The growth of Ge on Si(111)/Ge-(root 3 x root 3)Ag substrates was investigated for Ge coverages up to 1 monolayer (ML). The root 3Ag substrate was obtained by depositing 0.2 ML Ag on Si(111)/Ge( 111)-5 x 5 surfaces. Because of the low Ag coverage, three types of regions - root 3Ag 'island', root 3Ag 'hole' and exposed Ge(111)-5 x 5 - are produced. This has allowed investigation of Ge growth simultaneously on these three types of surface features by scanning tunneling microscopy. Ge has been found to grow as bilayers almost exclusively on the root 3Ag 'hole' regions, with its surface terminated by a root 3Ag structure. This indicates that Ag behaves like a surfactant and segregates to the top of the deposited Ge via Ag-Ge exchange. At higher Ge coverages the root 3Ag surface undergoes a transformation to a (3 x 1) Ag phase. The deposited Ge hardly grows on the exposed Si/Ge-5 x 5 regions, in contrast to the expected growth behavior on bare Si/Ge-5 x 5 surface. (C) 2015 Elsevier B.V. All rights reserved.