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

本项目旨在研究纳米结构与脉冲激光辐照的相互作用。一方面研究了纳米结构周围电磁场的分布，另一方面研究了电磁场对纳米结构性能的影响，特别是电子通过原子尺寸的接触和金属纳米结构之间可控尺寸的纳米间隙的传递。由于金属尖端的场增强（取决于入射波的极化）可能非常明显，因此在直流-电压特性非线性的情况下，预计会对通过结的电流产生很大的影响。需要解决的一个问题是，在低频非线性结的交流测量中所知道的整流效应是否也存在于光频上。其他可能被研究的效应包括产生表面等离子体，光电流或电子的强非平衡能量分布，以及纳米触点中的光学控制隧道电流。为了量化热膨胀的影响，将研究不同的样品几何形状，如机械可控断结几何中的悬浮纳米桥，以及领结几何中的膜和纳米间隙上的纳米结构。期望的结果是一个模型系统来研究纳米光电机械效应，并探索其作为光机械驱动控制电子输运的工具的适用性。该模型系统具有电偏的等离子体纳米粒子之间的纳米间隙，其精度为1-10 nm，将用于研究等离子体增强因子的极化、强度和波长依赖性及其对机械控制间隙中电子传输的影响。此外，等离子体介导的光化学反应将在横截面为几十纳米的体积中进行（一个案例研究：光聚合）。

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).