Ultraviolet to Infrared Dielectric Function of Ultrathin VO₂ Films Grown by Atomic Layer Deposition

Accurate optical modeling of VO 2 thin films requires reliable knowledge of the complex dielectric function, which is known to depend sensitively on the fabrication method, substrate, and post–deposition processing. In this work, we report a phenomenological dielectric function model for ultrathin (below 50 nm thick) VO 2 films deposited by atomic layer deposition and crystallized by post–deposition annealing. Dielectric function models for both the insulating and metallic phases are provided, along with an effective medium description that enables optical modeling through the phase transition. Variable–angle spectroscopic ellipsometry measurements spanning from the ultraviolet to infrared are used to extract the complex dielectric function in both the insulating and metallic phases of VO 2 . The dielectric response is parameterized using Kramers–Kronig consistent oscillator models, yielding a single complex dielectric function that provides excellent agreement with all measurements across the full spectral range. The dielectric function reported here provides the input necessary for optical modeling of ultrathin atomic layer deposition-grown VO 2 layers.