Automatic Deposition of Oriented Copper Hydroxide Nanobelt Films for the Heteroepitaxial Growth of Metal-Organic Frameworks

Abstract

One of the key challenges that the field of metal-organic frameworks (MOFs) faces today is the possibility of processing these materials as thin films to enable their integration into existing technologies [1-4]. This is particularly important for devices that exploit anisotropic properties obtained from highly oriented materials. Based on a previously described procedure to obtain centimetre-scale oriented MOF films [5], we hereby report the optimization and extension of this procedure into an automated, operator-independent method that affords higher yields without compromising the long-range orientation. The procedure is based on the deposition of crystalline copper hydroxide nanobelts that can be aligned to obtain substrates with preferential orientation. The influence of different deposition parameters on the coverage and orientation of the films was studied and tuned in order to obtain reproducible samples with higher yields. With applications in fields such as gas storage, catalysis and light harvesting, among others, these oriented ceramic substrates can be converted on demand to different MOFs by exploiting a rapid heteroepitaxial growth [6]. This automatic method introduces the attractive prospect of the potential implementation of MOFs in large-scale thin-film processing. Figure 1: Comparison between manual and automated procedures for the deposition of oriented copper hydroxide films on silicon substrates. Left: Azimuthal angle dependence of intensity profiles of the (020) reflection of Cu(OH)2 at a diffraction angle of 23.8°corresponding to a typical sample obtained by each method, showing the superior alignment of the automatic procedure. Right: Optical images showing the surface coverage and long range (centimetre-scale, top) and micro alignment of the substrate (by polarized-light optical microscopy, bottom).