NOT AVAILABLE

STATION 1.1
HESGM

Description

• NEXAFS: Near edge x-ray absorption fine structure.
• SEXAFS: Surface x-ray absorption spectroscopy
• XPS: X-ray photoelectron spectroscopy
• XPD: X-ray photoelectron diffraction
• XMCD: X-ray magnetic circular dichroism
• XMLD: X-ray magnetic linear dichroism
• SOXMAS: Soft x-ray magnetic scattering
• OD-XAS: Optically detected x-ray absorption spectroscopy

News

New High Energy Grating Funded
Funding has now been agreed to replace the existing high energy spherical diffraction grating, covering the energy range 500eV - 1000eV.
The existing grating has deteriorated in performance in recent years, an it is anticipated that the replacement will provide flux enhancements of about a factor of 4-5.

Functional Description

Station 1.1 at the Daresbury SRS is a soft x-ray UHV spectroscopy beamline, providing monochromatic photons over the energy range 175 - 1200 eV.

The station is suitable for surface x-ray absorption (SEXAFS and NEXAFS) experiments, photoelectron spectroscopy and photoelectron diffraction experiments, and studies in the area of structural material science (EXAFS).

The energy range encompasses the 1s binding energies of carbon, nitrogen and oxygen atoms, which have a central importance in many areas of catalytic chemistry.

The station can be configured to produce light of a high degree of circular polarisation (~85%), which also makes it suitable for experiments in the field of Magnetic Circular Dichroism (MXD). The station covers the 2p core levels of the transition metals and the 3d core levels of the rare earths.

Recent experiments on the station have also included work in the expanding field of Soft X-ray Magnetic Scattering (SOXMAS).

Technical Description

The heart of the beamline is the HESGM - the High Energy Spherical Grating Monochromator, an entrance slitless instrument providing high photon flux and coverage of the energy range 175 eV to about 1200 eV.

The optical elements are:

• horizontally deflecting water cooled cylindrical mirror (Pt coated CVD SiC).
• 3 interchangeable spherical gratings of line density 1050, 1500 and 1800 lines per mm. The high energy grating (1800 lines/mm) has 2 coatings, gold and nickel, the latter for use in the suppression of higher order light content at energies below the nickel L-edge. The low energy grating (1050 lines/mm) also has 2 coatings, gold and chromium, with the latter particularly useful at energies below the chromium L edge at 574 eV. The medium energy grating is gold coated.
• an exit slit with variable size from zero to >1 mm.
• post-focussing mirror (Pt coated spectrosil ellipsoid with 2:1
• demagnification).

In normal configuration, the light available in an end chamber is > 97% linearly polarised. The use of a retractable grating baffle allows the selection of circularly polarised radiation of degree > 85%.

A permanently installed vessel behind the postfocussing mirror allows continuous monitoring of the 'I0' signal - the photon flux passing into the user's end chamber. A range of carbon, gold and copper meshes and foils are available, and an argon ion gun is permanently installed in the vessel for cleaning.

Data acquisition and control is provided by a dedicated PC-CAMAC-GPIB-RS232 system, running DL developed software.

Proposed Development

Replacement high energy diffraction grating, which should enhance the available flux between 500eV and 1000 eV by about a factor of 4-5.

Benchmark

Low Energy Grating (all values are for a 100 micron exit slit): Flux up to 3.5 * 10^10 photons/second/100mA beam current.
Resolution is 100meV at 250 eV, and 300meV at 500eV.

High Energy Grating (all values are for a 100 micron exit slit): Flux is around 1.5 * 10^10 photons/sec/100mA beam current.
Resolution is 200meV at 500eV, and 500meV at 800eV.