Angle-resolved photoelectron spectrometer and method

Abstract

An angle-resolved photoelectron spectrometer and a method for such a spectrometer are described. The spectrometer comprises an electrostatic lens system (101) having a first end (1) and a second end (2) and arranged to form a beam of electrons emitted from a measurement area (A) on a sample surface (Ss) of a solid sample (3) and to transfer the electrons to the second end (2), and a first lens element (4) is configured to be arranged at a positive voltage with respect to the sample (3). The spectrometer comprises at least a first shielding electrode (17) having a limiting aperture (18) arranged such that, as viewed from a point on the sample surface (Ss) at the optical axis (6), an angle between the optical axis (6) and any point on the limiting aperture (18) is greater than 45° and less than 70°, and at least one compensation electrode (7) arranged around the optical axis (6) at a greater distance from the measurement area (A) than the first lens element (4). According to the method, the compensation electrode (7) is configured to be placed at a negative voltage with respect to the sample (3).

Description

Technical Field

[0001] The present invention relates to an angle-resolved photoelectron spectrometer arranged to analyze electrons emitted from a sample surface of a solid sample that emits particles, comprising a lens system having a first lens element and configured to place a positive voltage on the first lens element with respect to the sample surface in order to increase the emission angle from the sample surface for electrons that can enter the lens system. The present invention also relates to a method for an angle-resolved photoelectron spectrometer.

Background Art

[0002] The investigation of the electronic properties of surfaces has been a long-standing research field. There are several different techniques available for the investigation of the electronic properties of surfaces. Photoemission spectroscopy is a sensitive method in which photons are used to eject electrons from a sample. The electrons thus ejected are called photoelectrons. Photoelectrons are ejected from the surface of the sample in all directions. An electrostatic lens system is used to collect and focus the photoelectrons into an analyzer. The photoelectrons enter the lens system through an aperture.

[0003] The photoelectrons are accepted into the lens system at a certain acceptance angle. The acceptance angle can be increased by increasing the size of the aperture and / or by reducing the distance between the aperture and the sample. For different reasons, increasing the size of the aperture or reducing the distance between the aperture and the sample is not always desirable. Another way to increase the acceptance angle is to apply a voltage between the sample and the lens to create an extraction field between the sample and the lens entrance, which accelerates the photoelectrons into the aperture of the electrostatic lens system. An electrostatic lens system having such an extraction field is commonly called an oil-immersion lens, because the sample is part of the lens system.

[0004] The problem with using an extraction field is that non-uniform or waveform samples distort electron trajectories, thereby preventing the acquisition of an angularly resolved image of the sample. Furthermore, the electric field surrounding the sample influences the electron trajectories, further distorting them. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide an angle-resolved photoelectron spectrometer, which is arranged for the analysis of electrons emitted from the sample surface of a solid sample, the spectrometer which achieves a large receiving angle for electrons while still maintaining a near-zero electric field on the sample surface and preserving the integrity of the angular distribution.

[0006] Another objective is to provide a method and an angle-resolved photoelectron spectrometer lens system, which is arranged to analyze electrons emitted from the sample surface of a solid sample, the method of which maintains the integrity of the angular distribution while still keeping a near-zero electric field on the sample surface, while increasing the receiving angle for electrons. [Means for solving the problem]

[0007] At least one of these objectives is achieved by the angle-resolved photoelectron spectrometer and method according to the independent claim.

[0008] Further advantages are realized through the features of the dependent claims.

[0009] According to a first aspect of the present invention, an angle-resolved photoelectron spectrometer is provided, comprising an electrostatic lens system having a first end and a second end, the first end comprising a first lens element having a lens aperture to be positioned facing the sample surface of a solid sample. The angle-resolved photoelectron spectrometer comprises a measurement area for analyzing electrons at the second end. The electrostatic lens system comprises an optical axis extending from the first end to the second end through the lens aperture. The electrostatic lens system is positioned to form a beam of electrons emitted from the measurement area on the sample surface and entering through the lens aperture. The electrostatic lens system is positioned to transfer electrons to the second end. The first lens element is configured to be positioned with a positive voltage relative to the sample. The angle-resolved photoelectron spectrometer is characterized in that it comprises at least one shielding electrode having a limiting aperture. The shielding electrode is positioned between the sample and the first lens element, with the limiting aperture located within a distance from the sample surface of no more than 1 / 5 of the distance between the sample surface and the first lens element, the limiting aperture surrounding the optical axis, and the size of the limiting aperture and the distance between the sample surface and the limiting aperture such that the angle between the optical axis and the line between the sample surface and any point on the limiting aperture on the optical axis is greater than 45° and less than 70°. The angle-resolved photoelectron spectrometer includes at least one compensating electrode positioned around the optical axis at a longer distance from the measurement area than the first lens element. The compensating electrode is configured to be positioned with a negative voltage relative to the sample.

[0010] Coulomb's law states that the field from a point charge in a vacuum is proportional to the inverse square of the distance from the charge. In the simple and naive case, where point 0 is in the same direction, with a point charge q at a distance of 1 and a charge -4q at a distance of 2, the field at point 0 is 0. However, the field along the line between point 0 and charge q points away from charge q and increases with decreasing distance relative to charge q. This means that an electron placed between point 0 and charge q is accelerated towards q. What is achieved in this invention, where point 0 is the sample and charge q is the lens entrance, is a similar field distribution.

[0011] In the angle-resolved photoelectron spectrometer according to the first aspect of the present invention, it is possible to essentially cancel the electric field at the sample surface. Thus, when electrons are close to a surface where the electric field may be distorted by surface irregularities, the electric field does not affect the electrons.

[0012] The voltage applied to the compensating electrode is preferably such that a lower electric field is realized in the measurement area on the sample surface compared to the electric field produced by the voltage on the first lens element. Preferably, the voltage is selected such that the electric field in the measurement area is less than 10%, preferably less than 5%, and most preferably less than 1% of the electric field in the measurement area when the compensating electrode is at the same potential as the sample surface. The voltage on the compensating electrode may be such that the electric field in the measurement area satisfies one of these limits. It is preferable that the electric field in the measurement area remains positive so that no electron repulsion occurs. The positive voltage accelerates electrons toward the lens, which results in a larger detection angle. The voltage on the compensating electrode also realizes a lens effect that allows electrons with a larger emission angle to enter the lens aperture.

[0013] The inventors have observed that electrons with very large emission angles from the sample surface contribute to higher levels of noise. This is partly because the electrons enter the lens aperture at too large an angle. Thus, the lensing effect of the compensating electrode results in higher levels of noise. By introducing at least one shielding electrode having a limiting aperture according to the first embodiment, electrons with emission angles greater than 70° are removed. Since this setup is electrostatic, its size can be scaled up or down. To keep the size of this setup manageable, it is preferable that the limiting aperture be close to the sample surface and within 1 / 5, preferably 1 / 10, of the distance between the sample surface and the first lens element. This enables effective removal of electrons, thereby reducing the noise level.

[0014] When the voltage is applied to the first lens element and the compensating electrode, the compensating electrode can be configured such that the potential increases monotonically along the optical axis from the measurement area to the first lens element. In this way, during operation, a lower electric field will affect the electrons emitted from the sample surface. Furthermore, when the voltage is applied to the first lens element and the compensating electrode, if the potential increases monotonically along the optical axis from the measurement area to the first lens element, even lower energy particles can enter the lens aperture of the lens system.

[0015] The distance from the compensating electrode to the measurement area is preferably longer than the distance from the first lens element to the measurement area. Unless the area of ​​the compensating electrode is larger than the area of ​​the first lens element, a higher voltage of opposite polarity and sign to the sample surface must be applied to the compensating electrode in the measurement area, according to Coulomb's law, in order to cancel the voltage caused by the voltage on the first lens element. If the area of ​​the compensating electrode is much larger than the area of ​​the first lens element, the magnitude of the voltage on the compensating electrode may be smaller than the magnitude of the voltage on the first lens element. As the distance to the first lens element decreases, the influence of the electric field from the first lens element increases faster than the field from the compensating electrode. Therefore, when a voltage that cancels the electric field in the measurement area is applied to the compensating electrode, a monotonically increasing potential is realized.

[0016] At least one compensating electrode can be arranged symmetrically around the optical axis. Such a symmetrical arrangement of compensating electrodes makes it easier to achieve the desired compensation of the electric field in the measurement area.

[0017] The emission of electrons from the sample surface is caused by electromagnetic radiation from a light source. It is advantageous to provide electromagnetic radiation toward the sample surface at the steepest possible angle so as to focus on the sample surface. To achieve this, the electromagnetic radiation beam needs to pass close to the outside of the first lens element. The compensating electrode can be placed between the sample and the first lens element, along the optical axis, at a distance from the sample along the optical axis that is less than half the distance between the sample surface and the first lens element. By positioning the compensating element in this way, room remains for electromagnetic radiation to reach the sample. It also increases the distance between the element focusing on the electromagnetic radiation and the compensating electrode, which in turn reduces crosstalk between the element focusing on the electromagnetic radiation and the compensating electrode.

[0018] An angle-resolved photoelectron spectrometer can be positioned such that the shortest distance between the compensating electrode and the optical axis is less than twice, preferably less than 1.5 times, and most preferably less than 1 time, the longest distance from the periphery and optical axis of the lens system. In this way, the overall dimensions of the angle-resolved photoelectron spectrometer are kept small.

[0019] The shortest distance between the compensating electrode and the optical axis may be longer than the longest distance between the edge of the lens aperture and the optical axis. In this way, the risk of the compensating electrode limiting the maximum angle at which particles can be emitted from the sample surface but still enter the lens aperture is eliminated.

[0020] An angle-resolved photoelectron spectrometer may include at least one shielding electrode that blocks the line of sight from the compensating electrode to the measurement area on the sample surface. With such a shielding electrode arrangement, the effect of the electric field from the compensating electrode can also be controlled by the geometry and position of the compensating electrode, the shielding electrode, and the sample. This also results in the magnitude of the voltage on the compensating electrode being lower than the magnitude of the voltage on the first lens element, while enabling the cancellation of the electric field in the measurement area.

[0021] An angle-resolved photoelectron spectrometer may have at least two compensating electrodes, which are configured to allow movement of the position of the maximum electric field induced by the compensating electrodes by applying different voltages. Preferably, when the angle-resolved photoelectron spectrometer has more than one compensating electrode, the number of compensating electrodes is four. Two of the compensating electrodes can be used to move the position of the minimum electric field in a first direction on the sample surface, while the other two electrodes can be used to move the position of the minimum electric field in a second direction on the sample surface, the second direction being perpendicular to the first direction.

[0022] An angle-resolved photoelectron spectrometer may include at least one compensator electrode, which is symmetrically arranged around the optical axis and includes a compensator margin positioned along the optical axis between the lens aperture and the sample surface, the compensator margin defining an aperture through which electrons can pass, and each point on the compensator margin is at a greater distance from the optical axis than each point on the lens aperture margin.

[0023] An angle-resolved photoelectron spectrometer can be configured to apply a higher positive voltage to the compensating electrode than to the first lens element. The main function of the compensating electrode is to attract electrons emitted from the measurement area at a large angle toward the optical axis. In this way, the electrons are prevented from entering through the lens aperture. Due to their angles, the electrons do not reach the second end of the lens element. Therefore, noise is reduced by the compensating electrode.

[0024] According to a second aspect of the present invention, there is provided a method for an angle-resolved photoelectron spectrometer comprising an electrostatic lens system having a first end and a second end, the first end comprising a first lens element having a lens aperture to be disposed facing a sample surface of a solid sample, and the second end comprising a measurement region for analyzing electrons. The electrostatic lens system comprises an optical axis extending from the first end to the second end through the lens aperture. The electrostatic lens system is arranged to form a beam of electrons emitted from a measurement region on the sample surface and entering through the lens aperture. The electrostatic lens system is arranged to transfer the electrons to the second end. The method includes applying a positive voltage to a sample that emits particles onto the first lens element. The method is characterized in that it includes providing at least one shielding electrode having a restricted aperture between the sample and the first lens element, the restricted aperture being within a distance from the sample surface that is 1 / 5 or less of the distance between the sample surface and the first lens element, and the restricted aperture surrounding the optical axis. The size of the restricted aperture and the distance between the sample surface and the restricted aperture are such that the angle between the optical axis and a line between the sample surface at the optical axis and any point on the restricted aperture is greater than 45° and less than 70°. The method is also characterized in that it includes providing at least one compensation electrode arranged around the optical axis and arranging the compensation electrode at a negative voltage with respect to the sample that emits particles such that a lower electric field is achieved in the measurement region on the sample surface as compared to the electric field caused by the voltage on the first lens element.

[0025] With the method according to the second aspect of the present invention, it is possible to substantially cancel the electric field at the sample surface. Thus, when electrons are close to a surface where the electric field may be distorted by surface irregularities, the electric field does not affect the electrons.

[0026] The voltage applied to the compensation electrode is preferably of such a magnitude that a lower electric field is realized in the measurement area on the sample surface as compared to the electric field brought about by the voltage on the first lens element. In a setup according to the prior art, the compensation electrode is at the same potential as the sample surface and a voltage is applied on the first lens element. This results in an electric field being brought about in the measurement area. Preferably, according to a preferred embodiment, the voltage applied to the compensation electrode is selected such that the electric field in the measurement area is less than 10%, preferably less than 5%, most preferably less than 1% of the electric field in the measurement area when the compensation electrode is at the same potential as the sample surface, and the same voltage as in the first example is applied to the first lens element. The voltage on the compensation electrode may be of such a magnitude that the electric field in the measurement area satisfies one of the above limitations. It is preferable that the electric field in the measurement area remains positive so that electron repulsion does not occur. The voltage of the compensation electrode also realizes a lens effect that allows electrons with a larger emission angle to enter the lens aperture.

[0027] The inventor has noticed that electrons having a very large emission angle from the sample surface contribute to a higher level of noise. This is partly because the electrons enter the lens aperture at an angle that is too large. Thus, the lens effect of the compensation electrode results in a higher level of noise. By introducing at least one shielding electrode having a restricted aperture according to the first aspect, electrons having an emission angle greater than 70° are removed. Since this setup is electrostatic, its size can be enlarged or reduced. To keep the size of this setup manageable, it is preferable to have the restricted aperture close to the sample surface, within 1 / 5, preferably 1 / 10 of the distance between the sample surface and the first lens element. This enables effective removal of electrons. As a result, the noise level is reduced.

[0028] When the voltage is applied to the first lens element and the compensating electrode, the electrodes can be configured such that the potential increases monotonically along the optical axis from the measurement area to the first lens element. In this way, a lower electric field will affect the emission of electrons from the sample surface. Furthermore, when the voltage is applied to the first lens element and the compensating electrode, if the potential increases monotonically along the optical axis from the measurement area to the first lens element, even lower energy particles can enter the lens aperture of the lens system.

[0029] The negative voltage on the compensating electrode can be greater than the positive voltage on the first lens element. With such a voltage, the electric field on the sample surface can be completely canceled at a single point.

[0030] The method may include the step of providing at least one shielding electrode that electrically and partially shields the compensating electrode from the measurement area on the sample surface. With such a shielding electrode arrangement, the effect of the electric field from the compensating electrode can also be controlled by the geometry and position of the compensating electrode, the shielding electrode, and the sample. This also results in the voltage on the compensating electrode being lower than the voltage on the first lens element, while allowing for the cancellation of the electric field in the measurement area.

[0031] The method may include the step of providing at least two compensating electrodes, the voltage applied to the compensating electrodes being varied to move the position of the minimum electric field on the sample surface generated by all electrodes.

[0032] The method may include providing a corrective electrode having a corrective edge that is symmetrically arranged around the optical axis and positioned between the lens aperture and the sample surface along the optical axis. The corrective edge defines an aperture that allows electrons to pass through the corrective electrode, and each point on the edge is at a greater distance from the optical axis than each point on the lens aperture edge.

[0033] A higher positive voltage than that applied to the first lens element can be applied to the compensating electrode. The main function of the compensating electrode is to attract electrons emitted from the measurement area at a large angle toward the optical axis. In this way, the electrons are prevented from entering through the lens aperture. Due to their angles, the electrons do not reach the second end of the lens element. Therefore, noise is reduced by the compensating electrode.

[0034] With a higher positive voltage applied to the correction electrode, the potential will not increase monotonically along the optical axis from the measurement area to the first lens element.

[0035] Preferred embodiments of the present invention are described below with reference to the drawings. [Brief explanation of the drawing]

[0036] [Figure 1a] This figure schematically shows an angle-resolved photoelectron spectrometer according to an embodiment of the present invention. [Figure 1b] This is a magnified view of a portion of Figure 1a. [Figure 2] This is a cross-sectional view showing a portion of the spectrometer shown in Figure 1a, which has electron orbits resulting from the electric field under the first setting. [Figure 3] This is a cross-sectional view showing a portion of the spectrometer shown in Figure 2, which has electron orbits resulting from the electric field under the second setting. [Figure 4] This is a cross-sectional view showing a portion of the spectrometer shown in Figure 2, which has electron orbits resulting from the electric field under the second setting. [Figure 5] This is a cross-sectional view showing a portion of a spectrometer according to a different embodiment, having electron orbits resulting from an electric field according to a third setting. [Figure 6] This is a cross-sectional view showing a portion of a spectrometer according to a different embodiment, having electron orbits resulting from an electric field according to a fourth setting. [Figure 7] This is a perspective view showing some of the spectrometers in different embodiments. [Figure 8] This is a cross-sectional view showing a portion of an angle-resolved photoelectron spectrometer according to a different embodiment. [Figure 9] This is a cross-sectional view showing a portion of an angle-resolved photoelectron spectrometer according to a different embodiment. [Figure 10] This is a cross-sectional view showing a portion of an angle-resolved photoelectron spectrometer according to a different embodiment. [Modes for carrying out the invention]

[0037] The present invention is described in the following illustrative and non-limiting detailed description of exemplary embodiments with reference to the accompanying drawings. In the drawings, similar features in different drawings are indicated by the same reference numerals. The drawings are not to scale.

[0038] Figure 1a schematically shows an angle-resolved photoelectron spectrometer 100 according to an embodiment of the present invention. Figure 1b is an enlarged view of a portion of Figure 1a. The angle-resolved photoelectron spectrometer 100 comprises an electrostatic lens system 101 having a first end 1 and a second end 2 at a certain distance from the first end 1. A particle-emitting solid sample 3 is placed on a manipulator 16. The particle-emitting sample 3 is positioned so that its sample surface Ss faces the first end 1 of the electrostatic lens system 101. The electrostatic lens system 101 comprises a first lens element 4 having a lens aperture 5 and a further lens element 12. An optical axis 6 extends through the lens aperture 5 from the first end 1 to the second end 2. The electrostatic lens system 101 also comprises compensating electrodes 7 arranged symmetrically around the optical axis 6. The compensating electrode 7 is configured to be positioned at a voltage relative to the particle-emitting sample Ss in order to reduce the electric field in the measurement area A on the sample surface Ss compared to the electric field produced by the voltage on the first lens element 4. In Figure 1b, the measurement area is marked with a thick line. The measurement area is the area where electrons are emitted. The angle-resolved photoelectron spectrometer 100 includes a shielding electrode 17 having a limiting aperture 18. The shielding electrode 17 can be divided into two or more parts. The shielding electrode 17 is positioned between the sample 3 and the first lens element 4, with the limiting aperture 18 located within a distance 20 from the sample surface Ss that is no more than 1 / 5 of the distance D between the sample surface Ss and the first lens element 4, and the limiting aperture 18 surrounds the optical axis 6. The shielding electrode 17 can extend beyond 1 / 5 of the distance D between the sample surface Ss and the first lens element 4, as long as the aperture is within 1 / 5 of the distance D between the sample surface Ss and the first lens element 4. As shown in Figure 1b, the size of the limiting aperture 18 and the distance 20 between the sample surface and the limiting aperture 18 are such that the angle α between the optical axis 6 and the line 27 between the sample surface Ss on the optical axis 6 and any point on the limiting aperture 18 is greater than 45° and less than 70°, preferably less than 60°. In Figure 1b, the angle α is approximately 60°. In Figure 1b, the measurement area A is shown as a thick line on the sample surface Ss. Sample 3 is positioned such that the distance between the sample surface Ss and the limiting aperture 18 is independent of that of sample 3.Particles can be generated by electromagnetic radiation 25, which may be visible, ultraviolet, or X-rays, emitted from the sample surface Ss. The electrostatic lens system 101 is positioned to form a beam of electrons emitted from a measurement area A on the sample surface Ss of the sample 3 emitting the particles, entering the lens system through a lens aperture 5 at a first end 1, and transferring the electrons to a second end 2. After reaching the second end, the particles pass through an inlet 21 into a measurement area 22 and are analyzed by an analytical device 11, which may be, for example, an electrostatic hemisphere or a time-of-flight analyzer. The analyzer is not part of the lens system 101. The lens system 101 comprises a first lens element 4 at the first end 1 having a lens aperture 5, which is positioned facing the sample surface Ss to allow at least a portion of the particles to enter the lens system 101. The number of particles that enter through the lens aperture 5 is determined by the size of the lens aperture 5 and the emission angle of the particles from the sample 3 emitting the particles. If there is no electric field applied between the first lens element 4 and the sample emitting particles, the solid angle of the lens aperture 5 as viewed from the measurement area determines the emission angle for particles entering through the lens aperture 5. To increase the emission angle of particles entering through the lens aperture 5, the first lens element 4 is configured to be positioned with a voltage relative to the sample surface Ss that attracts particles from the sample surface Ss. By applying such a positive voltage to the first lens element 4, particles emitted from the measurement area A are accelerated toward the first lens element 4. This results in particles with a larger emission angle entering the lens aperture 5.

[0039] When the voltage is applied to the first lens element 4 and the compensation electrode 7, the compensation electrode 7 is configured such that the potential increases monotonically along the optical axis 6 from the measurement area A to the first lens element 4.

[0040] Apart from the first lens element 4, the electrostatic lens element 101 comprises a further lens element 12. The further lens element is not described in detail in this application because the focus of this application is on the field between the sample surface Ss and the first lens element 4.

[0041] The function of the electric field is described in more detail with respect to Figures 2 and 3. The voltage on the first lens element 4 should be positive in order to attract electrons. The electric field on the compensating electrode 7 should be negative in order to compensate for the electric field in sample 3 that is brought about by the positive electric field on the first lens element 4.

[0042] Figure 2 is a cross-sectional view of a portion of the angle-resolved photoelectron spectrometer 100 shown in Figure 1, which has electron orbits 13 resulting from the electric field under the first setting. Further lens elements are indicated by 12. In the embodiment shown in Figure 2, the kinetic energy of the electrons is 10 eV, and a positive voltage of 200 V is applied to the first lens element 4 relative to the sample surface Ss. This positive voltage results in strongly curved electron orbits close to the sample surface Ss. This causes electrons emitted from the sample surface Ss at angles within + / - 45 degrees from the optical axis 6 to enter through the lens aperture 5, compared to only + / - 15 degrees where there is no positive electric field. No voltage is applied to the compensating electrode 7. The electric field at 0.2 mm from the sample surface Ss is 8200 V / m in this case.

[0043] Figure 3 is a cross-sectional view of a portion of the angle-resolved photoelectron spectrometer 100 shown in Figure 1, which has electron orbits 13 resulting from the electric field under the second setting. In the embodiment shown in Figure 2, a positive voltage of 200 V is applied to the first lens element 4 relative to the sample surface Ss. A negative voltage of -386 V is applied to the compensating electrode 7. These electric fields produce an electric field of 0.3 V / m at 0.2 mm from the surface, which is considerably lower than the electric field under the first setting. If the kinetic energy of the electron is 100 eV, a tenfold increase in voltage will result in the same orbit. Therefore, the combination of the negative electric field from the compensating electrode and the positive electric field from the first lens element results in a weaker, more curved electron orbit closer to the sample surface Ss compared to the electric field under the first setting. However, as the electron moves toward the first lens element, the combined electric fields from the compensating electrode 7 and the first lens element 4 will bend the electron orbit. This results in electrons emitted from the sample surface Ss at angles within + / - 45 degrees from the optical axis 6 entering through the lens aperture 5 in an usable orbit, that is, electrons emitted from the sample surface Ss at angles within + / - 45 degrees from the optical axis 6 being transported to the second end 2 of the lens system 101 (Figure 1).

[0044] As can be seen in Figures 2 and 3, the compensating electrode 7 is positioned on the sample surface Ss on the same side as the first lens element 4. The distance R from the compensating electrode to the optical axis 6. C The distance R between the first lens element and the optical axis is the distance R between the first lens element and the optical axis. A It is longer. Furthermore, the compensating electrode 7 is positioned at a longer distance from the sample surface Ss along the optical axis 6 than the first lens element. This results in a considerably longer distance from the compensating electrode 7 to the measurement area A. The negative voltage on the compensating electrode 7 must be considerably higher than the positive voltage on the first lens element 4, as this allows the electric field from the compensating electrode to cancel out the electric field from the first lens element 4.

[0045] Figure 4 is a cross-sectional view of a portion of the angle-resolved photoelectron spectrometer 100 shown in Figure 3, which has electron orbits 13 resulting from an electric field under a second setting. Figure 4 also shows electron orbits for electrons with emission angles greater than 45 degrees with respect to the optical axis 6. As seen in Figure 4, some of the electron orbits with large emission angles will enter the lens aperture 5. These electron orbits 14 will have deviations that are too large for proper handling by the lens system 101. Typically, some of them will be transported to the second end 2 by back-folding mapping. Such electrons will introduce noise into the signal in the analyzer 11 at the second end 2 of the lens system 101. In Figure 4, only half of the shielding electrode 17 is shown to illustrate the block of electrons with large emission angles. In the embodiment in Figure 4, a focusing element 24 that focuses the electromagnetic radiation 25 onto the measurement area A is also shown. Depending on the choice of wavelength and implementation form, the focusing element may be a capillary tube for X-rays, an optical fiber, a lens, or a mirror.

[0046] Figure 5 shows a cross-sectional view of a portion of an angle-resolved photoelectron spectrometer 100 according to a different embodiment, having electron trajectories resulting from an electric field according to a third setting. In the embodiment shown in Figure 5, the compensating electrode 7 is positioned between the sample 3 and the first lens element 4 within a distance 23 from the sample 3 along the optical axis 6, where the distance 23 is less than half the distance D between the sample surface Ss and the first lens element 4 along the longitudinal axis 6. The portion of the angle-resolved photoelectron spectrometer 100 shown in Figure 5 includes a second shielding electrode 8 that blocks the line of sight from the compensating electrode 7 to the measurement area A on the sample surface Ss. The second shielding electrode 8 allows for the blocking of additional electrons, separate from those already blocked by the shielding electrode 17. In the embodiment shown in Figure 5, the kinetic energy of the electrons is 10 eV, and a voltage of -2.1 V is applied on the second shielding electrode. The function of the voltage on the second shielding electrode 8 is to repel electrons from the second shielding electrode 8. The compensating electrode is perpendicular to the optical axis 6 and provides acceleration along the optical axis 6. The shielding electrode also absorbs electrons emitted from the measurement area at a large angle with respect to the optical axis 6. A voltage of -30V is applied to the compensating electrode and a voltage of +80V is applied to the first lens element 4. As can be seen in Figure 5, electrons emitted from the measurement area at a large angle with respect to the optical axis 6 are absorbed by the first shielding electrode 17 and do not enter through the lens aperture 5. In the embodiment in Figure 6, a focusing element 24 is also shown that focuses the electromagnetic radiation 25 onto the measurement area A.

[0047] Figure 6 shows a cross-sectional view of a portion of an angle-resolved photoelectron spectrometer 100 according to a different embodiment, having electron trajectories resulting from an electric field according to a fourth setting. In the embodiment shown in Figure 6, the shielding electrode 8 has a frustoconical shape close to the sample 3. The embodiment in Figure 6 also shows a focusing element 24 that focuses the electromagnetic radiation 25 onto the measurement area A. As seen in Figure 6, the arrangement of the compensating electrode 7 closer to the sample than the first lens element 4 allows the focusing element 24 that focuses the electromagnetic radiation 25 to be positioned at a distance from the compensating electrode that is favorable from an electrostatic viewpoint. Furthermore, the focusing element can be positioned closer to the first lens element 4 compared to the embodiment in Figure 4. This results in the electromagnetic radiation 25 being incident on the sample surface Ss3 at a steeper angle, which in turn results in a smaller spot of electromagnetic radiation 25 on the sample surface Ss.

[0048] The angle-resolved photoelectron spectrometer 100 shown in Figure 6 includes a correction electrode 9 which is symmetrically arranged around the optical axis 6 and has a correction edge 10 positioned between the lens aperture 5 and the sample surface Ss along the optical axis 6. The lens aperture 5 has a lens aperture edge E A The corrective edge 10 defines an aperture that allows electrons to pass through the corrective electrode 9. Each point of the corrective edge 10 is defined by the lens aperture edge E A It is located at a longer distance from optical axis 6.

[0049] In the embodiment shown in Figure 6, the kinetic energy of the electrons is 10 eV, a voltage of +100 V is applied to the first lens element, a voltage of +104 V is applied to the correction electrode 9, a voltage of -9 V is applied to the shielding electrode 8, and a voltage of -1000 V is applied to the compensation electrode 7. The main function of the correction electrode is to attract electrons emitted from the measurement area at a large angle toward the optical axis 6. In this way, the electrons are prevented from entering through the lens aperture 5. In this way, noise is reduced.

[0050] Figure 7 shows a perspective view of a portion of an angle-resolved photoelectron spectrometer 100 according to a different embodiment. The portion of the angle-resolved photoelectron spectrometer 100 according to the embodiment of Figure 7 has four compensating electrodes 7, 7', 7'', 7''' and four corresponding second shielding electrodes 8, 8', 8'', 8''''. The portion of the angle-resolved photoelectron spectrometer 100 shown in Figure 7 also has four compensating electrodes 9, 9', 9'', of which only three are shown in Figure 7. In operation, different voltages can be applied to different compensating electrodes 7, 7', 7'', 7''' to move the point of lowest electric field across the sample surface. When the same voltage is applied to all compensating electrodes 7, 7', 7'', 7''', the point of lowest electric field becomes the optical axis.

[0051] Figure 8 shows a cross-sectional view of part of an angle-resolved photoelectron spectrometer 100 according to a different embodiment. The angle-resolved photoelectron spectrometer 100 in Figure 8 is similar to the one shown in Figure 5. The main difference between the embodiment in Figure 8 and the embodiment in Figure 5 is that the photoelectron spectrometer 100 in Figure 8 is equipped with a third shielding electrode 26, and the third shielding electrode 26 in this embodiment is similar to the first shielding electrode in Figure 8. The third shielding electrode 26 is positioned between the first shielding electrode 17 and the second shielding electrode 8. In Figure 8, the manipulator cover constitutes the first shielding electrode 17. It is possible to have the first shielding electrode 17 with a limiting aperture 18 at a different position by changing its location on the shielding electrode. However, it is preferable to have the limiting aperture 18 as close to the sample as possible, because such an arrangement effectively shields the sample from the surrounding environment.

[0052] Figure 9 shows a cross-sectional view of part of the angle-resolved photoelectron spectrometer 100 according to a different embodiment. The only difference from Figure 8 is that the compensating electrode 7 is moved downstream of the lens aperture 5, i.e., as shown in Figures 2 to 4.

[0053] Figure 10 shows a cross-sectional view of a part of the angle-resolved photoelectron spectrometer 100 according to a different embodiment. The embodiment in Figure 10 is similar to the embodiment shown in Figure 5, except that the first shielding electrode 17 is composed of the manipulator cover.

[0054] The embodiments described above can be modified in many ways without departing from the scope of the invention, limited only by the appended claims and their limitations. [Explanation of Symbols]

[0055] 1. First end 2. Second end 3. Solid samples, samples that release particles 4. First lens element 5 Lens aperture 6. Optical axis, longitudinal axis 7 Compensation electrode 7' compensation electrode 7'' compensation electrode 7''' compensation electrode 8. Second shielding electrode 8' Second shielding electrode 8'' Second shielding electrode 8'' Second shielding electrode 9 Correction electrode 9' correction electrode 9'' correction electrode 10 Correction edge 11. Analytical devices, analyzers 12 Further lens elements 13 Electron orbitals 14 Electron Orbitals 16 Manipulators 17. First shielding electrode 18 Restricted opening 20 distance 21 Entrance 22 Measurement area 23 distance 24 Focusing Elements 25 Electromagnetic radiation 26 Third shielding electrode 27 lines 100-angle resolved photoelectron spectrometer 101 Electrostatic lens system, electrostatic lens element

Claims

1. An electrostatic lens system (101) comprising a first lens element (4) having a first end (1) and a second end (2), the first end (1) having a lens aperture (5) positioned facing the sample surface (Ss) of a solid sample (3), The second end (2) has a measurement area (22) for analyzing electrons and Equipped with, The electrostatic lens system includes an optical axis (6) that passes through the lens aperture (5) and extends from the first end (1) to the second end (2), The electrostatic lens system is arranged to form a beam of electrons emitted from the measurement area (A) on the sample surface (Ss) and entering through the lens aperture (5), The electrostatic lens system is arranged to transfer the electrons to the second end (2), An angle-resolved photoelectron spectrometer (100) is configured such that the first lens element (4) is positioned with a positive voltage relative to the sample (3), A first shielding electrode (17) having a limiting aperture (18), wherein the shielding electrode (17) is positioned between the sample (3) and the first lens element (4), the limiting aperture (18) is located within a distance (20) from the sample surface (Ss) that is less than or equal to 1 / 5 of the distance (D) between the sample surface (Ss) and the first lens element (4), the limiting aperture (18) surrounds the optical axis (6), and the size of the limiting aperture (18) and the distance between the sample surface and the limiting aperture (18) are determined such that the angle between the optical axis (6) and the line between the sample surface (Ss) and any point on the optical axis (6) and the limiting aperture (18) is greater than 45° and less than 70°, At least one compensating electrode (7) is arranged around the optical axis (6) and To be equipped, An angle-resolved photoelectron spectrometer (100) characterized in that the compensation electrode (7) is configured to be positioned with a negative voltage relative to the sample (3).

2. The spectrometer (100) according to claim 1, wherein when the voltage is applied to the first lens element (4) and the compensating electrode, the compensating electrode (7) is configured such that the potential increases monotonically along the optical axis from the measurement area (A) to the first lens element (4).

3. The spectrometer (100) according to claim 1 or 2, wherein at least one compensating electrode (7) is arranged symmetrically around the optical axis (6).

4. The spectrometer (100) according to any one of claims 1 to 3, wherein the compensating electrode is positioned between the sample (3) and the first lens element (4) along the optical axis (6), within a distance from the sample (3) along the optical axis (6), and this distance is less than or equal to half the distance (D) between the sample surface (Ss) and the first lens element (4).

5. The shortest distance (R) between the compensating electrode (7) and the optical axis (6) Ｃ ) is the longest distance (R) from the periphery of the lens system (101) and from the optical axis (6). Ｌ A spectrometer (100) according to any one of claims 1 to 4, wherein the value is less than twice, preferably less than 1.5 times, and most preferably less than 1 time.

6. The shortest distance (R) between the compensating electrode (7) and the optical axis (6) Ｃ ) is the edge (E) of the lens aperture (5). Ａ A spectrometer (100) according to any one of claims 1 to 5, wherein the distance between the optical axis (6) is longer than the longest distance between the optical axis (6).

7. The spectrometer (100) according to claim 4, further comprising a second shielding electrode (8) that blocks the line of sight from the compensating electrode (7) to the measurement area (A) on the sample surface (Ss).

8. The spectrometer (100) according to claim 4, comprising at least two compensating electrodes (7', 7''), wherein the compensating electrodes are configured to allow the position of the minimum electric field on the sample surface generated by all electrodes (7', 7'') to move by applying different voltages.

9. The lens system comprises at least one corrective electrode (9) having a corrective edge (10) symmetrically arranged around the optical axis (6) and positioned between the lens aperture (5) and the sample surface (Ss) along the optical axis (6), wherein the corrective edge (10) defines an aperture that allows electrons to pass through the corrective electrode (9), and each point on the corrective edge (10) is on the edge (E) of the lens aperture. Ａ The spectrometer (100) according to claim 4, which is located at a longer distance from the optical axis than each of the points on the above.

10. An electrostatic lens system (101) comprising a first lens element (4) having a first end (1) and a second end (2), the first end (1) having a lens aperture (5) positioned facing the sample surface (Ss) of a solid sample (3), The second end (2) has a measurement area (22) for analyzing electrons and Equipped with, The electrostatic lens system includes an optical axis (6) that passes through the lens aperture (5) and extends from the first end (1) to the second end (2), The electrostatic lens system is arranged to form a beam of electrons emitted from the measurement area (A) on the sample surface (Ss) and entering through the lens aperture (5), A method for an angle-resolved photoelectron spectrometer (100), wherein the electrostatic lens system is arranged to transfer the electrons to the second end (2), The process includes the step of applying a positive voltage to the sample (3) on the first lens element, A step of providing a first shielding electrode (17) having a limiting aperture (18) between the sample (3) and the first lens element (4), wherein the limiting aperture (18) is located within a distance (20) from the sample surface (Ss) that is 1 / 5 or less of the distance (D) between the sample surface (Ss) and the first lens element (4), the limiting aperture (18) surrounds the optical axis (6), and the size of the limiting aperture (18) and the distance between the sample surface and the limiting aperture (18) are determined such that the angle between the optical axis (6) and any point on the limiting aperture (18), as viewed from a point on the sample surface (Ss) on the optical axis (6), is greater than 45° and less than 70°. The steps include providing at least one compensating electrode (7) arranged around the optical axis (6), The steps include: positioning the compensating electrode (7) with a negative voltage relative to the particle-emitting sample (Ss) such that a lower electric field is realized in the measurement area (A) on the sample surface (Ss) compared to the electric field produced by the voltage on the first lens element (4); A method characterized by including

11. The method according to claim 10, wherein when the voltage is applied to the first lens element (4) and the compensating electrode (7), the compensating electrode (7) is configured such that the potential increases monotonically from the measurement area (A) to the first lens element (4) along the optical axis (6).

12. The method according to claim 10 or 11, wherein the negative voltage on the compensating electrode (7) is greater than the positive voltage on the first lens element (4).

13. The method according to any one of claims 10, 11, or 12, wherein the voltage of the compensating electrode 7 is such that the electric field in the measurement area (A) is less than 10%, preferably less than 5%, and most preferably less than 1% of the electric field in the measurement area (A) when the compensating electrode (7) is at the same potential as the sample surface (Ss).

14. The method according to any one of claims 10 to 13, wherein the compensating electrode is positioned between the sample (3) and the first lens element (4) along the optical axis (6), within a distance from the sample (3) along the optical axis (6), and is less than or equal to half the distance (D) between the sample surface (Ss) and the first lens element (4).

15. The method according to claim 14, further comprising the step of providing a second shielding electrode (8) that blocks the line of sight from the compensating electrode (7) to the measurement area (A) on the sample surface (Ss).

16. The method according to claim 14, wherein the spectrometer comprises at least two compensating electrodes (7', 7''), and the voltage applied to the compensating electrodes is varied to move the position of the maximum electric field generated by the compensating electrodes (7', 7'').

17. The step includes providing a corrective electrode (9) having a corrective edge (10) symmetrically arranged around the optical axis (6) and positioned between the lens aperture (5) and the sample surface (Ss) along the optical axis (6), wherein the corrective edge (10) defines an aperture that allows electrons to pass through the corrective electrode (9), and each point on the edge (10) is on the edge (E) of the lens aperture. Ａ The method according to claim 14, wherein each of the points is located at a longer distance from the optical axis than the points on the above.

18. The method according to claim 17, wherein a positive voltage higher than that on the first lens element (4) is applied to the corrective electrode (9).

Images