Crystalline thin film growth in anisotropic mixtures: a combined approach by experiment, theory and simulation

• Applicants: Professor Dr. Martin Oettel; Professor Dr. Frank Schreiber
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Experimental Condensed Matter Physics
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271660218

We will investigate thin film growth in mixtures of anisotropic particles on substrates using a combined approach by experiment, theory and simulation. The first central goal is to explore and explain the crossover between near-equilibrium growth and kinetically determined growth by analyzing suitable coarse-grained models with different theoretical and simulation methods on different length and time scales. Insights and findings from these investigations shall be applied to the experimental systems of two-component mixtures of organic semiconductors on different substrates, varying in their attraction strength for the organic molecules. These systems are relevant for potential applications in organic electronics. We want to understand growth in these particular systems in the context of surface thermodynamics and surface phase diagrams. These surface phase diagrams will be a central result of the theoretical and simulation-based investigations. As the second central goal, we aim at control over structures in anisotropic film growth through variation of substrate temperature and growth rate protocol by exploiting the bulk and surface thermodynamics of the anisotropic material. The proposed methods of investigation are: (i) classical density functional theory on the basis of Fundamental Measure Theory, ideally suited for the determination of bulk and surface thermodynamics in coarse-grained models of anisotropic mixtures, (ii) on-lattice and off-lattice simulations to determine phase diagrams and to cover different time and length scales in the film growth process and (iii) real-time interface-sensitive scattering techniques (X-ray reflectivity [XRR], grazing incidence X-ray diffraction [GIXD], grazing incidence small-angle X-ray scattering [GISAXS] / diffuse scattering) combined with post-growth atomic force microscopy (AFM) for the characterization of grown structures. Special emphasis lies on the interconnected approach: theory and off-lattice simulations will establish phase diagrams and provide parameters for more coarse-grained on-lattice simulations of Kinetic Monte Carlo type, and experiments will be carried out to explore growth conditions near surface phase transitions which have been determined correspondingly. Thus we expect to obtain a comprehensive picture of growth in such systems.

• DFG Programme: Research Grants
• International Connection: Luxembourg
• Partner Organisation: Fonds National de la Recherche
• Cooperation Partner: Professorin Dr. Tanja Schilling