All-optical control of hybrid plasmonic semiconductor-metal nanostructures

Abstract

This thesis is dedicated to the study of linear and nonlinear properties of closely spaced gold nanoparticle dimers, so-called nanoantennas, and hybrid nanoantenna devices consisting of metals and semiconductors. Coupled nanoparticles are of particular interest for nanophotonics because of their ability to focus light into subwavelength volumes and the associated large field enhancement in the gap.The samples used in this thesis are gold rectangles designed by electron-beam lithography, with both symmetric and asymmetric arms, as well as symmetric closely spaced 100 nm disk dimers which were fabricated by colloidal lithography in combination with angle-dependent evaporation. We investigate the linear interplay of modes in the two arms with Spatial Modulation Microscopy, an experimental technique which results in a measure directly proportional to the extinction cross-section. We find a variety of constructive and destructive interference between different order modes, which we can better understand by comprehensive simulations of antennas, varying the parameter space of gap size (coupling strength) and length-length ratio using advanced numerical methods such as the Fourier Domain Time Difference and the Boundary Element Method. We find that the presence of nonradiative modes is made visible by Electromagnetically Induced Transparency.In order to probe the nonlinear properties of the antennas and their interaction with Indium Tin Oxide substrates, a pump-probe setup is used to get an insight into ultrafast nonlinear response with picosecond resolution. These measurements (and corresponding fits using numerical simulations) lead us to identify a new energy transfer mechanism where fast electrons are injected from the nanoparticles into the semiconductor, resulting in a refractive index change due to heating of the surroundings. In follow-up experiments, we find this mechanism to be universal (and versatile) for other types of transparent conductive oxides. These results open new avenues towards application of nanoantennas for ultrafast switching