Spectroscopic light scattering was used to monitor periodic ripple evolution on Si(001) in situ during ${\mathrm{Ar}}^{+}$ sputtering. Analysis indicates that under high flux the concentration of mobile species on the surface is temperature and ion flux independent. This is due to an effect of ion collision cascades on the concentration of mobile species. We thereby measure the migration energy on the surface to be $1.2\pm 0.1\mathrm{eV}$. The technique is generalizable to any material, including high temperature and insulating materials for which surface migration energies are notoriously difficult to measure.

• Received 2 November 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.2330