The surface structure of plasma-modified self-assembled monolayers is studied by x-ray photoelectron spectroscopy. The measurements show that the oxygen postplasma gas produces gradual chemical modifications in a pure polyethylene-type monolayer. Different oxygenated functions are observed and quantitatively, they are measured to be denser at shorter distances from the plasma source. Used as liquid crystal alignment layers, these surfaces present a fast transition between the homeotropic and planar anchorings. The average distance between the oxygen atoms on the organic layer is found to be at the anchoring transition.
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