Nitrogen Concentration Profiles

The measured nitrogen concentration profiles are shown in Fig. 1. For all intents and purposes, the profile peaks at the surface, with a peak concentration of 40-45%. The concentration actually decreases very near the surface, but this has little effect on the finite element solution and it has been ignored. This profile decreases roughly linearly to the bulk concentration at 100-125 nm. The nitrogen concentration profile is shallower than one might expect from conventional ion implantation because the PSII process implants a mixture of N and N. Computer simulations of the implantation have been performed, and the agreement between the simulations and the measured nitrogen profile was excellent [12]. This provides some indication that the profile measurement is reliable. Based on this result, the finite element model included a yield stress profile that peaked at the surface and decreased linearly to the bulk value at 100 nm. This model thus assumes that the primary hardening mechanism is the formation of titanium nitride, as has been found in prev studies [16]. It should be made clear, though, that there was no attempt to directly assess the existence of titanium nitride in the samples used for this study.