Hard coatings to protect silicon nanostructures for durable water-repellency

Abstract

Superhydrophobic surfaces and their additional properties such as anti-icing or selfcleaning are used, e.g., on aircraft, solar panels or in oil-water filtration. A key to the mechanism of superhydrophobicity is the existence of micro and nanostructures on the surface. However, these surface structures are exposed and easily damaged. This is currently one of the main limitations preventing the widespread use of superhydrophobic surfaces in applications.

This thesis aimed to protect the superhydrophobic micro and nanostructures with a hard material coating. The studied coatings were titanium silicide (TiSi2 C54 phase) and titanium nitride (TiN), both formed by annealing in argon or nitrogen of a radio frequency sputtered titanium thin film. Their protection was tested with linear abrasion. X-ray diffraction (XRD) and resistivity measurements showed that the annealing atmosphere affects the composition of the samples in that additional TiN is present at the samples annealed in nitrogen. Dynamic contact angle, sliding angle measurements and scanning electron microscope images after the abrasion tests showed that all coatings improved the durability greatly compared to the non-coated micro and nanostructures. The difference between the coatings were small but TiSi2 C54 phase combined with TiN performed slightly better than only TiSi2 C54 phase or Ti in the abrasion tests.