Atom probe tomography enables atomic-resolution characterization of sample structure and elemental composition. This technique, which removes individual atoms from the sample surface (as ions) and measures their identity with a mass spectrometer, requires that the sample is in the form of a sharp tip to eject the ions for analysis. Focused ion beam (FIB) milling is well suited for this particular type of sample preparation as it can remove highly precise quantities of material. When coupled with a scanning electron microscope (SEM), as in DualBeam (FIB-SEM) instruments, the milling process can be visually monitored in real-time.
The fundamental criteria for a good APT sample are:
- Needle-shaped specimen with tip radius typically less than 50 nm
- Uniform, circular cross-section of the tip to produce a radially symmetric electric field
- Correct taper angle for significant evaporation events to occur
- Minimal damage introduced to the tip during specimen preparation (apex region of needle should represent original sample in terms of microstructure and composition)
Thermo Scientific DualBeam instruments offer gallium FIB and plasma FIB (PFIB) milling for high-quality APT sample preparation. With the Thermo Scientific Helios Hydra DualBeam, a range of plasma ion species (oxygen, argon, nitrogen, or xenon) can uniquely be applied within the same instrument to determine which ion is best suited for milling a given sample. The process can also be automated with Thermo Scientific Autoscript Software, greatly reducing the burden of repetitive sample preparation.
Novel materials are investigated at increasingly smaller scales for maximum control of their physical and chemical properties. Electron microscopy provides researchers with key insight into a wide variety of material characteristics at the micro- to nano-scale.
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