Strong excitons in novel two-dimensional crystals: Silicane and germanane O. Pulci, P. Gori, M. Marsili, V. Garbuio, R. Del Sole and F. Bechstedt EPL, 98 3 (2012) 37004 Published online: 11 May 2012 DOI: 10.1209/0295-5075/98/37004