Theoretical foundations for size and shape selective laser-based manipulation of supported metal nanoparticles

Tigran Vartanyana, Johannes Bosbachb, Christian Hendrichb, Frank Stietzb, Frank Trägerb
aState Optical Institute, St. Petersburg, Russia; bFachbereich Physik, Universität Kassel, Germany

Abstract
We demonstrate that laser-based thermal processing of an ensemble of metal nanoparticles on a transparent substrate can be highly selective with regard to the dimensions of the particles. The selectivity originates from the resonant dependence of the absorption cross section for surface plasmon excitation of a metal nanoparticle on its size and shape. This makes possible resonant heating by selective absorption and subsequent rapid quenching of the deposited energy by electron-phonon coupling. As a result, the temperature rise of a nanoparticle is determined by the absorbed photon energy and by the thermal properties of the substrate rather than by the heat flow between the particles, provided their number density and the laser pulse duration are properly chosen. Finally, desorption and diffusion activated by the temperature rise cause substantial changes of the particle size and shape. These laser-induced modifications are even more selective than laser-stimulated heating due to a threshold-like dependence of the thermally activated processes on the temperature of an individual particle. Altogether this can be exploited in a novel technique to control the size and shape distribution of supported metal nanoparticles through laser illumination in a very precise manner. Here, we present a detailed theoretical treatment of all aspects of selective laser-induced thermal processing of nanoparticles.

Keywords: Nanoparticles; laser processing; ultrafast electron dynamics; spectral hole burning; surface plasmon; dephasing time, © SPIE