  We investigate the (0001) surface of single crystal quartz with a
submonolayer of Rb adsorbates. Using Rydberg atom electromagnetically induced
transparency, we investigate the electric fields resulting from Rb adsorbed on
the quartz surface, and measure the activation energy of the Rb adsorbates. We
show that the adsorbed Rb induces a negative electron affinity (NEA) on the
quartz surface. The NEA surface allows low energy electrons to bind to the
surface and cancel the electric field from the Rb adsorbates. Our results are
important for integrating Rydberg atoms into hybrid quantum systems and the
fundamental study of atom-surface interactions, as well as applications for
electrons bound to a 2D surface.
