Thermodynamic properties of supported and embedded metallic nanocrystals: gold on/in SiO2

We report on the calculations of the cohesiveenergy, melting temperature and vacancy formation energyfor Au nanocrystals with different size supported on andembedded in SiO2. The calculations are performed crossingour previous data on the surface free energy of the supportedand embedded nanocrystals with the theoreticalsurface-area-difference model developed by W. H. Qi forthe description of the size-dependent thermodynamicsproperties of low-dimensional solid-state systems. Suchcalculations are employed as a function of the nanocrystalssize and surface energy. For nanocrystals supported onSiO2, as results of the calculations, we obtain, for a fixednanocrystal size, an almost constant cohesive energy,melting temperature and vacancy formation energy as afunction of their surface energy; instead, for thoseembedded in SiO2, they decreases when the nanocrystalsurface free energy increases. Furthermore, the cohesiveenergy, melting temperature and vacancy formation energyincrease when the nanocrystal size increases: for thenanocrystals on SiO2, they tend to the values of the bulkAu; for the nanocrystals in SiO2 in correspondence tosufficiently small values of their surface energy, they aregreater than the bulk values. In the case of the melting temperature, this phenomenon corresponds to the experimentallywell-known superheating process.