Extreme superheating and supercooling of encapsulated metals in fullerenelike shells.

Nanometer-sized tin and lead crystals exhibit drastically altered melting and solidification behavior when encapsulated in fullerenelike graphitic shells. The melting transitions of encapsulated Sn and Pb nanocrystals are shown in an in situ electron microscopy study to occur at unexpectedly high temperatures, significantly higher than the melting point of the corresponding bulk materials. Atomistic simulations are used to show that the driving force for superheating is a pressure buildup of up to 3 GPa, that prevails inside graphitic shells under electron irradiation.