Growth Inhibition of Hexagonal Silver Nanoplates by Localized Surface Plasmon Resonance

Characteristic light absorption occurred in silver citrate solution irradiated by ffionochromatic visible light above a threshold fluence (Phi(thes)) due to the localized surface plasmon resonance (LSPR) of hexagonal silver nanoplates. The peak energy of the predominant absorption (E-hex) at Phi(thes) was nearly the same as the incident energy (E-irrad) and showed a slow decrease with the fluence (Phi). Transmission electron microscopy indicated that the edge length of the hexagons (D-hex) increased from 25 to 58 nm with a decrease in E-hex, but the thickness was constant at about 8 nm despite the difference in D-hex. The slow decrease in E-hex with Phi suggests gentle planar growth of the hexagonal nanoplates. When E-irrad switched successively from 2.34 to 2.46 eV during light irradiation, the slow decrease in E-hex. with Phi showed a temporal stagnation. Thus, the LSPR acted as an inhibitory agent for the planar growth of hexagonal nanoplates. Some precursors formed below Phi(thes) begin to transform into critical seeds, and the growth of critical seeds is inhibited when the size is sufficient for LSPR excitation by E-irrad. Hence, hexagonal nanoplates are size-selectively formed by monochromatic light irradiation.