Structural and Optical Properties of ZnO Nanotips Grown on GaN Using Metalorganic Chemical Vapor Deposition

ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction (XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO||(0002)GaN and (101̄0)ZnO||(101̄0)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are 11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni’s equation to study the variation of energy bandgap versus temperature.     

Strategies to Improve Field Emission Performance of Nanostructural ZnO

Nanostructural ZnO is a good candidate for field emission (FE) because of its high aspect ratio, controllable electrical conductivity, and good thermal and chemical stability. In order to improve the FE performance, ZnO nanopins, gallium-doped nanofibers, periodic nanorod arrays, and aligned nanotubes were designed and fabricated by a vapor-phase transport method using ZnO + C and ZnO + C + Ga₂O₃ powder mixtures, electrochemical deposition, and hydrothermal decomposition, respectively. The FE behaviors including threshold of electric field, emission current density, field enhancement factor, and stability are reviewed in this paper based on our previous works. Some strategies to improve the performance of the nanostructural ZnO field emitters are demonstrated.     

Controlled synthesis of porous spinel cobalt manganese oxides as efficient oxygen reduction reaction electrocatalysts

In this article, we report a facile precursor pyrolysis method to prepare porous spinel-type cobalt manganese oxides (Co _x Mn_3-x O₄) with controllable morphologies and crystalline structures. The capping agent in the reaction was found to be crucial on the formation of the porous spinel cobalt manganese oxides from cubic Co₂MnO₄ nanorods to tetragonal Co₂Mn₄ microspheres and tetragonal Co₂Mn₄ cubes, respectively. All of the prepared spinel materials exhibit brilliant oxygen reduction reaction (ORR) electrocatalysis along with high stability. In particular, the cubic Co₂MnO₄ nanorods show the best performance with an onset potential of 0.9 V and a half-wave potential of 0.72 V which are very close to the commercial Pt/C. Meanwhile, the cubic Co₂MnO₄ nanorods present superior stability with negligible degradation of their electrocatalytic activity after a continuous operation time of 10,000 seconds, which is much better than the commercial Pt/C electrocatalyst.

Open image in new window

     

Electrochemical growth of flowerlike gold nanoparticles on polydopamine modified ITO glass for SERS application

A functional biopolymer - polydopamine (Pdop) layer was easily modified on the surface of indium tin oxide substrates by spontaneous oxidative polymerization in a dopamine solution. The Pdop layer functions as a novel and promising protector for electrochemical growth of flowerlike gold nanostructures (AuNFs). Electrochemical investigations and SEM results demonstrate that Pdop coating is favored to rapid gold nucleation. The application of AuNFs in surface-enhanced Raman scattering is investigated by using rhodamine 6G as probe molecule. Its detection limit reaches as low as 10⁻¹² M. Pdop coating as a functional platform to prepare AuNFs is promising for potential applications in sensitive optical chemical sensors.     

Recent progress in electrospun nanofibers and their applications in heavy metal wastewater treatment

Novel adsorbents with a simple preparation process and large capacity for removing highly toxic and nondegradable heavy metals from water have drawn the attention of researchers. Electrospun nanofiber membranes usually have the advantages of large specific surface areas and high porosity and allowing flexible control and easy functionalization. These membranes show remarkable application potential in the field of heavy metal wastewater treatment. In this paper, the electrospinning technologies, process types, and the structures and types of nanofibers that can be prepared are reviewed, and the relationships among process, structure and properties are discussed. On one hand, based on the different components of electrospun nanofibers, the use of organic, inorganic and organic−inorganic nanofiber membrane adsorbents in heavy metal wastewater treatment are introduced, and their advantages and future development are summarized and prospected. On the other hand, based on the microstructure and overall structure of the nanofiber membrane, the recent progresses of electrospun functional membranes for heavy metal removal are reviewed, and the advantages of different structures for applications are concluded. Overall, this study lays the foundation for future research aiming to provide more novel structured adsorbents.     

Controlled synthesis of one-dimensional Au-Ag porous nanostructures

The fabrication of a new type of one-dimensional Au-Ag porous nanotube (NPT) structure was presented based on a facile combination of nanocrystal growth and surface modification. Ag nanowires with various diameters were firstly served as the chemical plating templates via a polyol-process. Then, one-dimensional (1D) Au-Ag porous nanostructures with tailored structural features could be prepared by controlling the individual steps involved in this process, such as nanowire growth, surface modification, thermal diffusion, and dealloying. Structural characterizations reveal these Au-Ag porous nanotubes, non-porous nanotubes and porous nanowires possess novel nano-architectures with multimodal open porosity and excellent structural continuity and integrity, which make them particularly desirable as novel 1D nanocarriers for biomedical, drug delivery and sensing applications.     

锂离子电池Cu6Sn5负极的研究进展

综述了锂离子电池Cu6Sn5合金的研究进展。介绍了锡铜合金体系作为锂离子电池负极的优势,并指出其循环性能对比石墨负极仍然不够理想。对此,还概述了目前国内外改进锡铜合金材料循环性能的方法,主要包括实现纳米化、薄膜化以及多孔结构。     

氧化石墨烯表面的饱和池沸腾强化传热实验

利用氧化石墨烯（GO）纳米片沸腾自组装法（self-assembly）制备出GO纳米表面,以蒸馏水为液体工质,对常压下GO纳米表面和光滑铜平面的饱和池沸腾换热特性进行了对比实验研究,并用高速摄像机拍摄了汽泡的动态行为。结果表明,GO纳米表面降低了换热壁面的过热度,其临界热流密度（CHF）和换热系数（HTC）分别达到了208W/cm²和7.25W/(cm²?K),较光滑铜平面分别提高了66.4%和86.9%。分析认为,是铜基底表面沉积的润湿性优异的高导热二维GO层状结构促使了CHF提高。汽泡可视化观察发现,相比于光滑铜平面,较低热流密度时,相同热流下GO纳米表面上汽泡脱离直径较小,脱离频率较高,汽化核心增多;较高热流密度时,光滑铜平面汽泡合并现象更严重,即GO纳米表面能延缓导致CHF产生的表面蒸汽膜的出现。     

MnO2/NiCo2O4复合材料的控制合成及其电化学性能研究

采用两步合成法制备了MnO_2/NiCo_2O_4核壳结构纳米棒,使用场发射扫描电子显微镜、X射线衍射和电化学工作站研究了其形貌特征和电化学性能。研究结果表明,在α-MnO_2纳米棒上生长了均匀的NiCo_2O_4纳米片,这种核壳结构纳米棒所制备的电极在充放电电流密度为0.5A/g时比电容达到了434F/g,明显比纯α-MnO_2的比电容(256F/g)高,循环测试2 000次后,比电容保留量为91.8%,表现出了优秀的电化学性能,具有广阔的应用前景。     

超亲水毛细芯环路热管启动及热性能分析

为解决电子设备高热通量下的散热问题,采用H₂O₂氧化法对烧结毛细芯进行了超亲水改性,研究了毛细芯表面润湿性对吸液性能的影响。并将改性后的超亲水毛细芯应用到环路热管内,研究了倾斜角度及加热功率对超亲水毛细芯环路热管的换热特性的影响。实验结果表明:超亲水毛细芯的吸液速度增加,吸液时间较亲水毛细芯减小了3.52ms;与普通亲水毛细芯环路热管相比,在加热功率Q=200W时,超亲水毛细芯环路热管蒸发器中心温度降低了约6.0℃,在Q=20W时启动时间与温度分别降低了33s与2.5℃。同时发现超亲水毛细芯环路热管在正重力状态时的运行温度更低,热阻较小,最低热阻仅为0.084℃/W。