Intramolecular Force Contrast and Dynamic Current-Distance Measurements at Room Temperature.

Area of Science:

• Surface Science
• Atomic Force Microscopy
• Organic Electronics

Background:

• Scanning probe microscopy (SPM) is crucial for probing the atomic structure of molecules.
• Previous SPM studies of molecular internal structure were limited to cryogenic temperatures (liquid helium/nitrogen).
• This limitation hindered room-temperature applications and investigations of dynamic molecular behaviors.

Purpose of the Study:

• To demonstrate the capability of SPM for atomic-level imaging of organic molecules at room temperature.
• To investigate intramolecular and intermolecular forces and contrasts in organic molecular systems.
• To explore the potential of SPM for characterizing molecular charge states.

Main Methods:

• Utilized an unreactive tip in scanning probe microscopy.
• Employed an oscillating force sensor to dynamically measure the vertical decay constant of tunneling current.
• Quantified transimpedance of the current-to-voltage converter and accounted for tip oscillation for enhanced precision.

Main Results:

• Achieved intramolecular and intermolecular force contrast at room temperature for PTCDA molecules on a Ag/Si(111)-(√[3]×√[3]) surface.
• Demonstrated clear contrast between neighboring PTCDA molecules.
• Attributed the observed molecular contrast to differences in molecular charge states.

Conclusions:

• SPM can effectively probe internal atomic structure and intermolecular forces of organic molecules at ambient conditions.
• The developed method provides high precision for analyzing molecular properties, including charge states.
• This advancement opens new avenues for studying molecular interactions and electronic properties at the nanoscale.