Researchers from DTU Nanotech and collaborators at DTU Danchip, DTU Energy, Columbia University USA and Aixtron Ltd, UK have found a greener, more sustainable way of producing graphene. Their method not only reduces the amount of copper needed for growth but also reuses the copper.
The scientists minimized the amount of copper needed for growth from 50 µm thick foils to 100 nm thick layers supported by silicon wafers. To transfer the graphene, they used a novel electrochemical method in a liquid electrolyte. This method involves oxygen from the atmosphere, dissolved in a liquid electrolyte in between the copper and graphene layer. By applying a reducing potential, the oxidised copper surface is changed back to copper without dissolving it, and at the same time releasing the graphene. This works well because graphene does not tend to stick to copper oxide and reducing the copper oxide results in a volume decrease which helps further to release the graphene from the catalyst surface.When turned into electronic devices, the graphene layers produced by this new method show better properties than devices made by dissolving the copper. DTU representative says that each time the copper layer is reused, its surface actually improves, becoming flatter and more pure, so in this instance reusing less material gives a real advantage.
Reducing the amount of copper needed to much less can make graphene growth much less expensive and far more sustainable. The time previously needed to clean and optimise the copper layer by heat treatment has been substantially reduced, saving energy. Also, only non-toxic salt water or some other simple electrolyte is needed to remove the graphene from the catalyst.
In September 2014, IBM explored using graphene as a reusable substrate for semiconductor growth.