New research from the University of Pennsylvania demonstrates a more consistent and cost-effective method for making graphene Other methods make expensive custom copper sheets in an effort to get them as smooth as possible; defects in the surface cause the graphene to accumulate in unpredictable ways. Instead, Johnson’s group “electropolished” their copper foil, a common industrial technique used in finishing silverware and surgical tools. The polished foil was smooth enough to produce single-layer graphene over 95% of its surface area.
The growth of large-area graphene on catalytic metal substrates is a topic of both fundamental and technological interest. We have developed an atmospheric pressure chemical vapor deposition (CVD) method that is potentially more cost-effective and compatible with industrial production than approaches based on synthesis under high vacuum. Surface morphology of the catalytic Cu substrate and the concentration of carbon feedstock gas were found to be crucial factors in determining the homogeneity and electronic transport properties of the final graphene film. The use of an electropolished metal surface and low methane concentration enabled the growth of graphene samples with single layer content exceeding 95%. Field effect transistors fabricated from CVD graphene made with the optimized process had room temperature hole mobilities that are a factor of 2−5 larger than those measured for samples grown on as-purchased Cu foil with larger methane concentration. A kinetic model is proposed to explain the observed dependence of graphene growth on catalyst surface roughness and carbon source concentration.
Working with commercially available materials and chemical processes that are already widely used in manufacturing could lower the bar for commercial applications.
“The overall production system is simpler, less expensive, and more flexible” Luo said.
The most important simplification may be the ability to create graphene at ambient pressures, as it would take some potentially costly steps out of future graphene assembly lines.
“If you need to work in high vacuum, you need to worry about getting it into and out of a vacuum chamber without having a leak,” Johnson said. “If you’re working at atmospheric pressure, you can imagine electropolishing the copper, depositing the graphene onto it and then moving it along a conveyor belt to another process in the factory.”