Evolution from mono-dispersed to mound-like structures of size-selected Ag-nanocluster films

In this report, morphology of the film grown by size-selected Ag-nanoclusters (Ag-NCs) on Si/SiOx is investigated. The size-selected Ag-NCs films are produced by using a gas-aggregation type magnetron based nanocluster source and the size-selection is done by a Quadrupole Mass Filter (QMF). In this experiment we choose Ag-NCs with a diameter of ∼ 4 nm with corresponding mass= 211227 amu and number of atoms, n=1958 atoms/cluster. A constant deposition time of 15 minutes for each sample is chosen, whereas the ion current were varied from 0.3±0.1 nA to 1.6±0.1 nA. The deposited surfaces are investigated by atomic force microscopy (AFM) in tapping mode and scanning electron microscopy (SEM) to get information of height and lateral features of the surfaces respectively. From the observations, it is found that initially the film is mono-dispersed for a cluster-beam current of 0.3±0.1 nA which turns into mound-like structure for higher ion current. The roles of surface diffusion and agglomerations of deposited clusters are discussed for the formation of mound-like structures.