Ag（100）表面α-6T分子的自组装和STM诱导发光

Self-assembly of α-6T Molecule on Ag（100） and Related STM Induced Luminescence

利用扫描隧道显微镜诱导发光技术，对有机分子α-6T在Ag（100）表面的自组装和光子发射特性进行了研究．发现在极低的覆盖率下，α-6T分子以四个分予形成一种独特的风车形状的异构体．随着覆盖率的增加，α-6T分子倾向于肩并肩紧密排列形成条纹状结构．进。步增加覆盖率时，分子以低层分了的条纹结构作为模板，一层一层往上生长，在五层分子厚度的样品上，利用光致方法可以获得分子荧光，这说明顶层分子已经被有效脱耦合．然而在同样的样品上，STM诱导发光光谱却只展现出类似等离激元的发射特性．在这种情况下，分子荧光的消失说明了仅仅满足电子脱耦合条件还不足以产生分子荧光．分子动态偶极矩的方向以及分子．金属界面的能级排列对分子荧光的发生可能也是至关重要的，这样分子才可以通过与局域等离激元场有效耦合而被激发，并打开向分子注入空穴的通道，产生分子本征发光．

We have investigated the self-assembly and light emission properties of organic α- sexithiophene （α-6T） molecules on Ag（100） under different coverage by scanning tunneling microscopy （STM）. At very low coverage, the α-6T molecules form a unique enantiomer by grouping four molecules into a windmill supermolecular structure. As the coverage is increased,α-6T molecules tend to pack side by side into a denser stripe structure. Further increase of the coverage will lead to the layer-by-layer growth of molecules on Ag（100） with the lower-layer stripe pattern serving as a template. Molecular fluorescence for α-6T molecules on Ag（100） at a coverage of five monolayers has been detected by light excitations, which indicates a well decoupled electronic states for the top-layer α-6T molecules. However, the STM induced luminescent spectra for the same sample reveal only plasmonic-like emission. The absence of intramolecular fluorescence in this case suggests that the electronic decoupling is not a sufficient condition for generating photon emission from molecules. For intramolecular fluorescence to occur, the orientation of the dynamic dipole moment of molecules and the energy-level alignment at the molecule-metal interface are also important so that molecules can be effectively excited through efficient dipolar coupling with local plasmons and by injecting holes into the molecules.