Development of Combined Chemical Imaging Approaches for Application in Materials Science

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a widely recognized technique for high-resolution chemical imaging, with extensive applications across various scientific fields. This method has been applied to a broad range of solid samples and typically requires minimal to no sample preparation. LA-ICP-MS ablates a small amount of sample and enables spatially resolved characterization of elemental distribution with high lateral and depth resolution. Yet, LA-ICP-MS faces several limitations, including laser ablation parameter optimization, matrix effects, elemental fractionation, and instrumental sensitivity drift. These limitations become most pronounced when pursuing quantitative, spatially resolved visualization of complex, heterogeneous materials. Diffusive gradients in thin films (DGT) is a passive, non-destructive sampling technique that, in combination with LA-ICP-MS, has become a powerful tool for the two-dimensional (2D) visualization and quantification of chemical processes in heterogeneous systems. To date, the majority of DGT LA-ICP-MS studies have been focused on environmental systems, with only one report on application in materials science. This thesis presents two new studies utilizing the DGT LA-ICP-MS approach for the application in materials science. In addition, this thesis includes an examination of laser parameters optimization on the example of LA-ICP-MS analysis of four different materials - NIST 612 glass, DGT gel, graphite pellet, and copper alloy. The study assessed the signal intensity, stability, and crater morphology based on LA-ICP-MS analysis of selected samples with different spot sizes or fluences. The results highlight that both laser parameters and material-specific properties (surface polishing, material homogeneity, and sample thickness) play a crucial role in achieving reliable and reproducible analytical outcomes. Furthermore, the standard addition calibration strategy was developed for LA-ICP-MS of carbon-based materials, enabling the use of matrix-matched calibration standards for analyte quantification in graphite samples. The results showed excellent linear regression (R² > 0.99) for several trace elements (Be, Se, Te, Tl, and Bi) and rare earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu). The use of 13C as an internal standard enabled consistent normalization, compensating for signal fluctuations and correcting for elemental fractionation. Finally, this thesis contains three research publications, including two first-author studies. The first study is focused on the assessment of DGT LA-ICP-MS lateral resolution capabilities and limitations for imaging of metal solutes, and the second study develops and applies a novel DGT LA-ICP-MS method for mapping of elemental solutes at sub-picogram levels during localized corrosion of Al alloys exposed to NaCl solution. The third second-author study is focused on the application of LA-ICP-MS for spatially resolved trace element analysis of two macroscopic inclusions in steel ingots, assessing their potential source. Overall, the presented PhD thesis advances the analytical capability of LA-ICP-MS-based method and provides valuable insights for the method¿s application in materials science, particularly in the area of localized metal corrosion and microstructural characterization.