Atomistic investigation of FIB-induced damage in diamond cutting tools under various ion irradiation conditions

Focused Ion Beam (FIB) has been demonstrated as a promising tool to the fabrication of micro- and nanoscale diamond cutting tools. In-depth understanding of the ion-solid interaction in diamond leading to residual damage under different processing parameters are in high demand for the fabrication of nanoscale diamond tools. Molecular dynamics (MD) simulation method has long been regarded as a powerful and effective tool for analysing atomistic interactions with regard to its capacity of tracking each atom dynamically. Developing on the previous research work on single ion collision process in diamond, a novel Gauss random distribution multi-particle collision MD model was developed in this paper to study FIB-induced damage in diamond under various ion irradiation conditions. A multi-timestep algorithm was developed to control the whole collision process.
The results show that the proposed model can effectively track the impulse of each single ion leads to atomic displacements in diamond and finally to a U-shape residual damaged layer at the core irradiation area. The multi-timestep algorithm can increase the computing efficiency by 12 times while still holding high simulation accuracy in terms of the thickness of residual damaged layer and the range of incident gallium distribution. The simulation model was further used to study the ion-induced damage layer in diamond under various beam voltages (5 kV, 8 kV, and 16 kV) and incident angles (0˚, 15˚, 30˚, and 45˚). Less damage range were found under the beam energy of 5 kV with the ion incident angle of 45˚, which indicated that a post ion beam polishing process (low beam energy with large incident angle) would be an effective way in practice to remove/minimise the residual damage layer when shaping the diamond cutting tools.