Thin Film Growth of nbo MOFs and their Integration with Electroacoustic Devices

Metal-organic frameworks (MOFs) with the “nbo” topology constitute a diverse suite of more than 100 nanoporous materials, but their use in applications such as chemical sensing and membranes is inhibited by a lack of methods for growing them as thin films. Here, layer-by-layer (LBL) and solvothermal growth of “nbo” films is demonstrated and it is established for the first time that interlinker steric hindrance is a critical factor in determining the effectiveness of the LBL method. Film growth is demonstrated for three “nbo” MOFs: NOTT-100 and NOTT-101, which have the R-3m space group and are deposited by the LBL method, and PCN-14, with the R-3c space group, which is deposited by a solvothermal approach. Continuous and dense films of NOTT-100 and NOTT-101 are obtained and LBL growth is verified by observing deposition with a quartz crystal microbalance technique, which also yields the temperature dependence. Oxygen plasma treatment is found to be a useful tool for promoting the MOF film growth under solvothermal conditions. Effective mechanical coupling of these films to the substrate is demonstrated by growing them on surface acoustic wave sensors, which respond reversibly to vapors of water, acetone, and n-hexane.