Surface phase transitions at metal–semiconductor interfaces: a revisit is needed M.E. Da ´vila a , J. Avila a,b , H. Ascolani c , G. Le Lay d , M. Go ¨thelid e , U.O. Karlsson e , M.C. Asensio a,b,* a Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain b LURE, Centre Universitaire Paris-Sud, Ba ˆt. 209 D, B.P. 34, 91898 Orsay Cedex, France c Centro Ato ´mico Bariloche, CNEA, 8400 Bariloche, Argentina d CRMCN-CNRS, Campus de Luminy, Case 913, 13288 Marseille Cedex 09, France e Material och Halvledarfysik, IMIT Electrum 229, 164 40 Kista, Sweden Abstract In this article, we review some of the most recent progress and understanding in the low temperature surface phase transitions at prototypical metal–semiconductor interfaces. We essentially focus on quantitative surface structural information obtained by using a significant variety of specialised techniques for the individual phases of a model system, namely, tin on Ge(1 1 1) substrates. The strengths and limitations of the structural results obtained by using scanning tunnelling microscopy, photo- electron diffraction and surface X-ray diffraction are discussed in relation to their support with respect to possible mechanisms recently invoked in the literature as being at the origin of the phase transition. These investigations show that a large progress has been made in this field, taking into account the very valuable experimental and theoretical contributions provided by different groups. There remain, however, essential unresolved problems, which will be analysed in the light of the limitations of these structural methods and the difficulty presented by the complex adsorbate systems studied. # 2004 Elsevier B.V. All rights reserved. PACS: 79.60.Dp; 71.15.Pd; 68.35.p Keywords: Dynamical fluctuations; Phase transitions; Metal–semiconductor interfaces; Photoelectron diffraction; Surface X-ray diffraction 1. Introduction The origin of surface phase transitions has been a matter of intense dispute among both theoreticians and experimentalists, during the last years [1–3]. This subject has generated an enormous interest due to its impact in a wide variety of fields ranging from technologically key catalytic processes to the com- prehension of some trends observable in high-T c superconductors, besides many other complex beha- viours related to nano-objects, as well as the relation between low dimensional leading materials and cor- relation effects. Particularly, in the field of surface and interface science, the study of phase transitions in simple model systems has resulted in astonishing advances in the last years [4–7]. However, thanks to Applied Surface Science 234 (2004) 274–285 * Corresponding author. Tel.: þ33 1 6446 8012; fax: þ33 1 6446 4148. E-mail address: asensio@lure.u-psud.fr (M.C. Asensio). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.06.001