When a charged particle penetrates a target, it rapidly loses energy both through interactions with the atoms of the target and to the electronic system. The electronic system can then rapidly redistribute energy throughout the target reducing the energy available for the creation of defects. These electronic energy losses can be implemented in molecular dynamics as additional forces on the atoms. This can be done in several ways. 2TMD is a method that has been previously used in literature, defining the electronic energy losses as a simple drag force. The new non-adiabatic model uses a more complex form for the electronic energy losses allowing the damping force to have a direction that may not be opposite in direction to the ion's velocity. In this thesis we implement the new non-adiabatic model in the molecular dynamics code LAMMPS and compare it to 2TMD using primary knock-on atoms of both 5 and 15 keV. We find find that there is no significant difference in the peak and residual number of defects between 2TMD and the non-adiabatic model although, both models yield significant differences in defect behaviour over simply ignoring the electronic energy losses. We do, however, find a difference in the variation of the electronic temperatures. We then compare copper and nickel using both models finding the peak number of defects is similar in both copper and nickel. However, the residual number of defects is significantly more in copper across the models. Again, there were no significant differences found between 2TMD and the non-adiabatic model.
|Date of Award||31 Dec 2019|
- The University of Manchester
|Supervisor||Joseph Robson (Supervisor) & Christopher Race (Supervisor)|