AN INTEGRATED NANO-AUGER ELECTRON SPECTROSCOPY SYSTEM: SURFACE TO BULK CHARACTERIZATION OF MATERIALS

Auger electron spectroscopy (AES) is a surface sensitive analytical method that is routinely used in material science, but has only rarely been applied to geological materials. Among the signals that derive from e-beam particle interactions (e.g., secondary and back-scattered electrons, CL, and characteristic X-rays), Auger electrons are typically ignored, yet yield significant information of the elemental composition of only a few atomic monolayers (<1 nm) on material surfaces due to their short mean free path in the volume of materials. The advantages of AES are: 1) ability to analyze all elements with high yield with Z>2; 2) quantitative analysis of surface components using published sensitivity factors; 3) sub-micron scale compositional mapping of components on material surfaces; and 4) depth profiling capabilities using an Ar-ion sputter gun to determine chemical stratigraphy on surfaces. Issues of charging of insulating materials using AES encountered in early studies have been somewhat overcome by advanced charge compensation, so the surfaces of a full range of non-metallic minerals can now be studied.

We have equipped a PHI 710 Scanning Auger Nanoprobe System with a field emission electron source and high performance EDS and EBSD detectors. This combination of detectors allows us to acquire at a given location: 1) nano-scale images, 2) “bulk” analysis of materials and elemental X-ray maps using EDS, 3) identification and crystallographic orientation of phases using EBSD, and 4) composition, elemental maps and depth profiling of surface components using AES on micron-scale grains, in situ, and in near real-time. These capabilities will extend research opportunities in characterization of minerals involved with surface-mediated processes such as sorption, catalysis, dissolution/precipitation, and redox reactions. Example applications that will be presented include biocorrosion of steel and sorption of heavy metals on ferri-oxyhydroxide minerals. This instrument is housed at the Imaging and Chemical Analysis Laboratory at Montana State University (http://www.physics.montana.edu/ical) and is part of the MONT National Nanotechnology Coordinated Infrastructure network. We welcome proposed collaborative research projects from across the Earth and environmental sciences.