Principle

The Scanning X-ray microscope can be operated in an energy range from 2-7 keV, thus giving access to the K-edges of Phosphorus to Iron, and to the L- and M-edges of some heavier elements for micro-fluorescence and micro-XANES measurements. Please consult the following periodic table for further details.

A fixed exit double crystal monochromator equipped with Si<111>, Si<220> crystals or NiB4C multilayers is used to select and/or scan the energy of the x-ray beam. The monochromatic beam is then focussed to a submicron probe using a Fresnel zone plate. Typically, the spot size varies between 0.3 to 1 micron depending on the energy, with a beam flux of the order of 10⁸- 10⁹photons/s/Si<111> bandwidth. The rejection of unwanted focussing orders of the zone plate is ensured by the combined use of a central stop and an Order Selecting Aperture (OSA).

The sample is aligned in the focal plane of the zone plate and raster scanned in the micro-beam to collect 2D images. Silicon photodiodes are used for transmission measurements. The SXM is also equipped with two energy dispersive detectors, a high purity germanium detector (HpGe) from Princeton Gamma-Tech and a Silicon Drift Diode (SDD) XFLASH 2001 from Röntec. Transmission signal as well as a full fluorescence spectra can be recorded for each pixel of the map.