Grazing incidence small-angle x-ray scattering and atomic force microscopy have been used to systematically investigate the evolution of Si(100) surface morphology during normal-incidence Ar+ sputtering as a function of ion energy in the range of 100–500 eV. For ion energy ranges of 100–300 eV, two structures with distinct individual length scales and behaviors form on the surface. There is a smaller scale (lateral size of 20–50 nm) morphology that grows in scattering intensity and coarsens with time. There is also a larger scale (lateral size of approximately 100 nm) morphology that grows in scattering intensity but does not coarsen significantly in the time scales studied. At higher energies (400–500 eV), sputtering causes the Si(100) surface to become smoother on length scales smaller than 200 nm. © 2002 American Institute of Physics.