EAGER: Exploration of a New Class of Semiconductor Nanocrystals with Aliovalent Magnetic Dopants

摘要：该项目支持开发一类多功能纳米晶体的化学和物理，这些纳米晶体可以导致基于先进磁性材料的新技术。更具体地说，该项目旨在阐明含有一定量金属离子（掺杂剂）的地球丰富纳米晶体的材料化学和电子结构。这种独特的目标掺杂离子需要在纳米晶体结构中存在额外的变化。这些材料在纳米尺度上具有独特的电子结构，可以通过改变掺杂离子的类型和通过外力（如光）共改变电子的浓度来控制。为了完成这项工作，本科生和研究生正在接受训练，学习如何制作新材料，并使用复杂的光谱学和电子显微镜测量它们的电子结构。特别值得一提的是，麻省大学阿姆赫斯特分校的能源本科合作研究中心（CURE） REU站点能够从代表性不足的群体中招募和培训本科生参与该项目。技术摘要：水热合成胶态铬（III）掺杂钛酸锶纳米立方体，应用于多种已知的过渡金属掺杂离子替代体中钛（IV）的位置。研究这些多功能材料作为纳米晶体可以影响许多不同的应用研究领域，从可见光光催化到固态存储器，也可以作为多铁组件的潜在构建块。由于钛酸锶带隙内的潜在氧化还原水平，与传统的等价掺杂剂相比，这些稀释磁性半导体的电子结构是独一无二的。作为胶体纳米晶体，这些材料通过改变表面的缺陷化学来释放改变电子结构的新潜力，并为通过溶液处理技术制造器件提供了一条途径。本工作的目标是：(1)优化合成，以产生和确定一系列共价稀释磁性半导体纳米晶体的电子结构；(2)确定纳米晶体中的费米能级对电子结构和掺杂-缺陷相关性的影响。在这项工作中，材料的独特电子结构也允许在纳米晶体和散装粉末之间比较电荷补偿缺陷的性质。

Non-technical Abstract:This project supports an effort to develop the chemistry and physics of a class of multifunctional nanocrystals that can lead to new technologies based on advanced magnetic materials. More specifically, the project aims to elucidate the materials chemistry and electronic structures of earth-abundant nanocrystals containing specific amount of metal ions (dopants). This unique class of targeted dopant ions requires the presence of additional changes in the structure of nanocrystals. These materials have unique electronic structures at the nanoscale that can be controlled by varying the type of dopant ions and cochanging the concentration of electrons by external forces such as light. To accomplish this work, undergraduate and graduate students are being trained in both making the novel materials and measuring their electronic structures using sophisticated spectroscopy and electron microscopy. In particular, the recruitment and training of undergraduates from underrepresented groups to work on this project is enabled by the Collaborative Undergraduate Research in Energy (CURE) REU site at the University of Massachusetts Amherst. Technical Abstract:The hydrothermal synthesis of colloidal chromium(III)-doped strontium titanate nanocubes is applied to a variety of transition metal dopant ions known to substitute at the titanium(IV) site in the bulk. Examining these multifunctional materials as nanocrystals can impact a number of diverse applied research fields from visible-light photocatalysis to solid-state memories, and also serve as potential building blocks for multiferroic assemblies. The electronic structures of these diluted magnetic semiconductors are unique with aliovalent dopants compared to traditional, isovalent dopants, due to the potential redox levels that are within the band gap of the strontium titanate. As colloidal nanocrystals, these materials unlock new potential for altering the electronic structure through altering the defect chemistry at the surface, and providing a path for device fabrication by solution processing techniques. The objectives of this work are to (1) optimize the synthesis to yield and determine the electronic structures of a series of aliovalent diluted magnetic semiconductor nanocrystals, and (2) determine the effect of the Fermi level in the nanocrystals on the electronic structures and dopant-defect correlations. The unique electronic structures of the materials in this work also allows the nature of the charge-compensating defects to be compared between nanocrystals and bulk powders.