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.


IXAS Strategy toward Standardization

Hiroyuki Oyanagi
Electronics and Photonics Research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan

The rapid growth of synchrotron radiation (SR) facilities, particularly since the advent of the 3rd generation (3G) followed by accumulating number of experimenters has led to a significant increase of output of XAFS research. Unfortunately, the quality divide of users has in effect lead to the degradation of publications and loss of reliability. Expertise is achieved only through a slow process (learning and experience), although communication and information sharing technology dramatically progressed. Since the first meeting on “standards and criteria in x-ray absorption spectroscopy” in 1988 followed by a publication [1], round table discussions have been frequently held at previous XAFS conferences, under the same philosophy but with limited success [2].

The use of standardization is to implement guidelines, a design, or measurements in order to obtain solutions to an otherwise disorganized system. According to ISO, “when standards are absent, we soon notice,” implying our keen awareness of products (data) with poor quality, which do not fit, or are incompatible with the quality level (standard) that we already have. In our community, for example, a phase shift calculation code “FEFF” might be considered as one such “standards”, while some of the data analysis packages are close to this level. If data format is standardized as well, users can exchange resources with each other, making collaborations more possible between distant institutions and giving opportunities to researchers who have no access to the SR facilities. Other fields that need standardization or recommendations to improve quality are: criteria in energy scale accuracy, SR beam purity and stability, detector linearity, sample preparation and procedures etc.

How can we implement standards and recommendations? We need to reach a consensus on solutions that meet both the requirements of common science as well as the community. With a standard in place, users will be ensured with desirable characteristics of data and services such as quality, user friendliness, safety, reliability, efficiency and interchangeability - and at an economical cost. The necessary first step would be for the community to share a common understanding on the merits of standardization. The IXAS and IUCr can work together to discuss their roles to form and implement standardization. The results of the IXAS questionnaire show majority view of experts expect the implementation of standardization in data collection, data format, data analysis, and database within 3-5 years.

The impact of workshop in Tsukuba in its role as the first kick-off opportunity for relevant experts representing various categories of application will be significant. Efforts will be continued by annual workshops to yield draft documents and approval in the XAFS16 meeting (Karlsruhe, 2015). I have high expectations that the voluntary efforts will produce fruitful outcome towards achieving necessary actions for standardization. Urgent need of standardization in data format is widely recognized. For this purpose, a special working group focusing on data format is to be formed which will evaluation several possible candidates to be reported in XAFS15 (Beijing, 2012).

[1] F.W. Lytle, D.E. Sayers and E.A. Stern, Physica B 158, 701 (1989)
[2] July, 2000 report, D.E. Sayers, unpublished. (downloadable pdf file )



Updated documentations on XAFS data format
following the Q2XAFS2011

1. The XAS Data Interchange Specification

Data format working group


2. XAFS format and CIF

James Hester