Atomic Level Characterization of Organic Molecule-Semiconductor Heterostructures by High-resolution Soft Probes

在这个项目中，我们旨在阐明半导体衬底上有机薄膜生长过程的原子图，为制造高质量的有机薄膜获得有用的知识。基于我们在表征和控制各种半导体-半导体和金属-半导体表面外延生长方面的经验和技术，我们试图提取新的知识和指导原则，这些知识和指导原则应该有助于实现高质量的有机分子束外延。导电软材料，如硅衬底上的有机半导体，作为下一代微电子器件的重要组成部分，已经变得越来越重要。这些软质材料不适合通过传统的表面敏感电子探针（如反射高能电子衍射（RHEED））和其他使用电子束或隧道电子的显微镜技术进行研究。在本项目中，我们使用了高灵敏度的慢电子束软探针，如高分辨率电子能量损失谱（HREELS）、斑点分析低能电子衍射（SPA LEED）、低能电子显微镜（LEEM）和非接触原子力显微镜（nc-AFM）。这些新的分析工具对有机薄层无损，为我们研究有机异质结构的结构和功能特性提供了重要的信息。在本项目中，我们系统地寻找了用于并五苯覆盖层高质量生长的良好无机衬底，如阶梯硅表面、高折射率硅表面、金属单层涂层表面等。具有金属表面的衬底不适合形成突发性界面，因为分子是平躺的，大多形成无序的润湿层。同样的情况也发生在绝缘衬底上，比如二氧化硅。我们发现最好的系统是Si(111) -7x7衬底上的Bi多层，它对分子具有相当惰性的化学性质，但由于其半金属电子和键性质，仍然具有高导电性。在该模板表面上，我们发现并五苯完全外延生长在Si（111）衬底上，其畴尺寸范围超过几十微米。我们已经发现了多种其他的有机分子和几种很好的组合，适合于形成p-n有机结，电致发光器件结构等。我们认为我们的项目非常成功，为OMBE的原子表征和精确控制提供了新的知识，从而为未来微电子器件应用的新型低维功能材料的开发开辟了广阔的道路。少

In this project, we aimed at elucidating the atomistic picture of the growth process of the organic thin films on semiconductor substrates to obtain useful knowledge for the fabrication of highquality organic thin films. Based on our experience and techniques for characterizing and controlling the epitaxial growth of various semiconductor-on-semiconductor and metal-on-semiconductor surfaces, we tried to extract new knowledge and guiding principles which should be useful for realizing high-quality organic molecular beam epitaxy '(OMBE). Conductive soft materials such as organic semiconductor on Si substrates has become more and more important these days as a promising building blocks for the next generation microelectronics devices. These soft materials are not suited to be studied by conventional surface-sensitive electron probes such as reflection high-energy electron diffraction (RHEED) and other microscopy techniques using electron beams or tunneling electrons. In this context, high … More -sensitivity soft probes without, or with extremely low electron dose has been strongly desired, In the present project, we utilize high-sensitivity soft probes with slow electron beam such as high-resolution electron energy loss spectroscopy (HREELS), spot-profile-analyzing low-energy electron diffraction (SPA LEED) and low-energy electron microscopy (LEEM) and non-contact atomic force microscopy (nc-AFM). These novel analytical tools are nondestructive against organic thin layers and provides us important information on the structural and functional properties of organic heterostructures. In this project, we have systematically searched for good inorganic substrates for the high-quality growth of pentacene overlayer, such as stepped silicon surfaces, high-index silicon surfaces, metal monolayer coated surfaces, etc. Substrates with metallic surfaces are concluded to be not suited for the formation of abrupt interfaces since the molecules lies down and mostly forms disordered wetting layer. The same happens for the insulating substrates such as silicon dioxide. The best system we found was the Bi multi layers on Si(111) -7x7 substrate, which has rather inert chemical nature against the molecule but still highly conductive due to its semimetallic electronic and bond nature. On this template surface, we have found that the pentacene growth perfectly epitaxially to the Si(111) substrate and its domain size ranges more than a few tens of micrometers. We have found various other organic molecules and several good combinations for the hetemepitaxial OMBE growth which will be suited to form p-n organic junction, electroluminescence device structure, etc. We judge our project as very successful one which provided new knowledge on the atomistic characterization and precise control of the OMBE and thus opens up a wide avenue towards the development of new low-dimensional functional materials for the future microelectronics device application. Less