Figure 4

AFM sequence of images for experiment Cd.6 performed at a load of 25 nN. Each pair of images shows a topography image on the left and a friction image in the right, corresponding to the same scan. a) calcite surface before switching to the Cd²⁺(aq) rich solution. The position of steps 1 and 2 are highlighted in both images. b) Growth of a first layer of calcian otavite (Ot-1) as well as the formation of calcian otavite nuclei (Ot-2) over Ot-1, 50 min after the introduction of a CdCO₃ supersaturated solution. The right image shows the contrast in friction between the two calcian otavite layers and the original calcite. Also clear is the initial position of step 1 prior to its advancement (labelled 1') c) Calcite surface nearly completely covered by a layer of calcian otavite (Ot-1) 145 minutes after introduction of supersaturated solution. The position of step 2 has advanced over the original position of step 1, forming a double layer of calcian otavite (Ot-2). The areas occupied by two layers of calcian otavite show a much higher friction signal than those where only one layer of calcian otavite has grown. Image size: 5 μm × 5 μm.