Figure 1. Phase diagram showing STM induced surface modifications at different tip voltage and different tip-to-surface distance mainly constructed using ref. [5], [12] and ref. [17].

In drawing the lines for mound formation we have assumed that it is the electric field that decides if some particular kind of mound will be formed. Mounds will form at positive voltages, area A. From our model assuming field induced diffusion of adatoms we can calculate the threshold electric field for mound formation for area A to 2 V/nm. In area B we have transfer of tip materials to the surface making a mound of tip material on the surface. For pits, area C, we have assumed that they are formed at constant independent of the tip-to-surface distance in agreement with Kondo et al. [17]. At short distances and low electric fields, area D, the van der Waals force will contribute in creating a mound [22]. Close to the U-axis (not shown) at electrical fields above 20–50 V/nm field evaporation will occur [18].