Optical contrast from InN nanodots grown on nitrided sapphire is investigated using apertureless near-field scanning optical microscopy at two different visible wavelengths, 633 nm and 532 nm. The dependence of the near-field signal on the size of the dots is described using a coupled dipole model expanded to four dipoles. The near-field signal from InN dots with a height of < 1 nm is detected due to dipole-dipole coupling. (c) 2007 Elsevier B.V. All rights reserved.