Buckling reversal of the Si(111) bilayer termination of 2-dimensional ErSi2 upon H dosing

Laboratoire de Physique et de Spectroscopie Electronique-URA CNRS 1435, Faculté des Sciences et Techniques - 4 rue des Frères Lumière, 68093 Mulhouse Cedex, France

Received: 27 January 1997
Accepted: 3 April 1997

Abstract

Hydrogen-induced reconstruction of 2-dimensional (2D) epitaxially grown on Si(111) is studied by Auger-electron diffraction (AED) and low-energy electron diffraction (LEED). The intensity of the Er MNN Auger line is measured vs. polar angle along the and azimuths for clean and H-saturated silicides. The atomic structure of clean 2D silicide, previously established by AED as well as other techniques, consists of a hexagonal monolayer of Er located underneath a buckled Si layer comparable to the Si(111) substrate double layers. Moreover, for clean 2D only the B-type orientation is observed, i.e. the buckled Si top layer is always rotated by around the surface normal relative to the relevant double layers of the substrate. After atomic H saturation, AED reveals drastic changes in the silicide structure involving a major most remarkable reconstruction of the Si bilayer termination. The latter is found to switch from B-type to A-type orientation upon H dosing, i.e. H-saturated 2D exhibits a buckled Si top layer oriented in the same way as the substrate double layers. A comparison with single scattering cluster simulations demonstrates that the latter phenomenon is accompanied by a large expansion of the Er-Si interlayer spacing close to 0.3 Å.