J. Gil-Rostra, M. Cano, J.M. Pedrosa, F.J. Ferrer, F.J. García-García, F. Yubero, A.R. González-Elipe
ACS Applied Materials and Interfaces, 4 (2012) 628-638
doi: 10.1021/am2014629

This work reports the synthesis at room temperature of transparent and colored W_xSi_yO_z thin films by magnetron sputtering (MS) from a single cathode. The films were characterized by a large set of techniques including X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), Fourier transform infrared (FT-IR), and Raman spectroscopies. Their optical properties were determined by the analysis of the transmission and reflection spectra. It was found that both the relative amount of tungsten in the W–Si MS target and the ratio O₂/Ar in the plasma gas were critical parameters to control the blue coloration of the films. The long-term stability of the color, attributed to the formation of a high concentration of W⁵⁺ and W⁴⁺ species, has been related with the formation of W–O–Si bond linkages in an amorphous network. At normal geometry (i.e., substrate surface parallel to the target) the films were rather compact, whereas they were very porous and had less tungsten content when deposited in a glancing angle configuration. In this case, they presented outstanding electrochromic properties characterized by a fast response, a high coloration, a complete reversibility after more than one thousand cycles and a relatively very low refractive index in the bleached state.