Highly localized photothermal conversion in two-dimensional Au nanoparticle arrays

Abstract

We have investigated, both theoretically and experimentally, highly localized photothermal conversions in Au nanoparticle array/dielectric layer/Ag mirror sandwiches, namely local plasmon resonators. The depth profile of the optical absorption in the local plasmon resonators was calculated using a simple model comprising homogeneous multilayers. The calculation results show highly localized light absorption in the ∼ 10-nm-thick Au nanoparticles layer (more than 99% of total optical absorption). The photoacoustic measurements, which are sensitive to the surface temperature of the sample, were performed on the fabricated local plasmon resonators. The photoacoustic amplitude of the local plasmon resonator possessing a high optical absorption (A = 0.97) was 15 times larger than the absorbance of the bulk Si wafer (A = 0.67) and 8 times larger than the absorbance of graphite (A = 0.85). These results suggest that the photothermal conversion is localized in the thin Au nanoparticles layer, which enables rapid modulation of the temperature of the surrounding fluid.