Chemical and morphological characterization of photoactive SiOx films electrodeposited on Pt substrate

Abstract

SiOx films electrodeposited on platinum (Pt) substrate were shown to exhibit n-type photoactivity while placed both in aqueous and organic solutions. The films were obtained via potentiostatic deposition at potential values ranging from −2.25 to −2.75V. The mechanism of the electrodeposition involved reactions with the used electrolyte and with traces of water as sources of oxygen and hydrogen, as interpreted from Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The photoactivity of the deposits deceased at potential −2.75V. The highest observed photocurrent was ca. 60μA/cm2 and it was registered in organic solution. The band gap energies determined by XPS technique were approximately 2.5, 2.3 and 3.7eV for films electrodeposited at −2.25, −2.5 and −2.75V, respectively. The depth profiles of Si, O and H in the films were registered by glow discharge optical emission spectroscopy (GD-OES), which showed that the film thickness was ca. 0.4μm. The n-type photoactivity was associated with oxygen evolution from the aqueous solution (0.1M HClO4, pH1), whereas the time instability as a function of time observed for the photocurrent was associated with morphological changes of the films as seen by scanning electron microscopy (SEM) and their oxidation detected by XPS and FTIR spectroscopies.