Atom Probe Tomography (APT) is a technique that provides both three-dimensional (3-D) tomographic images and chemical identification at the atomic scale. This technique combines both high spatial resolution and high chemical sensitivity. The spatial resolution is 0.3 nm in depth and 0.5 nm in lateral. The chemical sensitivity is tens of ppm for most of the elements.
The sample needs to be prepared into a needle shape with the tip radius of 50-100 nm at the apex. The cryogenic cooled needle specimen (25-100K) is biased with DC voltage (2-15 kV). The resulting electrostatic field (tens V/nm) at the apex of needle, in combination with pulsed laser or pulsed voltage, triggers the evaporation of one or more atoms from the surface of the apex. The position of each detected ion is recorded using Position Sensitive Detector (PSD), while the chemical identity is calculated based on the time of flight.
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