Formation and commensurate analysis of "incommensurate" superstructures of Pb on Si(111)

Using high resolution low-energy electron diffraction for spot profile analysis we have investigated dense phases (close to one monolayer) of Pb on Si(1 1 1)7 x 7 substrates within the temperature range of 25-600 degreesC. The observed diffraction pattern from these superstructures can be explained by models basing on root3 x root3 overlayers with almost perfectly ordered domain walls. Using the kinematical approximation we obtain very good agreement between experiments and model calculations (considering both the position and the diffraction spot intensities). In this paper both structures, the Si(1 1 1)-root 31 x root3-Pb superstructure and Si(1 1 1)-13 x \/5-Pb superstructure are revealed as commensurate with root3 unit cells and regularly arranged domain walls. In matrix form these phases should be designated as Si(1 1 1)-((6)(-1) (5)(1))-Pb and Si(1 1 1)-((13)(-1) (13)(1))-Pb phase. (C) 2001 Elsevier Science B.V. All rights reserved.