X-ray scattering and diffraction from ion beam induced ripples in crystalline silicon

We report on periodic ripple formation on Si(001) surfaces after bombardment with Xe+ ions with energies between 5 and 35 keV under incidence angles of 65 degrees and 70 degrees. The sputter process leads to the formation of a rippled amorphous surface layer, followed by a rippled interface toward crystalline material. Using grazing-incidence small-angle scattering and diffraction, we show that the surface morphology is exactly reproduced at the interface. In addition, we observe that the crystal lattice close to the interface is anisotropically expanded. The lattice expansion parallel to the ripples is larger than those perpendicular to them.