Identification of chemical species on plasma-treated polytetrafluoroethylene surface by ab-initio calculations of core-energy-level shift in X-ray photoelectron spectra

Abstract

X-ray photoelectron spectroscopy (XPS) measurements and ab-initio calculations of the XPS chemical shift were performed to identify chemical species on plasma-treated polytetrafluoroethylene (PTFE) surfaces. The obtained C1s-XPS and O1s-XPS spectra confirmed the generation of oxygen-containing functional groups on plasma-treated PTFE surfaces. We investigated the effect of the substitution of F atoms in a CF2– chain by H atoms on the C1s core level binding energy in PTFE; our calculations showed that the C1s core level binding energy is linearly dependent on the number of substituted F atoms. This finding enables us to infer the number of substituted F atoms from the experimentally observed C1s-XPS spectra. We deconvoluted the experimentally observed C1s-XPS spectra of the plasma-treated PTFE surfaces using the calculated binding energies of various functional groups. It is impossible to reproduce the C1s-XPS spectra using the C1s core level binding energies of functional groups in the CF2– chain. However, they can be well reproduced by adding the calculated binding energies of the functional groups in the CH2– chain, indicating the substitution of the F atoms by the H atoms by plasma treatment. Furthermore, the time-of-flight secondary ion mass spectrometry confirmed the existence of H atoms on the plasma-treated PTFE surfaces.