Semiconductor Belts, Sheets, and Wires Having Idealized Optical and Transport Properties

William E. Buhro在化学系大分子、超分子和纳米化学项目的支持下，对一维和二维胶体半导体纳米晶体的合成和光学特性进行了全面的实验研究，这些纳米晶体被优化为远距离电荷和能量（激子）传输。一维和二维纳米晶体具有扩展长度维度的一个令人兴奋的方面，如量子线、量子带、纳米带和纳米片，是它们在接近毫米尺度的长度上传输能量和电荷的潜力。由于输运与纳米电子学、纳米光子学和太阳能转换密切相关，因此在这些应用中使用一维和二维纳米晶体存在巨大的潜在优势。半导体一维和二维纳米晶体领域正处于快速发展的阶段。由于最近在表面钝化方面取得的进展，其中一些是由美国国家科学基金会先前对PI的资助造成的，量子线和纳米线现在具有出色的钝化和光学性能，并且进一步的快速发展迫在眉睫。二维胶体纳米晶体领域尚处于起步阶段，表面钝化性能和光学性能初步良好，发展速度很快。目前正在构建具有高效远程传输能力的一维和二维纳米晶体目录，以及相应的合成和结构策略。这项工作致力于解决目前可用的一维胶体纳米线的一个长期存在的问题，即钝化不良，相应的传输性能也较差。该工作的具体目标是：(1)通过氧化取代和新的胶体原子层沉积（c-ALD）方法，提出优化半导体量子线光学性能和光致发光效率的核壳策略；(2)分离并进一步表征魔术大小的II-VI纳米团簇，以提供实验结构和光谱数据；(3)研究魔术大小的纳米团簇作为低温纳米晶体前驱体。(4)开发控制量子带长度、宽度和厚度的方法；(5)探索II-VI、IV-VI和I-III-VI半导体的量子薄片和薄片的合成和光谱特性。将半导体纳米晶体整合到下一代太阳能转换设备中，引起了相当大的兴趣。由半导体纳米结构构建的太阳能电池有望比传统的硅基器件更经济地制造，并具有其他应用优势。太阳能电池的功能是通过捕获光能并将其转化为高能的正电荷和负电荷，然后将其分离并传输到电池中的相反电极。它为电池充电或操作电器提供电能。因此，关键的步骤是有效地分离正电荷和负电荷，并将这些电荷有效地传输到电极上。一维和二维半导体纳米晶体是用于新的太阳能电池设计的目标，因为它们原则上可以长距离传输能量和电荷。然而，有效的传输要求电荷不被困在纳米晶体的缺陷位置。该项目旨在识别和消除这些陷阱缺陷，使1D和2D半导体纳米晶体在太阳能电池、纳米电子学以及用于光探测和产生的小型设备中的应用成为可能。更广泛的影响包括技术进步，以帮助解决国家的能源挑战。PI在培训妇女和代表性不足群体成员方面也有出色的记录，从而增加了该国技术劳动力的多样性。PI正在华盛顿大学共同领导一项努力，以增加科学、技术、工程和数学（STEM）领域的本科女性留用率。

William E. Buhro is supported by the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry to perform a thorough experimental study of the synthesis and optical properties of 1D and 2D colloidal semiconductor nanocrystals optimized for long-range charge and energy (exciton) transport. An exciting aspect of 1D and 2D nanocrystals having extended length dimensions, such as quantum wires, quantum belts, nanoribbons, and nanosheets, is their potential for transporting energy and charge over lengths approaching the millimeter scale. As transport is intimately involved in nanoelectronics, nanophotonics, and solar-energy conversion, large potential advantages exist for the use of 1D and 2D nanocrystals in such applications. The semiconductor 1D and 2D nanocrystal fields are now poised for rapid development. As a result of recent advances in surface passivation, some resulting from the prior NSF funding to the PI, quantum wires and nanowires are now available with excellent passivation and optical properties, and further rapid advances appear imminent. The 2D colloidal nanocrystal field is in its infancy, surface passivation and optical properties are initially good, and the field is developing at a very fast pace. A catalog is being constructed of 1D and 2D nanocrystals capable of efficient long-range transport as well as corresponding synthetic and structural strategies. This work strives to solve a long-standing problem with the currently available 1D colloidal nanowires, which are poorly passivated and have correspondingly poor transport properties. The specific goals of the proposed work are to (1) advance core-shell strategies for optimizing the optical properties and photoluminescence efficiencies of semiconductor quantum wires, by oxidative substitution, and by the new colloidal atomic-layer-deposition (c-ALD) method, (2) isolate and further characterize magic-size II-VI nanoclusters to provide experimental structural and spectroscopic data, (3) investigate magic-size nanoclusters as low-temperature nanocrystal precursors, (4) develop methods for gaining control over quantum-belt lengths, widths, and thicknesses, and (5) explore the synthesis and spectroscopic properties of quantum platelets and sheets of II-VI, IV-VI, and I-III-VI semiconductors.There is considerable interest in incorporating semiconductor nanocrystals into next-generation devices for solar-energy conversion. Solar cells constructed from semiconductor nanostructures are expected to be fabricated more economically than the traditional silicon-based devices, and to have other application advantages. A solar cell functions by capturing light energy and converting it to energetic positive and negative electric charges, which are then separated and transported to opposite electrodes in the cell. This provides electrical energy for charging a battery or operating an electrical appliance. The critical steps are thus the efficient separation of the positive and negative charges and the efficient transport of those charges to the electrodes. 1D and 2D semiconductor nanocrystals are targeted for use in new solar-cell designs because they can in principle transport energy and charge over long distances. However, efficient transport requires that charges not be trapped at defect sites in the nanocrystals. This project is aiming to identify and eliminate those trap-site defects, enabling the application of 1D and 2D semiconductor nanocrystals in solar cells, nanoelectronics, and in small-scale devices for light detection and generation. The broader impacts include technological advances to assist in addressing the nation's energy challenge. The PI also has an excellent record of training women and members of underrepresented groups, thereby increasing the diversity of the nation's technological work force. The PI is co-leading an effort at Washington University to increase the retention of undergraduate women in science, technology, engineering, and math (STEM) fields.