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Home » Page 795

Massachusetts carbon tax ‘would save 340 lives’

A carbon tax on fuel used in transport, buildings and industry in Massachusetts, US, would save 340 lives over 23 years from reduced air pollution, according to an analysis by researchers in the US.

The tax analysed by the researchers, which is based on several proposals in the Massachusetts legislature, would have dual climate and health benefits, cutting carbon emissions by 33 million metric tons while simultaneously curbing air pollutants.

“Climate policies, even at the state or local level, can have substantial, basically immediate, and local benefits to health,” says Jonathan Buonocore at the Harvard T.H. Chan School of Public Health, US. “By improving air quality, these policies can especially protect children, the elderly, and others that are more vulnerable to air pollution.”

Many studies have investigated the health impacts of large-scale US climate policies. But since the US withdrawal from the Paris Agreement, it is state and local governments that have been most active in curbing greenhouse-gas emissions, according to Buonocore and colleagues. For this reason, they say, analysis of climate-policy impacts should also focus on the state and local level.

“Policy makers [need] to understand the full impact of their decisions – not only how they can reduce emissions, but also how they can usher in immediate health benefits to residents across a state or region,” says Buonocore. “It also becomes more important for residents to understand how their health is affected by bills that pass through their state houses and town halls.”

Recently, the Massachusetts legislature has considered the imposition of a carbon fee-and-rebate bill, which would use a fee on carbon emissions either to reduce people’s taxes elsewhere, or to support energy-efficiency and renewable-energy programmes.

Buonocore and colleagues modelled how such a bill would affect carbon emissions and the consumption of fossil fuels for 2017–2040, and how these changes would affect the prevalence of the air pollutants sulphur dioxide, nitrogen oxides, fine particulate matter and volatile organic compounds. In the final step, the researchers estimated the resultant health benefits, based on previous work.

“Air pollution causes harm by increasing the risk of many health conditions including respiratory and cardiovascular disease, and it also increases the risk of premature death,” Buonocore explains. “Decreasing air pollution reduces people’s risk of dying from these diseases. When the benefits of decreased air pollution and reduced risk of dying is spread across the population, it ends up working out to being 340 lives saved from the policy.”

These lives saved had a monetary value of $2.9 bn (£2.3 bn). This is potentially higher than the monetary value of climate benefits at $2.0 bn (£1.6 bn), although the researchers point out that the health-value estimate rests on uncertain factors, such as the amount of methane that leaks from the natural-gas supply chain.

Now the researchers want to study in greater detail how natural-gas leakage affects the policy’s health benefits. “We would like to work on better assessing the impacts of natural gas, so that impacts of extraction, transmission, distribution, and these other ‘upstream’ impacts can be included in assessments of health benefits of climate policies,” Buonocore says.

The team reported the findings in Environmental Research Letters (ERL).

Levelling the physics field

We can all surely agree that everyone who wants a career in physics – men and women alike – should be given the opportunity to do so. Unfortunately, this is not the case. The underrepresentation of women in science, technology, engineering and mathematics (STEM) subjects, and especially in physics, is well documented, despite there being plenty of evidence that the presence of women in a team enhances group collaboration and performance (Interdisciplinary Science Reviews 36 2). Indeed, Aarhus University science historian Mathias Wullum Nielsen, and University of California, Merced sociologist Sharla Alegri, together with colleagues at a workshop held at Stanford University in February 2016, found that having more women in science leads to an “innovation dividend”. Their research showed that gender diversity leads to smarter and “more creative” teams, all of which ultimately has a positive impact on scientific discovery itself (PNAS 114 1740).

Even more recently, a report published in January 2018 by management consulting firm McKinsey & Company – entitled Delivering through Diversity – re-examined the link between diversity (both gender and racial) and a company’s company financial outperformance. Having analysed global datasets of more than 1000 firms in 12 countries, they found there are clearly more beneficial financial results for companies with more diversity in top management and on the board. Correlation does not equal causation, but the study concludes that “more diverse companies…are better able to win top talent, improve their customer orientation, employee satisfaction, and decision-making and all that leads to a virtuous cycle of increasing returns”.

So, there is growing evidence that diverse teams are more productive and inspire more creativity, which , in turn, is likely to result in tangible benefits to the physics and wider scientific community. Yet, a recent Royal Society Career Pathway Tracker report – which followed the careers of those who had been awarded a University Research Fellowship or Dorothy Hodgkin Fellowship from the society – found that 73% of male research fellows had become professors, as compared to 58% of female fellows. The report also found that men took a shorter time to achieve a chair or a similarly senior position, obtaining it in 4.6 years on average, compared to 5.8 years for women. All this suggests that we need to do more to get more women into STEM subjects, and that we have a way to go to ensure that we keep them here.

At the Institute of Physics (IOP), we have been working on these issues for more than a decade, embarking on an ambitious programme to improve uptake of A-level physics among girls in schools. Through our Improving Gender Balance project, we trialled different school interventions – separately and combined – to help boost the confidence and resilience of girls, to improve their experience in the physics classroom, and address the impact of unconscious bias and gender stereotyping.

We found that a combined approach that includes addressing confidence and resilience, improving experiences, and dealing with unconscious bias, radically affected the number of girls taking AS-level physics in the participating schools, with the number more than trebling over two years. With research from the Institution of Engineering and Technology (IET) showing that boys are three times more likely than girls to be given a STEM toy for Christmas, it is clear that we need to address gender stereotyping at all ages, so that boys and girls have parity in career choices.

Alongside our Improving Gender Balance work is Project Juno – the IOP’s initiative to recognize and reward good practice in addressing the under-representation of women at all levels in physics, be it at university departments or research institutes. Launched in 2007, the Juno award is based on six principles that organizations work towards addressing, to achieve their Juno Practitioner or Juno Champion status. Applications are “peer reviewed” by a panel of physicists, and we conduct site visits to provide supportive and constructive feedback on progress.

But Juno is more than a project about fixing only the gender imbalance. It is based on openness, transparency and improving the working environment for all, and the project aims to promote the development of our next generation of physics leaders. Some of the Juno work in universities has been transformational, opening up recruitment, promotions and leadership selection, ensuring that everyone in physics has the opportunity to progress. A head of a physics department in a university once said that taking part in Juno “gives a message of equality, that women can do it based on capability, that promotion is open to any gender”.

Over the course of a PhD, women report feeling more isolated and having less contact with their supervisors

Research done by the IOP as well as other institutions has also found that over the course of a PhD (and any subsequent postdoctoral contracts), women’s aspirations to remain in scientific research decline, as they report less satisfaction with their doctorate, feeling more isolated and they have less contact with their supervisors or principal investigators. To help with this, the IOP runs career workshops for physics students that promote leadership development and highlight career pathways in and out of academia. We also provide a Carers’ Fund – a grant of up to £250 – that any members of the IOP who wish to attend an event or conference can apply to.

Others across the science community are also doing their bit. We know that returning from a career break can be daunting, and the IOP works closely with the Daphne Jackson Trust – a charity dedicated to helping STEM professionals who have taken a career break of two years or more and want to return to research. Its fellowship scheme is open to both men and women who have taken a career break for a number of reasons, including raising a child, looking after an elderly parent or health issues. The Women Into Science and Engineering (WISE) campaign encourages companies to engage with its Ten Steps framework that ensures women in STEM have the same career progression opportunities as men. AdvanceHE, a higher-education charity in the UK, runs the Aurora leadership initiative for women in higher education, and many physicists have benefited from taking part in this year-long programme.

These and many other initiatives will support and encourage women to pursue lifelong physics and STEM careers. This will, in turn, hopefully ensure that a future in science is inviting, open and inclusive to everyone, which will ultimately benefit the whole of physics.

Deep learning improves optical storage

A new ultrahigh-density optical storage technology that can store up to nine bits of information per diffraction-limited area that works thanks to a deep learning approach has been put forward by researchers in Toulouse in France. The technology overcomes the physical constraints of compact disks (CDs), DVDs and Blu-ray disks, which can only store one bit per diffraction-limited area. It is based on silicon and could thus be produced on a large scale using mass-market-ready complementary metal-oxide-semiconductor (CMOS) technology.

The storage capacity of magnetic hard disk drives is reaching its limits and it will soon no longer be able to meet the demand of the increasing volumes of data being generated each day. Optical data storage is a promising alternative because it can store much higher volumes (over 10 terabytes) and for longer periods (hundreds of years compared to just five to ten years for hard disk drives).

The storage capacity of current optical data storage technologies such as the CD, DVD and Blu-ray disk is, however, restricted by the diffraction limit of the laser used to write to the disk. This means that they can store just a single bit per diffraction-limited area (“0” or “1”) to reach 200 gigabytes per disk at best. Ways to increase optical information density – such as using polarization-sensitive digits, near-field optical recording, two-photon point excitation or holographic memory – do exist but no commercial product based on these technologies is yet available.

Encoding information in subwavelength silicon nanostructures

A team of researchers from CEMES and LAAS-CNRS, both in Toulouse, has now put forward a new way to encode multiple bits of digital information in subwavelength silicon nanostructures. Thanks to the high refractive index of silicon, these nanostructures scatter light with little loss. The researchers retrieve the information stored in these particles using a machine-learning-based approach in which an artificial neuronal network (ANN) analyses their scattering spectra.

ANNs are computational schemes that can be trained to efficiently solve problems that are challenging for a classical computer, explains study lead author Peter Wiecha of CEMES. “Although ANNs have many applications – including, for example in modern smartphones or for interpreting medical images – research in nano-optics has only begun to harness the tremendous potential of machine learning.”

The researchers studied a 300 x 300 nm2 square of nanoparticles subdivided into smaller blocks measuring 120 x 120 nm2 that encode the information bits. “Our approach is simple,” explains Wiecha. “We made a small checker-board-like nanostructure surrounded by an asymmetric border. If a block in this nano-array is occupied by a silicon nanoparticle, then the according bit is ‘1’. If it is empty, the encoded bit is ‘0’.”

A four-bit array (four blocks) can be used to encode four bits (a “nibble” or half-byte) of information.

Reading out the encoded data

Once they had defined the nano-geometry for encoding multiple bits in the diffraction-limited area in their blocks, the researchers then needed to read out the encoded data using a simple optical set up that is robust to unavoidable structural defects in the material and instrumental noise. They did this by collecting the optical spectra of their arrays with a dark-field microscope and postprocessing these spectra with an ANN. “The asymmetric border around the checker-board nanostructure renders each pattern unique and gives it an exclusive optical scattering response when probed with polarized light in our microscope,” explains Wiecha.

“Our idea is to train a deep ANN on a large number of nanostructures and their experimentally measured scattering spectra,” he tells Physics World. “We found that it is indeed possible to read out, quasi-error-free, up to nine bits per diffraction-limited area using such a deep learning approach. And that is not all: once trained, the ANN is extremely fast.”

The researchers say that they do not even need to analyse the full spectra from the nanostructures but can accurately retrieve the information by probing just three to five specific wavelengths. “For example, the red, green and blue (RGB) spectral windows from microscopy images is all we require,” says Wiecha. “This type of analysis might be done using hand-held smartphone-microscopy (a field that has seen some important advances recently), making the technique easily accessible to all.”

Compatible with CMOS

The new work could help open the way towards high-density optical information storage using planar silicon nanostructures, says Wiecha. “Importantly, the technique we have developed is also compatible with mass-production-ready CMOS technology.

“We are now looking at how small we can make our nanostructures without introducing significant error rates, and trying to find out if we can increase the number of bits per diffraction-limited area,” he reveals.

The present research is detailed in Nature Nanotechnology.

Double-slit interference boosts resonant inelastic X-ray scattering

A new twist on the classic Young’s double-slit experiment has been performed by an international team of physicists, who have measured interference in resonant inelastic X-ray scattering (RIXS). The experiment provides important insights into the symmetry and character of electronic excitations in solids and could provide scientists with a useful tool for probing complex materials.

In his original experiment done in 1801, Thomas Young placed two slits a variable distance apart, illuminated them with light, and projected the light emerging from the slits onto a screen. When the slits were far apart, he simply observed two patches of light. When he brought the slits closer together, however, he noticed a series of bright and dark fringes on the screen. He concluded these were caused by constructive and destructive interference between the light from each slit. This provided crucial evidence that light comprised waves, and later experiments using beams of particles such as electrons confirmed the wave-particle duality of quantum mechanics.

The traditional double-slit experiment is an “elastic” process, which means that no energy is exchanged between the light and the slits. This is unlike RIXS, which is a relatively new and rapidly developing “inelastic” technique that analyses the energy lost by X-ray photons when they scatter from a material. Energy is lost to electronic excitations and therefore a RIXS energy spectrum provides valuable information about the intrinsic properties of materials.

Dimers as double slits

But that is not the end of the story because the interference of scattered X-rays should carry additional information about the target material. In 1994, Faris Gel’mukhanov and Hans Ågren predicted that it should be possible to disentangle the symmetry of electronic excitations using the interference patterns observable in RIXS from gaseous molecular dimers. In 1995, Yanjun Ma and Martin Blume beautifully rephrased this in terms of the double-slit experiment. The two atoms of a dimer would act as a double slit and interference occurs if the excitation is delocalized over both atoms. Until now, however, this effect has not been observed in the lab because the random orientation of gas molecules tends to blur the interference pattern.

“RIXS is well understood, but a clear realization of a spatial double-slit interference was still missing,” explains Markus Grüninger of the University of Cologne, who led the latest research.

Grüninger and colleagues eliminated the problem of random orientation by growing a crystal of an iridium oxide-based material that contains dimers of iridium atoms with a well-defined orientation. The researchers irradiated the crystal with X-rays from the European Synchrotron Radiation Facility in Grenoble. Choosing the appropriate X-ray energy, confines scattering to the iridium atoms and creates excitations within individual dimers. By recording the scattered X-rays, the researchers reconstructed the interference pattern for each excitation.

Out of phase

Young’s experiment gives an intensity maximum at the midpoint on the screen between the two slits as the two path lengths are equal and add in phase. For atoms, the situation is more complex. The phase of an emitted photon depends on the phase of the wavefunction at the point of emission. Therefore, emission from an antisymmetric dimer state occurs in antiphase from the two atoms and produces an intensity minimum at the midpoint.

“In terms of symmetry, all dimer states are either even or odd,” explains Grüninger, “This technique determines the symmetry of the excitations which helps us to characterize them. For the iridium dimers we learned that the states are spin-orbit entangled, in contrast to previous assumptions for dimers. This is of general interest for related iridate compounds that are studied as promising candidates for new quantum states of matter: quantum spin liquids with fractional excitations.” The double slit serves as the most fundamental model system, the researchers now hope to study more complex, multi-atomic states using the same technique.

Stephen Kevan of Lawrence Berkeley National Laboratory in California, who was not involved, says that, initially, many researchers believed that inelastic scattering would not conserve momentum at all. Numerous experiments have refuted this, so he says that “in one sense this result, which demonstrates transverse coherence – at least between two atoms – shouldn’t be that surprising.” Nevertheless, he describes the finding as “important” as “some will say ‘I thought it was obvious’ and others will say ‘My goodness! I thought it was the other way around.'”

The research is described in Science Advances.

Implantable device shows potential as epilepsy treatment

Epilepsy is one of the most common neurological conditions, affecting millions of individuals of all ages, and characterized by debilitating seizures. Current antiepileptic drugs are ineffective in one third of all patients, who often experience an increased frequency of seizures that may become associated with cognitive decline and psychiatric disorders.

Motivated by the need for an effective and well-tolerated epilepsy therapy, a research team from the University of Ferrara and Gloriana Therapeutics has developed an implantable device that delivers high and consistent levels of therapeutic protein directly to the brain. The slender device can be implanted into diseased areas of the brain where it secretes protein through its permeable distal tip.

Giovanna Paolone and colleagues have investigated the use of this Gloriana targeted cellular delivery system to deliver glial cell line-derived neurotrophic factor (GDNF) — a protein that may help suppress epileptic activity — directly to the hippocampus of epileptic rats (J. Neuroscience 10.1523/JNEUROSCI.0435-18.2018).

When implanted into a rat’s hippocampus, the device continued to secrete GDNF and produced high levels in hippocampal tissue. The treatment rapidly and progressively reduced seizures — by 75% within two weeks and ultimately leading to a 93% reduction at three months. This effect persisted even after the researchers removed the device, suggesting potential disease-modifying benefits.

In addition to seizure reduction, the implant improved the rats’ anxiety-like symptoms and their performance in an object recognition task, indicating an improvement in cognition. Immunohistochemical analyses revealed that the GDNF treatment also corrected abnormalities in brain anatomy associated with epilepsy.

Overall, these results support ongoing development and pre-clinical evaluation of this technology, paving the way for eventual clinical translation into a new treatment for epilepsy.

Community energy: a local solution?

Over the years there have been many grass-roots community energy projects in the UK and elsewhere, often with an emphasis on local ownership. This provides an economic reward and incentive for investing in local projects and the opportunity for direct local control as well as wider local economic, social and environmental benefits. Local ownership has also helped to avoid opposition at the local level to wind farms elsewhere, as is evident from Denmark, where most wind projects are locally-owned and usually welcomed and, indeed, sought after. As the Danes say, “your own pigs don’t smell”.

There are, of course, a range of factors shaping how easy it is to move to local ownership, including the availability of suitable support schemes and local orientations. Although there are many constraints, there are also opportunities, and across the EU there are many community energy projects.

Some of these involve local ownership. In addition to the wind co-ops in Denmark, nearly 40% of German renewable capacity is now locally owned, some by household domestic photovoltaic (PV) “prosumers”, some by local co-ops, with many hundreds of village and town-based schemes in place. Some see this as prefiguring a new form of decentralized socio-economic power, with local social entrepreneurship challenging the existing energy market system. Certainly, in some countries, local ownership and self-generation mean that the existing power utilities are losing control of some parts of their market and local ownership clearly opens up a wide range of technical, social and political issues.

Community capacity

The situation in the UK, however, is not quite so dramatic. There is maybe nearly 4 GW of FiT-backed small, privately-owned “prosumer” PV. But in terms of community ownership, although local energy projects have involved a lot of people in local activism and networking — 48,000 according to a recent “State of the Sector” report — in all, there is only around 249 MW of locally-owned/community project capacity so far.

What’s more, the prognosis for the future is mixed. The second edition of the “State of the Sector” review by Community Energy England and Community Energy Wales notes that, while there was 168 MW of locally-owned project capacity in England, Wales and Northern Ireland, only one new community organization was constituted in 2017, with 30 fewer successful projects and 31% less generation capacity installed or acquired than in 2016. The cuts to the Feed-In Tariff (FiT) were a major problem.

The UK government has only made limited commitment to local projects, following the publication of DECC’s Community Energy Strategy report in 2104. The situation in Scotland is better, given its more supportive government, with 666 MW of local power in place. Following the early attainment of the Scottish Government’s 500 MW target for community and locally owned energy in 2017, Scotland, which has a Community & Renewables Energy Scheme (CARES), set an increased target of 1 GW by 2020. And it seems to be well on the way to reaching that. Although only 81 MW of the 666 MW of local power capacity in place so far was community-owned, it did represent a 12% increase in community-owned renewables capacity between 2016 and 2017 across more than 500 separate installations.

With ideas for smart-grid demand management in development, it could be that local energy projects will at long last come into their own

Dave Elliott

However, while CARES has clearly helped in Scotland, the Feed-Tariff has been a key element in all of this, and with that cut back and soon to go entirely, the prognosis does not look good. The State of the Sector review noted that: “At present it seems likely that the slowdown in the sector will continue into 2018. Despite ongoing innovation, the greater risks and hurdles associated with such projects mean that the number of financially viable projects in 2017 has been low. Communities are calling for better support for renewable energy projects, as well as reduced barriers to project development. Critically, clearer and more supportive government strategy is required, with greater support at the regional and local levels from local authorities.”

External support

The point is that, while self-help is important, there is also a need for external assistance. The State of the Sector review said, “improved policy support must be offered throughout the sector to improve project margins and viability and realize the benefits of local low-carbon projects. Whether through financial interventions — including reviewed subsidies, investment incentives, innovative support and early stage funding — or through greater engagement with the community energy sector (e.g. local authority partnerships), the public sector must play a central role in enabling community energy. Improved strategies and support will allow communities to continue to develop their low-carbon ideas to the benefit of local people and areas, whether through traditional routes or by establishing more innovative paths towards low-carbon community development”.

Nevertheless, looking to the future, the sector review concluded on a hopeful note: “An increasing focus on new business models, including behind-the-meter renewables, direct or local energy supply and a more collaborative approach to community energy, is driving forward a new agenda in the community energy sector”. That might include branching out from power generation via PV solar, which has been the main focus so far. There have also been 1.9 MW of local heat-supply projects and many energy efficiency/demand management projects. With ideas for smart-grid demand management in development, it could be that local energy projects will at long last come into their own. That’s what seems to be happening in some places in Germany, with attempts to move into distribution as well as generation, in some cases via municipal schemes.

In the UK context, some local councils have been exploring local power project options, developing out of the pioneering schemes in place in Nottingham and Bristol and that idea is part of the Labour party’s proposals for “public power”, with municipal projects running alongside community energy co-operatives. The prescription of local cooperative/community ownership does assume there would be demand for this form of involvement. That may not be the case. Most people may be happy just to buy whatever power is offered. Certainly, few people, wherever they lived, have in the past shown much interest in where their energy came from. However, issues relating to the costs, as well as the health and environmental impacts of power generation, as currently organized, have led to political pressures for change, with co-operatives and local ownership, along with other forms of democratic control, being one approach.

The loss of the FiT may make it harder for local projects of any kind to get going but, as I noted in my last post, the government is now proposing a “Smart Export Guarantee” as a replacement for the FiT export tariff, creating a local market for excess electricity. That might help community energy projects. But it’s still some way off, and not everyone will welcome the replacement of the FiT with a competitive market. The proposed new system is based on the power utilities, who run the trades and set the market prices, not on “peer to peer” transactions between prosumers, which some see as a potentially more progressive way ahead, possibly expanded to include community groups.

Commonly uncommon

Exoplanet Kepler-62f
Earth-like?: Artist’s impression of the extrasolar planet Kepler-62f. (Courtesy: NASA Ames/JPL-Caltech/T. Pyle )

Ten billion – that is the estimated number of Earth-like planets in orbit around Sun-like stars in the Milky Way. In One of Ten Billion Earths: How we Learn About our Planet’s Past and Future from Distant Exoplanets, astrophysicist Karel Schrijver takes a detailed look at what we know about exoplanets, and what this rapidly growing body of knowledge tells us about the Earth and its place in the solar system.

We have known about exoplanets for about 25 years and Schrijver points out that the earliest discoveries were made in the most unlikely places. In 1992, for example, the first ever confirmed observation of an exoplanet involved an object about four times the mass of Earth orbiting a neutron star. Rather than surviving the supernova explosion that preceded the formation of the neutron star, Schrijver explains that the exoplanet and its two subsequently discovered companions were probably formed from the remnants of the explosion. So even in death, a star can acquire exoplanets.

Another early surprise with possible implications for our solar system is the existence of “hot Jupiters” – gas giants that orbit much closer to their stars than Mercury does to the Sun. The first one was discovered in 1995, when it was thought that such planets must form far away from their stars, where it is cold enough for water, ammonia, methane and other volatile substances to freeze. We now know of many hot Jupiters, and a likely explanation for their existence is that they formed far from their stars and wandered inwards. Indeed, there is evidence that Jupiter may have done this long ago, sculpting the inner solar system as it lumbered through.

A strong theme of One of Ten Billion Earths is the constant stream of surprising exoplanet discoveries that have been made by astronomers. We are surprised, of course, because before 1992 we only knew about the solar system and had assumed that it was somehow normal. Even though we can make an educated guess that there are 10 billion Earth-like planets in the Milky Way, Schrijver describes Earth as “common and exceptional”. He points out that factors such as the migration of Jupiter and the presence of the Moon may have played crucial roles in creating Earth’s life-friendly environment – and we just do not know how many other exoplanets would have enjoyed a similar evolution.

  • 2018 Oxford University Press 480pp £25

Can 2D materials contribute to consumer electronics?

“Industry is not going to accept mechanical exfoliation as a path forward for manufacturing these devices,” says Joshua Robinson, Associate Professor of Materials Science and Engineering at Penn State University in the US. This conclusion is informed by over a decade working in the 2D materials research community, and in particular the past two years spent preparing a roadmap on electronic grade 2D materials, largely led by his graduate students Natalie Briggs and Shruti Subramanian.

Mechanical exfoliation refers to the fabrication approach Andre Geim and Kostya Novoselov used in the first experiments on isolated graphene. At the time researchers would routinely recover a pristine graphite substrate surface for their experiments by removing the top layer with a bit of sticky tape and throwing it away. The curiosity to investigate these discarded scraps one Friday night, thereby revealing a host of wonder properties in the single atomic layer of carbon – graphene – earnt them the Nobel Prize in 2010.

Graphene and 2D materials remain the subject of multibillion euro research across the world. Yet while mechanical exfoliation can yield high quality graphene that is useful for research purposes, fabrication techniques with more scope for industrial scaling than a bit of sticky tape are critical to gaining economic returns on research investment.

Beyond sticky tape

In terms of scale and cost progress in industrially viable fabrication methods has been great. The past decade has seen the cost of graphene plunge from the hundreds of thousands of US dollars per kilogram of graphene at the time it was first isolated to around just 50 US dollars per kilogram. The snag is that graphene from most of these more scalable fabrication methods is prone to defects, which although they may not greatly affect the material’s mechanical properties, significantly compromise the material’s electronic properties.

“2D materials constitute an entire zoo of materials, and within those types of materials are widely ranging qualities – 2D materials for mechanical properties or in composites you want defects so they interact,” Robinson tells Physics World. “In electronics you either don’t want defects or if there are defects we want to know they are very controlled and purposely put there. Random defects do not help us.”

Over the past couple of years there have been various initiatives to help manage this “zoo” of materials, such as the ISO Graphene Standard, an internationally recognized definition of graphene, and the Graphene Service, which offers characterization and advice for graphene users to match materials to suitable applications. When it comes to electronic applications a lot of the graphene produced simply does not hit the grade.

Hope for electronic grade 2D materials

Consequently, Robinson agrees with those who suggest that applications exploiting the more forgiving mechanical properties of 2D materials have a head start in making their way into high street products. However he adds, “There’s been a lot of improvements in the past couple of years – looking at chemical vapour deposition (CVD) and molecular beam epitaxy (MBE) – these are some of the approaches that are going to grow electronic grade 2D materials, so we thought it was time to ask what are the number one challenges that we have to address so that these 2D materials can make an impact.”

The roadmap recently published in the journal 2D Materials outlines a series of applications of electronic grade 2D materials including electronics, Internet of Things devices, computing and solar energy, highlighting the potential for commercial progress and the remaining challenges in both theory and experiment for understanding and mastering the fabrication techniques required.

Standing on the shoulders of silicon

Robinson also points out how techniques for fabricating electronic grade 2D materials are largely compatible with existing semiconductor fabrication techniques, which as he suggests is arguably the number one reason why their fascination has been so persistent in industry.

“For quantum dots, nanowires and nanotubes you have to put them on a surface by spin coating etc and it’s hard to do this deterministically,” says Robinson. “The key with 2D materials is you can grow them directly on a substrate and use the same processes to make devices as developed with silicon. Manufacturers of semiconductor devices can utilize the same techniques without major changes to their fabrication lines.”

This CMOS-compatible manufacture strengthens the potential for exploiting 2D materials to augment, complement or enhance existing semiconductor technology. In fact Robinson is more than sceptical of the chance of 2D materials – or anything else – replacing silicon in the next 10-20 years, favouring instead a scenario where 2D materials develop alongside conventional electronics.

Could they match the ubiquity of silicon technology in the next decade? Robinson suggests they may have a greater impact in some areas than others, promising avenues being the post-fabrication processes in transistor technology, sometimes described as Back-End-Of-the-Line (BEOL), and certain computer memory technologies.

“I think one of the big things is being able to do the manufacturing in a manner that is compatible with silicon technology and that is the real trick for the things we are trying to do,” says Robinson. “This roadmap is focused on how to make these materials electronics grade because if we can’t make them high enough quality – controlled properties low defects etc – they will never be ubiquitous even if the intrinsic properties are revolutionary.”

The full roadmap is available in the journal 2D Materials.

Multiple excitons make a surprise appearance in 2D hybrid perovskites

Semiconductor devices based on hybrid organic–inorganic perovskites (HIOPs) are growing in popularity due to their potential applications in efficient light-emitting diodes, solar cells, lasers, and more. These hybrid materials are soft and flexible, and are much easier to fabricate in the bulk than comparable semiconductors. As a result, thin films of HIOPs could even be used for future electronic devices that could be painted onto a surface.

Particular interest has focused on 2D metal halide HIOPs, since they have been shown to host high-energy excitons – typically hundreds of meV. Now, an international team led by researchers from the Georgia Institute of Technology, US, has made the surprising discovery that multiple excitons with distinct properties can coexist in these hybrid materials. This finding could open up a range of novel device applications, but also raises many questions about the mechanisms that give rise to this phenomenon.

Excitons are quasiparticle excitations that have no net charge but can transport energy. “Using the standard formalism,” comments team member Srinivasa Srimath from the Istituto di Tecnologia in Milan, Italy, “ the coexistence of multiple excitons cannot be predicted.” Srimath explains that the main focus of the research was to investigate how excitons are affected by the lattice, and the team was surprised to find that that distinct excitons can exist in the same material.

Two single-layer hybrids of lead iodide were considered, (PEA)2PbI4 and (NBT)2PbI4, where PEA is phenylethyl ammonium and NBT is n-butylammonium. The organic component is usually host to high-frequency vibrations, or phonons, whereas lower frequencies should dominate in the inorganic part of the materials. This suggests that there should be a sharp change in the vibrational spectrum at the boundary between the materials, which in turn implies that the electronic properties of 2D HIOPs should be heavily influenced by phonons.

Scientists usually turn to Raman spectroscopy to probe the vibrational spectrum of materials. But HIOPs generate a rich photoluminescent response, which makes the weaker Raman signal difficult to isolate. To overcome this obstacle, the researchers exploited ultrashort light pulses, a variation of the method that is known as resonant impulsive stimulated Raman spectroscopy (RIRS).

Using RIRS, the researchers found a set of coexisting excitons that couple to the lattice in different ways. Some are coupled to vibrations in the crystal plane, while others to out-of-plane motion – which results in excitons that could be useful for novel laser designs.

Although the researchers have confirmed the coexistence of excitons with vastly different properties, it is not clear which type of quasiparticle would be excited in the material at any given time. However, notes Srimath, that remains an active line of enquiry. “To some degree the nature of these excitons seems to depend on the choice of the organic cation,” he comments. Changing the organic cation used could affect the relative intensities of the excitonic peaks, which would make it possible to design materials that tune in or out specific excitonic responses. With the growing interest in the field of 2D HIOPs, these highly tunable electronic devices may soon become reality.

The full results are reported in Nature Materials.

Physics World 30th anniversary podcast series – fusion energy

Physics World has recently turned 30 and we are celebrating with a 5-part series podcast series exploring key areas of physics. This third episode in the series explores the prospects for fusion energy ­­– a carbon-free form of energy generation that may finally be on the cusp of becoming practical.

For the past few decades, the running joke has been that despite the excitement, fusion energy is “always 30 years away.” In the January episode of Physics World Stories, Andrew Glester meets fusion researchers at the UK company Tokamak Energy to learn about the practical challenges and the technology that could make fusion a reality within the next 15 years.

Melanie Windridge, a communication consultant (and adventurer), explains the science behind the two main approaches to achieving fusion. The first is known as inertial confinement fusion and its feasibility is being investigated at the National Ignition Facility (NIF) in the US. The alternative involves using intense magnetic fields to confine hot plasma inside a device known as a tokamak. This is the approach taken at the International Thermonuclear Experimental Reactor (ITER), an international collaboration based in southern France.

In contrast to the much larger tokamak ITER tokamak, the technology being developed by Tokamak Energy could lead to a compact tokamak that can run at much higher plasma pressure. Glester visits the company in Oxfordshire to meet the company’s chief executive David Kingham, who believes this smaller-scale approach could make fusion energy more economically viable. Both Kingham and Windridge believe that practical fusion energy has become more realistic due to two key factors – the growing global consensus that we need to act on climate change coupled with the arrival of private enterprise in this space.

If you enjoy the podcast, then take a listen to the first two podcasts in the 30th anniversary series. Glester began in October by looking at the past and future of particle physics. Then in November he explored gravitational waves by looking at the exciting future for multimessenger astronomy. Don’t forget you can also subscribe to Physics World Stories via the Apple podcast app or your chosen podcast host.

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