Speaker
Description
Solvent-free on-surface synthesis approach allows to design and study new materials with unrivaled resolution, but it is traditionally limited to materials of monolayer thickness. Here, we demonstrate that multilayer metal-organic frameworks (MOFs) can be grown on surfaces in ultrahigh vacuum, and these materials can be characterized at the atomic-scale using the established surface science methodology. By Scanning Tunneling Microscopy, Low Energy Electron Diffraction and X-Ray Photoemission Spectroscopy combined with Density Functional Theory computations, we show that an on-surface prepared multilayer Fe-TCNQ MOF structure is well-defined at the atomic scale, and features both in-plane and out-of-plane chemical bonding. The interlayer chemical interaction affects the structural and electronic properties of the material, making this system distinct from the monolayer case, and comparable to the materials studied in applied materials chemistry.
The multilayer growth is partially independent of the support, as we demonstrate its feasibility on two substrates: Au(111) and graphene/Ir(111). However, the support defines the growth mode of the MOF, which is Volmer-Weber (island) on graphene/Ir(111) and Stranski-Krastanov (layer-plus-island) on Au(111). We rationalize these observations by the different interaction strengths between the MOF components and the supports. Despite these differences, MOF thicknesses up to 3-4 monolayers were achieved on both supports, with no hints of any issues that would prevent growth of thicker structures. Overall, our results bridge the gap between fundamental atomically-resolved models and application-relevant materials.