The effect of dimethylglyoxime on Co electrodeposition was investigated with cyclic voltammetry, chronopotentiometry, quartz microbalance as well as electrochemical impedance. A potential dependent suppression effect was observed at low potential with a breakdown of the suppression at high potential, resulting in a hysteresis in CV. The addition of dimethylglyoxime not only causes a fast and strong suppression in potential transients but also modifies the impedance spectra. Additional capacitive loops and inductance loops emerged depending on the applied potential, suggesting a competitive adsorption between different surface adsorbed intermediates. A relaxation of suppression effect was observed in absence of agitation and a strong suppression was re-established upon agitation. A reverse relation between Co deposition rate and rotation rate was observed when the rotation rate is below a critical value, providing a path to enable the preferential deposition at the bottom of a small damascene feature. (C) The Author(s) 2016. Published by ECS. All rights reserved.