Theoretical investigation of toxic-metal-free nanocrystals for technological applications

研究背景：纳米技术的核心是在纳米尺度上设计材料的能力(即操纵典型尺寸约为人类头发厚度的1/10万的结构)，用于技术应用。胶体量子点(Qds，又名纳米晶体，NCs)是一种典型尺寸为几纳米的单晶球形半导体纳米结构，其尺寸可调的光学特性使其能够应用于非常不同的领域，如光电子学(在激光和LED中)，以及生物和医学(作为有机分子标志物)，以及光伏，使其吸收能量被定制为最大限度地吸收太阳光子；(Ii)其胶体(即化学)性质使其能够低成本和大规模生产；(3)在合成过程中可实现高度的尺寸单分散性(小于5%)，这提供了可重复性和生长控制。这些特性也使它们与现有的光纤技术兼容，并可用作各种光学和电子设备的自下而上组装的构建块，包括光学放大器、激光器和单电子晶体管。然而，在这类应用中开发的大多数纳米晶体是由镉和铅基材料(即镉和铅基材料，其中X=S，Se，Te)制成的，对人类和环境都是剧毒的。因此，最重要的是找到无毒的替代品，能够代表这些具有良好特性和良好性能的材料的可行替代品。目的和目标：应用美国国家可再生能源实验室固体理论小组发展的原子半经验赝势方法(SEPM)，从理论上筛选不同的(“新颖的”和更传统的)无Cd和Pb型胶体材料和替代拓扑结构，用于纳米级的技术应用，从光伏到纳米电子学。可能的材料包括基于Ga和In的材料(即GaX和InX，其中X=As、Sb和P)，而可能的结构包括棒状和四足(可能更适合于薄膜传输)，以及球形纳米晶体。潜在的应用和好处：对不同材料的四脚体的研究可能产生的许多影响之一可能是增强量子点薄膜中微带的形成和传输，其应用范围从光伏到纳米电子(晶体管)。其他可能涉及利用镓材料的长载流子寿命的新型生物传感器的设计。此外，学生将在使用最先进的理论建模方法方面发展深厚的知识和能力，并通过与国内和国际实验小组的合作以及参加会议，开始建立一个合作者网络。

Context of research: Nanotechnology centers around the ability to engineer materials at the nanoscale (that is, to manipulate structures with typical dimensions of the order of 1/100,000 of the thickness of a human hair), for technological applications. Colloidal quantum dots (QDs, aka nanocrystals, NCs) are chemically synthesised single-crystalline spherical semiconductor nanostructures with typical dimensions of a few nanometers which exhibit several characteristics that make them attractive for this field: (i) their size-tunable optical properties enable their application in very different fields such as optoelectronics (in lasers and LEDs), as well as biology and medicine (as organic molecule markers), and PV, allowing their absorption energies to be tailored to maximise solar photon absorption; (ii) their colloidal (i.e., chemical) nature enables low cost and large scale production; (iii) the very high degree of size monodispersity (less than 5%) achievable in their synthesis provides reproducibility and growth control. These properties make them also compatible with existing fibre-optic technologies and useful as building blocks for bottom-up assembly of various optical and electronic devices, including optical amplifiers, lasers and single-electron transistors. However, most of the nanocrystals exploited in such applications are made of Cd- and Pb-based materials (i.e., of CdX and PbX, where X=S, Se, Te), which are highly toxic for humans and the environment. It is therefore paramount to find non-toxic alternatives that can represent viable substitutes to such well characterised and well performing materials. This is the aim of this project.Aims and objectives:To apply the atomistic semiempirical pseudopotential method (SEPM) developed in the Solid State Theory group at the National Renewable Energy Lab, Golden (CO) U.S.A., to theoretically screen different ("novel" and more conventional) Cd- and Pb-free colloidal materials and alternative topological structures for technological applications at the nanoscale, ranging from PV to nanoelectronics. Possible materials include Ga- and In- based ones (i.e., GaX and InX, where X=As, Sb and P), whereas possible structures include rods and tetrapods (potentially better suited for transport in films), as well as spherical nanocrystals. Potential applications and benefits:One of the many possible implications of the study on tetrapods of different materiasl could be the enhancement of miniband formation and transport in QD films, with applications ranging from PV to nanoelectronics (transistors). Others could involve the design of novel biosensors exploiting the long carrier lifetimes in Ga-based materials.Furthermore, the student will develop a deep knowledge and competence in the use of a state-of-the-art theoretical modelling method and, through collaborations with national and international experimental groups and attendance to conferences, will start building a network of collaborators.