| AVS 66th International Symposium & Exhibition | |
| Chemical Analysis and Imaging Interfaces Focus Topic | Friday Sessions |
| Session CA+AS+NS+SE+SS-FrM |
| Session: | Novel Applications and Approaches in Interfacial Analysis |
| Presenter: | David Mueller, Forschungszentrum Juelich GmbH, Germany |
| Authors: | D.N. Mueller, Forschungszentrum Juelich GmbH, Germany M. Giesen, Forschungszentrum Juelich GmbH, Germany D. Stadler, University of Cologne, Germany T. Duchon, Forschungszentrum Juelich GmbH, Germany F. Gunkel, Forschungszentrum Juelich GmbH, Germany V. Feyer, Forschungszentrum Juelich GmbH, Germany S. Mathur, University of Cologne, Germany C.M. Schneider, Forschungszentrum Juelich GmbH, Germany |
| Correspondent: | Click to Email |
Spectroscopic imaging techniques are becoming more and more accurate and available, which results in an increase of data to handle and analyze. Near Edge X-Ray absorption spectroscopy, especially in the soft X-Ray regime, has the ability to identify inhomogeneities in chemistry and electronic structure, which is mostly done by fingerprinting or using internal standards. In a spectromicroscopic image, each pixel contains such a spectrum, and by the lack of rigorous fitting routines that are for example present in XPS, reduction and preevaluation of data is needed. Principal Component Analysis (PCA) of X-PEEM data affords this in an unambiguous and unbiased way by identifying and highlighting spectroscopic features which contribute to a spectrum.1
Two cases where PCA revealed information that might have been missed otherwise are presented here: Firstly, iron oxide thin films grown by CVD showed a considerable influence of an external magnetic field on chemistry and crystallinity. Combination of O-K- and Fe-L-Edge X-PEEM unambiguously identified different iron oxide polymorphs (Fe3O4 and α-Fe2O3) depending on field strength during deposition. The former XAS Edge showed subtle spatial variations in the EXAFS regime that could be identified as the breakdown of long-range ordering, pointing to incomplete crystallization when films are deposited without magnetic field assistance.2
The second example is the surface decomposition of Pr0.5Ba0.5CoO3-δ (PBCO), a promising material for the use as water splitting catalyst and solid oxide electrochemical cell electrode. Using spatially resolved O-K-, Co-L-, and Ba- and Pr-M-Edge XAS, changes in surface chemical composition upon annealing and its impact on the electronic structure were observed. Laterally resolved by X-PEEM, PCA could reveal that exposing thin films of the material to technologically relevant conditions (1073 K, 20 mbar of O2) leads to a more complex decomposition pathway than simple spinodal unmixing to the end members BaCoO3 and PrCoO3 as the spectromicroscopic dataset could only be described satisfactory by a linear combination of three components.