Interrelation between Substrate Roughness and Thin-Film Structure of Functionalized Acenes on Graphite

Breuer, Tobias; Salzmann, Ingo; Götzen, Jan; Oehzelt, Martin; Morherr, Antonia; Koch, Norbert; Witte, Gregor

doi:10.1021/cg200894y

Cited by 29 publications

(62 citation statements)

References 31 publications

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“…(b) Specular XRD scans of PFP/graphene (top) and PFP/HOPG as reference (bottom) both showing the PSP(002) reflection. For PFP/HOPG, the HOPG(002) reflection dominates the spectrum (higher harmonics of the substrate marked by stars), while no such diffraction is observed for PFP/graphene; there, minor contributions of standing PFP grown in the TFP, likely related to nucleation on substrate defects, 40 are found. (c) Top: GIXRD-RSM of PFP/graphene yielding the PSP unit cell dimensions.…”

Section: Resultsmentioning

confidence: 99%

Epitaxial Growth of π-Stacked Perfluoropentacene on Graphene-Coated Quartz

et al. 2012

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Chemical-vapor-deposited large-area graphene is employed as the coating of transparent substrates for the growth of the prototypical organic n-type semiconductor perfluoropentacene (PFP). The graphene coating is found to cause face-on growth of PFP in a yet unknown substrate-mediated polymorph, which is solved by combining grazing-incidence X-ray diffraction with theoretical structure modeling. In contrast to the otherwise common herringbone arrangement of PFP in single crystals and “standing” films, we report a π-stacked arrangement of coplanar molecules in “flat-lying” films, which exhibit an exceedingly low π-stacking distance of only 3.07 Å, giving rise to significant electronic band dispersion along the π-stacking direction, as evidenced by ultraviolet photoelectron spectroscopy. Our study underlines the high potential of graphene for use as a transparent electrode in (opto-)electronic applications, where optimized vertical transport through flat-lying conjugated organic molecules is desired.

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Section: Resultsmentioning

confidence: 99%

Epitaxial Growth of π-Stacked Perfluoropentacene on Graphene-Coated Quartz

et al. 2012

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“…Considering that the TDMs corresponding to excitationsi nto p*o rbitals (typically found in the energetic range from 282 to 292 eV for aromatic hydrocarbons) are oriented perpendicular to the molecular backbone, the orientation of the molecules can be determinedbycomparing absorption spectra measured at different sample orientations. [39] For PEN, [40,41] PFP [42,43] and pentacene-5,7,12,14-tetrone (P-TET), [43] it has been reported that the molecular orientation is strongly influenced by the supporting substrate;the molecules adopt upright orientations on SiO 2 whilet hey crystallize in lying configurations on graphite surfaces. Due to the high expenditure of time of the NEXAFS measurements and limited synchrotron beam time these analyses could only be performed for al imited number of compounds.F or this purpose 3, 30 and 42 have been chosen since they represent different types of substitution and the complementary experiments have verifiedt heir processability by vacuum sublimation.…”

Section: Thin-film Studiesmentioning

confidence: 99%

Efficient Syntheses of Novel Fluoro‐Substituted Pentacenes and Azapentacenes: Molecular and Solid‐State Properties

Schwaben

Münster

Klues

et al. 2015

Chemistry A European J

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Non-symmetrical 6,13-disubstituted pentacenes bearing trifluoromethyl and aryl substituents have been synthesized starting from pentacenequinone. Diazapentacenes with a variety of fluorine substituents were prepared either via a Hartwig-Buchwald aryl amination route or by a SNAr strategy. As a result of a non-symmetric substitution pattern containing electron-donating substituents in combination with electron-accepting fluorine substituents, the synthesized compounds feature distinct molecular dipoles. All compounds are analyzed regarding their optoelectronic properties in solution with special focus on the frontier orbital energies as well as their molecular packing in the crystal structures. The analyses of isolated molecules are complemented by thin-film studies to examine their solid-state properties. A precise comparison between these and the molecular properties gave detailed insights into the exciton binding energies of these compounds, which are explained by means of a simple model considering the molecular packing and polarizabilities.

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“…30 The effect of the quality of the graphene substrate on the CuPc thin film morphology and crystal structure could plausibly be extrapolated to other organic films on graphene, especially those with planar aromatic groups. 31 With the many methods of transparent graphene electrode production currently being explored for organic device applications, such as CVD graphene, 32 functionalized graphene, 33 and solutioncast graphene, 34 we show that it is crucial to consider how the distribution of extended defects like steps, wrinkles and etch pits on graphene will impact the properties of subsequent thin film formation. Notable among the graphene variants under heavy investigation in recent years is epitaxial graphene on SiC 35 which is a platform that is intrinsically highly crystalline and also transparent to visible light.…”

Section: Discussionmentioning

confidence: 93%

Toward Single-Crystal Hybrid-Carbon Electronics: Impact of Graphene Substrate Defect Density on Copper Phthalocyanine Film Growth

McAfee

Gann

Guan

et al. 2014

Crystal Growth & Design

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Graphene has long been recognized as a potential replacement for indium tin oxide as a transparent conducting substrate that may not only be cheaper to manufacture but also may provide mechanical flexibility and templating for preferential organic film growth. Here, we report the discovery that the thin film growth mode and crystal structure of copper phthalocyanine (CuPc), a prototype organic semiconductor, is extremely sensitive to even atomic-scale defects (e.g., steps) on the graphene surface and that high quality films can be grown with a well-defined crystal orientation that should be favorable for optimized solar cell applications. The initial growth involves flat-lying copper phthalocyanine molecules in a triclinic brickstone crystal with (012̅ ) orientation. Thicker films on pristine graphite, as well as thin films on lower quality graphene, show an orientational transition to the flat-lying (112̅ )-oriented brickstone, which nucleates near film defects and grows in more compact 3D islands. The thickness dependent transition between these two flat-lying crystal orientations is sensitive to substrate defect density since this determines the extent to which initial island elongation along the substrate can alleviate strain in the film. The sensitivity of copper phthalocyanine film morphology demonstrates the extreme importance of graphene substrate quality to controlling organic film growth. The high crystallinity and optimal molecular orientation achieved here implies a new driving force for high performance organic optoelectronics based on substrate-controlled crystal engineering.

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Interrelation between Substrate Roughness and Thin-Film Structure of Functionalized Acenes on Graphite

Cited by 29 publications

References 31 publications

Epitaxial Growth of π-Stacked Perfluoropentacene on Graphene-Coated Quartz

Epitaxial Growth of π-Stacked Perfluoropentacene on Graphene-Coated Quartz

Efficient Syntheses of Novel Fluoro‐Substituted Pentacenes and Azapentacenes: Molecular and Solid‐State Properties

Toward Single-Crystal Hybrid-Carbon Electronics: Impact of Graphene Substrate Defect Density on Copper Phthalocyanine Film Growth

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