Acquisition of a Low Energy Electron Microscope (LEEM)

该项目将向亚利桑那州立大学提供一台商用低能电子显微镜(LEEM)。它将是设在美国大学的两个这样的工具之一。该仪器将安装在物理大楼内，紧挨着NSF支持的高分辨率电子显微镜中心，将补充扫描隧道显微镜和电子显微镜。LEEM有几个特点与其他显微镜不同：(A)它使用能量很低的照明束，约为10 eV；(B)低束能通常低于电子刺激脱附的阈值，并且几乎不会对表面造成损害；(C)它使用静态光束而不是扫描束，因此以并行探测模式运行，从而能够以5纳米的横向分辨率以视频速率实时成像表面动力学过程。物理和天文学系表面科学研究小组提出了几个实验，旨在实时研究表面过程的动力学，如温度变化和/或吸附覆盖引起的表面重建和相变，表面化合物的形成和外延生长，外加应力引起的台阶运动，以及缺陷结构和缺陷密度对薄膜形核和生长的影响。他们在LEEM中观测到的理论模型和模拟将补充实验工作，以实现对表面过程的充分理解。

This project will provide a commercial Low Energy Electron Microscope (LEEM) to Arizona State University. It will be one of two such instruments located at Universities in the United States. The instrument will be located in the Physics building, next to the NSF supported Center for High Resolution Electron Microscopy, and will complement the scanning tunneling microscopes as well as the electron microscopes. Several features distinguish the LEEM from other microscopes: (a) it uses very low energy illuminating beam, about 10 eV; (b) the low beam energies are usually below the threshold of electron stimulated desorption and do practically no damage to the surface; (c) it uses a static rather than a scanning beam, and thus operates in a parallel detection mode which allows real-time imaging of surface kinetic processes at video rates with a lateral resolution of 5 nm. The surface science research group in the Department of Physics and Astronomy has proposed several experiments aimed at studying the dynamics of surface processes in real time, such as surface reconstructions and phase transitions induced by temperature change and/or adsorbate coverage, surface compound formation and epitaxial growth, step motions induced by externally applied stress, and influence of defect structure and defect density on nucleation and growth of thin films. Theoretical models and simulations of their observations in the LEEM will complement the experimental effort in order to achieve a full understanding of the surface processes.