Atom probe
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The atom probe is an atomic-resolution microscope used in materials science that was invented in 1967 by Erwin Müller.
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 atoms from a sharp tip (corresponding to specimen volumes of 10,000-1,000,000 nm3).
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.
[edit] External links
- Northwestern University Center for Atom-Probe Tomography
- Metallic Nanostructure group of the National Institute for Materials Science (Japan)
- Field ion microscopy and atom probes, Rouen University (France)
- Imago Scientific Instruments [1]
- Oxford nanoScience Ltd [2]
- Cameca [3]
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