Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators.

Area of Science:

• Surface Science
• Molecular Spectroscopy
• Nanotechnology

Background:

• Electron transfer is fundamental to numerous chemical reactions like photosynthesis and corrosion.
• Mapping redox-state transitions at the single-molecule level is challenging due to substrate limitations.
• Existing techniques like Scanning Tunnelling Microscopy (STM) require conductive substrates, hindering redox studies, while Atomic Force Microscopy (AFM) typically lacks electronic state access.

Purpose of the Study:

• To develop a novel method for mapping single-molecule orbital structure as a function of redox state.
• To overcome the limitations of conductive substrates in studying electron transfer.
• To visualize electronic transitions and polaron formation in isolated molecules.

Main Methods:

• Synchronized voltage pulses were applied to steer electron tunneling between an AFM tip and a substrate.
• Tip oscillation was synchronized with voltage pulses to enable tunneling experiments on non-conductive substrates.
• This technique allows for sub-ångström resolution mapping of molecular orbital structure and electronic states.

Main Results:

• Successfully performed tunneling experiments on non-conductive substrates, mapping orbital structure of isolated molecules.
• Resolved previously inaccessible electronic transitions in both space and energy.
• Visualized the effects of electron transfer and polaron formation on individual molecular orbitals.

Conclusions:

• The developed synchronized tunneling AFM technique enables redox-state-resolved electronic structure mapping of single molecules.
• This approach overcomes substrate limitations, opening new avenues for studying electron transfer dynamics.
• The method is anticipated to be valuable for investigating complex redox reactions and charging phenomena with high resolution.