Synthesis and stability of indium nanoclusters formed in silica by ion implantation

In this work, we report on the synthesis of indium crystalline nanoparticles by ion implantation of In2+ ions (2 × 1017In2+/cm2, 320 keV) in silica. The thermal stability of the nanoparticles is investigated during a post-implantation thermal annealing cycle in vacuum by means of in situ techniques based on X-ray diffraction (XRD) and transmission electron microscopy (TEM). The measurements were carried out in a temperature range from room temperature up to 473 K, which is above the bulk melting point of In (429.8 K). The experimental results demonstrated that the In nanocrystals embedded in the silica matrix exhibit a range of melting temperatures between a lower limit of 423 K corresponding to a melting point depression of 7 K and an upper limit of 443 K corresponding to a superheating of 13 K. During the thermal cycle, all the particles remain stable in their positions and no clusters growth was observed. When the sample was cooled down a remarkable supercooling was observed, indicating the presence of a hysteresis cycle.