Shape transformation of self-assembled Au nanoparticles by the systematic control of deposition amount on sapphire (0001)

The shape and size dependent optical, physical and chemical properties of isotropic and anisotropic gold nanoparticles (Au NPs) have attracted significant research interest for their application in various optoelectronic devices. In this paper, we systematically study the evolution of shape and size of self-assembled Au NPs by the variation of Au deposition amount on sapphire (Al₂O₃) (0001). With sufficient thermal energy (1000 °C) provided, dome shaped Au NPs are fabricated on sapphire based on the Volmer-Weber growth model, due to the isotropic surface energy distribution. Furthermore, we observe the incremental variation of Au deposition amount is responsible for the transformation of isotropic to anisotropic Au nanoparticles (nanocrystals). An anisotropic nanoparticles reflect variant properties in their different crystalline surfaces and thus the utilization of anisotropic nanoparticles can lead to the comparatively high efficiency of related device applications. The addition of Au deposition amount leads to facet formation on the lowest possible energy crystalline planes of NPs such that the orientation of top facet of Au NPs is the (111) plane parallel to the (0001) plane of sapphire. However, due to many other higher index facet formation, the NPs look almost dome shaped at high amounts of Au deposition. Overall, the shape transformation of NPs from dome, truncated hexagonal pyramid, elongated truncated hexagonal pyramid, truncated cone to multifaceted dome is observed along with the variation of Au deposition amount on sapphire (Al₂O₃) (0001).