LATERAL AND DEPTH SCALE CALIBRATION OF THE POSITION-SENSITIVE ATOM-PROBE

In this paper a method is outlined to calibrate both the lateral and depth scales using a combination of FIM and PoSAP microanalysis. Results are given for the following alloy systems: Fe-45at%Cr, Cu-1at%Co, Al-3at%Zn-3 at%Mg-1at%Cu and Fe-1.3wt%Cu-1.4wt%Ni. For each system a direct relationship between the applied voltage and tip radius was found from indexed FIM images and estimates of the image compression factor. The reconstructed PoSAP data was divided into a series of frames in which each represented a fraction of an atomic layer evaporated. Individual rings were seen to collapse inwards when the frames were displayed in succession. The visual effect is similar to watching ring collapse in a FIM image when DC field evaporation occurs. A depth scale calibration was determined directly from the number of ions detected per plane evaporated. The lateral resolution of the wedge and strip anode was analysed by placing a thin mask, consisting of a series of small circular apertures, arranged in a concentric ring pattern, in front of the double channel plate assembly. A series of FIM images was generated and compared with a simulation of the expected distribution of ion impacts. In order to simulate a uniform detector resolution a Gaussian scatter was added to each coordinate in the x and y directions of the simulated impact positions. A comparison between the observed impact positions and simulations showed that approximately 96% of observations would be located to within one atomic spacing during a typical PoSAP experiment.