US2447260A

US2447260A - Electron microspectroscope

Info

Publication number: US2447260A
Application number: US600761A
Authority: US
Inventors: Marton Ladislaus
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1945-06-21
Filing date: 1945-06-21
Publication date: 1948-08-17
Anticipated expiration: 1965-08-17

Description

Aug. 17, 1948. I I L. MARTON 2,447,260

ELECTRON MI CROSPECTROSCOPE Filed June 21, 1945 2 Sheets-Sheet 1 1948. MARTON 2,447,260

ELECTRON MICROSPECTROSCOPE Filed June 21, 1945 2 Sheets-Sheet 2 Y w k v Patented Aug. 17, 1948 uN-Ifrw car s ELno'rnoN MIoRosP o'rRosooPE corporation .oflN w Whichvmay bemade visible by allowing vthe beam;

toimpinge on a layer of fluorescent substance or: a photographic plate. p I A purpose. of the present invention is to provide..;apparatus for. determinin the composition of a specimen .by. subjecting an electron beam: which has passed through a small selected area of the specimen to spectral velocity analysisw Another purpose of theinvention isto provide meansv ,for analyzing the velocity.distributionof. electrons which have passed through asmall se--: e ted areacf a specimen. e fl'lhe velocity losses suffered by electrons passing through a specimen are characteristicof the atoms comprising the specimen and byanalyzing. the velocityhdistribution of the electrons after. passing through the specimen the atomic constitution of thespecimen may be determined, a 5.

, {Ihe purposesof theinventionmay .be accomplished by, subjecting, a selected narrowportion. of a beam of electrons, which has passed through." a specimen and has been. highly magnified, toa deflecting field... After deflection the electrons of different velocities williollow divergent .paths and will establish on an electron sensitive-layer, such as a fluorescent or photographic layer, positionedin the focal plane ofthe. deflected beam, a pattern corresponding to the, velocity distribution of electrons inthe beam and, therefore,:.to.the.. atomic constitution. of the. portion of. the-specimen-through which thedeflected portionof. the. beamhas passed, v The. principles of the invention Will be more fully described withreferenceto the accompany-. ing drawings in which: r

Fig. lis adiagrammatic representation of anelectron microspectroscopa embodying. thelprinciples of the invention; a .c

Fig. 2 is an elevation in partial sectionof the I electron velocity analyzer of the invention, and .50 Fig, 3 isa sectional elevation of the beam -.de-: fiector on line 3.,3 of Fig.2.

In the diagrammatic representation of Fig. 1, A represents a conventional.electronmicroscope, and 3 represents the; electron .velocityianalyzer tbscrefin at mositionL-Zfl; :and the: :spectrum canzsb 11 era-,onby placing:anphotographiciiemulsidnFlay I riff assignor of the invention, a typical embodiment of which sents;an= electron source; such as the typical lelec' s tron sgun :lz'lrisr a magnetictcondenser which": col limateszthe eiectron-ioeamiiirofit source" k0; l'2oisi at specimen to be examined; I13. is amagiieticobjec tivei whichproduceszaniintermediate' image at: 1|:- and'- .I5 is afinagnetic image projector-which pro-i duces'at iE; a highly magnifiedimage'of aportion: ofr...the. intermediate. images-i Any: aorlalaill otsthe magneticilenszelementsiimayzbereplaced by-elec tros'tatic.lenstelements, "as istwell known, tprovided; that: 1the xhigh.:ipotntia1: 11sedefomaoceleratingithe electrons and; -forithe'roperation fcthe' iensi elements is keptjiconstant it'o ithe idegree required foritheelimination *of: -thezchromatic aberration.

If thisucon'dition isniot satisfied,ranaeleotrostatici deflecting; system Foam be a used by openalizing the analyzerzwithithe same variable potenti microscope-elements Incaccordancewith the invention, there is provided in the plane of the highly magnified image:-

lfi; agnarroimslit 1:01: other smalleaperture pa sing; arbeam-il 8 of 'GIBCtIDllSEfIlOIHSIQhVEIY-FSmQIUQ'fiOI Q tioni oi the .spe cirnen:;which.-mayiabez-selected by q. varying the position sof islit. T air-1 the n'iagnified ima'gep; iThe .electronibeamxxlil is-isubjectedrto: J. deflecting fildl: l.9;.rwhich may? be" magnetic ":or i electrostatic .or; combined magnetic and electro static. The: defie'otioni of theelecti'ons forming:

-. i the beam, is; :pnoportion-ah to the zstrength Ofi'ith'eil :1 corresponding to-:,the.-:ve1-ocit'y species :.composing:

the beam? 1:8. 11,,8- distance o-f:,the;dflecting fifeldi from the slit is preferably ichosemsothat thesys 1i tern focuses,,=without%the.=use:lofriurther'lens.ele ments, Since" the ifocah distance;-ionftheielece-rV tron components of different velocities willzdifieni the electron-:sensitivedayerflfl is'rinclinedaat an angle Which-3111913??? be .-readily ideterminediar The:- electron velocity spectrum: producedzbyithe anaeis lyzer man; be iobservedzby. :meansi of sa'ziluorscentz i recorded :by-photographing thedluoresoentsscre'e by meansiot' ate-conventionalphotographic-cam .1

By shifting the slit l'l with e. image fonlyielectrons. passing- 'throughra s-sel cted stage of the electron microscope or by shifting the slit. The size of the analyzed area of the specimen can be varied by changing the magnification of the image at the position of the slit or by changing the width of the slit or by a combination of the two.

The typical embodiment of the electron velocity analyzer of the invention shown in Figs. 2 and 3 comprises a disk 22 provided with two

holes

23 and 24. The disk fits into a circular recess 25 in the lower end of electron microscope 2i and is fastened thereto by means of a clamping ring 26 attached with bolts 21. A rubber gasket 28 is provided for sealing the two parts in a vacuumtight manner. The top surface of the disk 22 is coated with fluorescent material and provided with an adjustable slit 29 in front of the circular hole 23. The slit blades are also coated with fluorescent material.

The divergent electron beam 30 producing an image on the fluorescent surface is adjusted so that the part of the image to be analyzed enters the slit 29. The electron beam entering the slit travels downward through tube 3| to enter a flat chamber 32 where it is deflected at 135 angle by means of a magnetic field perpendicular to the plane of the drawing. After deflection, it enters tube 33 which is attached by means of a flexible metallic bellows 34 to a small chamber 35. The metallic bellows is provided for orientation of chamber 35 by means of adjusting screws 34. Chamber 35 is provided with a transparent fluorescent screen 36 on which the analyzed beam can be observed. Due to the fact that slit l9 provides too small a cross-section for producing the required high vacuum in the deflecting chamber, another tube 3'! is provided which interconnects the different lower parts of the deflecting chamber and through which the same vacuum is maintained as in the electron microscope The magnetic field necessary for deflection of the beam is produced by means of an external electromagnet, shown in detail in Fig. 3. In Fig. 2, 38 indicates the location of the pole pieces shown in Fig. 3. These pole pieces 38 forming part of a conventional electromagnet consisting of a. yoke 39 and coil 40 provide a relative homogeneous field. The whole electromagnet is mounted on a base 4| provided with three adjusting screws 42. These screws 42 permit the necessary alignment of the magnetic field for proper deflection.

It has been found advantageous to shield parts of the tubes 3| and 33 from the stray magnetic field produced by the electromagnet in order to localize its action to the deflecting chamber 32 alone. For this purpose, shields made of high permeability material 43 and 44 are placed around the tubes 3| and 33.

It has been found that relative motion of the magnetic field with respect to the remainder of the apparatus greatly impairs the resolution of the microspectroscope so that care should be taken to mount the electron microscope and the elements of the velocity analyzer in such a way as to eliminate the influence of external vibration.

The dispersion requirements and the resolving power of the analyzing system are largely determined by the velocity of the main beam and the velocity diiferences to be determined. In apparatus constructed in accordance with the invention, utilizing a main beam velocity of 70,000 electron-volts, velocity losses as low as electron- Yolts can be determined.

With the arrangement shown in the drawing, the homogeneous deflecting field will concentrate all electrons of the same velocity at a definite distance varying with the velocity. The plane on which the images of the slit are properly focussed for electrons of different velocity is inclined at an angle of approximately 70 when the middle ray is deflected the middle ray being defined as the ray for which the distance of the image from the field is equal to the distance of the slit from the field.

Permanent magnets may be used instead of the electro-magnet shown by way of illustration or suitable electrostatic fields or combinations of magnetic and electrostatic fields may be used for deflecting the electron beam and focussing the divergent velocity components.

It will be seen that the apparatus of the invention makes possible the simultaneous observation of a highly magnified image of a specimen and of its characteristic electron velocity spectrum. A further advantage lies in the extremely small area of the specimen which can be selected for analysis, areas of the order of 1/l00,000,000 of a square inch in magnitude having been observed with the apparatus of the invention.

Inasmuch as the apparatus of the invention may be readily utilized in the production of a record of the electron velocity spectrum, for example, by photographic recordation as was pointed out above, Without altering in any manner the principles of operation of the apparatus, the term microspectroscope as used in the specification and claims is intended to include modifications of the apparatus for graphic recording or microspectrographs.

I claim:

1. An electron microspectroscope comprising means providing a magnified electron image of a specimen, means defining a narrow aperture in the electron image plane, means providing an electron deflecting field in the path of the electron beam emerging I'rom the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

2. An electron microspectroscope comprising means providing a magnified electron image of a specimen, means defining a narrow aperture in the electron image plane, means providing an electron deflecting field in the path of the electron beam emerging from the aperture, and support means located adjacent the path of the deflected electron beam for positioning an electron-sensitive layer in the focal plane of the defiected electron beam.

3. An electron microspectroscope comprising means providing a magnified electron image of a specimen, means defining a narrow aperture in the electron image plane, means providing an electron deflecting magnetic field in the path of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

4. An electron microspectroscope comprising means providing a magnified electron image of a specimen, means defining a narrow aperture in the electron image plane, means providing a substantially uniform constant rectilinear magnetic field normal to the path of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

5. An electron microspectroscope comprising means providing a magnified electron image of a specimen, means defining a narrow aperture in the electron image plane, means for varying the position of said aperture in the electron image plane, means providing an electron deflecting field in the path of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

6. An electron velocity analyzer comprising means defining a narrow aperture in the plane of a magnified electron image, means providing an electron deflecting field in the path of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

7. An electron velocity analyzer comprising means defining a narrow aperture in the plane of a magnified electron image, means providing an electron deflecting field in the path of the electron beam emerging from the aperture, and support means located adjacent the path of the deflected electron beam for positioning an electron-sensitive layer in the focal plane of the deflected electron beam.

of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

9. An electron velocity analyzer comprising means defining a narrow aperture in the plane of a magnified electron image, means providing a substantially uniform constant rectilinear magnetic field normal to the path of the electron beam emerging from the aperture, and an electron-sensitive layer positioned in the focal plane of the deflected electron beam.

10. An electron velocity analyzer comprising means defining a narrow aperture in the plane of a magnified electron image, means for varying the position of said aperture in the electron image plane, means providing an electron de-- fleeting field in the path of the electron beam emerging from the aperture, and an electronsensitive layer positioned in the focal plane of the deflected electron beam.

LADISLAUS MARTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,058,914 Rudenberg Oct. 27, 1,936 2,260,041 Mahl et a1. Oct. 21, 1941 2,372,422 Hillier Mar. 27, 1945