Comparative study of different tip materials for surface modification by the scanning tunneling microscope

When short pulses are superimposed on the bias voltage of a scanning tunneling microscope, Au tips produce hillocks on an Au surface, as has already been shown. Other tip materials such as Fe, Ni, or Pt also seem to create features on an Au surface-mounds or holes-but with less reliability. The strong electrostatic force between the tip and the surface during a voltage pulse is considered to account for the observed surface modifications and reliabilities. Furthermore, the rate of diffusion of some created hillocks has been measured. The determined values for the coefficient of diffusion are similar for all hillocks produced with different tips. Possible implications for the composition of the created structures are discussed.