Molecular Dynamics Simulation of Ultrasonic Vibration-assisted Polishing of Gallium Nitride
The present work aims at investigating the microscopic mechanism of ultrasonic vibration-assisted polishing(UVAP)of gallium nitride(GaN)and providing guidelines for optimizing ultrasonic parameters to enhance material removal and surface quality.Thus,molecular dynamics(MD)method was applied to investigate the removal behavior of GaN material scratched by individual abrasive particles at different periods and amplitudes.As the rising of the UVAP vibration period,the average tangential force decreases,the average normal force initially increases and then decreases,and the thickness of the damage layer decreases and then tends to flatten out.With a vibration period of 40 ps,the number of atoms removed after UVAP is 5.6 times higher than conventional polishing,while the depth of the damaged layer is only 15.85 Å.Moreover,as the UVAP amplitude increases,the average tangential force decreases and then increases,the average normal force continuously decreases,and both the scratch width and damage layer thickness increase nonlinearly.Under 8 Å amplitude,the thickness of the damaged layer remained essentially the same as in conventional polishing,and the number of atoms removed after UVAP increased by a factor of 4.6 compared to conventional polishing.In summary,UVAP offers advantages over conventional polishing,including reduced average grinding force,increased scratch width,and improved atom removal,resulting in excellent polishing results.Both increasing the UVAP vibration period and amplitude rising the types of dislocations at the bottom of the scratch.In addition,the total length of dislocations is mainly influenced by the amplitude,while the vibration period has less impact.Finally,better surface quality and higher material removal efficiency can be ensured by regulating the UVAP vibration period and amplitude to 40 ps and 8 Å,respectively.
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