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

在本项目中，我们旨在阐明半导体衬底上有机薄膜生长过程的原子图，为制备高质量的有机薄膜提供有用的知识。根据我们在表征和控制各种半导体和金属表面外延生长方面的经验和技术，我们试图提取有助于实现高质量有机分子束外延(OMBE)的新知识和指导原则。硅基有机半导体等导电软材料作为下一代微电子器件的重要组成部分越来越受到人们的重视。这些软材料不适合用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技术来研究。在这种情况下，高…在本项目中，我们迫切需要灵敏度更高的无电子剂量或极低电子剂量的软探测器，如高分辨率电子能量损失谱(HREELS)、光斑轮廓分析低能电子衍射(SPA LEED)、低能电子显微镜(LEEM)和非接触原子力显微镜(NC-AFM)等具有慢电子束的高灵敏度软探测器。这些新的分析工具对有机薄层是无损的，为我们提供了关于有机异质结构的结构和功能性质的重要信息。在本项目中，我们系统地寻找了高质量生长并五苯覆盖层的良好的无机衬底，如阶梯状硅表面、高折射率硅表面、金属单层涂层表面等。金属表面的衬底不适合形成陡峭的界面，因为分子平躺着，主要形成无序的润湿层。同样的情况也发生在二氧化硅等绝缘衬底上。我们发现最好的体系是Si(111)-7x7衬底上的铋多层膜，它对分子具有相当惰性的化学性质，但由于它的半金属电子和成键性质，它仍然具有很高的导电性。在该模板表面上，我们发现并五苯在Si(111)衬底上完全外延生长，其微区尺寸在几十微米以上。我们发现了适合于形成p-n有机结、电致发光器件结构等异质外延OMBE的各种有机分子和几种良好的组合。我们认为我们的计划是非常成功的，这为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的应用开辟了一条新的低维功能材料的发展道路。较少

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