Tuning wettability of Si surface by ion beam induced silicon nitride formation and nanopatterning

Abstract

The transformation of a hydrophilic surface to a hydrophobic surface due to chemical modification and periodic nano pattern formation on silicon surface by 5–12 keV N+ ion bombardment is reported. The reactive N+ ion bombardment at oblique angle incidence leads to form silicon nitride (Si3N4) on the surface. Also, a periodic wave-like ripple pattern is formed on Si surface at nanoscale range whose wavelength and surface roughness can be regulated by varying the ion energy (5–12 keV). It is found that the contact angle of water droplet on such patterned surface increases with the increase of ripple wavelength and surface roughness. In contrast, the contact angle does not change for the same energy Ar+ bombarded Si surfaces, where such type of surface nano patterns are absent and also surface roughness remains almost the same. The morphologies of the irradiated and un-irradiated Si surfaces are examined by Atomic Force Microscopy (AFM), whereas the surface chemical composition is investigated by X-ray photoelectron spectroscopy (XPS). The chemical modification in terms of Si3N4 formation on the surface, periodic wave-like ripple pattern formation and high increase of root mean square (rms) roughness for N+ bombarded Si surfaces result in hydrophilic to hydrophobic transformation. The tuning of wettability in terms of ion beam parameters for the patterned and chemically modified Si surfaces is discussed in detail.