  We present a general formalism of ultrafast diffractive voltammetry approach
as a contact-free tool to investigate the ultrafast surface charge dynamics in
nanostructured interfaces. As case studies, the photoinduced surface charging
processes in oxidized silicon surface and the hot electron dynamics in
nanoparticle-decorated interface are examined based on the diffractive
voltammetry framework. We identify that the charge redistribution processes
appear on the surface, sub-surface, and vacuum levels when driven by intense
femtosecond laser pulses. To elucidate the voltammetry contribution from
different sources, we perform controlled experiments using shadow imaging
techniques and N-particle simulations to aid the investigation of the
photovoltage dynamics in the presence of pho- toemission. We show that
voltammetry contribution associated with photoemission has a long decay tail
and plays a more visible role in the nanosecond timescale, whereas the
ultrafast voltammetry are dominated by local charge transfer, such as surface
charging and molecular charge transport at nanostructured interfaces. We also
discuss the general applicability of the diffractive voltammetry as an integral
part of quantitative ultrafast electron diffraction methodology in researching
different types of interfaces having distinctive surface diffraction and
boundary conditions.
