The mobility of indium on the Zn-polar (0001) surface of single crystal ZnO wafers was investigated using real-time x-ray photoelectron spectroscopy. A sudden transition in the wettability of the ZnO(0001) surface was observed at similar to 520 degrees C, with indium migrating from the (000 (1) over bar) underside of the wafer, around the non-polar (1 (1) over bar 00) and (11 (2) over bar0) sidewalls, to form a uniform self-organized (similar to 20 angstrom) adlayer. The In adlayer was oxidized, in agreement with the first principles calculations of Northrup and Neugebauer that In2O3 precipitation can only be avoided under a combination of In-rich and Zn-rich conditions. These findings suggest that unintentional In adlayers may form during the epitaxial growth of ZnO on indium-bonded substrates. (C) 2015 AIP Publishing LLC.