Surface hardening in N+ implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N+ ions at a beam current of 1 μA/cm2 in the dose range of 1 × 1015 to 1 × 1017 ions cm−2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 1017 ions cm−2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (I D/I G ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 1017 N+ cm−2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.