Controllable fabrication of polygonal micro and nanostructures on sapphire surfaces by chemical etching after femtosecond laser irradiation

We fabricate two different types of micro and nanostructures with either pyramid-like or tetrahedron-like geometry on the sapphire surface, through the use of thechemical etching process after femtosecond laser irradiation. The distinct features of the structures are measured with both scanning electron microscopy and atomic force microscopy. The dynamic regions for the formation of the two surface structures are experimentally obtained to indicate their tunability by varying the laser average fluence and etching temperature. With the help of discussions and analyses, we propose a model to explain the formation mechanisms of the two kinds of structures, in which the competition between the growth of the alunogen (Al-2 (SO4)(3)center dot 17H(2)O) crystals and the anisotropic etching rate of the sapphire material plays an important role. In addition, it is confirmed that the tetrahedron-like structures can be used to activate the sapphire substrate for the enhancement of Raman scattering and the hydrophobic properties. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement