Coherent Oscillations of Breathing Modes in Metal Nanoshells

Abstract

ABSTRACTWe study coherent oscillations of radial breathing modes in metal nanoparticles with a dielectric core. Vibrational modes are impulsively excited by a rapid heating of the particle lattice that occurs after laser excitation, while the energy transfer to a surrounding dielectric leads to a damping of the oscillations. In nanoshells, the presence of two metal surfaces leads to a substantially different energy spectrum of acoustic vibrations. The lowest and first excited modes correspond to in-phase (n=0) and anti-phase (n=1) contractions of shell-core and shell-matrix interfaces respectively. We calculated the energy spectrum as well as the damping of nanoshell vibrational modes in the presence of surrounding medium, and found that the size-dependences of in-phase and anti-phase modes are different. At the same time, the oscillator strength of the symmetric mode is larger than that in solid nanoparticles leading to stronger oscillations in thin nanoshells.