Femtosecond Time-Resolved Transient Absorption Spectroscopy with Sub-Diffraction-Limited Spatial Resolution Reveals Accelerated Exciton Loss at Gold-Poly(3-Hexylthiophene) Interface
Femtosecond Time-Resolved Transient Absorption Spectroscopy with Sub-Diffraction-Limited Spatial Resolution Reveals Accelerated Exciton Loss at Gold-Poly(3-Hexylthiophene) Interface
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具有亚衍射有限空间分辨率的飞秒时间分辨瞬态吸收光谱揭示了金-聚（3-己基噻吩）界面处的激子损失加速
DOI：
10.1021/acs.jpcc.7b11385
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发表时间：
2018
影响因子：
3.7
通讯作者：
A. Materny
中科院分区：
文献类型：
--
作者：
T. Z. Khan;P. Donfack;M. Namboodiri;M. M. Kazemi;S. Bom;V. Wagner;A. Materny
已知分子在与金属表面接触时会改变性质。因此，半导体中的光诱导分子激子的动力学也预期受到金属接触的影响。这种效果，这是相当大的兴趣，也为应用程序，是有限的界面激子内产生的几个纳米接近的金属层。然而，到目前为止，一个高度本地化的访问这样的激子事件还没有提出，衍射有限的显微光谱学没有产生任何模式的激子动力学以外的散装激子，无论现有的金属界面。在我们的工作中，我们结合了飞秒时间分辨光谱与扫描近场光学显微镜（SNOM）研究的界面动力学的金-聚（3-己基噻吩）系统（Au-P3 HT）利用尖端增强的超短激光脉冲的光场周围的SNOM光纤尖端，收集信号光的黄金边缘。在P3 HT中的自由激子的湮灭旁边，这是在所采用的激光功率下的有效损耗机制，已经观察到在Au-P3 HT界面处的近场范围内高度限制的直接激子衰减。我们表明，发生的金涂覆的SNOM尖端诱导的近场增强的光场允许选择性地访问高度受限的界面激子衰减。实验表明，早期的超快损失的电荷对P3 HT变得更快的Au-P3 HT界面，因为一个额外的途径。
Molecules are known to change properties when in contact with metal surfaces. Therefore, dynamics of photoinduced molecular excitons in a semiconductor also are expected to be influenced by a metal contact. This effect, which is of considerable interest also for applications, is limited to interface excitons generated within just a few nanometer proximity to a metal layer. Up to now, however, a highly localized access to such excitonic events has not been presented, and diffraction-limited microspectroscopy did not yield any pattern in exciton dynamics other than that of bulk excitons, irrespective of an existing metal interface. In our work, we have combined femtosecond time-resolved spectroscopy with scanning near-field optical microscopy (SNOM) to study the interfacial dynamics of a gold-poly(3-hexylthiophene) system (Au–P3HT) making use of tip-enhancement of the light fields of the ultrashort laser pulses by a gold rim surrounding the SNOM fiber tip, which collects the signal light. Next to annihilation of free excitons in P3HT, which is an efficient loss mechanism at the laser powers employed, a direct exciton decay highly confined within the near-field range right at the Au–P3HT interface has been observed. We show that the occurrence of the gold-coated SNOM-tip-induced near-field enhancement of the optical fields permits selective access to the highly confined interfacial exciton decay. The experiments reveal that the early ultrafast loss of charge pairs in P3HT becomes significantly faster at the Au–P3HT interface because of an additional pathway.