Atom probe - Definition and Overview

Atom probe is an analysitical technique in materials science.

Varieties

One Dimensional

A kind of microscopy combining time-of-flight spectroscopy and field ion microscopy (FIM).

As in FIM, a sharp tip is made, placed in vacuum at cryogenic temperature (<50 K). A Positive pulsed voltage is applied, causing individual atoms at the surface of the tip to ionize and be 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 thus the element (or elements) of the ion. From the collection of many of these atoms, a chemical profile of the sample can be made with relative position accuracy of less than one atomic spacing, from a probe size in the range of 1 to 5 nm.

Three Dimensional

aka Tomographic Atom Probe (TAP), 3D Atom Probe (3DAP), Atom Probe Tomograph (APT), and Position Sensitive Atom Probe (POSAP)

This type is similar to the One Dimensional Atom Probe, except that a position sensitive detector is used when collecting, and a 3D reconstruction can be made of the sample (which comprises millions of atoms and volumes of approximately 10,000 nm³).

See Also

• Field ion microscope