Role of Combustion Chemistry in Low-Temperature Deposition of Metal Oxide Thin Films from Solution

Metal-oxide thin films find many uses in (opto)electronic and renewable energy technologies. Their deposition by solution methods aims to reduce manufacturing costs relative to vacuum deposition while achieving comparable electronic properties. Solution deposition on temperature sensitive substrates (e.g., plastics), however, remains difficult due to the need to produce dense films with minimal thermal input. Here, we investigate combustion thin-film deposition, which has been proposed to produce high-quality metal-oxide films with little externally applied heat, thereby enabling low temperature fabrication. We compare chemical composition, chemical structure, and evolved species from reactions of several metal nitrate [In(NO3)(3), Y(NO3)(3), and Mg(NO3)(2)] and fuel additive (acetylacetone and glycine) mixtures in bulk and thin-film forms. We observe combustion in bulk materials but not in films. It appears acetylacetone is removed from the films before the nitrates, whereas glycine persists in the film beyond the annealing temperatures required for ignition in the bulk system. From analysis of X-ray photoelectron spectra, the oxide and nitrate content as a function of temperature are also inconsistent with combustion reactions occurring in the films. In(NO3)(3) decomposes alone at low temperature (similar to 200-250 degrees C) without fuel, and Y(NO3)(3) and Mg(NO3)(2) do not decompose fully until high temperature even in the presence of fuel when used to make thin films. This study therefore distinguishes bulk and thin-film reactivity for several model oxidizer-fuel systems, and we propose ways in which fuel additives may alter the film formation reaction pathway.