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The thermal stability of metal nanoparticles is discussed in both melting thermodynamics and interface thermodynamics. Emphases are put on the size and shape dependence of melting temperature, critical size and vacancy-formation energy of both freestanding and embedded metal nanoparticles. The melting temperature depression and superheating phenomena for reported nanoparticle systems are explained. Critical sizes of Fe, Co, Ni metal nanocrystals that the crystals keep their crystallinity are calculated and the corresponding minimum melting temperatures predicted. The vacancy-formation energies of Fe, Co, Ni small particles are also calculated as a reference. Theoretical predictions are consistent with experimental results. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Some potential problems in our recent letter [D. Xie et al., phys. stat. sol. (b) 242, R76 (2005)], which have been pointed out by a comment [W. H. Qi, phys. stat. sol. (b) 242, R129 (2005)] are discussed in detail. Furthermore, the formation enthalpies of nanocrystals are calculated by using the equation of surface energies established in the mentioned letter, and the fact that the predicted formation enthalpy values are consonant with the corresponding experimental results of Mo and W nanocrystals verifies the appearance of the higher surface energy of nanocrystals in return. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple but valid equation for the higher surface energies of metallic nanocrystals is obtained. The calculated values on surface energies of Ag and Au nanocrystals are in excellent agreement with the corresponding newest experimental values. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)