Molecular Orbital Tomography: Organic Interfaces and Surface Reaktions

分子的性质受最高占据轨道和最低未占据轨道的影响。因此，这些轨道的空间分布的成像在科学上是非常有趣的。最近，角分辨光电子能谱（ARPES）已经建立了实验访问这个空间轨道信息。与其他技术如高次谐波产生、电子动量谱或扫描隧道显微镜相比，ARPES的这种分子轨道层析成像具有重要的优势，例如，更快的数据采集。ARPES的理论描述通常是复杂的。然而，使用平面波近似的最终状态，它可以被带入一个简单的形式，这使得角度依赖的ARPES强度分布作为各自的分子轨道的傅里叶变换。这种方法允许直接将分子轨道与ARPES测量结果联系起来，从而解释实验数据。自2014年以来，在DFG资助的SCHO 1260/4-1项目中，我们在过去的两年半中取得了非常成功的工作，部分成果已经在六份出版物中发表。这些结果和特别及时的主题提供了几个链接，为这个继续的建议，其中以下调查的目的：（一）方法方面：限制的应用程序的平面波近似：的限制-轨道层析成像直接连接到近似的最后状态的平面波。有迹象表明，在某些能量的出射电子偏离这个平面波的最终状态。在这个子项目中，光子能量和角度相关的数据将被记录在一个大的动量和能量区域，以区分和量化相邻原子上的前向散射，后向散射或衍射的可能贡献。此外，还将在模型系统C60上测试轨道层析成像对非平面系统的适用性。由于该分子的球形对称性，在这种情况下预期散射效应的显著影响。(ii)轨道层析成像技术在特殊系统中的应用：高能量分辨率的轨道成像：在振动激发的情况下，分子骨架的运动导致电子波函数几何分布的变化。为了在真实的空间中对这些扭曲的轨道进行成像和相位重建，我们计划对弱耦合、低对称性的分子进行实验。分子-分子-界面的杂化及其对轨道的影响：通过轨道层析术，我们将研究分子-分子-界面可能的新杂化态，这将对理解有机半导体材料中的掺杂有重要的贡献。

The properties of molecules are crucially influenced by the highest occupied and lowest unoccupied molecular orbitals. Imaging of the spatial distribution of these orbitals is thus scientifically highly interesting. Recently angle resolved photoelectron spectroscopy (ARPES) has been established to experimentally access this spatial orbital information. Against other techniques like higher harmonics generation, electron-momentum spectroscopy or scanning tunneling microscopy this molecular orbital tomography by ARPES has essential advantages such as, e.g., a faster data acquisition. The theoretical description of ARPES is generally complicated. However, using a plane-wave approximation for the final state it can be brought into a simple form, which renders the angle dependent ARPES intensity distribution as a Fourier transform of the respective molecular orbital. This approach allows rather directly connecting the molecular orbital with the ARPES measurement and thus interpreting the experimental data. Within the project SCHO 1260/4-1, funded by the DFG since 2014, we have been able to work very successfully in the last 2½ years and parts of the achieved results have been published already in six publications. These results and the particular timeliness of the topic provide several links for this continuation proposal, in which the following investigations are intended:(i) Methodological Aspects: Limitations for the Application of the Plane-Wave-Approximation:The limitations of -orbital tomography are immediately connected to the approximation of the final state by a plane wave. There are indications for deviations from this plane wave final state at certain energies of the outgoing electrons. In this subproject photon energy- and angle-dependent data will be recorded over a large momentum and energy region to distinguish and quantify possible contributions from forward scattering, back scattering, or diffraction on neighboring atoms. The applicability of orbital tomography to non-planar systems will furthermore be tested on the model system C60. Due to the spherical symmetry of this molecule a pronounced influence of scattering effects is expected in this case.(ii) Application of Orbital Tomography to Particular Systems:Imaging of orbitals with high energy resolution: In case of excitation of vibrations the motion of the molecular backbone leads to a change of the geometric distribution of the electronic wave function. To image these distorted orbitals in real space and reconstruction of the phase, experiments on weakly coupled, low-symmetric molecules are planned.Hybridization at molecule-molecule-interfaces and its influence on orbitals: By means of orbital tomography possible new hybrid states at molecule-molecule-contacts will be investigated, which will crucially contribute to the understanding of doping in organic semiconductor materials.