Investigation of edge effect on wurtzite gallium nitride in nanoindentation using molecular dynamics simulation

In practical applications, block materials frequently experience edge collapse, yet our grasp of this phenomenon at the nanoscale remains limited. Understanding this is crucial, as nanoscale material behaviors can trigger intricate microscale effects that elude easy observation or comprehension at the macroscopic level. This work researched the edge effect of the wurtzite GaN with {0001} surface crystal orientation at different nanoindentation distances by molecular dynamics simulation. The results show that the GaN indentation edge effect is anisotropic. The atomic displacement directions prolonged [2-1-10], [-12-10], and [-1-120], which is hexagonal distributing, similar to the crystal structure. The dislocations are around the indenter and close to the upper surface, similar to the negative von Mises stress distributions. The closer the indenter is to the edge of the sample, the more atoms are extruded from the specimen edge, and the more serious the damage is to the edge generally. However, analysis of the mechanical response and phase transition shows that the damage to the edge can be weakened while the crystal structure is destroyed more severely at some specific locations of the indenter. This work reveals the evolution of GaN crystal structure under different nanoindentation distances and the mechanism of squeeze-out atoms from the edge at the atomic scale.