Nanometer-thick crystalline and amorphous zeolitic imidazolate framework films for membrane and patterning applications

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal-organic frameworks (MOFs) with more than 200 characterized crystalline and amorphous networks made of divalent transition metal centers (e.g., Zn2+ and Co2+) linked by imidazolate linkers. ZIF thin films have been pursued intensively motivated by the desire to prepare membranes for selective gas and liquid separations. To achieve membranes with high throughput, as in Å-scale biological channels with nanometer-scale pathlengths, ZIF films with the minimum possible thickness, down to just one unit cell, are highly desired. Control of ZIF film thickness at the 10-nm-scale may also enable emerging, MOF-inspired, applications including patterned crystalline MOF films, and amorphous organic-inorganic resists for high-resolution electron-beam (e-beam) and extreme UV (EUV) lithography. However, the state-of-the-art methods yield ZIF films with thicknesses exceeding 40 nanometers. Here, we report a deposition method from ultra-dilute precursor mixtures that within minutes yields uniform ZIF deposits with nm-scale thickness control. On crystalline substrate such as graphene, two-dimensional crystalline ZIF (2DZIF) film with thickness of a unit-cell could be achieved, which composed of a six-membered zincimidazolate coordination ring enabling record-high H2 permselective separation performance. Deposition under identical conditions on amorphous substrates yields macroscopically smooth amorphous ZIF (aZIF) films, which can be used as negative- and positive-tone resists yielding pattern features down to 20 nm. The method reported here will likely accelerate the development of 2D crystalline and ultrathin amorphous MOF films for applications ranging from separation membranes to sensors and patterning for microelectronic applications.

Liu, Q., Miao, Y., Villalobos, L. F., Li, S., Babu, D. J., Chen, C., Chi, H.-Y., Vahdat, M. T., Hao, J., Song, S., Han, Y., Tsapatsis, M., & Agrawal, K. V. (2023). Nanometer-thick crystalline and amorphous zeolitic imidazolate framework films for membrane and patterning applications.

The authors acknowledge Dr. Dmitry Chernyshov and Dr. Diadkin Vadim at beamline BM01, the-Swiss-Norwegian Beamlines (SNBL), European Synchrotron Radiation Facility (ESRF) for assistance with synchrotron GIXRD experiments (doi:10.15151/ESRF-ES-670011338.), Dr. Pascal Alexander Schouwink from EPFL for the help of XRD data. Dr. Mounir Mensi and Mojtaba Rezaei from EPFL for the help of XPS and AFM. This project is primarily supported by European Research Council Starting Grant (805437-UltimateMembranes). Parts of the work was supported by Swiss National Science Foundation (SNSF) Assistant Professor Energy Grant (PYAPP2_173645) and SNSF project (514601); Y. M. and M. T. acknowledge funding by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-SC0021212.

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