Phase stability of Co nanowires prepared by electrodeposition via AAO templates

Cobalt nanowires with average diameters of 40nm, 55nm, 70nm, 90nm, 250nm were prepared by electrodeposition using anodic aluminum oxide (AAO) templates. The as-deposited Co nanowires were dense and presented hcp monocrystal structure. Austenite transformation finish (Af) temperature of the nanowires was investigated with in-situ XRD. Af temperature of nanowires with diameter of 250nm was found almost the same as bulk Co. While, there was a sudden dramatic increase (over 300K) in Af temperature when the diameter decreased from 90nm to 70nm, gaining a great enhancement in the stability of hcp phase. However, Af temperature decreased slightly when the diameter became smaller than 70nm. Possible reasons of this phenomenon were discussed.