The stacking of different two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) allows to realize novel 2D heterostructures with tailored properties for application in atomically thin optoelectronic, electronic, and sensing devices. To achieve a high-density, bottom-up integration of such heterostructures in future technologies, the synthesis of 2D layers on top of each other via van der Waals epitaxy (vdWE) is a promising alternative to flake exfoliation followed by mechanical transfer, which is problematic in terms of scaling and reproducibility. However, due to the weak bonding between 2D crystals, vdWE is sensitive to various surface defects, usually leading to uncontrolled nucleation and thus non-uniform growth of polycrystalline material. Hence, the control over nucleation location is one of the key challenges to achieve scalable and high-quality fabrication of 2D heterostructures.
In this work, we report on the use of a focused ion beam (FIB) within a He ion microscope as a novel tool to deliberately create atomic-scale defects in graphene on SiC(0001), which act as nucleation centers for h-BN grown via molecular beam epitaxy. Thereby, we demonstrate a mask-less, selective-area growth of h-BN/graphene heterostacks, in which nucleation yield and crystal quality of h-BN is controlled by the ion beam parameter used for the defect formation in graphene. Importantly, the epitaxially grown h-BN exhibits electron tunneling characteristics comparable to those of h-BN flakes exfoliated from state-of-the-art bulk crystals. These results open a new pathway for the scalable fabrication of not only h-BN/graphene systems, but also of other vdW heterostructures composed of layered materials that can be synthesized via vdWE, such as magnetic 2D materials.
Author: M. Heilmann , V. Deinhart , A. Tahraoui , K. Höflich , J. M. J. Lopes
Title: Spatially controlled epitaxial growth of 2D heterostructures via defect engineering using a focused He ion beam
Source: npj 2D Mater. Appl. , 5 , 70 ( 2021 )