Beckman Institute researchers have given new insight into the electronics behavior of graphene with grain boundaries that could guide fabrication methods toward lessening their effect. The researchers grew polycrystalline graphene by chemical vapor deposition (CVD), using scanning tunneling microscopy (STM) and spectroscopy for analysis, to examine at the atomic scale grain boundaries on a silicon wafer.
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.”
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 electron impinges on the electron’s movement at the grain boundary, leading to variations in their scattering.
“More scattering means that it is making it more difficult for an electron to move from one grain to the next,” he said. “The more difficult you make that, the lower the quality of the electronic performance of any device made from that graphene.”
The researchers work is aimed not just at understanding, but also at controlling grain boundaries. One of their findings – that GBs are aperiodic – replicated other work and could have implications for controlling them, as they wrote in the paper: “Combining the spectroscopic and scattering results suggest that GBs that are more periodic and well-ordered lead to reduced scattering from the GBs.”
This story is reprinted from material from Beckmann Institute, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.