Ion beam sputtering (IBS) is a versatile nanofabrication process that uses an ion source to sputter a target material (semiconductors, metals and insulators) onto a substrate to produce a nanostructured surface. This work studies the metal co-deposition of Fe or Mo impurities in the nanodot pattering dynamics of silicon by normal-incidence IBS. The morphological and compositional evolution is studied simultaneously. Atomic force microscopy (AFM) shows the surface morphological after irradiation and latter is operated in conductive mode with Kelvin prove measurements (KPFM) using tips from NEXT-TIP. Conductive mode AFM measurements achieved at the initial and asymptotic stages show that nanodot structures are metal-rich allowing a correlation between the morphology and composition. These results permit to debate the mechanisms of patterns formation are complex due to many processes can come into play with a different relative importance depending on the specific patterning conditions.