Automated Spin-Assisted Layer-by-Layer Epitaxy Produces Highly Oriented Mixed-Linker MOF Thin Films.

Control over crystallographic orientation in metal-organic framework (MOF) thin films is crucial for exploiting their anisotropic properties in sensing, catalysis, and separation. Achieving reproducible, highly oriented films remains challenging, especially for mixed-linker, pillared-layered frameworks. Here we present an automated, spin-assisted layer-by-layer liquid-phase epitaxy (LbL-LPE) strategy that enables rapid, ambient-condition fabrication of highly oriented, mixed-linker MOF thin films, demonstrated for Zn2BDC2DABCO (BDC = terephthalate, DABCO = 1,4-diazabicyclo[2.2.2]octane). Correlative process monitoring by grazing-incidence wide-angle x-ray scattering (GIWAXS), grazing-angle infrared (GI-IR) and UV-Vis spectroscopy, contact-angle measurements, scanning electron microscopy (SEM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) ensures formation of uniform films with exceptional out-of-plane (001) orientation (degree of orientation > 85%, Hermans orientation parameter ∼0.95) and excellent reproducibility. This strategy enables high-throughput fabrication of orientation-controlled MOF thin films, providing a generalizable alternative to conventional LbL approaches. The resulting highly oriented Zn2(BDC)2(DABCO) thin films retain their crystallinity after prolonged exposure to 80% and short-term exposure up to 90% relative humidity, whereas defect-rich films undergo rapid degradation. Thus, this reproducible, automated strategy establishes the role of crystallographic orientation in humidity stability and advances the integration of oriented MOFs into optoelectronic, sensing, and membrane devices.