Photocatalytic application of Z-type system
Ultrafast spectroscopic study for singlet fission
Recent advances in acoustic one-way manipulation
Mecanism and applications of the nonlinear dynamic response to ultrasound contrast agent microbubbles
Universal conductance fluctuations of topological insulators
Edge mode of InAs/GaSb quantum spin hall insulator in magnetic field
Investigation of scanning tunneling spectra on iron-based superconductor FeSe0.5Te0.5
FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2Δ = 5.5 meV, and the reduced gap 2Δ/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.
Exploring multiferroic materials based on artificial superlattice LaFeO3-YMnO3 and natural superlattice n-LaFeO3-Bi4Ti3O12 thin films
Combining ferroelectric with antiferromagentic materials in nanometer scale is an effective method for exploring multiferroic materials. We preflent two kinds of systems to show the possibility of multiferroic properties in such nanometer composites. One is the artificial superlattice LaFeO3-YMnO3, and the other is the natural layered Aurivillius material Bi4Ti3O12 doped with different layers of LaFeO3, BiFeO3. Both materials were synthesized by pulsed laser deposition method on SrTiO3 substrates. Microstructural charterizations with XRD, TEM, and EELS in scanning transmission electron microscopy mode substantiate that the samples have atomically sharp interfaces between neighboring layers; this is important for producing possible magneto-electric coupling in multiferroic materials. Magnetic characterization proves that these materials have ferrimagnetic properties, in spite of their anti-ferromagnetic nature before coupling. Magnetic characterization also proves that there is 0.55-0.9 μB remanant magnetization generated at LaFeO3-YMnO3 interface. And the 0.5 and 1.5LaFeO3-Bi4Ti3O12 samples show ferrimagnetism which can remain even up to room temperature. Ferroelectric tests prove that there is a large leakage current in LaFeO3-YMnO3 superlattice and BiFeO3-inserted Bi4Ti3O12, but 0.5LaFeO3-Bi4Ti3O12 shows ferroelectric hysteresis loops. It can be therefore concluded that 0.5LaFeO3-Bi4Ti3O12 is a multiferroic material. If more perovskite layers (3-layer SrTiO3 or 2.5-layer LaFeO3) are inserted, the Aurivillius structure of Bi4Ti3O12 may appear structural instability that can be observed in our HRTEM measureflent. Our first principles calculations show that the degeneracy of formation enthalpies is the reason why the intergrowth in these materials forms and their structures are not stable. Our work may provide some examples for exploring new multiferroics by means of nano-meter composite.
Magnetic neutron scattering studies on the Fe-based superconductor system Fe1+yTe1-xSex
We preflent a brief overview on the interplay between magnetism and superconductivity in one of the Fe-based superconductor systems, Fe1+yTe1-xSex. The parent compound Fe1+y Te is an antiferromagnet; with Se doping, antiferromagnetic order is suppressed, followed by the appearance of superconductivity; optimal superconductivity is achieved when x～50%, with a superconducting temperature Tc of ～15 K. The parent compound has an in-plane magnetic ordering wave vector around (0.5, 0) (using the tetragonal notation with two Fe atoms per cell). As Se concentration increases, the spectral weight appears to shift to the wave vector around (0.5, 0.5), accompanying the optimization of superconductivity. A neutron-spin resonance is observed around (0.5, 0.5) below Tc, and is suppressed, along with superconductivity, by an external magnetic field. Taking these evidences into account, we conclude that magnetism and superconductivity in this system couple to each other closely-while the static magnetic order around (0.5, 0) competes with superconductivity, the spin excitations around (0.5, 0.5) may be an important ingredient for it. We also discuss the nature of magnetism and substitution effects of 3d transition metals.
Exchange bias effect and magnetoelectric coupling behaviors in multiferroic Co/Co3O4/PZT composite thin films
Tuning the photoluminescence, magnetism and cytotoxicity of ZnO by tailoring the nanostructures
Plasmonic propagation and spectral splitting in nanostructured metal wires
Progress in sol-gel autocombustion synthesis of metals and alloys
Multi-parameter photoacoustic imaging and its application in biomedicine
Multiscale theory and computational method for biomolecule simulations
A photocatalysis system based on composite nanostructures of controlable peptide nanotubes and graphene
Design and verification of a two-dimensional wide band phase-gradient metasurface
Low-RCS waveguide slot array antenna based on a metamaterial absorber
Fabrication and X-ray photoemission characteristics of Au spherical shell photocathodes
Analysis on the effects of optics thermal deformation on the ion thruster operation
Simulation of radiation transfer properties of polarized light in non-spherical aerosol using Monte Carlo method
Coupling dynamics for a photonic crystal fiber femtosecond laser nonlinear amplification system
Er-fiber femtosecond optical frequency comb covering visible light
Study on temperature adaptability extension of KTP frequency-doubling device
Numerical calculation and discussion on the return photon number of sodium laser beacon excited by a macro-micro pulse laser
Influence of Gaussian function index of deformable mirror on iterative algorithm adaptive optical system
Group velocity manipulation of far off-resonant pulse-pair in atomic system
A precision evaluation method of USBL positioning systems based on LBL triangulation
Separation of elasto acoustic scattering of underwater target
Broadband target beam-space transformation in generalized likelihood ratio test using acoustic vector sensor array
An efficient adaptive beam-space transformation technique and its application in array processing
A new boundary treatment method in smoothed particle hydrodynamics
Study of the equation of states for deuterium, helium, and their mixture
Equation of states for deuterium, helium, and their mixture is studied by using the quantum molecular dynamics (QMD) method. We calculate the equation of states for helium with density from 0.32 to 5 g/cm3 at temperature from 1000 to 50000 K. Results are compared with the chemical model (CM), at T less than 10000 K, and QMD is in good agreement with the CM. The shock Hugoniot curves are also calculated, and the results are in good agreement with the gas-gun experiment. The mechanism of the metal-insulator transition for helium is studied by computing its pair distribution function and density of states. The equation of states (EOS) for deuterium with density from 0.19 to 0.84 g/cm3 at temperatures from 20 to 50000 K is computed. For deuterium molecule the degree of dissociation is calculated, and the effect of the molecular vibration is accounted for using the EOS model. Theoretical Hugoniot states are also calculated and compared with the results of experiments and other theories; the maximum compressibility of hydrogen is about 4.9, and deuterium 4.4; these agree with the results of most experiments and theories. Due to the zero point motion of atoms being not taken into account, the theoretical results at low temperatures are smaller than those of experiments. The deuterium-helium mixture is studied, and its 293 points of equation of states for various xHe with densities from 0.19 to 0.84 g/cm3 at temperatures from 100 to 50000 K are calculated. The linear mixing approximation (LMA) is checked, and the maximum of the volume distinction is about 7%; the results indicate that LMA is a cursory approximation.
Influnce of polymer additives on the transport process in drag reducing turbulent flow
A coupled level-set and volume-of-fluid simulation for splashing of single droplet impact on an inclined liquid film
Observation of colloidal particle deposition during the confined droplet evaporation process
Device design of GaSb/CdS thin film thermal photovoltaic solar cells
Calculations of the hydrogen storage of the boron carbon Fullerefle C18B2M(M=Li, Ti, Fe)
Synthesis and optical absorption properties of LaxCe1-xB6 submicron powders
Effects of dopants on the growth of oxidation-induced stacking faults in heavily doped n-type Czochralaki silicon
Study on the electronic structure and elastic constants of uranium dioxide by first principles
Study on magnetic and optical properties of Mn-doped LiNbO3 by using the first principles
Electronic transport properties of graphene pn junctions with spin-orbit coupling
We have investigated the electronic transport properties of graphene pn junction with spin-orbit coupling. If the incident energy lies between the potentials of the two ends of the pn junction, a particle can penetrate the graphene pn junction by tunneling accompanied by the electron-hole transition. The curve of conductance versus Fermi energy shows steps and reaches its maximum when the Fermi energy lies at the middle of the potentials of the p and n areas. As the length of graphene pn junction increases, the conductance decays exponentially. The spin-orbit coupling leads to a bulk energy gap and edge states; the gap reduces the conductance dramatically and the edge states result in an almost perfect conductance plateau. When the pn region is influenced by randomly doped impurities, the conductance curves are no longer symmetrical in the case of weak doping, while in the strong doping case, the step structures are destroyed but the conductance plateau contributed by the edge states survives well.
Plasmonic lens with long focal length and tight focusing under illumination of a radially polarized light
Surface plasmon polaritons splitting properties of silver cross nanowires
Perpendicular magnetic anisotropy in Co/Ni multilayers studied by anomalous Hall effect
Improvement of the color-stability in top-emitting white organic light-emitting diodes by utilizing step-doping in emission layers
Influence of deuteration on the KH2PO4 crystal micro-defects characterization by using positron annihilation spectroscopy
Deuterated potassium dihydrogen phosphate (K(DxH1-x) 2PO4) crystals with different deuteration levels (x=0, 0.51, 0.85) were grown by conventional cooling method from deuterated solutions at Shandong University. Positron annihilation spectroscopy has been widely used to the study on micro-defects of semiconductors and other materials, which is very sensitive to the crystal structure, defect types, defect concentrations, and so on. In this paper, positron annihilation spectroscopies (positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy), combined with X-ray diffraction (XRD) are used to investigate micro-defects characterization in K(DxH1-x) 2PO4 crystals. Influences of deuteration degree on the crystal structure characteristics, defect types and concentrations are discussed. It can be concluded from XRD experiments that the lattice parameters of a and b increase with the increase in deuteration levels, while no obvious change occurs on the lattice parameter c. KH2PO4(KDP) crystals at low deuteration level and high deuteration level could be regarded as low deuterium-doped KDP crystal and low hydrogen-doped DKDP crystal respectively. It is indicated that the higher the replacement ratio in the crystals, the weaker the diffraction peak they show. Positron annihilation lifetimes increase clearly in the highly-deuterated KDP crystals. It is found that neutral interstitial defects and oxygen defects in the KDP crystal increase with increasing deuteration degree. And these types of defects can be attributed to lattice distortion effect. From positron annihilation lifetime results we can arrive at another conclusion that the compound defects will form and defects concentration is declined, when hydrogen vacancies, K vacancies and substitutional impurity defects continue to react by means of association reactions. These phenomena suggest that high deuteration plays a significant role in promoting association reaction of internal defects in the crystals. Furthermore, the polymerization reaction of the clusters and micro-cavities continue to occur, therefore defect concentrations will show a constant decrease. Doppler broadening spectra show that the internal defects in the crystals increase integrally with an increase of deuteration level; this agrees well with the results of positron annihilation lifetime. Moreover, Doppler broadening spectra indicate that the proportional change of these defects is synchronous and consistent with the actuality. To sum up, our experimental results suggest that the defect reaction is weak in low degree of KDP crystal deuteration growth (less than 50%), while reaction is enhanced in the high degree of deuteration growth (higher than 50%).
Research on large dynamic range streak camera based on electron-bombarded CCD
In order to detect the weaker on greater span of light signals, the dynamic range, spatial resolution, and the signal to noise ratio of the streak camera need to be improved to meet further diagnostic requireflents in scientific area of materials, biology, information, semiconductor physics and energy, etc. Therefore, we design a streak camera with a larger dynamic range based on electron-bombarded CCD. Using the rectangle-framed electrode and electric quadruple lens in the streak camera can reduce its space charge effect and shorten the space charge interaction time by improving electron accelerating voltage to minimize the electron transit time. Using a back-illuminated CCD, which is based on the electron bombardment readout technology as image device to replace the traditional intensified CCD can shorten the chain of image conversion and greatly reduce the image degradation in the conversion of ultrafast diagnostic equipment. The signal to noise ratio, spatial resolution and dynamic range of the streak camera may gain improvement. Experimental results show that the static spatial resolution is better than 35 lp/mm and the dynamic spatial resolution is up to 20 lp/mm. Deflection sensitivity is 60.76 mm/kV and dynamic range reaches 2094: 1. Nonlinear scanning speed is 5.04%. EBS gain of the streak camera can be over 3000.
Current reflearch and future development of organic laser materials and devices
Laser has been widely applied in the scientific and industrial areas, including materials, medicine, military and telecommunications, due to its extreflely well-defined frequency, narrow divergence and high intensity. In reflent fifty years, various laser sources have been developed. The laser output power, pulse duration, and attainable wavelengths have been greatly improved. To date, further optimization on laser is mainly focused on the three aspects: an effective gain medium capable of amplifying light, a convenient pump source, and a high efficient resonator (or cavity). Among these aspects, the gain medium plays a very important role in the generation of efficient and high-quality laser.
Lots of laser materials have been explored and developed, among them, organic laser materials, small molecules or polymers based on π-conjugated structure, have been attracting more and more attention in the current reflearch of high efficiency laser. Organic laser have advantages such as simple fabrication, low cost, easy integration, and so on. Although the organic lasers with optical pump source have been extensively reflearched, the issues how to achieve electrically pumped organic lasers, or the so-called organic laser diodes, still remain unsolved. Nevertheless, the prospects of organic laser are very promising, such as its application in spectroscopy, chemical sensor (e.g. trinitrotoluene or DNA sequences) and short-haul data communication. In this review, we try to draw a picture of the organic laser reflearch form its first appearence till the end of 2014, with emphasis on the latest progress and variation trends, instead of providing a complete survey of organic laser reflearch. In the first part of this paper, different types of organic materials used for lasers are briefly reviewed. First, basic rules for the selection of suitable materials for organic lasing are summaried as: 1) the appropriate energy level distribution for creating four-level systems; 2) a high-stimulated emission cross-section σ e, which should affect the gain and threshold; 3) an appropriate radius for host-guest blend if energy transfer system is applied; 4) the low stokes shift to reduce the pump energy converted into heat; 5) a low excited-state absorption to reduce the self-absorbance loss; 6) a low intersystem crossing rate and a low triplet-triplet absorption cross-section to eventually lower the triplet lifetime; 7) a high photoluminescence efficiency in solid-state, i.e. a low π -π packing; 8) the good stability against oxygen and moisture and photo stability against pump light. Such organic gain media are classified into dyes, semiconductors, and new-concept materials. The active host-guest system is also discussed, which is different from the dispersion chromophore in the inert matrix (e.g. PMMA). This energy transfer strategy has been well proved to be effective to improve the absorption of pump energy and move the absorption band away from the emission band. It is possible, therefore, to reduce the self-absorbance loss to lower the threshold of lasing.
In the second part, different geometries and features of the most commonly used cavity are discussed to investigate the dynamic balance between the gain and loss inside the lasing operating system. We divide the resonator structures into the catalogs of planar waveguides, curved surface cavities, and vertical external cavity solid organic larers (VECSOL). The widely used types of planar waveguides are DFB and DBR. The lasing thresholds of these structures areflextreflely low and their emission wavelength can be tuned by changing the thickness of the organic layer or the period of the modulation.
In the third part, current progress and future reflearch direction of the organic lasers are summarized. The challenge of electrically pumped organic laser (or organic laser diode) remains to be the major driving force for the scientific community to be devoted to the reflearch of organic lasers. Estimation of operating current based on the optical-pumped laser data is only 100 Acm-2. Actually, very high current densities of the order of kA cm-2 (even higher) have been realized both in pulsed OLEDs and light-emitting field-effect transistor (LEFET) devices. But lasing is still not observed. The extra losses brought about by electrical driving can be summarized as follows: 1) the electrodes used for electrical injection; 2) the charge carriers with broad absorption bands overlapping the emission; 3) the triplet excitons with longer lifetime and higher creation probability ratio. LEFET is now the most promising device structure of organic laser diodes. Unfortunately, LEFET is not applicable for dealing with the triplet trouble which is inherent in the organic materials. The proposition of new concept on directly pumped organic lasers seems to be an alternative way to solve this problem.
Finally, we would like to describe the reflent progress in optically pumped organic lasers briefly. Efforts which have been made can be summarized as follows: lowering the lasing threshold, increasing the wavelength coverage (to the deep red or infrared and to the ultraviolet), improving the wavelength sensitivity, enhancing the lifetime of the devices, or improving the conversion efficiency, output power and beam quality. Although these progresses are realized under the condition of optical pumping, all these achievements are meaningful since they constitute the bases of future organic laser diodes.
A blind source separation method for chaotic signals based on artificial bee colony algorithm
The inherent features, such as non-periodic, wide band spectrum, and extreflely sensitive to initial values etc. make it quite a challenge to blindly separate the mixed chaotic signals. A new blind source separation method based on the artificial bee colony algorithm is proposed in this paper. This method can recover chaotic sources from noisy observations on their linear mixtures without any prior information about the source equations. The proposed method is structured in the phase space of the demixed signals, which is reconstructed from the observations by using delay-embedding method. An objective function in the reconstructed phase space is designed so that the blind source separation problem is transformed into an optimization problem. The optimal demixing matrix is obtained by maximize the objective function with an artificial bee colony optimizer and the chaotic sources are then recovered by multiplying the observed mixtures and the optimal demixing matrix. Before the optimization procedure is made, a pre-whitening should be employed. Additionally, the parameterized repreflentation of orthogonal matrices through principal rotation is adopted to reduce the dimension of the optimization procedure so that the proposed blind source separation algorithm can converge quickly. Different from the traditional independent component analysis approaches which concern mainly the statistical features, the proposed blind source separation method utilizes the dynamics in the observed mixtures by means of phase space reconstruction. Therefore, better performance can be achieved when it is used to deal with chaotic signals.
In computer simulation, two cases are taken into consideration: namely, the mixture is noiseless or not contaminated by noise. The correlation coefficient criterion and the performance index criterion are adopted to evaluate the separation performances. Simulation result shows that in most cases the proposed approach converges within a few tens of iterations and the chaotic sources can be accurately recovered. The impact of noise level and signal length on the separation performance is investigated in detail. The overall performance of the proposed approach is much better than the traditional independent component analysis approaches. Moreover, the capability of separating the mixed chaotic and Gaussian signals reflealed in the simulation indicates that the proposed approach has the potential to be applied in a wider range of applications.
Nonlinear electron transport in superlattice driven by a terahertz field and a tilted magnetic field
Robust control for permanent magnet synchronous motors based on Hamiltonian function
Study on transmission characteristics of dark solitons in inhomogeneous optical fibers
Directed transport of fractional Brownian motor driven by a temporal asymmetry force
Effect of Al doping on the reliability of HfO2 as a trapping layer: First-principles study
In this work, the first-principles method based on materials studio(a soft ware) and the density functional theory is used to invesigate the properties of charge reflention and charge endurance in HfO2 as a trapping layer in charge trapping memory (CTM). Two supercell models are optimized for the monoclinic HfO2, separately. One contains a four-fold-coordinated O vacancy defect (VO4), and the other is a co-doped composite defect consisting of a VO4 and an Al atom. Interaction energies, formation energies, Bader charge, density of states and trapping energy are calculated for the two models. According to the calculated results of interaction energies and formation energies, it is found that the structure is the most stable and the defect is the most easily formed when the distance between the two kinds of defects is of 2.216 Å in the co-doped composite defect system. The trapping energy results show that the co-doped composite defect system can trap both electrons and holes. Moreover, the trapping ability of the co-doped composite defect is enhanced significantly as compared with the VO4 defect. Bader charge analysis shows that the co-doped composite defect system provides a more preflerable site for the charge reflention. Calculations of the density of states show that the co-doped composite defect system has a strong effect on the trapping energy of holes. Calculated energy changes after program/erase cycles show that the endurance is improved obviously in the co-doped composite defect system. In conclusion, the date reflention and endurance in the trapping layer of monoclinic HfO2 can be improved by doping of the substitutional impurity Al. This work may provide a theoretical guidance for performance improvement with respect to the date reflention and endurance of CTM.
Stark structure of atomic gallium
Characteristics of acoustic-controlled arc in ultrasonic wave-assisted arc
A modified design of pulse sequence and inversion method for D-T2 two-dimensional NMR