具有新光学性质的Zn-Zn_2SiO_4纳米同轴线阵列

Unique Optical Properties of Aligned Zn-Zn_2SiO_4 Core-shell Nanocables

采用气相沉积技术在Si衬底上生长了Zn-Zn2SiO4芯-壳结构纳米同轴线阵列。根部呈笋状的纳米同轴线,直径约100nm,长度可以超过10μm;同轴线芯直径约50nm、壳层厚约25nm。通过X射线衍射的表征以及能量色散谱的线扫描,确定纳米同轴线的芯为Zn,壳层为Zn2SiO4。我们提出了一种新的生长机制,同时也为生长均匀的纳米同轴线提供一种新的技术。观察阴极荧光谱发现,纳米同轴线有三个主要发光带:强度最大的中紫外300nm发光、较弱的可见光区560nm以及红外谱区865nm的发光。对纳米同轴线截面的300nm发光峰观测发现,中紫外发光来源于Zn2SiO4壳层。正是这种同轴线的结构,使得其具备特殊的光学性质。

Recently, there is much interest in the development of wide band gap semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of photons, electrons, and holes make them particularly attractive as potential building blocks for nanoscale optoelectronic devices. Semiconductor nanostructures with modulated composition have been known to enhance new functions and properties, such as GaAs/GaP superlattice, core-shell structured Si-Ge nanowires, and core-shell Zn-ZnO nanobehs. To composite nanowires, especially, coaxial nanocables will provide a great possibility to take advantage of different function and properties of different material within a single nanoscale component. Aligned coaxial nanocables were grown on Si substrates by a vapor deposition technique. Zn powders were placed on a quartz boat and positioned at the center of a quartz tube in a horizontal furnace. After the quartz boat was inserted, the furnace was ramped to 1 100 ℃ and kept at that temperature for 2 h under a N2 flow rate of 500 sccm. The obtained nanocable arrays had average diameters of about 100 nm and length up to more than 10 μm. Both the shell thickness and the core radius were almost the same, about 25 nm. It has been revealed that the nanocable is grown from the sprout-shaped root and the top ends of the nanocables were typically round without droplet. Together with the XRD pattern and EDS mapping analysis, it can be suggested that the nanocable had a Zn2SiO4 shell and a Zn core. A unique growth mechanism was proposed for the homogeneous crystallization of Zn-Zn2SiO4 core-shell nanocables. The CL spectra exhibited three distinct peaks： one strong peak at middle-UV region（300 nm） and another two weak bands at visible（560 nm） and infrared （865 nm） regions. The UV emission was attributed to the thin double-layer structure in the Zn-Zn2SiO4 coreshell nanocable where the Zn2SiO4 shell has the potential to serve as more ideal luminophors.