Al2O3(11(2)over-bar0) surface as a template for the ordered growth of Ni and Co nanoclusters

Abstract

The morphology and thermal stability of Ni and Co nanoclusters grown by physical vapour deposition on a reconstructed (11 (2) over bar0) surface of alpha-Al2O3 is investigated using non-contact atomic force microscopy (NC-AFM). NC-AFM images reveal that the clean alpha-Al2O3(11 (2) over bar0) substrate adopts a characteristic (12 X 4) reconstruction when prepared in vacuum at high temperature. Subsequent deposition of Ni and Co onto this substrate at room temperature facilitates the growth of well-ordered metal nanocluster arrays with a preferred inter-cluster distance determined by the (12 X 4) periodicity of the substrate surface. The order in the cluster arrangement remains intact even upon annealing the system to temperatures up to 500 degrees C indicating a high resistance against sintering. The reconstructed alpha-Al2O3(11 (2) over bar0) surface can, therefore, serve as an appropriate insulating template for studies of size-dependent magnetic or catalytiWc effects in a well-defined ensemble of metallic nanoclusters.