PHYSICAL REVIEW MATERIALS 6, 033403 (2022) Influence of partial fluorination on growth modes of organic molecules on amorphous silicon dioxide Mila Miletic Research Group Simulations of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany and Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, 12489 Berlin, Germany Karol Palczynski * Research Group Simulations of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany Joachim Dzubiella † Applied Theoretical Physics - Computational Physics, Albert-Ludwigs-Universität Freiburg, Hermann-Herder Straße 3, D-79104 Freiburg, Germany and Research Group Simulations of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany (Received 21 October 2021; revised 9 March 2022; accepted 9 March 2022; published 24 March 2022) We study the influence of fluorination on nucleation and growth of the organic parasexiphenyl molecule ( p-6P) on amorphous silicon dioxide (a-SiO 2 ) 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-SiO 2 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. DOI: 10.1103/PhysRevMaterials.6.033403 I. INTRODUCTION Hybrid structures of organic and inorganic semiconductors (HIOS) have shown enormous application potential in recent years [1–3]. Combining the favorable properties of individual materials into a single conjugate makes it possible to realize device properties that cannot be achieved with either material class alone. To control the properties and functions of HIOS, it is necessary to know the molecular structure and to understand the molecule-molecule interactions and the molecule-surface interactions at the hybrid interface during the interface for- mation. Then controlling the properties and functions of HIOS can be accomplished by a combination of chemical functionalization of the organic adsorbates and a careful se- lection of the underlying surface. * karol.palczynski@helmholtz-berlin.de † joachim.dzubiella@physik.uni-freiburg.de For instance, the hydrogens in the meta positions of both terminal phenyl groups of the prototypical organic parasex- iphenyl ( p-6P) molecule can be substituted by fluorine atoms to introduce two local dipole moments at both terminal groups [4,5]. This, in turn, changes the degree of diffusion-anisotropy of the molecule on the inorganic zinc oxide (10 10) sur- face, which leads to differences in the growth morphology [6]. Films of p-6P are characterized by a three-dimensional (3D) morphology with mound-like crystalline islands and a rather rough surface. In contrast, the fluorinated derivative ( p-6P4F) grows in a layer-by-layer mode with a smooth, two- dimensional (2D) morphology [7]. Various other fluorinated derivatives of p-6P show a strong impact of the fluorine posi- tions on the structures of the thin films and on their energetics [8]. Strong molecule-surface interactions can lead to further interesting growth phenomena: surface-induced polymorphs [7,9–16], wetting layers, i.e., flat-lying molecules at the inter- faces [17,18], or the formation of defective islands with tilted or disordered edges [19]. 2475-9953/2022/6(3)/033403(12) 033403-1 ©2022 American Physical Society