Ž . Thin Solid Films 323 1998 158–162 Friction and wear behaviour of carbon ion-implanted PS against steel Weimin Liu a, ) , Shengrong Yang a , Changlin Li b , Youmei Sun b a Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China b Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China Received 31 December 1996; accepted 14 November 1997 Abstract Ž . 14 15 15 15 A 25 mm thick polystyrene PS film was implanted with 120 keV ions of carbon to doses of 1 =10 ,1 =10 ,3 =10 ,5 =10 16 y2 Ž . and 1 =10 ions cm , respectively. The structure of the implanted PS was characterized by X-ray photoelectron spectroscopy XPS , whereas the friction and wear behaviour of both implanted and unimplanted PS were investigated using an one-way reciprocating friction tester against a steel ball. Friction results indicate that ion implantation at a dose of 1 =10 14 ions cm y2 increases friction coefficient, whereas the ion implantation at a dose of 1 =10 15 ions cm y2 or higher decreases friction coefficient, and all the tests show that ion implantation lowers wear rate. XPS analyses reveal that ion implantation at dose of 1 =10 14 ions cm y2 results in partial break of benzene ring, and at a dose of 1 =10 16 ions cm y2 results in complete break of benzene ring. q 1998 Elsevier Science S.A. All rights reserved. Keywords: Polystyrene; Ion implantation; Carbon; Friction and wear; XPS analyses 1. Introduction Ion implantation significantly alters surface properties of materials. Recent studies at Oak Ridge National Labora- tory as well as some other laboratories have shown that ion Ž . implantation of polymers such as PI, polycarbonate PC , Ž . Ž . polyethylene PE , polystyrene PS and polytetrafluo- Ž . roethylene PTFE can improve surface hardness, wear and w x other surface-sensitive properties 1–5 , and it is assumed that the improvement of surface hardness and wear resis- tance is mainly related to the cross-linking of polymers. Previous investigation in Laboratory of Solid Lubrication has found that nitrogen ion implantation decreases friction coefficient and improves wear resistance of PI, and the wx formation of CN bonds was suggested 6 . In this work, the effect of carbon ion implantations on both friction and wear properties of PS, and the impact of implantation dose have been investigated. Since X-ray Ž . photoelectron spectroscopy XPS is very sensitive to in- vestigate the chemical composition and chemical environ- ment of the elements on the surface of a material, the change of the structure of the treated specimen was investi- gated using XPS, and the results of XPS were correlated to ) Corresponding author. the tribological behaviour of the PS. It is expected that this investigation would be helpful to understand the friction and wear properties of ion implanted polymers. 2. Experimental details The PS used in this test is a sheet with a thickness of 25 m m and its molecular structure of the repeating units is: The ion implantations were performed on a 400 keV implanter in the Institute of Modern Physics in Lanzhou, China. The sheets of PS were implanted with 120 keV ions of carbon to doses of 1 = 10 14 ,1 = 10 15 ,3 = 10 15 ,5 = 10 15 16 y2 y3 Ž y5 . and 1 = 10 ions cm in a 1.33 = 10 Pa 10 Torr vacuum, respectively, using an ion current of approxi- mately 1 mA cm y2 . The ion beam was scanned uniformly over a 40 = 40 cm 2 area of the PS sheet during the process of implantation. The implanted depth is about 0.3 m m to 0.5 m m, and the implantation resulted in a color change of the PS with increasing dose, from light brown to grey at a dose of 1 = 10 16 ions cm y2 . 0040-6090r98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.