Paper AS-ThM13
Multi-Technique Surface Analysis of Geological Samples, Including sub-10 Micron Spectroscopic XPS Imaging

Thursday, October 22, 2015, 12:00 pm, Room 212D

A single geological sample may have multiple phases, each with different chemical bonding environments. Geologists will typically have access to SEM-EDS, giving them elemental information from the different grains (from bulk depths). When it comes to chemical information, however, XPS provides a unique ability to easily acquire data from these small grains. It offers quantitative chemical bonding data with a probe size small enough to acquire data from individual phases.

In this work, rock cross-sections were analysed with XPS to quantify the elements in different phases and to identify and quantify the oxidation states of elements in these regions. The analysis can be divided into four main sections: 1) Finding the features of interest, 2) Aligning the X-ray spot on the features, 3) Acquiring the XPS data and 4) Processing the XPS data to answer the key questions about chemical bonding states.

Any XPS tool used for this analysis needs to have a high quality optical system, enabling to geologist to rapidly find the features of interest, with a live optical feedback system. The grains were typically 10s of microns in size, so a small X-ray analysis area is required. This small area analysis was achieved in two different ways: shrinking the

X-ray spot to match the feature size or collecting spectroscopic parallel imaging data. In the latter case, every pixel in the image has full XPS data allowing the analyst to perform sub-10mm area analysis directly from the X-ray image.

Techniques complementary to XPS can also help provide a more complete characterization of geological samples. SEM/Auger can offer analysis with a much smaller probe size than XPS, but it is necessary to charge compensate during the experiment. Charge compensation methodology will be discussed in this work.