We demonstrate that the morphology of crystalline surfaces during ion sputtering and thermal annealing can be monitoredin situwith an oblique-incidence polarization-modulated optical reflectance difference technique. Such a technique is effective under high ambient pressures as well as ultrahigh vacuum. We studied the Ne ion sputtering and thermal annealing of Ni(111) from 623 to 823 K. We found that the rate-limiting step (with an activation energy of 1.1 eV/atom) during annealing is most likely to be direct evaporation of Ni atoms from step edges. ©1998 American Institute of Physics.