A wide energy range photoelectron spectroscopy system with soft and hard X-ray confocal

Abstract

The invention relates to a wide energy range photoelectron energy spectrum system with co-focusing of soft and hard X-rays, comprising a first undulator, a second undulator and a white light deflection mirror which are arranged in sequence, wherein the first undulator provides hard X-ray light to form a first light path through which the hard X-ray light beam passes; the second undulator provides soft X-ray light, and the white light deflection mirror is used to deflect the soft X-ray light provided by the second undulator, and after deflection, a second light path through which the soft X-ray light beam passes is formed; on the first light path, a first slit, a first deflection focusing mirror, a first monochromator, a second monochromator and a second deflection focusing mirror are arranged in sequence along the transmission direction of the hard X-ray light beam; on the second light path, a second slit, a third monochromator and a third deflection focusing mirror are arranged in sequence along the transmission direction of the soft X-ray light beam; the hard X-ray light beam deflected and focused by the second deflection focusing mirror and the soft X-ray light beam deflected and focused by the third deflection focusing mirror are irradiated to a sample together, and an electron energy analyzer is arranged behind the sample.

Description

Technical Field

[0001] The present invention relates to the field of synchrotron radiation X-ray spectroscopy devices, and more specifically to a soft and hard X-ray co-focusing wide energy range photoelectron energy spectrum system. Background Art

[0002] X-ray photoemission spectroscopy (XPS) is a characterization technique widely used in many fields because of its excellent surface sensitivity and element sensitivity. It realizes non-destructive detection of the elemental composition and chemical state of the sample surface by exciting the sample with photons and detecting the intrinsic information of the escaping photoelectrons (i.e., the photoelectric effect). Traditional XPS uses soft X-rays as the light source (soft X-rays generally refer to photons with energy less than 2000eV), and its analysis depth is generally within 10nm of the surface, with distinct surface and interface sensitivity characteristics. However, traditional XPS cannot directly realize deep analysis involving deeper buried layer interfaces and bulk structures, and generally requires the use of ion beam etching methods. However, XPS depth analysis based on ion etching is a sample-destructive analysis process, which inevitably leads to the destruction of the chemical state and produces illusions.

[0003] According to the relationship between the inelastic scattering mean free path (IMFP) of photoelectrons escaping from the sample surface and their kinetic energy, when the kinetic energy of the escaping photoelectrons is above 100eV, its IMFP and kinetic energy show a quasi-linear relationship. In order to increase the escape depth of photoelectrons and achieve in-depth analysis of samples without damage, a simple and feasible method is to continuously and controllably increase their kinetic energy. According to the principle of Einstein's photoelectric effect: photoelectron kinetic energy = excitation photon energy - electron binding energy - sample work function, the photoelectron kinetic energy is directly determined by the energy of the excitation X-ray light. Therefore, the continuous adjustment of the energy of X-ray light over a wide range is the key to achieving XPS characterization in a wide energy range: by continuously changing the energy of the incident light, from soft X-ray light (such as 200eV) to hard X-ray light (above 2000eV, up to above 10000eV), the escape depth of the emitted photoelectrons is continuously changed, thereby achieving non-destructive and direct detection characterization of different interfaces deep in the buried solid.

[0004] At present, the common XPS characterization equipment at home and abroad is mainly based on synchrotron radiation X-ray sources or laboratory X-ray sources. The photon energy of synchrotron radiation X-ray sources is generally below 2000eV. Laboratory X-ray sources are mainly based on characteristic X-ray fluorescence of Mg target (1254eV), Al target (1486eV) and less commonly used Cr target (5415eV), Ga target (9251eV). Although laboratory X-ray sources based on Cr target or Ga target can provide X-ray sources with relatively high photon energy, they have the disadvantages of low photon flux (108phs / s), limited and fixed photon energy value, and inability to change continuously, and cannot cover the entire energy range from 130eV to 18000eV. Summary of the invention

[0005] In view of the above-mentioned defects in the prior art, the present invention provides a wide energy range photoelectron energy spectrum system with soft and hard X-ray confocalization to achieve ultra-wide energy range XPS characterization with soft and hard X-ray confocalization.

[0006] The present invention provides a wide-energy-range photoelectron energy spectrum system for co-focusing hard and soft X-rays, comprising a first undulator, a second undulator and a white-light deflection mirror which are arranged in sequence, wherein the first undulator is used to provide hard X-ray light to form a first optical path through which the hard X-ray beam passes; the second undulator is used to provide soft X-ray light, and the white-light deflection mirror is used to deflect the soft X-ray light provided by the second undulator to form a second optical path through which the soft X-ray beam passes after deflection; on the first optical path, a first slit, a first deflection focusing mirror, a first monochromator, a second monochromator and a second deflection focusing mirror are arranged in sequence along the transmission direction of the hard X-ray beam; on the second optical path, a second slit, a third monochromator and a third deflection focusing mirror are arranged in sequence along the transmission direction of the soft X-ray beam; the hard X-ray beam deflected and focused by the second deflection focusing mirror and the soft X-ray beam deflected and focused by the third deflection focusing mirror are irradiated to a sample together, and an electron energy analyzer is arranged behind the sample.

[0007] Preferably, the first undulator adopts undulator IVU24 to provide photons in the energy range of 1500 eV-18000 eV.

[0008] Preferably, the second undulator adopts the undulator EPU60 to provide photons in the energy range of 130 eV-1500 eV.

[0009] Preferably, the angle between the first undulator and the second undulator is set to 2 mrad.

[0010] Preferably, the first monochromator adopts a liquid nitrogen grating monochromator to monochromatize hard X-ray light with a photon energy in the range of 1500eV to 2500eV; the second monochromator adopts a liquid nitrogen double crystal monochromator to monochromatize hard X-ray light with a photon energy in the range of more than 2500eV.

[0011] Furthermore, when hard X-ray light with a photon energy in the range of 1500eV to 2500eV is needed, the double crystals in the liquid nitrogen double crystal monochromator are completely pulled apart to allow light in the energy range of 1500eV to 2500eV to pass directly through the liquid nitrogen double crystal monochromator.

[0012] Furthermore, when hard X-ray light with a photon energy range above 2500 eV is required, the plane reflector inside the liquid nitrogen grating monochromator is moved to the leftmost or rightmost side of the cavity to allow light with an energy range above 2500 eV to pass directly through the liquid nitrogen grating monochromator.

[0013] Preferably, the third monochromator is a water-cooled grating monochromator to monochromatize soft X-ray light with a photon energy in the range of 130 eV-1500 eV.

[0014] Preferably, the angle between the electron energy analyzer and the hard X-ray beam is 70 degrees.

[0015] Preferably, the angle between the electron energy analyzer and the soft X-ray beam is 68 degrees.

[0016] The present invention realizes in-situ XPS characterization analysis with continuously adjustable photon energy in a wide range (130eV-10000eV or above, without interruption). The optical path design of the dual beam line deflection focusing of the present invention makes the photon flux at the soft and hard co-focusing point as high as 4×10 12 phs / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of a wide energy range photoelectron energy spectrum system of soft and hard X-ray confocalization according to the present invention.

[0018] Figure 2 It is a wide energy range XPS spectrum from low energy to high energy based on the Au(111) single crystal surface. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0020] In order to achieve continuous adjustment of photon energy within an ultra-wide range, and further realize XPS characterization technology that fully covers low-kinetic energy electrons to high-kinetic energy electrons, the present invention adopts the physical design of soft and hard X-ray beam deflection and focusing, the parallel operation of dual undulators, and the series-parallel operation of three monochromators.

[0021] Specifically, Figure 1 As shown, a wide energy range photoelectron energy spectrum system of soft and hard X-ray co-focalization provided by the present invention comprises a first undulator 10, a second undulator 20 and a white light deflection mirror 30 which are arranged in sequence, wherein the first undulator 10 is used to provide hard X-ray light to form a first optical path through which the hard X-ray light beam passes; the second undulator 20 is used to provide soft X-ray light, and the white light deflection mirror 30 is used to deflect the soft X-ray light provided by the second undulator 20 to form a second optical path through which the soft X-ray light beam passes after deflection.

[0022] In this embodiment, the first undulator 10 uses an undulator IVU24 to provide photons in the energy range of 1500 eV-18000 eV; the second undulator 20 uses an undulator EPU60 to provide photons in the energy range of 130 eV-1500 eV. Since the thermal power load of the undulator IVU24 is large, gas molecules are easily released in its cavity, resulting in vacuum deviation. Therefore, the undulator IVU24 must be set upstream of the undulator EPU60 (that is, in front of the undulator EPU60) to reduce the impact of the undulator IVU24 on the vacuum of the undulator EPU60.

[0023] In order to enable the above two undulators to work independently without interfering with each other, and the emitted X-rays can be transmitted through their respective vacuum pipes, in this embodiment, the angle between the first undulator 10 and the second undulator 20 is set to 2mrad (milliradians, 1mrad is approximately equal to 0.0573 degrees), that is, one of the undulators is deflected by 2mrad relative to the other undulator. In this way, under the setting of this high-precision angle, the light generated by the undulator IVU24 can pass through the cavity of the undulator EPU60 behind it without loss and influence and be transmitted with high quality, thereby ensuring a wide energy range X-ray with both soft and hard X-ray light.

[0024] In this embodiment, the white light deflection mirror 30 has a length of 250 mm and a width of 20 mm. It deflects the soft X-ray light, thereby increasing the angle between the soft and hard X-ray light, thereby ensuring that the soft and hard light beams can be effectively separated.

[0025] On the above-mentioned first optical path, the first slit 11, the first deflection focusing mirror 12, the first monochromator 13, the second monochromator 14 and the second deflection focusing mirror 15 are sequentially arranged along the transmission direction of the hard X-ray beam. Among them, the first slit 11 is used to intercept the spot of the hard X-ray beam and block stray light according to the size requirements of the sample for the spot. The first slit 11 moves in the up and down and left and right directions in a vacuum, with a range of ±50 mm, a movement accuracy of less than μm level, and requires water cooling. The first deflection focusing mirror 12 and the second deflection focusing mirror 15 are used to deflect and focus the hard X-ray beam, so that the hard X-ray beam and the soft X-ray beam finally reach the sample 40 together.

[0026] In this embodiment, the first monochromator 13 adopts a liquid nitrogen grating monochromator, which is used to monochromatize hard X-ray light with a photon energy in the range of 1500eV to 2500eV; the second monochromator 14 adopts a liquid nitrogen double crystal monochromator, which is used to monochromatize hard X-ray light with a photon energy in the range of 2500eV or more. In order to achieve the separate monochromatization of different energy ranges, both the liquid nitrogen grating monochromator and the liquid nitrogen double crystal monochromator adopt a direct-through mode design. Specifically, if hard X-ray light with a photon energy in the range of 1500eV to 2500eV is required, the double crystals in the liquid nitrogen double crystal monochromator are completely pulled apart to allow light in the energy range of 1500eV to pass directly. At this time, the hard X-ray light monochromatized by the liquid nitrogen grating monochromator will not be affected when it reaches the liquid nitrogen double crystal monochromator behind. Similarly, if hard X-ray light with a photon energy above 2500eV is needed, the plane mirror inside the liquid nitrogen grating monochromator is moved to the far left or far right of the cavity. At this time, the hard X-ray light will not be reflected or dispersed in the liquid nitrogen grating monochromator, so it can pass directly to the liquid nitrogen double crystal monochromator behind for monochromatization. In this way, the grating and crystal can be moved within a large range (±100 mm) in the vacuum to ensure the repeatability of the movement, the stability of the vacuum, etc., so as to obtain monochromatized X-rays of different energies as needed.

[0027] In the above-mentioned second optical path, a second slit 21, a third monochromator 22 and a third deflection focusing mirror 23 are sequentially arranged along the transmission direction of the soft X-ray beam. Among them, the second slit 21 is used to intercept the light spot of the soft X-ray beam and block stray light according to the size requirements of the light spot of the sample. The second slit 21 moves in the up and down and left and right directions in a vacuum, with a range of ±50mm, a movement accuracy of less than μm level, and requires water cooling. The third deflection focusing mirror 21 is used to deflect and focus the soft X-ray beam so that the soft and hard X-ray beams reach the sample 40 together.

[0028] In this embodiment, the third monochromator 22 is a water-cooled grating monochromator, which is used to monochromatize the soft X-ray light with a photon energy in the range of 130 eV-1500 eV.

[0029] To complete the in-depth analysis of the sample 40, an electron energy analyzer 50 is disposed behind the sample 40. The electron energy analyzer 40 can receive and effectively analyze electrons with a kinetic energy range of 5eV-10000eV, which meets the characterization and research requirements of wide energy range XPS.

[0030] In this embodiment, the angle between the electron energy analyzer 50 and the hard X-ray beam is 70 degrees, and the angle between the electron energy analyzer 50 and the soft X-ray beam is 68 degrees. Generally, in order to maximize the photoelectron collection efficiency in XPS characterization, for soft X-rays, the optimal value of the angle between the electron energy analyzer and it is 54.7 degrees (i.e., the "magic angle"). For high-kinetic energy photoelectrons, since the dipole approximation effect at the interface cannot be ignored, the X-rays need to be incident on the sample surface at the smallest possible angle or at a grazing incidence angle, that is, the angle between the X-rays and the energy analyzer needs to be close to 90 degrees. In other words, the angle requirements between soft X-rays and hard X-rays and the electron energy analyzer are different. Therefore, in order to achieve the purpose of satisfying both low-energy XPS detection efficiency and high-energy XPS detection efficiency, this embodiment adopts the above-mentioned angles of 68 degrees and 70 degrees.

[0031] In this embodiment, in order to protect against soft X-rays and hard X-rays, a protective wall 60 may be further provided between the white light deflecting mirror 30 and the two slits 11 and 21 to ensure the safety of the system.

[0032] In the technical solution of the present invention, soft X-ray light and hard X-ray light are transmitted independently, and then deflected and focused respectively before reaching the sample, so as to focus on the same position of the sample (100% overlap of X-ray spots). The optical path design of the two beams of X-rays transmitted independently effectively avoids the mutual influence between soft X-rays and hard X-rays, especially the intersection of light and cross-contamination of vacuum pipes, while ensuring that soft and hard X-rays can reach the sample at the same time for detection XPS research. The present invention truly realizes in-situ XPS characterization analysis with continuously adjustable photon energy over a wide range (130eV-10000eV or more, without interruption), and the optical path design of dual beam line deflection and focusing makes the photon flux at the soft and hard common focus as high as 4×10 12 phs / s (photons per second).

[0033] like Figure 2 As shown, the photon energy is increased from 244 eV to 3998 eV, 4997 eV, and finally to 7994 eV, and then the Au 4f core state peak is measured based on the Au (111) single crystal plane, wherein the spin-orbit splitting peak shape, half-width, and spectrum peak area of ​​4f5 / 2 and 4f7 / 2 remain relatively unchanged at different photon energies, which is consistent with the molecular orbital theory, thereby proving the feasibility, reliability, and universality of the ultra-wide energy range XPS technical solution of the present invention.

[0034] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A soft and hard X-ray confocal wide energy range photoelectron spectroscopy system, characterized in that: It comprises a first undulator, a second undulator and a white light deflection mirror which are arranged in sequence, wherein the first undulator is used to provide hard X-ray light to form a first light path through which the hard X-ray light beam passes; the second undulator is used to provide soft X-ray light, and the white light deflection mirror is used to deflect the soft X-ray light provided by the second undulator to form a second light path through which the soft X-ray light beam passes after deflection; On the first optical path, a first slit, a first deflection focusing mirror, a first monochromator, a second monochromator and a second deflection focusing mirror are sequentially arranged along the transmission direction of the hard X-ray beam; On the second optical path, a second slit, a third monochromator and a third deflection focusing mirror are sequentially arranged along the transmission direction of the soft X-ray beam; The hard X-ray beam deflected and focused by the second deflection and focusing mirror and the soft X-ray beam deflected and focused by the third deflection and focusing mirror are irradiated to the sample together, and an electron energy analyzer is arranged behind the sample.

2. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The first undulator uses an undulator IVU24 to provide photons in the energy range of 1500 eV-18000 eV.

3. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The second undulator uses the undulator EPU60 to provide photons in the energy range of 130 eV-1500 eV.

4. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The angle between the first undulator and the second undulator is set to 2 mrad.

5. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The first monochromator adopts a liquid nitrogen grating monochromator to monochromatize hard X-ray light with a photon energy in the range of 1500eV to 2500eV; the second monochromator adopts a liquid nitrogen double crystal monochromator to monochromatize hard X-ray light with a photon energy in the range of more than 2500eV.

6. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 5, characterized in that: When hard X-ray light with a photon energy in the range of 1500eV to 2500eV is needed, the double crystals in the liquid nitrogen double crystal monochromator are completely pulled apart to allow light in the energy range of 1500eV to 2500eV to pass directly through the liquid nitrogen double crystal monochromator.

7. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 5, characterized in that: When hard X-ray light with a photon energy range above 2500 eV is needed, the plane reflector inside the liquid nitrogen grating monochromator is moved to the leftmost or rightmost side of the cavity to allow light with an energy range above 2500 eV to pass directly through the liquid nitrogen grating monochromator.

8. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The third monochromator is a water-cooled grating monochromator to monochromatize soft X-ray light with a photon energy in the range of 130 eV-1500 eV.

9. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The angle between the electron energy analyzer and the hard X-ray beam is 70 degrees.

10. The soft and hard X-ray confocal wide energy range photoelectron spectroscopy system according to claim 1, characterized in that: The angle between the electron energy analyzer and the soft X-ray beam is 68 degrees.

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