X-ray study of ion-beam induced amorphous-crystalline ripples in silicon

Ripple formation with a spatial periodicity in the sub-micrometer range on obliquely ion-bombarded solid surfaces has become a topic of intense research in the context of fabrication of nanoscale textured materials [1]. Ion-beam induced ripples are produced by the interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by thermally or ion-induced surface diffusion. Recently we have shown that Ar- ion irradiation of Si (001) surfaces under an angle of about 60° with respect to surface normal and using ion energies of about 60keV results in periodic crystalline ripple formation where the crystalline ripples are covered by a partially amorphous surface layer [2, 3]. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe-ions using ion-energies between 5 and 40keV. Besides AFM measurements, the structure of the amorphous layer and the amorphous-crystalline interface were studied by means of grazing-incidence small-angle scattering (GISAXS) and grazing-incidence diffraction (GID) using synchrotron-radiation. The data reveal that both surface and crystalline ripples appear for all ion energies used. These ripples show asymmetric side-facets where the degree of asymmetry decreases for increasing ion-energy. They show short-range ordering; the ripple wavelength and thickness of the amorphous layer increase as a function of the ion-energy.

Acknowledgement: One of the authors (A.B.) would like to thank the ESRF for financial support and the ID01 beamline-staff for providing beamtime and valuable help.

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[3] S. Grigorian, J. Grenzer, D. P. Datta, S. Hazra, T.K. Chini, M. K. Sanyal and U. Pietsch, Appl. Phys. Lett 89, 231915 (2006).