Optothermoelectric assembly of plasmonic nanoparticles

Abstract

Reversible agglomeration of plasmonic nanoparticles has a plethora of applications in material science, nanophotonics and life sciences. Very high power density requirement and increased temperature of trapped metal particle make conventional optical tweezers operating in the visible regime an unfavourable choice to achieve reversible plasmonic aggregate. In this thesis, we elaborately study another mechanism, optothermoelectric trapping, with which metal particles can be reversibly aggregated at very low optical power. It relies on the differential movement of ions in a thermal gradient that arises due to the plasmonic heating of a metal nanostructure when illuminated by light. In the thesis, we first discuss preliminaries, chemical synthesis methods and experimental techniques to setup an optothermoelectric trap. Next, through systematic experimentation and analysis, we study the effect of surfactant concentration, power density, and the excitation wavelength on the metal nanoparticle aggregate. We explore the possibility of in-situ surface-enhanced Raman scattering (SERS) with this assembly. This study has laid down the foundation for multiple future research directions. There is an effort towards creating optothermoelectric trap using a single metal nanoparticle. We are also trying to push the limit of in-situ SERS up to the single-molecule level with the plasmonic aggregate.