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 $2.68\ \mu \mathrm{m},\ 3.16\ \mu \mathrm{m}$, and $3.61\ \mu\mathrm{m}$. 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.