GB2460664A - A surface ionization ion source - Google Patents
A surface ionization ion source Download PDFInfo
- Publication number
- GB2460664A GB2460664A GB0810166A GB0810166A GB2460664A GB 2460664 A GB2460664 A GB 2460664A GB 0810166 A GB0810166 A GB 0810166A GB 0810166 A GB0810166 A GB 0810166A GB 2460664 A GB2460664 A GB 2460664A
- Authority
- GB
- United Kingdom
- Prior art keywords
- ion source
- source according
- reservoir
- filament
- ion
- 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- Withdrawn
Links
- 239000000463 material Substances 0.000 claims abstract description 22
- 238000010438 heat treatment Methods 0.000 claims description 7
- 229910052783 alkali metal Inorganic materials 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- -1 alkali metal salt Chemical class 0.000 claims 1
- 239000008188 pellet Substances 0.000 claims 1
- 239000000126 substance Substances 0.000 claims 1
- 150000002500 ions Chemical class 0.000 abstract description 23
- 230000000694 effects Effects 0.000 abstract description 3
- 230000008016 vaporization Effects 0.000 abstract 1
- 238000009834 vaporization Methods 0.000 abstract 1
- 239000000919 ceramic Substances 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 239000002585 base Substances 0.000 description 3
- 230000005684 electric field Effects 0.000 description 3
- 238000010884 ion-beam technique Methods 0.000 description 3
- 150000001340 alkali metals Chemical class 0.000 description 2
- FJDQFPXHSGXQBY-UHFFFAOYSA-L caesium carbonate Chemical compound [Cs+].[Cs+].[O-]C([O-])=O FJDQFPXHSGXQBY-UHFFFAOYSA-L 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 239000010937 tungsten Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910000024 caesium carbonate Inorganic materials 0.000 description 1
- 229910001417 caesium ion Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229910052702 rhenium Inorganic materials 0.000 description 1
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000001004 secondary ion mass spectrometry Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J27/00—Ion beam tubes
- H01J27/02—Ion sources; Ion guns
- H01J27/26—Ion sources; Ion guns using surface ionisation, e.g. field effect ion sources, thermionic ion sources
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Electron Sources, Ion Sources (AREA)
Abstract
A thermal contact surface ionisation source having separate reservoir 11 and emitter 9 regions. A single electrical filament 12 is used to effect both vaporization of the species to be ionized, and the thermal contact ionization event itself. The filament 12 may comprise different sizes and materials to optimise the performance and maintain the correct thermal gradient along the device. The ionising part of the filament 8 may include devices to reduce the energy spread of the emitted ions, such as indirectly heated sections. The end-cap 6 of the ion source can be electrically biased from the filament or otherwise to improve ion emission and reduce space charge in the vicinity of the surface.
Description
Source of Ions
Background
Sources of ions have a wide range of applications in industry, providing charged particles for ion beam machining, integrated circuit fabrication, materials analysis (such as secondary ion mass spectrometry), spacecraft thrusters, surface modification and as component parts in sputter ion sources.
A wide variety of ion source types are known, many of which are described in the book "Physics and Technology of Ion Sources" by 1G. Brown published by Wiley lnterscience in 1989. A popular source of ions for species possessing a relatively low ionisation potential is the thermal surface contact type. In this source, the easily ionised material, often an alkali metal, is first vaporised and is then made to contact a hot metal surface having a high work function (typically, tungsten at >1000°C). On contact, the vaporised material becomes ionised and can then be swept away by an electric field to be formed into an ion beam.
Typically, ion sources of this type comprise four main components, a reservoir of material, a reservoir heater to vaporise the material, an emitter surface on which ionisation occurs and a second heater to raise the temperature of the emissive surface. In operation the emissive surface is heated to a fixed temperature and then the reservoir temperature is used to control the vapour pressure of the volatilised material and hence the source output ion flux. Thus M'o separate heater power supplies and control circuits are required for operation. Heating can either be resistive, using traditional wire-wound elements, or by electron impact. This type of source has the advantage that the reservoir can be made to almost any size and large ion currents can be extracted over an extended period of time. The emitting surface can be made quite small which provides a good ion-optical match to beam forming ion guns.
Statement of the invention
The present invention is a surface contact ionisation source using a single electrical supply to drive a filament which heats both the reservoir and the emitter stages. The reservoir may either contain the material to be ionised, or a material which, on heating, releases a species that may be subsequently ionised. The emitter may either be part of the filament wire or a separate surface heated by the filament which may or may not be electrically connected to it.
Advantages Use of a single power supply makes operation of the device easier and permits it to be used with ion gun power supplies designed for other types of ion sources.
The reservoir will permit a long lifetime of the source at high emitted current and will preferably be refillable.
Emission takes place from a small area which can be matched to ion beam forming optics.
Confining the emission to a small area limits the amount of non-ionised material that can escape the source providing both a better local vacuum environment, reducing contamination and giving longer operating time.
The entire source can be constructed as a replaceable cartridge that is stable in air, permitting easy maintenance of an ion gun.
The source can be made physically small to permit installation where space is restricted, which may be the case if it is used in an ion gun as a replacement for a source of a different type.
Introduction to Drawings
Figure 1 shows a cross section of a preferred embodiment of the ion source.
Figure 2 shows schematically how the source may be connected electrically.
Figure 3 shows details of possible filament and emitter configurations.
Detailed description
One embodiment of the invention is shown is figure 1. The source is built on a base plate (1) which also serves as a heatsink and is most likely constructed of metal. A ceramic end plug (2) is mounted on the baseplate and a twin bore ceramic tube (4) of 2mm outside diameter passes through its centre. The purpose of this tube is to provide electrical insulation of the filament (12) and to uniformly distribute the heat from the filament. A tube (3), most likely of ceramic with an outside diameter of 5 mm and 20mm in length, is also fixed to the end plug (2) and a second end plug (5) is fitted at the end away from the base plate. The end-plug nearest the baseplate (2) is sealed tightly to the two ceramic components so as to prevent gas escape; or is made in one piece together with items 3 and 4. The end-plug at the emitter end of the source (5) has a tight fit to the outer tube and either a loose fit, or preferably a small groove (10), to permit gas to escape from the reservoir and enter the emitter chamber (11) formed by the metal end-cap (6). A small aperture, typically of 0.5mm, in the end-cap (7) permits ions and atoms to escape from the source.
The metal end-cap may be connected to one side of the filament power supply such that it is slightly electrically biased and will tend to draw ions from the emitter.
A current flowing through the filament (12) heats both the reservoir, via the twin bore tube (4), and the emitter (8). The emitter may either be part of the filament (known as directly heated) as in figure 3a or may be a separate plate (known as indirectly heated) as shown in figure 3(b+c). In the case of the indirectly heated emitter the emissive surface (8) may be electrically connected to the filament in just one place (13) such that the whole emitter surface is at one electrical potential.
Alternatively (as shown in figure 3c), it may be electrically isolated from the filament by a suitable medium (14) which may be solid or vacuum, and may be electrically connected to another supply We) which could be the same as the end-cap. . This will allow a narrower energy spread of emitted ions to be extracted from the source as there is no potential gradient across the emitter surface, it is a principle used in thermionic electron emission devices.
The simplest embodiment uses a directly heated emissive surface which can be the same material, or different from that of the filament. Generally, the exposed nature of the emitter and the heat-sinking effect of the centre tube (4) means that the emitter surface will be significantly hotter than the reservoir. A more advanced design uses a flat tungsten or rhenium ribbon as the emitter, connected to a tantalum filament. The sizes of the individual components are chosen to ensure the correct balance of heating between the emitter and the filament as well as suitable surface and mechanical properties.
The space between the outer tube (3) and the inner ceramic (4) is filled with the source material.
This may either be an element that is easily ionised, such as, but not limited to, an alkali metal; or more usually, a salt of the material which decomposes under heating to produce the required species. For example, in use as a source of Cs ions, Cs2CO3 is a favoured material as it decomposes at 630°C liberating gaseous species. However many other compounds may be used, including mixtures designed to getter the liberated gasses, such as oxygen in the previous
example.
In some embodiments there may be provision to replenish the reservoir as it is emptied using conveniently shaped moulded or pressed material.
In operation, the source is mounted in vacuum and connected as shown in figure 2. A current, of typically 1 to 2 amps is passed through the filament and emitter to cause heating. Heat is generated by the filament and the emitter, and is lost by conduction through the base-plate and by radiation from the source body. The source may be placed within a thin walled metal tube to control radiation loss. The heatsinking effect of the base-plate leads to the emitter end of the source becoming hotter than the base, with a thermal gradient along the source itself. This means that decomposition or evaporation will begin towards the emitter end of the reservoir and the "decomposition zone" can be extended towards the base-plate by simply increasing the current. It is desirable for the emitter to be >1000°C before there is significant generation of ionisable material.
Species to be ionised escape from the reservoir chamber via the small gap or canal (10) and enter the emitter chamber (9). Direct line-of-sight exit from this chamber is blocked by the emitter and neutral atoms are forced to diffuse around the hot chamber until some finally contact the emitter surface and are ionised. The electric field set up by connection of the end-cap to the negative part of the filament supply, or to an external voltage source, encourages the positive ions to exit through the aperture and then to enter the strong electric field that exists between the end-cap and the extraction electrode. The end-cap is sufficiently hot to re-evaporate any ions striking it and these join material diffusing around the chamber until being re-lonised and again having the possibility of exiting the source.
Claims (4)
- Claims 1 A thermal surface ionisation source having separate reservoir and ionisation regions where the reservoir and emitter temperatures are controlled using a single current.
- 2 An ion source according to claim 1 where the reservoir is filled with material for direct evaporation.
- 3 An ion source according to claim 1 where the reservoir is filled with an alkali metal salt or other material which thermally decomposes to provide the species for ion emission.
- 4 An ion source according to claim 1 where the reservoir contains a mixture of materials which chemically react when heated to liberate species for ion isation.A filament, fitted to an ion source according to claim 1, comprising materials of differing size and composition so as to tailor the thermal, electrical, mechanical and chemical properties to those suitable for both heating the reservoir and causing surface ionisation, 6 An ion source according to claim 1 where a filament of a single material causes both heating of the reservoir and ionisation.7 An ion source according to claim 1 where the emissive surface is held at a single electrical potential by direct electrical connection to the filament at one point.8 An ion source according to claim 1 where the emissive surface is electrically isolated from the heat source and is connected to another electrical supply.9 An ion source according to claim 1, where the end-cap is electrically biased by connection to one of the filament supplies.An ion source according to claim 1, where the end-cap is connected to another electrical supply.11 An ion source according to claim 1 where the reservoir can be replenished when exhausted.12 An ion source according to claim 11 where replenishment is via moulded or compressed pellets.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0810166A GB2460664A (en) | 2008-06-04 | 2008-06-04 | A surface ionization ion source |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0810166A GB2460664A (en) | 2008-06-04 | 2008-06-04 | A surface ionization ion source |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0810166D0 GB0810166D0 (en) | 2008-07-09 |
| GB2460664A true GB2460664A (en) | 2009-12-09 |
Family
ID=39638126
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0810166A Withdrawn GB2460664A (en) | 2008-06-04 | 2008-06-04 | A surface ionization ion source |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2460664A (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3864575A (en) * | 1970-07-25 | 1975-02-04 | Nujeeb Hashmi | Contact ionization ion source |
| JPS61148739A (en) * | 1984-12-24 | 1986-07-07 | Hitachi Ltd | Surface ionization type-ion source |
| JPS61203535A (en) * | 1985-03-06 | 1986-09-09 | Hitachi Ltd | Surface ionization type cesium ion source |
| US4801849A (en) * | 1984-05-16 | 1989-01-31 | Office National D Etudes Et De Recherches | Ion source operating by surface ionization in particular for providing an ion probe |
-
2008
- 2008-06-04 GB GB0810166A patent/GB2460664A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3864575A (en) * | 1970-07-25 | 1975-02-04 | Nujeeb Hashmi | Contact ionization ion source |
| US4801849A (en) * | 1984-05-16 | 1989-01-31 | Office National D Etudes Et De Recherches | Ion source operating by surface ionization in particular for providing an ion probe |
| JPS61148739A (en) * | 1984-12-24 | 1986-07-07 | Hitachi Ltd | Surface ionization type-ion source |
| JPS61203535A (en) * | 1985-03-06 | 1986-09-09 | Hitachi Ltd | Surface ionization type cesium ion source |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0810166D0 (en) | 2008-07-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |