US2405306A - Electronic microanalyzer monitoring - Google Patents

Description

Aug 9 1% J. HILLKER ET AL ELECTRONIC MIQROANALYZER MONITORING Filed Jan. 51, v1944' 3 Sheets-Sheet l AZ .59 a 24 I? are)? Aug. 6, W46. J. HILLIER ETAL, 7' O ZAOSEOQ ELECTRONIC MICROANALYZER MONITORING Filed Jan. 51', 1944 3 Sheets-Sheet 2 van ' INVENTOR$ Jamal! :5 dfifialr- J. HELLIER ETAL. ELECTRONIC MICROANALYZER MONITORING Filed Jan. 51 1944 s Sheets-Sheet 3 nvvgzvrqzas I Mali 191' TO/f/VE Y A also are provided for adjusting the position of The thus scattered electrons have lost energy due .croanalysis offers several advantages over orstill further object includes an improved method dinary methods of microanalysis. Sub-micrm of and means for subjecting a minute area of a 'scopic regions of a specimen can be analyzed substance to electron irradiation, subjecting Patented Aug. 6, ices 2,45,306

UNITED STATES PATENT QFFICE ELECTRONIC MICROANALYZER MONITORING James Hillier, Cranhury, and Richard F. Baker, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application January 31, 1944, Serial No. 520,410

17 Claims. (01. 250-495) 1 2 This invention relates generally to electron op- By means of the improved electron microscope tics and more particularlyto an improved method associated with the analyzer, as described in deof and means for monitoring the microanalyzing tail hereinafter, the area of the specimen anaof materials by electron irradiation. lyzed can be observed and monitored at all The invention is an improvement over the sys- 5 times, so that the relationship of the region extems described in acopending, U. S. application amined to the remainder of the specimen can be of James Hillier, Serial No. 505,572, filed October determined continuously, independently of and 3, 1942, entitled Electronic microanalyzer, simultaneously with the electron velocity analwhich describes the generation of an electron ysis. probe, having extremely minute cross-sectional The apparatus required for electronically area, which is focused upon a minute area of the analyzing materials is similar in many respects electron permeable material to be analyzed. to the conventional electron microscope. The

reflected from the material by the impinging trons which impinge upon or penetrate the sub electrons, are subjected to an electrical or magstance under observation are subjected to denetic deflecting field which deflects the electrons fleeting electric or magnetic fields whereby they as a function of their velocities. The deflected are deflected amounts proportional to th ir ve electron-s impinge upon a fluorescent screen for locitie before impingement upon the observation visual observation of the electron velocity disscreen. Accordingly, if desired, the invention tribution pattern, or the electrons impinge upon may take the form of a relatively simple attacha photographic plate for providing a permanent ment for conventional electron microscopes to record of the pattern. Means are included for permit microanalysis by electronic methods. observing upon an auxiliary fluorescent screen Furthermore, the electrons which are velocity the portion of the specimen upon which the analyzed are those which are scattered in passelectron probe impinges only during intervals ing through the specimen to some predetermined when the deflecting field is not present. Means angle from the irradiating electron beam axis.

the material under observation with respect to to inelastic collisions with the specimen, hence the axisof the electron probe. they are especially suitable for the desired micro- The operation of the electronic microanalyzer 3 analysis, thereby providing improved velocity inis based on the fact that when electrons pass dications over the analysis of directly transmitthrough matter some of the energy of the elected electrons as described in said ccpending aptrons is transformed into X-ray radiation energy. plication. Since this transformation of energy takes place Among the object of the invention are to proaccording to the accepted quantum theory, it vide an improved method of and means for microfollows that for an electron to excite a photon analyzing materials permeable to electron irraof the characteristic X-ray radiation of an elediation. Another object of the invention is to ment the electron must lose energy in an amount provide an improved method of and means for equal to or greater than that contained in the electronically analyzing minute specimens of X-ray photon. Thus among the electrons leavto materials. A further object of the invention is ing a specimen containing a certain element there to provide an improved method of and means for will be a predominance of those electrons which electronically analyzing materials by subjecting h e 1 s n amount Of Energy qual to or slight y 2. minute area of the material to electron irragreater than the energy contained in a single diation, subjecting electrons derived from said photon of the characteristic X-ray radiation of irradiated area to the effects of a deflecting field. that element. The velocity spectrum of the elecand indicating the relative velocities of the electrons leaving a point of the specimen will have trons subjected to said field. Another object is lines corresponding to the important X-ray to provide improved means for securing a perlines of all the elements contained in the area manent record of the relative velocities of said of the specimen being examined. Electron mielectrons subjected to said deflecting field. A

without removing the region from the specimen electrons transmitted by said substance to a unior withoutchangingitin any way. .55 form magnetic field, and indicating th relative said selected electrons to a deflecting field, indicating the relative velocities of said electrons subjected to said field and forming an enlarged optical image of the specimen continuously, independently of and simultaneously with said electron velocity indications. Another object is to provide an improved method of and means for electronically microanalyzing materials wherein electrons derived from a minuteportion' of said materials are velocity analyzed, and other electrons derived from said material form continuously and independently of said velocity analysis an enlarged visual image of said material, and controlling said visual image by external adjustment of a light optical lens system. I The invention will be further described by reference to the accompanying drawings of which Figure 1 is a schematic diagram of one embodiment thereof, Figure 2 is a schematic diagram of a second embodiment thereof, Figure 3 is a crosssectional elevational view of a preferred embodiment of the invention according to the schematic diagram of Figure 1, Figure 4 is an enlarged fragmentary elevational View of a portion of Figure 3, andFigure 5 is a plan view of the devices of Figure 4. Similar "reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1, an electron source L which may be provided by a conventional thermionic cathode which is maintained at a relatively high negative potential with respect to an 'apertured anode electrode, neither of which are shown herein, is imaged by a pairof electron lenses 2, 3 respectively, to irradiate an extremely 'minute area of an electron permeable object 4. The electron lenses 2, 3, respectively, may be of either the electromagnetic or electrostatic types customarily employed in electron optical apparatus such as, for example, electron microscopes. Ii electromagnetic lenses are employed, as shown in; the drawings, the focus of said lenses may be adjusted by means of series resistors 5, 5' connected between one terminal of each of the magnetic lenses and an energizing current source such as, for example, a battery 6.

A third electron lens 8, which may be energized through a third variable resistor 9 by current from the battery 6, is disposed coaxially with the first and second electron lenses 2, 3.

The electrons transmitted by the specimen 4 may be selectively subjected to a magnetic field within a deflection chamber l3. The magnetic field will cause the transmitted electrons to follow substantially semi-circular paths and impinge upon an image screen or The magnetic field within the deflection chamber l3 will deflect the electrons different amounts determined by their respective velocities whereby a velocity distribution pattern will be provided upon the image screen Id. The focus of the pattern is controlled by varying the current through the third lens 8 by adjusting the resistor 9.

A pair of deflecting coils 2|, 2| energized by the battery 6 through an adjustable fourth resistor 22 are symmetrically disposed adjacent the specimen 4 and between the specimen and the -deflection chamber |3. The deflecting coils 2 2 photographic plate M.

provide deflection oi the principal electron beam transmitted by the specimen to an auxiliary fluorescent screen It, adjustably positioned within the specimen chamber but displaced from the main beam axis. A prism or mirror l2, cooperating with aconve tional lightmicroscope permits an enlarged image of theelectronirradiated portion of the specimen 4 to be observed continuously, also independently of and simultaneously with the velocity analysis of the electrons introduced into the deflection chamber l3. Some of the electrons transmitted by the specimen are scattered or reflected thereby at angles other than the electron beam axis. These scattered electrons are deflected by the deflecting coils 2|, 2|, and are passed into the deflection chamber to be velocity analyzed. It therefore will be seen that an axial portion of the specimen transmitted electrons may be employed for continuously observing an enlarged image of the specimen, while other transmitted electrons from the specimen are velocity analyzed during desired intervals.

It should be understood that the magnetic field within the deflection chamber i3 may be established in any desired manner. It also should be understood that the electron lens system described may be modified in any known manner to provide a suitable electron probe of convenient cross-sectional area for irradiation of the specimen 4, and that the third electron lens 8 may be omitted entirely if the deflection chamber l3 and image screen I l are disposed in close relation with the specimen 4.

Figure 2 is similar to Figure 1, diiiering in that an electric field is substituted for the magnetic field Within the deflection chamber l3 of the device of Figure 1 for deflecting the electrons derived irom the specimen 4 in accordance with their relative electron velocities. In order to provide relatively long electron paths through an electrostatic field, two arcuate concave electrodes |8, |9, separated by an air gap 20, are disposed in cooperative relation to provide an arcuate tubular electrostatic deflecting element which will cause the deflected electrons to impinge upon the screen Hi to provide a velocity distribution pattern thereon. A pair of deflecting coils 2|, 2|, symmetrically disposed adjacent the specimen 4 between the specimen and the deflection chamber |3, provide deflection of the principal electron beam transmitted by the specimen to an auxiliary fluorescent screen I0, which, cooperating with a prism or mirror |2 and a, light microscope provides an enlarged image of the electron irradiated portion of the specimen continuously in the same manner as described in Figure 1. Similarly, some of the electrons transmitted by the specimen but refracted or scattered from the beam axis, due to inelastic collisions within the specimen, are deflected by the deflecting coils 2|, 2| to enter the a 28 between the electrostatic deflecting elements |8, |5 for the electron velocity analysis described heretofore.

Figure 3 is a preferred embodiment of the device described in Figure 1 constructed according to conventional electron microscope practice. The electron source includes a thermionic cathode 25 which is supported by a high potential insulator 26 and connected to a terminal 21 which is maintained at high negative potential. An apertured anode electrode 28, which is maintained at a high positive potential with respect to the thermionic cathode 25, provides an electron beam having relatively high electron velocity. The first electron lens 2 is illustratedasa COHVBhtiOnalleOl- 2,405,306 tromagnetic electron microscope lens including port 55v extending between the'walls 31 of the a winding 29 having a pole piece aperture 30. object o amber, supports two parallel disposed The second electron lens 3 forms a-unitary strucguide rods 57, 59 which are journalled in aperture with the first electron lens 2 and includes tures in the transverse support 55, and disposed a second windingil and a second pole piece aperture 32; the specimen 4. The remaining end .of the :first -'-I'he specimen 4 is supported by a conventional guide rod 51 is supported in aperture 6| in the specimen supporting element 33 which may be specimen chamber wall 31, and the remainingv by an external adjusting knob 34 operating 10 a bushing 63 in thespecimen chamber wall 31 adjacent an aperture 36 in the outer wall 31 f ing 63 includes a packing gasket 65 which eifecthe supporting structure. The third electron tively seals the vacuum within the specimen len 8cmay be similar to the first and second elecchamber. A portion 51 of thesecond guide rod tron lenses 2, 3 respectively, and includes a third 59 is threaded to receive a complementarily winding 38 and a relatively large pole piece aperthreaded bushing on the movable support 24 ture 39. A shutter 40, operated by an externally which carries the light microscope objective lens controlled knob 4|, is interposed between the assembly 23, the mirror 12 and the auxiliary wall of a deflection chamber 43 which is secured 29 mg knob 50 thereby provides transverse adjustto .t e supportingstructure of the third electron ment of the light microscopenobjective 213, the

lens. a c

A magnetic winding 44, disposed external to with respect to the central axis of the specimen the deflection chamber 43, provides a magnetic hambe The eye piece portion of the light microscope aperture 42 and for causing them to impinge upon is supported on the exterior of the specimen which is sealed :in the specimen chamber wall 37. or any other structure customarily employed in The movable specimen support 33 which is adconventional electron microscopes. A hinged J' a e by m ans of th spec men-'adju t g-knob fluorescent screen 46, pivoted adjacent one edge 4 up to the Spe m pp '33 through of the photographic plate 45, may be rotated to the sylphon 5, supports the ma ne ic d fle t cover the plate 45 for providing a visual image C011 assemblies 2!, 2! Which are symmetrically position 41, shown in dash lines, may be observed offset slightly from the electron beam axi B8.

through a window 48 adjacent to and normal Thedeflecting coil assemblies 2|, 2l' include therewith. parallel-disposed magnetic pole pieces 69, 679',

The auxiliary beam deflecting coils 2i, 2!, dis- Which support windings H, H respectively. Adposed within the specimen chamber, may be supjustment of the spe Supp t 33 th reby ported by the adjustable specimen supporting adjusts the position of the deflecting coil assemelement 33 symmetrically with respect to the blies 2|, 2|, and the spec men Simultaneously specimen The auxiliary fluorescent screen It, w h p t o the electron beam axis 58. prism or mirror l2 and the objective lens 23 of the As explained heretofore, the normal electron specimen chamber on a movable support 24, the by the deflecting coils 2|, 2| to impinge upon the position of which may be adjusted by an external auxiliary fluorescent screen I 0 for continuous adjusting knob 50. The remainder of the light 50 observation of the electron-irradiated portion of ber wall 31. The details of the preferred emcidence of th irradiat el tr s nt th u h t ap tu 42 d for the electromagnetic deflecting field of the position, as indicated in the drawings. The shut- Thus the invention described comprises several ter 40 may then-be opened for a desired interval modifications of an improved method ofand to expose the photographicplate 45. means for microanalyzing materials by electron Referring to Figures 4 and 5, a transverse supirradiation wherein continuous observation- 0f screen and said object means the minute electron irradiated portion of the specimen is provided independently of and, if desired, simultaneously with'the velocity analysis of electrons derived from said irradiated specimen. Improved electron velocity analysis is provided by utilizing electrons scattered within predetermined angular limits in passing through the specimen due to inelastic collisions within said specimen.

. We claim as our invention:

1. In an electron microanalyzer including means for providing an electron probe having extremely minute cross-sectional area, means for supporting an object, means for irradiating said object by said electron probe, an electron sensitive screen responsive to electrons from said object, and means-interposed between said screen and said object means providing a field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, the improvement comprising electronic means for continuously providing a visible image of said electron probe irradiated portion of said object means independently of and simultaneously with said deflection of said electrons.

2. An electron microanalyzer including electron beam generating means and electron beam focusing means for providing an electron probe having extremely minute cross-sectional area, means for supporting an object, means for irradiating said object by said electron probe, an electron sensitive screen responsive to electrons from said object, means interposed between said providing a field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, and electronic means for continuously providing a visible image of said electron probe irradiated portion of said object means independently of and simultaneously with said deflection of said electrons as a function of their velocity.

3. In an electron microanalyzer including electron beam generating means and electron beam focusing means for providing an electron probe having extremely minute cross-sectional area, means for supporting an object substantially permeable to electron irradiation, means for irradiating said object by said electron probe, an electron sensitive photographic screen responsive to electrons from said object, and means interposed between said screen and said object means providing a field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, the improvement comprising electronic means for continuously providing a visible image of said electron probe irradiated portion of said object means independently of and simultaneously with said deflection of said electrons as a function of their velocity.

4. Apparatus of the typedescribed in claim 1 including means disposed within said deflecting means selectively providing a visual image of said screen. t

5. Apparatus of the type described in claim 3 characterized in that said image means includes a fluorescent screen for-continuously observing said electron probe irradiation of 'said object,.and means for optically magnifying said image on said fluorescent screen. v V

6. Apparatus of the type described in claim 3 characterized in that said image means includessaid image formation a fluorescent screen for continuously observing said electron probe irradiation oi said object, means for optically magnifying said image on said fluorescent screen and externally a justable means for orienting said optical magnifying means and said fluorescent screen with respect to said electron irradiated portion of said object.

7. 'In an electron microanalyzer including means for providing an electron probe having extremely minute cross-sectional area, an object substantially permeable to electron irradiation, means for irradiating said object by said electron probe, an electron sensitive screen responsive to electrons from said object, and means interposed between said screen and said object means providing a field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, the improvement comprising electronic means for continuously providing a visible image of said electron probe irradiated portion of said object independently of and simultaneously with said deflection of said electrons.

8. In an electron microanalyzer including means for providing an electron probe having extremely minute cross-sectional area, means for supporting an object substantially permeable to electron irradiation, means for irradiating said object by said electron probe, an electron sensitive screen responsive to electrons from said object, and means interposed between said screen and said object means providing a magnetic field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, the improvement comprising means for continuously providing a second lectron image of said electron probe irradiated portion of said object means independently of and simultaneously with said deflection of said electrons.

9. In an electron microanalyzer including means for providing .an electron probe having extremely minute cross-sectional area, means for supporting an object substantially permeable to electron irradiation, means for irradiating said object by said electron probe, an electron sensitive screen responsive to electrons from said object, and means interposed between said screen and said object means providing an electrostatic field for deflecting said electrons derived from said object as a function of their velocity to provide an electron velocity distribution image on said screen, th improvement comprising electron optical means for continuously providing a visible image of said electron probe irradiated portion of said object means independently of and simultaneously with said deflection of said electrons.

10. Apparatus of the type described in claim 2 including an externally operable shutter interposed between said object supporting means and said screen for controlling the electron exposure time for said screen, said object second image means being independent of said shutter.

ll. The method of electron microanalyzing a material comprising generating an electron probe of minute cross-sectional area, electron irradiating said material by said electron probe, subjecting electrons derived from said object to a field to deflect said electrons as a function of electron velocity, of said derived electrons, and forming continuously and electron optically a visual image of said electron irradiated portion of said material, being independent of said indicating the relative velocities I 10 electron deflection as a function of electron screen responsive to electrons deflected from said velocity. object for continuously providing a visible image 12. The method of electron microanalyzing a of said electron probe irradiated portion of said material comprising electron irradiating aminute object means independently of and simultanecross-sectional area of said material, indicating ously with said deflection of said electrons as a the relative velocities of the electrons derived function of their velocity. from said area of said material in response to said 15. Apparatus of the type described in claim 3 irradiation and continuously forming electron characterized in that said image means includes indications an enlarged visual image of said said electron probe irradiation of said object,

irradiating said object by said electron probe, an respect to said electron irradiated portion of said electron sensitive screen responsive to electrons object.

from said object, means interposed between said 16. The method of electron microanalyzing a screen and said object means providing a field for material comprising electron irradiating a minute between said object supporting means and said and which have been scattered between predeterportion of said object means independently of 17. In an electron microanalyzer including and simultaneously with said deflection of said ans r pr v ding a electron probe h vi electrons as a function of their velocity. xtr m y minu e r ss-se t na a ea, means for 14 An electron microanalyzer mcludmg elecsupporting an obje t, m an for irradiating said posed between said screen and said object means n?! me s rp se tw en Sa d Obj ct mea s prising magnetic beam deflecting means inter JAMES H LLIER. posed between said object supporting means and RICHARD F, BAKER.

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