Time-Resolved Measurements of the Interfacial Charge Transfers by Capacitive Voltage Probe

TL;DR

This study introduces a capacitive voltage probe technique to measure and visualize interfacial charge transfer dynamics in real-time, providing insights into photoinduced redox reactions on silicon surfaces.

Contribution

It demonstrates a novel application of a capacitive probe for time-resolved measurement of surface photovoltage in redox chemistry, independent of semiconductor optical properties.

Findings

Electron injection into silicon is extremely fast ( >10^9 s^-1).

Back electron transfer exhibits a broad range of time constants, from microseconds to over a second.

The method allows quantitative analysis of charge transfer rates in surface redox reactions.

Abstract

When redox active molecules are covalently tethered to the surface of the n-doped silicon, light induces their oxidation by the semiconductor. To visualize this charge separation we have followed the formation and decay of the surface photovoltage by an auxiliary transparent electrode, which serves as a capacitive probe that picks up the transient surface photovoltage. This method has been used in electronics and biophysics but is novel for the surface redox chemistry. The probe provides both the direction of the charge transfer and the resolution of the dynamics. Its application is independent of the optical properties of the semiconductor. Laser initiation of the reaction permits quantitative measurements of the reactions with the rate constants ~108-103 s-1. The electron injection from covalently tethered NTCI(A) molecules into silicon was fast (k >109 s-1). The back electron transfer is poly-disperse with the components ranging from ~10 microseconds and up.