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

Using high resolution low-energy electron diffraction for spot profile anal ysis 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. Th e 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 agree ment between experiments and model calculations (considering both the posit ion and the diffraction spot intensities). In this paper both structures, t he Si(1 1 1)-root 31 x root3-Pb superstructure and Si(1 1 1)-13 x \/5-Pb su perstructure are revealed as commensurate with root3 unit cells and regular ly 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.