Thickness Induced Structural Phase Transition of Gold Nanofilm

Transition of gold (001) nanofilm to a (111) was observed in an ultrahigh vacuum electron microscope. The critical thickness of the nanofilm was measured by electron holography to be eight atom layers. These nanofilms ranged from 2 to 20 nm in length. Analyzing the nanofilms by high resolution electron microscopy and electron diffraction, the lattice spacing of the film was isotropically compressed by $3.1%$-- $3.6%$, similar to a hexagonal lattice in 5×20 surface reconstruction. The experiments show that the nanofilm structure is dominated by surfaces.