DE2213719A1 - Device for spectroscopy with charged particles - Google Patents

Description

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ASSOCIATED ELECTRICAL INDUSTRIES LIMITED, London, England

Device for spectroscopy with charged particles

The invention relates to a device for use in Charged particle spectroscopy and in particular apparatus for use in electron spectroscopy.

The device for charged particle spectroscopy consists in particular of a pair of coaxial tubular or partially tubular electrodes that are opposed to one another are electrically isolated so that during operation between them to generate a radial electric field between the Electrodes a voltage can be applied, whereby charged particles, which from a predetermined origin zone in get into the radial field, be deflected by the field in the direction of the axes of the electrodes and particles with. a given energy to be focused in this way; a collector opening located at the focal point so that Particles with the given energy are selected; and a detector for determining the particles passing through the collector opening step through. A device of this type is hereinafter referred to as a cylindrical mirror analyzer.

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Such a device can be used to analyze the energy spectrum of the particles by sweeps the voltage between the electrodes over an area and thus the output of the detector as a function that measures time.

If the zone of origin for the charged particles is a point which is arranged on the axis of the analyzer, it can be seen that all particles are in radial planes, i.e. planes which contain the axis of the analyzer, migrate. In general, however, some of the particles entering the radial Field, wander on inclined paths, i.e. paths that do not lie in a single radial plane. These obliquely wandering particles are not focused on the same place we * cause non-skewing of the same energy and consequently undesirable aberrations in the analyzer.

Although a point-like point of origin on the axis has the advantage that no particles wandering at an angle from it such a place of origin has a very small area and therefore leads to a very low sensitivity.

The aim of the invention is to reduce the deviations or ■ Aberrations associated with the wandering particles in a cylindrical mirror analyzer.

The subject of the invention is a cylindrical mirror analyzer with a pair of at least partially tubular electrodes, which are arranged coaxially and electrically isolated from one another, so that between them a voltage for generating a radial electric field can be applied between the electrodes, means for generating and injecting charged particles in the radial field, causing the particles to be deflected by the field on the axis and particles of a given energy be brought to a focal point, a part with a collector opening which is arranged at the focal point to

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to select surfaces with the given energy, as well as a Detector for detecting particles that pass through the collector opening go through. The analyzer is characterized by that he has another part with an opening, the so-called ·, ß-opening, which is arranged at a point where the Contains particles with the given energy that change in radial planes and cross the axis.

Through the O-opening arranged in front of the detector, at least the majority of the particles running on inclined paths prevented from entering the detector.

The collector opening is preferably arranged at a distance from the analyzer axis. This interferes with the collector opening not the function of the ß-opening. The collector opening expediently coincides essentially with the inner one of the electrodes together.

Furthermore, the ß-opening is preferably arranged at one point j which is reached by the particles when they are reached by the radial field have been deflected.

In a preferred embodiment, the analyzer is according to the invention arranged in such a way that the particles in operation after passing the ß-opening again in the radial electrical Enter the field and be deflected again by the field towards the detector, which is located on the axis.

The particles preferably pass on their way from the point of origin through a further opening, hereinafter referred to as "Opening and which limits the divergence angle of the trajectories of those particles that" reach the detector. The α-opening is preferably arranged at a distance from the analyzer axis so that it functions as the β-opening does not interfere, and is preferably upstream of the collector opening. Appropriately, the α opening practically falls with the inside of the electrodes.

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Furthermore, the collector opening is preferably ring-shaped and arranged symmetrically with respect to the analyzer axis. Such an annular design allows that the sensitivity of the analyzer is optimized for a given resolution.

The analyzer is preferably arranged in such a way that the angle that the path of the particles makes with the analyzer axis forms before the particles enter the radial electric field, useful for focusing the particles from given energy at the collector opening optimally.

Conveniently, a means is provided which can be operated selectively to decelerate the particles before they enter the radial field, thereby improving the sensitivity of the analyzer without affecting the resolving power is affected, as will be described below. The means for retarding the particles is expedient a charged-particle lens.

The invention is explained in more detail below with reference to drawings in which

Figures 1 to 6 each a schematic elevation of a cylindrical Mirror analyzer according to the invention

represent.

Referring to Fig. 1, the illustrated cylindrical mirror analyzer includes a pair of coaxial tubular metal electrodes 1 and 2 of radii r. or r _? . The electrodes 1 and 2 are electrically insulated from one another so that, during operation, the outer electrode 2 can be kept at a negative potential with respect to the inner electrode 1, whereby a radially directed electric field is produced in the space between the electrodes 1 and 2 .

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Line sample 3 is on a sample carrier 15 within the inner electrode 1 on the common axis 4 of the electrodes arranged. When the analyzer is in operation, the sample 3 is bombarded with radiation, such as X-rays, Ultraviolet radiation or with electrons from a radiation source 14 so that the sample is caused "electrons to emit. The energies of these emitted electrons depend on the chemical structure of the sample and the nature of the bombarding radiation. The sample 3 is surrounded by a screen 5 which has a small opening 6 through which the electrons emitted by the sample pass through and which in this way form a point-shaped electron source represents.

After passing through the source opening 6 pass the electrons have a further opening 7, which in this case is arranged in the inner electrode 1, but which is also in a separate part may be present. This opening 7 is used to set the divergence angle 2 "of the orbits of those electrons to limit that of the source opening 6 through .die Pass through opening 7. The opening 7 is consequently referred to as -opening. Electrons passing through the α opening 7 pass through, get into the radial electric field between electrodes 1 and 2 and are caused by the field to " the axis 4 of the analyzer is too deflected. The deflected electrons pass through an exit opening 8 in the inner electrode 1, which is sufficiently wide so as not to have a limiting effect on the electrons; The electron optics of a cylindrical mirror analyzer are such that electrons of a predetermined, of the strength of the radial Electric field dependent energy migrating in radial planes with respect to the analyzer at one point be focused. This focal point is a second order focal point, i.e. the focusing of the electrons on the point

2

is independent of α and a , ie the main aberration is proportional to α. A collector opening 10 is provided at this point to select the electrons of the predetermined energy. 209840/0835

Electrons passing through this opening enter an electron detector 11, which generates an output signal, which is proportional to the extent to which it picks up electrons.

It goes without saying that the analyzer has the ability to resolve between electrons of different energies to distinguish, among other things, depending on the extent of the collector opening 10 in the axial direction and the extent the source opening 6 in the axial direction. The smaller these openings, the greater the resolution. However reducing the size of these openings also reduces the sensitivity of the analyzer, see above that in practice the sizes of the openings must represent a compromise.

The radial position of the focal point 9, ie its radial distance I ₂ from the inner electrode 1, depends on 1., the radial distance of the source opening 6 from the inner electrode 1 and also on the mean angle θ that the trajectories of the electrons make with the axis 4 form before they get into the radial electric field. For a given angle θ we get the distances] L · and 1 _? by the equation

I ₁ + I ₂ = Dr ₁ . (1)

where η is a constant dependent on θ. In the present example, where 1. + I ₉ = 2r «. and therefore η = 2, the corresponding angle θ is 42 and 20 minutes.

It follows that with this geometry the electrons reach the analyzer axis 4 somewhere between the exit opening and must cross the focal point 9. However, this only applies to electrons whose orbits run in radial planes, so that electrons with inclined orbits which are not in radial planes do not cross the axis 4, whereby the distance its closest approach to the axis is a direct measure of the inclination of its orbit, i.e. the angle eleven,

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by which they deviate from a radial plane. A major part this inclined electron is by means of a circular opening 12, the β-opening, which is on the axis 4 at a point where the non-skewed electrons cross the axis, from the reaching of the Detector 11 excluded.

It is clear that the O opening 12 is the oblique electrons the smaller it is, the more effectively it intercepts, although at the same time the number of electrons also becomes smaller reaches the detector 11, thereby reducing the sensitivity of the analyzer. Hence the size of the ß-opening 12 also a compromise in practice. The effect the β opening 12 is that aberrations or deviations, the oblique electrons are attributable, strong can be reduced and thereby the effectiveness of the analyzer is improved.

Since the source opening 6, the α-opening 7 and the collector opening 10 are arranged away from the axis 4, they interfere not the function of the A-opening 12. If the collector opening 10 were arranged, for example, on "the axis, it would be whole generally restrict the flow of non-axial electrons more than is necessary to achieve the required resolution in this way would unnecessarily reduce the sensitivity of the analyzer.

The energy spectrum of the electrons emitted by the sample v / ground can be analyzed by measuring the voltage applied between electrodes 1 and 2 through a suitable range varies and the output of the electron detector 11 records as a function of time.

According to FIG. 2, in which the same features have the same reference numerals as in FIG. 1, are in a modification of the arrangement According to FIG. 1, the gullet opening 6, the α-opening 7, the exit opening 8, the focal point 9, the collector opening 10 and the Detector 11 are all ring-shaped and extend over a

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azimuthal angle of 2π coaxial to axis 4. The electron optics this arrangement is analogous to that according to FIG. However, it turns out that in this case the area of the source opening 6 is much larger than in the case of FIG. 1 and thereby greatly increases the sensitivity of the analyzer v / ird. As in the embodiment described above, the analyzer contains a circular β-opening 12 at the point at which the non-skewed electrons cross the axis.

In other embodiments of the arrangement according to FIG. 1, the arrangement may only be partially ring-shaped and thus extend over an azimuthal angle that is smaller than is.

In modifications of the arrangements, as shown in FIGS. 1 and 2, the factor η in the above equation (1) can remain constant if the distances I ₁ and Ip are both changed, but the sum 1. + 1 _? is kept constant, so that the angle Θ, which is required for focusing at the collector opening in the second order, remains the same, ie is about 42 ° and 20 minutes. In addition, the aberration coefficients remain the same and the dispersion expression, ie the relationship between electron energy and applied voltage, also remains the same for the analyzer. A limiting case for this is in Fig. 3 for the case in which 1. = 0 and therefore 1_ = 2r. are shown.

Referring to Fig. 3, the analyzer consists of a pair of coaxial tubular electrodes 21 and 22 for generating a radial electric field. A sample "23 is by means of a sample carrier 35 arranged on the analyzer axis 24 such that they can be bombarded with radiation from a radiation source 34 and caused to emit electrons. The emitted electrons pass through an annular opening 25 in the Inner electrode 21, this opening being a ring-shaped electron source forms. Another annular opening 26 is arranged between sample 23 and source opening 25 and is used as a-opening, the .Divergence angle 2 ο of the electrons, the

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step through the source opening, limited.

Electrons from the source opening 25 enter the radial electric field between the electrodes 21 and 22 and v / ground deflected towards the axis 24, whereby it is deflected by a pass through annular outlet opening 27 in the inner electrode 21, which is large enough that they do not have a limiting Influences the electrons. Electrons of a given energy are shaped in this way in a ring Focal point 28 brought second order. There in this case

Ip = 2r . , the focal point 28 lies on the inner electrode 21. An annular opening 29 is provided in the inner electrode 21 and serves as a collector opening which selects the focused electrons of a given energy. The selected electrons are detected by an annular electron detector 30.

As described above, the electrons cross the analyzer axis 24 at a point between the exit opening 2? and denr Focal point 28, and an annular opening 31 is provided on the axis at this point so that the majority of the oblique electrons is excluded and thereby the Aberrations from this. Reason to be reduced.

In a modification of the arrangement shown in FIG For example, the opening 27 can be arranged so that it serves as a "ce opening and effectively limits the divergence of the electron beam. In this case, the opening 26 is chosen to be large is enough not to have a restrictive influence on the electrons, or it can be omitted entirely, whereby more working space around the sample 23 is created.

In other modifications of the arrangements according to FIGS. 1 and 2, the distances I ^ and 1_ can be changed independently of one another, so that the factor η in equation (1) is no longer 2. In such an arrangement the angle Q * must have a value other than 42 ° 20 minutes ^ so that a second order focusing can be achieved »Γ ^! '

2 09840/0 83 5. ^

One such variation is shown in Figure 4 which shows a cylindrical mirror analyzer which, v / ie described above, a pair of coaxial tubular ketal electrodes 41 and 42 as well as an annular electron source 43 which has a source opening v / ie opening 6 according to FIGS 1 and 2 may have. Electrons emerge from source 43 through an annular opening 44 in the inner electrode 41 and ground through the radial electric field between the electrodes through an annular outlet 46 in the inner electrode which does not restrict the electrons the analyzer axis 45 is deflected, with electrons of a predetermined energy moving in radial planes brought a second order focal point 47. In the example shown, the angle θ and the distance 1 " chosen so that the focal point 47 is a point-like focal point which lies on the axis 45. In other arrangements can however, this focal point may be ring-shaped or partially ring-shaped. An annular collector opening 48 is at the focal point arranged and selected focused electrons of the given energy. The selected electrons enter an electron detector 49.

In this arrangement, the electrons cross the axis 45 at a point between the source 43 and the α-opening 44, i.e., before they enter the radial electric field. An annular P-port 50 is located at this point on the axis to to prevent most of the oblique electrons from reaching detector 49.

In the example shown in FIG. 4, 1. is greater than r * and I ₂ = r, so that the factor η in equation (1) is greater than. For example, η = 2.5 when L = 1.5r ..

Referring to Figure 5, there is shown a preferred analyzer in accordance with the invention having a pair of coaxial tubular electrodes 62 and 63 for generating a radial electric field. A sample 60 is by means of a sample holder 75 on the Analyzer axis 64, arranged in such a way that it emits radiation

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shot at a radiation source 74 and emit electrons can be initiated. The emitted electrons pass through an annular source opening 61 in the inner electrode 62 through, so that this opening represents an annular electron source.

Electrons from the source opening 6i enter the radial one electric field between the electrodes 62 and 63 and are deflected towards the axis 64 to. The electrons kick through an annular opening 65 in the inner electrode 62 through, this opening serving as the α-opening and the effective Divergence angle 2 α of the electrons from the source opening

61 limited.

The radial electric field focuses electrons of a given amount Energy on an annular focal point 66 of the second order, which coincides with the inner electrode 62. One annular collector opening 68 in the inner electrode selects the focused electrons of predetermined energy.

The electrons cross the analyzer axis 64 at one point between the opening 65 and the focal point 66, and an annular one The β-opening is arranged on the axis at this point, so that the majority of the oblique electrons are shielded and in this way - the aberration for that reason is reduced will. .

As previously described, the arrangement according to FIG. 5 is analogous to that according to FIG. 3. However, according to FIG. 5, the electrons do not enter an annular detector after passing through the collector opening 68. Instead, they enter the radial electric field between the electrodes 62 and 63 again and are again deflected by this field towards the axis 64, so that they pass through an exit opening 69 in the irnial electrode

62 step through. The electrons converge on a ring-shaped one Detector opening 71 on the axis 64 and step through they pass through and are then deflected by a tubular electrode 72 into an electron detector 70 '* Neither' the output

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passage opening 69 nor the detector opening has a limiting effect on the electrons.

When the electrons pass through the radial field for the second time, they can be reduced to a relatively narrow one Area so that a single detector can be used. This makes the use of an annular Detector, as is required in the embodiments according to FIGS. 2 or 3, avoided.

In a modification of the arrangement according to FIG. 5, the collector opening be arranged where the electrons exit the radial field for the second time, i.e. it can be the exit opening 69 replace.

In the arrangements described above, the various Openings, such as the openings 61, 65 and 68 according to FIG. 5, through the inner electrode of the analyzer is limited. In modifications of these arrangements, however, the openings can be separated by separate Plates be limited, which can then be mounted on the inner electrode. This will allow the openings to replace, if desired, other dimensions should have. Such separate plates can be kept at the same potential as the inner cylinder, or they can be kept at a potential little different therefrom, so that small corrections of the insertion angle are possible θ made and the effect of fringing fields at the openings can be compensated.

In the individual embodiments as described above, the effective electron source is through an opening limited, such as the opening 6 according to FIG. 1. In modifications of these arrangements, however, the effective source be the surface of a sample from which the electrons actually originate. Alternatively, the Device contain an electron optical lens arranged to focus the electrons (on a point or ring-shaped or partially ring-shaped focus),

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where then the focus is the. effective electron source for the Arrangement forms. In addition to its electron-focusing effect, the electron-optical lens can also use electrons delay, i.e. lower their energies. The advantage of the delay of the electrons in the device for electron spectroscopy is, as in patent 2 105 805 (patent application ' P 21 05 805 * 9) explains that it is under certain circumstances it is possible to increase the sensitivity of the device, at least for relatively high-energy electrons, without that the resolving power is impaired. /.

According to FIG. 6, in such an embodiment, the one according to the invention. Device a cylindrical mirror analyzer is provided which contains two tubular electrodes -80 and 81, which are arranged coaxially to the axis 82 and between which a radial electric field can be generated. A sample 83 is arranged on the axis on a sample carrier 96 in such a way that it can be bombarded with radiation from a radiation source 94 in order to emit electrons from it. The electrons pass through an annular source opening 84 in the inner electrode 80, are deflected by the radial electric field in the direction of the axis 82 and pass through an annular opening 85 in the inner electrode. Electrons be einer'vorgegebenen energy gebraclit in this way an annular focus 8 &, dei · coincides with the inner electrode 80 electrons of these: |!. '_ given energy are selected by eineir Kollelttöröffnung 95, d4e in the inner electrode 80 is arranged "the of the collector opening 95 selected electrons pass either annular in a (not shown) electron detector a, as in the case of the arrangement of Figure 3 success. ^: or enter a "second time · by the radial field and be set to a (not shown) detector converges towards the axis 82, as is the case in the device according to FIG. 6. As before, a ^ opening 87 is provided at a location where the electrons cross the axis 82 before arriving at the focus 86 to prevent the bulk of the oblique electrons from reaching the focus 86 *

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Between the sample 83 and the opening 84 there is an electron-optical Lens assembly 88 is arranged, which consists of three metal components 89, 90 and 91, each of which has the shape has a truncated cone, which with the electrodes 80 and 81 ■ ■ is coaxial, and each of which has an annular opening 92 through which the electrons pass one by one. By applying suitable potentials to the components 89 and 91, the lens arrangement 88 can be caused to To cause electrons emitted from the sample 83 to impinge on an annular focus 93 at the opening 84 as well as decelerating the electrons before they enter the radial field. This focus 93 acts in this way as a ring-shaped electron source.

The lens assembly is selectively operable by changing the electrical connections to it to either provide a ' To achieve delay or no delay and either practically unity or electron optical magnification to produce one that is practically greater than one (substantially unit or substantially greater than unity). The delay is achieved by setting the potentials of components 89, 90 and 91 such that the potential of the last component 91 is more negative than that of the sample

The delay is applied for the reasons explained above,

when analyzing relatively high-energy electrons;

are, while for the analysis of relatively low-energy elec-

no delay is applied. j j

Magnification over one is used in one of two cases. In the case where the sample is irradiated with a very fine radiation (i.e. a "microprobe"), the The area of the sample that emits electrons is very small, so that the application of a magnification of well over one allows more of the electrons emitted from this small area to pass through the analyzer and thereby the sensitivity of the analyzer is increased. In the second case where the sample is exposed to radiation

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flooding means the application of magnification. of much more than one, that the electrons, which by the Source opening 84 pass through, only originate from a very small area of the sample. This latter arrangement causes a so-called virtual micro-sample and can do something similar In the same way as conventional microsampling arrangements can be used.

A magnification of practically unity, on the other hand, is applied when the sample is flooded with radiation to remove it to cause electrons to emit over an extended area.

Of course, the lens 88 can be arranged in modifications 6 contain more than three parts or, alternatively, only two components. In addition, the components of the lens have a considerable thickness, so that the openings 92. become channels of considerable length.

Of course, the arrangement according to the invention in in the same way also to spectroscopy with other types of charged particles, for example to ion spectroscopy can be applied.

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Claims (9)

«6 Claims Cylindrical mirror analyzer having a pair of at least partially tubular electrodes arranged coaxially and are electrically isolated from one another, so that between them a voltage for generating a radial electric field can be applied between the electrodes, means for generating and injecting charged particles into the radial field, whereby the particles are deflected by the field towards the axis and particles of a given energy are brought to a focal point, a part with a collector opening, which is arranged at the focal point in order to select particles with the predetermined energy, and a detector to find particles that pass through the collector opening, characterized in that it has a further part with an opening (12, 31, 50, 67, 87), the so-called ß-opening, which is arranged at a point where the particles with the given energy, in radial Hiking planes that cross axis (4, 24, 45, 64, 82) contains. 2. Analyzer according to claim 1,
characterized in that the collector opening (10, 29, 68, 95) is arranged away from the analyzer axis (4, 24, 45, -64, 82). 3. Analyzer according to claim 2,
characterized in that the collector opening (29, 68, 95) practically coincides with the inner one of the electrodes (21, 62, 80). 209840/0835 4. Analyzer according to one of the preceding claims, characterized in that that the β-opening (12, 31, 67, 87) is arranged in one place which is reached by the particles after they have been deflected by the radial field. " 5. Analyzer according to claim 4 ,. characterized, " that it is arranged in operation in such a way that the particles after passing the β-opening (67) re-enter the radial field and again from the field to the detector (70) to be deflected, which is arranged on the axis (64). 6. Analyzer according to one of the preceding claims, characterized, that it includes means (88) which are selectively operable to decelerate the particles before they enter the field. 7. analyzer according to claim 6,
characterized in that the means (88) for retarding the particles consists of a charged-particle.lens. 8. Analyzer according to claim 7 »
characterized in that the lens (88) is an electrostatic lens comprising a number of metal parts (89, 90, 91) having respective openings (92) through which the particles pass one after the other. . 9. analyzer according to claim 8,
characterized in that the metal parts (89, 90, 91) are conically shaped in the broadest sense. Wa / Gu. 209840/0835