physics – Page 2 – Lightsources.org

Kilian Peter Heeg wins ESRF Young Scientist award

2018/02/062018/02/07

Kilian Peter Heeg has been awarded the title of Young Scientist 2018 by the ESRF User Organisation in recognition of his pioneering work on light-matter interactions enabling resonant brilliance enhancement of X-ray pulses. This award is presented every year at the ESRF annual User Meeting to a scientist aged 37 or younger for outstanding work conducted at the ESRF.

Kilian Heeg is a physicist and postdoctoral researcher at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Aged just 31, Kilian has already significantly shaped the field of X-ray quantum optics.

Kilian says: “I wanted to be a mathematician when I was a child and I was always fascinated by natural sciences. However in my final years in school I fell in love with physics and very quickly became fascinated with quantum mechanics and especially quantum optics. I feel very honoured and pleased to have been chosen as the winner of this year’s ESRF Young Scientist Award.”

>Read more on the ESRF website

Image: Kilian on ESRF’s ID18 beamline
Credit: ESRF/C. Argoud

High coherence and intensity at FERMI enables new X-ray interfacial probe

2018/02/052018/03/14

Interfaces are involved in a wide range of systems and have significant implications in many fields of scientific and technological advancement, often determining device performance or chemical reactivity. Vital examples include solar cells, protein folding, and computer chips. A class of commonly used surface science techniques are comprised of even-ordered nonlinear spectroscopies (i.e., second harmonic and sum frequency generation) which exhibit no response in centrosymmetric media due to symmetry constraints.As a result, they have been widely used at optical wavelengths to explore physical and chemical properties of interfaces, where centrosymmetry is broken. Extending this to x-ray wavelengths would effectively combine the element specificity and spectral sensitivity of x-ray spectroscopy with the rigorous interfacial/surface specificity of optical even-ordered nonlinear spectroscopies. Unfortunately, at hard x-ray energies (x-ray wavelength order of the spacing between atoms) these even-ordered nonlinear spectroscopies are effectively bulk probes, as each individual atom breaks inversion symmetry. As soft x-ray wavelengths fall in between the UV and hard x-ray regimes, there has been uncertainty regarding the interface specificity of soft x-ray second harmonic generation.

>Read more on the FERMI webpage

Figure: (extract) Experimental Design. X-ray pulses are passed through a 2 mm iris and focused onto the graphite sample at normal incidence. The transmitted beam is then passed through a 600 nm aluminum filter and onto a spectrometer grating, spatially resolving the second harmonic signal from the fundamental. Inset: A schematic energy level diagram of the second harmonic generation process. (entire figure here)

Magnetic trick triples the power of SLAC’s X-ray laser

2018/01/312018/02/01

The new technique will allow researchers to observe ultrafast chemical processes previously undetectable at the atomic scale.

Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to triple the amount of power generated by the world’s most powerful X-ray laser. The new technique, developed at SLAC’s Linac Coherent Light Source (LCLS), will enable researchers to observe the atomic structure of molecules and ultrafast chemical processes that were previously undetectable at the atomic scale.

The results, published in a Jan. 3 study in Physical Review Letters (PRL), will help address long-standing mysteries about photosynthesis and other fundamental chemical processes in biology, medicine and materials science, according to the researchers.

“LCLS produces the world’s most powerful X-ray pulses, which scientists use to create movies of atoms and molecules in action,” said Marc Guetg, a research associate at SLAC and lead author of the PRL study. “Our new technique triples the power of these short pulses, enabling higher contrast.”

>Read more on the LCSL website

Picture: The research team, from left: back row, Yuantao Ding, Matt Gibbs, Nora Norvell, Alex Saad, Uwe Bergmann, Zhirong Huang; front row, Marc Guetg and Timothy Maxwell.
Credit: Dawn Harmer/SLAC

Questioning the universality of the charge density wave nature…

2018/01/312018/02/02

… in electron-doped cuprates

The first superconductor materials discovered offer no electrical resistance to a current only at extremely low temperatures (less than 30 K or −243.2°C). The discovery of materials that show superconductivity at much higher temperatures (up to 138 K or −135°C) are called high-temperature superconductors (HTSC). For the last 30 years, scientists have researched cuprate materials, which contain copper-oxide planes in their structures, for their high-temperature superconducting abilities. To understand the superconducting behavior in the cuprates, researchers have looked to correlations with the charge density wave (CDW), caused by the ordered quantum field of electrons in the material. It has been assumed that the CDW in a normal (non-superconducting) state is indicative of the electron behavior at the lower temperature superconducting state. A team of scientists from SLAC, Japan, and Michigan compared the traits of superconducting and non-superconducting cuprate materials in the normal state to test if the CDW is correlated to superconductivity.

>Read more on the SSRL website

Picture: explanation in detail to read in the full scientific highlight (SSRL website)

Scientists discover material ideal for smart photovoltaic windows

2018/01/222018/01/24

Berkeley Lab researchers make thermochromic windows with perovskite solar cell

Smart windows that are transparent when it’s dark or cool but automatically darken when the sun is too bright are increasingly popular energy-saving devices. But imagine that when the window is darkened, it simultaneously produces electricity. Such a material – a photovoltaic glass that is also reversibly thermochromic – is a green technology researchers have long worked toward, and now, scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a way to make it work.

Researchers at Berkeley Lab, a Department of Energy (DOE) national lab, discovered that a form of perovskite, one of the hottest materials in solar research currently due to its high conversion efficiency, works surprisingly well as a stable and photoactive semiconductor material that can be reversibly switched between a transparent state and a non-transparent state, without degrading its electronic properties.

Image Credit: iStock

G. Ghiringhelli and L. Braicovich win 2018 Europhysics Prize of Condensed Matter

2018/01/222018/01/24

Giacomo Ghiringhelli and Lucio Braicovich were awarded the 2018 Europhysics Prize of the Condensed Matter Division of the European Physical Society (EPS), for their groundbreaking work « for the development and scientific exploration of high-resolution resonant inelastic x-ray scattering (RIXS) ».

Awarded once every 2 years, the EPS Condensed Matter Europhysics Prize is one of Europe’s most prestigious prizes in the field of condensed matter physics. The Prize will be presented on Tuesday March 13th, 2018, at the Awards Session of the 27th General Conference of the EPS Condensed Matter Division, to be held in Berlin.

>Read more on the ESRF website

X-ray detector for studying characteristics of materials

2018/01/182018/03/12

Sol M. Gruner’s group, Physics, has been a leader in the development of x-ray detectors for scientific synchrotron applications, and the team’s technology is used around the world. Their detectors utilize pixelated integrated circuit silicon layers to absorb x-rays to produce electrical signals. The wide dynamic range, high sensitivity, and rapid image frame rate of the detectors enable many time-resolved x-ray experiments that have been difficult to perform until now.

The detectors are limited by the silicon layer. Low atomic number materials such as silicon become increasingly transparent to x-rays as the energy of the x-rays rises. Gruner’s group is now developing a variant of their detector that will use semiconductors comprised of high atomic weight elements to absorb the x-rays and produce the resultant electrical signals. The Detector Group, led by Antonio Miceli, at the United States Department of Energy’s Advanced Photon Source (APS) will simultaneously develop the ancillary electronics and interfacing required to produce fully functional prototypes suitable for high x-ray energy experiments at the APS and CHESS.

>Read more on the CHESS website

Image: Sol M. Gruner, Physics, College of Arts and Sciences
Credit: Jesse Winter

Scientists decipher key principle behind reaction of metalloenzymes

2018/01/15

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how important bioinorganic electron transfer systems operate. Using a combination of very different, time-resolved measurement methods at DESY’s X-ray source PETRA III and other facilities, the scientists were able to show that so-called pre-distorted states can speed up photochemical reactions or make them possible in the first place. The group headed by Sonja Herres-Pawlis from the RWTH Aachen University Michael Rübhausen from the University of Hamburg and Wolfgang Zinth from Munich’s Ludwig Maximilian University, is presenting its findings in the journal Nature Chemistry.

The scientists had studied the pre-distorted, “entatic” state using a model system. An entatic state is the term used by chemists to refer to the configuration of a molecule in which the normal arrangement of the atoms is modified by external binding partners such that the energy threshold for the desired reaction is lowered, resulting in a higher speed of reaction. One example of this is the metalloprotein plastocyanin, which has a copper atom at its centre and is responsible for important steps in the transfer of electrons during photosynthesis. Depending on its oxidation state, the copper atom either prefers a planar configuration, in which all the surrounding atoms are arranged in the same plane (planar geometry), or a tetrahedral arrangement of the neighbouring ligands. However the binding partner in the protein forces the copper atom to adopt a sort of intermediate arrangement. This highly distorted tetrahedron allows a very rapid shift between the two oxidation states of the copper atom.

>Read more on the PETRA III website

Image Caption: Entatic state model complexes optimize the energies of starting and final configuration to enable fast reaction rates (illustrated by the hilly ground). The work demonstrates that the entatic state principle can be used to tune the photochemistry of copper complexes.
Credit: RWTH Aachen, Sonja Herres-Pawlis

First Pilot Experiment at SwissFEL-Alvra

2017/12/172018/03/15

UV photo-induced charge transfer in OLED system

On the 17th of December 2017 SwissFEL saw its first pilot experiment in the Alvra experimental station of the SwissFEL ARAMIS beamline. A team of scientists from the University of Bremen, Krakow and PSI, led by Matthias Vogt (Univ. Bremen) and Chris Milne (PSI)in collaboration with J. Szlachetko, J. Czapla-Masztafiak, W. M. Kwiatek (Inst. of Nucl.Phys. PAN (Krakow), successfully did the first pilot experiment at SwissFEL-Alvra on UV photo-induced charge transfer in OLED system.

With ever-increasing demands on low-cost, low-power display technology, significant resources have been invested in identifying OLED materials that are based on Earth-abundant materials while maintaining high internal quantum efficiencies. The recent pilot experiment performed at SwissFEL’s Alvra experimental station aimed to use X-ray spectroscopy to investigate a promising OLED candidate based on copper and phosphorus. This molecule, synthesized by Dr. Matthias Vogt from the University of Bremen, is based on a physical phenomenon called thermally activated delayed fluorescence, which allows for extremely high energy efficiencies to be achieved. The experiment probed how the phosphorus atoms are involved in the fluorescence process as a complement to longer-timescale measurements on the copper atoms performed at the Swiss Light Source’s SuperXAS beamline by Dr. Grigory Smolentsev and collaborators. The SwissFEL measurements confirm that the phosphorus atoms are directly involved in the charge transfer process in the molecule, and lay the foundation for future investigations of the mechanisms behind the efficiency of the delayed fluorescence process.

>Read more on the SwissFEL website

Figure: please find here the full figure

Ruling out Weyl points in MoTe2

2017/12/142018/01/18

Sometimes the hunt for new kinds of fundamental particles takes place in the low-energy degrees of freedom of exotic quantum materials

Over the past decade, such strange entities as magnetic monopoles, Majorana fermions, and even Higgs modes have been predicted and identified inside materials at low temperatures. The goal of learning to manipulate these new quanta for technological purposes is a grand challenge for science, predicted to spark a “second quantum revolution”. Among the intriguing zoo of new particles which exploit the topological properties of electronic wavefunctions, the Weyl fermions (which are charged, massless, and chiral) were originally postulated in the 1920s but have never been observed in high-energy physics experiments. However, compelling evidence for Weyl physics inside certain classes of semi-metals has accumulated over the past three years. The material TaAs, for example, has been shown to host special electronic band crossings (“nodes”) where the quasiparticles act like Weyl fermions. Subsequently, a second type of Weyl semimetal (called “type-II”) was theoretically predicted to exist in the material MoTe₂. Weyl semi-metals are predicted to host Fermi surface lines with non-trivial topological properties at the material surface. Initial support for the type-II Weyl picture of MoTe₂ has been published in the form of ARPES experiments, but the full, bulk electronic structure was until recently unknown.

>Read more on the CHESS website

Synchrotron “X-ray Micromechanics” course now online

2017/12/122018/01/17

An online course for novice X-ray users with backgrounds in engineering

As part of the mission of InSitμ@CHESS, the ONR-funded center focused on developing new High Energy X-ray Diffraction (HEXD) users and methods, the staff has developed and made available an online course for novice X-ray users with backgrounds in engineering.

>Read more on the CHESS website

Ferromagnetism Emerges to Alleviate Polar Mismatch

2017/12/042018/01/17

Alchemists dreamed of turning boring, base metals into exotic, noble metals. Although such dreams were never realized, scientists today can induce unexpected properties at the interface between two materials—including properties not present in either parent material. For example, researchers have discovered that if they combine SrTiO3 (a dielectric and paramagnetic material) together with LaMnO3 (an insulating and antiferromagnetic material) in just the right way, they can induce an insulating ferromagnetic state at the interface.

NSRRC User, Jennifer Kung elected as a MSA Fellow

2017/11/282017/11/29

First female scientist ever awarded MSA fellowship in Asia.

NSRRC user, Jennifer Kung is among the 11 new elected fellows for 2018, announced by the Mineralogical Society of America (MSA) Council at its Fall Council Meeting in Seattle, WA, USA. She is the only recipient from Taiwan, as well as the first female scientist ever awarded MSA fellowship in Asia.

Prof. Kung is an Associate Professor in Earth Science at National Cheng-Kung University. She runs “Mineral and Rock Physics Lab” to investigate the behaviors of earth materials under high pressure and high temperature using the knowledge of crystal chemistry, mineral physics to understand the interior of the Earth. The major research methods she employs include X-ray diffraction, vibrational spectroscopy and ultrasonic measurements in conjunction with high pressure facilities, like large volume high pressure apparatus or diamond anvil.

>Read More on the NSRRC website

2017 ANSTO, Australian Synchrotron Stephen Wilkins Medal awarded

2017/11/272017/12/07

Leonie van ‘t Hag has been awarded the Australian Synchrotron S. Wilkins Medal for her PhD thesis

The award recognises her research to improve the method to crystallise proteins and peptides in order to study their structure, using a technique called crystallography. “Leonie’s insights into crystallisation processes could significantly help the development of treatments for a variety of illnesses,” said Australian Synchrotron Director, Professor Andrew Peele.

Most solid material in the world is made of crystalline structures. Crystals are made up of rows and rows of atoms or molecules stacked up like boxes in a warehouse, in different arrangements.

The science of determining these atomic or molecular structures from crystalline materials is called crystallography.

Scientists Named 2017 American Physical Society Fellows

2017/11/222017/12/07

Five Brookhaven Lab Scientists recognized for their outstanding contributions

The American Physical Society (APS), the world’s largest physics organization, has elected five scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory as 2017 APS fellows. With more than 53,000 members from academia, government, and industry, APS seeks to advance and share physics knowledge through research journals, scientific meetings, and activities in education, outreach, and advocacy. Each year, a very small percentage of APS members are elevated to the status of fellow through a peer nomination process. Fellows are recognized for their exceptional contributions to physics, including in research, applications, leadership and service, and education.

The 2017 APS fellows representing Brookhaven Lab are Anatoly Frenkel, Morgan May, Rachid Nouicer, Eric Stach, and Peter Steinberg.

Anatoly Frenkel, APS Division of Materials Physics

“For seminal contributions to in situ X-ray absorption spectroscopy, transformative development of structural characterization methods for nanoparticles, and their pioneering applications to a broad range of functional nanomaterials in materials physics and catalysis science.”

Anatoly Frenkel holds a joint appointment as a senior chemist in Brookhaven Lab’s Chemistry Division—where he serves as principal investigator of the Structure and Dynamics of Applied Nanomaterials Group—and tenured professor in Stony Brook University’s Materials Science and Chemical Engineering Department. Frenkel’s research focuses on the application of synchrotron-based x-ray methods to characterize materials and study how their structures and properties relate.

>Read more on the NSLS II website

Image: Anatoly Frenkel

Quantum spectroscopy, for the measurements of dynamical current current thermalization

2017/11/172018/01/16

Nearly all spectroscopic measurements deals with the measurements of the average properties of the material. As an example, the reflectivity of a material is simply defined by the ratio between the number of photons which are reflected by the sample divided by the number of those arriving on it. The interest in measuring mostly average properties is the main drive of the standard scientific practice of repeating the measurements a lot of times so that the error made in one single measurements is averaged out by the repetition of the measurements. In this context the noise which determines fluctuation of the repeated measurements have always been considered as an impediment to a good quality measurements which needs to be mitigated by careful experimentalists.
The approach of repeated measurements is employed conspicuously in pump-probe experiments which are the prime way to study condensed matter out of its equilibrium state. In standards optical pump-probe experiments, ultrashort pulses are always used in pairs. The pump triggers the dynamical response and the probe is used to detect changes in the optical properties of the sample.