Collaborative Research: Remote epitaxy on van der Waals materials: unveiling adatom interaction, growing single-crystal membranes, and producing unconventional heterostructures

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

PART 1: NON-TECHNICAL DESCRIPTION Science and technology have developed alongside with discovery of new materials platform, such as carbon nanotubes, or synthetic polymers. Instead of chasing after a completely new materials, the research team targets a novel twist, making currently existing materials to become flatter, thinner, and lighter. Back in 2017, the principal investigator invented remote epitaxy, which allows growing nanoscale materials on graphene-coated templates to be exfoliated afterwards. These thin freestanding materials can become building blocks for lightweight, flexible devices having unprecedented performance. Until now, studies on remote epitaxy have been mostly limited to empirical observations on materials such as gallium nitride and gallium arsenide typically used in semiconductors. To utilize remote epitaxy as an ideal platform for growth and hetero-integration between various materials systems, the research team aims to study the mechanism of remote epitaxy at a fundamental level. By exploring the mechanism on various two-dimensional (2D) and three-dimensional (3D) materials, the research team expects to create a wider range of materials systems available for remote epitaxy. Also, being able to combine different materials systems together can benefit the physical sciences by discovering new functionalities, bringing advancements in engineering sciences and industry by improving current device fabrication techniques and their performances. PART 2: TECHNICAL DESCRIPTION The research team plans to focus on answering three major questions to understand remote epitaxy further: (1) the nature of the adatoms interaction with the underlying 2D/3D substrates, (2) the impacts of 2D materials and interfaces on remote epitaxy, and (3) the dynamic processes involved in adatom/nuclei migration and defect formation on 2D surfaces. To answer these questions, the research team will first reveal whether the remote epitaxy truly occurs in a ‘remote’ sense, which is the most fundamental conundrum that precedes any other questions. This has been difficult to answer because one can easily observe only the results of epitaxy, not the nucleation of adatoms. This issue is tackled by intentionally patterning the 2D layer and employing various materials with different growth properties as the epilayers. Second, impact of 2D layers is explored by studying how the type, crystallinity, and thickness of 2D interlayers alter the remote interaction of adatoms and substrates. In order to show the intrinsic role of 2D layers, direct growth of 2D layers is attempted on various substrates having different ionicity. Third, thermodynamics and kinetics of adatoms, their mergence to form nuclei, and nucleus-nucleus interaction on 2D layers are studied by understanding the nucleation mechanism, performing defect analysis, and exfoliating epilayers. Based on these results, the research team plans to demonstrate high-quality ultrathin films grown by remote epitaxy on directly-grown 2D layers with engineered nucleation conditions. As remote epitaxy allows mixed dimensional heterostructures, further study is done on 3D/various 2D/3D sandwiched structures to investigate new physical couplings between electronic states and magnetic properties. To the scientific community, these results are expected to utilize remote epitaxy for studying multifunctional and coupled material platforms that were not achievable by conventional methods. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.