Abstract
Scanning probe microscopy has become an essential tool to not only study pristine surfaces but also on-surface reactions and molecular self-assembly. Nonetheless, due to inherent limitations, some atoms or (parts of) molecules are either not imaged or cannot be unambiguously identified. Herein, we discuss the arrangement of two different nonplanar molecular assemblies of para-hexaphenyl-dicarbonitrile (Ph6(CN)2) on Au(111) based on a combined theoretical and experimental approach. For deposition of Ph6(CN)2 on Au(111) kept at room temperature, a rhombic nanoporous network stabilized by a combination of hydrogen bonding and antiparallel dipolar coupling is formed. Annealing at 575 K resulted in an irreversible thermal transformation into a hexagonal nanoporous network stabilized by native gold adatoms. However, the Au adatoms could neither be unequivocally identified by scanning tunneling microscopy nor by noncontact atomic force microscopy. By combining van’t Hoff plots derived from our scanning probe images with our density functional theory calculations, we were able to confirm the presence of the elusive Au adatoms in the hexagonal molecular network.
Highlights
Scanning probe microscopy has been developed over the past decades into an inherently valuable tool to gain insights into both surface-confined molecular self-assembly and on-surface reactions
Scanning tunneling microscopy (STM) has been routinely used to visualize organic molecules even with submolecular resolution for more than 30 years.[1−4] As a result, profound knowledge has been obtained on molecular conformation, intermolecular bonding, and electronic properties of molecular self-assembly on surfaces
“qPlus”[12] noncontact atomic force microscopy, by probing the Pauli repulsion forces between the tip and sample, has been emerged as an enormously powerful tool to unveil the chemical structure of molecules in real-space based on the seminal work by Gross et al.[13]
Summary
Scanning probe microscopy has been developed over the past decades into an inherently valuable tool to gain insights into both surface-confined molecular self-assembly and on-surface reactions. Scanning tunneling microscopy (STM) has been routinely used to visualize organic molecules even with submolecular resolution for more than 30 years.[1−4] As a result, profound knowledge has been obtained on molecular conformation, intermolecular bonding, and electronic properties of molecular self-assembly on surfaces. This knowledge enables the understanding and tuning of various processes, for example, on-surface reactions,[5−8] molecular recognition,[9,10] and molecular spin states,[11] among others. The main approach to overcome this limitation consists in acquiring multiple images at variable tip−sample distances.[20−22] since the CO molecule at the tip apex exhibits a certain flexibility and can move, image artifacts have to be considered.[23−25]
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