Bimodal atomic force microscopy for the characterization of thiolated self-assembled monolayers

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Molecular coatings, particularly self-assembled monolayers (SAMs), offer versatile applications in materials science.
• Understanding the structure-property relationships of SAMs under realistic conditions is crucial but challenging.
• Atomic Force Microscopy (AFM) is a key technique for nanoscale surface analysis.

Purpose of the Study:

• To develop and validate a methodology for simultaneous topographical and nanomechanical characterization of SAMs.
• To quantitatively measure surface elasticity and correlate it with molecular ordering.
• To investigate phase separation in binary SAMs at the nanoscale.

Main Methods:

• Utilized a commercially available bimodal atomic force microscopy (AFM) setup.
• Performed simultaneous topographical imaging and nanomechanical measurements.
• Measured effective surface elasticity (E*) and localized chemical species.

Main Results:

• Effective surface elasticity (E*) was found to scale with monolayer formation-time and ligand-length, indicating correlation with molecular ordering.
• The developed method allowed for quantitative measurement of surface elasticity.
• Phase separation in thiolated binary SAMs was observed down to approximately 10 nm domains in both topography and elasticity channels.

Conclusions:

• The bimodal AFM methodology provides accurate and quantitative insights into SAM structure-property relationships.
• Surface elasticity is a sensitive indicator of molecular ordering and monolayer formation.
• The technique is capable of resolving nanoscale chemical heterogeneity in complex SAM systems.