Tunable ferromagnetism in a 2D material at room temperature

Breakthroughs in next-generation spintronic logic and memory devices could hinge on our ability to control spin behavior in two-dimensional materials—stacks of ultrathin layers held together by relatively weak electrostatic (van der Waals) forces. The reduced dimensionality of these so-called “van der Waals materials” often leads to tunable electronic and magnetic properties, including intrinsic ferromagnetism. However, it remains a challenge to tune this ferromagnetism (e.g. spin orientation, magnetic domain phase, and magnetic long-range order) at ambient temperatures.

In this work, researchers performed a study of Fe3GeTe2, a van der Waals material that consists of Fe3Ge layers alternating with two Te layers. The material’s magnetic properties were characterized using a variety of techniques, including x-ray absorption spectroscopy (XAS) with x-ray magnetic circular dichroism (XMCD) contrast at Beamline 6.3.1 and photoemission electron microscopy (PEEM) at Beamline 11.0.1.

>Read more on the Advanced Light Source (ALS) at LBNL website

Image: PEEM images for unpatterned and patterned Fe3GeTe2 samples at 110 K and 300 K. The unpatterned samples formed stripe domains at 110 K, which disappeared at 300 K. The patterned samples formed out-of-plane stripe domains at 110 K and transitioned to in-plane vortex states at 300 K, demonstrating control over magnetism at room temperature and beyond.

Direct Observation of the Kinetics of Gas–Solid Reactions

… using in-situ kinetic and spectroscopic techniques.

Copper oxide is a widely used adsorptive material that removes trace amounts of H2S from various process streams via chemical reaction to form copper sulfide. At room temperature the thermodynamics favor a near complete conversion of CuO to copper sulfide in the presence of H2S. However, in application, the extent of conversion of the CuO to copper sulfide during reaction can be influenced by many factors, including the initial crystalline state of the CuO, and the rate at which solid products accumulate on the reactive surfaces or within pores of the CuO particles. This incomplete utilization of CuO is problematic for industrial applications because it typically leads to oversized equipment and/or frequent process shutdowns. Developing fundamental insight at the atomic scale for this reaction could overcome these limitations by providing a rational basis for the design of new materials and by leading to predictive models that allow for current materials to be operated toward their thermodynamic limits. Thus, experiments that combine reaction kinetic testing while also simultaneously capturing chemical and structural changes in the solid phase at multiple length scales are necessary to elucidate the fundamentals of these reactions at various length scales.

Previous studies were successful in semi-quantitatively relating properties of materials to performance in fixed-bed systems, however, differences in performance were often attributed to physical properties at the >10 mm scale (e.g., surface area, pore volume, bulk density). The effects of molecular scale material characteristics (e.g., microscopic shape, metal oxide crystallite size, and surface composition) were rarely investigated, thus, it is difficult to extend the conclusions from these studies across a broad range of conditions and materials.

>Read more on the SSRL at SLAC website

Image (extract): (A) CuO and CuS concentration maps derived from XANES analysis of TXM images of individual CuO particle during reaction with 1000 ppm H2S. (B) Fractional conversion versus time (derived from linear combination fitting of Cu K-edge XANES) of fixed beds of CuO particles consisting of 2 different crystallite sizes (red circles are 2.8 nm and blue squares are 28 nm) and of individual CuO particles. See the entire figure here.

High-caliber research launches NSLS-II beamline into operations

Pratt & Whitney conduct the first experiments at a new National Synchrotron Light Source II beamline.

A new experimental station (beamline) has begun operations at the National Synchrotron Light Source II (NSLS-II)—a U.S. Department of Energy (DOE) Office of Science User Facility at DOE’s Brookhaven National Laboratory. Called the Beamline for Materials Measurement (BMM), it offers scientists state-of-the-art technology for using a classic synchrotron technique: x-ray absorption spectroscopy.

“There are critical questions in all areas of science that can be solved using x-ray absorption spectroscopy, from energy sciences and catalysis to geochemistry and materials science,” said Bruce Ravel, a physicist at the National Institute of Standards and Technology (NIST), which constructed and operates BMM through a partnership with NSLS-II.

X-ray absorption spectroscopy is a research technique that was developed in the 1980s and, since then, has been at the forefront of scientific discovery.

“The reason we’ve used this technique for 40 years and the reason why NIST built the BMM beamline is because it adds a great value to the scientific community,” Ravel explained.

The first group of researchers to conduct experiments at BMM came from jet engine manufacturer Pratt & Whitney. Senior Engineer Chris Pelliccione and colleagues used BMM to study the chemistry of jet engines.

>Read more on the National Synchrotron Light Source II (NSLS-II) website

Image: Pratt & Whitney Senior Engineer Chris Pelliccione (left) with NIST’s Bruce Ravel (right) at BMM’s workstation.

Insight into catalysis through novel study of X-ray absorption spectroscopy

An international team has made a breakthrough at BESSY II.

For the first time, they succeeded in investigating electronic states of a transition metal in detail and drawing reliable conclusions on their catalytic effect from the data. These results are helpful for the development of future applications of catalytic transition-metal systems. The work has now been published in Chemical Science, the Open Access journal of the Royal Society of Chemistry.

Many important processes in nature depend on catalysts, which are atoms or molecules that facilitate a reaction, but emerge from it themselves unchanged. One example is photosynthesis in plants, which is only possible with the help of a protein complex comprising four manganese atom sites at its centre. Redox reactions, as they are referred to, often play a pivotal role in these types of processes. The reactants are reduced through uptake of electrons, or oxidized through their release. Catalytic redox processes in nature and industry often only succeed thanks to suitable catalysts, where transition metals supply an important function.

>Read more about on the BESSY II at HZB website

Image: Manganese compounds also play a role as catalysts in photosynthesis.
Credit: HZB

New class of single atoms catalysts for carbon nanotubes

They exhibit outstanding electrochemical reduction of CO2 to CO.

Experiments using X-rays on two beamlines at the Australian Synchrotron have helped characterise a new class of single atom catalysts (SACs) supported on carbon nanotubes that exhibit outstanding electrochemical reduction of CO2 to CO. A weight loading of 20 wt% for the new class, nickel single atom nitrogen doped carbon nanotubes (NiSA-N-CNTs), is believed to be the highest metal loading for SACs reported to date.

Single atoms of nickel, cobalt and iron were supported on nitrogen doped carbon nanotubes via a one-pot pyrolysis method and compared in the study.

A large international collaboration, led by Prof San Ping Jiang, Deputy Director of the Fuels and Energy Technology Institute at the Curtin University of Technology and associates from the Department of Chemical Engineering, have developed a new synthesis and development process for nitrogen-doped carbon nanotubes with a nickel ligand that demonstrate high catalytic activity.

The study was published in Advanced Materials and featured on the inside cover of the publication.

Dr Bernt Johannessen, instrument scientist on the X-ray absorption spectroscopy (XAS) beamline at the Australian Synchrotron was a co-author on the paper, which also included lead investigators from Curtin University of Technology and collaborators at the University of Western Australia, Institute of Metal Research (China), Oak Ridge National Laboratory (US), University of the Sunshine Coast, University of Queensland, Tsinghua University (China) and King Abdulaziz University (Saudi Arabia). Technical support and advice on the soft X-ray spectroscopy experiments was provided by Australian Synchrotron instrument scientist Dr Bruce Cowie.

>Read more on the Australian Synchrotron website

Image: extract of the cover of Advanced Materials.

Toward control of spin states for molecular electronics

Investigation of metal deposition in organs after joint replacement

Synchrotron analysis shows potentially harmful metals from implants can find their way into human organs.

The hip replacement is considered to be one of the most successful orthopaedic interventions, with 75,000 performed each year by the NHS alone. However, the implants used to replace hips contain metals, such as chromium and cobalt, which are potentially toxic and which can be deposited into tissues around the implant site due to wear and corrosion. A team of researchers used X-ray absorption spectroscopy (XAS) on the I18 beamline to show that these metals can also find their way into organ tissues. Their results suggest that chronic diseases, such as diabetes, may create conditions in which mildly toxic trivalent chromium (CrIII) particles from replacement joints are reoxidised within the body to form carcinogenic hexavalent chromium (CrVI). Their results have been published in the Journal of Trace Elements in Medicine and Biology.

>Read more on the Diamond Light Source website

Image: Overview of the study (entire figure to see here).