Acetylene plasma-polymer films treated by argon plasma immersion ion implantation

Abstract

Structural and surface properties of acetylene plasma polymer films were studied as a function of treatment time via Plasma Immersion Ion Implantation (PIII). The polymer films were obtained from acetylene and argon mixture using radiofrequency glow discharge and then treated by argon PIII. XPS (X-ray photoelectron spectroscopy) was used to analyze the composition of the films before and after PIII treatment. With rising exposure time, XPS revealed an increase of oxygen-to-carbon (O/C) atomic ratio from 0.23 to 2.43. It can be explained by recombination processes between dangling bonds or radicals created in the polymer structure and atmospheric water and/or oxygen. It was observed that the film structure was predominantly formed C-H and C-C bonds, but there was an increment of the C=O proportion bonds upon argon PIII treatment. The wettability of the polymer films was investigated using contact angle measurements for water and diodimethane droplets on the film surface. After the argon ion implantation, the contact angle was reduced from 55 to 24 degrees, attributed to incorporation of polar groups in the polymer structure. Upon aging in atmosphere, all samples lost the high wettability, but the hydrophilic character of the films was maintained. It was used atomic force microscopy (AFM) to investigate the roughness of the samples. After argon PIII treatment, the roughness of the polymer films decreased from 8.1 to 5.5 nm, mainly due to ablation processes like sputtering one. The hardness and elastic modulus of the polymer films were investigated by nanoindentation technique. The hardness was enhanced from 0.68 to 5.35 GPa and the elastic modulus increased from 28 to 97 GPa. In general, the results show that argon PIII turned acetylene plasma polymer films smoother and mechanically more resistant, but its effect depends on treatment time.