High Resolution Structural Studies of Single Crystal Metal and Ordered Alloy Surfaces
One of the current challenges faced by surface science is the accurate measurement of the three dimensional structure of surfaces on the scale of hundredths of Angstroms. This thesis describes measurements of the three dimensional geometrical structures of single crystal metal and ordered alloy surface using Medium Energy Ion Scattering with Channeling and Blocking (MEIS/CB). Comparison of the results of this work to results of another high resolution structural probe, Low Energy Electron Diffraction (LEED) intensity analysis, show excellent agreement. This provides the groundwork for the study of more complex surfaces such as ordered alloys and adsorbate covered surfaces. The analysis of each study includes full-crystal Monte Carlo simulations of the MEIS/CB experiment. Surface structural probes are reviewed and two methods of ion detection are discussed and compared. The results can be summarized as follows: (I) Ni(110): Measurements of the first two interlayer spacings (9.0% (+OR-) 1.0% first layer contraction and a 3.5% (+OR -) 1.5% expansion of the second layer) show excellent agreement with the most recent LEED results. Previous discrepancies are explained. (II) Fe(111): Contraction of the first layer with the respect to the bulk is measured to be 20% (+OR-) 5% which is in excellent agreement with the most recent LEED analysis of this surface. (III) NiAl(110): A high sensitivity to the first layer ripple (10% ripple with the Al on top) is reported and a multilayer model is proposed. The present results are in excellent agreement with a recent single layer LEED intensity analysis. (IV) Al(110): MEIS/CB measurements of the Al(110) surface are consistent with the models proposed by LEED studies but suffer in sensitivity because of the fact that the measurements were carried out at room temperature. Simulations are provided which show that the surface sensitivity should be sufficient when the experiment is repeated at 100K. The results of this thesis have advanced the credibility of MEIS/CB as an accurate technique for the determination of three dimensional surface structure of ordered metal surfaces. Furthermore, the results have laid the groundwork for the extending the applicability of MEIS/CB to systems inaccessible to other structural techniques such as LEED intensity analysis.
- Pub Date:
- Physics: Condensed Matter