Molecular dynamics simulation and experimental investigation on deformation anisotropy of gallium nitride Ga-plane and N-plane nano-scratching

Abstract

Gallium nitride(GaN) is a typical anisotropic material. Therefore, in order to guide the processing of GaN, it is important to investigate the effect of anisotropy on its frictional properties and deformation mechanism. Hexagonal wurtzite c-GaN has a periodicity of 60°; therefore, in this study, only the [1‾010] and [1‾21‾0] crystal directions of the Ga and N planes were investigated through molecular dynamics simulations, and corresponding nano-scratch experiments were conducted to validate the simulation results. The results indicated that the entire scratching process could be divided into three phases: elastic deformation, plastic deformation, and brittle fracture. The GaN N-plane [1‾21‾0] crystal direction was the first to undergo plastic and brittle deformation, and the incision depth corresponding to the elastic-plastic transition was 0.62 nm and the normal force was 264.1 nN. The brittle-plastic transition corresponded to an incision depth of 55 nm and normal force of 1.4 mN. At the same time, when brittle-plastic transition occurred, the friction coefficient of the material increased abruptly, and the corresponding friction coefficient of the N plane was generally larger than that of the Ga plane. Moreover, distribution of cracks was determined by scanning electron microscopy. In terms of deformation mechanism, when scratching along the [1‾010] crystal direction, the removed materials got mainly accumulated on both sides of the scratched groove; when scratching along the [1‾21‾0] crystal direction, the removed material mainly got accumulated in front of the indenter.