Structural effect of nitrogen plasma-based ion implantation on ultra-high molecular weight polyethylene

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 mus duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp(3)/sp(2) bonded carbon in the modified layer was obtained by suitable fitting of the XPS C Is energy peak, using a four-curve fitting procedure, which recognizes a portion of C-O and C=O surface bonding. The XPS results for N Is peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering. (C) 2004 Elsevier B.V. All rights reserved.