Morphology, optical, and adsorption properties of copper-oxide layers deposited from complex compound solutions

A technique for synthesizing gas-sensing copper-oxide layers by layer-by-layer deposition onto glass and plastic substrates is considered. Deposition is based on the oxidation of a copper–ammonia complex by hydrogen peroxide. Layers synthesized at various numbers of deposition cycles are studied by atomicforce microscopy and transmission spectroscopy methods (300–1000 nm). The spectral shape indicates the mixed nature of the oxide with predominant copper oxide (I) Cu$_2$O with a corresponding band gap of 2.1 eV. The layers have a continuous granular structure. The surface concentration of Brönsted acid adsorption sites with $pK_{a}\approx$ 2.5 (OH acid groups), determined by the indicator method, is 560 $\mu$mol/m$^2$ for the initial films, and threefold increases after heat treatment at 80$^\circ$C for 30 min. The results obtained are interesting for the use of the described technology for fabricating copper-oxide active layers in gas-sensing sensors operating at room temperature.