Copper and iron based thin film nanocomposites prepared by radio-frequency sputtering. Part II: elaboration and characterization of oxide/oxide thin film nanocomposites using controlled ex-situ oxidation process

CuO/CuFe2O4 thin films were obtained on glass substrate by ex situ oxidation in air at 450 A degrees C for 12 h from various starting metal/oxide nanocomposites by radio-frequency sputtering technique. The structure and microstructure of the films were examined using grazing incidence X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies, X-ray photoelectron spectroscopy, and electron probe microanalysis. These studies reveal that a self-organized bi-layered microstructure with CuO (surface layer) and CuFe2O4 (heart layer) was systematically obtained. Due to the porosity of the upper layer formed during annealing, an increase in total thickness of the film was observed and is directly correlated to the oxidation of the metallic copper content initially present in the as-deposited sample. A self-organization in two stacked layers CuO/CuFe2O4 with various void fractions ranging from 0 to 41 % can be obtained by controlling the as-deposited elaboration step described in the part I of this paper. The highest porosities were observed for films deposited at low argon pressure and low target-to-substrate distance. Due to their specific self-organization in p- and n-type layers associated with their high porosity, such structured films exhibited the best electrical sensitivity to CO2 gas sensing. The obtained results demonstrated the importance of microstructure control to improve the response of sensing layers.