Imaging the charge distribution within a single molecule.

Area of Science:

• Surface Science
• Nanotechnology
• Physical Chemistry

Background:

• Scanning probe microscopy (SPM) techniques like Scanning Tunnelling Microscopy (STM) and Atomic Force Microscopy (AFM) provide atomic-scale insights into surface and nanostructure properties.
• However, these methods cannot directly visualize charge distribution within molecules or on surfaces.

Purpose of the Study:

• To investigate the charge distribution of naphthalocyanine molecules on an insulating NaCl layer on Cu(111) using advanced SPM techniques.
• To demonstrate the capability of Kelvin probe force microscopy (KPFM) in mapping local contact potential differences with submolecular resolution.

Main Methods:

• Utilized a combination of Scanning Tunnelling Microscopy (STM), Atomic Force Microscopy (AFM), and Kelvin probe force microscopy (KPFM).
• Examined naphthalocyanine molecules adsorbed on a thin NaCl film grown on a Cu(111) substrate.
• Performed density functional theory (DFT) calculations to corroborate experimental findings.

Main Results:

• Achieved submolecular resolution imaging of the local contact potential difference using KPFM.
• Experimental KPFM maps were validated by DFT calculations, confirming they reflect intramolecular charge distribution.
• Successfully visualized the charge distribution within naphthalocyanine molecules.

Conclusions:

• KPFM is a powerful tool for mapping local contact potential differences with high resolution, revealing charge distribution at the molecular level.
• This combined SPM and theoretical approach provides fundamental insights into charge redistribution during single-molecule switching and bond formation.
• The study opens avenues for understanding and manipulating charge dynamics in molecular systems.