Exfoliation of 2D van der Waals crystals in ultrahigh vacuum for interface engineering

Two-dimensional (2D) materials and their heterostructures have been intensively studied in recent years due to their potential applications in electronic, optoelectronic, and spintronic devices. Nonetheless, the realization of 2D heterostructures with atomically flat and clean interfaces remains challenging, espe-cially for air-sensitive materials, which hinders the in-depth investigation of interface-induced phenom-ena and the fabrication of high-quality devices. Here, we circumvented this challenge by exfoliating 2D materials in an ultrahigh vacuum. Remarkably, ultraflat and clean substrate surfaces can assist the exfo-liation of 2D materials, regardless of the substrate and 2D material, thus providing a universal method for the preparation of heterostructures with ideal interfaces. In addition, we studied the properties of two prototypical systems that cannot be achieved previously, including the electronic structure of monolayer phospherene and optical responses of transition metal dichalcogenides on different metal substrates. Our work paves the way to engineer rich interface-induced phenomena, such as proximity effects and moire superlattices. CO 2022 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Automated summary

Two-dimensional materials and their heterostructures have been widely studied for their potential applications in electronic, optoelectronic, and spintronic devices. However, achieving atomically flat and clean interfaces in 2D heterostructures remains challenging. This study overcomes this challenge by exfoliating 2D materials in an ultrahigh vacuum, providing a universal method for preparing heterostructures with ideal interfaces and enabling the investigation of previously unattainable properties of different systems.