Tunable resonance transmission modes in hybrid heterostructures based on porous silicon

ABSTRACT: In this work, we report the experimental results and theoretical analysis of strong localization of resonance transmission modes generated by hybrid periodic/quasiperiodic heterostructures (HHs) based on Porous Silicon (PSi). The HHs are formed by stacking a quasiperiodic Fibonacci (FN) substructure between two Distributed Bragg Reflectors (DBRs). FN substructure defines the number of strong localized modes that can be tunable at any given wavelength and be unfolded when a partial periodicity condition is imposed. These structures show interesting properties for biomaterials research, biosensor applications and basic studies of adsorption of organic molecules. We also demonstrate the sensitivity of HHs to material infiltration.     

Enhanced mobility in LaAlO3/SrTiO3 heterostructures with layer-modulated patterning

Overcoming the unintentional doping of defect-related carriers induced from low oxygen partial pressure is a major challenge to realize multifunctional oxide electronics. In this work, we demonstrate that the two-step deposition in conjunction with layer modulated patterning process can enhance several properties of LaAlO₃/SrTiO₃ (LAO/STO) heterostructures grown under a low oxygen partial pressure of 5?×?10^?8 Torr. Specifically, our patterned samples exhibit extraordinary electronic properties including positive colossal magnetoresistance of ～3500% under 10?T, and enhanced carrier mobility ~5000?cm²/Vs at 2?K without using buffer layer or using additional elements. These unique phenomena are resulted from inhibition of the multiband conducting behaviour, which likely originates from oxygen vacancy related defects in the STO layers, through the two-step fabrication method. Consequently, by controlling defect behaviour through the two-step deposition jointly with modulated patterning process, several properties for oxide-based electronics can be induced in a single platform even under a low oxygen condition.     

Bi2O3-sensitized hierarchically mesoporous ZnO nanoparticles for Hg(II) reduction

Herein, an affordable and novel approach to design Bi₂O₃-sensitized hierarchically mesoporous ZnO nanoparticles (NPs) with a variety of Bi₂O₃ contents is achieved for Hg(II) reduction upon visible light exposure. TEM images of both ZnO and 3% Bi₂O₃/ZnO samples exhibit nanoscale spherical-like structures with a regular shape and a particle size of ~30 nm. The incorporation of Bi₂O₃ on hierarchically mesoporous ZnO networks allows visible light to be harvested in a broad range, and the mesoporous 3% Bi₂O₃/ZnO heterostructure demonstrates the best photocatalytic efficiency for Hg(II) reduction with a value of ~100% after 60 min. The photoreduction rate over the 3% Bi₂O₃/ZnO heterostructure is enhanced 10 and 20 times more than that of TiO₂-P25 and ZnO NPs. The rate constant of the 3% Bi₂O₃/ZnO heterostructure is 16.8 and 33.6 fold larger than that of TiO₂-P25 and ZnO NPs. The superior Hg(II) photoreduction performance could be ascribed to the synergistic effect, excellent visible-light harvest, large surface area, and pore volume provided by incorporating Bi₂O₃ and the heterojunction design between p-type Bi₂O₃ and n-type ZnO. This alignment of the electronic bands provides charge carrier separation, thereby decreasing the recombination rate. Finally, the mechanisms and kinetics for the photocatalytic reduction of Hg(II) are proposed.     

转盘式反应器光催化氧化含酚废水的试验研究

设计的新型转盘式光反应器采用同轴多层转盘作为TiO2膜的载体,很大程度上扩大了光与催化剂的接触面积,对光源系统进行优化布置,使光均匀分布在各转盘叶片之间,不仅可以提高光辐射强度还具有良好的传质性能.利用该反应器光催化氧化苯酚废水,考察了反应器各参数对苯酚降解率的影响,试验结果表明该反应器对低浓度苯酚废水具有良好的降解效果,出水水质可以达到国家一级排放标准.同时从工业放大的角度考虑,多叶转盘式光反应器的结构和降解能力决定了它具有潜在的优势.     

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 10⁶ V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The E_c-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at E_c-0.24 eV is 0.39 eV.     

TiO2光催化材料的超亲水性原理及应用

介绍了TiO2光催化材料的催化氧化和表面超亲水性的原理,并着重探讨了其在表面超亲水性方面的应用,同时还分析了光催化剂应用的关键技术。     

结合多种光催化产品的开发以提高光催化技术在室内环境净化中的应用效果

本文介绍了近年来关于二氧化钛光催化在室内环境净化中的应用研究，初步探讨了目前二氧化钛光催化剂净化室内环境应用中所存在的问题，认为结合光催化剂的不同利用方式及其开发出的多种光催化产品，将有利于提高光催化技术在室内环境净化中的应用效果，特别是将光催化技术与室内装饰产品的结合、开发出自身具有光净化功能的环保型装饰产品将是光催化技术在室内环境净化中的趋势。     

光催化技术在污水处理方面的应用

光催化技术是一种新兴的高效节能现代污水处理技术,本文从半导体光催化方法,反应机理、各类污染物光催化降解的现状,提高半导体光催化剂活性途径,光催化技术发展中存在问题等方面分别论述了半导体光催化技术现状及发展趋势。     

以玻璃珠为载体的负载型二氧化钛的制备及光催化活性研究

在溶胶-凝胶法制备。TiO2胶体溶液的基础上,用玻璃珠作载体制备了负载型TiO2光催化剂,利用SEM对玻璃珠载体和玻璃珠负载TiO2膜的粒径进行了表征分析;同时对玻璃珠负载TiO2的光催化活性进行了研究。     

光催化膜反应器用于亚甲基蓝的降解

研究了催化剂颗粒粒径对降解速率的影响,并将光催化反应和膜分离技术相结合,开发了光催化膜反应器。利用该反应器对亚甲基蓝进行降解的结果表明,亚甲基蓝可被很快地降解,而悬浮在反应液里的催化剂颗粒同时可被有效地分离回收并连续地在反应器里使用。     

Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two: quantum wires and quantum dots, in order to realize novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use self-organized three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. This article is intended to convey the flavour of the subject by focussing on the structural, optical and electronic properties and device applications of self-assembled quantum dots and to give an elementary introduction to some of the essential characteristics.     

Structural and compositional evolution of FePt nanocubes in oganometallic synthesis

In this study, the mechanisms for the formation of FePt nanocubes via pyrolysis of iron pentacarbonate [Fe(CO)₅] and platinum(II) acetylacetonate [Pt(acac)₂] were investigated. The time evolution of the structure, morphology, and composition of the FePt nanocubes was probed by transmission electron microscopy (TEM) at different reaction stages. On the basis of the detailed characterization, we determined the following aspects of the reaction mechanism: (1) The FePt nanocubes are rapidly formed at 160°C to 180°C by the decomposition of the precursors, and the formation of the FePt nanocubes is dominated by the nucleation of Pt-rich species followed by a slow deposition process of Fe atoms. (2) A thin Fe atomic layer is present on the FePt nanocubes, which does not influence their phase transition into a fct structure. (3) The use of Fe(CO)₅ is the key factor leading to the anisotropic growth of the FePt nanocubes, and the Fe(CO)₅/Pt(acac)₂ molar ratio not only determines the composition of the resulting FePt nanocubes but also affects their morphology and structures.     

光催化技术在降解有机染料污染物方面的应用

光催化技术是一种新兴的高效节能现代污水处理技术,本文从半导体光催化技术研究现状、反应机理、反应动力学、光催化技术发展及其存在的问题等方面对半导体光催化技术在降解常见有机染料方面的应用加以综述.     

Three-dimensional heterostructure of metallic nanoparticles and carbon nanotubes as potential nanofiller

ABSTRACT: The effect of the dimensionality of metallic nanoparticle-and carbon nanotube-based fillers on the mechanical properties of an acrylonitrile butadiene styrene (ABS) polymer matrix was examined. ABS composite films, reinforced with low dimensional metallic nanoparticles (MNPs, 0-D) and carbon nanotubes (CNTs, 1-D) as nanofillers, were fabricated by a combination of wet phase inversion and hot pressing. The tensile strength and elongation of the ABS composite were increased by 39% and 6%, respectively, by adding a mixture of MNPs and CNTs with a total concentration of 2 wt%. However, the tensile strength and elongation of the ABS composite were found to be significantly increased by 62% and 55%, respectively, upon addition of 3-D heterostructures with a total concentration of 2 wt%. The 3-D heterostructures were composed of multiple CNTs grown radially on the surface of MNP cores, resembling a sea urchin. The mechanical properties of the ABS/3-D heterostructured nanofiller composite films were much improved compared to those of an ABS/mixture of 0-D and 1-D nanofillers composite films at various filler concentrations. This suggests that the 3-D heterostructure of the MNPs and CNTs plays a key role as a strong reinforcing agent in supporting the polymer matrix and simultaneously serves as a discrete force-transfer medium to transfer the loaded tension throughout the polymer matrix.