May 21, 2008

2008 Joint NSLS-CFN Users' Meeting Workshop

Interfacial Chemistry in Environmental Sciences

As part of the 2008 Joint NSLS/CFN Users’ Meeting, a workshop on “Interfacial Chemistry in Environmental Sciences,” organized by Brookhaven National Laboratory scientists Jeffrey Fitts and Paul Northrup, was held on Wednesday, May 21. Reactions at mineral-water interfaces are integral to a diverse array of environmental processes including element cycling in the oceans, contaminant transport in groundwater, and aerosol formation in the atmosphere. Atomic-level details of these processes have only recently begun to emerge as a result of the parallel development and application of probe microscopy and synchrotron-based methods adapted to the study of mineral-water interfaces. Workshop speakers presented results from the application of a variety of techniques used today to study the structure of hydrated mineral surfaces, adsorbate ions and water composition profiles at environmental interfaces. The workshop also looked at how these applications, along with current efforts at the NSLS and CFN, will benefit from the unique characteristics of NSLS-II.

Participants of the Interfacial Chemistry in Environmental Sciences Workshop

Professor Young-Shin Jun, from Washington University in St. Louis, opened the morning session by providing an overview of interfacial geochemistry and the application of crystal truncation rod (CTR) scattering and grazing incidence x-ray absorption spectroscopy (GI-XAS) to study interfacial phenomena. Professor Jun’s results demonstrated the progression of the field by confirming the oxide surface structure using CTR prior to recording grazing-incidence XAS measurements (at NSLS beamline X15B) of the adsorbates. Dr. Jun highlighted the applicability of these methods to the study of nanoscale materials – a theme that repeatedly emerged throughout the workshop.

Professor Dan Strongin, from Temple University, combined probe microscopy, x-ray absorption spectroscopy and x-ray photoelectron spectroscopy to study pyrite oxidation in order to understand mechanisms to devise methods to passivate pyrite and limit sulfuric acid production in mine drainage sites. Science drivers that emerged during the morning session included particle (nanoparticle) nucleation, which occurs at surfaces/interfaces at a greater rate than in solution (homogeneous vs. heterogeneous), as well as buried interfaces, self assembly, inter-particle mobility, particle morphology, and ligand density.

NSLS resources currently available were reviewed by NSLS scientist Lin Yang. Beamlines X21 and X6B are currently open for general user proposals, and include capabilities to perform CTR. Beamline X9, for small-angle, wide-angle, solution and surface scattering applications, will have higher intensity, higher x-ray energy to get through solution, and smaller focused beam. This beamline is expected to be operational and open for general users in the winter 2009 cycle. Strong interest was expressed by the environmental science community to utilize this new facility. Dr Yang presented an example of arrays of virus (nano)particles on ordered lipid layers on a substrate. These surface measurements (at NSLS X21) were made under solution and provided information on lipid order and particle spacing.

Following the coffee break, this workshop was joined by participants in the workshop on “New Experimental Techniques for Hard X-ray Studies of In-situ Film Growth and Surface Processing” for a joint session. Dr. Paul Fenter, from Argonne National Laboratory, gave the first talk of the joint session and described exciting work by his group to develop computational approaches that will dramatically reduce data processing time and enable nearly real-time structural output from scattering data while at the beamline. Dr. Fenter also showed some of the first data collected on an x-ray reflection interface microscope being developed at the APS, capable of correlating surface topography with scattering intensity at a spatial resolution of 100-200 nm. These developments promise to provide new perspectives on a wide range of interfacial phenomena in environmental sciences and also should make these techniques available to the broader user community.

The final invited speaker was Dr. Gyula Eres from Oak Ridge National Laboratory. Eres described the use of time-resolved surface x-ray diffraction to study interlayer transport in epitaxial growth of STO by pulsed laser deposition.

Following lunch, the joint workshop continued with a short discussion led by Randy Headrick (University of Vermont), Paul Northrup, and Jeff Fitts. It quickly became clear that these two communities – thin-film and surface materials processes and environmental interface science – share many key interests and analytical needs. The discussion initially focused on resources needed at the NSLS and CFN to improve interfacial studies and grow these user communities. A number of participants who currently or would like to use resources available at both facilities for the same experiment encouraged efforts to improve the synergy between the two facilities including joint proposals and operating hours. The group also reviewed current and proposed beamline designs for interfacial studies at NSLS-II. The ability to study dynamics in heterogeneous systems was identified as important common ground between the two communities that should be used to justify and drive development in detectors, electronics, data processing, and microscopy. A number of model beamlines at other synchrotrons dedicated to interfacial studies were discussed.

For more information:
Jeffrey Fitts
Brookhaven National Lab
Email: fitts@bnl.gov

Paul Northrup
Brookhaven National Lab
Email: northrup@bnl.gov