Insight into Atomic-Scale Adhesion at the C-Cu Interface During theInitial Stage of Nanoindentation

Adhesion is a common phenomenon in nanomachining which affects processing accuracy and repeatability.As material removal approaches the atomic or close-to-atomic scale,quantum mechanics becomes the dominant principle behind the atomic-level interaction.However,atomic-scale effects cannot be properly described by empirical potential function-based molecular dynamics simulations.This study uses a first-principles method to reveal the atomic-scale adhesion between a diamond tip and a copper slab during initial-stage nanoindentation.Using a simplified tip and slab model,adhesion energy,electronic distribution,and density of states are analyzed based on quantum chemistry calculation.Results show that atomic adhesion is primarily due to the covalent bonding interaction between C and Cu atoms,which can induce structural changes to the diamond tip and copper slab.The effects of tip position and angles on adhesion are further studied through a series of simulations.The results show that adhesion between the tip and slab is sensitive to the lattice structure and a variant in angstroms is enough to cause different adhesion and structural changes.The actual determinants of adhesion can only be the atomic and electronic structures at the tip-slab interface.Bond rotation and breakage are observed during simulation and their effects on adhesion are further discussed.To conclude,the first-principles method is important for the analysis of an atomic-scale interaction system,even if only as an aid to describing adhesion at atomic and electronic scales.