Local electronic structure of single-layer Kagomé MOFs on carbon surfaces

Metal–organic frameworks (MOFs) are crystalline lattices that exhibit metal nodes bridged by π-conjugated organic ligands. The 2D molecular connectivity of MOFs provides a chemically programmable platform for engineering lattice symmetry and band structure. We have realized single-layer Kagomé-type Ni-HITP MOFs on highly oriented pyrolytic graphite (HOPG) using dual-source chemical vapor epitaxy (CVE). Scanning tunneling microscopy imaging reveals long-range Kagomé order for this 2D system. Spatially resolved dI/dV spectra show frontier states consistent with Kagomé-band physics, i.e., a flat-band feature and a Dirac-like crossing that are reproduced by density-functional calculations. 2D device compatibility of this MOF was demonstrated by also using monolayer graphene/hBN devices with prepatterned contacts and back-gates as Kagomé growth substrates via CVE. This resulted in well-ordered Kagomé MOFs with characteristic local spectral features. The aim of this approach is to enable electrostatic tuning of single-layer Kagomé materials via backgating of a graphene device support in the absence of reactive metal substrates. These results establish a new route for interrogating single-layer Kagomé phenomena.