From Northwestern University Center for Atom-Probe Tomography
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These are answers to frequently asked questions from the AtomProbe mailing list and other sources.

File formats


An atomlist is an ASCII text file (typically, but not always, with Mac line endings). It was created by NUCAPT for ADAM/Apex. Values are separated by whitespace and the header row says which each column represents:

index (incremented int) pulse number (int) element type (int) mass/charge (amu as a float) voltage x (ang) y (ang) z (ang)


A POS file is a simple binary file (big endians) consisting of 4-byte IEEE float32s representing the x, y, and z position (in nm), and mass/charge (in amu) of every atom in a dataset. It is used by many atom probe groups and software packages and is the current de facto exchange method.


These files are the minimally documented files collected by the LEAP and used in Imago's IVAS and their reconstruction backend ROOT.


Scripts to convert between atomlists and POS files are available from NUCAPT. Apex can import and export both of these types, but some versions skip ions in the conversion process.