Growth Mechanisms and Anisotropic Softness-dependent Conductivity of Orientation-controllable Metal-organic Framework Nanofilms

Conductive metal-organic frameworks (MOFs) manifest great potential in modern electrical devices due to their porous nature and the ability to conduct charges in a regular network. MOFs applied in electrical devices normally hybridize with other materials, especially a substrate. Therefore, the precise control of the interface between MOF and a substrate is particularly crucial. However, the unexplored interface chemistry of MOFs makes the controlled synthesis and advanced characterization of high-quality thin films, particularly challenging. Herein, we report the development of a simplified synthesis method to grow "face-on" and "edge-on" MOF nanofilms on substrates, and the establishment of operando characterization methodology using atomic force microscopy and X-ray, thereby demonstrating the relationship between the soft structure of surface-mounted oriented networks and their characteristic conductive functions. As a result, crystallinity of MOF nanofilms with a thickness down to a few nanometers is obtained, the possible growth mechanisms are proposed, and the interesting anisotropic softness-dependent conducting properties (over 2 orders of magnitude change) of the MOF are also illustrated.