Experiments with Supersonic Beams as a Source of Cold Atoms

(c) (d)
Figure 3.2: An AFM image of a passivated Si(111) crystal. Image (a) and (b) are
2 μm by2μm regions of the same wafer, 15 minutes and 43 minutes after etching
respectively. Image (a) shows atomically flat regions separated by bilayer steps between
crystal planes, each of which are 3.8 ˚A high. The increased noise seen in image
(b) shows the surface contamination (most likely oxidation) from the additional 28
minutes the wafer spent in atmosphere. The height profiles shown in (c) and (d) are
taken along the white lines in (a) and (b) respectively. The roughness of the crystal
terraces in (a) and (c) are likely noise in the AFM, but the increased roughness seen in
(b) and (d), showing grains approximately 2˚A high, show the increased contamination
of the surface.
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