| Oxford nanScience Ltd, UK, has recently introduced 3DAP atom probe that brings a unique approach to materials characterisation at the nanoscale level. The instrument offers simultaneous mapping of the 3-dimensional position and chemical identity of individual atoms within a conductive sample. The atom probe uses the principle of Field Ion Microscopy where a high-voltage is applied to a cooled, needle-shaped sample under ultra-high vacuum. The introduction of an inert gas results in individual atoms being ionised and removed. These are projected onto a phosphor screen to give an image with a magnification of 106 to 107 times.
For 3DAP applications, information is obtained by counting, identifying and spatially locating individual atoms. This is achieved using a patented position detector and time-of-flight mass spectroscopy. Since each atom is evaporated and identified individually, the technique gives atomic resolution in the z-direction nd subnanometre resolution in the x-y plane and is capable of very high sensitivity (10ppb). The instrument is supplied with proprietary software for real-time data acquisition, data processing and data analysis with full 3-dimensional visualisation of the atomic arrangement in the sampled volume. The software allows particular regions of interest in the sample to be examined in detail by allowing slices to be created and moved through the image in any plane.
Applications for the 3-D atom probe include the analysis of nanoparticles and nanophases, the study of nanocrustalline materials, quantitative analysis of segregation at grain boundaries and interfaces, investigation of multi-layer thin film structures, as well as surface chemistry and catalysis.
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