Crystalline clusters of Bi and Sn with the diameters ranging from 100 to 5 nm were prepared by in situ evaporation on to different kinds of substrates in a transmission electron microscope. These metal clusters were then heated to the molten state and behaviour of the metal liquid clusters observed in situ in the transmission electron microscope. The contact angle of liquid clusters of Bi and Sn on different kinds of substrates changes as a function of the size of liquid metal clusters. It was concluded that the interfacial energy between the substrates and liquid metals depends on the size of liquid metal clusters and changes significantly at around 20 nm. (c) 2006 Springer Science + Business Media, Inc.