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Title: Thermally driven smoothening of molecular thin films: Structural transitions in n-alkane layers studied in real-time

We use thermal annealing to improve smoothness and to increase the lateral size of crystalline islands of n-tetratetracontane (TTC, C{sub 44}H{sub 90}) films. With in situ x-ray diffraction, we find an optimum temperature range leading to improved texture and crystallinity while avoiding an irreversible phase transition that reduces crystallinity again. We employ real-time optical phase contrast microscopy with sub-nm height resolution to track the diffusion of TTC across monomolecular step edges which causes the unusual smoothing of a molecular thin film during annealing. We show that the lateral island sizes increase by more than one order of magnitude from 0.5 μm to 10 μm. This desirable behavior of 2d-Ostwald ripening and smoothing is in contrast to many other organic molecular films where annealing leads to dewetting, roughening, and a pronounced 3d morphology. We rationalize the smoothing behavior with the highly anisotropic attachment energies and low surface energies for TTC. The results are technically relevant for the use of TTC as passivation layer and as gate dielectric in organic field effect transistors.
Authors:
; ; ; ; ;  [1] ; ;  [2] ; ;  [3]
  1. Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin (Germany)
  2. Institut für Physik, Universität Augsburg, 86135 Augsburg (Germany)
  3. Max-Planck-Institut für Kolloid- und Grenzflächenforschung, 14476 Potsdam-Golm (Germany)
Publication Date:
OSTI Identifier:
22493177
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 16; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALKANES; ANISOTROPY; ANNEALING; DIFFUSION; FIELD EFFECT TRANSISTORS; LAYERS; MICROSCOPY; SURFACE ENERGY; TEMPERATURE RANGE; THIN FILMS; X-RAY DIFFRACTION