Role of Phase Stabilization and Surface Orientation in 4,4 '-Biphenyl-Dicarboxylic Acid Self-Assembly and Transformation on Silver Substrates

Molecular functionalization of nanoparticles and metallic substrates can be used to tune their properties for specific applications. However, polycrystalline substrates and nanoparticles exhibit surface planes with distinct crystallographic orientations. Therefore, the development of reliable strategies for molecular functionalization requires knowledge of the role of the surface plane orientation in the growth kinetics, structure, and properties of the molecular layer. Here, we apply a combination of low-energy electron microscopy and diffraction, scanning tunneling microscopy, and photoelectron spectroscopy to investigate the self-assembly of 4,4'-biphenyl-dicarboxylic acid (BDA) on Ag(111) and critically discuss the difference to Ag(100). The structural motifs for intact and fully deprotonated BDA are similar on both surfaces, however, the intermediate phases comprising partially deprotonated BDA differ in structure and chemical composition. A real-time view of the phase transformations enables us to present a generalized picture of the phase transformations between the self-assembled molecular phases on the surfaces and underline important features such as the phase stabilization of the chemical composition and the mechanism of the related burst transformation. The influence of the substrate orientation on the structure of molecular layers and phase transformations provides the necessary background for developing functionalization strategies of the substrates displaying multiple surface planes and kinetic models for the growth near thermodynamic equilibrium.