Applications for TiAlN- and TiO2-coatings with nanoscale surface topographies

This paper reports on the development of nanostructured, multifunctional TiAlN- and TiO2-coatings where the multifunctionality stems from their nanoscale surface topography. The coatings were sputter-deposited on silicon and steel substrates by a reactive RF-magnetron-process. For both types of coatings deposition parameters which led to a columnar growth with mean column diameters between 100 nm and 500 nm were elaborated. The columns itself were terminated by pyramid-shaped tips where the geometric forms of the pyramids were determined by the crystal system of the coating material. Investigations of microstructure and surface morphology were carried out with scanning electron microscopy, atomic force microscopy and X-ray diffraction techniques. A power law was found for the dependence of the mean column diameter on coating thickness in qualitative agreement with phenomenological models for thin film growth. In order to test the coating's suitability for industrial applications, both coating materials were deposited on steel tools and replicated into the surfaces of PMMA sheets. The resulting sheet's surface morphologies proved to be comparable to the antireflective surfaces of motheyes and led to a pronounced decrease in reflectivity. A second possible application, namely the modification of wetting properties of surfaces due to their structuring, was tested by fluorination of the nanostructured TiO2-surface which led to an ultrahydrophobic surface with water contact angles up to 150°.