Some characteristics of materials surface-modified by ions beam bombardment

Abstract

Abstract Ion implantations with energies less than 100 keV and current densities of 10 15 –10 18 ions/cm 2 were conducted to polymers, metals, and diamond gemstone. Physical and chemical phenomena and mechanical properties of the implanted materials were investigated. Single or mixed ions of N, He, C were implanted onto polyethylene terephtalate (PET) to see the surface hardening effects. Multiple ion-implantation resulted in more increase in the surface hardness than single ion implantation at the same ion energy and dose. Implantation of C + N ions increased the surface hardness by about three times as compared to implantation of N or C ions alone. XPS analysis showed that C–N compounds were formed when both N and C ions are implanted into PET, implying that hard particle formation by reactions between the implanted ions and/or between the implanted N ions and carbon in PET in addition to the cross linking may be the mechanism of this significant increase in hardness. Ion implantation with 70 keV N ions of >5 × 10 16 /cm 2 into the surface-polished stainless steel reduced the average surface roughness ( R a ) from 0.04 μm to 0.02 μm. The implanted nitrogen was detected up to at least 300 nm from the surface of the stainless steel as measured with Auger electron spectroscopy. X-ray photo-electron spectroscopy analysis showed that the implanted N formed mostly Cr 2 N without post irradiation annealing. Hardness depth profiles obtained with nano-indentation technique showed that the peak hardness of 14 Gpa formed at ≈50 nm depth from the N ion implanted surface was about at least 2 times higher than non-irradiated specimen. N ions were implanted into the diamond in order to change the optical band gap and then to change the emitted color. In spite of the restricted ion penetrated depth, uniform and vividly changed color was observed after heat treatment of the nitrogen-implanted diamond in the vacuum or inert gas atmosphere. The changed color appeared to be black. Chemical states of the implanted nitrogen were N–N and 4N-vacancy as characterized with FTIR. Band structure calculation shows that band gap of the diamond reduced by 25% after N doping.