EP0165140B1 - Source d'ions opérant par ionisation de surface, notamment pour la réalisation d'une sonde ionique - Google Patents

Source d'ions opérant par ionisation de surface, notamment pour la réalisation d'une sonde ionique Download PDF

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Publication number
EP0165140B1
EP0165140B1 EP85400969A EP85400969A EP0165140B1 EP 0165140 B1 EP0165140 B1 EP 0165140B1 EP 85400969 A EP85400969 A EP 85400969A EP 85400969 A EP85400969 A EP 85400969A EP 0165140 B1 EP0165140 B1 EP 0165140B1
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EP
European Patent Office
Prior art keywords
ions
source according
ion source
active surface
ionization
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.)
Expired
Application number
EP85400969A
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German (de)
English (en)
French (fr)
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EP0165140A1 (fr
Inventor
Georges Slodzian
Bernard Daigne
François Girard
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.)
Office National dEtudes et de Recherches Aerospatiales ONERA
Universite Paris Sud
Original Assignee
Office National dEtudes et de Recherches Aerospatiales ONERA
Universite Paris Sud
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Application filed by Office National dEtudes et de Recherches Aerospatiales ONERA, Universite Paris Sud filed Critical Office National dEtudes et de Recherches Aerospatiales ONERA
Publication of EP0165140A1 publication Critical patent/EP0165140A1/fr
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    • 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

Definitions

  • the invention relates to ion sources operating by surface ionization.
  • Ion sources of this type are already known which include, under vacuum, a source of neutral particles of the same nature as the ions to be produced, an ionization support which has at least one active surface suitable for adsorption of the particles. neutrals, followed by their desorption in the form of ions, means for bringing the neutral particles to the ionization support, which transforms them into ions by adsorption / desorption, and means for channeling most of the ions thus produced in a beam emitted in a chosen direction of space.
  • the degree of ionization obtained during such a desorption is governed by the law of Saha-Langmuir. This law expresses an exponential dependence according to the difference between the work of exit of the heated support and the potential of ionization for positive ions or the electronic affinity for negative ions.
  • a suitable choice of the material of the ionization support makes it possible to obtain a probability of ionization close to unity.
  • the temperature of the support then has only a weak influence on the probability of ionization.
  • it plays a decisive role in the desorption process. In particular, it influences the residence time of an atom adsorbed on the surface of the support.
  • a hot surface which receives for example a jet of alkaline atoms such as potassium, rubidium or cesium, will have, in steady state, and in a situation of equilibrium where there is no accumulation, a cover (number of atoms adsorbed per unit area) which will depend on the incident flux of neutral atoms and the temperature of the support. But the presence of these adsorbed atoms then modifies the output work and can therefore influence the probability of ionization, in particular causing it to decrease sharply. It thus appears that the ion sources have a complex functioning.
  • dl is the intensity of the beam emitted by a surface element of in a solid angle dQ defined around a direction characterized by angles 0 and ⁇ , and in an energy band located between E and E + dE.
  • Gloss B is a function of 0, ⁇ and E.
  • Ion sources are already known in which the ionizing member is a sintered tungsten pellet.
  • An alkaline vapor passes through the interstices which remain between the tungsten grains and the pellet is brought to a temperature of the order of 1,200 ° C., while being placed in an electric field intended to accelerate the ions which emerge between the grains.
  • the source of neutral particles is a reservoir of liquid cesium, the temperature of which is adjusted to obtain a pressure of cesium vapor sufficient to force the diffusion of this vapor through the pores of the sintered tungsten pellet.
  • This first known source of ions has the particularity that the atoms to be ionized cross the ionization support.
  • This type of ion source makes it possible to reach high intensities, provided that a large emissive surface is used.
  • Sources of ions using a hot filament are also known. Their assembly is analogous to that of an electron gun: a filament, folded back in a hairpin, is placed in the center of a circular orifice pierced in an electrode which plays the role of screen and Wehnelt electrode. The filament and the Wehnelt are brought to high positive voltage and arranged in front of an electrode at the potential of the earth pierced with a circular hole (equivalent to the anode of an electron gun). The space between the filament and this "anode” is filled with cesium vapor produced by an annex furnace.
  • Ion sources are also known in which the ionization support is arranged in a baffle, which obstructs the passage of neutral particles in the beam of emitted ions.
  • United States patent 3,283,193 can, under certain reservations, be considered as also describing a baffle, in the rather special context of the catalytic production of nascent hydrogen.
  • Electronic bombardment ionizes part of the hydrogen atoms before they have had time to recombine into molecules.
  • the ion source thus produced is not very bright, wide, and fairly dispersed in energy. It is also not very stable, and vapors are released out of the ionizer itself, since few hydrogen atoms are actually ionized.
  • the ionization support is defined by thin conductive parts, all thin parts except one having a central hole and being stacked so that they internally form a cylindrical passage coaxial with the orifice of outlet, and of cross section smaller than that of said closed conduit;
  • the baffle is defined by the fact that said part without central hole is a plate pierced only with peripheral holes inside the passage, which it crosses, while its central part defines said active surface opposite the outlet orifice ; this achieves a quasi-perfect baffle preventing the direct passage of neutral particles in the emitted beam, without them having struck the active surface of the ionization support.
  • the ionization support is housed inside a conductive cap, mounted at the end of said conduit, which is completely closed by the cap except at the outlet orifice of the latter. .
  • the dimensions of the duct are adapted to preserve the chicane effect obtained in the ionization support.
  • the focusing means comprise an external focusing electrode, pierced and arranged to establish between the active surface and the outlet orifice, an electric field suitable for accelerating the ions to constitute the emission beam.
  • the potential difference between the active surface and the external electrode is of the order of at least 10 kilovolts, the size of the outlet orifice being a few tenths of a millimeter, and the latter being flared outwards.
  • the ion source comprises means suitable for heating the ionization support, preferably to a temperature of between 1000 and 1500 ° C.
  • the source of neutral particles may comprise a solid compound capable of delivering said particles by pyrolysis and, preferably, without gassing.
  • the active surface of the ionization support is curved, opposite the outlet orifice.
  • this ion source can function in particular with alkaline atoms, positively ionized, as well as with halogen atoms ionized negatively.
  • a particular arrangement of the active ionization surface makes it possible to obtain a beam which is as rich in ions on its periphery as in its center or, on the contrary, a beam whose ions are essentially concentrated in the emission axis. .
  • the source of neutral particles is designated by 1. It comprises a container consisting of a cylindrical side wall 11 and a bottom 12, integral with a sleeve 14 facing downward, and suitable for being housed on a support of alumina 15. Apart from this alumina support 15, all the parts of the ion source in FIGS. 1 and 2 are metallic.
  • the container 1 is surmounted by a bell 31 communicating with a tubular metal conduit 30 which defines means 3 for bringing neutral particles to the ionization support 2.
  • the bell 31 is screwed to the wall 11, with interposition of a copper gasket 19.
  • tank 1 a solid compound has been shown at 10, but which could be in the form of discrete particles, capable of producing by pyrolysis of vapors (ionized or not).
  • the corresponding neutral atoms can be produced by pyrolysis of a compound such as an alumino-silicate, an iodide, or a carbonate, for example.
  • alumino-silicate is particularly advantageous in that it leaves only solid residues and does not produce gas emissions.
  • the upper end of the tube 30 is provided with a cap 51, which closes it completely, except in an outlet orifice 50 which flares upwards in a flat V-shaped cross section.
  • the periphery of the cap extends axially over a substantial length of the tube 30.
  • a groove machined in the internal wall of the molybdenum cap 51 loqe a nickel seal 53 formed by electron bombardment to obtain a weld.
  • the whole of the ion source itself is brought for example to a potential of 10 kilovolts, which can be applied to the tube 30, or at the level of the reservoir 1 (FIG. 3).
  • a potential of 10 kilovolts which can be applied to the tube 30, or at the level of the reservoir 1 (FIG. 3).
  • an electrode 55 placed at the earth potential is placed. The structure of this electrode 55 will be described in more detail with reference to FIG. 3.
  • the cap 51, the orifice 50 and the electrode 55 define means 5 for focusing the ions produced in a beam which is emitted in a chosen direction of space.
  • ionization support generally designated by 2, and inserted between the cap 51 and the upper end of the tube 30.
  • This ionization support will now be described with reference to FIG. 2A. It comprises, bearing on the tube 30, a first annular washer 61, surmounted by a plate 62, pierced with four holes 65 to 68, then a second washer 63, which can be further surmounted by a last washer 64 , the assembly being held by the underside 25 of the top of the cap 51.
  • the surfaces 21 to 24 as well as 25 are also made of metallic material and, consequently, also capable of adsorption / desorption generating ions.
  • the ions thus created can again adsorb / desorb on the main active surface 20, or possibly exit through the orifice 50, at least for some of them.
  • the material cone of the cap 51 and which defines the orifice 50 here has an angle of 30 °. This leaves room for fairly inclined ion trajectories, at the start, with respect to the main direction of emission D of FIG. 2A.
  • the applied electric field which accelerates the ions in the direction D, of course bends this trajectory so that it returns thereafter on the axis.
  • the direct passage of neutral particles between the tube 30 and the orifice 50 could be made impossible by removing the washer 24, which, like the other stacked members 21 to 23, has a thickness of 0.1 mm. This further decreases the distance between surfaces 20 and 25.
  • the baffle is provided essentially by the fact that the plate 62 has four holes 65 to 68, off-center and drilled in a regularly distributed manner.
  • this embodiment is not limiting. A greater number of holes can be provided, possibly placed irregularly, provided that they are suitably off-center. It is also possible to make annular recesses in the plate 62, reserving the necessary fasteners for the maintenance of its central part 20.
  • the end of the tube 30, the cap 51, and the plate 62 (as well as the washers 61, 63 and 64) are heated to a temperature of between 1000 and 1500 °. C.
  • the tank 1 must for its part be heated to allow the pyrolysis of the compound which it contains. This heating can be independent of the previous one.
  • the heating is ensured by electronic bombardment by means of a filament F, supplied in an adjustable manner with electric current to be brought to the desired temperature.
  • a filament F supplied in an adjustable manner with electric current to be brought to the desired temperature.
  • Independent heating of the reservoir is not therefore essential, since the section and the length of the tube 30 can be provided so that the thermal leak occurring during the heating of the ionization support itself is sufficient to supply the reservoir 1 with l energy needed to bring the compound (alumino-silicate-cesium) it contains to an adequate temperature.
  • FIG. 3 shows a metal support 80 on which is mounted an alumina spacer 81, which in turn supports a metal electrode 82, protected by a heat shield 83.
  • the electrode 55 which here takes on an annular shape pierced with a central hole 58 for the passage of the ions produced. Slightly downstream of this hole 58, the electrode 55 supports a tantalum heat shield 56 pierced with a central hole. Still downstream, a fixing 59 of the grounded electrode 55 supports a lens shown diagrammatically at 90, and receiving a positive high voltage supply 95. Finally, on the bottom side, the electrode 55 is connected to an enclosure shown schematically in 89, isolating the ion source from the atmosphere, and making it possible to create a partial vacuum desirable for its operation.
  • the lens 80 is chosen according to the use for which the ion source is intended.
  • the lens 90 is used to create a real image of the virtual point source that constitutes the ion source of the invention.
  • the core of the probe consists of the cap 51, the baffle, which must be as thin as possible (distance between the surfaces 20 and 25), and the extraction electrode 55 whose role is to establish an electric field as large as possible at the surface 20 of the ionizer to ensure the extraction of ions.
  • a very strong extractor field makes it possible to obtain a high gloss without the need to increase the diameter of the orifice 50.
  • the electrode 55 is made of a material, such as Tantalum , emitting few negative ions due to the bombardment of positive ions in the beam. But this positive ion bombardment will create electrons which return to bomb the cap 51 at + 10 kV.
  • This parasitic phenomenon creates heating additional cap (and the entire ionizer). This increases the feed rate, and may make it impossible to control the temperature of the ionizer.
  • FIGS. 4 and 4A takes advantage of the parasitic phenomenon which has just been described.
  • an insulating insert 57A is placed supporting a ring electrode 57 whose internal, free edge is coaxial with the orifice 58;
  • the operation of the ion source is then started by heating the cap 51 using the filament F, as before. Then, the polarization of the additional electrode 57 is adjusted in order to focus the secondary electrons on the ionizing surface 20. It is then possible to stop the heating by the filament F, or decrease it for an auxiliary heating ensuring the compensation of the heat losses of the external walls of the ionizer assembly (organs 1 to 5).
  • the role of active surface of the ionizer is played essentially by surface 20. But this role can also be played, to a certain extent, by any surface of the same metal brought to a sufficient temperature, which is the case for the internal face 25 of the cap, and for the lateral surfaces 21 to 24, as previously indicated.
  • the ions thus produced laterally can go to the active surface 20, leave again in the same state (of ions) and then undergo the acceleration which will make them exit by the exit orifice 50, then by the hole 58 (FIG. 3) .
  • the emitted ion beam does not have a substantially Gaussian distribution centered on its main direction D, but on the contrary a fairly wide, rather reinforced, distribution on a peripheral ring of this beam;
  • any reduction in beam size by this means produces an increase in the aperture angle and therefore an increase in aperture aberrations, which defeats the purpose, at know how to produce a small probe.
  • This effect makes it necessary to reduce the opening angle, by interposing suitably arranged diaphragms. Under these conditions, as the ions coming from the abovementioned circular crown do not feed the smallest opening angles, they are not useful for the creation of an ion probe.
  • the invention provides (FIG. 2C) that a thin disc of lanthanum hexaboride, denoted 64A, is placed on the internal face 25 of the cap and pierced with a central hole substantially the same size as the orifice 50.
  • the disk 64A can be replaced by a deposit of lanthanum hexaboride produced by vacuum evaporation. The thickness being less, the electric field of extraction is increased.
  • lanthanum hexaboride has a lower output work than the ionization energy of cesium (for example).
  • cesium for example
  • the cesium atoms which have struck the lanthanum hexaboride disc leave in the form of neutral atoms, and then strike the actie surface 20A, which is the only ionizing surface.
  • the ion beam thus obtained is then particularly suitable for producing an ion probe.
  • the source of the invention also allows the production of negative ions, by of course passing the voltage between the ionizer and the electrode 55 to -10 kilovolts.
  • the additional electrode 57 polarized at + 320 V, is used to block positive ions.
  • FIG. 2A has a metal surface 25 and a surface 20 in lanthanum hexaboride.
  • an ion beam starting from the surface 20 will then be produced.
  • This ion beam is of the very point type suitable for ion probes.
  • iodine crystals are placed in the tank, which produce iodine vapor by gentle heating. Iodine atoms do not ionize on metal, whereas they will ionize on lanthanum hexaboride.
  • negative ions can be created from halogens, namely not only iodine, but also chlorine for example. It is also conceivable to produce negative ions from alkaline atoms, although their interest is then more limited.
  • the probability of ionization for positive ions is high when the material of the active surface has, for these ions, an output work greater than their ionization potential.
  • the material of the active surface has, for these ions, an output work lower than their electronic affinity.
  • the geometry of the orifice 50 is not necessarily circular. This geometry may depend on the shape of the ion beam which is desired for working downstream.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Electron Sources, Ion Sources (AREA)
EP85400969A 1984-05-16 1985-05-15 Source d'ions opérant par ionisation de surface, notamment pour la réalisation d'une sonde ionique Expired EP0165140B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8407606A FR2564636B1 (fr) 1984-05-16 1984-05-16 Source d'ions operant par ionisation de surface, notamment pour la realisation d'une sonde ionique
FR8407606 1984-05-16

Publications (2)

Publication Number Publication Date
EP0165140A1 EP0165140A1 (fr) 1985-12-18
EP0165140B1 true EP0165140B1 (fr) 1988-05-18

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ID=9304048

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Application Number Title Priority Date Filing Date
EP85400969A Expired EP0165140B1 (fr) 1984-05-16 1985-05-15 Source d'ions opérant par ionisation de surface, notamment pour la réalisation d'une sonde ionique

Country Status (6)

Country Link
US (1) US4801849A (enrdf_load_stackoverflow)
EP (1) EP0165140B1 (enrdf_load_stackoverflow)
JP (1) JPS6151729A (enrdf_load_stackoverflow)
DE (1) DE3562842D1 (enrdf_load_stackoverflow)
FR (1) FR2564636B1 (enrdf_load_stackoverflow)
SU (1) SU1473724A3 (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11031205B1 (en) 2020-02-04 2021-06-08 Georg-August-Universität Göttingen Stiftung Öffentlichen Rechts, Universitätsmedizin Device for generating negative ions by impinging positive ions on a target

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IL81375A (en) * 1987-01-23 1990-11-05 Univ Ramot Method and apparatus for producing ions by surface ionization of energy-rich molecules and atoms
US4954750A (en) * 1988-07-07 1990-09-04 Albert Barsimanto Flexible ion emitter
JPH042031A (ja) * 1990-04-18 1992-01-07 Matsushita Electric Ind Co Ltd イオン源装置
GB2460664A (en) * 2008-06-04 2009-12-09 Hiden Analytical Ltd A surface ionization ion source

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486452A (en) * 1945-04-30 1949-11-01 Cons Eng Corp Mass spectrometry
FR65999E (enrdf_load_stackoverflow) * 1954-05-25 1956-03-27
US3283193A (en) * 1962-05-14 1966-11-01 Ellison Company Ion source having electrodes of catalytic material
US3336475A (en) * 1964-02-05 1967-08-15 Electro Optical Systems Inc Device for forming negative ions from iodine gas and a lanthanum boride contact ionizer surface
US3864575A (en) * 1970-07-25 1975-02-04 Nujeeb Hashmi Contact ionization ion source
DE2222396B2 (de) * 1972-05-06 1975-04-30 Bodenseewerk Perkin-Elmer & Co Gmbh, 7770 Ueberlingen Selektiver lonisationsdetektor
JPS57205953A (en) * 1981-06-12 1982-12-17 Jeol Ltd Ion source

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11031205B1 (en) 2020-02-04 2021-06-08 Georg-August-Universität Göttingen Stiftung Öffentlichen Rechts, Universitätsmedizin Device for generating negative ions by impinging positive ions on a target

Also Published As

Publication number Publication date
US4801849A (en) 1989-01-31
FR2564636B1 (fr) 1990-07-06
FR2564636A1 (fr) 1985-11-22
JPS6151729A (ja) 1986-03-14
JPH0451929B2 (enrdf_load_stackoverflow) 1992-08-20
SU1473724A3 (ru) 1989-04-15
EP0165140A1 (fr) 1985-12-18
DE3562842D1 (en) 1988-06-23

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