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Renewed investigation of a molecule that was originally synthesized with the goal of creating a unique light-absorbing pigment has led to the establishment of a novel design strategy for efficient light-emitting molecules with applications in next-generation displays and lighting.

Researchers at Kyushu University’s Center for Organic Photonics and Electronics Research (OPERA) demonstrated that a molecule that slightly changes its chemical structure before and after emission can achieve a high efficiency in organic light-emitting diodes (OLEDs).

In addition to producing vibrant colors, OLEDs can be fabricated into everything from tiny pixels to large and flexible panels, making them extremely attractive for displays and lighting.

In an OLED, electrical charges injected into thin films of organic molecules come together to form packets of energy – called excitons – that can produce light emission.

The goal is to convert all of the excitons to light, but three-fourths of the created excitons are triplets, which do not produce light in conventional materials, while the remaining one-fourth are singlets, which emit through a process called fluorescence.

Inclusion of a rare metal, such as iridium or platinum, in a molecule can enable rapid emission from the triplets through phosphorescence, which is currently the dominant technology for highly efficient OLEDs.

An alternative mechanism is the use of heat in the environment to give triplets an energetic boost that is sufficient to convert them into light-emitting singlets.

This process, known as thermally activated delayed fluorescence (TADF), easily occurs at room temperature in appropriately designed molecules and has the added advantage of avoiding the cost and reduced molecular design freedom associated with rare metals.

However, most TADF molecules still rely on the same basic design approach.

“Many new TADF molecules are being reported each month, but we keep seeing the same underlying design with electron-donating groups connected to electron-accepting groups,” says Masashi Mamada, lead researcher on the study reporting the new results.

“Finding fundamentally different molecular designs that also exhibit efficient TADF is a key to unlocking new properties, and in this case, we found one by looking at the past with a new perspective.”

Currently, combinations of donating and accepting units are primarily used because they provide a relatively simple way to push around the electrons in a molecule and obtain the conditions needed for TADF.

Although the method is effective and a huge variety of combinations is possible, new strategies are still desired in the quest to find perfect or unique emitters.

The mechanism explored by the researchers this time involves the reversible transfer of a hydrogen atom – technically, just its positive nucleus – from one atom in the emitting molecule to another in the same molecule to create an arrangement conducive to TADF.

This transfer occurs spontaneously when the molecule is excited with optical or electrical energy and is known as excited-state intramolecular proton transfer (ESIPT).

This ESIPT process is so important in the investigated molecules that quantum chemical calculations by the researchers indicate that TADF is not possible before transfer of the hydrogen.

After excitation, the hydrogen rapidly transfers to a different atom in the molecule, leading to a molecular structure capable of TADF.

The hydrogen transfers back to its initial atom after the molecule emits light, and the molecule is then ready to repeat the process.

Although TADF from an ESIPT molecule has been reported previously, this is the first demonstration of highly efficient TADF observed inside and outside of a device.

This vastly different design strategy opens the door for achieving TADF with a variety of new chemical structures that would not have been considered based on previous strategies.

Interestingly, the molecule the researchers used was most likely a disappointment when first synthesized nearly 20 years ago by chemists hoping to create a new pigment only to discover that the molecule is colorless.

“Organic molecules never cease to amaze me,” says Professor Chihaya Adachi, Director of OPERA. “Many paths with different advantages and disadvantages exist for achieving the same goal, and we have still only scratched the surface of what is possible.”

The advantages of this design strategy are just beginning to be explored, but one particularly promising area is related to stability.

Molecules similar to the investigated one are known to be highly resistant to degradation, so researchers hope that these kinds of molecules might help to improve the lifetime of OLEDs.

To see if this is the case, tests are now underway.

While only time will tell how far this particular strategy will go, the continually growing options for OLED emitters certainly bode well for their future.

Javier Vela, scientist at the U.S. Department of Energy’s Ames Laboratory, believes improvements in computer processors, TV displays and solar cells will come from scientific advancements in the synthesis of low-dimensional nanomaterials.

Ames Laboratory scientists are known for their expertise in the synthesis and manufacturing of materials of different types, according to Vela, who is also an Iowa State University associate professor of chemistry. In many instances, those new materials are made in bulk form, which means micrometers to centimeters in size. Vela’s group is working with tiny, nanometer, or one billionth of a meter sized, nanocrystals.

“We’re trying to find out what happens with materials when we go to lower particle sizes, will the materials be enhanced or negatively impacted, or will we find properties that weren’t expected,” Vela said. “Our goal is to broaden the science of low-dimensional nanomaterials.” In an invited paper published in Chemistry of Materials entitled, “Synthetic Development of Low Dimensional Materials”, Vela and coauthors Long Men, Miles White, Himashi Andaraarachchi, and Bryan Rosales discussed highlights of some of their most recent work on the synthesis of low dimensional materials.

One of those topics was advancements in the synthesis of germanium-based core-shell nanocrystals. Vela says industry is very interested in semiconducting nanocrystal-based technologies for applications such as solar cells.

Small particle size can affect many things from transport properties (how well a nanocrystal conducts heat and electricity) to optical properties (how strong it interacts with light, absorbs light and emits light). This is especially true in photovoltaic solar cells “Let’s say you’re using a semiconductor material to make a solar device, there’s often different performance when solar cells are made from bulk materials as opposed to when they are made with nanomaterials. Nanomaterials interact with light differently; they absorb it better. That’s one way you can manipulate devices and fine tune their performance or power conversion efficiency,” said Vela.

Beyond solar cells, Vela says there’s tremendous interest in using nanocrystals in quantum dot television and computer displays, optical devices like LEDs (light-emitting diodes), biological imaging, and telecommunications.

He says there are many challenges in this area because depending upon the quality of the nanocrystals used, you can see different emission properties, which can affect the purity of light. “Ultimately the size of the nanocrystals being used can make a huge difference in the cleanliness or crispness of colors in TV and computer displays,” said Vela. “Television and computer technology is a multibillion dollar business worldwide, so you can see the potential value our understanding of properties of nanocrystals could bring to these technologies.”

In the paper, Vela’s group also discussed advancements made in the study of synthesis and spectroscopic characterization of organolead halide perovskites, which Vela says are some of the most promising semiconductors for solar cells because of their low cost and easier processability. He adds photovoltaics made of these materials now reach power conversion efficiencies of greater than 22 percent. Vela’s research in this area has focused on mixed-halide perovskites. He says his group has discovered these materials exhibit interesting chemical and photo physical properties that people hadn’t realized before, and now they are trying to better understand the correlation between the structure and chemical composition of perovskites and how they behave in solar cells. “One of our goals is to use what we’ve learned to help lower the cost of solar cells and produce them more reliably and readily,” Vela said.

In addition, Vela’s group is studying how to replace lead in traditional organolead halide perovskites with something less toxic, like germanium. “In principle, this is an area that should be much better known, but it’s not,” said Vela. “When we’ve been able to substitute germanium for lead, we have been able to produce a lighter perovskite, which he says could positively impact the automotive industry, for example.

“This could have great implications for transportation applications where you don’t want a lot of lead because it’s so heavy,” said Vela. Going forward Vela says his group’s focus will be on advancing the science in low-dimensional materials.

“We’re not working with well-known materials, but the newest; the most recently discovered,” Vela said. “And every time we can advance the science we’re one step closer to opportunities for more commercialization, more production, more manufacturing and more jobs in the U.S.”

UPV/EHU-University of the Basque Country’s researchers have explored superelasticity properties on a nanometric scale based on shearing an alloy’s pillars down to nanometric size. In the article published by the prestigious scientific journal Nature Nanotechnology, the researchers have found that below one micron in diameter the material behaves differently and requires much higher stress for it to be deformed. This superelastic behaviour is opening up new channels in the application of microsystems involving flexible electronics and microsystems that can be implanted into the human body.

Superelasticity is a physical property by which it is possible to deform a material to a considerable extent, up to 10%, which is much higher than that of elasticity. So when stress is applied to a straight rod, the rod can form a U-shape and when the stress applied is removed, the rod fully regains its original shape. Although this has been amply proven in macroscopic materials, “until now no one had been able to explore these superelasticity properties in micrometric and nanometric sizes,” explained José María San Juan, lead researcher of the article published by Nature Nanotechnology and a UPV/EHU professor.

Researchers in the UPV/EHU’s Department of Condensed Matter Physics and Applied Physics II have managed to see that “the superelastic effect is maintained in really small devices in a copper-aluminium-nickel alloy”. It is an alloy with shape memory on which the research team has been working for over 20 years on a macroscopic level: Cu-14Al-4Ni, an alloy that displays superelasticity in ambient temperature.

Pillars were built using the Cu-Al-Ni alloy, each one with a diameter measuring about 500 nm (half a micrometre). Credit: José María San Juan / UPV/EHU

Pillars were built using the Cu-Al-Ni alloy, each one with a diameter measuring about 500 nm (half a micrometre). Credit: José María San Juan / UPV/EHU

By using a piece of equipment known as a Focused Ion Beam, “an ion cannon that acts as a kind of atomic knife that shears the material”, explained San Juan, they built micropillars and nanopillars of this alloy with diameters ranging between 2 μm and 260 nm –a micrometre is one millionth of a metre and a nanometre one thousand-millionth of a metre–. And to them they applied a stress using a sophisticated instrument known as a nanoindenter, which “allows extremely small forces to be applied,” and then they measured their behaviour.

The researchers have for the first time confirmed and quantified that in diameters of less than a micrometre there is a considerable change in the properties relating to the critical stress for superelasticity. “The material starts to behave differently and needs a much higher stress for this to take place. The alloy continues to display superelasticity but for much higher stresses”. San Juan highlights the novelty of this increase in critical stress linked to size, and also stresses that they have been able to explain the reason for this change in behaviour: “We have proposed an atomic model that allows one to understand why and how the atomic structure of these pillars changes when a stress is applied”.

Microsystems involving flexible electronics and devices that can be implanted in the human body

The UPV/EHU professor highlighted the importance of this discovery, “spectacular superelastic behaviour on a small scale”, which opens up new channels in the design of strategies for applying alloys with shape memory to develop flexible microsystems and electromechanical nanosystems. “Flexible electronics is very much present on today’s market, it is being increasingly used in garments, sports footwear, in various displays, etc.” He also affirmed that all this is of crucial importance in developing smart healthcare devices of the Lab-on-a-chip type that can be implanted into the human body. “It will be possible to build tiny micropumps or microactuators that can be implanted on a chip, and which will allow a substance to be released and regulated inside the human body for a range of medical treatments.”

It is a discovery that “is expected to have great scientific and technological repercussions and offer the potential to revolutionise various aspects in related fields,” concluded San Juan, and he welcomed the fact that “we have managed to transfer all the necessary knowledge and to acquire the working tools that the most advanced centres can avail themselves of to open up a new line of research which can be fully developed at the UPV/EHU”.

As electronics become increasingly pervasive in our lives – from smart phones to wearable sensors – so too does the ever rising amount of electronic waste they create. A United Nations Environment Program report found that almost 50 million tons of electronic waste were thrown out in 2017–more than 20 percent higher than waste in 2015.

Troubled by this mounting waste, Stanford engineer Zhenan Bao and her team are rethinking electronics. “In my group, we have been trying to mimic the function of human skin to think about how to develop future electronic devices,” Bao said. She described how skin is stretchable, self-healable and also biodegradable – an attractive list of characteristics for electronics. “We have achieved the first two [flexible and self-healing], so the biodegradability was something we wanted to tackle.”

The team created a flexible electronic device that can easily degrade just by adding a weak acid like vinegar. The results were published May 1 in the Proceedings of the National Academy of Sciences.

A newly developed flexible, biodegradable semiconductor developed by Stanford engineers shown on a human hair. Credit: Bao Lab

A newly developed flexible, biodegradable semiconductor developed by Stanford engineers shown on a human hair. Credit: Bao Lab

“This is the first example of a semiconductive polymer that can decompose,” said lead author Ting Lei, a postdoctoral fellow working with Bao.

In addition to the polymer – essentially a flexible, conductive plastic – the team developed a degradable electronic circuit and a new biodegradable substrate material for mounting the electrical components. This substrate supports the electrical components, flexing and molding to rough and smooth surfaces alike. When the electronic device is no longer needed, the whole thing can biodegrade into nontoxic components.

Biodegradable bits

Bao, a professor of chemical engineering and materials science and engineering, had previously created a stretchable electrode modeled on human skin. That material could bend and twist in a way that could allow it to interface with the skin or brain, but it couldn’t degrade. That limited its application for implantable devices and – important to Bao – contributed to waste.

Bao said that creating a robust material that is both a good electrical conductor and biodegradable was a challenge, considering traditional polymer chemistry. “We have been trying to think how we can achieve both great electronic property but also have the biodegradability,” Bao said.

Eventually, the team found that by tweaking the chemical structure of the flexible material it would break apart under mild stressors. “We came up with an idea of making these molecules using a special type of chemical linkage that can retain the ability for the electron to smoothly transport along the molecule,” Bao said. “But also this chemical bond is sensitive to weak acid – even weaker than pure vinegar.” The result was a material that could carry an electronic signal but break down without requiring extreme measures.

In addition to the biodegradable polymer, the team developed a new type of electrical component and a substrate material that attaches to the entire electronic component. Electronic components are usually made of gold. But for this device, the researchers crafted components from iron. Bao noted that iron is a very environmentally friendly product and is nontoxic to humans.

The researchers created the substrate, which carries the electronic circuit and the polymer, from cellulose. Cellulose is the same substance that makes up paper. But unlike paper, the team altered cellulose fibers so the “paper” is transparent and flexible, while still breaking down easily. The thin film substrate allows the electronics to be worn on the skin or even implanted inside the body.

From implants to plants

The combination of a biodegradable conductive polymer and substrate makes the electronic device useful in a plethora of settings – from wearable electronics to large-scale environmental surveys with sensor dusts.

“We envision these soft patches that are very thin and conformable to the skin that can measure blood pressure, glucose value, sweat content,” Bao said. A person could wear a specifically designed patch for a day or week, then download the data. According to Bao, this short-term use of disposable electronics seems a perfect fit for a degradable, flexible design.

And it’s not just for skin surveys: the biodegradable substrate, polymers and iron electrodes make the entire component compatible with insertion into the human body. The polymer breaks down to product concentrations much lower than the published acceptable levels found in drinking water. Although the polymer was found to be biocompatible, Bao said that more studies would need to be done before implants are a regular occurrence.

Biodegradable electronics have the potential to go far beyond collecting heart disease and glucose data. These components could be used in places where surveys cover large areas in remote locations. Lei described a research scenario where biodegradable electronics are dropped by airplane over a forest to survey the landscape. “It’s a very large area and very hard for people to spread the sensors,” he said. “Also, if you spread the sensors, it’s very hard to gather them back. You don’t want to contaminate the environment so we need something that can be decomposed.” Instead of plastic littering the forest floor, the sensors would biodegrade away.

As the number of electronics increase, biodegradability will become more important. Lei is excited by their advancements and wants to keep improving performance of biodegradable electronics. “We currently have computers and cell phones and we generate millions and billions of cell phones, and it’s hard to decompose,” he said. “We hope we can develop some materials that can be decomposed so there is less waste.”

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

Scanning Electron Microscope Images of architectured carbon nanotube (CNT) textile made at Illinois. Colored schematic shows the architecture of self-weaved CNTs, and the inset shows a high resolution SEM of the inter-diffusion of CNT among the different patches due to capillary splicing. Credit: University of Illinois

Scanning Electron Microscope Images of architectured carbon nanotube (CNT) textile made at Illinois. Colored schematic shows the architecture of self-weaved CNTs, and the inset shows a high resolution SEM of the inter-diffusion of CNT among the different patches due to capillary splicing. Credit: University of Illinois

“The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including biological and structural health monitoring sensors,” explained Sameh Tawfick, an assistant professor of mechanical science and engineering at Illinois. “Aligned carbon nanotube sheets are suitable for a wide range of application spanning the micro- to the macro-scales including Micro-Electro-Mechanical Systems (MEMS), supercapacitor electrodes, electrical cables, artificial muscles, and multi-functional composites.

“To our knowledge, this is the first study to apply the principles of fracture mechanics to design and study the toughness nano-architectured CNT textiles. The theoretical framework of fracture mechanics is shown to be very robust for a variety of linear and non-linear materials.”

Carbon nanotubes, which have been around since the early nineties, have been hailed as a “wonder material” for numerous nanotechnology applications, and rightly so. These tiny cylindrical structures made from wrapped graphene sheets have diameter of a few nanometers–about 1000 times thinner than a human hair, yet, a single carbon nanotube is stronger than steel and carbon fibers, more conductive than copper, and lighter than aluminum.

However, it has proven really difficult to construct materials, such as fabrics or films that demonstrate these properties on centimeter or meter scales. The challenge stems from the difficulty of assembling and weaving CNTs since they are so small, and their geometry is very hard to control.

“The study of the fracture energy of CNT textiles led us to design these extremely tough films,” stated Yue Liang, a former graduate student with the Kinetic Materials Research group and lead author of the paper, “Tough Nano-Architectured Conductive Textile Made by Capillary Splicing of Carbon Nanotubes,” appearing in Advanced Engineering Materials. To our knowledge, this is the first study of the fracture energy of CNT textiles.

Beginning with catalyst deposited on a silicon oxide substrate, vertically aligned carbon nanotubes were synthesized via chemical vapor deposition in the form of parallel lines of 5μm width, 10μm length, and 20-60μm heights.

“The staggered catalyst pattern is inspired by the brick and mortar design motif commonly seen in tough natural materials such as bone, nacre, the glass sea sponge, and bamboo,” Liang added. “Looking for ways to staple the CNTs together, we were inspired by the splicing process developed by ancient Egyptians 5,000 years ago to make linen textiles. We tried several mechanical approaches including micro-rolling and simple mechanical compression to simultaneously re-orient the nanotubes, then, finally, we used the self-driven capillary forces to staple the CNTs together.”

“This work combines careful synthesis, and delicate experimentation and modeling,” Tawfick said. “Flexible electronics are subject to repeated bending and stretching, which could cause their mechanical failure. This new CNT textile, with simple flexible encapsulation in an elastomer matrix, can be used in smart textiles, smart skins, and a variety of flexible electronics. Owing to their extremely high toughness, they represent an attractive material, which can replace thin metal films to enhance device reliability.”

In addition to Liang and Tawfick, co-authors include David Sias and Ping Ju Chen.

Physicists at the Institute for Quantum Information and Matter at Caltech have discovered the first three-dimensional quantum liquid crystal — a new state of matter that may have applications in ultrafast quantum computers of the future.

These images show light patterns generated by a rhenium-based crystal using a laser method called optical second-harmonic rotational anisotropy. At left, the pattern comes from the atomic lattice of the crystal. At right, the crystal has become a 3-D quantum liquid crystal, showing a drastic departure from the pattern due to the atomic lattice alone. Credit: Hsieh Lab/Caltech

These images show light patterns generated by a rhenium-based crystal using a laser method called optical second-harmonic rotational anisotropy. At left, the pattern comes from the atomic lattice of the crystal. At right, the crystal has become a 3-D quantum liquid crystal, showing a drastic departure from the pattern due to the atomic lattice alone. Credit: Hsieh Lab/Caltech

“We have detected the existence of a fundamentally new state of matter that can be regarded as a quantum analog of a liquid crystal,” says Caltech assistant professor of physics David Hsieh, principal investigator on a new study describing the findings in the April 21 issue of Science. “There are numerous classes of such quantum liquid crystals that can, in principle, exist; therefore, our finding is likely the tip of an iceberg.”

Liquid crystals fall somewhere in between a liquid and a solid: they are made up of molecules that flow around freely as if they were a liquid but are all oriented in the same direction, as in a solid. Liquid crystals can be found in nature, such as in biological cell membranes. Alternatively, they can be made artificially — such as those found in the liquid crystal displays commonly used in watches, smartphones, televisions, and other items that have display screens.

In a “quantum” liquid crystal, electrons behave like the molecules in classical liquid crystals. That is, the electrons move around freely yet have a preferred direction of flow. The first-ever quantum liquid crystal was discovered in 1999 by Caltech’s Jim Eisenstein, the Frank J. Roshek Professor of Physics and Applied Physics. Eisenstein’s quantum liquid crystal was two-dimensional, meaning that it was confined to a single plane inside the host material — an artificially grown gallium-arsenide-based metal. Such 2-D quantum liquid crystals have since been found in several more materials including high-temperature superconductors — materials that conduct electricity with zero resistance at around -150 degrees Celsius, which is warmer than operating temperatures for traditional superconductors.

John Harter, a postdoctoral scholar in the Hsieh lab and lead author of the new study, explains that 2-D quantum liquid crystals behave in strange ways. “Electrons living in this flatland collectively decide to flow preferentially along the x-axis rather than the y-axis even though there’s nothing to distinguish one direction from the other,” he says.

Now Harter, Hsieh, and their colleagues at Oak Ridge National Laboratory and the University of Tennessee have discovered the first 3-D quantum liquid crystal. Compared to a 2-D quantum liquid crystal, the 3-D version is even more bizarre. Here, the electrons not only make a distinction between the x, y, and z axes, but they also have different magnetic properties depending on whether they flow forward or backward on a given axis.

“Running an electrical current through these materials transforms them from nonmagnets into magnets, which is highly unusual,” says Hsieh. “What’s more, in every direction that you can flow current, the magnetic strength and magnetic orientation changes. Physicists say that the electrons ‘break the symmetry’ of the lattice.”

Harter actually hit upon the discovery serendipitously. He was originally interested in studying the atomic structure of a metal compound based on the element rhenium. In particular, he was trying to characterize the structure of the crystal’s atomic lattice using a technique called optical second-harmonic rotational anisotropy. In these experiments, laser light is fired at a material, and light with twice the frequency is reflected back out. The pattern of emitted light contains information about the symmetry of the crystal. The patterns measured from the rhenium-based metal were very strange–and could not be explained by the known atomic structure of the compound.

“At first, we didn’t know what was going on,” Harter says. The researchers then learned about the concept of 3-D quantum liquid crystals, developed by Liang Fu, a physics professor at MIT. “It explained the patterns perfectly. Everything suddenly made sense,” Harter says.

The researchers say that 3-D quantum liquid crystals could play a role in a field called spintronics, in which the direction that electrons spin may be exploited to create more efficient computer chips. The discovery could also help with some of the challenges of building a quantum computer, which seeks to take advantage of the quantum nature of particles to make even faster calculations, such as those needed to decrypt codes. One of the difficulties in building such a computer is that quantum properties are extremely fragile and can easily be destroyed through interactions with their surrounding environment. A technique called topological quantum computing–developed by Caltech’s Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics–can solve this problem with the help of a special kind of superconductor dubbed a topological superconductor.

“In the same way that 2-D quantum liquid crystals have been proposed to be a precursor to high-temperature superconductors, 3-D quantum liquid crystals could be the precursors to the topological superconductors we’ve been looking for,” says Hsieh.

“Rather than rely on serendipity to find topological superconductors, we may now have a route to rationally creating them using 3-D quantum liquid crystals” says Harter. “That is next on our agenda.”

Graphene Flagship researchers from AMBER at Trinity College Dublin have fabricated printed transistors consisting entirely of layered materials. Published today in the leading journal Science, the team’s findings have the potential to cheaply print a range of electronic devices from solar cells to LEDs with applications from interactive smart food and drug labels to next-generation banknote security and e-passports.

Led by Professor Jonathan Coleman from AMBER (the Science Foundation Ireland-funded materials science research centre hosted in Trinity College Dublin), in collaboration with the groups of Professor Georg Duesberg (AMBER) and Professor Laurens Siebbeles (TU Delft, Netherlands), the team used standard printing techniques to combine graphene flakes as the electrodes with other layered materials, tungsten diselenide and boron nitride as the channel and separator (two important parts of a transistor) to form an all-printed, all-layered materials, working transistor.

All of these are flakes are a few nanometres thick but hundreds of nanometres wide. Critically, it is the ability of flakes made from different layered materials to have electronic properties that can be conducting (in the case of graphene), insulating (boron nitride) or semiconducting (tungsten diselenide) that enable them to create the building blocks of electronics. While the performance of these printed layered devices cannot yet compare with advanced transistors, the team believe there is a wide scope to improve the performance of their printed TFTs beyond the current state-of-the-art.

Professor Coleman, who is an investigator in AMBER and Trinity’s School of Physics, said, “In the future, printed devices will be incorporated into even the most mundane objects such as labels, posters and packaging. Printed electronic circuitry will allow consumer products to gather, process, display and transmit information: for example, milk cartons will send messages to your phone warning that the milk is about to go out-of-date. We believe that layered materials can compete with the materials currently used for printed electronics.”

All of the layered materials were printed from inks created using the liquid exfoliation method previously developed by Professor Coleman and already licensed. Using liquid processing techniques to create the layered materials inks is especially advantageous in that it yields large quantities of high quality layered materials which helps to enable the potential to print circuitry at low cost.

An innovative new technique to produce the quickest, smallest, highest-capacity memories for flexible and transparent applications could pave the way for a future golden age of electronics.

Engineering experts from the University of Exeter have developed innovative new memory using a hybrid of graphene oxide and titanium oxide. Their devices are low cost and eco-friendly to produce, are also perfectly suited for use in flexible electronic devices such as ‘bendable’ mobile phone, computer and television screens, and even ‘intelligent’ clothing.

Crucially, these devices may also have the potential to offer a cheaper and more adaptable alternative to ‘flash memory’, which is currently used in many common devices such as memory cards, graphics cards and USB computer drives.

The research team insist that these innovative new devices have the potential to revolutionise not only how data is stored, but also take flexible electronics to a new age in terms of speed, efficiency and power.

The research is published in the leading scientific journal ACS Nano.

Professor David Wright, an Electronic Engineering expert from the University of Exeter and lead author of the paper said: “Using graphene oxide to produce memory devices has been reported before, but they were typically very large, slow, and aimed at the ‘cheap and cheerful’ end of the electronics goods market.

“Our hybrid graphene oxide-titanium oxide memory is, in contrast, just 50 nanometres long and 8 nanometres thick and can be written to and read from in less than five nanoseconds — with one nanometre being one billionth of a metre and one nanosecond a billionth of a second.”

Professor Craciun, a co-author of the work, added: “Being able to improve data storage is the backbone of tomorrow’s knowledge economy, as well as industry on a global scale. Our work offers the opportunity to completely transform graphene-oxide memory technology, and the potential and possibilities it offers.”

To realize the next generation of devices for information processing based on new phenomena such as spintronics, multiferroics, magnetooptics, and magnonics, their constituent materials need to be developed. Recent rapid progress in nanotechnology allows us to fabricate nanostructures that are impossible to obtain in nature.

However, complex magnetic oxides are one of the most complicated material systems in terms of development and analysis. In addition, the detailed mechanism is unknown by which changes in atomic composition that do not affect overall structure lead to drastic changes in material characteristics even though the material structure is similar.

Now, researchers at Spin Electronics Group at Toyohashi Tech and at Myongji University, Harbin Institute of Technology, Massachusetts Institute of Technology, Universidad Técnica Federico Santa María, University of California, San Diego, and Trinity College Dublin found that nanoscale pillar-shaped distribution of iron in strontium titanate (STF) changes its magnetic and magnetooptical response drastically. Surprisingly, the polycrystalline sample showed stronger magnetism than single crystalline film.

Image of nanopillar-like poly-crystalline STF film obtained by transmission electron microscopy. Credit: TOYOHASHI UNIVERSITY OF TECHNOLOGY.

Image of nanopillar-like poly-crystalline STF film obtained by transmission electron microscopy.
Credit: TOYOHASHI UNIVERSITY OF TECHNOLOGY.

“In usual oxide systems, magnetic and magnetooptical effects are stronger in highly ordered structures. In other words, single crystalline material is better for obtaining better magnetic properties,” explains Assistant Professor Taichi Goto, “However, iron-substituted strontium titanate deposited at certain oxygen pressure is different.”

The STF films were prepared by pulsed laser deposition at various pressures directly on silicon substrate, and crystalline structure and magnetic properties were characterized systematically. A sample deposited at a certain pressure showed significantly stronger magnetism and larger Faraday rotation angle (magnetooptical effects) at room temperature. Several tests analyzing the oxygen stoichiometry and the corresponding Fe valence states, the structure and strain state, and the presence of small-volume fractions of iron revealed that the nanostructure and clustering of the elements enhanced magnetism.

These results show the broad possibility of polycrystalline films being used in silicon-based devices. In this paper, the integration of STF film with 0.1 mm scale optical resonator was demonstrated. Further, the integration of such novel oxides with conventional device concepts would pave a way for interesting systems in the future.

Quantum dots are very small particles that exhibit luminescence and electronic properties different from those of their bulk materials. As a result, they are attractive for use in solar cells, optoelectronics, and quantum computing. Quantum computing involves applying a small voltage to quantum dots to regulate their electron spin state, thus encoding information. While traditional computing is based on a binary information system, electron spin states in quantum dots can display further degrees of freedom because of the possibility of superposition of both states at the same time. This feature could increase the density of encoded information.

Readout of the electron spin of quantum dots is necessary to realize quantum computing. Single-shot spin readout has been used to detect spin-dependent single-electron tunneling events in real time. The performance of quantum computing could be improved considerably by single-shot readout of multiple spin states.

A Japanese research collaboration based at Osaka University has now achieved the first successful detection of multiple spin states through single-shot readout of three two-electron spin states of a single quantum dot. They reported their findings in Physical Review Letters.

To read out multiple spin states simultaneously, the researchers used a quantum point contact charge sensor positioned near a gallium arsenide quantum dot. The change in current of the charge sensor depended on the spin state of the quantum dot and was used to distinguish between singlet and two types of triplet spin states.

“We obtained single-shot ternary readout of two-electron spin states using edge-state spin filtering and the orbital effect,” study first author Haruki Kiyama says.

That is, the rate of tunneling between the quantum dot and electron reservoir depended on both the spin state of the electrons and the interaction between electron spin and the orbitals of the quantum dot. The team identified one ground state and two excited states in the quantum dot using their setup.

The researchers then used their ternary readout setup to investigate the spin relaxation behavior of the three detected spin states.

“To confirm the validity of our readout system, we measured the spin relaxation of two of the states,” Kiyama explains. “Measurement of the dynamics between the spin states in a quantum dot is an important application of the ternary spin readout setup.”

The spin relaxation times for the quantum dot measured using the ternary readout system agreed with those reported, providing evidence that the system yielded reliable measurements.

This ternary readout system can be extended to quantum dots composed of other materials, revealing a new approach to examine the spin dynamics of quantum dots and representing an advance in quantum information processing.