Engineering:Field emission probes

Field emission probes are used in scanning electron microscopy 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 a vacuum, the geometry of the surface of the body is unknown. Upon further study, the field emission probes are kept, which emit electrons as soon as a voltage is applied across them. As a result, this causes the emission of secondary electrons from the surface of the body subject to ion milling. By collecting these secondary emitted electrons, a clear image of the surface of the ion-milled body can be obtained. This technique is also used in scanning electron microscopes (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. To resolve details at the atomic level, it should have a small aspect ratio to reduce mechanical vibration while scanning, contain a stable atomic configuration at its apex to yield reliable and reproducible images, and be clean enough to ensure a stable tunnel junction since the presence of contaminants like oxides or etching by-products could alter its metallic behavior.

Despite the various well-known methods to make field emission probes, such as the drop-off method, it is still difficult to get an ideal probe.

See also

• Field emission
• Electron microscope
• Scanning electron microscope
• Scanning tunneling microscope