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The construction of van der Waals heterostructures based on 2D polarized materials is a unique technique to achieve enhanced photocatalytic performance. We have investigated the intrinsic electric field and photocatalytic properties of the MoTe2/GeS heterostructure via first-principles calculations. The results showed that a dipole-induced electric field induced by the GeS monolayer and an interface-induced electric field induced by the interface between the GeS monolayer and the MoTe2 monolayer emerge in the 2D polarized MoTe2/GeS heterostructure. The dipole-induced electric field contributes mainly to the total intrinsic electric field. Moreover, the 2D polarized MoTe2/GeS heterostructure possesses many excellent and distinguished photocatalytic performance parameters, such as a direct semiconductor bandgap of 1.524 eV, a wide light spectrum ranging from the ultraviolet to near-infrared region with a high absorption coefficient (about 106 cm−1), a total intrinsic electric field, which reduces the probability of the recombination of photo-generated electron–hole pairs effectively, and a suitable band alignment for the water-splitting reaction. These indicate that the 2D polarized MoTe2/GeS van der Waals heterostructure is a potential novel high-efficient photocatalyst for water-splitting.

Cation substitution in spinel cobaltites (e.g., ACo2O4, in which A = Mn, Fe, Co, Ni, Cu, or Zn) is a promising strategy to precisely modulate their electronic structure/properties and thus improve the corresponding electrochemical performance for water splitting. However, the fundamental principles and mechanisms are not fully understood. This research aims to systematically investigate the effects of cation substitution in spinel cobaltites derived from mixed-metal-organic frameworks on the oxygen evolution reaction (OER). Among the obtained ACo2O4 catalysts, FeCo2O4 showed excellent OER performance with a current density of 10 mA·cm−2 at an overpotential of 164 mV in alkaline media. Both theoretical calculations and experimental results demonstrate that the Fe substitution in the crystal lattice of ACo2O4 can significantly accelerate charge transfer, thereby achieving enhanced electrochemical properties. The crystal field of spinel ACo2O4, which determines the valence states of cations A, is identified as the key factor to dictate the OER performance of these spinel cobaltites.

The structural, electronic, dipole-induced internal electric field, optical and photocatalytic properties of monolayer GeS and GeSe under external biaxial strain were investigated by using first-principles calculations. The monolayer GeS and GeSe are indirect semiconductors with the band gaps of 3.265 eV and 2.993 eV, respectively. The band alignment of the monolayer GeS and GeSe manifests the photocatalytic activity for water splitting. Especially, it is effective to tune the properties including structures, band gaps, surface potential difference, dipole moment P, dipole-induced internal electric field, absorption and photocatalytic activity of the monolayer GeS and GeSe via biaxial strain. Our results suggest that monolayer GeS and GeSe possess photocatalytic properties for water splitting, and strain engineering, especially tensile strain, can enhance the photocatalytic activity under ultraviolet and visible light.

The modulation of exciton recombination is one of the core issues for the electronic/optoelectronic devices. Here, we investigate the exciton recombination and surface depletion of ZnO nanowires under various interface conditions in terms of continuum medium mechanics and bond relaxation method. We find that the enhancement of donor concentration, nanowire dimension and external temperature can modify the carrier recombination, surface barrier height and surface depletion depth. Moreover, coated a thin epitaxial layer on the nanowires is of great benefit to reduce the surface state for suppression of recombination rate. The related mechanism on the interface confinement has also been clarified. Our predictions agree well with the experimental measurements, which provide an effective guidance for the organization of electronic device design.

K-ion batteries (KIBs) have become one of the promising alternatives to lithium ion batteries. In this work, we are the first to utilize reduced graphene oxide (RGO) wrapped metal organic framework-derived FeS2 hollow nanocages (FeS2@RGO) as an anode for KIBs. Owing to the synergistic effect from FeS2 nanocages and RGO shells, our FeS2@RGO sample exhibited superior electrochemical performance. Such FeS2@RGO electrodes demonstrate a high capacity of 264 mA h g-1 after 50 cycles at 50 mA g-1 and 123 mA h g-1 after 420 cycles even at a large current density of 500 mA g-1. More importantly, we also explain the electrochemical reaction process about FeS2 and believe that these results would open the door for a novel class of long cycling performance anode materials in the KIB field.

Superlattice-like(SLL) phase-change films have attracted increasing attention because they can provide more controllable degree of freedoms besides composition. At present the cycle number manipulating effect on crystallization temperature of SLL phase-change films is discussed less and the analysis method should be further improved. Here, four new SLL samples, [Ge(1 nm)/Ge 8 Sb 92 (9 nm)] n (n = 1,2,3,4), are prepared. Cycle number manipulating effect on crystallization temperature of the four SLL films is investigated by coherent phonon spectroscopy (CPS) and the sheet resistance measurement. Both kinds of measurements prove the effect of cycle number on T c and show that T c decreases with the increasing n of the SLL films, following an exponential law. Based on the combination of alloying effect and equivalent interfacial effect, the cycle number manipulation effect on T c of SLL films is explained. Our work further improves the analysis method of cycle number manipulating effect on crystallization temperature of SLL films.

A concise bead-based microfluidic system has been developed for joint detection in TORCH screening at point-of-care testing. Assisted by five functionalized polycarbonate single beads, totally five critical infections including TOX, RUB, CMV, HSV-1 and HSV-2 can be simultaneously detected with the microfluidic chip based on chemiluminescence. The microfluidic chip consists of multiple reaction chambers respectively for different reaction steps of the sandwiched chemiluminescence immunoassay, and each reaction chamber is divided into five interconnected independent cells to respectively hold five single beads in different position. With a guiding path, each single bead with a ferrous core can be easily transported between each two adjacent reaction chambers through magnetic control to consecutively react with the serum sample or other different reagents. Meanwhile, with magnetic control, each single bead within the reaction chamber can be moved back and forth to improve the detection sensitivity with enhanced mixing. In one time test, joint detection with five infections to one serum sample can be simultaneously implemented by introducing synchronous manipulation to five single beads. Chemiluminescence signal from five single beads is collected by a sensitive CCD camera in parallel. Qualitative detection is achieved by comparing the detection signal amplitude with the corresponding cutoff value for each infection. Experimental results show that accurate, simple, convenient and efficient TORCH screening can be achieved with the easy-to-operate and low-cost microfluidic system at resource-poor settings.

We investigate the Auger recombination (AR) rate in CdSe/CdS core/shell nanocrystals (NCs) under different interface confinements in terms of the interface bond relaxation mechanism and Fermi’s golden rule. We find that the epitaxial layer of CdS can not only depress the influence of the Coulomb interaction between electrons and holes, but can also change the wave function and quantum confinement, resulting in the reduction of the AR rate. Moreover, the AR lifetime of CdSe/CdS core/shell NCs at a fixed entire dimension is lower than that of bare CdSe because of interface confinement of the wave function. A great drop of the AR rate can be achieved by adding an alloying layer that depresses the interface effect. Our predictions are in agreement with the available evidence, suggesting that the proposed approach could provide a general method to explore the AR process in core/shell NCs.

In order to clarify the interface adhesion properties between graphene (Gr) membrane and curved substrate, we investigate three kinds of systems, including Gr/Si nanowire, Gr/Si nanotube and Gr/silicene in terms of continuum medium mechanics and nanothermodynamics. We find that the interface adhesion energy is determined by the thickness of the Gr and curvature of the substrate. The coupling role of the surface effect and interface confinement affects the strain energy and induces the strain redistribution in the Gr and curved substrate, resulting in the interface adhesion energy increasing with diminishing thickness of Gr and increasing curvature of the substrate. Our findings can be expected to be applied to the design of Gr-based electronic devices.

A principle study on reducing the depolarization loss in a single-frequency Nd:YAG ring laser by a novel ring resonator configuration is reported. In the resonator, one cavity mirror with 99.5% reflectivity at 1064 nm for 45-degree incident s-polarized light and about 75% transmissivity for 45-degree incident p-polarized light was employed. Besides, the transmissivity for the 45-degree incident p-polarized and s-polarized light for the output-couple mirror were 32% and 3.5%, respectively. The cavity mirror and the output-couple mirror were utilized as the polarizer to enforce the s-polarized beam unidirectionally operating in the resonator. 2.1 W single-frequency output at 1064 nm with elliptical polarization was obtained from this ring resonator. Compare with the existent Nd:YAG ring resonator, this novel resonator has a potential advantage in reducing depolarization loss and increasing the efficiency.

Femtosecond laser-irradiation-induced phase change of new environment friendly Te-free amorphous Ga-Sb-Se films is studied by coherent phonon spectroscopy. New coherent optical phonons (COP) occur when laser irradiation power reaches some threshold, implying laser-induced phase change taken place. Pump power dependence of COP dynamics reveals the phase change as crystallization and crystallization quality is comparable to one of annealing crystallization, showing application potential of Ga-Sb-Se films in optical phase change memory. The laser-irradiated crystallization of different component Ga-Sb-Se films is studied. It is found crystallization threshold power depends on Sb content, implying Sb-content control of the crystallization temperature of Ga-Sb-Se films.

Multiple parameters of nanocomposite Si/Sb80Te20 multilayer films are possibly optimized simultaneously to satisfy the development of ideal phase-change memory devices by adjusting chemical composition and physical structure of multilayer films. The crystallization and structure of the films are studied by coherent phonon spectroscopy. Laser irradiation power dependence of coherent optical phonon spectroscopy reveals laser-induced crystallization of the amorphous multilayer film, while coherent acoustic phonon spectroscopy reveals the presence of folded acoustic phonons which suggests a good periodic structure of the multilayer films. Laser irradiation-induced crystallization shows applicable potentials of the multilayer films in optical phase change storage.

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes of crystalline Sb2Te3, enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb2Te3-like topological insulators., Comment: 16 pages, 4 figures

The periodic number dependence of the femtosecond laser-induced crystallization threshold of [Si(5nm)/Sb80Te20(5nm)] x nanocomposite multilayer films has been investigated by coherent phonon spectroscopy. Coherent optical phonon spectra show that femtosecond laser-irradiated crystallization threshold of the multilayer films relies obviously on the periodic number of the multilayer films and decreases with the increasing periodic number. The mechanism of the periodic number dependence is also studied. Possible mechanisms of reflectivity and thermal conductivity losses as well as the effect of the glass substrate are ruled out, while the remaining superlattice structure effect is ascribed to be responsible for the periodic number dependence. The sheet resistance of multilayer films versus a lattice temperature is measured and shows a similar periodic number dependence with one of the laser irradiation crystallization power threshold. In addition, the periodic number dependence of the crystallization temperature can be fitted well with an experiential formula obtained by considering coupling exchange interactions between adjacent layers in a superlattice. Those results provide us with the evidence to support our viewpoint. Our results show that the periodic number of multilayer films may become another controllable parameter in the design and parameter optimization of multilayer phase change films.