Resonant Photoemission on Organic Thin Films and Interfaces

有机材料的独特物理性质受到单分子与其局部环境耦合的关键影响。特别是，决定宏观输运特性或光学性质的动态过程受到复杂相互作用机制的影响。最终，对这些机制的微观理解是对系统特性进行特定控制的基础。与完全远程有序固体相比，在凝聚有机体系中各自的机制可能不太清楚地区分，因此需要昂贵的制备和分析方法。本课题将共振光电子能谱（ResPES）应用于有机半导体薄膜电子结构的系统研究。该方法是基于一个核心电子的局部激发。从理论角度理解的诱导多粒子过程具有特征谱信息，可以分别对电子系统或分子系统的动力学性质作出结论。这些许多粒子过程发生在比初级激发小得多的能量尺度上，并且可以包含例如核心空穴的局部筛选，分子间电荷转移或集体振动或电子激发。在这个项目中，我们将具体研究：-在弱结合情况下，respes光谱对外部影响分子的敏感性：respes光谱显示出特有的精细结构，这可归因于激发态与分子振动的耦合。如果在不同的环境中检测分子，即使化学键很弱，这种振动特征也会显示出差异。-通过“核心-空穴时钟”方法的电荷转移过程的时间序列：电子激发后的电荷转移将在薄分子膜、分子/金属界面和异质界面（分子A/分子B）中进行研究。本项目旨在系统研究特定有机分子与周围环境的物理耦合及其对振动和电子激发的影响。它将提高对有机分子材料的微观认识。

The unique physical properties of organic materials are crucially influenced by the coupling of the single molecule to its local surrounding. In particular, dynamic processes, which determine e.g. the macroscopic transport characteristics or the optical properties, are influenced by complex interaction mechanisms. Ultimately, a microscopic understanding of these mechanisms is the basis for a specific control of the system properties. In contrast to perfectly long-range ordered solids, the respective mechanisms can be less clearly distinguished in condensed organic systems, thus requiring expensive preparation and analysis methods. In this project resonant Photoelectron Spectroscopy (ResPES) will be applied for the systematic investigation of the electronic structure of organic semiconductor films. The method is based on the local excitation of a core electron. The induced many particle processes, which are generally well understood from a theoretical viewpoint, bear characteristic spectral information, which allow conclusions on the dynamic properties of the electronic or molecular system, respectively. These many particle processes occur on a much smaller energy scale than the primary excitation and can contain e.g. a local screening of the core hole, intermolecular charge transfer, or collective vibronic or electronic excitations. In this project we will specifically investigate: - The sensitivity of the ResPES-spectra for external influences on molecules in case of weak binding: ResPES-spectra show characteristic fine structures, which can be attributed to the coupling of the excited intermediate state to molecular vibrations. This vibronic signature shows differences if the molecules are examined in different surrounding, even if the chemical bonding is weak. - The temporal sequence of charge transfer processes via the ‘core-hole clock ‘-method: the charge transfer following the electronic excitation will be investigated in thin molecular films, at molecule/metal-interfaces, and at heterointerfaces (molecule A/molecule B). This project aims on the systematic investigation of the physical coupling of particular organic molecules to the surrounding and its effect on vibronic and electronic excitations. It will improve the microscopic understanding of organic molecular materials.