  Clean oxide surfaces are generally hydrophilic. Water molecules anchor at
undercoordinated surface metal atoms that act as Lewis-acid sites, and they are
stabilized by H bonds to undercoordinated surface oxygens. The large unit cell
of In2O3(111) provides surface atoms in various configurations, which leads to
chemical heterogeneity and a local deviation from this general rule.
Experiments (TPD, XPS, ncAFM) agree quantitatively with DFT calculations and
show a series of distinct phases. The first three water molecules dissociate at
one specific area of the unit cell and desorb above room temperature. The next
three adsorb as molecules in the adjacent region. Three more water molecules
rearrange this structure and an additional nine pile up above the OH groups.
Despite offering undercoordinated In and O sites, the rest of the unit cell is
unfavorable for adsorption and remains water-free. The first water layer thus
shows ordering into nanoscopic 3D water clusters separated by hydrophobic
pockets.
