Sept. 24, 1946., 2,408,287 c. H. BACHMAN ELECTRON MICROSCOPE Filed Feb. 1, ‘1944 'Fi 2. F33.” .30 3.9 33 Inventor“: Charles H. Bachman, 61 Hus Attor‘neg. 2,408,287 Patented Sept. 24, 1946 ~ UNITE-D STATE S PATIENT-‘OFFICE ~ Charles II. General Bachman,“ Scotia,'-YYN-.‘Y., assignor to I Electric ‘Company, I a >7 corpor tion ‘_ of New York vApplication February 1, 19411, _$erial Nor ' 5 Claims.v '" ' (Cl. 250-495) ~ It is .an'objectvof the invention to provide a new in the appended claims. The invention itself together “with vfurther objects and advantages thereof'may best be_understood- by reference to the following description-taken in connection with thegacco'mpanying' drawing in which Fig. 1 repre and‘ improved ?uorescent screen for an electron ' sents ‘diagrammatically ‘an end section of an elec microscope.‘ Fig.‘ 2 is‘ a cross-sectional view showing'the ?u ' The present invention relates to electron opti cal apparatus particularly adapted for themiOl‘U scopic examination of electron pervious objects. _ _ v tron optical system'employing my invention ‘and p f It, is known that objects may be microscopically orescent"scre'en supporting arrangement of ‘the examined by the rays of an electron beam which transra'diates the object,’ ‘the, beam' ‘passing 710 invention. ’ ' ' ‘ ' providedwith thelch'aracteristics thereof. Such , “Referring ‘to Figs. 1" and 2 jointly‘, ‘there is shown ‘an ‘electron microscope 'comprising an ‘ that there ‘are two fundamental limitations in con?nes the" emitted electrons to a "narrow beam throughithe object and in'this passage being elongatedvacuum-t'ight container H] of a tubular an "electron beam may be refracted by appro metal‘ construction; Atone end’ of ‘the‘container, priately conditioned ?elds and the’ beam may be impinged upon a ?uorescent screen; an image 115 there isi'provided a glass insulator I l’ which serves to support‘ an electron source in" the :form of ‘a being‘ constructed on. the > screen, in accordance ?lamentary ‘cathode-121 The cathode I2 is sur withthe characteristics given to 'the'bea'm in ‘its rounded by ‘a tubularm‘etal member'l? which passage ‘through the, object. It hasbeen observed. ' with 'res'pect'to an the use of ?uorescent screenin? electron micros- , 20 and is ‘cooperatively ‘positioned M which is in contact with copy where an‘ electron beamjis impingedjupon ' apertured electrode‘ I the metal envelope part l0.- The opposite end of theen'velo'pe I0‘ is sealed ‘by ‘a glass window ‘I5. are ‘thecsize of thejphosphor or fluorescent par ticlesf and the" physical thickness'of the screen.‘ ' ' A-?uorescentviewing screen" I 6 is positioned with" and passes through the ‘screen; ' These limitations in thejtubel?- in front of vvthe window [5. The limitations of course are of consequence only when optical magni?cation of an’ image on ‘the screen is desired7 In ‘this'case,>as;the_image_on ‘a ?uorescent screen ' Inthe'normal use of‘ the'apparatus, the en velope l0 and the apertured electrode I4 ‘are maintained at "g'round-potentialand the cathode enlarged to magni?cations of the order of, 25 diameters,_ thethickness 0f the ‘screen,‘that is,‘ the number of layers'of phosphor or ?uorescentparticles causes the edges of the is ‘maintained at a high negative potential, for @330 example; being ‘connected to 'a ‘potential source ‘ hand,'the sizeof the individual phosphor particles can beso controlled that this factor ‘does not enter 'as/a limitation of magni?cation until‘ enlarge ments of the order of several hundreddiameters ' "l1 "so that electrons the cathode are promoted axially of the contain‘er-with'the objector producing a ‘image tolbecome blurred or fuzzy. ' Onthe other 35 ' are‘ reached.’ Improved magni?cation may be at visible image ‘on the fluorescent vscreen l8. Between the cathode I2 and the image-‘repro ducing'screenl‘lt there is provided object sup l‘9.c In the ‘porting- means ' indicated generally at intended use of the apparatus, this means is to~be tained, therefore; if asu?iciently thin fluorescent screen,“ preferably consisting of: a single player of 1 employed as a support for an object to be trans ‘?uorescent particles, may be constructed satis :40 radiated *by an electron beam, the beam being ‘factorily without the occurrence of tiny‘ holes due to ‘incomplete coverage of a screen surface dele teriously a?ecting satisfactory‘imaging of ‘the ' passed-through the object and in the passage as suming the characteristics of the object. A sup porting ‘structure may ‘be ‘provided in connection ~ 7 .withr-the object supporting means l9 and may :It is an .iobject of my invention to provide im- _, rlikewise employ appropriate clamps or other "proved' means by which very thin - ?uorescent ‘ 'means (notshown) forholding an object with its 'magnified object.’ 1 screens may be successfully‘emplo'yed in electron ‘optical studies or .objects.‘ ‘ ~ .I '"An‘ important feature ‘of the invention consists vinran apparatus arrangement by which thin ?u crescent screens used in electron optical' studies‘ a ‘are movedilaterally' to effect a smoothing out of Tall irregularities in the screen structure'and with surface, in exposed position to the electron beam20. ‘I , v y. _ . . , V In order that the electron beam,_after modi? cation in accordance with the structural charac ter ofrthe object under investigation as the beam caused to pro 'transradiate's' the-object, may' beofthe visible image object in videv an enlarged the micro l-s'u?lcient frequency to eliminate visual effects. ' accordance with the ‘intended: use ofthrough‘ the ' ' The features of the'inv'ention' whichIdesi‘re to 155 “scope; the beam 20,v after passing \protect herein‘ are pointed out with particularity: 2,408,287 3 object, is caused to pass through an electron lens system of known character. In the drawing, the lens system is illustrated as of the electrostatic type, although a lens system of the magnetic type may be ‘employed. The lens system comprises a series of three diaphragms, numbered 22-24, in clusive. The diaphragms 22 and 24 are main production of the electron image are encoun tered. To eliminate any possible visual defects in the reproduction of the electron image, as the screen I6 is moved laterally, the frequency of motion of screen l6 Of course must be greater than the ?icker frequency of the human eye. To this end, a frequency ofv 20 cycles-per second or greater at ground potential and the intermediate dia phragm 23 may be insulatingly supported and is _10_ should be employed in movement of rod 35. Such vibration of the rod 35 may be obtained by means biased to cathode potential through a connection 'of an electrical coil 40 energized from a suit 25 which is brought into the microscope enclosure able source of alternating voltage 4| through a through an insulating bushing 26. Because of the ‘ ‘control switch 42. An armature 43 may be pro resultant di?‘erence in potential between the dia vided at they lower. end of rod 36 to be vibrated phragm 23 and diaphragms" 22 and 2‘, lens ?elds 15 by coil 40'. ~ are established between these diaphragms which When the lens .system 29 is replaced by a cam have the eifect of refracting the electron beam in era for photographing the image produced on a manner analogous to the refraction of a light screen IS, the need for eliminating ?icker effect beam by an optical lens. Additional lens ?elds is no longer present so that at such times the may be employed in the electron microscope 20 frequency of vibration of screen [6 may be re where so desired. duced and the screen may be moved manually Means are provided for optical magni?cation tained at the potential of the casing H1, that is, during the exposure time. of the image formed on the ?uorescent screen I6 and this means is represented conventionally as » 'By the present invention, in an electron mi croscope of the type described above, a ?uores an optical lens 29 through which the beam of 25 cent screen may be employed. which is made up visible radiation 28. projected through window of a single layer of ?uorescent particles; Such I5 from ?uorescent screen I6. is caused to pass. a screen usually is not suitable for electron mi The fluorescent screen I 5 shown in plan View croscopic examinations, since the coverage of the in Fig. 2 comprises a frame member 30 which screen under such conditions is only about 60% Inav be either circular or recta'ngnlar in shape 30 complete. In the normal microscope, therefore, and which supports a transparent window 3| more effective coverage of the screen surface is upon which is deposited a thin coating of a suit_ able ?uorescent material 32. Preferably. the obtained by adding additional layers of‘ ?uores cent material. In a microscope, however, in coating 32 consists of a minimum number of lateral shaking of the screen is provided, lavers of small particles Of'a suitable phosphor. 35 awhich single layer of ?uorescent particles may be em The frame 30 is suspended within member In by ployed and the shaking produces the effect of means of a set of swine members 33 which pro a completely covered very thin screen having re_ virie a good conductive connection, between duced light output because of the decreased screen l6 and tube H). To one edge of the frame number of ?uorescent particles. ' 30. there is attached a rod member 35 which ex 40 While I have shown a particular embodiment tends through an opening 35 in tube 10 and of my invention, it will of course be understood passes through a bellows device 31. the bellows 31 that I do not wish to be limited thereto since providing a seal across opening 36. The member various modi?cations may be vmade, and I con 35 has a nnrtirm extending pwterio-rlv of the he] lows 31 by which motion may be imparted to 45 template by the appended claims to cover any such modi?cations as fall within the true spirit screen [6 to produce lateral movement of this and scope of my invention. screen. What I claim as new and desire to secure by In order to prevent any motion imparted to Letters Patent of the United States is: screen I6 bv actuating rod 35 from producing 1. The combination, in an electron micro axial motion of the screen to aiTect either the 50 scope, of a viewing screen coated with a thin electronic or optical focus. a plurality of guide layer of ?uorescent material and means for pro members 39 are attached to the inner surface ducing lateral motion of said screen to reduce of container Ill. The guide members‘ 39 may be blurring of images produced on said screen. provided with slots or ?ngers at one of their ends 2. An electron microscope comprising an evac and the screen I 6 may be restrained by these 55 uated container having a ?uorescent screen po~ ?ngers from axial movement and yet permitted sitioned therein, means for projectingv a beam to move in a plane perpendicular to the axis of of electrons upon said screen, means for sup the container I0. porting an object to be examined in the path Bv the screen supporting arrangement de of said beam, and means for vibrating said screen scribed, the screen 16 may be moved laterally 60 in a plane substantially transverse to said beam and the eifect of any kind of screen irregulari to reduce blurring of the image of said object ties, such as holes, dirt specks, and similar de produced on said screen. ‘ fects in the phosphor coating on screen l6, which would normally produce distortion in optically 3. An electron microscope system comprising enlarged images on the ?uorescent screen I 6 is 65 an evacuated container having a transparent wall, a ?uorescent screen supported within said eliminated, Since the electron beam 20 always container‘ in front of said wall, means for pro bombards the same points in space, as the screen I6 is shifted in a plane perpendicular to the beam, the effect of smoothing out all the irreg ularities of the above-mentioned type in the 70 screen structure is obtained. So long as the mo tion is con?ned to a lateral direction and there is not su?icient axial motion to a?'ect either elec tronic or optical focus, no ill effects inv the re screen, means external of said container for pro ducing optical enlargement of the' image on said screen, and means for vibrating said screen in 75 a plane substantially transverse to said beam to reduce blurring of said enlarged image due to 2,408,281 non-uniform distribution of ?uorescent particles on said screen. 4. In combination, a viewing ‘screen coated with a thin layer of fluorescent particles, means for producing an image to be viewed on said screen, optical means for enlarging said image to a degree such that irregularities in the depo sition of said particles on said screen produce objectionable blurring of said enlarged image, and means for vibrating said screen in a plane transverse tov the optical axis of said optical means to reduce said blurring. 5. The combination, in an electron microscope having a vacuum-tight container, of a ?uorescent screen resiliently supported within said con ' tainer, means for projecting an electron beam on an image thereon, means said screen to produce said image, and means for for optically enlarging vibrating said screen in a plane transverse to ' said beam to reduce image. blurring in said enlarged _ CHARLES H. BACHIVLAN.