Self-assembly of molecules under confinement conditions at liquid-solid interface

Promovendus/a: Lihua Yu

Promotor(en): Prof. dr. Steven De Feyter

Two-dimensional molecular self-assembly is a promising research area that involves the non-covalent attachment of molecular units on substrates. Numerous factors have been shown to significantly influence the assembly behavior and the resulting structures. One of the dominant themes within this field is to reveal the role of interfacial and intermolecular interactions that occur during the assembly process. Specifically, special confinement conditions on the substrate surface offer a unique platform for studying molecular assembly within a controlled environment.

In this thesis, we investigate both simple alkane systems and complex molecules featuring two alkyl chains adsorbed onto highly oriented pyrolytic graphite (HOPG). Our goal is to explore the impact of lateral spatial confinement conditions imposed by the substrate on the formation of self-assembled molecular networks at the liquid/graphite interface. Scanning tunnelling microscopy (STM) is employed not only to visualize the structure and dynamic behavior of these assemblies in real space and time, but also as a lithography tool to fabricate well-defined lateral confinement conditions (referred to as corrals) on covalently modified graphite substrates.

By restricting the assembly of molecules within well-defined spaces (in-situ corrals and ex-situ corrals) and continuously monitoring the dynamics, we observe different molecular behaviors compared to those on infinite pristine graphite. In addition to the well-defined nanoshaved corrals, the “fences” or confined spaces created by randomly distributed chemisorbed molecules with low density on the graphite substrate can also act as stabilizing environments for the molecular assemblies. The stability of assembly domains and transient structures can be studied in detail, allowing for a better understanding of the underlying kinetics and thermodynamics.

This thesis provides novel insights into the nucleation, growth, and Ostwald ripening of molecular assemblies, shedding light on the fundamental principles governing supramolecular chemistry on surfaces.