Spectroscopy endstation

The spectroscopy endstation is used for high resolution XPS and NEXAFS measurements on clean surfaces and surface adsorbates under ultra high vacuum (UHV) conditions. It consists of separate analyser and preparation chambers accessible via a long-travel manipulator. The preparation chamber includes the usual equipment for preparation and characterization of surfaces (Ar+ ion sputter gun, LEED optics, mass spectrometer), and is connected to a gas-inlet system that allows the storage of up to 4 gases simultaneously, plus argon. The hemispherical electron energy analyser (SCIENTA SES200) is the main instrument used for photoelectron spectroscopy. The sample drain current can also be used for obtaining electron yield NEXAFS.

Prep chamber

Scienta SES200 analyser

The analyser is, of course, set up for ordinary photoemission spectra, but can also operate in constant final state (CFS) mode to measure NEXAFS; constant initial state (CIS) to record f.i. resonant photoemission spectra; and can be run in angle resolved mode to record ARPES spectra. In "add dimension" mode consecutive sweeps of a spectrum can be stored individually such that time dependence can be monitored f.i. as a function of heating, beam exposure or gas exposure.

Due to the spherical symmetry of the analyser a straight entrance slit will be imaged onto a curved line at the detector, with a radius which is half that of the analyzer. Since the detector in the non-angle resolved mode is integrating the signals along one pixel line for each energy channel, this curvature gives a contribution to the energy broadening. For relatively wide slits (> 1 mm) the curvature can be neglected, but for narrower slits it can be more significant. In order to eliminate this effect, some of the entrance slits are curved with the appropriate radius to produce straight lines at the detector. The resolution of the analyser can be calculated from the pass energy and slit width using:
Res (eV) = PassE ∗ w / 2R, with R the radius of the analyser (200 mm)

• Analyser Slit Dimensions (w and l) in mm (.txt)

Manipulator and sample mounting

The 600 mm travel OMNIAX manipulator can be fitted with two cryostats. The default insert is the LN₂ crysostat, which has 4 large power connector feedthroughs (max 20 A each), and two thermocouple feedthroughs: both with 2 pairs of K type (chromel-alumel) spade connectors. A feedthrough with a single pair of C type (tungsten-rhenium) spades is available, but no longer mounted on the cryostat.

NEW! (Sep 09) The LHe cryostat has three large power connectors (max 20 A each), as well as one BNC connector, plus 2 pairs of K type spades on a single feedthrough. Lowest sample temperature reached: 17K. With the crystal on a W wire described below you'll end up around 45K.
∗ Note that LN₂ is available free of charge, but LHe should be ordered (at least 2-3 days in advance) and paid for by the users. Ask the beamline manager how to go about this.

Both cryostats terminate in a copper cylinder with an M6 threaded hole in the centre. You can fit your own sampleholder directly here (advised: max 10 cm length), or also use our piece "A", which has two holes of 3 mm diameter, spaced 6.5 mm centre-to-centre. For crystals with a groove, mounting piece "B" is often used in addition (see schematic example).
NEW! (Oct 09) If you need all the measures of A and B, click here.