Focusing on microbeam: Initial installment of CRLs at CHESS

A great challenge is to direct x-rays into a very small, very clean footprint while maintaining high photon flux.

A great challenge at many x-ray beamlines is to direct x-rays into a very small, very clean footprint while maintaining high photon flux. This is especially important when illuminating very small samples, as in protein microcrystallography where crystals can be on the order of a micron across and diffract weakly compared to larger crystals. Any excess scatter in these conditions will contribute unwanted noise and decrease the overall signal-to-noise ratio – an important measure of data quality. Consider an experiment where you first must take the water from a firehose and somehow get a water thread thinner than a human hair without any mist! That is akin to the scale of creating x-ray microbeam at CHESS.

One solution would be to simply block the x-rays down to the size desired, but this has the unfortunate side effect of throwing away vast numbers of photons. Fortunately, x-rays can be manipulated similar to visual light and therefore focused using optical components such as mirrors and lenses. Recently, an optical design of interest at CHESS incorporates the focusing power of x-ray compound refractive lenses (CRLs) to create an x-ray beam on the order of microns across – effectively, a microbeam.

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Picture: The assembled and aligned lenses in their casing. Two brass pinholes bookend the stack of lenses, which all sit in a v-groove designed to be sub-micrometer in accuracy.

Great experience at BioMAX

“It was a fantastic experience”, Jette Sandholm Kastrup.

On June 30, 2017 Professor Jette Sandholm Kastrup, University of Copenhagen was granted two shifts of beamtime at BioMAX by the Program Advisory Committee (PAC) and the MAX IV Laboratory Management for the project “Molecular recognition of agonists, antagonists and positive allosteric modulators at ionotropic glutamate receptors”.

The ionotropic glutamate receptors (iGluRs) are highly abundant in the central nervous system (CNS) and mediate fast synaptic neurotransmission. Dysfunction of the glutamatergic system has been associated with various diseases in the CNS, e.g. depression, Parkinson’s and Alzheimer’s diseases and epilepsy. The iGluRs are for example considered an attractive and appropriate target for the discovery of cognitive enhancers.

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X-ray experiments reveal two different types of water

The strangest liquid of all is even more unusual than we thought

Liquid water exists in two different forms – at least at very low temperatures. This is the conclusion drawn from X-ray experiments carried out at DESY and at the Argonne National Laboratory in the US. An international team of researchers headed by the University of Stockholm now reports its findings in the Proceedings of the National Academy of Sciences (PNAS).

The scientists led by Anders Nilsson had been studying so-called amorphous ice. This glass-like form of frozen water has been known for decades. It is quite rare on earth and does not occur in everyday life; however, most water ice in the solar system actually exists in this amorphous form. Instead of forming a solid crystal – as in an ice cube taken from the freezer – the ice takes on the form of disordered chains of molecules, more akin to the internal structure of glass. Amorphous ice can be produced, for example, by cooling liquid water so rapidly that the molecules do not have enough time to form a crystal lattice.

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Picture: Liquid water has two variants: High Density Liquid (HDL) and Low Density Liquid (LDL) which have now been observed at extremely low temperatures, but can not be bottled. Photo: Gesine Born, DESY

Liquid-phase chemistry: Graphene nanobubbles

X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption Spectroscopy (XAS) provide unique knowledge on the electronic structure and chemical properties of materials.

Unfortunately this information is scarce when investigating solid/liquid interfaces, chemical or photochemical reactions in ambient conditions because of the short electron inelastic mean free path (IMFP) that requires a vacuum environment, which poses serious limitation on the application of XPS and XAS to samples operating in atmosphere or in the presence of a solvent. One promising approach to enable the use of conventional electron spectroscopies is the use of thin membrane, such as graphene (Gr), which is transparent to both X-ray photons and photoelectrons. For these purposes, this work proposes an innovative system based on sealed Gr nanobubbles (GNBs) on a titanium dioxide TiO2 (100) rutile single crystal filled with the solution of interest during the fabrication stage (Figure 1a).

The formation of irregularly shaped vesicles with an average height of 6 nm and lateral size of a few hundreds of nanometers was proved by using a multi-technique approach involving Atomic Force Microscopy (AFM, see Figure 1b,c,d), Raman (Figure 1e) and synchrotron radiation spectroscopies (Figure 2), which have unequivocally demonstrated the presence of water inside the GNBs and the transition to a flat Gr layer after water evaporation by thermal heating up to 350 °C in ultra high vacuum (UHV).

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