Preparation method of medium-energy-region X-ray bent crystal monochromator based on lithium niobate crystal

Abstract

The invention discloses a preparation method of a medium-energy-region X-ray bent crystal monochromator based on a lithium niobate crystal, which comprises the following steps of: 1, determining a working crystal orientation index of the lithium niobate crystal according to a working angle and a working energy region of the medium-energy-region X-ray bent crystal monochromator; 2, determining the crystal orientation of the lithium niobate crystal, and measuring the Bragg angle of the lithium niobate crystal to determine the x axis, y axis and z axis of the lithium niobate crystal; the x-axis cutting direction Xcut, the y-axis cutting direction Ycut and the z-axis cutting direction Zcut of the lithium niobate crystal are perpendicular to the corresponding planes of the x axis, the y axis and the z axis, the included angles between the determined crystal orientation indexes and the Miller-Brayer indexes [2-1-10], [1-100] and [0001] are calculated respectively, then the lithium niobate crystal is cut according to the included angles, and a wafer is obtained; and step 3, bending and curing the wafer to obtain the medium energy region X-ray bent crystal monochromator.

Description

Technical Field

[0001] The present invention belongs to the field of synchrotron radiation X-ray spectroscopy and relates to a method for preparing a medium-energy X-ray bent crystal monochromator based on a lithium niobate crystal. Background Art

[0002] Lithium niobate (LiNbO3) is an important optoelectronic material with a high Curie temperature, excellent optoelectronic properties, good physical and chemical stability, and the ease of preparing large, high-quality crystals. It is widely used in harmonic generation and frequency-doubling devices, making it an ideal candidate for mid- and low-energy X-ray monochromators. Mid- and low-energy X-rays (1–6 keV) are widely used in synchrotron radiation sources, materials characterization, medical imaging, and spectroscopic instruments such as X-ray spectrometers. However, traditional monochromators rely on silicon- or germanium-based crystals, which suffer from low integrated reflectivity and a lack of available matching crystal orientations.

[0003] Traditional silicon-based bent crystal monochromators use Si(111) or Si(220) crystal planes to achieve monochromation through back diffraction. In addition, Baxter Abraham mentioned the use of Crystal orientation measurement of sulfur element X-ray emission spectrum (2.3 KeV, Bragg angle 80°). In addition, in 2014, Yan Wenchao proposed the use of highly oriented pyrolytic graphite crystals to develop a new type of reflection X-ray spectrometer with high reflection efficiency, high energy spectrum resolution, and a relatively wide energy spectrum measurement range.

[0004] The above-mentioned highly oriented pyrolytic graphite crystals are based on mosaic crystals and have low energy resolution. In addition, pyrolytic graphite is expensive and cannot be applied to X-ray absorption spectrometers and X-ray emission spectrometers.

[0005] Currently, commonly used single crystal materials have limited coverage in the low- to mid-energy range (1-6 keV). For example, common single crystal materials such as silicon and germanium single crystals are applicable in the range of 4-20 keV. Below 2 keV, it is difficult to find suitable crystal planes that match the specific Bragg angle. Furthermore, although quartz crystal belongs to the non-cubic crystal system and has many diffraction planes, it has a large thermal expansion coefficient and poor temperature stability. Other materials, such as LiF, have problems with easy deliquesce and low mechanical strength. Mica single crystals are of low quality, layered materials are difficult to process, and the ultra-pure crystal growth process is complex.

[0006] In summary, the current problems with bent crystal monochromators include a limited number of optional materials and an inability to effectively cover the energy range of the low and medium energy regions of X-rays. Summary of the Invention

[0007] To address the challenges of the prior art, the present invention provides a method for fabricating a mid-energy X-ray bent-crystal monochromator based on lithium niobate crystals. This method utilizes lithium niobate crystals with specific crystal orientations to achieve coverage of the 1-6 keV energy range, with a Bragg angle range of 65-85 degrees, suitable for use in Rowland circle or Von Hamos configuration X-ray absorption or reflection spectrometers.

[0008] The present invention utilizes a series of diffraction surfaces of lithium niobate crystals to cover the X-ray energy range of 1-6keV, so that the crystals can be used for bent crystal monochromators of X-ray absorption and emission spectrometers.

[0009] The invention uses VESTA software to calculate the angle between the crystal surface to be cut and the crystal appearance surface through the steps of orientation and cutting of lithium niobate, and prepares a bent crystal monochromator using lithium niobate single crystal material.

[0010] The technical solution of the present invention is:

[0011] A method for preparing a mid-energy X-ray bent crystal monochromator based on lithium niobate crystal, comprising the following steps:

[0012] Step 1. Determine the crystal orientation index of the lithium niobate crystal based on the working angle and working energy range of the medium-energy X-ray bent crystal monochromator; the lithium niobate is a hexagonal crystal with its z-axis parallel to the c-axis of the unit cell, the x-axis coincides with one of the three equivalent translation vectors of the hexagonal unit cell, and its Miller index is (u, v, w) and the Miller-Bravais index is [2u-v, -u+2v, -uv, 3w].

[0013] Step 2: Determine the crystal orientation of the lithium niobate crystal, measure the Bragg angle of the lithium niobate crystal to confirm the x-axis, y-axis, and z-axis of the lithium niobate crystal; then, orient the x-axis cutting direction Xcut, the y-axis cutting direction Ycut, and the z-axis cutting direction Zcut of the lithium niobate crystal perpendicular to the planes of the corresponding x-axis, y-axis, and z-axis, respectively calculate the angles between the crystal orientation index determined in step 1 and the Miller-Bravais index [2-1-10], [1-100], and

[0001] , and then cut the lithium niobate crystal according to the angles to obtain wafers;

[0014] Step 3: Press and bend the wafer to solidify it to obtain a medium-energy X-ray bent crystal monochromator.

[0015] Furthermore, the method for cutting the lithium niobate crystal is:

[0016] Step 21: Open the crystal structure CIF file of the lithium niobate crystal, determine the indices of the [u, v, w] crystal plane to be cut, and if they are Miller-Bravais indices, convert them into Miller indices;

[0017] Step 22: confirm the x-axis, y-axis, z-axis and Miller-Bravais indices [2-1-10], [1-100] and

[0001] of the lithium niobate crystal according to the crystal orientation of the crystal rod;

[0018] Step 23: Calculate the angles between the [u, v, w] crystal plane and the Miller-Bravais indices [2-1-10], [1-100], and

[0001] ; and cut the lithium niobate crystal according to the angles to obtain wafers.

[0019] Furthermore, the method for bending and curing the wafer is as follows: ① double-sided polishing of the wafer; ② bending the polished wafer, and when the curvature radius is less than or equal to the set curvature radius, dicing the bent wafer into a strip shape; when the curvature is greater than the set curvature radius, no dicing is required; ③ processing a concave spherical borosilicate glass substrate to support the crystal material; ④ bonding the crystal processed in step ② to the concave spherical borosilicate glass substrate, and applying a certain pressure and temperature for curing.

[0020] The advantages of the present invention are as follows:

[0021] 1. The single crystal quality of lithium niobate crystal is high, and large-size single crystal materials can be obtained, which is suitable for the development of bent crystal monochromators for X-ray absorption and emission spectrometers.

[0022] 2. The present invention provides a complete technical process of crystal orientation selection, crystal orientation and cutting, and bent crystal monochromator preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flow chart of the method of the present invention.

[0024] Figure 2 This is the energy coverage diagram of different crystal orientations of lithium niobate crystals in the 1-8KeV energy range.

[0025] Figure 3 This is the correspondence diagram between the X, Y axes, crystal directions and unit cells of lithium niobate crystal. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0027] like Figure 1 As shown, the process of manufacturing a bent crystal monochromator in the low and medium energy range using lithium niobate crystal includes the following steps:

[0028] 1. Energy range coverage and crystal orientation selection of lithium niobate crystals.

[0029] According to the common working angle range of Rowland spectrometer is 65-85 degrees, lithium niobate crystals with different crystal orientations are selected. The corresponding working energy list is shown in Table 1, and the energy range coverage is shown in Figure 2 , which can cover the medium and low energy areas very well.

[0030] Table 1. Index planes and working energies of lithium niobate crystals corresponding to the energy range of 1-8 KeV

[0031] <![CDATA[LiNbO3 crystal orientation index]]> Face spacing 65° corresponds to energy 85° corresponds to energy (002) 6.9315 986.50566 897.49299 (100) 4.4583 1533.76082 1395.36917 (004) 3.46575 1973.01132 1794.98599 (110) 2.574 2656.55166 2416.8503 (006) 2.3105 2959.51698 2692.47898 (200) 2.22915 3067.52163 2790.73834 (008) 1.73288 3946.02264 3589.97197 (210) 1.68508 4057.94969 3691.79982 (300) 1.4861 4601.28246 4186.10753 (0010) 1.3863 4932.5283 4487.46496 (220) 1.287 5313.10332 4833.70061 (400) 1.11457 6135.04329 5581.47671 (500) 0.89166 7668.80405 6976.84583 (330) 0.858 7969.65499 7250.55091

[0032] 2. Directional cutting of lithium niobate crystals:

[0033] Lithium niobate belongs to the hexagonal crystal system, with its z-axis parallel to the c-axis of the unit cell and the x-axis coincident with one of the three equivalent translation vectors of the traditional hexagonal unit cell. The conversion relationship between its Miller index (three-digit crystal plane index) and Miller-Bravais index (four-digit index, usually a common crystal plane index representation method for trigonal and hexagonal crystal systems) is: (u, v, w) → [2u-v, -u+2v, -uv, 3w]. The x-axis cutting direction Xcut, y-axis cutting direction Ycut and z-axis cutting direction Zcut of lithium niobate are planes perpendicular to the x, y and z axes, respectively characterized by Miller-Bravais index [2-1-10], [1-100] and

[0001] . The angles between the crystal direction index determined in step 1 and the Miller-Bravais index [2-1-10], [1-100] and

[0001] are calculated respectively, and then the lithium niobate crystal is cut according to the angle to obtain a wafer; the corresponding relationship of the crystal directions is shown in Figure 3 Since Bravais indices are sometimes used, converting them into Miller indices is helpful for the subsequent determination of crystal cutting angles.

[0034] Specific orientation steps: Taking the Z-axis 4-inch lithium niobate single crystal rod as an example, the crystal Z-axis is the vertical direction of the crystal rod. Rotate the crystal and cut a small piece of crystal along the axial direction to determine the crystal orientation. Use a Cu target X-ray spectrometer to measure the Bragg angle of the crystal. The diffraction angle equals 9.949, which is the X-axis.

[0035] Cutting steps:

[0036] 21) Opening the crystal structure CIF file of the lithium niobate crystal, determining the indices of the [u, v, w] crystal plane to be cut, and converting them into Miller indices if they are Miller-Bravais indices;

[0037] 22) Determine the x-axis, y-axis, z-axis, and Miller-Bravais indices of the lithium niobate crystal as [2-1-10], [1-100], and

[0001] based on the crystal orientation of the crystal rod;

[0038] 23) Calculate the angles between [u,vw] and the Miller-Bravais indices [2-1-10], [1-100], and

[0001] . Use VESTA software to draw the [u,v,w] crystal plane and use the software's built-in tools to measure the angles between the crystal plane and the Miller-Bravais indices [2-1-10], [1-100], and

[0001] .

[0039] Lithium niobate curved crystal manufacturing process: ① The crystal is rounded and cut into 4-inch, 300um thick single wafers, and then double-sided polished. ② When manufacturing curved crystals with a curvature radius of less than or equal to 500mm, the crystal needs to be sliced into strips with a strip width of 10-15mm. When manufacturing curved crystals with a crystal curvature greater than 500mm, the crystal does not require slicing. ③ Process the concave spherical borosilicate glass substrate to support the crystal material. The processing technology requirements are a thickness of 10-15 mm and a surface accuracy of one-quarter wavelength. ④ Bond the crystal to the concave spherical borosilicate glass and apply a certain pressure and temperature for curing.

[0040] While specific embodiments of the present invention have been disclosed for illustrative purposes, intended to facilitate understanding and implementation of the present invention, those skilled in the art will appreciate that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the disclosure of the preferred embodiments, and the scope of protection claimed in the present invention shall be determined by the scope of the claims.

Claims

1. A method for preparing a mid-energy X-ray bent crystal monochromator based on lithium niobate crystal, comprising the following steps: Step 1. Determine the crystal orientation index of the lithium niobate crystal based on the working angle and working energy range of the medium-energy X-ray bent crystal monochromator; the lithium niobate is a hexagonal crystal with its z-axis parallel to the c-axis of the unit cell, the x-axis coincides with one of the three equivalent translation vectors of the hexagonal unit cell, and its Miller index is (u, v, w) and the Miller-Bravais index is [2u-v, -u+2v, -uv, 3w]. Step 2: Determine the crystal orientation of the lithium niobate crystal, measure the Bragg angle of the lithium niobate crystal to confirm the x-axis, y-axis, and z-axis of the lithium niobate crystal; then, orient the x-axis cutting direction Xcut, the y-axis cutting direction Ycut, and the z-axis cutting direction Zcut of the lithium niobate crystal perpendicular to the planes of the corresponding x-axis, y-axis, and z-axis, respectively calculate the angles between the crystal orientation index determined in step 1 and the Miller-Bravais index [2-1-10], [1-100], and [0001], and then cut the lithium niobate crystal according to the angles to obtain wafers; Step 3: Press and bend the wafer to solidify it to obtain a medium-energy X-ray bent crystal monochromator.

2. The method according to claim 1, characterized in that The method for cutting the lithium niobate crystal is as follows: Step 21: Open the crystal structure CIF file of the lithium niobate crystal, determine the indices of the [u, v, w] crystal plane to be cut, and if they are Miller-Bravais indices, convert them into Miller indices; Step 22: confirm the x-axis, y-axis, z-axis and Miller-Bravais indices [2-1-10], [1-100] and [0001] of the lithium niobate crystal according to the crystal orientation of the crystal rod; Step 23: Calculate the angles between the [u, v, w] crystal plane and the Miller-Bravais indices [2-1-10], [1-100], and [0001]; and cut the lithium niobate crystal according to the angles to obtain wafers.

3. The method according to claim 1 or 2, characterized in that The method for bending and curing the wafer is as follows: ① double-sided polishing of the wafer; ② bending the polished wafer, and when the curvature radius is less than or equal to the set curvature radius, dicing the bent wafer into a strip shape; when the curvature is greater than the set curvature radius, no dicing is required; ③ processing a concave spherical borosilicate glass substrate for supporting crystal materials; ④ bonding the crystal processed in step ② to the concave spherical borosilicate glass substrate, and applying a certain pressure and temperature for curing.

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