Study of nucleation and growth mechanism of the metallic nanodumbbells

We propose a general nucleation and growth model that can explain the mechanism of the formation of CoPt(3)/Au, FePt/Au, and Pt/Au nanodumbbells. Thus, we found that the nucleation event occurs as a result of reduction of Au(+) ions by partially oxidized surface Pt atoms. In cases when Au(3+) is used as a gold precursor, the surface of seeds should be terminated by ions (e.g., Co(2+), Pb(2+)) that can reduce Au(3+) to Au(+) ions, which can further participate in the nucleation of gold domain. Further growth of gold domain is a result of reduction of both Au(3+) and Au(+) by HDA at the surface of gold nuclei. We explain the different ability of CoPt(3), Pt, and FePt seeds to serve as a nucleation center for the reduction of gold and further growth of dumbbells. We report that the efficiency and reproducibility of the formation of CoPt(3)/Au, FePt/Au, and Pt/Au dumbbells can be optimized by the concentration and oxidation states of the surface ions on metallic nanocrystals used as seeds as well as by the type of the gold precursor.