Chemical vapor deposition of metal-organic frameworks for sensing

Metal-organic frameworks are crystalline porous materials composed of metal ion nodes interconnected by organic linker molecules. Displaying uniform pores and record-breaking surface areas, MOFs are very attractive for both large-scale applications (e.g., adsorption, gas storage, catalysis) and high-value applications (e.g., gas sensors, low-k dielectrics). Suitable methods for their synthesis as powders and deposition as thin films on surfaces are necessary to realise their application potential. Conventional solvothermal processes present several compatibility issues, in particular with device microfabrication: use of toxic organic solvents, corrosion of electronic circuits, particle contamination,… which can be overcome through vapour-phase instead of solution-based processing.

Vapour-phase processing represents a major technological breakthrough in processing MOF materials. Several solvent-free or vapour-assisted powder synthesis procedures exist. However, it was only recently that a MOF was successfully deposited as thin film entirely from the vapour-phase. The method, called MOF chemical vapour deposition (MOF-CVD), was only demonstrated for a prototypical MOF based on zinc ions and imidazolate linkers.

In this work, vapour-phase powder synthesis and MOF-CVD were expanded to materials based on other chemistries, including zinc (bipyridyl-)imidazolates, copper and aluminium dicarboxylates. For the first time, thin films of a mesoporous crystalline material, or with preferential crystallite orientation on the surface, were deposited entirely from the vapour-phase. These achievements were made possible through the use of novel types of reaction chambers allowing control on reaction temperature and atmosphere composition, and through extensive in and ex situ material characterization using conventional and advanced methods, in some cases for the first time.