Using scanning gate microscopy (SGM), we probe the scattering between a beam of electrons and a two-dimensional electron gas (2DEG) as a function of the beams injection energy, and distance from the injection point. At low injection energies, we find electrons in the beam scatter by small-angles, as has been previously observed. At high injection energies, we find a surprising result: placing the SGM tip where it back-scatters electrons increases the differential conductance through the system. This effect is explained by a non-equilibrium distribution of electrons in a localized region of 2DEG near the injection point. Our data indicate that the spatial extent of this highly non-equilibrium distribution is within ~1 micrometer of the injection point. We approximate the non-equilibrium region as having an effective temperature that depends linearly upon injection energy.
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