Clean, H-induced and N-induced reconstructions of the (100) surface were studied by means of surface core-level spectroscopy. It was found that the clean and N-induced shifts were consistent with a simple local re-structuring of the surface layer which was based upon coordination numbers. On the other hand, the H-induced reconstruction involved an anomalously large surface core level shift; all the way to the high binding-energy side of the bulk peak. The latter result was compatible with an inward displacement of the surface potential barrier. The cause of this inward displacement was unknown.

K.G.Purcell, J.Jupille, D.A.King: Surface Science, 1991, 251-252, 660-3