Probing the electronic properties of the electrified silicon/water interface by combining simulations and experiments

Silicon (Si) is used in electrochemical and photoelectrochemical devices, and capacitive and Faradaic reactions at the Si/water interfaces are critical for signal transduction or noise generation. However, probing these interfaces at the microscopic level remains a challenging task. Here we focus on hydrogenated Si surfaces in contact with water, relevant to transient electronics and photoelectrochemical modulation of biological cells and tissues. We show that by carrying out first principles molecular dynamics simulations of the Si(100)/water interface in the presence of an electric field, we can realistically correlate the computed flat-band potential and tunneling current images at the interface with experimentally measured capacitive and Faradaic currents. Specifically, we validate our simulations in the presence of bias by performing pulsed chronoamperometry measurements on Si wafers in solution. Consistent with prior experiments, our measurements and simulations indicate the presence of voltage dependent capacitive currents at the interface. We also find that Faradaic currents are weakly dependent on the applied bias, and we relate these currents to surface defects present in newly prepared samples.