When light shines on a semiconductor, its energy is absorbed. As a result, negatively charged electrons and positively charged holes combine in the semiconductor to form pairs, known as excitons. In the most modern two-dimensional semiconductors, these excitons have an extraordinarily high binding energy. In their study, the researchers set themselves the challenge of investigating the hole of the exciton. As physicist and first author Jan Philipp Bange from the University of Göttingen explains: “In our laboratory, we use photoemission spectroscopy to investigate how the absorption of light in quantum materials leads to charge transfer processes. So far, we have concentrated on the electrons that are part of the electron-hole pair, which we can measure using an electron analyser. Up to now, we didn’t have any way to directly access the holes themselves. So, we were interested in the question of how we could characterise not just the electron of the exciton but also its hole.”

To answer this question, the researchers, led by Dr Marcel Reutzel and Professor Stefan Mathias at Göttingen University’s Faculty of Physics, used a special microscope for photoelectrons in combination with a high-intensity laser. In the process, the breaking up of an exciton leads to a loss of energy in the electron measured in the experiment. Reutzel explains: “This energy loss is characteristic for different excitons, depending on the environment in which the electron and the hole interact with each other.” In the current study, the researchers used a structure consisting of two different atomically thin semiconductors to show that the hole of the exciton transfers from one semiconductor layer to the other, similar to a solar cell. Professor Ermin Malic’s team at the University of Marburg was able to explain this charge transfer process with a model to describe what happens at a microscopic level.

Mathias summarises: “In the future, we want to use the spectroscopic signature of the interaction between electrons and holes to study novel phases in quantum materials at ultrashort time and length scales. Such studies can be the basis for the development of new technologies and we hope to contribute to this in the future.”

This research benefited from the German Research Foundation (DFG) funding for the Collaborative Research Centres “Atomic scale control of energy conversion” and “Mathematics of Experiment” in Göttingen and “Structure and Dynamics of Internal Interfaces” in Marburg.

According to a new study, these so-called “Snowball” Earth periods, in which the planet’s surface was covered in ice for thousands or even millions of years, could have been triggered abruptly by large asteroids that slammed into the Earth.

The findings, detailed in the journal Science Advances, may answer a question that has stumped scientists for decades about some of the most dramatic known climate shifts in Earth’s history. In addition to Yale, the study included researchers from the University of Chicago and the University of Vienna.

Climate modelers have known since the 1960s that if the Earth became sufficiently cold, the high reflectivity of its snow and ice could create a “runaway” feedback loop that would create more sea ice and colder temperatures until the planet was covered in ice. Such conditions occurred at least twice during Earth’s Neoproterozoic era, 720 to 635 million years ago.

Yet efforts to explain what initiated these periods of global glaciation, which have come to be known as “Snowball Earth” events, have been inconclusive. Most theories have centered on the notion that greenhouse gases in the atmosphere somehow declined to a point where “snowballing” began.

“We decided to explore an alternative possibility,” said lead author Minmin Fu, the Richard Foster Flint Postdoctoral Fellow in the Department of Earth and Planetary Sciences in Yale’s Faculty of Arts and Sciences. “What if an extraterrestrial impact caused this climate change transition very abruptly?”

For the study, the researchers used a sophisticated climate model that represents atmospheric and ocean circulation, as well as the formation of sea ice, under different conditions. It is the same type of climate model that is used to predict future climate scenarios.

In this instance, the researchers applied their model to the aftermath of a hypothetical asteroid strike in four distinct periods of the past: preindustrial (150 years ago), Last Glacial Maximum (21,000 years ago), Cretaceous (145 to 66 million years ago), and Neoproterozoic (1 billion to 542 million years ago).

For two of the warmer climate scenarios (Cretaceous and preindustrial), the researchers found that it was unlikely that an asteroid strike could trigger global glaciation. But for the Last Glacial Maximum and Neoproterozoic scenarios, when the Earth’s temperature may have been already cold enough to be considered an ice age — an asteroid strike could have tipped Earth into a “Snowball” state.

“What surprised me most in our results is that, given sufficiently cold initial climate conditions, a ‘Snowball’ state after an asteroid impact can develop over the global ocean in a matter of just one decade,” said co-author Alexey Fedorov, a professor of ocean and atmospheric sciences in Yale’s Faculty of Arts and Sciences. “By then the thickness of sea ice at the Equator would reach about 10 meters. This should be compared to a typical sea ice thickness of one to three meters in the modern Arctic.”

As for the chances of an asteroid-induced “Snowball Earth” period in the years to come, the researchers said it was unlikely — due in part to human-caused warming that has heated the planet — even though other impacts could be as devastating.

The research was supported by the Flint Postdoctoral Fellowship at Yale and the ARCHANGE project. Co-authors of the study are Dorian Abbot of the University of Chicago and Christian Koeberl of the University of Vienna.

The researchers, from the University of Cambridge, developed sensors made from highly porous materials known as aerogels. By precisely engineering the shape of the holes in the aerogels, the sensors were able to detect the fingerprint of formaldehyde, a common indoor air pollutant, at room temperature.

The proof-of-concept sensors, which require minimal power, could be adapted to detect a wide range of hazardous gases, and could also be miniaturised for wearable and healthcare applications. The results are reported in the journal Science Advances.

Volatile organic compounds (VOCs) are a major source of indoor air pollution, causing watery eyes, burning in the eyes and throat, and difficulty breathing at elevated levels. High concentrations can trigger attacks in people with asthma, and prolonged exposure may cause certain cancers.

Formaldehyde is a common VOC and is emitted by household items including pressed wood products (such as MDF), wallpapers and paints, and some synthetic fabrics. For the most part, the levels of formaldehyde emitted by these items are low, but levels can build up over time, especially in garages where paints and other formaldehyde-emitting products are more likely to be stored.

According to a 2019 report from the campaign group Clean Air Day, a fifth of households in the UK showed notable concentrations of formaldehyde, with 13% of residences surpassing the recommended limit set by the World Health Organization (WHO).

“VOCs such as formaldehyde can lead to serious health problems with prolonged exposure even at low concentrations, but current sensors don’t have the sensitivity or selectivity to distinguish between VOCs that have different impacts on health,” said Professor Tawfique Hasan from the Cambridge Graphene Centre, who led the research.

“We wanted to develop a sensor that is small and doesn’t use much power, but can selectively detect formaldehyde at low concentrations,” said Zhuo Chen, the paper’s first author.

The researchers based their sensors on aerogels: ultra-light materials sometimes referred to as ‘liquid smoke’, since they are more than 99% air by volume. The open structure of aerogels allows gases to easily move in and out. By precisely engineering the shape, or morphology, of the holes, the aerogels can act as highly effective sensors.

Working with colleagues at Warwick University, the Cambridge researchers optimised the composition and structure of the aerogels to increase their sensitivity to formaldehyde, making them into filaments about three times the width of a human hair. The researchers 3D printed lines of a paste made from graphene, a two-dimensional form of carbon, and then freeze-dried the graphene paste to form the holes in the final aerogel structure. The aerogels also incorporate tiny semiconductors known as quantum dots.

The sensors they developed were able to detect formaldehyde at concentrations as low as eight parts per billion, which is 0.4 percent of the level deemed safe in UK workplaces. The sensors also work at room temperature, consuming very low power.

“Traditional gas sensors need to be heated up, but because of the way we’ve engineered the materials, our sensors work incredibly well at room temperature, so they use between 10 and 100 times less power than other sensors,” said Chen.

To improve selectivity, the researchers then incorporated machine learning algorithms into the sensors. The algorithms were trained to detect the ‘fingerprint’ of different gases, so that the sensor was able to distinguish the fingerprint of formaldehyde from other VOCs.

“Existing VOC detectors are blunt instruments — you only get one number for the overall concentration in the air,” said Hasan. “By building a sensor that is able to detect specific VOCs at very low concentrations in real time, it can give home and business owners a more accurate picture of air quality and any potential health risks.”

The researchers say that the same technique could be used to develop sensors to detect other VOCs. In theory, a device the size of a standard household carbon monoxide detector could incorporate multiple different sensors within it, providing real-time information about a range of different hazardous gases. The team at Warwick are developing a low-cost multi-sensor platform that will incorporate these new aerogel materials and, coupled with AI algorithms, detect different VOCs.

“By using highly porous materials as the sensing element, we’re opening up whole new ways of detecting hazardous materials in our environment,” said Chen.

The research was supported in part by the Henry Royce Institute, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Tawfique Hasan is a Fellow of Churchill College, Cambridge.

Researchers from ECU’s Centre for Research in Aged Care and HammondCare’s The Dementia Centre noted that behaviours and psychological symptoms of dementia (BPSD), such as agitation and aggression, are common; however, its presentation may be influenced by the cultural background of the person.

A study investigated differences in clinical and demographics characteristics and BPSD between immigrants and non-immigrants living with dementia in residential aged care homes who were referred to Dementia Support Australia (DSA) programs. The study found that immigrants were more likely to present with agitation or aggression, while non-immigrants were more likely to present with hallucinations and delusions.

DSA, a free, Australian Government-funded dementia behaviour support program, has supported over 60,000 clients and 98 percent of aged care homes in every state and territory since 2016.

BPSD were common between the groups, with language barriers and cultural considerations frequently observed for immigrants, adding to the contributing factors.

“In Australia, over 400,000 people are living with dementia, a number projected to double by 2058, At least 54% of people living in residential aged care homes (RACHs) in 2019 — 2020 had a dementia diagnosis,” said lead researcher Pelden Chejor.

“Over 31% of aged care residents were also born overseas, and 9.2% of people using aged care preferred a language other than English. In 2019 — 2020, 21% of people living with dementia in RACHs were immigrants from non-English speaking countries. International studies have reported that immigrants experience a higher prevalence of dementia due to differing life experiences including those related to trauma, low literacy, and socioeconomic status.”

Chejor and his colleagues noted that loneliness, boredom, language barriers, and cultural considerations significantly contributed to BPSD for non-English-speaking immigrants compared with non-immigrants, with the largest significant differences being for language barriers and cultural considerations. There were no differences in the prevalence of contributing factors between English-speaking immigrants and non-immigrants.

“Our findings indicated a significantly lower rate of hallucinations for immigrants and non-English-speaking immigrants compared to non-immigrants. Additionally, non-English-speaking immigrants were significantly lower on delusions and disinhibition than non-immigrants.

“The higher severity of agitation or aggression is likely driven by communication difficulties as there was no difference for the English-speaking immigrants. Cognitive decline can impair both the ability to express and comprehend spoken language and people living with dementia who have English as their additional language may lose their ability to communicate in English and subsequently use their first language as the primary language of communication,” said Chejor.

“Our study calls for increased awareness and education on the impact of culture and language for people receiving residential care and exhibiting BPSD. Future research should explore related factors such as length of stay in Australia and English language proficiency to learn more about BPSD presentations for different immigrant groups. By doing so, we can better manage these symptoms.”

Head of DSA Marie Alford said the study reinforced the importance of understanding the person living with dementia, including their cultural background and experiences, likes, dislikes and routines when responding to BPSD.

“Communicating effectively with the person living with dementia, and taking the time to know them, including their language background and culture, is essential,” Alford said. “In many cases this can mean responding with support without the need for a pharmacological intervention.”

In his chemical engineering lab in UC’s College of Engineering and Applied Science, Associate Professor Jingjie Wu and his team found that a modified copper catalyst improves the electrochemical conversion of carbon dioxide into ethylene, the key ingredient in plastic and a myriad of other uses.

Ethylene has been called “the world’s most important chemical.” It is certainly among the most commonly produced chemicals, used in everything from textiles to antifreeze to vinyl. The chemical industry generated 225 million metric tons of ethylene in 2022.

Wu said the process holds promise for one day producing ethylene through green energy instead of fossil fuels. It has the added benefit of removing carbon from the atmosphere.

“Ethylene is a pivotal platform chemical globally, but the conventional steam-cracking process for its production emits substantial carbon dioxide,” Wu said. “By utilizing carbon dioxide as a feedstock rather than depending on fossil fuels, we can effectively recycle carbon dioxide.”

The study was published in the journal Nature Chemical Engineering.

Wu’s students, including lead author and UC graduate Zhengyuan Li, collaborated with Rice University, Oak Ridge National Laboratory, Brookhaven National Laboratory, Stony Brook University and Arizona State University. Li received a prestigious graduate student award last year from the College of Engineering and Applied Science.

The electrocatalytic conversion of carbon dioxide produces two primary carbon products, ethylene and ethanol. Researchers found that using a modified copper catalyst produced more ethylene.

“Our research offers essential insights into the divergence between ethylene and ethanol during electrochemical CO2 reduction and proposes a viable approach to directing selectivity toward ethylene,” lead author Li said.

“This leads to an impressive 50% increase in ethylene selectivity,” Wu said. “Ideally, the goal is to produce a single product rather than multiple ones.”

Sponsored by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy. Its Industrial Efficiency and Decarbonization Office is leading efforts to reduce fossil fuels and carbon emissions in industry wherever possible.

Li said the next step is refining the process to make it more commercially viable. The conversion system loses efficiency as byproducts of the reaction such as potassium hydroxide begin forming on the copper catalyst.

“The electrode stability must be improved for commercial deployment. Our next focus is to enhance stability and extend its operation from 1,000 to 100,000 hours,” Li said.

Wu said these new technologies will help make the chemical industry greener and more energy efficient.

“The overarching objective is to decarbonize chemical production by utilizing renewable electricity and sustainable feedstock,” Wu said. “Electrifying the conversion of carbon dioxide to ethylene marks a significant stride in decarbonizing the chemical sector.”

However, storing and transporting H₂ safely and efficiently remains a challenge. Compressed gaseous hydrogen poses a significant risk of explosion and leakage, whereas liquid hydrogen must be maintained at extremely low temperatures, which is costly. But what if we could store hydrogen directly in the molecular composition of other liquid or solid materials?

This was the focus of a team of scientists from Japan, who, in a recent study published in the journal Small, investigated the potential of hydrogen boride (HB) sheets as practical hydrogen carriers. Storing hydrogen in HB sheets is not an entirely new concept, and many aspects of their potential applications as hydrogen carriers have already been studied. However, getting the hydrogen out of the sheets is the tricky part. Heating at high temperatures or strong ultraviolet (UV) illumination is required to release hydrogen (H₂) from HB sheets. However, both approaches have inherent disadvantages, such as high energy consumption or incomplete H₂ release.

Thus, the team delved into a potential alternative: electrochemical release. Based on the mechanism of UV-induced H₂ release from HB sheets, the team speculated that electron injection from a cathode electrode into HB nanosheets by an electric power supply could be a superior way to release H₂ compared to UV irradiation or heating.

Based on this theory, the researchers dispersed HB sheets into acetonitrile — an organic solvent — and applied a controlled voltage to the dispersion. These experiments revealed that nearly all of the electrons injected into the electrochemical system were used to convert H⁺ ions from the HB sheets into H₂ molecules. Notably, the Faradaic efficiency of this process, which measures how much electrical energy is converted into chemical energy, was over 90%.

The team also conducted isotope tracing experiments to confirm that the electrochemically released H₂ originated from the HB sheets and not through some other chemical reaction. Moreover, they also employed scanning electron microscopy and X-ray photoelectron spectroscopy to characterize the sheets before and after H₂ release, yielding further insights into the underlying mechanisms of the process.

These findings contribute to the development of safe and lightweight hydrogen carriers with low energy consumption. Although the team studied the dispersed form of the HB sheets in the published paper, the current findings are applicable to film or bulk-based HB sheet systems for H₂ release. Moreover, the team will investigate the rechargeability of HB sheets after dehydrogenation in a future study.

With any luck, this line of research will help pave the way to cleaner energy sources and more sustainable societies!

As many real-world quantum sensing devices are emerging, one promising direction is the use of microscopic defects inside diamonds to create “qubits” that can be used for quantum sensing. Qubits are the building blocks of quantum devices.

Researchers at MIT and elsewhere have developed a technique that enables them to identify and control a greater number of these microscopic defects. This could help them build a larger system of qubits that can perform quantum sensing with greater sensitivity.

Their method builds off a central defect inside a diamond, known as a nitrogen-vacancy (NV) center, which scientists can detect and excite using laser light and then control with microwave pulses. This new approach uses a specific protocol of microwave pulses to identify and extend that control to additional defects that can’t be seen with a laser, which are called dark spins.

The researchers seek to control larger numbers of dark spins by locating them through a network of connected spins. Starting from this central NV spin, the researchers build this chain by coupling the NV spin to a nearby dark spin, and then use this dark spin as a probe to find and control a more distant spin which can’t be sensed by the NV directly. The process can be repeated on these more distant spins to control longer chains.

“One lesson I learned from this work is that searching in the dark may be quite discouraging when you don’t see results, but we were able to take this risk. It is possible, with some courage, to search in places that people haven’t looked before and find potentially more advantageous qubits,” says Alex Ungar, a PhD student in electrical engineering and computer science and a member of the Quantum Engineering Group at MIT, who is lead author of a paper on this technique, which is published today in PRX Quantum.

His co-authors include his advisor and corresponding author, Paola Cappellaro, the Ford Professor of Engineering in the Department of Nuclear Science and Engineering and professor of physics; as well as Alexandre Cooper, a senior research scientist at the University of Waterloo’s Institute for Quantum Computing; and Won Kyu Calvin Sun, a former researcher in Cappellaro’s group who is now a postdoc at the University of Illinois at Urbana-Champaign.

Diamond defects

To create NV centers, scientists implant nitrogen into a sample of diamond.

But introducing nitrogen into the diamond creates other types of atomic defects in the surrounding environment. Some of these defects, including the NV center, can host what are known as electronic spins, which originate from the valence electrons around the site of the defect. Valence electrons are those in the outermost shell of an atom. A defect’s interaction with an external magnetic field can be used to form a qubit.

Researchers can harness these electronic spins from neighboring defects to create more qubits around a single NV center. This larger collection of qubits is known as a quantum register. Having a larger quantum register boosts the performance of a quantum sensor.

Some of these electronic spin defects are connected to the NV center through magnetic interaction. In past work, researchers used this interaction to identify and control nearby spins. However, this approach is limited because the NV center is only stable for a short amount of time, a principle called coherence. It can only be used to control the few spins that can be reached within this coherence limit.

In this new paper, the researchers use an electronic spin defect that is near the NV center as a probe to find and control an additional spin, creating a chain of three qubits.

They use a technique known as spin echo double resonance (SEDOR), which involves a series of microwave pulses that decouple an NV center from all electronic spins that are interacting with it. Then, they selectively apply another microwave pulse to pair the NV center with one nearby spin.

Unlike the NV, these neighboring dark spins can’t be excited, or polarized, with laser light. This polarization is a required step to control them with microwaves.

Once the researchers find and characterize a first-layer spin, they can transfer the NV’s polarization to this first-layer spin through the magnetic interaction by applying microwaves to both spins simultaneously. Then once the first-layer spin is polarized, they repeat the SEDOR process on the first-layer spin, using it as a probe to identify a second-layer spin that is interacting with it.

Controlling a chain of dark spins

This repeated SEDOR process allows the researchers to detect and characterize a new, distinct defect located outside the coherence limit of the NV center. To control this more distant spin, they carefully apply a specific series of microwave pulses that enable them to transfer the polarization from the NV center along the chain to this second-layer spin.

“This is setting the stage for building larger quantum registers to higher-layer spins or longer spin chains, and also showing that we can find these new defects that weren’t discovered before by scaling up this technique,” Ungar says.

To control a spin, the microwave pulses must be very close to the resonance frequency of that spin. Tiny drifts in the experimental setup, due to temperature or vibrations, can throw off the microwave pulses.

The researchers were able to optimize their protocol for sending precise microwave pulses, which enabled them to effectively identify and control second-layer spins, Ungar says.

“We are searching for something in the unknown, but at the same time, the environment might not be stable, so you don’t know if what you are finding is just noise. Once you start seeing promising things, you can put all your best effort in that one direction. But before you arrive there, it is a leap of faith,” Cappellaro says.

While they were able to effectively demonstrate a three-spin chain, the researchers estimate they could scale their method to a fifth layer using their current protocol, which could provide access to hundreds of potential qubits. With further optimization, they may be able to scale up to more than 10 layers.

In the future, they plan to continue enhancing their technique to efficiently characterize and probe other electronic spins in the environment and explore different types of defects that could be used to form qubits.

This research is supported, in part, by the U.S. National Science Foundation and the Canada First Research Excellence Fund.