Document Z8oqQg3p6DZagrkVNqk2wNrbp

E. I. DU PONT DE NEMOURS & COMPANY KREBS PICMENTS DEPARTMENT 256 VANDERPOOL STREET NEWARK. NEW JERSEY Serial No. KN~46"*76 Copy No. 1 NEWARK PLANT PIGMENT COLOR RESEARCH REPORT ELECTRON DIFFRACTION STUDIES PART I CONSTRUCTION AND OPERATION OF CAMERA Period Covered: June 1943 - June 1946* FILE: DATE: 10/13/46 P f NJ6*7S N39957 Serial Mo. OMt-T* Copy Ho# 1 Copy to* #1 - Ntoerleal File 2 - Research Office (145.2) 3 library File (145*2) 4 Inpsriml Cfeenieal Industries, US# 5. * m m m ** ! w# r. Speagenen Physics Lab. 9 * A. V. Kenney* Bxperlaental Station 10 - Extra NEWARK, fUM PI0MENT COLOR RESEARCH REPORT Final Report Titles SIS6TR0H DIFFRACTION STUDIES PART I CONSTRUCTION AND ^OPERATION OF CAMERA Period Covered! June 1943 * June 1946# SUBMITTED BYs F. Kaxush Cb APPROVED BY i H. Perkins DATS SUBMITTEDI Sept. 20, 1946 DATS ISSUED* 10/18/46 N39957.01 DUP050150100 PART I HM.1M A Introduoti B General Ga*U*rkleBila Blctrw Diffraction C Camera Construction B Vacuus Systcn B Hi# Voltage Supply F Electron don ft Im Voltage ElectronOun H Operation of Camera ! Preparation of epeeiaeae 2* Bjuudnation and recording of diffraction pattern* 3 Diffraction date l 2 4 5 6 7 8 DUP050150101 .1* A. mvn Xa 1942* a report ea electron diffraction, entitled "Electron Diffraction In Figment Research?1* KH-42-147* ms issued* This was a survey report designed to indicate the possible applications of electron diffraction to pigment rosearoh* Bone time after the preparation of this report* the construction of as electron diffraction camera at undertaken at Beeark and me eueeeeefuily oocpleted* following this, a considerable amount of experimental work waa carried out ia the attei|jt to ascertain the applicability of the diffraction technique to various pljpwrt problems. Xa presenting a formal report on the electron diffraction studies* it has seemed preferable to issue it in two parte* the first part* which ia eon* tdiaddla this report* ia devoted to the construction end operation of the camera* Xt lo intended to serve a a description of both the variouo parte of the camera* and* to acme extent* the problems involved ia their construction* Xn addition* it will* function ae a fairly detailed manual. for the eperatlea and maintenance of the instrument* The second port* dddi will be presented in a future report* will describe the detailed applications which have been made to date of the diffraction technique* This will include a discussion of results obtained and* wherever possible* their interpretation ia terms of pigment properties* literature references relevant to this report can be found In KR-42-14?* B* The diffraction of electrons is in many respects similar to the diffraction of X-rays. The scattering of electrons can be described as the interaction bctveea matter and a periodic wave with a definite wavelength* If the scattering material is periodically distributed on an atomic scale then diffraction effects will be observed. Compared to X-rays* the scattering of fast electrons of the same range of wavelength is a much mere efficient process* being of the order of a million times greater. This arises from the fact that the scattering of electrons is largely due to the interaction between the intense localized elec trostatic fields surrounding the atomic nuclei and the charged beam elections which are strongly deflected* Because of the efficiency of scattering of electrons by matter* electron diffraction is especially suitable for the study of the structure of thin films and surfaces* This is indicated by the fact that cry- stalllne films of only a few atoms thickness yield strong diffracted rays* In addition to the elaetie scattering of electrons which gives rise to diffraction* there are inelastic collisions* i*e** collisions in which the electron loses part of its energy thru exaltation or ionisation of the strut# atom* Those inelastically scattered electrons are responsible for the considerable background which appears in electron diffraction patterns* The fraction of electrons under going inelastic collisions is increased by a decrease in the accelerating voltage and by an increase in specimen thickness. far 30*000 volt electrons the offestiva free path in a solid is a few huadrtd Angstroms* Unlike the X-ray diffraotioa tdehnlquc* the lev penetrating power of electrons requires that electron diffraction experiments be carried out in an cvacuatodd chamber* For the usual size camera* and with accelerating voltages above 10*000 volts, a vacuum of the order of 10"4 mm. of Hg. is satisfactory. DUP050150102 As indicate* above* associated with the mayo oharaotor of electrons ia a wavelength for the electros* this wavelength A la related ta the Avelocity of the electron v thru the da Broglie relatiett * h/m, where a ia the paaa and h ia PlnMh'o constant* In teraa of the aaeolaratiag voltage F, which la need to inpart velocity to the electron bean* the wavelength ia given br i , '' of 1*5* Angstroms freqacatly ee^lepdd .in X-rpy work*' Xt ia of particular ' advantage that ia electron diffraetioa work it ia poaaiblo to alter the wave- r length j&agtly *F changing the aeoeleratiag voltage* A variation of voltage alee means a change in the penetrating power of the electron bean* a fact which ean be pat to good nao in studying thin aurfnea layers* Since in pigment work* pelyeryetalline epeelmans of nero or lose randomly ordered particles are ordinarily employed, the usual fcdka of the diffraetioa pattern obtained io n series of eenoentrie circles with an intense central spot and with a background dlminiehing in intensity away from the center* The width of the diffraetioa ring or circle depends, among other things, on the width of the electron beam or spot else and is often limited by it* Xn order to obtain beat resolution therefore it io of great importance to reduce the Spot else to a minimum* C* CWftuCTTOTOga The earners at Newark wee built on the basic of blueprints supplied by U* L* roller of tho Research Division, New Jersey Bine Co* A sohematide diagram of the camera is shewn in Fig* 21* It is essentially an evacuated chamber oontaining a source of electrons, a means for manipulating the specimen and a device for photographically rooordiag the diffraction pattern* The main features of the earners ean be seen in the photographs of Figs* 1 and 2* The main section of the camera consists of a brass tube aita Inches in diameter and two feet in length* Attached to the front end of the tube it the eleotron gun, most of which is within the metal sage* To the rear end la connected the plate holder housing* The samara is constructed entirely of tease exeept for platinum jaws on the aperture and parts of the electron gun* "Sylphon" bellows have been employed to permit tho transmission of motion into tho evacuated chamber* Two types of electron guns which will be described later have been used* With the original gun it was accessary to employ apertures to limit the spot site* These apertures consist of two pairs of platinum jags, each pair mounted separately* The jaws fora a slit with a width of approximately 0*1 mm* Tho elite are placed at right angles to each other in such a way that the beam after passing through them hue u square cross section with a length of 0*1 am* en the side* The positions of the elite can be altered from the outside by manipulation of the bellow to whleh they are attached* The elite are placed close to each other and about three inches from the eleotron source. Fig* 3 shows a photograph of the apertures, and their position ia the camera is indicated by A en Fig* 1* DUP050150103 Bines the eleeiren beam at It smergss from the apertures Is divergent! it it necessary to foou* it in order to obtain a minimum spot also* For this purpose a foeusisg ooil it used* a photograph of whioh is shown in Fig* * It oonsiete shyly of a brats eore( with a eat lath disaster hole, on whioh hat beta wound several hundred tftrae et #10 BIB insulated eopper wire* One end of the sail it grounded! while the ether it eoaneoted to a tin volt storage battery through a one ohm rheostat* A current ef between 3 end 4 tuyeres ie uted te fooue the beam* She foeueing eoil ie plaeed iawedlatly before the apeetaea terrier and gives a diamond shaped spot on th# fluorescent toreen whioh represente a slightly enlarged and distorted image of the crossed slits* She insulated lead-in poet for the ooil ie indioaied by B in Fig* 1* In tho original eonstructlen of tho ooaova too yaire of dofleotlon platoo vert placed between the elite and the feeuslsg ooil* By tho ue of a variable potential between the plate# ef eaeh pair it ie possible to deflect the bean both horizontally and vertically! and that te center it on the oereea* With the installation ef the new gun these plate* have beta removed* together with the elite and foeueing ooil* It appears likely that these parts will net be aeeeesary with the new gen* She specimen carrier (0) is shown attached te the betten side of the camera in Fig* 1* Fig* 5 is a photograph of the carrier with three traneaissien type mount** By the notion ef the two bellows it is possible to effeot a vortical movement ef the specimens and* independently! a rotation about an horisental salt perpendicular to tho boom direction* The Utter motion ie required only with reflection type specimens* To eueoeesively place the three specimens in the path of the beam* a pushing defies! indicated by D in Fig* 1* ie employed to move the epeeimen mensdnr in a horisental plane perpendicular to the electron been* On the opposite side of the pushing define and in line with it* there ie located a window?: whioh permits viewing of the specimens under vacuum* At the rear end ef the camera is mounted the puts holder housing indicated by B la Fig* % Within this unit la contained the pUte and pUta holder (Fig* 13) and the mechanism for the motion ef the plate holder* She Utter is introduced into the camera at F9 Fig* 1* and ie moved horizontally thru a gear and reek arrangement by means ef the bellows at 0* Fig* 2* She plate holder carries a 4 a 5 in* plate and ie light-tightt so that leading of the diffraction camera does net require darkness* Immediately is front of tho plato ie a metal disk with a rectangular opening ef 1 in* x 5 in* This derate to limit the area of the photographic pUte exposed te the -dififranti*tefe*tyi particular time and thereby make* possible the recording ef three patterns on a single plate* the plate to specimen distance ie 30*9 m* When the plate' holder ie in its extreme jpbsltisM^leftUHidm|' Kbgsihk, Fig* 2) the beam falls upon a fluorescent soreea (Ht Fig* 2) which readers visible the undeviated beam* and* in many ease*, also ernes of the diffraction rings* Viewing of the screen has te be done in a darkened room* She fluorescent screen ie prepared by spraying a dispersion of e fluoresoent pigment ea te a circular place of leaded glass* She pigment used, together with directions for its application* is obtainable from RCA, end is the same material as that used in fluorescent screens far the RCA electron raircro- eeepee* DUP050150104 The instrument panel, which is shewn la Fig* 6t carries all the electrical controls exoept the four additional ones necessitated toy the nev eleotron gun* The latter are loeated Just above the top of the plate holder heaving* the panel le arranged ao that any of the controls eaa he manipulated while viewing the fluereeeeat screen* in ladieated above, it it neoooeary to operate the fiffraetiea camera under high vacuum. In the neighborhood of 10*4 an* of Hg* Furthermore, elnoo frequent exposure of the earners to atmospheric preeeure is essential, it ie deelrable te reduce to a minima the tine required te pnsg doen to operating preeeure* A satisfactory arrangement uhieh is cqplcyed uith the diffraction oamera ie indicated sehematieally in fig* T* the foropunp ie a "Genes llegavatf* operated at 600 RPH and pevered by e 1/2 h*p* aster* It eenree both for the initial evacuation of the eaoera te a proaaure at which the diffusion pusp ean operate, and alee aa a backing punp* The diffusion poop la a high cpaod all-astal eil pimp aold by Distillation Product# Co*, (type HD 275)* The pimp is vater-ooolsd and has a speed of 275 liters/sea* at 104sm* It requires a fercproecure of 100 microns and uses about 200 grama of "Amoil-B* a the distilling liquid* The pump heater rsquires about 3 asperse and is operated directly fron the 110? line through several ohms of external resistance* The valve arrangement illustrated in fig* 7 is designed to permit the diffusion pump to remain in operation while the camera ia at atmospheric pressure, and during the pre-pumping period* Valve A ie e wide-bere two-say glaso stop cock which eennooto the fere pump wither to the lev vaeuum side of the diffusion pump or directly to the earners through valve 8* Valve C on the high vacuum side of the diffusion punp ie used to seal off this pusp from the camera* Both valves B and 0, 1/2 inch and 11/2 inch recpeetively, are paeklees radiator valves of the believe type vhleh have been adapted far vaeuum verk* The eyele for evacuation of the earners ie ae follows* With the oamera at atmospheric pressure and the diffusion pump at Operating temperatura, valve C (already elosed) remains eleead, while valve A, Vhleh has connected the forepump to the diffusion punp, is opened* This isolates the diffusion pump and opens the camera te the forepump after valve B has been opened* When the pressure in the camera has reached a value between *2 end'd an* (Kg), valve 8 is closed, valve A turned te connect the diffusion punp te the forepump and valve C opened* The oamera is then evacuated te operating pressure end maintained there while the diffraction experiment ie being oarried out* Valve B serves to prevent the rubber hose connection between valve A and the oamera from being exposed te the high vaouum* However, it dees net seem to be essential* Finally, te open the camera te the atmosphere, valve G ie closed end sir permitted te leak through a small opening until the inside end outside pressures are equal* Fig* 8 gives e photographic view of the vaouua system showing valves A, B and 0 and the oil diffusion pimp D* The forepump is located at F where it ie enclosed in a sound-proof box* The evacuating system is connected to the body of the camera by e pair of two inch braes pipes fitted with Sylphon" bellows* These permit alight motion of the camera relative to the vacuum system* The time required to punp the camera from atmospheric pressure down to operating preeeure ranges from 10 to 15 minutes* DUP050150105 Two types of vasuun gauges or* ss^loyed for the measurement of tbs low pressures used in the camera* The thermocouple vaeutm gauge meaeures pressures in the range from 200 aierons to about one mieron (Hg)* it is Identified ns 3 in Tig* l|atbe aseoeiated meters on the instrument panel can he sew in Tig* 6* in which the heater current meter* labeled *T*G* H&MER*, is la the lover right hand corner* St is a 8*200 nisreaaaeier shunted by a 1/2 ehn resistor oo that a reading of 1Q0, vhioh oorrespends to a heater eurrent ef about 70 ailiiaaperes thru the thermocouple gauge* gives a reading of the themo-ourrent of 195 microamperes uhoa the pressure is less than 10*3 o k , ef mercury* This is read in the low resistance (55 ohms) 8*200 micreammeter* labeled "VACUUM?*, sheen in the upper left tend eomer of Fig* 6* Ter the measurement of pressures la the range of 10*3 to 10"^bs b. (8g) an ionisation gauge la employed* A portion of this gauge eon bo seen in Tig* 1 at 1* The filament auvrent for this gauge ie supplied by a six welt storage battery* Tig* 6 shove the asseeiatsd asters aad rheostat* The meter labeled *1*0* iShKH* indicates the filament current* usually about 1*6 amperes* which io controlled by the rheostat with the same identification* When the reading on the meter mashed "X*G GRID* is 9 mlllioaperee* corresponding to on actual grid current of 21 nUllaaporoo because of a 2 ohm shunt resistor across the motor* the pressure in the samara in mm* ef mercury is approximately five times the positive ion eurrent in asgeres* This ie road on the nderoammeter labeled "1*0* FIATS** Thus a reading of 20 miereasEperes on this meter corresponds to a pressure of about 1 x 10** mm* of mercury* The satisfactory operation of the ionisation gauge requires the removal of adsorbed gas after exposure to air* This io carried out by placing the voltage available from the battery chargor la series with that from the storage battery and passing a current of 2*5 amperes thru the filament* The DPDT toggle 0*itoh at the left of the *1*0* (HUD* meter in Fig* 6 servos to make this connection when it io in the upper position. The lower position is used for normal operation of the gauge and for charging of the storage battery* Both the grid current and plate eurrent meters must be shunted during the degassing period* The farmer metdr is shunted when the above toggle switch is in the degassing position and the latter is shunted by the toggle switch at the upper right ef the "1*0* PLATE* meter* The circuit diagrams for the thermocouple gauge and the ionisation gauge are given in Figs* 9 and 10 respectively* e . mAJsmm.mmiL To furnish the constant high DC* voltage required for the operation of the oamera* a used medical X-ray high voltage supply was purchased, together with a constant voltage transformer aad a high voltage condenser* A circuit diagram of the high voltage supply io given in Fig* 11 and a photographic view of the high voltage equipment in Fig* 12, The high voltage transformer* the reotifier tube and its filament transformer, and the filament transformer for the electron souroe are enclosed in a cylindrical metal container (A* Fig* 12) and submerged in oil* The $00 watt "Sola" constant voltage transformer can just bo seen at B in Fig* 12* It serves to maintain eonetant the voltage supplied to the primary of the high voltage transformer and thus stabilises the accelerating voltage of the oamera* The high voltage condenser (C, Fig* 12) has a capacity of *012 microfarads and can withstand 50,000 volts* It is mounted on an Insulated base and io grounded thru a 10*000 ohm, 100 watt resistor (S* Fig* 12) to prevent surges. DUP050150106 The primary voltage for the high voltage transformer it supplied from a aute-traniformer adL0 it notated on the panel tad it labeled "BSG8 TOLTAffl8 in Fig* 6* Tbit permits the selection of tap accelerating voltage la the range fWw 0 to 50 kilovolttf although 40 XT it usually eBployod* For reasons of safety all tbs Ugh voltage equipment it teatataed within a metal eage* Vhaa tit* dear to thie oage le opened an interloek ewiteh ekute off the power' aad at the same time a grounding eap grenade the high voltage tide ef the condenser* The value of the high voltage eta be read directly ia kilovolte on the 0-JO microsmmster labeled "BEQ8 V0I3ASB" in Fig* 6* One aide ef thla meter le eonneoted to ground while the other is tied to the high voltage thru a 10' ohm, 100 OT realator. Thia measurement ef the high voltage it net very accurate* la the original construction ef the camera, a relatively simple design was asployed far the eleetron seurce. This eeasieta of a toagstoa filament of 6 mil diaailwr oonaeeted to two long insulated niekol rods* Details oaa bo 00m in Fig* 14 whloh alum tha old eloetron gun disassembled* lunrouadiat these rods, and extending Just btysnd the filament, is a copper tube on which is mounted a aided disk oeataiaiag a reotangular slit* Both the tube and disk are at a potential of 45 votes positive with reepeet to the filament, thee nerving to enhance the electron emission from the filament* The amission current is measured by a sderoaameter which is contained, together with faces and a 45 volt battery, in the copper sphere placed at the top of the high voltage condenser* Thie is visible ia Fig* 12, in which the slot to permit reading the aderoanmeter may also be seen* The gun described above was not wholly satisfactory baeansa it required frequent replacement of the tungsten filament, and also, because of inadequate intensity, particularly at lower voltages* Xn ardor to 4#ereome these disadvantages, and especially to diminish the spot siso and thus istprovo tha resolution of ths esmera, a now and more elaborate electron gun was installed* This gun was taken from a "DuMont- typo 5<JP eathedo*ay tube and adapted far use in the camera* Thia change involved the substitution ef a tungsten filament far the oxide-coated cathode originally present, because the latter loses its emitting power after a few exposures to the atmosphere* A photographic view of the gun and associated parte ie shown in Fig* 15} some details are partially obscured however by the wide silver band coated on the inside ef the glace tube in which the gun is enclosed* The electron beam is focused by the adjustment ef the potential on the focusing electrode and the intensity regulated by the voltage en the control eleotrode* This voltage must always be negative relative to the eathodo potential* Tha direction of the beam, and consequently the poeitioa ef the spot on the fluorescent screen, eon be altered by varying the potential# on the two pairs ef deflection plates* *beee plates permit adjustment in both the horiiontal and vertioal directions and thus make possible aoourate centering of the beam* The controls for the guneare enclosed in a braes box shewn at the right in Fig* 15* Thie ben is maintained at high potential, usually 40K7, and contains ths required potentiometers, resistere, eoadeaeers and batteries* The manipulation of the potentiometers while viewing the screen is possible by the insulated extensions from the box, as is evident in Fig* 1* The circuit diagram for the gun ia shown in Fig* 16 Share the portion enclosed by the broken linos corresponds to the equip ment contained withint the braes box* The gun ie maintained DUP050150107 scat contained within the braea hex* The gun 1* maintained at high potential with a maximum drop aeroas it e$|f 2KF* the voltage for the difleetion plates is supplied by two 0Y batteries thru a pair of dual 1 megohm oontrols* A toggle switch qhich ean be reaehsd at the bath of the high voltage box la provided to avoid eentinuous drain of urrent from the batteries* The dual potentiometers are arranged as aa te make the voltage drop between the deflection plates of each pair syanstrieal with reepeot to the electron bean and thus te minimise distortion* To avoid distortion and defoeusing of the electron beam and spot* the pyres tube within which the gun ie contained is seated on its Inside eurfaoe with a wide silver band and three silver rings shown in fig* 15* Electrical eenneotione te the latter sen be aade with the rounded brans paste which make ooctaot with the rime thru wire-glass seals* The wide band la at the potential ef the aooelerating eleetrede of the gun and makes contact with it ineide the tube* It serves to shield the gnat* particularly the deflection plates* from the aooelerating voltage* The silver rings permit the 40KV aooelerating voltage bo bo applied In steps ef lOKf by the nee ef 200 megohm resistors between them* as shown in the oireuit diagram of fig* Id* The silver rings and bend were seated on the tube by appl|il|f with a camel's hair brush te the tubs mounted on a laths* a pasts ef colloidal silver in turpentine* For this purpose silver paste no* 38 from Honoris Chemical i Hfg* Co* is used after it has been thinned to brushing consisteasy with turpentine* After the paste has been applied*'the tube ie placed in an even end heated te between 600 and 650*C* This heating removes all organic material and leaves a strongly bonded silver film* o. In the examination of massive speeimeae where the reflection technique must be employed* difficulty in obtaining diffraction patterns is often encountered due to the development of an electrostatic charge on the sample* This problem ean be avoided by bombarding the specimen with low voltage electrons (a few . hundred volte) simultaneously with its exposure te the high voltage eleotron beam* For this purpose a low voltage electron gut has been incorporated in the diffraction oamera* It can ba seen at the top of fig* 1 connected te the main body by mesas of bellows* which is used for aladng the gun* For the construction of the gun* sa ell-metal RCA cathode ray tube (Me* 913) use used* The ease was removed together with the cathode* heater sad control eleetrede* As with the main gun* e tungsten filament was installed as the source of electrons* (holy one pair of deflection plates is used since it is sufficient te direct the beam to the specimen* The circuit diagram for the low voltage gen is shown in Fig* 17* a. i* fywwpliflB.?? nmfownB The preparation ef mounts for the diffraction earners ie a critical and sometimes a difficult matter* Pigment samples* aa well as ether powdered materials* ere almost invariably examined by the transmission technique* In this ease the ideal mount ooasiete of a densely peeked moaopartieular (one particle thick) DUP050150108 layer thru which the electron team it transmitted. The first step in the usual preparation of aerate of pigment w 1m Is to deposit thin fils of uitroeoliuloso (about 400 sgggtsejiS^ w a Q0 neoh stainless rteel screen dieh, 1/4 iaoh is disaster* This is dons by plaeiig oas drop of a p solution of nitrocellulose in npl asotato on the surface of distilled water contained in a sis inch eva porating dish. After the solvent has evaporated, leaving a thin nitrooellulose film on the surface, a screen carried by a serosa support is brought v free below the water surface to just above the surfaoe causing the film to root on the screen. The film te then severed with a sharp point and the soreen support lq lifted out of the water. la Fig. 18, rev A shows a photograph of throe sereena, and row-B, throe oereea supports. The moat oasoooofal technique found for preparing the pigment film has bora to first dispores the powder la ethyl aootato, with a snail amount of aitroeel|lose as a dispersing agrat if neeesaary (as in ehrone yellows) Then a drop op two of the dispersion is plaesd on the surfaoe of hot water in a beaker* Thors is almost instantaneous evaporation of the solvent such that, if the operation is done properly, the pigment remains on the surface in the form of a coherent file usually without ouch flocculation having occurred. Xa the ease of ohromo .yellows( electron microscope examination has shown that a densely packed film of about one particle thickness can actually be prepared by this procedure. The next step is to place the pigneat ra the preformed nitrooellulose film simply by raising the latter, resting ra a soreen end soreen support, from below the surface of the water thru the pigment film* This action causes the film to break around the edge of the support with a circular eeotioa of the film remaining on the nitrocellulose. When the mount thus prepared boo dried it ie ready for use* After examination in the camera, the screen with the pigment specimen on it is removed from its support and is filed in a numbered gelatin capsule for possible future reference. Two kinds of ooroes supports are employed, ae shown in rows B and C of Fig. 18. Those in row B are used when it ie desired that the electron beam Strike the mount at perpendicular incidence. When evidence of the orientation of pigment particles Is being sought, the supports in row 0 are used. In this ease the beam makes an angle of 4with the normal to the pigment film and if -tiie particles are net randomly oriented, ares appear in the diffraction pattern instead of rings. Bush results are useful in oonneetira with the study of the shape of pigment particles. In Fig. 18, D is the soreen rapport holder which is attached to the specimen carrier for examination in the camera. It has previsions for three samples* The examination of pigment samples by the reflection technique can be executed by placing the samples ra solldf.polished stainless steel supports which have been made for the purpose. These fit into the screen support holder. 2* Examination and Recording of Diffraction Pattern After the specimens and a photographic plate hove been placed in the camera the latter must be evacuated to a pressure of about 10** mm. of Hg. before the electron beam and high voltage are turned on. Usually the ionisation gauge is not used, but the system ie regarded ae having reached a working vacuum when the thermocouple gauge gives its maximum reading 1195) on the meter labeled DUP050150109 "VACUtar is rig* 6* fa obtain tha high voltage* the witches la rig* 6 marked *wmwm* and "MOS VOtrAGE* ara turned on and* after a moment, the veltagp trm the autetransfemsr ia slowly iasrsaned if turning the knob marled "KSH TOLTAfias* astil the high voltage meter indicates the desired voltage* Although the direat beafa aha always bo swan a the fluereeoent aeraea* with tha aid gaa diffraction ringa would ha eaaa with rOlatlvely dew sables* With the new gm it ia ejected that tha diffraction ring* will ha viaihle with prqetleally all samplee wldah shew diffraction* far photographic recording of tha pattern a plato ia ahlftad lat^rf position in front af tha aaraaa* A Barker aa tha hallewa controlling tha action af tha plate holder indicate* tha correct position far aaah af the exposures to he recorded aa a single plats* The type of plate mat frequently used ia tha Bastaaa Kodak 4x5 Presets plate* Tha plates art dehydrated befora wsaL kept la a desiccator so that tha moisture eoataiaad la then will not unduly \ lengthen tha evacuation tine* Tha exposure oondltiena for phetegrai$ie reoordlng wary for diffw|t patterns* hut rang# from 10 seconds to 2 sdautoe with aa asdsoiett current batmen 100 and 200 mleroasfarea* With the now gm It ia anticipated that exposure tines of a few seconds will he sufficient. The plates era developed at 88*T* for l\l/2 minutes in Kastman D-8 developer and hardened ia a hath of chrome aim for eqoi!j` 1 minute. Several typical patterns are reproduced ia fig* 19* 3* S>UfrftgU9ft.Pfita In general tha information which it ia desired to secure tram a diffraction pattern is the interplansr spaeings corresponding to the diffractioln rings and their relative intensities* The accurate measurement of the ring , diameter#* uddeh range trim a fraction of a oentimetor to 3 or 4 oentiaotoro* if required for thief calibration of tha apparatus with a standard at the particular voltage employed io also nseeoosvy* A device for measuring ring diameters was! constructed and ia ahem la Tig* 20* It ia essentially a low power travelling! microscope and measurements to aa aoeuraey of 0*1 millimeter aan ho made with Ter the calibration of the diffraction apparatus* iron bine io very' suitable sines it gives a strong and sharp pattern of about 28 rings and la addition* its lattice constant is accurately known (of X6X Report Rl*4030 / "A Oeaeral Account of an X-ray Examination of Prussian Blnol"* 12-5-35) This has a value of 10*2 Angstroms which* for example* gives a conversion, faster af. 4*42 Angstrom-centimeters for 40KT electrons. Thus, by dividing the ring diameter into tide footer* the corresponding value af tha interplansr spacing ia Angstroms eaa he computed* | / To facilitate the estimation of relative intensities* a photographic seals waa prepared by jlg&ograptdag eeveral times the electron beam* in the form of a narrow line, at constant intensity at various known exposure times. Fourteen exposure steps covering a 11-fold range of intensity were obtained* By matching the lines oftshft scale against the diffraction rings it is possible to make rough quantitative estimates of the relative intensities of the rings ia any given pattern* This eaa he done in spite of the feet that in most patterns the back ground intensity varies considerably from ring to ring* DUP050150110 FIG. 1 - GENERAL VIEW OF RIGH'J? SIDE OP CAMERA ! I i i j PIG. 2 - GENERAL VIEW OP LEFT SIDS OP CAMERA | DUP050150111 FIQ S - ADJUSTABLE APERTURES FIG 4 - FOCUS BIG COIL DUP050150112 PIG. 5 SPECIMEN CARRIER DUP050150113 DUP050150114 tbmwsmm* PIG* 9 - THERMOCOUPLE VACUUM GAUGE CIRCUIT msTm e is c t r io DUP050150115 so<m miw& mrnm tv rm im, PIG' 11 * HSOS VOLTAGE SUP PI!3f OIROtflf DUP050150116 FIGi 12 - HIGH VOLTAGE EQTJIPMEWr FIG, I'3 - PLATE GOGHia DUP050150117 ' I FIS, 15 - IMsF SL2C2H0II Gull DUP050150118 # % *; ;jf-y ... ^*7 'V'l DUP0501 50119 '*'?**?> '( ,}*/ ... ,i'lr* 'i'"t **.;*'V ;>-} 4V fy-S-'i DUP050150119 %m m PIG. 17 - um VOLTAGE E&DGOTOIJ GOB CXBCCIXV f ig . 18 somssrs* soirai CSiTCSES & HOUSE DUP050150120 7T<5 19 - DIPF/<C?XO)F PhT9mn OF rSOaffitfSK DUP050150121 DUP050150122