XPEEM is a parallel (full-field), surface-sensitive imaging method using photo-excited electrons, and is therefore related to the photoemission process. The surface sensitivity of the technique arises from the limited inelastic mean-free path of the characteristic photoelectrons in matter. In this technique, X-ray or UV photons shine the sample surface, and an electron optical column (the PEEM) makes, with the emitted photoelectrons, a magnified image of the surface which can be further filtered in energy with an imaging spectrometer or energy filter. Depending on whether secondary electrons or true core-level electrons (both element- and bonding state-specific) are used for microscopy, the image can be characteristic either of the work function anisotropy, or of heterogeneities in elemental distribution and chemical changes at the surface of interest. Besides imaging in real space, reciprocal space microscopy can also be performed by imaging the diffraction plane of the PEEM, which is equivalent to imaging the parallel component of the valence band photoelectron momentum. The so-called kPEEM technique is equivalent to micro-ARPES and now competes it regarding energy resolution, but is much faster since parallel, angular spectroscopic valence band imaging is performed without any sample rotation.
If many PEEM instruments can be found at synchrotron radiation beamlines, most of them use the absorption channel for element-specific microscopy (XANES-PEEM), and are rarely fitted with an effective (i.e, maintaining energy resolution at high lateral resolution) imaging spectrometer to exploit the photoemission channel. Mature, advanced instrumentation is now available with laboratory sources (including X-rays), without significant degradation of the resulting energy and lateral resolutions, and enhancing very much the accessibility of the technique to research teams.
XPEEM, LEEM - SIM Beamline @ Swiss Light Source Synchrotron
The permanent endstation of the SIM (Surfaces/Interfaces Microscopy) beamline is a Photoemission Electron microscope (PEEM), it allows to image samples using the photoelectric effect with very high spatial resolution
Pure permanent magnet helical undulators, flux 1015 photon/s/0.1%BW/0.4A, focused spot size 30µm x 100µm (V x H), polarization linear: 0 deg (horizontal) to 90 deg (vertical), circular: right / left
Diameter<10mm, thickness 0.1-3 mm, flat, conducting surfaces for high resolution, temperature between 120 K and 1800 K