Table of Contents
What are electron field emitters?
Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum.
What are the materials used for thermionic emitter?
Considering the above-mentioned properties, we normally use, tungsten, thoriated tungsten, oxide-coated metals for constructing cathode of thermionic emission.
How are electrons emitted?
In physics, electron emission is the ejection of an electron from the surface of matter, or, in beta decay (β− decay), where a beta particle (a fast energetic electron or positron) is emitted from an atomic nucleus transforming the original nuclide to an isobar.
How thermionic emission is produced?
Thermionic emission (archaically known as the Edison effect) is the flow of charged particles called thermions from a charged metal or a charged metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface.
Why is a Schottky field emitter so called?
At very high values of the applied field, however, the electron emission undergoes an excessive increase because of the onset of a different type of emission, called high-field emission or, simply, field emission. The effect is named after its discoverer, the German physicist Walter Schottky.
Which metal is suitable for thermionic emission?
tungsten
The best pure metal thermionic emitter is tungsten which has a work function of 4.54 eV which at 1500K can provide 1.5 × 10−7 A/cm2.
Why is tungsten used for thermionic emission?
Tungsten is a suitable metal for Thermionic emission, has a high melting point of 3655 K but its work function is high at about 4.52 eV(electron volt-energy unit). It starts emission at 2500 K. If thoriated tungsten (coated with carbon and thorium) is used work function reduces to 2.6 eV and emission begins at 2000 K.
How many types of electron emissions does 3?
Electron emission from a material surface occurs through three main possible processes; photoemission, thermionic emission, and field emission (Jensen, 2007b).
How do you increase your Armionic emissions?
The large surface area provides more space for electrons to emit. Thus, if large surface area metals are used the rate of thermionic emission will increase proportionally.
Is tungsten a good thermionic emitter?
The best pure metal thermionic emitter is tungsten which has a work function of 4.54 eV which at 1500K can provide 1.5 × 10−7 A/cm2.
Is tungsten used for electron emission?
Answer: Tungsten is used as an electron emitter as it has a very high melting point (3655 K) and moderate work function. Tungsten is a suitable metal for Thermionic emission, has a high melting point of 3655 K, but its work function is high at about 4.52 eV. It starts emission at 2500 K.
Which emission is the heaviest?
The first is an alpha particle. These particles consist of two protons and two neutrons and are the heaviest type of radiation particle. Many of the naturally occurring radioactive materials in the earth, like uranium and thorium, emit alpha particles.
Is graphene an efficient electron emitter?
Introduction Graphene, a single-layer hexagonal lattice consisting of carbon atoms, can be used as a efficient electron emitter due to its abundant edge structures, high electrical and thermal conductivity and superior mechanical strength.
How do you identify graphene field emitters?
Characterization The morphologies of the prepared graphene field emitters are often characterized by scanning electron microscope (SEM) or transmission electron microscopy (TEM) [90], [47], [91], [92], [93], [94]. The image and the thickness of graphene are also investigated by atomic force microscope (AFM).
What are the active materials used in graphene Electron Devices?
For flexible graphene based electron devices construction, the combination of graphene and organic semiconductors or inorganic nanomaterials is often used as the active materials with graphene. The high-performance flexible patterned RGO field emitters with vertically aligned tip structures are successful fabricated [51].
What are the advantages of vertical alignment of graphene sheet arrays?
The vertical alignment of graphene sheets arrays arranged along the direction of external electric field can guarantee superior efficient electrons emission performance. The large-scale and low-cost fabrication of the graphene is another critical issue for their industrial-scale production.