Atomically thin 2D materials incorporated into van der Waals heterostructures are a promising platform to deterministically engineer quantum materials with atomically resolved thickness and abrupt interfaces across macroscopic length scales while retaining excellent material properties. Because 2D materials exhibit a wide range of electronic characteristics with properties that often rival conventional electronic materials — e.g., metals, semiconductors, insulators, and superconductors — it is possible to combine them in virtually infinite variety to achieve diverse heterostructures. Many of these heterostructures would be otherwise infeasible through direct growth.
The Mannix Group is developing a unique set of in-house capabilities to systematically elucidate the fundamental structure-property relationships underpinning the growth of 2D materials and their inclusion into van der Waals heterostructures. These specific techniques are discussed below:
Materials growth is the foundation for all subsequent science and engineering. Much of the progress in 2D materials has been enabled by micromechanical exfoliation, a facile but stochastic method of sample preparation. The Mannix lab will be equipped with extensive sample growth facilities to enable deterministic study of the key parameters for high-quality, reproducible growth. We intend to employ two primary techniques for the synthesis of atomically thin films:
Molecular Beam Epitaxy (MBE)
MBE involves physical vapor deposition onto atomically-clean surfaces under ultra-high vacuum (UHV, pressures < 10-9 mbar) from solid or gas sources with precisely calibrated fluxes. MBE is amenable to in-situ monitoring during growth (e.g., RHEED, QMS, QCM, BFM) and samples can be characterized without leaving vacuum (e.g., STM). The Mannix lab will be equipped with state-of-the-art MBE facilities for exploring the growth of 2D chalcogenide and pnictide materials.
Chemical Vapor Deposition (CVD)
CVD involves the deposition of vapor-phase precursors (supplied by solid, liquid, or gas sources) on a growth substrate at elevated temperatures. Metal-organic chemical vapor deposition (MOCVD) is a subset of CVD which provides access to a diverse array of precursors to grow a variety of materials. The Mannix lab is starting out with two MOCVD and one UHV-CVD systems to grow a wide range of 2D materials (e.g., mono- and dichalcogenide semiconductors).
Assembly of van der Waals Heterostructures (vdWHS)
Atomically-resolved solids constructed sequentially from layered 2D materials have generated a flood of discoveries in condensed matter physics. Such devices show great promise for future applications, but the large-scale fabrication of these devices remains a critical challenge. The Mannix group will develop techniques to enable the scalable production of vdWHS.
The growth of electronic-grade materials requires precise characterization to enable iterative optimization. Defects dominate the properties of electronic materials, but it has been challenging to elucidate the role that specific defects play in many 2D materials. This is especially important for functional defects, such as the quantum emitters observed in hBN and transition metal dichalcogenides (e.g., WS2). The Mannix group will utilize a cryogenic, UHV scanning tunneling microscope (STM) to characterize these defects, and correlate their presence with the operation of devices. The STM will be equipped with a quartz tuning fork AFM to provide complementary topographical characterization. Non-equilibrium phenomena may be probed with STM/AFM on operational devices. Complementary information will be obtained from (scanning) transmission electron microscopy (S/TEM) in the SNSF user facilities.
The intersection between these techniques will enable us to deterministically study and engineer the properties of 2D materials and their heterostructures, thus providing a platform for engineering the properties of matter at the atomic scale. The resulting capabilities will be of great relevance to emerging platforms for quantum information science based on defects or topological matter.