The growth of GaAs nanowires was investigated by molecular beam epitaxy assisted by the pre-deposition of An on a clean GaAs (1 1 1)B surface. Before growth was started, we observed the formation of nanoparticles consisting of AuGa alloys. The transition between their solid and liquid phases was evidenced by in situ reflection high energy electron diffraction. Regular nanowires were obtained only for growth temperatures above the melting temperature of the metallic particle which was observed near 400 degrees C. The kinetics of this nanowire growth is discussed. (c) 2006 Elsevier B.V. All rights reserved.