  We used x-ray photoemission spectroscopy to investigate the electronic
structure of the Mott insulator LaVO3 embedded in LaAlO3. By limiting the upper
layer of LaAlO3 to 3 unit cells, the underlying LaVO3 could be probed. The V 2p
core-level spectra had both V3+ and V4+ components, and above 2 unit cell thick
LaVO3, the structures exhibited spectra similar to bulk samples. The atomically
flat surfaces enabled study of the emission angle dependence, which indicates
the V4+ is localized to the topmost layer. These results demonstrate the
potential for probing interface electronic structure in oxide ultrathin films
by surface spectroscopy.
