Aspect ratio of heavy ion tracks in mica and CR-39 plastic

Ion track technique has recently been developed as an important lithographic technique and has found wide application in microstructure technology. Aspect ratio, defined as the ratio of track depth to its diameter, is of great significance in 3-dimensional structures, where deep trenches or high ridges are required. Samples of muscovite mica and CR-39 plastic were irradiated at GSI UNILAC using 197Au(11.4 MeV/u) and 14N(10.83 MeV/u) ion beams of fluence 104 to 109 ions cm-2 at normal incidence. Track depth and diameter are determined after etching the irradiated samples. It is observed that in case of mica, aspect ratio first increases monotonically and then decreases gradually. However, in case of CR-39, the aspect ratio is found to be almost constant and decreases abruptly, once the full depth of track is revealed. (author). 7 refs., 5 figs., 5 tabs