Surface-Stress-Driven Lattice Contraction Effects on the Extinction Spectra of Ultrasmall Silver Nanowires

Abstract

We utilize numerical simulations based on the discrete dipole approximation to study the effects of surface-stress-driven lattice contraction on the extinction spectra of silver nanowires with a square cross section of length 2 nm. The novel finding of the present work is the determination that the blue shift that is induced in the silver nanowires due to surface-stress-driven lattice contraction increases with an increase in the nanowire aspect ratio; the blue shift in the longitudinal plasmon resonance wavelength reaches 20 nm in air and 30 nm in water when the nanowire aspect ratio increases to six. Furthermore, we have delineated the lattice contraction effects on the relative contributions of the free (conduction) electrons and the ionic core (bound) electrons to the observed blue shift; specifically, due to the increasingly free electron optical response of the nanowires with increasing aspect ratio, the blue shift due to the contraction-driven increase in the free electron density is found to dominate the red shift due to the increase in the core electron density for larger nanowire aspect ratios. The results collectively indicate that surface-stress-driven lattice contraction plays an important role in blue shifting the longitudinal plasmon resonance wavelength for ultrasmall silver nanowires.