U.Valbusa, F. Buatier, S.Rusponi, G,Costantini and C. Boragno

INFM-Unità di Genova, and Dipartimento di Fisica

Via Dodecaneso 33 , 16146 Genova Italy

The mostly pursued way to pattern a surface on the nanometric scale is via the control of self-assembly in growth processes as Molecular Beam Epitaxy (MBE) 1 or in controlled chemical etching 2. The resulting nano-structures are generally aligned along thermodynamically favored orientations. On the other hand non-equilibrium oriented nano-structures can be of great interest as for example in catalysis: surface defects are known to be chemical active sites 3 and are strictly related to the local orientation of the surface morphology. We demonstrate that surface etching by ion sputtering, besides producing equilibrium oriented patterns which resemble the surface symmetry and are similar to those obtained by MBE, can also be used to pattern the surface along non-equilibrium orientations, thus extending the possibilities of MBE. For example in the case of Ag(001), by properly tuning the competition between ion erosion and surface diffusion, it is possible to pass from a checkerboard of pits to a rippled structure aligned along the ion beam direction. In the case of rectangular lattice surfaces as Ag(110) [4] or Cu(110) [5] [6] ripples are obtained whose direction depends both on temperature and on the sputtering geometry. We also show the generality of the obtained results and indicate some possible applications for the produced nanostructures.

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[2] K.Pohl, M.C.Bartelt, J. de la Figuera, N.C.Bartelt, J.Hrbek and R.Q.Hwang Nature 397 (1999) 238-240

[3] T.Zambelli, J.Wintterlin, J.Trost and G.Ertl, Science 273 (1996) 1688-1690

[4] S. Rusponi, C. Boragno and U.Valbusa Physical Review Letters 7 (1997):2795

[5] S. Rusponi, G.Costantini, C. Boragno and U. Valbusa Physical Review Letters 81 (1998) 2735

[6] S. Rusponi, G.Costantini, C. Boragno and U. Valbusa Physical Review Letters 81 (1998) 4184.