  The process of creating an atomically defined and robust metallic tip is
described and quantified using measurements of contact conductance between gold
electrodes and numerical simulations. Our experiments show how the same
conductance behavior can be obtained for hundreds of cycles of formation and
rupture of the nanocontact by limiting the indentation depth between the two
electrodes up to a conductance value of approximately $5G_{0}$ in the case of
gold. This phenomenon is rationalized using molecular dynamics simulations
together with density functional theory transport calculations which show how,
after repeated indentations (mechanical annealing), the two metallic electrodes
are shaped into tips of reproducible structure. These results provide a crucial
insight into fundamental aspects relevant to nano-tribology or scanning probe
microscopies.
