Atomic Layer Deposition of Organic–Inorganic Hybrid Materials Based on Unsaturated Linear Carboxylic Acids

Abstract

The atomic layer deposition (ALD) technique has been further developed as a tool for producing thin films of organic–inorganic hybrid materials. Trimethylaluminium (TMA) and unsaturated linear carboxylic acids such as maleic acid, fumaric acid and trans,trans-muconic acid have been used as precursors, providing the possibility of also exploring the possible effect of cis- and trans configurations of the precursors. Quartz crystal microbalance measurements of the growth dynamics indicate that all systems are of a self-limiting ALD-type. Nevertheless, temperature-dependent growth, with decreasing growth rates with increasing deposition temperature, was observed. Growth rates were found to be in the range 0.24–1.19 nm/cycle. FTIR spectroscopy proved that the deposited films have a hybrid character. The carboxylic acids formed either bidentate or bridging complexes, and the cis- and trans configuration of the precursor influenced the preference for the type of bonding to the cation. All films were X-ray amorphous as deposited. The films were further analyzed by atomic force microscopy to determine the surface roughness and topography, UV/Vis spectroscopy and ellipsometry to evaluate the optical properties, and the goniometer method was employed to measure sessile drops for the surface wetting properties. All films are stable in contact with water. The films are generally smooth, transparent and have a refractive index in the range 1.5–1.6. Although the obtained films are dense when compared to attractive porous metal–organic framework (MOF) bulk materials, the present work shows that controlled growth of functionalized hybrid materials is offered by the ALD technique.