Page 63 – Physics World

Home » Page 63

Green concrete: paving the way for sustainable structures

Grey, ugly, dull. Concrete is not the most exciting material in the world. That is, until you start to think about its impact on our lives. Concrete is the second most consumed material on the planet after water. Humanity uses about 30 billion tonnes of the stuff every year, the equivalent of building an entire new New York City every month. Put another way, there is so much concrete in the world and so much being made that by the 2040s it will outweigh all living matter.

As the son of a builder, I have made a few concrete mixes over the years myself, usually following my father’s tried and trusted recipe. Take one part cement (fine mineral powder), two parts sand, and four parts aggregate (crushed stone), then mix and add enough water until it all goes gloopy.

The ubiquity and low cost of these simple ingredients are just two of the reasons for concrete’s global reach. In liquid form, it can be moulded into almost any shape, and once set, it is as hard and durable as stone. What’s more, it doesn’t burn, rot or get eaten by animals.

These factors make concrete the ideal material for everything from vast imposing dams to sleek kitchen floors. However, its gargantuan presence across society comes at an equally epic environmental cost. If concrete were a country, it would rank third behind only the US and China as a greenhouse gas emitter.

Though raw material processing and transport of concrete are part of the problem, concrete’s biggest environmental impact comes from the heat and chemical processes involved in producing cement. Ordinary cement clinker (the raw form of cement before it is ground to a powder) is the product of heating limestone up to 1450 °C until it breaks apart into lime and carbon dioxide (CO₂). This heating requires lots of energy and the chemical process releases huge amounts of the greenhouse gas CO₂ – meaning that cement makes up around 90% of the carbon footprint of an average concrete mix.

Cement factory at twilight — **Tricky ingredient** Concrete’s biggest environmental impact comes from the heat and chemical processes involved in making cement. It’s very energy-intensive and produces vast quantities of carbon dioxide. (Courtesy: Shutterstock/Bilanol)

In the UK and some other parts of the world, this climate impact is well recognized, with the industry having made significant efforts to decarbonize over the last few decades. “Since 1990, the UK concrete industry has decreased its direct and indirect environmental impacts by over 53% through various technology levers,” says Elaine Toogood – an architect and senior director at the Mineral Products Association’s Concrete Centre, the UK’s technical hub for all things concrete.

This reduction has been achieved through actions such as fuel switching, decarbonizing electricity and transport networks, and carbon capture technology. “For example, over 50% of all the heat that’s needed to make cement is now supplied by waste-derived fuels,” Toogood adds.

Yet the sheer scale of the global concrete industry means that much more needs to be done to fully mitigate concrete’s carbon impact. Can physics, and more specifically AI, lend a hand?

Low-carbon replacements

Replacing cement – concrete’s least green ingredient – with low-carbon alternatives seems like a good place to start. Two well-proven options have been available for decades.

Fly ash – the by-product of burning coal at power plants – can replace about 30% of cement in concrete mixes. It has been used in the construction of many prominent structures including the Channel Tunnel, which opened in 1994. Blast furnace slag – the by-product of iron and steel production – is another capable replacement, and can make up to 70% of cement content. Slag was used in 2009 to substitute half of the regular cement in the precast concrete units that now make up the sea defences on Blackpool beach.

Yet although these waste materials are currently extensively used as cement or concrete additions in the UK and elsewhere, they rely on very polluting sources (coal-fired power plants and blast furnaces) that are gradually being phased out globally to meet climate targets. As a result, fly ash and blast furnace slag are not long-term solutions. New low-carbon materials are needed, which is where physics can play a decisive role.

Based in Debre Tabor University in Ethiopia, Gashaw Abebaw Adanu is an expert in innovative construction materials. In 2021 he and colleagues investigated the potential of partially replacing (0%, 5%, 10%, 15% and 20%) standard cement with ash from burning lowland Ethiopian bamboo leaf, a common local construction waste material (Adv. Civ. Eng 10.1155/2021/6468444). The findings were encouraging. Though the concrete took longer to set with increased bamboo leaf ash content, the material’s strength, water absorption and sulphate attack (concrete breakdown caused by sulphate ions reacting with the hardened cement paste) improved for 5–10% bamboo leaf ash mixes. The results suggest that up to 10% of cement could be swapped for this local low-carbon alternative.

Steel, copper – or hair?

More recently, Adanu has turned his focus to concrete fibre reinforcement. Adding small amounts of steel, copper or polyethene fibres is known to increase concrete’s ductility and crack resistance by up to 200% and 90%, respectively. The tiny fibres act like micro-stitches throughout the entire mix, transforming concrete from a brittle material into a tough, energy-absorbing composite.

Fibre reinforcement also leads to major cost savings and a reduced carbon footprint, primarily by removing the need for traditional steel rebar and mesh, where 50 kg of steel fibres can often do the work of 100 kg+ of traditional rebar. Eliminating this expensive material also reduces labour and maintenance costs.

In his latest research, Adanu has explored an unexpected alternative fibre reinforcement material that would decrease costs further as it would otherwise go to landfill: human hair (Eng. Res. Express 7 015115). Adanu took waste hair from barbershops in Debre Tabor (with permission, of course), and added small amounts of it in different quantities to standard concrete mixes. “It’s not biodegradable, it’s not compostable, but as a fibre reinforcement material, we found that using 1–2% human hair improves the concrete’s tensile strength, compressive strength, cracking resistance and reduces shrinkage,” says Adanu. “It makes concrete more clean and sustainable, and because it improves the quality of the concrete, it reduces cost at the same time.”

Research like Adanu’s, involving experimentation with local materials, has been the driving force for innovation in construction for millennia. From the ancient Neolithic practice of boosting mudbricks’ strength by adding local straw, to the Romans using volcanic dust as high-quality cement for concrete constructions like the Pantheon in Rome – a structure that still stands to this day, with its 43.3-m diameter non-reinforced concrete dome remaining the largest in the world. But testing one material at a time is no longer the only way.

Four photos of concrete buildings — **Shapely material** Concrete is ubiquitous in modern buildings, from generic office blocks (top left) to some of the world’s most creative architecture, such as (top right) the Auditorio de Tenerife in Santa Cruz (designed by Santiago Calatrava) and (bottom left) the Metropolitan Cathedral Nossa Senhora Aparecida in Brasilia (designed by Oscar Niemeyer). But it can be found in much older buildings as well. The largest unreinforced concrete dome in the world (bottom right) is on the Pantheon in Rome, built in 126 CE. This structure uses volcanic dust as its cement. (Courtesy: Shutterstock/Snide12; Shutterstock/Framalicious; Shutterstock/Marcelo Moryan; Shutterstock/Sean Pavone)

Taking a more modern, wide-ranging approach, a team of researchers led by Soroush Mahjoubi and Elsa Olivetti of Massachusetts Institute of Technology (MIT), recently mined the cement and concrete literature, and a database of over one million rock samples, looking for cement ingredient substitutes (Communications Materials 6 99). The study not only confirmed the potential of the well-known alternatives fly ash and metallurgic slags, but also various biomass ashes like the bamboo leaf ash Adanu investigated, as well as rice husk, sugarcane bagasse, wood, tree bark and palm oil fuel ashes.

The meta-review in addition identified various other waste materials with high potential. These include construction and demolition wastes (ceramics, bricks, concrete), waste glass, municipal solid waste incineration ashes, and mine tailings (iron ore, copper, zinc), as well as 25 igneous rock types that could significantly reduce cement’s carbon impact.

AI to the rescue

Although a number of these alternative concrete materials have been known for some time, they have struggled to make an impact, with very few being used to partially replace regular cement in ready-mix concretes. Getting construction companies or concrete contractors to give them a try is no simple task.

“Concrete contractors are used to using certain mixes for certain jobs at certain times of the year, so they can plan a site and project based on how those materials are going to behave,” says Toogood. “Newer mixes act slightly differently when fresh,” she adds, which makes life tricky for those running a construction site, where concrete that behaves in a predictable manner is critical so that things run smoothly and efficiently.

Two physicists – Raphael Scheps and Gideon Farrell – aim to build this trust in low-carbon alternatives through their UK construction technology company Converge. Starting out using sensors to measure the real-time performance of different mixes of concrete in situ, they have built one of the world’s largest datasets on the performance of concrete.

Two photos of sensors on building sites - a macro shot of a probe and a wider shot of a person wearing hi-vis and a hard hat crouched on a concrete surface — **Watch and learn** UK construction technology company Converge uses sensors to measure the real-time performance of different mixes of concrete *in situ*, then adds the data to its AI program to model untested concrete mixes. (Left) Signal Long Range is Converge’s LoRaWAN-enabled, fully embedded concrete-monitoring sensor for large-scale construction. (Right) Installation of Converge’s Helix system at HS2 Old Oak Common – a long-range, reusable concrete-monitoring solution. (Courtesy: Converge)

They can now apply an AI model underpinned by physics principles. The program simulates the physical and chemical interactions of different components to predict the performance of a vast number of concrete mixes in a wide range of situations to a high level of accuracy. And this is key, as it builds trust to experiment with lower-carbon mixes. “With projects in the UK and Australia, we’ve helped people tweak the mix that they’re using and achieve quite major carbon savings,” says Scheps. “Anywhere from 10% all the way up to 44%.”

Currently used to recommend existing cost-saving concrete recipes, Scheps sees Converge’s AI model becoming more sophisticated over time. “As it starts to uncover the real fundamental physics-based rules for what drives concrete chemistry, our model will make projections for entirely new materials,” he enthuses.

Also exploring the power of AI to optimize concrete production is US company Concrete.ai. Like Converge, Concrete.ai was born from the idea of applying physics principles to optimize traditional materials and industries; specifically, how AI can be used to reduce the carbon footprint of concrete. And also like Converge, the company’s technology rests on one of the world’s largest concrete databases, consisting of vast amounts of different recipes and materials, alongside their associated performances.

Trained on this dataset, Concrete.ai’s generative AI model creates millions of possible mix designs to identify the optimal concrete recipe for any particular application. “The main difference between a solution like Concrete.ai’s and general models like ChatGPT or Gemini is that our goal is really to create recipes that don’t exist yet,” explains chief technology officer and co-founder Mathieu Bauchy. “Popular large language models regurgitate what they have been trained on and tend to hallucinate, whereas our model discovers new recipes that have never been produced before without breaking the laws of physics or chemistry, and in a reliable way.”

Bauchy sees Concrete.ai’s role as a bridge between concrete producers keen to cut their costs and carbon footprint, and innovators like Adanu or the MIT group exploring new low-carbon concrete materials who are unable to demonstrate the performance of these materials in real-world scenarios and at scale.

Circular benefits

It is perhaps apt that the industry most in need of AI insights from the likes of Converge, Concrete.ai and their growing number of competitors is the AI industry itself. New data centres being used to train, deploy and deliver AI applications and services are the cause of a huge spike in the greenhouse gas emissions of tech giants such as Google, Meta, Microsoft and Amazon. And one of the biggest contributors to those emissions is the concrete from which these hyperscale facilities are built.

Aerial view of large industrial building complex next to a solar farm — **Feedback loop** The Google Hyperscale Data Center for AI and Sustainable Energy opened in Winschoten, Netherlands, in November 2025. The massive growth in AI is leading to many more of these huge structures, and though the electricity they run on is increasingly from renewable sources, the concrete from which they are built is decidedly less green. But AI is also potentially the best resource we have to reduce the carbon cost of concrete. (Courtesy: Shutterstock/Make more Aerials)

This is the reason Meta recently partnered with concrete maker Amrize to develop AI-optimized concrete. For Meta’s new 66,500 m² data centre in Rosemount, Minnesota, the partners applied Meta’s AI models and Amrize’s materials-engineering expertise to deliver concrete that met key criteria including high strength and low carbon content, as well as practical performance characteristics like decent cure speed and surface quality. The partners estimate that the custom mix will reduce the total carbon footprint of this concrete by 35%.

“There is an interesting synergy between concrete and AI,” says Bauchy. “AI can help design greener concrete, and on the other hand, concrete can be used to build more sustainable data centres to power AI.” With other tech giants exploring AI’s potential in reducing the carbon footprint of the concrete they use too, it may well be that the very places in which AI is developed become the testbeds for AI-derived sustainable green concrete solutions.

New journal aims to advance the interdisciplinary field of personalized health

Personalized health – the use of individualized measurements to address each patient’s specific needs – is a research field that’s evolving at pace. Bringing this level of personalization into the clinic is an interdisciplinary challenge, requiring the development of sensors that generate clinically meaningful data outside the hospital, new imaging modalities and analysis techniques, and computational tools that address the uncertainties of dealing with just one individual.

Much of the most impactful work in this field sits in the spaces between established disciplines. And for researchers looking to publish their findings or read about the latest breakthroughs, this work is often scattered across discipline-specific journals. A new open access journal from IOP Publishing – Medical Sensors & Imaging (MSI) – aims to remedy this shortfall, providing a dedicated home for authors working across sensing, imaging, modelling and data-driven healthcare.

**New launch** *Medical Sensors & Imaging* is fully open for submissions. (Courtesy: IOP Publishing)

“We want a journal where physicists, engineers, computer scientists, biomedical researchers and clinicians can publish and read work that advances personalized health, without confinement into traditional silos,” explains founding editor-in-chief Marco Palombo from Cardiff University. “MSI also aims to play an important role in strengthening interdisciplinary exchange.”

“The community needs a specialized forum that doesn’t just report on new materials or a clinical trial, but validates innovations that can specifically solve complex biomedical challenges,” adds deputy editor Xiliang Luo from Qingdao University of Science and Technology. “I think this journal is a perfect fit for that gap.”

Connecting communities

Published by IOP Publishing on behalf of the Institute of Physics and Engineering in Medicine (IPEM), MSI aims to dismantle the barriers between engineering innovation and clinical application by creating a community of experts that work together to translate innovative technology into clinical settings.

MSI sits within IPEM’s journal portfolio that includes Physics in Medicine & Biology, Physiological Measurement and Medical Engineering & Physics. Its aims and scope were designed to complement, rather than overlap with, these existing journals and provide a dedicated venue for translational work and practical applied research that may otherwise struggle to fit a traditional scope.

**Marco Palombo**: “We have been discussing green AI and green healthcare for at least 10 years. I think MSI can be one of the first journals to push this area forward.”

Being part of this established family of journals brings with it strong editorial standards, an established readership base and a commitment to scientific integrity. The journal also offers rapid, high-quality peer review, with feedback that’s constructive, rigorous and fair. MSI is fully open access, which maximizes the visibility, reach and impact of its published papers.

“For a new journal in a dynamic field, ensuring content is discoverable and barrier-free is essential for building an audience quickly and establishing credibility,” says Palombo. “We also wanted MSI to support global participation. Many excellent groups operate with limited budgets but make major scientific contributions. Open access reduces inequities in who can read and build on published work.”

“For the authors, we can provide a specialized platform for scientists whose work transcends traditional boundaries, offering visibility to a broad audience that’s eager for translational solutions,” says Luo. “And for the readers, I think we will be the go-to resource for academic researchers, industry R&D leaders, and healthcare innovators seeking the latest breakthroughs in personalized health monitoring and advanced diagnostics.”

Hot topics

Palombo contributed to the strategic development of the journal at an early stage, drawing upon his experience in healthcare and medical imaging research and engaging with the research community to identify the scientific niche that MSI could fill. Working with IOP Publishing, he helped shape the journal’s aims and scope and assembled a diverse, internationally recognized editorial board with knowledge aligned with the journal’s mission – including Lui, who brings specialist expertise in wearable technologies and biosensors.

**Xiliang Luo**: “We hope to establish a forum where advanced sensing technology and imaging techniques can enable the next generation of personalized and predictive health.”

The journal will publish high-quality research on novel biomedical sensing and imaging techniques, along with the algorithms, validation frameworks and translational studies that demonstrate their application in real-world medicine. MSI also provides a platform to showcase research on hot topics such as wearable and implantable sensors for continuous physiological monitoring, for example, or microneedle-based sensing technologies and breath analysis.

The development of flexible and biocompatible materials will be key for the growth of bio-integrated devices and biodegradable or transient electronics, as will anti-fouling strategies that enable use of sensors in complex biological environments. On the imaging side, the journal scope encompasses mainstay medical imaging techniques such as MRI, CT, ultrasound, PET and SPECT, as well as emerging multimodal and hybrid approaches, with a focus on technical innovation and translational relevance.

“Given my own background, I’m particularly keen to see strong submissions in the area of MRI, including advanced quantitative biomarkers and approaches that probe tissue microstructure,” notes Palombo. “I also see huge potential in connecting imaging to computational modelling – particularly digital twins – and in building imaging pipelines that enable personalized diagnosis and prognosis.”

“Other exciting areas include combining sensing and imaging technologies into one system, and closed-loop ‘sense then act’ systems, which sense something and can then release medicine to treat the disease,” says Luo.

The rise of AI

Artificial intelligence (AI) is becoming increasingly central to both sensing and imaging, and will likely play a major role in the evolution of personalized health, enabling a shift towards multimodal fusion of sensor streams, imaging and clinical data. AI could also facilitate the introduction of integrated sensor systems that collect data and interpret signals in real time, and digital twins that link patient-specific data with computational models to simulate disease progression or treatment response.

Palombo emphasizes the importance of trustworthy AI: methods that don’t just provide an output, but are explainable, robust and explicitly handle uncertainty. This is a direction seen in the general field of AI, but is especially important within healthcare. He also cites the increasing momentum around green healthcare and green AI, with personalized health technologies designed to reduce waste and minimize energy consumption, and clinical models developed with far greater computational efficiency.

“It would be fantastic to have an AI model running directly on the sensor, for example, and this ties in with the environmental impact of AI,” he explains. “If we keep AI small and manageable, then it pollutes less, is more affordable for everybody and can be deployed on small, lightweight devices.”

A community focal point

Looking ahead, Palombo hopes that MSI will becomes a leading platform for interdisciplinary innovation in personalized health, and the routine home for publishing major advances in sensing, imaging, modelling and trustworthy AI. “Over time, I’d like the journal to build depth in core areas, while also actively shaping emerging directions such as digital twins, uncertainty-aware and explainable AI, multimodal integration and technologies that are genuinely deployable in clinical workflows.”

“Currently, the fields of sensor engineering and clinical medicine often run on parallel tracks. My hope is that this journal will force these tracks to converge over time,” adds Luo. “I see the journal fostering a new language where chemists, physicists, engineers and doctors can understand each other by publishing papers in MSI.”

Medical Sensors & Imaging is fully open for submissions, with the first issue expected to publish in Q2/Q3 of this year. During the launch phase, IOPP is covering the article processing charge (APC) for all accepted papers, enabling early contributors to publish at no cost while helping the journal establish a strong foundation of high-quality inaugural content. Beyond this period, many authors will benefit from support through IOPP’s transformative agreements, while others may be eligible for APC waivers and discounts.

Olympian Eileen Gu rules the piste with physics and international relations

Here at Physics World we are always on the look out for physicists with extraordinary talents outside of science. In 2023, for example we were in awe of Harvard University’s Jenny Hoffman who ran across the US in 47 days, 12 hours and 35 minutes – shattering the previous record by one week.

Now, coverage of the Winter Olympics in Italy has revealed that the Chinese freestyle skier Eileen Gu had studied physics at Stanford University. The most decorated female Olympic freestyle skier in history, US-born Gu bagged two gold medals and a silver at the 2022 Beijing games and added three silvers at Milano Cortina.

Gu has subsequently switched majors to international relations at Stanford, but we can still celebrate her as an honorary physicist.

Physics-rich event

Indeed, freestyle skiing is quite possibly the most physics-rich of all Olympic events. Athletes must consider friction, gravity and the conservation of momentum and angular momentum to perfect their skiing.

Now, I’m not suggesting that studying free-body diagrams of freestyle manoeuvres is essential for Olympic success, but I live in hope that an understanding of classical mechanics can improve one’s skiing. (I’m not sure why I believe this, because a PhD and decades of writing about physics certainly hasn’t improved my skiing!).

As well as being lauded for her prowess on the snow, Gu has found herself at the centre of an international furore regarding her choice of competing for China rather than for the US. So, international relations combined with physics seems like a very good course of study!

Article has been updated to include Gu’s third silver medal at Milano Cortina.

Wobbling gyroscopes could harvest energy from ocean waves

A new way of extracting energy from ocean waves has been proposed by a researcher in Japan. The system couples a gyroscope to an electrical generator and could be fine tuned to extract energy from a wide range of wave conditions. A prototype of the design is currently being built for testing in a wave tank. If successful, the system could be used to generate electricity onboard ships.

Ocean waves contain huge amounts of energy and humans have tried to harness this energy for centuries. But, despite the development of myriad technologies and a number of trials, the widespread commercial conversion of wave energy remains an elusive goal. One important problem is that most generation schemes only work within a narrow range of wave conditions – and the ocean can be a very messy place.

Now, Takahito Iida at the University of Osaka has proposed a new energy-harvesting technology that uses gyroscopic flywheel system that can be tuned to absorb energy efficiently over a broad range of wave frequencies.

“Wave energy devices often struggle because ocean conditions are constantly changing,” says Iida. “However, a gyroscopic system can be controlled in a way that maintains high energy absorption, even as wave frequencies vary.”

Wobbling top

At the heart of the technology is gyroscopic precession, whereby a torque on a rotating object causes the object’s axis of rotation to trace out a circle. This is familiar to anyone who has played with a spinning top, which will wobble (precess) when perturbed.

Iida’s device is called a gyroscopic wave energy converter and comprises a spinning flywheel mounted on a floating platform (see figure). On calm seas, the gyroscope’s axis of rotation points in a fixed direction thanks to the conservation of angular momentum. However, waves will cause the platform to pitch from side-to-side, exerting torques on the gyroscope and causing it to precess. It is this precession that drives a generator to deliver electrical power.

To design the system, Iida used linear wave theory to model the coupled interactions between waves, the platform, the gyroscope and the generator. This allowed him to devise a scheme for tuning the gyroscope frequency and generator parameters so that an energy conversion efficiency of 50% is achieved for a variety of wave conditions.

The effect of the generator was modelled as a spring-damper. This is a system that responds to a torque by storing and then returning some energy to the gyroscope (the spring), and removing some energy by converting it to electricity (the damper). Iida discovered that a maximum conversion of 50% occurs when the spring coefficient of the generator is adjusted such that the gyroscope’s resonant frequency matches the resonant frequency of the floating platform.

Fundamental constraint

Iida explains that 50% is the maximum efficiency that can be achieved. “This efficiency limit is a fundamental constraint in wave energy theory. What is exciting is that we now know that it can be reached across broadband frequencies, not just at a single resonant condition.”

Turning water into watts

Iida tells Physics World that a small prototype (approximately 50 cm³ in size) is being built and will be tested in a 100 m-long tank.

The next step will be the development of a system with a generating capacity of about 5 kW. Iida says that the ultimate goal is a 300 kW generator.

Iida also explains that the gyroscopic wave energy converter is designed to operate untethered to the seabed. As a result he says the system would be ideal for use as an auxiliary power system for a ship. “The target output of 300 kW is based on the assumed auxiliary power demand of a typical commercial vessel,” says Iida.

The research is described in the Journal of Fluid Mechanics.

World’s smallest QR code paves the way for ultralong-life data storage

A team headed up at TU Wien in Austria has set the Guinness World Record for creating the world’s smallest QR code. Working with industry partner Cerabyte, the researchers produced a stable and repeatedly readable QR code with an area of just 1.977 µm². When read out – using an electron microscope, as its structure is too fine to be seen with a standard optical microscope – the QR code links to a scientific webpage at TU Wien.

But this wasn’t just a ploy to get into the record books, the QR code was created as part of the team’s research into ceramic data storage materials. Unlike conventional magnetic or electronic data storage media, which degrade within decades, ceramic-based storage is designed to withstand extreme temperatures, radiation, chemical corrosion and mechanical damage.

As such, information stored in ceramic materials could endure for centuries, or even millennia. And in contrast to today’s data centres, ceramics preserve stored information without any energy input and without requiring cooling.

Electron microscope image of QR code — **Invisible code** The world’s smallest QR code can only be read out using an electron microscope. (Courtesy: TU Wien)

To create these ultralong-life data storage systems, the researchers use focused ion beams to mill the QR code into a thin film of chromium nitride, a durable ceramic often used to coat high-performance cutting tools. As each individual pixel is just 49 nm in size, roughly 10 times smaller than the wavelength of visible light, the code cannot be imaged using visible light. But when examined with an electron microscope, the QR code could indeed be read out reliably.

After the writing process, the entire stack of ceramic films is subjected to extreme conditions, such as high temperatures, corrosive environments and mechanical stress, to evaluate the material’s long-term durability and readout stability.

Pushing storage to its limits

Creating a “tiny QR code” was not the team’s initial goal, but emerged as a natural outcome of pushing this storage technology to its limits, says Paul Mayrhofer from TU Wien’s Institute of Materials Science and Technology.

“During a discussion with one of my PhD students, Erwin Peck, we realised that the writing procedure we had developed already produced features smaller than what had previously been reported for QR codes,” he explains. “This sparked the idea: if we can reliably write structures at that scale, why not intentionally create the smallest QR code possible?”

To claim its place in the record books, the QR code was successfully milled and read out in the presence of witnesses and its size independently verified using calibrated scanning electron microscopy at the University of Vienna. It is now officially recognized by Guinness as the world’s smallest QR code, and is roughly one third the size of the previous record holder.

Mayrhofer points out that the storage capacity of the ceramic data storage technology far surpasses that of a single QR code. “Based on current estimates, a cartridge of 100 x 100 x 20 mm with ceramic storage medium could potentially store on the order of 290 terabytes of raw data,” he says.

As well as offering this impressive raw capacity, for practical applications it’s also crucial that the ceramic storage offers high writing speed, which determines how efficiently large datasets can be stored, and low energy consumption during writing, which will influence the potential for scalability and sustainability. The researchers are currently working to optimize both of these parameters.

“Humanity has preserved information for millennia when carved in stone, yet much of today’s digital information risks being lost within decades,” project leader Alexander Kirnbauer tells Physics World. “Our long-term goal is to create an ultrastable, sustainable data storage technology capable of preserving information for extremely long times – potentially thousands to millions of years. In essence, we want to develop a form of storage that ensures the knowledge of our digital age does not disappear over time.”

Quantum Systems Accelerator focuses on technologies for computing

Developing practical technologies for quantum information systems requires the cooperation of academic researchers, national laboratories and industry. That is the mission of the Quantum Systems Accelerator (QSA), which is based at the Lawrence Berkeley National Laboratory in the US.

The QSA’s director Bert de Jong is my guest in this episode of the Physics World Weekly podcast. His academic research focuses on computational chemistry and he explains how this led him to realise that quantum phenomena can be used to develop technologies for solving scientific problems.

In our conversation, de Jong explains why the QSA is developing a range of qubit platforms − including neutral atoms, trapped ions, and superconducting qubits – rather than focusing on a single architecture. He champions the co-development of quantum hardware and software to ensure that quantum computing is effective at solving a wide range of problems from particle physics to chemistry.

We also chat about the QSA’s strong links to industry and de Jong reveals his wish list of scientific problems that he would solve if he had access today to a powerful quantum computer.

This podcast is supported by Oxford Ionics.

Metallic material breaks 100-year thermal conductivity record

A newly identified metallic material that conducts heat nearly three times better than copper could redefine thermal management in electronics. The material, which is known as theta-phase tantalum nitride (θ-TaN), has a thermal conductivity comparable to low-grade diamond, and its discoverers at the University of California Los Angeles (UCLA), US say it breaks a record on heat transport in metals that had held for more than 100 years.

Semiconductors and insulators mainly carry heat via vibrations, or phonons, in their crystalline lattices. A notable example is boron arsenide, a semiconductor that the UCLA researchers previously identified as also having a high thermal conductivity. Conventional metals, in contrast, mainly transport heat via the flow of electrons, which are strongly scattered by lattice vibrations.

Heat transport in θ-TaN combines aspects of both mechanisms. Although the material retains a metal-like electronic structure, study leader Yongjie Hu explains that its heat transport is phonon-dominated. Hu and his UCLA colleagues attribute this behaviour to the material’s unusual crystal structure, which features tantalum atoms interspersed with nitrogen atoms in a hexagonal pattern. Such an arrangement suppresses both electron–phonon and phonon–phonon scattering, they say.

Century-old upper limit for metallic heat transport

Materials with high thermal conductivity are vital in electronic devices because they remove excess heat that would otherwise impair the devices’ performance. Among metals, copper has long been the material of choice for thermal management thanks to its relative abundance and its thermal conductivity of around 400 Wm⁻¹ K⁻¹, which is higher than any other pure metal apart from silver.

Recent theoretical studies, however, had suggested that some metallic-like materials could break this record. θ-TaN, a metastable transition metal nitride, was among the most promising contenders, but it proved hard to study because high-quality samples were previously unavailable.

Highest thermal conductivity reported for a metallic material to date

Hu and colleagues overcame this problem using a flux-assisted metathesis reaction. This technique removed the need for the high pressures and temperatures required to make pure samples of the material using conventional techniques.

The team’s high-resolution structural measurements revealed that the as-synthesized θ-TaN crystals had smooth, clean surfaces and ranged in size from 10 to 100 μm. The researchers also used a variety of techniques, including electron diffraction, Raman spectroscopy, single-crystal X-ray diffraction, high-resolution transmission electron microscopy and electron energy loss spectroscopy to confirm that the samples contained single crystals.

The researchers then turned their attention to measuring the thermal conductivity of the θ-TaN crystals. They did this using an ultrafast optical pump-probe technique based on time-domain thermoreflectance, a standard approach that had already been used to measure the thermal conductivity of high-thermal-conductivity materials such as diamond, boron phosphide, boron nitride and metals.

Hu and colleagues made their measurements at temperatures between 150 and 600 K. At room temperature, the thermal conductivity of the θ-TaN crystals was 1100 Wm⁻¹ K⁻¹. “This represents the highest value reported for any metallic materials to date,” Hu says.

The researchers also found that the thermal conductivity remained uniformly high across an entire crystal. H says this reflects the samples’ high crystallinity, and it also confirms that the measured ultrahigh thermal conductivity originates from intrinsic lattice behaviour, in agreement with first-principles predictions.

Another interesting finding is that while θ-TaN has a metallic electronic structure, its thermal conductivity decreased with increasing temperature. This behaviour contrasts with the weak temperature dependence typically observed in conventional metals, in which heat transport is dominated by electrons and is limited by electron-phonon interactions.

Applications in technologies limited by heat

As well as cooling microelectronics, the researchers say the discovery could have applications in other technologies that are increasingly limited by heat. These include AI data centres, aerospace systems and emerging quantum platforms.

The UCLA team, which reports its work in Science, now plans to explore scalable ways of integrating θ-TaN into device-relevant platforms, including thin films and interfaces for microelectronics. They also aim to identify other candidate materials with lattice and electronic dynamics that could allow for similarly efficient heat transport.

Nickel-enhanced biomaterial becomes stronger when wet

Synthetic materials such as plastics are designed to be durable and water resistant. But the processing required to achieve these properties results in a lack of biodegradability, leading to an accumulation of plastic pollution that affects both the environment and human health. Researchers at the Institute for Bioengineering of Catalonia (IBEC) are developing a possible replacement for plastics: a novel biomaterial based on chitin, the second most abundant natural polymer on Earth.

“Every year, nature produces on the order of 10¹¹ tonnes of chitin, roughly equivalent to more than three centuries of today’s global plastic production,” says study leader Javier G Fernández. “Chitin and [its derivative] chitosan are the ultimate natural engineering polymers. In nature, variations of this material produce stiff insect wings enabling flight, elastic joints enabling extraordinary jumping in grasshoppers, and armour-like protective exoskeletons in lobsters or clams.”

But while biomaterials provide a more environmentally friendly alternative to conventional plastics, most biological materials weaken when exposed to water. In this latest work, Fernández and first author Akshayakumar Kompa took inspiration from nature and developed a new biomaterial that increases its strength when in contact with water, while maintaining its natural biodegradability.

Metal matters

In the exoskeletons of insects and crustaceans, chitin it is secreted in a gel-like form into water and then transitions into a hard structure. Following a chance observation that removing zinc from a sandworm’s fangs caused them to soften in water, Kompa and Fernández investigated whether adding a different transition metal, nickel, to chitosan could have the opposite effect.

By mixing nickel chloride solution (at concentrations from 0.6 to 1.4 M) with dispersions of chitosan extracted from discarded shrimp shells, the researchers entrapped varying amounts of nickel within the chitosan structure. Fourier-transform infrared spectra of resulting chitosan films revealed the presence of nickel ions, which form weak hydrogen bonds with water molecules and increase the biomaterial’s capacity to bond with water.

“In our films, water molecules form reversible bridges between polymer chains through weak interactions that can rapidly break and reform under load,” Fernández explains. “That fast reconfiguration is what gives the material high strength and toughness under wet conditions: essentially a built-in, stress-activated ‘self-rearrangement’ mechanism. Nickel ions act as stabilizing anchors for these water-mediated bridges, enabling more and longer-range connections and making inter-chain connectivity more robust”.

The nickel-doped chitosan samples had tensile strengths of between 30 and 40 MPa, similar to that of standard plastics. Adding low concentrations of nickel did not significantly impact the mechanical properties of the films. Concentrations of 1 M or more, however, preserved the material’s strength while increasing its toughness (the ability to stretch before breaking) – a key goal in the field of structural materials and a feature unique to biological composites.

**Increased strength** Testing a nickel-doped chitosan film using a 20 kg dumbbell. (Courtesy: Institute for Bioengineering of Catalonia)

Upon immersion in water, the nickel-doped films exhibited greater tensile strength, increasing from 36.12±2.21 MPa when dry to 53.01±1.68 MPa, moving into the range of higher-performance engineering plastics. In particular, samples created from an optimal 0.8 M nickel concentration almost doubled in strength when wet (and were used for the remainder of the team’s experiments).

Scaling production

The manufacturing process involves an initial immersion in water, followed by drying for 24 h and then re-wetting. During the first immersion, any nickel ions that are not incorporated into the material’s functional bridging network are released into the water, ensuring that nickel is present only where it is structurally useful.

The researchers developed a zero-waste production cycle in which this water is used as a primary component for fabricating the next object. “The expelled nickel is recovered and used to make the next batch of material, so the process operates at essentially 100% nickel utilization across batches,” says Fernández.

Nickel-doped chitosan structures — **Zero waste production** The team created structures including a 3 m² nickel-doped chitosan film and a cup that can retain water as effectively as common plastics. (Courtesy: Institute for Bioengineering of Catalonia)

They used this process to produce various nickel-doped chitosan objects, including watertight containers and a 1 m² film that could support a 20 kg weight after 24 h of water immersion. They also created a 244 x 122 cm film with similar mechanical behaviour to the smaller samples, demonstrating the potential for rapid scaling to ecologically relevant scales. A standard half-life test revealed that after approximately four months buried in garden soil, half of the material had biodegraded.

The researchers suggest that the biomaterial’s first real-world use may be in sectors such as agriculture and fishing that require strong, water-compatible and ultimately biodegradable materials, likely for packaging, coatings and other water-exposed applications. Both nickel and chitosan are already employed within biomedicine, making medicine another possible target, although any new medical product will require additional regulatory and performance validation.

The team is currently setting up a 1000 m² lab facility in Barcelona, scheduled to open in 2028, for academia–industry collaborations in sustainable bioengineering research. Fernández suggests that we are moving towards a “biomaterial age”, defined by the ability to “control, integrate, and broadly use biomaterials and biological principles within engineering applications”.

“Over the last 20 years, working on bioinspired manufacturing, we have been able to produce the largest bioprinted objects in the world, demonstrated pathways for resource-secure and sustainable production in urban environments, and even explored how these approaches can support interplanetary colonization,” he tells Physics World. “Now we are achieving material properties that were considered out of reach by designing the material to work with its environment, rather than isolating itself from it.”

The researchers report their findings in Nature Communications.

2D materials help spacecraft electronics resist radiation damage

Electronics made from certain atomically thin materials can survive harsh radiation environments up to 100 times longer than traditional silicon-based devices. This finding, which comes from researchers at Fudan University in Shanghai, China, could bring significant benefits for satellites and other spacecraft, which are prone to damage from intense cosmic radiation.

Cosmic radiation consists of a mixture of heavy ions and cosmic rays, which are high-energy protons, electrons and atomic nuclei. The Earth’s magnetic field protects us from 99.9% of this ionizing radiation, and our atmosphere significantly attenuates the rest. Space-based electronics, however, have no such protection, and this radiation can damage or even destroy them.

Adding radiation shielding to spacecraft mitigates these harmful effects, but the extra weight and power consumption increases the spacecraft’s costs. “This conflicts with the requirements of future spacecraft, which call for lightweight and cost-effective architectures,” says team leader Peng Zhou, a physicist in Fudan’s College of Integrated Circuits and Micro-Nano Electronics. “Implementing radiation tolerant electronic circuits is therefore an important challenge and if we can find materials that are intrinsically robust to this radiation, we could incorporate these directly into the design of onboard electronic circuits.”

Promising transition-metal dichalcogenides

Previous research had suggested that 2D materials might fit the bill, with transistors based on transition-metal dichalcogenides appearing particularly promising. Within this family of materials, 2D molybdenum disulphide (MoS₂) proved especially robust to irradiation-induced defects, and Zhou points out that its electrical, mechanical and thermal properties are also highly attractive for space applications.

The studies that revealed these advantages were, however, largely limited to simulations and ground-based experiments. This meant they were unable to fully replicate the complex and dynamic radiation fields such circuits would encounter under real space conditions.

Better than NMOS transistors

In their work, Zhou and colleagues set out to fill this gap. After growing monolayer 2D MoS₂ using chemical vapour deposition, they used this material to fabricate field-effect transistors. They then exposed these transistors to 10 Mrad of gamma-ray irradiation and looked for changes to their structure using several techniques, including cross-sectional transmission electron microscopy (TEM) imaging and corresponding energy-dispersive spectroscopy (EDS) mapping.

These measurements indicated that the 2D MoS₂ in the transistors was about 0.7 nm thick (typical for a monolayer structure) and showed no obvious signs of defects or damage. Subsequent Raman characterization on five sites within the MoS₂film confirmed the devices’ structural integrity.

The researchers then turned their attention to the transistors’ electrical properties. They found that even after irradiation, the transistors’ on-off ratios remained ultra-high, at about 10⁸. They note that this is considerably better than a similarly-sized Si N-channel metal–oxide–semiconductor (NMOS) transistors fabricated through a CMOS process, for which the on-off ratio decreased by a factor of more than 4000 after the same 10 Mrad irradiation.

The team also found that MoS₂ system consumes only about 49.9 mW per channel, making its power requirement at least five times lower than the NMOS one. This is important owing to the strict energy limitations and stringent power budgets of spacecraft, Zhou says.

Surviving the space environment

In their final experiment, the researchers tested their MoS₂ structures on a spacecraft orbiting at an altitude of 517 km, similar to the low-Earth orbit of many communication satellites. These tests showed that the bit-error rate in data transmitted from the structures remained below 10^-8 even after nine months of operation, which Zhou says indicates significant radiation and long-term stability. Indeed, based on test data, electronic devices made from these 2D materials could operate for 271 years in geosynchronous orbit – 100 times longer than conventional silicon electronics.

“The discovery of intrinsic radiation tolerance in atomically thin 2D materials, and the successful on-orbit validation of the atomic-layer semiconductor-based spaceborne radio-frequency communication system have opened a uniquely promising pathway for space electronics leveraging 2D materials,” Zhou says. “And their exceptionally long operational lifetimes and ultra-low power consumption establishes the unique competitiveness of 2D electronic systems in frontier space missions, such as deep-space exploration, high-Earth-orbit satellites and even interplanetary communications.”

The researchers are now working to optimize these structures by employing advanced fabrication processes and circuit designs. Their goal is to improve certain key performance parameters of spaceborne radio-frequency chips employed in inter-satellite and satellite-to-ground communications. “We also plan to develop an atomic-layer semiconductor-based radiation-tolerant computing platform, providing core technological support for future orbital data centres, highly autonomous satellites and deep-space probes,” Zhou tells Physics World.

The researchers describe their work in Nature.

Rethinking how quantum phases change

In this work, the researchers theoretically explore how quantum materials can transition continuously from one ordered state to another, for example, from a magnetic phase to a phase with crystalline or orientational order. Traditionally, such order‑to‑order transitions were thought to require fractionalisation, where particles effectively split into exotic components. Here, the team identifies a new route that avoids this complexity entirely.

Their mechanism relies on two renormalisation‑group fixed points in the system colliding and annihilating, which reshapes the flow of the system and removes the usual disordered phase. A separate critical fixed point, unaffected by this collision, then becomes the new quantum critical point linking the two ordered phases. This allows for a continuous, seamless transition without invoking fractionalised quasiparticles.

The authors show that this behaviour could occur in several real or realistic systems, including rare‑earth pyrochlore iridates, kagome quantum magnets, quantum impurity models and even certain versions of quantum chromodynamics. A striking prediction of the mechanism is a strong asymmetry in energy scales on the two sides of the transition, such as a much lower critical temperature and a smaller order parameter where the order emerges from fixed‑point annihilation.

This work reveals a previously unrecognised kind of quantum phase transition, expands the landscape beyond the usual Landau-Ginzburg-Wilson framework, which is the standard theory for phase transitions, and offers new ways to understand and test the behaviour of complex quantum systems.

Read the full article

Continuous order-to-order quantum phase transitions from fixed-point annihilation

David J Moser and Lukas Janssen 2025 Rep. Prog. Phys. 88 098001

Do you want to learn more about this topic?

Dynamical quantum phase transitions: a review by Markus Heyl (2018)