Tip-enhanced near-field optical microscopy with a parabolic mirror microscope: Enhancing luminescence emission and Raman scattering by inelastic tunneling

在成功落实前两个资助期的研究计划的基础上，我们在下一个资助期的目标是将抛物面反射镜辅助近场光学显微镜与扫描隧道显微镜相结合。主要目的是用尖端增强发光光谱和拉曼光谱研究隧道结中(单)分子(S)的结构、光学和电学性质随偏压的变化。更具体地说，我们将从我们的初步工作中调查导致新的和重要的观测结果的潜在基本物理机制。例如，1)化学吸附在金衬底上的分子的拉曼光谱随偏压的变化；2)隧道结的增强发光和拉曼散射随偏压的变化；3)相对位置能级相对于偏置电压的影响。例如：i)Au衬底的最高占据分子轨道(HOMO)和d带的相对能量排列；以及ii)金属的虚态(拉曼)或最低未占据分子轨道(LUMO)的能级和费米能级。此外，我们将探索在什么条件下，针尖和衬底之间的等离子体振荡反馈可以导致受激拉曼散射和发光。总的来说，我们的目标是更深入地了解分子与金属表面相互作用的基本过程，例如分子的结合、极化、电荷转移、分子的电子激发和从能隙发射光子，以及另一方面附近分子之间的相互作用。本项目中探索的观测和机理将在以下领域得到广泛的应用：具有单分子空间分辨率和化学对比度的光学显微镜和光谱学；高效的单分子光开关和高效稳定的单分子点状光源。

Based on the successful implementation of the research plans of the previous two funding periods, we aim in the next funding period at combining parabolic mirror assisted near-field optical microscopy with scanning tunneling microscopy. The main goal is to investigate the structure, the optical and the electronic properties of (single) molecule(s) in a tunneling junction as a function of bias voltage by tip-enhanced luminescence- and Raman-spectroscopy. More specifically we will investigate the underlying fundamental physics mechanisms responsible for the novel and important observations from our preliminary work. Such as 1) the modification of Raman spectra of molecules chemisorbed to the gold-substrate as a function of the bias voltage; 2) the enhanced luminescence emission and Raman scattering from tunneling junctions as a function of the bias voltage; 3) the influence of the relative position energy levels with respect to the bias-voltage. For instance: i) the relative energetic arrangement of the highest occupied molecular orbital (HOMO) and the d-band of the Au substrate; and ii) the energetic levels of the virtual state (Raman) or the lowest unoccupied molecular orbital (LUMO) and the Fermi-level of the metal. Furthermore, we will explore under what conditions feedback from the plasmon oscillations between a tip and a substrate can lead to stimulated Raman-scattering and luminescence emissinon. In general, we target at a deeper understanding of the fundamental processes governing the interaction of molecules with a metal surface such as binding, polarization, charge transfer, electronic excitation of the molecule and emission of photons from the gap on one hand and the interaction between nearby molecules on the other hand. The observations and the mechanisms explored in this project will find a variety of applications in the following fields: optical microscopy and spectroscopy with single molecule spatial resolution and chemical contrast; efficient single-molecule optical switches and efficient and stable single-molecule point-like light sources.