US3612861A - Method of and apparatus for the automatic refocusing of x-ray spectrometers - Google Patents

Method of and apparatus for the automatic refocusing of x-ray spectrometers Download PDF

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Publication number
US3612861A
US3612861A US769511A US3612861DA US3612861A US 3612861 A US3612861 A US 3612861A US 769511 A US769511 A US 769511A US 3612861D A US3612861D A US 3612861DA US 3612861 A US3612861 A US 3612861A
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voltage
electron beam
crystal
improvement
sawtooth
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US769511A
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Gerhard Dorfler
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/20—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
    • G01N23/207—Diffractometry using detectors, e.g. using a probe in a central position and one or more displaceable detectors in circumferential positions
    • G01N23/2076—Diffractometry using detectors, e.g. using a probe in a central position and one or more displaceable detectors in circumferential positions for spectrometry, i.e. using an analysing crystal, e.g. for measuring X-ray fluorescence spectrum of a sample with wavelength-dispersion, i.e. WDXFS

Definitions

  • the invention relates to a method of and apparatus for the automatic refocusing of X-ray spectrometers in which the crystal axis, the detector and the X-ray source (formed by the scanning electron beam of a microsonde at the points of impact on the surface of the sample), are disposed on a Rowland circle.
  • the electron beam controlled by deflecting voltages, scans surface of the sample lineby-line; and the x-rays, generated by the electron beam, are reflected from the crystal into the detector and, further, the crystal axis is rotated in such a manner that the angle formed by the line connecting the impact point of the electron beam with the crystal axis and the line normal to the latter is constant for all positions of the electron beam with respect to the sample.
  • the effect is geometrical which may be compensated by resetting the angular position of the goniometer (the mechanical device in the spectrometer which carries and moves the defracting crystal and the X-ray detector). The resetting is automatically and independently performed for he individual spectrometers secured to the microsonde.
  • FIG. 1 is a perspective schematic view of parts of the preferred apparatus showing the principle of operation
  • FIG. 2 is a schematic diagram showing control means incorporated in the preferred embodiment.
  • a sample 1 is scanned line-by-line 0 with an electron beam 2.
  • the electron beam 2 may consecutively travel along perpendicular paths.
  • the focusing point F of the electron beam 2 on the sample I forms an X-ray source which travels with the scanning beam and which emits X-rays whose wavelength is measured by means of an X-ray spectrometer.
  • the spectrometer used for this purpose is of the fully focusing type for which the Bragg condition applies and in which the X-ray source (the focusing point F), the detector 3 and the crystal 4 lie on the Rowland circle R, the plane of which is normal to the surface of the sample 1.
  • the crystal 4 is arranged in such a manner on a goniometer head 5 that the crystal axis A and two edge faces of crystal 4 are disposed normal to the plane of the Rowland circle R and intersect or almost intersect the area within the Rowland circle.
  • the other two edge faces of the crystal 4 extend in a plane parallel to the plane of the Rowland circle.
  • the crystal axis A thus extends practically parallel to the surface of the sample I so that during a scanning of the surface of sample I in a direction parallelto the crystal axis A, the angle 8 which is formed, on the one hand, by the line B connecting the focusing point F with the crystal axis A and, on the other hand, the line N normal to A, remains constant.
  • the angle Y complementing the angle ,3 to is the Bragg-angle which, in the aforementioned scanning process, also remains constant.
  • the Bragg-angle Y changes during a scanning of the sample I in a direction normal to the scanning just described.
  • the direction of such scanning coincides with one chord of the Rowland circle R so that the angle a which is formed between the direction of motion and the line connecting the travelling focusing point F with the crystal axis A varies. It is a result of this angular variation that, for example, in a constant position of crystal 4--i.e., the Bragg-angle is set to a characteristic X-ray line-the scanning of the sample 1 yields erroneous data (concentration of a certain element in the entire sample I).
  • the intensity (count rate) of the X-ray radiation decreases since, due to the aforenoted change in angle, an intensity is measured which is outside the range of the maximum of a line which, in an ideal case, is a bell-shaped ascending curve.
  • the line intensity is measured as a function of the Bragg-angle. Relating this to the entire sample I, a concentration of a certain substance would be simulated which lies under the real value.
  • this erroneous measuring is eliminated by rotating the crystal axis A and thus the crystal 4 synchronously with the change in angle occurring during the scanning in a chordal direction.
  • This synchronous movement proceeds in the direction of cancelling the change in angle.
  • the rotational movements of the crystal axis A in the direction of the line connecting the crystal axis A with the focusing point F.
  • This translational motion is not essential to the solution of the problem.
  • a synchronous rotational movement of the crystal 4 alone is sufficient.
  • FIG. 1 As seen, the crystal 4 is secured to a goniometer head 5 to which there is affixed a worm wheel 6 meshing with worm 7.
  • a sawtooth generator 11 which delivers a voltage U, for the deflection of the electron beam 2 in the direction of a chord of the Rowland circle R, also delivers the same varying DC voltage U, to one input terminal of differential amplifier 12.
  • a DC voltage U taken from a potentiometer 13 by means of a slider 14.
  • the potentiometer 13 is connected to a DC voltage source V.
  • the two voltages U, and U are adjusted with respect to one another in such a manner that for extreme or peak values (maximum or minimum) of the voltage U, the two voltages U, and U, are in balance at the input terminals of the differential amplifier 12. Consequently, in such cases the voltage at the output terminal G of the differential amplifier 12 is zero.
  • the maxima and minima of the sawtooth voltage U correspond to the maximum excursions of electron beam 2 on sample 1. This then means that for each peak value of the sawtooth voltage U, the angular deviation from the Bragg-angle Y is at its maximum if the angular position of crystal 4 is fixed.
  • the crystal 4 in order to correct the aforenoted angular deviation, the crystal 4, while maintaining a constant position with respect to the line connecting the travelling focusing point F with the crystal axis A, has to be rotated clockwise or counterclockwise into extreme positions. It is to be noted that in linear spectrometers a translational movement in the direction of said connecting line is superimposed on the rotational movements. Such translational movement, however, does not give rise to additional errors.
  • the measuring bridge (not shown) in difierential amplifier 12 becomes unbalanced so that the latter supplies a voltage AU (proportional to the voltage difference U,U at the input terminals of amplifier 12) to the electromotor 10.
  • the electromotor 10 rotates in a direction depending upon the voltage polarity MU and moves the slider 14 of the potentiometer 13 as well as the goniometer head 5 through the worm 7 of the shaft 8.
  • the shaft 8 is disconnected from the electromotor 10 by opening the clutch 9 and the maximum intensity of the selected X-ray line in one extreme position of the electron beam 2 is manually adjusted at the goniometer. Further, the slider 14 of the potentiometer 13 is set to zero. Thereafter, the electromotor l0 and the goniometer head 5 are connected and the electron beam 2 is brought into its other extreme position by changing the setting at the sawtooth generator 11 accordingly. At the same time, the slider 14 rotates into a determined position between the two terminals of the potentiometer 13. Thus, the slider 14 and the crystal 4 on the goniometer head 5 have rotated through a determined angle. The intensity of the X-ray line measured in this position in most cases does not correspond to the maximum of the X-ray line.
  • the required rotation of the goniometer head is set by means of an appropriate adjustment of the variable voltage source V.
  • Such an arrangement may be made purely empirically or may be based on tabulated data depending upon the Bragg-angle Y, the
  • the sawtooth voltage U required for the control of the deflection of electron beam 2 may be used as a second, control voltage generated in the same sawtooth generator 11 and synchronized with the deflecting voltage U,. Further, the sawtooth voltage U for the differential amplifier 12 may be generated independent of the generator that produces the deflecting voltage for the electron beam 2.
  • an X-ray spectrometer of the type having an X-ray source, a diffracting crystal and a detector all lying on a Rowland circle, said X-ray source being formed by an electron beam at the point of impact on the surface of a sample being scanned by said beam, the method of automatically refocusing said spectrometer comprising the following steps:
  • a method as defined in claim 2, wherein said voltage for energizing said means is derived from a comparison of said sawtooth voltage with a DC voltage which is a function of the angular position of said crystal.
  • an X-ray spectrometer of the type having an X-ray source, a diffracting crystal and a detector, all lying in a Rowland circle, said X-ray source being formed by an electron beam at the point of impact on the surface of a sample being scanned by said electron beam, the improvement for automatically refocusing said spectrometer, comprising,
  • A. sawtooth voltage generator means for producing a first, sawtooth voltage utilized to effect a deflection of said electron beam in the direction of a chord of said Rowland circle,
  • D. differential amplifier having 1. a first input terminal receiving said sawtooth voltage
  • said potentiometer includes a slider, said electric motor is connected to said slider to vary said second DC voltage as a function of the angular position thereof.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Dispersion Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US769511A 1967-10-24 1968-10-22 Method of and apparatus for the automatic refocusing of x-ray spectrometers Expired - Lifetime US3612861A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT958367A AT289428B (de) 1967-10-24 1967-10-24 Einrichtung zur automatischen Fokussierung von Röntgenspektrometern für Elektronenstrahl-Mikrosonden

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US3612861A true US3612861A (en) 1971-10-12

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US769511A Expired - Lifetime US3612861A (en) 1967-10-24 1968-10-22 Method of and apparatus for the automatic refocusing of x-ray spectrometers

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US (1) US3612861A (de)
AT (1) AT289428B (de)
CH (1) CH485217A (de)
DE (1) DE1801656A1 (de)
FR (1) FR1589853A (de)
GB (1) GB1236987A (de)
NL (1) NL6815217A (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3898455A (en) * 1973-11-12 1975-08-05 Jr Thomas C Furnas X-ray monochromatic and focusing system
US4028547A (en) * 1975-06-30 1977-06-07 Bell Telephone Laboratories, Incorporated X-ray photolithography
US4697080A (en) * 1986-01-06 1987-09-29 The United States Of America As Represented By The United States Department Of Energy Analysis with electron microscope of multielement samples using pure element standards
US20110188631A1 (en) * 2010-02-01 2011-08-04 P. N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI) X-ray spectrometer
WO2025006670A1 (en) * 2023-06-27 2025-01-02 University Of Washington Method of operating a spectrometer

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1030042A (en) * 1963-04-25 1966-05-18 Cie D Applic Mecaniques A L El Improvements in or relating to microanalysers

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1030042A (en) * 1963-04-25 1966-05-18 Cie D Applic Mecaniques A L El Improvements in or relating to microanalysers

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3898455A (en) * 1973-11-12 1975-08-05 Jr Thomas C Furnas X-ray monochromatic and focusing system
US4028547A (en) * 1975-06-30 1977-06-07 Bell Telephone Laboratories, Incorporated X-ray photolithography
US4697080A (en) * 1986-01-06 1987-09-29 The United States Of America As Represented By The United States Department Of Energy Analysis with electron microscope of multielement samples using pure element standards
US20110188631A1 (en) * 2010-02-01 2011-08-04 P. N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI) X-ray spectrometer
US8675816B2 (en) * 2010-02-01 2014-03-18 P. N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI) X-ray spectrometer
WO2025006670A1 (en) * 2023-06-27 2025-01-02 University Of Washington Method of operating a spectrometer

Also Published As

Publication number Publication date
DE1801656B2 (de) 1970-09-17
AT289428B (de) 1971-04-26
NL6815217A (de) 1969-04-28
FR1589853A (de) 1970-04-06
GB1236987A (en) 1971-06-23
DE1801656A1 (de) 1969-06-26
CH485217A (de) 1970-01-31

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