Scanning electron microscopy or SEM utilizes focused electron beam to obtain three-dimensional images up to nano-scale which provides compositional, morphological and topographical information. Whereas, Auger electron spectroscopy obtains quantitative elemental and chemical composition of the surface of the sample. Coupling these features, SEM with AES demonstrates that it can be an excellent tool for surface analysis.
In the study of Liu, Yang, et. al, SEM and AES were utilized to examine the surface morphologies and chemistry of Mg-Ca alloy implanted with bioactive elements. The Mg and its alloys are investigated as biodegradable materials due to their mechanical support, biocompatibility, and biodegradation. Several scientific reports showed the beneficial compatibility of Mg-Ca as an implant material for enhancement of osteogenesis upon Ca addition. However, living cells enhance the degradation process of the said alloy. To improve the performance of the implant material, physical and chemical surface variations are required. Implantation of metal ions of Mg-Ca proved to be valuable for corrosion and oxidation resistance, cytotoxicity and biocompatibility. It also helps with the post-surgery healing.
Through high-resolution imaging using SEM, surface showed slight modification with the roughness after implantation of Ag and Fe ion implantation. Shutter-like surface morphology with similar orientation and cracks which divide the surface area were observed after Y ion implantation. Implanted Ag with the oxidized layer of about 50 nm showed low Ag concentration. The Fe-implanted sample showed a slightly higher oxidized layer of about 110-120 nm while Y-implantation layer resulted in more than 200 nm. It was also observed that Y distribution is exceptionally homogeneous from 10% atomic concentration at the surface then steadily decreases upon ion implantation.
Corrosion behavior after implantation was also observed through SEM. Out of the three metal ion implantation, Y showed the most enhanced corrosion resistance and homogenous corrosion morphology. EDS analysis of untreated Mg-Ca matrix and ion-implanted samples after 14-day immersion in Hank solution demonstrated that existence of corrosion product layer on the four samples. It also reveals that Y implanted samples produced needle-like corrosion products in lesser amounts compared to the Ag- and Fe-implanted samples.
In conclusion, the surface alteration was observed after metal ion implantation. This is due to heat-effect and oxidation. For Ag and Fe, it followed Gaussian form while Y showed uniform distribution. After Y implantation, Y2O3 was also observed with brief protective influence. Of the three metal ion implants, Y provided promising outcomes for orthopedic applications.