Synthesis of Large-scale 2D Organic Framework/graphene Heterostructure with Observing Dirac and Flat Bands

The current strategies for building 2D organic-inorganic heterojunctions involve mostly wet-chemistry processes or exfoliation and transfer using PMMA, leading to interface contaminations, poor crystallizing, or limited size. Here, we report a bottom-up procedure to fabricate 2D large-scale heterostructure, with clean interface and highly-crystalline sheets in ultrahigh vacuum (UHV). As a prototypical example, a well-ordered self-assembled hydrogen-bond organic framework (HOF) of 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) is grown on the highly-oriented-pyrolytic-graphite (HOPG) substrate. Interestingly, the topmost layer of HOPG is self-lifted by THPB-HOF monolayer via strong interlayer coupling, to form effectively a floating HOF/graphene heterostructure. The HOF adopts a honeycomb lattice with faulted and unfaulted halves in a unit cell, a form of molecular "graphene". The individual layers of heterostructure inherit their intrinsic properties, exhibiting distinct Dirac bands of graphene folded into the Brillouin zone (BZ) of HOF and narrow bands of THPB-HOF. Intriguingly, the HOF/graphene heterostructure displays density-of-state (DOS) peaks near EF in tunneling spectra, which is interpreted as the local magnetic states induced via removing pz orbital in π-conjugated systems. Our results demonstrate a promising approach to fabricate 2D organic-inorganic heterostructure with large-scale uniformity and long-range order via the self-lifting effect, which should be generally applicable to most of van der Waals (vdW) materials.