Recent developments in position-sensitive atom-probe microanalysis

Abstract

The difficulties associated with the aperture geometry of the conventional atom probe have been overcome by the introduction of a new generation of wide-angle, single-atom sensitivity, positionsensitive detectors. With the aid of such detectors, it is now possible to map the locations and identitiesof atoms over regions of solid surface up to 50 nm in diameter. The nanometer-scale chemistry of successive atomic layers can be investigated during the process of field evaporation. We therefore have the new and exciting ability to investigate the atomic-scale chemistry of solids in three dimensions. The first three-dimensional atom probe is the PoSAP (Position Sensitive Atom Probe), developed at Oxford by Cerezo and Smith. In this instrument, position sensing is carried out by means of a wedge-and-strip anode assembly, located directly behind the double microchannel plate used for primary ion detection and time of flight measurement. The detector readout functions in serial mode. Only one ioncan be successfully detected and identified for each evaporation pulse which is applied to the specimen