Figure 4. Growth mechanism analysis for gold nanorods.

a, Simulated growth rate distribution of nanorods in the diffusion-limited regime. The diffusion-limited hypothesis yields a distribution of growth rates not observed experimentally, and incorrectly predicts that 47% of nanoparticles dissolve while 24% grow at a rate too fast to form nanorods. b, Simulated growth rate distribution of nanorods in nucleation-limited regime. The nucleation-limited hypothesis yields accurate predictions of distributions tightly centered about the experimentally observed growth rate. c, High-resolution transmission electron micrographs (HRTEM) of gold nanorods. The end facets exhibit re-entrant grooves, while the side facets are stepped, but relatively smooth by comparison. The grooves are known to catalyze monolayer nucleation, which explains the faster nucleation rate on the {111} facets. See Figure S1 for additional details about re-entrant grooves. d, Experimental length and width of nanoparticles fit to nucleation-limited growth. The curves are the best theoretical fits for anisotropic growth starting from a 4 nm seed (dashed line) and a 7.5 nm seed (solid line). The best fit to data occurs for a seed that begins growing into a rod once it reaches 7.5 nm in diameter.