Supersonic cluster beam deposition (SCBD) with a pulsed microplasma cluster source (PMCS) was used to deposit cobalt porous carbon-nanocomposite thin films (Co:ns-C), on silicon substrates at room temperature and under vacuum. The films find applications due to their magnetic properties. Analytical images and mass spectra of secondary ions were obtained using the University of Chicago-scanning ion microprobe (UC-SIM). This instrument, using a liquid gallium ion source and a magnetic sector mass spectrometer, makes it possible to obtain images of secondary ions with a lateral resolution of 50 nm. Mass spectra indicate a low levels of contamination at the surface and inside the film and the presence of metallic cobalt and cobalt oxides. The images show the distribution of Co+ and CoO- at different depths. We observe the distribution and the relative size of cobalt and cobalt oxide aggregates inside the film. The capability to control the presence of cobalt is relevant for the films magnetic properties. (C) 2004 Elsevier B.V. All rights reserved.