Automatic LbL-LPE Spin-Coating Strategy for the Fabrication of Highly Oriented Mixed-Linker MOF Thin Films for Orientation-Dependent Applications

Abstract: Control over crystallographic orientation in metal-organic framework (MOF) thin films is essential, as many of their functional properties critically depend on exact alignment along a defined crystallographic direction. Spin-assisted layer-by-layer liquid-phase epitaxy (LbL-LPE) offers significant advantages over conventional synthesis approaches, including reduced chemical consumption, shorter processing times, and operation under ambient conditions. In this work, this LbL-LPE spin-coating is established as a robust, high-throughput fabrication protocol suitable for application-ready materials. The flexible pillar-layered framework Zn2BDC2DABCO serves as a proof-of-concept framework for the development of an automated spin-assisted LbL-LPE workflow enabling reproducible fabrication of homogeneous and highly oriented MOF thin films with integrated monitoring of critical processing steps. The protocol incorporates correlative characterization combining grazing-incidence wide-angle X-ray scattering (GIWAXS), infrared and UV-Vis spectroscopy, scanning electron microscopy (SEM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to ensure control over surface chemistry, reactant delivery, and film growth. Determination of the degree of orientation and the Hermans orientation parameters provides a key quality metrics for assessing crystal alignment and reproducibility. The automated experimental workflow significantly accelerates the fabrication of thin films whose properties depend on crystal orientation, providing processing optimizations and control that can be readily extended to increasingly complex MOF architectures.