Low Energy Wiggler Beamline (7-22 keV)


 

All three endstations at the LE Beamline are now open for general user operation.

 

Layout and performance

 

 

Measured performance

  • Energy range:                                       7 – 22 keV
  • Flux, @ 250 mA, minimum gap:         1012 photons/s with Si(111), or 1011 with Si(311)
  • Beam size, FWHM:                              150 μm V × 500 μm H
  • Energy resolution, ΔE/E:                    2.5 – 6.4 × 10-4
  • Divergence:                                           200 – 300 μrad V × 730 μrad H

 

The beamline paper is now published in Journal of Synchrotron Radiation! For more details about the beamline, click here to download a pdf copy. DOI: 10.1107/S1600577521002496

 

Endstations and techniques

Endstations at the LE beamline operate at fixed energies, and support the following diffraction and scattering techniques,

  • "Huber" endstation, 15.1 keV, a 4 circle general purpose diffractometer, optimized for high-resolution powder X-ray diffraction (PXRD), but with great flexibility to accommodate a variety of experiments including GISAXS/WAXS, in-situ setups, reflectometry, and reciprical space mapping.
  • "IBM" endstation, 7.9 or 15.1 keV, optimized for in-situ rapid thermal annealing experiments on thin films and multilayer structures.
  • "Bruker" endstation, 9.5 or 18.2 keV, optimized for single crystal small molecule structure determination.

 

High-resolution powder X-ray diffraction (PXRD)

  

We operate this endstation at a fixed photon energy of 15120 eV (λ = 0.8201 Å) using Si(111). However, it is possible to move the endstation and change to another fixed energy within the range approximately 10 - 16 keV using Si(111), or 19 - 21 keV using Si(311). If you would like an energy other than 15.1 keV, please discuss with beamline staff in advance of your beamtime. The default detector is a Dectris Mythen2 X series 1K. We also offer a range of devices for temperature control and gas flow.

PXRD sample preparation and mounting

Our standard method of mounting powder samples is within Kapton capillaries, sealed on both ends. Capillaries are sourced from Cole Parmer. We have several inner diameters available on site: 0.30 mm, 0.50 mm, 0.63 mm and 0.81 mm. We can supply capillaries and help with loading. The choice of capillary diameter is dependent on the X-ray absorption of the sample. Samples with a large fraction of high Z elements may produce the best data within small diameter capillaries. This APS website provides useful guidelines. We use the free program MAC 3.0 for this purpose at the beamline.

IMPORTANT: The capillary should be no more than 25 mm long, no less than 10 mm long, and with a plug of material at least 4 mm long (preferably more). The capillary should be sealed on both ends with wax or superglue, even if the compound is not air sensitive. Take care not to form a bead of glue at the end which is wider than the capillary, or it may not be possible to fit it in the magnetic stub holder. Grind your samples well before loading, as large grains will reduce the quality of the data.

 

The sealed capillary is then mounted on a reusable magnetic stub with a small amount of wax or modelling clay. The magnetic stubs are from Mitigen, Goniometer Base Type B3S-R, GB-B3S-R-40. We will provide the stubs for users. The capillaries are typically measured while spinning at a rate of about 3.5 rotations per second.

For best results, we encourage users to,

  1. If working with samples in powder form, load your samples in capillaries ahead of the beamtime (see instructions above).
  2. Create a priority list ahead of your scheduled beamtime: Determine which samples and which measurements are the most important. We want to ensure that your most important measurements get done in case there are unexpected problems. Typical PXRD samples can be measured at a rate of about 3 samples per hour.
  3. Use a very simple naming convention for your samples (A1, A2, A3, B1, B2, C1, etc.). This makes it much easier for staff who receive hundreds of samples a week.

PXRD data format and how to view your data

When you receive your data we will typically include three types of files:

  • Files with the extension .xye are the PXRD data. The format is essentially that of TOPAS data with no header. The first column is 2θ, the second column is intensity in counts/s, and the third column is error. We use the free program GSAS-II for most PXRD data workup. These files open in GSAS-II (import, powder data, guess format from file). When it asks for an instrument parameter file, choose cancel, and then select “defaults for 0.7Å synchrotron data”. Now the data file should open. By refining the data for the calibration standard LaB6, you can create, save, and apply your own instrument parameter file to the data. PyMCA is a free program also useful for quickly viewing the patterns.
  • The files with no extension are the individual frames from the scan, and can be viewed with PyMCA. These frames get merged together to form the .xye files. Typically users do not need these, but they can sometimes be useful.
  • Lastly, there are files that end in _spec. These contain additional information collected during the scans, such as ion chamber readings and the ring current for each point in the scan.

 

SAXS/WAXS

   

Small and/or wide angle X-ray scattering measurements use our Huber 4 circle diffractometer as the sample holder. Measurements are made at a fixed energy of 15120 eV (λ = 0.8201 Å), and can be performed in grazing incidence or transmission geometry. A multi-sample holder is available for high-throughput grazing incidence measurements (8 - 10 planar samples per hour). The default detector is a Rayonix MX300, with 300 mm × 300 mm active area, typically operated in 2×2 binning mode (73.242 μm pixel size). The maximum detector distance is 2400 mm and the minimum is 250 mm.

For best results, we encourage users to,

  1. Let us know in advance the q (Å-1) and d (nm) range, and angles of incidence, you are most interested in. This will minimize setup time and we can optimize the setup for your specific problem. Our currently available q and d range is tabulated above.
  2. Create a priority list: Determine which samples and which measurements are the most important. We want to ensure that your most important measurements get done in case there are unexpected problems. If the samples are all about the same size, we can measure about 8 samples per hour with the multi-sample stage. Also, switching from WAXS to SAXS or vice versa involves a few hours of setup and tuning, so samples should be grouped by technique.
  3. Use a very simple naming convention for your samples (A1, A2, A3, B1, B2, C1, etc.). This makes it much easier for staff who receive hundreds of samples a week.

SAXS/WAXS data format and how to view your data

Data/images from the Rayonix detector are in the .tif file format. The files are 33 Mb each, so take care to manage the amount of unnecessary images collected. For example, avoid collecting images during initial alignment scans or delete them. The free program ImageJ is installed at the beamline for a quick visual check of the image quality. We use the free program GSAS-II for some SAXS/WAXS data workup. The .tif files open in GSAS-II (import, image, from TIF image file). Now the data file should open. By refining the data for the calibration standard such as silver behenate or LaB6, you can calibrate the detector, and then apply the calibration to your data to perform azimuthal integrations in units of q. GSAS-II has excellent turtorials which fully describe these steps (help, tutorials, browse tutorial on web, calibration of an area detector, and integration of area detector data). The free Matlab program GIXSGUI is also popular for more advanced data workup,

 

In-situ rapid thermal annealing (IBM endstation)

  

This highly specialized endstation can perform simultaneous in-situ diffraction, four point probe resistivity measurements, and surface roughness measurements on thin films during rapid annealing, up to 1100°C. We currently offer a choice of two energies, 7.9 keV with Si(111), or 15.1 keV with Si(311).

 

Small molecule crystallography (Bruker endstation)

single crystal data

The endstation is a commerical SMART APEX II instrument from Bruker. It has a D8 goniometer, APEX II CCD detector, and modern APEX 3 software for data aquistion and analysis. We currently offer a choice of two fixed energies, 9.5 keV (Cu Kα-like) with Si(111), or 18.2 keV (Mo Kα-like) with Si(311).

We have a selection of stacked pinhole collimators: 0.05, 0.2, 0.3 and 0.5 mm. 0.05 mm is the default. We also have two available Oxford Cryostream 800 Plus systems (80 - 500 K) that can be reserved for your beamtime. Our standard sample mount is part # HR8-176 from Hampton Research.

 

Our detectors

Scintillator

FMB Oxford C30NA50B, with Oxford C400 detector electronics. This detector is excellent for measuring weak signals, but has a low dynamic range of about 4 orders of magnitude

Photodiode

We have a selection of photodiodes available at the beamline. The output can be monitored using Keithley 6485 picoammeters or Stanford Research SR570 current preamplifiers. The good sensitivity and high dynamic range of 6 - 8 orders of magnitude is well suited to single crystal and reflectivity measurements. We also use them in active beamstops for SAXS/WAXS.

Mythen

Dectris Mythen2 X series 1K with DCS4. This Si pixel detector has an active area of 8 mm × 64 mm, consisting of a linear strip of 1280 pixels, 50 µm wide, with 1000 μm sensor thickness. The maximum count rate is 1,000,000 counts/s, however it has a linear response up to 100,000 counts/s. It has almost no dark noise and has an acquisition rate up to 1000 Hz. This the default detector for PXRD measurements at the LE beamline.

We have several lengths of detector arm tubes to hold the scintillator, diode or mythen detectors. The tube can be evacuated, and motorized slits can be added to the upstream and downstream ends.

Rayonix

Rayonix MX300. The CCD area is 300 mm × 300 mm with 8192 × 8192 pixels (36.621 μm × 36.621 μm pixels). We typically operate in 2×2 binning (4096 × 4096), or 73.242 μm × 73.242 μm pixel size with 1 s acquisition rate. The acquisition rate increases to 0.3 s with 4×4 binning. The maximum counts per pixel is 216 = 65536. This is our main SAXS/WAXS detector.

Hitachi Vortex

X-ray fluorescence detector, just arrived and being commissioned.