Effect of thiourea and saccharin on the roughness of electrodeposited ultrathin nickel and cobalt layers

Ni and Co films were produced by electrodeposition from plating baths containing either thiourea or saccharin. The effect of the organic additives on surface roughness was studied for the Ni-thiourea, Ni-saccharin, Co-thiourea and Co-saccharin systems. Layer thicknesses were varied from 1 to 10 nm and the additive concentration was varied from about 1 M to 1 mM. Contact mode atomic force microscopy was used to measure both the root mean square (RMS) peak height (nm) and the areal peak density (m^–2) of each film. Although the RMS peak height and areal density were both influenced by film thickness and by additive concentration, the two roughness measures provide complementary information on the layer morphology and growth mechanisms. The four systems studied responded differently to changes in the concentration of the added organic. For example, for films 8 nm thick, addition of 1.22 × 10^–3 thiourea reduced the Ni peak density about 80%; in contrast, the Co peak density was increased over 180% by addition of 1.25 × 10^–3 thiourea. Use of peak height and peak density data to infer growth mechanisms for ultrathin films is discussed.