Like just about every other material, graphene has imperfections that impair its abilities. Researchers across the planet are working to perfect graphene production methods, but thus far they have had limited success. That is why researchers at the Beckman Institute for Advanced Science and Technology have decided to study one kind of imperfection, to see how to minimize its effects, if not presence.
A common means to produce atom-thick sheets of graphene is Chemical Vapor Deposition (CVD), in which carbon atoms arrange themselves into graphene as they fall onto a substrate. The catch is that multiple graphene crystals can form and grow on the substrate, eventually connecting at odd angles. These connections are called Grain Boundaries (GBs) and act as resistors within the graphene sheet. A GB is like a potential hill, that electrons may not be able to climb, and when they fall back down the electrons interfere with themselves, creating a standing wave pattern. In the end the effect is to slow the electrons down, which is not at all desirable if graphene is to be used in electronics.
While the grain boundaries are inescapably detrimental to graphene's performance, the researchers do have some good news. If the GBs are aligned and periodic, instead of randomly occurring along a sheet or wafer of graphene, then there should be less scattering, and thus less resistance.