Investigation of conductive nanostructures on ta-C films made by FIB lithography

Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 10¹⁶ cm^-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 10¹⁷ cm^-2. Investigations of the conduction mechanism were done by Hall-mobility measurements on Van der Pauw and Hall test structures. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 200 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 0.3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
[1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.