Size-dependent melting and supercooling of Ge nanoparticles embedded in a SiO2 thin film

Melting of Ge nanocrystals embedded in a 20 nm SiO2 film is analyzed using a highly sensitive nanocalorimetric technique. Fast heating rates of ∼5 × 104 K/s between room temperature and 1200 K and cooling rates of 8 × 103 K/s at the onset of solidification are used to probe the phase transitions. A melting point reduction of 125 K with respect to the bulk melting temperature is observed upon heating. A size-dependent supercooling has also been observed with an onset of solidification that ranges from 890 to 935 K depending on the maximum size of the previously melted nanoparticles. For a given nanocrystal size the melting hysteresis is around 225 K.