Researchers from Columbia University have shown that graphene, even if stitched together from many small crystalline grains, is the strongest material in the world. This experiment brings to a successful conclusion that contradiction between theoretical models, which predicted that grain boundaries can be very strong, and earlier experiments, which suggested that they were a lot weaker than the perfect lattice.
According to CNN, graphene is a one-atom thick layer of carbon atoms arranged in a honeycomb lattice. This arrangement gives graphene unique properties. For instance, electrical currents in graphene travel faster than in any other material known to man.
Study leader James Hone, professor of mechanical engineering at Columbia University, notes that the researchers’ first Science paper examined the strength graphene can achieve if it has no defects, but defect-free, pristine graphene exists only in very small areas. Large-area sheets needed for applications must contain numerous small grains connected at grain boundaries.
This study examines the strength of large-area graphene films created utilizing chemical vapor deposition (CVD). The findings confirm that frequently used techniques for post-processing CVD-grown graphene weaken grain boundaries, which explains why earlier studies found that grain boundaries were a lot weaker than the perfect lattice.
To avoid this problem, the researchers created a new process that prevents the graphene from being damaged during transfer.
“We substituted a different etchant and were able to create test samples without harming the graphene,” says lead author Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab. “Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications.”
The researchers say that in its perfect crystalline form, graphene is so strong that it would take an elephant, placed on top of a pencil, to pierce through a sheet of graphene as thick as a piece of Saran Wrap.
At the moment, researchers can grow sheets of graphene as big as a television screen by utilizing CVD, in which single layers of graphene are grown on copper substrates in a high-temperature furnace.
According to Jeffrey Kysar, professor of mechanical engineering, CVD graphene is “stitched” together from numerous small crystalline grains at grain boundaries that contain defects in the atomic structure. Naturally, these grain boundaries can curtail the strength of large-area graphene if they come apart more easily than the perfect lattice.
Upon closer examination, the researchers found that that the chemical frequently utilized to remove the cooper substrate also results in damage to the graphene, severely limiting its strength.
Their experiments showed that CVD graphene with large grains is just as strong as exfoliated graphene. In addition, the experiments revealed that CVD graphene with tiny grains, even when tested right at a grain boundary, is approximately 90 percent as strong as the ideal crystal.
The researchers believe that grain boundaries in 2D materials can be a lot more sensitive to processing than in 3D materials. However, they note that with the right type of processing that prevents surface damage, grain boundaries in 2D materials can be almost as strong as the perfect lattice.
Large-area graphene can be utilized for a number of different applications such as flexible electronics and strengthening components. What about hypothetical applications? Researchers posit that this material could fulfill the science fiction idea of a space elevator, in which an orbiting satellite is connected to Earth by a long cord that might be made up of sheets of CVD graphene.
The study’s findings are described in detail in the journal Science.