Coalescence aspects of cobalt nanoparticles during in situ high-temperature annealing

In this work we investigate the coalescence aspects of Co nanoparticles. It was observed that nanoparticles in contact with the substrate are relatively immobile, whereas those on top of other Co particles can rearrange themselves during high-temperature annealing and further coalesce. Indeed, similar size particles prior to coalescence come at close proximity forming an arc-shaped area, which leads to finite-size necking and thereafter to coalescence towards a single partially spherical particle. This is in contrast to the theoretical predictions where necking occurs following an initial pathway of a point contact. Moreover, it was shown that after necking a transient period of relatively fast coalescence occurs followed by a slower coalescence rate at constant speed towards a single particle with partial spherical shape. In addition, the coalescence is faster with decreasing particle size, where in the case of unequal size the smallest particle is mainly absorbed by an adjacent large one in an Ostwald ripening process.