THE 3X1-LI TO 7X7 STRUCTURAL TRANSFORMATION OF SI(111) DUE TO LI DESORPTION

A combined investigation using thermal desorption spectroscopy (TDS) a nd low-energy electron diffraction (LEED) shows that the area of the L i-induced 3 x 1 reconstruction on Si(111) depends linearly on the amou nt of adsorbed Li. This is in contrast to the concept of an impurity-s tabilized 3 x 1 reconstruction by a small amount of Li through a long- ranged mechanism. The desorption energy of the Li atoms involved in th e reconstruction is 3.2 eV. This is substantially higher than that of Li desorbing from the Si(111)7 x 7 surface (2.5 eV). The high desorpti on energy points to saturation of dangling bonds by Li chemisorption, which also explains the passivation of the Si(111)3 x 1-Li surface aga inst oxidation. (C) 1998 Elsevier Science B.V. All rights reserved.