atom probe tomography

**APT** (Atom Probe Tomography) is a **destructive 3D characterization technique that provides atom-by-atom chemical analysis** — field-evaporating individual atoms from a needle-shaped specimen and detecting their mass-to-charge ratio to reconstruct atomic-scale 3D composition maps. **How Does APT Work?** - **Specimen**: FIB-prepared needle with tip radius < 100 nm. - **Field Evaporation**: High voltage (+ laser pulse) evaporates surface atoms one by one. - **Time-of-Flight**: Mass-to-charge ratio identifies the chemical species. - **Position-Sensitive Detector**: Hit position + evaporation sequence reconstructs 3D positions. **Why It Matters** - **Atomic Resolution**: The only technique that provides both 3D position and chemical identity of individual atoms. - **Dopant Distribution**: Maps individual dopant atoms in a semiconductor volume — statistical fluctuation analysis. - **Interface Analysis**: Characterizes abrupt interfaces, grain boundary segregation, and clustering at the atomic scale. **APT** is **the atom census** — counting, identifying, and locating every single atom in a nanoscale semiconductor volume.