GB2190786A - Liquid metal field emission electron source - Google Patents

Liquid metal field emission electron source Download PDF

Info

Publication number
GB2190786A
GB2190786A GB08612305A GB8612305A GB2190786A GB 2190786 A GB2190786 A GB 2190786A GB 08612305 A GB08612305 A GB 08612305A GB 8612305 A GB8612305 A GB 8612305A GB 2190786 A GB2190786 A GB 2190786A
Authority
GB
United Kingdom
Prior art keywords
liquid metal
field emission
electrons
electron
cathode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08612305A
Inventor
Roy Clampitt
Peter Hanley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
OXFORD APPL RES Ltd
Oxford Applied Research Ltd
Original Assignee
OXFORD APPL RES Ltd
Oxford Applied Research Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by OXFORD APPL RES Ltd, Oxford Applied Research Ltd filed Critical OXFORD APPL RES Ltd
Priority to GB08612305A priority Critical patent/GB2190786A/en
Publication of GB2190786A publication Critical patent/GB2190786A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02Main electrodes
    • H01J1/30Cold cathodes, e.g. field-emissive cathode
    • H01J1/304Field-emissive cathodes

Landscapes

  • Cold Cathode And The Manufacture (AREA)

Abstract

Liquid metal wetted to a cathode anchor in the point-in-a-plane geometry is field-formed into a sharp liquid metal point by application of a high electric field, to produce continuous and stable microampere levels of electron current in an ordinary high vacuum environment. The liquid metal may be gallium, tin or indium on a tungsten or molybdenum anchor. The anchor may be a sharply pointed needle or a small bore tube.

Description

SPECIFICATION Liquid metal field emission electron source This invention relates to field emission of electrons from liquid metal cathodes in vacuum.
Positive metal ions can be extracted from the surface of a sharp solid metal, termed an anode, in vacuo by subjecting the anode to a high negative electric field. The phenomenon is known as "field evaporation". By reversing the polarity of the electric field electrons can be extracted from the surface of such a sharp solid point, termed a cathode. This phenomenon is known as "field emission". The ion or electron currents so obtained are generally very low (--nanoamps), the threshold field for electron emission being lower, typically by one order of magnitude, than that for ion emission. Despite that the ion or electron currents from such respective anodes or cathodes are low, these solid emitters find practical application in, for example, electron microscopes, particularly since the sources are of high brightness.In order to sustain stable beams, however, such sharp metal point emitters must be maintained in an ultra-high vacuum environment (typically 10-'0 torr).
Positive metal ions can also be extracted from the surface of sharp liquid metal points in vacuo by application of a high electric field.
The positive ion current so produced is orders of magnitude greater than that from sharp solid metal points, typically several microamperes. This ion source also is of very high brightness, but in contrast to its solid metal anode counterpart, it does not require an ultra-high vacuum environment for stable operation. Ion sources of this type are called liquid metal ion sources. Conventional field evaporation theory does not predict that such high ion currents will be obtained from sharp liquid metal points, nor that stable ion currents will be sustained ordinary high vacuum (10-5-10-5 torr). An example of prior art on liquid metal ion sources is embodied by one of us in British Patent No.1,574,611.
By reversing the polarity of the electric field we have now discovered that microamperes of electrons, (i.e. very high in comparison with conventional field emission), can be obtained continuously and that stable electron currents can be sustained in ordinary high vacuum (10-5-10-6 torr). Conventional field emission theory does not predict that such high electron currents will be obtained from sharp liquid metal points, nor that stable electron currents will be sustainable in ordinary high vacuum. We find, however, that the threshold field for electron emission from a liquid metal point is lower, typically by an order of magnitude, than that for ion emission from a liquid metal point, suggesting that the mechanism of electron emission from liquid metal points is phenomenologically similar to field (electron) emission from solid metal points.We have not directly measured the brightness of this electron source. However, by reference to the body of knowledge on liquid metal ion sources which rely for their operation on a field-forming point and which differ from the mentioned electron sources only by a reversal of the polarity of the point-forming electric field, we can predict that the electron source will be of comparable brightness.
Prior art on electron emission in vacuo from field-deformed liquid metal surfaces teaches that very high pulsed electron currents (hundreds of amperes) only are obtained, by a phenomenon known generally as explosiveelectron emission. One group of research workers, whilst studying pulsed electron emission, observed oscillographically the growth profile of the current pulse. In the temporal region of onset of electron emission, typically in the nanosecond time-scale and immediately prior to the almost-step function surge of current leading to explosive emission, they observed electron emission which was attributed by them to transient field emission. However this work does not teach that continuous and stable currents of electrons will be sustainable in this regime of current growth, without leading on to the pulsed explosive electron emission regime.
A specific embodiment of the invention will now be described: The design, geometry and fabrication techniques required to produce liquid metal electron sources are identical to those of the prior art of liquid metal ion sources. The geometric arrangement of a liquid metal electron emitting cathode source is identical to that of the corresponding liquid metal ion emitting anode source i.e. that of a point-in-a-plane. A feature common to both types of liquid metal sources, and to those other devices of the prior art, such as the mercury-wetted relay, which depend for their operation on electricfield induced extrusion of the liquid metal surface into a sharp point, is the need for a cathode anchor. This may typically be a sharp solid electrode to which the liquid metal is anchored by wetting or equally a fine hollow metal tube filled and likewise wetted to it by the liquid metal.In order to preserve the point-in-a-plane geometry i.e. to provide a high electric field to the liquid metal surface at modest applied voltages, (typically less than 10 kV) the preferred aforementioned embodiment of liquid metal-containing electrodes should be of small diameter, typically less than 0.5 mm. In the case of the fine hollow tube embodiment of the cathode electrode wetted at its periphery by liquid metal, the surface of which assumes the concave shape which characterises a wetted surface deformed by surface tension forces, the application of a sufficient voltage difference between the cathode and an adjacent, typically planar electrode results in the extrusion of the wetted surface into a conical form, the apex of which constitutes the sharp liquid metal point.
In the case of the sharp solid electrode embodiment of the cathode it is generally necessary in the prior art to ensure that the radius of curvature of the point of the electrode is less than, typically, 10 microns in order to avoid the production of more than a single sharp liquid metal point on application of the aforementioned electric field, although it is recognised that for some applications not requiring a single emitting point, such multiple emission points may be a desirable feature.
When the voltage difference, typically 4 kV, is of a polarity, in either of the above embodiments of the cathode, to favour electron emission therefrom, it is observed that electron currents of greater than one microampere can be produced and sustained stably in an ordinary vacuum environment, typically 10-5 torr.
In principle any liquid metal element or alloy would make a suitable cathode material provided that its vapour pressure at the melting point is sufficiently low (10-4 torr) as to avoid vapour discharge or arc formation; and that it wets well and substantially non-corrosively to the cathode holder. Convenient liquid metals are gallium, tin or indium, which all exhibit low melting points, very low vapour pressures at their respective melting-points and which also wet readily and substantially non-corrosively to cathode holders made of, for example, tungsten or molybdenum.
In order to maintain the cathode in a molten state it can be heated by any of the standard procedures, such as resistively, radiatively or by electron bombardment. In one embodiment, the cathode anchoring structure is almost identical to that of a thermionic electron emitting filament used in, for example, scanning electron microscopes. Such a structure comprises a hair-pin filament mounted on a ceramic base. To the apex of this filament a needle-shaped tungsten wire electrode is spotweided, the radius of curvature of which, however, is much larger than that of a thermionically-operated electron emitter and is typically ten microns. The needle-shaped wire electrode and the spotweld juncture of the hair-pin filament are wetted with liquid metal by any of the standard wetting practices such as dipping momentarily, in a high vacuum environment, into a pool of very hot liquid metal, which in the example of indium would typically be 1000"C. In this embodiment of the cathode, the indium metal is maintained in a molten state by resistively heating the tungsten hair-pin filament.
The cathode can be operated as in prior art electron or ion sources in either a diode or triode configuration, the latter possessing a 'Wehnelt' or grid control electrode.

Claims (7)

1. A liquid metal field emission point source of electrons producing continuous and stable microampere levels of electron current in ordinary high vacuum from a sharp liquid metal point formed in a high electric field.
2. A liquid metal field emission point source of electrons as claimed in Claim 1 wherein the liquid metal cathode comprises a solid tungsten needle of ten microns radius wetted by a film of liquid metal.
3. A liquid metal field emission point source of electrons as claimed in Claim 1 wherein the liquid metal cathode comprises a small bore tube filled with and wetted by liquid metal.
4. A liquid metal field emission point source as claimed in any preceding claim wherein the liquid metal cathode is of gallium.
5. A liquid metal field emission point source of electrons as claimed in any preceding claim wherein the cathode structure takes the form of a filament and base as commonly used in scanning electron microscopes.
6. A liquid metal field emission point source of electrons as claimed in claim 5 wherein the electron emitting source forms part of a triode electrode structure.
7. A liquid metal field emission source of electrons substantially as described herein.
GB08612305A 1986-05-21 1986-05-21 Liquid metal field emission electron source Withdrawn GB2190786A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08612305A GB2190786A (en) 1986-05-21 1986-05-21 Liquid metal field emission electron source

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08612305A GB2190786A (en) 1986-05-21 1986-05-21 Liquid metal field emission electron source

Publications (1)

Publication Number Publication Date
GB2190786A true GB2190786A (en) 1987-11-25

Family

ID=10598173

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08612305A Withdrawn GB2190786A (en) 1986-05-21 1986-05-21 Liquid metal field emission electron source

Country Status (1)

Country Link
GB (1) GB2190786A (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2214345A (en) * 1988-01-06 1989-08-31 Jupiter Toy Co "Generating and utilising electric discharge entities"
US5018180A (en) * 1988-05-03 1991-05-21 Jupiter Toy Company Energy conversion using high charge density
US5054046A (en) * 1988-01-06 1991-10-01 Jupiter Toy Company Method of and apparatus for production and manipulation of high density charge
US5054047A (en) * 1988-01-06 1991-10-01 Jupiter Toy Company Circuits responsive to and controlling charged particles
US5123039A (en) * 1988-01-06 1992-06-16 Jupiter Toy Company Energy conversion using high charge density
US5153901A (en) * 1988-01-06 1992-10-06 Jupiter Toy Company Production and manipulation of charged particles

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB332734A (en) * 1929-07-04 1930-08-07 Anthony Aloysius Joseph Crowne Improvements in electric discharge devices
GB1136144A (en) * 1965-04-12 1968-12-11 Asea Ab Electronic beam generating devices
GB2057300A (en) * 1979-08-23 1981-04-01 Atomic Energy Authority Uk Improvements in or relating to sources for spraying liquid metals
GB2115604A (en) * 1982-02-22 1983-09-07 Atomic Energy Authority Uk Liquid metal ion sources
GB2150745A (en) * 1983-11-28 1985-07-03 Hitachi Ltd Liquid metal ion source
GB2151071A (en) * 1983-11-11 1985-07-10 Hitachi Ltd Liquid metal ion source

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB332734A (en) * 1929-07-04 1930-08-07 Anthony Aloysius Joseph Crowne Improvements in electric discharge devices
GB1136144A (en) * 1965-04-12 1968-12-11 Asea Ab Electronic beam generating devices
GB2057300A (en) * 1979-08-23 1981-04-01 Atomic Energy Authority Uk Improvements in or relating to sources for spraying liquid metals
GB2115604A (en) * 1982-02-22 1983-09-07 Atomic Energy Authority Uk Liquid metal ion sources
GB2151071A (en) * 1983-11-11 1985-07-10 Hitachi Ltd Liquid metal ion source
GB2150745A (en) * 1983-11-28 1985-07-03 Hitachi Ltd Liquid metal ion source

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2214345A (en) * 1988-01-06 1989-08-31 Jupiter Toy Co "Generating and utilising electric discharge entities"
US5054046A (en) * 1988-01-06 1991-10-01 Jupiter Toy Company Method of and apparatus for production and manipulation of high density charge
US5054047A (en) * 1988-01-06 1991-10-01 Jupiter Toy Company Circuits responsive to and controlling charged particles
US5123039A (en) * 1988-01-06 1992-06-16 Jupiter Toy Company Energy conversion using high charge density
US5153901A (en) * 1988-01-06 1992-10-06 Jupiter Toy Company Production and manipulation of charged particles
GB2214345B (en) * 1988-01-06 1992-10-28 Jupiter Toy Co Apparatus for producing and manipulating charged particles.
US5018180A (en) * 1988-05-03 1991-05-21 Jupiter Toy Company Energy conversion using high charge density

Similar Documents

Publication Publication Date Title
US3631291A (en) Field emission cathode with metallic boride coating
US5773921A (en) Field emission cathode having an electrically conducting material shaped of a narrow rod or knife edge
US7888654B2 (en) Cold field emitter
US3374386A (en) Field emission cathode having tungsten miller indices 100 plane coated with zirconium, hafnium or magnesium on oxygen binder
US3720856A (en) Binary material field emitter structure
US9082578B2 (en) Electron emission element and method for manufacturing the same
JP2002334662A (en) Ion source and driving method of the same
EP0151588B1 (en) Electron emission system
GB2190786A (en) Liquid metal field emission electron source
US8232716B2 (en) Field emission cathode capable of amplifying electron beam and methods of controlling electron beam density
US7828622B1 (en) Sharpening metal carbide emitters
US2916668A (en) Heat stabilized field emission electron sources
KR100499120B1 (en) Triode structure field emission display using carbon nanotube
US4591754A (en) Electron gun for brightness
Lee et al. CNT field emitter based high performance X-ray source
Dyke Progress in electron emission at high fields
US11935720B1 (en) Field-emission type electron source and charged particle beam device using the same
RU151235U1 (en) ACUTE FIELD EMITTER
Mousa Effect of an internally conductive coating on the electron emission from glass tips
US3521113A (en) Electron beam apparatus incorporating a hollow pyramidal indirectly heated cathode member
Kuznetsov Cathodes for electron guns
Kellogg I n situ cleaning of nickel field‐ion surfaces by neon ion bombardment
KR910005219Y1 (en) Electrode of electron gun
RU2288520C1 (en) Method for producing positive ion current
Latham The Point-Plane Field Emitting Diode

Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)