Subsurface contrast due to friction in heterodyne force microscopy

Area of Science:

• Nanotechnology
• Materials Science
• Surface Science
• Microscopy

Background:

• Nondestructive imaging of subsurface nanostructures is crucial for science and industry.
• Combining ultrasound with atomic force microscopy (AFM) shows feasibility, with heterodyne force microscopy offering high contrast and resolution.
• The physical contrast mechanism in ultrasound-AFM has remained unknown, hindering quantitative analysis.

Purpose of the Study:

• To identify the physical mechanism responsible for contrast formation in heterodyne force microscopy.
• To enable quantitative analysis of subsurface nanostructures using ultrasound-AFM.
• To validate the proposed contrast mechanism through quantitative analysis and simulations.

Main Methods:

• Experimental investigation of contrast formation in heterodyne force microscopy.
• Quantitative analysis comparing experimental observations with simulations and calculations.
• Ruling out alternative proposed contrast mechanisms such as Rayleigh scattering, viscoelasticity, tip motion damping, and ultrasound attenuation.

Main Results:

• Friction at material boundaries within the sample is identified as the primary mechanism for contrast formation.
• This friction-based mechanism explains the observed contrasts in experimental data.
• Other commonly assumed mechanisms were experimentally and theoretically ruled out.

Conclusions:

• The physical contrast mechanism in subsurface-AFM is friction at material boundaries.
• This finding resolves a long-standing question in nanoscale imaging.
• The developed analytical description enables quantitative subsurface-AFM imaging.