(169a) Thin Films of Metal Organic Frameworks Interfaces Obtained By Laser Evaporation

Properties such as large surface area, pore volume, high chemical and thermal stability, and structural flexibility render zeolitic imidazolate frameworks (ZIFs) as well-suited materials for gas separation, chemical sensors, and optical and electrical devices. However, for such applications, film processing is a prerequisite.

Several methods demonstrated controlled film formation and relied on pulsed-laser deposition (PLD), atomic layer deposition (ALD), molecular layer deposition (MLD), liquid-phase epitaxy (LPE), chemical solution deposition (CSD) or Langmuir-Blodgett layer-by-layer (LBL) deposition, just to name a few. However, such methods failed to demonstrate that resulting films were uniform in nature. Moreover, several of these techniques required long reaction times and were not able to provide user-controlled, consistent morphologies or crystallinities for the deposited films. Furthermore, PLD for instance, is known to lead to high degradation of some of the films because of the vapor-related condition encountered during such specimen’s growth. With above listed limitations, developing the next generation of controlled deposition means capable to ensure maximum heterogeneity as well as continuous, highly oriented film formation, with control over film functionality and integrability, is urgently needed.

Herein, Matrix Assisted Pulsed Laser Evaporation (MAPLE) was successfully used as a single-step deposition process to fabricate ZIF-8 films. MAPLE versatility was previously demonstrated during the deposition of magnetite silica, organic targets, SnO₂ colloidal, TiO₂ nanoparticle, kanamycin functionalized magnetite nanoparticles and polyaniline, just to name a few. Using MAPLE was expected to reduce the logistical burden associated with ZIF-8 thin film deposition which is made as brittle crystals or insoluble powders that are not amenable to common surface-processing techniques. By correlating laser fluency and controlling the specific transfer of lab-synthesized ZIF-8, films with user-controlled physical and chemical properties were obtained. Films’ characteristics were evaluated by Scanning Electron Microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies, respectively. Analysis showed that frameworks of ZIF-8 can be deposited successfully and controllably using the gentle MAPLE technique to yield to polycrystalline films on selective substrates. Deposited films maintained the integrity of individual ZIF-8 framework, while undergoing minor crystalline and surface chemistry changes. No significant changes in particle size homogeneity and uniformity were however observed. Our study demonstrated control over both the MAPLE deposition conditions and the outcome, as well as the suitability of the deposition method to create composite architectures. We envision that controlled deposition of MOF films using MAPLE could be tuned to create structures with application in sensors or membrane or to form seeding layers in which such deposited films serve as nucleation centers for growth of catalytic precursors. Such tuning capability combined with the ability to deposit on a variety of substrates from metals to oxides, or polymers, all at room temperature, could allow for increased versatility of deposited thin films while largely maintaining their physico-chemical characteristics.