Sectional area-dependent plasmonic shifting in the truncated process of silver nanoparticles: from cube to octahedron

A silver nanocube with sub-40 nm edge length was truncated by {111} planes and transformed into octahedron gradually. The extinction cross-section spectra corresponding to this process were studied by using the discrete dipole approximation (DDA) method. Non-monotonous shifting (blue shifts first and then red shifts) of the surface plasmon resonance (SPR) bands was observed. It was found that the sectional area of {111} facets could be a new and better factor to characterize the shape-dependent non-monotonous shifting of the SPR. The area of {111} facet increases while the SPR peak red shifts, whereas decreases while the SPR peak blue shifts. Similar results were also observed while an octahedron has been truncated into a smaller cube. The physical mechanism was illuminated by analyzing the local field distribution of the nanoparticles with different truncated ratios. The distance of the charge center was one of the most important reasons to affect the shift of SPR as the sectional area of {111} facet is changed. We believe the sectional area factor could be widely used to investigate the SPR shifting in other kinds of truncated process.