Engineers link lower graphene quality to oxygen levels during the processing stage and develop new techniques to make less flawed carbon nanomaterial at scale.

Engineers at Columbia University School of Engineering and Applied Science, the University of Montreal, and the National Institute of Standards and Technology have developed an oxygen-free chemical vapor deposition (OF-CVD) method for producing high-quality graphene that can create samples at scale.

Their work, published May 29 in Nature, has demonstrated for the first time how even trace amounts of oxygen poorly affect the quality of graphene growth rate during production.

Graphene has consistently made headlines as a miracle material in all manner of new technologies since its discovery in 2004. This nanomaterial – a single layer of carbon atoms – whose properties include exceptional electrical conductivity and tensile strength, has been transforming electronics, energy storage, sensors and biomedicine, to name only a few technologies being disrupted by its arrival on the engineering scene, and the raft of continuing discoveries across numerous fields.

Graphene is extremely pliable, stretchable, and incredibly strong (roughly 150 times stronger than its equivalent in steel.)

Around 15 years ago, researchers developed large-area graphene synthesis for real-world applications. This process, known as CVD growth, passes carbon-containing gas over a heated copper surface (about 1,000 degrees Celsius), enabling the carbon atoms to deposit on the sheet as a single honeycomb-shaped layer as graphene.

CVD growth can be scaled up to create graphene samples that are up to several meters in size. However, CVD-synthesized samples have suffered from variable quality and reproducibility concerns.

The answer is less oxygen

Co-authors Richard Martel and Pierre Levesque from Montreal suggested in previous publications that oxygen can slow the growth process and even etch the graphene. To overcome this setback, Christopher DiMarco designed and built a CVD growth system that controls the amount of oxygen introduced during the deposition process.

Current Ph.D. students Xingzhou Yan and Jacob Amontree continued DiMarco's work, further improving the system. With trace oxygen eliminated completely, CVD growth was much faster, with consistent results.

"We both became fascinated by graphene and its potential as undergraduates. We conducted countless experiments and synthesized thousands of samples over the past four years of our Ph.D.s," the researchers said. "Seeing this study finally come to fruition is a dream come true."

"We show that eliminating virtually all oxygen from the growth process is the key to achieving reproducible, high-quality CVD graphene synthesis," said senior author James Hone, Wang Fong-Jen Professor of Mechanical Engineering at Columbia. "This is a milestone towards large-scale production of graphene."

Moving forward, the team's next challenge is to develop a method of cleanly transferring the delicate graphene sheets from their metal growth catalysts to other functional substrates such as silicon – the final step in driving down price and taking full advantage of this wonder material.