A sizeable proportion of the samples and experiments brought to the beamline benefit from a microfocus capacity, which has been designed, constructed and commissioned as an optional ‘drop-in’ end station. This optional configuration for I22 provides additional demagnification and focusing of the primary beam to a spot size of approximately 10 μm2. The microfocus end station consists of secondary focusing optics, an independent sample stage and positioning motors, an inline microscope camera, a beamstop, and a detector, all of which are detailed here. The entire end station is self- contained on two free-standing steel frames, one for the optics and sample position and one for the detector platform. The energy range available is currently 14-20 keV, as the sample positioning area and flight path are in air. We have recorded a flux of 5.645 x 1010 photons/sec in the focused beam at 14 keV. Ongoing work on the main bimorph mirrors on I22 will lead to smaller focal spot sizes with the microfocus end station, with an overall goal of 3-5 μm2 at the sample. We are currently able to achieve a maximum resolution of 220Å.
The microfocus capacity is currently in the optimisation phase, and available to users; to discuss a microfocus experiment, contact a member of the beamline team.
Sample positioning and environment
Inline sample viewing on the microfocus table is provided with a GigE camera attached to a Keyence lens, which can be used to align samples in the beam as well as view samples during data collection and plan mapping experiments. For alignment, a tantalum wire cross is used to locate the beam centre. Directions for the alignment procedure can be found on the sample viewing and alignment page.
The microfocus station has a standalone positioning system comprising two PI high-precision linear stages and a vertical high-precision elevation stage, for XYZ positioning to 0.1µm. We have recently added a small piezo rotation stage with 0.2µrad minimum increment and 360° travel, which can be placed on the linear stages if required.
The microfocus station also benefits from some custom-designed sample environments, including an optical trap for objects 1-20 µm in size, and a tensile tester and cantilever bender. If your experiment would benefit from these, please contact a member of the beamline team so we can ensure availability. We are also equipped to house custom or user-supplied commercial sample environments on the microfocus station, up to a maximum weight of 10 kg; please discuss this with beamline staff in advance to ensure correct mounting and connectivity on the table.
Beamstop, detector and camera
A 1mm tungsten wire beamstop is placed behind the sample position to stop the primary beam from hitting the detector. A drain current measured from the tungsten wire should provide an indication of flux after the sample, and will eventually be calibrated to provide a transmitted intensity measurement. Alternatively, a lead square placed on the detector face can also provide the necessary beamstop.
The microfocus station has a separate detector table that can accommodate either the Rayonix SX-165 HE CCD detector or the PILATUS 2M detector. The detector position can be changed easily to vary the camera lengths between 400 mm and 1175 mm for combined SAXS/WAXS. As there is no evacuated flight tube on the microfocus station, camera length changes require minimal intervention. With the present setup, we are able to achieve a maximum D-spacing of greater than 225Å on the detector at the maximum camera position; this will increase as the focal spot is reduced in size during the optimisation process.