Local Atomic Arrangements at Alloy Surfaces

合金表面的局部原子排列是本研究的主要主题。特别感兴趣的是环境的变化，如重建或面间距垂直于表面或分离，如何影响相变，如有序和聚类。应变在这种反应中起着重要的作用，阿贡实验室的新同步加速器（先进光子源，或APS）的光束线采用了x射线掠射技术。x射线样品在较浅的深度范围内产生漫射散射，在位置敏感探测器中进行分析。从这些数据中得到了短范围的有序参数和畸变。样品包括铝合金的单晶，这些单晶被制备成具有不同可能弛豫的几个面。经过热处理产生区域后，确定浓度与深度的关系，并使用俄歇电子能谱和低能电子衍射来寻找表面重建或松弛的证据。漫射散射随深度的变化被测量，表面结构和位移被建模并与体结构进行比较。对表面结构的了解有助于分析相关现象，如金属合金的腐蚀和裂纹萌生。＊＊＊

9700674 Cohen The local atomic arrangements at surfaces of alloys is the major theme of this research. Of particular interest is how changes in the environment, such as reconstruction or interplanar spacing normal to the surface or segregation ,affect phase transitions such as ordering and clustering. Strain plays an important role in such reactions, and a beam line at Argonne Laboratory's new Synchrotron (the Advanced Photon Source, or APS) is used employing an X-ray glancing incidence technique. The X-rays sample a shallow range of depths producing diffuse scattering that is analyzed in a position-sensitive detector. From these data short range order parameters and distortions are obtained. Samples include single crystals of aluminum alloys that are prepared featuring a few facets with different possible relaxations. After heat treatment to produce zones, concentration profiles vs. depth are determined and Auger electron spectroscopy and low energy electron diffraction are used to look for evidence of surface reconstruction or relaxation. Diffuse scattering is measured vs. depth, and the surface structures and displacements modeled and compared to the bulk structure. %%% An understanding of surface structure aids in analysis of related phenomena, such as corrosion of metal alloys and crack initiation. ***