Large area arrays of dots have been patterned in Au/Co/Au(lll) sandwiches with ultrathin Co layers (0.6 to 2 nm) and a perpendicular easy magnetization axis. Dot dimensions down to 0.2 mu m have been achieved using x-ray lithography, with either positive resist and direct ion beam etching or a lift-off process with aluminum mask. Both processes have been tested against the damages they induce to the fragile structure of the samples. The magneto-optical effects and magnetization reversal processes in the arrays have been characterized versus Co thickness, dot dimension, and lattice aspect ratio. For high quality samples, the domain walls propagation mechanism that drives magnetization reversal in as-grown films is drastically modified in dot arrays, leading to a large increase of the coercive field with dot diameter reduction, together with changes in the shape of the hysteresis loops.