Effects of nonlinear forces on dynamic mode atomic force microscopy and spectroscopy

Area of Science:

• Physics
• Materials Science
• Surface Science

Background:

• Atomic Force Microscopy (AFM) is a high-resolution surface imaging technique.
• Dynamic mode AFM utilizes cantilever oscillations to probe tip-sample interactions.
• Understanding nonlinear forces is crucial for accurate AFM measurements and spectroscopy.

Purpose of the Study:

• To investigate the impact of nonlinear tip-sample forces on dynamic mode AFM.
• To explain the observed jumps and hysteresis in amplitude-distance curves.
• To elucidate the relationship between oscillation frequency and hysteresis phenomena.

Main Methods:

• Experimental dynamic mode atomic force microscopy and spectroscopy.
• Numerical analysis of the fundamental dynamic equation governing cantilever oscillations.
• Analysis of vibration amplitude (A) versus tip-sample distance (h) curves.

Main Results:

• Nonlinear tip-sample forces lead to bistability in the AFM cantilever's resonance curve.
• This bistability directly causes the observed jumps and hysteresis in A-h curves.
• The specific location of hysteresis is dependent on the driving oscillation frequency relative to the cantilever's natural frequency.

Conclusions:

• Bistability in the resonance curve is the primary cause of hysteresis in dynamic mode AFM.
• Frequency-dependent behavior is a key factor in understanding and mitigating these nonlinear effects.
• This research provides a framework for interpreting complex AFM data and improving spectroscopic analysis.