Molecular Identification, Bond Order Discrimination, and Apparent Intermolecular Features in Atomic Force Microscopy...

Area of Science:

• Surface Science
• Computational Chemistry
• Microscopy

Background:

• Atomic Force Microscopy (AFM) is crucial for nanoscale imaging.
• Simulating HR-AFM with CO probes requires accurate modeling of short-range interactions.
• Distinguishing molecular structures and chemical identities remains a challenge.

Purpose of the Study:

• To introduce an efficient and accurate simulation method for HR-AFM using CO probes.
• To investigate the role of charge density and Pauli repulsion in molecular imaging.
• To clarify the origin of intermolecular features in AFM images.

Main Methods:

• Developed a simulation model incorporating sample and probe charge densities for short-range interactions.
• Utilized a two-parameter model retaining ab initio accuracy.
• Applied the model to simulate HR-AFM images of molecules, including C60.

Main Results:

• The simulation method shows strong dependence on stoichiometry and bonding, limiting atom identification by force-distance curves.
• Identified features in 2D images and 3D force maps reflecting anisotropic charge density decay for molecular identification.
• Pinpointed Pauli repulsion as key for bond order discrimination in C60.
• Attributed intermolecular features to wave function overlap, not H-bond charge redistribution.

Conclusions:

• The new HR-AFM simulation method provides accurate insights into molecular structure and interactions.
• Anisotropic charge density decay features offer a pathway for molecular identification.
• Pauli repulsion and wave function overlap are critical factors in AFM imaging of molecular bonds.