A Paradigm Shift from 2D to 3D: Surface Supramolecular Assemblies and Their Electronic Properties Explored by Scanning Tunneling Microscopy and Spectroscopy

Abstract

Exploring supramolecular architectures at surfaces plays an increasingly important role in contemporary science, especially for molecular electronics. A paradigm of research interest in this context is shifting from 2D to 3D that is expanding from monolayer, bilayers, to multilayers. Taking advantage of its high‐resolution insight into monolayers and a few layers, scanning tunneling microscopy/spectroscopy (STM/STS) turns out a powerful tool for analyzing such thin films on a solid surface. This review summarizes the representative efforts of STM/STS studies of layered supramolecular assemblies and their unique electronic properties, especially at the liquid–solid interface. The superiority of the 3D molecular networks at surfaces is elucidated and an outlook on the challenges that still lie ahead is provided. This review not only highlights the profound progress in 3D supramolecular assemblies but also provides researchers with unusual concepts to design surface supramolecular structures with increasing complexity and desired functionality.

3D Directional Assembly of Liquid Crystal Molecules

“…In these fundamental building blocks, the manipulation and study of molecules in 3D space through advanced self‐assembly methods, such as supramolecular chemistry and host–guest processes, can significantly contribute to the advancement of multidimensional and multifunctional nanostructures and biomaterials. [ 13–24 ] These interactions used for molecular self‐assembly are inherently short‐range ordering and relatively weak, posing challenges in assembling them into programmable, long‐range ordered structures with high degree of freedom and applying them to various functional devices, such as soft actuators, proton transport membranes, and high‐strength materials. [ 25–28 ] To address this issue, directional assembly methods [ 29 ] such as the template method, [ 30–35 ] solution evaporation, [ 36 ] and shear flow field [ 37–40 ] have all been employed to assemble small molecules into ordered structures.…”

Conformation-Dependent Monolayer and Bilayer Structures of an Alkylated TTF Derivative Revealed using STM and Molecular Modeling

“…Two-dimensional (2D) self-assembled molecular networks (SAMNs) of organic molecules on atomically flat, and often conductive, surfaces have been studied extensively over the past decades due to their potential applicability in different areas ranging from organic photonic or electronic devices to single-molecule switches. − In these reports, it has been demonstrated that during their formation, the surface interacts with molecules and acts as a template facilitating the formation of highly ordered supramolecular networks. Combined with other noncovalent intermolecular forces, such as hydrogen bonding, , van der Waals (vdW), − electrostatic, − dipolar, , and π–π interactions, , molecular assemblies with complex architectures have been built.…”

Formation of Supramolecular Heterostacks at the Liquid–Solid Interface: Impact of Symmetry Mismatching on Structural Growth

“…5 Most previous reports described the epitaxial growth of the same molecular component. 5,6 Those featuring a different component on the first SAMN layer are limited, 7,8 particularly at the liquid/solid interface.…”

“…Self-assembled molecular networks (SAMNs) formed by organic molecules on solid surfaces are not only the subject of curiosity driven interest but may have also interesting applications. − One recent challenge is the construction of three-dimensional (3D) architectures through the epitaxial structural growth from surface-confined SAMNs, not only from a crystal engineering viewpoint but also for the fabrication of functional materials such as 3D metal–organic frameworks and molecular devices . Most previous reports described the epitaxial growth of the same molecular component. , Those featuring a different component on the first SAMN layer are limited, , particularly at the liquid/solid interface.…”