Anisotropic Vanadium Dioxide Nanogratings by Direct Laser-Induced Periodic Surface Structuring (LIPSS)

Thermochromic vanadium dioxide (VO₂) films have attracted enormous attention in the past decade owing to their high potential in active optical filters, sensors, anevices. VO₂ patterned at the micro- and nanoscale is an evident route toward next-generation devices justifying the need for scalable, straightforward, and high-performing nanofabrication technologies being easily applied for this material. Herein, precise and nondestructive femtosecond laser nanopatterning of the VO₂ films in both direct ablation and plasmon-assisted self-organization regimes is reported under ambient conditions. Our studies unveil formation of the spatially uniform subwavelength nanogratings (or laser-induced periodic surface structures) with a periodicity of around 100 nm through optical excitation and interference of the surface plasmons in the VO₂ film upon its multipulse irradiation. Plasmon-assisted nanotexturing preserves pristine composition of the film, strongly modulating its optical properties toward enhanced visible-range transmittance and evident thermochromic anisotropy in the near-IR spectral range. Overall, our study not only sheds light onto the origin of the laser-driven self-organization in the VO₂ films, but also unveils huge potential of scalable nondestructive direct fs-laser patterning for creating novel optoelectronic and sensing devices based on the optically anisotropic nanotextured VO₂ films.