Category Archives: Materials

Rice University scientists are counting on films of carbon nanotubes to make high-powered, fast-charging lithium metal batteries a logical replacement for common lithium-ion batteries.

Rice University graduate student Gladys López-Silva holds a lithium metal anode with a film of carbon nanotubes. Once the film is attached, it becomes infiltrated by lithium ions and turns red. Credit: Jeff Fitlow/Rice University

The Rice lab of chemist James Tour showed thin nanotube films effectively stop dendrites that grow naturally from unprotected lithium metal anodes in batteries. Over time, these tentacle-like dendrites can pierce the battery’s electrolyte core and reach the cathode, causing the battery to fail.

That problem has both dampened the use of lithium metal in commercial applications and encouraged researchers worldwide to solve it.

Lithium metal charges much faster and holds about 10 times more energy by volume than the lithium-ion electrodes found in just about every electronic device, including cellphones and electric cars.

“One of the ways to slow dendrites in lithium-ion batteries is to limit how fast they charge,” Tour said. “People don’t like that. They want to be able to charge their batteries quickly.”

The Rice team’s answer, detailed in Advanced Materials, is simple, inexpensive and highly effective at stopping dendrite growth, Tour said.

“What we’ve done turns out to be really easy,” he said. “You just coat a lithium metal foil with a multiwalled carbon nanotube film. The lithium dopes the nanotube film, which turns from black to red, and the film in turn diffuses the lithium ions.”

“Physical contact with lithium metal reduces the nanotube film, but balances it by adding lithium ions,” said Rice postdoctoral researcher Rodrigo Salvatierra, co-lead author of the paper with graduate student Gladys López-Silva. “The ions distribute themselves throughout the nanotube film.”

When the battery is in use, the film discharges stored ions and the underlying lithium anode refills it, maintaining the film’s ability to stop dendrite growth.

The tangled-nanotube film effectively quenched dendrites over 580 charge/discharge cycles of a test battery with a sulfurized-carbon cathode the lab developed in previous experiments. The researchers reported the full lithium metal cells retained 99.8 percent of their coulombic efficiency, the measure of how well electrons move within an electrochemical system.

Solar cells are a cost-effective, alternate source of energy. A subtype of these, organic solar cells make use of organic polymers inside the cell. Using these polymers makes the cells light-weight and increases their flexibility. Organic solar cells are produced by two different chemical methods: dry processing and wet processing, with the latter being a faster method. There are several parameters used to assess the efficiency of solar cells with absorption of light and transportation of charge being widely used.

A prevailing problem with the structure of organic cells is that molecules in the active organic layer responsible for light absorption and charge transport tend to face both towards the edges of cells, as well as towards the light absorbing substrate. Maximizing the number of molecules facing the substrate, however, is the key to maximising absorption and conductivity of the cell. Scientists have modified the dry processing method to achieve such an orientation, but it has not been possible with the wet method. The research team led by Tetsuya Taima at Kanazawa University, is the first to successfully do so.

The premise of their method is the introduction of a copper iodide (CuI) layer between the active molecules and the substrate. In their study, the researchers used a film of active molecules called DRCN5T and coated them onto either CuI/PEDOT: PSS (30 nm)/indium tin oxide (ITO) mixed substrates, or substrates without the CuI layer. The ratio of substrate facing to edge facing DRCN5T molecules was then compared between both. Subsequent high-resolution imaging revealed that the CuI containing cells had active molecules with a ten times higher substrate facing orientation, along with enhanced light absorption. The researchers attributed this altered orientation of the molecules to strong chemical interactions between the DRCN5T and CuI atoms. To further confirm this, DRCN5T molecules with bulky side chains that do not interact with CuI were used, and a higher substrate facing ratio was not seen.

This is the first study that effectively demonstrates a method of producing such efficient organic solar cells using the wet processing method. Besides saving time, the wet method also results in larger film areas. “This technique is expected to greatly contribute to the development of organic thin film solar cells fabricated by wet processing in the future”, conclude the authors. Their approach paves the way for producing high-performance solar cells faster.

Air Liquide Advanced Materials Inc. was joined by local officials and members of the community to inaugurate a new speciality chemical production facility in Upper Mount Bethel, Pennsylvania, on October 19, 2018.

This new facility marks an expansion of Air Liquide’s operations in the community, adding 105,000 sq. ft. of production space. Featuring multiple manufacturing suites and updated infrastructure, the new site offers next generation specialty chemical operations that complement our global manufacturing base. Air Liquide worked closely with the Governor of Pennsylvania’s Action Team to reinforce its commitment to the region and bring this project to fruition.

Commented Paul Burlingame, President & CEO, Air Liquide Advanced Materials Inc.: “Air Liquide Advanced Materials is experiencing strong global growth, and the inauguration of the second state-of-the-art Advanced Materials Center in Upper Mount Bethel, Pennsylvania further enhances our ability to serve customers with innovative products and technologies. This facility comes to life thanks to the men and women of ALAM focused on safety, quality, and our customers along with the strong support of the Commonwealth of Pennsylvania, Lehigh Valley Economic Development Corporation, and the local Upper Mount Bethel community.”

Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials together with their international colleagues have proved it possible to change the structural and conductive properties of nanotubes by stretching them. This can potentially expand nanotubes’ application into electronics and high-precision sensors such as microprocessors and high-precision detectors. The research article has been published in Ultramicroscopy.

Carbon nanotubes can be represented as a sheet of graphene rolled in a special way. There are different ways of «folding» it, which leads to the graphene edges interconnecting at different angles, forming either armchair, zigzag or chiral nanotubes (Pic.1).

Nanotubes are considered to be promising materials for use in electronics and sensors because they have high electrical conductivity, which would work well in things like microprocessors and high-precision detectors. However, when producing carbon nanotubes it is hard to control their conductivity. Nanotubes with metallic and semiconducting properties can grow into a single array while microprocessor-based electronics require semiconducting nanotubes that have the same characteristics.

Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials jointly with a research team from Japan, China and Australia, led by Professor Dmitri Golberg, have proposed a method that allows for the modification of the structure of ready-made nanotubes and thus changes their conductive properties.

«The basis of the nanotube – a folded layer of graphene – is a grid of regular hexagons, the vertices of which are carbon atoms. If one of the carbon bonds in the nanotube is rotated by 90° degrees, a pentagon and a heptagon are formed at this [junction] instead of a hexagon, and a so-called Stone-Wales defect is obtained in this case. Such a defect can occur in the structure under certain conditions. Back in the late 90s, it was predicted that the migration of this defect along the walls of a highly heated nanotube with the application of mechanical stress could lead to a change in its structure – a sequential change in the chirality of the nanotube, which leads to a change in its electronic properties. No experimental evidence for this hypothesis has previously been obtained, but our research paper has presented convincing proof of it», said Associate Professor Pavel Sorokin, Doctor of Physical & Mathematical Sciences and head of the «Theoretical Materials Science of Nanostructures» infrastructure project at the NUST MISIS Laboratory of Inorganic Nanomaterials.

Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials have conducted simulations of the experiment at the atomic level. At first, the nanotubes were lengthened to form the first structural defect consisting of two pentagons and two heptagons (a Stone-Wales defect, pic.2a), where the prolonged lengthening of the tube began to «spread» to the sides, rearranging other carbon bonds (pic.2b). It was at this stage that the structure of the nanotubes changed. With further stretching, more and more Stone-Wales defects began to form, eventually leading to a change in the nanotubes’ conductivity (Pic. 2).

«We were responsible for the theoretical modeling of the process on a supercomputer in the NUST MISIS Laboratory for Modeling and Development of New Materials for the experimental part of the work. We are glad that the simulation results [support] the experimental data», added Dmitry Kvashnin, co-author of the research work, Candidate of Physical & Mathematical Sciences and a researcher at the NUST MISIS Laboratory of Inorganic Nanomaterials.

The proposed technology is capable of helping in the transformation of «metallic» nanotubes’ structure for their further application in semiconductor electronics and sensors such as microprocessors and ultrasensitive detectors.

Exagan, an innovator of gallium nitride (GaN) semiconductor technology enabling smaller and more efficient electrical converters, has established Exagan Taiwan Ltd. with a new sales and applications center in Taiwan – the company’s first step in its global market deployment – to accelerate the development and use of fast, intelligent GaN power solutions in the region.

The facility in Taipei’s Nankang Software Park officially opened today during ceremonies attended by Exagan’s president and CEO Frédéric Dupont, COO Fabrice Letertre and Asia sales director Ralf Kilguss. Kilguss is heading up regional sales in Asia, leveraging his 20 years of experience in the semiconductor and power electronics markets.

“With this new application center, our company experts will be able to work closely with local customers on evaluating and designing GaN-based solutions while speeding the technology’s adoption in the rapidly growing charger and server sectors, which are being driven by a very dynamic Asian market,” Dupont said.

Since its creation in 2014, Exagan has developed multiple partnerships in Asia to support its product design, development and manufacturing, thus establishing a robust supply chain with proven solutions for the targeted markets.

Earlier this year, Exagan launched its safe, powerful G-FET™ power transistors and G-DRIVE™ intelligent and fast-switching solution featuring an integrated driver and transistor in a single package. These are designed for easy system implementation in applications including servers and USB chargers.

The number of devices with at least one USB type C port for the simultaneous transfer of electrical power, data and video is forecasted to grow to nearly five billion units by 2021, according to market research firm IHS Markit, while total server shipments are expected to expand at a CAGR of 14 percent over the period of 2018 to 2023, as forecasted by Digitimes Research.

Graphene Flagship researchers have shown in a paper published in Science Advanceshow heterostructures built from graphene and topological insulators have strong, proximity induced spin-orbit coupling which can form the basis of novel information processing technologies.

Scanning Electron Microscope micrograph of a fabricated device showing the graphene topological insulator heterostructure channel. Credit: Dmitrii Khokhriakov, Chalmers University of Technology

Spin-orbit coupling is at the heart of spintronics. Graphene’s spin-orbit coupling and high electron mobility make it appealing for long spin coherence length at room temperature. Graphene Flagship researchers from Chalmers University of Technology (Sweden), Catalan Institute of Nanoscience and Nanotechnology – ICN2 (Spain), Universitat Autònoma de Barcelona (Spain) and ICREA Institució Catalana de Recerca i Estudis Avançats (Spain) showed a strong tunability and suppression of the spin signal and spin lifetime in heterostructures formed by graphene and topological insulators. This can lead to new graphene spintronic applications, ranging from novel circuits to new non-volatile memories and information processing technologies.

“The advantage of using heterostructures built from two Dirac materials is that, graphene in proximity with topological insulators still supports spin transport, and concurrently acquires a strong spin-orbit coupling,” said Associate Professor Saroj Prasad Dash, from Chalmers University of Technology.

“We do not just want to transport spin we want to manipulate it,” said Professor Stephan Roche from ICN2 and deputy leader of the Graphene Flagship’s spintronics Work-Package, “the use of topological insulators is a new dimension for spintronics, they have a surface state similar to graphene and can combine to create new hybrid states and new spin features. By combining graphene in this way we can use the tuneable density of states to switch on/off – to conduct or not conduct spin. This opens an active spin device playground.”

The Graphene Flagship, from its very beginning, saw the potential of spintronics devices made from graphene and related materials. This paper shows how combining graphene with other materials to make heterostructures opens new possibilities and potential applications.

“This paper combines experiment and theory and this collaboration is one of the strengths of the Spintronics Work-Package within the Graphene Flagship,” said Roche.

“Topological insulators belong to a class of material that generate strong spin currents, of direct relevance for spintronic applications such as spin-orbit torque memories. As reported by this article, the further combination of topological insulators with two-dimensional materials like graphene is ideal for enabling the propagation of spin information with extremely low power over long distances, as well as for exploiting complementary functionalities, key to further design and fabricate spin-logic architectures,” said Kevin Garello from IMEC, Belgium who is leader of the Graphene Flagships Spintronics Work-Package.

Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its Management Panel added “This paper brings us closer to building useful spintronic devices. The innovation and technology roadmap of the graphene Flagship recognises the potential of graphene and related materials in this area. This work yet again places the Flagship at the forefront of this field, initiated with pioneering contributions of European researchers.”

Organic semiconductor materials have the potential to be used in innovative applications such as transparent and flexible devices, and their low cost makes their potential use particularly attractive. The properties of organic semiconductor materials can be tuned by controlling their structure at the molecular level through parts of the structure known as electron-accepting units. A group of researchers centered at Osaka University has specifically tailored an electron-accepting unit that was then successfully used in an organic semiconductor applied in solar cell device that showed high photovoltaic performance. Their findings were published in NPG Asia Materials.

Chemical structures and photovoltaic characteristics. Credit: Osaka University

“Electron-accepting units are important elements of organic semiconductors,” study corresponding author Yoshio Aso says. “Through the controlled addition of electronegative fluorine groups to a widely used electron-accepting material, we were able to show precise control of the energy levels within the resulting semiconductor. This ability to tune the band gap translates to selectivity over the injection and transport of holes and/or electrons within the material, which is important in potential applications.”

The fluorinated electron-acceptor unit was used to prepare a thin film solar cell that was compared with a cell based on a non-fluorinated analogue. The researchers found that the fluorinated material showed enhanced power conversion efficiency, up to 3.12%. The morphology of the fluorinated film was also found to be good, which supported the efficient charge generation and transport that is necessary for successful application.

“The more we are able to fine tune organic semiconductor behavior on the molecular level, the more possibilities there will be for demonstrating their macroscopic applications,” co-author Yutaka Ie says. “It is our hope that the band gap control and high photovoltaic performance we have demonstrated will lead to our material being applied in devices such as organic light-emitted diodes, field-effect transistors, and thin film solar cells.”

The straightforward demonstration of the link between high electronegativity, greater electron-accepting tendency, and enhanced semiconductor performance, highlights both the potential and versatility of organic semiconductors. Further elegant solutions such as this one could substantially broaden the range of ƒÎ-conjugated materials, and reinforce the case for organic electronics.

Researchers from Graduate School of Bio-Applications and Systems Engineering at Tokyo University of Agriculture and Technology (TUAT) have sped up the movement of electrons in organic semiconductor films by two to three orders of magnitude. The speedier electronics could lead to improved solar power and transistor use across the world, according to the scientists.

They published their results in the September issue of Macromolecular Chemistry and Physics, where the paper is featured on the cover.

Led by Kenji Ogino, a professor at Graduate School of Bio-Applications and Systems Engineering at TUAT, Japan, the team found that adding polystyrene, commonly known as Styrofoam in North America, could enhance the semiconducting polymer by allowing electrons to move from plane to plane quickly. The process, called hole mobility, is how electrons move through an electric field consisting of multiple layers. When a molecule is missing an electron, an electron from a different plane can jump or fall and take its place.

Through various imaging techniques, it’s fairly easy to follow the electron trail in the crystal-based structures. In many semiconducting polymers, however, the clean, defined lines of the crystalline skeleton intertwine with a much more difficult-to-define region. It’s actually called the amorphous domain.

“[Electrons] transport in both crystalline and amorphous domains. To improve the total electron mobility, it is necessary to control the nature of the amorphous domain,” Ogino said. “We found that hole mobility extraordinarily improved by the introduction of polystyrene block accompanied by the increase of the ratio of rigid amorphous domain.”

The researchers believe that the way the crystalline domain connects within itself occurs most effectively through the rigid amorphous domain. The addition of polystyrene introduced more amorphous domain, but contained by flexible chains of carbon and hydrogen atoms. Even though the chains are flexible, it provides rigidity, and some degree of control, to the amorphous domain.

Electrons moved two to three times quicker than normal.

“The introduction of a flexible chain in semicrystalline polymers is one of the promising strategies to improve the various functionalities of polymer films by altering the characteristics of the amorphous domain,” Ogino said. “We propose that the rigid amorphous domain plays an important role in the hole transporting process.”

Enhanced hole mobility is a critical factor in developing more efficient solar devices, according to Ogino. Next, Ogino and the researchers plan to examine how the enhanced hole mobility affected other parameters, such as the chemical composition and position of the structures within the polymer film.

Researchers at the universities in Linköping and Shenzhen have shown how an inorganic perovskite can be made into a cheap and efficient photodetector that transfers both text and music. “It’s a promising material for future rapid optical communication”, says Feng Gao, researcher at Linköping University.

The film in the new perovskite, which contains only inorganic elements (caesium, lead, iodine and bromine), has been tested in a system for optical communication, which confirmed its ability to transfer both text and images, rapidly and reliably. Credit: Thor Balkhed

“Perovskites of inorganic materials have a huge potential to influence the development of optical communication. These materials have rapid response times, are simple to manufacture, and are extremely stable.” So says Feng Gao, senior lecturer at LiU who, together with colleagues who include Chunxiong Bao, postdoc at LiU, and scientists at Shenzhen University, has published the results in the prestigious journal Advanced Materials.

All optical communication requires rapid and reliable photodetectors – materials that capture a light signal and convert it into an electrical signal. Current optical communication systems use photodetectors made from materials such as silicon and indium gallium arsenide. But these are expensive, partly because they are complicated to manufacture. Moreover, these materials cannot to be used in some new devices, such as mechanically flexible, light-weight or large-area devices.

Researcher have been seeking cheap replacement, or at least supplementary, materials for many years, and have looked at, for example, organic semi-conductors. However, the charge transport of these has proved to be too slow. A photodetector must be rapid.

The new perovskite materials have been extremely interesting in research since 2009, but the focus has been on their use in solar cells and efficient light-emitting diodes. Feng Gao, researcher in Biomolecular and Organic Electronics at LiU, was awarded a Starting Grant of EUR 1.5 million from the European Research Council (ERC) in the autumn of 2016, intended for research into using perovskites in light-emitting diodes.

Perovskites form a completely new family of semi-conducting materials that are defined by their crystal structures. They can consist of both organic and inorganic substances. They have good light-emitting properties and are easy to manufacture. For applications such as light-emitting diodes and efficient solar cells, most interest has been placed on perovskites that consist of an organic substance (containing carbon and hydrogen), metal, and halogen (fluorine, chlorine, bromine or iodine) ions. However, when this composition was used in photodetectors, it proved to be too unstable.

The results changed, however, when Chunxiong Bao used the right materials, and managed to optimise the manufacturing process and the structure of the film. The film in the new perovskite, which contains only inorganic elements (caesium, lead, iodine and bromine), has been tested in a system for optical communication, which confirmed its ability to transfer both text and images, rapidly and reliably. The quality didn’t deteriorate, even after 2,000 hours at room temperature.

“It’s very gratifying that we have already achieved results that are very close to application,” says Feng Gao, who leads the research, together with Professor Wenjing Zhang at Shenzhen University.

When chemists from the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw were starting work on yet another material designed for the efficient production of nanocrystalline zinc oxide, they didn’t expect any surprises. They were greatly astonished when the electrical properties of the changing material turned out to be extremely exotic.

The exotic transformations causes that one of the precursors of zinc oxide, initially an insulator, at approx. 300 degrees Celsius goes to a state with electrical properties typical of metals, and at ~400 degrees Celsius it becomes a semiconductor. Credit: IPC PAS

The single source precursor (SSP) approach is widely regarded as one of the most promising of the various strategies employed for the preparation of semiconductor nanocrystalline materials. However, one of the key obstacles hampering both the rational design of SSPs and their controlled transformation to the desired nanomaterials with highly controlled physicochemical properties is the scarcity of mechanistic insights during the transformation process. Scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Faculty of Chemistry of Warsaw University of Technology (WUT) have revealed that in the thermal decomposition process of a pre-organized zinc alkoxide precursor the nucleation and growth of the semiconducting zinc oxide (ZnO) phase is preceded by cascade transformations involving the formation of previously unreported intermediate radical zinc oxo-alkoxide clusters with gapless electronic states. Up to now, these types of clusters have not been considered either as intermediate structures on the path to the semiconductor ZnO phase or as a potential species accounting for the various defect states of ZnO nanocrystals.

“We discovered that one of the groups of ZnO precursors that have been studied for decades, zinc alkoxide compounds, undergo previously unobserved physicochemical transformations upon thermal decomposition. Originally, the starting compound is an insulator, when heated it rapidly transforms into a material with conductor-like properties, and a further increase in temperature equally rapidly leads to its conversion into a semiconductor,” says Dr. Kamil Soko?owski (IPC PAS).

The design and preparation of well-defined nanomaterials in a controlled manner remains a tremendous challenge and is acknowledged to be the biggest obstacle for the exploitation of many nanoscale phenomena. Professor Lewiski’s (IPC PAS, PW) group has for many years been engaged in the development of effective methods of producing nanocrystalline forms of zinc oxide, a semiconductor with wide applications in electronics, industrial catalysis, photovoltaics and photocatalysis. One of the studied approaches is based on the single source precursors. The precursor molecules contain all components of the target material in their structure and only temperature is required to trigger the chemical transformation.

“We dealt with a group of chemical compounds with the general formula RZnOR, as single source pre-designed ZnO precursors. A common feature of their structure is the presence of the cubic [Zn4O4] core with alternating zinc and oxygen atoms terminated by organic groups R. When the precursor is heated, the organic parts are degraded, and the inorganic cores self-assemble, forming the final form of the nanomaterial,” explains Dr. Soko?owski.

The tested precursor had the properties of an insulator, with an energy gap of about five electronvolts. When heated, it eventually transformed into a semiconductor with an energy gap of approximately 3 eV.

“An exceptional result of our research was the discovery that at a temperature close to 300 degrees Celsius the compound suddenly transforms into almost gap-less electronic state, showing electrical properties rather more typical of metals. When the temperature rises to approximately 400 degrees, the energy gap suddenly expands to a width characteristic of semiconductor materials. Ultimately, thanks to the combination of advanced synchrotron experiments with quantum-chemical calculations, we have established all the details of these unique transformations,” says Dr. Adam Kubas (IPC PAS), who carried out the quantum-chemical calculations.

The spectroscopic measurements were carried out using methods developed by Dr. Jakub Szlachetko (Institute of Nuclear Physics PAS, Cracow) and Dr. Jacinto Sa (IPC PAS and Uppsala University) at the Swiss Light Source synchrotron facility at the Paul Scherrer Institute in Villigen, Switzerland. The material was heated in a reaction chamber, and then its electron structure was sampled using an X-ray synchrotron beam. The set-up allowed for real-time monitoring of the transformations taking place.

This detailed in situ study of the decomposition process of the zinc alkoxide precursor, supported by computer simulations, revealed that any nucleation or growth of a semiconducting ZnO phase is preceded by cascade transformations involving the formation of previously unreported intermediate radical zinc oxo-alkoxide clusters with gapless electronic states.

“In this process homolytic cleavage of the R-Zn bond is responsible for the initial thermal decomposition process. Computer simulations revealed that the intermediate radical clusters tend to dimerise though an uncommon bimetallic Zn-Zn-bond formation. The following homolytic O-R bond cleavage then leads to sub-nano ZnO clusters which further self-organise to the ZnO nanocrystalline phase,” says Dr. Kubas.

Up to now, the radical zinc oxo clusters formed have not been considered either as intermediate structures on the way to the semiconductor ZnO phase or as potential species accounting for various defect states of ZnO nanocrystals. In a broader context, a deeper understanding of the origin and character of the defects is crucial for structure-property relationships in semiconducting materials.

The research, funded by the National Science Centre and the TEAM grant of the Foundation for Polish Science co-financed by the European Union, will contribute to the development of more precise methods of controlling the properties of nanocrystalline zinc oxide. So far, with greater or lesser success, these properties have been explained with the help of various types of material defects. For obvious reasons, however, the analyses have not taken into account the possibility of forming the specific radical zinc-oxo clusters discovered by the Warsaw-based scientists in the material.