  The effects of surface chemical doping on spin transport in graphene are
investigated by performing non-local measurements in ultrahigh vacuum while
depositing gold adsorbates. We demonstrate manipulation of the gate-dependent
non-local spin signal as a function of gold coverage. We discover that charged
impurity scattering is not the dominant mechanism for spin relaxation in
graphene, despite its importance for momentum scattering. Finally, unexpected
enhancements of the spin lifetime illustrate the complex nature of spin
relaxation in graphene.
