Non-Technical: The ability to design new materials in which the flow of electricity and heat can be tailored in a controllable way is fundamentally important for addressing the challenges of modern science and technology. It is essential to numerous fields including microelectronics, optoelectronics and thermoelectrics. Two-dimensional (2D) layered materials open new opportunities for addressing this important need. While the vast amount of research on 2D layered structures has been focused on the 2D carbon crystal, graphene, the goal of the current project will be to fabricate and to understand the properties of 2D layered structures based on Germanium (Ge) and tin (Sn). These Ge/Sn graphane analogue structures offer the possibility to manipulate the electronic, optical and heat transport properties by adjusting the number of layers, chemical composition of constituent layers and tunable chemical bonding between layers, as well as showing great promise for a wide range of electronic and thermoelectric applications. State-of-the-art materials synthesis, measurements and theoretical modeling methodologies will be established for understanding how to tune electronic and thermal transport in 2D materials beyond graphene. Furthermore, we will develop a novel, scalable route towards integrating 2D materials directly into existing semiconductor growth and fabrication technology. Complementing the project's major research goals are its broader aims, which include efforts to enhance thermal science education in the participating institutions, and to increase awareness in local communities of the importance and excitement of cutting edge research in thermal sciences, which has often been perceived as a mature field because of insufficient interactions between the research community and the public. Finally, this multi-institutional collaboration will allow the research team to carry out a joint effort to recruit and retain students from underrepresented groups across multiple scientific and engineering disciplines.
The overall research objective of this project is to develop the fundamental knowledge needed for enhancing the coupled electronic and thermal properties of Ge/Sn graphane analogues, a promising system that offers the ability to vary the anisotropic electronic and thermal properties along both the in-plane and cross-plane directions by using different main group elements and different surface-terminating ligands. To accomplish this, a novel, scalable synthesis method will be developed for the direct integration of Ge/Sn van der Waals heterostructures into existing semiconductor fabrication processes, by combining the epitaxial growth of precursor thin films on Ge(111) wafers with their topotactic conversion into the van der Waals material. These "epitopotaxial" structures will facilitate a comprehensive suite of cutting edge measurements of in-plane and cross-plane electronic, thermal, and thermoelectric properties of single sheets, multilayer heterostructures, bulk 2D crystals, and different substrate-2D interfaces. These measurements will in turn be supported by first-principle theoretical calculations to verify, predict and establish the underlying principles for controlling anisotropic thermal and electronic properties of these 2D van der Waals heterostructured materials. Elucidating the key mechanisms for controlling anisotropic thermal, electronic, and thermoelectric properties in single and multilayered 2D van der Waals systems will facilitate the development of next-generation electronic and thermoelectric devices.
