In this study the structural and morphological properties of perylene films deposited on different substrates have been investigated. The film properties have been studied by employing a range of techniques including atomic force microscopy, x-ray diffraction, and drop shape analysis for the determination of the surface free energy. For films deposited on top of Al2O3, the perylene molecules have a fiber texture ordering perpendicular to the substrate, while for films deposited on top of a Au(111) layer, only for thicker films above 400nm were diffraction peaks observed. The different growths of perylene on top of these substrates are attributed to the different strengths of the molecule-substrate interaction.
We investigate the temperature-and flux-dependent roughening of amorphous organic thin films of N,N-diphenyl-N,N-bis(1-naphthyl)-1-1 biphenyl-4,4 diamine (α-NPD) molecules grown by organic vapor phase deposition. We find that organic thin films become unstable at high temperatures and low deposition rates as well as at low temperatures and high deposition rates. Based on a detailed stochastic analysis of the morphology we suggest probable mechanism for the roughening phenomena. Indeed, this result allows us to identify the optimum deposition conditions for relevant technological applications.
Intermolecular interactions in crystalline perylene films on Au(111) have been investigated by Fourier transform infrared spectroscopy. Dimer modes of vibrations are observed in the crystalline film, in contrast to the monomer modes found for isolated perylene molecules. These dimers are formed via hydrogen bonding in the sandwich herringbone structure of the crystalline α-phase. Davydov splitting of both the monomer and the dimer modes is observed due to resonance dynamic intermolecular interaction. The splitting of monomer modes into three distinct vibrations and the occurrence of the dimer modes confirm that the film crystallizes in the α phase, which is in line with the x-ray diffraction results. The frequency shift and band broadening at elevated temperature have been attributed to the cubic and quartic anharmonic interactions.
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