Fast Dynamic Synthesis of MIL-68(In) Thin Films in High Optical Quality for Optical Cavity Sensing

Abstract

Fabrication of metal−organic framework (MOF) thin films rigidly anchored on suitable substrates is a crucial prerequisite for the integration of these porous hybrid materials into electronic and optical devices. Thus, far, the structural variety for MOF thin films available through layer-by-layer deposition was limited, as the preparation of those surface-anchored metal− organic frameworks (SURMOFs) has several requirements: mild conditions, low temperatures, day-long reaction times, and nonaggressive solvents. We herein present a fast method for the preparation of the MIL SURMOF on Au-surfaces under rather harsh conditions: Using a dynamic layer-by-layer synthesis for MIL-68(In), thin films of adjustable thickness between 50 and 2000 nm could be deposited within only 60 min. The MIL-68(In) thin film growth was monitored in situ using a quartz crystal microbalance. In-plane X-ray diffraction revealed oriented MIL-68(In) growth with the pore-channels of this interesting MOF aligned parallel to the support. Scanning electron microscopy data demonstrated an extraordinarily low roughness of the MIL-68(In) thin films. Mechanical properties and lateral homogeneity of the layer were probed through nanoindentation. These thin films showed extremely high optical quality. By applying a poly(methyl methacrylate) layer and further depositing an Au-mirror to the top, a MOF optical cavity was fabricated that can be used as a Fabry−Perot interferometer. The MIL-68(In)-based cavity showed a series of sharp resonances in the ultraviolet−visible regime. Changes in the refractive index of MIL-68(In) caused by exposure to volatile compounds led to pronounced position shifts of the resonances. Thus, these cavities are well suited to be used as optical read-out sensors.

Trendbericht Festkörperchemie und Materialforschung 2024

“…32) Das Team um Knebel hat mit einer Quarzmikrowaage die direkte Synthese für ein MOF auf einem Goldsubstrat optimiert und baut damit nun einen optischen Sensor für Gase. 33) Gase speichern ist eines der wichtigsten MOF-Anwendungsgebiete. Dass sich toxische Gase wie SF 6 bei Normalbedingungen in MOFs speichern lassen, zeigen Bunzen und Mitarbeitende am Beispiel der porösen Verbindung ZIF-8: Auch nach 60 Tagen gibt diese kein SF 6 frei.…”

Fabrication of Oriented Polycrystalline MOF Superstructures

“…[133,134] Indeed, IP orientation has been observed first by using synchrotron facilities and then by using laboratory X-ray diffractometers. [60,134,135] The simultaneous IP and OOP orientations have become progressively more common in LbL deposition obtained on functionalized substrates through different fabrication methods (e.g., LbL-Liquid Phase Epitaxy (LPE), [136] combinations of Langmuir-Blodgett and LbL, [133] continuous flow dynamic LbL, [137] spray and spin-coating depositions). [80,138] Textural analyses have confirmed, in a few cases, the existence of oriented polycrystalline systems.…”

Thickness and Humidity on Proton Conductivity in MOF-508 Thin Film by Twin-Zinc-Source Method

“…There have been several achievements in MOF materials with high proton conductivity by systematic design modifications, such as the introduction of NH 4 + , H 3 O + , and HSO 4 − into the pores of the framework [8]. However, there have been few studies on the physical properties of MOF thin films [9][10][11], such as adjusting the film morphology and the fabrication of dense MOF films [12][13][14]. Therefore, the simple preparation of stable and high proton conductive MOF thin films remains a great challenge [15].…”