Immersion infrared reflection-absorption spectroscopy studies on diamond-like carbon surfaces. I. Formation of electrophilic groups on surfaces of amorphous carbon films aging in ambient air

To study chemical functional groups on surfaces of diamond-like carbon (DLC) films, a highly sensitive infrared reflection-absorption spectroscopic technique, immersion infrared reflection-absorption spectroscopy (IRRAS), is applied in the present study. The method employs (i) a conventional attenuated total reflection (ATR) accessory with a Ge crystal as an immersion medium and (ii) an aluminum underlayer beneath the 50-70 nm thick DLC film. Sensitivity, selectivity, and quantifiability of the method can be enhanced by chemical derivatization (CD), coupling chemical moieties with strong characteristic vibrational bands to specific functional groups on the DLC surface. The method is applied to amorphous sputtered carbon films (a-C) to demonstrate that electrophilic groups, most probably epoxy groups, are formed during aging under ambient conditions.