Hough Transform Based Accurate Composition Extractions From Correlation Histograms in Atom Probe Tomography

Atom probe tomography (APT) has enabled key insights into material properties and design, by providing accurate nanoscale chemical composition in three dimensions. APT uses a time-of-flightbased mass-spectrometry to decipher the chemical identity of the atoms. The field evaporated ions are collected at a position-sensitive detector, and later back reconstructed in to a three dimensional point cloud. The times of flight are measured in a pulsing window, where the field evaporation of an ion (ideally) is triggered by the application of a single high-voltage pulse or a fast laser pulse. Experimentally, the rates of evaporation are kept actually as low as 0.01 ion(s) per pulse on average. However, the field evaporation triggered by either a high voltage pulse or a laser pulse usually have a decay time. This leads to multiple evaporations not only at the peak of one pulse but also during the decay of the pulse. This causes the departed ions to have a deficit compared to the highest possible kinetic energy or simply a delay, and, these ions are registered with a time of flight incommensurate with their mass-to-charge, making it impossible to label them properly. Field evaporation from phases that are ionically or covalently bonded also often lead to the formation of metastable molecular ions that can dissociate during the flight [1, Such dissociations also cause kinetic energy deficiencies leading to inaccurate identification of the ions. These inaccuracies can cause bias in the extracted compositions.