CAREER: Two-Dimensional Phase Change Materials

Stanford University, Stanford CA

Investigators

Abstract

NON-TECHNICAL SUMMARY Phase change materials have the property that they can be switched between multiple atomic configurations, yielding different properties like electrical conductivity. They are critical for electronic and energy applications, but it is rare for nature to provide one that can be readily switched near ambient conditions. This project builds on the recent prediction that some two-dimensional materials exhibit phase change properties near ambient conditions. These materials are nearly atomically thin, an aspect that provides potentially useful properties that ordinary phase change materials lack. The two-dimensional nature of these materials provides fundamentally new physical mechanisms for controlling the transformations that do not exist in known, bulk materials. In this project, the PI and his team will explore the phase change properties of two-dimensional materials and their potential for applications in energy, information storage, electronic, optical, and other important applications with broad societal benefit. The project will also elucidate the scientific theory of two-dimensional structural phase transformations, which is likely to be quite different from conventional theories for bulk materials. In the process, the research team will tackle some of the most challenging problems in computational materials science by extending the accuracy and scale of computational methods for predicting the properties of materials. To integrate outreach with this research, the PI will host and mentor a group of college-bound, under-represented minority high school students during the summers and involve them in aspects of this project. The PI will develop interactive Java applications that run real-time atomistic materials simulations aimed at broad research dissemination and materials education at the undergraduate and K-12 levels. These applications represent an exciting new paradigm for materials education that has potential to transform the way in which students learn about materials by putting them in the driver seat. These activities will have a high quality mentoring impact on a few students as well as broad dissemination of the research and teaching tools, potentially reaching thousands or more students. Some of the activities will be facilitated by Stanford's Office of Science Outreach which will assist the research team with post-experience success metrics. TECHNICAL SUMMARY Phase change materials like GeSbTe alloys are critical for electronic and energy applications but it is rare for nature to provide one with phase boundaries close enough to ambient conditions to be useful. Phase change materials can be switched between multiple atomic configurations that have different properties. This project builds on the recent prediction that some of the newly discovered two-dimensional (2D) materials exhibit such phase change properties and may provide new opportunities for energy, electronic, information storage, optical, and other important applications with broad societal benefit. The nearly atomically-thin nature of these materials provides fundamentally new physical mechanisms for controlling the transformations that do not exist in known, bulk materials. Furthermore, this project will elucidate the purely scientific theory of 2D structural phase transformations, which is likely to be quite different from conventional theories for bulk materials. The objectives are to discover how 2D phase change materials can be controlled and reduced to practice in experiments and device applications. This project seeks to understand the role of substrate interactions, electrostatic gating, temperature, and chemical alloys in the control and stabilization of these phases. In the process, the research team will tackle some of the most challenging problems in computational materials science by exploring new statistical techniques for systematically improvable analytical interatomic potentials and advancing density functional theory approaches for monolayers on substrates with van der Waals interactions. To integrate outreach with this research, the PI will host and mentor a group of college-bound, under-represented minority high school students during the summers and involve them in aspects of this project. The PI will develop interactive Java applications that run real-time atomistic materials simulations aimed at broad research dissemination and materials education at the undergraduate and K-12 levels. These applications represent an exciting new paradigm for materials education that has potential to transform the way in which students learn about materials by putting them in the driver seat. These activities will have high quality mentoring impact on a few students as well as broad dissemination of the research and teaching tools, potentially reaching thousands or more students. Some of the activities will be facilitated by Stanford's Office of Science Outreach which will assist the research team with post-experience success metrics.