Surface chemistry and initial growth of Al2O3 on plasma modified PTFE studied by ALD

•Ambient air plasma as an effective method to enhance the ALD nucleation process.•Initial growth of atomic layer deposited Al2O3 on PTFE was studied by XPS.•Plasma surface pre-treatment of PTFE showed significantly faster nucleation.•Nucleation behaviour correlated with the surface oxygen-containing groups induced by plasma.•ALD as a diagnostic tool to study of surface chemistry on plasma-modified polymers.

This paper reports on the growth of ultra-thin Al2O3 layers deposited on polytetrafluoroethylene (PTFE) surfaces pre-treated by atmospheric pressure ambient air plasma. Al2O3 thin films were deposited by a thermal atomic layer deposition (ALD) process using trimethylaluminium and water at 100 °C. The concentration of elements and the bonding structures in layers resulting from up to 350 ALD cycles was measured by X-ray photoelectron spectroscopy. It was disclosed that the concentration of oxygen-containing groups increased initially as surface carbon contamination was oxidised, then decreased as the surface composition approached pure PTFE. In general, the plasma-treated samples showed significantly faster nucleation; 300 cycles were necessary for the formation of a complete film on untreated PTFE, whereas only 150 cycles were needed to create uniform films on plasma-pre-treated PTFE surfaces. The swiftest nucleation behaviour was associated with the highest number of oxygen-containing groups on the surface rather than complete removal of contamination. As demonstrated here, the state of a plasma-activated surface may easily be studied by means of deposition of atomic layers by the ALD method.