Shape‐Controlled Synthesis of Polyhedral Nanocrystals and Their Facet‐Dependent Properties

Growth of inorganic polyhedral nanocrystals with excellent morphology control presents significant synthetic challenges, especially when the development of synthetic schemes to make nanocrystals with systematic shape evolution is desired. Nanocrystals with fine size and shape control facilitate formation of their self‐assembled packing structures and offer opportunities for examination of their facet‐dependent physical and chemical properties. In this Feature Article, recent advances in the synthesis of nanocrystals with systematic shape evolution are highlighted. The reaction conditions used to achieve this morphology change offer insights into the growth mechanisms of nanocrystals. A novel class of polyhedral core–shell heterostructures fabricated using structurally well‐defined nanocrystal cores is also presented. Facet‐dependent photocatalytic activity, molecular adsorption, and catalytic and electrical properties of nanocrystals have been examined and are discussed. Nanomaterials with enhanced properties and functionality may be obtained through continuous efforts in the synthesis of nanocrystals with well‐defined structures and investigation of their plane‐selective properties.     

温度对飞秒激光沉积ZnO/Si薄膜的结构和性能的影响

通过飞秒脉冲激光(50 fs,800 nm,1 kHz,2 mJ)沉积技术在n型Si(100)单晶基片上制备了ZnO薄膜.详细研究了基片温度变化以及退火处理对ZnO薄膜的结构、表面形貌及光学性质的影响.X射线衍射(XRD)结果表明,不同温度下(20~350℃)生长的ZnO薄膜具有纤锌矿结构,并且呈c轴择优取向;当基片温度为80℃时,薄膜沿(002)晶面高度择优生长;当基片温度为500℃时薄膜沿(103)晶面择优生长,场发射扫描电子显微镜(FEEM)结果表明薄膜呈纳米晶结构,并观察到了ZnO的六方结构.进一步通过透射光谱的测量讨论了基片温度及退火处理对ZnO薄膜光学透射率的影响,结果表明退火后薄膜的透射率增大.     

The Role of oxygen diffusion in photoinduced changes of the electronic and optical properties in amorphous indium oxide

A stable increase by as much as 10⁸ in the conductivity of amorphous indium oxide to σ≥ 10³Ω^-1 cm₋₁ can be achieved by ultraviolet photoreduction. This treatment also increases the absorption coefficient, α(hυ), by up to a factor of 10₃ for hυ <1.5 eV due to free carrier absorption and causes a 0.1 eV shift of the absorption edge to the blue. These changes are controlled by the Fermi level, EF, which is presumably determined by doping due to oxygen vacancies. A diffusion constant D >3 x 10⁻¹² cm²/s for oxygen at 300K is determined from a constant flow experiment. Oxygen diffusion is verified by secondary ion mass spectrometry with ¹⁸O. The functions α(hυ) and σ(T) are simulated as E_F is varied using a simple density of states model appropriate for amorphous semiconductors. These simulations qualitatively agree with the experimental data if transitions from the conduction band tail to the conduction band are assumed to be forbidden.     

Recyclable,Flexible, Low‐Power Oxide Electronics

The ability to process and dimensionally scale field‐effect transistors with and on paper and to integrate them as a core component for low‐power‐consumption analog and digital circuits is demonstrated. Low‐temperature‐processed p‐ and n‐channel integrated oxide thin‐film transistors in the complementary metal oxide semiconductor (CMOS) inverter architecture are seamlessly layered on mechanically flexible, low‐cost, recyclable paper substrates. The possibility of building these circuits using low‐temperature processes opens the door to new applications ranging from smart labels and sensors on clothing and packaging to electronic displays printed on paper pages for use in newspapers, magazines, books, signs, and advertising billboards. Because the CMOS circuits reported constitute fundamental building blocks for analog and digital electronics, this development creates the potential to have flexible form factor computers seamlessly layered onto paper. The holistic approach of merging low‐power circuitry with a recyclable substrate is an important step towards greener electronics.     

Functional Free‐Standing Graphene Honeycomb Films

Fabricating free‐standing, three‐dimensional (3D) ordered porous graphene structure can service a wide range of functional materials such as environmentally friendly materials for antibacterial medical applications and efficient solar harvesting devices. A scalable solution processable strategy is developed to create such free‐standing hierarchical porous structures composed of functionalized graphene sheets via an “on water spreading” method. The free‐standing film shows a large area uniform honeycomb structure and can be transferred onto any substrate of interest. The graphene‐based free‐standing honeycomb films exhibit superior broad spectrum antibacterial activity as confirmed using green fluorescent protein labeled Pseudomonas aeruginosa PAO1 and Escherichia coli as model pathogens. Functional nanoparticles such as titanium dioxide (TiO₂) nanoparticles can be easily introduced into conductive graphene‐based scaffolds by premixing. The formed composite honeycomb film electrode shows a fast, stable, and completely reversible photocurrent response accompanying each switch‐on and switch‐off event. The graphene‐based honeycomb scaffold enhances the light‐harvesting efficiency and improves the photoelectric conversion behavior; the photocurrent of the composite film is about two times as high as that of the pure TiO₂ film electrode. Such composite porous films combining remarkably good electrochemical performance of graphene, a large electrode/electrolyte contact area, and excellent stability during the photo‐conversion process hold promise for further applications in water treatment and solar energy conversion.     

用二次离子质谱和扩展电阻探针技术测量硅中注入硼的深度分布及扩展电阻探针技术分辨率的估算

利用二次离子质谱和扩展电阻探针技术测量了硅中注入硼的深度分布 .在适当的测量深度 ,用扩展电阻探针技术测得的结果对二次离子质谱技术测量的结果进行了标定 ,从而得到硅片中硼原子的深度分布 .用近似模型估算了扩展电阻探针针尖半径对测试分辨率的影响 .若探针针尖半径为r0 ,测量斜面的角度为 ξ ,在用扩展电阻探针技术测量载流子浓度的深度分布时 ,可以近似认为深度分辨率为 7 86r0 sinξ.还定性讨论了样品表面耗尽层对扩展电阻探针技术的影响.     

热处理温度对片状ZnO晶体结构和光学性质的影响

采用均匀沉淀法,在无任何催化剂的条件下,两步合成片状ZnO晶体。105℃干燥得到ZnO晶体前驱物,400℃煅烧得到纯ZnO晶体。通过XRD、SEM、TEM、UV-vis和PL光谱等测试手段对ZnO晶体在两个不同热处理温度下的结构和光学性质进行表征。结果显示:ZnO晶体为六方纤锌矿结构,(0001)面形貌为规则的片状正六边形。热处理温度由105℃升至400℃,样品直径增加,透射率降低,禁带宽度减小,光致发光近带边发射峰强度减弱,位置红移。实验结果表明,热处理温度对均匀沉淀法合成ZnO晶体的光学性质存在一定影响。     

980nm垂直腔面发射激光器的外延生长

模拟了垂直腔面发射激光器(VCSEL)的反射谱和量子阱增益谱,采用金属有机物化学气相沉积设备外延生长了980 nm的垂直腔面发射激光器,制作了氧化孔径为14 μm的内腔式氧化限制型VCSEL器件,其阈值电流为3.3mA,阈值电压为1.8V,斜率效率为0.387 W/A,室温直流电流为22.8 mA时,输出光功率为5 mW.     

锂离子电池用聚合物电解质的最新进展I.干态聚合物电解质

聚合物锂离子电池的发展对聚合物电解质提出了更高的要求,促使人们开发性能优良的干态聚合物电解质。综述了近年来干态聚合物电解质的研究进展,包括:(1)以改性聚氧化乙烯-锂盐复合体系为代表的耦合体系;(2)导电机理完全不同的解耦合体系;(3)阴离子移动受限的单离子体系。其中,解耦合体系与单离子体系的研究得到了特别的关注。