Alkyl chain assisted thin film growth of 2,7-dioctyloxy-benzothienobenzothiophene

DOI: 10.1039/C9TC01979K

Authors: Harald Spreitzer (Technische Universität Graz) , Benjamin Kaufmann (Institut für Physik, Montanuniversität Leoben) , Christian Ruzié (Université Libre de Bruxelles (ULB)) , Christian Rothel (Technische Universität Graz) , Thomas Arnold (University Bath; ISIS Neutron and Muon Source; Diamond Light Source; European Spallation Source ERIC) , Yves H. Geerts (Université Libre de Bruxelles (ULB)) , Christian Teichert (Institut für Physik, Montanuniversität Leoben) , Roland Resel (Technische Universität Graz) , Andrew O. F. Jones (Technische Universität Graz; Anton Paar GmbH)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Materials Chemistry C , VOL 26

State: Published (Approved)
Published: June 2019
Diamond Proposal Number(s): 13569

Abstract: An understanding of the thin film growth modes of substrate-induced polymorphs allows a deeper insight into the origin of this class of materials. Their onset of crystallisation, the subsequent crystal growth, the evolution of the thin film morphology and the transfer to the equilibrium bulk structure are still not fully understood. This work investigates the thin film formation of a conjugated molecule with terminal alkyl chains. Thin films of 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene were grown by physical vapor deposition on silicon oxide surfaces with varying the film thicknesses from the sub-monolayer regime up to 33 layer thick films. Additionally, the substrate temperature and deposition rate were varied. The films were investigated by atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. The first growth stage is a closed monolayer with a thickness of 3 nm formed by upright-standing molecules. It is found that the substrate-induced crystal structure is already formed within the first monolayer and continues its growth up to the largest investigated film thickness. The characteristic morphology is terraced islands over the whole thickness range. On top of the first monolayer a morphology with several terrace levels appears, which is associated with a rapid increase of the surface roughness. At larger film thicknesses (≥13 nm) the number of terrace steps does not increase significantly, so that the surface roughness only increases slowly. This work shows that molecules with terminal alkyl chains can form a substrate-induced phase up to large film thicknesses without the appearance of the equilibrium bulk phase.

Subject Areas: Materials, Chemistry


Instruments: I07-Surface & interface diffraction

Documents:
fhfh4b4b4.pdf