衬底上原子级凸起对隧道结中分子发光的影响

Inuence of Atomistic Protrusion on the Substrate on Molecular Luminescence in Tunnel Junctions

扫描隧道显微镜诱导发光可以用于研究单分子的各种光电现象,理解所涉及的基本光物理机制.为了清楚地观察具有分子特征的发光,提高分子在金属纳腔中的量子效率非常重要.本文采用电磁学模拟的方法,从理论上研究了在银纳腔中衬底上原子级凸起对平行于衬底的点偶极发射特性的影响.这种衬底凸起结构可以大幅提高水平偶极发光体的量子效率,具有跟针尖尖端带有原子级凸起的情况类似的增强效应.本文还考察了在针尖和衬底都具有原子级凸起的双凸起隧道结结构,并发现这种结构与没有凸起情况相比,确实提供了显著增强的发光,但与单凸起的情况相比,似乎没能进一步提高量子效率.这些结果对今后的单分子扫描隧道显微镜诱导电致和光致发光研究具有指导意义.

Scanning tunneling microscope(STM)induced lu-minescence can be used to study various optoelec-tronic phenomena of single molecules and to under-stand the fundamental photophysical mechanisms involved.To clearly observe the molecule-speci c luminescence,it is important to improve the quan-tum eciency of molecules in the metallic nanocav-ity.In this work,we investigate theoretically the inuence of an atomic-scale protrusion on the sub-strate on the emission properties of a point dipole oriented parallel to the substrate in a silver plas-monic nanocavity by electromagnetic simulations.We nd that an atomic-scale protrusion on the substrate can strongly enhance the quantum eciency of a horizontal dipole emitter,similar to the situation with a protrusion at the tip apex.We also consider a double-protrusion junction geometry in which there is an atomic-scale protrusion on both the tip and the substrate,and nd that this geometry does provide signi cantly enhanced emission compared with the protrusion-free situation,but does not appear to improve the quantum ef-ciency compared to the mono-protrusion situation either at the tip apex or on the substrate.These results are believed to be instructive for future STM induced electroluminescence and photoluminescence studies on single molecules.