Bonding Geometry of Large Pi-Conjugated Molecules on Insulator Surfaces

我们想要确定离子绝缘材料（电介质）表面上大的有机偶联分子的键合几何（吸附位置加上内部结构修饰）。与金属表面相比，迄今为止，关于绝缘体表面大分子的键合几何形状的定量信息很少。这一信息对于一般离子宽禁带材料的分子键的基本理解是必不可少的。它将进一步允许根据实验数据测试密度泛函理论（DFT）对这些系统进行的计算，这不是微不足道的，因为相关的范德华相互作用目前在DFT中通过不同的经验修正来描述。此外，在本项目中获得的结构数据将有助于解释离子表面分子的许多其他实验结果（例如，通过STM，光电发射或光谱学）。特别感兴趣的是模型分子PTCDA在不同碱卤化物（AH）（即NaCl和KCl）表面的吸附。我们的问题是：什么是吸附位点？部分带电分子官能团和表面离子之间的库仑相互作用是什么？这些相互作用对原来的平面分子的扭曲程度有多强？这种键与金属表面上的键又是如何一致的？在方法论方面，该项目将使用低能电子衍射（LEED-IV）和正入射x射线驻波（NIXSW）的强度与能量分析，并结合AH的薄外延膜。LEED-IV技术的应用和开发将与G博士教授（英国雷丁大学）共同进行。将LEED-IV应用于大型有机分子的表面结构需要进一步开发该方法，并使用NIXSW的早期结果进行基准测试。本项目基于申请人的项目成果：pi共轭分子在表面（So407/6-1）上的垂直键合几何，将对其进行描述。

We want to determine the bonding geometry (adsorption site plus internal structural modifications) of large organic pi-conjugated molecules on surfaces of ionic insulating materials (dielectrics). In contrast to metal surfaces, very little quantitative information is available on the bonding geometries of large molecules on insulator surfaces so far. This information is essential for a fundamental understanding of molecular bonding on ionic wide bandgap materials in general. It will further allow for testing density functional theory (DFT) calculations performed for these systems against experimental data, which is not trivial since the relevant van der Waals interactions are presently described in DFT by different empirical corrections. In addition, the structural data obtained in this project will help to interpret results from many other experiments on molecules on ionic surfaces (e.g., by STM, photoemission, or optical spectroscopy). Particular interest is on the adsorption of the model molecule PTCDA on the (100) surfaces of different alkali halides (AH), namely, NaCl and KCl. Our questions are: What are the adsorption sites? What is the role of the Coulombic interactions between partially charged molecular functional groups and surface ions? How strongly do these interactions distort the originally planar molecule, and how does this bonding comply with that on metal surfaces? Concerning the methodology, the project will use the intensity versus energy analysis of low energy electron diffraction (LEED-IV) and normal-incidence x-ray standing waves (NIXSW) in combination with thin epitaxial films of the AH. The application and development of the LEED-IV technique will be conducted together with Prof. Dr. G Held (University of Reading/GB). Applying LEED-IV to surface structures of large organic molecules requires further development of this method and benchmarking using earlier results from NIXSW. This project is based on results of the project: Vertical bonding geometry of pi-conjugated molecules on surfaces (So407/6-1) of the applicant, which will be described.