Low power 2-phase AC plasma polymerization has been used to surface modify glassy carbon substrates that are used as an experimental model for carbon fibers in reinforced. composites. In order to probe the role of carboxylic acid density on the interfacial adhesion strength a combination of different plasma powers and monomer compositions was used. Maleic anhydride (MAH) and 1,2-methylenedioxybenzene (MDOB) were plasma deposited separately and as mixtures to create layers with different surface compositions. In all cases the MAH was hydrolyzed to form carboxylic acid groups. Some carboxylic acid are present on the MDOB surface as a result of the fragmentation processes in the plasma. Chemical and physical changes were investigated as a function of plasma power at constant polymerization time. Surface chemistry analysis was performed with x-ray photoelectron spectroscopy and attenuated total veflectance Fourier transform infrared spectroscopy. Atomic force microscopy was used to measure the thickness of the plasma films and to monitor the surface roughness for the different polymerization conditions. Finally, preliminary results of fracture energy measurements of the plasma modified surfaces determined by a double cantilever method are presented. (c) 2007 American Vacuum Society.