The material is grown on copper, which is not unusual.
What is different about the process, is that every scrap of copper oxide is removed from the metal surface while deposition is underway.
In a reduced pressure environment, hydrogen plasma removes any oxide while a small amount of methane in the atmosphere decomposes on the surface to form graphene.
With earlier techniques, “typically, it takes about ten hours and nine to ten different steps to make a batch of high-mobility graphene using high-temperature growth methods”, said Professor Nai-Chang Yeh (left in photo). “Our process involves one step, and it takes five minutes.”
According to Caltech, work by Yeh’s group and international collaborators has revealed fewer defects than graphene made using conventional methods, and the highest electrical mobility yet measured for synthetic graphene.
This plasma-enhanced CVD, operating below 420°C, produced graphene with room-temperature electrical mobility up to 6.0(±1.0)x104cm2 /Vs, said to be better than CVD-grown single crystal graphene.
The team thinks one reason their technique works is that a reaction between the hydrogen plasma and air molecules generates cyano radicals (carbon-nitrogen ions) that effectively scour the copper of surface imperfections providing a pristine surface on which to grow graphene.
They also discovered that the graphene grows in a special way.
“Graphene produced using conventional thermal processes grows from a random patchwork of depositions,” said Caltech. “But graphene growth with the plasma technique is more orderly. The graphene deposits form lines that then grow into a seamless sheet, which contributes to its mechanical and electrical integrity.”
Strain engineering is now a possibility by controlled addition of defects.
“If you can strain graphene by design at the nanoscale, you can artificially engineer its properties. But for this to work, you need to start with a perfectly smooth, strain-free sheet of graphene,” said Yeh. “You can’t do this if you have a sheet of graphene that has uncontrollable defects in different places.”
According to Yeh, the technique could extend to larger areas. “We have created sample sizes of a few square centimeters, and since we think that our method is scalable, we believe that we can grow sheets that are up to several square inches or larger,” she said.
Written with Caltec scientist David Boyd, who first made the high quality graphene, Yeh has a paper on the work in Nature Communications: ‘Single-step deposition of high-mobility graphene at reduced temperatures‘.
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