Direct absorption spectroscopy of individual nanostructures

圣母大学的Masaru K. Kuno得到了化学系大分子、超分子和纳米化学项目的支持，致力于解决纳米科学界对单个纳米结构进行直接吸收光谱的现有需求。虽然现在存在测量单个分子和纳米颗粒的发射强度和光谱的可靠技术，但存在非荧光或具有低发射量子产率的整个材料类别。因此，这些物种对于当前的单分子成像技术来说是不可见的。除了开发单纳米结构吸收方法外，这项工作的主要目标之一将是测量单CdSe纳米线和纳米棒从1D到0D（量子点）系统转变时的长度依赖吸收光谱。这将使我们第一次能够在这个（或任何其他）低维系统中完整地描绘出约束、介电对比和介电约束之间的竞争。我们将进一步研究单个纳米结构的缺陷吸收，如CdS纳米线，其中在系综消光光谱中存在明显的厄巴赫尾。鉴于低维材料的表面体积比的增强以及缺陷在影响其光学和电学性能方面所起的重要作用，这些缺陷研究触及了现代纳米科学中一个重要但尚未得到充分研究的领域。二十年来，人们一直致力于探测单个分子和纳米结构。这些研究的动机是寻找方法来探索这些物种的个性。在这方面，就像我们都喜欢冰淇淋一样，上面的研究本质上是为了找出为什么你最喜欢香草而我最喜欢巧克力。不幸的是，几乎所有现有的单分子检测技术都依赖于监测被探测物种的发射。问题是并不是所有的分子（或纳米结构）都是发光的。因此，我们必须找到新的方法来研究它们。要做到这一点，最普遍但也最具挑战性的方法之一就是观察他们的吸收情况。这是我们提出的研究主题，通过成功实现这一目标，我们相信我们将学习到关于半导体纳米结构基本行为的重要新物理学，为现代纳米科学奠定基础。拟议的工作也与PI在本科教育方面的教育计划联系在一起，该计划的重点是通过开发新的实验室模块来提高学生对纳米科学和显微镜的兴趣。最后，这项研究有助于培养对美国国家安全至关重要的未来科学和技术重要领域的国内研究生。

Masaru K. Kuno at the University of Notre Dame is supported by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry in work addressing an existing need in the nanoscience community to conduct the direct absorption spectroscopy of individual nanostructures. While robust techniques now exist for measuring the emission intensity and spectrum of individual molecules and nanoparticles, entire classes of materials exist that are non-fluorescent or which possess low emission quantum yields. These species are therefore invisible to current single molecule imaging techniques. Apart from developing single nanostructure absorption methodologies, one of the primary goals of the work will be to measure the length-dependent absorption spectrum of single CdSe nanowires and nanorods as the system transitions from a 1D to a 0D (quantum dot) system. This will allow us to fully map out the competition between confinement, dielectric contrast and dielectric confinement in this (or any other) low dimensional system for the first time. We will furthermore investigate the defect absorption of individual nanostructures such as CdS nanowires where an apparent Urbach tail exists in the ensemble extinction spectrum. These defect studies touch on an important, yet underserved, area of modern nanoscience, given the enhanced surface-to-volume ratios of low dimensional materials and the important role played by defects in influencing their optical and electrical properties.There have been two decades of research devoted to detecting individual molecules and nanostructures. The motivation for such studies has been to find ways to probe the individuality of these species. In this regard, just like we all like ice cream, the above research essentially aims to find out why you like vanilla best whereas I like chocolate. Unfortunately, nearly all existing single molecule detection techniques rely on monitoring the emission of the probed species. The problem then is that not all molecules (or nanostructures) are emissive. Hence we must find new ways to study them. One of the most universal, yet challenging, approaches to do this involves looking at their absorption. This is the topic of the proposed research and, by successfully achieving this goal, we believe that we will learn important new physics about the fundamental behavior of semiconductor nanostructures underpinning modern nanoscience. The proposed work also ties into the PI's educational initiatives in undergraduate education, which focus on increasing student interest in nanoscience and microscopy through the development of new laboratory modules. Finally, the study aids the training of domestic graduate students in an important area of future science and technology vital to US national security.