Spontaneous dissolution at room temperature of gold nanoparticles

We have studied gold nanoparticles evaporated on NaCl. We examined the sample before and after an annealing at room temperature for seven months. We found that most of the small particles with square shape disappear after the annealing. Many of the particles remaining correspond to multiple twinned particles (MTP), i.e., particles with icosahedral or decahedral shapes. We also found that the size of the icosahedral and decahedral particles did not change with the room-temperature annealing. The only consistent explanation is a spontaneous dissolution of the square-shaped nanoparticles at room temperature. This indicates that the binding energy of the atoms in such particles is much lower than the bulk value. The reason why such a particle would rather be dissolved instead of undergoing quasimelting is not clear. Room-temperature dissolution of square-shaped particles is another example of nanoparticles instability.