Effect of pH at Early Formed Structures in Cobalt Electrodeposition

摘要

The electrodeposition of cobalt on platinum wafer substrates was studied versus electrolyte pH. The crystallographic structure of electrodeposited cobalt films found to be very sensitive on the electrolyte pH value. During the first stage of growth, at pH = 2 a mixture of Co_(fcc) and Co_(hcp) are formed with the prevailing Co_(fcc) phase. By increasing the pH (3.0 < pH < 4.0), Co_(hcp) becomes the major fraction with good crystallization state and large grain sizes. Electrochemical impedance spectroscopy technique was used to describe the interface's behaviour and the passage steps of electrodeposition process. It was found that at pH = 2, the impedance spectra are characterized by the presence of a semicircle feature at high frequencies and by complex inductance at low frequencies. At pH (3.0 < pH < 4.0), the inductive feature disappears and replaced by capacitive feature indicating the control of electrodeposition by the deposition process.