Surface-Controlled Crystal Alignment of Naphthyl End-Capped Oligothiophene on Graphene: Thin-Film Growth Studied by In Situ X-ray Diffraction

Mathias Huss-Hansen, Martin Hodas, Nada Mrkyvkova, Jakub Hagara, Bjarke B. E. Jensen, Andreas Osadnik, Arne Lützen, Eva Majková, Peter Siffalovic, Frank Schreiber, Luciana Tavares, Jakob Kjelstrup-Hansen, Matti Knaapila

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We report on the microstructure, morphology, and growth of 5,5′-bis(naphth-2-yl)-2,2′-bithiophene (NaT2) thin films deposited on graphene, characterized by grazing incidence X-ray diffraction (GIXRD) and complemented by atomic force microscopy (AFM) measurements. NaT2 is deposited on two types of graphene surfaces: custom-made samples where chemical vapor deposition (CVD)-grown graphene layers are transferred onto a Si/SiO 2 substrate by us and common commercially transferred CVD graphene on Si/SiO 2. Pristine Si/SiO 2 substrates are used as a reference. The NaT2 crystal structure and orientation depend strongly on the underlying surface, with the molecules predominantly lying down on the graphene surface (face-on orientation) and standing nearly out-of-plane (edge-on orientation) on the Si/SiO 2 reference surface. Post growth GIXRD and AFM measurements reveal that the crystalline structure and grain morphology differ depending on whether there is polymer residue left on the graphene surface. In situ GIXRD measurements show that the thickness dependence of the intensity of the (111) reflection from the crystalline edge-on phase does not intersect zero at the beginning of the deposition process, suggesting that an initial wetting layer, corresponding to 1-2 molecular layers, is formed at the surface-film interface. By contrast, the (111) reflection intensity from the crystalline face-on phase grows at a constant rate as a function of film thickness during the entire deposition.

Original languageEnglish
Issue number8
Pages (from-to)1898-1906
Publication statusPublished - 3. Mar 2020


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