Calculation of an Atomically Modulated Friction Force in Atomic-Force Microscopy

Abstract

We investigate the microscopic mechanism of energy dissipation in the friction force microscope (FFM), which is a modification of the atomic-force microscope for application to friction. Based on ab initio results for the interaction between Pd and graphite, we determine the atomic-scale modulation of the friction force and the corresponding stick-slip molion at the interface during the relative motion between these solids. We propose two idealized versions of the FF1\1 and show that the friction force depends not only on the Pd-graphite interaction potential, but even more critically on the construction parameters of such a microscope. Friction between two solids is one of the most important and complex processes which affect everyday's life. So far, the science of friction-tribology-has described this phenomenon mainly in a macroscopic and phenomenological way [1]. More recently, successful attempts have been undertaken to observe friction forces on the atomic scale [2] and to understand the underlying microscopic mechanisms in case of sliding friction without wear [3]. Independently, the availability of supercomputers has made predictive calculations [4,5] of atomic-scale friction forces possible. The recent experimental progress in nanotribology has been facilitated by the development of a modified version of the atomic-force microscope [6] (AFM) for application to friction, which is sometimes called the friction force microscope (FFM). Like the AFM, the FFM consists of an «atomically sharp" tip of a material A, suspended on a soft cantilever, which is brought into nondestructive contact with a well-defined substrate B. Measuring the vertical deflection of the cantilever is used to keep the applied load F..xl constant during the sLUface scan. An independent measurement of the cantilever deflection in the direction of

Stress-augmented thermal activation: Tribology feels the force

“…Initial work focussed on the stick-slip behaviour generally observed in this system and this was analysed in terms of the PrandtlTomlinson model [90]. However, in many cases, both mean and maximum friction also increased with log(speed) and in 1990 this was analysed by Gnecco et al [91] using a stress-augmented thermal activation model very similar to Prandtl's 1928 concept [2].…”

Superlubricity in Layered Nanostructures

“…The stick-slip phenomena is the major process, which contributes to the dissipation of the mechanical energy through sudden or non-adiabatic transitions between bi-stable states of the sliding surfaces [1,2,6,7]. During a sudden transition from one state to another, the velocities of the surface atoms exceed the center of mass velocity sometimes by orders of magnitudes [8].…”

Nanotribology, nanomechanics and nanomaterials characterization

“…(A wave of atoms vibrating in concert is termed a phonon.) The stick-slip phenomenon, resulting from irreversible atomic jumps, can be theoretically modelled with classical mechanical models ( Tomlinson 1929;Tomanek et al 1991). (Ruan & Bhushan 1994a) and (b) schematic of a model for a tip atom sliding on an atomically flat periodic surface.…”

“…The Tomanek-Zhong-Thomas model (Tomanek et al 1991) is the starting point for determining friction force during atomic-scale stick-slip. The AFM model describes the total potential as the sum of the potential acting on the tip due to interaction with the sample and the elastic energy stored in the cantilever.…”