Formation and stability of highly conductive semitransparent copper Meso-grids covered with graphene

We report on the formation of highly stable and robust hybrid semitransparent electrodes based on a percolated mesoscale copper grid covered with graphene. Copper films sputtered on transparent substrates are used to synthesize graphene by CVD and annealed to form metallic grids covered with graphene. The copper grid density can be controlled by varying annealing temperature and time, obtaining excellent sheet resistance (<0.7 Ω/sq). The single layer graphene that covers the whole sample modifies the preferred crystalline orientation favoring (110) copper grains when treated up to 1050 °C. However, when annealed few degrees below bulk copper melting temperature, graphene is partially eliminated, probably due to the high pressure of copper vapor generated underneath, and copper forms isolated dots with mainly (111) orientation. During graphene synthesis, ~70% of the copper film is evaporated but, once graphene layer is completed the remaining copper fraction is constant up to almost bulk copper melting temperature demonstrating that graphene is an excellent barrier against copper evaporation. Contrary to the enhanced oxidation of copper foils with graphene, these graphene-Cu grids are extremely stable in ambient conditions maintaining an almost unchanged performance for years. The copper based meso-grids are highly stable and robust and present a suitable surface for organic- and bio-molecules provided by the continuous graphene layer.