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Nanometre-sized (hereafter n-) Pb particles embedded in an Al matrix were prepared by ball milling, and the surface melting behaviour was studied by the internal friction technique using a dynamic mechanical analyser. There is an internal friction peak appearing around Pb melting point and the height of the internal friction peak decreases with the increase of Pb particle size. Surface melting of n-Pb particles accounts for the internal friction peak. The study may throw light on the nature of surface melting in condensed matter physics. In addition, the present work makes a beneficial attempt at exploring internal friction as an experimental method for studying surface melting.

The size effect of materials on the phase structure has been proved by many experiments, and here for the first time, we proposed a size-temperature phase diagram of gallium (Ga). We found that liquid Ga as well as its solid-liquid phase transition (PT) is size dependent. This PT phenomenon was successfully explained in terms of nucleation theory. The size-temperature phase diagram offered a universal phenomenological explanation for the size-related phase selection of Ga. This finding would enrich the general knowledge about the new phenomena induced by the finite-size effect.