What are 2D materials?
When thinking about the properties and applications of a material, we tend to start with what a material is made of. For example, metals conduct electricity because electrons can move freely within them. The same cannot be said for rubber, making it a good electrical insulator.
But size also matters. When shaved down to the nanoscale, the properties and behaviour of materials can differ hugely when compared to their 3D form.
A material is classed as 2D when one of its dimensions is on the nanoscale but the others are larger. It helps to imagine a sheet of paper that is large in surface area, but only around one nanometer (one billionth of a metre) thick.
The poster child of 2D materials is graphene, a new form of carbon discovered in 2004. Graphene is the 2D version of graphite, but has very different properties to its parent material. For example, graphene has the largest tensile strength of any material recorded whereas graphite is very brittle.
Since the discovery of graphene, research into 2D nanomaterials has exploded as scientists begin to understand the amazing properties and applications of these materials. At the University of Sheffield, two PhD students are undertaking projects looking at two very different potential uses of nanomaterials.
Exploring nanophotonics
Working within Professor Sasha Tartakovskii’s research group in the Department of Physics and Astronomy, Sam Randerson is a PhD student with an impressive track record when it comes to working with nanomaterials.
As an undergraduate, Sam joined Sasha’s research group on a Student Undergraduate Research Experience (SURE) placement in the summer after his second year. He worked with the team on a project which used a variety of specialist techniques to look at how a group of metals called transition metal dichalcogenides (TMDs) could be characterised on the nanoscale.
“When I did that placement I actually got to do a bit of research that led to me being a co-author on one of their papers which is pretty cool, especially when you're a student,” Sam said.
This experience led Sam to transfer from a three-year BSc to an MPhys course that comes with an additional year of research experience. Since then he has also gained experience in the field of bio-physics, using atomic force microscopy (AFM) in his masters project to build images of microscopic structures like bacterial cell walls.
Doing a PhD was not really at the forefront of Sam's mind until Sasha approached him with an opportunity to rejoin the research group he worked with in second year.
“I did a bit of research into the projects that Sasha was working on and I found it really interesting,” he said. “I had already had experience in this field and working with the group from my second year placement, so it felt like a very natural progression.”
Now, he is undertaking exciting research looking at how monolayers of tungsten disulphide, only 0.4-0.7 nanometers thick, can be used to control and manipulate light on the nanoscale.
“If we can control light exactly how we want it, there are infinite possibilities for structures you could make to do different tasks like quantum computing or biosensing,” Sam explained.
Sam started off with simulating the structures he could make with the nanomaterials, before moving on to actually building them himself. Now he is using optical equipment in the lab to measure his results and prove that his simulations are actually happening in real life.
Although this field of research is still in the exploratory stages, the results are so far very promising.
“It's working so far and we’re getting good agreement, which is always nice!” Sam said. “I’m actually going to present this at a conference in Barcelona this summer, so that's really cool too.”
The Engineering and Physical Sciences Research Council recently awarded a grant of £6.1 million to Sheffield researchers as investment into quantum research at the university. This grant is being used to install cutting edge equipment, allowing researchers to investigate the light emitting semiconductor nanostructures which could underpin the next generation of quantum technologies.
Realising the potential of metal organic nanosheets
Also exploring the properties and uses of nanomaterials is PhD student Amelia Wood, who is working with supervisor Dr Jona Foster in the field of metal organic nanosheets (MONs). Dr Jona Foster was recently awarded a Leverhulme grant of £193,610 for his work on nanomaterials entitled “Harnessing supramolecular interactions to make molecularly thin nanosheets”.
Amelia did her undergraduate degree in Chemistry, opting to do a placement year in industry when she saw the options available. It was while working for functional polymer manufacturers, Scott Bader, that she first thought about doing a PhD.
“I really enjoyed my time there and engaged with the company,” she said “I didn't really know what a PhD entailed, but my supervisor at Scott Bader had done a PhD at Sheffield and this got me thinking about it.”
On her return to Sheffield, Amelia worked with Dr Sarah Staniland in chemical biology for her fourth year MChem project and her PhD now builds on this biological training as she investigates how MONs can be used to create biosensors.
Amelia works specifically with zinc-based MONs, but there is the full range of metals in the periodic table to choose from and over 90,000 metal-organic frameworks known. The biosensors made from MONs can have a wide range of medical applications due to how tunable and changeable MONs are, allowing scientists to alter their individual properties.
For example, the COVID-19 lateral flow tests we have all become familiar with over the last two years are based on nanomaterials. Pregnancy tests are also based on gold nanoparticles, as they can detect biomarkers in urine.
“Whether it's urine, saliva, there'll be a lot of things in there that are quite similar and you're trying to differentiate between them and make sure you're detecting something very selectively, often in very low concentrations,” Amelia explained. “So what nanomaterials provide is a very dense collection of possible binding sites that can be tuned for a given target, and they can be more sensitive than other materials.”
Blurring the subject lines
Although Amelia's background is in chemistry, within this she found herself really attracted to the biomedical side of things.
Happily, Amelia's PhD research marries both of these subjects. She is now looking at nanosurface interactions and fine tuning the binding sites of her own MONs in a bid to make them smaller and even more selective.
Many biosensors, such as lateral flow tests, typically use antibodies to bind to target molecules in a sample. More specifically, a small part of the target molecule, called the epitope, will bind to a small section on the antibody, called the paratope.
Amelia’s goal is to go one step smaller and create MONs that contain just the epitope or paratope sites vital for the recognition of biomolecules.
“It's all about shrinking,” she explained. “If you can mimic the epitope and paratope, which are often only five or six amino acids, then you can avoid sticking really bulky antigens and antibodies to your nanosurface. It also means you can create a device that can test for more than one thing by having different binding sites on the same tiny nanomaterial.”
The main thing that attracted Amelia to do her PhD in this field was the real world applications of the technology she is researching. Despite having a chemistry background, she was fascinated by the potential medical applications of her research.
“I genuinely think nanomaterials are the future,” she said. “They can be used to carry drugs to a specific part of the body, or they can be designed to fluoresce so you can identify and target things like cancer. There's definitely a big drive toward using nanomaterials in biomedical applications, like imaging and drug delivery.”
Learning things not taught in the classroom
Sam and Amelia's academic careers have been hugely shaped by the opportunities for experience and research that are available to students at Sheffield.
From short term placements with the SURE scheme to year long placements in industry, these opportunities equip students with unique skills and independence that can only be gained through ‘doing’.
In Sam's case, doing a SURE placement showed him what he could do with the knowledge he was learning in lectures, and how this could be applied in the real world.
“I definitely think the placement was worth it because it's completely different to doing an undergraduate degree,” Sam said. “Undergraduate labs are fun, but can be quite tailored, whereas here I had more freedom to explore other techniques and questions.”
Work placements like the one Amelia completed also give students the unique opportunity to test out a career path they may not have considered before. In Amelia's case, doing a year in industry, along with her placement experience, grew her confidence and showed her that being a successful researcher requires more than just good grades.
“You don't have to be able to get 100% on exams to be a good researcher,” Amelia said. “Hard work and resilience will get you a lot further than being the cleverest person in the room. It made me realise that scientists aren't just one type of person, there are lots of different qualities that go into being a good scientist and seeing that has given me a lot more confidence in my own abilities.”
Written by Louise Elliott
