Field emission probes
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Field emission probes are used in scanning electron miscroscopy for imaging. When a voltage is applied to these probes, electrons are emitted from the tips through a process known as field electron emission.
When a body is subjected to ion milling in vacuum, we do not get to know about the geometry of the surface of the body. So to study it we will keep the field emission probes which will emit electrons as soon as a voltage is applied across it. This in turn will cause emission of secondary electrons from the surface of the body that is subjected to ion milling, by collecting these secondary emitted electrons we get a clear image of the surface of the ion milled body.
This is the technique that is used in the or scanning electron microscope(SEM).
There exist various well defined techniques for preparing field emission probes. Ideally, a field emission probe should be extremely sharp, possibly terminating in a single atom, in order to resolve details at the atomic level; it should have a small aspect ratio to reduce mechanical vibration while scanning, have a stable atomic configuration at its apex to yield reliable and reproducible images, and be clean to ensure a stable tunnel junction, since the presence of contaminants like oxides or etching by products could alter its metallic behavior. Our experimental setup helps us obtain tips with an apex radius of a few nanometres.
There are various well-known methods to make field emission probes but still it is difficult to get an ideal probe. One of them is the Drop-off method.
- Anne-Sophie Lucier (2004), Preparation and Characterization of Tungsten Tips Suitable for Molecular Electronics Studies (PhD thesis), McGill University, Center for the Physics of Materials