Using EELS to reveal ferric iron content from a Chang’e-5 lunar surface sample

Gatan instrument used

The Continuum S is an electron energy-loss spectroscopy (EELS) system that combines high-speed XCR™ sensor stack technology and advanced acquisition hardware to acquire shift-corrected, dual-energy range EELS (DualEELS™) data at ~8,000 spectra per second with near-zero dead time. Utilizing the advanced features of the DigitalMicrograph^® software, 3D chemical state maps can be quickly and reliably generated.

Background

Using the presence of iron in lunar regolith, researchers can record and reveal the oxygen potential of our solar system. Previous research on Apollo samples showed that the lunar surface and interior are highly reducing and mainly contained ferrous (Fe²⁺) or metallic iron (Fe0), with only a tiny amount (<1 wt.%) of ferric iron (Fe³⁺). However, a much higher Fe³⁺ concentration in lunar glass beads has been recently revealed. The mechanisms for the creation and stability of Fe³⁺ in the highly reductive environment of the moon’s surface are still under debate. Using EELS chemical state mapping and tomography, the authors propose an explanation.