  Understanding the ultra-fast transport properties of hot charge carriers is
of significant importance both fundamentally and technically in applications
like solar cells and transistors. However, direct measurement of charge
transport at the relevant nanometre length scales is challenging with only a
few experimental methods demonstrated to date. Here we report on molecular
nanoprobe experiments on the Si(111)-7x7 at room temperature where charge
injected from the tip of a scanning tunnelling microscope (STM) travels
laterally across a surface and induces single adorbate toluene molecules to
react over length scales of tens of nanometres. A simple model is developed for
the fraction of the tunnelling current captured into each of the surface
electronic bands with input from only high-resolution scanning tunnelling
spectroscopy (STS) of the clean Si(111)-7x7 surface. This model is
quantitatively linked to the voltage dependence of the molecular nanoprobe
experiments through a single manipulation probability (i.e. fitting parameter)
per state. This model fits the measured data and gives explanation to the
measured voltage onsets, exponential increase in the measured manipulation
probabilities and plateau at higher voltages. It also confirms an ultrafast
relaxation to the bottom of a surface band for the injected charge after
injection, but before the nonlocal spread across the surface.
