Epitaxial In$_{2}$O$_{3}$ and Sn-doped In$_{2}$O$_{3}$ thin films with (100) and (111) orientation

In$_{2}$O$_{3}$ and Sn-doped In$_{2}$O$_{3}$ (Indium-Tin Oxide, ITO) have optical transparency and low electrical resistivity. Relatively little is known about their atomic-scale surface properties because of challenges in preparing single crystal samples. We have grown epitaxial In$_{2}$O$_{3}$ and ITO films on Yttrium Stabilized Zirconia. The (100) surface has polar character and the (111) orientation is non-polar. Films were prepared using oxygen-plasma assisted e-beam epitaxy under UHV conditions and the growth was monitored by RHEED. \textit{In-situ} characterization with XPS, ARXPS, LEED and synchrotron-based UPS was used. In$_{2}$O$_{3}$ (100) facets while ITO(100) stays with a 1x1 termination and Sn segregates to surface. In$_{2}$O$_{3}$ and ITO (111) exhibit a 1x1 termination. On both orientations valence band maximum is 2.7 eV below the Fermi level. For the ITO films resonant photoemission measurements indicate a Sn-derived band gap state.