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This work proposes a low-profile circularly polarized folded reflectarray antenna (CPFRA). Compared to traditional CPFRA that comprise the main reflectarray, a polarization grid (PG), and a linear-to-circular polarization (LP-CP) converter, the proposed CPFRA utilizes a polarization-sensitive LP-CP converter that plays the roles of both PG and LP-CP converter to minimize the CPFRA profile. One period of the polarization-sensitive LP-CP converter consists of an LP and a CP patch on the bottom and top layer of the substrates, respectively, which are connected by a metalized via. Due to its frequency-selective characteristic, the polarization-sensitive LP-CP surface can simultaneously reflect the x-polarized waves and transfer the received y-polarized waves into the CP state. A 1-bit unit cell at the bottom layer is adopted for polarization conversion and phase shift. A planar patch antenna is integrated as the primary feeding source. A high-gain circularly polarized folded reflectarray antenna at the X-band is designed, fabricated, and measured. Both simulated and measured results demonstrate the advantages of high gain and a lower profile of the proposed CPFRA compared to those in its traditional counterparts.

According to the strange quark matter hypothesis, pulsars may actually be strange stars composed of self-bound strange quark matter. The normal matter crust of a strange star, unlike that of a normal neutron star, is supported by a strong electric field. A gap is then presented between the crust and the strange quark core. Therefore, peculiar core-crust oscillation may occur in a strange star, which can produce distinctive gravitational waves. In this paper, the waveforms of such gravitational waves are derived using a rigid model. We find that the gravitational waves are extremely weak and undetectable, even for the next-generation detectors. Therefore, the seismology of a strange star is not affected by the core-crust oscillation. Observers will have to search for other effects to diagnose the existence of the crust., Comment: 9 pages, 1 figure, published in the journal Universe as a contribution to the special issue "Advances in Astrophysics and Cosmology - in Memory of Prof. Tan Lu"

Recently developed solid-state catalysts can mediate carbon dioxide (CO

In this paper, we extend the single-step pseudo-spectral method for nonlinear Volterra integral equations of the second kind to the multistep pseudo-spectral method. We also analyze the convergence of the hp-version of the multistep pseudo-spectral method under the L 2-norm, and the result shows that the scheme enjoys high order accuracy and can be implemented in a stable and efficient manner. In addition, it is very suitable for long time calculations and large step size situations. Numerical experiments confirm the theoretical expectations.

Disponible preprint en: arXiv:1812.04023v1 [astro-ph.HE] [v1] Mon, 10 Dec 2018 19:00:52 UTC (4,376 KB), In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.© 2018, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature., This work was supported by the Royal Society, ERC Starting (Grant No. 639217), the European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Global Fellowship (Grant No. 703916), the National Natural Science Foundation of China (Grant Nos. 11233001, 11773014, 11633007, 11403074, 11333005, 11503008, and 11590781), the National Basic Research Program of China (Grant No. 2015CB857100), NASA (Grant No. NNX13AD28A), an ARC Future Fellowship (Grant No. FT120100363), the National Science Foundation (Grant No. PHY-1430152), the Spanish MINECO (Grant No. AYA2016-76012-C3-1-P), the ICCUB (Unidad de Excelencia 'Maria de Maeztu') (Grant No. MDM-2014-0369), EU's Horizon Programme through a Marie Sklodowska-Curie Fellowship (Grant No. 702638), the Polish National Science Center (Grant Nos. 2015/17/B/ST9/03422, 2015/18/M/ST9/00541, 2013/10/M/ST9/00729, and 2015/18/A/ST9/00746), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA15020100), and the NWO Veni Fellowship (Grant No. 639.041.647).

With the distinct electronic and optical properties, multiwall carbon nanotubes (MWCNTs) are identified as an outstanding catalyst support, which can effectively improve the performance of the TiO2 photocatalysts. Herein, the unique one dimensional TiO2@MWCNTs nanocomposites have been prepared by a facile hydrothermal method. The TiO2 coating layers are extremely uniform and the thickness is adjustable for different nanocomposites. XPS measurements confirm that intimate electronic interactions are existed between MWCNTs and TiO2 via interfacial Ti O C bond and the photoluminescence intensity of the TiO2@MWCNTs nanocomposites are effectively quenched compared with pure TiO2, suggesting the fast electron transfer rates. The thickness of TiO2 coating layers of the TiO2@MWCNTs nanocomposites plays a significant role in the photocatalytic degradation of organic pollutants, such as methylene blue (MB) and Rhodamine B (RhB), and photocatalytic H2 evolution from water. Due to the formation of one dimensional heterojunction of TiO2@MWCNTs nanocomposites and the positive synergistic effect between TiO2 and carbon nanotubes, it is found that the photocatalytic activity of the system is significantly improved.

The characteristics of fundamental and mutipole dark solitons in the nonlocal nonlinear couplers are studied through numerical simulation in this work. Firstly, the fundamental dark solitons with different parameters are obtained by the Newton iteration. It is found that the amplitude and beam width of the ground state dark soliton increase with the enhancement of the nonlocality degree. As the nonlinear parameters increase or the propagation constant decreases, the amplitude of the fundamental dark soliton increases and the beam width decreases. The power of the fundamental dark soliton increases with the nonlocality degree and nonlinear parameters increasing, and decreases with the propagation constant increasing. The refractive index induced by the light field decreases with the nonlocality degree increasing and the propagation constant decreasing. The amplitudes of the two components of the fundamental dark soliton can be identical by adjusting the coupling coefficient. These numerical results are also verified in the case of multipole dark solitons. Secondly, the transmission stability of fundamental and mutipole dark solitons are studied. The stability of dark soliton is verified by the linear stability analysis and fractional Fourier evolution. It is found that the fundamental dark solitons are stable in their existing regions, while the stable region of the multipolar dark solitons depends on the nonlocality degree and the propagation constant. Finally, these different types of dark dipole solitons and dark tripole solitons are obtained by changing different parameters, and their structures affect the stability of dark soliton. It is found that the multipole dark soliton with potential well is more stable than that with potential barrier. The refractive-index distribution dependent spacing between the adjacent multipole dark solitons favors their stability.

Development of coherent X-ray source, especially X-ray free electron laser (XFEL), offers a new approach to reaching a strong X-ray field. High field laser physics will extend from optical to X-ray regime since the X-ray beam has high photon energy, high intensity and ultrashort pulse duration. Till now, nonlinear atomic physics and nonlinear molecular physics have been explored based on intense X-ray beam sources. They will extend to relativistic physics and quantum electrodynamics (QED) physics area with X-ray intensity increasing, and thus offering a new opportunity to innovatively investigate the particle acceleration and radiation, QED vacuum, dark matter generation and vacuum birefringence. This review provides an overview of the wake field acceleration, vacuum birefringence as well as axion generation and detection based on strong X-ray laser field. Intense X-ray pulse will show unique potential both in basic science and in practical applications. Finally, an outlook for the future development and perspectives of high-field X-ray physics is described. The invention of chirped pulse amplification results in the generation of the light intensity in the relativistic regime (> 1018 W/cm2). Laser-plasma interaction in this regime motivates multiple disciplines such as laser-driven particle acceleration, laser secondary radiation sources, strong-field physics, etc. While petawatt (PW) lasers have been established in various institutions, several projects of building 10 PW or even 100 PW lasers are proposed. However, pushing the laser power to the next level (EW) confronts significant challenges. Current technology is approaching to its limit in producing large aperture size optics due to the damage threshold of optical material. Alternatively, plasma is considered as a potential medium to amplify or compress laser pulses. This requires further validation in future studies. In recent years, XFEL has made significant progress of producing high brightness light sources. Based on self-amplified spontaneous emission (SASE) or self-seeding in undulators, the XFEL provides a brightest light source up to the hard X-ray wavelength. The existing major XFEL facilities are LCLS-II in USA, EuXFEL in Europe, SACLA in Japan, Swiss FEL in Switzerland and PAL-XFEL in South Korea. In China, a new facility SHINE consisting of a high-repetition rate hard X-ray FEL and ultra-intense optical laser is under construction. After implementing the tapered undulator in XFEL, the peak power of X-ray pulses now reaches multi-terawatt. The pulses can also be compressed to an attosecond level. Following this trend, it is expected that the coherent XFEL will be able to generate a super strong light field, thus pushing strong-field physics to the X-ray regime. The relativistic threshold for 1-nm X-ray is about 1024 W/cm2, which we believe will be achievable in the near future. Such relativistic X-ray pulses can be used to stimulate relativistic dynamics in solid materials, realizing high-gradient low-emittance particle acceleration in solids. This may open a new path towards high-energy physics, advanced light sources, fast imaging, etc. In addition, the combination of strong X-rays and ultra-intense lasers offers a new opportunity to study the light-by-light scattering in vacuum and detecting the candidate particles for dark matter. The field of strong-field X-ray physics is largely unexplored realm. In this review, we show a few key science cases brought up by high power X-rays and shed light on this important direction.The ultra-intense coherent X-ray laser with a wavelength in a range from 100 nm to less than 0.1nm can interact directly with the nanostructured materials with solid density. Benefiting from the ultra-intense field and ultra-high critical density, acceleration field with gradient of TeV/cm can be stimulated on a nanometer scale, and thus ultra-high energy particle beams can be obtained. The available nanometer material technique promotes such a development. For example, the recent research reported that high-repetition/few-attosecond high-quality electron beams can be generated from crystal driven by an intense X-ray laser. Beside electrons, ions including protons are expected to be accelerated to ultra-high energy via target normal sheath or light pressure acceleration mechanisms on a nanometer scale if the X-ray is intense enough. It should be noted that ultra-high acceleration gradient is not the unique advantage of the X-ray laser driven acceleration. A more important quality is the beam emittance that can be low enough because of the small size of the beam source. This is very significant for ultrafast microscopy to achieve a high resolution.In classical physics, photon-photon interaction is prohibited in vacuum. However, according to the QED theory, vacuum is full of quantum fluctuation, in which virtual particle-antiparticle pairs emerge and annihilate in ultra-short instants. When excited by strong fields, the vacuum fluctuation appears as a weak nonlinear medium and allows photon-photon interaction therein, which is referred to as vacuum polarization. Based on the effective field theory, the vacuum polarization can be described by Euler-Heisenberg Lagrangian density, and then classical Maxwell equations are modified. Vacuum polarization can induce some novel physical effects, including vacuum birefringence, light-by-light scattering, vacuum diffraction, etc. Up to now, none of these effects has been verified experimentally under strong fields. The XFEL is regarded as a promising probe to explore these vacuum polarization effects. In this paper, the research progress of vacuum polarization driven by strong fields is summarized, the potential detection proposal using XFEL is discussed.Dark matter is one of the puzzles in contemporary physics. Till now, we still have not known what particles constitute it. Axion is a spinless massive hypothetical boson that is proposed as the solution to strong CP problem. It is the particle beyond the standard model and has extremely weak interaction with the standard-model particle like photon, and hence there appears a significant obstacle to detecting it. Therefore, axion and axion-like-particles (ALPs) are a kind of promising candidate of dark matter. In this paper, we summarize the research progress of axions and ALP detection, including detecting the axions sources from universe, the production and detection of artificial axions and ALPs. It is shown that the XFEL is a potential tool for detecting the artificial axions and ALPs under strong electromagnetic fields.The XFEL provides a coherent ultrafast X-ray beam for exploring particle acceleration and radiation, QED vacuum, dark matter generation, vacuum birefringence, etc. The probing of these dynamics requires different X-ray diagnoses, including the measurement of polarization purity, spectrum, pulse duration and focal condition. The X-ray polarization purity has been improved to a 10-10 level by using 6 reflections based on channel-cut silicon crystal and it will efficiently probe the vacuum birefringence. The pulse duration of isolated X-ray pulse in FEL reaches as short as 200 as, which allows probing ultrafast electron dynamics. A new self-seeding scheme using the Bragg reflection in SACLA is developed to obtain a narrow spectrum of 3 eV, 10 times smaller than that in the current SASE scheme. Therefore, the fast development of X-ray diagnostics will finely characterize X-ray beam itself and offer a unique tool for understanding the underlying phenomena for different applications.The peak intensity of coherent X-ray beam will reach to a relativistic level in future. A possible way is CPA technology, which is well developed in intense near-infrared laser system and may produce an ultrahigh intense attosecond X-ray pulse. High field X-ray laser physics will offer new opportunities both for basic science and for revolutionary application.

Melting of the dielectric phase change material inside a closed square enclosure is numerically investigated. The fully coupled equations including Navier-Stokes equations, Poisson's equation, charge conservation equation and the energy equation are solved using the lattice Boltzmann method (LBM). Strong charge injection from a high temperature vertical electrode is considered and the basic characteristics of fluid flow, charge transport and heat transfer in solid-liquid phase change process under the coupling of Coulomb force and buoyancy force are systematically studied. Emphasis is put on analysing the influence of multiple non-dimensional parameters, including electric Rayleigh number T, Stefan number \begin{document}$Ste$\end{document}, mobility number M, and Prandtl number \begin{document}$Pr$\end{document} on electrohydrodynamic (EHD) solid-liquid phase change. The numerical results show that comparing with the melting process driven by buoyancy force, the applied electric field will not only change the flow structure in liquid region and the evolution of the liquid-solid interface, but also increase the heat transfer efficiency of dielectric phase change material and thus enhance the solid-liquid phase change process. In particular, we find that this phenomenon becomes more pronounced when T is larger. Further, the dimensionless parameter \begin{document}$\varPhi$\end{document} is introduced to characterize the effect of EHD enhanced solid-liquid phase change, and the results indicate that the effect of EHD enhancement solid-liquid phase change is weakened with the increase of Stefan number \begin{document}$Ste$\end{document}, However the change of \begin{document}$Ste$\end{document} does not make much difference in EHD enhancement solid-liquid phase change for a sufficiently high electric Rayleigh number T, and it is attributed to the fully developed convection cells at a very early stage of the melting process. Moreover, it is found that the effect of EHD enhancement solid-liquid phase change is negatively related to the mobility number M and that the effect of Prandtl number \begin{document}$Pr$\end{document} on the EHD enhancement solid-liquid phase change largely depends on the mobility number M, which is due to the simultaneous influence of electric field force and buoyancy force. In general, the electric field has a significant influence on the melting process of dielectric phase change material, especially at high T,\begin{document}$Pr$\end{document} and low \begin{document}$Ste$\end{document}, M. And quantitatively, in all tested cases, a maximum melting time saves about 86.6% at \begin{document}$T=1000$\end{document}, \begin{document}$Ra=10000$\end{document}, \begin{document}$M=3$\end{document}, \begin{document}$Pr=20$\end{document}, and \begin{document}$Ste=0.1$\end{document}.

Ship magnetic field modeling is not only beneficial to understanding the characteristics of ship magnetic field, but also can predict the space distribution of ship magnetic field, which has an important application in ship protection and underwater weapons. Aiming at the problems of low modeling accuracy and poor stability in establishing the ship magnetic field hybrid model, a method of establishing a high precision stablity model is proposed in this paper. A hybrid model of magnetic field of a ship is established by using a uniformly magnetized rotating ellipsoid and a magnetic dipole array. Since the number and positions of magnetic dipoles in the hybrid model have an important effect on the modeling accuracy and stability, the fitting error function representing the modeling accuracy and the coefficient matrix condition number function representing the stability of the model are constructed by taking the magnetic dipole parameters as unknown variables. The multi-objective function is constructed by combining the fitting error function with the coefficient matrix conditional number function, which indirectly transforms the modeling problem into a multi-objective optimization problem. The multi-objective function is solved by using the multi-objective particle swarm optimization algorithm, and an optional set of modeling solution results is obtained. In order to select the best results from the optional set, the corresponding selection rules are designed based on the modeling accuracy. The proposed method is validated by the measured data of three kinds of ship models, the modeling results show that the relative error of the model is less than 3%, and the conversion error is less than 6%, which verifies that the proposed method can effectively model the ship magnetic field. Though the measurement data error exists, the modeling solution results from the proposed method have the best stability, which verifies that the modeling method proposed in this work has good stability. Compared with the two existing modeling methods, the proposed method has very good modeling accuracy and stability. Finally, the actual data of a ship on the sea are used for modeling, and the modeling results further verify that the proposed method has high modeling accuracy and conversion accuracy, and can be effectively applied to the relevant projects.

Many previous researches on the plasma sheath were based on the fact that the electrons satisfy the classical Maxwell velocity distribution function, while the particles in the plasma have long-range electromagnetic interactions. It is more appropriate to use the non-extensive distribution proposed by Tsallis to describe the electrons. In this paper, a collisional magnetized plasma sheath model with non-extensive distribution of electrons is established. Bohm criterion is derived theoretically. With the ion drift motion in the plasma pre-sheath region taken into consideration, the ion Mach number is only related to the angle of the magnetic field, the collision parameters, the electric field at the sheath edge, and non-extensive parameter \begin{document}$ q $\end{document}. The influence of parameter \begin{document}$ q $\end{document} on the criterion is discussed in this paper. The lower limit of the ion Mach number changes with the value of parameter \begin{document}$ q $\end{document}. The lower limit of the ion Mach number increases for \begin{document}$ q < 1 $\end{document}. And the lower limit of the ion Mach number decreases for \begin{document}$ q>1 $\end{document}. With the increase of \begin{document}$ q $\end{document}, the number of electrons with lower speed increases, ions need less kinetic energy to enter into the sheath and thus enter into the sheath more easily. Through numerical simulation, it is found that compared with the structure of the plasma magnetized sheath with Maxwell distribution (\begin{document}$ q=1 $\end{document}), the structure of the plasma magnetized sheath with super-extensive distribution (\begin{document}$ q < 1 $\end{document}) and that with sub-extensive (\begin{document}$ q>1 $\end{document}) are different, including the distribution of the space potential, the ion density, the electron density, and the space charge density. When \begin{document}$ q < 1 $\end{document}, the space potential, the electron density and the ion density fall more slowly, and the peak of the space charge density curve is closer to the wall. When \begin{document}$ q>1 $\end{document}, the space potential and the ion electron density fall faster, especially the electron density drops to zero faster, and the peak of the space charge density curve is far away from the wall. The simulation results show that the non-extensive parameter \begin{document}$ q $\end{document} has a significant influence on the structure of collisional plasma magnetized sheath. The influence of the collision on the magnetized plasma sheath with non-extensive distribution is similar to that with the Maxwell distribution. These conclusions may be useful in solving the problems of plasma boundary.

Silicon heterojunction (SHJ) solar cells have attracted much attention in the international photovoltaic market due to their high efficiencies and low costs. The quality of amorphous silicon/crystalline silicon (a-Si:H/c-Si) interfaces of SHJ solar cells has a key influence on the device performance. Therefore, the carrier recombination rate of a-Si:H/c-Si interface needs to be effectively controlled. In addition, as the important component of SHJ solar cells, the p-type emitter must meet the requirements for high conductivity, high light transmittance, and energy band matching with c-Si. The research contents and the relevant achievements of this paper include the following aspects. Firstly, in order to reduce the surface defects and realize the energy band alignment of a-Si:H/c-Si interface, the effect of passivation layer on passivation effect is studied. An ultra-thin buffer layer deposited by a low power and a high hydrogen dilution ratio is inserted between the conventional passivation layer and c-Si to improve the passivation effect and broaden the process window of passivation layer. The effects of the buffer layer thickness and hydrogen dilution ratio on passivation quality are further studied, and the best experimental conditions of buffer layer are obtained. The experimental results show that the sample with double-layered passivation layer is more stable than the conventional passivation layer. The minority carrier lifetime of the sample with single conventional passivation layer is 3.8 ms and the iVOC is 712 mV, while the minority carrier lifetime of the sample with double-layered passivation layer is 4.197 ms and the iVOC is 726 mV.Secondly, for the p-type emitters of silicon heterojunction solar cells, the effects of doping level on the photoelectric properties of p-type hydrogenated nanocrystalline silicon (nc-Si:H) thin films are studied. On this basis, the p++-nc-Si:H/p-nc-Si:H double-layer emitter with wide band gap and high conductivity is designed and fabricated. By analyzing the optical and electrical properties of different emitters, it is found that p-nc-Si:H has good electrical and optical properties. Owing to the high doping efficiency of nc-Si, a small amount of doping can obtain high conductivity. Lightly doped p-nc-Si:H provides a better contact with the passivation layer, while heavily doped p++-nc-Si:H can not only provide enough built-in electric field, but also improve the contact characteristics of p/ITO, thus enhancing the output characteristics of the cell. At the same time, the deposition of p-nc-Si:H layer with high hydrogen dilution ratio can also implement the hydrogen plasma treatment on the passivation layer, the reduction of the dangling bonds on the surface of the c-Si, the enhancement of the chemical passivation effect, and thus improving the open circuit voltage of the cell. Finally, a silicon heterojunction solar cell with an efficiency of 20.96% is obtained based on the commercial czochralski silicon wafer, with an open circuit voltage of 710 mV, a short circuit current density of 39.88 mA/cm2 and filling factor of 74.02%.

With the rapid development of the information age, the demand for information storage capacity and miniaturization of memory units has been being increased. However, the commonly used silicon-based flash memory has nearly approached to its physical limit. The resistive switching random access memory (ReRAM) has become one of the promising candidates for the next-generation non-volatile memory due to its simple structure, fast operation speed, excellent flexibility, and long endurance. Recently, we witnessed that the lead halide perovskites, as hot star materials, have been widely used in optoelectronic fields owning to their advantages of low cost, excellent photoelectric properties, and solution process ability. Moreover, the lead halide perovskite has been successfully used as the active layer in ReRAM device because of its tunable bandgap, long charge carrier diffusion length, fast ion migration, and high charge carrier mobility. Whereas the toxicity of lead in halide perovskite is a very horrible problem in lead halide perovskite-based ReRAM devices. The lead-free halide perovskite is considered to be the most promising material for perovskite-based ReRAM devices because it does not contain lead element. Most recently, a large number of scientists from different groups have begun to study lead-free perovskite-based ReRAM devices. For example, tin, bismuth, antimony, and copper-based halide perovskite materials have been utilized in ReRAM devices and exhibited excellent resistance switching (RS) performances. Here in this paper, the recent development of lead-free perovskite and its RS performance are reviewed, including lead-free halide perovskite materials, RS performances, and RS mechanisms of lead-free perovskite-based ReRAM. Finally, the key problems and development prospects of lead-free perovskite-based ReRAM are also presented, which provides a fundamental step towards developing the RS performance based on lead-free halide perovskites.

Solid-state lithium-ion batteries have attracted much attention due to their high safety, high energy densities and other advantages. However, solid-state lithium-ion batteries cannot realize large-scale commercial use. There are key scientific and technical issues that have not been resolved, especially interface issues, such as high resistance and instability of the interface. The X-ray photoelectron spectroscopy (XPS), as an important surface analysis method, can perform qualitative and semi-quantitative chemical analysis of the interface, which makes XPS can be widely used to study the solid-state lithium-ion battery interfaces. In this paper, we review the recent research progress of solid-state lithium-ion battery interfaces by using XPS, and summarize and review the XPS experimental principle, experimental method, experimental results and their effects on interface performance. The XPS analysis methods for solid-state lithium-ion batteries include ex-situ XPS, in-situ XPS reflecting the real-time changes of the battery interface, and operando XPS based on the actual working conditions of the battery. The ex-situ XPS can study oxide solid electrolyte interfaces, sulfide solid electrolyte interfaces and artificial solid electrolyte interface (SEI) layers to access information about the chemical composition of the interface, predict the performance of the interface, obtain the chemical distribution in space, and evaluate the chemical structure and irregularity of the interface. With ultraviolet photoemission spectroscopy (UPS) the interface work function, energy band bending and energy structure of the full battery can be obtained. In-situ XPS can effectively study the process of chemical reactions between the electrolyte and the electrode. The key prerequisite is the controllable in-situ construction of the electrolyte/electrode interface. In-situ XPS research can directly study the electrochemical changes of the interface. In-situ XPS/UPS can study the energy level alignment of solid-state lithium-ion batteries, indicating that a space charge layer is formed at the solid electrolyte interface, and the energy band bending occurs. The degree of energy band bending is reflected in the binding energy shifts of the related elements at the interface. The change of the energy structure in the deposition process can be determined by the binding energy shifts of the related elements at the interface and the change of the interface work function. Operando XPS performs XPS characterization at the same time under the working condition of the battery. Operando XPS can be combined with electrochemical characterization to observe the effects of interface reaction and solid electrolyte decomposition products on electrochemical performance, thereby determining the main components that affect electrochemical performance. It can also be combined with the ex-situ XPS to study the interface reaction mechanism and influencing factors. The information obtained includes the chemical states of elements after the interface reaction has occurred, the evolution of interface elements in the process of real-time interface reaction, the energy structure change and interface component overpotential, thus having a better understanding of interface composition, interfacial structure change, kinetics of interface reaction, and interfacial ion migration of the solid-state lithium ion batteries.

Penta-graphene is a new two-dimensional metastable carbon allotrope composed entirely of carbon pentagons with unique electronic and mechanical properties. In this work, molecular dynamics simulations are carried out to investigate the effects of functionalization by hydrogen, epoxide or hydroxyl groups on the mechanical properties and failure mechanism of penta-graphene, as well as the effects of different functionalization coverages. The effects of functionalization on the structural transformation of free-standing penta-graphene triggered by increasing temperature have also been studied. The results indicate that each of the three functional groups considered can effectively tune the mechanical properties and the failure mechanism of penta-graphene. Both the Young's modulus and elastic limit of penta-graphene first decrease sharply and then increase slowly with the increase of the functionalization coverage, while the ultimate elastic strain increases monotonically. Like the pristine penta-graphene, partially functionalized penta-graphene still exhibits a plastic deformation failure behaviour under tensile load, which is caused by the irreversible pentagon-to-polygon structural transformation occurring during tensile loading. Temperature can trigger structural reconstruction for free-standing partially functionalized penta-graphene, and the corresponding critical transition temperature is higher than that of pristine penta-graphene. However, complete functionalization can change the deformation mechanism of penta-graphene from plastic deformation to brittle fracture. For fully functionalized penta-graphene by each of the three functional groups, the structural transformation is not observed when tensile strain is applied or environmental temperature is increased. These findings are expected to provide important guidelines for effectively tuning the mechanical properties of two-dimensional nanomaterials including penta-graphene.

A broadband continuously tunable semiconductor disk laser is reported in this paper. The active region of gain chip is composed of InGaAs multiple quantum wells with resonant periodic gain structure, and its fluorescence peak wavelength is around 965 nm. Using the wideband characteristics of the quantum wells in gain chip, along with the simple linear cavity that is formed by a high reflectivity external mirror, the laser has a low cavity loss and a wide tuning range. The continuously tunable laser wavelength can be obtained by inserting birefringent filters with different thickness into the cavity. When the thickness of the birefringent filter is 2 mm, the wavelength tuning range of the laser is 45 nm, the maximum output power is 122 mW, and the beam quality M2 factors in the X- and the Y-directions are 1.00 and 1.02, respectively. The temperature characteristics of the surface-emitting spectra of gain chip and the narrowing effect of birefringent filter on laser linewidth h are also discussed.

The inner shell process produced by the collision of highly charged ion with medium atoms near the Bragg peak is an important frontier area of atomic physics under extreme conditions such as celestial plasmas and controlled nuclear fusion plasmas. Because of the special complexity of the inner shell process produced by the collision of ions with atoms in the Bragg peak energy region and the relevant experimental research is less, limited by the experimental conditions, there remain some interesting and unanswered questions.We report the experimental data of X-ray spectra produced by the impact of Xe20+ with 6.0 MeV kinetic energy on V, Fe, Ni, Cu, and Zn surface in the National Laboratory of Heavy Ion Research Facility in Lanzhou, China. The generation mechanism of X-ray with energy of 1.60 keV is analyzed. The results show that when Xe20+ without initial holes interacts with different targets, the Mα X-ray of Xe is not observed, but X-ray with energy twice as great as that of Xe Mα X-ray is observed in the experiment, which is called Xe Mαα X-ray and considered to be generated by the two-electron-one-photon process of Xe on the upper surface of the target. The existence time of the first-generation hollow atoms on the upper surface is calculated by using the classical over-barrier model when Xe20+ interacts with different targets, which is consistent with the variation of Mαα X-ray yield with the atomic number of target, therefore it is further proved that Mαα X-ray is formed by the two-electron one-photon process of Xe on the upper surface of the target. Of course, this conclusion needs further analyzing and verifying with more experimental data.

This paper obtains the lowest-energy geometric structures and the electronic and magnetic properties of small CuNiN clusters by using all-electron density functional theory. The calculated results reveal that the Cu atom prefers to occupy the apical site when N ≤ 9 and for the clusters with N = 10, the Cu atom starts to encapsulate in the cage. The CuNi7 and CuNi9 are magic clusters. The magnetism correlates closely with the symmetry of the clusters. For these clusters, the charge tends to transfer from the nickel atoms to the copper atoms. It finds that the doping of Cu atom decreases the stability of pure NiN clusters.

In recent years, nano-structures used as light harvesting have been widely used in perovskite cells to enhance the photon absorption of cells. The introduction of trapping structures in perovskite cells can change the photon propagation in the cell and the photon energy absorbed by the cell. The nano-structure used in different interfaces of perovskite cells can increase the absorption of light by the device to different degrees, and ultimately improve the efficiency of the solar cell. Therefore, the effective light trapping structure has become trending in the application of perovskite cells. How to effectively apply the such nano-structure is the key to improve the power conversion efficiency(PCE) of perovskite cells. So far, there is three ways including surface antireflection nanostructure, texture structure and plasmon nanostructure to apply to perovskite solar cell. The first one is ordered and disordered antireflection nanostructure that enhance the absorption of light on the surface of perovskite cells and makes visible light scatter at the interface of the nanostructure to reflection probability, the second one is texture structure that can not only improve the light absorption but avoid the formation of short-circuit channel inside the cell, the third one is plasmon nanostructure that can further improve the absorption of the thin film absorption material in the long band, so as to achieve the effect of improving the light utilization and cell efficiency. The trap structure is expected to achieve good photon absorption performance in wide spectral range and wide incidence angle range under the condition of reducing the thickness of active layer. At the same time, it has the advantages of good repeatability, easy to simulate and easy to change the structure. Therefore, using various trap technologies to design efficient trap structure has become a research hotspot in the field of solar cells. So far, most of the reports on the trapping structure have been applied to the silicon-based thin film solar cells, but few of them have been reported on the perovskite cells. This paper starts from the description of the perovskite cell with different nano-structures, comparing and summarizing the different structures, and analyzes the advantages and Disadvantage.

Relaxation oscillations are ubiquitous in various fields of natural science and engineering technology. Exploring possible routes to relaxation oscillations is one of the important issues in the study of relaxation oscillations. Recently, the pulse-shaped explosion (PSE), a novel mechanism which can lead to relaxation oscillations, has been reported. The PSE means pulse-shaped sharp quantitative changes related the variation of system parameters in branches of equilibrium points and limit cycles, which leads the system’s trajectory to undertake sharp transitions and further induces relaxation oscillations. Regarding externally and parametrically excited nonlinear systems with different frequency ratios, some work on PSE has been reported. The present paper focuses on the PSE and the related relaxation oscillations in a externally and parametrically excited Mathieu-van der Pol-Duffing system. We show that if there is an initial phase difference between the slow excitations with the same frequency ratio, the fast subsystem may compose of two parts with different expressions, each of which determines a different vector field. As a result, the bistable behaviors are observed in the system. In particular, one of the vector fields exhibits two groups of bifurcation behaviors, which are symmetric with respect to the positive and negative PSE, and each can induce a cluster in the relaxation oscillations. Based on this, we present several routes to compound relaxation oscillations, and obtain new types of relaxation oscillations connected by pulse-shaped explosion, which we call compound “subHopf/fold-cycle” relaxation oscillations and compound “supHopf/supHopf” relaxation oscillations, respectively. Our results show that the two clusters in the resultant relaxation oscillations are connected by the PSE, and the initial phase difference plays an important role in transitions to different attractors and the generation of relaxation oscillations. Although the research in this paper is based on a specific nonlinear system, we would like to point out that the bistable behaviors, the PSE and the resultant compound relaxation oscillations can also be observed in other dynamical systems. The reason is that the fast subsystem composes of two different vector fields induced by the initial phase difference, which dose not rely on a specific system. The results of this paper deepen the research about PSE as well as the complex dynamics of relaxation oscillations.

Based on the excellent optoelectronic properties of organic-inorganic hybrids perovskite materials, the power conversion efficiency of perovskite solar cells (PSCs) is rapidly increasing. However, factors that restrict the performance of PSCs still exist, such as interface and stability problems. Problems, such as band mismatching, carrier recombination and chemical reaction between interfaces, could be alleviated by introducing a buffer layer (BL) with a proper band structure between different layers. Moreover, stability as well as charge separation and collection could also be efficiently improved in PSCs. In this paper, an overview of the most contemporary strategies of BLs was provided. The passivation mechanism of BLs at different interfaces are highlighted and discussed in detail. Furthermore, the performances of recently developed BLs in PSCs are compared. Finally, we elaborate on the remaining challenges and future directions for the development of BLs to achieve high-efficiency and high-stability PSCs.

By introducing redox active substances into electrolyte, the energy density can be effectively increased without reducing the power density. Considering the influence of ionic conductivity and environmental safety, we introduce the redox small molecule hydroquinone (HQ) into the PVA/H3PO4 gel electrolyte, which then will recombine with the carbon nanotube arrays (ACNT) possessing high specific surface area and vertical orientation structure. The symmetrical “sandwich” type redox-enhanced solid-state super capacitor is then designed and prepared. We systematically study the effects of oriented structure and pore space on the electrochemical properties of the ACNT@PVA@HQ device and charge storage mechanism. With the addition of hydroquinone (0.1%, mol%), the specific capacitance of ACNT@PVA@HQ composite device increases 6.4 times compared with that of the ACNT@PVA, and maintains the extremely high rate performance and cyclic stability. When the current density increases 10 times, the specific capacitance of the device still possesses 85% of the original value. The energy storage mechanism is mainly ascribed to a diffusion-control behavior at a low scan rate while it will change into a capacitive behavior at a high scan speed. Furthermore, we prepare highly densified oriented carbon nanotube arrays (DACNT) by solvent evaporation, enhancing the mechanical stability of carbon nanotube arrays and improving the specific capacitance and energy density of the devices. Compared with the specific capacitance of ACNT and random carbon nanotube (CCNT), that of DACNT@PVA@HQ device under the current density of 11.1 mA·cm–2 increases up to 385 mF·cm–2 (1674 mF·cm–3), which is 6.6 times higher than that of the CCNT@PVA@HQ device and 18 times higher than that of the ACNT@PVA device. The maximum energy density can finally reach as high as 0.06 mW·h·cm–2 (0.26 mW·h·cm–3), which is much better than those of many other reported CNTs-based devices. The oriented structure of the arrays effectively shortens the ion migration path of the device, achieving a good rate performance and lower internal resistance. This new type of redox-enhanced solid-state supercapacitor not only has excellent electrochemical energy storage properties, but also meets the requirements for environmental protection and safety. This design provides a new idea for developing the new energy devices in the future, which has a good prospect in practical applications.

Soliton is an exotic topological excitation, and it widely exists in various nonlinear systems, such as nonlinear optics, Bose-Einstein condensates, classical and quantum fluids, plasma, magnetic materials, etc. A stable soliton can propagate with constant amplitude and velocity, and maintain its shape. Two-dimensional and three-dimensional solitons are usually hard to stabilize, and how to realize stable two-dimensional or three-dimensional solitons has aroused the great interest of the researchers. Ring dark soliton is a kind of two-dimensional soliton, which was first theoretically predicted and experimentally realized in nonlinear optical systems. Compared with the usual two-dimensional solitons, ring dark solitons have good stability and rich dynamical behaviors. Owing to their highly controllable capability, Bose-Einstein condensates provide a new platform for studying the ring dark solitons. Based on the recent progress in Bose-Einstein condensates and solitons, this paper reviews the research on the analytic solutions, stability, as well as the decay dynamics of ring dark solitons in Bose-Einstein condensates. A transform method is introduced, which generalizes the analytic solutions of ring dark solitons from a homogeneous system with time-independent nonlinearity to a harmonically trapped inhomogeneous system with time-dependent nonlinearity. The stability phase diagram of the ring dark soliton under deformation perturbations is discussed by numerically solving the Gross-Pitaevskii equations in the mean-field theory. A method of enhancing the stability of ring dark solitons by periodically modulating the nonlinear coefficients is introduced. It is also shown that the periodically modulated nonlinear coefficient can be experimentally realized by the Feshbach resonance technology. In addition, we discuss the dynamics of the decay of ring dark solitons. It is found that the ring dark soliton can decay into various vortex clusters composed of vortices and antivortices. This opens a new avenue to the investigation of vortex dynamics and quantum turbulence. It is also found that the ring dark solitons combined with periodic modulated nonlinearity can give rise to the pattern formation, which is an interesting nonlinear phenomenon widely explored in all the fields of nature. Finally, some possible research subjects about ring dark solitons in future research are also discussed.

Fluorescence lifetime imaging microscopy (FLIM) is widely used in biomedical, materials and other fields. It not only has strong specificity and high sensitivity, but also has the capability of quantitative measurement because the fluorescence lifetime is not affected by the intensity of excitation, the concentration of fluorophores and photobleaching, and consequently is able to monitor the changes of microenvironment and reflecting the interaction between molecules. However, its application is limited to some extent by the complexity of data analysis. In order to make FLIM technology more suitable for fast analysis of high-throughput data, a variety of new algorithms for fluorescence lifetime analysis have emerged in recent years, such as phasor analysis, maximum likelihood estimation, first-order moment, Bayesian analysis, and compressed sensing. Among them, the phasor analysis (PA) method obtains the fluorescence lifetime by converting the fitting in the time domain to the direct calculation in the frequency domain. Compared with traditional least-square fitting method, it is not only simpler and faster, but also more suitable for the case of low photon counts. In addition, in the PA approach to FLIM, the fluorescence decay is directly converted into a phasor diagram by simple mathematics, where the phasor points originating from different pixels in the image are represented by the positions in the phasor plot, and thus the graphical representation obtained by PA method is convenient for data visualization and cluster analysis. Therefore, it has become a simple and powerful analysis method for FLIM, and is increasingly favored by researchers. In this paper, the basic principle of PA method and how we can use it are described in detail. And on this basis, the latest application research progress of the method in cell metabolism state measurement, protein interaction study, cell microenvironment measurement, auxiliary pathological diagnosis, and resolution improvement in super-resolution imaging are introduced and summarized. The advantages of PA method in these FLIM applications are focused on, providing useful reference for the research in related fields. Finally, the phasor analysis method for FLIM data analysis and the development trend of its application are prospected.

In this paper, the progress of micro-energy harvesters by using piezoelectret-based transducers as a core element is reviewed, including basic physical principle and properties of piezoelectrets, and their applications in micro-energy harvesting. Piezoelectret is electret-based piezoelectric polymer with a foamed structure. The piezoelectric effect of such material is a synergistic effect of the electret property of the matrix polymer and the foam mechanical structure in the material. Piezoelectret, featuring strong piezoelectric effect, flexibility, low density, very small acoustic impedance and film form, is an ideal electromechanical material for lightweight flexible sensors and mechanical energy harvesters. The piezoelectret prepared by means of grid, template patterning, supercritical CO2 assisted low-temperature assembly, lithography mold combined with rotary coating and hot pressing has regular voids and good piezoelectric properties. Piezoelectret has been used to harvest vibrational energy, human motion energy and sound energy. According to the stress direction applied to the piezoelectrets, operating modes of energy harvesters can be divided into 33 and 31 modes. The vibrational energy harvesters based on piezoelectret are utilized to harvest medium frequency vibrational energy generated by factory machines, aircrafts, automobiles, etc. Such energy harvesters can generate considerable power even in a small size. Human motion energy harvesters are generally used to power wearable sensors. The high sensitivity, lightweight, and flexibility of the piezoelectret make such a material a promising candidate for harvesting human motion energy. Owing to very small acoustic impedance, high figure-of-merit, flat response in audio and low-frequency ultrasonic range, the piezoelectrets are more appropriate for acoustic energy harvesting in air medium than conventional PZT and ferroelectric polymer PVDF.In the future, specific micro-energy harvesters using piezoelectrets as transduction material can be designed and fabricated according to the practical application environment, and their performance can be enhanced by using flexible connections of transduction elements.

Based on the theory of surface lattice dynamics, the surface phonon spectrums along three symmetrical directions of \begin{document}$\bar \varGamma \bar L$\end{document}, \begin{document}$\bar L\bar M$\end{document} and \begin{document}$\bar \varGamma \bar M$\end{document} are simulated for the W(100) surface by using the modified analytic embedded atom method. The polarization vectors at different symmetrical points are also calculated. According to the criterion and marking method of surface mode, the surface modes along different symmetrical directions are drawn, the distribution range and mode coupling of surface modes are discussed as well. The vibration frequencies of surface modes calculated by us have been compared to available experimental datum and some theoretical values correspondingly. The results display that the present results are general agreement with the referenced experimental or theoretical results. Based on the calculated polarization vector, the surface vibration states are constructed for the atomic layers in the neighboring surface. And the polarization and local features of the surface modes along different symmetrical directions are analyzed. The results show that there are some coupling phenomena between surface mode dispersion, such as avoid crossing and independence crossing. The avoid crossing is found between the surface-mode branch S1 and the surface-mode branch S2 near \begin{document}${\bar \zeta _y} = 0.32$\end{document} along \begin{document}$\bar L\bar M$\end{document} direction. In the region, going from \begin{document}$\bar L$\end{document} to \begin{document}$\bar M$\end{document}, S1 changes from y polarization to z polarization, and S2 changes from z polarization to y polarization. The independence crossings exist between surface-mode branch S1 and surface-mode branch S2 at \begin{document}${\bar \zeta _x} = 0.5$\end{document} along \begin{document}$\bar \varGamma \bar L$\end{document} direction, and surface-mode branch S2 and surface-mode branch S3 at \begin{document}${\bar \zeta _x} = 0.5$\end{document} along \begin{document}$\bar L\bar M$\end{document} direction, respectively. Before and after the crossings, the polarization and local features of the surface modes have not changed. Inspection of the polarization vectors, the coupling phenomena are iconically demonstrated.

Dual-wavelength laser sources have important applications in the interferometry and the nonlinear-frequency-conversion generated mid-infrared or terahertz-band coherent radiation. Vertical-external-cavity surface-emitting lasers own outstanding advantages such as high output power, good beam quality and flexible emission wavelength, which make them very suitable for dual-wavelength running. In this paper, we employ a collinear Y-type cavity to produce a dual-wavelength laser. There are two semiconductor gain chips in the resonant cavity, one has an active region of In0.185Ga0.815As/GaAs strained multiple quantum wells and a designed wavelength of 960 nm, and the other has an active region of In0.26Ga0.74As/GaAsP0.02 strained multiple quantum wells and a target wavelength of 1080 nm. The peak wavelength of the photoluminescence of chip 1 is 950 nm, which is 10 nm shorter than the designed wavelength under weak pump, and the peak wavelength of the photoluminescence of chip 2 is 1094 nm, which is 14 nm longer than the target wavelength under low pump. When the pump power is increased, the peak wavelengths of the photoluminescence of two gain chips are both red-shifted. The oscillating laser wavelengths are centered at 953 nm and 1100 nm, the corresponding full width at half maximum (FWHM) values of the laser spectra are 1.1 nm and 2.7 nm, respectively. The wavelength spacing of the dual-wavelength is 147 nm, and the related mid-infrared coherent radiation is about 7.1 μm on the assumption that the dual-wavelength laser is used for difference frequency generation. When the absorbed pump power of each gain chip is 5.8 W, the total output power of the dual-wavelength laser reaches 293 mW at room temperature.

Organometal halide perovskites featuring solution-processable characteristics, high photoluminescence quantum yield (PLQY), and color purity, are an emerging class of semiconductor with considerable potential applications in optoelectronic devices. Electron injection layer is an important component of perovskite light-emitting device, which determines the growth of perovskite film directly. In this paper, the perovskite light-emitting diodes (PeLEDs) based on n-type nanocrystalline silicon oxide (n-nc-SiOx:H) electron injection layer are designed and realized. This novel electron injecting material is prepared by the plasma enhanced chemical vapor deposition (PECVD), and its smooth surface and matched energy band result in superior perovskite crystallinity and low electron injection barrier from the electron injecting layer to the emissive layer, respectively. However, the external quantum efficiency (EQE) of PeLED is as low as 0.43%, which relates to defects and leakage current due to the incomplete surface coverage of perovskite film. The fast exciton emission decay (< 10 ns) stems from strong non-radiative energy transfer to the trap states, and represents a big challenge in fabricating high-efficiency PeLEDs. In order to obtain desirable perovskite film morphology, an excessive proportion of methylammonium bromide (MABr) is incorporated into the perovskite solution, and a volume of benzylamine (PMA) is added into the chlorobenzene antisolvent. The perovskite films suffer low PLQY and short PL lifetime if only MABr or PMA is introduced. When the molar ratio of MABr is higher than 60%, the luminescence quenching arising from Joule heating is depressed by employing PMA, contributing to a higher PLQY (> 30%) and a longer carrier lifetime. The synergistic effect of MABr and PMA increase the coverage and reduce the trap density of perovskite film, inhibit the luminescence quenching in the annealing process, and thus facilitating the perovskite film with higher quality. Finally, the n-i-p PeLED exhibits green-light emission with a maximum current efficiency of 7.93 cd·A-1 and a maximum EQE up to 2.13% is obtained. These facts provide a novel electron injecting material and a feasible process for implementing the PeLEDs. With further optimizing the perovskite layer and device configuration, the performance of n-i-p type PeLEDs will be improved significantly on the basis of this electron injection material.

Lead halide perovskite has attracted much attention due to its high absorption coefficient, long carrier diffusion length, low binding energy, and low cost. The stability of intrinsic crystal structure in I-based perovskite can be theoretically estimated by calculating cubic structures factor and octahedral factor. Experimental methods to solve the stability of structure in I-based perovskite could be mainly to either incorporate anions (e.g. Cl–, Br–) or mix cations (e.g. Cs+) into I-based perovskite matrix. Moreover, incorporating Br– into I-based perovskite leads its band gap to widen, which might be used as a top-cell material to tandem solar cell. However, in order to understand photo-physics process of anion-mixed and/or cation-mixed perovskites, it is essential to further investigate the optical properties such as absorption spectrum, photoluminescence (PL), temperature-dependent PL (TPL) behavior, etc. In this work, anion-mixed and/or cation-mixed perovskite thin films with high quality crystallization and (110) prereferral orientation are synthesized by one-step solution method. All mixed perovskite films are characterized by using X-ray diffraction (Rigaku D MAX-3C, Cu-Kα, λ = 1.54050 Å) and X-ray photoelectron spectroscopy (XPS) (Thermo Scientific Escalab 250Xi). A set of strong peaks of the mixed perovskite films at 14.12° and 28.48°, is assigned to (110) and (220) lattice plane of orthorhombic crystal structure of I-based perovskite, due to preferred orientation. The Pb 4f and I 3d doublet peaks, corresponding to Pb+2 and I– states, are observed in XPS spectra. It should be noted that in the absence of other valence states of Pb and I component at lower/upper binding energy, the chemical element composition ratio of Pb+2 and I– are close to stoichiometric proportion. For optical absorptionspectra, the optical bandgaps of the perovskite films increase with doping concentration of Br– increasing. For TPL, the perovskite films with x = 0 and x = 0.05 show abnormal red-shifts in a temperature range from 10 to 100 K. The following blue shifts in a temperature range from 125 to 350 K emerge, which is mainly attributed to band gap widening. However, incorporating more Br– into I-based perovskite leads the TPL spectra to monotonically blue-shift. A linear relationship between the TPL peak position and the doping concentration of Br– ions is observed at the same temperatures. This indicates that the Br– anion in I-based perovskite plays a crucial role in determining the optical properties. The low-temperature and high-temperature (HT) excitonic binding energy at x = 0 are 186 meV and 37.5 meV, respectively. The HT excitonic binding energy first increases and then decreases with the Br– concentration in I-based perovskite film increasing. The minimal variation of TPL peak position and FWHM (full width at half maximum) at x = 0.0333 are 13 nm and (25.8 ± 0.5) meV, respectively, suggesting higher temperature stability in optical property. This should contribute to understanding the relationship between temperature-dependent electrical and optoelectronic performance for hybrid mixed perovskite materials and devices.

Due to the rapid development of dopant free asymmetric heterogeneous contacts in recent years, the theoretical conversion efficiency can reach 28%, which has large room for development and has attracted one’s attention. With the expectation of low cost and green pollution-free solar cell, the traditional crystalline silicon solar cell has many limitations due to its high equipment cost and flammable and explosive raw materials. It greatly increases the necessity of research and development of new solar cells with no doping and asymmetric heterogeneous contacts. The new solar cell is safe and environmental friendly due to the multi-faceted advantages of dopant-free asymmetric heterogeneous contact (DASH) solar cells constructed by transition metal oxide (TMO): the TMO has been widely studied as an alternative option, because of its wide band gap, little parasitic absorption, as well as repressed auger recombination, and conducing to the increase of the short-circuit current density of the solar cells; the DASH solar cell has high efficiency potential, its theoretical efficiency has reached 28%, and it can be produced by low-cost technology such as thermal evaporation or solution method; it always avoids using flammable, explosive and toxic gases in the manufacturing process. Our group proposed using MoOx as a hole selective contact and ZnO as an electron selective contact to construct a new and efficient DASH solar cell. It has achieved a conversion efficiency of 16.6%. Another device, in which MoOx is used as the hole selective contact and n-nc-Si:H as the electron selective, was fabricated, and its efficiency has reached 14.4%. In order to further speed up the research progress of the dopant-free asymmetric heterogeneous contact crystalline silicon solar cell, the development status is reviewed, and the basic principle and preparation technology of selective transport of transition metal oxide (TMO) carriers are discussed. And the effect of the hole transport layer, the electron transport layer and the passivation layer on the performance of the TMO dopant-free asymmetric heterogeneous contact (DASH) solar cells are discussed in order to have an in-depth understanding of the working mechanism and material selection of the battery, thereby providing guidance in preparing new and efficient DASH solar cells.

As a new energy storage device, supercapacitor (or electrochemical capacitor) has an ultra-long cycle life, extremely high power density and enhanced energy density. It fills the gap in the energy-power spectrum between traditional capacitor and battery. In general, the traditional energy storage and conversion device cannot have a perfect trade-off between high energy density and high power density. With the rapid development of modern society, developing light, portable, safe and environmentally friendly high-performance energy storage devices has become increasingly vital. Therefore, there are numerous researches of flexible solid supercapacitors emerging at this historic moment. The selection of flexible electrode materials and that of electrolytes are crucial factors in designing the flexible solid state supercapacitors, which have been the research hotspots in recent years. Carbon nanotube array has been widely used in electrode material of super capacitors due to its excellent electrical conductivity, large specific surface area and super high chemical stability. But in assembly process, carbon nanotube array easily collapses and breaks its neat orientation because of its poor mechanical strength. In consideration of environmental contamination and practical demands, in this paper the neutral gel electrolyte is adopted to embed carbon nanotube array to form flexible composite film electrode. Besides the fact that we use hydrophilic flexible carbon cloth as current collector and neutral gel electrolyte as separator to prepare flexible devices, we compare the electrochemical properties among different devices by changing the electrolyte salt added in gel electrolyte. Meanwhile, after continuous bending and folding, the properties of flexible devices have not been significantly damaged, indicating good flexibility and mechanical stability. The specific capacity of the whole device with PVA-NaCl used as gel electrolyte increases up to 104.5 mF·cm–3, which is much higher than the specific capacity of the composite device formed by organic ionic gels with carbon nanotube array and that of the composite device formed by commercial short carbon nanotubes with hydrogels. A maximum energy density of 0.034 mW·h·cm–3 is obtained at the same time. In addition, it has good rate performance, cycling stability, suppressing self-discharge property, and good chemical stability at a high voltage of 1.6 V. Neutral gel/carbon nanotube array composite devices not only meet the needs of the era of green safety, flexible and portable folding, but also open up the future application prospects of medical implants.

Acquisition, tracking and pointing (ATP) is an important subsystem of satellite-based optical communication system. It controls the direction of the beam passing through the mirror, and then completes the alignment and stabilization of intersatellite/satellite-ground light path. As is well known, the ordinary mirror changes the polarization of photons, so the ATP mirrors must be specially processed in quantum communication system and coherent optical communication system. For example, in order to counteract the change of photon polarization caused by the mirror, it is usually necessary to coat the mirror. However, this membrane structure must be tested by the radiation and temperature change from the space environment. A polarization-independent reflector based on two magneto-optical crystals and two mirrors is proposed. This structure does not need any special treatment (such as coating) for the reflector. It can realize polarization-independent reflection at any angle only through the reasonable configuration of the ordinary reflector and 90° rotatory crystal. In addition, it is found that the structure has self-stability, that is, when the polarization characteristics of optical devices change due to environmental change, the overall polarization reflection characteristics of the reflective structure remain unchanged. The polarization equation of reflected light of reflector based on two magneto-optical crystal and two mirrors is derived. The polarization of reflected light under environmental influence is simulated, and the polarization independent reflection self-stability of double-rotating double-reflection structure is found. The polarization-independent self-stabilization of this structure is verified by temperature and radiation experiment. The experimental results show that the average polarization retention of the reflecting light of the reflector based on two magneto-optical crystal and two mirrors can reach 99.77% when the temperature varies from －45 ℃ to 85 ℃. The mirrors and the magneto-optical crystals are irradiated by cobalt 60 with a total dose of 400 Gy, and the average polarization retention of the reflective structure is also 99.35%. The experimental results show that the polarization-independent reflectance can be kept stable for a long time in the space environment where radiation and temperature change dramatically. Relying on this self-stability, the reflector based on two magneto-optical crystals and two mirrors can maintain high polarization-independent reflection capability for a long time in a space environment. This makes it a new option for polarization-preserving reflective components in satellite-based optical communication systems.

Graphene is believed to have promising applications in many fields because of its unique properties. At present, graphene films are mainly prepared on Cu substrates by chemical vapor deposition. The graphene films prepared in this way need to be transferred to the target substrates for further applications, while the transfer process inevitably induces contamination on graphene, which affects the properties of graphene and the performance of devices. Therefore, how to reduce or avoid contamination and realize the clean transfer of graphene is an important topic for the development of graphene transfer technology, which is the major topic of this review. Here, firstly, the transfer techniques of graphene are briefly reviewed, which can be classified according to different rules. For example, it can be classified as direct transfer, with which graphene is directly stuck to the target substrate, and indirect transfer, with which graphene is indirectly transferred to the target substrate with a carrier film. According to the way of separating graphene and the growth substrate, it can also be classified as dissolving transfer, with which the substrate is dissolved by chemical etchant, and delaminating transfer, with which graphene is delaminated from the substrate. Then the origins of contamination are discussed followed with how contamination affects graphene properties. The main contaminations induced by transfer are ions from the etchant and electrolyte, undissolved metal or metal oxide particles, and organic residues from carrier films. Contaminations have a great influence on the electrical, thermal and optical properties of graphene. Then the up-to-date progress of techniques for clean transfer is reviewed, including modifying the cleaning process or using alternative etchant/electrolyte to remove or suppress metal contamination and annealing graphene or using alternative carrier films (e.g., more dissoluble materials) to remove or suppress organic residues. Finally, the challenges of clean transfer of graphene are summarized, and future research directions and opportunities are prospected. This review not only contributes to the research of graphene film transfer technology, but also has great reference value for the clean fabrication of the whole two-dimensional materials and devices.

An interaction potential for an N2(X1σ+g) molecule is constructed by using the highly accurate valence internally contracted multireference configuration interaction method and the largest basis set, aug–cc–pV6Z, in the valence range. The potential is used to investigate the elastic scattering of two N atoms at energies from 1.0×10−11 to 1.0 × 10−4 a.u. The derived total elastic cross sections are very large and almost constant at ultralow temperatures, and the shape of total elastic cross section curve is mainly dominated by the s-partial wave at very low collision energies. Three shape resonances are found in the total elastic cross sections. Concretely, the first one is very sharp and strong. It results from the g-partial-wave contribution and the resonant energy is 3.645 × 10−6 a.u. The second one is contributed by the h-partial wave and the resonant energy is 1.752 × 10−5 a.u. This resonance is broadened by those from the d- and f-partial waves. The third one comes from the l = 6 partial wave contribution and the resonant energy is 3.522 × 10−5 a.u. This resonance is broadened by those from the g- and h-partial waves. The N2(X1σ+g) molecular parameters, which are determined at the current theoretical level, achieve very high accuracy due to the employment of the largest correlation-consistent basis set in the valence range.

A scheme of generating energetic ions by the interaction of an ultrahigh-intensity laser pulse and a thin solid foil is studied. The combination of the effects of radiation pressure and Coulomb explosion makes the ion acceleration more effective. The maximum ion velocity variation with time is predicted theoretically while the temporal evolution of the electrostatic field due to the Coulomb explosion is taken into consideration. Two-dimensional particle-in-cell simulations are done to verify the theory.

In this paper, we consider spatial-temporal correlation functions of the turbulent velocities. With numerical simulations on the Gledzer–Ohkitani–Yamada (GOY) shell model, we show that the correlation function decays exponentially. The advecting velocity field is regarded as a colored noise field, which is spatially and temporally correlative. For comparison, we are also given the scaling exponents of passive scalars obtained by the Gaussian random velocity field, the multi-dimensional normal velocity field and the She–Leveque velocity field, introduced by She, et al. We observe that extended self-similarity scaling exponents H(p)/H(2) of passive scalar obtained by the colored noise field are more anomalous than those obtained by the other three velocity fields.

This paper studies boron contamination at the interface between the p and i layers of μc-Si:H solar cells deposited in a single-chamber PECVD system. The boron depth profile in the i layer was measured by Secondary Ion Mass Spectroscopy. It is found that the mixed-phase μc-Si:H materials with 40% crystalline volume fraction is easy to be affected by the residual boron in the reactor. The experimental results showed that a 500-nm thick μc-Si:H covering layer or a 30-seconds of hydrogen plasma treatment can effectively reduce the boron contamination at the p/i interface. However, from viewpoint of cost reduction, the hydrogen plasma treatment is desirable for solar cell manufacture because the substrate is not moved during the hydrogen plasma treatment.

This paper investigates the entanglement dynamics of the system, composed of two qubits A and B with Heisenberg XX spin interactation. There is a third controller qubit C, which only has Dzyaloshinskii–Moriya (DM) spin-orbit interaction with the qubit B. It is found that depending on the initial state of the controller qubit C and DM interaction, the entanglement of the system displays amplification and sudden birth effects. These effects indicate that one can control the entanglement of the system, which may be helpful for quantum information processing.

This paper reports that high-rate-deposition of microcrystalline silicon solar cells was performed by very-high-frequency plasma-enhanced chemical vapor deposition. These solar cells, whose intrinsic μc-Si:H layers were prepared by using a different total gas flow rate (Ftotal), behave much differently in performance, although their intrinsic layers have similar crystalline volume fraction, opto-electronic properties and a deposition rate of ~ 1.0 nm/s. The influence of Ftotal on the micro-structural properties was analyzed by Raman and Fourier transformed infrared measurements. The results showed that the vertical uniformity and the compact degree of μc-Si:H thin films were improved with increasing Ftotal. The variation of the microstructure was regarded as the main reason for the difference of the J−V parameters. Combined with optical emission spectroscopy, we found that the gas temperature plays an important role in determining the microstructure of thin films. With Ftotal of 300 sccm, a conversion efficiency of 8.11% has been obtained for the intrinsic layer deposited at 8.5 A/s (1 A = 0.1 nm).

This paper presents a novel approach to hyperchaos control of hyperchaotic systems based on impulsive control and the Takagi–Sugeno (T–S) fuzzy model. In this study, the hyperchaotic Lu system is exactly represented by the T–S fuzzy model and an impulsive control framework is proposed for stabilizing the hyperchaotic Lu system, which is also suitable for classes of T–S fuzzy hyperchaotic systems, such as the hyperchaotic Rossler, Chen, Chua systems and so on. Sufficient conditions for achieving stability in impulsive T–S fuzzy hyperchaotic systems are derived by using Lyapunov stability theory in the form of the linear matrix inequality, and are less conservative in comparison with existing results. Numerical simulations are given to demonstrate the effectiveness of the proposed method.

This paper reports that the mesoscopic inductance and capacitance coupling LC circuit is quantized by means of the canonical quantization method. Using the 'invariant eigen-operator' method, it deduces the energy-level transition rule when the system is disturbed by an external electromagnetic field. At the same time, the quantum fluctuations for the system at finite temperature are examined by virtue of the generalized Hellmann–Feynman theorem.

This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres (PBGFs) by using a full-vector finite element method. By simulation we found that theoretically the zero dispersion wavelength can be tailored by respectively changing the rounded diameter of air holes, pitch, refractive index, normalized thickness of core rings, and hole diameter to pitch ratio. At the same time the tailoring of dispersion slope can also be realized by changing the rounded diameter of air holes or pitch or normalized thickness of core rings. To illustrate the reasonability of fibre designs, this paper also gives the variance of normalized interface field intensity which measures the scattering loss relatively versus wavelength for different designs. From the viewpoint of loss, varying the rounded diameter and the thickness of core ring could shift zero wavelength but it is difficult to get the required parameters within so tiny range in practical drawing of PBGFs, on the other hand, it is possible in practice to respectively alter the pitch and refractive index to shift zero wavelength. But varying hole diameter to pitch ratio is not worthwhile because they each induce large increase of loss and narrowness of transmission bandwidth. The zero dispersion wavelength can be engineered by respectively varying the rounded diameter of air holes, pitch, refractive index, and normalized thickness of core rings without incurring large loss penalties.

Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, the Wigner functions of the even and odd binomial states (EOBSs) are obtained. The physical meaning of the Wigner functions for the EOBSs is given by means of their marginal distributions. Moreover, the tomograms of the EOBSs are calculated by virtue of intermediate coordinate-momentum representation in quantum optics.

We propose a quantum error-rejection scheme for direct communication with three-qubit quantum codes based on the direct communication of secret messages without any secret key shared in advance. Given the symmetric and independent errors of the transmitted qubits, our scheme can tolerate a bit of error rate up to 33.1%, thus the protocol is deterministically secure against any eavesdropping attack even in a noisy channel.

We propose new coefficients for the Sellmeier equations of 1.0 mo1% Mg-doped stoichiometric LiTaO3. The extraordinary refractive indices for the wavelength range 0.5?4.0?m and for temperature 30?170?C are based on measured data derived from quasi-phase-matched (QPM) optical parametric oscillator (OPO) and second-harmonic generation (SHG) based on periodically poled Mg-doped stoichiometric LiTaO3 with a pump wavelength of 1064 nm. The corrected refractive indices are in good agreement with our experimental data obtained from QPM OPO and SHG pumped at 1064?m at different temperatures.

In this work, the stability issues of the equilibrium points of the cellular neural networks with multiple time delays and impulsive effects are investigated. Based on the stability theory of Lyapunov–Krasovskii, the method of linear matrix inequality (LMI) and parametrized first-order model transformation, several novel conditions guaranteeing the delay-dependent and the delay-independent exponential stabilities are obtained. A numerical example is given to illustrate the effectiveness of our results.

The entanglement dynamics of system, where atoms A and B interact with single mode cavity fields a and b respectively, is studied. The interaction between atom A and cavity a may be described by using the typical Jaynes–Cummings model, while that between the atom B and cavity b filled with a Kerr medium is of a two-photon process. For a certain initial atom entanglement state, there is an entanglement sudden death effect between the two atoms. The Kerr medium in the cavity b can effectively prevent the undesirable entanglement sudden death from occurring. Also, from the viewpoint of the population dynamics, we discuss why the Kerr medium can do so.

Photoinduced birefringence in a liquid-crystalline azobenzene side-chain polymer is investigated. It is observed that the birefringence does not show any decay but increases after switching off the pump light at room temperature. The magnitude of the birefringence relaxation is found to depend on the exposure dose of the pump light. A discussion about the mechanism of the inverse relaxation of birefringence is presented.

Using two typical types of polarization controller, this paper analyses theoretically and experimentally the fact that it is necessary to adjust at least three instead of two waveplates in order to transform any state of polarization to any other output covering the entire Poincare sphere. The experimental results are exactly in accordance with the theory discussed in this paper. It has corrected the conventional and inaccurate point of view that two waveplates of a polarization controller are adequate to complete the transformation of state of polarization.