The (root 3 x root 3) to (3 x 3) phase transition in Sn/Ge(1 1 1)-(root 3 x root 3)R30 degrees and Sn/Si(1 1 1)-(root 3 x root 3)R30 degrees systems was investigated for the first time using a non-contact atomic force microscope (NC-AFM). Observations show the occurrence of the phase transition with small (3 x 3) domains on the Sn/Ge(1 1 1) surface at low temperatures of 78 and 6 K. However, no evidence was found to support the presence of the phase transition for the Sn/Si(1 1 1) system, even when the temperature was lowered to 6 K. The (3 x 3) domains present two patterns, one hexagonal and the other honeycomb, depending on the tip to sample distance. (c) 2006 Elsevier B.V. All rights reserved.