Revealing a spontaneous two-stage process in femtosecond laser-induced fully-oxidized nanostructures

Abstract

Femtosecond laser interactions with matter facilitate the creation of diverse structures on material surfaces, including laser induced periodic surface structures (LIPSS), ablation nanoparticles, sub-diffraction nanogrooves, and plasmonic nanostructures. In this study, we reveal a unique nanostructure on silicon induced by femtosecond laser irradiation, distinguished by its pea-shaped morphology. At the center of this nanostructure, a nano-slit is oriented perpendicular to the laser polarization. The nano-slit penetrates the pea-shaped nanostructure and an underlying layer with a depth of approximately 600 nm. Energy dispersive X-ray spectroscopy (EDS) analysis confirms that the nanostructure and the underlying layer consist entirely of silicon oxide. A spontaneous two-stage oxidation process is proposed to explain the formation mechanism of fully-oxidized nanostructures. The presence of nano-slits endows the oxide nanostructures with polarization sensitivity, which shows the potential in applications such as optical encryption and data storage. In addition, the spontaneous two-stage oxidation process allows for the maskless fabrication of oxide nanowires with a precision down to hundreds of nanometers, providing the flexibility to produce arbitrary nanostructures. This capability opens up new possibilities for manipulating light beams and enabling on-chip nano-glass printing.