Graphene, known worldwide as a potential wonder material, is asserting its dominance across nanotechnology, materials science, chemistry and physics fields. New research is being published all the time, be it in small open-access journals or high impact paywall journals. Industry is advancing at a fast pace and is being governed by organizations such as the National Graphene Association (NGA, Mississippi, USA) and the National Graphene Institute (NGI, Manchester, UK).
The emergence of graphene research centers and associations such as the NGI and NGA have helped to steer graphene from simple academic merit, since its creation in 2004, to a material of huge commercial worth. The potential for graphene and its many derivatives is huge. There are currently many applications that graphene could potentially be used in commercially, and new ideas are arising daily.
The future looks bright for commercial graphene applications through the bridging of industry and academia at specially designed research institutions. One such example currently under construction is the Graphene Engineering Innovation Centre (GEIC) from the NGI, which looks to create an atmosphere for both industry and academia to collaborate. Whilst this is the first institute of its kind dedicated to graphene, there are talks of similar institutes to be created in both the United States and Australia.
The emergence of the new International Organization for Standardization (ISO) for graphene published by National Physical Laboratory (NPL) is also set to allow the graphene industry to grow in a controlled way and help to set the standard for all companies.
Whilst the commercial potential of graphene could be discussed at great length, this article primarily looks at some of the academic work that has recently come out. Why is it so significant, the research itself only presents a small step towards new ideas and properties? What is represented is the fact that 3 papers come out on the same day, only in Nature open access journals (Nature Communications and Scientific Reports), showcases a widespread use in terms of applications– and this is only just one day for one publishing house. It should also be noted that these papers all work using different forms of graphene – a showcasing of versatility of the highest calibre.
What does it show? It shows that graphene is a hotbed of research and the application and research output from academia may be more than many people think. Will most of the research make it to the commercial sector? Probably not, but a lot of research is starting to. The interest towards graphene from the commercial sector is growing and it is only a matter of time before more academic research becomes a commercial reality, whether it is governed by associations like the NGI and NGA, or not.
The Faces of Graphene
Graphene presents itself in many forms and in many different applications. One type of graphene, or one application of graphene, can rarely be directly compared with another. So, the different graphene derivatives and their applications have many faces, so to speak, from a central point of ‘graphene’.
Graphene comes in many forms, from conventional chemical vapor deposition (CVD) grown sheets, to graphene nanoribbons (GNRs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoplatelets (GNPs), graphene quantum dots (GQDs), graphene aerogels and graphene nanowalls.
The applications of graphene are even more diverse and each individual application is not dependent upon a single graphene type. So far, graphene is used in at least 15 kinds of sensor devices, Li-ion batteries, supercapacitors, composites, conductive inks, catalyst supports, electron emission displays, solar cells, energy storage devices and water filtration membranes, to name a few. This is but a small number of the actual and potential applications that graphene can be used in.
One Day, One Publishing House
Here, the article looks at the publications that came out all on the same day and how one material can have such a wide effect and research potential.
- Measuring the Quantum Numbers in Graphene
Firstly, a team of Researchers from the USA and Japan have used a cryogenic impedance transformer to measure the layer-resolved charge density and the valley and orbital polarization within the zero-energy Landau level of bilayer graphene (van der Waals bilayers).
Layer polarizations were found to occur in discrete steps in 32 electric field-tuned phase transitions. The transitions included states with varying degrees of valley, spin and orbital order. This included previously unobserved orbitally polarized states that were stabilized by skew interlayer hopping.
The Researchers also used Hartree-Fock calculations to map a complete picture of the correlated electron system. The model captured single-particle and interaction-induced anisotropies to create a roadmap that could be used for deterministic engineering of fractional quantum Hall states. The technique is also applicable to other 2D materials, including twisted bilayer graphene and homobilayer and heterobilayer and transition metal dichalcogenides (TMDCs).
- Kondo Resonance using Graphene Nanoribbons
In this piece of research, Scientists from the USA have used a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) methods to observe an unusually well-defined Kondo resonance from a variety of magnetic molecules.
The Researchers separated magnetic molecules from a (111) gold surface plane using vertically stacked graphene nanoribbons. The Kondo resonance on the graphene-mediated surfaces was found to be almost identical to when the magnetic molecules were directly absorbed onto the gold plane.
The extremely strong spin-coupling effect is unusual for graphene nanoribbons as the band gap structure does not normally allow for free electrons to interact with molecular spins, but instead decouple. DFT calculations revealed that no spin-electron interactions occur when the graphene nanoribbons are removed and the research offers insights towards potential applications in graphene-mediated spintronics.
- Barocaloric Effect on Graphene
Finally, Researchers from China, Brazil and Portugal have theoretically analyzed the barocaloric effect of graphene, i.e. the capacity of the graphene sheet to exchange heat with a thermal reservoir under mechanical strain.
The calculations took into account all of the planar orientations of the sheet and calculated the mechanical strain as a function of an induced pseudo-magnetic field using a 2D Dirac Hamiltonian. The induced magnetic field was found to be directly responsible for barocaloric effects in graphene.
The barocaloric effect was found to be greater at higher temperatures (>40 Kelvin) and effects have been shown so far in temperatures up to 300 K. The computations look to introduce a new property into the existing group of multi-caloric effects on graphene, alongside the already established magneto- and electro-caloric effects.
“Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene”- Hunt B. M., et al, Nature Communications, 2017, DOI: 10.1038/s41467-017-00824-w
“Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure”- Li Y., et al, Nature Communications, 2017, DOI: 10.1038/s41467-017-00881-1
“Barocaloric effect on graphene”- Ma N., and Reis M. S., Scientific Reports, 2017, DOI:10.1038/s41598-017-13515-9
National Graphene Association (NGA): https://www.nationalgrapheneassociation.com/
National Graphene Institute (NGI): http://www.graphene.manchester.ac.uk/collaborate/national-graphene-institute/
Graphene Engineering Innovation Centre (GEIC): http://www.graphene.manchester.ac.uk/collaborate/geic/