Simulations of atomic-scale sliding friction

Abstract

Simulation studies of atomic-scale sliding friction have been performed for a number of tip-surface and surface-surface contacts consisting of copper atoms. Both geometrically very simple tip-surface structures and more realistic interface necks formed by simulated annealing have been studied. Kinetic friction is observed to be caused by atomic-scale stick and slip which occurs by nucleation and subsequent motion of dislocations preferably between close-packed ͕111͖ planes. Stick and slip seems to occur in different situations. For single crystalline contacts without grain boundaries at the interface the stick and slip process is clearly observed for a large number of contact areas, normal loads, and sliding velocities. If the tip and substrate crystal orientations are different so that a mismatch exists in the interface, the stick and slip process is more fragile. It is then caused by local pinning of atoms near the boundary of the interface and is therefore more easily observed for smaller contacts. Depending on crystal orientation and load, frictional wear can also be seen in the simulations. In particular, for the annealed interface necks which model contacts created by scanning tunneling microscope/ atomic force microscope tip indentations the sliding process involves breaking contacts leaving tip material behind on the substrate.

Molecular scale analysis of dry sliding copper asperities

“…Zhong et al (2003) also reported that the wear decreased significantly when the sliding surfaces where parallel to the (111) planes compared to the (100) planes. Further, Sorensen et al (1996) have shown that between a Cu tip and Cu surface, with non-matching surfaces parallel to the (111) plane the wear is minimum. Although, the most favorable case of (111) parallel to the sliding direction is not considered in this work, the results are comparable.…”

“…Song and Srolovitz (2007) performed MD simulations of single asperity contact and deformation on a flat surface over single-and multi-cycle loading and unloading. In an extensive study, Sorensen et al (1996) conducted MD simulations on atomic-scale friction of sliding copper surfaces. The dependence of the normal load, contact area, sliding velocity, temperature, and lattice mismatch was investigated with an emphasis on observing slip-stick for different tip-surface and surfacesurface contacts.…”

Friction between solids

“…Carpick & Salmeron 1997;Gnecco et al 2007) including diamond (Germann et al 1993). Insight into the atomic-scale stick-slip phenomenon has been provided by MD simulations of two contacting diamond surfaces (Harrison et al 1992a, of a tip and a Si surface (Landman et al 1989), metal surfaces (Sorensen et al 1996) and two infinite surfaces of organic monolayers in sliding contact (Glosli & McClelland 1993;Mikulski & Harrison 2001a,b;Chandross et al 2004;Harrison et al 2004;Mikulski et al 2005a,b).…”

Numerical tribology of a dry contact

“…To investigate atomic scale asperities and finite contact areas, many authors (such as [119], see figure 1) have modelled AFM-like tips-on-substrate contacts. Since the shearing velocity in classical MD simulations is very high compared to real AFM experiments, Large Scale Molecular Dynamics simulations are still under development, involving massive parallel programming [120].…”