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

TL;DR

This paper presents a universal ultrahigh vacuum exfoliation method for creating atomically flat, clean interfaces in 2D material heterostructures, enabling advanced studies of interface phenomena and device applications.

Contribution

It introduces a novel ultrahigh vacuum exfoliation technique that produces high-quality 2D heterostructures with pristine interfaces, overcoming previous air-sensitive material limitations.

Findings

Successful exfoliation of 2D materials in ultrahigh vacuum.

Observation of electronic structure of monolayer phosphorene.

Analysis of optical responses of TMDs on metal substrates.

Abstract

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, especially for air-sensitive materials, which hinders the in-depth investigation of interface-induced phenomena 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 exfoliation 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 moir\'{e} superlattices.