Instrument control

• FMB Beamline Software (beamline control and NEXAFS measurement)
• SPECSlab2 (X-ray Photoelectron Spectroscopy and NEXAFS measurement)

Energy range

In order to achieve an x-ray beam of adequate stability and energy resolution, it is considered that the energy range sought should be restricted to 100-2500 eV.

The insertion device will be a variable polarisation undulator, capable of supplying linear vertical, linear horizontal, left and right circularly polarised light. The device will work in the 1st, 3rd and 5th harmonics. Limited tapering of the undulator is desirable for producing a broader range of energies in the harmonic peak, but is not essential. It is expected that it will be an 'Apple' type, as fast switching of polarisation is not needed. The device may have either a single period or consist of two modules of different periods to cover the entire energy range required. A design study of the insertion device will provide quantitative data for deciding the preferred specification.

Such an insertion device will meet the needs of the x-ray absorption community by allowing the measurement of linear and circular dichroism without the necessity to rotate the sample.

Elliptically polarising undulators are currently the most advanced general-purpose insertion devices. The provision of circularly polarised light ensures that the beamline will be sufficiently flexible to cater for future developments in the scientific areas of interest to the Australian user community.

The resolving power will be 20,000, which is relatively easy to achieve with modern monochromators. In addition there will be provision for lower dispersion gratings with reduced resolution but correspondingly higher flux for experiments that require maximum flux at moderate resolution.

Special features

A soft x-ray beamline and end-station must be maintained under a clean, ultra high vacuum (UHV).

There must be vacuum continuity between the analysis chamber and the synchrotron ring. Therefore, the vacuum in the beamline and end-station must be comparable with that in the ring, in terms of both pressure and quality. It is important that the UHV in both the beamline and end-station be as carbon-free as possible, not only to maintain the reflectivity of the optical components at higher photon energies, but also to facilitate XAS at the carbon K-edge.

The necessity to work under clean UHV conditions means that synchrotron soft x-ray spectroscopy is more demanding and time-consuming than hard x-ray spectroscopy. As a consequence, typical beam access periods are longer, and fewer users can be accommodated. The strategy proposed to address this problem is to have two end-stations, in a branched rather than in-line configuration, sharing one monochromator. The two end-stations proposed are the ASRP soft x-ray spectroscopy end-station, and the other an XPS/XAS end-station optimised for industrial (especially minerals) research. A mirror could switch the radiation between the two end-stations, so that measurements could be made in one end-station while specimen preparation or vacuum recovery was taking place in the other.

In addition, allowance will be made for the ability to connect specialist end-stations in the future.

The soft x-ray spectroscopy end stations

The ASRP soft x-ray spectroscopy end-station is currently being built in Germany at a cost of ~$A1m, and is scheduled to be completed by August 2004. It will be used at the NSRRC in Taiwan until the Australian Synchrotron is operational, when it will be transferred to Australia. Thus, a fully commissioned end-station would be available, at minimal cost in addition to the beamline itself, as soon as beamline 6 becomes operational. This end-station has been designed, and is being constructed, to meet the stringent clean vacuum requirements noted above. In particular, the vacuum system will be as carbon-free as possible, and the end-station will allow the investigation of specimens that must be maintained at a low temperature while they are under vacuum, in order to retain moderately volatile material that might otherwise sublime or desorb.

The ASRP end-station has also been designed to accommodate a cell for the XAS of systems that need to be investigated in their wet environment. A conceptual design for this cell has been developed.

The second soft x-ray spectroscopy end-station will be a modified version of an ambient XPS facility at the Advanced Light Source (Berkeley, USA). The design is a result of collaboration by a consortium consisting principally of the University of South Australia, the Victorian and South Australian Governments, the University of Western Ontario, the Canadian Light Source and researchers at the Advanced Light Source.

Detectors

• SPECS Phoibos 150 Hemispherical Analyser
• Retarding Grid Analyser (Partial Electron Yield and Fluoresence Yield modes)
• Drain Current
• Photodiodes