THE TOMOGRAPHIC ATOM-PROBE - A QUANTITATIVE 3-DIMENSIONAL NANOANALYTICAL INSTRUMENT ON AN ATOMIC-SCALE

The physical architecture and the performance of a quantitative three- dimensional atom probe recently constructed are described. The develop ment of such an instrument relies on the design of a multi-impact posi tion sensitive detector. The multidetection system that we have develo ped is based on the use of a 10 x 10 anode array placed behind a two m icrochannel plate assembly in a chevron arrangement. The spread of cha rge between the microchannel plate and the multianode is used to deriv e the position of ion striking the detector. Spatial coordinates can b e calculated for multiple and simultaneous time-of-flight events. The procedure used for the derivation of ion positions from charge measure ments is given. Specific experiments were carried out in order to dete rmine the intrinsic spatial resolution of the multidetector. Three-dim ensional reconstruction of two-phase materials are provided and illust rate the performance of this new apparatus. The reconstructed images d emonstrate that atoms are positioned with a precision of a few tenths of a nanometer. The mass resolution M/DELTAM (FWHM) of the apparatus i s close to 200.