Dynamic Color Tuning with Electrochemically Actuated TiO₂ Metasurfaces.

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Dynamic tuning of metamaterials is crucial for advanced functionalities and broader bandwidths.
• Visible spectrum color tuning is limited by high absorption, especially at blue wavelengths, during index changes.
• Existing actuators like tungsten oxide (WO3) face challenges with absorption at high frequencies.

Purpose of the Study:

• To investigate the potential of electrochemically lithiated anatase titanium dioxide (TiO2) for dynamic visible color tuning.
• To demonstrate the performance of TiO2/LTO in optical devices like Fabry-Perot cavities and gap plasmon metasurfaces.
• To compare the TiO2/LTO system with established actuators in terms of dynamic range, speed, and cyclability.

Main Methods:

• Electrochemical lithiation of anatase TiO2 to form Li0.5TiO2 (LTO).
• Characterization of optical properties, including refractive index and absorption coefficient, particularly at visible wavelengths.
• Integration of the TiO2/LTO material into a Fabry-Perot cavity and a gap plasmon metasurface device configurations.

Main Results:

• LTO exhibits a significant refractive index change (0.65 at 649 nm) with low absorption (<0.1) in the blue wavelength region.
• The TiO2/LTO Fabry-Perot device achieved a reflectance shift exceeding 100 nm with a low applied bias of 2 V.
• The gap plasmon metasurface demonstrated enhanced switching speeds, and the TiO2/LTO system showed competitive dynamic range, speed, and cyclability.

Conclusions:

• Electrochemical lithiation of TiO2 to LTO provides a promising route for low-absorption, dynamic visible color tuning in metamaterials.
• The TiO2/LTO system is a viable alternative to WO3, offering advantages in reduced absorption at high frequencies.
• This material system holds potential for next-generation tunable optical devices and advanced functional metamaterials.