Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, 710119, China.
Phys Chem Chem Phys. 2018 Nov 28;20(46):29539-29548. doi: 10.1039/c8cp05621h.
We performed potential dependent second harmonic generation (SHG) measurements on the Si(111) electrolyte interface at different azimuthal angles and for different polarization combinations. When the external potential was biased from the equilibrium potential to the flatband potential (Efb), the SHG intensity decreased linearly with the potential when the azimuthal angle was oriented at 30°. This linearity extends well beyond the linear region of the Mott-Schottky plot as measured traditionally by capacitance measurements. When the external potential was scanned from Efb toward more negative potentials, the response of SHG intensity showed quadratic behavior and can be described by the parabolic model. The non-parabolic potential dependence cannot be explained with the parabolic model proposed from previous literature. Such asymmetric behavior only implied that the interfacial structure of the Si(111) electrode changes from semiconductor to metal with the applied electric potential biased negatively, i.e. with accumulation of electrons in the surface region. The anisotropic contribution from the Si(111) electrode can also significantly affect the SHG response as seen where the minimum of the potential dependent SHG curve shifts away from Efb.
我们在不同的方位角和不同的偏振组合下对 Si(111)电解质界面进行了依赖于势的二次谐波产生 (SHG) 测量。当外加电势从平衡电势偏置到平带电势 (Efb) 时，当方位角定向在 30°时，SHG 强度随电势线性减小。这种线性度远远超出了传统通过电容测量测量的 Mott-Schottky 图的线性区域。当外加电势从 Efb 扫描到更负的电势时，SHG 强度的响应表现出二次行为，可以用抛物模型来描述。非抛物电势依赖性不能用先前文献中提出的抛物模型来解释。这种不对称行为仅意味着 Si(111)电极的界面结构随着施加的负偏置电势从半导体变为金属而发生变化，即表面区域的电子积累。来自 Si(111)电极的各向异性贡献也会显著影响 SHG 响应，如电势相关 SHG 曲线的最小值偏离 Efb 时所示。
