Structural and mechanical properties of nitrogen ion implanted ultra high molecular weight polyethylene

The structural and mechanical properties have been studied for ultra high molecular weight polyethylene (UHMWPE) implanted by 80 keV N-2(+) (40 keV N+)with fluencies ranging from 1 x 10(14) to 5 x 10(15) ions/cm(2). Elastic recoil detection (ERD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) have been employed to study the structural change of UHMWPE before and after implantation. ERD results show that the high-energy edge of ERD spectra shifts to the lower energy with an increase in implantation fluence, indicating that a hydrogen deficient surface layer is formed after implantation. From Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion implantation and when the fluence exceeds 1 x 10(15) ions/cm(2), a layer of hydrogenated amorphous carbon is formed. The XPS result shows that the injected nitrogen atoms form chemical bonds with the polymer instead of forming precipitates by self-clustering. The hardness and Young's modulus of the UHMWPE determined by nanoindenter increase with increased fluence. The hardness and Young's modulus of the UHMWPE implanted with the fluence of 5x10(15) ions/cm(2) is four and two times higher than those of unimplanted UHMWPE, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.