Iridium ‘loses its identity’ whe…

Iridium ‘loses its identity’ when interfaced with nickel

Hey, physicists and materials scientists: You’d better reevaluate your work if you study iridium-based materials—members of the platinum family—when they are ultra-thin.

Iridium “loses its identity” and its electrons act oddly in an ultra-thin film when interfaced with nickel-based layers, which have an unexpectedly strong impact on iridium ions, according to Rutgers University-New Brunswick physicist Jak Chakhalian, senior author of a Rutgers-led study in the journal Proceedings of the National Academy of Sciences.

The scientists also discovered a new kind of magnetic state when they created super-thin artificial superstructures containing iridium and nickel, and their findings could lead to greater manipulation of quantum materials and deeper understanding of the quantum state for novel electronics.

“It seems nature has several new tricks that will force scientists to reevaluate theories on these special quantum materials because of our work,” said Chakhalian, Professor Claud Lovelace Endowed Chair in Experimental Physics in the Department of Physics and Astronomy in the School of Arts and Sciences. “Physics by analogy doesn’t work. Our findings call for the careful evaluation and reinterpretation of experiments on ‘spin-orbit physics’ and magnetism when the interfaces or surfaces of materials with platinum group atoms are involved.”

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Nylon as a building block for transparent el…

Nylon as a building block for transparent electronic devices?

Scientists at the Max Planck Institute for Polymer Research (MPI-P) led by Dr. Kamal Asadi have solved a four-decade-long challenge of producing very thin nylon films that can be used in electronic memory components, for instance. The thin nylon films are several hundred times thinner than a human hair, and could thus be attractive for applications in bendable electronic devices or for electronics in clothing.

As the microelectronics industry shifts toward wearable electronics and e-textiles, researchers are integrating electronic materials such as ferroelectrics with textiles. Nylons, a family of synthetic polymers, were first introduced in the 1920s for women’s stockings, and are today among the most widely used synthetic fibers in textiles. They consist of a long chain of repeated molecular units, i.e. polymers, in which each repeat unit contains a specific arrangement of hydrogen, oxygen and nitrogen with carbon atoms.

Nylons also exhibit so called “ferroelectric properties.” This means that positive and negative electric charges can be separated, and this state can be maintained. Ferroelectric materials are used in sensors, actuators, memory and energy-harvesting devices. The advantage in using polymers is that they can be liquified using adequate solvents and therefore processed from solution at low cost to form flexible thin films which are suitable for electronic devices such as capacitors, transistors and diodes. This makes ferroelectric polymers a viable choice for integration with e-textiles. Although nylon polymers have significant commercial applications in fabrics and fibers, their application in electronic devices has been hindered because it was impossible to create high-quality thin films of ferroelectric nylons by solution processing.

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New retroreflective material could be used i…

New retroreflective material could be used in nighttime color-changing road signs

A thin film that reflects light in intriguing ways could be used to make road signs that shine brightly and change color at night, according to a study that will be published on Aug. 9 in Science Advances.

The technology could help call attention to important traffic information when it’s dark, with potential benefits for both drivers and pedestrians, researchers say.

The film consists of polymer microspheres laid down on the sticky side of a transparent tape. The material’s physical structure leads to an interesting phenomenon: When white light shines on the film at night, some observers will see a single, stable color reflected back, while others will see changing colors. It all depends on the angle of observation and whether the light source is moving.

The research was led by Limin Wu, Ph.D., at Fudan University in China, whose group developed the material. Experts on optics at the University at Buffalo made significant contributions to the work, providing insight into potential applications for the film, such as employing it in nighttime road signs.

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Ultra-thin layers of rust generate electricity from flowing water

There are many ways to generate electricity – batteries, solar panels, wind turbines, and hydroelectric dams, to name a few examples. …. And now there’s rust.

New research conducted by scientists at Caltech and Northwestern University shows that thin films of rust – iron oxide – can generate electricity when saltwater flows over them. These films represent an entirely new way of generating electricity and could be used to develop new forms of sustainable power production.

Interactions between metal compounds and saltwater often generate electricity, but this is usually the result of a chemical reaction in which one or more compounds are converted to new compounds. Reactions like these are what is at work inside batteries.

In contrast, the phenomenon discovered by Tom Miller, Caltech professor of chemistry, and Franz Geiger, Dow Professor of Chemistry at Northwestern, does not involve chemical reactions, but rather converts the kinetic energy of flowing saltwater into electricity.

The phenomenon, the electrokinetic effect, has been observed before in thin films of graphene – sheets of carbon atoms arranged in a hexagonal lattice – and it is remarkably efficient. The effect is around 30 percent efficient at converting kinetic energy into electricity. For reference, the best solar panels are only about 20 percent efficient.

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Tuning the energy levels of organic semicond…

Tuning the energy levels of organic semiconductors

Physicists from the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and the Center for Advancing Electronics Dresden (cfaed) at the TU Dresden, together with researchers from Tübingen, Potsdam and Mainz were able to demonstrate how electronic energies in organic semiconductor films can be tuned by electrostatic forces. A diverse set of experiments supported by simulations were able to rationalize the effect of specific electrostatic forces exerted by the molecular building blocks on charge carriers. The study was published recently in Nature Communications.

In electronic devices based on organic semiconductors such as solar cells, light-emitting diodes, photodetectors or transistors, electronic excitations and charge transport levels are important concepts to describe their operation principles and performances. The corresponding energetics, however, are more difficult to access and to tune than in conventional inorganic semiconductors like silicon chips, which stands as a general challenge. This applies both to the measurement and to the controlled influence from outside.

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Creating ‘movies’ of thin film g…

Creating ‘movies’ of thin film growth

From paint on a wall to tinted car windows, thin films make up a wide variety of materials found in ordinary life. But thin films are also used to build some of today’s most important technologies, such as computer chips and solar cells. Seeking to improve the performance of these technologies, scientists are studying the mechanisms that drive molecules to uniformly stack together in layers—a process called crystalline thin film growth. Now, a new research technique could help scientists understand this growth process better than ever before.

Researchers from the University of Vermont, Boston University, and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have demonstrated a new experimental capability for watching thin film growth in real-time. Using the National Synchrotron Light Source II (NSLS-II)—a DOE Office of Science User Facility at Brookhaven—the researchers were able to produce a “movie” of thin film growth that depicts the process more accurately than traditional techniques can. Their research was published on June 14, 2019 in Nature Communications.

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A new quasi-2D superconductor that bridges a…

A new quasi-2D superconductor that bridges a ferroelectric and an insulator

Researchers at the Zavoisky Physical-Technical Institute and the Southern Scientific Center of RAS, in Russia, have recently fabricated quasi-2-D superconductors at the interface between a ferroelectric Ba0.8Sr0.2TiO3 film and an insulating parent compound of La2CuO4. Their study, presented in a paper published in Physical Review Letters, is the first to achieve superconductivity in a heterostructure consisting of a ferroelectric and an insulator.

The idea of forming a quasi-2-D superconducting layer at the interfacebetween two different compounds has been around for several years. One past study, for instance, tried to achieve this by creating a thin superconducting layer between two insulating oxides (LaAlO3 and SrTiO3) with a critical temperature of 300mK. Other researchers observed the thin superconducting layer in bilayers of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation.

“Here we put forward the idea that thin charged layer on the interface between ferroelectric and insulator is formed in order to screen the electric field,” Viktor Kabanov and Rinat Mamin, two researchers who carried out the study, told via email. “This thin layer may be conducting or superconducting depending on the properties of the insulator. In order to get a superconducting layer, we chose La2CuO4 – an insulator that becomes a high Tc superconductor when it is doped by carriers.”

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Ice lithography: Opportunities and challenge…

Ice lithography: Opportunities and challenges in 3-D nanofabrication

Nanotechnology and nanoscience are enabled by nanofabrication. Electron-beam lithography (EBL), which makes patterns down to a few nanometers, is one of the fundamental pillars of nanofabrication. In the past decade, significant progress has been made in electron-beam-based nanofabrication, such as the emerging ice lithography (IL) technology, in which ice thin-films are used as resists and patterned by a focused electron-beam. The entire process of IL nanofabrication is sustainable and streamlined because spin coating and chemical developing steps commonly required for EBL resists are made needless.

A fresh review “Ice lithography for 3-D nanofabrication” by Prof. Min Qiu at Westlake University is published in Science Bulletin. In this review, the authors present current status and future perspectives of ice lithography (IL). Different ice resists and IL instrument design are also introduced. Special emphasis is placed on advantages of IL for 3-D nanofabrication.

The IL technology was first proposed by the Nanopore group at Harvard University in 2005. Water ice is the first identified ice resist for IL, and it is still the only one positive-tone lithography resist so far. As shown in Fig.1, water ice is easily removed within the electron-beam exposure area. Organic ice condensed from simple organic molecules, such as alkanes, demonstrates a negative-resist-like capability, which means only exposed patterns remain on the substrate after heating the sample to room temperature.

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Researchers find a way to produce free-stand…

Researchers find a way to produce free-standing films of perovskite oxides

A team of researchers from Nanjing University in China, the University of Nebraska and the University of California in the U.S. has found a way to produce free-standing films of perovskite oxide. In their paper published in the journal Nature, the group describes the process they developed and how well it worked when tested. Yorick Birkhölzer and Gertjan Koster from the University of Twente have published a News and Views piece on the work done by the team in the same journal issue.

Birkhölzer and Koster point out that many new materials are made by going to extremes—making them really big or really small. Making them small has led to many recent discoveries, they note, including a technique to make graphene. One area of research has focused on ways to produce transition-metal oxides in a thinner format. It has been slow going, however, due to their crystalline nature. Unlike some materials, transition-metal oxides do not naturally form into layers with a top layer that can be peeled off. Instead, they form in strongly bonded 3-D structures. Because of this, some in the field have worried that it might never be possible to produce them in desired forms. But now, the researchers with this new effort have found a way to produce two transition-metal oxides (perovskite oxides strontium titanate and bismuth ferrite) in a thin-film format.

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New Flatland material: Physicists obtain qua…

New Flatland material: Physicists obtain quasi-2D gold

Researchers from the MIPT Center for Photonics and 2-D Materials have synthesized a quasi-2-D gold film, revealing how materials not usually classified as two-dimensional can form atomically thin layers. Published in Advanced Materials Interfaces, the study shows that by using monolayer molybdenum disulfide as an adhesion layer, quasi-2-D gold can be deposited on an arbitrary surface. The team says the resulting ultrathin gold films, which are only several nanometers thick, conduct electricity very well and are useful for flexible and transparent electronics. The finding might contribute to a new class of optical metamaterials with the unique potential to control light.

The first 2-D material discovered, graphene is a one-atom-thick sheet of carbon atoms in a honeycomb formation. Its synthesis and the study of its exciting properties have given rise to an entirely new field of science and technology. The groundbreaking experiments regarding graphene earned MIPT graduates Andre Geim and Kostya Novoselov the 2010 Nobel Prize in physics.

Since then, more than 100 graphene cousins have been discovered. Their intriguing properties had applications in biomedicine, electronics and the aerospace industry. These materials belong to the class of layered crystals whose layers are weakly bound to one another but have strong internal integrity. For example, the graphite in a pencil is essentially many stacked-up layers of graphene bound so weakly that Geim and Novoselov famously used sticky tape to peel them off.

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