In polycrystalline structural materials segregation at grain boundaries plays a significant role to control deformation, fracture and strength. With the atomic resolution of the tomographic atom probe nowadays even low amounts of impurities at interfaces that are beyond the detection limit of surface sensitive techniques such as Auger electron microscopy can be imaged. Additional crystallographic information required to describe the grain boundary character is usually obtained from transmission electron microscopy or transmission Kikuchi diffraction.
However, a calibrated reconstruction of atom probe data is necessary to ascertain an accurate analysis of the segregation content at grain boundaries, especially in materials with very low segregation contents such as technically pure molybdenum. Conventional reconstructions with default radii, image compression factors and field factors often create curved interfaces, therefore the impurity contents generally appear lower due to broadening of the one-dimensional concentration profiles. To determine more accurate segregation contents, a calibrated tomographic reconstruction has to be carried out to obtain a straight boundary without curvature artifacts.
In this study, transmission Kikuchi diffraction is used to facilitate site-specific atom probe specimen preparation. Molybdenum tips with grain boundaries are run in an atom probe equipped with a reflectron. A reconstruction method is applied where crystallographic features in the atom probe dataset are used to determine the image compression factor and geometric field factor for calibration. Furthermore, the deflection of the ions by the reflectron is taken into account. A virtual flight path is applied which describes the straight flight of the ions before they enter the reflectron as well as their bent trajectories after reflection. The accuracy of the method for reflectron data is discussed and compared to data obtained from transmission Kikuchi diffraction and field ion microscopy.