Aligned Co nanodiscs by electrodeposition on GaAs

Aligned cobalt nanodiscs have been electrodeposited on GaAs (1 1 0), (1 1 1), and (0 0 1) substrates from weakly acidic, cobalt sulphate (CoSO4) and ammonium sulphate [(NH4)2SO4] solutions. The thickness and diameter of the nanodiscs are about 50 and 500 nm, respectively. They have an HCP crystal structure with their [0 0 0 1] c-axis perpendicular to the disc normal and aligned with the low mismatch in-plane GaAs 〈1 1 0〉 directions. They dominate the growth after an initial layer containing a mixture of BCC and HCP cobalt. Random alignment results for deposition from pure CoSO4 electrolyte [no (NH4)2SO4], or acidic [by adding H2SO4], or basic [by adding (NH4)OH] CoSO4 solutions.