Actively Tunable Metasurfaces via Plasmonic Nanogap Cavities with Sub-10-nm VO 2 Films.

Actively tunable optical materials integrated with engineered subwavelength structures could enable novel optoelectronic devices, including reconfigurable light sources and tunable on-chip spectral filters. The phase-change material vanadium dioxide (VO 2 ) provides a promising solid-state solution for dynamic tuning; however, previous demonstrations have been limited to thicker and often rough VO 2 films or require a lattice-matched substrate for growth. Here, sub-10-nm-thick VO 2 films are realized by atomic layer deposition (ALD) and integrated with plasmonic nanogap cavities to demonstrate tunable, spectrally selective absorption across 1200 nm in the near-infrared (NIR). Upon inducing the phase transition via heating, the absorption resonance is blue-shifted by as much as 60 nm. This process is reversible upon cooling and repeatable over more than ten temperature cycles. Dynamic, ultrathin VO 2 films deposited by ALD, as demonstrated here, open up new potential architectures and applications where VO 2 can be utilized to provide reconfigurability including three-dimensional, flexible and large-area structures.