US2422041A - Electron microscope - Google Patents

Electron microscope Download PDF

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Publication number
US2422041A
US2422041A US522875A US52287544A US2422041A US 2422041 A US2422041 A US 2422041A US 522875 A US522875 A US 522875A US 52287544 A US52287544 A US 52287544A US 2422041 A US2422041 A US 2422041A
Authority
US
United States
Prior art keywords
cathode
specimen
tip
electron microscope
screen
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 - Lifetime
Application number
US522875A
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English (en)
Inventor
Ramo Simon
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.)
General Electric Co
Original Assignee
General Electric Co
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
Priority to BE479996D priority Critical patent/BE479996A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US522875A priority patent/US2422041A/en
Priority to GB3668/45A priority patent/GB637361A/en
Application granted granted Critical
Publication of US2422041A publication Critical patent/US2422041A/en
Priority to FR977856D priority patent/FR977856A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/27—Shadow microscopy

Definitions

  • My invention relates toelectron microscopes and has for its object to provide a new and improved-method and apparatus for obtaininghighly enlarged. images of very'small structures by: the use of electrons.
  • One of the features of. my invention is theuse in an electron. microscopy of. the. shadow microscopy typeof a cold cathode upon which is sup ported aspecimen to beobserved and ananode. or fluorescent screen closely spaced with respect to 7 Claims. (01. 250-495) said cathode.
  • a relatively low potential im pressed between the cathode and anode produces electron emission solely through. the actionof the electric field existing between these electrodes, the electrons being drawn from the portion of the cathode not covered by the small specimensto produce anenlarged shadow image of the specimen on the fluorescent screen.
  • Fig. 1 represents.diagram matically and in section an electron microscope
  • Fig. 2 illustrates an enlarged view of a portion of-the cathode. structure employed intthe. electron. microscope of Fig. 1
  • Fig. 3 illustrates a modification of an electron microscope employing an alternative energizing potential arrange,- ment.
  • FIG. 1 there is shown an electron microscope comprising a closed container I0 of tubular construction.
  • the container is. closed by a glass window ll having a fluorescent screen or material l2 on its inner surface, upon which is deposited as by evaporation a very thin film l 3 of a suitable metal suchv as for example aluminum.
  • a cathode l4 At the opposite endof the container... there is supported a cathode l4 so constructed as to. be easily inserted and withdrawn from the container.
  • the container l0 may be formed of glass and may have at its cathode end. a flanged member l5 formed of a suitable alloy,.such asan iron-nickele-cobalt alloy, for uniting with the glass container Ill.
  • the container H may be formed of a borosilicate glass which unites readily with the alloy material l5.
  • the anode M' may be provided with a circular metallic ringlfi at" its end external to the container [0 which is in opposed relation with the member l5; being secured thereto by a plurality of bolts IT.
  • a gasketor sealing material It may be interposed between the members I5 and 16 to provide an air-tight seal aroundthe cathode opening of the container.
  • the enclosure Hl may be evacuated by any-suitable means, such as a vacuum pump, attached to an outlet tubulation IS.
  • cathode 14- preferably is formed of asuit.- able metallicmaterial, such as tungsten, which is provided, at its inner extremity with: a smoothly rounded tip-or point 20.
  • the tip 20 may. be produced by etching a tungsten wire until the. tip
  • the container l may be of very small size, the enclosure having a volume of only a few cubic centimeters.
  • the tip 20 of the cathode shown in Fig. 2 is covered with an adhesive or plastic film 22 in which is embedded particles of very small structure or specimen 23 to be observed.
  • an electric field is established between cathode l4 and fluorescent screen l2 by any suitable means, such as battery 24, the positive terminal of which is connected to ground and to the metallic coating I3 which covers the fluorescent screen 12.
  • the negative terminal of the battery is connected. to the cathode I4 through any suitable energizing means, such as the switch 25.
  • the cathode I4 is of the cold cathode type and electrons are drawn from the point 20 solely by field emission and travel essentially in radial lines to the anode or fluorescent screen l2.
  • the radius of the tip 20 is sufhciently small and the surface of the tip is sufiiciently smooth that the electrons appear to come from a point very close to the surface of the tip.
  • the potential applied between the cathode and anode is held to a low value, of the order of 4 or 5 kilovolts or less, bein sufficient merely to provide field emission from the cold cathode tip.
  • a low value of the order of 4 or 5 kilovolts or less
  • bein sufficient merely to provide field emission from the cold cathode tip there is no question of the electrons penetrating the specimen 23 on account of their low velocity.
  • the electrons are emitted from the surface of the tip 20 which is not covered by the specimen, i. e they flow through the holes in the structure which covers the tip. Since the electron flow is of the rectilinearly accelerated field emission type, it creates an image of the surface of the tip 20, the specimen 23 participating as a part of the image. As a result, an enlarged shadow image of the specimen is produced. on the fluorescent screen. 1
  • a cold cathode is employed which may be easily positioned within and withdrawn from the microscope and the specimen which is placed upon the cathode is not subjected to the high temperature conditions encountered in cathodes of the thermionic type. Furthermore, since electron emission is of the rectilinearly accelerated field emitted type, the
  • the specimen material may become charged due to the electron emission of the cathode surface between the small specimen particles, and the specimen may show a tendency to fly off of the cathode surface due to repulsion of like charges, as Well as the attraction of the negatively charged particles to the positively charged anode.
  • the field applied between the screen 12 and the cathode i4 is pulsed repeatedly, the pulse being of the character indicated as applied between the terminals 30, 3!, and comprises a pulse of relatively high negative potential 32 applied for a short period of time followed by a pulse of less negative potential 33, which may be of zero or positive potential and which is applied for a longer period of time.
  • the duration of the pulse 32 is made shorter than the charging time of the specimen particles on the cathode tip.
  • the duration of the potential 33 when the potential is almost zero or slightly positive, is long enough to allow discharge of the specimen particles.
  • Use of a pulse of this type assures operation of the electron microscope without displacement of the specimen on the cathode tip.
  • the film 22 shown in Fig. 2 may be employed, the thickness of this film being of the order of angstrom units, as compared with the radius of the spherical tip 20 which is of the order of 10,000 angstrom units.
  • my invention provides a two-element electron microscope which is extremely small in size and of relatively simple construction.
  • the use of a cold cathode and an anode as the sole electrodes of the microscope obviates the requirement of large size and the 'difiiculty of insulation of a lens system.
  • a cold cathode structure comprising a metallic member having a smoothly rounded tip adapted to support a specimen to be examined, an electron sensitive plate mounted in spaced relation with said tip, and means for establishing an electric field between said cathode and said plate whereby electrons are emitted from said tip to produce on said plate a shadow image of a speci men supported on said tip.
  • An electron microscope comprising an evacuated chamber, a cathode supported in said chamber comprising a metallic member having a rounded tip adapted to support a specimen to be observed, a fluorescent screen supported adjacent said tip, and means for establishing an electric field between said cathode and said screen to produce electron emission from said tip, said electrons being emitted from the portions of said tip not covered by a specimen supported on said tip to produce on said screen a shadow image of a specimen so supported.
  • An electron microscope comprising a cathode constituted by a metallic member having a rounded point, an adhesive film covering the surface of said point and adapted to have embedded therein a specimen to be examined, an electron sensitive screen, and means for establishing an electric field between said cathode and said screen to produce an emission of electrons from the portions of said point not covered by a specimen whereby a shadow image of a specimen may be produced on said screen.
  • a cold cathode comprising a metallic member having a smoothly rounded end for supporting a specimen to be observed, a fluorescent screen in spaced relation with said end, and means for establishing an electric field between said screen and said cathode, said means comprising means for providing a pulse of negative voltage to said cathode of relatively short duration and a pulse of positive voltage for suflicient duration to permit discharging of a specimen supported on said end to remove electrons collected thereon during periods of said negative pulse.
  • a cold cathode comprising a metallic member having a smoothly rounded end for supporting a specimen to be observed, a fluorescent screen in spaced relation with said end, and means for establishing a cyclically varying electric field between said screen and said cathode, said means comprising means for providing a pulse of negative Voltage of relatively short duration for a portion of each cycle, and means to permit discharging of a specimen supported on said end during another portion of each cycle to remove electrons collected thereon during said portion of said negative pulse.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)
  • Electron Sources, Ion Sources (AREA)
US522875A 1944-02-18 1944-02-18 Electron microscope Expired - Lifetime US2422041A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE479996D BE479996A (en, 2012) 1944-02-18
US522875A US2422041A (en) 1944-02-18 1944-02-18 Electron microscope
GB3668/45A GB637361A (en) 1944-02-18 1945-02-14 Improvements in and relating to electron microscope
FR977856D FR977856A (fr) 1944-02-18 1947-12-22 Perfectionnements aux microscopes électroniques

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US522875A US2422041A (en) 1944-02-18 1944-02-18 Electron microscope

Publications (1)

Publication Number Publication Date
US2422041A true US2422041A (en) 1947-06-10

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
US522875A Expired - Lifetime US2422041A (en) 1944-02-18 1944-02-18 Electron microscope

Country Status (4)

Country Link
US (1) US2422041A (en, 2012)
BE (1) BE479996A (en, 2012)
FR (1) FR977856A (en, 2012)
GB (1) GB637361A (en, 2012)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2813991A (en) * 1952-11-05 1957-11-19 Gen Electric Electron emitting electrode
US5376792A (en) * 1993-04-26 1994-12-27 Rj Lee Group, Inc. Scanning electron microscope
US5654548A (en) * 1992-08-06 1997-08-05 International Business Machines Corporation Source for intense coherent electron pulses

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2249453A (en) * 1938-12-02 1941-07-15 Gen Electric Electron microscope
US2271990A (en) * 1939-07-29 1942-02-03 Rca Corp Electron microscope
US2274215A (en) * 1939-07-22 1942-02-24 Fides Gmbh Electronic microscope
US2363359A (en) * 1941-05-01 1944-11-21 Gen Electric Electron microscope

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2249453A (en) * 1938-12-02 1941-07-15 Gen Electric Electron microscope
US2274215A (en) * 1939-07-22 1942-02-24 Fides Gmbh Electronic microscope
US2271990A (en) * 1939-07-29 1942-02-03 Rca Corp Electron microscope
US2363359A (en) * 1941-05-01 1944-11-21 Gen Electric Electron microscope

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2813991A (en) * 1952-11-05 1957-11-19 Gen Electric Electron emitting electrode
US5654548A (en) * 1992-08-06 1997-08-05 International Business Machines Corporation Source for intense coherent electron pulses
US5376792A (en) * 1993-04-26 1994-12-27 Rj Lee Group, Inc. Scanning electron microscope

Also Published As

Publication number Publication date
GB637361A (en) 1950-05-17
FR977856A (fr) 1951-04-06
BE479996A (en, 2012)

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