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Conformal Ultrathin Film Metal–Organic Framework Analogues: Characterization of Growth, Porosity, and Electronic Transport

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journal contribution
posted on 30.10.2019, 12:36 by Jonathan Lau, Ashley E. Trojniak, Macy J. Maraugha, Alyssa J. VanZanten, Alexander J. Osterbaan, Andrew C. Serino, Monica L. Ohnsorg, Kevin M. Cheung, David S. Ashby, Paul S. Weiss, Bruce S. Dunn, Mary E. Anderson
Thin-film formation and transport properties of two copper-paddlewheel metal–organic framework (MOF)-based systems (MOF-14 and MOF-399) are investigated for their potential integration into electrochemical device architectures. Thin-film analogues of these two systems are fabricated by the sequential, alternating, solution-phase deposition of the inorganic and organic ligand precursors that result in conformal films via van der Merwe-like growth. Atomic force microscopy reveals smooth film morphologies with surface roughnesses determined by the underlying substrates and linear film growth of 1.4 and 2.2 nm per layer for the MOF-14 and MOF-399 systems, respectively. Electrochemical impedance spectroscopy is used to evaluate the electronic transport properties of the thin films, finding that the MOF-14 analogue films demonstrate low electronic conductivity, while MOF-399 analogue films are electronically insulating. The intrinsic porosities of these ultrathin MOF analogue films are confirmed by cyclic voltammetry redox probe characterization using ferrocene. Larger peak currents are observed for MOF-399 analogue films compared to MOF-14 analogue films, which is consistent with the larger pores of MOF-399. The layer-by-layer deposition of these systems provides a promising route to incorporate MOFs as thin films with nanoscale thickness control and low surface roughness for electrochemical devices.