Measurement of Sb diffusion using shadow profiles created by a STM tip

The diffusion of a nanostructured Sb layer on Si(111) was measured at room temperature. We used the tip of a scanning tunneling microscope (STM) as a shadow mask to create a nanostructured Sb film by deposition from a molecular beam. The profiles of the shadow edges were measured as a function of Sb layer thickness. We observed: (i) an Sb layer outside the shadow region, which is rough on a length scale of 100 إ; and (ii) diffusion of Sb several hundred إngstroms in the shadow. This can be explained consistently by a highly diffusive Sb precursor which decays and becomes immobile after a certain lifetime. Kinetic Monte Carlo calculations including only one fit parameter (the decay time) describe the form and the width of the measured shadow edge profiles.