Multipeak-structured photoluminescence mechanisms of as-prepared and oxidized Si nanoporous pillar arrays

Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O₂ atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.     

氧化锌/硅纳米孔柱阵列的结构和光致发光特性研究

以硅纳米孔柱阵列(Si-NPA)为衬底、用化学气相沉积法制备了具有规则阵列结构特征的ZnO/Si-NPA纳米复合体系，并对其结构和光致发光性质进行了表征. 实验结果显示，组成ZnO/Si-NPA表面阵列的每个柱子均呈现层壳结构. 不同于衬底Si-NPA的红光和蓝光发射，ZnO/Si-NPA在紫外光区和蓝绿光区呈现出两个强的宽发光峰. 分析表明，紫外光发射应归因于ZnO晶体的带边激子跃迁；而蓝绿光发射则来自于ZnO晶体本征缺陷所形成的两类深能级复合中心上载流子的辐射跃迁.     

硅纳米孔柱阵列的结构和光学特性研究

采用水热腐蚀技术在单晶硅衬底上制备出一种新的硅微米／纳米结构复合体系——硅纳米孔柱阵列(Si-NPA)，并对其表面形貌、结构及光学特性进行研究.Si-NPA的结构复合性体现为 在微米和纳米两个尺度上形成了三个分明的结构层次，即微米尺度的硅柱阵列结构、硅柱上 的纳米多孔结构以及组成孔壁的硅纳米晶粒.积分光反射谱和荧光光谱测试表明，Si-NPA具 有良好的光吸收和光致发光特性.依据Si－NPA积分反射谱的实验数据，采用Kramers-Kronig 变换关系计算得到了Si-NPA的复折射率和复介电函数、吸收系数等光学常数，并由此讨论了 Si-NPA相对于单晶硅的光学特性发生显著变化的原因.最后，通过分析Si-NPA的光吸收系数 与入射光子能量之间的关系，揭示出Si-NPA具有直接带隙半导体的电子结构特征，而且理论 计算得到的Si-NPA的带隙能与其光致发光谱的峰位能很好符合. 关键词： 硅纳米孔柱阵列 光学特性 电子结构 水热腐蚀     

An effective surface-enhanced Raman scattering template based on gold nanoparticle/silicon nanowire arrays

A large-scale Si nanowire array （SiNWA） is fabricated with gold （Au） nanoparticles by simple metal-assisted chemical etching and metal reduction processes. The three-dimensional nanostructured Au/SiNWA is evaluated as an active substrate for surface-enhanced Raman scattering （SERS）. The results show that the detection limit for rhodamine 6G is as low as 10-7 M, and the Raman enhancement factor is as large as 105 with a relative standard deviation of less than 25%. After the calibration of the Raman peak intensifies of rhodamine 6G and thiram, organic molecules could be quantitatively detected. These results indicate that Au/SiNWA is a promising SERS-active substrate for the detection of biomolecules present in low concentrations. Our findings are an important advance in SERS substrates to allow fast and quantitative detection of trace organic contaminants.     

Quantitative and sensitive detection of prohibited fish drugs by surface-enhanced Raman scattering

Rapid and simple detections of two kinds of prohibited fish drugs, crystal violet(CV) and malachite green(MG),were accomplished by surface-enhanced Raman scattering(SERS). Based on the optimized Au/cicada wing, the detectable concentration of CV/MG can reach 10~(-7) M, and the linear logarithmic quantitative relationship curves between log I and log C allows for the determination of the unknown concentration of CV/MG solution. The detection of these two analytes in real environment was also achieved, demonstrating the application potential of SERS in the fast screening of the prohibited fish drugs, which is of great benefit for food safety and environmental monitoring.     

多孔泡沫铜和硫脲协同作用构筑无枝晶锂负极

锂金属作为下一代储能电池的理想负极材料一直受到极大的关注,然而锂枝晶的不可控生长和负极副反应带来的低库伦效率问题严重限制了锂金属电池的发展。这里,我们提出了一种多孔泡沫铜和硫脲协同作用的策略,利用硫脲分子的超填充作用实现锂金属在多孔泡沫铜表面的均匀沉积。在电解液中添加0.02 mol·L^-1硫脲作为电解质添加剂,采用多孔泡沫铜的Li||Cu半电池在循环300圈以后,库伦效率仍保持在98%以上。此外,在5C的高倍率条件下,Li||Li FePO4全电池循环300圈以后仍有94%的容量保持率。本工作为锂金属负极保护提供了一种新的策略并且该策略也可以扩展到其他金属负极保护中,非常有利于下一代高能量密度储能电池的开发。     

Preparation, structural and electrical properties of zinc oxide grown on silicon nanoporous pillar array

Polycrystalline thick film of zinc oxide (ZnO) is grown on a unique silicon substrate with a hierarchical structure, silicon nanoporous pillar array (Si-NPA), by using a vapour phase transport method. It is found that as-grown ZnO film is composed of closely packed ZnO crystallites with an average size of $\sim$10\,\mu$m. The film resistivity of ZnO/Si-NPA is measured to be $\sim$8.9\Omega\cdot$\,cm by the standard four probe method. The lengthwise $I$-$V$ curve of ZnO/Si-NPA heterostructure is measured. Theoretical analysis shows that the carrier transport across ZnO/Si-NPA heterojunction is dominated by two mechanisms, i.e. a thermionic process at high voltages and a quantum tunnelling process at low voltages.