First steps on the way to a superconductive organic layer

Since solid coronene was recently discovered to exhibit superconductive properties by intercalation with potassium, we investigated the potassium doping of ultrathin coronene layers in the (sub-) monolayer regime on Ag(111). The doping process was controlled using in situ differential reflectance spectroscopy (DRS) during the preparation. We show that before the formation of monoanions starts, a primary phase seems to appear which shows a stronger hybridization than the undoped molecules. Higher potassium concentration leads to the occurrence of dianions. Trianions or higher doped species were never observed. After stopping the potassium deposition the dianions decay into monoanions and into molecules in the primary phase. All species up to monoanions are stable and could be further investigated electronically via scanning tunneling microscopy / spectroscopy (STM, STS). While the potassium atoms are not resolved in the STM images, the doping process is evidenced by characteristic features in the related STS data we want to show. We also observed a new well-ordered structure of undoped coronene on Ag(111) for a coverage below 1ML determined by low energy electron diffraction (LEED) and STM.