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Topic: Thermionic emission

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	THERMIONIC EMISSION. The Columbia Encyclopedia: Sixth Edition. 2000 (Site not responding. Last check: 2007-11-05)
		The number of thermions emitted increases rapidly as the temperature of the substance rises.
		At temperatures below red heat (see fl body), thermionic emission from uncharged bodies is chiefly positive; at higher temperatures it is negative.
		Thermionic emission’s most important practical application in electronics is in the electron tube, since it is the mechanism by which electrons are emitted from the cathode.
	www.bartleby.com /aol/65/th/thermion.html (142 words)

	Thermionic emission - Wikipedia, the free encyclopedia
		Thermionic emission (archaically known as the Edison effect) is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface.
		The thermionic diode can also be configured as a device that converts a heat difference to electric power directly without moving parts (a thermionic converter, a type of heat engine).
		The thermionic emission equations are of fundamental importance in electronics, significantly affecting both older vacuum tube technology (e.g.
	en.wikipedia.org /wiki/Thermionic_emission (925 words)

	Thermionic Emission (Site not responding. Last check: 2007-11-05)
		Thomas Edison, an American physicist, was the first to observe a phenomenon, since known as thermionic emission or the thermionic effect.
		Thermionic emission is the emission of electrons from a hot metal.
		In 1883, while experimenting with an electric lamp which contained a metal plate near the filament and connected to it via a galvanometer and battery, Edison found that a current flowed through the galvano- meter when the plate was positive with respect to the filament.
	homepage.eircom.net /~ncl/thermionic_emission.htm (485 words)

	Cathode Emissions in CPO
		When a thermionic cathode is called for, a finely-divided 'cathode space-charge region' is created by the program in front of the cathode.
		For extended Schottky emission, a modification of the Richardson-Dushman equation is used.
		A User-supplied data file could be used to define parameters such as the maximum current density of a thermionic cathode or the work function of a field-emission cathode, although this is not done in the present examples (where the values entered in the databuilder are used instead).
	www.simion.com /cpo/cathodes.html (864 words)

	Thermionic Emission of Single-Wall Carbon Nanotubes Measured
		So that the thermal emission could be measured, the nanotube paper was used as the electron emitter in a parallel plate configuration with a tantalum collector.
		Emission was studied for temperatures ranging from 25 to 1207 °C. The emission plots obtained from a purified nanotube paper are shown in the following graph.
		By developing a technique to produce a thin sheet of highly purified nanotube emitter and measuring the electron emission as a function of temperature and applied field strength, we are making significant progress toward the development of higher efficiency and greater power devices for NASA and commercial applications.
	www.grc.nasa.gov /WWW/RT/2003/5000/5410landis2.html (772 words)

	Electron Emission
		Electron emission is actually the basic of tube working principal, it is defined as liberation of free electron from a surface of a substance caused by the externak energy transfered to the electrons.
		Electron emission tends to occur on metal, because metal is a substance with much free electron in between its molecul.
		Electron emission from a metalic surface by the bombardment of high speed electrons or other particles is known as secondary emission.
	www.geocities.com /tube_theory/ElectronEmission.htm (984 words)

	Thermionic Emission - Search Results - MSN Encarta (Site not responding. Last check: 2007-11-05)
		Thermionic Emission, emission of electrons from a hot metal surface under the influence of an external potential difference.
		That electric charges were carried by extremely small particles had already been suspected in the 19th century, and electrochemical experiments that...
		- electron emission: the emission of electrons or ions from a solid or liquid as a result of its thermal energy
	uk.encarta.msn.com /Thermionic_Emission.html (124 words)

	untitled
		The thermionic emission current density is determined by the 'work function' of the material, which is basically the magnitude of the surface potential.
		In this model it is assumed that electrons are emitted from the insulator by the thermionic process and the temperature is described in terms of the electric field that has accelerated them through the insulator.
		The gas, primarily consisting of cathode material, expands into the vacuum where it is ionised by bombardment from the thermionic emission due to the very hot underlying cathode.
	reld.phys.strath.ac.uk /bwi2.htm (997 words)

	Thermionic converter - Wikipedia, the free encyclopedia
		A thermionic converter consists of a hot emitter electrode from which electrons are vaporized by thermionic emission and a colder collector electrode into which they are condensed after conduction through the interelectrode plasma.
		Substantial thermionic space reactor development programs were conducted in the U.S. France and Germany in the period 1963-1973, and the US resumed a significant thermionic nuclear fuel element development program in the period 1983-1993.
		The electrode surface properties determine the magnitude of electron emission current and electric potential at the electrode surfaces, and the plasma properties determine the transport of electron current from the emitter to the collector.
	en.wikipedia.org /wiki/Thermionic_converter (1042 words)

	[No title]
		Electron emission processes are central to many effects at surfaces and interfaces, and to many techniques for examining the near-surface region.
		Thermionic emitters in the form of pointed wires or rods are used as electron sources in many electron optical devices such as oscilloscopes, TV and terminal displays, and both scanning and transmission varieties of electron microscopes.
		The Field F plays a similar role to the temperature in thermionic emission, and the governing equation is that by Fowler and Nordheim, derived in 1928 from free electron theory (see Woodruff and Delchar, pages 326-7 or Modinos, p 16).
	venables.asu.edu /sphy/sectA2.doc (2741 words)

	McGraw-Hill AccessScience: Thermionic emission (Site not responding. Last check: 2007-11-05)
		In its broadest meaning, thermionic emission includes the emission of ions, but since this process is quite different from that normally understood by the term, it will not be discussed here.
		Thermionic emitters are used as cathodes in electron tubes and hence are of great technical and scientific importance.
		Of the metals, tungsten is an important practical thermionic emitter; in most electron tubes, however, the oxide-coated cathode is used to great advantage.
	www.accessscience.com /Encyclopedia/6/68/Est_689800_frameset.html (157 words)

	Thermionic Valves - Theory
		Thermionic emission which occurs when a conductor is heated.
		The use of the thermionic diode is thus restricted to its linear region AB.
		When the anode potential falls below that of the screen, secondary emission of electrons from the anode are collected by the screen, causing a sharp drop in anode current and producing the 'kink' in its characteristics.
	www.livinginthepast.demon.co.uk /vtheory/vtheory.htm (3854 words)

	Thermionic Emission (Site not responding. Last check: 2007-11-05)
		In thermionic emission, electrons have energies barely above the vacuum level (internally, E very close to I).
		That means that not only the electrons must be in the tail of the energy distribution to be emitted, but they also must be traveling nearly perpendicular to the surface.
		The equation is dominated by the exponential factor which is a very small number, since a typical work function is much larger than thermal energies.
	www.virginia.edu /ep/SurfaceScience/thermion.html (849 words)

	Applied Diamond Conference
		Thermionic Emission of Carbon/Diamond Surfaces at Low Temperature
		Thermionic emission sources that operate at temperatures less than 800C may prove appropriate for many applications such as thermionic energy converters, microwave amplifiers, CRTs and even light sources.
		In all cases the emission is uniform over the entire surface, which is characteristic of conduction band emission.
	www.eng.auburn.edu /ADC-FCT2001/ADCFCTabstract/023.htm (211 words)

	Field emission - Wikipedia, the free encyclopedia
		Also known as Fowler-Nordheim tunneling, field emission is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field.
		In the field of vacuum electronics, field emission is seen as an alternative to thermionic emission, with advantages such as dramatically higher efficiency, less scatter of emitted electrons, faster turn-on times, compactness, and, in many cases, redundancy.
		Vacuum tubes based on thermionic emission require several minutes to warm up before they can be used; by contrast, the function of field emission devices is effectively instantaneous, allowing switching times of many megahertz.
	en.wikipedia.org /wiki/Field_emission (375 words)

	Electronics 27
		Thermionic diodes, like semiconductor diodes, are divided into signal diodes that handle small currents at low voltages, and rectifier diodes that handle large currents, often with large inverse voltages.
		A large part of this plate current drop is caused by secondary emission from the plate, which seems quite efficient when the electrons impact with the energy corresponding to 60 V. As the plate voltage is lowered, the impact becomes less severe, and the number of secondary electrons decreases, so the plate current rises again.
		The actual emission to the anode comes from the minimum of this potential well, which is several volts negative, and so the plate may be slightly more positive than this minimum, in spite of contact potentials.
	www.du.edu /~etuttle/electron/elect27.htm (23318 words)

	Schottky diode current
		The thermionic emission theory on the other hand postulates that only energetic carriers, those, which have an energy equal to or larger than the conduction band energy at the metal-semiconductor interface, contribute to the current flow.
		The thermionic emission theory assumes that electrons, with an energy larger than the top of the barrier, will cross the barrier provided they move towards the barrier.
		The thermionic emission theory assumes that electrons, which have an energy larger than the top of the barrier will cross the barrier, provided they move towards the barrier.
	ece-www.colorado.edu /~bart/book/book/chapter3/ch3_4.htm (1088 words)

	3.3.2 Thermionic emission current (Site not responding. Last check: 2007-11-05)
		Thermionic emission is the process where electrons are emitted across a barrier.
		The driving force of this process is the thermal energy which provides a non-zero density of carriers at energies larger than the confining barrier.
		The expression for the current due to thermionic emission can also be written as a function of the average velocity with which the electrons at the interface approach the barrier.
	ece-www.colorado.edu /~bart/book/msthermi.htm (338 words)

	CURRENT TRANSPORT IN W AND WSIX OHMIC CONTACTS TO INGAN AND INN (Site not responding. Last check: 2007-11-05)
		The data indicates the conduction mechanism is field emission for these contact schemes for all but as-deposited metal to InN where thermionic emission appears to be the dominant mechanism.
		Theoretical curves for the temperature dependence of specific contact resistance of contacts in which thermionic emission, thermionic field emission, or field emission are the dominant conduction mechanism.
		The thermionic field emission does have a slight upward slope with increasing reciprocal temperature, but it is less than the error found in the experimental measurements on the samples.
	nsr.mij.mrs.org /MRS/S97-D/3.4 (1489 words)

	Information Bridge: DOE Scientific and Technical Information - - Document #286293 (Site not responding. Last check: 2007-11-05)
		Recently Klots and Compton have reviewed the evidence for thermionic emission from small aggregates where mention was also made of experiments designed to determine the effects of externally applied electric fields on thermionic emission rates.
		The increase in fullerene ion signal relative to that of Cs{sup+} is attributed to field enhanced thermionic emission.
		Thermionic emission from neutral clusters has long been known for autodetachment from highly excited negative ions.
	www.osti.gov /bridge/product.biblio.jsp?osti_id=286293 (432 words)

	thermionic emission — Infoplease.com
		by substances that are highly heated, the charged particles being called thermions.
		), thermionic emission from uncharged bodies is chiefly positive; at higher temperatures it is negative.
		Thermionic emission's most important practical application in electronics is in the
	www.infoplease.com /ce6/sci/A0848439.html (145 words)

	Thermionic Emission
		A thermionic energy converter is a device consisting of two electrodes placed near one another in a vacuum.
		As long as the potential difference between the electrodes is maintained, there will be a steady current flow from the cathode to the plate.
		The simplest example of a thermionic device is a vacuum tube diode in which the only electrodes are the cathode and plate, or anode, as shown in Figure 17.
	www.tpub.com /doeelecscience/electricalscience223.htm (460 words)

	[No title]
		It was the purpose of this investigation to determine the feasibility and suitability of substituting reconstituted mica for natural mica splittings in receiving tubes.
		emissions Stoney, Johnstone, a letter in Philosophical Magazine 1894 first use of the word electron to denote the molecule of electricity van der bijl says it was 1891 Thompson, Edward P., M. E., “Chemistry of the Carbon Filament,” American Institute of Electrical Engineers, Transactions, vol.
		From the first paragraph: “The object of this article is to review the principles of audio frequency transformers, to apply these principles to simple and practical methods of design, and finally to describe the essential tests which should be applied to a finished transformer.” 5.
	www.triodeel.com /biblio.txt (15833 words)

	Quantum Electronic - Research
		Thermionic Energy Conversion Center’s goal is to design, fabricate and characterize direct energy conversion systems that meet the above requirements.
		Materials design is focused on increasing the efficiency of heterostructure thermionic power generators using embedded quantum dot structures and metal/semiconductor superlattices and the development of thermionic energy conversion based on thermionic-field emission from nanostructured carbon surfaces and low work function n-type wide band gap semiconductor collectors.
		Measurements of electrical, optical and thermal transport at both the device and nanostructure level will be used to verify model predictions and thereby lay the foundation for improved device and materials design.
	quantum.soe.ucsc.edu /research/TEC/tec.html (555 words)

	AllRefer.com - thermionic emission (Electrical Engineering) - Encyclopedia
		You are here : AllRefer.com > Reference > Encyclopedia > Electrical Engineering > thermionic emission
		thermionic emission[thUrm´´Ion´ik] Pronunciation Key, emission of electrons or ions by substances that are highly heated, the charged particles being called thermions.
		More articles from AllRefer Reference on thermionic emission
	reference.allrefer.com /encyclopedia/T/thermion.html (264 words)

	Carbon Nanotubes Monthly - January 2006 - Field Emission Applications of Carbon Nanotubes
		Field emission represents a type of quantum tunnelling in which electrons pass through a barrier in the presence of a high electric field.
		As opposed to thermionic emission, field emission does not require any heat for extracting the electrons.
		As an alternative to thermionic emission, field emission promises dramatically higher efficiency, less scatter of emitted electrons, faster turn-on times, and the possibility to build more robust and compact devices.
	www.nanosprint.com /nanotubes/newsletter/monthly_0106 (536 words)

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