Modeling the preferred shape, orientation and aspect ratio of gold nanorods

It has been widely shown that gold nanorods produced via a variety of methods may have average aspects between ∼2-40, depending on the synthetic conditions, and other thermodynamic considerations. This is significant, since the optical properties are highly dependant on the aspect of the nanorods. Furthermore, the number of different shapes and axial orientations produced depend partially on the aspect ratio, which clearly indicates that the relationship between shape, orientating and aspect is also significant. Presented here are the results of a systematic study of this relationship, using 30 candidate nanorod structures and an analytical shape-dependent thermodynamic model with input from relativistic first-principles calculations. The results show that gold nanorods with principle axes in the ±[011] orientation are energetically preferred over alternative ±[001] and ±[111] orientations (under ambient conditions), but that the stability of the ±[111] orientation increases significantly with both aspect and temperature, in agreement with other experimental and computational studies on selected types of structures reported in the literature.