**2. Electrically controlled optical responses of silicon-based nanoantennas**

In this chapter, we will discuss the applications of silicon-based Mie resonators into electro-optical modulation. This chapter can be divided into two parts:

First, we demonstrated the electrically tunable scattering of a single silicon nanoparticle at visible wavelengths. To build the nanoantennas, gold interdigital electrodes with separation distances between 100 and 200 nm were fabricated using photolithography and focused ion beam (FIB) milling. After trapping silicon nanoparticles with different sizes between adjacent two electrodes, the scattering spectra under different voltages can be measured. Interestingly, the scattering experiences blueshift and obvious intensity attenuation when increasing the applied voltages from 0 to 1.5 V. In theory, MIS (metal-insulator-semiconductor) junctions can be formed at Au-SiO2-Si interfaces [28]. Once the bias voltage increases, the inversion and accumulation effect would produce much more free carriers at interfaces [29–31] and then change the permittivity based on Drude model [32, 33]. The proposed hybrid nanoantennas represent a new method to build optoelectronic devices based on Mie resonators.

Second, we combined silicon nanostripes, a typical Mie resonator, with WS2 to realize active PL manipulation. In the proposed electro-optical modulator, suspended monolayer and bilayer WS2 are covered on a Si nanostripe. The Si nanostripe not only acts as a nanoscale gate electrode but also a Mie resonator. For both monolayer and bilayer WS2, the PL intensities on the nanostripes are much stronger than those of the suspended one. After applying gate voltages, both the electrostatic doping and strain come into effect. This new tuning mechanism leads to abnormal control of exciton emission from WS2, which is clearly different from that in previous works [34–36]. Considerable PL tuning can also be observed in bilayer WS2 gated by Si nanostripes. Based on the modulation capability, we believe the proposed electro-optical modulator will bring new possibilities for future nanophotonic devices.
