US2305761A - Electron-optical lens - Google Patents

Electron-optical lens Download PDF

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US2305761A
US2305761A US260296A US26029639A US2305761A US 2305761 A US2305761 A US 2305761A US 260296 A US260296 A US 260296A US 26029639 A US26029639 A US 26029639A US 2305761 A US2305761 A US 2305761A
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electron
lens
plates
magnetic
magnets
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US260296A
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Bodo V Borries
Ruska Ernst
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/10—Lenses
    • H01J37/14—Lenses magnetic
    • H01J37/143—Permanent magnetic lenses

Definitions

  • the invention relates to electron-optical devices and more in particular to magnetic lenses of small focal length to be employed for magnifying or reducing images produced by electron rays.
  • the resolving power of electron microscopes may be increased considerably by providing objectives of very small focal length.
  • the aperture fault as well as the chromatic aberration are proportional to the focal length so that magnetic systems with which relatively small focal lengths cannot be attained are not suitable for electron microscopes.
  • This is the reason why heretofore permanent magnets have not been used for electron-optical magnifying or reducing lenses. It was believed, in particular, that when using permanent magnets the necessary small focal length could not be attained, and it was generally assumed that when using permanent magnets the magnet field could not be controlled to a sufiicient extent.
  • Fig. 1 a perspective and sectional view of a lens system according to the invention, and in Fig. 2 a top View of the same embodiment.
  • Fig. 3 shows an axial cross section of a second embodiment.
  • Fig. 4 illustrates a third possibility by an axial cross section showing only one-half of the symmetrical structure.
  • Figs. 5 and 6 represent a sectional side elevation and a top view, respectively, of a further example which, in general, is similar to that of Fig. 4.
  • the electron-optical lens structure shown in Fig. 1 contains two ferromagnetic pole pieces in the form of circular plates.
  • the plates are rigid- 1y connected with each other and held in spaced relationship by a tubular supporting member 3 which consists of non-magnetic material, for instance brass, and forms a wall portion of the vacuum vesselof the electron-optical instrument containing the lens structure.
  • the two pole plates 2 have a central portion ll provided with an aperture 5 for the passage of the electron rays.
  • the two central portions are funnelshaped and project inwardly so that the perforated centers closely approach each other.
  • Several permanent magnets l are arranged along the periphery of the plates outside the vacuum wall 3.
  • a coarse regulation of the strength of the magnetic field effective in the air gap may be effected by varying the number of the permanent magnets employed.
  • one or more of the magnets I may be designed to be easily removable.
  • An example of a device for effecting a fine regulation is shown in Fig. 21.
  • one or more of the permanent magnets may be movably arranged so that their contacts with the plates 2 may be varied as indicated by a dot-and-dash line, for instance by means of a screw 6 or another adjusting device. It is advisable to use an adjusting device having sufiiciently long lever arms in order to attain the desired sensitiveness.
  • the strength of the magnetic field may be varied in accordance with any desired sensitiveness.
  • the same effect may be obtained by movably arranging the permanent magnets in such a manner that they may be displaced in parallel relation to the outer surface of the lens structure. It has been found convenient to design two or three of the magnets employed in the above-described manner. The range of regulation thus obtained is, as a rule, sufficient in view of the fact that for effecting a coarse regulation some of the magnets may be removed from the lens.
  • the permanent magnets I are arranged at the front faces of the cylindrical lens structure.
  • the outer peripheral surface of the lens is formed by a portion of the metal wall I of the electron-optical instrument.
  • annular inserts are provided as indicated at 9. They consist of a ferro-magnetic material, for instance iron.
  • permanent magnets l are arranged in axial direction at the outer peripheral surface as well as radially at the front faces of the lens structure. Rings l0 serve to close the magnetic circuit between the magnets.
  • 6 denotes a spacing member consisting of a vacuum wall of non-magnetic material.
  • 1 denotes the wall proper of the electron-optical instrument and 3 the pole pieces.
  • the radially arranged magnets i should be sector shaped in order to arrange as great a number of magnets as possible in the manner shown. In some cases it may be preferable to render the crosssection of the radially arranged magnets uniform throughout their lengths in order to create the necessary flux without thereby varying the flux density. This is shown, for instance, in Fig. 5 in which I denotes the magnets and 8 the pole pieces. In this case the ends of the permanent magnets near the axis are narrow and high, whereas the opposite ends thereof are relatively broad and fiat. Particularly when designing the lens according to the invention in the manner as shown in Figs. i and 5 a very high magnetomotive force may be obtained with a relatively small height of the entire arrangement.
  • cobalt magnets or also the ironnickel-aluminum alloy known under the tradename Oerstite are employed in the manufacture of permanent magnets to be used according to the invention.
  • Electron-optical lenses according to the invention are simpler and more economical in construction and manufacture, and less space-consuming than the known electromagnetic lens systems. Lenses according to the invention further eliminate faults due to voltage fluctuations or other irregularities of electrical arrangements and do not require an energy supply when in operation.
  • the magnetic lenses according to the invention may not only be employed for influencing electron rays but also for other corpuscular rays, for instance ion or proton rays.
  • a magnetic lens of small focal length comprising two annular pole plates of high magnetic permeability arranged in said vacuum vessel coaxially with the electron-optical axis and spaced from each other in the direction of the electron-optical axis in fixed relation to each other, each of said plates being provided with a centrally aperture pole piece approaching the pole piece of said other plate, and permanent magnet bodies forming the magnetomotive source of the lens and being arranged in parallel to said axis and around said pole piece to form a substantially cylindrical arrangement of magnets, said magnet bodies being connected with said plates to form a closed magnetic circuit between said two pole pieces and including a magnet body movable relative to said plates, and means for adjusting said movable body in order to regulate the magnetic field effective between said pole pieces.
  • an electron-optical lens of small focal length comprising two circular disc-like plates of highly permeable magnetic material arranged in said vessel concentrically to the electron-optical axis and spaced from each other along said axis in fixed relation to each other, two centrally apertured pole pieces of highly permeable magnetic material arranged centrally with respect to said plates and being magnetically integral therewith respectively, said pole pieces facing each other to forma lens gap along and close to said axis, and permanent magnet means arranged at the periphery of said plates to form a substantially cylindrical arrangement and connecting said plates magnetically in order to energize the gap between said pole pieces.
  • an electron-optical lens or" small focal length comprising two circular plates of highly permeable magnetic material arranged in said vessel concentrically to the electron-optical axis and. spaced from each other along said axis in fixed relation to each other, two centrally apertured pole pieces of highly permeable magnetic material arranged centrally with respect to said plates and being magnetically integral therewith respectively, said pole pieces facing each other to form a lens gap along and close to said axis, and a plurality of permanent magnet bars disposed round the periphery of said pole members and in parallel to said axis so as to form a substantially cylindrical magnet arrangement, said bars being magnetically connected with said plates to energize the gap between said pole pieces.
  • said lens structure comprising two substantially circular and axially symmetrical pole plates of magnetically-soft material spaced from each other along the optical axis of the microscope, said plates being arranged in said vacuum vessel and having their central portions, respectively, provided with an axial aperture and shaped to approach each other to form a lens gap along and close to said axis, and permanent magnet means forming a magnetic circuit with said lens gap, said means including permanent magnet bodies disposed in parallel to said axis so as to form a substantially cylindrical arrangement around said plates, and other magnet bodies extending radially to said axis between said former magnet bodies and said plates for energizing said pole plates.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Beam Exposure (AREA)
  • Electron Sources, Ion Sources (AREA)

Description

Dec. 22, I942.
ELECTRONOPTICAL LENS Filed March 7, 1939 (3011 A!" Mi W M B. v. BORRIES ET AL 2,305,751
Patented Dec. 22, 1942 ELECTRON-OPTICAL LENS Bodo v. Borries and Ernst Ruska, Berlin-Spandau, Germany; vested in the Alien Property Custodian Application March '7, 1939, Serial No. 260,296 In Germany March '7, 1938 7 Claims.
The invention relates to electron-optical devices and more in particular to magnetic lenses of small focal length to be employed for magnifying or reducing images produced by electron rays.
It is well known to influence the electron rays in electron-optical instruments with the aid of magnet coils. In some cases, particularly in magnetic electron microscopes, it is necessary to avoid voltage fluctuations of the power sources energizing the magnet coils, as such fluctuations represent one of the faults which must be eliminated in order to obtain a higher resolving power than attainable in a light-optical microscope. It has been proposed to employ regulating devices for maintaining the energizing voltage of the magnetic lens systems of an electron microscope at a constant value; the result, however, is not satisfactory.
As is well known, the resolving power of electron microscopes may be increased considerably by providing objectives of very small focal length. For instance, the aperture fault as well as the chromatic aberration are proportional to the focal length so that magnetic systems with which relatively small focal lengths cannot be attained are not suitable for electron microscopes. This is the reason why heretofore permanent magnets have not been used for electron-optical magnifying or reducing lenses. It was believed, in particular, that when using permanent magnets the necessary small focal length could not be attained, and it was generally assumed that when using permanent magnets the magnet field could not be controlled to a sufiicient extent.
Our invention is based on the discovery that these prejudices are unjustified, and that it is readily possible to avoid the above-mentioned drawbacks of the known electron-optical lens systems by employing a particular lens structure comprising permanent magnets in combination with ferromagnetic pole pieces, which will be described in the following in conjunction with the drawing showing in Fig. 1 a perspective and sectional view of a lens system according to the invention, and in Fig. 2 a top View of the same embodiment. Fig. 3 shows an axial cross section of a second embodiment. Fig. 4 illustrates a third possibility by an axial cross section showing only one-half of the symmetrical structure. Figs. 5 and 6 represent a sectional side elevation and a top view, respectively, of a further example which, in general, is similar to that of Fig. 4.
The electron-optical lens structure shown in Fig. 1 contains two ferromagnetic pole pieces in the form of circular plates. The plates are rigid- 1y connected with each other and held in spaced relationship by a tubular supporting member 3 which consists of non-magnetic material, for instance brass, and forms a wall portion of the vacuum vesselof the electron-optical instrument containing the lens structure. The two pole plates 2 have a central portion ll provided with an aperture 5 for the passage of the electron rays. The two central portions are funnelshaped and project inwardly so that the perforated centers closely approach each other. Several permanent magnets l are arranged along the periphery of the plates outside the vacuum wall 3. By providing the plates 2 with openings 4, the advantage is obtained over the known magnet coils that when exhausting the vacuum vessel not only the aperture 5 but a considerably greater cross-section is available for the passage of the gas.
A coarse regulation of the strength of the magnetic field effective in the air gap may be effected by varying the number of the permanent magnets employed. To this end, one or more of the magnets I may be designed to be easily removable. An example of a device for effecting a fine regulation is shown in Fig. 21. According to the invention one or more of the permanent magnets may be movably arranged so that their contacts with the plates 2 may be varied as indicated by a dot-and-dash line, for instance by means of a screw 6 or another adjusting device. It is advisable to use an adjusting device having sufiiciently long lever arms in order to attain the desired sensitiveness. If, for instance, the length of the magnet is correspondingly increased or themagnet is provided with an extension which may be employed as a lever when regulating, the strength of the magnetic field may be varied in accordance with any desired sensitiveness. The same effect may be obtained by movably arranging the permanent magnets in such a manner that they may be displaced in parallel relation to the outer surface of the lens structure. It has been found convenient to design two or three of the magnets employed in the above-described manner. The range of regulation thus obtained is, as a rule, sufficient in view of the fact that for effecting a coarse regulation some of the magnets may be removed from the lens.
In the embodiment shown in Fig. 3 the permanent magnets I are arranged at the front faces of the cylindrical lens structure. The outer peripheral surface of the lens is formed by a portion of the metal wall I of the electron-optical instrument. In order to protect the electron ray passing through the aperture 5 against disturbing interferences caused by extraneous magnetic fields, annular inserts are provided as indicated at 9. They consist of a ferro-magnetic material, for instance iron.
In the embodiment shown in Fig. 4-. permanent magnets l are arranged in axial direction at the outer peripheral surface as well as radially at the front faces of the lens structure. Rings l0 serve to close the magnetic circuit between the magnets. 6 denotes a spacing member consisting of a vacuum wall of non-magnetic material. 1 denotes the wall proper of the electron-optical instrument and 3 the pole pieces. By the use of horse-shoe magnets the same effect may be obtained as by the arrangement of the magnets shown in Fig. 4.
In the embodiment shown in Fig. 4 the radially arranged magnets i should be sector shaped in order to arrange as great a number of magnets as possible in the manner shown. In some cases it may be preferable to render the crosssection of the radially arranged magnets uniform throughout their lengths in order to create the necessary flux without thereby varying the flux density. This is shown, for instance, in Fig. 5 in which I denotes the magnets and 8 the pole pieces. In this case the ends of the permanent magnets near the axis are narrow and high, whereas the opposite ends thereof are relatively broad and fiat. Particularly when designing the lens according to the invention in the manner as shown in Figs. i and 5 a very high magnetomotive force may be obtained with a relatively small height of the entire arrangement.
Preferably cobalt magnets or also the ironnickel-aluminum alloy known under the tradename Oerstite are employed in the manufacture of permanent magnets to be used according to the invention.
Electron-optical lenses according to the invention are simpler and more economical in construction and manufacture, and less space-consuming than the known electromagnetic lens systems. Lenses according to the invention further eliminate faults due to voltage fluctuations or other irregularities of electrical arrangements and do not require an energy supply when in operation. The magnetic lenses according to the invention may not only be employed for influencing electron rays but also for other corpuscular rays, for instance ion or proton rays.
What is claimed is:
1. In combination with an electron microscope having a vacuum vessel, a magnetic lens of small focal length comprising two annular pole plates of high magnetic permeability arranged in said vacuum vessel coaxially with the electron-optical axis and spaced from each other in the direction of the electron-optical axis in fixed relation to each other, each of said plates being provided with a centrally aperture pole piece approaching the pole piece of said other plate, and permanent magnet bodies forming the magnetomotive source of the lens and being arranged in parallel to said axis and around said pole piece to form a substantially cylindrical arrangement of magnets, said magnet bodies being connected with said plates to form a closed magnetic circuit between said two pole pieces and including a magnet body movable relative to said plates, and means for adjusting said movable body in order to regulate the magnetic field effective between said pole pieces.
2. In an electron microscope having a vacuum vessel, an electron-optical lens of small focal length comprising two circular disc-like plates of highly permeable magnetic material arranged in said vessel concentrically to the electron-optical axis and spaced from each other along said axis in fixed relation to each other, two centrally apertured pole pieces of highly permeable magnetic material arranged centrally with respect to said plates and being magnetically integral therewith respectively, said pole pieces facing each other to forma lens gap along and close to said axis, and permanent magnet means arranged at the periphery of said plates to form a substantially cylindrical arrangement and connecting said plates magnetically in order to energize the gap between said pole pieces.
3. In an electron microscope having a vacuum vessel, an electron-optical lens or" small focal length comprising two circular plates of highly permeable magnetic material arranged in said vessel concentrically to the electron-optical axis and. spaced from each other along said axis in fixed relation to each other, two centrally apertured pole pieces of highly permeable magnetic material arranged centrally with respect to said plates and being magnetically integral therewith respectively, said pole pieces facing each other to form a lens gap along and close to said axis, and a plurality of permanent magnet bars disposed round the periphery of said pole members and in parallel to said axis so as to form a substantially cylindrical magnet arrangement, said bars being magnetically connected with said plates to energize the gap between said pole pieces.
4. In an electron microscope having a vacuum vessel and a magnetic lens structure, said lens structure comprising two substantially circular and axially symmetrical pole plates of magnetically-soft material spaced from each other along the optical axis of the microscope, said plates being arranged in said vacuum vessel and having their central portions, respectively, provided with an axial aperture and shaped to approach each other to form a lens gap along and close to said axis, and permanent magnet means forming a magnetic circuit with said lens gap, said means including permanent magnet bodies disposed in parallel to said axis so as to form a substantially cylindrical arrangement around said plates, and other magnet bodies extending radially to said axis between said former magnet bodies and said plates for energizing said pole plates.
5. In an electron microscope having a vacuumtight enclosure formed in part of a pair of annular magnetic members positioned in mutually spaced end-to-end relation to provide a lens gap between them and tapered conically towards each other, magnetic means associated with said members for energizing said lens gap, and peripheral means externally sealing said gap to maintain the vacuum-tight qualities of the enclosure.
6. In an electron microscope having a vacuumtight enclosure formed in part of a pair of annular magnetic members positioned in mutually spaced end-to-end relation to provide a lens gap between them and tapered conically towards each other, magnetic means externally connected between said members for energizing said lens gap, and non-magnetic means peripherally sealing the interstice between said members to maintain said enclosure vacuum-tight.
7. In an electron microscope having a vacuumtight enclosure formed in part of a pair of annular magnetic members positioned in mutually spaced end-to-end relation to provide a lens gap between them and tapered conically towards each other, magnetic means associated with said members for energizing said lens gap, and a ring of non-magnetic material interposed between said members for peripherally sealing the interstice between said members.
BODO v. BORRI S. ERNST RUSKA.
US260296A 1938-03-08 1939-03-07 Electron-optical lens Expired - Lifetime US2305761A (en)

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DES6773D DE973258C (en) 1938-03-08 1938-03-08 Magnetic pole shoe lens with a small focal length for electron-optical enlargements in electron microscopes

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Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2455676A (en) * 1946-05-21 1948-12-07 Rca Corp Electron lens correction device
US2503173A (en) * 1946-10-18 1950-04-04 Rca Corp Permanent magnetic electron lens system
US2533688A (en) * 1950-01-31 1950-12-12 Quam Nichols Company Focusing device
US2533687A (en) * 1949-05-27 1950-12-12 Quam Nichols Company Magnetic focusing device
US2533689A (en) * 1950-06-28 1950-12-12 Quam Nichols Company Magnetic focusing device
US2550592A (en) * 1948-08-10 1951-04-24 Emi Ltd Focusing coil for cathode-ray tubes
US2579273A (en) * 1949-05-21 1951-12-18 Rca Corp Magnetic lens for electron optical systems
US2592185A (en) * 1950-12-09 1952-04-08 Quam Nichols Company Focusing device
US2619607A (en) * 1951-03-10 1952-11-25 Glaser Steers Corp Internal focusing device
US2624022A (en) * 1944-05-31 1952-12-30 Siemens Ag Device for regulating the focal length of magnetostatic pole shoe lenses
US2627589A (en) * 1950-10-30 1953-02-03 Rca Corp Focusing of electron optical apparatus
US2640868A (en) * 1950-11-04 1953-06-02 All Star Products Inc Magnetic focusing device for cathode-ray tubes
US2664514A (en) * 1952-03-10 1953-12-29 All Star Products Inc Magnetic focusing mechanism
US2681421A (en) * 1952-03-04 1954-06-15 Gen Electric Magnetic focusing structure for electron beams
US2723362A (en) * 1953-03-18 1955-11-08 Gen Electric Electron gun of the ion trap type
US2733364A (en) * 1956-01-31 flory
US2761991A (en) * 1950-08-29 1956-09-04 Siemens Ag Electron microscopes
US2804548A (en) * 1948-10-01 1957-08-27 Siemens Ag Device for adjusting the refractive power of electron lenses operating with permanent magnet excitation
US2844750A (en) * 1954-09-22 1958-07-22 Siemens Ag Focused electron flow electron tube for very high frequencies
US2858443A (en) * 1954-09-15 1958-10-28 Hitachi Ltd Permanent magnet lens and lens system
US2910603A (en) * 1955-10-04 1959-10-27 Philips Corp Device for compensating astigmatism in a magnetic electron lens
US3268648A (en) * 1962-09-25 1966-08-23 Heraeus Gmbh W C Apparatus for vaporizing materials by an electron beam
US3387241A (en) * 1966-10-11 1968-06-04 Centre Nat Rech Scient Permanent magnet multipole magnetic lens with variable convergence
US3689796A (en) * 1968-06-27 1972-09-05 Bbc Brown Boveri & Cie Electromagnetic lens for high speed electron beams
US4639597A (en) * 1983-10-24 1987-01-27 Anelva Corporation Auger electron spectrometer capable of attaining a high resolution
US6573817B2 (en) 2001-03-30 2003-06-03 Sti Optronics, Inc. Variable-strength multipole beamline magnet
CN104299872A (en) * 2013-07-18 2015-01-21 Fei公司 Magnetic lens for focusing a beam of charged particles

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL147885B (en) * 1949-02-24 Matsushita Electric Ind Co Ltd DRY CELL.
DE1114944B (en) * 1952-06-13 1961-10-12 Siemens Ag Arrangement for the bundled guidance of an electron beam
DE1010057B (en) * 1954-09-24 1957-06-13 Ruetgerswerke Ag Process for the regulation of rectifying columns connected in series which are heated by the utilization of broth

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE720927C (en) * 1937-02-25 1942-05-19 Telefunken Gmbh Magnetic electron lens

Cited By (30)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733364A (en) * 1956-01-31 flory
US2624022A (en) * 1944-05-31 1952-12-30 Siemens Ag Device for regulating the focal length of magnetostatic pole shoe lenses
US2455676A (en) * 1946-05-21 1948-12-07 Rca Corp Electron lens correction device
US2503173A (en) * 1946-10-18 1950-04-04 Rca Corp Permanent magnetic electron lens system
US2550592A (en) * 1948-08-10 1951-04-24 Emi Ltd Focusing coil for cathode-ray tubes
US2804548A (en) * 1948-10-01 1957-08-27 Siemens Ag Device for adjusting the refractive power of electron lenses operating with permanent magnet excitation
US2579273A (en) * 1949-05-21 1951-12-18 Rca Corp Magnetic lens for electron optical systems
US2533687A (en) * 1949-05-27 1950-12-12 Quam Nichols Company Magnetic focusing device
US2533688A (en) * 1950-01-31 1950-12-12 Quam Nichols Company Focusing device
US2533689A (en) * 1950-06-28 1950-12-12 Quam Nichols Company Magnetic focusing device
US2761991A (en) * 1950-08-29 1956-09-04 Siemens Ag Electron microscopes
US2627589A (en) * 1950-10-30 1953-02-03 Rca Corp Focusing of electron optical apparatus
US2640868A (en) * 1950-11-04 1953-06-02 All Star Products Inc Magnetic focusing device for cathode-ray tubes
US2592185A (en) * 1950-12-09 1952-04-08 Quam Nichols Company Focusing device
US2619607A (en) * 1951-03-10 1952-11-25 Glaser Steers Corp Internal focusing device
US2681421A (en) * 1952-03-04 1954-06-15 Gen Electric Magnetic focusing structure for electron beams
US2664514A (en) * 1952-03-10 1953-12-29 All Star Products Inc Magnetic focusing mechanism
US2723362A (en) * 1953-03-18 1955-11-08 Gen Electric Electron gun of the ion trap type
US2858443A (en) * 1954-09-15 1958-10-28 Hitachi Ltd Permanent magnet lens and lens system
US2844750A (en) * 1954-09-22 1958-07-22 Siemens Ag Focused electron flow electron tube for very high frequencies
US2910603A (en) * 1955-10-04 1959-10-27 Philips Corp Device for compensating astigmatism in a magnetic electron lens
US3268648A (en) * 1962-09-25 1966-08-23 Heraeus Gmbh W C Apparatus for vaporizing materials by an electron beam
US3387241A (en) * 1966-10-11 1968-06-04 Centre Nat Rech Scient Permanent magnet multipole magnetic lens with variable convergence
US3689796A (en) * 1968-06-27 1972-09-05 Bbc Brown Boveri & Cie Electromagnetic lens for high speed electron beams
US4639597A (en) * 1983-10-24 1987-01-27 Anelva Corporation Auger electron spectrometer capable of attaining a high resolution
US6573817B2 (en) 2001-03-30 2003-06-03 Sti Optronics, Inc. Variable-strength multipole beamline magnet
CN104299872A (en) * 2013-07-18 2015-01-21 Fei公司 Magnetic lens for focusing a beam of charged particles
EP2827357A1 (en) * 2013-07-18 2015-01-21 Fei Company Magnetic lens for focusing a beam of charged particles
US9595359B2 (en) 2013-07-18 2017-03-14 Fei Company Magnetic lens for focusing a beam of charged particles
CN104299872B (en) * 2013-07-18 2018-02-16 Fei 公司 For focusing on magnetic lenses and the method for charged particle beam

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FR850878A (en) 1939-12-28
DE973258C (en) 1959-12-31
BE433010A (en) 1939-04-29
NL57283C (en) 1946-04-15

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