December 5, 2008

Introduction to XAFS: Experiment, Theory, Data Analysis

The short course in x-ray absorption fine-structure (XAFS) spectroscopy was offered on October 30-November 1 at the NSLS. It continued the annual NSLS tradition of gathering a group of scientists, active in the field, to share their expertise with those interested in learning about the possible use of XAFS in their research. The course was geared toward beginners with overall familiarity with other structural techniques and have read basic literature about XAFS but needed hands-on practice. The course included beamline experiments, lectures by experts in the field, tutorials, and data analysis sessions. Emphasis was made on applications of EXAFS and XANES to typical problems in nanocatalysis, environmental, materials, and life sciences.

Participants of the 2008 XAFS Workshop

The course was oversubscribed by a factor of two, and 30 registered participants were selected on the basis of their project descriptions and diversity of research interests. In addition, about 25 auditors attended lectures and data analysis sessions.

The first two days of the course began with morning lectures on “Basic Principles and Application of EXAFS” (Anatoly Frenkel, Yeshiva University), “Theory of EXAFS and XANES” (John Rehr, University of Washington), “XAFS Instrumentation and Sample Preparation” (Syed Khalid, NSLS), “Principles of EXAFS Data Modeling” (Scott Calvin, Sarah Lawrence College), and “Firsth Shell Analysis Using IFEFFIT” (Bruce Ravel, NIST). After lunch, the participants were divided into five groups and participated in beamline experiments led by Joe Woicik (NIST), Trevor Tyson (New Jersey Institute of Technology), John Kirkland (SFA, Inc.), Faisal Alamgir (NIST), Kumi Pandya (SFA, Inc.), Nebojsa Marinkovic (University of Delaware), Qi Wang (Yeshiva University), Calvin, Khalid, and Frenkel. Although NSLS beamlines X23A2, X23B, X11B, X18B, and X19A were officially designated for the course, we also were able to use X18A since it was recently upgraded for energy scanning.

Beamline projects varied between different instructors, and participants were divided into groups led by instructors with research interests that best matched their own. For example, Tyson led a two-day long mini-research project focused on temperature-dependent EXAFS studies of MnO. Woicik demonstrated the use of fluorescence EXAFS technique in measuring local structure of alloy thin films. Marinkovic prepared several solution samples (concentrated and dilute ones) to demonstrate how to measure the local structure of metal complexes in liquid phase. And Wang, Alamgir, Calvin, Frenkel, Khalid, and Pandya provided guidance in sample preparation methods, beamline operation, and data acquisition procedures using standard materials – metal foils and metal oxides – as examples.

On Friday, after the beamline session, participants gathered in the large auditorium of the Medical Building and participated in an analysis session with the data they collected at the beamlines. Data analysis instructors were Tyson, Alamgir, Calvin, Khalid, Marinkovic, Wang, Ravel, and Frenkel. During the data analysis session, participants were trained in using the XAFS analysis packages IFEFFIT and FEFF8.

On Saturday morning, the organizers ran several parallel discussion sessions aimed at helping participants develop a better understanding of how to incorporate EXAFS and XANES in their research programs. Rehr’s session was focused on XANES modeling, Alamgir’s discussed electrochemistry applications, Frenkel led a discussion session on the problems in catalysis, and Ravel focused on environmental science. That afternoon, the course participants continued analyzing the data they collected during the workshop.

All course members thoroughly enjoyed friendly and professional support by the NSLS Users Administration Office members Gretchen Cisco, Liz Flynn, and Mercy Baez.