NSF/DMR-BSF: Artificial Semiconductor Nanocrystal Molecules for Charge Carrier Separation

非技术总结该奖项支持理论和计算研究，旨在利用新的计算方法对一种新开发的半导体纳米晶体的电子和光学性质有一个基本的了解。半导体纳米晶体是纳米尺寸(约十亿分之一米)的颗粒，每个颗粒包含数百到数千个原子，它们以规则的框架排列，就像硅这样的固体半导体一样。这些纳米晶体通常被称为人造原子。值得注意的是，它们的化学和物理性质，如它们发出的颜色，只需改变它们的大小就可以灵活地调节，这与真正的原子不同。这导致它们被广泛用作各种设备中的积木，例如用于丰富颜色和增强最先进显示屏的节能特性。在这个项目中，研究团队将利用半导体纳米晶体的人造原子特性来极大地扩展其功能。精心定制的半导体纳米晶作为人造原子，将与其他原子结合起来，创造出一个新的人造分子家族。该项目的特别重点是研究在这种人造分子中，由于光吸收而产生的正电荷和负电荷是如何相互分离的。在空间上分离半导体中的正负电荷对于收集太阳能(例如在太阳能电池中)并以清洁和可持续的方式将其转化为其他有用的形式是至关重要的。PI和他的研究团队将与一个实验小组合作，将他们的理论和计算研究集中在理解电荷分离作为人造分子原子结构、组成和物理尺寸的函数的机制上，并帮助设计由具有理想功能的半导体纳米晶体制成的新人造分子。这个项目将产生计算工具和基础理解，其用途超出了所研究的特定材料。这项研究将作为理解纳米结构中电荷转移的基本机制和设计涉及光致电荷分离的新型光催化和光伏器件的基础。该项目将涉及材料、化学和工程跨学科接口的本科生和研究生的培训。国际和平研究所还将在Telluride科学研究中心举办一次暑期班，重点是现代电子结构技术。国内和国际专家在这所学校的演讲将被转换为在线开放获取的视频，以进一步传播教育材料。技术总结该奖项支持理论和计算研究，目的是利用最先进的随机电子结构技术，对新开发的胶体量子点异质二聚体的电子和光学性质有一个基本的了解。研究小组将专注于以下问题：(I)纳米尺度的电荷转移机制，(Ii)如何通过改变材料的尺寸和组成来控制电荷分离效率，以及(Iii)如何在解释所有必要物理过程的最小模型下对这种复杂的量子动力学模型进行建模。计算方法的验证将基于准粒子激发以及中性单粒子和多粒子激发。经过验证的模型将被用来探索长度尺度和时间尺度对电荷转移机制的相互作用。该项目还将专注于改变施主/受主胶体量子点的大小和连接它们的脖子的作用，并探索俄歇与马库斯类电荷转移机制的相互作用。这个项目将产生计算工具和基本理解，其用途超出了所研究的特定材料。这项研究将作为理解纳米结构中电荷转移的基本机制和设计涉及光致电荷分离的新型光催化和光伏器件的基础。该项目将涉及材料、化学和工程跨学科接口的本科生和研究生的培训。国际和平研究所还将在Telluride科学研究中心举办一次暑期班，重点是随机电子结构技术。国内和国际专家在这所学校的演讲将被转换为在线开放获取的视频，以进一步传播教育材料。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research with an aim to develop a fundamental understanding of the electronic and optical properties in a newly developed family of semiconductor nanocrystals using novel computational methods. Semiconductor nanocrystals are nano-sized (of the order of one billionth of a meter) particles, each containing hundreds to thousands of atoms arranged in a regular framework as in a solid semiconductor such as silicon. These nanocrystals are often referred to as artificial atoms. Remarkably, their chemical and physical properties, such as the color they emit, are flexibly tunable merely by changing their size, unlike real atoms. This has led to their widespread use as building blocks in diverse devices, e.g. to enrich color and enhance energy saving characteristics of the most advanced display screens. In this project, the research team will greatly extend the functionality of semiconductor nanocrystals by taking advantage of their artificial atom character. Carefully tailored semiconductor nanocrystals, serving as artificial atoms, will be combined with others to create a new family of artificial molecules. The particular focus of the project is the investigation of how positive and negative charges, which are created upon light absorption, separate from each other in such artificial molecules. Spatially separating the positive and negative charges in a semiconductor is central for harvesting solar energy (e.g. in solar cells) and transforming it into other, useful forms of energy in a clean and sustainable manner. Working in collaboration with an experimental group, the PI and his research team will focus their theoretical and computational research on understanding the mechanisms of charge separation as a function of the artificial molecules' atomic structure, composition and physical dimensions, and help design new artificial molecules made of semiconductor nanocrystals with desirable functionalities.This project will generate computational tools and fundamental understanding whose utility extends beyond the specific materials investigated. The research will serve as a basis for understanding the basic mechanisms of charge transfer in nanostructures and for designing new photocatalytic and photovoltaic devices that involve light induced charge separation. The project will involve the training of undergraduate and graduate students at the interdisciplinary interface of materials chemistry and engineering. The PI will also organize a summer school at the Telluride Science Research Center focused on modern electronic structure techniques. The lectures given by national and international experts in this school will be converted into online open-access videos for further dissemination of the educational material.TECHNICAL SUMMARYThis award supports theoretical and computational research with an aim to develop a fundamental understanding of the electronic and optical properties in a newly developed family of colloidal quantum dot heterodimers using state-of-the-art stochastic electronic structure techniques. The research team will focus on questions regarding (i) the mechanism of charge transfer at the nanometer scale, (ii) how to control the charge separation efficiencies by changing the dimensions and composition of materials, and (iii) how to model such complex quantum-dynamical models at the minimal model that accounts for all necessary physical processes. Validation of the computational approach will be based on quasiparticle excitations as well as neutral single- and multi-particle excitations. The validated models will then be used to explore the interplay of length scales and timescales on charge transfer mechanisms. The project will also focus on the role of changing the size of the donor/acceptor colloidal quantum dots and the neck connecting them and explore the interplay of Auger- vs. Marcus-like charge transfer mechanisms.This project will generate computational tools and fundamental understanding whose utility extends beyond the specific materials investigated. The research will serve as a basis for understanding the basic mechanisms of charge transfer in nanostructures and for designing new photocatalytic and photovoltaic devices that involve light induced charge separation. The project will involve the training of undergraduate and graduate students at the interdisciplinary interface of materials chemistry and engineering. The PI will also organize a summer school at the Telluride Science Research Center focused on stochastic electronic structure techniques. The lectures given by national and international experts in this school will be converted into online open-access videos for further dissemination of the educational material.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.