As we enter an era of folding screens and better ways of monitoring our health, technology and the way it’s applied needs to move fast to keep up with the ever-evolving demands placed upon it. Ing. Anthea Agius Anastasi, a Maltese researcher within the Department of Metallurgy and Materials Engineering (DMME), Faculty of Engineering, University of Malta, has put her doctoral research to fantastic use by investigating the properties of graphene.
The research is being done under the supervision of Prof Ing Glenn Cassar, Head of Department of DMME, and Dr Matthew K. Borg from The University of Edinburgh.
If you’re asking what this material is, what it can be used for and what experiments Agius Anastasi is getting up to, strap yourself in, because there’s much to unpack and it could reshape the future of how certain electronics are built!
Stronger than steel yet highly flexible
Partially funded by the ENDEAVOUR Scholarships Scheme, the study focuses on the mechanical properties of graphene, a carbon allotrope consisting of a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice. What makes it so interesting is the wide range of exceptional electrical, chemical and mechanical properties graphene exhibits.
“For starters,” Agius Anastasi explains, “it’s optically transparent, very flexible, and exhibits a very high electrical conductivity. These properties make graphene ideal for use in flexible display screens, taking folding tablets and phones to the next level, and wearable electronics, such as non-invasive stickers which will monitor blood glucose levels in diabetics and administer drugs when required.”
Graphene also has a very high tensile strength (the stress required to fracture a material). And by high, Agius Anastasi reveals, it’s around 200 times stronger than construction industry-level steel. The elastic modulus of graphene (a material’s resistance to elastic deformation) is also one of the highest known, of around 1 TPa (terapascals). This is equivalent to the elastic modulus of diamond, and around 5 times higher than that of steel.
“This means graphene can be used to produce nanocomposites with very high strength-to-weight ratios”, Agius Anastasi tells us. “With these properties, it can be used in the aerospace and vehicle industries, as well as in sports equipment”.
Another thing, before the (minor) catch
A perfect sheet of graphene is impermeable to all atoms, which means no atoms will be able to pass through.
“If we introduce nanopores or small holes in the graphene sheet, we will be able to create nanosieves or filtration membranes. This will allow smaller atoms & molecules to pass through and filter out the larger ones. In the case of desalination, pores of around 0.8 nanometres will be able to filter out the larger salt ions from the smaller water molecules, to produce clean potable water from saline water.”
So, apart from using graphene to create stronger devices and structures, it can also be used to solve a longstanding problem in Malta: producing clean water for a variety of uses. There is, however, one minor catch, that Agius Anastasi is looking to address in her research.
“To adequately and effectively use graphene in any of the above applications, we still need to fully understand the mechanical behaviour of graphene”, Agius Anastasi states. While the scientific community at large needs to develop a testing procedure to measure the mechanical properties of graphene and obtain accurate, repeatable results, Agius Anastasi is focusing on her own part.
“In my research work, I focused on the elastic modulus of graphene. So far, one of the methods that has been used to measure the elastic modulus of graphene is by nanoindentation using atomic force microscopy (AFM)”, she divulges.
In this technique, the graphene is suspended over a hole in a substrate to create a drum-like membrane. A very sharp probe of the AFM is then used to indent or push the centre of the graphene membrane and the AFM records the force required to indent the graphene membrane. From this, one can calculate the elastic modulus of graphene.
Any progress to share?
Several testing parameters were used and the variation in the values of elastic modulus obtained for the same graphene sample proved that the testing parameters affect the final results. Therefore, Agius Anastasi clarifies, results show that small changes in the method parameters, for example, the depth to which the graphene membrane is indented and the type of indentation probes used, affect the results obtained.
In summary, this means that a methodology that can be used by other researchers to measure the elastic modulus of graphene and repeatedly obtain comparable results is being established. More work, however, is still required.
“Currently, we are working on improving the nanoindentation method guidelines to ensure that the results obtained are accurate and repeatable across different graphene samples and laboratories all over the world”, Agius Anastasi tells us in conclusion. “Apart from that, we have ongoing work on developing graphene-based filtration membranes.”
The results are published in a peer-reviewed journal:
A. Agius Anastasi, A. Valsesia, P. Colpo, M. K. Borg, and G. Cassar, “Raman spectroscopy of gallium ion irradiated graphene,” Diamond and Related Materials, vol. 89, pp. 163-173, 2018.