Characterization of aluminium surfaces with and without plasma nitriding by X-ray photoelectron spectroscopy

Substrates of aluminium alloy 2011 have been plasma nitrided using an inductively coupled plasma source and then characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD analysis confirmed the presence of a crystalline aluminium nitride (AlN) layer on the substrates surfaces. Both AlN and Al2O3 were observed by XPS on the surface of the nitrided Al substrates. The binding energy (BE) of the C 1s photoelectron of adventitious hydrocarbon was found to be dependent on the thickness of the insulating AlN/Al2O3 surface layer. None of the Al 2p, N 1s or O 1s BEs showed any shifts due to surface charge build up. The BE values of the Al 2p photoelectron for AlN, Al2O3 and metallic Al were determined to be 74.5, 75.5 and 72.7 eV, respectively. The charge shifting of the BEs of all the photoelectrons occurs simultaneously only for oxidised Al substrates (not nitrided) with a sufficiently thick oxidised surface layer. For a thinner oxidised surface layer the adventitious hydrocarbon C 1s photoelectron BE still shows charge shifting but this is not reflected in the BE of the Al 2p and O 1s XPS components.