Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

Hexagonal boron nitride (h-BN), an insulating two-dimensional material, is a promising building block as a dielectric layer in novel, atomically thin and flexible two-dimensional (2D) electronic devices such as graphene-based capacitors or field-effect transistors. Furthermore, it is preferentially used as a substrate or as a van der Waals (vdW) bonded encapsulating layer for other 2D materials, because it improves their electronic properties by shielding them from environmental influences. So far, such 2D layered structures have been demonstrated by mechanically stacking h-BN and graphene sheets, which were exfoliated from their bulk counterparts. However, this approach is time-consuming, inherently non-scalable and the interfaces may suffer from impurities. To advance heterostructures comprising different 2D materials with clean interfaces and processing them on large-area, a heteroepitaxial growth within a controlled environment will be crucial.

AFM image of h-BN monolayer islands grown on epitaxial graphene on SiC. The inset shows the height profile along the red dotted line, which reveals a second h-BN layer close to a nanoparticle in the center of the first extended monolayer, which nucleated at a wrinkle in graphene.

We present a direct growth approach for h-BN/graphene heterostructures under controlled conditions using molecular beam epitaxy. The comprehensive growth study (covering various temperatures and growth times) reveals the evolution of 2D h-BN layers during van der Waals epitaxy on graphene from nucleation to coalesced layers. As a substrate high quality epitaxial graphene on SiC was selected for its good reproducibility. A detailed investigation using various correlated atomic force microscopy (AFM) techniques as well as Raman and X-ray photoemission spectroscopy revealed a nucleation which is mediated by morphological defects (wrinkles and step edges) and point defects in epitaxial graphene from where the 2D h-BN layers expand laterally (as a monolayer) and vertically (as multiple layers). Therefore, this study helps understanding the nucleation behavior during van der Waals epitaxy at elevated temperatures, which is a first step towards a controllable and scalable fabrication of 2D heterostructures. 

1 Author M. Heilmann , M. Bashouti , H. Riechert , J. M. J. Lopes

Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

Source 2D Mater. , 5 , 025004 ( 2018 )
DOI : 10.1088/2053-1583/aaa4cb | 2962 Cite : Bibtex RIS
M. Heilmann, M. Bashouti, H. Riechert, and J. M. J. Lopes