Superconducting MgB2 films were prepared by sequential e-beam evaporation of boron and magnesium on randomly oriented sapphire, glassy carbon and silicon substrates followed by an in-situ annealing. Ion beam analysis (IBA) methods using a 2530 keV He-3(+) beam were applied to obtain the Mg and B film profiles by Rutherford backscattering (RBS) and nuclear reaction analysis (NRA). It was found that Mg and B diffuse rather deeply into the substrates due to the annealing process. A presence of O and C in the MgB2 films was detected, apparently as formation of MgO and eventually B2O3. The zero resistance critical temperatures T-infinity values were 28 K for MgB2/Al2O3 and 25 K for MgB2 /C samples. Because of a rather high annealing temperature of 700 degreesC, we obtained T-co = 8 K only in the case of MgB2/Si(111) sample. (C) 2003 Elsevier Science B.V. All rights reserved.