Controlling In-Plane Isotropic and Anisotropic Orientation of Organic Semiconductor Molecules on Ionic Fluoride Dielectrics

Year: 2017

Authors: Jiang T.M., Koshmak K., Giglia A., Banshchikov A., Sokolov N.S., Dinelli F., Capelli R., Pasquali L.

Autors Affiliation: Univ Paris 11, ISMO, UMR 8214, Inst Sci Mol Orsay, Batiment 351, F-91405 Orsay, France; Univ Modena & Reggio Emilia, Dipartimento Ingn E Ferrari, Via Vivarelli 10, I-41125 Modena, Italy; CNR, IOM Ss 14, Km 163-5 AREA Sci Pk, I-34149 Trieste, Italy; Russian Acad Sci, Ioffe Phys Tech Inst, Solid State Phys Div, 26 Polytech Skaya Str, St Petersburg 194021, Russia; CNR, INO Area Ric Pisa S Cataldo, Via Moruzzi l, I-56124 Pisa, Italy; Univ Johannesburg, Dept Phys, POB 524, ZA-2006 Auckland Pk, South Africa.

Abstract: alpha-Sexithiophene (6T) ultrathin films have been grown on CaF2(111)/Si(111) planar surfaces and on CaF2(110)/Si(001) ridged surfaces by molecular beam epitaxy. The growth mode has been studied by means of atomic force microscopy (AFM), photoemission, and near edge X-ray absorption fine structure (NEXAFS). AFM reveals a substantial difference in the film morphology on the two substrates: on CaF2(111) large islands with flat terraces form with no in-plane preferential growth direction; on CaF2(110) narrow and elongated islands develop following the substrate corrugation. Photoemission and X-ray absorption at Ca L-2,L-3 and F K edges indicate that the interaction with the substrate is negligible. Near-edge X-ray absorption (NEXAFS) flanked by DFT calculations of the angular-resolved absorption cross section of 6T at the carbon K-edge reveal that the molecules on both substrates have their long axis vertically oriented with respect to the substrate plane. In addition, in-plane anisotropy of the molecular orientation has been observed on CaF2(110), and it has been interpreted in terms of well aligned molecules in the elongated islands.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY C

Volume: 121 (8)      Pages from: 4426  to: 4433

More Information: T. Jiang thanks the Chinese Scholarship Council for his Ph.D. scholarship. This work was partly supported by Italian FAR 2015. The research leading to some of these results has received funding from the European Community´s Seventh Framework Program (FP7- IRSES-2009) grant agreement no. 247518 (ONDA). Parts of the experiments were carried out in proposal n. 20150163 at Elettra. S. Nannarone is acknowledged for useful discussions and suggestions.
KeyWords: ELECTRONIC-STRUCTURE; ALPHA-SEXITHIOPHENE; EPITAXIAL-GROWTH; CAF2; ADSORPTION
DOI: 10.1021/acs.jpcc.6b12926

Citations: 3
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