Growth and electronic properties of a potential organic superconductor on Cu(111)

Several polycyclic aromatic hydrocarbons (PAHs) become superconducting after the intercalation of alkali metal atoms. The number of promising candidates has increased in the last few years. Among them, K_3.451,2:8,9-dibenzopentacene (trans-DBPen, C₃₀H₁₈) is the one with the highest critical temperature of 33.1 K reported so far. Nevertheless, the microscopic mechanisms of superconductivity in K-doped PAHs are still under debate. One open question is, for example, the effect of structural order in bulk materials as well as two-dimensional layers. Our work deals with the growth of trans-DBPen on Cu(111) in the monolayer (ML) regime. The self-assembled thin films were prepared using organic molecular beam epitaxy. The structure was characterized by means of low energy electron diffraction (LEED). X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) were used to study the interaction of the molecules with the substrate. In the sub-ML range we observe a 2D gas-like behavior, whereas the first ML is characterized by a highly ordered structure. The results are compared to measurements of trans-DBPen on Au(111) and Ag(111) in terms of the molecule-substrate interaction.