February 1, 2008

X9 CFN Endstation Near Completion

The construction of the endstation at the new small angle x-ray scattering (SAXS) X9 beamline is almost complete and ready for acceptance by the Center for Functional Nanomaterials (CFN). X9 is an undulator-based beamline capable of carrying out SAXS measurements in both transmission and grazing incidence geometry within a wide x-ray energy range from 2 to 20keV and spot sizes as small as 10 microns in the sample. Its construction is funded by multiple sources including a Department of Energy instrumentation grant for beamline optics, and a contribution from the CFN as a Contributing User (CU) for endstation equipment.

The layout of the endstation

The X9 endstation features several instrumentation innovations. The beamline utilizes two-stage focusing optics that can be configured to optimize either beam divergence when low scattering background is needed, or a small spot size for measurements on small samples or samples with micron-scale structural textures. A custom-made charge-couple device (CCD) detector, located only 20mm from the sample, is used to collect scattering data at wide angles simultaneously with data collection at small angles on the detector located at the end of the flight path up to 5m away from the sample. For thin film samples that contain two-dimensional structures, a hexapod will be used as the sample positioner. The hexapod utilizes six actuators to realize sample translation and rotation. Compared to sample positioners that utilize rotary stages, a hexapod has the great advantage that the rotation center of motion can be arbitrarily chosen by the software to be any point on the sample. The limitation of finite rotation range of the hexapod is compensated by the use of a full circle rotary stage under the hexapod. Finally, the endstation is equipped with a PILATUS pixel array detector. This photon-counting detector does not have dark and readout noises that are typical in CCD detectors. It is therefore ideal for measurements such as protein solution scattering in which low detect noise is crucial. The PILATUS detector is also capable of capturing a stream of scattering patterns at frame rates as fast as 100 frames per second.

The hexapod that will be used as the sample manipulator.

View from the end of the hutch that shows the flight tube and the sample/detector chamber.

The mechanical design of the beamline itself is currently in progress. The installation of the undulator and the front end will take place during the May shutdown, and the monochromator and mirror system are scheduled for delivery in May and June. The beamline is expected to come into operation toward the end of 2008.

Upon its completion, X9 will host the SAXS program that currently exists at beamline X21. The beam time at X21 is currently shared by two endstations and three different scientific programs. As a result, SAXS beam time is severely over-subscribed. The operation of X9 will provide much-needed beam time for the life sciences, soft condensed matter physics, and nanoscience communities.

ARTICLE BY: Lin Yang