Understanding the Adsorption Energetics of Growth Polymorphs of FerroceneDerivatives: Microscopic Thermal Desorption Analysis

The ultra-thin films of 2-ferrocenyl-1,3-dithiolane (FcS2C3) and 2-ferrocenyl-1,3-dithiane (FcS2C4) drop-casted from toluene on highly oriented pyrolytic graphite (HOPG) surface are investigated using atomic force microscopy (AFM). Two types of growth polymorphs have been observed, which are distinctly different based on their nature of growth and the molecular level packing. We have developed a new type of temperature dependent desorption experiment named as “Microscopic Thermal Desorption Analysis” (MTDA) for understanding the adsorption energetics related to the observed growth polymorphs on the surface. Using MTDA, we have calculated the adsorption energies of growth polymorphs of both molecules and further revealed that their formation requires an activation energy. The subtle relation between the adsorption energies and activation energies of growth polymorphs account for their average abundance on the surface. The experimental observations are further supported by density functional theory (DFT) ca...