Optical characterization of sputtered YBaCo_4O_(7+δ) thin films

摘要

Thin films of YBaCo_4O_(7+δ) were deposited on r (1012)-oriented Al_2O_3 substrates by dc magnetron sputtering. The as-grown films were characterized after their structural, morphological and optical properties. Special attention is devoted to the analysis of the optical response of these films as reports on optical properties of YBaCo_4O_(7+δ), especially in thin film form, are not frequently reported in the literature. Transmittance/absorbance measurements allow for determining two well defined energy gaps at 3.7 and 2.2 eV. In turn, infrared (IR) measurements show infrared transparency in the wave length range 4000 -2500 nm with a sharp absorption edge at wave lengths less than 2500 nm. Complementary Raman spectra measurements on the thin films allowed for identifying bands associated with vibrating modes of C0O_4 and YO_6 in tetrahedral and octahedral oxygen coordination, respectively. Additional bands which seemed to stem from Co ions in octahedral oxygen coordination were also clearly identified.