Abstract:

Scanning transmission x-ray microscopy (STXM) is a synchrotron-based non-invasive x-ray microscopy technique that can be employed for the investigation of micro- and nanostructured materials. This technique combines a high spatial resolution (for soft x-rays on the order of 10-15 nm) with a high temporal resolution (depending on the filling pattern of the synchrotron light source, either on the order of 10 or 100 ps). Furthermore, thanks to the use of monochromatic x-rays as probing mechanism, element-sensitive imaging can be carried out with STXM. The typical soft x-ray photon energies available (between ca. 100 eV and 2000 eV) allow the investigation of both carbon-based systems (e.g. polymers) and metallic systems (e.g. based on 3d transition metals). Furthermore, the elemental sensitivity of this technique, combined with the x-ray magnetic circular dichroism (XMCD) effect, allows for the investigation of the local magnetic configuration of magnetic materials and multilayers with sub-μm spatial and sub-ns temporal resolution.

In this presentation, an overview of the PolLux and NanoXAS endstations of the Swiss Light Source, both equipped with a STXM, will be given. In particular, the FPGA-based time-resolved acquisition system installed at the PolLux endstation, which allows for the acquisition of time-resolved images with sub-ns temporal resolution, and the combined STXM-AFM installed at the NanoXAS beamline will be presented in detail.

Finally, two examples of projects that employed the instrumentation available at the PolLux/NanoXAS beamline will be presented:

• In the first project, the PolLux and NanoXAS endstations were employed for the quantitative imaging at the micro- and nanoscale of polymeric films. Here, with combined STXM and AFM imaging, and NEXAFS spectroscopy, it was possible to investigate the variations of composition in a F8BT:PFB polymer blend with nanoscale spatial resolution.
• In the second project, the PolLux endstation was employed for the time-resolved investigation of the influence of the magneto-elastic coupling effect on the magnetic vortex core dynamics in micro- and nanostructured CoFeB elements. Here, to allow for the application of a mechanical strain to the microstructured CoFeB elements, an alternative approach to the use of piezoelectric crystals (unfeasible for STXM imaging due to the requirement of having x-ray transparent samples) was developed: the strain is generated by the in-situ bending of a thin Si₃N₄ membrane, by applying a pressure difference between the two sides of the membrane with a pressure-controlled environmental cell. After an overview of the membrane bending setup, the main results on the investigation of the effect of the magneto-elastic coupling on the vortex core dynamics will be presented.