Charged particle detector

Abstract

This charged particle detector comprises: a microchannel plate having an input surface through which charged particles enter, a multiplication unit that performs electron multiplication on the basis of input of the charged particles while maintaining positional information of the charged particles with respect to the input surface, and an output surface through which electrons multiplied by the multiplication unit are outputted; a resistive anode that, when electrons outputted through the output surface enters therein, outputs a charge signal corresponding to the entering position of the electrons; and an anode that is disposed in a spatial region between the output surface and the resistive anode, has an electron passage unit through which the electrons outputted through the output surface are allowed to pass, and is for collecting the electrons outputted from the resistive anode.

Description

Charged particle detector

[0001] The present disclosure relates to a charged particle detector.

[0002] Patent Document 1 describes an electron multiplier device. This electron multiplier device includes a stack of microchannel plates and a second multiplication stage disposed behind the stack. The second multiplication stage includes a dynode and an anode. The anode allows electrons emitted from the stack to pass through. Secondary electrons emitted from the dynode are collected by the anode.

[0003] Patent Document 1 also describes an example in which the electron multiplier device is made sensitive to the determination of position information by configuring the dynode in the form of a mosaic structure composed of independent elements. In this case, the dynode includes a plurality of independent elements disposed on an insulating substrate. Each element is provided with a conductor for leading out a signal to the outside.

[0004] Japanese Patent Application Laid-Open No. 57-196466

[0005] In Patent Document 1 described above, as described above, in order to make it sensitive to the determination of position information, the dynode is divided into a plurality of independent elements. In this case, when trying to improve the spatial resolution, in order to arrange a larger number of elements, it is necessary to make each element smaller while maintaining the space (for insulation) between the elements. In this case, the utilization efficiency of electrons decreases.

[0006] An object of the present disclosure is to provide a charged particle detector capable of improving the spatial resolution while avoiding a decrease in the utilization efficiency of electrons.

[0007] The charged particle detector according to this disclosure is a [1] "microchannel plate having an input surface into which charged particles are incident, a multiplication unit that multiplies electrons based on the input of charged particles while maintaining positional information of the charged particles with respect to the input surface, and an output surface that outputs electrons multiplied by the multiplication unit, a resistive anode that receives electrons incident from the output surface and outputs a charge signal corresponding to the incident position of the electrons, and an anode disposed in the spatial region between the output surface and the resistive anode and having an electron passage unit that allows electrons output from the output surface to pass through, for collecting electrons output from the resistive anode, wherein the resistive anode includes a multiplication layer that performs electron multiplication and outputs electrons multiplied by the multiplication layer toward the anode."

[0008] In this charged particle detector, electrons amplified and output in the microchannel plate pass through the electron passage of the anode and are incident on the resistive anode. The resistive anode then outputs a charge signal corresponding to the incident position of the electron. This allows the incident position of the charged particle to be detected. In particular, this charged particle detector uses a resistive anode for position detection. Therefore, compared to the case where multiple dynodes are divided and used as described above, the space required for insulation between dynodes is eliminated (i.e., they can be configured as a single unit), and spatial resolution can be improved while avoiding a decrease in electron utilization efficiency.

[0009] The dynamic range of a microchannel plate is determined by the upper limit of its output current (output linearity: MCP Output linearity), which is expressed as the product of the microchannel plate's multiplication factor (MCP gain) and the counting rate. The upper limit of the output current is defined by the strip current. Therefore, there is a trade-off relationship between the microchannel plate's gain and the counting rate. In other words, increasing the MCP gain reduces the counting rate.

[0010] In contrast, this charged particle detector has a resistive anode with a multiplication layer that performs electron multiplication. Therefore, when the secondary electron emission efficiency at the resistive anode is δ, the counting rate can be improved by δ while maintaining the MCP gain. Thus, this charged particle detector improves the dynamic range.

[0011] The charged particle detector relating to this disclosure may also be [2] "the charged particle detector according to [1] above, wherein the anode is a mesh anode." In this case, electrons can be passed through without adversely affecting the positional information that the resistive anode is to detect.

[0012] The charged particle detector relating to this disclosure may also be [3] "the charged particle detector according to [1] above, wherein the anode is a position-detection type anode." In this case, the position detection accuracy can be improved.

[0013] The charged particle detector relating to this disclosure may also be [4] "the charged particle detector according to [3] above, wherein the position-detecting anode is a delay-line anode." In this case, the electron transmittance can be increased, so that a high detection efficiency can be obtained.

[0014] The charged particle detector according to this disclosure may also be [5] "the charged particle detector according to any one of [1] to [4] above, wherein the resistive anode has a plurality of terminals for outputting the charge signal and a resistive layer for distributing the amount of charge according to a resistance value corresponding to the distance to the terminals, and the multiplier layer is provided on the resistive layer." In this case, the secondary electron emission efficiency δ can be reliably ensured by using a multiplier layer provided separately from the resistive layer for charge distribution of the resistive anode.

[0015] The charged particle detector according to this disclosure may also be [6] "the charged particle detector according to any one of [1] to [4] above, wherein the resistive anode has a plurality of terminals for outputting the charge signal and a multiplier layer which is a resistive layer for distributing the amount of charge according to a resistance value corresponding to the distance to the terminals." In this case, the configuration is simplified by having the resistive layer for charge distribution of the resistive anode function as a multiplier layer.

[0016] The charged particle detector relating to this disclosure may also be the "charged particle detector according to [5] or [6] above, wherein the plurality of terminals are arranged in a two-dimensional manner when viewed from a direction intersecting the output surface, and the resistive layer extends in a two-dimensional manner across the plurality of terminals when viewed from a direction intersecting the output surface." In this case, two-dimensional position detection becomes possible.

[0017] The charged particle detector according to this disclosure may also be [8] "a charged particle detector according to any one of [1] to [7] above, wherein the voltage applied to the multiplier layer is greater than the voltage applied to the output surface of the microchannel plate and less than the voltage applied to the anode." In this case, it becomes possible to more reliably secure the secondary electron emission efficiency δ.

[0018] According to this disclosure, it is possible to provide a charged particle detector that can improve spatial resolution while avoiding a decrease in electron utilization efficiency.

[0019] Figure 1 is a diagram showing an XPS apparatus according to one embodiment. Figure 2 is a cross-sectional view showing the configuration of the charged particle detector shown in Figure 1. Figure 3 is a plan view showing the mesh anode shown in Figure 2. Figure 4 is a plan view showing the resistive anode shown in Figure 2. Figure 5 is a graph showing the output signal of a charged particle detector according to a comparative example. Figure 6 is a graph showing the output signal of a charged particle detector according to this embodiment. Figure 7 is a plan view showing a delay line anode as an example of a position-detection type anode.

[0020] An embodiment will be described in detail below with reference to the drawings. In the description of each figure, the same or equivalent elements will be denoted by the same reference numeral, and redundant explanations may be omitted. In addition, each figure may show a Cartesian coordinate system consisting of an X-axis defining the X direction, a Y-axis defining the Y direction intersecting the X direction, and a Z-axis defining the Z direction intersecting the X and Y directions.

[0021] Figure 1 shows an XPS apparatus (X-ray photoelectron spectroscopy apparatus) according to one embodiment. As shown in Figure 1, the XPS apparatus 100 comprises a charged particle detector 1, a photoelectron generator 2, and an energy analyzer 3. The photoelectron generator 2 has an electron lens 4, an aperture 5, and a deflection plate 6. A sample A is placed in the photoelectron generator 2.

[0022] In the photoelectron generation unit 2, photoelectrons Pe are emitted from sample A by irradiating it with, for example, monochromatic X-rays. The electron lens 4 images the photoelectrons Pe emitted from sample A onto the aperture 5. The deflection plate 6 is provided between the electron lens 4 and the aperture 5. Depending on the applied voltage, the deflection plate 6 can deflect the photoelectrons Pe, thereby creating a state in which the photoelectrons Pe cannot pass through the aperture 5. On the other hand, depending on the applied voltage, the deflection plate 6 can stop the deflection of the photoelectrons Pe, thereby creating a state in which the photoelectrons Pe can pass through the aperture 5.

[0023] The energy analyzer 3 is formed in a hemispherical shape, and an electric field Fe is formed within it along the radial direction. In response to the electric field Fe, the energy analyzer 3 forms a trajectory corresponding to the kinetic energy of the photoelectron Pe incident through the aperture 5. In this way, the energy analyzer 3 spatially decomposes the energy of the photoelectron Pe.

[0024] The charged particle detector 1 is located at the end of the energy analyzer 3 opposite to the aperture 5, and receives photoelectrons Pe that have been brought to a position corresponding to their kinetic energy by the energy analyzer 3. The charged particle detector 1 detects the incident position of the photoelectrons Pe. Therefore, in this embodiment, the charged particles to be detected by the charged particle detector 1 are electrons (photoelectrons Pe). In this way, the XPS apparatus 100 measures the kinetic energy of photoelectrons Pe emitted by the irradiation of sample A with X-rays, and provides insights into the types, abundances, and chemical bonding states of elements present on the extreme surface of the sample.

[0025] Figure 2 is a cross-sectional view showing the configuration of the charged particle detector shown in Figure 1. As shown in Figure 2, the charged particle detector 1 has a microchannel plate 10, a resistive anode 20, and a mesh anode 30 (anode). The microchannel plate 10, the mesh anode 30, and the resistive anode 20 are arranged in this order along the Z direction.

[0026] The microchannel plate 10, when viewed from the Z direction, has a shape that is, for example, a disk. It has an input surface 10a into which electrons (charged particles) are input, a plurality (two in this case) of multiplication units 11 and 12 that perform electron multiplication (secondary electron multiplication) based on the input electrons while maintaining the positional information of the electrons relative to the input surface 10a, and an output surface 10b that outputs the electrons multiplied by the multiplication units 11 and 12. Each of the multiplication units 11 and 12 is a secondary electron multiplication unit having a plurality of independent microchannel structures. In the multiplication units 11 and 12, the plurality of microchannel structures are arranged in a two-dimensional array.

[0027] Each channel in the multiplication units 11 and 12 has an inner diameter of about 10 μm and is tilted at about 10° with respect to the normal direction of the input surface 10a (the direction of electron input, for example, the Z direction). The tilt direction of each channel is reversed between the multiplication unit 11 and the multiplication unit 12. In the multiplication units 11 and 12, the output surface 10b side has a higher potential than the input surface 10a side. Electrons generated in response to electrons reaching the input surface 10a are multiplied in the multiplication units 11 and 12, and these multiplied electrons are output from the output surface 10b.

[0028] The resistive anode 20 is an example of a charge-partitioning position detector, and receives incident electrons e1 output from the output surface 10b and outputs a charge signal corresponding to the incident position of the electrons e1. The resistive anode 20 includes a substrate 21, a resistive layer 22 formed on the substrate 21, a multiplier layer 23 provided on the resistive layer 22, and a plurality (four in this case) of terminals 24. The multiplier layer 23 receives incident electrons e1 output from the output surface 10b and multiplies them, outputting the multiplied electrons e2 toward the mesh anode 30.

[0029] The mesh anode 30 is positioned in the spatial region between the output surface 10b and the resistive anode 20. The mesh anode 30 allows electrons e1 output from the output surface 10b to pass through and collects electrons e2 output from the resistive anode 20.

[0030] The charged particle detector 1 is electrically connected to an external power supply and a bleeder circuit (not shown). The bleeder circuit applies a voltage with a predetermined potential gradient to the microchannel plate 10, the resistive anode 20, and the mesh anode 30. The applied voltage is highest at the mesh anode 30, followed by the resistive anode 20 (multiplier layer 23), and then the output surface 10b of the microchannel plate 10. That is, the voltage applied to the multiplier layer 23 is greater than the voltage applied to the output surface 10b of the microchannel plate 10, and less than the voltage applied to the mesh anode 30.

[0031] Figure 3 is a plan view showing the mesh anode shown in Figure 2. As shown in Figures 2 and 3, the mesh anode 30 has a disc shape when viewed from the Z direction. The mesh anode 30 is an electrode that collects electrons e2 amplified by the resistive anode 20 and prevents them from returning to the resistive anode 20 side. The mesh anode 30 has a collection section 31 that collects electrons e2 amplified by the resistive anode 20, and an opening 32 (electron passage section) that allows electrons e1 output from the output surface 10b to pass through to the resistive anode 20 side. In the illustrated example, the collection section 31 has a stripe-like pattern. The opening 32 is formed between adjacent collection sections 31.

[0032] Figure 4 is a plan view showing the resistive anode shown in Figure 2. As shown in Figures 2 and 4, the resistive anode 20 has four terminals 24. Each terminal 24 is electrically connected to at least the resistive layer 22 and is brought out to the outside via the substrate 21. Therefore, the resistive anode 20 can output a charge signal to the outside using these terminals 24.

[0033] The four terminals 24 are arranged in a two-dimensional manner when viewed from the Z direction (for example, the direction intersecting the output surface 10b). In the illustrated example, the four terminals 24 are positioned at locations corresponding to the vertices of a square, with equal distances from each other. The resistive layer 22 extends two-dimensionally across the four terminals 24 when viewed from the Z direction. The resistive layer 22 is integrally constructed so that it overlaps the entire microchannel plate 10 (output surface 10b) when viewed from the Z direction. The multiplier layer 23 may be provided across the entire resistive layer 22 when viewed from the Z direction. The secondary electron emission efficiency δ (multiplier) of the multiplier layer 23 is, for example, about 5 to 10. The substrate 21 is made of alumina as an example, and the resistive layer 22 is made of ruthenium oxide (RuO) as an example. ２ The multiplier layer 23 is composed of, for example, magnesium fluoride (MgF ２ ) is composed of (i.e., MgF ２ (It is a membrane.)

[0034] The four terminals 24 consist of a first X terminal 24a, a second X terminal 24b, a first Y terminal 24c, and a second Y terminal 24d. The first X terminal 24a is located at a first position in the X direction and a second position in the Y direction. The second X terminal 24b is located at a second position in the X direction and a first position in the Y direction. The first Y terminal 24c is located at a first position in the X direction and a first position in the Y direction. The second Y terminal 24d is located at a second position in the X direction and a second position in the Y direction. Therefore, the first X terminal 24a and the second Y terminal 24d, and the first Y terminal 24c and the second X terminal 24b are arranged in the X direction. Also, the first X terminal 24a and the first Y terminal 24c, and the second Y terminal 24d and the second X terminal 24b are arranged in the Y direction.

[0035] When an electron e1 is incident on the resistive layer 22, its charge is distributed according to the resistance value corresponding to the distance to each of the terminals 24. At this time, if the amount of charge distributed to the first X terminal 24a is X1, the amount of charge distributed to the first Y terminal 24c is Y1, the amount of charge distributed to the second X terminal 24b is X2, and the amount of charge distributed to the second Y terminal 24d is Y2, then the incident position of the electron e1 can be determined in the X direction by (X1 + X2) / (X1 + X2 + Y1 + Y2) and in the Y direction by (X2 + Y1) / (X1 + X2 + Y1 + Y2). As a result, the charged particle detector 1 can detect the incident position of the photoelectron Pe in two dimensions.

[0036] Specifically, the charge amount of electrons e1 incident on the resistive layer 22 is the positive charge amount corresponding to the charge amount of electrons e2 output from the multiplier layer 23 by electron multiplication in response to the incidence of electrons e1 on the multiplier layer 23.

[0037] Figure 5 is a graph showing the output signal of a charged particle detector according to a comparative example. Figure 6 is a graph showing the output signal of a charged particle detector according to this embodiment. In the comparative example in Figure 5, the resistive anode does not have a multiplication layer 23, and a mesh anode is not provided between the microchannel plate and the resistive anode. Also, in Figure 5, the voltage of the output surface of the microchannel plate is set to -200V, and the voltage of the resistive anode is set to Ground (0V). In Figure 6, the voltage of the output surface 10b of the microchannel plate 10 is set to -200V, the voltage of the resistive anode 20 is set to Ground (0V), and the voltage of the mesh anode 30 is set to +200V. As shown in Figures 5 and 6, in the charged particle detector 1 according to this embodiment, the polarity of the output signal is reversed and an increase in amplitude is confirmed compared to the charged particle detector according to the comparative example.

[0038] As described above, in the charged particle detector 1 according to this embodiment, electrons e1 that are multiplied and output in the microchannel plate 10 pass through the opening 32 of the mesh anode 30 and are incident on the resistive anode 20. The resistive anode 20 then outputs a charge signal corresponding to the incident position of the electrons e1. This allows the incident position of the charged particle (in this case, photoelectrons Pe) to be detected. In particular, the charged particle detector 1 uses the resistive anode 20 for position detection. Therefore, compared to the case in which multiple dynodes are used, space for insulation between dynodes is not required (i.e., they can be configured as a single unit), and spatial resolution can be improved while avoiding a decrease in electron utilization efficiency.

[0039] Furthermore, the charged particle detector 1 has a resistive anode 20 with a multiplication layer 23 that performs electron multiplication. Therefore, when the secondary electron emission efficiency at the resistive anode 20 is δ, the counting rate can be improved by δ while maintaining the MCP gain. Thus, the charged particle detector 1 improves the dynamic range.

[0040] In the charged particle detector 1 according to the present disclosure, a mesh anode 30 is used as the anode. Therefore, electrons e1 can pass through without adversely affecting the position information to be detected by the resistive anode 20.

[0041] In the charged particle detector 1 according to the present embodiment, the resistive anode 20 includes a plurality of terminals 24 for outputting a charge signal, and a resistive layer 22 for distributing the charge amount according to the resistance value corresponding to the distance to the terminals 24. The multiplication layer 23 is provided on the resistive layer 22. Therefore, the secondary electron emission efficiency δ can be surely ensured by using the multiplication layer 23 provided separately from the resistive layer 22 for charge distribution of the resistive anode 20.

[0042] In the charged particle detector 1 according to the present embodiment, the plurality of terminals 24 are arranged two-dimensionally when viewed from the direction (for example, the Z direction) intersecting the output surface 10b. The resistive layer 22 extends two-dimensionally so as to cover the plurality of terminals 24 when viewed from the direction intersecting the output surface 10b. Therefore, two-dimensional position detection is possible.

[0043] Furthermore, in the charged particle detector 1 according to the present embodiment, the voltage applied to the multiplication layer 23 is larger than the voltage applied to the output surface 10b of the microchannel plate 10 and smaller than the voltage applied to the mesh anode 30. Therefore, it is possible to more surely ensure the secondary electron emission efficiency δ.

[0044] The above embodiments illustrate one aspect of the present invention. Therefore, the present invention is not limited to the above embodiments and can be arbitrarily modified.

[0045] For example, in the above embodiment, an example in which the charged particle detector 1 has the mesh anode 30 has been described. However, the charged particle detector 1 may have a position detection type anode instead of the mesh anode 30. In this case, as shown in FIG. 7, the charged particle detector 1 can have a (one-dimensional) delay line anode 30A (anode) as an example of a position detection type anode. The delay line anode 30A is arranged in the space region between the output surface 10b of the microchannel plate 10 and the resistive anode 20, similarly to the above-described mesh anode 30.

[0046] The delay line anode 30A includes a wire portion 31A folded in a rectangular wave shape (zigzag), an electron passage portion 32A formed between the wire portions 31A and allowing electrons output from the output surface 10b to pass therethrough, and terminals 33a and 33b provided at both ends of the wire portion 31A, respectively. The wire portion 31A is a collection portion that collects the electrons e2 multiplied by the resistive anode 20. In the delay line anode 30A, when the electrons e2 hit the wire portion 31A, charges move from that position toward the terminals 33a and 33b at both ends of the wire portion 31A. The delay line anode 30A can detect one-dimensional position information based on the time difference at which the charges reach the terminals 33a and 33b.

[0047] Thus, when the charged particle detector 1 has a delay line anode 30A as a position-detecting anode, the electron transmittance can be increased, and therefore high detection efficiency can be obtained. In particular, the delay line anode 30A can operate at a maximum of 40 MHz for position detection, and multi-hits are less likely to be a problem (because only the arrival time of the pulse output (charge) at terminals 33a and 33b is detected, multi-hits are not a problem). Note that multi-hit is a phenomenon in which two-dimensional position information cannot be obtained when there are two or more signal inputs / outputs to the microchannel plate 10 simultaneously. Therefore, when the charged particle detector 1 has a delay line anode 30A, that is, when the charged particle detector 1 uses both a resistive anode 20 and a delay line anode 30A, the above advantages of the resistive anode 20 can be utilized, while the multi-hit problem that may occur with the resistive anode 20 can be overcome by the delay line anode 30A, thereby improving position detection accuracy. Although Figure 7 illustrates the case where the conductor portion 31A is rectangular wave-shaped, the conductor portion 31A may also be spiral-shaped, for example.

[0048] Furthermore, in the above embodiment, an example was given in which the resistive anode 20 has a multiplier layer 23 in addition to the resistive layer 22. However, the resistive layer 22 has an electron multiplication function, and the multiplier layer 23 may be omitted. In other words, the resistive anode 20 may have a multiplier layer, which is a resistive layer for distributing the amount of charge according to the resistance value corresponding to the distance to the terminal 24. In this case, the configuration is simplified because the resistive layer for charge distribution of the resistive anode 20 also functions as a multiplier layer.

[0049] Furthermore, the above embodiment described a case in which the charged particle detector 1 performs two-dimensional position detection. However, the charged particle detector 1 may also perform one-dimensional position detection by, for example, combining (combining) the charge outputs of the first X terminal 24a and the first Y terminal 24c, and the charge outputs of the second X terminal 24b and the second Y terminal 24d into one, thereby treating them as two virtual terminals.

[0050] Furthermore, in the above embodiment, electrons (photoelectrons Pe) are exemplified as the charged particles detected by the charged particle detector 1, and the case in which the charged particle detector 1 functions as an electron detector is illustrated. However, the charged particle detector 1 can also be applied to other uses, such as an ion detector. When the charged particle detector 1 is used as an ion detector, the charged particles input to the charged particle detector 1 are ions. The input ions are converted into secondary electrons in the microchannel plate 10, and the resulting output is electrons e1.

[0051] 1... Charged particle detector, 10... Microchannel plate, 10a... Input surface, 10b... Output surface, 11, 12... Multiplication section, 20... Resistive anode, 22... Resistive layer, 23... Multiplication layer, 24... Terminal, 30... Mesh anode (anode), 30A... Delay line anode (anode, position-detecting anode), Pe... Photoelectron (charged particle), e1, e2... Electron.

Claims

1. A charged particle detector comprising: a microchannel plate having an input surface into which charged particles are incident, a multiplication unit that multiplies electrons based on the input of charged particles while maintaining positional information of the charged particles relative to the input surface, and an output surface that outputs electrons multiplied by the multiplication unit; a resistive anode that receives electrons incident from the output surface and outputs a charge signal corresponding to the incident position of the electrons; and an anode disposed in the spatial region between the output surface and the resistive anode, having an electron passage unit that allows electrons output from the output surface to pass through, and for collecting electrons output from the resistive anode, wherein the resistive anode includes a multiplication layer that performs electron multiplication and outputs electrons multiplied by the multiplication layer toward the anode.

2. The charged particle detector according to claim 1, wherein the anode is a mesh anode.

3. The charged particle detector according to claim 1, wherein the anode is a position-sensing anode.

4. The charged particle detector according to claim 3, wherein the position-detecting anode is a delay line anode.

5. The charged particle detector according to any one of claims 1 to 4, wherein the resistive anode has a plurality of terminals for outputting the charge signal and a resistive layer for distributing the amount of charge according to a resistance value corresponding to the distance to the terminals, and the multiplier layer is provided on the resistive layer.

6. The charged particle detector according to any one of claims 1 to 4, wherein the resistive anode has a plurality of terminals for outputting the charge signal and a multiplier layer which is a resistive layer for distributing the amount of charge according to a resistance value corresponding to the distance to the terminals.

7. The charged particle detector according to claim 5 or 6, wherein the plurality of terminals are arranged in a two-dimensional manner when viewed from a direction intersecting the output surface, and the resistive layer extends in a two-dimensional manner across the plurality of terminals when viewed from a direction intersecting the output surface.

8. The charged particle detector according to any one of claims 1 to 7, wherein the voltage applied to the multiplication layer is greater than the voltage applied to the output surface of the microchannel plate and less than the voltage applied to the anode.

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