ALS beamline 12.2.2

Synchrotron X-ray diffraction under non-ambient conditions

Beamline 12.2.2 at the Advanced Light Source is a synchrotron X-ray diffraction beamline for samples at non ambient conditions of pressure, temperature and atmospheric conditions.

The beamline photon energy range is 6-35keV with a minimal x-ray spot size of 5x5 um.

The beamline offers mainly three areas of expertise:

- High-pressure X-ray powder diffraction through diamond anvil cells in axial or radial diffraction. Both geometries can be combined with double-sided laser heating.

- Ambient pressure X-ray powder diffraction at temperatures up to ~ 1000 C and simultaneous controlled atmosphere.

- High-pressure X-ray single crystal diffraction allowing for large DAC's (BX90, symmetric cells). This capability is currently available in a single axis configuration. A 4-circle goniometer is being commissioned on endstation 1.

Widely used in catalysis, electronics, photonics, and sensing applications, metallic nanocrystals have properties that are highly dependent on their size, shape, and structure. Defects and structural transformations can benefit certain properties while impeding others. Using chemical methods, it’s possible to synthesize nanocrystals with defined shapes, sizes, and structures for specific applications, but our understanding of the stability of these synthesized structures under operational stresses is limited.

Here, researchers tested the stability of 3.9 and 6 nm gold nanocrystals under stress applied using a diamond anvil cell. They tracked structural changes in the nanocrystals using in situ x-ray diffraction (XRD) at Beamline 12.2.2 of the Advanced Light Source (ALS). By observing changes in the width and position of XRD peaks, the researchers measured elastic strain, defects, and structural transformations.

For the 3.9 nm nanocrystals, peaks (200) and (220) got wider with pressure cycling and remained at higher values after unloading. This indicated the formation of stacking faults, which were shown using molecular dynamics (MD) simulations to be formed via surface-nucleated partial dislocations. For the 6 nm nanocrystals, all peak positions recovered completely with pressure cycling except one, the (200) peak. This peak position was significantly affected by the degree of twinning in the nanocrystal. The irreversible change indicated that the initial multiply twinned nanocrystal transformed into a single-crystalline nanocrystal. Using theoretical calculations and MD simulations, the researchers showed how this transformation is thermodynamically feasible under high pressure. The results indicate that large-scale structural transformation is possible in nanocrystals and must be considered when designing structures at the nanoscale.

Beamline acknowledgement policy:

  • Any publication connected to work on beamline 12.2.2 or the high-pressure lab (6-2241) must be acknowledged in the following manner:

Beamline 12.2.2 at the Advanced Light Source is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.

  • Any publication benefiting from the use of the 12.2.2 laser mill in the preparation lab 6-2241 must be acknowledged in the following manner:

This research was partially supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856

Please note that failure to include these acknowledgment may jeopardize future access to beamline 12.2.2 and/or its support facilities.

Financial Support

U.S. Department of Energy - The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

COMPRES - Beamline 12.2.2 is partially supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856"