Optoelectromechanic effects in nanocontacts: Electric-field enhancement and mechanically driven conductance changes

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This project aims at the investigation of nanostructures interacting with pulsed laser irradiation. One aspect is the distribution of electromagnetic fields around nanostructures, another one the influence of these fields on the properties of the nanostructures, in particular the electron transport through atomic-size contacts and nanogaps of controllable size between metallic nanostructures. Since the field enhancement at metallic tips - depending on the polarization of the incident wave - can be very pronounced, a large influence on the current through the junction is to be expected in those regimes where the dc l-V characteristics are nonlinear. A question to be addressed is whether the rectification effect known from ac measurements with nonlinear junctions at low frequencies also persists at optical frequencies. Other possible effects to be studied include the creation of surface plasmons, photo-currents or a strong non-equilibrium energy distribution of the electrons, and optically controlled tunneling currents in nanocontacts. In order to quantify effects of thermal expansion, different sample geometries like suspended nanobridges in the mechanically controllable break-junction geometry as well as nanostructures on membranes and nanogaps of bowtie geometry will be investigated. The expected outcome is a model system to study nano-opto-electromechanic effects and to explore its suitability as a tool for controlling electronic transport by optomechanical drive. This model system with electrically biased nanogaps between plasmonic nanoparticles made with precision of 1-10 nm will be used to investigate the polarization, intensity, and wavelength dependence of the plasmon enhancement factor and its effects on the electron transport in the mechanically controlled gaps. Also, plasmon-mediated photochemical reactions in the volumes with cross-sections of tens-of-nm will be carried out (a case study: photopolymerization).