Morphological evolution of silver nanoprisms in presence of halide ions under photoexcitation of LSPR modes

Silver nanoparticles exhibit localised surface plasmon resonance (LSPR) in the visible region of the electromagnetic spectrum owing to collective oscillation of free electrons under incident electromagnetic fields. The LSPR profile of silver nanoprisms can be tuned through visible and near infrared regions by controlling the morphology (edge length, thickness) of the prisms. Excitation of these LSPR modes has remarkable consequences such as near Efield enhancement, hot electron injection and photothermal heating. These effects can be used to drive chemical transformations on or close to nanoparticle surfaces. Silver nanoparticles are etched readily by halide ions, with etching occurring predominantly on the high surface energy {100} and {110} facets, while the lower surface energy {111} basal planes are relatively unaffected. By selectively exciting the different LSPR modes of Ag nanoprisms, we show that the etching by halide ions can be spatially biased either at the nanoprisms tips or the edges. We further investigate the kinetics of the reaction of the Ag nanoprisms with halide ions (X= Cl-, Br-, I-) at varying Ag:X molar ratios and under different photoexcitation conditions to demonstrate how the interplay between halide ion etching and LSPR excitation can be creatively utilised to tune the morphology and consequently optical properties of Ag nanostructures. The ability to sculpt the nanostructures has applicability in generating plasmonic and chemical hotspots with potential application in sensing (e.g. SERS) and plasmon-driven surface-confined chemical reactions.