The role of composition, structure and morphology on the electrical, optical and electrochemical responses of AlNxOy films

Metallic (Me) oxynitrides (MeNxOy) are an attractive class of materials due to a unique set of versatile properties in different technological domains such as protective applications (wear, diffusion and corrosion-resistance), decorative coatings, gas barriers, microelectronics, optoelectronics, solar cells, etc. Among the group of oxynitrides, aluminium oxynitride (AlNxOy) presents some interesting characteristics to be used in different technological fields, since it may combine the behaviour of metallic aluminium, and those of the base binary systems: aluminium nitride, known for its semiconducting and piezoelectric properties and aluminium oxide, for its protective and insulating performances. In this work, thin films of AlNxOy were prepared by reactive DC magnetron sputtering, using a pure Al target and an Ar/(N2,O2) gas mixture. The overall set of results suggests the formation of a nanocomposite-like material for some stoichiometries, with Al nanoparticles embedded in an AlNxOy matrix, forming a percolating network. This particular microstructure induced a wide variation in electrical properties [1], such as a gradual transition from positive to negative temperature coefficients of resistance (TCR) as the (N+O)/Al atomic ratio increases; as well as distinct optical responses [2], such as an unusual low and constant optical reflectance nearly independent of the wavelength (250 – 2500 nm), which opens the possibility of using the AlNxOy films in different applications, either in electrical or optical-based devices. The films were also tested in terms of electrochemical and corrosion behaviour, focusing this study on the influence of the immersion in NaCl solutions, which simulate the effect of sweat, on the electrochemical and optical performance of the coatings. Results showed that the films electrochemical and optical responses are very stable, even when immersed for several weeks.Fundação para a Ciência e a Tecnologia (FCT