Optothermal Effect Of Plasmonic Nanostructure And Applications

In recent years,metal nanostructures have attracted a lot of attention due to their unique optical properties caused by surface plasmon polaritons.Surface plasmons are hybrid modes of free electrons and light at metal-dielectric interfaces.The wavelength of its resonance peak can be regulated by changing the size,shape and material of the nanostructure.Particularly,the local electromagnetic fields can be greatly enhanced at the resonance frequency.This resonance effect makes metal nanostructures an efficient nanoscale broadband light absorber with extraordinarily strong photothermal effects.Today,photothermal effects have found many important applications,such as cancer treatment,solar energy utilization,photothermal imaging and so on.Thermal properties at the nanoscale define the performance of modern processors and thermoelectric nanomaterials,and affect the performance of sensors.Therefore,the study of heat transfer processes and temperature measurements at the nanometer scale is crucial.In this paper,heat transfer phenomena were investigated in different metal nanostructure systems.We also discussed the application in biochemical detection,and scanning probe microscope based nano-thermometer.In the introduction,brief introductions are provided on the principle and related applications of plasmon polaritons,current nanoscale local temperature characterization methods and a commercial finite element method solver,COMSOL Multiphysics.In the second chapter,we systematically studied the optothermal effects and the application of high efficiency optical absorber Au/AAOs on surface-assisted laser desorption/ionization mass-spectrometry(SALDI-MS).The light absorption and the temperature under laser irradiation were measured,and we found that Au/AAOs with larger diameter had better light absorption and photothermal conversion efficiency.Theoretical analysis indicate that the local high temperature is largely caused by the pore size dependent light absorption,thermal conductance and thermal capacity of the Au/AAOs.These optical and thermal properties make the large aperture Au/AAO a promising substrate for SALDI-MS.In the measurement of neurotensin,we obtained a signal with a signal-to-noise ratio of 394,which is 4 times better than the result obtained using the conventional MALDI-MS technique.In addition,we found that the Au/AAO sample with larger pores shows much less fragmentation of the analyte in SALDI-MS measurements than the case with smaller pores.In the third chapter,we investigated the heat transfer of the tip-sample coupled system of a scanning probe thermal microscope.The results indicate that there is a considerable temperature difference between the measured temperature and the undisturbed sample,and this temperature different is sensitive to multiple parameters of the system,including the size of the tip,tip-sample gap,heating power and the dimension of the heat source.Particularly in the case of a small heat source,large discrepancy(up to 30%)is found between the measured results and the temperature of the unperturbed heat source.To understand the numerical result,a simplified model is constructed,and we show that the temperature discrepancy between the perturbed and unperturbed system can precisely predicted using an explicit formula.