Graphene enables the ideal chemical sensor

Researchers from the University of Illinois at Chicago (UIC) developed a graphene-based highly sensitive chemical sensor (an electronic "nose" if you will). The graphene enabled the researchers to increase the sensitivity to absorbed gas molecules by 300 times compared to current technology.

Interestingly, the graphene's grain boundaries are key to this achievement. The researchers discovered that the gas molecules are attracted to these grain boundaries, and so this is the ideal spot for the detection of these molecules. They explain that the irregular nature of the grain boundary produces hundreds of electron-transport gaps with different sensitivities - as if there are multiple switches all working in parallel.

Researchers find way to fix graphene grain-boundary defects

Researchers from Korea's Ulsan National Institute of Science and Technology developed a technique to repair graphene line defects by selectively depositing metal (Platinum). Graphene grain boundary defects harm the material's properties, and the new method can be used to address this issue.

Using Atomic Layer Deposition (ALD), the researchers managed to use the platinum metal and deposit it on the line defects. The researchers used the new improved sheets to develop electrodes and hydrogen gas sensors at room temperature. In these two applications, the enhanced sheets outperformed the original graphene sheets three times over.

The researchers now say they want to try different metals (such as gold and silver), and also test other applications.

Researchers use surface plasmons to see and study graphene grain boundaries

Researchers from the US, Germany, Singapore and Spain developed a new way to image and study grain boundary defects in graphene using surface plasmons. The idea is that by analyzing how the surface plasmons are reflected and scattered you can understand more about those defects. The researchers discovered that grain boundaries act as electronic barriers around 10–20 nm in size and they are responsible for the CVD-grown graphene's low electron mobility.

In addition, the researchers say that the grain boundaries may actually be useful in the future - perhaps used as tuneable plasmons reflectors and phase retarders in "plasmonic circuits".

Experiments prove that graphene Boundaries do not weaken the graphene sheet

Researchers from Columbia demonstrated that a graphene sheet that is stitched together from many small crystalline grains is almost as strong as perfect graphene (this depends on the processing method, though). This solves the question whether graphene defects harm its mechanical strength (some theoretical simulations predict that grain boundaries are strong while other indicated they weaken the graphene sheet).

Commonly used methods for post-processing CVD-grown graphene may indeed weaken the grain boundaries and create a low-strength graphene. But the researchers developed a new transfer process (using a different etchant) that prevents any damage to the graphene.

Graphene defects can make it weak as the material exhibits a Pseudo Hall-Petch effect

Researchers from Rice University and Tsinghua University discovered (using theoretical calculations) that defects in graphene can cause it to become weak - if they occur at the grain boundaries of graphene sheets. Those grain boundaries occur because graphene grown in labs (usually using CVD) are not perfect and this creates several "islands" of graphene that merge together. The researchers say that at these points, graphene is about half as strong as perfect graphene.

The atoms on the lines that connect those islands are called grain boundaries - and the atoms at those lines usually bond in five- and seven- atom rings. These are weaker than the normal hexagon rings of graphene. The weakest points are seven-atom rings. These are found at junctions of three islands, and that's where cracks in graphene are most likely to form.