EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Metal Organic Frameworks (MOF), hybrid microporous crystalline materials are attractive for a large panel of applications due in part to their high specific surface area and physico-chemical stability. Recently, vapor phase-based routes were reported for the synthesis of MOF thin films. Vapour-phase process are usually preferred to obtain conformal coatings and they present a good compatibility with the Si technology. These breakthroughs have paved the way for the use of MOF in micro- and nanotechnologies but much remains to be done to control the growth and understand the potential and limits of these growth methods.
Here we developed a process to grow conformal ZIF-8 coatings with thicknesses up to 200 nm. This growth method is based on the deposition of ZnO layers by atomic layer deposition (ALD) on a substrate followed by ZIF-8 formation using cyclic exposure to water vapour and organic ligand in the gas phase. It was observed that this approach allowed formation of thin films with tunable thickness between 5 and 200 nm, independently of the initial ZnO thickness. The deposition was performed on several devices that can be used for gas analysis such as Quartz Crystal Microbalance and Si micro-pillars arrays.
Continuous ZIF-8 films were obtained and the composition, roughness and structure of the films were studied by FTIR, XRD and AFM experiments. Moreover, the growth mechanism was investigated by XPS and Tof-SIMS. Finally, the porosity was assessed using ellipsometric-porosimetry and the adsorption capacity and behaviour of the films towards several gases (methanol, acetone, water) were also established using gravimetric gas sensors in order to determine the benefit of ZIF-8 thin films for sensors.