  When plasmonic nanoparticles are coupled with semiconductors, highly
energetic hot carriers can be extracted from the metal-semiconductor interface
for various applications in light energy conversion. Hot charge-carrier
extraction upon plasmon decay using such an interface has been argued to occur
after the formation of an intermediate electron population with a uniform
momentum distribution. The efficiency of the charge separation process is thus
discussed to be limited by this spatial homogeneity in certain plasmon-induced
applications. Here we demonstrate using visible pump, near-infrared probe
transient absorption spectroscopy that increases in the contact area between
metal and semiconductor leads to an increase in the quantum yield for hot
electron injection that is inconsistent with the homogeneous energy-momentum
distribution of hot-electrons. Instead, further analysis of the experimental
data suggests that the highly energetic electrons are emitted across the
interface via a surface charge emission mechanism that occurs via a plasmon
excitation
