Active-layer-selective resonant absorption lowers the modeled photothermal drive in a Si/VO₂ metasurface

Here we establish a material-resolved numerical workflow for a square silicon (Si) resonator on a 150-nm VO₂ film supported by sapphire. Geometry maps identify a continuously tunable long-wavelength resonance and select a period P = 2.30 μm, a duty ratio D = 0.62, and a resonator side length L = DP = 1.43 μm.

At 4.08 μm, the optimized metasurface reaches an absorptance of 0.8446, whereas the paired bare VO₂/sapphire film absorbs approximately 0.0420. A Cartesian multipole analysis identifies a magnetic-dipole-dominated current topology, with 74.6% of the retained relative magnitude assigned to the magnetic dipole, while the electric field penetrates the VO₂ layer. Direct integration of the periodic-boundary-corrected VO₂ loss gives absorptances of 0.841044 and 0.0419874 for the metasurface and bare film, respectively, corresponding to a 20.0309-fold active-layer enhancement; 80% of the metasurface VO₂ power is carried by 48.8% of the active-layer volume.