Surface induced crystallographic order in sexiphenyl thin films

• Published in: Journal of physics. Condensed matter Vol. 20; no. 18; pp. 184009 - 184009 (10)
• Main Author: Resel, R
• Format: Journal Article
• Language: English
• Published: IOP Publishing 07.05.2008
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/20/18/184009

The crystallographic order in sexiphenyl thin films on dielectric surfaces (like thermally oxidized silicon, KCl(100), TiO2(110) mica (001)) and on metallic surfaces (like Au(111), Al(111)) are summarized. The combination of the surface science studies considering the first molecular layers on the substrate surfaces with crystallographic studies on sexiphenyl films reveals the influence of the first molecular layers on the thin-film structure. The interaction strength of the molecules with the substrate has a large influence on the preferred orientation of the crystallites relative to the substrate surface. In the case of metallic surfaces, the orientation of the molecules at the first monolayer determines the alignment of the crystallites in the thin film. In the case of dielectric surfaces, other types of preferred crystal orientations are observed, which is connected with the increasing importance of the intermolecular interaction strength in the first monolayers. Generally, it is observed that the bulk crystal structure is already present in thin films with a nominal thickness slightly larger than the monolayer thickness. The orientation and alignment of the initial crystal clusters at the surface determine the layer growth. The thin films show specific morphologies: depending on the orientation of the molecules relative to the substrate surface, either terraced islands or needle-like structures appear. The crystallite size parallel to the surface varies in a range from nanometres up to several tens of microns, depending on the type of substrate and the thin-film growth conditions. In the case of terraced islands, the crystallite size perpendicular to the surface is comparable with the nominal film thickness.