XAFS Standards & Criteria –Background


Q2XAFS Meetings as a means of experimental XAFS standardization

Original manuscript: Aug. 26, 2016, Revised: Feb. 22, 2017

Hiroyuki Oyanagi (KEK) and Steve Heald (APS)


For reliable state-of-the-art (time-resolved, spectro-imaging, and operando) XAFS applications with high brilliance of the 3rd + and 4th generation storage rings, it is desirable for the XAFS community to update and continue efforts toward experimental standardization. Here the authors would like to propose regular-basis of holding an international workshop hosted by synchrotron radiation facilities, or as satellite meetings to the XAFS and IUCr conferences. As a step toward this effort, we would like to propose organizing a scheme of holding a series of workshops of motivated researchers, hopefully at the next workshop to be held at Diamond in 2017. Considering the previous standardization efforts described briefly below, and the new and upgraded synchrotron facilities that are expected to provide us unprecedented high brilliance beams for which special care should be taken, it is apparent that updating the previous efforts is timely.

XAFS Standard and Criteria
The first meeting of XAFS Standards and Criteria was held during March 7-9, 1988, as a workshop held at Brookhaven National Laboratory to discuss the need for developing standards and criteria for the field of x-ray absorption spectroscopy (XAS) and to recommend methods to implement any suggestions. The workshop proposed by Dale Sayers and Ed Stern and organized by one of the authors (S.H.) was attended by 28 motivated participants from 7 countries including H.O. They represented both a broad geographical distribution and also a range of interests and points of view regarding both experimental and theoretical aspects of XAS. The participants were divided into four working groups: i) experiment, ii) data analysis, iii) theory, iv) and XAS standards database. The report is published at: F.W, Lytle, D.E. Sayers and E.A. Stern, Physica B 158, 701 (1989). More recent documentation is found at: http://ixs.iit.edu/subcommittee_reports/sc/ which includes the July, 2000 report.

Standard and Criteria Subcommittee of IXS (present IXAS)
One of the four sub-groups of the IXS (present IXAS), Standards and Criteria Committee, held the first meeting in Seattle on July 31 and August 1, 1997 to plan its agenda and to begin its work focusing, in the short term, on a report to the XAFS X Conference in Chicago. It met again in August 1998 in Chicago but did not finalize its report. A third meeting was held at LURE in July 1999 to further discuss both the committee report and the error reporting recommendations as well as to plan the activities prior to the XAFS XI Conference in Japan. It met again in July 2000 to finalize reports for the Akoh conference and to plan for the future. Report on Activities of Committee on Standards and Criteria in XAFS Spectroscopy is published at: D.C. Koningsberger, Jpn. J. Appl. Phys. 32 877 (1993).

Q2XAFS Workshop and IXAS Data Format Working Group
The XAFS Data Format Working group of the IXAS (Matt Newville, Bruce Ravel, V. Armando Sole and Gerd Wellenreuther) was formed after “International Workshop on Improving Data Quality and Quantity for XAFS Experiments (Q2XAFS)” held at the Photon Factory, in December 8-9, 2011 focusing on experimental and analytical quality control. The Q2XAFS2011 summarized discussions among experts on the experimental data format resulted in the IXAS Data Format Working Group finalizing a standard experimental format XDI (https://github.com/XraySpectroscopy/XAS-Data-Interchange/wiki/Xdispec). In 2015, the follow-up workshop “Data acquisition, treatment, storage- quality assurance in XAFS spectroscopy” was held at DESY organized by Edmund Welter during Aug. 21-22 period as a satellite conference of XAFS XVI conference. A similar workshop aimed at quality control is also planed at Diamond in 2017 organized by Sofia Diaz-Moreno.

Toward reliable XAFS data taking
For exchanging experimental data among collaborators, or for researchers who have difficulty of accessing reference data, the XAFS database would be quite useful if the data is provided with accurate energy scale and vertical axis linearity. The methodology for a standard energy scale has been a topic of past efforts and owing to dedicated work of staffs and modern instrumentation at synchrotron facilities, users now can record spectra with an established energy scale. Modern near-edge experiments can measure minute spectral changes with much smaller quantity of samples along with time- and/or space dependence. Thus, more strict energy scale or minimized uncertainty are naturally required. As quick scans with micron and sub-micron beams with an unprecedented photon flux are becoming routine, the experimental standardization in energy scale and transmission linearity as well as other spectral response functions should continually be updated. The authors believe continuing XAFS standardization efforts will be fruitful for researchers fully making use of the availability of latest XAFS facilities at the 3rd + and 4th generation synchrotron light sources. Taking the opportunity of XAFS17 in Krakow where experts will get together, in addition to the workshop on data analysis, the experimental methods following the spirit of the previous “Standards & Criteria “ and recent activities, a similar workshop would be fruitful and timely for sustainable XAFS research.

Hiroyuki Oyanagi and Steve Heald, based on a private conversations at NSRL in April, 2016; The blue lines were added by H.O., on Feb. 22, 2017.