A method for preparing nanodiamond rare earth vacancy color centers by grafting

Abstract

The present application discloses a method for preparing nano-diamond rare earth vacancy color centers by grafting, comprising the following steps: growing a diamond film on the surface of a silicon substrate; removing amorphous impurities such as graphite and extracting hydrogen terminal dangling bonds from the surface of the diamond substrate; adding a strong acid to a diamond crystallization solution to prepare a carboxylic diamond crystallization solution; stirring the carboxylic diamond crystallization solution and a rare earth aqueous solution to form a mixed crystallization solution of diamond grafted rare earth; implanting mixed crystal seeds on the surface of the diamond substrate; growing a nano-diamond film on the surface of the diamond substrate after the crystallization is completed and a rare earth metal target; then annealing the grown sample; and finally cleaning the surface of the sample to obtain relatively pure nano-diamond rare earth color centers. The present invention breaks through the barrier that rare earth atoms cannot enter diamond due to their large radius.

Description

Technical Field

[0001] The present invention relates to the field of diamond color centers, and in particular to a method for preparing nano-diamond rare earth vacancy color centers by grafting. Background Art

[0002] Nanodiamonds (NCDs) retain the excellent properties of single-crystal diamond while also possessing high refractive index, low optical absorption and scattering (especially in the near-infrared region), high hardness, thermal conductivity, and biocompatibility. Diamonds exhibit a unique color due to their strong near-infrared transmittance. Laser excitation can absorb defects at specific points, called color centers. These color centers in diamonds exhibit strong and stable luminescence, operate at room temperature, are simple to operate, and have controllable spins. Diamonds also possess strong acid and alkali resistance, high temperature resistance, ultra-high hardness, and are non-toxic, making them a hot topic for researchers.

[0003] Of the more than 500 color centers discovered so far, the most studied is the diamond nitrogen (NV) vacancy color center, which has the advantages of good fluorescence stability at room temperature, a long spin coherence time and a small size. However, the luminescence spectrum of the diamond nitrogen (NV) color center is seriously affected by the surrounding crystal field environment. The phonon spectrum is broadened in the range of 400-800nm, and only 4% of the fluorescence is concentrated on the zero phonon line (ZPL), resulting in low magnetic field response accuracy. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing nanodiamond rare earth vacancy color centers by grafting, which solves the problems existing in the background technology of using diamond nitrogen (NV) vacancy color centers through diamond rare earth vacancy color centers.

[0005] The present invention discloses a method for preparing nanodiamond rare earth vacancy color centers by grafting, comprising the following steps:

[0006] Step 1, preliminary preparation: clean the substrate with an ultrasonic cleaning machine; plant diamond crystals on the substrate with diamond planting liquid; take out the substrate and blow dry it with hot air.

[0007] Step 2, diamond substrate preparation: using microwave plasma chemical vapor deposition equipment, grow a diamond film with a thickness of about 1000nm-12000nm on the substrate in step 1 as a diamond substrate.

[0008] Step 3, diamond surface pretreatment: use a vacuum / atmosphere tubular annealing furnace to remove surface graphite from the diamond substrate prepared in step 2; after adjusting the microwave power, use a microwave plasma chemical vapor deposition device to introduce hydrogen, and then introduce methane after ignition; nucleation for 10 minutes, adjust the hydrogen and methane flow rates to grow for 3 hours; vacuum annealing at 850°C for 30 minutes and hydrogen etching for 1 hour, the temperature is 800°C.

[0009] Step 4: Diamond rare earth crystal solution preparation

[0010] Preparation of carboxylic diamond: Diamond powder with a particle size of 3-4 nm was used to prepare a nano-diamond aqueous solution with 100 mL of deionized water and 1 g of nano-diamond powder at 3000 r·min. -1 Centrifuge, discard the lower precipitate, freeze-dry; take nano-diamond fine powder and add mixed acid, 10000r·min -1 Centrifuge and discard the supernatant; add 15mL of 0.1mol·L-1N a OH and 0.1 mol·L-1HCL; heating temperature in a water bath to 90 ℃, holding time for 2h, remove the supernatant to obtain carboxyl nanodiamond; wash with deionized water 3-6 times until neutral, 3000r·min -1 Centrifugation was performed to obtain fine carboxyl nanodiamond powder.

[0011] Carboxylic diamond and rare earth crystal solution ratio: carboxylic diamond and deionized water were mixed to form 42.25mL of nanodiamond rare earth suspension with a concentration of 0.69wt%; ultrasonic treatment was performed; and the suspension was mixed with 300mL of 1.43wt% cerium acetate solution and stirred for 20min and ultrasonic treatment was performed for 5min; the indicator was used to detect Ln 3+ ion content; the nanodiamond rare earth suspension was placed on a rotary evaporator to dry; placed in a neutral dehumidifier to dry to constant weight, the yield was about 0.28-0.29g; the obtained 0.05g nanodiamond rare earth solid was placed in 50mL deionized water and ultrasonicated.

[0012] Step 5: Diamond rare earth vacancy color center growth

[0013] Secondary growth of diamond: the diamond substrate in step 3 is placed in the step 5 for ultrasonic treatment for 40 minutes, and the planted diamond substrate is placed in a microwave plasma chemical vapor deposition device for growth to grow a diamond film with a thickness of 200nm-400nm.

[0014] Formation of diamond rare earth vacancy color centers: The diamond substrate grown in step 5 is placed in a vacuum / atmosphere tubular annealing furnace for annealing to form vacancies in diamond rare earth color centers.

[0015] As a further limitation of step 1, the substrate in step 1 is a single-polished quartz glass sheet of Φ50 mm×0.5 mm.

[0016] As a further limitation to step 1, the cleaning solution in step 1 is anhydrous ethanol.

[0017] As a further limitation of step 1, the crystal planting time of the diamond crystal planting solution in step 1 is 40 minutes, and the particle size of the nano-diamond particles in the diamond crystal planting solution is 3-4 nm.

[0018] As a further limitation of the steps, in step 3, the surface graphite of the diamond substrate is removed by heating and oxidation in air, with a heating and cooling rate of 300°C / h, a heating temperature of 650°C, and a holding time of 1h.

[0019] As a further limitation of step 3, in step 3, the microwave power is adjusted to 600 W, and 200 sccm of hydrogen is introduced through the microwave plasma chemical vapor deposition equipment, and methane is introduced after ignition.

[0020] As a further limitation of step 4, in step 4, 300 mg of nano-diamond fine powder is added to 30 mL of mixed acid, and the ratio of the mixed acid is concentrated sulfuric acid: concentrated nitric acid = 3:1.

[0021] As a further limitation of step 4, in step 4, the Ce content in the supernatant is controlled by UV spectrophotometry using Azo I and Azo III indicators. 3+ Ion content.

[0022] As a further limitation of step 5, in step 5, the heating temperature is 900° C. and the annealing time is 30 min.

[0023] The beneficial effects of the present invention are:

[0024] The present invention's method for preparing nanodiamond cerium vacancy color centers by grafting overcomes the barrier that prevents rare earth atoms from entering diamond due to their large atomic radius. By introducing cerium into the diamond growth environment through grafting, the present invention offers low-cost, high-efficiency advantages, while simultaneously preventing contamination of the deposition chamber and increasing the concentration of rare earth color centers. The method can be further expanded to include other rare earth metal elements with larger atomic radii and is well-suited for quantum devices. Compared to existing diamond nitrogen (NV) vacancy color centers, the diamond rare earth vacancy color centers of the present invention effectively address the challenges associated with diamond nitrogen (NV) vacancy color centers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of the present invention.

[0026] Figure 2 This is the AFM image of diamond.

[0027] Figure 3 This is the Raman map of diamond.

[0028] Figure 4 This is the Diamond-COOCe SEM image.

[0029] Figure 5 This is the Diamond-COOCeEDS diagram.

[0030] Figure 6 The UV absorption spectra of the supernatant of cerium acetate and Diamond-COOCe.

[0031] Figure 7 This is the CeV color center energy level diagram of diamond.

[0032] Figure 8 This is the energy band structure diagram of the CeV color center in diamond.

[0033] Figure 9 This is the CeV color density map of diamond. DETAILED DESCRIPTION

[0034] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with the specific embodiments. Preferred embodiments of the present invention are provided in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. 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.

[0036] Example 1

[0037] Combine Figure 1 The flow chart of the present invention is shown in FIG. 1 , and this embodiment provides a method for preparing rare earth vacancy color centers in nanodiamonds by grafting, comprising the following steps:

[0038] Step 1, preliminary preparation: Use an ultrasonic cleaning machine (using existing products on the market, which will not be described here) to clean the substrate (for example, the substrate can be a Φ50mm×0.5mm single-polished quartz glass sheet); specifically, the ultrasonic cleaning temperature is 25°C, the ultrasonic frequency is 800Hz, the ultrasonic cleaning time is 2 minutes, and the cleaning liquid can be directly selected from anhydrous ethanol. Plant diamond crystals on the above substrate; specifically, the diamond crystal planting liquid planting time is 40 minutes, and the nano-diamond particles in the diamond crystal planting liquid (nano-diamond colloid solution) have a particle size of 3-4nm; after taking out the above substrate, blow dry it with hot air.

[0039] Step 2, diamond substrate preparation: using microwave plasma chemical vapor deposition equipment, with specific parameters of CH4 is 2.5sccm, H2 is 250sccm, temperature is 900℃, and pressure is 4500Pa, a diamond film with a thickness of about 1000nm-12000nm is grown on the substrate in step 1 as a diamond substrate.

[0040] Step 3, diamond surface pretreatment (diamond substrate purification): using a vacuum / atmosphere tubular annealing furnace, the diamond substrate (nanodiamond) prepared in step 2 is graphitized by heating and oxidizing in air, with a heating and cooling rate of 300°C / h, a heating temperature of 650°C, and a holding time of 1h; after adjusting the microwave power to 600W, a microwave plasma chemical vapor deposition device is used to pass into 200sccm of hydrogen, and methane is passed into the device after ignition (normal operation step of the microwave plasma chemical vapor deposition device), with a final power of 1200W and a pressure of 4.5kPa; nucleation for 10min, and adjusting the hydrogen and methane flow rate to grow for 3 hours; vacuum annealing at 850°C for 30min and hydrogen etching for 1h, at a temperature of 800°C.

[0041] Step 4: Diamond rare earth crystal solution preparation

[0042] (1) Preparation of carboxylated diamond: Diamond powder with a particle size of 3-4 nm was used to prepare a nanodiamond aqueous solution with 100 mL of deionized water and 1 g of nanodiamond powder. The solution was then stirred at 3000 r / min. -1 Centrifuge and discard the lower precipitate. Freeze-dry for 24 hours. Take 300 mg of nanodiamond fine powder and add 30 mL of mixed acid (concentrated sulfuric acid: concentrated nitric acid = 3:1). Ultrasonic temperature is 50 ° C, ultrasonic frequency is 800 Hz, ultrasonic time is 24 hours, and then 10000 r min -1 Centrifuge and discard the supernatant; add 15mL of 0.1mol·L-1N aOH and 0.1mol·L-1HCL, NaOH and HCl in the process of preparing carboxyl compounds mainly play the role of neutralization reaction and adjusting pH to neutral; heating temperature in a water bath pot is 90℃, holding time is 2h, and the supernatant is removed to obtain carboxyl nanodiamond. Wash with deionized water 3-6 times until neutral, then 3000r·min -1 The mixture was centrifuged and freeze-dried for 24 h to obtain carboxyl nanodiamond fine powder.

[0043] (2) Proportioning of carboxylic diamond and rare earth crystallization solution: First, carboxylic nanodiamonds were mixed with deionized water to form 42.25 mL of nanodiamond rare earth suspension (Diamond-COOH) with a concentration of 0.69 wt%. Then, ultrasonic treatment was performed with an ultrasonic temperature of 25 ° C, an ultrasonic frequency of 800 Hz, and a cleaning ultrasonic time of 2 h. The mixture was stirred with 300 mL of 1.43 wt% cerium acetate solution (Ce(OOCCH3)3·4H2O) for 20 min and ultrasonic treatment was performed for 5 min. There were no other metal impurity atoms in the cerium acetate solution (Ce(OOCCH3)3·4H2O), which avoided the formation of other color centers. The cerium acetate solution (Ce(OOCCH3)3·4H2O) was soluble in water and could be fully grafted onto the carboxylic diamond. Finally, the solid and liquid were dispersed in deionized water by centrifugation, and the Ce in the supernatant was controlled by ultraviolet spectrophotometry using azo I and azo III indicators. 3+ Ion content, used to detect Ce 3+ ion content; the nano-diamond rare earth suspension was placed in a rotary evaporator and dried at a temperature of 50°C and a pressure of 104 Pa; and dried in a neutral dehumidifier to constant weight, with a yield of approximately 0.28-0.29 g; the obtained 0.05 g nano-diamond rare earth solid was placed in 50 mL of deionized water and ultrasonicated at a temperature of 25°C, an ultrasonic frequency of 800 Hz, and a cleaning ultrasonic time of 1 h.

[0044] Step 5: Diamond rare earth vacancy color center growth

[0045] (1) Diamond Secondary Growth: The diamond substrate prepared in step 3 was placed in the ultrasonic treatment in step 5 for 40 minutes. The seeded diamond substrate was then placed in a microwave plasma chemical vapor deposition apparatus for growth, using the following parameters: CH₄ 1 sccm, H₂ 100 sccm, temperature 900°C, and pressure 4500 Pa, to grow a diamond film with a thickness of 200 nm to 400 nm. The present invention achieves a thinner diamond film through secondary deposition, making it easier to excite the rare earth vacancy color centers near the surface of the diamond, which is more beneficial for device applications.

[0046] The plasma ionizes the H atoms in H2, causing them to decompose and combine with the H atoms in CH4 to form H2, leaving only C atoms, which is the principle of diamond deposition.

[0047] (2) Formation of diamond rare earth vacancy color centers: The diamond substrate grown in step 5 (1) is placed in a vacuum / atmosphere tubular annealing furnace for annealing at a heating temperature of 900°C for 30 minutes to promote the formation of vacancies in diamond rare earth color centers.

[0048] In summary, the present invention's method for preparing nanodiamond cerium vacancy color centers via grafting overcomes the barrier that prevents rare earth atoms from entering diamond due to their large atomic radius. This method introduces cerium into the diamond growth environment through grafting, offering low cost, high efficiency, no pollution to the deposition chamber, and increased rare earth color center concentration. The method can be further expanded to include other rare earth metal elements with larger atomic radii, and is well-suited for applications in quantum devices.

[0049] Compared with the diamond nitrogen (NV) vacancy color center in the prior art, the diamond rare earth vacancy color center in the present invention can effectively solve the problems of diamond nitrogen (NV) vacancy color center. Since rare earth lanthanides have a unique electronic structure, electrons are filled in the 4f orbital and are shielded by the 5s2 and 5p6 outer shells, so that their ff transitions are almost unaffected by the external crystal field, showing "atomic-like properties" and having unique optical and magnetic properties. And the high localization of 4f electrons gives it an optical transition with high quantum efficiency, and the spectrum is sharp, with high color purity and long fluorescence lifetime. Among them, the rare earth Kramers ion has a non-integer spin, showing high magnetic anisotropy and large angular momentum, and will produce large spin splitting and long spin coherence time under an external magnetic field. The electron Zeeman splitting and hyperfine energy level transition are rich, and under radio frequency or microwave control, the electron spin state can be initialized. Based on this, the excellent electronic structure, optical and magnetic properties of rare earth elements have a good application prospect.

[0050] like Figure 2 As shown in , the diamond surface morphology and roughness qa = 0.12nm are measured, as Figure 3 As shown in the figure, the characteristic peaks of diamond are measured. In the figure, 1333 cm-1 is the characteristic peak of diamond, and 1552 cm-1 is the G peak of graphite phase; Figure 2 、 Figure 3 It can be proved that good diamond can be prepared by the method of the present invention; wherein, Figure 2 This is a diamond AFM (atomic force microscope) image. Figure 3 This is the Raman image of diamond.

[0051] like Figure 4 As shown in , the main test sample Diamond-COOCe is the morphology of the crystal on the diamond surface after formation, proving that Diamond-COOCe can be crystallized onto the diamond substrate; Figure 5As shown in the figure, the content of Ce in Diamond-COOCe was mainly detected, proving that there was a trace amount of Ce in Diamond-COOCe. Figure 4 This is a Diamond-COOCeSEM (scanning electron microscope) image. Figure 5 This is the Diamond-COOCeEDS (X-ray energy spectrum) diagram.

[0052] Figure 6 The UV absorption spectra of the supernatant of cerium acetate and Diamond-COOCe prove the formation of Diamond-COOCe. The addition of carboxylated diamond can reduce the Ce content.

[0053] Figure 7-9 It is proved that the C atoms of diamond can form bonds with Ce atoms well and produce energy level transitions. The zero phonon line of the transition is 2.528eV. Figure 7 is the diamond CeV color center energy level diagram, Figure 8 This is the energy band structure diagram of the CeV color center of diamond. Figure 9 This is the CeV color density map of diamond.

Claims

1. A method for preparing rare earth vacancy color centers in nanodiamonds by grafting, characterized in that: The steps include: S1, preliminary preparation: cleaning the substrate with an ultrasonic cleaning machine; planting diamond crystals on the substrate with diamond planting liquid; taking out the substrate and drying it with hot air; S2, diamond substrate preparation: using microwave plasma chemical vapor deposition equipment, growing a diamond film with a thickness of 1000nm-12000nm on the substrate in step 1 as a diamond substrate; S3, diamond surface pretreatment: using a vacuum / atmosphere tubular annealing furnace, remove the surface graphite of the diamond substrate prepared in step 2; after adjusting the microwave power, use a microwave plasma chemical vapor deposition device to introduce hydrogen, and then introduce methane after ignition; nucleation for 10 minutes, and adjust the hydrogen and methane flow rates to grow for 3 hours; vacuum annealing at 850°C for 30 minutes and hydrogen etching for 1 hour at a temperature of 800°C; S4, diamond rare earth crystal solution preparation, carboxylated diamond preparation: using diamond powder with a particle size of 3-4 nm, nano-diamond aqueous solution was prepared with 100 mL deionized water: 1 g nano-diamond powder, 3000 r·min -1 Centrifuge, discard the lower precipitate, freeze-dry; take nano-diamond fine powder and add mixed acid, 10000r·min -1 Centrifuge and discard the supernatant; add 15mL of 0.1mol·L-1N a OH and 0.1 mol·L-1HCL; heating temperature in a water bath to 90 ℃, holding time for 2h, remove the supernatant to obtain carboxyl nanodiamond; wash with deionized water 3-6 times until neutral, 3000r·min -1 Centrifugation was performed to obtain carboxyl nanodiamond fine powder; Carboxylic diamond and rare earth crystal solution ratio: carboxylic diamond and deionized water were mixed to form 42.25mL of nanodiamond rare earth suspension with a concentration of 0.69wt%; ultrasonic treatment was performed; and the suspension was mixed with 300mL of 1.43wt% cerium acetate solution and stirred for 20min and ultrasonic treatment was performed for 5min; the indicator was used to detect Ln 3+ ion content; the nanodiamond rare earth suspension was placed on a rotary evaporator to dry; placed in a neutral dehumidifier to dry to constant weight, the yield was 0.28-0.29g; the resulting 0.05g nanodiamond rare earth solid was placed in 50mL deionized water and sonicated; S5, diamond rare earth vacancy color center growth, diamond secondary growth: the diamond substrate in step 3 is placed in step 5 for ultrasonication for 40 minutes, and the planted diamond substrate is placed in a microwave plasma chemical vapor deposition device for growth to grow a diamond film with a thickness of 200nm-400nm; Formation of diamond rare earth vacancy color centers: The diamond substrate grown in step 5 is placed in a vacuum / atmosphere tubular annealing furnace for annealing to form vacancies in diamond rare earth color centers.

2. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: The substrate in step 1 is a single-polished quartz glass sheet of Φ50 mm×0.5 mm.

3. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: The cleaning solution in step 1 is anhydrous ethanol.

4. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: The crystal planting time of the diamond crystal planting solution in step 1 is 40 minutes, and the particle size of the nano-diamond particles in the diamond crystal planting solution is 3-4 nm.

5. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: In step 3, the surface graphite of the diamond substrate is removed by heating and oxidation in air, with a heating and cooling rate of 300°C / h, a heating temperature of 650°C, and a holding time of 1h.

6. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: In step 3, the microwave power is adjusted to 600 W, and 200 sccm of hydrogen is introduced through the microwave plasma chemical vapor deposition equipment, and methane is introduced after ignition.

7. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: In step 4, 300 mg of nano-diamond fine powder was added to 30 mL of mixed acid, and the ratio of the mixed acid was concentrated sulfuric acid: concentrated nitric acid = 3:

1.

8. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: In step 4, the Ce content in the supernatant was controlled by UV spectrophotometry using Azo I and Azo III indicators. 3+ Ion content.

9. The method for preparing nanodiamond rare earth vacancy color centers by grafting according to claim 1, characterized in that: In step 5, the heating temperature is 900° C. and the annealing time is 30 min.

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