Highly oriented pyrolytic graphite chemical bonding structure after gallium implantation

Highly oriented pyrolytic graphite (HOPG) structural changes caused by gallium (Ga) implantation at room temperature were investigated. Ga ions were implanted into HOPG at different energies (10, 20, and 30 keV) and fluences (ranging from 2 × 10¹⁵ to 5 × 10¹⁶ Ga⁺/cm²). To monitor structural changes in the samples post-implantation, Raman spectroscopy was employed. The Raman spectra of the pristine HOPG sample displayed low-intensity D peaks at 1359 cm⁻¹ and high-intensity G peaks at 1582 cm⁻¹. After implantation with 10 keV at a fluence of 5 × 10¹⁶ Ga⁺/cm², a decrease in G peak intensity was observed, accompanied by an increase in its full width at half maximum (FWHM), indicating defect formation in the HOPG structure. In contrast, implantation with 30 keV at the same fluence (5 × 10¹⁶ Ga + /cm²) resulted in the merging of the D and G peaks into a broad peak, signifying the amorphization of HOPG. These results confirm that ion energy plays a significant role in the amorphization of HOPG. Furthermore, implantation with 20 keV Ga ions at fluences ≤ 2 × 10¹⁶ Ga⁺/cm² introduced some defects in the HOPG structure, while higher fluences (≥ 4 × 10¹⁶ Ga⁺/cm²) led to complete amorphization. After comparing the Raman results with the threshold displacement per atom (dpa) values calculated using the SRIM (Stopping and Range of Ions in Matter) software, it is evident that the HOPG used in this study required a very high dpa (exceeding 35 dpa) for complete amorphization, significantly exceeding the previously suggested range of 0.2 dpa to 3 dpa. The findings of this study align with very few prior results, where no amorphization was observed above 3 dpa. However, further research and testing are necessary to quantify the dpa required for HOPG amorphization.