Here we clearly show the remarkable resistance to oxidation of highly crystallized hcp Co nanocrystals close packed in 2D compared to the same nanocrystals either disordered or isolated on the substrate. From a magnetic point of view, these core–shell structures with a high crystalized hcp core are expected to lead to a significant change in the exchange compared to the fcc systems. This intriguing behavior of Co nanocrystals that is related to the permeability of the coating chains to O2 constitutes the first intrinsic property due to their 2D organization.
Source : Enhanced stability against oxidation due to 2D self organization of hcp Co nanocrystals: A New intrinsic property. I.Lisiecki, S.Turner, S.Balls, M.P.Pileni and G.Van Tendeloo. Chem. Mat., 2009, 21, 2335-2338.