S.  Kundu, Yadav, R. Manohar, Narayanan, T. N., Shelke, M. V., Vajtai, R., Ajayan, P. M., and Pillai, V. K., ?Synthesis of N, F and S co-doped graphene quantum dots?, Nanoscale, vol. 7, no. 27, pp. 11515-11519, 2015.