Angle-resolved photoelectron spectrometer and method

Abstract

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

Description

Technical Field

[0001] This invention relates to an angle-resolved photoelectron spectrometer arranged to analyze electrons emitted from the sample surface of a particle-emitting solid sample. The spectrometer includes a lens system with a first lens element and is configured to apply a positive voltage to the first lens element relative to the sample surface to increase the emission angle of electrons that can enter the lens system from the sample surface. The invention also relates to a method for using the angle-resolved photoelectron spectrometer. Background Technology

[0002] The detection of surface electronic properties has long been a research area. Many different techniques can be used to examine the electronic properties of surfaces. Photoelectron emission spectroscopy is a sensitive method that uses photons to emit electrons from a sample. Electrons emitted in this way are called photoelectrons. Photoelectrons are emitted from the sample surface in all directions. An electrostatic lens system is used to collect the photoelectrons and focus them onto the analyzer. The photoelectrons enter the lens system through an aperture.

[0003] Photoelectrons are received in a lens system at a receiving angle. The receiving angle can be increased by increasing the aperture size and / or by decreasing the distance between the aperture and the sample. However, increasing the aperture size or decreasing the distance between the aperture and the sample is not always desirable for various reasons. Another method to increase the receiving angle is to apply a voltage between the sample and the lens to create an extraction field between the sample and the lens inlet, which accelerates the photoelectrons into the aperture of the electrostatic lens system. Electrostatic lens systems with such an extraction field are often called immersion lenses because the sample is part of the lens system.

[0004] The problem with using an extraction field is that an inhomogeneous or wavy sample distorts the electron trajectory, preventing the acquisition of an angle-resolved image of the sample. Furthermore, the surrounding electric field will affect the sample and distort the electron trajectory. Summary of the Invention

[0005] The purpose of this invention is to provide an angle-resolved photoelectron spectrometer arranged to analyze electrons emitted from the sample surface of a solid sample, which provides a large receiving angle for electrons while maintaining a near-zero electric field at 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 arranged to analyze electrons emitted from the sample surface of a solid sample, which increases the electron reception angle while still maintaining a near-zero electric field on the sample surface and preserving the integrity of the angular distribution.

[0007] According to a first aspect of the invention, an angle-resolved photoelectron spectrometer is provided, comprising an electrostatic lens system having a first end and a second end, and a first lens element at the first end having a lens aperture arranged to face a sample surface of a solid sample. The second end of the angle-resolved photoelectron spectrometer includes a measurement region for analyzing electrons. The electrostatic lens system includes an optical axis extending from the first end through the lens aperture to the second end. The electrostatic lens system is arranged to form an electron beam emitted from the measurement region on the sample surface and entering through the lens aperture. The electrostatic lens system is arranged to transport electrons to the second end. The first lens element is configured to be arranged with a positive voltage relative to the sample. The angle-resolved photoelectron spectrometer is characterized by including at least one shielding electrode with a limiting aperture. A shielding electrode is positioned between the sample and the first lens element, wherein a limiting aperture is located at a distance from the sample surface no greater than one-fifth of the distance between the sample surface and the first lens element, wherein the limiting aperture surrounds the optical axis, and wherein the size of the limiting aperture and the distance between the sample surface and the limiting aperture are such that the angle between the optical axis and the line between any point on the limiting aperture and the sample surface at the optical axis is greater than 45° and less than 70°. The angle-resolved photoelectron spectrometer includes at least one compensation electrode positioned around the optical axis at a greater distance from the measurement region than the first lens element. This compensation electrode is configured to be positioned with a negative voltage relative to the sample.

[0008] Coulomb's law states that the field of a point charge in a vacuum is proportional to the reciprocal of the square of the distance from the charge. In the simple, primitive case where there is a point charge q at a distance 1 in the same direction from point 0 and a charge -4q at a distance 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 this field increases as the distance to charge q decreases. This means that electrons located between point 0 and charge q are accelerated toward q. This invention achieves a similar field distribution, where point 0 is the sample and charge q is the lens entrance.

[0009] Using the angle-resolved photoelectron spectrometer according to the first aspect of the invention, the electric field at the sample surface can be substantially eliminated. Thus, when electrons approach the surface, no electric field affects them, whereas at the surface, the electric field would be distorted due to surface irregularities.

[0010] The voltage applied to the compensation electrode preferably has a value such that it achieves a lower electric field at the measurement region on the sample surface compared to the electric field caused by the voltage on the first lens element. Preferably, when the compensation electrode and the sample surface are at the same potential, the voltage is selected such that the electric field at the measurement region is less than 10%, preferably less than 5%, and most preferably less than 1%. The voltage on the compensation electrode can have a value such that the electric field at the measurement region satisfies one of these limitations. Preferably, the electric field at the measurement region is still positive, so that electrons do not experience repulsion. With a positive voltage, electrons are accelerated toward the lens, resulting in a larger reception angle. Therefore, the voltage of the compensation electrode also provides a lens effect, which allows electrons with a larger emission angle to enter the lens aperture.

[0011] The inventors have recognized that electrons with very large emission angles from the sample surface contribute to higher levels of noise. This is partly because they enter the lens aperture at excessively large angles. Therefore, the lensing effect of the compensating electrode will result in even higher levels of noise. By introducing at least one shielding electrode with a limiting aperture according to the first aspect, electrons with emission angles greater than 70° are removed. Since the device is electrostatic, its size is scalable. To keep the device size manageable, it is preferable to position the limiting aperture close to the sample surface and within one-fifth, preferably one-tenth, of the distance between the sample surface and the first lens element. This provides for effectively removed electrons. This reduces the noise level.

[0012] The compensation electrode can be configured such that when a voltage is applied to the first lens element and the compensation electrode, the potential increases strictly along the optical axis from the measurement region to the first lens element. Therefore, during operation, a lower electric field will affect electrons emitted from the sample surface. Furthermore, when a voltage is applied to the first lens element and the compensation electrode, because the potential increases strictly along the optical axis from the measurement region to the first lens element, even low-energy particles may enter the lens aperture of the lens system.

[0013] The distance from the compensation electrode to the measurement area is preferably greater than the distance from the first lens element to the measurement area. To eliminate the voltage at the measurement area caused by the voltage on the first lens element, according to Coulomb's law, a higher voltage with the opposite sign to the sample surface must be applied to the compensation electrode, unless the area of ​​the compensation electrode is larger than the area of ​​the first lens element. If the area of ​​the compensation electrode is much larger than the area of ​​the first lens element, the value of the voltage on the compensation electrode can be less than the value of the voltage on the first lens element. When the distance to the first lens element is small, the effect of the electric field from the first lens element will increase faster than the electric field from the compensation electrode. Therefore, when a voltage is applied to the compensation electrode to cancel the electric field at the measurement area, a strictly increasing potential is achieved.

[0014] The at least one compensation electrode can be arranged symmetrically about the optical axis. Such a symmetrical arrangement of the compensation electrodes makes it easier to achieve the desired compensation of the electric field in the measurement area.

[0015] Electron emission from the sample surface is induced by electromagnetic radiation from the light source. It is advantageous to provide electromagnetic radiation to the sample surface at the steepest possible angle and focus it onto the sample surface. For this purpose, the electromagnetic radiation beam needs to pass close to the outer edge of the first lens element. A compensation electrode can be arranged along the optical axis between the sample and the first lens element, within a distance no greater than half the distance between the sample surface and the first lens element along the optical axis from the sample. By arranging the compensation element in this way, it leaves space for the electromagnetic radiation to reach the sample. It also increases the distance between the element focusing the electromagnetic radiation and the compensation electrode, which in turn reduces crosstalk between the element focusing the electromagnetic radiation and the compensation electrode.

[0016] An angle-resolved photoelectron spectrometer can be arranged such that the minimum distance between the compensation electrode and the optical axis is less than twice the maximum distance between the periphery of the lens system and the optical axis, preferably less than 1.5 times, and most preferably less than 1 times. In this way, the overall size of the angle-resolved photoelectron spectrometer remains small.

[0017] The minimum distance between the compensation electrode and the optical axis can be greater than the maximum distance between the lens aperture edge and the optical axis. This eliminates the risk that the compensation electrode will limit the maximum angle at which particles can be emitted from the sample surface and still enter the lens aperture.

[0018] An angle-resolved photoelectron spectrometer may include at least one shielding electrode that blocks the line of sight from the compensation electrode to the measurement area on the sample surface. With this arrangement of shielding electrodes, the influence of the electric field from the compensation electrode can be controlled by the geometry and position of the compensation electrode, the shielding electrode, and the sample. This also results in a voltage on the compensation electrode that can be lower than the voltage on the first lens element, while simultaneously eliminating the electric field at the measurement area.

[0019] The angle-resolved photoelectron spectrometer may include at least two compensation electrodes, wherein the compensation electrodes are configured to be applied different voltages to enable movement of the position of the maximum electric field induced by the compensation electrodes. Preferably, when the angle-resolved photoelectron spectrometer includes more than one compensation electrode, the number of compensation electrodes is four. Two compensation electrodes can be used to move the position of the minimum electric field on the sample surface along a first direction, while the other two electrodes can be used to move the position of the minimum electric field on the sample surface along a second direction, wherein the second direction is perpendicular to the first direction.

[0020] The angle-resolved photoelectron spectrometer may include at least one correction electrode arranged symmetrically about the optical axis, including a correction edge arranged along the optical axis between the lens aperture and the sample surface, wherein the correction edge defines an opening that allows electrons to pass through the correction electrode, and wherein each point on the correction edge is at a greater distance from the optical axis than each point on the edge of the lens aperture.

[0021] An angle-resolved photoelectron spectrometer can be configured to apply a higher positive voltage to the correction electrode than to the first lens element. The primary function of the correction electrode is to attract electrons emitted from the measurement region at a large angle relative to the optical axis. This prevents the electrons from entering through the lens aperture. The electrons, due to their angle, do not reach the second end of the lens element. Therefore, noise is reduced by the correction electrode.

[0022] According to a second aspect of the invention, a method for an angle-resolved photoelectron spectrometer is provided, the spectrometer comprising an electrostatic lens system having a first end and a second end, and including at the first end a first lens element having a lens aperture arranged to face a sample surface of a solid sample, and at the second end a measurement region for analyzing electrons. The electrostatic lens system includes an optical axis extending from the first end through the lens aperture to the second end. The electrostatic lens system is configured to form an electron beam emitted from the measurement region on the sample surface and entering through the lens aperture. The electrostatic lens system is arranged to transport electrons to the second end. The method includes the step of applying a positive voltage relative to the particle-emitting sample on the first lens element. The method is characterized in that it includes the step of providing at least one shielding electrode having a limiting aperture between the sample and the first lens element, wherein the limiting aperture extends from the sample surface at a distance not greater than one-fifth of the distance between the sample surface and the first lens element, and wherein the limiting aperture surrounds the optical axis. The size of the limiting aperture and the distance between the sample surface and the limiting aperture are such that the angle between the optical axis and a line between any point on the limiting aperture and the sample surface at the optical axis is greater than 45° and less than 70°. The method is further characterized by comprising the following steps: providing at least one compensation electrode arranged around an optical axis; and arranging the compensation electrode relative to the particle emission sample with a negative voltage to achieve a lower electric field at the measurement area on the sample surface compared to the electric field caused by the voltage on the first lens element.

[0023] Using the method according to the second aspect of the invention, the electric field at the sample surface can be substantially eliminated. Thus, when electrons approach the surface, no electric field affects them, where the electric field would be distorted due to surface irregularities.

[0024] The voltage applied to the compensation electrode preferably has a value such that a lower electric field is achieved at the measurement region on the sample surface compared to the electric field caused by the voltage on the first lens element. In the prior art apparatus, the compensation electrode is at the same potential as the sample surface, and a voltage is applied to the first lens element. This generates an electric field in the measurement region. Preferably, according to a preferred embodiment, the voltage applied to the compensation electrode is selected such that when the compensation electrode and the sample surface are at the same potential and the same voltage is applied to the first lens element as in the first example, the electric field at the measurement region is less than 10%, preferably less than 5%, and most preferably less than 1%. The voltage on the compensation electrode can have a value such that the electric field at the measurement region satisfies one of the aforementioned limitations. Preferably, the electric field at the measurement region remains positive, and electrons do not experience repulsion. The voltage of the compensation electrode also provides a lensing effect, which allows electrons with a large emission angle to enter the lens aperture.

[0025] The inventors have recognized that electrons with very large emission angles from the sample surface contribute to higher levels of noise. This is partly because they enter the lens aperture at excessively large angles. Therefore, the lensing effect of the compensating electrode will result in even higher levels of noise. By introducing at least one shielding electrode with a limiting aperture according to the first aspect, electrons with emission angles greater than 70° are removed. Since the device is electrostatic, its size is scalable. To keep the device size manageable, it is preferable to place the limiting aperture close to the sample surface and within one-fifth, preferably one-tenth, of the distance between the sample surface and the first lens element. This provides for effectively removed electrons. This reduces the noise level.

[0026] The electrode can be configured such that when the voltage is applied to the first lens element and the compensation electrode, the potential increases strictly along the optical axis from the measurement region to the first lens element. Therefore, 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 compensation electrode, because the potential increases strictly along the optical axis from the measurement region to the first lens element, even low-energy particles may enter the lens aperture of the lens system.

[0027] The negative voltage on the compensation electrode can be greater than the positive voltage on the first lens element. Using such a voltage, the electric field at the sample surface can be completely canceled out at a single point.

[0028] The method may include the step of providing at least one shielding electrode that partially electrically shields the compensation electrode from the measurement area on the sample surface. With this arrangement of the shielding electrode, the influence of the electric field from the compensation electrode can also be controlled by the geometry and position of the compensation electrode, the shielding electrode, and the sample. This also results in the voltage on the compensation electrode being lower than the voltage on the first lens element, while simultaneously eliminating the electric field at the measurement area.

[0029] The method may include providing at least two compensation electrodes, wherein the voltage applied to the compensation electrodes is varied to move the position of the minimum electric field on the sample surface generated by all the electrodes.

[0030] The method may include the step of providing a correction electrode arranged symmetrically about an optical axis, the correction electrode including a correction edge disposed along the optical axis between a lens aperture and a sample surface. The correction edge defines an opening that allows electrons to pass through the correction electrode, wherein each point on the edge is at a greater distance from the optical axis compared to each point on the edge of the lens aperture.

[0031] A higher positive voltage than that applied to the first lens element can be applied to the correction electrode. The main function of the correction electrode is to attract electrons emitted from the measurement region at a large angle relative to the optical axis. This prevents the electrons from entering through the lens aperture. The electrons do not reach the second end of the lens element due to their angle. Therefore, noise is reduced by the correction electrode.

[0032] When a higher positive voltage is applied to the calibration electrode, the potential will not increase strictly along the optical axis from the measurement area to the first lens element.

[0033] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Attached Figure Description

[0034] Figure 1a An angle-resolved photoelectron spectrometer according to an embodiment of the present invention is illustrated schematically.

[0035] Figure 1b yes Figure 1a A magnified view of a portion of it.

[0036] Figure 2 It shows Figure 1a The cross-section of a portion of the spectrometer is shown, in which electron trajectories are generated by an electric field according to a first setting.

[0037] Figure 3 It shows Figure 2 The cross-section of a portion of the spectrometer is shown, in which electron trajectories are generated by an electric field according to a second setting.

[0038] Figure 4 It shows Figure 2The cross-section of a portion of the spectrometer is shown, in which electron trajectories are generated by an electric field according to a second setting.

[0039] Figure 5 A cross-section of a portion of a spectrometer according to different embodiments is shown, wherein electron trajectories are generated by an electric field configured according to a third method.

[0040] Figure 6 A cross-section of a portion of a spectrometer according to different embodiments is shown, wherein electron trajectories are generated by an electric field configured according to a fourth method.

[0041] Figure 7 A perspective view of a portion of a spectrometer according to different embodiments is shown.

[0042] Figure 8 A cross-section of a portion of an angle-resolved photoelectron spectrometer according to different embodiments is shown.

[0043] Figure 9 A cross-section of a portion of an angle-resolved photoelectron spectrometer according to different embodiments is shown.

[0044] Figure 10 A cross-section of a portion of an angle-resolved photoelectron spectrometer according to different embodiments is shown. Detailed Implementation

[0045] The 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 figures are indicated by the same reference numerals. The drawings are not drawn to scale.

[0046] Figure 1a An angle-resolved photoelectron spectrometer 100 according to an embodiment of the present invention is schematically shown. Figure 1b yes Figure 1a A magnified view of a portion. The angle-resolved photoelectron spectrometer 100 includes an electrostatic lens system 101 having a first end 1 and a second end 2 spaced apart from the first end 1. A particle-emitting solid sample 3 is arranged on a manipulator 16. The particle-emitting sample 3 is arranged such that its sample surface Ss faces the first end 1 of the electrostatic lens system 101. The electrostatic lens system 101 includes a first lens element 4 having a lens aperture 5 and an additional lens element 12. An optical axis 6 extends from the first end 1 through the lens aperture 5 to the second end 2. The electrostatic lens system 101 also includes a compensation electrode 7 arranged symmetrically around the optical axis 6. The compensation electrode 7 is configured to be arranged with a voltage relative to the particle-emitting sample Ss to reduce the electric field at the measurement region A on the sample surface Ss compared to the electric field caused by the voltage on the first lens element 4. Figure 1bIn the diagram, the measurement area is marked with a thick line. The measurement area is the region where electrons are emitted. The angle-resolved photoelectron spectrometer 100 includes a shielding electrode 17 with a limiting aperture 18. The shielding electrode 17 can be divided into two or more parts. The shielding electrode 17 is arranged between the sample 3 and the first lens element 4, wherein the limiting aperture 18 is within a distance 20, the distance 20 from the sample surface Ss not exceeding one-fifth of the distance D between the sample surface Ss and the first lens element 4, wherein the limiting aperture 18 surrounds the optical axis 6. As long as the aperture is within the said one-fifth of the distance D between the sample surface Ss and the first lens element 4, the shielding electrode 17 can extend beyond the said one-fifth of the distance D between the sample surface Ss and the first lens element 4. Figure 1b As shown, the size of the limiting hole 18 and the distance 20 between the sample surface and the limiting hole 18 are such that the angle α between the optical axis 6 and the line 27 between the sample surface Ss located on the optical axis 6 and any point on the limiting hole 18 is greater than 45° and less than 70°, preferably less than 60°. Figure 1b In this case, angle α is approximately 60°. Figure 1b In the diagram, measurement area A is shown as a thick line on the sample surface Ss. Sample 3 is arranged such that the distance between sample surface Ss and limiting aperture 18 is independent of sample 3. Particles can be emitted from sample surface Ss by electromagnetic radiation 25, which can be visible light, ultraviolet light, or X-rays. Electrostatic lens system 101 is arranged to form an electron beam emitted from measurement area A on sample surface Ss of particle emission sample 3. This electron beam enters the lens system through lens aperture 5 at first end 1 and transmits electrons to second end 2. After reaching the second end, the particles pass through inlet 21 into electron measurement area 22 and are analyzed by analyzer device 11, which can be, for example, an electrostatic hemisphere or time-of-flight analyzer. The analyzer is not part of lens system 101. Lens system 101 includes a first lens element 4 at first end 1 with lens aperture 5 arranged facing sample surface Ss to allow at least a portion of the particles to enter lens system 101. The number of particles entering through the lens aperture 5 is determined by the size of the lens aperture 5 and the emission angle of the particles from the particle emission sample 3. Without any applied electric field between the first lens element 4 and the particle emission sample, the solid angle of the lens aperture 5 as seen from the measurement area determines the emission angle of the particles entering through the lens aperture 5. To increase the emission angle of the particles entering through the lens aperture 5, the first lens element 4 is configured with a voltage relative to the sample surface Ss, which 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 will be accelerated toward the first lens element 4. This will result in particles with larger emission angles entering the lens aperture 5.

[0047] The compensation electrode 7 is configured such that when the voltage is applied to the first lens element 4 and the compensation electrode 7, the potential increases strictly along the optical axis 6 from the measurement region A to the first lens element 4.

[0048] In addition to the first lens element 4, the electrostatic lens element 101 also includes an additional lens element 12. The additional lens element will not be described in detail in this application, as the focus of this application is on the field between the sample surface Ss and the first lens element 4.

[0049] Reference Figure 2 and Figure 3 The function of the electric field is described in more detail. The voltage on the first lens element 4 should be positive to attract electrons. The electric field on the compensation electrode 7 should be negative to compensate for the electric field at sample 3 caused by the positive electric field on the first lens element 4.

[0050] Figure 2 It shows Figure 1a The shown angle resolves a portion of the cross-section of the photoelectron spectrometer 100, where electron trajectories 13 are generated by an electric field according to a first setting. An additional lens element is designated 12. Figure 2 In the illustrated embodiment, the electron kinetic energy 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 generates a strongly curved electron trajectory near the sample surface Ss. Compared to only + / - 15° without any positive electric field, this causes electrons emitted from the sample surface Ss at an angle within + / - 45° with the optical axis 6 to enter through the lens aperture 5. No voltage is applied to the compensation electrode 7. In this case, the electric field at a distance of 0.2 mm from the sample surface Ss is 8200 V / m.

[0051] Figure 3 It shows Figure 1a The angle-resolved photoelectron spectrometer 100 shown is a portion thereof, wherein electron trajectories 13 are generated by an electric field configured according to a second setting. Figure 2In the illustrated embodiment, a positive voltage of 200V is applied to the first lens element 4 relative to the sample surface Ss. A negative voltage of -386V is applied to the compensation electrode 7. These electric fields result in an electric field of 0.3V / m at a distance of 0.2 mm from the surface, significantly lower than the electric field according to the first setting. With an electron kinetic energy of 100eV, the same trajectory is achieved if the voltage is increased tenfold. Therefore, compared to the electric field according to the first setting, the combination of the negative electric field from the compensation electrode and the positive electric field from the first lens element results in an electron trajectory that is less strongly bent near the sample surface Ss. However, as electrons travel toward the first lens element, the combined electric field from the compensation electrode 7 and the first lens element 4 will bend the electron trajectory. This causes electrons emitted from the sample surface Ss at an angle within + / -45° with the optical axis 6 to enter through the lens aperture 5 with a usable trajectory; that is, electrons emitted from the sample surface Ss at an angle within + / -45° with the optical axis 6 will be transmitted to the second end 2 of the lens system 101. Figure 1a ).

[0052] like Figure 2 and Figure 3 As shown, the compensation electrode 7 is arranged on the same side of the sample surface Ss as the first lens element 4. The distance R from the compensation electrode to the optical axis 6 is... C Greater than the distance R between the first lens element and the optical axis A Furthermore, the compensation electrode 7 is positioned along the optical axis 6 at a greater distance from the sample surface Ss than the first lens element. This results in a significantly larger distance from the compensation electrode 7 to the measurement area A. In order for the electric field from the compensation electrode to cancel the electric field from the first lens element 4, the negative voltage on the compensation electrode 7 must be significantly higher than the positive voltage on the first lens element 4.

[0053] Figure 4 It shows Figure 3 The cross-section of a portion of the angle-resolved photoelectron spectrometer 100 is shown, wherein the electron trajectory 13 is generated by an electric field according to a second setting. Figure 4 The electron trajectory of an electron with an emission angle greater than 45° relative to optical axis 6 is shown. For example... Figure 4 As shown, some electron trajectories enter the lens aperture 5 at large emission angles. These electron trajectories 14 deviate too much from the correct processing by the lens system 101. Typically, some of them will be transferred to the second end 2 during the backward-folding mapping. Such electrons will generate noise in the signal of the analyzer 11 at the second end 2 of the lens system 101. Figure 4 In the diagram, only half of the shielding electrode 17 is shown to illustrate the blocking of electrons with large emission angles. Figure 4In one embodiment, a focusing element 24 is also shown to focus electromagnetic radiation 25 onto the measurement region A. Depending on the wavelength and implementation, the focusing element may be a capillary, optical fiber, lens, or mirror used for X-rays.

[0054] Figure 5 A cross-section of a portion of an angle-resolved photoelectron spectrometer 100 according to different embodiments is shown, wherein electron trajectories are generated by an electric field configured according to a third setting. Figure 5 In the embodiment shown, the compensation electrode 7 is arranged along the optical axis 6 between the sample 3 and the first lens element 4, within a distance from the sample 3 along the optical axis 6 that is no greater than half the distance D between the sample surface Ss and the first lens element 4. Figure 5 The angle-resolved photoelectron spectrometer 100 shown includes a second shielding electrode 8, which blocks the line of sight from the compensation electrode 7 to the measurement region A on the sample surface Ss. The second shielding electrode 8 provides additional electrons separated from those already blocked by the shielding electrode 17. Figure 5 In the illustrated embodiment, the electron's kinetic energy is 10 eV, and a voltage of -2.1 V is applied to the second shielding electrode. The voltage on the second shielding electrode 8 serves to repel electrons from it. The compensation electrode provides acceleration perpendicular to and along the optical axis 6. The shielding electrode also absorbs electrons emitted from the measurement region at a large angle relative to the optical axis 6. A voltage of -30 V is applied to the compensation electrode, while a voltage of +80 V is applied to the first lens element 4. Figure 5 As shown, electrons emitted from the measurement area at a large angle relative to the optical axis 6 are absorbed by the first shielding electrode 17 and do not enter through the lens aperture 5. Figure 6 In one embodiment, a focusing element 24 is also shown that focuses electromagnetic radiation 25 onto the measurement area A.

[0055] Figure 6 A cross-section of a portion of an angle-resolved photoelectron spectrometer 100 according to different embodiments is shown, wherein electron trajectories are generated by an electric field configured according to a fourth setting. Figure 6 In the illustrated embodiment, the shielding electrode 8 has a truncated cone shape close to that of the sample 3. Figure 6 In one embodiment, a focusing element 24 is also shown that focuses electromagnetic radiation 25 onto the measurement region A. For example... Figure 6 As shown, the arrangement of the compensation electrode 7 closer to the sample than the first lens element 4 allows the focusing element 24 for focusing electromagnetic radiation 25 to be positioned at a certain distance from the compensation electrode, which is advantageous from an electrostatic point of view. Furthermore, compared to... Figure 4 Compared to the previous embodiment, the focusing element can be positioned closer to the first lens element 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.

[0056] Figure 6 The angle-resolved photoelectron spectrometer 100 shown includes a correction electrode 9 symmetrically arranged around the optical axis 6. This correction electrode 9 includes a correction edge 10 arranged along the optical axis 6 between the lens aperture 5 and the sample surface Ss. The lens aperture 5 is formed by the lens aperture edge E. A The correction edge 10 defines the opening that allows electrons to pass through the correction electrode 9. Each point of the correction edge 10 is adjacent to the lens aperture edge E. A Each point on it is at a greater distance from the optical axis 6 compared to when it is located on the optical axis.

[0057] exist Figure 6 In this embodiment, the kinetic energy of the electrons is 10 eV. A voltage of +100V is applied to the first lens element, a voltage of +104V is applied to the correction electrode 9, a voltage of -9V is applied to the shielding electrode 8, and a voltage of -1000V 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 relative to the optical axis 6. This prevents the electrons from entering through the lens aperture 5, thereby reducing noise.

[0058] Figure 7 A portion of an angle-resolved photoelectron spectrometer 100 according to different embodiments is shown in perspective view. Figure 7 The angle-resolved photoelectron spectrometer 100 of the embodiment has four compensation electrodes 7, 7', 7'', 7''' and four corresponding second shielding electrodes 8, 8', 8'', 8'''. Figure 7 The angle-resolved photoelectron spectrometer 100 shown also includes four calibration electrodes 9, 9', and 9''. Figure 7 Only three of them are shown in the diagram. During operation, different voltages can be applied to different compensation electrodes 7, 7', 7'', and 7''' to move the point of lowest electric field on the sample surface. When the same voltage is applied to all compensation electrodes 7, 7', 7'', and 7''', the point of lowest electric field is on the optical axis.

[0059] Figure 8 A cross-section of a portion of an angle-resolved photoelectron spectrometer 100 according to different embodiments is shown. Figure 8 Angle-resolved photoelectron spectrometer 100 and Figure 5 Similar to what is shown. Figure 8 Implementation examples and Figure 5 The main difference between the embodiments is that Figure 8 The photoelectron spectrometer 100 includes a third shielding electrode 26, which in this embodiment is similar to... Figure 8 The first shielding electrode is located in the first shielding electrode 17. The third shielding electrode 26 is disposed between the first shielding electrode 17 and the second shielding electrode 8. Figure 8 In this configuration, the manipulator cover forms the first shielding electrode 17. The position of the shielding electrode can be changed, and the first shielding electrode 17 can be located at a different position from the limiting hole 18. However, it is advantageous to place the limiting hole 18 as close to the sample as possible; such an arrangement will effectively shield the sample from the surrounding environment.

[0060] Figure 9 A cross-section of a portion of an angle-resolved photoelectron spectrometer 100, according to different embodiments, is shown. Figure 8 The only difference is that the compensation electrode 7 is moved downstream of the lens aperture 5, i.e. Figures 2 to 4 As shown.

[0061] Figure 10 A cross-section of a portion of an angle-resolved photoelectron spectrometer 100 according to different embodiments is shown. Figure 10 The embodiments are similar to Figure 5 The only difference in the embodiment shown is that the first shielding electrode 17 is formed by a manipulator cover.

[0062] The above embodiments can be modified in various ways without departing from the scope of the invention, the scope of which is defined only by the appended claims and their limitations.

Claims

1. An angle-resolved photoelectron spectrometer, comprising: - An electrostatic lens system having a first end and a second end, and including a first lens element at the first end having a lens aperture arranged to face the sample surface of a solid sample. - An electron measurement region at the second end for analyzing the electrons. in, The electrostatic lens system includes an optical axis extending from the first end through the lens aperture to the second end. The electrostatic lens system is arranged to form an electron beam emitted from the measurement area on the sample surface and entering through the lens aperture. The electrostatic lens system is arranged to transfer the electrons to the second end, and The first lens element is configured to be arranged with a positive voltage relative to the sample. The feature is that the angle-resolved photoelectron spectrometer includes... - At least one first shielding electrode having a limiting aperture is disposed between the sample and the first lens element, wherein the distance between the side surface of the limiting aperture near the sample surface and the sample surface is no greater than one-fifth of the distance between the sample surface and the first lens element, wherein the limiting aperture surrounds the optical axis, and wherein the size of the limiting aperture and the distance between the side surface of the limiting aperture near the sample surface and the sample surface are such that: from the intersection of the optical axis and the sample surface, the angle between the optical axis and the straight line connecting the intersection point and any point on the limiting aperture is greater than 45° and less than 70°. - At least one compensation electrode is arranged around the optical axis, and the compensation electrode is at a greater distance from the measurement area compared to the side of the first lens element closer to the sample surface. The compensation electrode is configured to be arranged with a negative voltage relative to the sample, and the value of the negative voltage is such that a lower electric field is achieved at the measurement area on the sample surface than the electric field caused by the voltage on the first lens element.

2. The angle-resolved photoelectron spectrometer according to claim 1, wherein, The compensation electrode is configured such that when a voltage is applied to the first lens element and the compensation electrode, the potential increases strictly along the optical axis from the measurement region to the first lens element.

3. The angle-resolved photoelectron spectrometer according to claim 1 or 2, wherein, The at least one compensation electrode is arranged symmetrically around the optical axis.

4. The angle-resolved photoelectron spectrometer according to claim 1, wherein, The compensation electrode is arranged along the optical axis between the sample and the side of the first lens element away from the sample surface, within a distance from the sample along the optical axis not greater than half the distance between the sample surface and the first lens element.

5. The angle-resolved photoelectron spectrometer according to claim 1, wherein, The minimum distance between the compensation electrode and the optical axis is less than twice the maximum distance from the periphery of the lens system to the optical axis.

6. The angle-resolved photoelectron spectrometer according to claim 5, wherein, The minimum distance between the compensation electrode and the optical axis is greater than the maximum distance between the edge of the lens aperture and the optical axis.

7. The angle-resolved photoelectron spectrometer according to claim 1, comprising: A second shielding electrode that blocks the line of sight from the compensation electrode to the measurement area on the sample surface.

8. The angle-resolved photoelectron spectrometer according to claim 1, wherein, The angle-resolved photoelectron spectrometer includes at least two compensation electrodes, wherein the compensation electrodes are configured to be applied with different voltages to enable the movement of the position of the minimum electric field generated on the sample surface by all electrodes.

9. The angle-resolved photoelectron spectrometer according to claim 1, wherein, The lens system includes at least one correction electrode arranged symmetrically about the optical axis, the correction electrode including a correction edge arranged along the optical axis between the lens aperture and the sample surface, wherein the correction edge defines an opening that allows electrons to pass through the correction electrode, and wherein each point on the correction edge is at a greater distance from the optical axis than each point on the edge of the lens aperture.

10. The angle-resolved photoelectron spectrometer according to claim 5, wherein, The minimum distance between the compensation electrode and the optical axis is less than 1.5 times the maximum distance between the edge of the electrostatic lens system and the optical axis.

11. The angle-resolved photoelectron spectrometer according to claim 10, wherein, The minimum distance between the compensation electrode and the optical axis is less than 1 times the maximum distance between the edge of the electrostatic lens system and the optical axis.

12. A method for an angle-resolved photoelectron spectrometer, comprising: - An electrostatic lens system having a first end and a second end, and including a first lens element at the first end having a lens aperture arranged to face the sample surface of a solid sample, and - An electron measurement region at the second end for analyzing electrons. The electrostatic lens system includes an optical axis extending from the first end through the lens aperture to the second end. The electrostatic lens system is arranged to form an electron beam emitted from the measurement area on the sample surface and entering through the lens aperture. The electrostatic lens system is arranged to transfer the electrons to the second end, and The method includes the following steps: - Apply a positive voltage to the first lens element relative to the sample. The method is characterized by comprising the following steps: - At least a first shielding electrode is provided between the sample and the first lens element, the first shielding electrode having a limiting hole, the distance between the side surface of the limiting hole closest to the sample surface and the sample surface being no greater than one-fifth of the distance between the sample surface and the first lens element, the limiting hole surrounding the optical axis, wherein the size of the limiting hole and the distance between the side surface of the limiting hole closest to the sample surface and the sample surface are such that: from the intersection of the optical axis and the sample surface, the angle between the optical axis and the straight line connecting the intersection point and any point on the limiting hole is greater than 45° and less than 70°, and - Provide at least one compensation electrode arranged around the optical axis, wherein the compensation electrode is at a greater distance from the measurement region than the side of the first lens element closest to the sample surface, and - The compensation electrode is arranged with a negative voltage relative to the particle emission of the sample to achieve a lower electric field at the measurement area on the sample surface compared to the electric field caused by the voltage on the first lens element.

13. The method according to claim 12, wherein, The compensation electrode is configured such that when the voltage is applied to the first lens element and the compensation electrode, the potential increases strictly along the optical axis from the measurement region to the first lens element.

14. The method according to claim 12 or 13, wherein, The negative voltage on the compensation electrode has a larger value than the positive voltage on the first lens element.

15. The method according to claim 12, wherein, The voltage on the compensation electrode makes the electric field in the measurement area less than 10% of the electric field in the measurement area when the compensation electrode is at the same potential as the sample surface.

16. The method of claim 12, further comprising the step of providing a second shielding electrode that blocks the line of sight from the compensation electrode to the measurement area on the sample surface.

17. The method according to claim 12, wherein, The spectrometer includes at least two compensation electrodes, wherein changing the voltage applied to the compensation electrodes moves the position of the maximum electric field caused by the compensation electrodes.

18. The method of claim 12, comprising the following steps: A correction electrode is provided symmetrically arranged around the optical axis, the correction electrode including a correction edge arranged along the optical axis between the lens aperture and the sample surface, wherein the correction edge defines an opening that allows electrons to pass through the correction electrode, and wherein each point on the edge is at a greater distance from the optical axis than each point on the edge of the lens aperture.

19. The method according to claim 18, wherein, A higher positive voltage than that applied to the first lens element is applied to the correction electrode.

20. The method of claim 15, wherein, The voltage on the compensation electrode is such that the electric field strength in the measurement area is less than 5% of the electric field strength in the measurement area when the compensation electrode is at the same potential as the sample surface.

21. The method according to claim 20, wherein, The voltage on the compensation electrode is such that the electric field strength in the measurement area is less than 1% of the electric field in the measurement area when the compensation electrode is at the same potential as the sample surface.

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