Quantitative comparison of two independent lateral force calibration techniques for the atomic force microscope

Area of Science:

• Metrology
• Surface Science
• Nanotechnology

Background:

• Accurate lateral-force calibration is crucial for atomic force microscopy (AFM) applications.
• Existing methods like the hammerhead (HH) technique and diamagnetic lateral force calibrator (D-LFC) offer independent approaches to traceable accuracy.
• Understanding the limitations and optimal implementation of these calibration methods is essential for reliable AFM measurements.

Purpose of the Study:

• To systematically compare the hammerhead (HH) technique and the diamagnetic lateral force calibrator (D-LFC) for AFM lateral-force calibration.
• To investigate the limitations and sources of uncertainty associated with each calibration method.
• To determine the preferred method and optimal experimental conditions for accurate lateral-force calibration.

Main Methods:

• Comparison of HH and D-LFC calibration methods using four different tee-shaped HH reference probes.
• Investigation of D-LFC performance under varying AFM feedback control modes (constant height and constant force).
• Analysis of the impact of normal load and cantilever stiffness on D-LFC calibration accuracy.

Main Results:

• HH and D-LFC methods agree within 5% but with a precision limited to approximately 15%.
• Inconsistent D-LFC values were observed with stiff cantilevers at high normal loads.
• Calibration in constant height mode introduced up to 14% error in D-LFC; constant force mode yielded better agreement with HH.
• A systematic error of ~4% per μN was noted in constant force mode for loads ≤ 1 μN with stiff cantilevers.

Conclusions:

• The D-LFC method is preferred over the HH method due to fewer associated uncertainties.
• Optimal D-LFC calibration requires using constant force mode and minimizing applied normal loads.
• Careful consideration of cantilever stiffness relative to the D-LFC setup is necessary to avoid errors from excessive loads.