Diamond and DLC thin films deposited using hot-filament chemical vapour deposition technique at various parameters were irradiated with 50 MeV ST’ ions. The resulting microstructural changes were studied using X-ray diffraction and scanning electron microscopy. All the samples showed the development of B-Sic and hexagonal carbon phases at the expense of the diamond/DLC phase. The ERD analysis was carried out to
determine the hydrogen concentration and its distribution in DLC films. The absolute hydrogen concentration in DLC samples is of the order of lti2 atoms/c& which gets depleted on irradiation. The DLC samples show a clear dependence of hydrogen content on the deposition parameters.