Diamond spin quantum sensor and preparation method thereof

Abstract

The invention belongs to the field of quantum sensors, and discloses a diamond spin quantum sensor and a preparation method thereof. The preparation method comprises the following steps: cleaning and polishing a monocrystal diamond substrate; a microwave plasma chemical vapor deposition method is adopted for preparing a diamond film with the nitrogen-vacancy color center density larger than 10 < 16 > cm <-3 > on the single crystal diamond substrate; and preparing an anti-ferromagnetic NiO film on the diamond film by adopting a radio frequency magnetron sputtering method to obtain the diamond spin quantum sensor. The diamond spin quantum sensor disclosed by the invention contains a high-concentration nitrogen-vacancy color center diamond film, and nitrogen-vacancy color center measurement has extremely high spatial resolution, so that the change of a nano-scale magnetic field can be detected; the diamond spin quantum sensor is applied to precise measurement of the magnetic moment of an antiferromagnetic film and the magnetic coupling effect of an antiferromagnetic / ferromagnetic heterojunction interface. And the preparation method is simple, economical and applicable, and provides possibility for application of the diamond nitrogen-vacancy color center material in the field of quantum magnetic sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum sensors, and particularly to a diamond spin quantum sensor and a preparation method thereof. Background Art

[0002] The magnetic moment of an antiferromagnetic thin film is usually small and localized, and it is difficult to accurately measure it by traditional magnetic measurement methods.

[0003] The nitrogen-vacancy color center in diamond has nanoscale spatial resolution and extremely high magnetic field sensitivity, can detect these tiny magnetic moments, and reconstruct the magnetic structure of the antiferromagnetic thin film by analyzing the changes in the optically detected magnetic resonance (ODMR) spectrum. First, the nitrogen-vacancy color center in diamond can directly image the antiferromagnetic domains, revealing the size, shape, and distribution of the antiferromagnetic domains; second, by measuring the temperature-dependent ODMR spectrum, the magnetic order phase transition process of the antiferromagnetic material can be studied. In addition, spin waves in the antiferromagnetic material can also be detected, thereby studying the propagation characteristics of spin waves. Finally, it can be used to study the interfacial magnetic coupling effect in antiferromagnetic / ferromagnetic heterojunctions, providing an important experimental basis for the development of new spin electronic devices. Based on the above technological developments, how to provide high-sensitivity and high-precision magnetic field measurement methods and their devices remains a problem to be solved at present.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the Invention

[0005] In view of the deficiencies of the above prior art, the purpose of the present invention is to provide a diamond spin quantum sensor and a preparation method thereof, aiming to solve the problem that it is difficult to accurately measure antiferromagnetic thin films by traditional magnetic measurement methods.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect of the present invention, a preparation method of a diamond spin quantum sensor is provided, including the steps of:

[0008] S10. Cleaning and polishing an Ib-type (111) single-crystal diamond substrate;

[0009] S20. Preparing a nitrogen-doped diamond film on the single-crystal diamond substrate processed in step S10 by microwave plasma chemical vapor deposition (MPCVD), and the nitrogen-vacancy color center density of the diamond film is greater than 10 16 cm-3 ;

[0010] S30. Prepare an antiferromagnetic NiO thin film on the nitrogen-doped diamond thin film by radio frequency magnetron sputtering to obtain the diamond spin quantum sensor.

[0011] Optionally, in step S10, the steps of cleaning and polishing the single-crystal diamond substrate include:

[0012] Put the Ib-type (111) single-crystal diamond substrate into a mixed solution of 95% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 3:1 for acid boiling, then repeatedly clean the single-crystal diamond substrate with acetone, ethanol and deionized water, dry it with nitrogen, and polish the surface of the single-crystal diamond substrate along the

[112] direction with a deviation angle of 2°.

[0013] Optionally, in step S20, the microwave plasma chemical vapor deposition method uses CH4 as the source gas, H2 as the carrier gas, and N2 as the nitrogen source for deposition on the single-crystal diamond substrate.

[0014] Optionally, the flow rate ratio of CH4 in H2 is 4%; the flow rate ratio of N2 in H2 is 0.002% - 0.04%.

[0015] Optionally, during the deposition process, the pressure range is 140 - 160 Torr, and the microwave power is 4.5 - 5.0 kw.

[0016] Optionally, during the deposition process, the temperature of the single-crystal diamond substrate is 1000 - 1100 °C, and the plasma temperature is 5000 K.

[0017] Optionally, in step S20, the thickness of the nitrogen-doped diamond thin film is 120 - 150 μm.

[0018] Optionally, in step S30, the steps of preparing the antiferromagnetic NiO thin film on the diamond thin film by radio frequency magnetron sputtering include: under the condition that the vacuum degree is less than 5x10 -8 mTorr, using Ar as the working gas and the NiO ceramic target as the target, and sputtering on the diamond thin film for 40 - 60 min by magnetron sputtering to obtain the antiferromagnetic NiO thin film.

[0019] Optionally, the thickness of the antiferromagnetic NiO thin film is 20 - 30 nm.

[0020] In the second aspect of the present invention, a diamond spin quantum sensor is provided, which is prepared by the preparation method of the diamond spin quantum sensor.

[0021] Beneficial effects:

[0022] The present invention provides a diamond spin quantum sensor and a preparation method thereof. By using microwave plasma chemical vapor deposition technology, a diamond film with a high concentration of nitrogen-vacancy color centers is prepared, and then a diamond spin quantum sensor is further prepared. Compared with traditional technologies, the measurement of nitrogen-vacancy color centers has extremely high spatial resolution, can detect magnetic field changes at the nanoscale, is very sensitive to weak magnetic fields, and can indirectly measure the magnetic properties of antiferromagnetic materials. Utilizing the ability of nitrogen-vacancy color centers to detect magnetic fields to study the spin transport mechanism of antiferromagnets is crucial for designing efficient spintronic devices. The diamond spin quantum sensor of the present invention can be applied to the precise measurement of the magnetic moment of antiferromagnetic thin films and the interfacial magnetic coupling effect of antiferromagnetic / ferromagnetic heterojunctions, realizing the measurement of weak magnetic moments. At the same time, its preparation method is simple, economical and applicable, suitable for industrial production, and provides the possibility for the application of diamond nitrogen-vacancy color center materials in the field of quantum magnetic sensors. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the preparation process of the diamond spin quantum sensor described in the embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram of the structure of the diamond spin quantum sensor described in the embodiment of the present invention. Detailed Embodiments

[0025] The present invention provides a diamond spin quantum sensor and a preparation method thereof. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] The embodiment of the present invention provides a preparation method of a diamond spin quantum sensor, as Figure 1 shown, including the steps:

[0028] S10. Clean and polish an Ib-type (111) single-crystal diamond substrate;

[0029] S20. Prepare a nitrogen-doped diamond film on the single-crystal diamond substrate processed in step S10 by using microwave plasma chemical vapor deposition method, and the nitrogen-vacancy color center density of the diamond film is greater than 10 16 cm -3 ;

[0030] S30. Prepare an antiferromagnetic NiO thin film on the nitrogen-doped diamond thin film by radio frequency magnetron sputtering to obtain the diamond spin quantum sensor.

[0031] In some embodiments, in step S10, the steps of cleaning and polishing the single-crystal diamond substrate include:

[0032] Put the Ib-type (111) single-crystal diamond substrate into a mixed solution of 95% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 3:1 for acid boiling, then repeatedly clean the single-crystal diamond substrate with acetone, ethanol, and deionized water. After drying with nitrogen, polish the surface of the single-crystal diamond substrate along the

[112] direction with a deviation angle of 2°.

[0033] The present invention selects a single-crystal diamond substrate with the (111) crystal orientation, so that the diamond nitrogen-vacancy color centers prepared by microwave plasma chemical vapor deposition will form a perfect arrangement along the

[111] direction, and a theoretical maximum contrast of about 30% can be achieved. The purpose of polishing the surface of the single-crystal diamond substrate along the

[112] direction with a deviation angle of about 2° in the present invention is to achieve step-flow growth, so that the concentration of diamond nitrogen-vacancy color centers is greater, thereby improving the magnetic detection sensitivity of the diamond spin quantum sensor. This is because the magnetic detection sensitivity (η) of the diamond spin quantum sensor can be expressed as where C is the contrast, N is the density of nitrogen-vacancy color centers, is the spin decoherence time, and V is the volume of the diamond thin film excited by the laser. Therefore, under the same conditions, increasing the density of nitrogen-vacancy color centers can improve the magnetic detection sensitivity of the diamond spin quantum sensor. On the contrary, if the polishing treatment is not carried out under these conditions, the concentration of nitrogen-vacancy color centers in the grown diamond thin film is relatively low.

[0034] In some embodiments, in step S20, the microwave plasma chemical vapor deposition method uses CH4 as the source gas, H2 as the carrier gas, and N2 as the nitrogen source to deposit on the single-crystal diamond substrate.

[0035] In some specific embodiments, the flow ratio of CH4 in H2 is 4%; the flow ratio of N2 in H2 is 0.002% - 0.04%.

[0036] In some specific embodiments, during the deposition process, the pressure range is 140 - 160 Torr, and the microwave power is 4.5 - 5.0 kw.

[0037] In some specific embodiments, during the deposition process, the temperature of the single-crystal diamond substrate is 1000 - 1100 °C, and the plasma temperature is 5000 K. Within this temperature range, a nitrogen-vacancy color center density greater than 10 16 cm-3 diamond thin film

[0038] In the present invention, by incorporating a controllable amount of N2, changing the ratio of N2 in H2, and controlling the plasma temperature and microwave power, the arrangement and concentration of nitrogen-vacancy color centers in the diamond thin film are optimized, thereby realizing the preparation of a nitrogen-doped diamond thin film with high concentration and high uniformity.

[0039] In some embodiments, in step S20, the thickness of the nitrogen-doped diamond thin film is 120 - 150 μm. The diamond thin film with the required thickness can be obtained by controlling the deposition time. Within a certain range, the longer the deposition time, the thicker the obtained diamond thin film.

[0040] In some embodiments, in step S30, the step of preparing an antiferromagnetic NiO thin film on the diamond thin film by radio frequency magnetron sputtering method includes: under the condition that the vacuum degree is less than 5x10 -8 mTorr, using Ar as the working gas and a NiO ceramic target as the target, sputtering on the diamond thin film for 40 - 60 min by magnetron sputtering method to obtain the antiferromagnetic NiO thin film.

[0041] In some specific embodiments, the thickness of the antiferromagnetic NiO thin film is 20 - 30 nm.

[0042] The embodiment of the present invention provides a diamond spin quantum sensor, which is prepared by the preparation method of the diamond spin quantum sensor. A microwave antenna is used to apply a uniformly changing microwave signal to the diamond / antiferromagnetic thin film heterojunction through a microwave signal generator. In a specific embodiment, when applying the microwave signal, a planar antenna is used. Compared with linear and spiral copper wires, the planar antenna can achieve a wide-range, high-intensity, and large-area uniform microwave magnetic field, obtain a relationship diagram of the characteristic peak corresponding to the nitrogen-vacancy color center in the PL spectrum changing with the microwave signal, and then combine relevant computer software to complete the acquisition of data. The diamond spin quantum sensor provided by the present invention can measure weak magnetic moments.

[0043] The following is a detailed description through specific examples.

[0044] Example 1

[0045] The specific steps for fabricating the diamond spin quantum sensor in this embodiment are as follows: Using a microwave plasma chemical vapor deposition device, with CH4 as the source gas, H2 as the carrier gas, and N2 as the nitrogen source, epitaxially grow diamond on an Ib-type HPHT (111) diamond as the substrate. The substrate size is 1 mm × 1 mm × 0.3 mm. Put the Ib-type (111) diamond substrate into a mixed solution of 95% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 3:1 for acid boiling to remove impurities on the diamond surface, then repeatedly clean the diamond with acetone, ethanol, deionized water, etc., and dry the substrate with nitrogen for standby. Subsequently, polish along the

[112] direction with a deviation angle of about 2° to achieve step-flow growth. Incorporate a controllable amount of N2, with the N2 content as the variable factor, the ratio of CH4 in H2 is 4%, the ratio of N2 in H2 is 0.04%, the substrate temperature is 1000 °C, the plasma temperature is 5000 K, deposit for 4 hours, and the film thickness is 130 μm. Use radio frequency magnetron sputtering to prepare an antiferromagnetic NiO film on the diamond film, with the vacuum degree less than 5x10 -8 mTorr, the substrate temperature is room temperature, the Ar gas flow rate is 32 sccm, the sputtering time is 60 min, obtain an NiO film with a thickness of 30 nm, and finally obtain the diamond spin quantum sensor, the schematic structural diagram of which is as Figure 2 shown.

[0046] Place the sample of the above diamond spin quantum sensor on a microwave antenna, and apply a uniformly varying microwave signal to it through a microwave signal generator, indicating that the diamond spin quantum sensor can measure weak magnetic moments. When applying the microwave signal, use a planar antenna. Compared with straight and spiral copper wires, the planar antenna can achieve a wide range, high intensity, and large area of uniform microwave magnetic field.

[0047] The ratio of CH4 in H2 is 4%, and the ratio of N2 in H2 is 0.002% - 0.04%. The film thickness is 130 μm.

[0048] In summary, the present invention prepares a high-concentration nitrogen-vacancy color center diamond film by using the microwave plasma chemical vapor deposition method, and further fabricates a diamond spin quantum sensor. The measurement of high-concentration nitrogen-vacancy color centers has extremely high spatial resolution, can detect magnetic field changes at the nanoscale, is very sensitive to weak magnetic fields, and can indirectly measure the magnetic properties of antiferromagnetic materials. The diamond spin quantum sensor of the present invention realizes the measurement of weak magnetic moments, providing the possibility for the application of diamond nitrogen-vacancy color center materials in the field of quantum magnetic sensors.

[0049] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or changes can be made according to the above description, and all such improvements and changes shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a diamond spin quantum sensor, characterized in that, Including the steps of: S10. Cleaning and polishing an Ib-type (111) single-crystal diamond substrate; S20. Prepare a nitrogen-doped diamond film on the single-crystal diamond substrate processed in step S10 by microwave plasma chemical vapor deposition method, and the nitrogen-vacancy color center density of the diamond film is greater than 10 16 cm -3 ; S30. Preparing an antiferromagnetic NiO thin film on the nitrogen-doped diamond thin film by radio frequency magnetron sputtering to obtain the diamond spin quantum sensor.

2. The preparation method of the diamond spin quantum sensor according to claim 1, characterized in that In step S10, the steps of cleaning and polishing the Ib-type (111) single-crystal diamond substrate include: Putting the Ib-type (111) single-crystal diamond substrate into a mixed solution of 95% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 3:1 for acid boiling, then repeatedly cleaning the single-crystal diamond substrate with acetone, ethanol and deionized water, drying it with nitrogen, and polishing the surface of the single-crystal diamond substrate along the [112] direction with a deviation angle of 2°.

3. The preparation method of the diamond spin quantum sensor according to claim 1, wherein In step S20, the microwave plasma chemical vapor deposition method uses CH4 as the source gas, H2 as the carrier gas, and N2 as the nitrogen source for deposition on the single-crystal diamond substrate.

4. The method for preparing a diamond spin quantum sensor according to claim 3, wherein The flow rate ratio of CH4 in H2 is 4%; the flow rate ratio of N2 in H2 is 0.002% - 0.04%.

5. The method for preparing a diamond spin quantum sensor according to claim 3, wherein, During the deposition process, the pressure range is 140 - 160 Torr, and the microwave power is 4.5 - 5.0 kw.

6. The preparation method of the diamond spin quantum sensor according to claim 3, characterized in that, During the deposition process, the temperature of the single-crystal diamond substrate is 1000 - 1100 °C, and the plasma temperature is 5000 K.

7. The preparation method of the diamond spin quantum sensor according to claim 1, wherein, In step S20, the thickness of the nitrogen-doped diamond thin film is 120 - 150 μm.

8. The preparation method of the diamond spin quantum sensor according to claim 1, characterized in that, In step S30, the step of preparing an antiferromagnetic NiO thin film on the diamond thin film by radio frequency magnetron sputtering method includes: under the condition that the vacuum degree is less than 5x10 -8 mTorr, using Ar as the working gas and a NiO ceramic target as the target, sputtering on the diamond thin film for 40 - 60 min by magnetron sputtering method to obtain the antiferromagnetic NiO thin film.

9. The method for preparing a diamond spin quantum sensor according to claim 8, characterized in that, The thickness of the antiferromagnetic NiO thin film is 20 - 30 nm.

10. A diamond spin quantum sensor, characterized in that, Prepared by the preparation method of the diamond spin quantum sensor according to claims 1 - 9.

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