Laser-irradiated (100) surfaces were studied by using an ultra-high vacuum scanning tunnelling microscopic system. The results indicated that only the dimerized outermost atomic layer was removed when the laser fluence was below the melting threshold at photon energies that were higher than the band gap. However, the newly exposed layer did not have a dimerized atomic structure but instead resembled that of a bulk-terminated structure. The revealed layer remained atomically smooth (with no vacancies) even when 90% of the outermost layer was removed. It was suggested that a possible explanation of the results was that atom removal occurred via preferential breaking of the atomic bonds in defect sites. When the laser fluence was increased to levels that were above the melting threshold, extensive surface roughening occurred.

J.Xu, S.H.Overbury, J.F.Wendelken: Journal of Vacuum Science and Technology B, 1996, 14[2], 918-24