A Multilayer Neutron Thin-Film Spin-Flip Element for a Neutron Spin Flipper and Its Manufacturing Method

Abstract

The present invention provides a multi-layer neutron thin film spin flip element for a neutron spin flipper and a manufacturing method thereof. A multi-layer neutron thin film spin flip element for a neutron spin flipper includes a super-smooth silicon wafer substrate with double-sided polishing, a multi-layer iron-silicon alloy thin film layer, and a multi-layer chromium thin film layer. The multi-layer iron-silicon alloy thin film layer and the multi-layer chromium thin film layer are alternately deposited on the surface of the super-smooth silicon wafer substrate in sequence, and the top layer of the multi-layer neutron thin film spin flip element is a chromium thin film layer. In the manufacturing method of the multi-layer neutron thin film spin flip element, the manufacturing processes of both the iron-silicon alloy thin film layer and the chromium thin film layer are magnetron sputtering. The present invention mainly focuses on the iron-silicon alloy thin film layer and uses the chromium thin film layer as an interlayer to improve the saturation magnetic induction intensity of the thin film, so that the saturation magnetic induction intensity of the thin film exceeds 1 T. The chromium thin film layer can effectively regulate the microstructure of the iron-silicon alloy thin film layer, promote the growth of reasonable crystal planes, and inhibit the growth of unnecessary crystal planes.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film preparation, and particularly relates to a multi-layer neutron thin film spin flip element for a neutron spin flipper and a manufacturing method thereof. Background Art

[0002] Neutron spin echo small angle scattering technology has the advantages of large scale, high intensity, and multiple scattering, and is widely used in fields such as colloid transformation, polymer fibers, biological structures, powders, etc. A neutron spin flipper is a core device in the small angle mode of a neutron spin echo spectrometer.

[0003] A neutron thin film spin flip element is composed of a soft magnetic thin film with a certain thickness and is magnetized by the magnetic field of the precession device itself, as Figure 7 shown. When the magnetized thin film is adjusted to an inclination almost perpendicular to the precession field, the demagnetizing magnetic field in the thin film will force the local magnetization direction to be restricted within the plane of the magnetized thin film. Before the neutron enters the thin film, the polarization vector precesses in the xy plane around the magnetic field. After the neutron passes through the magnetized thin film, the polarization vector of the light beam will flip from a direction parallel to the magnetic field to a direction perpendicular to the magnetic field. As long as the thickness and inclination angle of the magnetized thin film are adjusted, the polarization vector can flip an angle of π around the in-plane saturation magnetic field, as shown in the following formula.

[0004] Φ = cλBd / sinα

[0005] Where: c is a constant: 4.632×10 14 T -1 m -2 ; λ is the wavelength of the incident neutron, unit: 10 -10 m; B is the effective magnetic induction intensity, unit: T (Tesla); d is the thickness of the magnetic material thin film, unit: 10 -6 m; α is the angle between the incident neutron beam and the surface of the soft magnetic thin film, unit: rad.

[0006] The advantage of this flip element is that it confines the flipping of neutrons within the thin film region, can precisely control the flipping angle, and the device is simple and easy to install. In addition, the inclined soft magnetic thin film can generate a clear boundary of the precession region and can be measured at a spin echo correlation length of up to 20 μm. However, in the main magnetic field with a magnetic thin film as the flip element, if the magnetic field is too large, it will affect the synthetic field inside the thin film, thereby affecting the flipping efficiency and ultimately reducing the spin echo length, which is a key index of the spectrometer. Therefore, in order to achieve higher indexes, the magnetic induction intensity of the magnetic thin film needs to exceed 1 T to meet the requirements of a larger spin echo length index.

[0007] Permalloy was first used as a neutron thin - film spin - flip element on the spin - echo small - angle spectrometer of the Delft reactor source in the Netherlands. The thickness of these Permalloy thin films is 3 μm, which are deposited on a silicon wafer with a thickness of 0.4 mm by an electrochemical method. Three - dimensional neutron depolarization is used for measurement, and the coercivity of the thin film is less than 10 A / m, and the saturation magnetization is about 1 T. In the wavelength range of 0.2 - 0.5 nm, the polarization neutron flip - over efficiency is about 93%. However, the preparation method is not specifically reported in the papers published on the HOR reactor. At present, there are many studies on the effects of annealing temperature, seed layer, buffer layer, substrate material, doping elements, etc. on the soft magnetic properties to improve the soft magnetic properties of Permalloy thin films. However, the current process methods cannot increase the saturation magnetic induction intensity of micron - scale Permalloy thin films to 1 T. Moreover, the flip - over angle of the neutron thin - film spin - flip element is very sensitive to the application thickness of the magnetic thin film, so the measurement accuracy of the thickness is required to be high enough. Since the thickness of the required magnetic thin film reaches the micron scale, XRR and ellipsometers cannot penetrate the depth, the measurement accuracy of TEM is not enough, and measurement methods such as step profilers will damage the thin film. Using the intercalation method can not only improve the soft magnetic properties of the magnetic thin film, but also facilitate the precise thickness jump regulation. In addition, research shows that using the intercalation method can interrupt the growth of the magnetic thin film, making it maintain the soft magnetic characteristics below the critical thickness. However, for magnetic materials, different intercalation materials have different effects on their magnetism, and experimental optimization is needed. Therefore, how to overcome these problems is a difficulty in the process of developing multi - layer neutron thin - film spin - flip elements.

[0008] Therefore, in practical applications, there is an urgent need for a suitable multi - layer neutron thin - film spin - flip element for neutron spin flippers. Summary of the Invention

[0009] Aiming at the defects of the prior art, the purpose of the present invention is to provide a multi - layer neutron thin - film spin - flip element for neutron spin flippers and its manufacturing method.

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

[0011] A multi - layer neutron thin - film spin - flip element for neutron spin flippers includes a super - smooth silicon wafer substrate with double - sided polishing, multiple layers of iron - silicon alloy thin - film layers, and multiple layers of chromium thin - film layers. The multiple layers of iron - silicon alloy thin - film layers and the multiple layers of chromium thin - film layers are alternately deposited on the surface of the super - smooth silicon wafer substrate in sequence, and the top layer of the multi - layer neutron thin - film spin - flip element is a chromium thin - film layer.

[0012] Further, the thickness of the super - smooth silicon wafer substrate is less than or equal to 0.5 mm.

[0013] Further, the effective size of the super - smooth silicon wafer substrate is greater than or equal to 120 mm×60 mm.

[0014] Furthermore, the surface form error PV of the effective size of the ultrasmooth silicon wafer substrate is less than or equal to 10 μm.

[0015] Furthermore, the single-layer thickness of the iron-silicon alloy thin film layer is 100 nm - 130 nm.

[0016] Furthermore, the single-layer thickness of the chromium thin film layer is 10 nm.

[0017] A manufacturing method of a multi-layer neutron thin film spin flipper element for a neutron spin flipper, the preparation processes of the iron-silicon alloy thin film layer and the chromium thin film layer are both magnetron sputtering.

[0018] Furthermore, in the process of the magnetron sputtering, the inert gas is 99.99% Ar gas, and the sputtering gas pressure is 1 mTorr.

[0019] Furthermore, in the process of the magnetron sputtering, the background vacuum is better than 8.0×10-5 Pa; the target distance of the iron-silicon alloy target is 8 cm, and the target distance of the chromium target is 6 cm; the sputtering power of the iron-silicon alloy target is 40 W, and the sputtering power of the chromium target is 30 W.

[0020] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0021] 1. Based on the traditional single-layer permalloy used as a neutron spin flipper, the present invention uses an iron-silicon alloy with a higher saturation magnetic induction intensity and maintains a lower coercive force.

[0022] 2. The present invention mainly uses an iron-silicon alloy thin film layer, and adopts a method of using a chromium thin film layer as an interlayer to improve the saturation magnetic induction intensity of the thin film, so that the saturation magnetic induction intensity of the thin film exceeds 1 T. The chromium thin film layer can effectively regulate the microstructure of the iron-silicon alloy thin film layer, promote the growth of reasonable crystal planes, and inhibit the growth of unnecessary crystal planes.

[0023] 3. The multi-layer neutron thin film spin flipper element involved in the present invention is convenient for film thickness measurement. Small-angle X-ray reflection testing can accurately measure the iron-silicon alloy thin film layer with a thickness of about 100 nm. Using magnetron sputtering to prepare the multi-layer neutron thin film spin flipper element, the thickness of each iron-silicon alloy thin film layer is consistent, and magnetron sputtering can ensure the thickness accuracy of each iron-silicon alloy thin film layer, and regulate the thickness of the iron-silicon alloy thin film layer with sub-nanometer accuracy, so as to ensure the accuracy of the flipping angle of the multi-layer neutron thin film spin flipper element. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the multi-layer neutron thin film spin flipper element of the present invention;

[0025] Figure 2Hysteresis loop curve of the multi-layer neutron thin film spin flip element fabricated for Example 1;

[0026] Figure 3 Hysteresis loop curve of the multi-layer neutron thin film spin flip element fabricated for Example 2;

[0027] Figure 4 Hysteresis loop curve of the multi-layer neutron thin film spin flip element fabricated for Example 3;

[0028] Figure 5 Hysteresis loop curve of the multi-layer neutron thin film spin flip element fabricated for Example 4;

[0029] Figure 6 Polarized neutron flip efficiency curve of the multi-layer neutron thin film spin flip element fabricated for Example 1;

[0030] Figure 7 Schematic diagram of the neutron thin film spin flip element of the present invention.

[0031] Figure 1 In the figure, 1. Ultra-smooth silicon wafer substrate; 2. Iron-silicon alloy thin film layer; 3. Chromium thin film layer. Detailed implementation manners

[0032] The following will describe in more detail a multi-layer neutron thin film spin flip element for a neutron spin flipper and its manufacturing method of the present invention with reference to the schematic diagrams, in which the preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation to the present invention.

[0033] Example 1:

[0034] A multi-layer neutron thin film spin flip element for a neutron spin flipper, as Figure 1 shown, includes a double-sided polished ultra-smooth silicon wafer substrate 1, an iron-silicon alloy thin film layer 2 and a chromium thin film layer 3. The iron-silicon alloy thin film layer 2 and the chromium thin film layer 3 are alternately deposited on the ultra-smooth silicon wafer substrate 1 in sequence until the uppermost layer is the chromium thin film layer 3. The thickness of the double-sided polished ultra-smooth silicon wafer substrate does not exceed 0.5 mm, the effective size ≥ 120 mm × 60 mm, and the surface form error PV within the effective area ≤ 10 μm. The total thickness of the iron-silicon alloy thin film layer is 2000 nm, the single-layer thickness is 100 nm, and the number of layers is 20 layers. The single-layer thickness of the chromium thin film layer is 10 nm, and the number of layers is 20 layers.

[0035] The preparation processes of the iron-silicon alloy thin film layer and the chromium thin film layer are both magnetron sputtering. The sputtering gases for preparing the iron-silicon alloy thin film layer and the chromium thin film layer are both pure Ar gas, and the sputtering pressures are both 1 mTorr. The background vacuum in magnetron sputtering is better than 8.0×10 -5 Pa. The target distance of the iron-silicon alloy target is 8 cm, and the target distance of the chromium target is 6 cm. The sputtering power of the iron-silicon alloy target is 40 W, and the sputtering power of the chromium target is 30 W.

[0036] The chromium thin film layer as an interlayer can improve the soft magnetic properties of the iron-silicon alloy thin film. As Figure 2 shown, by inserting a chromium thin film layer into the micron-scale iron-silicon alloy thin film, the saturation magnetic induction intensity reaches 1.3 T, and the coercive force is 5.0 Oe.

[0037] Based on the above method, the polarization neutron flipping efficiency of the fabricated multi-layer neutron thin film spin flipper element was measured at the China Mianyang Research Reactor. The measured flipping efficiency is as Figure 6 shown, where the angle between the neutron beam and the initial position of the thin film is 6°, the abscissa is the wavelength of the neutron beam, and the ordinate is the polarization neutron flipping efficiency of the multi-layer neutron thin film spin flipper element. As Figure 6 can be seen, the multi-layer neutron thin film spin flipper element can achieve a polarization neutron flipping efficiency as high as 98%.

[0038] Example 2

[0039] A multi-layer neutron thin film spin flipper element for a neutron spin flipper, as Figure 1 shown, includes a super-smooth silicon wafer substrate 1 with double-sided polishing, an iron-silicon alloy thin film layer 2, and a chromium thin film layer 3. The iron-silicon alloy thin film layer 2 and the chromium thin film layer 3 are alternately deposited on the super-smooth silicon wafer substrate 1 in sequence until the top layer is the chromium thin film layer 3. The thickness of the double-sided polished super-smooth silicon wafer substrate does not exceed 0.5 mm, the effective size is ≥120 mm×60 mm, and the surface profile error PV in the effective area is ≤10 μm. The total thickness of the iron-silicon alloy thin film layer is 1950 nm, the single-layer thickness is 130 nm, and the number of layers is 15. The single-layer thickness of the chromium thin film layer is 10 nm, and the number of layers is 15.

[0040] The preparation processes of the iron-silicon alloy thin film layer and the chromium thin film layer are the same as those in Example 1.

[0041] The chromium thin film layer as an interlayer can improve the soft magnetic properties of the iron-silicon alloy thin film. As Figure 3 shown, by inserting a chromium thin film layer into the micron-scale iron-silicon alloy thin film, the saturation magnetic induction intensity reaches 1.5 T, and the coercive force is 1.2 Oe.

[0042] Example 3

[0043] A multi-layer neutron thin-film spin-flip element for a neutron spin flipper, as Figure 1 shown, comprising a double-sided polished ultra-smooth silicon wafer substrate 1, an iron-silicon alloy thin-film layer 2, and a chromium thin-film layer 3. The iron-silicon alloy thin-film layer 2 and the chromium thin-film layer 3 are alternately deposited on the ultra-smooth silicon wafer substrate 1 in sequence until the top layer is the chromium thin-film layer 3. The thickness of the double-sided polished ultra-smooth silicon wafer substrate does not exceed 0.5 mm, the effective size is ≥120 mm × 60 mm, and the surface form error PV in the effective area is ≤10 μm. The total thickness of the iron-silicon alloy thin-film layer is 1430 nm, the single-layer thickness is 130 nm, and the number of layers is 11. The single-layer thickness of the chromium thin-film layer is 10 nm, and the number of layers is 11.

[0044] The preparation processes of the iron-silicon alloy thin-film layer and the chromium thin-film layer are the same as those in Example 1.

[0045] The chromium thin-film layer can improve the soft magnetic properties of the iron-silicon alloy thin-film as an interlayer, as Figure 4 shown. By inserting the chromium thin-film layer into the iron-silicon alloy thin-film in the micron scale, the saturation magnetic induction intensity reaches 1.8 T, and the coercivity is 2.1 Oe.

[0046] Example 4

[0047] A multi-layer neutron thin-film spin-flip element for a neutron spin flipper, as Figure 1 shown, comprising a double-sided polished ultra-smooth silicon wafer substrate 1, an iron-silicon alloy thin-film layer 2, and a chromium thin-film layer 3. The iron-silicon alloy thin-film layer 2 and the chromium thin-film layer 3 are alternately deposited on the ultra-smooth silicon wafer substrate 1 in sequence until the top layer is the chromium thin-film layer 3. The thickness of the double-sided polished ultra-smooth silicon wafer substrate does not exceed 0.5 mm, the effective size is ≥120 mm × 60 mm, and the surface form error PV in the effective area is ≤10 μm. The total thickness of the iron-silicon alloy thin-film layer is 1170 nm, the single-layer thickness is 130 nm, and the number of layers is 9. The single-layer thickness of the chromium thin-film layer is 10 nm, and the number of layers is 9.

[0048] The preparation processes of the iron-silicon alloy thin-film layer and the chromium thin-film layer are the same as those in Example 1.

[0049] The chromium thin-film layer can improve the soft magnetic properties of the iron-silicon alloy thin-film as an interlayer, as Figure 5 shown. By inserting the chromium thin-film layer into the iron-silicon alloy thin-film in the micron scale, the saturation magnetic induction intensity reaches 1.7 T, and the coercivity is 1.1 Oe.

[0050] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A multi-layer neutron thin film spin flipping element for a neutron spin flipper, characterized in that, it includes a super-smooth silicon wafer substrate with double-sided polishing, a multi-layer iron-silicon alloy thin film layer, and a multi-layer chromium thin film layer. The multi-layer iron-silicon alloy thin film layers and the multi-layer chromium thin film layers are alternately deposited on the surface of the super-smooth silicon wafer substrate in sequence, and the top layer of the multi-layer neutron thin film spin flipping element is a chromium thin film layer; the thickness of the super-smooth silicon wafer substrate is less than or equal to 0.5 mm; the single-layer thickness of the iron-silicon alloy thin film layer is 100 nm - 130 nm.

2. The multi-layer neutron thin film spin flipping element for a neutron spin flipper according to claim 1, characterized in that, the effective size of the super-smooth silicon wafer substrate is greater than or equal to 120 mm × 60 mm.

3. The multi-layer neutron thin film spin flipping element for a neutron spin flipper according to claim 2, characterized in that, the surface form error PV of the effective size of the super-smooth silicon wafer substrate is less than or equal to 10 μm.

4. The multi-layer neutron thin film spin flipping element for a neutron spin flipper according to claim 1, characterized in that, the single-layer thickness of the chromium thin film layer is 10 nm.

5. A manufacturing method of a multi-layer neutron thin film spin flipping element for a neutron spin flipper, preparing the multi-layer neutron thin film spin flipping element for a neutron spin flipper according to any one of claims 1 - 4, characterized in that, the preparation processes of the iron-silicon alloy thin film layer and the chromium thin film layer are both magnetron sputtering.

6. The manufacturing method of the multi-layer neutron thin film spin flipping element for a neutron spin flipper according to claim 5, characterized in that, in the process of the magnetron sputtering, the inert gas is 99.99% Ar gas, and the sputtering pressure is 1 mTorr.

7. The manufacturing method of the multi-layer neutron thin film spin flipping element for a neutron spin flipper according to claim 5, characterized in that, During the process of magnetron sputtering, the background vacuum is better than 8.0×10 -5 Pa, the target distance of the iron-silicon alloy target is 8 cm, the target distance of the chromium target is 6 cm, the sputtering power of the iron-silicon alloy target is 40 W, and the sputtering power of the chromium target is 30 W.

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