Formation of cobalt hydroxide single-crystal platelets from pulsed laser deposited cobalt thin film

Uniform size hexagonal shaped cobalt hydroxide single crystals of about 100–200 nm thick were produced on glass substrates. They were formed by the reaction of a cobalt thin film with the sodium hydroxide solution. The film was prepared by the pulsed laser deposition (PLD) process of which the second harmonic of a pulsed Nd:YAG laser (wavelength = 532 nm) was employed to ablate the rotating cobalt target in vacuum. As revealed by SEM the smoothed surface of the as-prepared cobalt film changed into individual hexagonal platelets after the chemical reaction. The platelets were grown with the hexagonal planes mostly parallel to the substrate surface. From the XRD and FTIR results, as well as the SAED provided by TEM, these platelets are evidently the single crystals of β-cobalt hydroxide. It is believed that the formation of these single crystals is benefited from the nanosized grains of PLD cobalt, which promote the chemical reaction.