Thermo-optical Properties of Gold Nanoparticles: Shape and Size Effects

Plasmonic metal nanoparticles (NPs) have been proposed for many applications because of their fascinating optical properties related to the surface plasmon resonance (SPR) phenomenon. Due to the absorption of incident light, these objects are heated, intentionally or not, which may lead to the modification of their optical properties. In this study, the thermal variations of the absorption and scattering cross-sections of a gold NP are studied for different shapes and sizes. The results reveal that, in general, the SPR peak undergoes a redshift and its magnitude changes with increasing temperature. The maximum thermal variation of the NP optical properties is located around the SPR wavelength. Depending on the size and shape of NPs, these behaviors result in different profiles like valley-peak, valley, or peak, in the thermo-absorption and thermo-scattering spectra around the SPR wavelength. The results show that depending on the size and shape of NP, absorption and scattering cross-section thermal variation at SPR wavelength vary from - 14 x 10-2 to 19 x 10-2% per Kelvin. The thermal response of the differential far-field scattering is also investigated. Once again, the maximum values of the scattered far field and its thermal variation are found around the SPR wavelength, but there is no isotropic behavior; while they are uniform in the plane perpendicular to the incident electric field, they exhibit an angular dependence in the plane including the incident wave vector and electric field.