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. 2021 Mar 5;6(10):7034–7046. doi: 10.1021/acsomega.0c06321

Figure 3.

Figure 3

Control over the Pd shell morphology: switching between smooth and rough Pd layers to alter the plasmonic properties. (a) Schematic representation of the Pd overgrowth with increasing Na2PdCl4 concentration, leading to an increase in roughness of the Pd shell. (b) HAADF-SEM images and corresponding EDX intensity maps of Au@Pd@SiO2 NRs grown with 0.18 mM (XPd = 0.14) and 0.83 mM (XPd = 0.39). (c) Measured extinction spectra of the Au@Pd@SiO2 NRs in water, grown with 0–0.83 mM Na2PdCl4 and XPd = 0–0.39. (d, e) Finite-difference time-domain (FDTD)-calculated extinction spectra of Au@Pd@SiO2 NRs with a thin (d) and a thick (e) Pd shell as a function of the Pd packing fraction p of the shell, where p < 1 and p = 1 correspond to a discontinuous and continuous Pd shell, respectively (see the Experimental Section for details). The Au@Pd@SiO2 NRs with a thin and a thick Pd shell correspond to experimental results with 0.083 mM Na2PdCl4 (Au core: 58.5 × 17.7 nm; Au@Pd NR: 60.5 × 19.7 nm) and 0.83 mM Na2PdCl4 (Au@Pd NR: 78.6 × 19.4 nm), respectively. (f, g) HRTEM image and EDX intensity map of Au@Pd@SiO2 NRs with a rough shell morphology before (f) and after (g) thermal treatment for 1 h at 300 °C in H2. See Table S3 for the full set of experimental details.