Photoemission study of Ti O2/V O2 interfaces

We have measured photoemission spectra of two kinds of Ti O2 -capped V O2 thin films, namely, that with a rutile-type Ti O2 capping layer (r Ti O2/V O2) and that with an amorphous Ti O2 capping layer (a Ti O2/V O2). Below the metal-insulator transition temperature of the V O2 thin films, ∼300 K, Ti O2 and V O2 form an interface between a band insulator with the d0 electronic configuration and a Mott (or Mott-Peierls) insulator with the d1 electronic configuration. Metallic states were, however, not observed at the interfaces, in contrast to the interfaces between the d0 band insulator SrTi O3 and the d1 Mott insulator LaTi O3. We discuss possible origins of the difference between Ti O2/V O2 and SrTi O3/LaTi O3, and suggest the importance of the polarity discontinuity in the latter interface. The stronger incoherent part was observed in r Ti O2/V O2 than in a Ti O2/V O2, suggesting Ti-V atomic diffusion due to the higher deposition temperature for r Ti O2/V O2.