There are two common types of CVD graphene growth. These processes require similar growth conditions, however, the underlying mechanism governing the growth of graphene is different.
Monolayer graphene can be produced on a copper substrate, either a thin foil or an evaporated film. The substrates are annealed at high temperatures in a hydrogen atmosphere to clean the surface from oxides of copper. The graphene is then grown by introducing methane gas. The methane gas is cracked by the copper surface which creates carbon species that can either adsorb to the surface of the copper to seed a graphene island (a nucleation site), attach to an existing nucleation site or desorb from the copper surface.
From successive attaching, the graphene islands grow in size, therefore reducing the area of the exposed copper surface. This in turn reduces the rate of catalysis of the methane adsorption and reduces the graphene growth rate. Once a continuous layer is formed there is no exposed copper to catalyse the methane adsorption, hence stopping any further growth. The resulting film is therefore limited to monolayer graphene; however impurities and defects in the copper foil can cause multilayer patches to form.
a) The annealing of a copper substrate to prepare the surface for CVD graphene growth at high temperatures of 1035°C, b) the process of the formation of graphene on the copper surface, where CH4 is adsorbed at the copper surface to form carbon species, which can form a nucleation site, attach to an already formed nucleation site or desorb from the surface, c) the final formed film shown on both sides of the copper foil, d) the annealing of a nickel substrate to prepare the surface for CVD graphene growth at high temperatures, e) the CH4 gas adsorption is catalysed at the surface of the nickel and the resulting carbon species absorbed into the nickel substrate, f) the precipitation of few layer graphene after cooling the substrate to room temperature.
Few layer graphene can be grown on a nickel substrate, either on an evaporated film or on a thin nickel foil. The nickel substrates are annealed, as with copper, which cleans the surface of the nickel and modifies the crystalline structure of the film. This is performed by heating the substrate in a hydrogen atmosphere. When methane is introduced carbon adsorption is catalysed on the nickel surface. When the nickel substrate is cooled down to room temperature the carbon is precipitated on the surface in the form of mono and few layer graphene. It has been shown that the rate of cooling directly affects the thickness and uniformity of the produced films.
The grown graphene films are removed from the metal substrates using a wet etching technique. The graphene films, using this technique, can be transferred onto arbitrary substrates.
If you are interested in CVD graphene transfer check out our range of CVD graphene transfer machines on our online store.
Loading...