Heinz-Georg Flesch

Epitaxially Grown Films of Standing and Lying Pentacene Molecules on Cu(110) Surfaces

Here, it is shown that pentacene thin films (30 nm) with distinctively different crystallographic structures and molecular orientations can be grown under essentially identical growth conditions in UHV on clean Cu(110) surfaces. By X-ray diffraction, we show that the epitaxially oriented pentacene films crystallize either in the “thin film” phase with standing molecules or in the “single crystal” structure with molecules lying with their long axes parallel to the substrate. The morphology of the samples observed by atomic force microscopy shows an epitaxial alignment of pentacene crystallites, which corroborates the molecular orientation observed by X-ray diffraction pole figures. Low energy electron diffraction measurements reveal that these dissimilar growth behaviors are induced by subtle differences in the monolayer structures formed by slightly different preparation procedures.

Temperature stability of the pentacene thin-film phase

This work presents the influence of temperatures above 300 K on the crystal structure and morphology of pentacene thin films. The thermal expansion of the unit cell and the relative amount of different phases are investigated via grazing incidence x-ray diffraction. Geometrical considerations about the specific molecular packing of the thin-film phase explain the anisotropic non-linear expansion. Furthermore, around 480 K, a phase transformation of the thin-film phase to the bulk phase is observed. In contrast, only a weak influence of the temperature on the height distribution of the thin-film phase crystallites is found.

Structure and morphology of an organic/inorganic multilayer stack: An x-ray reflectivity study

The internal morphology and crystallographic properties of a complete organic thin film multilayer stack are characterized via x-ray scattering techniques, atomic force microscopy (AFM), and scanning electron microscopy. The stack consists of the three organic layers – copper(II)phthalocyanine (CuPc), perylene tetracarboxylic bisbenzimidazole (PTCBI), and aluminum-tris(8-hydroxychinolin) (Alq3) – sandwiched between an optically semitransparent gold layer and a top silver electrode. The interface roughness progress is determined by the x-ray reflectivity, which is confirmed by the surface roughness determination via AFM. The crystallographic properties are characterized via x-ray diffraction. The CuPc layer is highly crystalline with preferentially oriented crystallites but forms a rough interface (σRMS = 5.5 nm) toward the PTCBI layer. The PTCBI layer grows with randomly distributed crystallites in a worm-like morphology with an interface roughness of σRMS = 6.4 nm toward the Alq3 layer. The amorphous Alq...