The Effect of Surface Irregularities on Ordering

As long as nucleation is an important part of the adsorbate ordering process, surface roughness is likely to play an important role in preparing ordered surface structures. 

It is much easier to investigate the effect of surface irregularities on ordering using stepped crystal surfaces. Unlike in the case of uncontrolled surface defects on a (111) face of an fee metal for example, steps are readily detectable by LEED or FIM. They are likely to be ordered with a well-defined periodicity and surfaces can be prepared in such a way that steps are the predominant highest concentration surface defects. 

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Ideally, this method would be fairly simple to implement on flat specimens. However, all the specimens tested contained significant degrees of warp due to the effects of a vacuum-pressure exposure test. In many specimens, the magnitude of this distortion was several times that of the surface irregularities. Therefore, it was necessaiy to flatten the bondline by fitting a parabolic function to the cup and then subtract the fit from the raw data. Next, the data were sorted in ascending order to produce a cumulative distribution for all measured surface displacements. A thickness tolerance could then be specified to define the bondline region as well as a depth... 

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