Irradiation of polytetrafluoroethylene films with vacuum UV light in an ammonia gas atmosphere resulted in a hydrophilic surface, where abstraction of fluorine atoms, and introduction of nitrogen, oxygen, and hydrogen atoms occurred. We used Kr-2* and Xe-2* excimer lamps at wavelength of 146 and 172 nm, respectively. The reaction mechanism for chemical surface modification is discussed on the basis of x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy analyses. (C) 1996 American Institute of Physics.