A device emerges from the fusion of IGZO and…

A device emerges from the fusion of IGZO and ferroelectric-HfO2

As a part of JST PRESTO program, Associate professor Masaharu Kobayashi, Institute of Industrial Science, the University of Tokyo, has developed a ferroelectric FET (FeFET) with ferroelectric-HfO2 and ultrathin IGZO channel. Nearly ideal subthreshold swing (SS) and mobility higher than poly-silicon channel have been demonstrated.

FeFET is a promising memory device because of its low-power, high-speed and high-capacity. After the discovery of CMOS-compatible ferroelectric-HfO2 material, FeFET has been attracting more attention. For even higher memory capacity, 3-D vertical stack structure has been proposed as shown in Fig. 1(a).

For 3-D vertical stack structure, poly-silicon is typically used as a channel material. However, poly-silicon has very low mobility in nanometer thickness region due to grain boundaries and extrinsic defects. Moreover, poly-silicon forms a low-k interfacial layer with ferroelectric-HfO2 gate insulator. This results in voltage loss and charge trapping which prevents low voltage operation and degrades reliability, respectively as shown in Fig. 1(b).

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High reaction rates even without precious me…

High reaction rates even without precious metals

Non-precious metal nanoparticles could one day replace expensive catalysts for hydrogen production. However, it is often difficult to determine what reaction rates they can achieve, especially when it comes to oxide particles. This is because the particles must be attached to the electrode using a binder and conductive additives, which distort the results. With the aid of electrochemical analyses of individual particles, researchers have now succeeded in determining the activity and substance conversion of nanocatalysts made from cobalt iron oxide—without any binders. The team led by Professor Kristina Tschulik from Ruhr-Universität Bochum reports together with colleagues from the University of Duisburg-Essen and from Dresden in the Journal of the American Chemical Society, published online on 30 May 2019.

“The development of non-precious metal catalysts plays a decisive role in realising the energy transition as only they are cheap and available in sufficient quantities to produce the required amounts of renewable fuels,” says Kristina Tschulik, a member of the Cluster of Excellence Ruhr Explores Solvation (Resolv). Hydrogen, a promising energy source, can thus be acquired by splitting water into hydrogen and oxygen. The limiting factor here has so far been the partial reaction in which oxygen is produced.

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Electron (or ‘hole’) pairs may s…

Electron (or ‘hole’) pairs may survive effort to kill superconductivity

Scientists seeking to understand the mechanism underlying superconductivity in “stripe-ordered” cuprates—copper-oxide materials with alternating areas of electric charge and magnetism—discovered an unusual metallic state when attempting to turn superconductivity off. They found that under the conditions of their experiment, even after the material loses its ability to carry electrical current with no energy loss, it retains some conductivity—and possibly the electron (or hole) pairs required for its superconducting superpower.

“This work provides circumstantial evidence that the stripe-ordered arrangement of charges and magnetism is good for forming the charge-carrier pairs required for superconductivity to emerge,” said John Tranquada, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory.

Tranquada and his co-authors from Brookhaven Lab and the National High Magnetic Field Laboratory at Florida State University, where some of the work was done, describe their findings in a paper just published in Science Advances. A related paper in the Proceedings of the National Academy of Sciences by co-author Alexei Tsvelik, a theorist at Brookhaven Lab, provides insight into the theoretical underpinnings for the observations.

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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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Chemists could make ‘smart glass&rsquo…

Chemists could make ‘smart glass’ smarter by manipulating it at the nanoscale

An alternative nanoscale design for eco-friendly smart glass

“Smart glass,” an energy-efficiency product found in newer windows of cars, buildings and airplanes, slowly changes between transparent and tinted at the flip of a switch.

“Slowly” is the operative word; typical smart glass takes several minutes to reach its darkened state, and many cycles between light and dark tend to degrade the tinting quality over time. Colorado State University chemists have devised a potentially major improvement to both the speed and durability of smart glass by providing a better understanding of how the glass works at the nanoscale.

They offer an alternative nanoscale design for smart glass in new research published June 3 in Proceedings of the National Academy of Sciences. The project started as a grant-writing exercise for graduate student and first author R. Colby Evans, whose idea – and passion for the chemistry of color-changing materials – turned into an experiment involving two types of microscopy and enlisting several collaborators. Evans is advised by Justin Sambur, assistant professor in the Department of Chemistry, who is the paper’s senior author.

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Rice U. lab grows stable, ultrathin magnets: R…

Rice U. lab grows stable, ultrathin magnets: Rare iron oxide could be combined with 2D materials for electronic, spintronic devices

Rice University researchers have simplified the synthesis of a unique, nearly two-dimensional form of iron oxide with strong magnetic properties that is easy to stack atop other 2D materials.

[…]

The material, epsilon iron(III) oxide, shows promise as a building block for exotic nanoscale structures that could be useful for spintronic devices, electronic or storage applications that take advantage of not only the charge of electrons but also their spin states.

Researchers at Rice’s Brown School of Engineering and Wiess School of Natural Sciences reported in the American Chemical Society journal Nano Letters that they had produced oxide flakes through simple chemical vapor deposition. The flakes are easily transferable from their growth substrates and retain their magnetic properties over the long term at room temperature.

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Rare copper oxide exhibits unusual magnetic …

Rare copper oxide exhibits unusual magnetic properties and spin-orbit interactions

The scientists of Ural Federal University conducted a study in which they found that one of the copper oxides with a structure of a rare mineral spinel—CuAl2O4—is a material with unusual magnetic properties and structure due to significant spin-orbit interactions.

The scientists described the process and the results of the research in the article published in Physical Review B, the world’s largest specialized journal on solid state physics.

Spin-orbit interaction is due to the electromagnetic interaction of the electron spin with the magnetic momentum caused by electron spinning around a nucleus. The phenomenon is essential to 4d and 5d systems, which are based on the elements of the fifth and sixth groups in Mendeleev’s periodic table—from yttrium to cadmium and from hafnium to mercury, respectively. CuAl2O4 is a 3d system, because copperbelongs to 3d elements (from scandium to zinc in the periodic table) for which spin-orbit interaction is usually not so crucial. However, it turns out that in the case of c CuAl2O4, it is pivotal. The spin-orbit interaction not only brings about the magnetic properties, but also determines the crystal structure of the material.

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Colorful solution to a chemical industry bot…

Colorful solution to a chemical industry bottleneck

The nanoscale water channels that nature has evolved to rapidly shuttle water molecules into and out of cells could inspire new materials to clean up chemical and pharmaceutical production. KAUST researchers have tailored the structure of graphene-oxide layers to mimic the hourglass shape of these biological channels, creating ultrathin membranes to rapidly separate chemical mixtures.

“In making pharmaceuticals and other chemicals, separating mixtures of organic molecules is an essential and tedious task,” says Shaofei Wang, postdoctoral researcher in Suzana Nuñes lab at KAUST. One option to make these chemical separations faster and more efficient is through selectively permeable membranes, which feature tailored nanoscale channels that separate molecules by size.

But these membranes typically suffer from a compromise known as the permeance-rejection tradeoff. This means narrow channels may effectively separate the different-sized molecules, but they also have an unacceptably low flow of solvent through the membrane, and vice versa—they flow fast enough, but perform poorly at separation.

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Copper oxide photocathodes: Laser experiment reveals location of efficiency loss

Copper oxide (Cu2O) is a very promising candidate for future solar energy conversion: as a photocathode, the copper oxide (a semiconductor) might be able to use sunlight to electrolytically split water and thus generate hydrogen, a fuel that can chemically store the energy of sunlight.

Copper oxide has a band gap of 2 electron volts, which matches up very well with the energy spectrum of sunlight. Perfect copper oxide crystals should theoretically be able to provide a voltage close to 1,5 volts when illuminated with light. The material would thus be perfect as the top-most absorber in a photoelectrochemical tandem cell for water splitting. A solar-to-hydrogen energy conversion efficiency of up to 18 per cent should be achievable. However, the actual values for the photovoltage lie considerably below that value, insufficient to make copper oxide an efficient photocathode in a tandem cell for water splitting. Up to now, loss processes near the surface or at boundary layers have been mainly held responsible for this.

A team at the HZB Institute for Solar Fuels has now taken a closer look at these processes. The group received high-quality Cu2O single crystals from colleagues at the California Institute of Technology (Caltech), then vapour-deposited an extremely thin, transparent layer of platinum on them. This platinum layer acts as a catalyst and increases the efficiency of water splitting. They examined these samples in the femtosecond laser laboratory (1 fs = 10-15 s) at the HZB to learn what processes lead to the loss of charge carriers and in particular whether these losses occur in the interior of the single crystals or at the interface with the platinum.

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