A Superbend X-Ray Microdiffraction Beamline at the Advanced Light Source
Summary (2 min read)
Introduction
- Over the years, X-ray microdiffraction (uXRD) has become one of the several standard tools used at synchrotron facilities to identify and characterize materials at micron- and submicron scale.
- A typical modern microdiffraction setup delivers a focused monochromatic beam onto the sample and is equipped with an X-ray area detector mounted on a diffractometer t collect 2D diffraction patterns in transmission mode (requiring the use of a beam stop).
- Data are then analyzed via software such as Fit2D. [4].
- Along with groups at the APS and NSLS, the ALS has pioneered some of these techniques and has offered a dedicated poly/monochromatic station on the bending magnet beamline 7.3.3 open to the users community since 2001. [6].
- The energy range can be exte ded and the increased flux at high energy allows using a smaller source size and thus obtaining a smaller focus spot size by flux trade-off.
Beamline description
- The general design of the beamline is similar to the previous end-station on ALS beamline 7.3.3 [6].
- The beamline uses one of the three 6 Tesla superconducting magnet sources of the Advanced Light Source which provides a critical energy at about 12 keV, extending the photon spectrum range well into the hard x-ray regime.
- Water-cooled tungsten roll slits are used to adjust the virtual source size and therefore the size of the focused beam onto the sample.
- The KB mirrors assembly is Peltier-cooled to compensate for the heat load on the mirrors inside the optic box vacuum chamber.
- Using polychromatic radiation, strain states in the sample are obtained by fitting the angular differences between reflections using a non-linear least square method.
Beamline performance and capabilities
- Beam spot size has been minimized using an on-line KB adjustment system.
- The technique uses the Hartmann method to adjust the bends and pitch of the KB mirrors. [7].
- This focus however has slightly degraded over time but stays stable around 1 um for several months.
- Vibrations of the sample stage relative to the optics box have been measured at ~500 nm rms and are probably one of the main factor preventing us from obtaining a sub 500 nm spot size, although it is not the limiting factor for the current 1 um size beam.
- This software’s main feature is its ability to index thousands of patterns in an automated way and convert the information extracted from individual patterns (such as crystal orientation and strain) into two-dimensional maps.
Applications
- The beamline uses two modes of operations that can be employed in a complementary way (Fig 5).
- It was observed that grains which are sitting in a current crowding reg on at the anode corner of the solder ball show significant rotation of up to 0.4º over the length of the experiment, while no other grain in the sample displays such changes in orientation.
- Monochromatic beam mode X-ray microdiffraction is suitable for polycrystalline samples with grain size much smaller than the beam size (nanometric sizes).
- In that case, the diffraction patterns are powder patterns (Debye-Scherrer rings) for which the ring positions can be fitted against a crystal structure database allowing for phase identification.
- Other phases that have been identified in the slips are a spinel (MgAl2O4) in the yellow slip and corundum (Al2O3) in both layers, while hematite and anorthite are ingredients of the body.
Conclusions and future prospects
- Beamline 12.3.2 is a versatile X-ray microdiffraction station recently built at the Advanced Light Source on a superconducting magnet source.
- The beamline is fully operational and is now open to the user community.
- Some of the enhanced capabilities of the beamline compared to the old bending magnet beamline 7.3.3 are a higher photon flux on the sample, better strain resolution, broader energy bandpass, enhanced computing capabilities (use of 24 node dual processor Linux cluster) and enhanced sample positioning system.
- Problems currently or about to be addressed are: sub-500 nm spot size on the sample, sample stage vibrations issues, and reduced data collection time due to long detector readout time.
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Citations
36 citations
Cites methods from "A Superbend X-Ray Microdiffraction ..."
...We also acquired an 8 keV XRD map on ALS beamline 12.3.2 (Tamura et al. 2009) using a MAR133 CCD....
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35 citations
Cites background from "A Superbend X-Ray Microdiffraction ..."
...Our microdiffraction experiments were conducted at Beamline 12.3.2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory (LBNL), Berkeley, California [17]....
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...A detailed description of the synchrotron and the beamline construction are beyond the scope of this report and are readily available in references [16-20]....
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...2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory (LBNL), Berkeley, California [17]....
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32 citations
31 citations
Cites methods from "A Superbend X-Ray Microdiffraction ..."
...All 4900 Laue diffraction patterns were automatically indexed with rhombohedral lattice parameters (a=b=c=6.375 Å, α=β=γ=46.076°; Graf, 1961) using a custom developed software package XMAS (Tamura et al., 2009) and then converted to a hexagonal lattice to obtain the information of orientation and strain tensor at each scanning spot....
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...…were automatically indexed with rhombohedral lattice parameters (a=b=c=6.375 Å, α=β=γ=46.076°; Graf, 1961) using a custom developed software package XMAS (Tamura et al., 2009) and then converted to a hexagonal lattice to obtain the information of orientation and strain tensor at each scanning spot....
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...076°; Graf, 1961) using a custom developed software package XMAS (Tamura et al., 2009) and then converted to a hexagonal lattice to obtain the information of orientation and strain tensor at each scanning spot....
[...]
26 citations
References
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