AFM, SEM AND XPS CHARACTERIZATION OF PAN-BASED CARBON-FIBERS ETCHED IN OXYGEN PLASMAS

Atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) have been used to investigate changes in topography and surface chemical functionality on PAN-based carbon fibres exposed to low-temperature, low-power, oxygen plasmas. U nsized, type II, Cellion 6000 carbon fibres were treated in oxygen pla smas for 2-60 min at a power of approximately 25 W. Increasing treatme nt time caused an increase in oxidation from surface alcohol(ether) to carbonyl and carboxyl species, but the total amount of oxidized carbo n near the surface remained constant. SEM confirmed that treatments lo nger than 15 min resulted in pitting on the fibre surface, but even tr eatments of 60 min did not significantly reduce the overall fibre diam eter. AFM showed surface morphology changes after oxygen plasma treatm ents for 2 and 15 min. 1 mum x 1 mum AFM scans of untreated fibres sho wed processing grooves with a distribution of depths. Enlarged images along these grooves revealed that their walls were smooth. Oxygen plas ma.treatments of 2 min roughened fibre surfaces and created holes of t he order of 50 nm evenly distributed with a spacing of 150 nm along th e bottoms of the grooves. Treatment for 15 min smoothed the overall to pography and resulted in smaller holes, of the order of 5-10 nm, with a spacing of < 50 nm. Calculated RMS roughnesses from the AFM data sho wed an initial increase in roughness with treatment, followed by a dec rease to final values lower than those for untreated fibres.