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

在前两个资助期研究计划顺利实施的基础上，下一个资助期我们的目标是将抛物面镜辅助近场光学显微镜与扫描隧道显微镜相结合。主要目的是通过尖端增强发光和拉曼光谱研究隧道结中（单）分子的结构、光学和电子特性与偏置电压的关系。更具体地说，我们将调查潜在的基本物理机制，负责从我们的初步工作的新颖和重要的观察。例如：1)化学吸附到金衬底上的分子拉曼光谱随偏置电压的变化；2)隧道结的发光发射和拉曼散射随偏置电压的增强；3)相对位置能级对偏置电压的影响。例如：i) Au底物的最高已占据分子轨道（HOMO）和d带的相对能量排列；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，我们将探讨在什么条件下，从尖端和衬底之间的等离子激元振荡反馈可以导致受激拉曼散射和发光发射。总的来说，我们的目标是更深入地了解控制分子与金属表面相互作用的基本过程，如结合、极化、电荷转移、分子的电子激发和光子从间隙发射，以及附近分子之间的相互作用。本项目所探索的观察结果和机制将在以下领域得到广泛应用：单分子空间分辨率和化学对比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.