Problems with the use of surface reconstructions as indicators of a well-ordered surface

The presence of sharp surface reconstruction or diffraction spots is often taken as an indicator of a well-ordered surface. We present results obtained using transmission electron microscopy in ultra-high vacuum (UHV) which demonstrate that even if the surface is well-ordered and reconstructed, there may be very high defect concentrations just below the surface of the order of 10h1_1013 cm 2. The key point is that surface ordering takes place via surface diffusion, but the temperatures where this is active are too low to anneal out the near-surface defects through bulk diffusion.