Physics-based reconstruction algorithm for 3D atom probe microscopy

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Atom probe tomography represents a method of 3D material analysis in outstanding resolution that follows an unusual functional principle: Single atoms are desorbed from the sample as ions, accelerated in strong electric fields, detected by a spatially resolving detector setup, and identified by their time of flight. Subsequent to the measurement, a 3D map of the spatial arrangement of the atoms is generated by a numeric reconstruction. Up to now, the established reconstruction algorithms are based on a simple geometric projection. This leads to unacceptable artifacts and limits the accuracy of spatial positioning to about 1 nanometre. The primary goal of the project is the design and exploration of a new reconstruction method that is based on the physically exact calculation of the ion trajectories. In a first phase of the project, the original idea of exactly calculating the electrical fields and the ion trajectories for a particular sample geometry and then matching them with the positions of the detector events was tested. In the course of these investigations, an additional principle was derived to determine the positions of the atoms unambigously. Now this principle shall be tested with different sample geometries. Remaining parameters of the reconstruction shall be optimized so that the correct sample shape and microstructure is reconstructed. The accuracy of the procedure should be improved. It should be investigated whether even the measurement of the atomic lattice structure becomes possible. The numerical efficiency of the algorithms should be sufficiently improved so that the reconstruction can be processed on small multi-kernel CPU cards. Finally a software should be developed that allows the practical processing of experimental data sets.