Introduction to APT

The sample is prepared in the form of a very sharp tip. The cooled tip is biased at high DC voltage (3-15 kV). The very small radius of the tip and the High Voltage induce a very high electrostatic field (tens V/nm) at the tip surface, just below the point of atom evaporation. Under laser or HV pulsing, one or more atoms are evaporated from the surface, by field effect (near 100% ionization), and projected onto a Position Sensitive Detector (PSD) with a very high detection efficiency. Ion efficiencies are as high as 80%, the highest analytical efficiency of any 3D microscopy.

The above schematic illustrates the principle of atom probe tomography, showing the specimen and the 2D position sensitive detector. T(pulse) is a laser or voltage pulse acting on the tip of the specimen that triggers field evaporation of ions and T(event) is the time the ion reaches the detector.

The detector allows the user to simultaneously measure:

• the Time Of Flight of the ions: measuring the time between the laser or voltage pulse and the arrival on the PSD allows determining the m/q ratio (mass overcharge ratio).
• the (X,Y) position of the ion impact on the detector: measuring the X-Y position and the order of arrival of the ions on the PSD allows users to reconstruct the original position of the atoms on the tip.

By repeating this sequence, the atoms are progressively removed from the tip, and a 3D image of the material can be reconstructed at the atomic scale.

The CAMECA Atom Probe Tomography product line comprises the 6000 family, with the Invizo 6000 and the LEAP 6000 XR and the EIKOS family. The CAMECA Atom Probes are developed in collaboration with the GPM - Materials Research Group - of Rouen University, France.

To learn more, view our short introductory video below.