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Schottky-emitter electron source of an Electron microscope. A field emission gun (FEG) is a type of electron gun in which a sharply pointed Müller-type [clarification needed] emitter [1]: 87–128 is held at several kilovolts negative potential relative to a nearby electrode, so that there is sufficient potential gradient at the emitter surface to cause field electron emission.
Currently, attempts are being made to develop carbon nanotubes (CNTs) as electron-gun field emission sources. [40] [41] The use of field emission sources in electron optical instruments has involved the development of appropriate theories of charged particle optics, [37] [42] and the development of related modeling. Various shape models have ...
The Schottky effect or field enhanced thermionic emission is a phenomenon in condensed matter physics named after Walter H. Schottky. In electron emission devices, especially electron guns, the thermionic electron emitter will be biased negative relative to its surroundings. This creates an electric field of magnitude F at the
Electron gun from an oscilloscope CRT Setup of an electron gun. 1. Hot cathode.2. Wehnelt cylinder.3. Anode. A direct current, electrostatic thermionic electron gun is formed from several parts: a hot cathode, which is heated to create a stream of electrons via thermionic emission; electrodes generating an electric field to focus the electron beam (such as a Wehnelt cylinder); and one or more ...
A field emission source uses instead electrostatic electrodes called an extractor, a suppressor, and a gun lens, with different voltages on each, to control the electric field shape and intensity near the sharp tip. The combination of the cathode and these first electrostatic lens elements is collectively called the "electron gun".
A typical LEEM setup consists of electron gun, used to generate electrons by way of thermionic or field emission from a source tip. In thermionic emission, electrons escape a source tip (usually made of LaB 6) by resistive heating and application of an electric field to effectively lower the energy needed for electrons to escape the surface ...
The tip radius of this cone is extremely small (~2 nm). The huge electric field at this small tip (greater than 1 × 10 8 volts per centimeter) causes ionization and field emission of the gallium atoms. Source ions are then generally accelerated to an energy of 1–50 kiloelectronvolts (0.16–8.01 fJ), and focused onto the sample by ...
He investigated the need for a brighter electron source in the microscope, positing that cold field emission guns would be feasible. [9] Through this and other iterations, Crewe was able to improve the resolution of the STEM from 30 Ångstroms (Å) down to 2.5 Å. [10] Crewe's work made it possible to visualize individual atoms for the first ...