Scientists discover material ideal for smart photovoltaic windows

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.

>Read more on the Advanced Light Source website

Image Credit: iStock

 

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

>Read more on the ESRF website

 

X-ray detector for studying characteristics of materials

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

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

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

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

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

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.

Read more on the ALS website.

Illustration of the LaMnO3/SrTiO3 heterostructure, showing an LaMnO3 thickness of three unit cells (UC). Source: ALS website

NSRRC User, Jennifer Kung elected as a MSA Fellow

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.

 

2017 ANSTO, Australian Synchrotron Stephen Wilkins Medal awarded

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

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

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.

Read more on the Elettra website.

Image: Schematic view of the pump-probe set-up used for the experiments. The intensity of every single probe pulse was separately acquired with low-electronic-noise detectors for every pump-probe delay.

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

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

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.

>Read More on the Bessy II (HZB) website

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?

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

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.