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（也就是说，操纵典型尺寸为人类头发厚度的十万分之一的结构），用于技术应用。胶体量子点（QDs，又名纳米晶体，nc）是化学合成的单晶球形半导体纳米结构，其典型尺寸为几纳米，具有以下几个特征，使其在该领域具有吸引力：(i)它们的尺寸可调光学特性使它们能够应用于非常不同的领域，如光电子学（激光和led），以及生物学和医学（有机分子标记），以及光伏，允许它们的吸收能量被定制，以最大限度地吸收太阳光子；（ii）它们的胶体（即化学）性质使得低成本和大规模生产成为可能；（iii）在合成过程中可达到的高度尺寸单分散性（小于5%）提供了再现性和生长控制。这些特性使它们与现有的光纤技术兼容，并可作为自下而上组装各种光学和电子设备的基石，包括光放大器、激光器和单电子晶体管。然而，在此类应用中开发的大多数纳米晶体都是由基于Cd和pb的材料制成的（即CdX和PbX，其中X=S, Se, Te），它们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，可以代表这些具有良好特征和良好性能的材料的可行替代品。这就是这个项目的目的。目的和目标：应用美国Golden （CO）国家可再生能源实验室固态理论小组开发的原子半经验伪势方法（SEPM），从理论上筛选不同的（“新颖”和更传统的）无Cd和pb的胶体材料和替代拓扑结构，用于从光伏到纳米电子学的纳米级技术应用。可能的材料包括镓基和铟基材料（即GaX和InX，其中X=As， Sb和P），而可能的结构包括棒状和四足体（可能更适合在薄膜中传输），以及球形纳米晶体。潜在的应用和好处：不同材料的四足体研究的许多可能的影响之一可能是增强量子点薄膜中的微带形成和传输，其应用范围从PV到纳米电子学（晶体管）。其他可能涉及设计新型生物传感器，利用镓基材料的长载流子寿命。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和参加会议，将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.