Order-disorder phase change in embedded Si nanoparticles

We investigated the relative stability of the amorphous versus crystalline nanoparticles of sizes ranging between 0.8 and 1.8 nm. We found that (at variance from bulk systems) at low T, small nanoparticles are amorphous and they undergo an amorphous-to-crystalline phase transition at high T. On the contrary, large nanoparticles recover the bulklike behavior: crystalline at low T and amorphous at high T. We also investigated the structure of crystalline nanoparticles, providing evidence that they are formed by an ordered core surrounded by a disordered periphery. Furthermore, we also provide evidence that the details of the structure of the crystalline core depend on the size of the nanoparticle.