Epitaxial Electrodeposition of Cobalt on a Pt(111) Electrode Covered with a Cu(111) Film

Electrodeposition is an inexpensive alternative to the conventional molecular beam epitaxy technique used to fabricate artificial magnetic materials, such as cobalt thin film. Reported here is a scanning tunneling microscopy (STM) study on the electrodeposition of Co on a Pt(111) single-crystal electrode precoated with a Cu thin film in 0.1 M KClO4 + 1 mM HCl + 0.04 M CoCl2 (pH 3). Deposition of Co started with the nucleation of nanometer-sized clusters preferentially at pits on the Cu support, followed by lateral expansion and coalescence of Co nuclei to form a uniform Co layer. Normally a few Co layers would grow simultaneously to produce a smooth Co deposit until the 12th layer. Cobalt grew in three dimensions afterward. Atomic-resolution STM imaging showed that the first Co layer assumed a double-lined pattern, which was lifted by the deposition of another layer of Co. The second Co layer exhibited a hollow-ring pattern, which transformed into a moire pattern and triangular pits at the third Co layer. The moire pattern gained prominence at the expense of the triangular pits as the Co deposit thickened. The amplitude of the intensity modulation of the moire pattern decreased with the thickness of the Co deposit and eventually became indiscernible at the 12th layer. These restructuring events resulted from a gradual release of the stress at the Co/Cu interface. Since the morphology of the copper substrate was hardly changed by the deposition of cobalt, mixing at the Co/Cu interface seems to be negligible. Similar to the deposition process, dissolution of Co deposit proceeded in layers also.