DE2029141A1 - Fluorescent analysis radiation source for the simultaneous generation of fluorescent, soft X-ray radiation and a secondary electron emission characteristic of the analysis sample - Google Patents

Description

B. I. BO POMT SB NEMORS AMD COMPAaY 10th and Market Streets, Wilklngton, Delaware 19898, V.St.A.

Fluorescent analysis radiation source for simultaneous Generation of fluorescent, soft X-rays and one for the analysis sample that is characteristic

Electron emission

You spectral analysis of cheap compounds so far to obtain (1) total information by means of a Usual X-ray analysis and more recently (2) Electron Spectroscopy (ESCA) for cheap analysis limits which provides information about the atomic and molecular structure up to a depth of usually £ 100 and also information regarding the surface muatandea, d. h · of construction and binding. There was no lazy time Time required than for a single analysis, but vas

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is even less, it was not possible to do the same Area of the sample during both inaljeen under the same To investigate environmental conditions, which is disadvantageous.

The invention represents a powerful source of radiation x for the simultaneous emission of both fluorescent, soft X-rays as well as secondary electron emissions, whereby both types of analysis are available on the same sample area and under the same Examination conditions can be carried out

The invention relates to an Aiialysis radiation source for Simultaneous generation of fluorescent, soft X-rays and secondary electron emissions, which for the examined sample are characteristic · The invention is characterized by the combination of an evacuated Housing, a cooled metallic X-ray anode plate provided with a central opening, which has a concave rotationally symmetrical electron impact surface, a cooled metallic cathode block, which is equipped with an annular shielding ring in the form of an upside-down xrog, which is arranged coaxially opposite the opening of the anode plate, the shielding ring and the cathode block opposite the anode impact surface closely adjacent, but out of contact with the same, with a cooled, metallic sample holder, which is connected to the cathode block and has a flat sample holding surface, the facing the anode plate and coaxial with the opening and to the shielding ring is arranged in a position in which primary X-ray emission from a ring area of the Anode impact area is added, with a for high Emission of a suitable cathode filament, which is provided with a heating device to generate electrons,

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which is arranged opposite the specimen holder behind the shielding ring, with an electrical voltage source » which is sufficient to excite τοη X-rays and which is located in the anode plate and the cathode block, and with a device that has an electroetatiechea Fuhrunga- and condenser field as well as a straight line for electrons The field between the opening and the sample holder is maintained in order to limit the kinetic energy of the secondary electrons which enter and exit the opening this way hurry under a given speed "-" Suppress level emission su

A particularly sweeping analysis standard uses the erfindungagemasae radiation source with an improved Spectrograph in accordance with TJSA-Patantaehrift 3 418 466 der same applicant, which arrangement allows an X-ray analysis to be carried out, while at the same time a conventional one Arrangement for studying the energy of the secondary electrons after their selective suppression within the electron source is provided in order to make the analysis sharper.

Fluorescent X-ray radiation sources of known design have only a low inherent brightness compared to radiation sources excited directly with electrons. Me radiation sources use an IQ Radiation generator, which bombardes a sample, thereby stimulating a characteristic X-ray fluorescence will. At the same time, a number of secondary electron emissions are generated, which are referred to as photoelectrons, Auger electrons, splitting electrons and in a similar way.

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In a common, well-known X-ray analysis device is the number of S & secondary electrons that oppose the Diffuse detector system, negligibly small. However, if a high electron flow is generated and in sighting the X-ray beam directed, so can the secondary Electron emission obscures the X-ray signal so that suppression elements must be used to get a useful X-ray analysis. It is an important feature of the radiation source according to the invention that as a result of the special arrangement and Electron focusing the secondary electrons are used to contribute to the overall information about the sample, with the suppression element being the most important Component of the radiation source itself is used.

Fig. 1 shows a schematic elevation in section of a preferred embodiment of the invention Radiation source including the equipotentiallicien between anode and cathode as well as the adjacent electron delay element, together with the path boundaries of the incident electron flow,.

Fig. 2 shows a partially schematic, sectional elevation of the cathode arrangement, the sample holder and the associated cooling device for an arrangement which is constructed similarly to that of FIG. 1, apart from that the anode is grounded and the cathode is kept at a negative potential,

FIG. 3 shows a schematic elevation of the radiation source according to the invention according to FIG. 1, the evacuated Housing is omitted, with the associated analysis device for the fluorescent, soft X-ray radiation

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and the secondary electron emission outputs of the gate direction and

Fig. 4 shows a graphical representation of a tuning fork drive signal, the coordinates being given by the voltage and the time are displayed, and a typical detected signal which was obtained during the operation of the analysis device for the fluorescent, soft X-rays shown in Pig · 3.

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According to SIg. 1, in a preferred embodiment of the radiation source according to the invention, a metallic, cylindrical anode 10 is used, which is water-cooled by means of a device not shown, and which is an internal, conical anode. X-ray anode surface 10a, which is directed towards the metallic cathode block 11, which, as will be explained in FIG. 2 below, is water-cooled. The anode 10 has a central bore which has an opening 10b for exciting the analysis radiation. forms and the cathode block is provided with an upwardly projecting flat metallic sample holder 12 11 1st, which is arranged coaxially with respect to the UFF ä nung.lOb and opposite this usually at a distance of i, 9 has cm "wherein the sample holder of the anode 10 facing . The upper circumference of the cathode block is designed as a conical surface which corresponds to the anode cone and is arranged below it. The entire arrangement is thus rotationally symmetrical to the vertical axis AA.

The cathode filament 13 consists of a stiff, electron-donating wire with a circular cross-section, which is wound in a helical manner, for example one

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Wolf raadraht, which is coaxial with the opening 10b and the sample holder 12, the filament 13 being held in a sweeping manner by the cathode block 11, as will subsequently be described in connection with FIG. 2; however, the filament can be held independently if necessary. The cathode filament 13 is with a conventional device for generating electrons, for example a voltage source or a heating device, which are not shown in FIG.

A shielding ring 20 in the form of an inverted trough is two kilometers radially inside the circumferential Arranged portion of the cathode and is located above the cathode filament 13 »to thereby the anode 10 opposite shielding from an immediate Versehmetsimg by a tungsten evaporation from the filament.

Inside the opening 10b is a downwardly directed Metallic cap 16 provided with an opening is arranged, the opening 16a of which lies coaxial with the axis of symmetry A-A. A metallic ring electrode 14 which functions as a guide condenser and delay tube for the sletetronea and usually 6.25 mm in the lungs with an opening diameter of 2.04 mm is arranged coaxially .within the cap 16 and is isolated from it by an Ieolierriag 19 »wherein the Electrode 14 thus forms the analysis radiation output of the radiation source. The ring electrode 14 is at its inward focus on the located end with a naoft outward-facing » the chamfer 14a provided.

For reasons of electrical shielding and to simplify the electrical connections, the Anode 10 to a positive potential of usually

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10 kV, while the cathode is grounded. However can If necessary, the anode according to FIG. 2 can be grounded and the cathode must be kept at a suitable, negative voltage potential between these elements in order to make the tom Cathode filament 13 delivered electrodes accordingly. speed up su.

According to FIG. 1, the electrical voltage source 18 has two

independently adjustable ranges 18a and 18b

which via terminals of opposite polarity and * conductors 18c are both grounded, the positive inhibiting of section 18a via line I8d with anode 10 and the negative terminal of section 18b over the line 18e is connected to the hanging electrode 14 ·. This allows the number of the potential carried by the ring electrode 14- » in order to maintain a field »which those who are close to described »wipe the anode source and the cathode is directed in the opposite direction · Bas field of the ring electrode is represented by field lines f, which on semiconductors can be obtained on the recording PC, with the field a relatively strong electrostatic guide and

Condenser effect and an electron recovery effect -

on the secondary electron emission of the radiation source ' exercises

The electron flow directed from the cathode filament 13 to the anode surface 10a is indicated by the crescent-shaped cross-sectional section a indicated by dashed lines in FIG * wa4 - ιΗ »« »υι? η rmpi ^ In the representation according to FIG. 1, the electron flux is restricted to a region which is essentially at right angles to

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the equipotenti all earthen e lying within the space are present between anode and cathode, with typical photential values of the most important lines being entered, as they are supplied by the radiation source on semiconducting recording paper.

The accelerated electron flow strikes a substantially ring-shaped surface b of the anode surface 10a and generates a primary X-ray radiation substantially uniformly around the entire 360 ° circumference, which is directed against the specimen holding surface 12a of the sample holder 12 is directed within the boundary surfaces of a cross section which is shown in FIG fig · 1 is denoted by d · Therefore, one is on the face 12a attached sample exposed to primary X-ray radiation and emits a fluorescent «soft X-ray radiation, which is characteristic of the composition of the Sample is and is a rich source of secondary electrons, both together the excitatory. Analysis radiation represent the radiation source according to the invention. Of the Secondary electron shell this analysis radiation is through the Aüoeden-cathode potential difference accelerates and it a relatively concentrated radiation is present along the axis A-A of the detector system described below. The opening 16a serves to collimate the discharged secondary electron output.

The field f, which is directed opposite to the field e is, allows an adjustable delay of the secondary electron emission, so that that portion of the etaission that is below a predetermined end-side speed level, can be suppressed, while the remaining part passes through the ring electrode 14 at a relatively low top speed.

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The effect of the ring electrode 14 as a guide and condenser is achieved by the influence that the electrode has on the electrostatic field that is present between the electrode and the lower portion of the cap 16, that is, the equipotential lines f between these two elements are primarily line determined by the ratio of the diameters of the * elements and their distance, as well as by the potential difference between them. The potential gradients are arranged in such a way that the electrons next entering the field move into a diverging path until they experience a condenser effect together with a delay effect when they enter the upper half of the delay field before they exit the radiation source.

3 shows a preferred arrangement for the simultaneous analysis of a sample using both the fluorescent X-ray radiation and the secondary electron emission, in which the radiation source 50 according to the invention can be used hemispherical electrostatic deflector ä tables 28 outputs comprising the two ball elements shown with the specified potentials. A common design of the deflection device is given in the article "Electron Monochromator Design," Eeview of Scientific Instruments, Vol. 27 (January 1967) pages 103-111. However, other types can also be used, for example a type using a Wien filter and described by Boersch, H., Geiger, J. and Hellwig, H., in Physics letters, Vol. 3, No. 2 (1962), pages 64 to 66 is described. The deflector 28 isolates the excitatory secondary electron emission by

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this length of a path g is guided to a usual Detector 31 leads. Essentially all of the secondary electron emission that occurs above a given speed lies, strikes the walls of the deflector 28, so that the part of the Ea & ssion with a predetermined Speed delivered at outlet 29, represents a measure for the characteristic data of the examined sample.

The detector 31 has a collector 31a on which the secondary electron emission emerging from the outlet 29 impinges, which forms the input to a fimction amplifier 31b, which is provided with a HO-Hetsswerk siir negative I-kick coupling, with the amplifier model 301 across the board from Analog Devices Corporation can be used. The overall arrangement is arranged within an electrically grounded, evacuated housing, with an output signal being supplied via a line 31c to an oscilloscope shown in the figure.

At the same time, the fluorescent Bontgena radiation reaches caused by the electrostatic field of Abl@nkvprrieh.tung 28 remains completely unaffected «by an opening 30 that is then arranged on the singing electrode 14 and impinges on an X-ray diffusion element 26, wherein this trajectory is shown by the dashed line h.

As already mentioned above, the fluorescent one becomes X-rays analyzed through the Torriehtang according to the US patent 3 418 466 of the same applicant " This device has a detector 2? on, which is on a focussing, never-shown Bewland circle is arranged on which preselected! X-ray radiation picks up, which is reflected by the scattering luminaire 26,

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the device preferably incorporating all new features Stiiiiigabel visual vibration generator 32, which in a Nadeliochoffnung 34 swings transversely to the Höntgenetstrahlbündel supplied by the radiation source 30, if the prongs 33 move back and forth The entire door direction is arranged within an evacuated housing (not shown)

As is described in US Pat. No. 3,418,466, the X-ray beam hitting the scattering element 26 is prompted to pass through the critical angle, this being done automatically by the pinhole, which typically moves the radiation by about Deflects 1 ° if a streak lea ent with a length of 12.7 to 25.4 mm is used · Thereby the detector 27 picks up reflected X-rays of alternating strength as a result of the tuning fork oscillation, so that the detector generates an electrical electrical current signal whose size is proportional to the concentration of the element in the sample, which fluoresces with a characteristic wavelength. The detector 27 can be formed by an electron multiplier having an open window, the output of which is connected to an amplifier (not shown) and a band filter (not shown) and is made visible on an ossilloscope (also not shown). A special part of the system described is that the phase of the detector signal can be continuously controlled by triggering the oscilloscope via line 32a with the tuning fork drive signal input via line 32b.

A second embodiment of the radiation source according to the invention is only in Pig with regard to the cathode arrangement. 2 dar-

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placed, with the arrangement for the cooling, which also is used in the embodiment of FIG. 1, is specified here in detail. "

In this arrangement, the anode is kept at ground potential, while the cathode 11 * has a negative potential, for example -10 kV negative X-ray excitation voltage. A cut-off ring 20 * is integral with the cathode at an angle of inclination of approximately 30 ° to the horizontal formed and protrudes beyond the cathode filament 13 ', which surrounds a sample holder 12' and which by a A number of electrically conductive cantilever brackets are supported, two of which, 13a and 13b, are shown are whose radially outer ends are attached to the cathode. The holder 13a is electrical from the cathode isolated and is in the circuit with the feed line 38, which is also isolated by a sleeve 38a from the cathode is, and which supplies the energy for the filament 13 * to generate the electron flow .. A not shown Current return is also connected to the cathode.

The underside of the holder 12 * has an axial recess, and likewise the. middle section 39 of the cathode, whereby a chamber for cooling water is formed, which over Metellrohre 40 and 41 is circulated through the assembly. These pipes are together with the line 38 through holes a metal cap 42, which is arranged in a protruding insulating sleeve 43, which is the insulating sleeve surrounded by an insulating ring 44, which has a surface flashover prevented. The insulating sleeve 43 is at its upper end by attachment to a grounded metal flange 45 attached, the part of the evacuated housing is.

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The cooling water pipes 40 and 41 are both at high potential and are taken from the water pipe system by pipe sections made of polymeric plastic, e.g. polyethylene, .isolated, which are expediently 22.6 m long and not shown, the drill 41 with a clampable electrical feed line 46 is provided.

During operation, the equipotential lines e (Fig. 1) have a relatively constant gradient, as is the case with the essentially parallel course of the lines with respect to the anode surfaces and sample support surfaces according to Fig. 1 can be seen. Furthermore, the electron orbits are in accordance with the laws of the electric field of the primary electron flow a is arranged almost at right angles to the equipotential lines e, as long as the initial velocities compared to those resulting from the energy gain Velocities obtained from the electric field are small, as is the case with the specified arrangement. Under these circumstances, it becomes a typical X-ray impact surface a length b, which can be about 6.35 mm, coated, whereby a primary X-ray radiation is delivered over a full 360 ° angle, so that a very even distribution of radiation on the surface 12a attached sample is present.

The emission of the fluorescent, characteristic, soft X-rays and the secondary electrons generated by excitation of the sample occurs arbitrarily, whereby those X-rays passing up through opening 16a get through the needle hole 34, which is moved back and forth transversely in the beam path h, to an apparent point source «The axially parallel, secondary electrons are optionally decelerated and from the upper end

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of the ring electrode 14 "guided" into the deflection device 28 and analyzed in the manner described above.

Since the sample is continuously cooled on the surface 12a, the sample substance is caused by the incident X-rays not destroyed. As a result of the geometry of the radiation source and the special structure, equilateral exceeds and the relative position of their individual components determines the strength of the primary X-ray radiation effective on the surface 12a noticeably those values «those previously with fluorescent Radiation sources for the generation of soft X-rays were obtained.

example 1

The theoretical, critical angle in charcoal for fluorescent X-rays that strikes a paraffin mirror, which is used as a scattering element 26 according to FIG. 3, is approximately 3 ° 50 ' Angle is a characteristic signal for carbon, since for Q <O _c the entire radiation is reflected, while it is for 0> 0. into the paraffin

entry.

To test whether a critical angle for a graphite sample could be determined, the paraffin level (26) was originally set to 5 °. It became a small signal the same frequency as the tuning fork vibration generator 32, which, however, was 180 ° out of phase with the drive signal. The angle of incidence was then increased to 4 · ° by moving the mirror (26) lengthways of the Bowland circle was shifted slightly and the The process was repeated. In this case a strong

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kes, periodic signal obtained in phase with the drive signal, as shown in phantom in Fig. 4-. at a further increase in the angle of incidence to 5 ° »returns the signal to its previous state; h », it becomes small and is 180 ° out of phase with the drive signal This confirms the existence of a critical angle, which is sufficiently pronounced for the analysis to be based on it.

The graphite sample was replaced with an aluminum sample f

and all previous measurements were repeated. There was no angle of incidence within the angular range »Wipe 3 ° - 5 ° a signal that is in phase is determined.

When the graphite sample was used again, a strong signal in phase, which is characteristic of carbon, was immediately obtained.

The smaller, out of phase signal can by changing the stereo angle of the mirror

(26) the incident beam as a puncture of the incidence \

angles are explained. · ■

As a result of the little house and fluctuations in the emission flow there are also several modulation signals. However, these effects can be achieved by reducing the amplitude of the vibration can be reduced by the critical angle, as well as by stabilizing the filament current and of the emission current.

las * presence of nitrogen in another sample was established similarly confirmed, taking an I & thium fluoride level was used, which has a critical angle

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from approximate 4 ⁰ JQ ¹ resulted in «as the theory predicted.

Example 2

This example checks the adaptability of the inventive radiation source as an analysis device for use in. Secondary electron spectroscopy · « ■

First of all, it is known that an unknown sample can be determined by the energy analysis of the K, L, or M «electrons ejected from their orbits in the atoms that form the part of the sample irradiated with X-rays. A sample hit by high-energy X-rays also provides two different types of electrons, namely photoelectrons and Auger electrons. For example, a sample containing oxygen was irradiated by A1Ea X-rays with an energy of 14θ7 eV. The X-rays can eject a K electron from the oxygen, whereby the K excitation p: »tenti & l at 532e? lies. The kinetic energy of the electron emitted is thus 955 # V "which represents the difference between the energy of the electron pushed out and the energy of the incident X-rays" Photon old 52 $ e ^v exits (where the energy difference din is the bindon energy of the L-shell of 7eY). There is an approximate probability of 99 %% that the photon will be internally absorbed to expel a second electron from the L-shell and this electron is commonly known as the Auger electron, which has a kinetic energy of 518®Y.

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With an essentially monochromatic primary X-ray radiation the energy of both the photoelectron and the Auger electron is a parameter for the emitting Element and its bond state

To determine the energy difference of the electrons that were emitted by elements in the second row of the periodic table, the subsequent experiment) which serves performed using delay fields ^ became. . '

A hanging electrode 14 to achieve a retardation field was in the fluorescent radiation source after £ ig. 1 arranged and connected to an adjustable negative supply voltage 18. The diameter of the access opening of the ring electrode 14 was 2.03 mm and the electrode was friction fit within an opening 10b in a disc made of AIgQ *, the diameter of which is about 9.5 mm. The radiation source was operated with an anode-cathode voltage of 6 kV.

In a preliminary experiment, each of the four J. The following samples determine the voltage at the ring electrode 14, which leads to the reduction of the electron signal a minimum value (i.e. the reverse voltage) was required, determined. The samples consisted of: (1) polypropylene, (2) boron nitride, (3) quartz, and (4) rock salt and contained Each of the elements (1) carbon, (2) nitrogen, (3) Oxygen and (4) sodium. The results are in the following Table listed:

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sample element C. on Polypropy F. len 0 Boron nitride Ha Quars Rock salt

(willrorlieh © Units)

-2.7 C- 0.1)

-3.0 (£ O / l) ^ 520 -3.2 (i 0.1)

-3 »8. (t 0.1)

The specified error fairies relate only to the Meter reading, which as a result of difficulty the determination of an exact voltage point a occurred, because the intensity with sun & hsender negative tension falls off.

The lower the negative SperrspanniHig is required ", the ®τ to a sufficient delay electrons, to keep them within the Ctrahltmgsquelle, the lower the electron energy." From the above data it can be seen that the Auger energy, which gradually increases from iron carbon to sodium, corresponds to the corresponding increase in the blocking voltage. It is therefore concluded that the reduction in the electron signal is always caused by the trapping of the Auger electrons which is characteristic of each of the four important elements.

The anode arrangement used in the investigation has a conical Sntgenstrablen anode surface 10a; however, other arrangements, for example a spherical, parabolic or similar arrangements can generally be used in the same way, and in some cases even are more effective · In addition, sieh © ine gross® Mssahl electrical circuits and MM devices for cathode

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1*

and anode, so that there are no restrictions in this regard *

There is a wide variety of cathode filament arrangements suitable ^ including wire elements, dia in close-fitting wind cmgea. in flat, horizontal or vertical screws are arranged to form a high electron emission area.

In addition, the inventive radiation source " can advantageously only be used as a secondary electron radiation source, and was completely separate from the Use as an associated X-ray source described above

It is obvious that further changes of the invention are possible and these are included within the scope of the following claims by the invention.

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Claims (2)

2029H1 ED-249 "^ ~ June 12th Claims Fluorescent analysis radiation sources for simultaneous Generation of fluorescent, soft X-rays and a secondary electron emission characteristic of the analyzed sample by the combination of a cooled, metallic X-ray radiation anode plate provided with a central opening (10), which has a concave, rotationally symmetrical impact surface (10a) for the electrons, with a cooled, metallic one Cathode block (11), which is provided with a shielding ring (20) in the form of an inverted (Crogs, which is arranged coaxially opposite the opening (10b) of the anode plate, the shielding ring and the cathode block close to the impact surface, but out of contact with it, with a cooled, metallic sample holder (12), which is attached to the cathode block and a flat sample mounting surface (12a), which lies opposite the anode plate and is coaxial to said opening and is arranged in relation to the shielding ring in such a way that it emerges from the ring area of the anode surface Absorbs X-rays, with a cathode filament (15) for high emission, which with an electron generating heating device is provided, which is concentric opposite the sample holder behind the shielding ring (20) is located, with an electrical voltage source (18) with sufficient for X-ray excitation Large, which is connected between anode plate and cathode block, and with a device (14-) to maintain an electrostatic lead and condenser field as well as an electron delay - 20 - 009852/1942 field s between the mentioned opening and the sample carrier, the kinetic energy of the. Secondary electrons too limit that emerge from the opening and thereby suppress any emission that is below the specified speed level 2. Fluorescent analysis radiation source according to claim 1, characterized in that the rotationally symmetrical electron impact surface aas- | is formed 3 · Fluorescent analysis beam source according to address 1 or 2, characterized in that the cathode filament surface for high emission from a helical wound element. - 21 -00Θ852 / 19Α2 L e r s e j t e