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Müller's atom probe made one-dimensional compositional maps by combining Time-of-flight Spectroscopy and Field Ion Microscopy (FIM). The instrument now allows the three-dimensional reconstruction of up-to hundreds-of-millions of Atom s from a sharp tip (corresponding to specimen volumes of 10,000-1,000,000 Nm 3). As in FIM, a sharp tip is made, placed in Ultra High Vacuum at cryogenic temperature (typically 20-100 K). Individual atoms at the surface of the tip are ionized, either by a positive pulsed voltage or a laser. These ions are repelled from the tip electrostatically. A fast timing circuit is used to measure the time taken between the pulse and the impact of the ion on a detector, thus allowing the mass-to-charge ratio of the ion to be calculated and, therefore, the element (or elements) of the ion. From the collection of many of these ions, a chemical profile of the sample can be made with relative position accuracy of less than one atomic spacing. Atom-Probe Tomography (APT) uses a position-sensitive detector to deduce the lateral location of atoms. It was invented in 1988 by Alfred Cerezo , Terence Godfrey , and George D. W. Smith . EXTERNAL LINKS
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