The 'special sites' are separated from each other by typically 3-4 nm and are distributed at random over the surface. It is not clear why specific points on the Si surface should be so beam sensitive, whereas only 1 nm away the surface is very stable under the electron beam. This is at present a mystery that we are still working on. If this problem can be solved then there may be real potential for controlled direct EBL on Si on a nanometre-scale. A model for the hole formation process was proposed, based on the sputtering and desorption of molecules or clusters of MgO, which is strongly suggested by the evidence.
All surfaces contain surface steps.
Surface steps strongly influence catalysis, crystal growth by MBE, etc. The work reported above for Al, Si and MgO demonstrates that 100 keV electrons have a relatively high cross-section for the sputtering of atoms of the exit surface of the specimen. Sputtering should be easier down the edges or corners of surface steps than from flat surfaces since fewer bonds have to be broken. Thus if an intense electron beam is rastered across a specimen, and if the incident electron energy is chosen correctly, surface steps should be removed preferentially leaving the surfaces entirely free from such steps. We have demonstrated this in MgO crystals.