S. Stanescu

HERMES: a soft X‐ray beamline dedicated to X‐ray microscopy

The HERMES beamline (High Efficiency and Resolution beamline dedicated to X-ray Microscopy and Electron Spectroscopy), built at Synchrotron SOLEIL (Saint-Auban, France), is dedicated to soft X-ray microscopy. The beamline combines two complementary microscopy methods: XPEEM (X-ray Photo Emitted Electron Microscopy) and STXM (Scanning Transmission X-ray Microscopy) with an aim to reach spatial resolution below 20 nm and to fully exploit the local spectroscopic capabilities of the two microscopes. The availability of the two methods within the same beamline enables the users to select the appropriate approach to study their specific case in terms of sample environment, spectroscopy methods, probing depth etc. In this paper a general description of the beamline and its design are presented. The performance and specifications of the beamline will be reviewed in detail. Moreover, the article is aiming to demonstrate how the beamline performances have been specifically optimized to fulfill the specific requirements of a soft X-ray microscopy beamline in terms of flux, resolution, beam size etc. Special attention has been dedicated to overcome some limiting and hindering problems that are usually encountered on soft X-ray beamlines such as carbon contamination, thermal stability and spectral purity.

Tailoring the photocurrent in BaTiO3/Nb:SrTiO3 photoanodes by controlled ferroelectric polarization

We demonstrate on prototypical samples containing a ferroelectric layer (BaTiO3/Nb:SrTiO3) that the efficiency of the system, used as photoanode, substantially depends on the polarization state of the ferroelectric layer. We show a significant increase of the photocurrent by a factor larger than 2 when the BaTiO3 film is downward polarized. We explain this finding by the presence of an internal electric field which favors the separation of photo-generated charges.

Fast pole figure acquisition using area detectors at the DiffAbs beamline - Synchrotron SOLEIL

Errors in the article by Mocuta, Richard, Fouet, Stanescu, Barbier, Guichet, Thomas, Hustache, Zozulya & Thiaudiere [J. Appl. Cryst. (2013), 46, 1842–1853] are corrected.

Effect of optical lithography patterning on the crystalline structure of tunnel junctions

The crystalline structure of metal-oxide-based magnetic tunnel junctions patterned by optical lithography was resolved locally using a microfocused x-ray spot. We evidence several micron-sized lithography-induced distortion effects on the crystalline structure of the layers near the edges of the junction. The distortions translate into tilts (up to 1°) of the crystalline planes in the vicinity of the edges and propagate toward the center of the junction. They are attributed to the release of the elastic strain in the layers during the lithographical process. For the smallest junctions, size effects limiting the amplitude of the tilt are also evidenced.

X-ray diffraction imaging of metal–oxide epitaxial tunnel junctions made by optical lithography: use of focused and unfocused X-ray beams

Metal-oxide tunnel junctions made by optical lithography were studied by X-ray diffraction (imaging approach with diffraction contrast) to access local distortions of the crystalline planes of the constituting layers. The effect of the size (10–150 µm) and shape (disc, square and rectangle) of the junction was investigated.

Fast X-ray reflectivity measurements using an X-ray pixel area detector at the DiffAbs beamline, Synchrotron SOLEIL

This paper describes a method for rapid measurements of the specular X-ray reflectivity signal using an area detector and a monochromatic, well collimated X-ray beam (divergence below 0.01°), combined with a continuous data acquisition mode during the angular movements of the sample and detector. In addition to the total integrated (and background-corrected) reflectivity signal, this approach yields a three-dimensional mapping of the reciprocal space in the vicinity of its origin. Grazing-incidence small-angle scattering signals are recorded simultaneously. Measurements up to high momentum transfer values (close to 0.1 nm-1, also depending on the X-ray beam energy) can be performed in total time ranges as short as 10 s. The measurement time can be reduced by up to 100 times as compared with the classical method using monochromatic X-ray beams, a point detector and rocking scans (integrated reflectivity signal).

Two-dimensional resonant magnetic soft X-ray scattering set-up for extreme sample environment.

The newly built MagSAXS (magnetic small-angle X-ray scattering) set-up dedicated to the direct two-dimensional measurement of magnetic scattering using polarized synchrotron radiation in extreme sample environments is presented. Pure optical transport of the image is used to record the magnetic scattering with a two-dimensional CCD visible-light camera. The set-up is able to probe magnetic correlation lengths from the micrometer down to the nanometer scale. A detailed layout is presented along with preliminary results obtained at several beamlines at Synchrotron SOLEIL. The presented examples underline the wide range of possible applications spanning from correlation lengths determination to Fourier transform holography.

Evidence of the exchange coupling in the Co/α-Fe2O3 system

The magnetic exchange coupling in Co/α-Fe2O3(0001) interfaces has been studied. In this paper, we investigated magnetic properties at macroscopic (hysteresis loops) and microscopic (magnetic domain structure) scales. The system shows increased coercive fields and magnetic domain duplication likely mediated by the presence of a metallic interfacial Fe layer.

Development of a fluidic cell to image precipitation reactions by x-ray microscopy

We introduce an observation chamber dedicated to image, at the nanoscale, the kinetics of reactions taking place at the liquid/solid interface. The assembly of this microfluidic cell is straightforward and, most importantly, its design allow the operator to precisely regulate the hydrodynamic flow and control the concentration in reagents at the observation window.