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 mu A/cm(2) in the dose range of 1 x 10(15) to 1 x 10(17) 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 x 10(17) 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 x 10(17) 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.