Uncertainties in interfacial excess calculations from atom probe tomography data.

Atom probe tomography can be used to measure the excess of solute chemical species at internal interfaces, but common protocols do not usually consider the compositional uncertainty of the (usually dilute) solute. Here, general models are derived for the composition profile of a solute segregated to the interface between two grains or phases. This model is fit to experimental data, with the cumulative compositional uncertainty included in the calculation of the interfacial excess. It is shown that the relative uncertainty in the interfacial excess can be large for dilute solutes, even when segregation is obvious in the concentration profile. Different methods for estimating the extent of the boundary provide different estimates for the interfacial excess and its uncertainty. Some strategies are provided for the minimisation of uncertainties in typical data, though ultimately, a typical calculation will be limited by compositional uncertainty arising from the relatively few solute counts in the region-of-interest.