Near Field Nanoscale Temperature Measurement Using AlGaN:Er³⁺ Film via Photoluminescence Nanothermometry

Abstract

In this chapter we present a new optical temperature measurement and thermal imaging technique combining near-field microscopy and Er³⁺ photoluminescence spectroscopy. The technique is used with two different approaches towards local temperature measurement and thermal imaging. In the first approach, gold nanostructures on top of Al_0.94 Ga_0.06 N thin film embedded with Er³⁺ ions are optically excited through the SNOM tip with 532 nm CW laser to generate thermal images with the spatial resolution comparable to the true size of the nanostructures. In the second approach, nanostructures on top of thermal sensor film are excited with 532 nm CW laser through the substrate with a large spot size (FWHM ~ 10 µm). The Er³⁺ emission from the film is collected in transmission mode through the SNOM tip. In this chapter the steady state temperature change under optical illumination is measured for different sized clusters made from 40 nm diameter gold nanoparticles and it is found that the maximum temperature change and temperature decay length (r_1/2) into the surrounding medium increases linearly with cluster radius. Based upon this observation, we can conclude that if a large cell is embedded with optical heaters with a distance between heaters that allows for collective heating, then the thermal profile outside of the cell decays with a decay constant that is dependent upon the size of the cell. This chapter is reprinted (adapted) with permission from Nanoscale, 2017, 4(7), pp 1864–1869. Copyright 2017 Royal Society of Chemistry.