Nanomechanical mapping in air or vacuum using multi-harmonic signals in tapping mode atomic force microscopy

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Atomic Force Microscopy (AFM) is crucial for nanoscale material characterization.
• Tapping mode AFM is widely used but quantitative mechanical property mapping remains challenging.
• Existing methods often require specialized setups or complex analysis.

Purpose of the Study:

• To develop a quantitative method for mapping local mechanical properties using multi-harmonic AFM signals.
• To establish analytical formulas relating harmonic signals to mechanical properties.
• To validate the method on a polymer blend sample.

Main Methods:

• Acquisition of multi-harmonic signals (0th and 2nd) during tapping mode AFM scans.
• Measurement of driven harmonic amplitude and phase.
• Development of analytical/semi-analytical formulas for tip-sample interactions.
• Pixel-by-pixel least squares estimation of mechanical properties (elastic modulus, adhesion, indentation).

Main Results:

• Demonstrated quantitative mapping of elastic modulus, adhesion, and indentation.
• Successfully utilized 0th and 2nd harmonic signals with good signal-to-noise ratio.
• Validated the method computationally and experimentally on a polystyrene and polyolefin elastomer blend.

Conclusions:

• The presented multi-harmonic AFM method enables quantitative mapping of local mechanical properties.
• This approach offers a robust way to analyze tapping mode AFM data for material characterization.
• The validated technique provides valuable insights into the mechanical behavior of materials at the nanoscale.