Optimisation of a scanning atom probe with improved mass resolution using post deceleration.

In this paper, we present calculations and experimental results obtained using post deceleration of ions in a scanning atom probe (SAP) geometry to improve the mass resolution. Various electrode geometries, tip to electrode distances in the range 50-170 microm and three different pulse shapes have been evaluated. Experimental mass resolutions of 750 FWHM and 200 FWTM have been achieved reproducibly for the 184W3+ peak without the use of a reflectron lens. 3D finite element electrostatics software has been used to simulate the ion trajectories through the instrument and thus to calculate the variations in velocities for the different electrode configurations. The observed trends are found to agree well with experimental results.