Atom Probe - Limitations

Limitations

• Materials implicitly control achievable, spatial resolution
• Specimen geometry is uncontrolled, yet controls projection behaviour, hence little control over the magnification. This may induce strong distortions into the computer generated 3D model dataset.
• Limited volume selectability, unlike EM methods. Site specific preparation methods, e.g. using Focussed ion beam preparation, although more time consuming, may be used to bypass such limitations.
• Features of interest may evaporate in a physically different manner to the bulk sample, altering projection geometry and the magnification of the reconstructed volume.
• Ion overlap in some samples (e.g. between oxygen and ) may result in ambiguous analysed species. This may be mitigated by selection of experiment temperature or laser input energy to influence the ionisation number (+, ++, 3+ etc.) of the ionised groups.
• Low molecular weight gases (Hydrogen & helium) may be difficult to remove from the analysis chamber, and may be adsorbed and emitted from the specimen, even though not present in the original specimen. This may also limit identification of Hydrogen in some samples. However deuterated samples have been used to overcome this limitation.
• Results may be contingent on the parameters used to convert the 2D detected data into 3D. Subsequently spatial measurements can be greatly affected, and careful analysis of the reconstructed volume is needd to ensure the correct results. In more problematic materials, correct reconstruction may be impossible due to limited knowledge of the true magnification; particularly if zone or pole regions cannot be observed.