Fig. 4. Casting Ag and Au NPs with prescribed cross section shapes.

In (A) to (D), the top row shows the design and the bottom row shows the TEM images of the empty barrel (left), the seed-decorated barrel (middle), and the fully grown NP (right). In the top row of each panel, a small purple dot represents a Au seed. Cast Ag NP is shown in yellow and Au NP is shown in orange. (A) A Ag NP with a 25 nm equilateral triangular cross section. See figs. S32, S42, and S56 for large-field-of-view images. (B) A Ag NP with a 22 nm – 24 nm – 28 nm right-angled triangular cross section. See figs. S34, S43, and S58 for large-field-of-view images. (C) A Ag NP with a 25 nm circular shape cross section. See figs. S36, S44, and S59 for large-field-of-view images. (D) A Au NP with 19 nm by 14 nm rectangle cross section. See figs. S23, S39, and S61 for large-field-of-view images. (E) EELS measurement for a Ag NP with a 25 nm equilateral triangular cross section [black, as in (A)] and a Ag sphere with 25 nm diameter circular cross section [red, as in (C)]. (F) The simulated EELS amplitude map for the dipolar resonant modes for a Ag NP with a 25 nm equilateral triangular cross section [as in (A), left] and a Ag NP with 25 nm diameter circular cross section [as in (C), right]. Colors represent simulated amplitude. The white and black dashed lines show the contour of the NP and the DNA mold, respectively.