期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：47
页码：16670-16675
DOI：10.1073/pnas.1405613111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significancevan der Waals (vdW) heterostructures of dissimilar 2D material sheets held together by vdW interactions promise new physics and applications not necessarily associated with the constituent 2D materials. Only epitaxial growth can achieve the orientational alignment in vdW heterostructures needed to obtain certain novel phenomena. As a case study of vdW epitaxy, we experimentally find that hexagonal boron nitride strictly aligns to Cu(100), whereas crystallographically similar graphene is known to exhibit a wide spread of in-plane rotations. Theoretical investigation reveals that this stark difference occurs because the C-Cu interactions are stronger than the B-Cu and N-Cu interactions. This counterintuitive discovery sheds light on orientational relationships in vdW epitaxy and their case specificity. Using selected-area low-energy electron diffraction analysis, we showed strict orientational alignment of monolayer hexagonal boron nitride (h-BN) crystallites with Cu(100) surface lattices of Cu foil substrates during atmospheric pressure chemical vapor deposition. In sharp contrast, the graphene-Cu(100) system is well-known to assume a wide range of rotations despite graphene's crystallographic similarity to h-BN. Our density functional theory calculations uncovered the origin of this surprising difference: The crystallite orientation is determined during nucleation by interactions between the cluster's edges and the substrate. Unlike the weaker B- and N-Cu interactions, strong C-Cu interactions rearrange surface Cu atoms, resulting in the aligned geometry not being a distinct minimum in total energy. The discovery made in this specific case runs counter to the conventional wisdom that strong epilayer-substrate interactions enhance orientational alignment in epitaxy and sheds light on the factors that determine orientational relation in van der Waals epitaxy of 2D materials.
关键词：two-dimensional materials ; van der Waals epitaxy ; hexagonal boron nitride ; graphene ; orientational relation
