Growth Dynamics of Supramolecular Self-assembly on Surfaces

The proposed research aims to substantially improve the capability of forming high quality two-dimensional supramolecular self-assembled structures, in order to expand the potential of this very promising technology. The self-assembly of metal-ligand coordinated (MLC) supramolecular structures has for many years been used successfully for the bottom-up fabrication of novel three-dimensional (3D) functional materials. Recently, metal-ligand coordination has also proven to be a viable strategy for the design and assembly of two-dimensional (2D) supramolecular structures on metal surfaces. These 2D-MLC systems provide opportunities beyond those available with 3D systems, since 2D systems are particularly relevant for a wide range of technological applications such as solid state devices. However, fabrication of these 2D systems frequently generates inhomogeneities, such as structural defects, polymorphic phases and orientational domains, that would generally limit performance in practical device applications. The difficulty of fabricating high quality 2D-MLC systems can be attributed to insufficient control over their growth. In the proposed research, we will address this key issue by investigating pertinent factors that determine the growth dynamics and self-assembly of 2D-MLC systems. These investigations will be carried out by means of a close coupling of calculations using density functional theory and experimental measurements using scanning tunneling microscopy and low energy electron microscopy. Our complementary theoretical and experimental investigations will focus on understanding the fundamental intermolecular and molecule-substrate bonding interactions that give rise to 2D-MLC self-assembly and define the energy landscape on which growth takes place. We will also investigate experimentally the kinetics of 2D molecular mass transport, which plays an integral role in growth on crystalline surfaces. These experimental studies of kinetics are expected to provide quantitative information about kinetic energy barriers that originate in the intermolecular and molecule- substrate bonding energetics, which we will model at the first principles level. This research will contribute a deeper understanding of the growth dynamics of 2D-MLC supramolecular systems at metal surfaces. Such knowledge is crucial for optimizing the quality of 2D-MLC systems, an essential step toward realizing their potential in numerous applications.