Reactions of small cobalt clusters with N2: implications for cluster structure

Abstract

The geometrical structures of small cobalt clusters are probed via the adsorption of molecular nitrogen on their surfaces. In contrast to nickel clusters, the adsorption of nitrogen causes most cobalt clusters to change structure; in some cases multiple structural changes occur as the nitrogen coverage is increased. Although this complicates the determination of structure for the bare clusters, we are able to propose structures for most of the clusters in the Co3Co16 size range. Again in contrast to nickel, most cobalt clusters appear to adopt close-packed structures that resemble bulk packing. For example, while Ni13 is most likely an icosahedron, Co13 appears to have an fcc or hcp structure. The structural differences between the two metals probably reflects the increased importance of d-orbital binding in cobalt compared to nickel.