Impact of Synthetic Conditions on the Morphology and Crystallinity of FDMOF-1(Cu) Thin Films

Metal–organic frameworks (MOFs) have attracted a lot of interest for their numerous properties. However, they are usually obtained as a powder (bulk) or as single crystals, which complicates their implementation into devices that could further exploit these properties. The development of surface anchored MOFs (SURMOFs) allowed the synthesis of MOF thin films chemisorbed to a substrate, creating a viable solution to the device integration problem. Yet, the fundamental understanding of the mechanisms governing their growth remains limited, and the systematic optimization of synthetic parameters is tedious. More studies on SURMOFs growth are needed before MOF-based devices become the norm. In this paper, a pillared-layer MOF with fluorinated terephthalate linkers, Cu₂(fbdc)₂(dabco) or F-DMOF-1­(Cu), was synthesized on functionalized gold surfaces using a layer-by-layer method of liquid phase epitaxy (LPE). The effects of temperature, linker concentration, type of surface functionalization and sonication during the rinsing step on coverage, film morphology, and crystal orientation were studied. We found that the concentration of the linker has a strong impact on the morphology of the crystallites formed as well as on the surface coverage. It was noticed that the crystalline orientation is not just governed by the functionalization of the substrate, supporting the hypothesis that SURMOF thin films can switch their crystalline orientation during growth. This study adds information on which variables affect the formation of the first layers of a prototypical SURMOF.