Nanotribological Properties of the h-BN/Au(111) Interface: A DFT Study

Understanding the quantum-mechanical origins of friction forces has become increasingly important in the past decades with the advent of nanotechnology. At the nanometer scale, the universal Amontons-Coulomb laws cease to be valid, and each interface requires individual scrutiny. Because of the well-known lubricating properties of two-dimensional materials, a significant amount of research has been performed in an effort to understand interfaces they form with one another. However, the interfaces between these two-dimensional materials and metals red from a tribological point of view, important for such applications as friction force microscopy, have yet to be thoroughly investigated. In the current work, we present a detailed density functional theory investigation of the hexagonal BN/Au(111) interface. Because of a good agreement between their characteristic lengths, a high level of commensurability is achieved in a suitably constructed model between the bulk surfaces of the two materials. As a result of our calculations, we find that the corrugation in the potential energy surface and the lateral forces in this interface are low compared to other similar interfaces. The friction coefficient falls rapidly with increasing load down to 0.005 for the largest loads considered. In contrast, Au-n clusters (n = 1, 4, 13, and 19) sliding on the h-BN surface exhibit much larger lateral forces, indicating strong size and edge effects. The reduction of energy corrugation in going from the Au-4 to the Au-19 cluster may already indicate a decreasing trend with increasing size even at this very small scale.