The composition, structure and optical properties of weakly magnetic Co-containing amorphous Si and Ge films

Highlights: ► a-SiCo and a-GeCo thin films have been deposited by rf sputtering. ► The Co atoms were effectively and homogeneously incorporated into the amorphous hosts. ► Thermal treatments induce the crystallization of the samples and the formation of non-magnetic secondary phases in the films containing Co. ► The optical properties of the films are significantly affected by the insertion of Co and by the temperature of thermal annealing. ► The samples exhibited reduced magnetic signal at room temperature. - Abstract: This study investigated the composition, structure and optical properties of amorphous SiCo and GeCo films. The samples were prepared by radio frequency sputtering. Films were deposited with Co atomic concentrations in the range of 1.7–10.3 at.%. After deposition, the films were submitted to thermal treatments up to 900 °C and investigated by energy dispersive X-ray spectrometry, X-ray diffraction, Raman scattering and optical transmission spectroscopy. Additionally, magnetic force microscopy measurements were performed at room temperature. For comparison purposes, Co-free samples were also prepared, annealed and characterized following a similar procedure. The experimental results indicated the following: (1) the Co atoms were effectively and homogeneously incorporated into the amorphous hosts; (2) the as-deposited films (either pure or containing Co) were essentially amorphous; (3) annealing the films at high temperatures induced crystallization; (4) after crystallization, non-magnetic CoSi2 (silicide) and CoGe2 (germanide) phases were identified in the Co-containing Si and Ge films, respectively; (5) the optical properties of the films were significantly affected by the insertion of Co and by the annealing temperature; and (6) the samples exhibited a reduced magnetic signal at room temperature. These experimental observations were systematically studied, which are presented and discussed in this report.