A Study of Plasmon Coupled Emission from Molecules Confined in Plasmonic Nano-Cavities

Abstract

The hot-spots or the region of highly enhanced electric fields between nanostructures possess exciting properties. These cavity structures have electric fields that are highly confined and enhanced. Thus placing a fluorophore in this cavity will result in highly enhanced molecular emission. Depending on the nature of cavity the signals can be enhanced, and the molecular emissions can be re-directed due to the antenna effects of the nanostructures. This thesis addresses plasmon-coupled emission from molecules confined in a one-dimensional plasmonic cavity and the resultant enhancement in fluorescence and directionality of emission. The first chapter introduces the various concepts that are necessary to understand the problems addressed in this thesis. This includes an introduction to plasmonics, different types of plasmons, molecular emission processes and the basic theory of surface plasmon coupled emission. The second chapter deals with the materials and methods used to address the problems. This involves the synthesis of silver nanowires, deposition of gold films and a section on the concepts of Fourier plane imaging. The third chapter deals with the experiments performed on the cavity systems formed by the coupling of silver nanowires and plasmonic films. The molecular emission from a system of silver nanowire placed on a thick mirror is considered. Here the thick film acts as a mirror. The enhancement and polarization dependence of fluorescence and the effects of plasmonic film and the silver nanowire has on the intensity has been studied. This chapter also addresses the surface plasmon coupled emission from molecules confined in the cavity between the silver nanowire and a semi-transparent gold film. Highly directional emission from such kind of system is observed.