Time-resolved Temperature Measurements and Thermal Imaging Using Nano-thermometers in Different Environments

Book excerpt: Temperature is one of the fundamental variables which carries thermodynamic information of a system. Temperature sensing and monitoring in a sub-micron scale are crucial to understanding phenomena such as thermal profile, heat dissipation, and distribution and thermodynamic transitions. This dissertation focuses on real-time temperature measurements in the nanoscale regime in various environments. Two erbium-based luminescent nanothermometers were used as temperature sensors: upconverting nanoparticles (NaYF4:Er3+, Yb3+) and AlGaN:Er3+ films. These temperature sensors use the luminescence intensity ratio (LIR) technique which exclusively follows the Boltzmann distribution equation for the calculation of temperature. The upconverting particles were introduced with a new universal calibration method that can overcome the uncertainty issues in extreme environments (such as limited excitation period and short acquisition time). The reliability of the method was confirmed by its application in temperature measurement in an electrospray jet which has a fluid velocity that is changing as it moves towards the tip. We found out the there was a formation of a microcavity at the tip of the cone, where the temperature rise was observed. The findings were supported by time-resolved energy balance equations. Next, we used AlGaN:Er3+ film to study the heat dissipation process in two universal media: air and water. We used our newly developed time-resolved temperature measurement technique and thermal imaging technique (introduced in this dissertation) to investigate the systems. Two gold nanosamples with the various extent of adhesion to the film were used. Both cases showed that heat dissipates faster in the air than in water, but the rate of heat dissipation is faster for the particles that adhered well to the film than to the particles loosely placed on it. Finally, for the ongoing project, we modified our thermal imaging technique to study circular dichroism in chiral gold structures. We mapped the photothermal effect on the gold structures, caused by circular dichroism when illuminated with circularly polarized laser light.