Degradation and segregation: Thermal stability and highly ordered epitaxial thin films of large aromatic molecules

The authors present an investigation of highly ordered epitaxial thin films of large organic molecules, namely quaterrylene derivatives. Even though the raw material quaterrylene tetracarboxylic diimide (QTCDI) starts to decompose below its sublimation temperature, epitaxial monolayers could be grown. By modifying the preparation procedure, highly ordered domains of quaterrylene dicarboxylic monoimide, being the main decomposition product of QTCDI, could also be produced. Although both molecules bear strong similarities, they grow in a dissimilar fashion influenced by their substituents and molecular dipole and quadrupole moments. The structures are characterized by scanning tunneling microscopy and, in case of QTCDI, low energy electron diffraction.