Method for in-situ control of diamond nv color centers by microwave plasma

Abstract

This invention discloses a method for in-situ microwave plasma modulation of NV centers in diamond, comprising the following steps: S1 providing a nitrogen-containing diamond substrate grown by MPCVD, and classifying the substrate grade according to determined S-parameters and the effective nitrogen index (ENI); S2 cleaning the diamond substrate, and then placing it back into the MPCVD equipment for in-situ plasma heat treatment in a hydrogen atmosphere; wherein, the plasma parameters are adjusted according to the determined substrate grade; S3 performing deep polishing and cleaning on the plasma-treated diamond sample to obtain diamond material enriched with NV centers. Based on the nitrogen-containing diamond substrate grown by MPCVD, this invention efficiently activates NV centers through a simplified process of cleaning-microwave plasma in-situ treatment-polishing-re-cleaning, exhibiting high repeatability and controllability of the process and wide applicability.

Description

Technical Field

[0001] This invention belongs to the field of functional materials preparation technology, specifically relating to a method for in-situ modulation of diamond NV color centers based on microwave plasma. Background Technology

[0002] In the field of quantum technology, diamond, with its unique and excellent quantum coherence, has become one of the most promising core carriers for quantum sensing and quantum precision measurement. The NV color center in diamond is a typical point defect structure, consisting of a nitrogen atom replacing a carbon atom in the crystal lattice and an adjacent vacancy. It is one of the few solid-state ensemble quantum systems that can achieve efficient optical readout and quantum state manipulation at room temperature. Ensemble NV color centers possess outstanding advantages such as strong signal, fast response, and the ability to achieve high-sensitivity detection of magnetic fields, electric fields, and temperatures at room temperature, demonstrating irreplaceable application prospects in practical quantum technologies such as quantum precision measurement, biomagnetic detection, and weak field sensing.

[0003] Currently, the mainstream methods for preparing NV centers mainly fall into two categories: 1) using nitrogen-doped diamond substrates, introducing vacancies through high-energy electron beam irradiation, followed by annealing to form NV centers; 2) implanting nitrogen ions into high-purity diamond, followed by annealing to construct NV centers. However, both of these methods have significant limitations: the process is complex, requiring multiple sample transfers between different devices, which can easily introduce surface contamination or adsorbed impurities; the irradiation and implantation processes inevitably cause lattice damage, inducing non-target defects and reducing material quality and the optical stability of NV centers; more importantly, existing heat treatment processes do not fully consider the decisive influence of nitrogen doping concentration in diamond on vacancy migration kinetics and NV center formation efficiency.

[0004] Related studies and experiments have confirmed that low-nitrogen samples, due to the sparse vacancy trapping sites, require lower temperatures to avoid excessive vacancy recombination; while high-nitrogen samples tend to form electrically inert nitrogen clusters (such as A-centers and B-centers), necessitating higher temperatures to effectively activate isolated nitrogen and promote their binding with vacancies. Further research indicates that NV... - The formation efficiency of color centers does not increase monotonically with nitrogen content. When the nitrogen content is too low (e.g., <1 ppm), there is insufficient nitrogen precursor available for NV formation; while when the nitrogen content is too high (e.g., >25 ppm), even with high-temperature annealing, a large number of nitrogen atoms tend to form inactive clusters, which actually inhibits NV formation. - Generation. Traditional single-annealing curve optimization methods are difficult to apply to diamonds with different nitrogen contents, leading to NV (Noise, Intake, and Failure) issues. - The large fluctuations and poor repeatability of color center yield severely restrict the controllable preparation of material properties. Furthermore, simply adjusting annealing processes based on nitrogen concentration also has significant limitations. Nitrogen with different defect morphologies contributes drastically to the formation of NV color centers; only nitrogen existing in monosubstituted forms (such as C centers and their charged N states) contributes significantly.+ Nitrogen can combine with vacancies to form NV centers, while aggregated nitrogen (such as A centers and B centers) is electrically inert and does not participate in the formation of NV centers. However, the total nitrogen doping concentration cannot effectively reflect the specific form of nitrogen in diamond, resulting in samples with the same total nitrogen concentration having drastically different NV formation potentials due to different aggregation states. Therefore, selecting heat treatment parameters solely based on total nitrogen concentration is difficult to accurately match the actual needs of different diamond substrates.

[0005] Therefore, there is an urgent need to develop a post-processing method that does not require irradiation treatment, avoids sample transfer between multiple devices, and can dynamically match plasma parameter curves according to the actual nitrogen doping concentration of diamond. Summary of the Invention

[0006] The main objective of this invention is to provide an efficient, stable, and controllable method for preparing NV center diamonds, aiming to overcome the problems of traditional processes such as reliance on irradiation, multiple sample transfers, easy lattice damage, and low NV center yield. By performing targeted heat treatment and surface finishing on nitrogen-containing diamond substrates, the method achieves controllable preparation of high-concentration, high-purity NV center diamond materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for in-situ modulation of diamond NV color centers using microwave plasma includes the following steps: S1 provides nitrogen-containing diamond substrates grown by MPCVD and measures nitrogen doping and vacancy defect characteristics; determines S-parameters and effective nitrogen index (ENI) to classify substrate grades; S2 performs a first surface cleaning treatment on the diamond substrate to remove surface contaminants introduced during cutting, polishing, or transfer. The cleaned diamond substrate is then placed back into the MPCVD equipment and subjected to in-situ plasma heat treatment in the growth chamber and under a hydrogen atmosphere (the diamond substrate has completed all crystal growth and no further growth deposition is required). The plasma parameters are adjusted according to the determined substrate grade. S3. The diamond sample obtained in S2 is subjected to deep polishing to remove the surface carbonization layer formed during the process; then a second surface cleaning treatment is performed to remove surface contamination introduced by polishing; a diamond material with a clean surface and NV color center enrichment is obtained.

[0008] Preferably, the nitrogen-containing diamond substrate is oriented with a (100) crystal plane; the (100) plane is the main homoepitaxial growth plane, and the substitutional doping efficiency of nitrogen atoms on this crystal plane is relatively high, which is beneficial to improving the optical readout contrast of the NV color center and the ensemble quantum sensing performance.

[0009] In the above solution, the nitrogen-containing diamond substrate has a surface roughness of less than 10 nm, and its nitrogen doping concentration is 1 to 25 ppm.

[0010] Further, the growth process by the MPCVD method includes the following steps: introducing a carbon source (such as CH₄ or C₂H₂, etc.) and a nitrogen source (such as N₂, etc.) in a hydrogen atmosphere, adjusting the concentration ratio of the nitrogen source to the carbon source, and performing epitaxial growth on a single crystal diamond substrate at 750-1000°C; the nitrogen doping concentration is directly controlled by the nitrogen / carbon ratio (nitrogen concentration) in the intake gas, so as to obtain the nitrogen-containing diamond substrate with a nitrogen doping concentration of 1 to 25 ppm respectively.

[0011] Further, in S1, positron annihilation spectroscopy is used to analyze vacancy defects and extract the S parameter; Fourier transform infrared spectroscopy (FTIR) is used to characterize nitrogen-related defects to obtain 1332cm -1 and 1344 cm -1 net absorption coefficients μ at the positions 1332 and μ 1344 , and the effective nitrogen index ENI = μ is calculated 1332 / (μ 1332 +μ 1344 ); wherein the S parameter is the ratio of the count in the low momentum region at the center of the annihilation peak (511 keV) in the positron annihilation Doppler broadening spectrum to the total count of the whole spectrum.

[0012] Further, the present invention adopts the positron annihilation technology to realize the accurate characterization of vacancy-type defects. As a non-destructive characterization means highly sensitive to the defect charge state, it can effectively reflect the concentration and distribution characteristics of vacancies inside the diamond, and provide a key experimental basis for vacancy regulation and annealing parameter matching. A larger S parameter value represents a higher density of vacancy defects.

[0013] Further, the present invention establishes a joint criterion based on the above multi-dimensional characterization results: a main criterion is established according to the ENI value obtained by Fourier transform infrared spectroscopy FTIR analysis and the S parameter obtained by PALS, and the absolute peak areas of NV obtained by photoluminescence spectroscopy PL characterization are further used as auxiliary verification indicators, so as to classify the diamond substrate to be regulated into three categories: low-nitrogen type, medium-nitrogen type and high-nitrogen type. - and NV 0 absolute peak area as auxiliary verification indicators, to classify the diamond substrate to be regulated into three categories: low-nitrogen type, medium-nitrogen type and high-nitrogen type.

[0014] Further, when ENI ≤ 0.3 and the S parameter is lower than 0.45, the nitrogen-containing diamond substrate is classified as the low-nitrogen type (subsequent regulation for the low-nitrogen type diamond substrate is performed); when 0.3 < ENI < 0.7 and the S parameter is between 0.45 and 0.48, the nitrogen-containing diamond substrate is classified as the medium-nitrogen type; when ENI ≥ 0.7 and the S parameter is higher than 0.48, the nitrogen-containing diamond substrate is classified as the high-nitrogen type.

[0015] Furthermore, photoluminescence spectroscopy was used to characterize the initial defect luminescence features, and normalization was performed using the first-order Raman peak of diamond as an internal standard to obtain the NV. - With NV 0 The normalized PL characteristic intensity of the zero-phonon line, where the normalized PL characteristic intensity is the peak area, is used for auxiliary verification. Specific verification methods include: NV 0 Area ≤ 2 au corresponds to low nitrogen characteristics; 2 au <NV 0 Area <10 au corresponds to nitrogen characteristics; NV 0 An area ≥ 10 au corresponds to a high nitrogen characteristic; NV - Area ≤ 10 au corresponds to low nitrogen characteristics; 10 au <NV - Area <30 au corresponds to nitrogen characteristics, NV - Areas ≥ 30 au correspond to high nitrogen characteristics.

[0016] In the above scheme, the first surface cleaning treatment and / or the second surface cleaning treatment are used to remove organic or inorganic contaminants.

[0017] The specific surface cleaning steps in the above scheme include: ultrasonic cleaning in acetone, isopropanol, ethanol and deionized water for 4-6 minutes each, letting it stand for 4-6 minutes and then ultrasonic cleaning for 4-6 minutes again; blowing it dry with high-purity nitrogen and drying it at 60-120℃.

[0018] Furthermore, if there is graphite or amorphous carbon residue on the surface of the nitrogen-containing diamond substrate, it is treated with pickling solution at 150~200℃ for 60~150min, then neutralized with sodium bicarbonate solution, and ultrasonically cleaned with water before drying.

[0019] Furthermore, the pickling solution is a mixture of concentrated sulfuric acid, concentrated nitric acid, and concentrated sulfuric acid and concentrated perchloric acid. The reasonable volume ratio of the three is 1:0.9~1.1:0.9~1.1 (based on concentrated nitric acid). In actual preparation, it needs to be dynamically adjusted according to the sample size to avoid affecting the experimental results due to insufficient cleaning or excessive corrosion.

[0020] In the above scheme, the deep polishing process is used to remove the surface carbonization layer formed during the plasma treatment and to make the surface roughness of the final diamond sample less than 10 nm.

[0021] Further, the deep polishing process includes: employing a multi-stage mechanical polishing process, sequentially using diamond micro-powder suspensions with particle sizes of 30~40μm, 15~20μm, 8~12μm, 3~5μm, 1~2μm, 0.5~1μm, and 0.25~0.5μm, to grind the obtained diamond sample stage by stage on a cast iron or polyurethane polishing disc; the polishing disc rotation speed is 1500~3000 r / min, and the applied pressure is 0.5~2.0 kg / cm². 2 Each grinding stage lasts 15-60 minutes with a continuous supply of coolant. After each stage is completed, the surface is ultrasonically cleaned with water (deionized water), and then finer-grained micro-powder is used for the next polishing stage, ultimately achieving a surface roughness of less than 10 nm.

[0022] In the above scheme, in S2, the cleaned diamond substrate is placed in an MPCVD device and subjected to in-situ plasma heat treatment without being removed from the growth chamber. Specific parameters include: The in-situ plasma heat treatment process is carried out in a hydrogen atmosphere with a hydrogen flow rate of 60~120 sccm. This flow rate range is applicable to all the following classification types and treatment stages. The microwave plasma heat treatment employs a multi-stage stepped parameter curve, matching the corresponding curve type based on the classification results of the aforementioned joint criteria (low-nitrogen, medium-nitrogen, and high-nitrogen). The specific plasma heat treatment process steps include the following: 1) For low-nitrogen grade nitrogen-containing diamond substrates, a two-stage heat treatment process is adopted. The specific parameters are as follows: the first stage has a microwave power of 600~1000 W, a cavity gas pressure of 15~30 Torr, and a hydrogen flow rate of 60~90 sccm, and the treatment time is 1.5~2.5 h; the second stage has a microwave power of 1200~1600 W, a cavity gas pressure of 40~60 Torr, and a hydrogen flow rate of 60~90 sccm, and the treatment time is 1.5~2.5 h; the total treatment time is 3~5 h. 2) For nitrogen-containing diamond substrates of medium nitrogen type, a three-stage heat treatment process is adopted. The specific parameters are as follows: the first stage is 600~1000 W microwave power, 15~30 Torr cavity pressure, and 60~90 sccm hydrogen flow rate, with a treatment time of 1.5~2.5 h; the second stage is 2500~3000 W microwave power, 70~90 Torr cavity pressure, and 90~120 sccm hydrogen flow rate, with a treatment time of 0.5~1 h; the third stage is 1200~1600 W microwave power, 40~60 Torr cavity pressure, and 60~90 sccm hydrogen flow rate, with a treatment time of 1.5~2.5 h; the total treatment time is 3~6.5 h.

[0023] 3) For high-nitrogen-grade nitrogen-containing diamond substrates, a three-stage heat treatment process is adopted. The specific parameters are as follows: Stage 1: microwave power 600~1000 W, cavity pressure 15~30 Torr, hydrogen flow rate 60~90 sccm, treatment time 1.5~2.5 h; Stage 2: microwave power 2500~3200 W, cavity pressure 70~90 Torr, hydrogen flow rate 90~120 sccm, treatment time 1.5~3 h; Stage 3: microwave power 1200~1600 W, cavity pressure 40~60 Torr, hydrogen flow rate 60~90 sccm, treatment time 1.5~2.5 h; total treatment time 4.5~8 h.

[0024] The specific power, pressure, flow rate, and time values ​​for each of the above stages can be adjusted within the corresponding range based on the actual characterization results of the sample, but the relative order between each stage and the shape of the processing curve remain unchanged.

[0025] Furthermore, during the in-situ microwave plasma treatment, parameter coupling control is implemented, including microwave power, cavity pressure, gas flow rate, and treatment time; to avoid process abnormalities such as plasma instability, sample displacement, or surface damage caused by excessive increases or decreases in a single parameter.

[0026] In the above scheme, the microwave plasma in-situ treatment is followed by natural cooling or programmed temperature control to reduce the temperature to room temperature.

[0027] Preferably, the programmed temperature control cooling step includes: implementing stepwise gradient reduction control of microwave power, cavity gas pressure and hydrogen flow rate, and synchronously reducing each parameter to the baseline value according to a preset step size; wherein the single-step adjustment range of microwave power is 40~80W, the single-step adjustment range of cavity gas pressure is 3~6 Torr, and the single-step adjustment range of hydrogen flow rate is 5~10 sccm, to avoid plasma quenching, sample thermal shock or surface stress damage caused by sudden changes in parameters.

[0028] In the above scheme, the microwave plasma in-situ treatment process does not require the application of external high voltage.

[0029] The nitrogen-vacancy color center-containing diamond material prepared according to the above scheme, after deep polishing to remove the carbide layer, has a thickness of 0.3~1.5 mm and a planar dimension of 2×2 mm. 2 Up to 10×10 mm 2 NV in this diamond material - The concentration of color centers increased by more than 100% compared with that before treatment, and the intensity of the 637 nm zero phonon line characteristic peak after normalization was 2 to 3 times that of the untreated sample.

[0030] Furthermore, the normalized NV of the diamond material treated by the method of the present invention for the low-nitrogen sample... -The peak area is 10–16 au, the medium nitrogen type is 16–35 au, and the normalized peak height of the high nitrogen type is 4–6 au.

[0031] This invention eliminates the need for electron beam irradiation or ion implantation to introduce vacancies, and also eliminates the need for high-temperature, high-pressure annealing equipment. All heat treatment steps are completed within the MPCVD chamber. Through the aforementioned microwave plasma in-situ processing technology, combined with positron emission tomography (PET) characterization results, precise parameter matching is achieved, avoiding sample transfer between multiple devices, effectively preventing external contamination and surface adsorption, and significantly improving the NV (noise, vibration, and aging) of the obtained diamond material. - Color center concentration.

[0032] Compared with the prior art, the beneficial effects of the present invention include: (1) Based on the nitrogen-containing diamond substrate obtained by MPCVD growth, this invention does not require the introduction of traditional irradiation and multi-step transfer steps. It can efficiently activate NV color centers through a simplified process of "cleaning-microwave plasma in-situ treatment-polishing-re-cleaning". It can effectively avoid the problems of defects being introduced simultaneously in traditional growth methods, and can significantly shorten the process cycle and improve the controllability of NV color center formation.

[0033] (2) Through multi-dimensional joint characterization using PALS, FTIR, and PL, the main criterion of "ENI+S parameters" was established, classifying diamond substrates into three types: low-nitrogen, medium-nitrogen, and high-nitrogen. Corresponding plasma thermal treatment parameter curves were matched for each type to achieve precise control of vacancy migration and NV formation dynamics, significantly improving the NV of the obtained diamond material. - Color center concentration; (3) The present invention can avoid lattice damage caused by high-energy irradiation, maintain the integrity of diamond crystal, and improve the optical stability and spin coherence performance of NV color centers; (4) Plasma heat treatment is completed in situ in MPCVD equipment, with high process repeatability and controllability. It does not require sample transfer between multiple devices, avoiding external contamination and surface adsorption, and provides high-quality, reproducible NV color center diamond materials for quantum sensing and quantum information devices. Attached Figure Description

[0034] Figure 1 The images show the Raman spectra of the diamond materials obtained after in-situ microwave plasma treatment in Examples 1-3. Figure 2 The fluorescence spectra of the low-nitrogen ensemble NV color center diamonds obtained in Example 1, Comparative Example 1, and Comparative Example 4 are shown below. Figure 3 The fluorescence spectra of the nitrogen ensemble NV color centers of diamond obtained in Example 2, Comparative Example 2, and Comparative Example 5 are shown below. Figure 4The fluorescence spectra of the high-nitrogen ensemble NV color center diamonds obtained in Example 3, Comparative Example 3, and Comparative Example 6 are shown below. Figure 5 The Raman spectra of the diamond materials obtained in Comparative Examples 1-3 are shown. Figure 6 The infrared absorption spectra of the diamond materials obtained in Comparative Examples 1-3 are shown. Figure 7 The diagram shows the correlation analysis of positron annihilation spectra (PALS) and SW parameters of nitrogen-doped diamond substrates with different nitrogen doping concentrations as described in Comparative Examples 1-3. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings, embodiments and comparative examples, but the content of the present invention is not limited to the following embodiments.

[0036] This invention pre-characterizes defects in nitrogen-doped diamond substrates with different nitrogen doping concentrations. Specifically, infrared spectroscopy is used to characterize nitrogen-related defects, clarifying the existence form and distribution of nitrogen in the substrate. Photoluminescence spectroscopy is used to characterize the initial defect luminescence state, corresponding to the intrinsic NV characteristics of the samples. Positron annihilation spectroscopy is used to analyze the vacancy defect distribution, revealing the corresponding lifetime peaks for vacancy defects, whose intensity increases with increasing nitrogen content. S-parameter correlation analysis shows a close relationship between vacancy concentration and the defect environment. These characterization results provide data support for the dynamic matching of subsequent plasma heat treatment parameters.

[0037] Example 1 A method for preparing diamond NV color centers based on in-situ microwave plasma modulation includes the following steps: S1. Provide a (100) crystal diamond substrate grown by MPCVD with dimensions of 5mm × 5mm × 0.6mm and a surface roughness of less than 10 nm. Characterization analysis using FTIR showed an effective nitrogen index (ENI) < 0.3, PALS analysis yielded an S-parameter of 0.43775, and the normalized peak area (NV) of PL was [missing value]. 0 ≈1.1 au, NV - ≈4.2 au, classified as low nitrogen level; S2. The diamond substrate is ultrasonically cleaned in acetone, isopropanol, ethanol and deionized water for 5 minutes each, left to stand for 5 minutes and then ultrasonically cleaned again for 5 minutes. Then, the sample surface is obliquely blown with high-purity nitrogen gas (purity ≥99.99%) at a flow rate of 2L / min and a pressure of 0.08~0.1MPa for 45 seconds and dried in an oven at 60℃ for 30 minutes. The cleaned sample was placed in the MPCVD chamber, evacuated, and then hydrogen was introduced. The plasma was ignited at a low initial power of 500 W, a hydrogen flow rate of 40 sccm, and a chamber pressure of 5 Torr. After the plasma stabilized, the power and pressure were gradually adjusted to the target levels. A stable plasma was maintained at a hydrogen flow rate of 60 sccm, a chamber pressure of 15 Torr, and a microwave power of 800 W for 2 hours. Then, the microwave power was increased to 1400 W and the chamber pressure to 50 Torr, while maintaining a hydrogen flow rate of 60 sccm for another 2 hours. The plasma was then turned off, and the sample was allowed to cool naturally to room temperature. S3. The plasma-treated sample undergoes mechanical-chemical composite polishing to remove the surface carbonized layer: a multi-stage polishing process is employed, sequentially using diamond micro-powder suspensions with particle sizes of 30–40 μm, 15–20 μm, 8–12 μm, 3–5 μm, 1–2 μm, 0.5–1 μm, and 0.25–0.5 μm on a cast iron or polyurethane polishing disc; the polishing disc rotation speed is 2000 r / min, and a pressure of 1 kg / cm² is applied. 2 Each grinding stage lasts 60 minutes with a continuous supply of coolant. After each stage is completed, the surface is ultrasonically cleaned with deionized water and then replaced with finer-grained micro powder for the next polishing stage, ultimately achieving a surface roughness of less than 10 nm. Then repeat the cleaning process in S2 to obtain clean diamond material enriched with NV color centers.

[0038] The Raman spectrum of the diamond material obtained in this embodiment is shown in [reference needed]. Figure 1 1332 cm⁻¹ in Raman spectrum -1 The full width at half maximum (FWHM) of the characteristic peak is 4.6 cm. -1 It was 5.0 cm lower than the untreated control sample. -1 This indicates that plasma heat treatment did not introduce additional lattice damage.

[0039] The diamond material obtained in this embodiment was subjected to photoluminescence spectroscopy testing. The fluorescence spectrum of the obtained diamond material is shown in the figure. Figure 2 Its normalized NV - The zero-phonon line peak area was 10.5 au, which was 150% higher than that of the untreated control sample at the same concentration (Comparative Example 1).

[0040] Example 2 A method for preparing diamond NV color centers based on in-situ microwave plasma modulation, the specific steps of which are basically the same as those in Example 1, with the only difference being: 1) In S1, the effective nitrogen index ENI of the diamond substrate, determined by FTIR characterization, is approximately 0.44, and the normalized peak area NV of PL is approximately 0.44. -The nitrogen content was approximately 12.28 au, and the S-parameter measured by PALS was 0.46974, which determined it to be a medium nitrogen level. 2) In S2, based on the nitrogen level classification results in S1, the plasma heat treatment process steps were adjusted as follows: After the first stage of treatment in S2, the microwave power was increased to 2800 W, the cavity pressure to 80 Torr, and the hydrogen flow rate to 100 sccm, and the treatment was continued for 1 hour; then the microwave power was reduced to 1400 W, the cavity pressure to 50 Torr, and the hydrogen flow rate to 60 sccm, and the treatment was continued for 2 hours. After the treatment, the plasma was turned off, and the sample was allowed to cool naturally to room temperature.

[0041] The remaining steps (including cleaning, polishing, drying, etc.) are the same as in Example 1.

[0042] The Raman spectrum of the diamond material obtained in this embodiment is shown in [reference needed]. Figure 1 1332 cm⁻¹ in Raman spectrum -1 The full width at half maximum (FWHM) of the characteristic peak is 4.19 cm. -1 It was 5.19 cm lower than the untreated control sample. -1 This indicates that plasma heat treatment did not introduce additional lattice damage, NV - The increased strength stems from the optimization of the manufacturing process itself.

[0043] The diamond product obtained in this embodiment was subjected to photoluminescence spectroscopy testing, and its normalized NV... - The zero-phonon line peak area is 28.10 au, such as Figure 3 The result showed an improvement of 129% compared to the untreated control sample at the same concentration (12.28 au).

[0044] Example 3 A method for preparing diamond NV color centers based on in-situ microwave plasma modulation, the specific steps of which are basically the same as those in Example 1, with the only difference being: 1) In S1, after characterization, the effective nitrogen index ENI calculated by FTIR is >0.7, and the normalized NV - The characteristic peak height is 2.308 au, and the S-parameter measured by PALS is 0.49836, which confirms it as a high-nitrogen grade. 2) In S2, based on the classification results of the high-nitrogen level in S1, the plasma heat treatment process steps were adjusted as follows: After the first stage of treatment in S2, the microwave power was increased to 2800 W, the cavity pressure to 80 Torr, and the hydrogen flow rate to 100 sccm, and the treatment was continued for 2 hours; then the microwave power was reduced to 1400 W, the cavity pressure to 50 Torr, and the hydrogen flow rate to 60 sccm, and the treatment was continued for 2 hours. After the treatment, the plasma was turned off, and the sample was allowed to cool naturally to room temperature.

[0045] The remaining steps (including cleaning, polishing, drying, etc.) are the same as in Example 1.

[0046] The Raman spectrum of the diamond material obtained in this embodiment is shown in [reference needed]. Figure 1 1332 cm⁻¹ in Raman spectrum -1 The full width at half maximum (FWHM) of the characteristic peak is 4.56 cm. -1 It was 4.76 cm lower than the untreated control sample. -1 This indicates that plasma heat treatment did not introduce additional lattice damage, NV - The increased strength stems from the optimization of the manufacturing process itself.

[0047] The diamond product obtained in this embodiment was subjected to photoluminescence spectroscopy testing, and the normalized NV was obtained. - The characteristic peak height is 5.1205 au, such as Figure 4 The result showed an improvement of approximately 122% compared to the untreated control sample at the same concentration (2.308 au).

[0048] Comparative Example 1 This comparative example is basically the same as Example 1, except that the plasma heat treatment step is omitted, that is, the sample directly enters the polishing and cleaning steps after cleaning.

[0049] NV measured - The normalized PL peak area was 4.2 au, which was set as the baseline (100%) and used to calculate the improvement rate of Example 1.

[0050] like Figure 5 As shown, the 1332 cm⁻¹ Raman spectrum was measured simultaneously. -1 The full width at half maximum (FWHM) of the characteristic peak is 5.00 cm. -1 This is used to compare and confirm the integrity of the crystal structure obtained in this invention and whether the heat treatment process introduced lattice damage; positron annihilation tests are performed on the samples, such as... Figure 7 As shown, the parameters are used to characterize vacancy-type defects and obtain vacancy concentration-related parameters, which serve as a reference for the process control effect of the embodiments.

[0051] Comparative Example 2 This comparative example is basically the same as Example 2, except that the plasma heat treatment step is omitted, while the rest of the process is the same.

[0052] NV measured - The normalized PL peak area was 12.28 au, which was set as the baseline (100%) and used to calculate the improvement rate of Example 2.

[0053] like Figure 5 As shown, the 1332 cm⁻¹ Raman spectrum was measured simultaneously. -1 The full width at half maximum (FWHM) of the characteristic peak is 5.19 cm.-1 This is used to compare and confirm the integrity of the crystal structure obtained in this invention and whether the heat treatment process introduced lattice damage; positron annihilation tests are performed on the samples, such as... Figure 7 As shown, the parameters are used to characterize vacancy-type defects and obtain vacancy concentration-related parameters, which serve as a reference for the process control effect of the embodiments.

[0054] Comparative Example 3 This comparative example is basically the same as Example 3, except that the plasma heat treatment step is omitted, while the rest of the process is the same.

[0055] Normalized NV measured - The characteristic peak height was 2.308 au, set as the baseline (100%), and used to calculate the improvement rate of Example 3. Figure 7 As shown, the 1332 cm⁻¹ Raman spectrum was measured simultaneously. -1 The full width at half maximum (FWHM) of the characteristic peak is 4.76 cm. -1 This is used to compare and confirm the integrity of the crystal structure obtained in this invention and whether the heat treatment process introduced lattice damage; positron annihilation tests are performed on the samples, such as... Figure 7 As shown, the parameters are used to characterize vacancy-type defects and obtain vacancy concentration-related parameters, which serve as a reference for the process control effect of the embodiments.

[0056] Comparative Example 4 This comparative example is basically the same as Example 1, except that: In S2, based on the classification results of the low-nitrogen type in S1, after the first stage of treatment in S2, the microwave power was increased to 1050 W, the cavity pressure was increased to 28 Torr, and the hydrogen flow rate was maintained at 60 sccm for 2 hours. After treatment, the plasma was turned off, and the sample was allowed to cool naturally to room temperature.

[0057] The remaining steps are the same as in Example 1.

[0058] Diamond samples prepared using this process were subjected to photoluminescence spectroscopy testing, with normalized NV... - The zero-phonon line peak area is 3.58 au, such as Figure 3 As shown, the concentration decreased by approximately 15% compared to the untreated control sample at the same concentration (4.2 au).

[0059] Comparative Example 5 This comparative example is basically the same as Example 2, except that: In S2, based on the classification results of the nitrogen type in S1, after the first stage of treatment in S2, the microwave power was increased to 1050 W, the cavity pressure was increased to 28 Torr, and the hydrogen flow rate was maintained at 60 sccm for 2 hours. Subsequently, the microwave power was increased to 1400 W, the cavity pressure was increased to 50 Torr, and the hydrogen flow rate was maintained at 60 sccm for another 2 hours. After the treatment, the plasma was turned off, and the sample was allowed to cool naturally to room temperature.

[0060] The remaining steps are the same as in Example 2.

[0061] Diamond samples prepared using this process were subjected to photoluminescence spectroscopy testing, with normalized NV... - The zero-phonon line peak area is 20.79 au, as... Figure 3 As shown, the improvement was only about 69% compared to the untreated control sample at the same concentration (12.28 au).

[0062] Comparative Example 6 This comparative example is basically the same as Example 3, except that: In S2, based on the classification results of the high-nitrogen type in S1, after the first stage of treatment in S2, the microwave power was increased to 2800 W, the cavity pressure to 80 Torr, and the hydrogen flow rate to 100 sccm, and the treatment was continued for 1 hour. Subsequently, the microwave power was reduced to 1400 W, the cavity pressure to 50 Torr, and the hydrogen flow rate to 60 sccm, and the treatment continued for 2 hours. After the treatment, the plasma was turned off, and the sample was allowed to cool naturally to room temperature.

[0063] The remaining steps are the same as in Example 3.

[0064] Diamond samples prepared using this process were subjected to photoluminescence spectroscopy testing, with normalized NV... - The characteristic peak height is 3.84 au, such as Figure 4 As shown, the improvement was only about 66% compared to the untreated control sample at the same concentration (2.308 au).

[0065] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0066] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for in-situ modulation of diamond NV color centers using microwave plasma, characterized in that, comprising the following steps: S1 provides a nitrogen-containing diamond substrate. Positron annihilation spectroscopy was used to analyze vacancy defects and extract S-parameters. FTIR was used to characterize nitrogen-related defects, obtaining a 1332 cm⁻¹ sample. -1 and 1344cm -1 Net absorption coefficient μ after deducting baseline 1332 and μ 1344 Calculate the effective nitrogen index ENI=μ 1332 / (μ 1332 +μ 1344 Based on the determined S-parameters and effective nitrogen index (ENI), the substrate grade is defined as follows: when ENI ≤ 0.3 and S-parameters are below 0.45, it is classified as a low-nitrogen type. When 0.3<ENI<0.7 and the S parameter is in the range of 0.45 to 0.48, it is classified as a medium-nitrogen grade; when ENI≥0.7 and the S parameter is higher than 0.48, it is classified as a high-nitrogen grade; wherein the S parameter is the ratio of the count in the low-momentum region at the center of the annihilation peak to the total count of the full spectrum in the positron annihilation Doppler broadening spectrum; S2: performing surface cleaning on the diamond substrate, then placing it back into the MPCVD apparatus, and carrying out in-situ plasma heat treatment in a growth chamber under a hydrogen atmosphere, with process parameters adjusted according to the determined substrate grade, which specifically includes the following: For the low-nitrogen grade, a two-stage heat treatment process is adopted: the first stage has a microwave power of 600 to 1000 W and a chamber pressure of 15 to 30 Torr; the second stage has a microwave power of 1200 to 1600 W and a chamber pressure of 40 to 60 Torr; Both the medium-nitrogen grade and the high-nitrogen grade adopt a three-stage heat treatment process, specifically adding one heat treatment process stage between the first stage and the second stage described for the low-nitrogen grade, and the parameters of the added stage are as follows: for the medium-nitrogen grade, the microwave power is 2500 to 3000 W, and the chamber pressure is 70 to 90 Torr; for the high-nitrogen grade, the microwave power of the second stage is 2500 to 3200 W, and the chamber pressure is 70 to 90 Torr; S3: performing deep polishing and surface cleaning to obtain a diamond material enriched with NV color centers.

2. The method according to claim 1, characterized in that, The in-situ plasma heat treatment process is carried out under a hydrogen atmosphere, with a hydrogen flow rate of 60 to 120 sccm.

3. The method according to claim 1, characterized in that, The hydrogen flow rate control requirements for diamond substrates of different grades are as follows: for the low-nitrogen grade, the flow rate is 60 to 90 sccm in both stages; for the medium-nitrogen grade and the high-nitrogen grade, the flow rate is 60 to 90 sccm in the first and third stages, and 90 to 120 sccm in the second stage.

4. The method according to claim 1, characterized in that, The heat treatment time control requirements for diamond substrates of different grades are as follows: For the low-nitrogen grade, the first stage lasts 1.5 to 2.5 h, the second stage lasts 1.5 to 2.5 h; the total treatment time is 3 to 5 h; For the medium-nitrogen grade, the first stage lasts 1.5 to 2.5 h, the second stage lasts 0.5 to 1 h, the third stage lasts 1.5 to 2.5 h; the total treatment time is 3.5 to 6.5 h; For the high-nitrogen grade, the first stage lasts 1.5 to 2.5 h, the second stage lasts 1.5 to 3 h, the third stage lasts 1.5 to 2.5 h; the total treatment time is 4.5 to 8 h.

5. The method according to claim 1, characterized in that, The nitrogen-containing diamond substrate is grown by the MPCVD method, has a (100) crystal plane orientation, a surface roughness of less than 10 nm, and a nitrogen doping concentration of 1 to 25 ppm.

6. The method according to claim 5, characterized in that, The growth process by the MPCVD method includes the following steps: introducing a carbon source and a nitrogen source in a hydrogen atmosphere, and performing epitaxial growth on a single-crystal diamond substrate at 750 to 1000°C by adjusting the concentration ratio of the nitrogen source to the carbon source.

7. The method according to claim 1, characterized in that, The initial defect luminescence characteristics were further characterized using photoluminescence spectroscopy, and normalization was performed using the first-order Raman peak of diamond as an internal standard to obtain the NV. - With NV 0 The normalized PL characteristic intensity of the zero-phonon line, where the normalized PL characteristic intensity is the peak area, is used for auxiliary verification. Specific verification methods include: NV 0 Area ≤ 2 au corresponds to low-nitrogen type; 2 au <NV 0 Area <10 au corresponds to medium nitrogen type; NV 0 Area ≥ 10 au corresponds to high nitrogen type; NV - Area ≤ 10 au corresponds to low nitrogen type; 10 au <NV - Area <30 au corresponds to the medium nitrogen type class, NV - Area ≥ 30 au corresponds to high nitrogen type.

8. The method according to claim 1, characterized in that, The surface roughness obtained after the deep polishing treatment is less than 10 nm.

9. The diamond material enriched with NV color centers prepared by the method according to any one of claims 1 to 8, characterized in that, Its NV - The concentration of color centers increased by more than 100% compared to before treatment.

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