  The generation and utilization of hot charge carriers in plasmonic materials
have emerged as a topic of significant importance, with profound implications
across multiple disciplines, including optoelectronics, photovoltaics,
photocatalysis, and sensing. In this study, we investigate the hot electron
transfer from nanoporous gold (npAu) in dependence of the structure size,
utilizing both the nanoscale feature size and the interconnected nature of this
material. We employ photoelectron injection from nanoporous gold into the
electrolyte under UV illumination as a test electron transfer process.
Nanoporous gold thin films with sub-10 nm initial ligament diameter are
stepwise coarsened by potential cycles in a photoelectrochemical setup, thereby
allowing us to precisely probe the influence of ligament diameter on the
photocurrent response. The resulting ligament diameter variations are confirmed
by scanning electron microscopy (SEM) analysis. As the ligament diameter
increased from 8 to 16 nm, there was a corresponding decrease in quantum
efficiency proportional to the inverse ligament diameter squared. Such
dependency is expected for electrons excited by surface collisions. For the
small ligament diameter of 10 nm we estimate an emission efficiency of excited
6sp electrons as 3.14%, reaching 23% for the surface excited electrons.
