SPELEEM microscope

Microprobe diffraction

The sample is illuminated with x-rays or UV radiation, to excite photoemission, or with electrons. IL and P1 image the specimen image produced by the objective. A slit can be inserted in the dispersive plane of the analyzer, in order select the desired energy of the photoelectrons. The specimen image is finally projected onto the detector by the action of P2 and P3. The contrast aperture in the diffraction plane limits the angular acceptance for optimum lateral resolution.

µ−LEED
The SPELEEM is operated as a LEED instrument. Reflection of the e-beam by a crystalline surface results in the formation of a diffraction pattern in the back-focal plane of the objective lens. The beam energy is varied by changing the bias voltage between sample and electron emitter. The probed area can be restricted to 2µm either by inserting an aperture in the image plane in the input or exit side of the beam separator, respectively. LEED data yields information about the surface structure.

µ−PhD and µ−ARPES
In micro x-ray photoelectron diffraction (PhD) the photons are used as probe. The exit slit of the electron analyser must be used, in order to allow energy filtering. The field limiting aperture is used to select the probed area. By imaging diffraction from a core level, one can get information on the local order around the emitter. Diffraction imaging using photelectrons emitted from the valence band gives access to the electronic structure in the momentum space.