X-Treme / X07MA: X-ray absorption spectroscopy at high magnetic field and low temperature
The X-Treme beamline, run by the Microscopy and Magnetism Group, produces a high flux of soft x-rays with variable polarization (circular left, circular right and linear polarization in any angle between 0 and 90 degrees) from an Apple-II undulator source.
The end station is equipped with a superconducting 2D vector magnet operating at 7 T single direction or 2 T vectorial field and a 2 K sample insert. The end-station is also equipped with an in-situ sample preparation system and a variable-temperature scanning tunneling microscope. In order to prepare for their experiment, users are asked to look at the end-station webpage, at the user information webpage and at our frequently asked questions section.
The beamline mostly focuses on measurements involving x-ray magnetic circular and linear dichroism at transition metal L2,3-edges (transition 2p -> 3d), lanthanide M4,5 edges (transition 3d -> 4f) and oxygen or nitrogen K-edges (transition 1s -> 2p). Typical systems studied are single atoms on surfaces; molecules or single-molecule magnets in bulk or on surfaces; superlattices and ultra-thin films. Different detection modes are available: total electron yield, total fluorescence yield, transmission and x-ray excited optical luminescence.
The X-Treme beamline and end station were constructed by a consortium including PSI (Microscopy and Magnetism group, SLS) and the group of Prof. Harald Brune, Laboratory of Nanostructures at Surfaces at EPFL. The funding for the beamline construction was provided by PSI and the one for the end station from the EPFL and the Swiss National Science Foundation.
|Energy range||400-2000 eV|
|Flux (700eV)||4 x 10^15 photons / s / 0.1%BW / 0.4 A
typically 10^12 photons / s at sample position (0.1 eV energy resolution, 700 eV photon energy)
|Focused spot size||exit slit µm x 230 µm (V x H)|
|Spectral resolution||> 5000|
|Polarization||Linear: 0 deg (horizontal) to 90 deg (vertical)
Circular: right / left
Current Highlights and News
3d transition metals often exhibit a quenched orbital moment when in a solid state system. Therefore, the proposition of a large unquenched orbital moment for V in VI3 caused some surprise and discussion in the scientific community. Experimental and theoretical works diverge on the fact of whether the orbital moment is quenched or not. In our work we have been able to give an answer this open issue, proposing also a model for the ground state of VI3.
In an interdisciplinary project, researchers from the Laboratory of Nanoscale Biology in BIO and the Laboratory for Condensed Matter in PSD have revealed the reaction between the nitrogen atoms of the amyloid-beta peptide and copper/zinc ions by using soft X-ray absorption spectroscopy.
Lithium fluoride is an important material which is technologically exploited in spintronics and organic light emitting devices. It turns out that there is a vast difference between the morphologies of ultrathin lithium fluoride grown on the (100) facet of a silver single crystal. At room temperature dendrites are obtained while at elevated temperature lithium fluoride forms square islands. The system is an interesting model to study the crossover between diffusion limited aggregates and island growth.