circular dichroism – Lightsources.org

Diamond celebrates 10,000th paper – A breakthrough in chiral polymer thin films research

2021/01/202021/01/21

This could fundamentally change the technology landscape by enabling a new generation of devices

A recent paper in Nature Communications by an international team of collaborative researchers marks the 10,000th published as a result of innovative research at Diamond Light Source, the UK’s national synchrotron. This study presents disruptive insights into chiral polymer films, which emit and absorb circularly polarised light, and offers the promise of achieving important technological advances, including high-performance displays, 3D imaging and quantum computing.https://player.vimeo.com/video/502596383

Chirality is a fundamental symmetry property of the universe. We see left-handed (LH) and right-handed (RH) mirror image pairs in everything from snails and small molecules to giant spiral galaxies. Light can also have chirality. As light is travelling, its internal electric field can rotate left or right creating LH or RH circular polarisation. The ability to control and manipulate this chiral, circularly-polarised light presents opportunities in next-generation optoelectronics (Figs 1a and 1b). However, the origin of the large chiroptical effects in polymer thin films (Figs 1c and 2) has remained elusive for almost three decades. In this study, a group of researchers from Imperial College London, the University of Nottingham, the University of Barcelona, the Diamond Light Source and the J.A. Woollam Company made use of Diamond’s Synchrotron Radiation Circular Dichroism beamline (B23) and the Advanced Light Source in California.

Read more on the Diamond website

Image: In situ chiroptical response of ACPCA and cholesteric chiral sidechain polymers (CSCP) thin ﬁlms. In situ CD spectra recorded during heating and cooling of ACPCA (F8BT: aza[6]H) and CSCP (cPFBT) thin ﬁlms (note blue represents low temperatures and red represents high temperatures), (c) and (d) the CD intensity recorded at 480nm as a function of temperature during heating (red) and cooling (blue), and (e) and (f) CD intensity of thin ﬁlms held at 140°C as a function of time for [P] (turquoise) and [M] (purple) systems (note the different time on-axis).

Electric dipoles form chiral skyrmions

2019/06/142019/06/27

Control of such phenomena could one day lead to low-power, nonvolatile data storage as well as to high-performance computers.

A group of researchers, led by scientists from Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Materials Science and Engineering Department, set out to find ways to control how heat moves through materials. They fabricated a material with alternating layers of strontium titanate, which is an electrical insulator, and lead titanate, a ferroelectric material with a natural electrical polarization that can be reversed by the application of an external electric field.

When the group took the material to Berkeley Lab’s Molecular Foundry for atomic-resolution scanning transmission electron microscope (STEM) measurements, however, they found something completely unexpected: bubble-like formations had appeared throughout the material, even at room temperature.

>Read more on the ALS website

Image: (a) Hard x-ray studies showed the presence of two sets of ordering: regular peaks along the out-of-plane direction (Q_z), related to superlattice periodicity (about 12 nm), and satellite peaks in the in-plane direction (Q_y), corresponding to the in-plane skyrmion periodicity (about 8 nm). (b) RSXD studies were performed at the in-plane satellite peaks, which correspond to the periodic polarization texture of the skyrmions’ Bloch components. (c) Spectra from a satellite peak for right- (red) and left- (blue) circularly polarized light. (d) The same spectra with background fluorescence subtracted. (e) The difference spectrum shows a clear circular dichroism peak at the titanium L₃ t_2g edge.

Electric skyrmions charge ahead for next-generation data storage

2019/04/182019/04/22

Berkeley Lab-led research team makes a chiral skyrmion crystal with electric properties; puts new spin on future information storage applications.

When you toss a ball, what hand do you use? Left-handed people naturally throw with their left hand, and right-handed people with their right. This natural preference for one side versus the other is called handedness, and can be seen almost everywhere – from a glucose molecule whose atomic structure leans left, to a dog who shakes “hands” only with her right.

Handedness can be exhibited in chirality – where two objects, like a pair of gloves, can be mirror images of each other but cannot be superimposed on one another. Now a team of researchers led by Berkeley Lab has observed chirality for the first time in polar skyrmions – quasiparticles akin to tiny magnetic swirls – in a material with reversible electrical properties. The combination of polar skyrmions and these electrical properties could one day lead to applications such as more powerful data storage devices that continue to hold information – even after a device has been powered off. Their findings were reported this week in the journal Nature.

Image: Simulations of skyrmion bubbles and elongated skyrmions for the lead titanate/strontium titanate superlattice.
Credit: Berkeley Lab.

Magnetic vortices observed in haematite

2018/08/132018/09/03

Magnetic vortices observed in antiferromagnetic haematite were transferred into ferromagnetic cobalt.

Vortices are common in nature, but their formation can be hampered by long range forces. In work recently published in Nature Materials, an international team of researchers has used mapped X-ray magnetic linear and circular dichroism photoemission electron microscopy to observe magnetic vortices in thin films of antiferromagnetic haematite, and their transfer to an overlaying ferromagnetic sample. Their results suggest that the ferromagnetic vortices may be merons, and indicate that vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex–antivortex annihilation. Ferromagnetic merons can be thought of as topologically protected spin ‘bits’, and could potentially be used for information storage in meron racetrack memory devices, similar to the skyrmion racetrack memory devices currently being considered.

Image: Graphic outlining the antiferromagnetic rust vortices. The grayscale base layer represents the (locally collinear) magnetic order in the rust layer, and the coloured arrows the magnetic order imprinted into the adjacent Co layer.

New forensic DNA profiling technique on the horizon

2018/06/082018/06/18

A study recently conducted at the Circular Dichroism beamline (B23) here at Diamond Light Source could pave the way to a new forensic DNA profiling technique. Researchers hailing from the Ivanovo State University of Chemistry and Technology, Russia, The University of Southampton and Diamond investigated the application of specially designed DNA building blocks.

DNA is a versatile template that can be used for a variety of applications. It is made up of building blocks known as nucleotides (labelled A, C, G and T) which form long strands that bind to complementary sequences and give the familiar double helix. The nucleotides can be tailor made to build new functional molecules for biotechnology, analytics, or even materials science.

With help from a few friends

2018/02/152018/02/19

Researchers discover the precise make-up of a molecular chaperone complex

A complex made up of three proteins, Hsp90, Sgt1, and Rar1, is thought to stabilise an important immune protein known as nucleotide-binding domain and leucine-rich repeat containing protein. While the structure of the Sgt1-Hsp90-Rar1 protein is known, the stoichiometry of the complex has remained elusive. In a paper published in Frontiers in Molecular Biosciences, Dr Chrisostomos Prodromou of the University of Sussex and Dr Minghao Zhang of the University of Oxford worked with Professor Giuliano Siligardi at the Circular Dichroism beamline (B23) at Diamond Light Source to clarify the detailed make-up of the complex. Using synchrotron radiation circular dichroism, they revealed that it consists of an Hsp90 dimer, two Sgt1 molecules, and a single Rar1 molecule. The stoichiometry of the full complex potentially allows two NLR molecules to bind, a finding which may open avenues of research into how these proteins form dimers.

Figure: (extract) The structure of the Sgt1-Hsp90-Rar1 complex with an Hsp90 dimer, two Sgt1 molecules, and a single Rar1. Entire image here.