Effect of preparation angle on atom probe tomography of reactive multilayers
Regarding self-propagating reactions in reactive multilayers, the morphological signature of the starting material plays a significant role for the processes taking place within the reaction front on the one hand and the evolution of the product phase microstructure on the other hand. Therefore, an extensive characterization of the unreacted material is necessary in order to understand which morphological parameters beyond the bilayer thickness of a multilayer affects the self-propagating reaction. On the near-atomic level, atom probe tomography (APT) is a powerful technique to measure local concentrations at the interfaces between the different layers.
However, analyzing multilayers via APT can be very challenging. Especially regarding Ru/Al and Ni/Al multilayers, the high mechanical stresses caused by the external electrical field in combination with large differences in the fields for evaporation (Ru ~ 41 V nm-1, Ni ~ 35 V nm-1, Al ~ 19 V nm-1) can lead to the rupture of the samples. Furthermore, these differences in the evaporation field strengths as well as the morphological roughness known for this system may result in misaligned atom positions at the reconstructed interfaces or artifacts with respect to the depth coordinates of the ions.
Depending on the orientation of the interfaces between the individual multilayers to the main axis of the sample tip, the above mentioned reconstruction artifacts could be minimized while maintaining good mechanical stability. For this reason in this work several sample types with different angles between the bilayer interfaces and the main axis of the sample tips are prepared with FIB/SEM and systematically investigated with APT. The reconstructed data sets are presented and compared with TEM images with regard to possible artifacts.