Photovoltage Dynamics of the Hydroxylated Si(111) Surface Investigated by Ultrafast Electron Diffraction

TL;DR

This paper introduces a new ultrafast electron diffraction technique to measure transient photovoltage at nanointerfaces, revealing charge relaxation dynamics on hydroxylated silicon surfaces with high temporal and spatial resolution.

Contribution

The study develops and applies a novel ultrafast diffraction method to directly observe interfacial charge dynamics and photovoltage changes in hydroxyl-terminated silicon surfaces.

Findings

Transient surface voltage measured via Coulomb refraction changes.

Charge relaxation mechanism linked to carrier dynamics.

Method aligns with ultrafast photoemission results.

Abstract

We present a novel method to measure transient photovoltage at nanointerfaces using ultrafast electron diffraction. In particular, we report our results on the photoinduced electronic excitations and their ensuing relaxations in a hydroxyl-terminated silicon surface, a standard substrate for fabricating molecular electronics interfaces. The transient surface voltage is determined by observing Coulomb refraction changes induced by the modified space-charge barrier within a selectively probed volume by femtosecond electron pulses. The results are in agreement with ultrafast photoemission studies of surface state charging, suggesting a charge relaxation mechanism closely coupled to the carrier dynamics near the surface that can be described by a drift-diffusion model. This study demonstrates a newly implemented ultrafast diffraction method for investigating interfacial processes, with both charge and structure resolution.