Resonance Raman polarization and high-energy excitonic states in semiconductor nanocrystals

在化学系大分子、超分子和纳米化学（MSN）项目的支持下，加州大学默塞德分校的Anne Kelley教授和David Kelley教授正在探索半导体纳米晶体（nc）的大小、形状和组成如何影响它们与光的相互作用。当半导体粒子的大小只有几纳米，或者比这句话末尾的句号小一百万倍时，它会以独特的方式与光相互作用，这取决于纳米粒子的大小和形状。通常，nc被认为是具有光滑表面的完美球体或圆柱体，但实际上并非如此。Kelley和Kelley教授及其研究小组将合成具有各种形状和成分的nc，以探索形状和表面缺陷如何影响光吸收产生的激发态。他们的发现可能会导致光学发光二极管（oled）、人工照明和生物医学成像等显示器材料的改进。该项目将有助于研究生和博士后的教育和培训，并为不同背景的本科生提供研究机会。本研究将利用共振拉曼（RR）散射和光致发光的偏振来检测II-VI型半导体nc中激子的对称性，特别是其他技术难以获得的高能量激子。重点将放在纯CdSe和核/壳NCs上，它们生产高质量材料的合成路线已经很发达，并且形状各向异性的程度可以系统地改变。光谱学和光谱模拟将在不同形状的nc（量子点、立方体、纳米片、纳米棒和点状棒）上进行，并作为尺寸、表面配体和核/壳界面退火的函数。该项目将利用RR散射的极化特性来探测不同激子能量和内部与表面或界面区域激子态的局部环境。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professors Anne Kelley and David Kelley of the University of California, Merced are exploring how the size, shape, and composition of semiconductor nanocrystals (NCs) influence their interactions with light. When the size of a semiconductor particle is just a few nanometers, or about a million times smaller than the period at the end of this sentence, it interacts with light in unique ways that depend on the nanoparticle's size and shape. Usually, NCs are assumed to be perfect spheres or cylinders with smooth surfaces, but in actuality this is not the case. Professors Kelley and Kelley and their research group will synthesize NCs with a variety of shapes and compositions to explore how shape and surface imperfections affect the excited states created by light absorption. Their discoveries could lead to improved materials for displays such as optical light-emitting diodes (OLEDs), artificial lighting, and biomedical imaging. This project will contribute to the education and training for graduate students and postdoctoral scholars and provide research opportunities for undergraduate students from diverse backgrounds.The proposed research will use the polarization of resonance Raman (RR) scattering and photoluminescence to examine the symmetries of the excitons in II-VI semiconductor NCs, particularly the higher-energy excitons that are difficult to access by other techniques. The focus will be on pure CdSe and core/shell NCs for which synthetic routes to producing high-quality materials are well developed and where the extent of shape anisotropy can be varied systematically. Spectroscopy and spectroscopic simulations will be performed on NCs of different shapes (quantum dots, cubes, nanoplatelets, nanorods, and dot-in-rods) and as a function of size, surface ligands, and annealing of core/shell interfaces. The project will exploit the polarization properties of RR scattering to probe the local environment of the excitonic states at different excitonic energies and at interior versus surface or interface regions.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.