A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in September 2021 may now found on NTNU Nano's page for publications.

Researchers at NTNU have developed a new elastomer with unprecedented stiffness and toughness, inspired by spider silk 

Inspired by extremely strong spider silk, researchers at NTNU have developed a new material that defies previously seen trade-offs between toughness and stiffness. 

The material is a type of polymer known as an elastomer because it has a rubber-like elasticity. The newly developed elastomer features molecules that have eight hydrogen bonds in one repeat unit, and it is these bonds that help to evenly distribute stress put on the material and make it so durable.

“The eight hydrogen bonds are the origin of the extraordinary mechanical properties,” says Zhiliang Zhang, professor of mechanics and materials at NTNU’s department of structural engineering. The material was developed at NTNU NanoLab and partially funded by the Research Council of Norway. 

The idea to introduce a higher than usual number of hydrogen bonds came from nature. “Spider silk contains the same kind of structure,” says Yizhi Zhuo, who developed the new material as part of his PhD and postdoc work. “We knew it could result in very special properties.”

Scientists have previously noted that spider silk – specifically dragline silk, which provides the spokes and outer rim of a spider’s web – is both exceptionally stiff and tough. 

Stiffness and toughness are distinct properties in engineering and are often in opposition. Stiff materials can withstand a lot of stress before deforming, whereas tough materials can absorb a lot of energy before they break. Glass, for example, is stiff but not tough.

Until now, replicating the dual stiffness and toughness of spider silk in synthetic elastomers has not been possible. “With commercial materials, if you want to have higher stiffness, you have lower toughness. It’s a trade off. You cannot have both,” says Zhang. 

The team’s new elastomer features distinct hard and soft domains. After devising and making it, the team used an atomic force microscope – with a resolution of fractions of a nanometre – to look at the underlying structure of the material, and observe the interface between the hard and soft regions. 

They saw that as well as the eight hydrogen bonds distributing stress, the mismatch in stiffness between the hard and soft domains helped to dissipate energy further by encouraging any cracks to branch off instead of continuing along a straight path. “If you have a zig-zag, you create a large fracture surface and dissipate more energy, so you have higher toughness,” says Zhang.

Alongside it’s mechanical properties, the material is optically transparent and research suggests it could even self-heal at temperatures higher than 80 °C. If production can be scaled up, the new material could one day be used in flexible electronics – particularly wearable devices that are more prone to damage and breakages. 

Zhang and his colleagues filed a patent for their material in March, but they continue to work on introducing other desirable properties to it. The soft domains in their material are made up of a silicon-based polymer known as PDMS, but the researchers suspect they could improve the mechanical properties even further by experimenting with other substances.

They would also like to extend the material’s properties to include anti-icing – stopping ice sticking to it at low temperatures – and anti-fouling – preventing aquatic organisms like mussels and algae attaching to it –  so it could be used in extreme conditions, such as the Arctic. “This material is a good starting point, but we want to add some other functionality,” says Zhang.

Kelly Oakes, September 2021

The research was funded by Research Council of Norway grant numbers 255507 and 245963.

Reference: Zhuo, Y., Xia, Z., Qi, Y., Sumigawa, T., Wu, J., Šesták, P., Lu, Y., Håkonsen, V., Li, T., Wang, F., Chen, W., Xiao, S., Long, R., Kitamura, T., Li, L., He, J., Zhang, Z., Simultaneously Toughening and Stiffening Elastomers with Octuple Hydrogen Bonding. Adv. Mater. 2021, 33, 2008523. https://doi.org/10.1002/adma.202008523
 

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in June - August 2021 may now found on NTNU Nano's page for publications.

No conferences to travel to this year? Tired of watching long, long lectures on Zoom?

Then this year’s Norwegian NanoSymposium might be just the thing for you! The NanoSymposium will be a very different kind of on-line meeting, with a dynamic mix of invited speakers, short Pecha Kucha presentations, and plenty of breaks and interactive sessions. This is an excellent opportunity to learn a little about the parts of nanoscience that you don't get to study or research every day.

Our aim is to hold a fun meeting covering all areas of nanoscience, where students and researchers from many disciplines can share ideas and make new contacts.

What is a Pecha Kucha?? Glad you asked...

Pecha Kucha is a concentrated pitch where the participants present exactly 20 slides at a rate of 20 seconds per slide. The entire presentation lasts 6 minutes and 40 seconds. You may find information about the Pecha Kucha format and how to prepare one here and here. Be sure to check out the examples for inspiration!

Thanks to sponsorship from NTNU Nano, there is no participation fee, but you will need to register your attendance. 

Read more about the programme and registration here.

Researchers at NTNU are studying brain cells in the lab to investigate the foggy beginnings of diseases like Parkinson’s and Alzheimer’s. 

When the symptoms of neurodegenerative diseases like Parkinson’s become clear enough to make a diagnosis, there have already been significant changes in a person’s brain. That’s why researchers believe that finding a way to identify this turning point could be the key to better treatments.

“In theory, if you can pinpoint the onset of the disease, you might be able to stop it or reverse some of its effects,” says Ioanna Sandvig, co-leader of the integrative neuroscience group at NTNU’s Department of Neuromedicine and Movement Science. “By the time you actually have very strong indications that something is wrong, then it's a bit too late.”

Sandvig and her colleagues are growing interconnected brain cells in the lab, to study how these neural networks evolve and what happens when things go wrong. The research, supported by the NTNU program for Enabling Technologies, could help to pinpoint the very beginnings of neurodegenerative diseases.

Chip that mimics connectivity
Each neural network contains bundles of neurons – the cells that carry messages in our brains – housed in a microfluidic chip, the prototype of which was designed by Rosanne van de Wijdeven during her PhD at NTNU. These nodes are connected by tunnels in the chip through which axons – the wire-like protrusions of a neuron – can grow, but the main body of a neuron cannot. 

By connecting three nodes together the researchers can mimic the connectivity inside the human brain. But Sandvig is keen to stress that these neural networks are not in any way real brains. “We don’t have brains in the lab,” she says. “But we do have networks that are representative, and are very malleable to the perturbations we want to introduce.”

The chips contain microelectrode-arrays made in NTNU’s NanoLab that enable the researchers to measure the electrical activity of the network and gain insight into how signals are passing between the neurons. 

In one recent study, led by Vibeke Devold Valderhaug and detailed in a paper uploaded to the pre-print server bioRxiv, the researchers cultivated two groups of neural networks in parallel, one of which housed neurons with a gene mutation that has been linked to Parkinson’s disease known as LRRK2 G2019S. They saw that, in the network with the mutation, neurons grew and formed connections in a markedly different way, and displayed different electrical activity, to the healthy network.

Neurons typically navigate their environment in a very specific manner, says Sandvig, but in the network with the mutation the cells didn’t have the kind of directionality you would expect – they seemed confused. “The LRRK2 mutated networks seem to have some kind of aberrant growth,” says Sandvig. “They seem to interpret exactly the same cues – because it's the same substrate – in a totally different way than the healthy network.”

As well as those findings, Sandvig was pleased to see how clearly the subtle changes showed up in the team’s experimental set up. “What was surprising was how well we could pick it up with this interface,” she says. The interface also allowed the researchers to look at the connectivity within the nodes as well as between them. 

Studying these brain changes in a neural network has advantages over studying them in animals, though each method can inform the other. “You can have these snapshots of changes in the structure and function of the network much more easily than in animal models,” says Sandvig. 

With neural networks, it’s also possible to take cells from the same individual and derive them in two separate ways to compare how the networks evolve when age-related effects are removed. In fact, one of the follow up projects Sandvig is developing with integrative neuroscience group co-leader Axel Sandvig alongside colleagues at the Kavli Institute for Systems Neuroscience does exactly this for Alzheimer’s disease. “Diseases like Parkinson's, ALS, Alzheimer's are all different, but they share some very fundamental characteristics,” she says. 

By providing new insights into how our brains change in the early days of neurodegenerative disease, real life neural networks could set us on a path to new understanding, and perhaps, eventually, even new treatments.

Kelly Oakes, June 2021

RCN project number: 295864 (NorFab)
 

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in May 2021 may now found on NTNU Nano's page for publications.

Researchers from NTNU are shedding light on magnetic materials at small scales by creating movies with the help of some extremely bright x-rays.

Erik Folven, co-director of the oxide electronics group at NTNU’s Department of Electronic Systems, and colleagues from NTNU and Ghent University in Belgium set out to see how thin-film micromagnets change when disturbed by an outside magnetic field. The work, partially funded by NTNU Nano and the Research Council of Norway, was published in the journal Physical Review Research.

Tiny magnets

The tiny square magnets, created by NTNU PhD candidate Einar Digernes, are just two micrometers wide and split into four triangular domains, each with a different magnetic orientation pointing clockwise or anti-clockwise around the magnet. These domains meet at a central point – the vortex core – where the magnetic moment points directly in or out of the plane of the material.

“When we apply a magnetic field, more and more of these domains will point in the same direction,” says Folven. “They can grow and they can shrink, and then they can [merge] into one another.” 

Electrons almost at the speed of light 
Seeing this happen isn’t easy. The researchers took their micromagnets to an 80m-wide donut-shaped synchrotron, known as BESSY II, in Berlin, where electrons are accelerated until they are travelling at almost the speed of light. Those fast moving electrons then emit extremely bright x-rays. “We take these x-rays and use them as the light in our microscope,” says Folven.

Because electrons travel around the synchrotron in bunches separated by two nanoseconds, the x-rays they emit come in precise pulses. A scanning transmission x-ray microscope, or STXM, takes those x-rays to create a snapshot of the material’s magnetic structure. By stitching these snapshots together, the researchers can essentially create a movie showing how the micromagnet changes over time.

With the help of the STXM, Folven and his colleagues disturbed their micromagnets with a pulse of current that generated a magnetic field, and saw the domains change shape and the vortex core move from the centre. “You have a very small magnet, and then you poke it and try to image it as it settles again,” he says. Afterwards, they saw the core return to the middle – but along a winding path, not a straight line. “It will kind of dance back to the centre,” says Folven. 

One slip and it’s over 

The team’s biggest challenge was making the samples in the first place. “We were very, very uncertain whether it would even be possible when we started out,” says Folven. 
That’s because they study epitaxial materials, which are created on top of a substrate that allows researchers to tweak the properties of the material, but would block the x-rays in a STXM. 

To solve the substrate problem, the researchers buried their micromagnet under a layer of carbon to protect its magnetic properties. Then they carefully and precisely chipped away the substrate underneath with a focused beam of gallium ions until only a very thin layer remained. The painstaking process could take eight hours per sample – and one slip up could spell disaster.

“The critical thing is that, if you kill the magnetism, we won't know that before we sit in Berlin,” he says. “The trick is, of course, to bring more than one sample.”

From fundamental physics to future devices
Thankfully it worked, and the team used their carefully-prepared samples to chart how the micromagnet’s domains grow and shrink over time. They also created computer simulations to better understand what forces were at work.

As well as advancing our knowledge of fundamental physics, understanding how magnetism works at these length and time scales could be helpful in creating future devices. 

Magnetism is already used for data storage, but researchers are currently looking for ways to exploit it further. The magnetic orientations of the vortex core and domains of a micromagnet, for example, could perhaps be used to encode information in the form of 0s and 1s.

The researchers are now aiming to repeat this work with anti-ferromagnetic materials, where the net effect of the individual magnetic moments cancels out. These are promising when it comes to computing – in theory, anti-ferromagnetic materials could be used to make devices that require little energy and remain stable even when power is lost – but a lot trickier to investigate because the signals they produce will be much weaker. 

Despite that challenge, Folven is optimistic. “We have covered the first ground by showing we can make samples and look through them with x-rays,” he says. “The next step will be to see whether we can make samples of sufficiently high quality to get enough signal from an anti-ferromagnetic material.”

Kelly Oakes, May 2021

RCN project numbers: 221860 and 295864

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in April 2021 may now found on NTNU Nano's page for publications.

 As sunlight filters through a forest canopy, chlorophyll is hard at work capturing the energy of photons. Inspired by nature, researchers at NTNU are working on light-capturing dyes for solar cells to generate electricity.

These aren’t the kind of solar cells you’ll see on the roof of a building. In those silicon solar cells, light hits one of two semiconductor layers and frees up electrons to jump between the layers. It’s the movement of these electrons that creates an electrical current. A dye-sensitised solar cell (DSSC) works in a similar way, but one of the semiconductor layers is replaced with a photosensitive dye that absorbs the light and releases electrons instead.

Dye-sensitised solar cells tend not to be as efficient at converting light into electricity as their silicon counterparts. But they work in low light conditions, and can be transparent and flexible, so are better suited to some applications. To really take full advantage of DSSCs, a research project partially funded by the Research Council of Norway (RCN)* is looking for ways to step up their efficiency. 

In a paper published recently in the journal Dyes and Pigments, NTNU PhD candidate David Moe Almenningen and colleagues, Odd Reidar Gautun, Bård Helge Hoff and Svein Sunde have shown that adding a particular molecule to the dyes can increase its light harvesting properties – though so far the additional light comes at a cost.

To harvest light a dye needs to act as an electron donor and an electron acceptor. “When this molecule is struck by a ray of sunlight, then the electron moves from the electron-rich part to the electron-poor part,” says Almenningen. By adding something in-between the donor and acceptor, chemists are able to increase the amount of light the cell harvests. 

Almenningen’s research is investigating the addition of compounds featuring thiophenes, a molecule similar to benzene but containing sulphur. Thiophenes are electron-rich, so would be expected to increase the light harvesting properties of the dye, he says. And recent experiments show that they do: the dye with the most thiophenes was the one that harvested most light. 

However, it turns out that increasing the amount of light a dye captures doesn’t automatically mean better solar cells. Put simply: you might get more electrons, but they don’t necessarily go where you want them to. 

In his experiments, Almenningen found that though it absorbed the most light, the dye with the most thiophenes actually made the least efficient solar cell. “You think you're doing something brilliant by increasing the light harvesting ability, but then there are other reactions going on in the solar cell that are negatively affected by these modifications,” he says. 

He and his colleagues hope to find a way to avoid those counterproductive effects and take advantage of the improved light collection. Their next step is to try modifying the dye chemically so the electrons can only go in one direction. If this is successful, it could lead to more efficient solar cells.

Finding a way to increase the efficiency of DSSCs is one of the roadblocks to widespread use. The current highest efficiency is around 12%, compared with closer to 20% for a traditional commercial silicon solar cell. 

If researchers are able to harness the light captured by dyes in these solar cells more effectively, DSSCs would potentially offer an advantage over traditional crystalline solar cells when it comes to scaling up: they are cheap to make, because they don’t need a clean room or vacuum technology. 

One promising avenue for DSSCs would be to integrate them into buildings to capture the dimmer light that is typically found indoors. “That’s where these solar cells shine,” says Almenningen. “Also they look quite pretty. You can customise any colour you want, they can be see-through.”

For Almenningen, though, the reward is in figuring out how changing the chemical structure affects the performance of the dye: “The chemistry in itself is what's fascinating.”

*RCN project numbers: 262152, 226244 and 295864

Kelly Oakes, March 2021

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in March 2021 may now found on NTNU Nano's page for publications.

Modern-day computers rely on the fact that electrons have charge. But electrons have another fundamental property called spin – a measure of magnetic orientation – that researchers hope to harness to create a new generation of computer chips. Spintronics – short for spin transport electronics – could lead to faster, more stable, and less power-hungry devices. 

An electron’s spin is a bit like a compass needle that points north or south. Magnetic hard drives already use the spin of electrons to store information in the form of binary 0s and 1s, which your computer can then translate back into human-readable information. But traditional computer processing ignores spin entirely. Using spin for computation would mean processing and storage could happen on the same chip.

 In most materials, there are equal numbers of electrons with   spins that point in opposite directions, so from the outside   they all appear to cancel out. These materials are known as   antiferromagnetic, and Thomas Tybell, a professor in the   department of electronic systems at NTNU and his colleagues   are looking for ways to engineer them for use in future   spintronic devices. “If we use antiferromagnetic materials,   where the spins cancel, they are very robust against   perturbations,” he says.

That stability is a big plus. Let’s say you’re working on an important document, and just before you hit save there’s a power cut. With conventional computing, you have probably just lost your work. But the spin of an electron stays the same even when the power is lost, so on a spintronic computer your work would be preserved. 

But to create spintronic devices, we first need materials that allow us to reliably control spin. 

One big challenge is engineering materials without internal boundaries that could mess with the spin of electrons and result in lost information. These boundaries  – called domain walls – occur where the repeating pattern of atoms in the material doesn’t quite match up. 

Recently, Tybell and his colleagues have found a way to make thin films from antiferromagnetic materials that look like they have no domain walls at all. By changing the arrangement of atoms – known as the lattice – in the substrate onto which the thin film is deposited, they can ensure the crystal grows in such a way as to avoid creating those internal boundaries. “Our key to controlling the physical properties is the lattice,” says Tybell.
“This is just a grey, boring image but actually what’s important is that each pixel has the same magnetic axis,” he says. “Suddenly you have no domain walls.”

In recent years other researchers have shown that it’s possible to create a single crystal that doesn’t have domain walls. This new work shows it is possible in thin films, too. “That’s important because suddenly you have unprecedented new possibilities for devices,” says Tybell. “If you want to make a device that works you can’t work on a single crystal, you have to make thin films.” 

There are still a number of challenges to overcome before spintronics goes mainstream, and Tybell says he can’t be sure how long it will be until you’ll be able to hold an entirely spintronic computer in your hand. “It will depend on how well we can control the materials to allow them to be mass produced,” he says. “I hope it’s soon, but I fear it’s quite in the future.”

But, he points out, the concept behind the transistors that are present in every computer around the world was first patented in 1925. It then took two decades until the first working transistor was realised by researchers working Bell Labs in the US, and several more years until they were in widespread use.

In the meantime, the materials Tybell and his colleagues are developing will not go to waste: they can also be used by researchers studying quantum objects from a fundamental physics point of view. And while it’s not easy to predict where that could lead, there’s always a chance it might prove vital in the future, one way or another. 

“We should not forget that if you can grow single crystalline thin films, it opens up new avenues to study quantum phenomena and learn about these materials in a way that might be important for quantum technologies in the future,” he says. “I am sure there are many things still to discover.”

Kelly Oakes, February 2021
 

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in February 2021 may now found on NTNU Nano's page for publications.

This week's news articles describe the story behind the development of NTNU’s COVID-19 test, the new Norwegian Quantum Computing Centre, and how advances in silicon processing may lead to more environmentally friendly solar cells .

A list of NTNU papers related to nanoscience, nanotechnology and functional materials published in January 2021 may now found on NTNU Nano's page for publications.

Sometimes, when it comes to friction, less is more – at least that’s what several experiments over the last decade seem to have shown in the case of friction caused by layered materials. But it wasn’t until recently that researchers at NTNU figured out what was actually going on.

Friction probably isn’t something you think about on a daily basis, but as anyone who’s ever slipped over on an icy pavement could tell you, it can play a crucial role in many situations. The downside of friction, though, extends far beyond icy pavements: along with wear, it is responsible for approximately 23% of the world’s energy consumption. 

“Friction is a huge technological problem,” says Astrid de Wijn, a professor in the department of mechanical and industrial engineering at NTNU. “In industrialised societies, where we have machines that are moving constantly or very fast, friction is enormously costly.” 

Studying friction is not as simple as classroom physics demonstrations involving a wooden block on a ramp suggest. “What is really happening is that the surfaces are rough and they meet at some points that are typically quite small,” says de Wijn. “When we study friction we are thinking about these contact points and how they behave.” 

In order to really understand what they can see happening at the real world macroscale, researchers need to be able to explain the complex behavior of the materials at the nanoscale. “Many different things are happening at different length and time scales, and it makes friction very interesting,” says de Wijn.

Layered materials  – such as graphene, which is a single layer of carbon atoms arranged in a honeycomb pattern – generally have low friction. They are already used in lubricants, but learning more about how they work could enable us to make the world’s machinery run more smoothly and reduce our energy bill on a global scale. 

But in the last decade, researchers studying how friction works in materials like graphene have found that a single layer actually creates more friction than several layers. “People didn't understand that, and for years they were struggling with it,” says de Wijn. “They did simulations and they reproduced this behaviour but couldn't figure out what was really happening.” 

The problem was, while there were plenty of results apparently showing what was causing the material to behave like this in particular situations, the explanations proposed by different researchers seemed to contradict each other, and nothing stood out. “They all had good arguments and evidence that, in their system, it was their suggested mechanism that was doing it, says de Wijn.

In a recent paper published in Nature Communications, de Wijn and PhD student David Andersson solved the problem. It turns out that all of the proposed solutions are, in a way, right. 

One existing model that often proves helpful for understanding friction was first proposed in 1928 and consists of three elements: a support, a spring and a tip. The friction is then the force required to pull the tip across a sheet. While that works well for explaining many situations, it falls apart when layered materials are involved. So de Wijn and Andersson added just one variable to describe what is happening inside the layers of the sheet that the tip is being pulled across. “We didn't specify what that variable meant exactly – if it was a scrunching up of some kind, or some bending or one of the many possible things that people had proposed,” she says. 

That simple tweak turned out to be the key to explaining several previous results, both from real world experiments and computational models. “Suddenly all the pieces fell into place and we understood what was happening,” says de Wijn. “It could be different mechanisms giving rise to the same kind of dynamics.”

Unfortunately, because of travel restrictions due to the coronavirus pandemic, de Wijn and Andersson have not been able to present the work at many conferences or discuss it with colleagues as widely as they would otherwise have done – at least not in person. Nevertheless, now this puzzle has finally been solved, it opens up new avenues for investigating how friction works in layered materials, and could pave the way for new technology to reduce it. 

The work is not over yet, though. The next step for de Wijn is to figure out how thermal fluctuations affect the system. “It's not just an academic puzzle for us,” she says. “Solving this means that we are one step closer to making friction lower.”
 

Kelly Oaks, January 2021