Observation and control of potential-dependent surface state formation at a semiconductor-electrolyte interface via the optical anisotropy

TL;DR

This study demonstrates how optical anisotropy measurements can detect potential-dependent surface state formation at a semiconductor-electrolyte interface, providing a new method to understand and control these complex surface phenomena.

Contribution

The paper introduces an optical anisotropy-based technique to observe and control surface state formation at semiconductor-electrolyte interfaces under operational conditions.

Findings

Optical anisotropy shifts indicate surface state formation.

Surface states can be switched on or off with applied potential.

New electro-optical method for interface characterization.

Abstract

The interface between semiconductors and ion-conducting electrolytes is characterised by charge distributions and potential drops that vary substantially with the evolution of surface states. These surface states at the very interface to the liquid can form or be passivated, depending on the applied potential between electrode and electrolyte, and hereby fundamentally impact properties such as charge transfer. Characterisation and understanding of such potential-dependent surface states with high spatial and temporal resolution is a significant challenge for the understanding and control of semiconductor-electrolyte interfaces. Here, we show that the optical anisotropy of InP(100) can be used to detect the potential-dependent formation of highly ordered surface states under operating conditions. Upon formation of a surface state in the bandgap of the semiconductor, the potential drop and hence the electric field is shifted away from the semiconductor to the Helmholtz-layer of the electrolyte. This modifies the instantaneous response of the optical anisotropy to disturbances of the applied potential. We propose an electrochemical variant of the linear electro-optical effect and our findings open a novel route for understanding these interfaces. The results show how surface states from surface reconstructions at this reactive interface can be switched on or off with the applied potential.