Fig. 1. Air/Si(111) interface rotation diagram

Fig. 2. (a) SHG response curve of air/Si(111) interface with the pp polarization combination. The circles in the figure represent experimental data points and the solid line represents the fitted curves. (b) Polar map of the air/Si(111) interface. The red circle represents the intensity of the SHG signal and the polar axis represents the angle

Fig. 3. (a) Cyclic voltammogram (CV) curve measured from the Si(111)/CH\begin{document}$ _3 $\end{document}CN system with a scan rate of 50 mV/s. (b) The Mott-Schottky diagram from the Si(111)/CH\begin{document}$ _3 $\end{document}CN system measured at 1500 Hz. The red dots are the experimental data, and the red solid line is obtained by fitting using Eq.(5). The experiment temperature was 298 K

Fig. 4. The potential-dependent SHG intensity of the Si(111)/CH\begin{document}$ _3 $\end{document}CN system at azimuthal angles \begin{document}$ \phi $\end{document} = 0\begin{document}$ ^{\circ} $\end{document}, 30\begin{document}$ ^{\circ} $\end{document} and 60\begin{document}$ ^{\circ} $\end{document}. The red dots are the experimental data, and the black solid line is the fitting curve.

Table 1. Fitting results of potential dependent SHG response for different polarization combinations at $ \phi $=30$ ^{\circ} $

Table 2. Fitting results of potential dependent SHG response for different polarization combinations at $\phi$=0$^{\circ}$. The relative phase $\theta$ cannot be obtained by Eq.(6), and the values are not shown in the table.

Table 3. Fitting results of potential dependent SHG response for different polarization combinations at $ \phi $=60$ ^{\circ} $