We present results of X-ray fluorescence measurements (carbon Kalpha and Si L-2,L-3) of methylhydroxylsiloxane and phenylmethylhydroxylsiloxane films. The films are converted into amorphous ceramics by irradiation with 500 keV C and 3 MeV Au ions. Changes in the composition (O/Si ratio) of some polysiloxane films are found when treated with ion irradiation. It is shown that ion irradiation induces a segregation of carbon atoms from methyl groups into diamond-like clusters whereas carbon atoms from phenyl groups maintain their sp(2) configuration.