3-DIMENSIONAL FIELD-ION MASS-SPECTROMETRY

The three-dimensional atom probe (3 D-AP) is a new variant of the field ion microscope (FIM) combined with a time of flight mass spectrometer and single ion detection sensitivity (imaging atom probe). With the field ion microscope the topology of a surface, surface reactions and surface modifications can be studied in atomic detail. Using time of flight measurements, surface layers and interface layers can be chemically analyzed atom by atom and atomic layer by atomic layer. This three-dimensional atom probe permits the elemental reconstruction of a small volume of the specimen with near atomic resolution. This improvement is obtained by using the digitized video signal of the imaging atom probe detector and a separate time signal from the phosphor screen to achieve simultaneously the x and y position and the mass-to-charge ratio of individual ions striking the detector. Examples from a study on high speed steel are presented to demonstrate the usefulness of a recently built instrument.