Leading Research in Materials Science
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Modified nanocellulose paper has been shown to be excellent biodegradable substrate for flexible perovskite solar cells and potentially other green flexible devices. A team of Chinese scientists led by Prof Wei Huang from Institute of Advanced Materials, Nanjing Tech University fabricate flexible perovskite solar cells on transparent nanocellulose paper. This becomes feasible only after they develop a treatment recipe to improve the mechanical, optical properties and the waterproof ability of the pure nanocellulose paper. The flexible solar cells on the modified substrates show high specific power of 0.56 W g-1 and good stability and mechanical durability. Another key advantage of nanocellulose paper is its biodegradation capability, making it a better substrate compared to PEN and PET for the next generation green flexible electronics.
A solar-powered portable filtration unit is capable of treating ground and surface water to drinking standards in rural communities in Tanzania. Water treatment in remote communities is extremely challenging because establishing permanent infrastructure is often not viable. Instead, decentralized treatment systems are needed. Here, an international team of researchers demonstrate decentralized water treatment in rural communities in Tanzania, via a solar-powered membrane filtration unit. They find that it is possible to obtain potable water from surface and ground water, and that water quality was not affected significantly by non-constant sunlight. The filtration unit used was able to provide drinking water for approximately 200 people per day, demonstrating the viability of such portable approaches to water treatment in rural areas of developing countries.
To support oil and gas exploration, researchers sent hydrocarbon mixtures into space to obtain accurate data on how each component behaves. The group—led by Guillaume Galliero from the University of Pau and Pays de l’Adour, France—wanted to study the effect of temperature on the movement of individual hydrocarbons in mixtures under typical reservoir conditions. Eliminating the effects of gravity allowed them to collect more accurate data than has previously been obtained. The team showed that thermodiffusion has a large impact on the distribution of hydrocarbon reservoirs under the ground. They state that thermodiffusion should therefore be considered in computer models that assess analytical data collected at potential underground reservoirs. This would allow oil and gas companies to more accurately predict the suitability of the hydrocarbons at potential drilling sites.
The perovskite Cs2SnI6 has been investigated using numerous in-situ techniques to understand its environmental stability. While organic–inorganic perovskites show great promise for photovoltaic applications, their poor stability remains a problem. Perovskite Cs2SnI6 shows enhanced stability properties, however, how it degrades is not fully understood. Now a team lead by Jie Lian at the Rensselaer Polytechnic Institute, USA, has investigated the phase stability and decomposition mechanisms of Cs2SnI6 when exposed to moisture. This systematic study used in-situ synchrotron X-ray diffraction, environmental scanning electron microscopy and micro-Raman spectroscopy and discovered that there was a critical relative humidity of 80% above which Cs2SnI6 decomposes into SnI4 and CsI. They attribute the degradation process to etch pit formation on the surface of the crystals, which results in the dissolution of the entire crystal through a stepwave model.
A sharp thickness-dependent metal–insulator transition has been observed in CaVO3, which is a correlated metal in its bulk form, but an insulator in its ultrathin film form. Milan Radovic and Thorsten Schmitt from the Paul Scherrer Institute in Switzerland, and colleagues, used X-ray absorption spectroscopy and resonant inelastic X-ray scattering to study CaVO3 films deposited on a SrTiO3 substrate. They found that with a growing number of layers the electronic bandwidth changed continuously by up to 40%, affecting the degree of electron localization and eventually resulting in a thermal metal–insulator transition at a thickness of 10 unit cells. The ability to control this phase transition is potentially useful for applications, for example in transparent conductors and field-effect transistors, while understanding the role of reduced dimensionality is a necessary step towards the design of functional quantum materials.
Evolution of the low-temperature Fermi surface of superconducting FeSe1−xSx across a nematic phase transition
New measurements of quantum oscillations in FeSe1-xSx help understanding the nature of the nematic phase transition in Fe-based superconductors. Nematic order — an electronic order that breaks the rotational symmetry of the underlying substrate — is thought to play an important role in the appearance of superconductivity in Fe-based superconductors. A way to investigate the interplay between nematicity and superconductivity is to apply chemical pressure, in this case by substituting Se with S in FeSe samples. Amalia Coldea from the University of Oxford, UK, and colleagues used Shubnikov-de Haas oscillations to characterize the evolution of the Fermi surfaces across the nematic phase transition. They found a strongly correlated state inside the nematic phase and weakening electronic correlations outside it, and evidence for a Lifshitz transition that had not been detected before.
A collaborative international team led by Dr. Swati Sharma from Karlsruhe Institute of Technology, Germany demonstrates the first catheter-compatible, pH-based enzymatic urea sensor. The authors directly convert commercially available Kapton films into carbon using IR laser, and optimize the process for obtaining a high surface area material with hydrophilic functional groups for biosensor fabrication. These inexpensive flexible sensors are fabricated by enzyme absorption on to the carbon films, with or without an electrodeposited intermediate chitosan layer. They can be rolled-up to fit inside a catheter tube, and feature detection limit down to 10−4 M urea concentration that is 100 times lower than that in the blood serum of a healthy human. These sensors show promising applications as they are inexpensive, flexible, readily usable for in-vivo urea determination and easily extendable to multi- functional circuits.
The interplay between the electronic and spin degrees of freedom determines the removal of Weyl points in magnetic semimetal systems. A team led by Je-Geun Park at the Institute for Basic Science and Seoul National University used linear spin wave theory to obtain the full spin wave spectra of antiferromagnetic A-type Mn3Sn across a broad energy-momentum range. The magnetic Hamiltonian obtained via a local moment model was capable of explaining the experimental inelastic neutron scattering data. Additional density functional theory calculations indicated that the Mn3Sn low-temperature magnetic structure involves a helical ordering that eliminates the Weyl points, and consequently reduces Mn3Sn experimental anomalous Hall conductivity. These results indicate how topological Weyl points can be removed by introducing a minor change to the magnetic ground state.
Retained free energy as a driving force for phase transformation during rapid solidification of stainless steel alloys in microgravity
A model that describes the atomic-structure changes in a steel alloy as it rapidly changes from a molten to a solid state is developed by a scientist in the USA. Steel solidifies very quickly after being welded, during which process the atomic structure of the solid alloy can change multiple times. For example, an alloy of iron, chromium and nickel transforms from a ferrite atomic structure to one known as austenite. Classical nucleation theory does not explain this so-called double recalescence. Douglas Matson at Tufts University has developed a novel physical model to describe this microstructural evolution that is based on viewing the transformation as an accumulation of defects. The model predicts the time delay of the transformation, which Matson compares to observed values determined by microgravity experiments.
A metamaterial made from thousands of superconducting devices provides a configurable ultra-strongly coupled environment for qubits. An already achievable application of prospective quantum computing platforms is as bespoke simulators of difficult-to-solve theoretical models. Javier Puertas-Martínez and colleagues from Institut Néel in France and the University of the Witwatersrand in South Africa have designed a superconducting circuit that provides an idealised synthetic environment for qubits with an interaction strength that is tunable with an external magnetic field. Made from a one-dimensional chain of 4700 SQUIDs, their device overcomes physical limitations on the coupling between a qubit and the natural environment, reaching the ultra-strong regime where quantum many-body effects become relevant. Integration of the design in more complicated circuits will enable the study of previously-inaccessible many-body quantum optics phenomena.
A scheme for protecting the quantum states in a nanodiamond is demonstrated that improves readout fidelity by enabling repeated measurements. The ability to readout a quantum state is key to quantum technologies, such as quantum sensors, computation and secure communication. Readout fidelity can be enhanced by making multiple measurements, but this often has the unfortunate effect of changing the quantum state being measured. A team of researchers from the University of Cambridge led by Mete Atature now demonstrate a simple error-correction code to protect the electronic-spin state of a nitrogen-vacancy center in diamond from measurement backaction, enabling them to significantly enhance the readout fidelity. Aside from showing the potential of this platform, this approach for correcting errors could also be used to improve quantum algorithms that require a non-volatile local memory.
Superconducting circuits can realize “superstrong” coupling between qubits and transmission lines, changing the state of the quantum vacuum. Superconducting qubits can interact with their environment by emitting and absorbing photons. In the strong coupling regime, the interaction is stronger than the rate of loss, allowing coherent exchange between qubit and photonic excitations. This normally involves confinement inside a cavity so that a photon is reflected across the qubit multiple times. A team led by Vladimir Manucharyan at the University of Maryland, USA, have created a transmission line where a photon couples strongly to a qubit with a single pass. Under these superstrong coupling conditions, the qubit modifies the structure of the photonic modes. By incorporating more strongly nonlinear elements, their device should enable the simulation of many-body impurity models with nonperturbative effects.
Solvent-free thermoplastic polyurethanes (TPU) could be used to 3D-print artificial tissues saving time and money. Achala de Mel and colleagues at University College London used open-source 3D-modelling software and commercially available 3D printers to fabricate a bespoke tracheal stent from custom-made TPU. The team was able to control the material’s porosity with 3D-design, which could facilitate its vascularisation if implanted. The trachea was mechanically and structurally similar to that of an adult, showing longitudinal elasticity and radial rigidity. When attached to a ventilator system, it responded well to pressures similar to those of inspiration, forced expiration, coughing or crying. 3D-printed trachea was treated with bioactive molecules so cells could potentially adhere to and proliferate on its surface. This method could be used to fabricate bespoke elastic tissue substitutes, avoiding costly and time-consuming cell-culture techniques.
Biomaterials-enabled cornea regeneration in patients at high risk for rejection of donor tissue transplantation
A biomaterial implant supports the regeneration of severely damaged corneas in patients at high risk for rejecting conventional transplantation. An international team from Canada, China, India, Sweden, Ukraine and United Kingdom used mini-pigs to confirm the safety of implanting cell-free corneas made from recombinant human collagen and a synthetic lipid, before examining the effects of implantation on human vision in seven patients. The implants were well-tolerated and led to significant vision improvement in patients with damaged corneas due to infection. Furthermore, within two weeks of surgery the implants had relieved pain. Over two years, sensitivity to touch improved, suggesting an ability to promote nerve regeneration. This study supports the use of animal models to test biomaterials designed for medical applications and describes a safe and promising option for treating patients that not treatable by conventional corneal transplantation.
Rehabilitative exercise and spatially patterned nanofibrillar scaffolds enhance vascularization and innervation following volumetric muscle loss
A collagen scaffold designed to mimic skeletal muscle, together with rehabilitative exercise, can help regenerate nerves and blood vessels following traumatic muscle injury. Ngan Huang from Stanford University, California, USA, and colleagues created scaffolding composed of collagen nanofibers aligned in parallel, as natural muscle fibers are. They implanted these specially patterned collagen constructs into the shins of mice that had no tibialis anterior muscles. Mice given the opportunity to exercise formed far more nerve connections in their injured muscles compared to mice without exercise wheels in their cages. Active mice also developed significantly more blood vessels in their injured muscles with the parallel-aligned scaffolds compared to other animals with randomly oriented scaffolds, decellularized scaffolds or no implant at all. The findings highlight the potential of combining exercise and biomimetic scaffolds to treat muscle trauma.