Local Temperature Determination of Optically Excited Nanoparticles and Nanodots

A thin film of Al0.94Ga0.06N embedded with Er3+ ions is used as an optical temperature sensor to image the temperature profile around optically excited gold nanostructures of 40 nm gold nanoparticles and lithographically prepared gold nanodots. The sensor is calibrated to give the local temperature of a hot nanostructure by comparing the measured temperature change of a spherical 40 nm gold NP to the theoretical temperature change calculated from the absorption cross section. The calibration allows us to measure the temperature where a lithographically prepared gold nanodot melts, in agreement with the bulk melting point of gold, and the size of the nanodot, in agreement with SEM and AFM results. Also, we measure an enhancement in the Er3+ photoluminescence due to an interaction of the NP and Er3+. We use this enhancement to determine the laser intensity that melts the NP and find that there is a positive discontinuous temperature of 833 K. We use this discontinuous temperature to obtain an interface conductance of similar to 10 MW/m(2)-K for the gold NP on our thermal sensor surface.