Saudi Arabian researchers have grown single-crystal graphene on insulating substrates at a wafer scale. According to the researchers, this development is important because Field-effect transistors made from a sapphire-grown single-crystal graphene monolayer performed excellently, with better carrier mobilities.
“If graphene can be grown on an insulating substrate with a clean interface, certain devices might function better,” said project scientist Bo Tian of KAUST (King Abdullah University of Science and Technology). “This also opens the door to new types of graphene-based nanodevices. The superior electronic performance of the graphene grown on sapphire results from its higher crystallinity and fewer folds on the surface.”
Copper – a typical graphene growth catalyst – is deposited on top of a sapphire substrate in this method. After careful heat treatment, the polycrystalline copper is transformed into a single thin film-like Cu(111) crystal. When copper is placed in a methane atmosphere, the gas is decomposed into carbon atoms. Further heat treatment allows graphene to form on the copper’s upper surface, which is a conventional method of producing graphene. The team, on the other hand, is not interested in graphene. They’re more interested in the carbon atoms which diffuse into the copper and travel to the copper-sapphire interface. This interface serves as a template for the formation of well-oriented graphene islands.
The structure is repeatedly thermally shocked between liquid nitrogen and a furnace to remove the copper without destroying the graphene. The copper-graphene link is weakened and the copper film collapses, but the graphene-sapphire bond is not harmed. The copper covering on the sapphire wafer can eventually be peeled away, leaving a single graphene crystal.
“Our team is now trying to grow other two-dimensional materials on the insulator-supported graphene to build functionalised large-scale heterostructures,” added Tian “These heterostructures held together by van der Waals interactions are expected to be useful in future nanodevices.”
The entire study, “Wafer-scale single-crystal monolayer graphene grown on sapphire substrate“, is published in Nature Materials.