Controlling the Conductivity of Nanocrystal Solids through their Surface Chemistry

在这个由化学系的大分子、超分子和纳米化学项目资助的项目中，肖恩·T。得克萨斯大学奥斯汀分校的罗伯茨和他的研究生研究被称为半导体纳米晶体的非常小的无机粒子。 纳米晶体是包含数千个原子的微小颗粒。虽然它们比只包含几个原子的化学分子大得多，但它们仍然比包含数万亿个原子的固体材料小得多。纳米尺度材料是独特的，因为它们的尺寸介于分子和固体之间，但有时具有不容易通过平均两个极端尺寸来预测的特性。这些纳米晶体的光学性质可以通过改变它们的尺寸和形状来调节，这使得它们可用于显示器，光伏电池和光电探测器等应用。然而，将这些材料加工成电子产品所需的导电薄膜仍然很困难。研究人员通过将纳米晶体与表面结合的分子相结合来解决这一挑战，这些分子旨在提高纳米薄膜的导电性。使用光谱技术和光电导测量所得到的结构进行了研究。该项目还包括一项名为“得克萨斯州绿色能源”的外联工作，旨在通过向社区学院学生介绍绿色能源研究，吸引他们学习物理科学。该项目的具体目标是了解促进半导体纳米晶体与其表面配体之间电子耦合的关键因素，并使用这种类型的相互作用来改善半导体光电薄膜中的电荷传输。配体的性质可以影响半导体纳米晶体的带隙和光学性质。这表明纳米晶体和配体之间存在一定程度的电子耦合，涉及电荷转移。这个项目定量评估了配体促进薄膜中纳米晶体之间电荷转移的程度。为了实现这一目标，时间分辨的拉曼光谱被用来映射电荷密度的变化后，光激发的配体壳内。二维电子光谱和photo-CELIV（电荷提取线性增加电压）测量确定如何激子离域配体（EDLs）修改电荷载流子输运的薄膜。

In this project funded by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professor Sean T. Roberts of the University of Texas at Austin and his graduate students study very small inorganic particles called semiconductor nanocrystals. Nanocrystals are tiny particles that contain thousands of atoms. While they are much larger than chemical molecules, which contain only a few atoms, they are still much smaller than solid materials that are large enough to see with the naked eye, containing trillions of atoms. Nanoscale materials are unique because they have sizes intermediate between molecules and solids, but sometimes have properties not easily predicted by averaging the two size extremes. The optical properties of these nanocrystals can be tuned by altering their size and shape, which makes them useful for applications such as displays, photovoltaic cells, and photodetectors. However, processing these materials into conductive thin films needed for electronics remains difficult. The researchers approach this challenge by combining the nanocrystals with surface-bound molecules designed to improve the electrical conductivity of nanocrystal thin films. The resulting structures are studied using spectroscopic techniques and photoconductivity measurements. This project also includes an outreach effort entitled GReen Energy At Texas (GREAT) designed to attract Community College students to the physical sciences by introducing them to green energy research. The specific goals of this project are to understand the key factors that facilitate electronic coupling between semiconductor nanocrystals and their surface ligands and to use interactions of this type to improve charge transport in nanocrystal optoelectronic films. The nature of the ligand can impact the bandgap and optical properties of semiconductor nanocrystals. This suggests some degree of electronic coupling between the nanocrystals and the ligands that involves charge transfer. This project quantitatively assesses the degree to which ligands facilitate charge transfer between nanocrystals in thin film. To accomplish this goal, time-resolved Raman spectroscopy is used to map charge density changes within nanocrystal ligand shells following photoexcitation. Two-dimensional electronic spectroscopy and photo-CELIV (charge extraction by linearly increasing voltage) measurements determine how exciton-delocalizing ligands (EDLs) modify charge carrier transport in nanocrystal thin films.