Strategies for enhanced layer-by-layer growth of organic thin films
Linus Pithan
ESRF Grenoble
11:15 - 12:15 Wednesday 16 January 2019 PH01150 In this seminar two model systems will be discussed to shine light from different aspects on enhanced temperature control during - and after - organic thin films growth.
The first part of the talk focusses on a real-time study of thermal annealing to produce atomically flat n-alkane layers. The thermal annealing behavior of n-tetratetracontane (TTC, $C_{44}H_{90}$) is analysed in detail with the aim to improve surface smoothness and to increase the lateral size of crystalline islands of polycrystalline TTC films on SiO, a material system also of interest from a device perspective. In situ X-ray diffraction is used to find an optimum temperature leading to improved texture and crystallinity while avoiding an irreversible phase transition. Further, results of real-time optical phase contrast microscopy with sub-nm height resolution to track the diffusion of TTC across monomolecular step edges are used to show that the lateral island sizes increase by more than one order of magnitude. This desirable behavior of 2d-Ostwald ripening and the pronounced smoothing contrasts the one to many other organic molecular films where annealing leads to dewetting, roughening, and a pronounced 3d morphology. It is originated in the highly anisotropic attachment energies of n-alkanes combined with low surface energies.
The second part of the talk shines light on a novel concept to make use of real time temperature control on the timescale of individual monolayer growth. Varying the substrate temperature during the growth of individual monolayers of PTCDI-C8 ($C_{40}H_{42}N_2O_4$) allows one to control the nucleation and coalescence regimes and to enhance layer-by-layer growth. In situ X-ray reflectivity at the anti-Bragg point combined with GISAXS and post-growth atomic force microscopy show that dynamic heating consistently leads to smoother films compared films grown with static substrate temperatures.
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Institute of Solid State Physics
