Growth of Co Nanoclusters on Si₃N₄ Surface Formed on Si(111)

We have grown high density Co clusters with a narrow-sized distribution on the Si₃N₄(0001)-(8 x 8) surface. In the submonolayer regime, Co clusters tend to keep a certain size (～ 1.45 nm in diameter) irrespective of coverage. With increasing coverage above 0.92 ML, two new clusters with certain but larger sizes are formed. This novel growth behaviour can be explained by the quantum size effect Phys. Rev. Lett. 90 (2003) 185506. It is found that the Co cluster size distribution can be improved by post annealing. Even at high temperature (700°C), no reaction of Co with Si₃N₄ is observed, indicating that Si₃N₄(0001)-(8 x 8) is a promising substrate for growth of magnetic nanostructures.