The chemical structure of a molecule resolved by atomic force microscopy

Area of Science:

• Surface science
• Atomic force microscopy
• Molecular imaging

Background:

• Achieving atomic resolution in surface microscopy is a long-standing goal.
• Scanning tunneling microscopy (STM) images atomic features but struggles with resolving single atoms in adsorbed molecules due to sensitivity to electron density.
• Existing methods face challenges in discerning individual atomic structures within molecules.

Purpose of the Study:

• To demonstrate unprecedented atomic resolution imaging of molecules.
• To overcome the limitations of scanning tunneling microscopy in resolving single atoms within molecules.
• To utilize short-range chemical forces for high-resolution molecular imaging.

Main Methods:

• Employing noncontact atomic force microscopy (AFM).
• Functionalizing the AFM tip apex with atomically well-defined terminations, specifically CO molecules.
• Corroborating experimental findings with ab initio density functional theory (DFT) calculations.

Main Results:

• Achieved unprecedented atomic resolution in imaging molecules.
• Demonstrated that functionalizing the microscope tip is crucial for high resolution.
• Identified Pauli repulsion as the primary source of atomic resolution, with van der Waals and electrostatic forces contributing a background effect.

Conclusions:

• Noncontact atomic force microscopy with a functionalized tip enables atomic resolution imaging of molecules.
• The technique overcomes the limitations of scanning tunneling microscopy for resolving individual atoms within molecular adsorbates.
• Pauli repulsion is identified as the dominant force responsible for the observed atomic resolution.