Surface treatment of polyethylene by fast atom beams

Abstract

Ultra-high molecular-weight polyethylene (UHMWPE) was treated by fast atom beams (FAB) obtained from He, Ar, H2 and N2 with about 1 kV accelerating voltage and estimated fluence of 1017 particles cm−2. The modified surface layers were characterised by X-ray photoelectron spectroscopy (XPS or ESCA) and dynamic microhardness measurements. Each applied FAB treatment results in the increase of the bulk plasmon loss energy (EL) of the C 1s peak. This implies the formation of graphitic-type material and/or hydrogenated amorphous carbon (or carbon nitride in case of treatment by N atoms) in the modified surface layer. FAB treatment by N atoms leads to the incorporation of ≈35 at.% of N, which is about three times higher than the value obtained previously after low-kilo-electron-volt N2+ ion-beam treatment. The related C 1s peak shows that the overwhelming portion of C is bound to N, while the N 1s peak reflects that N is present in at least three chemical bonding states. Angle-dependent XPS studies of the nitrogen-FAB-treated UHMWPE reveal the presence of a N-rich subsurface layer with a topmost layer containing less N. This is in agreement with the calculated depth distribution of N atoms. Each applied FAB treatment leads to significant increase in the surface microhardness.