Electronic bond rupture of Si atoms on Si(111)-(2  1) induced by 1.16-eV photon excitation E. Inami a , K. Ishikawa a , J. Kanasaki b , K. Tanimura a, * a Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan b Department of Intelligent Materials Engineering, Osaka-City University, 3-3-138 Sugimoto-cho, Sumiyoshi, Osaka 558-8585, Japan Abstract Ascanningtunnelingmicroscopystudyhasrevealedthat1.16-eVphotonexcitationinduceselectronicbondrupture of Si atoms on Si(111)-(2  1) surface. Monovacancy formation at perfect surface sites is the primary step of the structural changes, and it is followed by efficient formation of vacancy clusters with two distinctive forms: a vacancy stringalignedontheSichainone-dimensionallyandavacancyislanddevelopedtwo-dimensionallyonthesurface.The mechanism and kinetics of this photoinduced process is discussed based on the experimental results. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Surface structure, morphology, roughness, and topography; Laser methods; Silicon; Scanning tunneling microscopy 1. Introduction Laser interaction with semiconductor surfaces has been studied extensively, motivated by both applications in material processing and by basic research on the light/matter interaction [1]. As a resultoftheinteraction,changesinsurface-atomic structures are often induced. Recent studies by means of high-sensitive detection of desorbed spe- cies[2–4]andofdirectatomicimagingoftheirra- diated surfaces by scanning tunneling microscopy (STM) [5–9] have proven that electronic processes areprimarilyinvolvedinthelaser-inducedchanges on semiconductor surfaces for laser intensities below the melt threshold. This sensitive structural response under the electronic excitation, which is characteristic of surfaces, is related to some prop- erties of surface structures where the reconstruc- tion is important. However, the origin of the instability is still far from being well understood; more studies for typical surfaces are highly desir- able to clarify the correlation between surface properties and direct consequences of the insta- bility from atomic levels. In this paper, we study the surface-structural changesinducedbylaserexcitationontheSi(111)- surface with (2  1) structure by means of STM. The Si(111)-(2  1), formed upon cleavage of Si crystalsinultra-highvacuum(UHV)conditions,is one of the best-understood reconstructed surfaces [10,11].Thissurfaceischaracterizedbyquasione- dimensional zigzag chains of Si atoms, associated withasubstantialbuckling,onthetop-mostlayer. The buckling is accompanied by a net charge transfer from the down to the up atoms of the chains, inducing a significant ionicity in the bonding [12,13]. Therefore, the quasi one-dimen- sional properties and the significant bond ionicity characterize this reconstructed surface. * Corresponding author. Fax: +81-6-6879-8509. 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0039-6028(02)02619-5 Surface Science 528 (2003) 115–120 www.elsevier.com/locate/susc