  We directly compare the effect of metallic titanium (Ti) and insulating
titanium dioxide (TiO2) on the transport properties of single layer graphene.
The deposition of Ti results in substantial n-type doping and a reduction of
graphene mobility by charged impurity scattering. Subsequent exposure to oxygen
largely reduces the doping and scattering by converting Ti into TiO2. In
addition, we observe evidence for short-range scattering by TiO2 impurities.
These results illustrate the contrasting scattering mechanisms for identical
spatial distributions of metallic and insulating adsorbates.
