X-ray Photoemission Electron Microscope (I06)

The Microscope

The Aberration-Corrected PhotoEmission Electron Microscope (AC-PEEM, from Elmitec Gmbh) forms energy-filtered images with the low energy electrons emitted by the sample surface on a MAPS detector (Medipix-3, from Amsterdam Scientific Instruments). The microscope operates in ultra-high vacuum (UHV) and is ideally suited for magnetic imaging, surface science, catalysis and thin film/self-assembled structure growth. The standard sample cartridges allow flash anneal up to 2000°, and custom cartridges provide additional sample environments and excitations (i.e. low temperatures, electric/magnetic fields, strain, wire-bonds contacting of patterned devices). In some cases, gas dosers and evaporators can be introduced in the main chamber and operated during real-time imaging. The sample stage has azimuthal rotation capability, which allows changing the in-plane incoming angle of the illumination source.
The electron optics can operate in different imaging modes: real space (full-field imaging of the sample surface), reciprocal space (angular distribution of emitted electrons) or dispersive plane (electron analyser dispersive plane).

By incorporating a diverse range of illumination sources, such as X-rays, UV-lamps, electrons, and lasers, a wide range of spatially resolved spectroscopic and imaging techniques become available. The soft x-rays with tuneable polarisation coming from the beamline provides:

• X-ray Absorption Spectoscopy (XAS)
• X-ray Magnetic Circular/Linear Dichroism  (XMCD/XMLD)
• X-ray Photoemission Spectroscopy (XPS)
• Pump-probe time resolved imaging (with fs laser excitation)

Typical applications of X-ray imaging are nanoscale magnetism (ferromagnets, antiferromagnets), ferroelectricity, multiferroics, phase transitions (i.e. metal insulator transitions), catalysis, ultrafast dynamics of electronic or magnetic orderings.

The electron gun enables the structural characterisation of the surface through Low Energy Electron Microscopy (LEEM) on crystalline samples, which is sensitive to surface topography, atomic step edges and surface termination. It typically monitors real-time thin film deposition, structural domain formation, gas absorption, and phase transitions. At very low electron energies, Mirror Electron Microscopy (MEM) has enhanced sensitivity to surface electric potential and topography on crystalline and amorphous surfaces, which can be used to image ferroelectric domains.

In reciprocal space mode, the electron gun enables Micro Low-Energy Electron Diffraction (m-LEED) from areas as small as 0.5mm using an illuminating aperture. By scanning the energy of the illuminating electrons, LEED intensity curves can be recorded very efficiently. It is also possible to select an off-normal LEED spot and form LEEM images in dark-field mode to enhance the contrast between structural islands.