| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 91 === We consider the effect of valence electron potential on the equilibrium lattice separation in nanoparticles systems having discrete electronic energy levels and the attractive binding energy Ue of thermally excited valence electrons embedded in a caubic lattice of ions, where the energy of nth level above Fermi energy, can be taken to be Dn(T)=a/d3 , where a depends on the distribution of the level. The variation of the attractive binding energy with unit cell parameter R(T) shows a minimum occurs at Tmin , indicating that the effect on the lattice parameter are different for temperatures below and above Tmin. This crossover from a postive thermal expansion to negative thermal expansion can then be anticipated at Tmin Our lattice temperature depentent experiment of 4 nm Au and Pb particles can be reasonably well fitted by the effect of valence electron potential on the equilibrium lattice separstion, with a weakly temperature dependent level spacing.
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