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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Atom probe | 4/4 | https://en.wikipedia.org/wiki/Atom_probe | reference | science, encyclopedia | 2026-05-05T10:03:43.942629+00:00 | kb-cron |
=== System layout === At a minimum, an atom probe will consist of several key pieces of equipment.
A vacuum system for maintaining the low pressures (~10−8 to 10−10 Pa) required, typically a classic 3 chambered UHV design. A system for the manipulation of samples inside the vacuum, including sample viewing systems. A cooling system to reduce atomic motion, such as a helium refrigeration circuit - providing sample temperatures as low as 15K. A high voltage system to raise the sample standing voltage near the threshold for field evaporation. A high voltage pulsing system, use to create timed field evaporation events A counter electrode that can be a simple disk shape (like earlier generation atom probes), or a cone-shaped Local Electrode. The voltage pulse (negative) is typically applied to the counter electrode. A detection system for single energetic ions that includes XY position and TOF information. Optionally, an atom probe may also include laser-optical systems for laser beam targeting and pulsing, if using laser-evaporation methods. In-situ reaction systems, heaters, or plasma treatment may also be employed for some studies as well as a pure noble gas introduction for FIM.
=== Performance === Collectable ion volumes were previously limited to several thousand, or tens of thousands of ionic events. Subsequent electronics and instrumentation development has increased the rate of data accumulation, with datasets of hundreds of million atoms (dataset volumes of 107 nm3). Data collection times vary considerably depending upon the experimental conditions and the number of ions collected. Experiments take from a few minutes, to many hours to complete.
== Applications ==
=== Metallurgy === Atom probe has typically been employed in the chemical analysis of alloy systems at the atomic level. This has arisen as a result of voltage pulsed atom probes providing good chemical and sufficient spatial information in these materials. Metal samples from large grained alloys may be simple to fabricate, particularly from wire samples, with hand-electropolishing techniques giving good results. Subsequently, atom probe has been used in the analysis of the chemical composition of a wide range of alloys. Such data is critical in determining the effect of alloy constituents in a bulk material, identification of solid-state reaction features, such as solid phase precipitates. Such information may not be amenable to analysis by other means (e.g. TEM) owing to the difficulty in generating a three-dimensional dataset with composition.
=== Semiconductors === Semi-conductor materials are often analysable in atom probe, however sample preparation may be more difficult, and interpretation of results may be more complex, particularly if the semi-conductor contains phases which evaporate at differing electric field strengths. Applications such as ion implantation may be used to identify the distribution of dopants inside a semi-conducting material, which is increasingly critical in the correct design of modern nanometre scale electronics.
== Limitations == Materials implicitly control achievable spatial resolution. Specimen geometry during the analysis is uncontrolled, yet controls projection behaviour, hence there is little control over the magnification. This induces distortions into the computer generated 3D dataset. Features of interest might evaporate in a physically different manner to the bulk sample, altering projection geometry and the magnification of the reconstructed volume. This yields strong spatial distortions in the final image. Volume selectability can be limited. Site specific preparation methods, e.g. using Focused ion beam preparation, although more time-consuming, may be used to bypass such limitations. Ion overlap in some samples (e.g. between oxygen and sulfur) resulted 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. Data analysis can be used in some cases to statistically recover overlaps. Low molecular weight gases (Hydrogen & Helium) may be difficult to be removed 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. For this reason, deuterated samples have been used to overcome limitations. Results may be contingent on the parameters used to convert the 2D detected data into 3D. In more problematic materials, correct reconstruction may not be done, due to limited knowledge of the true magnification; particularly if zone or pole regions cannot be observed.
== References ==
== Further reading == Miller, M. K.; Cerezo, A.; Hetherington, M. G.; Smith, G D W. (1996). Atom Probe Field Ion Microscopy. doi:10.1093/oso/9780198513872.001.0001. ISBN 978-0-19-851387-2. Miller, M. K. (2000). Atom Probe Tomography. doi:10.1007/978-1-4615-4281-0. ISBN 978-1-4613-6921-9. Atom Probe Microscopy. Springer Series in Materials Science. Vol. 160. 2012. doi:10.1007/978-1-4614-3436-8. ISBN 978-1-4614-3435-1. Larson, David J.; Prosa, Ty J.; Ulfig, Robert M.; Geiser, Brian P.; Kelly, Thomas F. (2013). Local Electrode Atom Probe Tomography. doi:10.1007/978-1-4614-8721-0. ISBN 978-1-4614-8720-3.
== External links == Video demonstrating Field Ion images, and pulsed ion evaporation www.atomprobe.com - A CAMECA provided community resource with contact information and an interactive FAQ MyScope Atom Probe Tomography - An online learning environment for those who want to learn about atom probe provided by Microscopy Australia