Atom Probe Tomography (APT or 3D Atom Probe) is the only material analysis technique offering extensive capabilities for both 3D imaging and chemical composition measurements at the atomic scale (around 0.1-0.3nm resolution in depth and 0.3-0.5nm laterally). Since its early developments, Atom Probe Tomography has contributed to major advances in materials science.
The sample is prepared in the form of a very sharp tip. The cooled tip is biased at high DC voltage (5-20 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, a few 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.
The detector allows to simultaneously measure:
the Time Of Flight of the ions: measuring the time between the laser flash and the arrival on the PSD allows to determine the m/q ratio (mass over charge 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 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 LEAP 4000X Si model (straight TOF mass analyzer) and the LEAP 4000(X) HR (Reflectron TOF mass analyzer). The CAMECA Atom Probes are developed in collaboration with the GPM - Materials Research Group - of Rouen University, France).
By courtesy of
GPM, Univ. of Rouen,