Vortex state in thermally-induced pinning patterns in superconducting film

We propose a way to manipulate the landscape of the superconducting condensate in thin films via stripe-like (1D) and checkerboard (2D) periodic patterns. Our approach is based on the spatially localized heating of the superconductor, which is reflected in sinusoidal variations of the local temperature, which can be produced via, e.g., a focused laser beam or nanoheaters. This simple approach provides a very good alternative for modulation of the vortex collective, emerging in the type-II superconductors as a natural response to the applied magnetic field and the transport current, which was, up to now, controlled mainly via nanofabricated static pinning centers, whose distribution cannot be changed once the landscape is defined.     

二维缺陷GaAs电子结构和光学性质第一性原理研究

采用基于密度泛函理论的第一性原理方法计算了存在Ga空位缺陷和掺杂B原子的二维GaAs的能带结构、态密度和光学性质.计算结果表明空位缺陷二维GaAs显示出金属特性,B原子的引入使体系变为间接带隙半导体,禁带宽度为0.35 eV.态密度计算发现体系低能带主要由Ga的s态、p态、d态和As的s态、p态构成;高能带主要由Ga和As的s态、p态构成.掺杂B原子与存在空位缺陷的二维GaAs相比,静态介电常数相对较低,变为8.42,且易于吸收紫外光,在3.90～8.63 eV能量范围具有金属反射特性,反射率达到52%.     

Nondestructive testing of external defects on Nanguo pear

In view of the common pests and diseases and irregularly shaped fruits of Nanguo pear, this paper fused the spectral information and image features to realize the rapid nondestructive testing and recognition of the external defects on Nanguo pear by hyperspectral imaging technology. Backpropagation neural network and support vector machine model was established to identify external defects, which are commonly used in classification and pattern recognition. The testing results show that recognition effect of support vector machine is better than backpropagation neural network. Among them, the recognition accuracy of fruits damaged by insects and rotten fruits of Nanguo pears reaches 100%. This study provides a theoretical basis for developing online grading system and quality detection of Nanguo pear based on multispectral imaging technique.     

Enhanced interface interaction between modified carbon nanotubes and magnesium matrix

Carbon nanotube (CNT)/metal interface interaction is critical to the mechanical properties of CNT-reinforced metal matrix composites (MMCs). In this paper, in order to realize the chemical modification of the interface interaction between CNTs and Mg matrix, different types of defects (monovacancy, carbon and oxygen adatoms, as well as p-type boron and n-type nitrogen substitution) are introduced in CNTs to investigate the effect of the defects on the interface interaction (E_ib) between CNT and Mg (0 0 0 1) surface. Moreover, two models (adsorption model and interface model) are compared and validated to investigate the interface interaction. It is revealed that the CNT with the carbon adatom has the highest E_ib with the Mg (0 0 0 1), and the effect of boron doping on E_ib is superior to the intermediate oxygen which has already been proved experimentally in the enhancement of the interface interaction in MMCs. In terms of the electronic structure analysis, we reveal the micro-mechanism of the increase of E_ib under the action of different types of defects, and propose that the presence of holes (boron dopant) and the unsaturated electrons in CNTs can generate the chemical interaction between CNT and Mg matrix effectively. Our results are of great scientific importance to the realization of robust interfacial bonding between CNTs and Mg matrix via the reinforcement modification, so as to enhance the mechanical properties of CNTs reinforced Mg matrix composites.     

Study on electrical defects level in single layer two-dimensional Ta_2O_5

Two-dimensional atomic-layered material is a recent research focus, and single layer Ta_2O_5 used as gate dielectric in field-effect transistors is obtained via assemblies of Ta_2O_5 nanosheets. However, the electrical performance is seriously affected by electronic defects existing in Ta_2O_5. Therefore, spectroscopic ellipsometry is used to calculate the transition energies and corresponding probabilities for two different charged oxygen vacancies, whose existence is revealed by x-ray photoelectron spectroscopy analysis. Spectroscopic ellipsometry fitting also calculates the thickness of single layer Ta_2O_5,exhibiting good agreement with atomic force microscopy measurement. Nondestructive and noncontact spectroscopic ellipsometry is appropriate for detecting the electrical defects level of single layer Ta_2O_5.     

Electronic transport of bilayer graphene with asymmetry line defects

In this paper,we study the quantum properties of a bilayer graphene with(asymmetry) line defects.The localized states are found around the line defects.Thus,the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel.By adding a bias potential along the direction of the line defects,we calculate the electric conductivity of bilayer graphene with line defects using the Landauer-Biittiker theory,and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene.This one-dimensional line electric channel has the potential to be applied in nanotechnology engineering.     

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Titanium dioxide (TiO₂) is regarded as an important prototype photocatalytic material for several decades. The charge carrier kinetics determines the photocatalytic properties of TiO₂ materials; this is found to be greatly dependent on electronic structures. It has been revealed that the intrinsic intermediate gap states (intrinsic GSs) play a significant role in charge carrier kinetics that drive the photocatalytic processes of TiO₂ materials, which are not well summarized until now. Motivated by this thought, the purpose of this review focuses on physiochemical science of the intrinsic GSs of TiO₂ materials and their important role in charge carrier kinetics. We first give a summary on the chemical resources of the intrinsic GSs in TiO₂ and their physiochemical nature. Their general energy distribution, charge carrier population, and the associated thermodynamic properties are also elaborated from an overall viewpoint. We further carefully summarize and compare the experimental studies on the energy and the density distribution of the intrinsic GSs and discuss the associated chemical resources and charge carrier localizations. Trapping is the dominant function of intrinsic GSs in the charge carrier kinetics of TiO₂ materials. The significant effect of trapping on the transport, recombination, and interfacial transfer of charge carriers are also comprehensive summarized. Furthermore, the effects of charge carrier kinetics on photocatalytic performances are also discussed to some extents. Because of the importance of intrinsic GSs in modulating charge carrier kinetics, it is expected to increase the photocatalytic activity by engineering the intrinsic GSs, not only for TiO₂ materials, but also for the other semiconductor photocatalysts.     

Recent Advances in the Use of Black TiO2 for Production of Hydrogen and Other Solar Fuels

Black TiO₂ has emerged as one of the most promising photocatalysts recently discovered. The reason behind its catalytic activity is considered to be due to the presence of defects and Ti³⁺ species at the surface of black TiO₂ nanostructures, which are crucial for its diverse applications. Moreover, disordered/crystalline surface layers and bulk regions have been identified and appear to influence the intrinsic properties of the material. Here, we present the latest studies on the use of black TiO₂ for metal free hydrogen production, as well as for CO₂ photoreduction and N₂ photofixation. After highlighting the structure/property relations, we conclude with some critical questions and suggest further topics of research in order to better understand the underlying mechanisms of light absorption in black TiO₂, especially towards solar fuels production.     

钇铝石榴石在高压下的光学性质第一性原理研究

本文采用基于密度泛函理论(DFT)的第一性原理方法,分别计算了120 GPa的压力范围内钇铝石榴石理想晶体和含氧空位点缺陷晶体的光学性质.计算数据表明:(1)在120 GPa的压力范围内其理想晶体和含2+价氧离子空位(形成能最低)的缺陷晶体在可见光区不存在光吸收(是透明的).(2)压力加载将导致其反射谱峰值强度降低,且空位缺陷的存在使其峰值强度进一步减弱.这些结果对进一步实验有重要的参考价值.