US 2418029 A
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ELECTRON PROBE ANALYSIS EMPLOYING X-RAY SPECTROGRAPHY Filed oct. 8, 19.43
Patented Mar. 25, 1947 ELao'raoN PROBE ANALYSIS EMPLoYiNG X-RAY SPECTROGRAPHY .I ames Hillier, Granbury, N. J assignor` to Radio Corporation of America, a
corporation of Dela- .appucaaon ottenere, 1943, serial No.5o5,573
7 Claims. (CL 25d-49.5)
This invention relates generally to electron optics and more particularly. to X-ray spectrographic means for analyzing materials irradiated by an electron beam having minute cross-sectional area,
Investigation of the characteristics of various materials by X-ray analysis is Well known. However', theinstant invention contemplates a unique improvement upon existing methods of X-ray analysis wherein a minute cross-sectional area of the surface of the material under observation is subjected `to irradiation by an extremely ne beam of high velocity electrons. The X-rays generated by the impingement otthe high velocity electrons uponthe minute electron irradiated material surface area are A.analyzed by means of any conventional photcgraphicor electrical X-ray spectrographic apparatus. From the wavelengths of thepcharacteristic radiation of the material, the` elements thereof may be determined., hence a point analysis of the specimen is desirab'l`e.
X-ray spectroscopes of the type described in X-rays in Theory and Experiment by Compton and Allison, may be employed to Vanalyze the X-ray radiation derived from the material under observation. The Von Laue type spectrometer, employing a zinc blonde crystal for forming a` diffraction pattern of the X-ray radiationupon a photographic plate, provides a satisfactory permanent record of the X-ray spectrographic characteristics of the material. Similarly, the Bragg type spectrometer, also described in 'the reference mentioned heretofore, employs an ionizationV chamber for indicating the X-ray refractionTi-rom a zinc blende crystal the angular relation of which is adjustable with respect to the axis of the derived X-ray radiation. Various other types of X-ray spectroscopes or X-ray spectrometers may be employed toequal advantage.
The instant invention is related to apnlicants copending U S. application, Ser. No. 505,572, led October 8, .1.943, which describes several methods of and means for electron irradiating extremely minute areas of either electron permeable or electron opaque substances. This copending application describes several methods oi and means for making a velocity analysis of electrons transmitted by or reiiected from said electron irradiated area. The instant invention contemplates means for spectrcanalyzing X-ray radiation de rived from a minute electron irradiated area of substances which may or may not be substantially opaque to electrons.
Among the objects of the invention are to provide an improved method of and means for micro- 2 scopically analyzing materials. `Another object of .the invention is to provide an improved method of and means for microscopically analyzingnia-` terals substantially opaqueto `irradiating elec- 5 trons. A further object of the invention is to provide animproved method of and means for microscopically analyzing materials by subjecting minute' areas of' said materials to high velocity electron irradiation, and spectroanalyzing X-rays generated in the vicinity of said electronic irradiation. A Further objects of theinventionjinclude improved means for electron'v irradiating minute areas of a substance to generate X-rays there.-` from and photographic X-ray spectrographic means for providing al permanentl record of the X-ray spectrographic characteristics of the said material'. Anadditional object of the invention is to provide an improved means for electron irradiating a* minute area of a material to generate Xfrays therefrom and electrical means for spec,- trcanalyzing said Xf-ray radiation. The invention will be further described` by ref-V erence to the accompanying drawing of which the single iigure is a schematic, diagram of a typical embodiment thereof.,
Referring to the drawing, an electron source I, which may comprise, for example, a thermionic cathode and an apertured anode having high 3 electron accelerating potentials therebetween, is focused by a conventional electron lens 2 toform a greatly" reduced image 3 of the electron source llj `The `image 3 is` further vfocused by means of a second electron lens 4 to form substantially a point image of the electron source l at thepoint `5 `o`n` the surfacel of `a` material 6 tcV be spectroanalyzed. It should be understood that the rst and second electron lenses 2, il, respectively, may be of either the conventional electromagnetic or electrostatic types employed in electron microscopes and similar apparatus. The electron lenses may be energized by any means known in the art.
The electron irradiation of the point 5 on the surface of the electron opaque material 6 provides X-ray radiation in the vicinity of the point 5 due to the energy released by the high velocity electrons comprising the electron beam. A portion of this X-ray radiation is intercepted. by an X-ray spectroscope 8 of any known type which will provide the desired X-ray spectroanalysis.
For the purpose of illustration, the X-ray spectroscope 8 shown in the drawing, comprises `a pair of lead collimating apertures 9, I0 for selecting an extremely minute X-ray beam for spectroanalysis. The selected X-ray radiation is applied to a crystal II, which may be composed,`
for example, of zinc blende. The crystal I I is arranged to be oriented with respect to the X-ray beam, in order that the X-rays may either be transmitted by the crystal or reflected therefrom.-
The Velocity of lthe X-rays impinging upon the crystals II will determine the refraction of the X-rays derived from the crystal. The X-ray radiation derived from the crystal may be applied to a photographic plate I2, to obtain a spectroscopic pattern characteristic of the material under observation. When employing a photographic plate in an X-ray spectroscope, of the type described, it is customary to orient the crystal so that it transmits the applied X-rays to the photographic plate.
However, if electrical indication of the X-ray characteristics is desired, an ionization chamber, not shown in the drawing, is substituted for the photographic plate I2. The X-rays are reflected from the crystal II, and the current derived from the ionization chamber is indicated in terms of the angular orientation of the crystal with respect to the axis of the applied X-rays.
Thus the invention described comprises a novel method of and means for spectroanalyzing eX- tremely minute surface areas of materials by focusing a high Velocity electron beam upon a minute area of the materialsurface, and spectroscopically analyzing X-rays generated by said electron bombardment.
I claimV as my invention:
y1. The `method of microscopically analyzing the atomic composition of amaterial comprising electron irradiating a minute cross-sectional area of said material,generating X-rays in the vicinity of said area in response to said irradiation, and spectroanalyzing said generated X-rays.
A 2. The method of microscopically analyzing the atomic composition of a material comprising generating an electron probe of minute cross-sectional area, electron irradiating said material by said electron probe, generating X-rays in the vicinity of said area in respons to vsaid irradiation, and spectroanalyzing said generated X-rays.
3. A spectroscope for analyzing the atomic composition of a material including means for supporting said material, means for electron irradiating a predetermined minute cross-sectional surface area of said material to generate X-rays in the vicinity of said irradiation,-and means for spectroanalyzing said generated X-rays.
A4 ing an electron probe of minute cross-sectional area, means for supporting an object, means for irradiating substantially only a minute surface area of said object by said electron probe to gene Y ating an electron probe of minute cross-section- 4. A spectroscope including means for generatal area., means for supporting an object, means for irradiating substantially only a minute surface area of said object by said electron probe to generate X-rays in the vicinity of said electron irradiation, and photographic means for spectroanalyzing said generated X-rays.
6. A spectroscope including means for generating an electron probe of minute cross-sectional area, means for supporting an object, means for irradiatingsaid object by said electron probe to generate X-rays in the Vicinity of said electron irradiation, and photographic means and an X-ray refracting crystal disposed intermediate said object and said photographic means for spectroanalyzing said generated X-rays.
7. A spectrometer for analyzing the atomic composition of a material including means for supporting said material, means for electron .irradiating s-ubstantially only a predetermined minute cross-sectional surface area of said material to generate X-rays in the vicinity of said irradiation, and electrical means for spectroanalyzing said generated X-rays.
. JAMES HILLIER..
REFERENCES CITED The following references are of lrecord in the iile of this paten Y UNITED STATES PATENTSV Number Name Date 2,079,900 Cohn May 11, 1937 2,131,536 Knoll et al Sept. 27,1938 2,281,325 Ramo Apr. 28, 1942 1,971,277 Rupp Aug. 21, 1934 2,341,108 McLachlan Feb. 8, 1944 2,025,488 Yap Dec. 24, 1935 2,257,774 Von Ardenne Oct. 7, 1941 1,596,305 Rentschler Aug. 17, 1926 1,997,356 Bryant Apr. 9,1935 2,197,033 Diels Apr. 16,1940 2,274,215 Ruska Feb. 24,1942
FOREIGN PATENTS Number Country Date 86,274 Swiss Aug. 16, 1920