Chemical vapor deposition growth of two-dimensional heterojunctions

The properties of two-dimensional (2D) layered materials with atom-smooth surface and special interlayer van der Waals coupling are different from those of traditional materials. Due to the absence of dangling bonds from the clean surface of 2D layered materials, the lattice mismatch influences slightly on the growth of 2D heterojunctions, thus providing a flexible design strategy. 2D heterojunctions have attracted extensive attention because of their excellent performance in optoelectronics, spintronics, and valleytronics. The transfer method was utilized for the fabrication of 2D heterojunctions during the early stage of fundamental research on these materials. This method, however, has limited practical applications. Therefore, chemical vapor deposition (CVD) method was recently developed and applied for the preparation of 2D heterojunctions. The CVD method is a naturally down-top growth strategy that yields 2D heterojunctions with sharp interfaces. Moreover, this method effectively reduces the introduction of contaminants to the fabricated heterojunctions. Nevertheless, the CVD-growth method is sensitive to variations in growth conditions. In this review article, we attempt to provide a comprehensive overview of the influence of growth conditions on the fabrication of 2D heterojunctions through the direct CVD method. We believe that elucidating the effects of growth conditions on the CVD method is necessary to help control and improve the efficiency of the large-scale fabrication of 2D heterojunctions for future applications in integrated circuits.     

Quest towards ultimate performance in superconducting nanowire single photon detectors

正In 2007,superconducting nanowire single photon detectors(SSPD or SNSPD)[1]made an outstanding impact in the field of quantum information technology by demonstrating quantum key distribution(QKD)over a 200-km optical fiber with a 42-dB optical loss using a practical SNSPD system[2].This successful demonstration was realized thanks to its extremely     

Two-dimensional matter-wave solitons and vortices in competing cubic-quintic nonlinear lattices

The nonlinear lattice — a new and nonlinear class of periodic potentials — was recently introduced to generate various nonlinear localized modes. Several attempts failed to stabilize two-dimensional (2D) solitons against their intrinsic critical collapse in Kerr media. Here, we provide a possibility for supporting 2D matter-wave solitons and vortices in an extended setting — the cubic and quintic model — by introducing another nonlinear lattice whose period is controllable and can be different from its cubic counterpart, to its quintic nonlinearity, therefore making a fully “nonlinear quasi-crystal”.A variational approximation based on Gaussian ansatz is developed for the fundamental solitons and in particular, their stability exactly follows the inverted Vakhitov–Kolokolov stability criterion, whereas the vortex solitons are only studied by means of numerical methods. Stability regions for two types of localized mode — the fundamental and vortex solitons — are provided. A noteworthy feature of the localized solutions is that the vortex solitons are stable only when the period of the quintic nonlinear lattice is the same as the cubic one or when the quintic nonlinearity is constant, while the stable fundamental solitons can be created under looser conditions. Our physical setting (cubic-quintic model) is in the framework of the Gross–Pitaevskii equation or nonlinear Schrödinger equation, the predicted localized modes thus may be implemented in Bose–Einstein condensates and nonlinear optical media with tunable cubic and quintic nonlinearities.     

The effect of anodising time on the electrochemical behaviour of the Ti/TiO<Subscript>2</Subscript> NTs/IrO<Subscript>2</Subscript>-RuO<Subscript>2</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> anode

Nowadays, mixed metal oxide (MMO) anodes are a superior alternative to lead alloys in electrowinning processes. Passivation of titanium substrate is the most common mechanism of deactivation in these anodes. In this research, titanium oxide nanotubes have been utilised as an interlayer between the substrate and a mixed metal oxide coating in order to improve the anode electrochemical behaviour and life via retardation of titanium passivation. Anodising of the substrate was done in 0.5 wt% hydrofluoric acid for 30, 60 and 240 min. The samples were subsequently coated with a coating composed of IrO₂-RuO₂-Ta₂O₅. The microstructure of different samples was observed by scanning with an electron microscope, and the electrochemical behaviour of the samples was studied by accelerated life test, cyclic voltammetry and electrochemical impedance spectroscopy. The studies showed that formation of titanium oxide nanotubes with anodising times of 60 and 240 min increases the life of the anode through the provision of a compact coating. The life of the anode which was anodised for 240 min lasted about 20% longer than the sample which had a substrate without any anodised layer.     

Fabrication of urchin-like NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres assembled by using SDS as soft template for anode materials of Lithium-ion batteries

In this paper, the urchin-like NiCo₂O₄ microspheres assembled by using sodium dodecyl sulfate (SDS) as soft template are successfully fabricated by a facile procedure including microemulsion-solvothermal reaction and subsequent calcination at 400 °C for 4 h. The structure and morphology of synthesized NiCo₂O₄ particles are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It has been clearly revealed that the prepared three-dimensional urchin-like NiCo₂O₄ microspheres are constituted by one-dimension nanowires. As it is applied to anode for lithium-ion batteries (LIBs), the initial coulombic efficiency is up to 75.7%, and the specific reversible capacity retains up to 1034.2 mAh/g even after 40 cycles at a current density of 100 mA/g. Furthermore, as the current density gradually increases to 800 mA/g, it still delivers the reversible capacity of 895.4 mAh/g. The high reversible specific capacity, perfect cyclability, and rate performance are attributed to the unique urchin-like NiCo₂O₄ microspheres, which can alleviate the volume expansion and shorten the diffusion path of ions and electrons during lithiation/delithiation process. The self-standing urchin-like NiCo₂O₄ microspheres may be a very promising candidate in place of the commercial graphite-based anode materials for high-performance LIBs.     

Spray pyrolysis-deposited TiO<Subscript>2</Subscript> thin films as high-performance lithium ion battery anodes

Focusing on additive-free electrodes, thin films are of typical interest as electrodes for lithium ion battery application. Herein, we report the fabrication of TiO₂ thin films by spray pyrolysis deposition technique. X-ray diffraction and transmission electron microscopic analysis confirms the formation of anatase TiO₂. Electrochemical evaluation of these sub-micron TiO₂ thin films exhibits high-rate performance and long cycling stability. At 1C rate (1C?=?335 mA/g), the electrode delivered discharge capacity of 247 mAh/g allowing about 0.74 lithium into the structure. The electrodes also delivered specific capacities of 122 and 72 mAh/g at 10 and 30C rates, respectively. Without conductive additives, this excellent performance can be attributed to the nanosize effect of TiO₂ particles combined with the uniform porous architecture of the electrode. Upon cycling at high rates (10 and 30C), the electrode exhibited excellent cycling stability and retention, specifically only <?0.6% capacity loss per cycle over 2500 cycles.     

Structural,electrical, and transport number studies of AgI-doped silver borotellurite fast ion conducting glass system

Silver ion conducting glass system composed of xAgI–(100???x)[0.444 Ag₂SO₄–0.555 (0.4TeO₂–0.6B₂O₃)] has been prepared by melt quenching method for x?=?0 to 80 in step of 10. XRD, DSC, FTIR, and SEM were carried out to understand some structural properties of prepared samples. XRD and DSC studies of the samples with x?≤?60 show predominantly glassy nature. Electrical parameters and activation energies of all the samples were evaluated by complex impedance analysis and Arrhenius plots of DC conductivity, respectively. Carrier concentration, mobility, inter-ionic distance, and ionic conductivity of samples were measured and discussed. It is observed that the conductivity varies with increasing the temperature and composition. The highest conductivity (1.8?×?10^?1 S cm^?1) and ionic current (8.33 μA) is observed for =?50 sample at room temperature; hence, it can be used as best electrolyte material for solid-state battery application.     

Characterization of Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript> Thin Films Prepared by RF Magnetron Sputtering

Zn₂SnO₄ (ZTO) is a stable semiconductor in ZnO–SnO₂ system and important transparent conducting oxide (TCO) predominantly used in optoelectronic devices. ZTO thin films were prepared by RF magnetron sputtering using Zn₂SnO₄ ceramic target in this paper. The effects of annealing temperatures and oxygen contents on characterization of ZTO thin films were studied. The results show that ZTO thin films prepared by RF magnetron sputtering are amorphous with an optical band gap of 3.22 eV. After annealing at 650°C in Ar atmosphere for 40 min, ZTO films possess a spinel structure with an optical band gap of 3.62 eV. The atomic force microscope (AFM) data of morphology reveals that the surface roughness of films is about 2 nm. The results of energy dispersive spectrometer (EDS) show that the concentration ratio of Zn to Sn is in the range from 1.44 to 1.57. The results of Hall-effect-measurement system reveal that the resistivity of films varies from 102 to 10–1 Ωcm, carrier concentration is about 10¹⁷ cm^–3, and mobility ranges from 10⁰ to 10¹ cm² v^–1 s^–1.     

Autaptic modulation-induced neuronal electrical activities and wave propagation on network under electromagnetic induction

Based on an improved HR neuron model, the effects of electrical and chemical autapses on the firing activities of single neurons are studied, and the wave propagation in forward feedback neural network is also discussed by considering autapstic regulation under different intensities of electromagnetic induction. It is found that the electrical activities of single neuron can be changed by exerting excitatory or inhibitory of electrical and chemical autapses. With different feedback gains of electromagnetic induction current, membrane potential shows the oscillatory solutions and steady states. Under the condition of different autapse or electromagnetic induction, the propagation of electrical activities caused by the central neuron is transformed in the forward feedback network. Moreover, the spatial synchronization of the network will be changed by choosing different coupling intensities and feedback gains. It is proved that the electrical and chemical autapses play a significant role in firing modes of single neuron and the wave propagation of the forward feedback networks under the electromagnetic induction.