The pH dependence of Co-Cu alloy thin films fabricated on amorphous substrate by DC electrodeposition

Bulk Co-Cu alloy thin films were fabricated on amorphous substrates, instead of the commonly employed metallic substrates, by dc electrodeposition. The stoichiometric distributions of thin films on both sides was estimated using bath parameters, e.g., current pulse amplitude and electrolyte pH by energy dispersive spectroscopy (EDS). The results obtained revealed that film Cu contents were much higher on the solution/film interface than at the substrate/film interface. This indicates that the metals exchange between Co and Cu occurred immediately after the end of cathodic pulse until the films completely separated from electrolyte contribution to the asymmetry of Cu distribution. On increasing the cathodic current density, the films became more and more Co rich in a low pH bath, whereas at above 80 mA/cm² Co content was as high as 90 wt.%. The significant variations in the compositions of thin films formed using conditions of identical current density were also observed when the pH value was varied, which indicates the presence of a strong relation between bath pH value and composition dependence for the Co/Cu electrodeposition process. Moreover, some films deposited from higher pH baths showed oxygen incorporation in films at the solution side of the deposited film. The coercive fields of films obtained under fixed current, e.g., 80 mA/cm², at varying thicknesses were measured by vibrating sample magnetometer, and a correlation between coercivity and film thickness was obtained.