Autore: ExtremeTech

Defect-free graphene (or not)

The imagined industrial applications for graphene are currently constrained by two things — cost and quality. There is no concrete roadmap to predict how quickly graphene-based devices will become available and how common they will be. The quality of a sample of grapheme depends not only on purity but also on the nature of defects in the geometry. A new method to control the orientation, edge geometry, and thickness of vapor-deposited graphene has just been discovered by a pan-European group of researchers. With continued advances and some newly announced funding initiatives graphene’s full potential as a commercial material is now beginning to come into focus.

elephant

The legendary strength of graphene is a strict function of the quality of the sample. It is often said to have a strength 300 times that of steel however strength is a really nebulous way to define a material. There is strength in tension, compression, hardness, toughness and fatigue just to name a few. What we really need to know for a sheet of graphene is how many elephants it can carry. Fortunately some researchers have estimated this from experiments in which they indented a sample of it with an atomic force microscope probe. They determined that a sheet the thickness of Saran wrap would support an elephant poised atop a pencil, in turn standing on the sheet.

Getting this kind of performance out of graphene is a little easier said than done. Single crystal structures are considerably more robust than a random hodgepodge of graphene flakes — and considerably more expensive to produce. Chemical vapor depostion (CVD) is a method of producing graphene that is cheaper and easier to scale up than the original mechanical exfoliation methods by which it was first produced. To produce graphene with CVD, a gaseous source of carbon is introduced to a chamber where it can react and then get deposited onto a surface as a coating. By controlling the crystallographic orientations of the underlying copper template, the researchers were able deposit defect-free graphene sheets of considerable size.

Hexagonal graphene domains Growing atomically perfect structures, like mono-crystalline sapphire or silicon, is an excruciatingly slow process. Provided the grain boundaries of the individual crystal structures in a sample line up properly, high quality material can still be made without it being a single crystal. Many of the special uses imagined for graphene depend on its unique electrical and optical properties. Defects disrupt electron flow, but so long as this disruption is predictable and controlled, it can be used to advantage. In theory, the size of graphene sheets made in this way is only limited by the size of the underlying copper substrate. Graphene is also notable for its ability to be incorporated into other nanostructures. Graphene-nanotube hybrid materials have been made and provide an interesting extension off the plane and into the third dimension.

Recently, another European project has been funded to the tune of 1.3 billion (Euro) over ten years to be centered at the University of technology in Gotherburg, Sweden. There, the researchers will be focusing on applications for graphene in computers, batteries, and sensors. Other reports indicate that Finland-based Nokia has been awarded a grant to begin study of more immediate commercial applications, and give the the feel that a mad scramble may be about to unfold. It is important to look at the bigger picture and realize that graphene is the latest in a long line of carbon-based materials that have captured our collective imagination — buckyballs, nanotubes, graphite, diamond — but with each iteration we seem to get a little closer to the next generation technology.

Now read: Hype-kill: Graphene is awesome, but a very long way from replacing silicon

Research Paper: Controlling the Orientation, Edge Geometry, and Thickness of Chemical Vapor Deposition Graphene