Plasmonic sensing of heat transfer at solid-liquid and solid-gas interfaces

This dissertation focuses on the development and application of combination of the pump-probe technique and plasmonic nanostructures for the experimental study of heat transfer at solid – liquid interface. We developed the technique to measure i) the heat transfer between solid and liquid that has combination of interface chemistries and liquid compositions and ii) the evaporation / condensation of the refrigerant on Au nanostructures. With the strong transient absorption signals that are created by Au nanostructures, we investigate heat transport of Au nanorods immobilized on a crystalline quartz substrate and immersed in organic fluids. We developed a numerical model to analyze the heat flow from Au nanorods to the surrounding fluid and to the high thermal conductivity solid support. For methanol, ethanol, toluene, and hexane, the thermal conductance of the nanorod / fluid interface falls within a narrow range, 20 < Gf < 40 MW m-2 K-1. Plasmon resonances of Au nanostructures are also sensitive to the index of refraction, and therefore temperature, of the layer of liquid near the interface. The increase in temperature of the liquid near the interface is a more sensitive probe of the interface conductance than the decay of the metal temperature. With Au nanodisks (120 nm diameter x 20 nm height) on fused silica substrates as the heat source and temperature sensor in pump probe experiments, we studied heat transport between Au, self-assembled-monolayers, and liquid mixtures. We developed an analytical model to analyze the heat flow from Au nanodisks to the surrounding fluid. The thermal conductance of the nanodisks / fluid interface for nanodisks coated with a hydrophilic self-assembled monolayer (SAM) of sodium 3-mercapto-1-propanesulfonate is 90 < G < 190 MW m-2 K-1 as the fluid mixture is varied from pure ethanol to pure water. We applied our new approach to test the hypothesis that G is linearly related to the work of adhesion W. For hydrophilic interfaces, W can be varied over a significant range by varying the concentration of ethanol or glucoside in water. For hydrophobic interfaces, we cannot significantly vary W using this approach. The thermal conductance G is largest when the work of adhesion W is greatest, but we do not observe a linear relations ship between G and W. In addition, we report experimental studies of adsorption / desorption phenomena for a system of Au nanodisks coated with hydrophilic / hydrophobic self-assembed monolayer, and pressurized with various pressure of R124. The Au nanodisks are heated by a 100 Hz modulated optical pulse; the thickness change of the adsorbed film on the Au surface is monitored by transient absorption of Au nanodisks. The thickness change of R124 film on the nanodisk coated with a hydrophilic self-assembled monolayer (SAM) increases to ≈ 1.5 Å as the pressure of R124 increase to 25 psi, while the change in the thickness of R124 film for the hydrophobic nanodisks is ≈ 0.9 Å at 25 psi. We relate the difference in the amount of evaporated molecules to the variations in inter-molecular force of each gas