US2257774A - Electronic-optical device - Google Patents

Electronic-optical device Download PDF

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US2257774A
US2257774A US190629A US19062938A US2257774A US 2257774 A US2257774 A US 2257774A US 190629 A US190629 A US 190629A US 19062938 A US19062938 A US 19062938A US 2257774 A US2257774 A US 2257774A
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electron
electrons
point
electrode
electronic
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Ardenne Manfred Von
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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
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • 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
    • H01J37/22—Optical, image processing or photographic arrangements associated with the tube
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/18—Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast

Definitions

  • Everymicroscopical observation of very small objects is absolutely limited, as is known, by diffraction phenomena, insofar as only such objects or details can be reproduced which have a sufficient size compared with the wave length of the reproducing beam.
  • the limit of the resolving capacity for the optical microscope lies, therefore, in the order of magnitude of the wave lengths of light.
  • the operation of the electron microscope is predicated on a wave length which is related to the electron velocity by the known de- Broglie relation have a certain thickness, so that the electrons are subjected within those objects to a noticeable retardation which is different at different points of the respective object.
  • a beam of rays hava comparatively broad speed spectrum ema- This formula furnishes, for instance, for an electron beam with a speed of 100 kilovolts, a wave length which is shorter by about 10000 than the mean wave length of the visible light. 'It should therefore be possible to build an electron microscope, the resolving capacity of which is by about four ten-powers stronger than the resolving capacity of the light-microscope with the same aperture.
  • the present invention overcomes the above mentioned difflculties by point-for-point scanning of the object with the aid of an electronbeam focal spot, the diameter of which is less than one-thousandth of a millimeter.
  • the electrons coming from the electronically-optically illuminated" image element are registered, a basis is established for the building-up of an electronic-optical image of the object, and, in fact, with a resolving factor which depends solely on the pointsharpness of the scanning focal spot in the object plane subjected to investigation.
  • Any desired indicator method may be used for registering the electrons coming from the object point on which the electronic beam focal spot impinges at any instant.
  • the electrons may be counted either singly, e. g., by means of an electrometric arrangement, or the use of a counting chamber of the Geiger type, respectively, or the mean value of the resulting electron current may be measured or traced with the aid of an integrating device.
  • the invention renders it possible to extend the resolving capacity-con- I siderably beyond that of light-microscopes even with objects, the thickness of which corresponds to the thickness of a microtome. It is therefore, possible to observe and investigate microscopically objects which could not be rendered If, on'
  • Fig. l is a representation of an electronicoptical system for the production .of a minute electron spot with which the object to be investigated is to be scanned;
  • Fig. 2 shows a tracing device for the registra tion of the image produced
  • Fig. 3 illustrates a scanning field
  • Fig. 4 represents a device for counting the electrons coming from the object
  • Fig. 5 is an illustration of another embodiment of the tracing device which renders it possible to make the electronical-optically obtained image directly visible in a corresponding magnification;
  • Fig. 6 shows an arrangement for the formation of a particularly small electron focal spot for scanning an object, in connection with an arrangement for the observation of objects in the open air;
  • Fig. 7 illustrates a particularly designed electron-multiplier
  • Figs. 8-10 show several different electrodes intended to serve for the trapping of the electrons coming from the scanned object.
  • the highly evacuated glass tube I (Fig. 1) contains an electron emissive cathode 2 standing in a cylinder 3 of the Wehnelt type. From this cathode proceeds an electron beam transformed into a narrow pencil by the coaction of the cylinder 4 which has a positive initial voltage and 01' the anode cylinder 5, said pencil being directed towards the diaphragm opening 6.
  • the passage opening of this diaphragm may have, for instance, a diameter of one-hundredth of a millimeter; it constitutes the electron delivery point which then is reproduced on a reduced scale on the object to be observed. In order to reproduce this electron delivery point on the object on a reduced scale, an electric or a magnetic electron object-lens may be used.
  • the electron beams arriving from the diaphragm opening I are, therefore, trained as accurately as possible upon the passage opening of the diaphragm l of the magnetic electron object-lens III, which is done by means of a magnetic adjusting device comprising the coils l and 8 and the associated batteries and adjusting resistances, the coils-being arranged perpendicularly with respect to each other.
  • the electron objective ID has a very short focal distance and therefore reproduces the passage opening of the diaphragm or shutter 6 on the surface of the object II to be investigated in about a fifty-fold reduction. A scanning focal spot is therefore caused at that point which has a diameter of only 5.10- mm., resulting in a resolving capacity of 5.10" for the scanning.
  • the electrons coming from the object II are trapped by an electrode I2 arranged preferably in the interior of a grounded cage ll of the Faraday type.
  • This cage has only a comparatively small window and acts consequently at the same time as a shutter or diaphragm.
  • the number of the electrons arriving at the trapping electrode I2 depends obviously at any moment on the electron stray and on the permeability to electrons of the object II at the point where the electron focal spot is located at any instant.
  • the object I I When the object I I is moved in the plane in which the electron focal spot arises, and if this movement is carried out in such a manner that the small field of the object II to be investigated is scanned by said spot, then the number of the electrons reaching the trapping electrode I2 varies according to the permeability to electrons of the object II from point to point. It is advisable to carbonize the surface of the electrode I2 in order to obviate errors that may be caused I at this trapping electrode through reflection and by a secondary emission. Faults of the kind just mentioned may also be diminished by connecting a voltage between the object-carrier II and the trapping electrode I2. In order to register the electrons taken by the trapping electrode, this electrode may be connected with the input circuit of an amplifier I4, as illustrated in Fig. 1.
  • the variations of the current are transmitted to an image-tracing device.
  • the output circuit of the amplifier I4 is for this purpose connected with a gaseous conduction or glow lamp I5, the luminous surface of which is reproduced upon the light-sensitive surface of the image roller ll by means of the objective I6.
  • the roller I'I rotates in the usual manner below the lamp I5 and is simultaneously shifted in the direction indicated by the arrow I8.v
  • Connected with the roller I1 is a rotary resistance I9 and a sliding resistance 20.
  • the resistance I8 passes through its entire range from zero to the maximum value, and inasmuch as this resistance is connected in the circuit of a magnetic deflecting device comprising two coils 2i and 22 which are wound in opposite directions, as shown in Fig. 1, the angle of incident of the electron beam entering into the diaphragm or shutter 9 in the manner indicated by the dotted line is periodically changed.
  • This causes the required line deflection whereby the image field J is scanned, according to Fig. 3, in the direction indicated by the arrow A1.
  • the image deflection in the direction of the arrow A: may be brought about by means of a suitably designed coil arrangement controlled by the resistance 20.
  • the object-carrier Ii may be secured on a strong bi-metallic rod 23 which is heated by a bifilar-wound resistance 24 located in the circuit of the sliding resistance 20. It is possible in this way to scan the object II in successive lines in accordance with the preceding continuous registration of the electrons trapped at i2 in the image-field J (Fig. 3).
  • An imagefield (I) covering on the object merely a square of 2.10 mm. can thus be scanned with an electron focal spot of 5.10- mm. and can be traced on the roller I'I in the size of x10 cm.
  • the amplification difiicultles are increased in proportion to the decrease in size of the electron focal spot which scans the object II.
  • a particularly sensitive arrangement e. g., an electron multiplier" or a Geiger
  • the latter may comprise a vacuum-tight cylindrical casing 25, along the axis of which is located the prepared filament electrode 26, and which has a Lenard window a directed toward the object II.
  • Every electron penetrating into the chamber will produce' a discharge impulse between the electrode electrode 25.
  • the inner surface of the electrode 25 may also be providedv with a suitable coating which produces a high secondary electron emission when the electrons impinge upon it so as to facilitate the discharge puncture.
  • the counting chamber 25-26 is preferably connected with an integrating amplifier device,-
  • every current impulse flowing through the counting chamber 25-26 will cause used at present in television receivers.
  • This tube therefore conducts a current which corresponds with the time integral of the electrons entering into the counting chamber. This current may, therefore, be utilized for the tracing of an image.
  • Fig. 5 shows a cathode ray tube of the type A cathode beam.” coming from the cathode 34 is ac celerated in theusual manner by the electrodes 36 and 31, and the rays are assembled in the plane of the fluorescent screen 38 where they form a focal spot.
  • the intensity of the cathode beam is controlled by means of the Wehnelt cylinder 39; two coils 40 and 4
  • the mean anode current fiowing in the tube 21 is thus a function of the number .of the current impulses flowing through the counting chamber 25-26 in the unit of time; it produces at the resistance 3i, which bridges the large condenser 32, a voltage drop for controlling the grid of the tube control.
  • the generator 42 which delivers the line frequency
  • and 22 (Fig. 1), and parallel to the coil 4
  • the cathode beam 35 which scans the fluorescent screen in accordance with the movements of the electron focal spot scanning the object II, will be modulated in accordance with the permeability to electrons of the object H which changes from point to point.
  • the magnification obtained corresponds in this case with the ratio between the scanning paths of the two electron beams on the surface of the object ,and on the fluorescent screen.
  • An output shutter or diaphragm 6 having the previously noted opening diameter of 0.01 mm. can be accurately manufactured only with very great difficulty; and it is, therefore, advisable to use instead of a real shutter a so-called potential shutter or diaphragm for a' primary electron delivery source which is then reproduced on a reduced scale.
  • the potential shutter can in this case be produced by the coaction of the anode and the Wehnelt cylinder. With an implement actually made in this way, the flat oxidecathode was located at a distance of 0.3 mm. in back of the opening of 0.6 mm. of the Wehneltcylinder which was located opposite the anode carrying 25,000 volts at a distance of .3 mm. With this arrangement could be obtained in the interior of' the passageway of 1 mm. diameter of the anode an electron focal spot, the diameter,
  • the distance between the source of the electrons and the electronic-optical object-lens must be chosen as great as possible.
  • the earth magnetic field constitutes a disturbing factor, insofar as it causes a curvature of the electron beam. This curvature can be considered to a certain extent in the manufacture of the device, or incident to adjusting it, but variations of the earth magnetic field give rise to considerable disturbances. In order to avoid these disturbances,
  • the electron beam may be disposed in-the direction of the earth magnetic lines of force, or the path of the beam may be screened by means of a suitably designed and arranged iron shell.
  • Another possibility is to compensate the earth magnetic field by the provision of a corresponding magnetic counterfield produced preferably by two flat coils (so-called Helmholtz coils) arranged coaxially with respect to the discharge tube and sufiiciently spaced therefrom. The passage of the current through these coils is then readjusted according to the variations of the earth magnetic field which may be ascertained by suitable measurement as desired.
  • a particularly important means for increasing the sharpness of the electron focal spot caused upon the object to be investigated consists in a multi-stage reduction of the reproduction of the original electron source. Such an arrangement is shown in Fig. 6.
  • the electrons emanating from the cathode 46 are assembled by the coaction of the Wehnelt cylinder 41 and the anode 48 in an electron focal spot P1, from which they pass through a magnetic screening tube 49 in the direction of the magnetic objective lens 50.
  • the iron-encased lens 50' produces by means of the magnetic field arising in its iron-free slot a strongly reduced real image of the electron focal point P1 in the point P2, from which the electrons pass through a second, particularly effective, screening tube toward a second magnetic objective lens 62, in front of which are arranged deflecting coils 53 and 54.
  • the lens 52 reproduces the additionally reduced electron focal point P: on the surface of the object to be investigated.
  • the object to be investigated is not housed within the extremely evacuated electron beam arrangement 49, 6
  • the arrangement 49, Si is closed by a disk 53a. which is provided with a tube having a minute aperture closed in turn by a Lenard window 54a.
  • This window need not consist of metal, but may be made, for instance, of collodium or the like, by reason of the slight total scanning electron current.
  • the window may be produced by the evaporation of a solvent down to a thickness of 5.10 In accordance with this invention, it may also serve as a support for the object to be investigated.
  • the Lenard window a is arranged as close as possible to the trapping electrode 55 which is directly connected with the grid of the tube 56.
  • FIG. 7 A particularly advantageousembodiment, which is distinguished by an exceedingly small initial current, is illustrated in Fig. 7.
  • This "electron-multiplier consists of a vacuum vessel 61, in the interior of which are provided the prepared grids Il-BI as well as the closing plate 62, the diameter of the latter increasing from step to step.
  • the diaphragm or shutter 63 In front of the first grid 68 is arranged the diaphragm or shutter 63, and over its aperture is disposed the Lenard I window 64. This is substituted for the trapping electrode I! of Fig. 1, or 66 of Fig. 6.
  • the rebounding electrodes 66-62 are connected with increasing positive voltage delivery points of the battery 65.
  • a resistance 66 In the supply connection to the last electrode 62 is provided a resistance 66, the voltage drop of which controls the amplifier ll. It was found that, by the use of such an electronmultiplier" for scanning the object to be investigated, about 20 electrons per image element are suflicient to control the amplifier H in a satisfactory manner.
  • the practical application of the invention has been described mainly in connection with the so-called penetration-radiation method".
  • the present improved devices not only permit a very high resolving capacity in connection with thin layers of an object, when using said method, but also render possible, while maintaining this capacity, an electronic-optical observation in plan view (exclusive observation with returning electrons), and also an electronicoptical observation after the so-called darkfield method (exclusive observation of the laterally strayed electrons).
  • Suitable embodiments of the trapping electrodes which serve as registering surface are shown in Figs, 8-10, whereby the known modes of illumination of the lightmicroscope are imitated.
  • the numeral 64a denotes, drawn to an enlarged scale, the Lenard window onto which impinges the electron beam 66a under a very narrow convergence angle.
  • the Lenard window carries the object 61 to be investigated. If, analogous to Fig. 1, a trapping electrode 66 located in agrounded cage 69 having a narrow window is arranged opposite the object 61, the electrons which penetrate the object 61 without being deflected, as well as a limited portion of the laterally straying electrons will obviously reach the electrode 69. This arrangement therefore corresponds with the bright-field transparent observation in case of the light microscope.
  • annular trapping -electrode II in front of the Lenard-window, this electrode trapping exclusively returning electrons.
  • This observation method which is used, for instance, for the investigation of the surface texture of ground metal parts, corresponds to the observation with incident light by means of a light microcope.
  • a grounded annular shutter or diaphragm II is provided, which surrounds the electron beam 66.
  • Fig. is shown an electron arrangement for .an observation method which corresponds with the dark-field observation" of the optical microscope.
  • the electrons which penetrate the object 61 to be investigated without being deflected are trapped by the grounded circular disk 12. Only the annular surface is therefore used as registering surface, which remains free between the disk 12 and the cage electrode 13. Only the straying or deflected electrons therefore reach the trapping electrode 14, which start from the object within the range of a predetermined angle. It is clear that this method yields images very rich in contrasts even with extremely thin object layers.
  • the electrodes shown in Fig. 10 may also be given such geometrical configuration that only those electrons exert an action incident to the image reproduction which correspond with certain distinct diffraction figures. The distribution of micro-crystalline particles in the object can be made visible in this manner.
  • object support itself (object-carrier I I, Lenard window 54) for a trapping electrode.
  • a pure electron absorption image may be attained in this manner.
  • a conducting object support which is sumciently insulated with respect to the other members of the apparatus.
  • the manufacture of conducting object supports can be effected, for instance, by means of cathode atomization. Making use of this method of manufacture is also recommended if separate trapping electrodes are employed and if it is desired to place between the trapping electrode and the object an acceleration potential (for instance, for the acceleration of secondary electrons), or a brake voltage as used, for instance, to keep oil! of the trapping electrode all electrons, the speed of which is below a certain limit.
  • apertures of the same value for generating a cathode ray means for focusing the ray to a point on an object to be examined, the diameter of said point being of the order of the wavelength of visible light, a target beyond the object in the direction of the ray for intercepting electrons thereof that pass through the object, a circuit in which current flow is established by electrons intercepted on said target, reproducing means controlled responsive to variations in said current flow, said reproducing means including an element movable in two directions, and means electrically responsive to movement of said element for producing corresponding and proportionate movements of microscopic dimensions of the focus point of said ray on said object.
  • An electronic microscope comprising means for generating a cathode ray.
  • the depth sharpness rises by two tens-powers and it is sufilcient to make the plane of the object to be scanned coincide with the observation plane with an accuracy of from 10- to 10- This accuracy is still within the range of what can be attained with electric or mechanical auxiliary means.
  • An electronic microscope comprising means wavelength of visible light, reproducing means controlled in accordance with the number of electrons of the ray which pass through the object at the point where the ray impinges.
  • said reproducing means including a movable element, means for producing movement of said element in two directions, and means electrically responsive to the movement of said element for producing corresponding but relatively microscopic movements of the focus point of the ray on said object.
  • means for producing an electron beam means for focusing said beam at a point on an object to be examined, the diameter of said point being-of the order of the wavelength of visible light, scanning means for causing said point to scan an area of said object whereby said impinging electron beam is modified by said object, a collecting electrode adjacent said object, and a shield interposed between said object and target, said shield having an annular aperture therein surrounding an opaque portion located in line with controllable in response to variations in said current flow, said reproducing means including a movable element, and means electrically responsive to the movements of said element for producing similar but greatly reduced movement between said object and said beam.
  • means for producing an electron beam means for focusing said beam on a point or an object to be examined to cause electrons to be released therefrom,
  • the diameter of said point being less than the ducing an electron beam
  • electrode means tor collecting said electrons an output circuit coupled to said electrode means in which a current flow is established proportional to the number of said electrons
  • reproducing means coupled to said output circuit having a reproducing surface and a recording element, means for producing relative movement between said surface and said element, and means electrically responsive to said relative movement for producing corresponding movement of microscopic proportions between said object and said beam whereby said beam scans a microscopic area of said object.

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  • Analytical Chemistry (AREA)
  • Engineering & Computer Science (AREA)
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  • Analysing Materials By The Use Of Radiation (AREA)
US190629A 1937-02-18 1938-02-15 Electronic-optical device Expired - Lifetime US2257774A (en)

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Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2418029A (en) * 1943-10-08 1947-03-25 Rca Corp Electron probe analysis employing X-ray spectrography
US2418228A (en) * 1943-10-08 1947-04-01 Rca Corp Electronic microanalyzer
US2464229A (en) * 1943-11-10 1949-03-15 Univ Leland Stanford Junior High-frequency apparatus and method
US2477307A (en) * 1946-11-09 1949-07-26 Mackta Leo Combined x-ray and fluoroscopic apparatus
US2561988A (en) * 1949-06-30 1951-07-24 Westinghouse Electric Corp Electron diffraction detector system
US2593925A (en) * 1948-10-05 1952-04-22 Sheldon Edward Emanuel Device for color projection of invisible rays
US2619598A (en) * 1949-06-29 1952-11-25 Westinghouse Electric Corp Electron diffraction detecting system
US2666890A (en) * 1950-07-27 1954-01-19 Bendix Aviat Corp Apparatus for testing geiger tubes
US2727153A (en) * 1949-06-29 1955-12-13 Westinghouse Electric Corp Electron diffraction camera
US2802948A (en) * 1954-09-22 1957-08-13 Haloid Co Prevention of ion-caused undercutting in xeroradiography
US2877353A (en) * 1954-07-14 1959-03-10 Gen Electric X-ray microscope
US2891166A (en) * 1954-03-15 1959-06-16 Phillips Petroleum Co Well logging
US3010021A (en) * 1959-02-24 1961-11-21 William C Roesch Method for measuring radiation
US3013467A (en) * 1957-11-07 1961-12-19 Minsky Marvin Microscopy apparatus
US3191028A (en) * 1963-04-22 1965-06-22 Albert V Crewe Scanning electron microscope
US3223837A (en) * 1961-07-10 1965-12-14 First Pennsylvania Banking And Beam probe system and apparatus
US3229087A (en) * 1961-09-25 1966-01-11 First Pennsylvania Banking And Electron microanalyzer and monitoring system
US3385967A (en) * 1967-09-07 1968-05-28 Welch Scient Company Electron diffraction apparatus for measuring wave length of electrons
US3389252A (en) * 1964-06-11 1968-06-18 Philips Corp Electron microscope having a four-pole electron-optical lens assembly and a scanning line-like electron beam
US3689766A (en) * 1969-09-05 1972-09-05 Atomic Energy Authority Uk Apparatus for bombarding a target with ions
US3737659A (en) * 1969-04-08 1973-06-05 Nihoa Denshi Field of view adjusting device

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2418029A (en) * 1943-10-08 1947-03-25 Rca Corp Electron probe analysis employing X-ray spectrography
US2418228A (en) * 1943-10-08 1947-04-01 Rca Corp Electronic microanalyzer
US2464229A (en) * 1943-11-10 1949-03-15 Univ Leland Stanford Junior High-frequency apparatus and method
US2477307A (en) * 1946-11-09 1949-07-26 Mackta Leo Combined x-ray and fluoroscopic apparatus
US2593925A (en) * 1948-10-05 1952-04-22 Sheldon Edward Emanuel Device for color projection of invisible rays
US2619598A (en) * 1949-06-29 1952-11-25 Westinghouse Electric Corp Electron diffraction detecting system
US2727153A (en) * 1949-06-29 1955-12-13 Westinghouse Electric Corp Electron diffraction camera
US2561988A (en) * 1949-06-30 1951-07-24 Westinghouse Electric Corp Electron diffraction detector system
US2666890A (en) * 1950-07-27 1954-01-19 Bendix Aviat Corp Apparatus for testing geiger tubes
US2891166A (en) * 1954-03-15 1959-06-16 Phillips Petroleum Co Well logging
US2877353A (en) * 1954-07-14 1959-03-10 Gen Electric X-ray microscope
US2802948A (en) * 1954-09-22 1957-08-13 Haloid Co Prevention of ion-caused undercutting in xeroradiography
US3013467A (en) * 1957-11-07 1961-12-19 Minsky Marvin Microscopy apparatus
US3010021A (en) * 1959-02-24 1961-11-21 William C Roesch Method for measuring radiation
US3223837A (en) * 1961-07-10 1965-12-14 First Pennsylvania Banking And Beam probe system and apparatus
US3229087A (en) * 1961-09-25 1966-01-11 First Pennsylvania Banking And Electron microanalyzer and monitoring system
US3191028A (en) * 1963-04-22 1965-06-22 Albert V Crewe Scanning electron microscope
US3389252A (en) * 1964-06-11 1968-06-18 Philips Corp Electron microscope having a four-pole electron-optical lens assembly and a scanning line-like electron beam
US3385967A (en) * 1967-09-07 1968-05-28 Welch Scient Company Electron diffraction apparatus for measuring wave length of electrons
US3737659A (en) * 1969-04-08 1973-06-05 Nihoa Denshi Field of view adjusting device
US3689766A (en) * 1969-09-05 1972-09-05 Atomic Energy Authority Uk Apparatus for bombarding a target with ions

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Publication number Publication date
NL53538C (fr)
FR833491A (fr) 1938-10-21
BE426347A (fr)

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