  Heat is a familiar form of energy transported from a hot side to a colder
side of an object, but not a notion associated with microscopic measurements of
electronic properties. A temperature difference within a material causes charge
carriers, electrons or holes, to diffuse along the temperature gradient
inducing a thermoelectric voltage. Here we show that local thermoelectric
measurements can yield high sensitivity imaging of structural disorder on the
atomic and nanometre scales. The thermopower measurement acts to amplify the
variations in the local density of states at the Fermi-level, giving high
differential contrast in thermoelectric signals. Using this imaging technique,
we uncovered point defects in the first layer of epitaxial graphene, which
generate soliton-like domain wall line patterns separating regions of the
different interlayer stacking of the second graphene layer.
