Song, Z.C., Wei, H.L., Liu, Y.H., Wang, J., Long, H., Wang, H.N., Qin, P.L., Zeng, W. and Fang, G.J. (2014) Enhanced field emission from aligned ZnO nanowires grown on a graphene layer with hydrothermal method. IEEE Transactions on Nanotechnology, 13, 167-171.