A method for preparing long aa-nv color centers in hexagonal diamond by directional ion implantation

Abstract

The present application belongs to the technical field of diamond material, and particularly relates to a method for preparing long AA-NV color centers of hexagonal diamond by directional ion implantation. The present application effectively solves the problem that the traditional ion implantation process is not suitable for hexagonal diamond by improving the ion implantation process and using grazing ion implantation method to implant nitrogen ions directionally, so as to realize the accurate synthesis of long AA configuration NV color centers. In combination with the strain assisted step-by-step annealing process, the targeted regulation of phased annealing is realized, and the efficient preparation and stabilization of NV color centers are realized at the same time. In the hexagonal diamond, the NV color center forms a unique long AA type configuration according to the relative position of the nitrogen atom and the vacancy in the ABAB stacking layer. The nitrogen atom and the vacancy of the long AA-NV color center are not directly connected to the nearest neighbor, but each has four nearest neighbor carbon atoms. The nitrogen atom and the vacancy are in the diagonal position in the six-membered ring. The existence of this configuration can be used as a clear feature for identifying the long AA-NV color center of hexagonal diamond.

Description

Technical Field

[0001] This invention belongs to the field of diamond material technology, specifically relating to a method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation. Background Technology

[0002] In diamond, the NV center is a point defect consisting of a substituted nitrogen atom and its nearest-neighbor carbon vacancy. Upon gaining an electron, the NV center transforms into a negatively charged NV state. - Color centers possess exceptional optical and spin properties. Therefore, they are widely used in fields such as single-photon source fabrication, quantum information science, and high-sensitivity quantum sensing.

[0003] Hexagonal diamond, commonly known as lensdaleite, is a rare carbon allotrope. Theoretically, it is 58% harder than cubic diamond, and its band gap of 4.5 eV is lower than cubic diamond's 5.6 eV. Its atomic packing structure is AB type (sp... 3 The hybrid bonding (hybridized bonds) and stacking mechanism endow NV centers with unique properties. In recent years, hexagonal diamond has been able to achieve high-quality preparation using high-temperature, high-pressure methods and chemical vapor deposition (CVD) technology, which can provide a high-quality substrate for the preparation of NV centers. However, the preparation technology of hexagonal diamond NV centers is still in its infancy, and there are no successful precedents for preparing NV centers in hexagonal diamond.

[0004] Existing mature methods for preparing NV centers are all geared towards cubic diamond systems, mainly including CVD, electron irradiation, and ion implantation. CVD growth with nitrogen doping for NV center preparation has very low efficiency, with a yield of approximately 0.1%. Electron irradiation methods result in random nitrogen distribution in diamond, making it impossible to control the position of NV centers. Ion implantation introduces nitrogen elements by injecting nitrogen ions into the diamond lattice; after annealing, the nitrogen recombines with vacancies to form NV centers. This method offers precise and efficient NV center formation, making it more suitable for the directional preparation of specific NV center configurations. However, due to the lack of control over specific crystal planes in hexagonal diamond and the lack of optimization of ion implantation parameters and annealing conditions, this method has compatibility issues when used for preparing hexagonal diamond NV centers. These issues are mainly reflected in the following aspects: (1) Mismatch between ion implantation parameters and hexagonal diamond lattice characteristics: Ion implantation mainly determines the implantation depth by shielding or focusing the ion beam and controlling the ion kinetic energy, thereby implanting ions at a specified location. However, the energy, dose, and angle of existing ion implantation are based on the ABC-type stacked lattice design of cubic diamond, without considering the hcp structure, interplanar spacing, and nitrogen solubility of hexagonal diamond. If the existing process is directly adopted, the actual penetration depth of the implanted ions may deviate from the expected value, causing lattice damage, which may in turn damage the stability of the NV color center.

[0005] (2) The substrate pretreatment is not adapted to the requirements of NV center preparation: The hexagonal diamond substrate prepared by CVD inevitably has defects such as dangling bonds and impurities (such as nickel particles) left over from the etching process. When ion implantation is performed to construct NV centers, these residual surface defects may introduce additional lattice distortion and impurities, which will affect the spin-lattice relaxation process of NV centers and lead to a decrease in the coherence time of NV centers.

[0006] (3) Annealing process cannot simultaneously achieve lattice repair and NV - Stability: Existing annealing processes are mostly designed for a single temperature. Low-temperature annealing cannot achieve effective migration of vacancies in hexagonal diamond. In the ion implantation damage area, high-temperature annealing can easily lead to graphitization of hexagonal diamond. Secondly, existing annealing processes only focus on the diffusion and recombination of vacancies and fail to effectively consider the conditions required to prepare NV centers with specific configurations. This may result in the generated NV center configurations exhibiting a random mixed state. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for preparing long AA-NV color centers in hexagonal diamond by directional ion implantation. This is the first time that such a special configuration of NV color centers has been prepared in hexagonal diamond using ion implantation, solving the problem that traditional ion implantation processes are unsuitable for hexagonal diamond.

[0008] In hexagonal diamond, NV centers, based on the relative positions of nitrogen atoms and vacancies in the ABAB stack, can form a unique long AA-NV configuration, as shown in Figure 1. In the long AA-NV center, the nitrogen atom and vacancy are diagonally positioned within the six-membered ring; they are not directly connected nearest neighbors, but rather each has four nearest-neighbor carbon atoms. The presence of this configuration serves as a clear characteristic for identifying long AA-NV centers in hexagonal diamond. Since this configuration can only exist in hexagonal structures, it is a novel configuration distinct from that of cubic diamond NV centers. Therefore, the implantation parameters of traditional ion implantation processes are not suitable for preparing this special NV center in hexagonal diamond. Therefore, in view of the characteristics of long AA-NV color centers in hexagonal diamond, this invention creatively proposes an ion implantation process that is compatible with it, so that the implantation parameters are matched with the hcp structure, (100) crystal plane characteristics and nitrogen solubility of hexagonal diamond, so as to achieve precise deposition of nitrogen ions at the target depth, avoid the formation of disorder due to excessive or shallow deposition, and thus achieve the purpose of directional preparation of long AA-NV color centers.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation, comprising the following steps: (1) Preparation of hexagonal diamond substrate: Hexagonal diamond substrate was prepared by CVD method; (2) Substrate pretreatment: The hexagonal diamond substrate is passivated by oxygen plasma to form an oxide layer. Excess oxide layer is removed to retain a single oxygen terminal. Then, surface impurities are removed by argon plasma treatment, followed by hydrochloric acid soaking, cleaning, drying, and finally a PMMA film with small pores is prepared on the surface. (3) Directed nitrogen ion implantation: under a vacuum of 1×10 -7 In the Torr environment, the pretreated hexagonal diamond substrate is fixed on the sample stage, and the incident direction of the nitrogen ion beam is 5-8°. 15 N + Directional nitrogen ion implantation is performed using ions as the implantation source, and the temperature of the hexagonal diamond substrate does not exceed 200°C during the implantation process. (4) Strain-assisted stepwise annealing: First, the injected sample is placed in a diamond anvil or a specially designed bending and pressurizing device, and uniaxial tensile stress is applied in the direction perpendicular to the c-axis. Then, stepwise annealing is performed to form hexagonal diamond long AA-NV color centers.

[0010] Further, in step (1), the CVD method for preparing the hexagonal diamond substrate includes the following steps: Hexagonal diamond single crystals or polycrystalline films with specific orientations were selected as homogeneous seed crystals. After chemical mechanical polishing and ultrasonic cleaning, nickel films were deposited by magnetron sputtering CVD and then heat-treated to transform them into discrete nickel particle masks. Hexagonal diamond nanorods were then prepared by ICP etching. Finally, the (100) step surface was exposed by hydrogen etching. Finally, MP-CVD equipment with a parallel laser source was used for growth, and methane and hydrogen of 5N purity were introduced to obtain hexagonal diamond single crystals / polycrystalline films with specific orientations.

[0011] Further, in step (2), the method for removing the excess oxide layer is as follows: the hexagonal diamond substrate after surface passivation is placed into an MP-CVD device and treated with 5N pure hydrogen gas.

[0012] By optimizing the hexagonal diamond substrate pretreatment process, dangling bonds, residual impurities, and etching defects on the substrate surface are eliminated, reducing the substrate noise level. Furthermore, by using focused ion beams or photomasks to control the distribution precision of implanted nitrogen elements, a low-defect lattice environment is provided for the directional formation of long AA-NV color centers, thereby improving their spin coherence.

[0013] Furthermore, in step (3), the implantation energy during directional nitrogen ion implantation is 5-30 keV.

[0014] Further, in step (3), the implantation dose during directional nitrogen ion implantation is 1×10⁻⁶. 13 -1×10 15 ions / cm 2 .

[0015] Furthermore, in step (3), the implantation rate during directional nitrogen ion implantation is 5 × 10⁻⁶. 11 -1×10 13 ions / (cm 2 ·s).

[0016] Furthermore, in step (4), the magnitude of the uniaxial tensile stress is 1 bar-10 GPa.

[0017] Further, in step (4), the segmented annealing includes a first step of repair, a second step of recombination, and a third step of stabilization; the first step of repair is to perform vacuum annealing to repair the lattice distortion and shallow surface defects caused by ion implantation, while avoiding excessive vacancy migration leading to aggregation, thus creating conditions for subsequent nitrogen-vacancy recombination; the second step of recombination is to anneal in an argon + hydrogen mixed atmosphere to promote vacancy migration and recombination with nitrogen atoms at the diagonal position of nitrogen atoms to form long AA-NV color centers; the third step of stabilization is to anneal in an argon atmosphere to stabilize the NV of the long AA-NV color centers. - Charge state, reduce NV 0 and NV + The ratio is increased, while eliminating residual P1 centers and improving the optical stability of NV color centers.

[0018] Furthermore, the annealing parameters for the first step of repair are: heating rate 4-5℃ / min, heating to 350℃-450℃, holding for 2-3 h, and slow cooling rate 1.5-2℃ / min; the annealing parameters for the second step of composite repair are: argon flow rate 80-100 sccm, hydrogen flow rate 10-15 sccm, total pressure 1 atm, heating rate 4-5℃ / min, heating to 750-800℃, holding for 4-6 h, and cooling rate 2.5-3℃ / min; the annealing parameters for the third step of stabilization are: argon flow rate 80-100 sccm, pressure 1 atm, heating rate 4-5℃ / min, heating to 850-900℃, holding for 1-1.5 h, and cooling rate 4-5℃ / min.

[0019] This invention designs a strain-assisted stepwise annealing process that breaks through the formation energy barrier of long AA-NV by externally modulating the lattice potential energy surface. Simultaneously, it combines the stepwise annealing process to address lattice damage repair, vacancy migration, nitrogen-vacancy recombination, and NV formation. - The charge state is stable, which increases the conversion of nitrogen atoms to NV. -The ratio and yield of NV ensure the optical stability of NV color centers.

[0020] The second aspect of this invention provides a hexagonal diamond long AA-NV color center structure prepared by the above method. In hexagonal diamond, the NV color center can form a unique long AA configuration based on the relative positions of nitrogen atoms and vacancies in the ABAB stack. The nitrogen atoms and vacancies of the long AA-NV color center are diagonally located in the six-membered ring. They are not the nearest neighbors directly connected by covalent bonds, but each has four nearest neighbor carbon atoms. The existence of this configuration can be used as a clear feature to identify the long AA-NV color center of hexagonal diamond.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention develops an ion implantation process for the directional preparation of long AA-NV color centers in hexagonal diamond, targeting the structural, crystal orientation, and nitrogen solubility characteristics of hexagonal diamond. By using small-angle nitrogen ion implantation, nitrogen ions are precisely deposited, increasing the probability of nitrogen atoms forming AA-type color centers with vacancies. This suppresses the formation of AB-type color centers from the source, solving the problem of mixed configurations of NV color centers in hexagonal diamond. At the same time, it effectively suppresses the non-ideal aggregation of nitrogen atoms, significantly increases the probability of nitrogen-vacancy recombination, and reduces the impact of impurities and defects on the performance of NV color centers.

[0022] (2) For the residual surface dangling bonds, residual impurities, and structural defects caused by etching in the hexagonal diamond substrate, the targeted substrate pretreatment process adopted in this invention can effectively eliminate these impurities. Through steps such as surface passivation, defect screening, and impurity removal, a low-noise lattice environment is provided for the preparation of NV centers. This significantly reduces the interference of external noise on the spin state and improves the coherence performance of the NV centers.

[0023] (3) Compared with the single-temperature annealing process in the preparation of cubic diamond NV color centers, the strain-assisted three-step annealing strategy proposed in this invention introduces strain field-assisted technology and utilizes the modulation effect of external physical fields on the lattice potential energy surface to guide the directional migration of vacancies, thus providing conditions for the formation of metastable long AA-NV structures in subsequent annealing. The three-step annealing process also achieves lattice distortion repair and promotes NV formation. - The formation and stabilization of color centers (NVs) - Targeting objectives such as charge state is unattainable with traditional single thermal annealing. This process can simultaneously achieve the directional fabrication of long AA-NV color centers and NV... - Increased production of color hearts. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the long AA-NV color center structure of the present invention (carbon, nitrogen and vacancies are represented by gray, blue and white, respectively). Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0027] Example 1: Preparation of long AA-NV color centers of hexagonal diamond by directional ion implantation (1) Preparation of hexagonal diamond substrate This step uses hexagonal diamond prepared by CVD as the substrate. The core objective is to obtain a substrate with exposed (100) crystal planes and step surfaces, low defects, and high purity, laying the foundation for the preparation of NV color centers. The specific process is as follows: Hexagonal diamond single crystals or polycrystalline thin films with specific orientations are selected as homogeneous seed crystals (5 mm in diameter and 1 mm in thickness). After chemical mechanical polishing (CMP) and ultrasonic cleaning, nickel films are deposited by magnetron sputtering CVD and heat-treated to transform them into discrete nickel particle masks. Then, 200 nm high hexagonal diamond nanorods are prepared by ICP etching. Finally, the (100) step surfaces are exposed by hydrogen etching. Finally, MP-CVD equipment with a parallel laser source is used for growth. 5N purity methane and hydrogen are introduced, the deposition pressure is 20 Kpa, the reaction chamber temperature is 450℃, and the substrate temperature is 550℃ to obtain single crystals with a diameter of up to 10 mm.

[0028] (2) Substrate pretreatment First, surface passivation is performed. The hexagonal diamond substrate is placed in a plasma cleaning device, and 5N pure oxygen is introduced at a flow rate of 50 sccm, a pressure of 10 Pa, a power of 50 W, and a treatment time of 5 min. The oxygen combines with surface dangling bonds to form an oxide layer, reducing the formation of surface defects during ion implantation. Then, the passivated substrate is placed in an MP-CVD device, and 5N pure hydrogen is introduced at a flow rate of 80 sccm, a pressure of 15 kPa, a substrate temperature of 500℃, and a treatment time of 3 min. This removes the excess oxide layer, retains a single layer of oxygen terminals, and balances surface stability and ion implantation compatibility.

[0029] Then, impurity removal was performed. The substrate was placed in an RF plasma cleaning device, and 5N pure argon gas was introduced at a flow rate of 30 sccm, a pressure of 5 Pa, a power of 80 W, and a treatment time of 10 min to remove surface-adsorbed water vapor, hydrocarbons, and other impurities. Subsequently, the substrate was immersed in 10% dilute hydrochloric acid for 10 min to remove residual nickel particles and nickel-carbon complexes. It was then repeatedly ultrasonically cleaned with acetone, isopropanol, and deionized water for 10 min and dried with nitrogen. A 300 nm thick PMMA (A4:A7=3:5) film was spin-coated onto the cleaned diamond surface, and then pores with a diameter of 45 nm were fabricated on the PMMA film using EBL. (3) Targeted nitrogen ion implantation To form long AA-NV color centers, nitrogen atoms and vacancies must be located diagonally within the same hexagonal ring. Traditional vertical implantation can lead to ion channeling effects, causing nitrogen ions to penetrate the interlayer barrier and form interlayer defects (such as AB-type defects). Therefore, this invention employs a small-angle implantation strategy, adjusting the incident direction of the nitrogen ion beam to 7°, almost parallel to the basal plane of the hexagonal diamond. The guiding effect of the interlayer potential field of the hexagonal lattice is used to restrict the movement of nitrogen ions, thereby achieving precise nitrogen ion deposition.

[0030] The specific injection parameters were optimized based on the crystal structure and (100) crystal plane characteristics of hexagonal diamond. The crystal parameters of hexagonal diamond were input into the SRIM simulation software, and the appropriate parameters were selected. 15 N + Ions were used as the injection source for simulation. 15 The N nucleus has a spin I = 1 / 2, compared to 14 Increasing N (I=1) can reduce the impact of nuclear spin noise on the coherence of the NV color center and improve the T2 time. SRIM simulations show: The injection energy varies depending on the depth of the target NV color center: 8 keV for shallow NV, 15 keV for mid-depth NV, and 25 keV for deep NV. This energy helps to accurately deposit nitrogen ions at the target depth, preventing ions from penetrating too deeply or depositing too shallowly. The injection dose can be adjusted according to the required concentration of the NV color center; for low-concentration NV, 3 × 10⁻⁶ keV is used. 13 ions / cm 2 For medium concentrations of NV, use 1×10 14 ions / cm 2 High-concentration NV is selected using 8×10 14 ions / cm 2 This dosage is matched to the nitrogen solubility of hexagonal diamond, thus preventing nitrogen atom aggregation; the injection rate is controlled at 5 × 10⁻⁶. 12 The temperature of the substrate is monitored in real time using an infrared thermometer to ensure that it does not exceed 200℃, thereby avoiding lattice structure distortion caused by high temperature.

[0031] The actual injection process was carried out at a vacuum of 1×10⁻⁶. -7 The process is carried out in a Torr environment, where the pretreated hexagonal diamond substrate is fixed on the sample stage, and then... 15 N + Ions are used as the injection source to maintain the angle between the substrate surface and the injection beam, thus avoiding uneven configuration distribution caused by injection angle deviation.

[0032] (4) Strain-assisted segmented annealing Since the long AA-NV configuration is not thermodynamically the lowest energy state, conventional annealing easily transforms it into the AB type. Therefore, this invention introduces a strain-assisted stepwise annealing process to reduce the transformation of the NV color center configuration: First, the implanted sample is placed in a diamond anvil cell or a specially designed bending and pressurizing device, and a uniaxial tensile stress of 8 GPa is applied in the direction perpendicular to the c-axis. Theoretical calculations show that this specific lattice distortion can significantly reduce the formation energy of the long AA-NV configuration, thereby inducing vacancies to preferentially migrate to the diagonal positions of nitrogen atoms.

[0033] Then comes the segmented annealing: The first step is low-temperature repair, which involves annealing in a vacuum annealing furnace at a heating rate of 5℃ / min, heating to 450℃, holding at that temperature for 3 h, and then slowly cooling at a rate of 2℃ / min. This repairs lattice distortion and shallow defects (such as dislocations and small vacancy clusters) caused by ion implantation, while preventing excessive vacancy migration that could lead to agglomeration, thus creating conditions for subsequent nitrogen-vacancy recombination.

[0034] The second step is intermediate-temperature recombination, which involves annealing in an argon + hydrogen mixed atmosphere with an argon flow rate of 80 sccm, a hydrogen flow rate of 10 sccm, a total pressure of 1 atm, a heating rate of 5℃ / min, heating to 750℃, holding at that temperature for 5 h, and a cooling rate of 3℃ / min. The role of hydrogen is to passivate surface defects, while argon can inhibit the graphitization of hexagonal diamond. The intermediate-temperature environment can promote vacancy migration and recombination with nitrogen atoms at diagonal positions to form long AA-NV color centers.

[0035] The third step is high-temperature stabilization, which is carried out in an argon atmosphere annealing furnace with an argon flow rate of 100 sccm, a pressure of 1 atm, a heating rate of 5℃ / min, heating to 900℃, holding at that temperature for 1 h, and a cooling rate of 5℃ / min to further stabilize the NV of the long AA-NV color centers. - Charge state, reduce NV 0 and NV + The ratio is increased, while eliminating residual P1 centers and improving the optical stability of NV color centers.

[0036] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation, characterized in that, Includes the following steps: (1) Preparation of hexagonal diamond substrate: Hexagonal diamond substrate was prepared by CVD method; (2) Substrate pretreatment: The hexagonal diamond substrate is passivated by oxygen plasma to form an oxide layer. Excess oxide layer is removed to retain a single oxygen terminal. Then, surface impurities are removed by argon plasma treatment, followed by hydrochloric acid soaking, cleaning, drying, and finally a PMMA film with small pores is prepared on the surface. (3) Directed nitrogen ion implantation: under a vacuum of 1×10 -7 In the Torr environment, the pretreated hexagonal diamond substrate is fixed on the sample stage, and the incident direction of the nitrogen ion beam is 5-8°. 15 N + Directional nitrogen ion implantation is performed using ions as the implantation source, and the temperature of the hexagonal diamond substrate does not exceed 200°C during the implantation process. (4) Strain-assisted stepwise annealing: First, the injected sample is placed in a diamond anvil cell or a special pressure device, and uniaxial tensile stress is applied in the direction perpendicular to the c-axis. Then, stepwise annealing is performed to form hexagonal diamond long AA-NV color centers.

2. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (1), the CVD method for preparing the hexagonal diamond substrate includes the following steps: Hexagonal diamond single crystal / specific orientation polycrystalline thin film was selected as homogeneous seed crystal. After chemical mechanical polishing and ultrasonic cleaning, nickel film was deposited by magnetron sputtering CVD and then heat-treated to transform it into discrete nickel particle mask. Hexagonal diamond nanorods were then prepared by ICP etching. Finally, the (100) step surface was exposed by hydrogen etching. Finally, MP-CVD equipment with parallel laser source was used for growth, and methane and hydrogen of 5N purity were introduced to obtain hexagonal diamond single crystal or specific orientation polycrystalline thin film.

3. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (2), the method for removing the excess oxide layer is as follows: the hexagonal diamond substrate after surface passivation is placed in an MP-CVD device and treated with 5N pure hydrogen gas.

4. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (3), the implantation energy during directional nitrogen ion implantation is 5-30 keV.

5. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (3), the injection dose during directional nitrogen ion implantation is 1×10⁻⁶. 13 -1×10 15 ions / cm 2 .

6. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (3), the implantation rate during directional nitrogen ion implantation is 5 × 10⁻⁶. 11 -1×10 13 ions / (cm 2 ·s).

7. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (4), the magnitude of the uniaxial tensile stress is 1 bar-10 GPa.

8. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 1, characterized in that, In step (4), the segmented annealing includes a first step of repair, a second step of recombination, and a third step of stabilization. The first step of repair involves vacuum annealing to repair lattice distortion and shallow surface defects caused by ion implantation, while avoiding excessive vacancy migration leading to aggregation, thus creating conditions for subsequent nitrogen-vacancy recombination. The second step of recombination involves annealing in an argon + hydrogen mixed atmosphere to promote vacancy migration and recombination with nitrogen atoms at the diagonal positions of nitrogen atoms to form long AA-NV color centers. The third step of stabilization involves annealing in an argon atmosphere to stabilize the NV of the long AA-NV color centers. - Charge state, reduce NV 0 and NV + The ratio is increased, while eliminating residual P1 centers and improving the optical stability of NV color centers.

9. The method for preparing hexagonal diamond long AA-NV color centers by directional ion implantation according to claim 8, characterized in that, The annealing parameters for the first step of repair are: heating rate 4-5℃ / min, heating to 350℃-450℃, holding for 2-3 hours, and slow cooling rate 1.5-2℃ / min; the annealing parameters for the second step of composite repair are: argon flow rate 80-100 sccm, hydrogen flow rate 10-15 sccm, total pressure 1 atm, heating rate 4-5℃ / min, heating to 750-800℃, holding for 4-6 hours, and cooling rate 2.5-3℃ / min; the annealing parameters for the third step of stabilization are: argon flow rate 80-100 sccm, pressure 1 atm, heating rate 4-5℃ / min, heating to 850-900℃, holding for 1-1.5 hours, and cooling rate 4-5℃ / min.

10. A hexagonal diamond long AA-NV color center structure prepared by the method according to any one of claims 1-9, characterized in that, In hexagonal diamond, the NV color center forms a long AA-type configuration based on the relative positions of nitrogen atoms and vacancies in the ABAB stacking layer. The nitrogen atoms and vacancies in the long AA-NV color center are diagonally located in the six-membered ring. They are not directly connected nearest neighbors, but each has four nearest neighbor carbon atoms. The existence of this configuration is a clear characteristic for identifying the long AA-NV color center in hexagonal diamond.

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