A plasmonic structure (10) comprising a layer of metal (14) in which the metal is selected from: a Group 8 to Group 11 transition metal, aluminium, germanium, antimony or bismuth, and a barrier layer (16) formed from a 2-D material disposed on a surface of the layer of metal (14). The metal layer has a roughness that permits the propagation of running plasmons along the interface of the metal layer and the barrier layer.