Low energy Ar+-ion irradiation at normal incidence is used to fabricate nanostructured GaAs surface. Atomic force microscopy (AFM) images reveal the formation of GaAs surface nanodots with an average size of about 25-35 nm. The swelling of irradiated surface is observed at a higher energy due to the ion beam-induced porosity in the amorphized GaAs surface. Micro-Raman scattering shows a gradual increase in the downward shift and line shape broadening of optical phonon modes from the nanostructured GaAs prepared with increasing ion dose and beam energy. The rapid broadening of the transverse-optical phonon mode at a higher energy and dose represents the onset of plastic deformation of the irradiated surface. Furthermore, the influence of rapid thermal annealing (RTA) shows a reverse LO and TO phonon peakshift and the change in the lineshape due to reduction of the amorphous disorder. (c) 2006 Elsevier B.V. All rights reserved.