CAREER: Structurally and Chemically Ordered States in Low Dimensional Crystals

Nontechnical description: This project aims to explore synthesis strategies by which ordered atomic chains can be created in sub-nanometer thin layers of materials containing atoms of more than two different chemical elements, often called alloys. By controlling the exact positions of the atoms in an alloy, the properties of the material can be tuned in different directions. The work utilizes advanced electron microscopy imaging and spectroscopy techniques to understand the mechanisms of chemical and structural ordering of these materials. The research has a potential to design materials with controllable thermal, electronic, optoelectronic, and magnetic properties in wide ranges and to provide the key to properly design devices for heat dissipation applications, energy storage, electronics, optoelectronics, and thermoelectrics. This project also promotes the scientific fundamentals of emerging technologies through various educational modules. In addition, the principal investigator engages with specific target audiences by providing research experience to high school, undergraduate, and graduate students, in particular focusing on women and other minority groups within under-served communities. Technical description: Alloying and doping are considered versatile strategies for tuning charge and heat transport in nanostructures. Whether the resulting alloy structure is random or ordered can have a profound impact on the macroscale electronic, optoelectronic, vibrational, and transport properties of the material. Structural and chemical ordering in superlattices and heterostructures have already been demonstrated and led to phonon anomalies and significant anisotropy in thermal and electrical transport. In the family of two-dimensional (2D) crystals, however, the structural degree of freedom, i.e. the spatial correlation between dissimilar elements on a given crystallographic site in the lattice remains largely unknown. This research explores chemical ordering as a mechanism to design anisotropy in 2D crystal alloys and beyond. Through a kinetically-driven synthesis mechanism, chemically and structurally ordered states are introduced in atomically thin 2D crystal alloys. Leveraging recent advancements in atomic resolution imaging and spectroscopy, this research elucidates how chemically and structurally ordered states and vacancy-dopant complexes at the atomic level can tune the macroscale charge and phonon transport anisotropy in 2D materials. Furthermore, the research has a potential to determine how the resulting chemical and structural degrees of freedom can tailor the macroscale optoelectronic, electronic, and thermal transport anisotropy in 2D crystal alloys. This understanding helps design structural anisotropy towards improved electronics, optoelectronics and thermoelectric response in low dimensional crystals.