  Low-temperature X-ray photoemission electron microscopy (X-PEEM) is used to
measure the electric potential at domain walls in improper ferroelectric
Er0.99Ca0.01MnO3. By combining X-PEEM with scanning probe microscopy and
theory, we develop a model that relates the detected X-PEEM contrast to the
emergence of uncompensated bound charges, explaining the image formation based
on intrinsic electronic domain-wall properties. In contrast to previously
applied low-temperature electrostatic force microscopy (EFM), X-PEEM readily
distinguishes between positive and negative bound charges at domain walls. Our
study introduces an X-PEEM based approach for low-temperature electrostatic
potential mapping, facilitating nanoscale spatial resolution and data
acquisition times in the order of 0.1-1 sec.
