In this article, the growth of cobalt at 150 degreesC on the Ga-rich (4x2) reconstructed GaAs(001) surface is studied, emphasizing particularly submonolayer coverage. The surfaces were analyzed using scanning tunneling microscopy, soft x-ray photoemission spectroscopy (SXPS), low-energy electron diffraction, and reflection anisotropy spectroscopy (RAS). Co deposition above 1 monolayer thickness leads to a highly reacted interface consisting of CoGa and CoAs compounds, as evidenced by SXPS. At submonolayer coverage, however, Co atoms are incorporated in the row-like structure of the clean, Ga-rich (4X2) surface, forming one-dimensional, ordered chains in the [110] direction. Scanning tunneling spectroscopy and RAS demonstrate that these rows act as one-dimensional metallic nanowires. (C) 2004 American Vacuum Society.