INDUSTRIAL UNIVERSITY COOPERATION: Surface and Thin Film Investigations With Low Energy Positrons

利用一种新的超高真空、低能量的自旋极化正电子束，研究金属薄膜、金属和半导体表面的结构、电子和磁性能。将采用两种主要技术：从表面重新发射的正电子的能量和角度分辨光谱；而表面电子被（自旋极化）正电子捕获形成正电子。电子性质（正电子功函数、电子激发和平均自由程）和磁性性质（表面临界指数和各向异性）将作为薄膜厚度和衬底组成的函数，随着薄膜从二维特征发展到三维特征。这两种技术对表面和近表面缺陷处的正电子捕获也很敏感，因此也可以研究负载薄膜的结构特性（表面粗糙度、岛状结构、成核密度、界面相互扩散）。最终，目标是将上述技术整合到扫描正电子微探针中，以允许薄膜和表面现象的成像空间分辨率低于1微米。薄膜和表面表现出的特性与材料的本体特性截然不同。这种差异可以在化学催化、磁性薄膜和摩擦学涂层等不同领域产生巨大的技术机会。

The structural, electronic, and magnetic properties of thin metal films and metallic and semiconductor surfaces will be investigated with a new ultra-high vacuum, low energy beam of spin-polarized positrons. Two principal techniques will be employed: energy and angle resolved spectroscopy of positrons re-emitted from surfaces; and surface electron capture by (spin- polarized) positrons to form positronium. The electronic properties (positron work function, electronic exitations, and mean free paths) and magnetic properties (surface critical exponents and anisotropies) will be studied as a function of film thickness and substrate composition as the film evolves from 2- dimensional to 3-dimensional character. Both techniques are also sensitive to trapping of positrons at surface and near surface defects and thus structural properties (surface roughness, island formation, nucleation densities, interface interdiffusion) of supported thin films can be studied as well. Ultimately, the goal is to incorporate the above techniques into a scanning positron microprobe to allow imaged spatial resolution of thin film and surface phenomena below 1 micron. Thin films and surfaces exhibit properties that can be distinctly different from a material's bulk properties. Such differences can produce great technological opportunities in such diverse areas as chemical catalysis, magnetic films, and tribological coatings.