Surface patterning by low-energy ion irradiation

The modification of the surface morphology by means of low-energy (0.1-10 keV) ion irradiation is a fascinating process that has been devoted to intense study during the last decades. The first implications of this process were considered due to secondary effects derived from the ion-modified roughness, such as secondary ion emission (SIMS). However, the ability to produce regular and self-organized patternings in the nanoscale range, related to the typical size of the ion collision cascade, has recently attracted the interest on this process due to its potential applications in Nanotechnology. Depending on the ion incidence angle, different morphologies can be induced on the surface, namely ripples and dots [1]. The universality of the process has been demonstrated by the production of patterns either on metals (Ag, Cu), semimetals (graphite), semiconductors (GaSb, GaAs, InP, Si, Ge) and insulators (glass, SiO2). The mechanisms leading to the formation of these patternings have also attracted intense theoretical studies [3]. The successful approach considers continuum equations where an instability results from the interplay between roughening, due to the dependence of the ion sputtering yield on the local surface curvature, and smoothing processes (thermal and ion-induced). Finally, the applications of these nanostructures are still to be exploited. Several applications as optical filters, quantum wires, quantum dots, magnetic nanostructures, and templates have been addressed. In addition, the latter application has been already realized, transferring the pattern from Si surfaces to polymeric and metallic films [4]. Complementary, the possible functionalization of the surface for biological or catalytic processes can also open a wide range of potential applications.

[1] Navez et al. C.R. Acad. Sci, Paris 254 (1962) 240; Facsko et al. Science 285 (1999) 1551.
[2] Gago et al. Appl. Phys. Lett. 78 (2001) 3316; Gago et al. Nanothecnology 13 (2002) 304.
[3] Bradley et al. J. Vac. Sci. Technol. A 6 (1988) 2390; Cuerno et al. Phy. Rev. Lett. 74 (1995) 4746.
[4] Azzaroni et al. Appl. Phys. Lett. 82 (2003) 457; Azzaroni et al. Nanotechnology (submitted)