An isotope approach to characterization of microwave water plasma modified polyimide surfaces

Water vapor plasma treatment of polymer surfaces has recently gained renewed interest for its potential applications in biomedical science and microelectronics. We have used an isotope technique to characterize the modified polyimide (PI) films by exposing them to microwave H₂O and D₂O plasmas. Data were obtained showing unambiguously that during treatment the PI surfaces were oxidized and hydroxylated. In situ x‐ray photoelectron spectroscopy measurement indicated increased oxygen coverage and formation of carboxylic and possibly hydroxyl bonds on the treated surfaces. Multiple internal reflection Fourier transform infrared spectra confirmed the presence of oxalic acidlike OD stretching band, and demonstrated the propensity of the modified surfaces toward water adsorption. A resonance forward recoil technique was used to monitor the deuterium incorporation in the surfaces after treatment, and the degree of hydroxylation, measured in terms of D uptake, was found to increase monotonically and reach a plateau with prolonged exposure time when the absorbed microwave power and operating pressure were kept constant. A correlation appears to exist between the surface concentration of hydroxyl functionalities and the development of surface morphology during the plasma treatment.