Amorphous to Crystalline Transition in Nanoimprinted Sol-Gel Titanium Oxide Metasurfaces

초록

Crystalline titanium dioxide (TiO2) (anatase and rutile) possesses a higher refractive index than amorphous TiO2 and near-zero absorption in the visible region, making them an ideal material for visible metasurfaces. However, fabrication limitations hinder their implementation into flat optics. In this work, a wafer-scale manufacturing platform is proposed for crystalline TiO2 metasurfaces. Sol-gel TiO2 is developed as a printable material in which its material phase can be precisely controlled to produce amorphous, anatase, or rutile, depending on the crystallization temperature. Therefore, anatase or rutile metalenses can be fabricated on a wafer scale using thermal nanoimprint lithography and sintering process. The high refractive index of the crystalline TiO2 contributes to the enhanced conversion efficiency of the fabricated metalenses. The fabricated metalenses exhibit diffraction-limited focusing and imaging capabilities, comparable to the theoretically ideal lenses. A wafer-scale manufacturing platform is introduced for crystalline TiO2 metasurfaces. Anatase or rutile metalenses are fabricated via thermal nanoimprint lithography and sintering. The high refractive index enhances conversion efficiency and numerical aperture. These metalenses demonstrate diffraction-limited focusing and imaging capabilities, showcasing the potential of crystalline TiO2 in advanced flat optics for improved performance in various applications. image

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