Molybdenum hexacarbonyl, Mo(CO)6, and molybdenum hexafluoride, MoF6, have been used as precursors, with hydrogen or methane as reductants, to produce thin, dense and largely uniform layers of amorphous structure, on silicon (100) substrates. A plasma enhanced chemical vapor deposition (PECVD) setup was used for the deposition. XPS and AES analysis showed that Mo(CO)(6) with CH4 produces a film containing a mixture of Mo compounds, mostly consisting of MoO2. Carbon appears to be present as Mo2C rather than elemental carbon, although the latter is thermodynamically favored. Similarly, Mo(CO)(6) and H-2 as the reactant mixture produce a film containing only one single, metastable compound, namely a Mo-oxycarbide. A mixture of MoF6 with hydrogen is capable of producing pure molybdenum deposits without fluorine surface contamination. With CH4 as the reductant, MoF6 is expected to produce a mixture of elemental Mo and Mo2C, while MoF6 with NH3 as the reductant is expected to yield predominantly Mo2N. (C) 2003 Elsevier B.V. All rights reserved.