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

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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.