Two-dimensional (2D) sheet-like materials composed of one or a few layers of atoms often display properties dramatically different from the same materials in bulk form. This project focuses on a new two-dimensional material, namely silicon telluride, which has unique variable structures where Si atoms form Si-Si pairs to fill the sites between surrounding Te atoms. Each Si pair has four possible orientations, with easily achievable rotations between each other. The flexibility in Si dimer orientations enables unique structural variability and opens opportunities for new phenomena, properties, and functionalities. The research team combines theoretical and experimental studies to develop 2D materials with desirable properties and to achieve a fundamental understanding of the unique phenomenon in silicon telluride, which is expected to make significant impacts on the field of low-dimensional materials and electronic and optoelectronic industry. The research activities are integrated with educational efforts, augmenting the undergraduate and graduate curriculums through hands-on projects, enriched course materials, and summer workshops on nanomaterials to inspire the students' interest in science. Additional project activities including outreach to high school students and teachers through summer research activities and demonstrations at local high schools further extend the impact of this project on the community.
Atomically thin, two-dimensional materials such as graphene, dichalcogenides, and black phosphorus offer unique properties and have attracted significant attention by the scientific community. Silicon telluride is a new 2D material, recently demonstrated with a thickness of a few atomic layers. It has a unique crystal structure in which the Te atoms form a hexagonal close-packed structure, and Si atoms form Si-Si dimers to fill the two-thirds of the interstitial sites between the Te atoms, with each Si dimer taking one of the four possible orientations: three in-plane and one out-plane. The Si dimers can easily rotate their orientations due to the small energy barriers and thus can enable dynamic structural variations, such as flipped Si dimers and domain boundaries between regions of different Si dimer orientations, which are expected to interact with charge carriers and excitons to give rise to new electronic and optical phenomena and properties. In this project, the team combines theoretical investigations based on first-principles calculations and experimental deposition and characterization approaches to develop a fundamental understanding of how structural variations in 2D silicon telluride affect the material properties by exploring various strain and doping optimization strategies.