Abstract
High resolution diffraction measurements reveal the emergence of anisotropic adatom islands during submonolayer homoepitaxial growth of Cu(001) at grazing incidence. This anisotropy is mimicked well in simulations only after the incorporation of attractive dipolar interactions between the surface and the atoms in the gas phase. The anisotropy of the islands depends markedly on the range of the attractive potential, which allows quantitative insight into the shape of the potential. The role of long- and short-ranged interactions is delineated.