Interfacial Pockels Effect of Solvents with a Larger Static Dielectric Constant than Water and an Ionic Liquid on the Surface of a Transparent Oxide Electrode

Abstract

The optical Pockels effect is a change in the refractive index proportional to an applied electric field. As a typical example of the interfacial Pockels effect occurring at interfaces where the spatial inversion symmetry is broken, it is known that water in the electric double layer (EDL) on the transparent oxide electrode surface has a large Pockels coefficient, but the physical factors that determine its size are not clear. Therefore, we experimentally studied the Pockels effect of water and other characteristic liquids—formamide (FA), methylformamide (NMF) (these two have larger static dielectric constants than water), dimethylformamide (DMF), and an ionic liquid that is itself salts (IL, [BMIM] [BF4])—and evaluated their Pockels coefficients in the EDL on the transparent electrode surface. The magnitude of the Pockels coefficient was found to be in the order of water, DMF, FA, NMF, and IL, with the magnitude of the static dielectric constant not being an important factor.

Pockels Effect at the Interface between Water and Ti Electrode

“…Space Charge Layer (SCL) The Ti surface oxide film is known to be an N-type semiconductor TiO 2 and many impedance measurements have been made on it [21][22][23][24]; the magnitudes of the resistance and capacitance components of the TiO 2 space charge layer (SCL) in Table 1 are in good agreement in order of magnitude with those values reported previously. The magnitudes of the resistance and capacitance components of the EDL of water are also in order of magnitude agreement with previously reported values [25].…”