DE2222339A1 - Device for spectroscopy with charged particles - Google Patents

Description

Patent attorneys

Dr.-Ing. Wilhelm Reiche! DipL-Ing. Wolfgang Esichel

6 Frankfurt a. M. 1

Parksiraßel 3

7064

ASSOCIATED ELECTRICAL INDUSTRIES LIMITED, London, England

Device for spectroscopy with charged particles.

In the older application P 21 05 805.9. iat a device for electron spectroscopy has been proposed for the chemical analysis of a sample, with a radiation source irradiating the sample, The electrons are released from the sample, using an energy analyzer, which determines the electrons depending on their Able to deflect energy to different degrees, and with a device that detects the deflected electrons, the electrons Before entering the analyzer, they go through an electron-optical treatment device, which is operated optionally can be, either in such a way that the electrons are delayed before entering the analyzer or in such a way that the Electrons are essentially not delayed before entering the analyzer. ''.

In one operating mode of the older device, the sample is with a fine radiation probe, called a "microprobe", to cause electrons to be irradiated only from a small one Area of the sample to be sent. The energy analysis of the

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Electron then provides information about the chemical Composition in this small area of the sample.

The present invention is based on the object of a device for spectroscopy with charged particles, electrons or ions, which allows the analysis of charged particles from a small area of a sample without that a fine radiation probe must be used for this.

The invention relates to an apparatus for spectroscopy with charged particles for the chemical analysis of a sample, the is equipped with means for irradiating an extended area of the sample to release charged particles from the entire extended area, with a focusing device for charged particles, which together with the charged particles form an image of the extended area in an image plane generated, with a perforated plate or aperture plate arranged in the image plane, which allows the charged Particles other than those emitted from a small area of the extended area, and with an energy analyzer for analyzing the energy of the particles that have passed through the pinhole.

In this ^T, 7eise the invention realizes a "virtual micro-probe" as analyzed as the device only those charged particles which originate from a small region of the sample, so that the effect is the same as when the sample is irradiated with a fine radiation probe would to release charged particles only in the irradiated small area. The invention can therefore be advantageously used in cases in which X-rays are to be used for irradiating the prob o, since X-rays are difficult to achieve

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focus and therefore difficult to use a microprobe can be bundled.

Preferably, the focusing device of the invention is operated in such a way that the image is compared to the sample is increased by a factor which is substantially greater than one. This enables a very small area to analyze the sample. In a particular device according to the invention, the focusing device in the Operated in such a way that the particles are decelerated so that they enter the analyzer with less energy than that which they had when released from the sample. The energy of the particles as they pass through the analyzer is therefore degraded. This enables the analyzer to have and / or greater resolution that a higher magnification is used in order to achieve a higher sensitivity. The focusing device in this use advantageously comprises at least two lens elements which are electrically isolated from one another and through which the im Operation the particles pass through one after the other, as well as means for applying corresponding potentials to these lens elements.

In another particular device according to the invention, the focusing device can be operated in such a way that the particles are essentially not delayed before entering the analyzer. Such a device can be used if the particles emitted by the sample are all low in energy and a delay is therefore not desired, In this case, the focusing device expediently comprises at least three partial lenses that are electrically isolated from one another, through which the particles pass one after the other during operation, so / io means for applying corresponding potentials to them Partial lenses.

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In a preferred device according to the invention, the focusing device can optionally be operated in two ways in which they either retard or substantially retard the particles not delayed before they enter the analyzer. The focusing device is preferably designed in such a way that between the first operating mode, in which the particles are decelerated, and the second operating mode, in which the particles are essentially not delayed merely by changing the electrical connections in the Device can be switched without changing the mechanical arrangement of the device, and preferably includes the focusing · device at least four partial lenses, electrically isolated from one another, through which, during operation, the particles are successively run through, as well as means for applying corresponding potentials to these partial lenses.

Various embodiments of the device of the invention are described below with reference to the drawing. In this demonstrate

Pig. 1 is a schematic representation of a device for electron spectroscopy for chemical analysis of a sample _t which is adapted for a first mode of operation;

Pi.g 2 another operating mode of the Pig. 1;

Pig. 3, 4

and Fig. 5 shows three variations of the Pig arrangement. 1.

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According to Mg. 1, a sample 1 is mounted in a sample chamber (not shown) and is arranged so that it is over a Extensive area is irradiated by means of an X-ray beam 2, which is under electron bombardment from a Anticathode 3 of an X-ray tube goes out. The electrons emitted by the irradiated sample 1 pass through a Source slit or gap 5, which is kept at the same potential as the sample 1 (earth potential), into an electron-optical Focusing or bundling device 6, the four cylindrical partial lenses 7, 8, 9, 10 comprises. The partial lens 7 is part of the sample chamber and is therefore located also at earth potential, while the three other partial lenses 8, 9, 10 are formed by special tubular elements, which are electrically isolated from grounded parts of the spectrometer 'are. The partial lenses 7 to 10 all have a uniform inner diameter (which is not the case in other embodiments Need to be case) and are coaxially arranged in alignment with the gap 5. ■. .

If suitable potentials are applied to the partial lenses 8 to 10 during operation, as will be described below, v / ground the electrons 4 are bundled by the focusing device 6, so .that an electron-optical "image of the irradiated area the sample 1 is generated in an image plane 11, the opposite of sample 1 is enlarged by a factor which is substantially greater than one. A perforated plate or aperture plate is arranged in the image plane 11 and leaves only a part the electrons forming the image pass through, i.e. the diaphragm 12 prevents the passage of the electrons 4 with the exception those emitted from a small area of Sample 1. The entrance slit 5, on the other hand, is wide enough not to have a limiting effect on the electrons that pass through the aperture 12.

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The angle of divergence of the electrons passing through the pinhole 12 is by means of an angled opening or 7 / angle aperture 13 limited, which is arranged in the partial lens 10 and electrically connected to this.

The image plane 11 coincides with the entry plane of a hemispherical one electrostatic analyzer 14 together, the. comprises a pair of metal hemispheres 15, 16 which are concentric are arranged to each other and electrically isolated from each other. For operation. There is a voltage between the hemispheres 15i 16 by means of a voltage source 17 for analyzer voltage applied as described in detail below, the outer hemisphere 15 being at the negative potential with respect to the inner hemisphere 16 is located, whereby the electrons entering through the diaphragm 12 into the space between the hemispheres be made to follow curved .bahnen, for example 18 and an electron-optical image of the opening of the diaphragm 12 in the exit plane 19 of the analyzer to design the the aperture 12 is diametrically opposite. It should be noted that in years there are a large number of overlapping images of the diaphragm in the exit plane 19, since electrons, which are more energetic, have paths with a larger radius of curvature describe and therefore be focused in different places.

In the exit plane 19, an exit slit 20 is provided which is used to select electrons whose energies are within of a certain limited range of the energy spectrum, whereupon the electrons selected in this way Electron multiplier 21 are detected. The output signal of the electron multiplier 21 is fed via a capacitor 22 to a counter 23 which has an output signal or a

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Provides output power proportional to the frequency or velocity of the electrons passing through the gap 20 is.

During operation, the voltage applied by the voltage source 17 between the hemispheres 15 »16 gives rise to a certain V / range with the aid of a scanning device 24 which controls the voltage source 17 with the result that the exit gap 20 causes a scan over the energy spectrum of the electrons. The output of the counter 23 becomes fed to the Y input of an X-Y recording device 25, for example a measuring strip recorder or recorder, whose X input from the scanner 24 is fed with a character proportional to the analyzer voltage. Thus generated the recorder keeps a record of the energy spectrum of electrons from the small area of the sample that is is selected by the pinhole 12, and thus enables an analysis of the nature of this small area.

Other small areas of the sample can be examined by placing the sample 1 and the pinhole 12 relative to one another be moved.

A plate 26 is on the base of the hemispheres 15, 16 arranged for the purpose of reducing the refractive or diffractive field effects at the edges of the analyzer 14 to prevent. This plate 26 has a flat circular shape with two openings 27, next to the perforated diaphragm 12 or the exit slit 20, in order to allow electrons to enter the analyzer and exit the analyzer allow. The plate 26 is at a potential between the potentials of the hemispheres 15, 16 by suitable means (not shown) held.

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It should be noted that all parts of the device through which the electrons pass are kept in a high vacuum Need to become. In addition, a paramagnetic shield (not shown) can be provided, for example made of mu-metal, a Uickel iron alloy with high magnetic susceptibility (Permalloy), which the analyzer and at least surrounds a part of the lens system 6 and serves to prevent magnetic and electromagnetic interference in the electron orbits to be kept low by stray fields.

In a first mode of operation is the electron-optical focusing device 6 designed so that it not only bundles the electrons to the image in the plane 11, but also the electrons are delayed by a factor R. As in Pig. 1 indicated, the partial lens 8 together with the partial lens 7 placed at ground potential, while the partial lenses 9 and 9 are electrically connected to one another and at a negative potential are held against earth, this potential being such that it is proportional at a given moment to the potential difference between the hemispheres 15, 16 and thus is proportional to the energy of the electrons entering the detector or multiplier 21 at that moment. Furthermore, the potential difference between the hemispheres laid out in such a way that the central electron path through the analyzer is essentially on the the same potential as the last partial lens 10 is so that the electrons no further deceleration or acceleration after going through the focusing device 6.

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It therefore appears that those entering the electron multiplier 21 at some point in the spectrum scan Electrons are delayed by the same predetermined factor R, which is constant across the spectrum. This delay allows the analyzer to have higher resolution and / or higher magnification to be used can and thus a higher sensitivity is achieved.

The bundling of the electrons to the image in the plane 11 is in this Pail by the electrical PeId in the gap 34 between the partial lenses 8 and 9 causes.

Pig. 1 shows one possibility of applying the potentials to the partial lenses 7 to 10 and, which are necessary for the first mode of operation 'Put on the hemispheres 15, 16. The voltage of the voltage source 17 is applied to the hemispheres 15, 16 via a voltage divider applied, the four resistors 29, 30, 31, 32, which in this order in series between the negative and positive terminal of the voltage source 17 lie. The positive end of the voltage divider is connected to ground and the negative. end at the outer hemisphere 15, while the inner hemisphere is connected to the common point of the resistors 31 and 32. The partial lens 8 is connected to the partial lens 7, while the partial lenses 9 and 10 with each other and with a sliding contact 33 are connected to resistor 30.

It can be seen that when the output voltage changes the voltage source 17 the potentials of the two hemispheres and the potential difference between the hemispheres change proportionally to the supply voltage. Likewise, the potential of the partial lenses 9 and 10 changes proportionally to the supply voltage, and by properly setting the sliding contact 33, this potential can be made substantially equal to the mean

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Potential of the hemispheres and thus the potential of the central Electron orbit 18 can be made. It also changes the voltage between the partial lenses 8 and 9, both for 'the Concentration as well as for the delay effect of the focusing device 6 is responsible, proportional to the supply voltage.

According to Mg. 2, a second mode of operation is electron-optical Focusing device essentially not on a retardation of the electrons, but only on a lens effect designed, duroh the electrons in plane 11 are bundled.

Here, the potential difference between the hemispheres 15, 16 is taken from a potentiometer 38, which is connected to the Voltage source 17 is connected. The center of the potentiometer 38 is grounded, which means that the hemispheres are in the be kept essentially at the same positive or negative potential to earth. Thus the central electron orbit becomes 18 is held at ground potential through the analyzer when the analyzer voltage passes through the range of change. The partial lens 10 is connected to earth potential together with the partial lens 7, while the middle partial lenses 8 and 9 are connected to one another and are connected to a tap point on potentiometer 38, which is either at a positive or at a negative potential can be set against earth.

As can be seen, in this mode of operation in the analyzer Electrons entering 14 and reaching electron multiplier 21 are bundled, but essentially not delayed.

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The bundling of the electrons to the image in the plane TT becomes in this pail caused by the electric fields in the Gap 35 between the partial lenses 7 and 8 and in the gap 36 between the partial lenses 9 and 10 ..

In a modification of the arrangement of FIG. 2 (not shown), the partial lens 9 can be connected to the partial lens 8 to be, together with the partial lenses 7 and 10 to earth, so that only the partial lens 8 to the positive or negative Potential is connected. In this pail the bundling caused by the fields in the gaps 34 and 35. Which of these two possibilities is used depends on the desired magnification.

The first mode of operation described above is for the case suitable, in .dem the electrons to be analyzed have high energies have, while the second mode of operation, in which no delay is caused, is suitable for the Pail, in which the electrons to be analyzed have relatively low energies, for example below 100 eV.

A switchover between these two modes of operation becomes obvious simply by changing the electrical connections achieved on the partial lens 7 to 10 and the hemispheres 15, 16 without any change in the mechanical design of the Analyzer.

It will also be understood that while in the example described above the sample is irradiated with X-rays, in other embodiments of the invention the sample may be irradiated by other forms of electromagnetic radiation such as ultraviolet light or other non-electromagnetic radiation such as electrons , 'they whine

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If irradiation takes place, for example, with ultraviolet light, the electrons emanating from the sample are generally Low in energy, so that in this case the analyzer is only operated in the non-decelerating mode.

The aperture plate 12 can be removable, so that in this case the device can also be operated in a manner similar to that described in the earlier patent application P 21 05 805.9, i.e., without the "virtual microprobe" of the present invention. However, in general the gaps 34 · »35» 36 are not located in the right places for operation in all of these additional modes.

In a modification of the arrangement according to FIG. 1 according to FIG. 3, this difficulty is overcome in that the focusing device 6 by an electron optical focusing device is replaced, which comprises five (or more) sub-lenses 41 to 45. By applying these partial lenses to suitable electrical potentials are connected, the device can be operated with inserted aperture plate 12 in each of the two described above Operating modes with a virtual microprobe or with the perforated diaphragm 12 removed according to each of the three in the application P 21 05 805.9 described modes of operation, the only changes - apart from removing and inserting the aperture plate 12 the to switch between these two modes of operation are necessary in the change of the applied electrical potentials exist. The device can also be operated with the perforated diaphragm 12 removed in a further form, the one mentioned above Application is not described, in which the electrons are essentially not delayed, but rather by the focusing device be bundled with a magnification much greater than one. This mode of operation is for example useful when a low energy, e.g. ultraviolet microprobe

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is used.

For some purposes it may be sufficient to configure the device in this way. suggest that it can only work with a "virtual microprobe" in one of the two ways described above. With another Modification of the arrangement of FIG. 1, according to FIG. 4, the focusing device 6 comprises only three partial lenses 51 »52, 53.

Such an arrangement can work with a virtual microprobe in the second operating mode, in which the focusing device a concentration of the electrons but essentially no delay. In this case they are the first partial lens 51 and the third partial lens 53 connected to ground potential, while the second partial lens 52 has a suitable potential, leads either positively or negatively to earth. This arrangement is only for the analysis of low-energy electrons suitable and can be used, for example, in conjunction with an ultraviolet radiation source. According to FIG. 5 can In a further modification of the arrangement according to FIG. 1, the focusing device 6 has only two partial lenses 61 and 62. Such an arrangement can only work according to the first mode of operation with a virtual microprobe, in which the focusing device bundles the electrons and also retards them. In this case, the first sub-lens 61 is grounded and the second Partial lens 62 connected to a suitable negative retardation potential.

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Claims (3)

Claims Device for spectroscopy with charged lights for the chemical analysis of a sample, with means for irradiating an extensive area of the sample for the purpose of Release of charged particles from throughout extensive area, as well as with an energy analyzer to analyze the energy of the charged particles, characterized by a focusing device (6) for charged particles, which with the charged particles an image of the expanded Area generated in an image plane (11) by a pinhole diaphragm arranged in the image plane (12), which prevents the charged particles from entering the analyzer (14) with the exception of those emitted from a small area of the vast area. 2. Device according to claim 1, characterized by this, that the SJokussierungs device (6) to the particles able to delay and they in the analyzer (14) with less energy than when they are released from the Sample (1) possessed, allowed to enter. 3. Device according to claim 2, characterized in that the focusing device (6) has at least two electrically isolated partial lines (7 - 10), through which the particles pass one after the other, 209848/0783 and means (17) for applying corresponding potentials to these partial lenses. Device according to claim 2 or 3t characterized, that the focusing device (6) is optional can be switched between two operating modes, of which the particles are delayed in the first, so that they enter the analyzer (14) with less energy than when they are released from the Sample (1) possessed, and in the second, the particles substantially before entering the analyzer not be delayed. Device according to claim 4, characterized in that the lOkussierungseinrichtung (6) between the first and second modes of operation by simply changing the electrical connections without changing them switchable according to the mechanical arrangement of the device Device according to claim 2, - characterized in that the focusing device (6) has at least four Partial lenses (7-10) that are electrically isolated from one another and through which the particles pass one after the other, and means (17) for applying corresponding potentials on these partial lenses. 209848/0783