Quasi-BIC resonance in TiO₂ metasurface for emission enhancement of two-dimensional material

Bound states in the continuum (BICs) are a category of localized states that exist within the continuum of radiating modes. The high Q-factor exhibited by these states makes quasi-BICs interesting for enhancing the emission from quantum emitters. Quasi-BICs have been experimentally realized in silicon for applications in the infrared wavelength range. Instead of silicon, hydrogenated amorphous silicon (a-Si:H) has been used for achieving quasi-BIC resonance in parts of visible spectra. Titanium dioxide (TiO₂) has emerged as an alternate material for fabricating dielectric metasurfaces with high Q-factor in the visible spectral range due to its lower absorptive losses and high refractive index. However, the fabrication process for TiO₂ nanostructures presents challenges compared to the well-established fabrication processes in silicon. Our work focuses on the design and fabrication of TiO₂ metasurfaces supporting a quasi-BIC mode around 795 nm, with a theoretical Q-factor of 353. Experimental results reveal a maximum Q-factor of 258 at 791 nm. We discuss encountered fabrication constraints and explore possibilities for improvement in both design and fabrication processes. This study contributes to the understanding of quasi-BIC resonance in TiO₂ metasurfaces, and opens avenues for further exploration in the utilization of TiO₂ for high-Q dielectric metasurfaces, offering i nsights i nto t he d esign and optimization of these structures.