Morphological, surface and optical properties of spin-coated IrOx films; influence of spin speed, annealing and (Cr, La) codoping
Year: 2019
Journal: Ceram. Int., Volume 45, MAY, page 8460–8470
Authors: El Sayed, Adel M.; Shaban, Mohamed
Keywords: IrOx thin films; Nanorods structure; Band gap engineering; Co-doping; Optical constants; Wettability
Iridium oxide (IrOx) is a fascinating metal oxide with superior chemical/physical properties. The present report is an attempt to tune the surface and optical properties of II % to widen its industrial and technological applications. The influences of substrates' rotational speed (RS), annealing temperature (AT), Cr-doping and (Cr, La) codoping on the surface morphology and wettability, structural as well as the optical properties of spin-coated IrOx films are discussed. Raman spectra of the films show a characteristic phonon mode at 552 cm(-1) , arising from the Ir-O-x stretching and influenced significantly by the preparative conditions (RS and AT) as well as (Cr, La) codoping. Energy-dispersive X-ray spectra were obtained to confirm the chemical compositions of prepared IrOx nanostructure thin films. Field emission-scanning electron microscopy images reveal the growth of un-doped, Cr-doped and (Cr, La) codoped nanorod-like IrO x structures. The annealed film at 500 degrees C and Cr-doped films showed the nanoporous nature of the grown nanorod-like structures. The films are hydrophilic and follow the Wenzel model. The wetting ability is enhanced by decreasing RS and increasing AT. Increasing RS results in increasing the transmittance (T%) due to decreasing the films' thickness. At wavelength lambda= 10(3) nm, the deposited film shows T% = 53.2 and the film annealed at 500 degrees C exhibits T% = 44.3. The optical band gap (E7) increased with increasing RS and decreased with increasing AT. Cr-doping redshifted E-g(OP) from 2.95 to 2.85 eV, while codoping with La blue shifted E-g(OP) to 3.14 eV. The effect of Cr and La doping on the optical constants of IrOx films was investigated and compared with those of other transition metal oxide films because no data are available in the literature for IrOx films.
