Magnetization ratchet in cylindrical nanowires

A team of researchers from Materials Science Institute of Madrid (CSIC), University of Barcelona and ALBA Synchrotron reported on magnetization ratchet effect observed for the first time in cylindrical magnetic nanowires (magnetic cylinders with diameters of 120nm and lengths of over 20µm).

These nanowires are considered as building blocks for future 3D (vertical) electronic and information storage devices as well as for applications in biological sensing and medicine. The experiments have been carried out at the CIRCE beamline of the ALBA Synchrotron. The results are published in ACS Nano.

The magnetic ratchet effect, which represents a linear or rotary motion of domain walls in only one direction preventing it in the opposite one, originates in the asymmetric energy barrier or pinning sites. Up to now it has been achieved only in limited number of lithographically engineered planar nanostructures. The aim of the experiment was to design and prove the one-directional propagation of magnetic domain walls in cylindrical nanowires.

>Read more on the ALBA website

Image: (extract) Unidirectional propagation of magnetization as seen in micromagnetic simulations and XMCD-PEEM experiments. See entire image here.

Insulator metal transition at the nanoscale

An international team of researchers has been able to probe the insulator-conductor phase transition of materials at the nanoscale resolution. This is one of the first results of MaReS endstation of BOREAS beamline.

Controlling the flow of electrons within circuits is how electronic devices work. This is achieved through the appropriate choice of materials. Metals allow electrons to flow freely and insulators prevent conduction. In general, the electrical properties of a material are determined when the material is fabricated and cannot be changed afterwards without changing the material. However, there are materials that can exhibit metal or insulator behaviour depending on their temperature. Being able switch their properties, these materials could lead to a new generation of electronic devices.

Vanadium Dioxide (VO2) is one such material. It can switch from an insulating phase to a metallic phase just above room temperature, a feature exploited already for sensors. However, the reason why the properties of this material change so dramatically has been a matter of scientific debate for over 50 years.

One of the challenges in understanding why and how this switch occurs is due to a process called phase separation. The insulator-metal phase transition is similar to the ice to liquid transition in water. When ice melts, both liquid and solid water can coexist in separate regions. Similarly, in VO2, insulating and metallic regions of the material can be coexisting at the same time during the transition. But unlike water, where the different regions are often large enough to see with the naked eye, in VOthis separation occurs on the nanoscale and it is thus challenging to observe. As a result, it has been hard to know if the true properties of each phase, or the mixture of both phases, are being measured.

>Read more on the ALBA Synchrotron website

Image: (extract, original here) reconstructed holograms at the vanadium and oxygen edges (518, 529, and 530.5 eV) used to encode the intensities of the three color channels of an RGB (red, green, blue) image. At 330 K, an increase in intensity of the green channel, which probes the metallic rutile phase (R) through the d∥ state, is observed in small regions. As the sample is heated further, it becomes increasingly clear that the blue channel, which probes a intermediate insulating M2 phase, also changes but in different regions. At 334 K, three distinct regions can be observed corresponding to the insulating monoclinic M1, M2, and metallic R phases. As the temperature increases, the R phase dominates. The circular field of view is 2 μm in diameter. (taken from Vidas et al, Nanoletters, 2018).

Video presentation of thesis at NanoMAX

In April 2018, Karolis Parfeniukas (image) defended the first thesis to be fully completed at one of the new MAXIV beamlines called NanoMAX Here’s an interview with Karolis about this project making zone plates to improve focusing of the X-ray beam. Thesis from KTH university, Royal Institute of Technology in Stockholm. PLease watch here the presentation of his research at MAX IV Laboratory:

>Read more here about MAX IV Laboratory

Scientists find ordered magnetic patterns in disordered magnetic material

Study led by Berkeley Lab scientists relies on high-resolution microscopy techniques to confirm nanoscale magnetic features.

A team of scientists working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has confirmed a special property known as “chirality” – which potentially could be exploited to transmit and store data in a new way – in nanometers-thick samples of multilayer materials that have a disordered structure.

While most electronic devices rely on the flow of electrons’ charge, the scientific community is feverishly searching for new ways to revolutionize electronics by designing materials and methods to control other inherent electron traits, such as their orbits around atoms and their spin, which can be thought of as a compass needle tuned to face in different directions.

These properties, scientists hope, can enable faster, smaller, and more reliable data storage by facilitating spintronics – one facet of which is the use of spin current to manipulate domains and domain walls. Spintronics-driven devices could generate less heat and require less power than conventional devices.

In the latest study, detailed in the May 23 online edition of the journal Advanced Materials, scientists working at Berkeley Lab’s Molecular Foundry and Advanced Light Source (ALS) confirmed a chirality, or handedness, in the transition regions – called domain walls – between neighboring magnetic domains that have opposite spins.

Scientists hope to control chirality – analogous to right-handedness or left-handedness – to control magnetic domains and convey zeros and ones as in conventional computer memory.

>Read more on the Advanced Light Source website

Image: (extract, here original image)The top row shows electron phase, the second row shows magnetic induction, and the bottom row shows schematics for the simulated phase of different magnetic domain features in multilayer material samples. The first column is for a symmetric thin-film material and the second column is for an asymmetric thin film containing gadolinium and cobalt. The scale bars are 200 nanometers (billionths of a meter). The dashed lines indicate domain walls and the arrows indicate the chirality or “handedness.” The underlying images in the top two rows were producing using a technique at Berkeley Lab’s Molecular Foundry known as Lorentz microscopy.
Credit: Berkeley Lab

World’s strongest bio-material outperforms steel and spider silk

Novel method transfers superior nanoscale mechanics to macroscopic fibres

At DESY’s X-ray light source PETRA III, a team led by Swedish researchers has produced the strongest bio-material that has ever been made. The artifical, but bio-degradable cellulose fibres are stronger than steel and even than dragline spider silk, which is usually considered the strongest bio-based material. The team headed by Daniel Söderberg from the KTH Royal Institute of Technology in Stockholm reports the work in the journal ACS Nano of the American Chemical Society.

The ultrastrong material is made of cellulose nanofibres (CNF), the essential building blocks of wood and other plant life. Using a novel production method, the researchers have successfully transferred the unique mechanical properties of these nanofibres to a macroscopic, lightweight material that could be used as an eco-friendly alternative for plastic in airplanes, cars, furniture and other products. “Our new material even has potential for biomedicine since cellulose is not rejected by your body”, explains Söderberg.

The scientists started with commercially available cellulose nanofibres that are just 2 to 5 nanometres in diameter and up to 700 nanometres long. A nanometre (nm) is a millionth of a millimetre. The nanofibres were suspended in water and fed into a small channel, just one millimetre wide and milled in steel. Through two pairs of perpendicular inflows additional deionized water and water with a low pH-value entered the channel from the sides, squeezing the stream of nanofibres together and accelerating it.

>Read more on the PETRA III at DESY website

Image: The resulting fibre seen with a scanning electron microscope (SEM).
Credit: Nitesh Mittal, KTH Stockholm

Freeze-framing nanosecond movements of nanoparticles

New method allows to monitor fast movements at hard X-ray lasers.

A team of scientists from DESY, the Advanced Photon Source APS and National Accelerator Laboratory SLAC, both in the USA, have developed and integrated a new method for monitoring ultrafast movements of nanoscopic systems. With the light of the X-ray laser LCLS at the research center SLAC in California, they took images of the movements of nanoparticles taking only the billionth of a second (0,000 000 001 s). In their experiments now published in the journal Nature Communications they overcame the slowness of present-day two-dimensional X-ray detectors by splitting individual laser flashes of LCLS, delaying one half of it by a nanosecond and recording a single picture of the nanoparticle with these pairs of X-ray pulses. The tunable light splitter for hard X-rays which the scientists developed for these experiments enables this new technique to monitor movements of nanometer size fluctuations down to femtoseconds and at atomic resolution. For comparison: modern synchrotron radiation light sources like PETRA III at DESY can typically measure movements on millisecond timescales.

The intense light flashes of X-ray lasers are coherent which means that the waves of the monochromatic laser light propagate in phase to each other. Diffracting coherent light by a sample usually results in a so-called speckle diffraction pattern showing apparently randomly ordered light spots. However, this speckle is also a map of the sample arrangement, and movements of the sample constituents result in a different speckle pattern.

>Read more on the DESY website

Image: Scheme of the experiment: An autocorrelator developed at DESY splits the ultrashort X-ray laser pulses into two equal intensity pulses which arrive with a tunable delay at the sample. The speckle pattern of the sample is collected in a single exposure of the 2-D detector
Credit: W. Roseker/DESY

Toward control of spin states for molecular electronics

NEXT project receives secretary’s achievement award

On Wednesday, Mar. 14, Under Secretary of Energy Mark Menezes presented the Secretary’s Achievement Award—a U.S. Department of Energy (DOE) Office of Project Management (PM) Award—to the National Synchrotron Light Source II (NSLS-II) Experimental Tools (NEXT) project management team for completing the project on schedule and under budget, and for delivering scientific instruments to NSLS-II that will benefit research for years to come.

The NEXT project team coordinated the development and construction of five new beamlines (experimental stations) at NSLS-II, a highly advanced synchrotron light source and a DOE Office of Science User Facility located at DOE’s Brookhaven National Laboratory. Scientists use NSLS-II’s ultra-bright light to study materials with nanoscale resolution and exquisite sensitivity. The five new beamlines developed through NEXT complement the existing beamline portfolio at NSLS-II, and offer new, unique, and cutting-edge scientific capabilities.

“These state-of-the-art beamlines support the DOE Office of Science mission to deliver scientific discoveries and major scientific tools to transform our understanding of nature and to advance the energy, economic, and national security of the United States,” said Robert Caradonna, DOE Brookhaven Site Office Federal Project Director. “This award reflects the drive and dedication of the NEXT project team that made this endeavor a huge success. It was an honor to work with such talented people on such an important a project.”

>Read more on the NSLS-II website

Image: The NEXT team celebrates the completion of the project in NSLS-II’s lobby.
Credit: NSLS II

Scientists have a new way to gauge the growth of nanowires

In a new study, researchers from the U.S. Department of Energy’s Argonne and Brookhaven National Laboratories observed the formation of two kinds of defects in individual nanowires, which are smaller in diameter than a human hair.

These nanowires, made of indium gallium arsenide, could be useful for a wide range of applications in a field scientists have termed optoelectronics, which encompasses devices that work by converting light energy into electrical impulses. Fiber optic relays are a good example.

The effectiveness of these devices, however, can be affected by tiny defects in their components. These defects, which can change both the optical and electronic properties of these materials, interest scientists who seek to tailor them to boost the functionality of future optoelectronics, including materials that will be able to manipulate quantum information.

>Read more on the NSLS-II website and the Advanced Photon Source website

Image: Argonne and Brookhaven researchers observed two kinds of defects forming in individual nanowires, depicted here. These nanowires are smaller in diameter than a human hair.
Credit: Megan Hill/Northwestern University

New technique simplifies creation of nanoparticle ‘magic-sized clusters’

One of the cool things about nanoparticles is also what makes them so difficult to work with: the fact that their properties are dependent on their size.

A critical challenge in translating nanomaterials from the laboratory into commercial applications, such as lighting or optical memory storage, is making a batch of nanoparticles all the same size. Two Cornell research groups have joined forces to lay out a solution for this issue.

Researchers in the labs of Richard Robinson and Tobias Hanrath – using X-ray analysis at the Cornell High Energy Synchrotron Source (CHESS) – have developed a new nanosynthetic pathway to achieve ultra-pure and highly stable groups of same-sized particles – known as “magic-sized clusters.”

Their paper, “Mesophase Formation Stabilizes High-Purity Magic-Sized Clusters,” published online Jan. 27 in the Journal of the American Chemical Society, and will be on a cover of the March 14 print edition. Lead authors are Curtis Williamson, doctoral student in both the Robinson and Hanrath groups, and Douglas Nevers, doctoral student in the Hanrath Group. Lena Kourkoutis, assistant professor of applied and engineering physics, also contributed.

>Read more on the Cornell Hight Energy Synchrotron Source (CHESS) website

Image: Schematic of the magic-sized clusters hexagonal mesophase. The mesophase (left) is an assembly of nanofibers (center), which are composed of magic-sized clusters (right).
Credit: Richard Robinson

Scientists observe nanowires as they grow

X-ray experiments reveal exact details of self-catalysed growth for the first time

At DESY’s X-ray source PETRA III, scientists have followed the growth of tiny wires of gallium arsenide live. Their observations reveal exact details of the growth process responsible for the evolving shape and crystal structure of the crystalline nanowires. The findings also provide new approaches to tailoring nanowires with desired properties for specific applications. The scientists, headed by Philipp Schroth of the University of Siegen and the Karlsruhe Institute of Technology (KIT), present their findings in the journal Nano Letters. The semiconductor gallium arsenide (GaAs) is widely used, for instance in infrared remote controls, the high-frequency components of mobile phones and for converting electrical signals into light for fibre optical transmission, as well as in solar panels for deployment in spacecraft.

To fabricate the wires, the scientists employed a procedure known as the self-catalysed Vapour-Liquid-Solid (VLS) method, in which tiny droplets of liquid gallium are first deposited on a silicon crystal at a temperature of around 600 degrees Celsius. Beams of gallium atoms and arsenic molecules are then directed at the wafer, where they are adsorpted and dissolve in the gallium droplets. After some time, the crystalline nanowires begin to form below the droplets, whereby the droplets are gradually pushed upwards. In this process, the gallium droplets act as catalysts for the longitudinal growth of the wires. “Although this process is already quite well established, it has not been possible until now to specifically control the crystal structure of the nanowires produced by it. To achieve this, we first need to understand the details of how the wires grow,” emphasises co-author Ludwig Feigl from KIT.

>Read more on the FLASH and PETRA III at DESY website

Image: A single nanowire, crowned by a gallium droplet, as seen with the scanning electron microscope (SEM) of the DESY NanoLab.
Credit: DESY, Thomas Keller

How can asbestos teach us about carbon nanotubes?

Carbon nanotubes (CNTs) are already used in industry.

They have a fibrous structure that resembles that of asbestos. A team from University ofTrieste, IRCCS Burlo Garofolo, University of Turin, Elettra (Italy) and ESRF has studied both materials at the ESRF’s beamline ID21 and Elettra and has found that the presence of iron impurities in CNTs causes an asbestos-like toxicity in pleural cells. The scientists publish their results in Scientific Reports today.

>Read more on the ESRF website

Image: An artistic impression of a carbon nanotube.

Bing-Joe Hwang received National Chair Professorship from Ministry of Education

Exceptional award for this NSRRC User

The Ministry of Education recently announced the recipients of the 21st National Chair Professorships and the 61st Academic Awards. Prof. Bing-Joe Hwang, a long-term user of NSRRC, was given the National Chair Professorship in the category of Engineering and Applied Sciences. Prof. Hwang is a Chair Professor in Chemical Engineering at National Taiwan University of Science and Technology. He is also an adjunct scientist of NSRRC. His research interests include electrochemistry, nanomaterials, nanoscience, fuel cells, lithium ion batteries, solar cells, sensors, and interfacial phenomena.