US2440640A - Electron microanalyzer - Google Patents

Description

April 27, 1948. MARTQN 2,440,640

ELECTRON MICRO-ANALYZER I Filed Nov. 27, 1946 IN V EN TOR.

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Patented Apr. 27, 1948 uN-i,

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of electronsemittedlbyi the specimen under excitation by 'X-rayslf It is, known t t, constitutipn of a ItQ'is furthermore know that 'the incident xgrayv minus lth'effenergy necessary to expel thel elec'tronl from the atoin.' The energy" of the emitted .photoeleetrongisthus character istic for lthe emittirigpatom andjaf dte'rmination of the atomic constitutionpf ja. specimen is possiblelif" the? energy of. fthe. exciting, photon,- and i the energy level irom'which the electronis ex? tracted,.are known, i

It hasQbeen ,ioun'd'that byqirrfldiating. a speciareem s mming the i hest ss l a centration of substantially menachromatic Xerays, This can advantageo 1y befefiectedbvexciting a selected .X-ray eniittef (target) under nditi ns provid ng. ll redm n nt ine s e um i h al elet jvel fweakcont uous( e kground; By the vuse:of "sill-table"filters; preferablvtp aced as close as possi le fto the specimen r p v poesible fm un g of radiant energy, it jis possible to? substantially improvegthe;monochromism ofthe irradiatin in erder'jto Obtain the high beam. The filter material'is selected to contain an element having a K-absorption limit at a slightly shorter wave-length than the K-line of the target. For example, with a molybdenum target, a, suitable element for the filter is zirconium,

Preferably the space between the target and the specimen is cooled and the filter element advantageously can form a wall of the cooling chamber adjacent the specimen thereby preventing contact of the coolant with the specimen.

The invention will be more particularly described for the purpose or illustration with reference to the accompanying drawing in which:

Fig. 1 is a diagrammatic elevation of apparatus embodying the principles of the invention;

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e ectron jdptical i e i the, dinerehtflatoms of hetqwhenasu ance i ir acl e d photoelectrbnsg are .emittedf by the gexnittedjelectron' will bl that of the f -1'2 s a fra mentaryldetaul i ele or no;

with; 1

, H t t, rorexempiee moly denurn foil .0

25 mmens .1 .3 er

ro'magne c" material "suchjas b as yond the coilTanf electron currentof suitable i'nten y coil."""1?h'e instrument may e focus eclicyicalibrat in'gjthe mag'netic lens curre with respect tovari ous" precalcu'lated' energies;. of thfem'itted photo electrons, using' electrons'generate tio'nal electron" gunfior" exa 1e, to, obtain elec' trons pf various known energ es "for th'e caiibration'and 'iisingja" fluorescen re 40 measuring the accelerating voltage andi'ther CHI-erent flowing through the magnetic lens coil,

In'this way a calibration table or curve is provided, from which theproper lens current can be ascertained for any precalculated value of emitted photoelectrons.

If the element to be determined is unknown, the electron beam can be focussed by placing a Geiger-Muller counter or other radiation recording device at the plane of the photographic film, and the counting rate determined for various magnet coil currents. The maximum counting rate will correspond to the proper focussing' current.

In order to increase the intensity of the image 65 and at the same time to reduce the amount of sen ion 12;; 05iIl,C, in thicknessarrd, the thin zire m filtggfoiluls'c h ma net c hiee iy ii5ii e l rrises'e @1 i tn nfeny V "ftodeterminethe focussingf' By observin thefimageof the uor'escent screen; corresponding valuesof focussing currents can beestablished for the diiierent electron energies-byspherical aberration it is advantageous to accelerate the photoelectrons immediately after they are emitted from the specimen. This may be effectively accomplished by means of an electrostatic immersion lens as shown at 30 in Fig. 3. An electrostatic focussing lens 3| is also provided.

The accelerating voltages used for X-ray generation and for the acceleration of the photoelectrons may be obtained from the same power supply. Both electron accelerating systems may be connected in parallel to the power supply. In order to reduce the problem of insulation presented by the close spacing of the target and the specimen it is advantageous to connect the target I to the specimen and to energize the apparatus by a potential divider, as shown in Fig. 3, whereby the target and the specimen are maintained-at an intermediate potential between the cathode potential and the ground.

I claim:

1. An electron microanalyzer comprising means for directing a beam of substantially monochromatic X-rays upon a specimen to be analyzed, means for accelerating photoelectrons emitted from the specimen; and means for iocussing the accelerated photoelectrons to form an electron image.

2. An electron microanalyzer comprising means for directing a beam of substantially monochromatic X-rays upon a specimen to be analyzed, and means providing a focussing field adjacent said specimento focus photoelectrons emitted by the specimen into an electron image.

3. An electron microanalyzer comprising means for directing a beam of substantially monochromatic X-rays upon a specimen to be analyzed and an electron focussing electrode adjacent said specimen. V v i 4. An electron microanalyzer comprising an electron gun, a target adapted to emit X-rays under electron bombardment from the electron' gun, means :for positioning a specimento be analyzed in the path of X-rays generated by said target, and means providing a focussing field adjacent the specimen to focus photoelectrons emitted by the specimen into an electron image.

5. An electron microanalyzer comprising an electron gun, a target adapted to emit X-rays under-electron bombardment from the electron gun, means for positioning a specimen to be analyzed in the path of X-rays generated by said target, a filter member in the path of the X-rays substantially impermeable to X-rays .of lower wave-length than the K-emission of the target, and means providing an accelerating and focussing field adjacent the specimen to focus photoelectrons emitted byjthe specimen into an electron image.

4 electin gun, a thin target foil cat a metal adapted to emit X-rays under electron bombardment from the electron gun, means for positioning a specimen to be analyzed in the path of X-rays emitted by the target, a filter member between the target and the specimen substantially impermeable to X-rays of lower wave-length than the K-ernission of the target, and means providing an accelerating and focussing field, adjacent the specimen to focus photoelectrons emitted by the specimen into an electron image.

'l j-An electron microanalyzer comprising an electron gun, a thin target foil of a metal adapted to emiftfX-rays under electron bombardment from the electron gun, means for positioning a specimen to be analyzed in the path of X-rays emitted by the target,'a filter member between the target and the specimen substantially impermeable to X-rays of lower wave-length than the K-emission of the target, means positioning the target foil and the filtermember in spaced relationand'cooperating therewith to definea chamber between the target foil and the filter member, means for passing a cooling medium through said chamber,

and means providing an accelerating and focussing field adjacent the specimen to focus photoelectrons emittedby the specimen into an electron image.

t 8. An electron 'microanalyzer comprising an electron gun, a thin target foil of molybdenum positioned in'the path of electrons from the electron gun, means for positioning a specimen to be analyzed in the path 06 X-rays emitted by the target,a thin filter foil of zirconium positioned 6. Anlelectron microanalyzer comprising an between the target foil andthe specimen, and means providing an accelerating and focus'sing field adjacent. the specimen .to focus photoelectrons emitted by the specimen into an electron image.

9. In an electron microanalyzer, a source of substantially monochromatic X-rays comprising a thin. target foilof a metal adapted'toemit X-rays under electronbomba-rdment, a thin filter foil substantially impermeable to X-rays of lower 'wave-lengththan the 'K-emission of theitarget, means positioning the target foil and the filter foil in spaced relation and'cooperating therewith to define achamber between the target, foil and the filter foil, and means for passing'a cooling medium through said chamber.

10. In an electronmicroanalyzer, a source of substantially monochromatic X-rays comprising a thin target foil or" molybdenum, a thin filter foil of zirconium means positioning the target foil and the filter foil in spaced relationand cooperat-;

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