Structural and optical characterization of undoped, doped, and clustered ZnO thin films obtained by PLD for gas sensing applications

Abstract

The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF * ( λ = 248 nm, τ FWHM ∼7 ns) excimer laser source, operated at 2.8 J/cm 2 incident fluence value, whilst the substrates consisted of SiO 2(0 0 1) wafers heated at 150 °C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10 Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% Au and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing.