• Canadian Centre for Electron Microscopy
  • +1 905 525 9140 (Ext. 20400)

Atom Probe Tomography

Staff responsible:

Brian Langelier

langelb@mcmaster.ca

atom-probe

Cameca LEAP 4000X HR

The Local Electrode Atom Probe (LEAP) 4000X HR allows for 3D analysis of materials at the sub-nanometer scale. Materials are examined by successive field-evaporation of ions. The collected data is then reconstructed to yield a 3D computer model of the material, offering an unparalleled combination of spatial and compositional accuracy. In addition to the traditional method of high-voltage pulsing to induce field evaporation, the LEAP 4000X HR also uses an ultraviolet laser (355nm wavelength). The capability for laser pulsing expands the range of potential materials for analysis from metals, alloys, semiconductors to ceramics, minerals and bio-materials. Analyses include dopants in semiconductors, alloying elements, concentration profiles with atomic sensitivity and clustering.

Atom Probe Tomography

The local electrode atom probe (LEAP) analyzes materials by successively evaporating surface atoms from the sample material. Field evaporation of atoms requires an extremely strong electric field, which necessitates a high voltage, and a needle-shaped specimen (to concentrate the field at the tip apex). Preparing specimens for atom probe can be done either by electropolishing or by annular milling with a focused ion beam (FIB). Electropolishing is suitable only for bulk metals and alloys, while FIB can be used with nearly any material. FIB is also required when precision in selecting the feature of interest is needed (e.g. for analyzing grain boundaries).

Field evaporation is controlled by pulsing either with an applied voltage, or by illumination with a UV laser. Adsorbed ions are detected by a position sensitive detector, and their time of flight is also measured. When a suitably large amount of material is evaporated, the data can be reconstructed to create an atom-by-atom model of the original material. The reconstructed model gives 3D information on the structure and composition of the material with sub-nanoscale resolution and near-ppm elemental sensitivity.

Top