Nanopatterning of Si surfaces by normal incident ion erosion: Influence of iron incorporation on surface morphology evolution

The surface morphology of Si(100) induced by 1200 eV Ar+ ion bombardment at normal incidence with and without Fe incorporation is presented. The formation of nanodot patterns is observed only when the stationary Fe areal density in the surface is above a threshold value of 8×10¹⁴ cm^-2 . This result is interpreted in terms of an additional surface instability due to locally nonuniform sputtering in connection with the presence of a Fe rich amorphous phase at the peak of the nanodots. At Fe concentrations below the threshold, smoothing dominates and pattern formation is inhibited. The transition from a k^-2 to a k^-4 behavior in the asymptotic power spectral density function supports the conclusion that under these conditions ballistic smoothing and ion-enhanced viscous flow are the two dominant mechanisms of surface relaxation.