Tuesday, June 2, 2015

Roll-to-Roll CVD manufacturing of graphene

New manufacturing process could take exotic material out of the lab and into commercial products

That could finally change with a new process described this week in the journal Scientific Reports by researchers at MIT and the University of Michigan. MIT mechanical engineering Associate Professor A. John Hart, the paper’s senior author, says the new roll-to-roll manufacturing process described by his team addresses the fact that for many proposed applications of graphene and other 2-D materials to be practical, “you’re going to need to make acres of it, repeatedly and in a cost-effective manner.”

Diagram of the roll-to-roll process (a) shows the arrangement of copper spools at each end of the processing tube, and how a ribbon of thin copper substrate is wound around the central tube. Cross-section view of the same setup (b) shows the gap between two tubes, where the chemical vapor deposition process occurs. Photos of the system being tested show (c) the overall system, with an arrow indicating the direction the ribbon is moving; (d) a closeup of the copper ribbon inside the apparatus, showing the holes where chemical vapor is injected; and (e) an overhead view of the copper foil passing through the system (MIT News).

The new process is an adaptation of a chemical vapor deposition method already used at MIT and elsewhere to make graphene — using a small vacuum chamber into which a vapor containing carbon reacts on a horizontal substrate, such as a copper foil. The new system uses a similar vapor chemistry, but the chamber is in the form of two concentric tubes, one inside the other, and the substrate is a thin ribbon of copper that slides smoothly over the inner tube.

Gases flow into the tubes and are released through precisely placed holes, allowing for the substrate to be exposed to two mixtures of gases sequentially. The first region is called an annealing region, used to prepare the surface of the substrate; the second region is the growth zone, where the graphene is formed on the ribbon. The chamber is heated to approximately 1,000 degrees Celsius to perform the reaction.

The researchers have designed and built a lab-scale version of the system, and found that when the ribbon is moved through at a rate of 25 millimeters (1 inch) per minute, a very uniform, high-quality single layer of graphene is created. When rolled 20 times faster, it still produces a coating, but the graphene is of lower quality, with more defects.

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