Shape design of supported Au nanorods through morphological evolution: Coalescence, instability, reshaping

The morphological evolution of surface supported Au nanorods, induced by thermal heating, has been examined. This study is focused on the establishment of the connection of the nanorods morphology to the annealing temperature, on the elucidation of the acting microscopic mechanisms and quantitative evaluation of the involved parameters leading to the morphology evolution. In particular, after depositing the nanorods on SiO2 surface, thermal processes were performed to induce their morphological evolution and we pointed out our attention on: a) the study of the morphological evolution of single isolated Au nanorods, which was identified as a reshaping process towards a spherical shape. The morphological analysis led us to establish the correlation between the annealing temperature and the nanorods aspect ratio and to elucidate the basic atomic driving mechanism for the reshaping process;b) the study of the morphological evolution of closely spaced nanorods (forming a film over the substrate surface). The analysis led us to the identification of the mechanisms governing the nanorods joining and evolution in larger architectures which, then, operate a reshaping process.On the basis of the results, we set a general framework for the design of complex morphology nanostructures on surfaces with desired shape and aspect ratio.