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Glass fibres do everything from connecting us to the internet to enabling keyhole surgery by delivering light through medical devices such as endoscopes. But as versatile as today’s fiber optics are, scientists around the world have been working to expand their capabilities by adding semiconductor core materials to the glass fibers.

Ursula Gibson, a professor of physics at the Norwegian University of Science and Technology, holds a glass fiber with a semiconductor core. Rapid heating and cooling of this kind of fiber allows the researchers to make functional materials with applications beyond traditional fiber optics. Credit: Nancy Bazilchuk

Ursula Gibson, a professor of physics at the Norwegian University of Science and Technology, holds a glass fiber with a semiconductor core. Rapid heating and cooling of this kind of fiber allows the researchers to make functional materials with applications beyond traditional fiber optics. Credit: Nancy Bazilchuk

Now, a team of researchers has created glass fibers with single-crystal silicon-germanium cores. The process used to make these could assist in the development of high-speed semiconductor devices and expand the capabilities of endoscopes says Ursula Gibson, a physics professor at the Norwegian University of Science and Technology and senior author of the paper.

“This paper lays the groundwork for future devices in several areas,” Gibson said, because the germanium in the silicon core allows researchers to locally alter its physical attributes.

The article, “Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres,” was published in Nature Communications on October 24.

Melting and recrystallizing

To understand what the researchers did, you need to recognize that silicon and germanium have different melting points. When the two substances are combined in a glass fiber, flecks of germanium-rich material are scattered throughout the fiber in a disorderly way because the silicon has a higher melting point and solidifies, or “freezes” first. These germanium flecks limit the fiber’s ability to transmit light or information. “When they are first made, these fibers don’t look very good,” Gibson said.

But rapidly heating the fiber by moving it through a laser beam allowed the researchers to melt the semiconductors in the core in a controlled fashion. Using the difference in the solidification behavior, the researchers were able to control the local concentration of the germanium inside the fiber depending upon where they focused the laser beam and for how long.

“If we take a fibre and melt the core without moving it, we can accumulate small germanium-rich droplets into a melt zone, which is then the last thing to crystalize when we remove the laser slowly,” Gibson said. “We can make stripes, dots… you could use this to make a series of structures that would allow you to detect and manipulate light.”

An interesting structure was produced when the researchers periodically interrupted the laser beam as it moved along their silicon-germanium fibre. This created a series of germanium-rich stripes across the width of the 150-micrometer diameter core. That kind of pattern creates something called a Bragg grating, which could help expand the capability of long wavelength light-guiding devices. “That is of interest to the medical imaging industry,” Gibson said.

Rapid heating, cooling key

Another key aspect of the geometry and laser heating of the silicon-germanium fibre is that once the fibre is heated, it can also be cooled very quickly as the fibre is carried away from the laser on a moving stage.

Controlled rapid cooling allows the mixture to solidify into a single uniform crystal the length of the fibre — which makes it ideal for optical transmission.

Previously, people working with bulk silicon-germanium alloys have had problems creating a uniform crystal that is a perfect mix, because they have not had sufficient control of the temperature profile of the sample.

“When you perform overall heating and cooling, you get uneven composition through the structure, because the last part to freeze concentrates excess germanium,” Gibson said. “We have shown we can create single crystalline silicon-germanium at high production rates when we have a large temperature gradient and a controlled growth direction.”

Transistors that switch faster

Gibson says the laser heating process could also be used to simplify the incorporation of silicon-germanium alloys into transistor circuits.

“You could adapt the laser treatment to thin films of the alloy in integrated circuits,” she said.

Traditionally, Gibson said, electronics researchers have looked at other materials, such as gallium arsenide, in their quest to build ever-faster transistors. However, the mix of silicon and germanium, often called SiGe, allows electrons to move through the material more quickly than they move through pure silicon, and is compatible with standard integrated circuit processing.

“SiGe allows you to make transistors that switch faster” than today’s silicon-based transistors, she said, “and our results could impact their production.”

Researchers at the Center for Multidimensional Carbon Materials (CMCM), within the Institute for Basic Science (IBS) have demonstrated graphene coating protects glass from corrosion. Their research, published in ACS Nano, can contribute to solving problems related to glass corrosion in several industries. Glass has a high degree of both corrosion and chemical resistance. For this reason it is the primary packaging material to preserve medicines and chemicals. However, over time at high humidity and pH, some glass types corrode. Corroded glass loses its transparency and its strength is reduced. As a result, the corrosion of silicate glass, the most common and oldest form of glass, by water is a serious problem especially for the pharmaceutical, environmental and optical industries, and in particular in hot and humid climates.

Although there are different types of glass, ordinary glazing and containers are made of silicon dioxide (SiO2), sodium oxide (Na2O) along with minor additives. Glass corrosion begins with the adsorption of water on the glass surface. Hydrogen ions from water then diffuse into the glass and exchange with the sodium ions present on the glass surface. The pH of the water near the glass surface increases, allowing the silicate structure to dissolve.

Scientists have been looking at how to coat glass to protect it from damage. An ideal protective coating should be thin, transparent, and provide a good diffusion barrier to chemical attack. Graphene with its chemical inertness, thinness, and high transparency makes it very promising as a coating material. Moreover, owing to its excellent chemical barrier properties it blocks helium atoms from penetrating through it. The use of graphene coating is being explored as a protective layer for other materials requiring resistance to corrosion, oxidation, friction, bacterial infection, electromagnetic radiation, etc.

IBS scientists grew graphene on copper using a technique previously invented by Prof. Rodney S. Ruoff and collaborators, and transferred either one or two atom-thick layers of graphene onto both sides of rectangular pieces of glass. The effectiveness of the graphene coating was evaluated by water immersion testing and observing the differences between uncoated and coated glass. After 120 days of immersion in water at 60°C, uncoated glass samples had significantly increased in surface roughness and defects, and reduced in fracture strength. In contrast, both the single and double layer graphene-coated glasses had essentially no change in both fracture strength and surface roughness.

“The purpose of the study was to determine whether graphene grown by chemical vapor deposition on copper foils, a now established method, could be transferred onto glass, and protect the glass from corrosion. Our study shows that even one atom-thick layer of graphene does the trick,” explains Prof. Ruoff, director of the CMCM and Professor at the Ulsan National Institute of Science and Technology (UNIST). “In the future, when it is possible to produce larger and yet higher-quality graphene sheets and to optimize the transfer on glass, it seems reasonably likely that graphene coating on glass will be used on an industrial scale.”

The Society for Information Display (SID) announced today the designation of a new award to honor the outstanding contributions of young researchers to the advancements of active matrix addressed information displays. The Peter Brody Prize will be awarded to a young researcher under age 40 who has made outstanding contributions in innovating the design and enhancing the performance of active matrix addressed information displays.

The award is named after the late professor Dr. Peter Brody, who was the pioneer of active matrix thin film transistors for information displays.

Dr. Brody demonstrated the world’s-first working CdSe TFT-EL and TFT-LCD panels in 1973 and 1974, respectively. He was the pioneer and great advocate for active matrix addressed information displays. He led a pilot line manufacturing TFT-EL panels at Westinghouse and commercial-scale manufacturing of TFT-LCD panels at Panelvision in 1980. He continued to develop low-cost TFT backplane technologies at Magnascreen and Advantech until the end of his life.

Dr. Brody was an SID Fellow and received the Karl Ferdinand Braun Prize from SID in 1987 for his outstanding technical achievement and contribution to information displays. He was also honored with the Rank Prize in optoelectronics (UK), the Eduard Rhein Prize (Germany), the IEEE Jun-Ichi Nishizawa Metal and thee NAE Charles Stark Draper Prize.

The Peter Brody Prize will recognize a young researcher, under the age of 40, for major contributions, which enhance the performance of active matrix addressed displays. It is the intention of the prize to recognize young researchers who have made ‘major-impact’ technical contributions to the developments of active matrix addressed displays in one or more of the following areas:

  • thin film transistor devices
  • active matrix addressing techniques
  • active matrix device manufacturing
  • active matrix display media
  • active matrix display-enabling components

Award recipients have to be less than 40 years of age at the time of nomination; and nominees are not required to be a member of SID.

Winners of the Peter Brody Prize will receive a $2,000 stipend, made possible through a generous grant of $40,000 from Dr. Fang-Chen Luo. Dr. Luo worked with Dr. Brody at Westinghouse R&D Center demonstrating the first working TFT-EL panel in 1973 and a TFT-LC panel in 1974. He is donating the money to honor Dr. Brody, who was his mentor, as well as to recognize young engineers for their innovative contributions to active matrix addressed information displays. The grant will be used to endow the award in perpetuity.

The award joins the lineup of prestigious honors bestowed by SID to outstanding innovators in the field of information displays, including the Karl Ferdinand Braun Prize for outstanding technical achievement in or contribution to display technology; the Jan Rajchman Prize for outstanding scientific or technical achievement in or contribution to research on flat-panel displays; the Otto Schade Prize for outstanding scientific or technical achievement in or contribution to the advancement of the functional performance and/or image quality of information displays; and, the Slottow-Owaki Prize for outstanding contributions to personnel training in the field of information display.

The deadline for nominations for the 2017 awards is Oct. 15, 2016. For more information on any of the SID Honors and Awards, including how to submit nominations, please visit www.sid.org and click “Awards.”

Nanoelectronics research center imec announces that Kris Myny, one of its young scientists, has been awarded an ERC Starting Grant. The grant of 1.5 million euros is earmarked to open up new research horizons in the field of thin-film transistor technology. This will allow a leap forward compared to current state-of-the-art and enable breakthrough applications in e.g. healthcare and the Internet-of-Things (IoT). ERC Starting Grants are awarded by the European Research Council to support excellent researchers at the stage at which they are starting their own independent research team after a stringent selection procedure; they are among the most prestigious of European research grants.

With his research, Kris Myny wants to realize a breakthrough in thin-film transistor technology, a technology used to create the large-area, flexible circuits that e.g. drive today’s flat-panel displays.

Specifically, he wants to introduce design innovations of unipolar n-type transistor circuits based on amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) as semiconductor. These are currently acknowledged as the most promising transistors for next-generation curved, flexible, or even rollable electronic applications.

Kris Myny said, “My goal is to use these transistors to introduce a new logic family for building digital circuits that will drastically decrease the power consumption compared to current flexible circuits. And this of course without compromising the speed of the electronics. At the same time, we will also make the transistors smaller, in a way that is compatible with large-area manufacturing. In addition, I will also look at new techniques to design ultralow-power systems in the new logic style. These will allow building next-generation large-area flexible applications such as displays, IoT sensors, or wearable healthcare sensor patches.”

In a recent press release, the European Commission announced that in 2017 it would invest a record 1.8 billion in its ERC grant scheme. A sizable part of the budget is earmarked for Starting Grants, reserved for young scientists with two to seven years of post-PhD experience. Jo De Boeck, imec’s CTO says “We congratulate Kris Myny for all his valuable research culminating in this grant. Imec goes to great lengths to select and foster our young scientists and provide them with a world-class infrastructure. These ERC Starting Grants show that their work indeed meets the highest standards, comparable to any in Europe.”

Lomonosov MSU physicists found a way to “force” silicon nanoparticles to glow in response to radiation strongly enough to replace expensive semiconductors used in display business. According to Maxim Shcherbakov, researcher at the Department of Quantum Electronics of the Moscow State University and one of the authors of the study, the developed method considerably enhances the efficiency of nanoparticle photoluminescence.

The key term in the problem is photoluminescence — the process, when materials irradiated by visible or ultraviolet radiation start to respond with their own light, but in a different spectral range. In the study, the material glows red.

In some of the modern displays, semiconductor nanoparticles, or the so-called quantum dots, are used. In quantum dots, electrons behave completely unlike those in the bulk semiconductor, and it has long been known that quantum dots possess excellent luminescent properties. Today, for the purposes of quantum-dot based displays various semiconductors are used, i.e. CdSe, etc. These materials are toxic and expensive, and, therefore, researchers have long been scrutinizing the far cheaper and much more studied silicon. It is also suitable for such use in all respects except one — silicon nanoparticles vaguely respond to radiation, which is not appealing for optoelectronic industry.

Scientists all over the world were seeking to solve this problem since the beginning of the 1990’s, but until now no significant success has been achieved in this direction. The breakthrough idea about how to “tame” silicon originated in Sweden, at the Royal Institute of Technology, Kista. A post-doctoral researcher Sergey Dyakov (a graduate of the MSU Faculty of Physics and the first author of the paper) suggested placing an array of silicon nanoparticles in a matrix with a non-homogeneous dielectric medium and cover it with golden nanostripes.

‘The heterogeneity of the environment, as has been previously shown in other experiments, allows to increase the photoluminescence of silicon by several orders of magnitude due to the so-called quantum confinement,’ says Maxim Shcherbakov. ‘However, the efficiency of the light interaction with nanocrystals still remains insufficient. It has been proposed to enhance the efficiency by using plasmons (quasiparticle appearing from fluctuations of the electron gas in metals — ed). Plasmon lattice formed by golden nanostripes allow to “hold” light on the nanoscale, and allow a more effective interaction with nanoparticles located nearby, bringing its luminescence to an increase.’

The MSU experiments with samples of “gold-plated” matrix with silicon nanoparticles made in Sweden brilliantly confirmed the theoretical predictions – the UV irradiated silicon for the first time shone bright enough to be used it in practice.

The first author of the paper Sergey Dyakov will present the findings on The 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (September 17-22, Crete). The work was also published in the Physical Review B (“Optical properties of silicon nanocrystals covered by periodic array of gold nanowires”).

Super cement’s secret


August 30, 2016

Simple cements are everywhere in construction, but researchers want to create novel construction materials to build smarter infrastructure. The cement known as mayenite is one smart material — it can be turned from an insulator to a transparent conductor and back. Other unique properties of this material make it suitable for industrial production of chemicals such as ammonia and for use as semiconductors in flat panel displays.

The secret behind mayenite’s magic is a tiny change in its chemical composition, but researchers hadn’t been sure why the change had such a big effect on the material, also known as C12A7. In new work, researchers show how C12A7 components called electron anions help to transform crystalline C12A7 into semiconducting glass.

The study, published Aug. 24 in Proceedings of the National Academy of Sciences, uses computer modeling that zooms in at the electron level along with lab experiments. They showed how the small change in composition results in dramatic changes of the glass properties and, potentially, allows for greater control of the glass formation process.

“We want to get rid of the indium and gallium currently used in most flat panel displays,” said materials scientist Peter Sushko of the Department of Energy’s Pacific Northwest National Laboratory. “This research is leading us toward replacing them with abundant non-toxic elements such as calcium and aluminum.”

Breaking the glass ceiling

More than a decade ago, materials scientist Hideo Hosono at the Tokyo Institute of Technology and colleagues plucked an oxygen atom from a crystal of C12A7 oxide, which turned the transparent insulating material into a transparent conductor. This switch is rare because the conducting material is transparent: Most conductors are not transparent (think metals) and most transparent materials are not conductive (think window glass).

Back in the crystal, C12A7 oxide’s departing oxygen leaves behind a couple electrons and creates a material known as an electride. This electride is remarkably stable in air, water, and ambient temperatures. Most electrides fall apart in these conditions. Because of this stability, materials scientists want to harness the structure and properties of C12A7 electride. Unfortunately, its crystalline nature is not suitable for large-scale industrial processes, so they needed to make a glass equivalent of C12A7 electride.

And several years ago, they did. Hosono and colleagues converted crystalline C12A7 electride into glass. The glass shares many properties of the crystalline electride, including the remarkable stability.

Crystals are neat and tidy, like apples and oranges arranged orderly in a box, but glasses are unordered and messy, like that same fruit in a plastic grocery bag. Researchers make glass by melting a crystal and cooling the liquid in such a way that the ordered crystal doesn’t reform. With C12A7, the electride forms a glass at a temperature about 200 degrees lower than the oxide does.

This temperature — when the atoms stop flowing as a liquid and freeze in place — is known as the glass transition temperature. Controlling the glass transition temperature allows researchers to control certain properties of the material. For example, how car tires wear down and perform in bad weather depends on the glass transition temperature of the rubber they’re made from.

Sushko, his PNNL colleague Lewis Johnson, Hosono and others at Tokyo Tech wanted to determine why the electride’s glass transition temperature was so much lower than the oxide’s. They suspected components of the electride known as electron anions were responsible. Electron anions are essentially freely moving electrons in place of the much-larger negatively charged oxygen atoms that urge the oxide to form a tidy crystal.

Moveable feat

The team simulated Hosono’s lab experiments using molecular dynamics software that could capture the movement of both the atoms and the electron anions in both the melted material and glass. The team found that that the negatively-charged electron anions paired up between positively charged aluminum or calcium atoms, replacing the negatively charged oxygen atoms that would typically be found between the metals.

The bonds that the electron anions formed between the metal atoms were weaker than bonds between metal and oxygen atoms. These weak links could also move rapidly through the material. This movement allowed a small number of electron anions to have a greater effect on the glass transition temperature than much larger quantities of minerals typically used as additives in glasses.

To rule out other factors as the impetus for the lower transition temperature — such as the electrical charge or change in oxygen atoms — the researchers simulated a material with the same composition as the C12A7 electride but with the electrons spread evenly through the material instead of packed in as electron anions. In this simulation, the glass transition temperature was no different than C12A7 oxide’s. This result confirmed that the network of weak links formed by the electron anions was responsible for changes to the glass transition temperature.

According to the scientists, electron anions form a new type of weak link that can affect the conditions under which a material can form a glass. They join the ranks of typical additives that disrupt the ability of the material to form long chains of atoms, such as fluoride, or form weak, randomly oriented bonds between atoms of opposite charge, such as sodium. The work suggests researchers might be able to control the transition temperature by changing the amount of electron anions they use.

“This work shows us not just how a glass forms,” said PNNL’s Johnson, “but also gives us a new tool for how to control it.”

A research team led by Professor Keon Jae Lee from the Korea Advanced Institute of Science and Technology (KAIST) and by Dr. Jae-Hyun Kim from the Korea Institute of Machinery and Materials (KIMM) has jointly developed a continuous roll-processing technology that transfers and packages flexible large-scale integrated circuits (LSI), the key element in constructing the computer’s brain such as CPU, on plastics to realize flexible electronics (Advanced Materials, “Simultaneous Roll Transfer and Interconnection of Flexible Silicon NAND Flash Memory”).

This schematic image shows the flexible silicon NAND flash memory produced by the simultaneous roll-transfer and interconnection process. (Image: KAIST)

This schematic image shows the flexible silicon NAND flash memory produced by the simultaneous roll-transfer and interconnection process. (Image: KAIST)

Professor Lee previously demonstrated the silicon-based flexible LSIs using 0.18 CMOS (complementary metal-oxide semiconductor) process in 2013 (ACS Nano, “In Vivo Silicon-based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers”) and presented the work in an invited talk of 2015 International Electron Device Meeting (IEDM), the world’s premier semiconductor forum.

Highly productive roll-processing is considered a core technology for accelerating the commercialization of wearable computers using flexible LSI. However, realizing it has been a difficult challenge not only from the roll-based manufacturing perspective but also for creating roll-based packaging for the interconnection of flexible LSI with flexible displays, batteries, and other peripheral devices.

To overcome these challenges, the research team started fabricating NAND flash memories on a silicon wafer using conventional semiconductor processes, and then removed a sacrificial wafer leaving a top hundreds-nanometer-thick circuit layer. Next, they simultaneously transferred and interconnected the ultrathin device on a flexible substrate through the continuous roll-packaging technology using anisotropic conductive film (ACF). The final silicon-based flexible NAND memory successfully demonstrated stable memory operations and interconnections even under severe bending conditions. This roll-based flexible LSI technology can be potentially utilized to produce flexible application processors (AP), high-density memories, and high-speed communication devices for mass manufacture.

Professor Lee said, “Highly productive roll-process was successfully applied to flexible LSIs to continuously transfer and interconnect them onto plastics. For example, we have confirmed the reliable operation of our flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. Out results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing.”

Dr. Kim added, “We employed the roll-to-plate ACF packaging, which showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. This can be a key process to the new era of flexible computers combining the already developed flexible displays and batteries.”

Imagine an electronic newspaper that you could roll up and spill your coffee on, even as it updated itself before your eyes.

It’s an example of the technological revolution that has been waiting to happen, except for one major problem that, until now, scientists have not been able to resolve.

Researchers at McMaster University have cleared that obstacle by developing a new way to purify carbon nanotubes – the smaller, nimbler semiconductors that are expected to replace silicon within computer chips and a wide array of electronics.

Artistic rendition of a metallic carbon nanotube being pulled into solution, in analogy to the work described by the Adronov group. Credit: Alex Adronov, McMaster University

Artistic rendition of a metallic carbon nanotube being pulled into solution, in analogy to the work described by the Adronov group. Credit: Alex Adronov, McMaster University

“Once we have a reliable source of pure nanotubes that are not very expensive, a lot can happen very quickly,” says Alex Adronov, a professor of Chemistry at McMaster whose research team has developed a new and potentially cost-efficient way to purify carbon nanotubes.

Carbon nanotubes – hair-like structures that are one billionth of a metre in diameter but thousands of times longer – are tiny, flexible conductive nano-scale materials, expected to revolutionize computers and electronics by replacing much larger silicon-based chips.

A major problem standing in the way of the new technology, however, has been untangling metallic and semiconducting carbon nanotubes, since both are created simultaneously in the process of producing the microscopic structures, which typically involves heating carbon-based gases to a point where mixed clusters of nanotubes form spontaneously as black soot.

Only pure semiconducting or metallic carbon nanotubes are effective in device applications, but efficiently isolating them has proven to be a challenging problem to overcome. Even when the nanotube soot is ground down, semiconducting and metallic nanotubes are knotted together within each grain of powder. Both components are valuable, but only when separated.

Researchers around the world have spent years trying to find effective and efficient ways to isolate carbon nanotubes and unleash their value.

While previous researchers had created polymers that could allow semiconducting carbon nanotubes to be dissolved and washed away, leaving metallic nanotubes behind, there was no such process for doing the opposite: dispersing the metallic nanotubes and leaving behind the semiconducting structures.

Now, Adronov’s research group has managed to reverse the electronic characteristics of a polymer known to disperse semiconducting nanotubes – while leaving the rest of the polymer’s structure intact. By so doing, they have reversed the process, leaving the semiconducting nanotubes behind while making it possible to disperse the metallic nanotubes.

The researchers worked closely with experts and equipment from McMaster’s Faculty of Engineering and the Canada Centre for Electron Microscopy, located on the university’s campus.

“There aren’t many places in the world where you can to this type of interdisciplinary work,” Adronov says.

The next step, he explains, is for his team or other researchers to exploit the discovery by finding a way to develop even more efficient polymers and scale up the process for commercial production.

Unique optical features of quantum dots make them an attractive tool for many applications, from cutting-edge displays to medical imaging. Physical, chemical or biological properties of quantum dots must, however, be adapted to the desired needs. Unfortunately, up to now quantum dots prepared by chemical methods could be functionalized using copper-based click reactions with retention of their luminescence. This obstacle can be ascribed to the fact that copper ions destroy the ability of quantum dots to emit light. Scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw and the Faculty of Chemistry of the Warsaw University of Technology (FC WUT) have shown, however, that zinc oxide (ZnO) quantum dots prepared by an original method developed by them, after modification by the click reaction with the participation of copper ions, fully retain their ability to emit light.

“Click reactions catalyzed by copper cations have long attracted the attention of chemists dealing with quantum dots. The experimental results, however, were disappointing: after modification, the luminescence was so poor that they were just not fit for use. We were the first to demonstrate that it is possible to produce quantum dots from organometallic precursors in a way they do not lose their valuable optical properties after being subjected to copper-catalysed click reactions,” says Prof. Janusz Lewinski (IPC PAS, FC WUT).

Quantum dots are crystalline structures with size of a few nanometers (billionth parts of a meter). As semiconductor materials, they exhibit a variety of interesting features typical of quantum objects, including absorbing and emitting radiation of only a strictly defined energy. Since atoms interact with light in a similar way, quantum dots are often called artificial atoms. In some respects, however, quantum dots offer more possibilities than atoms. Optical properties of each dot actually depend on its size and the type of material from which it is formed. This means that quantum dots may be precisely designed for specific applications.

To meet the need of specific applications, quantum dots have to be tailored in terms of physico-chemical properties. For this purpose, chemical molecules with suitable characteristics are attached to their surface. Due to the simplicity, efficacy, and speed of the process, an exceptionally convenient method is the click reaction. Unfortunately, one of the most widely used click reactions takes place with the participation of copper ions, which was reported to result in the almost complete quenching of the luminescence of the quantum dots.

“Failure is usually a result of the inadequate quality of quantum dots, which is determined by the synthesis method. Currently, ZnO dots are mainly produced by the sol-gel method from inorganic precursors. Quantum dots generated in this manner are coated with a heterogeneous and probably leaky protective shell, made of various sorts of chemical molecules. During a click reaction, the copper ions are in direct contact with the surface of quantum dots and quench the luminescence of the dot, which becomes completely useless,” explains Dr. Agnieszka Grala (IPC PAS), the first author of the article in the Chemical Communications journal.

For several years, Prof. Lewinski’s team has been developing alternative methods for the preparation of high quality ZnO quantum dots. The method presented in this paper affords the quantum dots derived from organozinc precursors. Composition of the nanoparticles can be programmed at the stage of precursors preparation, which makes it possible to precisely control the character of their organic-inorganic interface.

“Nanoparticles produced by our method are crystalline and all have almost the same size. They are spherical and have characteristics of typical quantum dots. Every nanoparticle is stabilized by an impermeable protective jacket, built of organic compounds, strongly anchored on the surface of the semiconductor core. As a result, our quantum dots remain stable for a long time and do not aggregate, that is clump together, in solutions,” describes Malgorzata Wolska-Pietkiewicz, a PhD student at FC WUT.

“The key to success is producing a uniform stabilizing shell. Such coatings are characteristic of the ZnO quantum dots obtained by our method. The organic layer behaves as a tight protective umbrella protecting dots from direct influence of the copper ions,” says Dr. Grala and clarifies: “We carried out click reaction known as alkyne-azide cycloaddition, in which we used a copper(l) compound as catalysts. After functionalization, our quantum dots shone as brightly as at the beginning.”

Quantum dots keep finding more and more applications in various industrial processes and as nanomarkers in, among others, biology and medicine, where they are combined with biologically active molecules. Nanoobjects functionalized in this manner are used to label both individual cells as well as whole tissues. The unique properties of quantum dots also enable long-term monitoring of the labelled item. Commonly used quantum dots, however, contain toxic heavy metals, including cadmium. In addition, they clump together in solutions, which supports the thesis of the lack of tightness of their shells. Meanwhile, the ZnO dots produced by Prof. Lewinski’s group are non-toxic, they do not aggregate, and can be bound to many chemical compounds – so they are much more suitable for medical diagnosis and for imaging cells and tissues.

Research on the methods of production of functionalized ZnO quantum dots was carried out under an OPUS grant from the Poland’s National Science Centre.

Soft electronic devices, such as a smartphone on your wrist and a folding screen in your pocket, are looking to much improve your lifestyle in the not-too-distant future. That is, if we could find ways to make electronic devices out of soft organic materials instead of the existing rigid inorganic materials.

Conducting polymers are a promising candidate that could be utilized for these next-generation applications because they are malleable, lightweight, and can conduct electricity, although their charge carrier mobility is intrinsically lower than that of inorganic materials. Various studies therefore have focused on how to boost the speed at which the charge carriers move in conducting polymers. Many researchers have attempted to enhance the charge carrier mobility by increasing polymers’ crystallinity, which is the degree of structural order. However, this approach is inherently restrictive in terms of mechanical properties. In other words, an increase in the crystallinity results in a decrease of the mechanical resilience, at least according to the conventional norm.

A team of researchers with the Dept. of Chemical Engineering at Pohang University of Science and Technology (POSTECH), consisting of Profs. Taiho Park and Chan Eon Park with their students Sung Yun Son and Yebyeol Kim, has found a way to solve this dilemma and developed a low crystalline conducting polymer that shows high-field effect mobility. Their findings were recently published as the cover article in the Journal of American Chemical Societyand highlighted in the Spotlights.

To improve charge transport in a low-crystalline conducting polymer, the researchers took a simple yet unconventional approach. They introduced monomers without side chains into the polymer and utilized unconventional localized aggregates as stepping-stones to expedite charge transport in the microstructure of the polymer. Park et al. found that the resulting increase in the backbone planarity and chain connectivity of the polymer gave rise to enhanced charge transport along and between the polymer chains.

Their findings provide not only a greater understanding of charge transport dynamics in low-crystalline conducting polymers but also a new strategy in molecular design that allows faster charge transport without the loss of mechanical advantages. Taiho Park and Chan Eon Park, the two corresponding authors of this research, anticipate that their study opens up numerous possibilities and will bring forth new research, solutions, and applications for soft electronics.