Regulation of High‐Index Crystal Facets with Laser‐Induced Periodic Surface Structures on CoFe₂O₄ Epitaxial Films for Ethanol Gas Sensing

Abstract Control of exposed crystal facets in nanostructures is scientifically important, but technically challenging due to the inherent difficulty in manipulating surface energy of crystals. Here, laser‐induced periodic surface structures (LIPSS) induced by femtosecond laser is applied to produce periodic subwavelength 1D nanostructures with high index crystal facets on epitaxial CoFe₂O₄ surfaces, providing an efficient, maskless, cost‐effective “top‐down” method for nanostructure fabrication. Homogenous 1D LIPSSs (1D‐LIPSSs) with a period of 131 ± 15 nm and a depth of 90 ± 5 nm are obtained. The orientation of LIPSS nanostructures is finely controlled by tuning the polarization of fs laser beam, therefore flexibly producing 1D‐LIPSSs along various crystallographic orientations. Gas sensing performance evaluation shows that the fabrication of 1D‐LIPSSs on CoFe₂O₄ enlarges its surface area and contributes to enhanced gas sensing response. Compared to CoFe₂O₄ with LIPSSs faceted along {100} orientation, CoFe₂O₄ with LIPSSs faceted along high‐index {110} facets exhibits further improved gas sensing performance, suggesting the critical role of high‐index crystal facets in promoting surface reactivity and sensing sensitivity. The development of a laser‐based nanostructure fabrication route with high controllability of exposed crystal facets provides a novel solution for high‐density film‐based gas sensing applications.