A novel diffractometer ushers in a new era at I19

Figure 1: verview of the sample point showing the detector in the background and robotic arm on the left.

The I19 beamline has been operational since 2008, providing a high photon flux that allows crystal structure studies of samples that are too weakly scattering to be studied with other X-ray sources. Such studies underpin chemistry and materials science, including research into energy storage and carbon capture materials, superconducting materials and pharmaceuticals.


I19 has two experiment hutches, with EH1 providing a high-throughput diffractometer for chemical crystallography studies. EH2 has a heavy-duty diffractometer and is used for experiments that require a complex setup or bulky sample environment equipment. EH1 was initially equipped with a CCD detector and a basic robotic sample changer, and a two year project has dramatically upgraded the equipment, increasing throughput, allowing an entirely different mode of operation and freeing up beamtime for more involved experiments on EH2.

A shutterless detector
One of the key upgrades to EH1 has been the replacement of the CCD detector with a Dectris Pilatus 2M pixel-array photon-counting detector. The Pilatus 2M offers rapid frame rates and image readout times, and can collect data in a ‘shutterless’ mode, all but eliminating the time overhead between images. Datasets that previously took several minutes to collect can now be completed in seconds.

The Pilatus 2M has increased sensitivity and lower inherent noise, leading to an improvement in data quality. It also offers a comparatively large sample-to-detector distance, a crucial element in reducing the background from air-scatter, allowing the best possible datasets to be collected from weakly scattering samples.

A novel dual air-bearing goniometer
The original goniometer on EH1 had a sphere-of-confusion slightly larger than the 10 µm necessary to ensure that sample crystals remain well aligned with the beam, meaning that a degree of beam focusing was necessary to accommodate drifts in the sample position. The goal for the replacement goniometer was that it would be far more mechanically stable, and would allow micron-sized sample crystals to be studied with a fully optimised beam.

The new design is thought to be the first dual air-bearing fixed-𝛘 goniometer to be built. Air bearings are routinely used for high-precision rotary stages, and are used exclusively for the single-axis goniometers on Diamond’s MX beamlines. Air bearings have smaller systematic errors than conventional mechanical bearings, which do not change with wear. They are the most promising means for achieving a small sphere-of-confusion, and they are used for the major rotation axes of the new goniometer.

A new robotic sample changer
A robotic sample changer is essential to a high-throughput system, as it removes the time overhead of a user having to enter the hutch, manually change samples, and search and interlock the hutch before the next measurements can be taken. I19 now uses a Mistubishi Melfa RV-6S arm, operated via a Mitsubishi Melfa CR2b-574 controller, as the core element of the sample changer. The auto-filling Dewar can hold up to 80 samples in unipcuks under liquid nitrogen. Users can now pre-mount samples at their home lab, and even ship them to Diamond and access the beamline remotely. Remote access not only save users travel time, but it makes it possible to allocate smaller, more frequent slots of beamtimes to regular users, so that they can study crystals more rapidly.

Figure 2: Natalie Johnson from Mike Probert's research group operating I19 from her desk at Newcastle University.

Superior software
Tying these key hardware upgrades together are improvements to the software for data acquisition and processing. High-level user interactions take place via the Diamond GDA software layer, and the new diffractometer and robotic sample changer are more fully integrated. This means it is now possible to queue up different settings (e.g. temperature changes) for samples in advance, and the upgraded robot is more robust and provides far better diagnostics.

The I19 EH1 GDA borrows many features already in use on Diamond’s MX beamlines, but includes significant modifications to cope with the multiple scans needed for SMX. Data processing is now also carried out automatically for routine cases. Diffraction images can be imported into different processing packages, or converted into different file formats, according to user requirements.  Image conversion can be spawned to Diamond’s centralised computer services, and runs fast enough to avoid a backlog.

A forthcoming GDA upgrade will enable the robot to handle room-temperate sample trays. In future, more SMX tools will be added to the in-house software, and the beamline team would like to increase the capacity of the robotic system. 
 

To find out more about the I19 beamline, or to discuss potential applications, please contact Principal Beamline Scientist Dave Allan: [email protected]