Real-space identification of intermolecular bonding with atomic force microscopy

Area of Science:

• Surface Science
• Molecular Assembly
• Chemical Physics

Background:

• Hydrogen bonding is crucial for molecular assembly and material properties.
• Understanding intermolecular interactions at the nanoscale is essential for designing new materials.

Purpose of the Study:

• To visualize and characterize hydrogen bonding in 8-hydroxyquinoline (8-hq) molecular assemblies on a Cu(111) surface.
• To elucidate the role of electronic states in hydrogen bond formation.
• To investigate intermolecular coordination with metal adatoms.

Main Methods:

• Noncontact atomic force microscopy (NC-AFM) for real-space visualization of molecular structures.
• Ab initio density functional theory (DFT) calculations for interpreting bonding characteristics and electron density.
• Submolecular resolution AFM for identifying local bonding configurations.

Main Results:

• Atomically resolved visualization of hydrogen bond formation in 8-hq assemblies.
• Precise determination of hydrogen bond characteristics: sites, orientations, and lengths.
• Identification of electron density contributions from hybridized electronic states in hydrogen bonds.
• Observation of intermolecular coordination between dehydrogenated 8-hq and Cu adatoms.

Conclusions:

• NC-AFM provides direct, high-resolution insights into hydrogen bonding and intermolecular interactions.
• DFT calculations successfully explain the electronic nature of observed hydrogen bonds.
• This approach facilitates detailed studies of complex molecular systems with multiple active sites.