Manipulation and Dynamics at the Atomic Scale: A Dual Use of the Scanning Tunneling Microscopy

Atomic scale modification of surfaces may trigger off dynamical processes. This is shown here by using the tip of a scanning tunneling microscope to extract an individual atom in a controlled manner from a predefined site of the reconstructed Ge(111)- c(2 ×8) surface. By thermally activated hopping of neighboring adatoms to the vacant site, the produced single-atom vacancy diffuses on the surface. From statistical analysis of the adatom configurations observed around the vacancy, we determine tiny ( <0.15 eV) differences in free energy between the configurations. A linear increase of the configuration free energy with the number of adatoms located at metastable T₄ sites is reported.