Deep investigation of two-dimensional structure arrays formed on Si surface

Femtosecond laser-induced micro and nanostructures have been widely explored, because of their exhibiting great potential applications in many areas. However, the flexible control of the surface structure in both morphology and arrangement regularity still needs further investigation. This paper presents a maskless method to fabricate the two-dimensional periodic arrays of nanostructures on silicon surface based on the surface wave self-regulatory effect upon irradiation of the circularly polarized femtosecond laser. The spatial period of the regular structure arrays exhibit the alterable and constant values in the directions parallel and perpendicular to the sample scanning, respectively, the latter of which is highly dependent on the laser scanning speed. The formation mechanisms of the periodic structure arrays are explored through simulations with both the finite-difference time-domain method and the dynamic interference positive feedback model. The dynamic modulation of the laser energy on Si surface is revealed to originate from the self-regulatory effect during the laser processing. In addition, the depth of the two-dimensional structure arrays can be further experimentally adjusted from 74.5 nm to 112 nm by HF etching process.