACT FROM AUTHOR]

We report the characteristics of HfAlO films deposited on S- and GeO2-passivated Ge substrates at 150 °C by atomic layer deposition technique using Hf(NO3)4 and Al(CH3)3 as the precursors. The x-ray photoelectron spectroscopic analyses reveal that GeO2 passivation is more effective to suppress GeOx formation than S passivation. It is demonstrated that the capacitors with GeO2 passivation exhibit better electrical properties with less hysteresis, improved interface quality, and reduced leakage current. These results indicate that using GeO2 as an interfacial layer may be a promising approach for the realization of high quality Ge-based transistor devices. [ABSTRACT FROM AUTHOR]

A dielectric-metal-dielectric (DMD) surface plasmon (SP) waveguide, in which the top and bottom dielectric layers are incorporated with scatters and optical gain, respectively, was realized to support random lasing action. For the DMD waveguide under 532 nm optical excitation, sharp peaks at around 590 nm were observed from the edge of the top dielectric layer. Furthermore, the number of sharp peaks increases with the pump intensity. The dependence of lasing threshold on the excitation area also agrees with the random laser theory. Hence, it is verified that the SP waves, which supported inside the DMD waveguide, exhibit random lasing action. [ABSTRACT FROM AUTHOR]

An analytical model is developed to study the subwavelength focusing characteristics of a binary phase Fresnel zone plate (FZP). The model shows that high numerical-aperture phase FZP under the illumination of linear polarized light produces rotationally asymmetric focal spot with beamwidth varying from 0.36λ to 0.79λ, where λ is the wavelength. On the other hand, rotationally symmetric focal spot with minimum beamwidth of 0.39λ can be obtained from the illumination of radial polarized light. [ABSTRACT FROM AUTHOR]

A surface-plasmon polariton (SPP) waveguide, which is composed of a high-index decoupling layer for the excitation of surface emission, a metal grating layer to achieve coherent optical feedback and guiding of SPP waves as well as a dye polymer medium for the light amplification, is proposed to achieve surface lasing emission. Finite-difference time-domain calculation is performed to design and optimize the lasing performance of the SPP waveguide. It is found that the corresponding laser threshold can be lower than 700 cm-1 and the quality factor can be larger than 700. [ABSTRACT FROM AUTHOR]

The paper presents a study on dynamic stabilization of filamentation instability driven by an electron beam introduced into a plasma. The results presented in the paper demonstrate that the filamentation instability is successfully stabilized by the dynamic stabilization mechanism, in which the electron beam axis oscillates. The dynamic stabilization mechanism for plasma instability was proposed in the paper [Kawata, Phys. Plasmas 19, 024503 (2012)]. In general, instabilities emerge from the perturbations of the physical quantity. Normally the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superimposition of perturbations imposed actively: if the perturbation is introduced by, for example, a driving beam axis oscillation or so, the perturbation phase can be controlled and the instability growth is mitigated by the superimposition of the growing perturbations. [ABSTRACT FROM AUTHOR]

A mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A double-layer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in single-target-based TNSA or BOA. The model has been verified by 2.5D-PIC simulations. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are employed to investigate the melting behavior and thermal stability of magnesium oxide clusters (MgO)(n) (n=18, 21, and 24). The rocksalt and hexagonal tube structures are two dominant low-energy structural motifs for small (MgO)(n) clusters and it results in the magic sizes n=3k (k is an integer). For n=6, 9, 12, and 15, the rocksalt and hexagonal tube structures have the same topological geometry, but for n>or=18, the two isomers are separated by high energy barriers. The simulations show a one-step melting process for the rocksalt structures of (MgO)(18,24) (no perfect rocksalt structure exists for n=21). The melting transition occurs sharply between 1800 and 1950 K for n=24 but gradually from 1400 to 2450 K for n=18. The relative root-mean-square bond length fluctuation reveals a premelting stage from about 700 K to the melting transition for the hexagonal tube structures of all the three clusters. The short-time averages of kinetic energy and a visual molecular dynamics package are used to monitor the structures along the trajectories. The low-energy isomers are identified by the quenching technique and the isomerization processes are traced. The results show that there exists a family of isomers which are only 0.1-0.4 eV higher in energy than the corresponding hexagonal tube structures and separated by low energy barriers. The premelting stage is caused by the isomerizations among these structures. The melting characteristics demonstrated in the simulations are clarified in terms of the energies of the isomers and the energy barriers separating them.

The current study investigated the ability of subjects to perceive source characteristics (the gender of a human walker) of a naturally occurring auditory event (human walking). A number of acoustic properties were measured and subjected to statistical analyses in order to identify those properties that differentiate male and female walking footsteps. A principal component analysis on the statistical properties of the spectral energy distributions then identified two classes of information that were important in determining subject perception of the gender of a walker: (1) the spectral peak which integrates the information about the spectral central tendency of frequency and shape of the spectral peak; and (2) the contribution of high-frequency spectral components. A follow-up experiment then manipulated these spectral properties to verify their contributions in the perceptual classification of walker gender. Additionally, the effect of shoe on the gender judgement in walking sequences was assessed by having both male and female walkers wear male's shoes.