Radiation damage of alkoxy and siloxy ligands bonded to silica

The pattern of radiation-induced bond dissociation in alkoxy and siloxy lig ands bonded to silica was studied using EPR spectroscopy. Bond-specific dam age to ligands was deduced from observation of grafted and physisorbed radi cals. Our results show that ligand damage predominates over desorption of l igands from the surface and are consistent with studies of radiation-induce d modification of self-assembled monolayers on various types of substrates. Dissociation of C-H bonds is the dominant process, followed by C-C dissoci ation. In siloxy ligands losses of hydrogen atoms and alkyl groups were bot h major processes. Direct excitation of dissociative excited states of the organic ligands and ionization are both important damage mechanisms.