training for advanced research


Glossary terms about Gun

In electron microscopy: the equipment that produces an electron beam: usually an emitter (electrode), a surrounding cathode (Wehnelt cylinder/ grid cap) and below this an anode with a central hole.

12 pages mention Gun

Beam Adjustment
This might include changing an aperture to a larger or smaller size, adjusting the gun controls to provide the brightest image, and adjusting the “wobbler” to align the beam axis. 
Electron column
The electron column focuses and illuminates the specimen using the electron beam generated by the electron gun
Electron gun
High vacuum mode and pump system
The SEM uses a beam of high energy electrons generated by an electron gun, processed by magnetic lenses, focused at the specimen surface and systematically scanned (rastered) across the surface of a specimen. 
Principles of SEM operation
A scanning electron microscope is a machine comprised of an electron generating component called the gun, a column through which the electron beam travels, a series of lenses to shape the electron beam, the sample chamber at the base, and a series of pumps to keep the system under vacuum. 
Role of sample height
The "trade-off" for an increased WD is that the electron beam must travel a greater distance from the gun and therefore has a larger spot size on the specimen. 
Saturating the filament
An important factor in using a thermionic gun is understanding saturation of the filament. 
Scan rate and signal to noise ratios
To overcome the limitation of W filaments, and to improve the S/N ratio, bright sources such as the field emission gun (FEG) have been developed. 
The electron gun
The electron gun refers to the top region of the SEM that generates a beam of electrons. 
Troubleshooting: edge effect, charging, sample damage
The number of electrons relates to a number of parameters including, beam current, the emission level of the gun, the spot size, and the apertures between the gun and the specimen. 
What is an SEM (Parts of the machine)?
the computer that drives the microscope, with the additional bench controls ancillary equipment that, for example, analyses composition.