  We have measured photoemission spectra of two kinds of TiO$_2$-capped VO$_2$
thin films, namely, that with rutile-type TiO$_2$ (r-TiO$_2$/VO$_2$) and that
with amorphous TiO$_2$ (a-TiO$_2$/VO$_2$) capping layers. Below the
Metal-insulator transition temperature of the VO$_2$ thin films, $\sim 300$ K,
metallic states were not observed for the interfaces with TiO$_2$, in contrast
with the interfaces between the band insulator SrTiO$_3$ and the Mott insulator
LaTiO$_3$ in spite of the fact that both TiO$_2$ and SrTiO$_3$ are band
insulators with $d^0$ electronic configurations and both VO$_2$ and LaTiO$_3$
are Mott insulators with $d^1$ electronic configurations. We discuss possible
origins of this difference and suggest the importance of the polarity
discontinuity of the interfaces. Stronger incoherent part was observed in
r-TiO$_2$/VO$_2$ than in a-TiO$_2$/VO$_2$, suggesting Ti-V atomic diffusion due
to the higher deposition temperature for r-TiO$_2$/VO$_2$.
