Development of segmented titanium oxynitride layer with spinform surfaces exhibiting antibacterial properties

We have developed the titanium oxynitride (TiON) layer which exhibits antibacterial activity against Escherichia coli without sunlight irradiation. This TiON layer with the segmented structure was formed on a pre-oxidized Ti substrate by the electron beam physical vapor deposition method while spraying the substrate and Ti target with N2-0.1 % O2 gas. An XRD pattern of the surface of the segmented layer revealed that the layer has a rock salt structure, which is preferentially deposited in a [111] direction to the substrate surface. TEM observation of the TiON layer showed that the columnar segments have a feather-like structure. The width of the segments near the surface was 100–500 nm, and their outermost surfaces were covered with nanometer-sized spines of 10–50 nm width. The TiON layer contained about 20 at % nitrogen as determined by XPS, and the surface was slightly negatively charged with a zeta potential of −0.9 mV at pH 7.2. The maximum average pressure in the elastic deformation region for the layer was over 100 MPa, which was much higher than the average occlusal pressure (<10 MPa). It is concluded that the segmental structure of the film facilitates the elastic deformation without distorting of the unique surface structure in response to external stress.