Conductivity through the disordered iron and ytterbium two-dimensional layers during their formation on Si(111)-7 x 7, Si(111)7 x 7-Cr and Si(111)-(root3 x root3)/30degrees-Cr surface phases was investigated. It was found in the case of Si(111)-7 x 7 surface that at submonolayer [1 monolayer (ML) - 7.8 x 10(18) at./m(2)] metal coverage iron and ytterbium atoms intermix with silicon surface atoms resulting in formation of silicide islands and silicide alloy layers which display the properties of a degenerated semiconductor. Deposition of small amounts (within one monolayer) of iron or ytterbium atoms onto the Si(111)-[(root3 x root3)/30degrees]-Cr surface phase results in growth of iron or ytterbium metal islands without formation of silicides. This fact indicates that this surface phase represents a diffusion barrier which blocks intermixing. It has been shown that metallic-type conductivity through the nearly continuous layer occurs at the coverage of 8.5 ML for Fe and 6.0 ML for Yb. For deposition of Fe or Yb atoms onto the Si(111)7 x 7-Cr surface phase, the 3D island growth mode without metallic-type layer conductivity was found within a coverage range extending Lip to 20-30 monolayers. (C) 2004 Published by Elsevier B.V.