  The interface of Pt/TiO$_2$ plays an essential role in device engineering and
chemical reactions. Here, we report the electrostatic potential distribution of
a Pt/TiO$_2$ interface by electron holography. The decrease of the
electrostatic potential exists at TiO$_2$ in the vicinity of the interface,
indicating the presence of negative charge due to electron transfer from
TiO$_2$ and Pt. The decrease of the electrostatic potential can be understood
in the difference in work functions between Pt and TiO$_2$. This study reveals
the interplay between Pt and TiO$_2$ and the usefulness of electron holography
for probing the potential in nanoscale interfaces.
