The Structure Dissection of Compacted CeO2/La2O3 Laminates by Spatially Offset Raman Spectroscopy

Abstract

To tackle the challenge of non-destructively analyzing complex oxide layers formed by atmospheric corrosion on active metals, we investigate the potential of inverse spatially offset Raman spectroscopy (inverse-SORS) to detect corrosion products and elucidate how the spectroscopic features of SORS vary. This study explores the utilization of inverse-SORS technology for longitudinal structural analysis of opaque CeO₂/La₂O₃ laminates, which serve as a proxy for corrosion products. Through a combination of experimental measurements and Monte Carlo simulation, it demonstrates the feasibility of inverse-SORS in non-destructively elucidating the layered structure of these laminates. With increasing the spatial offset of this technology, the Raman intensity ratio of La₂O₃-to-CeO₂ increases from 0.23 to 3.2 and then decreases to 0.27 for the CeO₂/La₂O₃ sample with a 34-μm-thick CeO₂ layer under 532-nm excitation, whereas the bottom La₂O₃ layer is hardly detected when the thickness of the upper La₂O₃ layer increases to 225 μm. The results reveal that a thinner CeO₂ layer facilitates the escape and detection of Raman signals originating from the bottom La₂O₃ layer, leading to an enhanced La₂O₃-to-CeO₂ signal ratio and a reduced offset at the characteristic peak. The research also sheds light on the intricate interplay among multiple variables, such as spatial offset, laser wavelength, the corresponding absorption factor, the thickness of the oxide layer, and the compactness. These insights suggest that SORS is a valuable and non-destructive approach for dissecting the structures of highly turbid composites of metallic compounds and semi-quantitatively deducing their thickness.