We study the formation mechanism and microstructure of nickel (Ni) atomic aggregates on the silicone oil surfaces by atomic force microscopy (AFM). Initially, the deposited atoms nucleate and form the compact dusters on the liquid surfaces. Then they perform Brownian motion and adhere upon impact. Finally the branched aggregates are formed. The Ni aggregates exhibit granular structure. The mean size of the granularities in the aggregates is of the order of 10 nm and it decreases with the nominal film thickness. The experiment shows that the Ni aggregates perform a directional diffusion towards the sample edge. The interpretation for this phenomenon is presented.