physics – Page 3 – Lightsources.org

Fuel cell X-Ray study details effects of temperature and moisture on performance

2017/11/132017/11/29

Experiments at Berkeley Lab’s Advanced Light Source help scientists shed light on fuel-cell physics

Like a well-tended greenhouse garden, a specialized type of hydrogen fuel cell – which shows promise as a clean, renewable next-generation power source for vehicles and other uses – requires precise temperature and moisture controls to be at its best. If the internal conditions are too dry or too wet, the fuel cell won’t function well.

But seeing inside a working fuel cell at the tiny scales relevant to a fuel cell’s chemistry and physics is challenging, so scientists used X-ray-based imaging techniques at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Argonne National Laboratory to study the inner workings of fuel-cell components subjected to a range of temperature and moisture conditions.

The research team, led by Iryna Zenyuk, a former Berkeley Lab postdoctoral researcher now at Tufts University, included scientists from Berkeley Lab’s Energy Storage and Distributed Resources Division and the Advanced Light Source (ALS), an X-ray source known as a synchrotron.

>Read More on the ALS website

Image: This animated 3-D rendering (view larger size), generated by an X-ray-based imaging technique at Berkeley Lab’s Advanced Light Source, shows tiny pockets of water (blue) in a fibrous sample. The X-ray experiments showed how moisture and temperature can affect hydrogen fuel-cell performance.
Credit: Berkeley Lab

Antiferromagnetic dysprosium reveals magnetic switching with less energy

2017/11/062017/11/13

HZB scientists have identified a mechanism with which it may be possible to develop a form of magnetic storage that is faster and more energy-efficient.

They compared how different forms of magnetic ordering in the rare-earth metal named dysprosium react to a short laser pulse. They discovered that the magnetic orientation can be altered much faster and with considerably less energy if the magnetic moments of the individual atoms do not all point in the same direction (ferromagnetism), but instead point are rotated against each other (anti-ferromagnetism). The study was published in Physical Review letters on 6. November 2017 and on the cover of the print edition.

Dysprosium is not only the atomic element with the strongest magnetic moments, but it also possesses another interesting property: its magnetic moments point either all the same direction (ferromagnetism) or are tilted against each other, depending on the temperature. This makes it possible to investigate in the very same sample how differently oriented magnetic moments behave when they are excited by an external energy pulse.

Image: A short laser pulse pertubates magnetic order in dysprosium. This happens much faster if the sample had a antiferromagnetic order (left) compared to ferromagnetic order (right). Credit: HZB

Where did those electrons go?

2017/11/022017/12/07

Decades-old mystery solved

The concept of “valence” – the ability of a particular atom to combine with other atoms by exchanging electrons – is one of the cornerstones of modern chemistry and solid-state physics. Valence controls crucial properties of molecules and materials, including their bonding, crystal structure, and electronic and magnetic properties.

Four decades ago, a class of materials called “mixed valence” compounds was discovered. Many of these compounds contain elements near the bottom of the periodic table, so-called “rare-earth” elements, whose valence was discovered to vary with changes in temperature in some cases. Materials comprising these elements can display unusual properties, such as exotic superconductivity and unusual magnetism.

But there’s been an unsolved mystery associated with mixed valence compounds: When the valence state of an element in these compounds changes with increased temperature, the number of electrons associated with that element decreases, as well. But just where do those electrons go?

>Read more on the CHESS website

Image: Illustration of ytterbium (Yb) atoms in YbAl3, where electrons transform from localized states (bubbles surrounding the yellow orbitals) to itinerant states (hopping amongst orbitals), as a function of temperature.

NSRRC Researchers receive Taiwan’s 2017 Presidential Science Prize

2017/10/312017/11/29

Former NSRRC Director C. T. Chen and NSRRC User Andrew H.-J. Wang

Established in 2001, the biennial Presidential Science Prize recognizes innovative researchers who have made outstanding contributions in the fields of mathematics and physical sciences, life sciences, social sciences, and applied sciences. It is considered the nation’s highest scientific honor.

According to the Eligibility and Selection Process of the Prize, the Committee is composed of 15 members, including the President of Academia Sinica as the chair, and the Minister of Science and Technology as the vice chair. This year three winners stood out among 13 nominees: Academician Chien-Te Chen (NSRRC) in mathematics and physical sciences, Academician Andrew H.-J. Wang (Academia Sinica) in life sciences, and Dr. Douglas Yu (Taiwan Semiconductor Manufacturing Company) in applied sciences. The awarding ceremony will be held in the Presidential palace and presented by the President in November.

>Read More on the NSRRC website

HZB launches the HI-SCORE international research school in collaboration with Israel

2017/10/232017/11/13

The Helmholtz-Zentrum Berlin is establishing the Helmholtz International Research School HI-SCORE, which will be oriented towards solar energy research.

To accomplish this, HZB is collaborating with the Weizmann Institute in Rehovot, the Israeli Institute of Technology (Technion) in Haifa, and three Israeli universities as well as universities in Berlin and Potsdam. The project is being funded by the Helmholtz Association.

The name “HI-SCORE” stands for “Hybrid Integrated Systems for Conversion of Solar Energy”. The research themes extend from novel solar cells based on metal-organic perovskites, to tandem solar cells, to complex systems of materials for generating solar fuels. These complex materials systems can convert the energy of sunlight to chemical energy so it can be easily stored in the form of fuel.

Joining forces to advance perovskite solar cells

2017/10/202017/11/16

Great Interest in the HySPRINT Industry Day

No fewer than 70 participants attended the first Industry Day of the Helmholtz Innovation Lab HySPRINT devoted to the topic of perovskite solar cells at Helmholtz-Zentrum Berlin (HZB) on 13 October 2017. This far exceeded the expectations of the event hosts. The knowledge shared on Industry Day will serve as the basis for deepening the collaboration even further with strategically important companies in the scope of HySPRINT.

“Seeing the industry partners’ active participation was very gratifying. We could feel in the lively discussions how there is great interest on both sides to collaborate even more closely on technology transfer,” says Dr. Stefan Gall, project manager of the Helmholtz Innovation Lab HySPRINT (“Hybrid Silicon Perovskite Research, Integration & Novel Technologies”). On the Industry Day, eight companies presented those topics that especially interest them. “From this, certain problems emerged that we are now going to work on targetedly with our industrial partners.”

Missing link between new topological phases of matter discovered

2017/10/172017/11/13

HZB-Physicists at BESSY II have investigated a class of materials that exhibit characteristics of topological insulators.

During these studies they discovered a transition between two different topological phases, one of which is ferroelectric, meaning a phase in the material that exhibits spontaneous electric polarisation and can be reversed by an external electric field. This could also lead to new applications such as switching between differing conductivities.

The HZB researchers studied crystalline semiconductor films made of a lead, tin, and selenium alloy (PbSnSe) that were doped additionally with tiny amounts of the element bismuth. These semiconductors belong to the new class of materials called topological insulators, materials that conduct very well at their surfaces while behaving as insulators internally. Doping with 1-2 per cent bismuth has enabled them to observe a new topological phase transition now. The sample changes to a particular topological phase that also possesses the property of ferroelectricity. This means that an external electric field distorts the crystal lattice, whereas conversely, mechanical forces on the lattice can create electric fields.

Image: The Bismut doping is enhanced from 0% (left) to 2.2% (right). Measurements at BESSY II show that this leads to increased bandgaps. Credit: HZB

Translation of ‘Hidden’ Information Reveals Chemistry in Action

2017/10/102017/10/16

New method allows on-the-fly analysis of how catalysts change during reactions, providing crucial information for improving performance.

Chemistry is a complex dance of atoms. Subtle shifts in position and shuffles of electrons break and remake chemical bonds as participants change partners. Catalysts are like molecular matchmakers that make it easier for sometimes-reluctant partners to interact.

Now scientists have a way to capture the details of chemistry choreography as it happens. The method—which relies on computers that have learned to recognize hidden signs of the steps—should help them improve the performance of catalysts to drive reactions toward desired products faster.

The method—developed by an interdisciplinary team of chemists, computational scientists, and physicists at the U.S. Department of Energy’s Brookhaven National Laboratory and Stony Brook University—is described in a new paper published in the Journal of Physical Chemistry Letters. The paper demonstrates how the team used neural networks and machine learning to teach computers to decode previously inaccessible information from x-ray data, and then used that data to decipher 3D nanoscale structures.

>Read More

First users welcomed to I21

2017/10/042017/10/26

Diamond’s Inelastic X-ray Scattering beamline has celebrated an important milestone.

This new beamline is dedicated to Resonant Inelastic X-ray Scattering (RIXS) producing highly monochromatised, focused and tunable X-rays. It is suited to investigate the electronic, magnetic and lattice dynamics of samples particularly those with magnetic and electronic interactions.

“Considering the exceptional progress of the RIXS technique in the last few years, and the unique capabilities that I21 will offer to our UK and international community, we are extremely pleased to celebrate first users on I21,” says Laurent Chapon, Physical Sciences Director at Diamond. “Dr Kejin Zhou and his team, Diamond’s engineers and all support groups have worked incredibly hard to deliver this new beamline with an energy resolution and count rates already very close to the expected final targets. This is just the start of a great adventure, and we are looking forward to exploiting I21’s high-resolution for measurements of local and collective excitations in solid state materials. Our future investments to extend the energy range as well as delivering a polarimeter will reinforce the position of I21 as a world-leading facility.”

Photo: The I21 beamline time with first users from university of Bristol.

Observation and Control of Laser-Enabled Auger Decay

2017/09/212017/10/12

When isolated atoms are electronically excited, they have two possible ways of releasing electronic energy: by radiation or by Auger decay. The Auger process, in which the decaying electron transfers its energy to another electron causing it to detach (ionization), has played an important part in modern physics, particularly surface science, because it is by far the strongest decay channel for core holes of light elements such as carbon, nitrogen, and oxygen. In some cases, the Auger process is energetically forbidden, because the energy being exchanged is not sufficient for ionization. In this case, new electronic mechanisms for deexcitation may be discovered that “borrow” energy from the surroundings. One of these is interatomic Coulombic decay (ICD) where the energy is “borrowed” from surrounding atoms. Another mechanism is laser enabled Auger Decay (LEAD), where the energy is “borrowed” from an ancillary laser field; up to now LEAD has been observed with low-energy photons, meaning that more than one photon must be absorbed to make the process possible.

>Read more

The miracle material graphene: convex as a chesterfield

2017/09/182017/10/09

Graphene possesses extreme properties and can be utilised in many ways.

Even the spins of graphene can be controlled through use of a trick. This had already been demonstrated by a HZB team some time ago: the physicists applied a layer of graphene onto a nickel substrate and introduced atoms of gold in between (intercalation).

The scientists now show why this has such a dramatic influence on the spins in a paper published in 2D Materials. As a result, graphene can also be considered as a material for future information technologies that are based on processing spins as units of information.

>Read More

Emergent magnetism at transition-metal-nanocarbon interfaces

2017/08/282017/10/09

Researchers have shed light on the origin of the magnetism arising at carbon/non-magnetic 3d,5d metal interfaces

These results may allow the manipulation of spin ordering at metallic surfaces using electro-optical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices.

Interfaces are key in solid state and quantum physics, controlling many fundamental properties and enabling emergent interfacial, bi-dimensional like phenomena. Therefore they offer potential opportunities for designing hybrid materials that profit from promising combinatory effects.

In particular, the fine-tuning of spin polarization at metallo–organic interfaces opens a realm of possibilities, from the direct applications in molecular spintronics and thin-film magnetism to biomedical imaging or quantum computing. This interaction at the interface can control the spin polarization in magnetic field sensors, generate magnetization spin-filtering effects in non-magnetic electrodes or even give rise to magnetic ordering when non-magnetic elements such as diamagnetic copper or paramagnetic manganese are put in contact with carbon/fullerenes at such interfaces.

>Read More

Solar hydrogen production by artificial leafs

2017/08/282017/10/09

Scientists analysed how a special treatment improves cheap metal oxide photoelectrodes

Metal oxides are promising candidates for cheap and stable photoelectrodes for solar water splitting, producing hydrogen with sunlight. Unfortunately, metal oxides are not highly efficient in this job. A known remedy is a treatment with heat and hydrogen. An international collaboration has now discovered why this treatment works so well, paving the way to more efficient and cheap devices for solar hydrogen production.

The fossil fuel age is bound to end, for several strong reasons. As an alternative to fossil fuels, hydrogen seems very attractive. The gas has a huge energy density, it can be stored or processed further, e. g. to methane, or directly provide clean electricity via a fuel cell. If it is produced using sunlight alone, hydrogen is completely renewable with zero carbon emissions.

>Read More

NSLS-II Welcomes New Tool for Studying the Physics of Materials

2017/08/172017/10/16

Versatile instrument for precisely studying materials’ structural, electronic, magnetic characteristics arrives at Brookhaven Lab.

A new instrument for studying the physics of materials using high intensity x-ray beams has arrived at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory. This new diffractometer, installed at beamline 4-ID at the National Synchrotron Light Source II (NSLS-II), a DOE Office of Science User Facility that produces extremely bright beams of x-rays, will offer researchers greater precision when studying materials with unique structural, electronic, and magnetic characteristics. Understanding these materials’ properties could lead to better electronics, solar cells, or superconductors (materials that carry electricity with almost no energy loss).

A diffractometer allows researchers to “see” the structure of a material by shooting highly focused x-rays at it and measuring how they diffract, or bounce off. According to Brookhaven physicist Christie Nelson, who worked with Huber X-Ray Diffraction Equipment to design the diffractometer, the new instrument has big advantages compared to one that operated at Brookhaven’s original light source, NSLS. Most significantly, it gives researchers additional ways to control where the beam hits the sample and how the x-rays are detected.

>Read More

Spectrally broad X-ray pulses can be “sharpened” by purely mechanical means

2017/07/312017/10/09

Abrupt motion sharpens X-ray pulses

A team of theoretical and experimental physicists, including scientists from DESY, lead by the Max Planck Institute for Nuclear Physics (MPIK in Heidelberg, Germany) has developed and realized a method to “sharpen” spectrally broad X-ray pulses by purely mechanical means. It is based on fast motions, precisely synchronized with the pulses, of a target interacting with the X-ray light. Thereby, photons are redistributed within the X-ray pulse to the desired spectral region, as the scientists demonstrated at DESYs X-ray source PETRA III and the European Synchrotron Radiation Facility ESRF (Grenoble, France). The researchers present their work in the journal “Science”.

The novel method can intensify the spectrally broad X-ray pulses in a narrow spectral region. Such X-ray pulses are desired for a number of fundamental physics experiments or are a prerequisite for some precision experiments. The key roles are played by a piezoelectric transducer which performs precise motions upon electric signals and by a thin iron foil. Precisely synchronized motions redistribute the photons within the X-ray pulse to a narrow wavelength region. “Our method doesn’t waste photons like a monochromator that only cuts off the undesired wavelengths”, explains Jörg Evers from the division of Christoph Keitel at MPIK. “On the other hand, we don’t need to increase the overall energy of the X-ray pulse.”

>Read More

Time-resolved measurement of interatomic Coulombic decay

2017/04/282017/12/04

… induced by two-photon double excitation of Ne2

On the 24th of March 2017, Tsukasa Takanashi gained his doctorate from the University of Tohoku (Japan), together with the President’s Award prize (総長賞). The prize is awarded each year to the best PhD students in recognition of their outstanding academic curriculum, and particularly for the excellent results obtained during their studies. Tsukasa carried out his studies under the supervision of Professor Kiyoshi Ueda, a leading figure on the international scene of atomic and molecular physics, and until recently, a member of the FERMI Review Panel. In his thesis, Tsukasa used the light from Free Electron Lasers (FELs) to study the dynamics of highly excited molecular systems; in his home country, he utilized the Japanese FEL SACLA, and he studied the Coulomb explosion of the molecule CH₂I₂ (diiodomethane). This process is the fragmentation by multiple ionization of a sample, and the successive repulsion of the ions by the positive charge which is generated.

An important part of his work was carried out at FERMI, currently the only FEL source in the world able to provide Tsukasa the wavelength (75.6 nm) and temporal resolution (10^-13 s) necessary to study the dynamics of his system: the Ne₂ molecule, which consists of two neon atoms bound by their weak van der Waals interaction. The apparent simplicity of this system allows the detailed study of complex phenomena, such as the exchange of energy after electronic excitation, which is basic to all photochemical processes.

>Read more on the FERMI website

Image: Schematic representation of the resonant absorption of two FEL photons by a neon dimer (upper panel) and the ICD relaxation process by ionization (lower panel).