The Poly(ethyl terephthalate) (PET) surfaces were modified by fluorocarbon plasmas.Angle dependent x ray photoelectron spectroscopy (XPS) and contact angle techniques were employed to determine the change of the surface structures and properties of the modified PET.Experiments show that the changing of F/C ratio and contact angle of the modified PET along with the CH 4/CF4 feed.It was found that the modified surfaces show more hydrophobic

and CF 4/CH 4 plasma exhibits more stronger hydrophobic effect than CF4plasmas alone.The structures and properties of the modified PET surface depend on the molar ratio of the CH4/CF4 feed.The plots of contact angle vs.molar ratio of the CH4/CF4 feed is the same with that of F/C ratio measured by angle-dependent XPS at 10 degree of taking-off angle.By conparison

the relationship of the sampling depth of XPS and contact angle can be obtained.