Published in Phys. Rev. Lett. 106, 067601 (2011).

Co-existence of negatively and positively buckled isomers on n+ doped Si(111)-2x1

G.Bussetti,1 B.Bonanni,1 S.Cirilli,1 A.Violante,1 M.Russo,1 C.Goletti,1 P.Chiaradia,1 O.Pulci,2 M.Palummo,2 R.Del Sole,2 P.Gargiani,3 M.G. Betti,3 C. Mariani,3 R.M. Feenstra,4 G. Meyer,5 and K.H. Rieder6
1Dipartimento di Fisica, NAST and CNISM, Università di Roma ‘Tor Vergata’, via della Ricerca Scientifica 1, 00133 Roma, Italy
2Dipartimento di Fisica, NAST, ETSF and MIFP, Università di Roma ‘Tor Vergata’, via della Ricerca Scientifica 1, 00133 Roma, Italy
3Dipartimento di Fisica and CNISM, Università di Roma, ‘La Sapienza’, Roma, Italy
4Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
5IBM Research Division, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland
6Department of Chemical Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany


A long-standing puzzle regarding the Si(111)-2x1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angleresolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps co-exist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results.

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