"If you had two pieces of fence, and you laid them on the ground next to each other but they weren't perfectly aligned, then they wouldn't match," he said. "That's a grain boundary, where the lattice doesn't match."
The research involved Pop's group, led by Beckman Fellow Josh Wood, growing the graphene at the Micro and Nanotechnology Lab, and transferring the thin films to a silicon (Si02) wafer. They then used the STM at Beckman developed by Lyding for analysis, led by first author Justin Koepke of Lyding's group.
Their analysis showed that when the electrons' itinerary takes them to a grain boundary, it is like, Lyding said, hitting a hill.
"The electrons hit this hill, they bounce off, they interfere with themselves and you actually see a standing wave pattern," he said. "It's a barrier so they have to go up and over that hill. Like anything else, that is going to slow them down. That's what Justin was able to measure with these spectroscopy measurements.
"Basically a grain boundary is a resistor in series with a conductor. That's always bad. It means it's going to take longer for an electron to get from point A to point B with some voltage applied."
Images from the STM reveal grain boundaries that suggest two pieces of cloth sewn together, Lyding said, by "a really bad tailor."
In the paper, the researchers were able to report on their analysis of the orientation angles between pieces of graphene as they grew together, and found "no preferential orientation angle between grains, and the GBs are continuous across graphene wrinkles and Si02 topography." They reported that analysis of those patterns "indicates that backscattering and intervalley scattering are the dominant mechanisms responsible for the mobility reduction in the presence of GBs in CVD-grown graphene."
Lyding said that the relationship between the orientation angle of the pieces of graphene and the wavelength of an el
|Contact: Steve McGaughey|
Beckman Institute for Advanced Science and Technology