Heterogeneous LiNbO3/Si Direct Bonding for Wavelength-Dependent Mid-Infrared Imaging

Lithium niobate (LiNbO3) is one of the most important multifunctional materials, which possesses excellent electro-optic and piezoelectric properties, as well as high transmittance in the mid-infrared (mid-IR) wavelength range. In this work, we developed a wet sequential plasma activated method for the heterogeneous direct bonding of single-crystal LiNbO3 and Si with a nanometer-scale (6.4 nm) interface. Both surface and interface characterizations are used for the exploration of the bonding mechanism. For the first time, atomic structures of the LiNbO3/Si direct bonding interface have been disclosed. Leveraging this direct bonding method, we creatively integrate the metasurface into the LiNbO3-based nanofluidics for wavelength-dependent imaging. Because of the accurate nanogap control between the nanoantenna and metal reflector, the quadrupole resonance can be well excited. Therefore, the mid-IR imaging with ultrahigh contrast has been achieved in the wavelength of 2.68, \ 3.16, and 3.61. Moreover, since the hot spots are completely exposed in the nanochamber, which can be filled with various types of liquids. More images can be designed and presented based on the light-matter interaction and changes of refractive index. Therefore, this hybrid LiNbO3-based nanofluidics has great potential in the applications of switchable optical devices and information encryption.