We have analyzed the height dependence of the Si and Sn atoms on the 1/6 monolayer (ML) Sn/Si(1 1 1)-(root3 x root3)R30degrees surface, also known as Sn/Si(1 1 1) mosaic phase, by means of non-contact atomic force microscopy (NC-AFM) technique. By preparing samples in which the Sn/Si(1 1 1) mosaic phase and the Si(1 1 1)-(7 x 7) surfaces coexist, and taking account of the proportion of bright and dim contrast atoms when comparing NC-AFM images of both surfaces, we have been able to discriminate between the two atom species forming the mosaic phase. Additionally, we have found a pronounced variation of the height of the Si adatoms with the number of first neighboring Sn adatoms in the Sn/Si(1 1 1) mosaic phase. (C) 2004 Elsevier B.V. All rights reserved.