C. Pareige

Tomographic Atom Probe: New Dimension in Materials Analysis.

: Materials science requires the use of increasingly powerful tools in materials analysis. The last 20 years have witnessed the development of a number of analytical techniques. However, among these techniques, only a few allow observation and analysis of materials at the nanometer level. The tomographic atom probe (TAP) is a three-dimensional atom-probe (3-DAP) developed at the University of Rouen. In this instrument, the specimen is field evaporated, atomic layer by atomic layer, and the use of a position-sensing system makes it possible to map out the chemical identity of individual atoms within each field-evaporated layer on a nearly atomic scale. After analysis, the volume of matter removed from the specimen can be reconstructed atom by atom in the three dimensions of real space. The main advantages of the 3-DAP is its single-atom sensitivity and very high spatial resolution. In addition to 3-D visual information on chemical heterogeneity, 3-D images give an accurate measurement of the composition of any feature without any convolution bias. This study first describes the history of the 3-DAP technique. Its main features and the latest developments of the TAP are then detailed. The performance of this instrument is illustrated through two recent applications in materials science. Possible ways to further improve the technique are also discussed.

Analysis of Radiation Damage in Light Water Reactors: Comparison of Cluster Analysis Methods for the Analysis of Atom Probe Data

Irradiation of reactor pressure vessel (RPV) steels causes the formation of nanoscale microstructural features (termed radiation damage), which affect the mechanical properties of the vessel. A key tool for characterizing these nanoscale features is atom probe tomography (APT), due to its high spatial resolution and the ability to identify different chemical species in three dimensions. Microstructural observations using APT can underpin development of a mechanistic understanding of defect formation. However, with atom probe analyses there are currently multiple methods for analyzing the data. This can result in inconsistencies between results obtained from different researchers and unnecessary scatter when combining data from multiple sources. This makes interpretation of results more complex and calibration of radiation damage models challenging. In this work simulations of a range of different microstructures are used to directly compare different cluster analysis algorithms and identify their strengths and weaknesses.