Ultrathin fluoropolymer films of about 4 nm in thickness were deposited on the HCl-etched (100)-oriented GaAs single-crystal substrates via radio frequency plasma sputtering of a poly(tetrafluoroethylene) (PTFE) target. X-ray photoelectron spectroscopy (XPS) results indicated that the sputter-deposited PTFE (s-PTFE) ultrathin film, having a dielectric constant comparable to that of the PTFE film (k similar to 2.1), could effectively passivate the HCl-etched GaAs(100) substrate under various environments. The growth of the oxide layer was effectively hindered by the s-PTFE barrier when the HCl-etched GaAs(100) surface was exposured to air for several hundred hours. The surface oxidation rate was also reduced significantly in the presence of the s-PTFE barrier when the HCl-etched GaAs(100) was exposed to water and the H2O2 solution. XPS and time-of-flight secondary mass spectrometry results indicated that the deposited s-PTFE film was oxygen-free and consisted of -(CF2)(n)-units with different end groups. The 180degreespeel adhesion test results suggested that the s-PTFE film adhered strongly to the GaAs(100) surface. (C) 2003 The Electrochemical Society.