Miletic, M.; Palczynski, K.; Dzubiella, J.: Influence of partial fluorination on growth modes of organic molecules on amorphous silicon dioxide. Physical Review Materials 6 (2022), p. 033403/1-12
10.1103/physrevmaterials.6.033403
Abstract:
We study the influence of fluorination on nucleation and growth of the organic parasexiphenyl molecule (p-6P) on amorphous silicon dioxide (a−SiO2) by means of atomistically resolved classical molecular dynamics computer simulations. We use a simulation model that mimics the experimental deposition from the vapor and subsequent self-assembly onto the underlying surface. Our model reproduces the experimentally observed orientational changes from lying to upright standing configurations of the grown layers. We demonstrate that the increase in the number of fluorinated groups inside the p-6P leads to a smoother, layer-by-layer growth on the a−SiO2 surface: We observe that in the first layers, due to strong molecule-substrate interactions the molecules first grow in chiral (fan-like) structures, where each consecutive molecule has a higher angle, supported by molecules lying underneath. Subsequently deposited molecules bind to the already standing molecules of the chiral structures until all molecules are standing. The growth of chiral islands is the main mechanism for growth of the fluorinated p-6P derivative, while the p-6P, due to the lower interaction with the underlying substrate, forms less chiral structures. The higher degree of chirality leads to a lower-energy barrier for step-edge crossing for the fluorinated molecules. We find that partial fluorination of the p-6P molecule can, in this way, significantly alter its growth behavior by modifying rough, three-dimensional growth into smooth, layer-by-layer growth. This has implications for the rational design of molecules and their functionalized forms, which could be tailored for a desired growth behavior and structure formation.