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

The structural and mechanical properties have been studied for ultra high m olecular 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 r ecoil detection (ERD), Raman spectroscopy and X-ray photoelectron spectrosc opy (XPS) have been employed to study the structural change of UHMWPE befor e and after implantation. ERD results show that the high-energy edge of ERD spectra shifts to the lower energy with an increase in implantation fluenc e, indicating that a hydrogen deficient surface layer is formed after impla ntation. From Raman spectra it is observed that the chain structure of UHMW PE 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. Th e XPS result shows that the injected nitrogen atoms form chemical bonds wit h the polymer instead of forming precipitates by self-clustering. The hardn ess and Young's modulus of the UHMWPE determined by nanoindenter increase w ith increased fluence. The hardness and Young's modulus of the UHMWPE impla nted with the fluence of 5x10(15) ions/cm(2) is four and two times higher t han those of unimplanted UHMWPE, respectively. (C) 2001 Elsevier Science B. V. All rights reserved.