Multimorphism in molecular monolayers: Pentacene on Cu(110)

The architecture of the contacting interface between organic molecular semiconductors and metallic or insulating substrates determines its cooperative properties such as the charge injection and the charge-carrier mobility of organic thin-film devices. This paper contributes a systematic approach to reveal the evolution of the different structural phases of pentacene on Cu(110) while using the same growth conditions. Complementary measurement techniques such as scanning tunneling microscopy and low-energy electron diffraction together with ab initio calculations are applied to reveal the complex multiphase behavior of this system at room temperature. For coverages between 0.2 and 1 monolayer (ML) a complex multiphase behavior comprising five different phases is observed, which is associated to the interplay of molecule/molecule and molecule/substrate interactions. Multimorphism critically depends on the thermodynamics and kinetics determined by the growth parameters as well as the system itself and arises from shallow energy minima for structural rearrangements. In consequence, the multimorphism affects the interface structure and therefore the interface properties.