Scanning tunneling microscopy at liquid helium temperature was used to image potassium adsorbed on graphite at low coverage (≈0.02 monolayer). Single atoms appear as protrusions on Scanning tunneling microscopy topographs. A statistical analysis of the position of the atoms demonstrates repulsion between adsorbates, which was quantified by comparison with molecular dynamics simulations. This gives access to the dipole moment of a single adsorbate, found to be 10.5±1  D. Time-lapse imaging shows that long-range order was broken by thermally activated diffusion, with a 30meV barrier to hopping between graphite lattice sites

Real-Time Imaging of K Atoms on Graphite - Interactions and Diffusion. J.Renard, M.B.Lundeberg, J.A.Folk, Y.Pennec: Physical Review Letters, 2011, 106[15], 156101