Stability and reactivity of Fe-DCA 2D metal-organic frameworks on chemically inert graphene support.

Atomically defined 2D Metal-Organic Frameworks (MOFs) show high promise for many applications, but their implementation is often hindered by their limited stability. Here, we provide an atomic-scale view on the structural stability and chemical reactivity of Fe-DCA 2D MOF placed on an inert graphene support. We use Scanning Tunneling Microscopy, Low-Energy Electron Microscopy/Diffraction, X-ray Photoemission Spectroscopy, and Density Functional Theory to unravel how the Fe-DCA reacts with oxygen and carbon monoxide in ultrahigh vacuum. We show that O2 exposure at room temperature causes structural collapse of the Fe-DCA framework, leaving oxidized Fe clusters and self-assembled DCA molecules on the surface. In contrast, CO does not stably adsorb on the defect-free Fe-DCA at room temperature, but larger CO doses induce slow disintegration of the Fe-DCA structure starting from domain boundaries and defects. Variable-temperature Scanning Tunneling Microscopy captures the atomic-scale details of this process at temperatures below 200 K, where the individual adsorbed CO molecules can be imaged. Overall, our results outline the stability limits of Fe-DCA networks on a technologically relevant graphene support; this knowledge is necessary for any potential application of similar materials, e.g., in spintronics, catalysis, or sensing.