Effect of surrounding environment on atomic structure and equilibrium shape of growing nanocrystals: gold in/on SiO2

We report on the equilibrium shape and atomicstructure of thermally-processed Au nanocrystals (NCs) asdetermined by high resolution transmission electronmicroscopy (TEM). The NCs were either deposited onSiO2 surface or embedded in SiO2 layer. Quantitative dataon the NCs surface free energy were obtained via theinverse Wulff construction. Nanocrystals inside the SiO2layer are defect-free and maintain a symmetrical equilibriumshape during the growth. Nanocrystals on SiO2 surfaceexhibit asymmetrical equilibrium shape that ischaracterized by the introduction of twins and more complexatomic defects above a critical size. The observeddifferences in the equilibrium shape and atomic structureevolution of growing NCs in and on SiO2 is explained interms of evolution in isotropic/anisotropic environmentmaking the surface free energy function angular and/orradial symmetric/asymmetric affecting the rotational/translational invariance of the surface stress tensor.