click image to enlarge

Imaging Technique Reveals Strains and Defects in Vanadium Oxide

Non-destructive imaging uses synchrotron light

Researchers led by Edwin Fohtung, an associate professor of materials science and engineering at Rensselaer Polytechnic Institute, have developed a new technique for revealing defects in nanostructured vanadium oxide, a widely used transition metal with many potential applications including electrochemical anodes, optical applications, and supercapacitors. In the research — which was published in an article in the Royal Chemical Society journal,CrystEngComm, and also featured on the cover of the edition — the team detailed a lens-less microscopy technique to capture individual defects embedded in vanadium oxide nanoflakes.

“These observations could help explain the origin of defects in structure, crystallinity, or composition gradients observed near grain boundaries in other thin-film or flake technologies,” said Fohtung, an expert in novel synchrotron scattering and imaging techniques. “We believe that our work has the potential to change how we view the growth and non-destructive three-dimensional imaging of nanomaterials.”

Vanadium oxide is currently used in many technological fields such as energy storage, and can also be used in constructing field-effect transistors owing to metal insulating transition behavior that can be adjusted with an electric field. However, strain and defects in the material can alter its functionality, creating the need for non-destructive techniques to detect those potential flaws.

The team developed a technique based on coherent X-ray diffraction imaging. This technique relies on a type of circular particle accelerator known as a synchrotron. Synchrotrons work by accelerating electrons through sequences of magnets until they reach almost the speed of light. These fast-moving electrons produce very bright intense light, predominantly in the X-ray region. This synchrotron light, as it is named, is millions of times brighter than light produced from conventional sources and 10 billion times brighter than the sun. Fohtung and his students have successfully used this light to develop techniques and capture minute matter such as atoms and molecules and now defects. When used to probe crystalline materials, this technique is known as Bragg coherent diffraction imaging (BCDI). In their research, the team used a BCDI approach to reveal nanoscale properties of electron densities in crystals, including strain and lattice defects.

Fohtung worked closely with Jian Shi, a Rensselaer associate professor of materials science and engineering. They were joined in the research on “Imaging defects in vanadium(III) oxide nanocrystals using Bragg coherent diffractive imaging” by Zachary Barringer, Jie Jiang, Xiaowen Shi, and Elijah Schold at Rensselaer, as well as researchers at Carnegie Mellon University.

Needle-Like Ferroelastic Domains in Individual Ferroelectric Nanoparticles

(Adv. Electron. Mater. 5/2020)

In article 1901300, Edwin Fohtung and co-workers demonstrate an X-ray Bragg coherent diffractive imaging technique to spatially resolve the evolution of nanoscopic ferroelastic needle-like domains in individual BaTiO3 nanocrystals under external pressure. This provides a new paradigm for domain-boundary engineering and potential for nanoscale functional devices aided by pressure-induce structural phase transitions and ferroelectric phase transformation.

Room temperature giant magnetostricon revealed in single crystal nanowires

Big Data Technique Reveals Previously Unknown Capabilities of Common Materials

New research reveals possible applications of nickel, from data storage to biosensors

TROY, N.Y. — When scientists and engineers discover new ways to optimize existing materials, it paves the way for innovations that make everything from our phones and computers to our medical equipment smaller, faster, and more efficient.

According to research published today by Nature Journal NPG Asia Materialsa group of researchers — led by Edwin Fohtung, an associate professor of materials science and engineering at Rensselaer Polytechnic Institute — have found a new way to optimize nickel by unlocking properties that could enable numerous applications, from biosensors to quantum computing.

They demonstrated that when nickel is made into extremely small, single-crystal nanowires and subjected to mechanical energy, a huge magnetic field is produced, a phenomenon known as giant magnetostriction.

Inversely, if a magnetic field is applied to the material, then the atoms within will change shape. This displacement could be exploited to harvest energy. That characteristic, Fohtung said, is useful for data storage and data harvesting, even biosensors. Though nickel is a common material, its promise in these areas wasn’t previously known.

“Imagine building a system with large areas of nanowires. You could put it in an external magnetic field and it would harvest a very huge amount of mechanical energy, but it would be extremely small,” Fohtung said.

The researchers uncovered this unique property through a technique called lensless microscopy, in which a synchrotron is used to gather diffraction data. That data is then plugged into computer algorithms to produce 3D images of electronic density and atomic displacement.

Using a big data approach, Fohtung said, this technique can produce better images than traditional microscopes, giving researchers more information. It combines computational and experimental physics with materials science — an intersection of his multiple areas of expertise.

“This approach is capable of seeing extremely small objects and discovering things we never thought existed about these materials and their uses,” Fohtung said. “If you use lenses, there’s a limit to what you can see. It’s determined by the size of your lens, the nature of your lens, the curvature of your lens. Without lenses, our resolution is limited by just the wavelength of the radiation.”

Fohtung used this same technique to show that barium hexaferrite — a universal and abundant material often used in tapes, CDs, and computer components — has spontaneous magnetic and electric polarization simultaneously that increases and decreases when exposed to an electric field. The property, known as ferroelectricity, is useful for fast-writing, power-saving, and data storage. Those findings were recently published in Physical Review B.

Fohtung believes that the lensless approach to studying substances will allow researchers to learn even more about solid state materials, like those used in technological devices. It may even enable deeper understanding of human tissue and cells, which could be viewed in a more natural habitat using this technique.

“What excites me so much about it is the potential for the future. There are so many existing materials that we are just not able to understand the potential applications,” Fohtung said.

Fohtung worked with researchers from Los Alamos National Laboratory, New Mexico State University, and Argonne National Laboratory on both publications.