Atomistic study of lateral contact stiffness in friction force microscopy

• A multi-spring model is used to study FFM tip–substrate contact system.
• Molecular dynamics simulations are used to calculate contact and tip apex stiffness.
• Tip apex stiffness decreases with size.
• Contact stiffness increases when the contact surfaces are well aligned.
• Contact stiffness is less than tip apex stiffness so dominates the overall stiffness.

The effective stiffness of a friction force microscope tip–substrate system is an important parameter that describes the relationship between lateral force and elastic deformation. In this study, we use a multi-spring model to simplify the system, where two contributions, the tip apex stiffness and the lateral contact stiffness, are discussed in detail. Molecular dynamics simulations are used to characterize stiffness by simulating a tip apex subject to shear or sliding over a substrate surface. The results show that, although the height of the tip apex and tip–substrate orientation affect the various stiffness contributions, the contact itself dominates the overall compliance.