Thin diamondlike films, deposited on (100) Si, have been examined by electron energy loss spectroscopy (EELS), Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis. Results indicate that films deposited at high partial pressures of H2, which have been found to be softer than those deposited at low partial pressures, have higher concentrations of oxygen but similar concentrations of hydrogen within their bulk. It is proposed that the oxygen is bound to the carbon matrix, thus modifying the extended sp2 network. Analysis of the substrate indicates a damaged region at the top surface of the Si. © 1990.