Femtosecond Laser-Induced Co3O4 Periodic Surface Structures of Active Facets for Gas Sensing

Abstract Achieving precise facet control in metal oxides is a critical challenge for advancing gas sensor performance, as high-energy crystal planes offer superior surface reactivity but are difficult to expose in a controlled manner on functional thin films. This work demonstrates facet engineering by employing a femtosecond laser-induced periodic surface structure (LIPSS) technique to selectively expose distinct, high-energy crystal facets on Co3O4 nanoscale films. Simply by adjusting the laser polarization in a single, maskless step, we fabricated Co3O4-LIPSS with identical nanoscale morphology but controlled exposure of either {100} or {110} facets, confirmed by detailed structural and epitaxial characterization. The nanoscale periodic structures provide an accessible surface with well-defined structural features, while the controlled crystallographic orientation enables selective exposure of different crystal facets. The significance of this facet control is directly quantified in gas sensing. Chemiresistive sensors based on {100} and {110}-faceted LIPSS exhibit dramatically enhanced sensitivities, 1.4 and 1.74 times higher, respectively, compared to conventional thin films, alongside faster response/recovery kinetics and excellent cyclic stability. This study not only establishes the direct, positive role of selective high-energy facet exposure in boosting gas sensing performance but also provides a scalable, lithography-free nano fabrication platform. The LIPSS technique enables precise facet control in oxides while integrating nanoscale surface structuring with crystallographic engineering, providing a design pathway for engineering next-generation, high-performance gas sensing materials.