  The linear band dispersion of graphene's bands near the Fermi level gives
rise to its unique electronic properties, such as a giant carrier mobility, and
this has triggered extensive research in applications, such as graphene
field-effect transistors (GFETs). However, GFETs generally exhibit a device
performance much inferior compared to the expected one. This has been
attributed to a strong dependence of the electronic properties of graphene on
the surrounding interfaces. Here we study the interface between a graphene
channel and SiO$_{2}$, and by means of photoelectron spectromicroscopy achieve
a detailed determination of the course of band alignment at the interface. Our
results show that the electronic properties of graphene are modulated by a
hydrophilic SiO$_{2}$ surface, but not by a hydrophobic one. By combining
photoelectron spectromicroscopy with GFET transport property characterization,
we demonstrate that the presence of electrical dipoles in the interface, which
reflects the SiO$_{2}$ surface electrochemistry, determines the GFET device
performance. A hysteresis in the resistance vs. gate voltage as a function of
polarity is ascribed to a reversal of the dipole layer by the gate voltage.
These data pave the way for GFET device optimization.
