半导体纳米结构的边缘效应及其光电性质调控的键弛豫理论研究

As compared to the nanostructures with perfect sphere, rodlike shape and their bulk counterparts, the nanostructures with different geometries, including nanocubes, nanoprisms and nanopencils, have attracted intensive attention in recent years due to their novel physical and chemical properties and potential applications in the fields such as material surface modification, micro- and nano-optoelectronic devices, etc. The end effects occurrence in these kind of semiconductor nanostructures play the crucial role for their structures and performances owing to a large fraction of under-coordinated atoms located at the end parts of nanostructures, including edges, vertexes, and side facets. In order to achieve effectively tunable the optoelectronic properties (e.g., band structure, optical absorption and photo-electric conversion efficiency, etc.) of semiconductor nanostructures, we will investigate systematically these geometrical factors, pursue the underlying mechanism and predict the suitable manipulation methods, which have great significance in the fields of energy and material science. Our goal is to investigate the end effects of semiconductor nanostructures by using ab initio calculation and atomic-bond-relaxation theory based on the nanothermodynamics and continuum mechanics. The modulation of optoelectronic properties of the kind of semiconductor nanostructures should be effectively achieved through understanding the principle of end effects. Furthermore, the results can be as guidance for the morphology and heterointerface designs of nanostructures, which also provide a new consideration and theoretical foundation for the photo-electric material in the aspect of high-efficient of energy utilization.

由于不同于理想的球形、棒形结构以及相应体材料的理化性质，不同形貌的纳米结构，包括纳米方块、棱柱和铅笔状纳米线等在材料表面改性和微纳光电子器件等领域展现出了一些重要的应用，近年来引起了科学家们强烈地关注。此种类型的半导体纳米结构具有的边缘效应，即在棱边、顶角和边界晶面的异常原子能态将极大影响体系的结构及性质。对这些因素展开系统研究，理解其理论机制，预测适合的调控手段，以实现对半导体纳米体系能带结构、光吸收和光电转换效率等性质的有效预测，对于半导体纳米结构在能源和材料等领域的应用具有重要的意义。本项目拟从基于纳米热力学和连续介质力学的原子键弛豫理论和第一性原理计算的角度，深入研究半导体纳米结构的边缘效应。通过理解边缘效应对纳米结构光电性质调控的物理机制，以此指导尺度、形貌和异质界面层的合理设计，实现对半导体纳米结构光电性能的有效调控，为光电转换材料在能源高效利用方面提供新思路和理论支撑。

为了深入理解半导体纳米结构体系的边缘效应，探索其宏观可测性能与微观键参数的联系，本项目主要围绕三个要点展开：（1）边界弛豫，（2）应力和电场调控和（3）电子结构和性质。我们基于纳米热力学和连续介质力学，结合基于密度泛函理论的第一性原理计算结果，发展了新的“几何-性能”的理论工具来计算边界问题，建立了部分宏观可测性能（如能级漂移、光电转换效率等）和微观键参数之间的理论关系，阐述了系列纳米结构体系边缘效应及其光电性质的调制机理。理论预测结果得到了部分实验验证，为新型功能器件的设计和能源的高效利用提供有效的理论依据。