Method for the production of site-specific shallow color centers in diamond using metalation with transition metals

Abstract

This invention utilizes transition metals to metallize diamond and prepare shallow, localized color centers. It addresses the challenges of existing methods for preparing diamond color centers, which require complex chemical vapor deposition (CVD) processes or large particle injection equipment, and struggle to control the positioning of the color centers. The method for preparing shallow, localized color centers includes: 1. Ultrasonic cleaning of the diamond containing impurities; 2. Etching of the cleaned diamond using argon plasma; 3. Patterning using photolithography or masking; 4. Sequential deposition of a transition metal layer and an anti-oxidation layer on the patterned diamond substrate using vacuum deposition; 5. High-temperature annealing of the diamond substrate with the double-layer structure; and 6. Acid pickling. This invention uses transition metals to metallize diamond, avoiding etching and surface damage. The near-destructive process ensures a smooth and flat surface after metallization, providing a stable environment for the luminescence of the color centers.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and quantum technology, and specifically relates to a method for preparing color centers in diamond. Background Technology

[0002] Diamond is a high-performance wide-bandgap semiconductor material. When a substitutional impurity atom is incorporated into a diamond lattice, and a vacancy exists around it, an impurity vacancy luminescent center is formed. For example, a nitrogen impurity would be called an NV color center, and a silicon impurity would be called a SiV color center, and so on. Unlike ordinary point defect luminescent centers, the electron spin state of these color centers can be manipulated using lasers and microwaves, and read out by optical systems through different fluorescence patterns, making them an excellent single-photon source. Importantly, as a solid-state quantum system, compared to quantum systems such as cold atoms, ion traps, and Josephus junctions that require extremely low temperatures or ultra-high vacuum environments, the diamond lattice's robust sp[s] state... 3 The stable environment provided by bonding allows color centers in diamond to perform quantum operations at room temperature and pressure. Among them, NV color centers exhibit relatively long coherence times in the millisecond range and are considered to be a very promising quantum computer system.

[0003] There are three traditional methods for preparing diamond color centers: incorporating impurity atoms during chemical vapor deposition, implanting impurity ions into high-purity diamond, and introducing carbon atom vacancies through electron irradiation. The first method can control the distribution of color centers vertically but not horizontally; the second method can control the distribution horizontally but not vertically. Both methods require large-scale equipment, resulting in high costs and technical requirements, thus limiting the development of diamond color centers. In terms of applications, color centers, as physically sensitive units, should be as close to the surface as possible, but traditional color center preparation methods often place them within the diamond matrix, significantly restricting practical applications. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of existing diamond internal color center preparation requiring complex chemical vapor deposition processes or large particle injection equipment, and difficulty in controlling the positioning of color centers. Instead, it provides a method for preparing shallow, fixed-point color centers by metallizing diamond with transition metals.

[0005] The present invention describes a method for preparing shallow color centers by metallizing diamond with transition metals, implemented according to the following steps:

[0006] 1. Cleaning: The diamond containing impurities is ultrasonically cleaned and dried to obtain the cleaned diamond substrate.

[0007] II. Etching: Argon plasma is used to bombard and etch the surface of the cleaned diamond to obtain the etched diamond substrate.

[0008] 3. Patterning process: The etched diamond substrate is patterned as needed using photolithography or masking processes to obtain a patterned diamond substrate.

[0009] IV. Transition metal deposition: A transition metal layer and an anti-oxidation layer are sequentially deposited on a patterned diamond substrate using a vacuum coating process to obtain a diamond substrate with a double-layer structure.

[0010] V. High-temperature annealing: The diamond substrate with a double-layer structure deposited is subjected to high-temperature annealing in an inert gas atmosphere at a temperature of 500-1200℃ to obtain a metallized diamond substrate.

[0011] VI. Acid pickling: The metallized diamond substrate is immersed in a mixed strong acid solution to remove the surface metal and expose the underlying metallized diamond. After washing and drying, shallow color centers are obtained in the diamond.

[0012] The transition metal layer is a rare earth metal or a refractory metal from Group IIIB (third subgroup) to VIIB (seventh subgroup); the anti-oxidation layer is a noble metal.

[0013] The transition metal layer described in this invention is a rare earth metal or refractory metal from Group IIIB (third subgroup) to VIIB (seventh subgroup), including rare earth metals such as Sc, Y, and La, and refractory metals such as Ti, Ta, Mo, and W. Its characteristic is that it can chemically react with carbon at high temperatures to form transition metal carbides, which then dissolve and diffuse into each other. In contrast, ferrous metals such as Fe, Co, and Ni, and platinum group metals such as Pt, Ir, and Ru readily react with diamond at high temperatures to form solid solutions and generate a large amount of sp. 2 Carbon phase disrupts the diamond lattice, creating an unstable environment for the luminescence of color centers, and produces etching sp in a hydrogen plasma environment. 2 Carbon phase leaves etching pits on diamond, causing macroscopic damage.

[0014] The anti-oxidation layer described in this invention is an inert material that is not easily oxidized, such as a precious metal, and is used to prevent the oxidation of transition metals from causing incomplete reactions and affecting the subsequent generation of vacancies and color centers.

[0015] Diamonds typically prepared using high temperature and pressure (HTHP) contain a large number of uniformly distributed substitutional nitrogen impurities, while diamonds prepared using chemical vapor deposition (CVD) can introduce dopants such as nitrogen, silicon, and germanium as needed. However, both methods lack vacancies, making it difficult to form effective color center structures. This invention utilizes the high reactivity of the unsaturated d-shell electrons of transition metals. At high temperatures, these electrons react with diamond, and the intense electron transfer between the transition metal and carbon atoms causes lattice relaxation in the diamond, resulting in the desorption of some carbon atoms and the formation of numerous vacancies. Driven by the concentration gradient, these vacancies diffuse into the diamond interior at high temperatures and are captured by the uniformly distributed substitutional impurity atoms, forming a more stable impurity-vacancy color center structure. The transition metals and their carbides, due to their large atomic radii, are mainly distributed on the diamond surface and can be removed by acid washing after the reaction.

[0016] Since the longitudinal distribution of color centers formed after diamond metallization depends on the inward diffusion depth of carbon vacancies, i.e., on the annealing time, a typical annealing time of one hour results in a vacancy diffusion depth only on the micrometer scale, while the lateral distribution on the surface depends on the patterned distribution of the transition metal, this invention uses a transition metallization process to prepare shallow color centers at specific points on the diamond surface. Compared to traditional methods such as ion implantation and electron bombardment, this method is lower in cost and simpler. Furthermore, compared to methods like iron etching that require hydrogen plasma etching of diamond to generate color centers, this invention uses transition metals to metallize diamond without etching or damaging the diamond surface. This near-destructive process ensures that the metallized diamond surface remains smooth and flat, providing a stable environment for the luminescence of the color centers. The method of preparing shallow color centers at specific points through metallization provides an innovative and low-cost preparation method for point defect luminescence centers, which are widely present in fundamental physics research and materials science. It also provides technical support for key engineering fields such as diamond-based NV, SiV, or GeV color center quantum sensors and single-photon sources, and has significant demonstrative and guiding effects. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the diamond substrate with a double-layer structure deposited in the embodiment;

[0018] Figure 2 This is a comparison of the diamond photofluorescence spectra of the metallized and non-metallized regions of refractory metal Ti used in Example 1;

[0019] Figure 3 NV in the metallized region of Example 1 - The relationship between the intensity ratio of the color center relative to the first-order Raman peak of diamond and the measurement depth;

[0020] Figure 4This is a comparison of the diamond photofluorescence spectra of the metallized and non-metallized regions using rare earth metal Sc in Example 2.

[0021] Figure 5 This is a comparison of the Raman spectra of diamonds after metallization with Pt in the comparative examples. Detailed Implementation

[0022] Specific Implementation Method 1: This implementation method for preparing shallow color centers by metallizing diamond with transition metals is carried out according to the following steps:

[0023] 1. Cleaning: The diamond containing impurities is ultrasonically cleaned and dried to obtain the cleaned diamond substrate.

[0024] II. Etching: Argon plasma is used to bombard and etch the surface of the cleaned diamond to obtain the etched diamond substrate.

[0025] 3. Patterning process: The etched diamond substrate is patterned as needed using photolithography or masking processes to obtain a patterned diamond substrate.

[0026] IV. Transition metal deposition: A transition metal layer and an anti-oxidation layer are sequentially deposited on a patterned diamond substrate using a vacuum coating process to obtain a diamond substrate with a double-layer structure.

[0027] V. High-temperature annealing: The diamond substrate with a double-layer structure deposited is subjected to high-temperature annealing in an inert gas atmosphere at a temperature of 500-1200℃ to obtain a metallized diamond substrate.

[0028] VI. Acid pickling: The metallized diamond substrate is immersed in a mixed strong acid solution to remove the surface metal and expose the underlying metallized diamond. After washing and drying, shallow color centers are obtained in the diamond.

[0029] The transition metal layer is a rare earth metal or a refractory metal from Group IIIB (third subgroup) to VIIB (seventh subgroup); the anti-oxidation layer is a noble metal.

[0030] In this embodiment, step two, the etching process, is used to clean the diamond surface to remove all surface-adhered chemical groups and other contaminants, promote sufficient contact between the transition metal and the diamond, and prevent the transition metal from oxidizing. The precious metal mentioned in step four is gold.

[0031] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the impurities contained in the diamond in step one are nitrogen impurities, silicon impurities, or germanium impurities.

[0032] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the diamond containing impurities in step 1 is high-temperature high-pressure diamond or chemical vapor deposition diamond.

[0033] In this embodiment, the high-temperature, high-pressure diamond itself contains nitrogen impurities.

[0034] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that in step one, deionized water, acetone, and anhydrous ethanol are used sequentially to ultrasonically clean the diamond containing impurities.

[0035] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the etching time in step 2 is 10 min to 1 h.

[0036] Specific Implementation Method Six: This implementation method differs from one of Specific Implementation Methods One to Five in that the vacuum coating process described in step three is a magnetron sputtering process or an electron beam evaporation process.

[0037] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the patterning process in step three forms a point matrix or a line matrix.

[0038] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that, in step four, when the transition metal layer is a rare earth metal, the rare earth metal is Sc, Y, or La; when the transition metal layer is a refractory metal, the refractory metal is Ti, Ta, Mo, or W.

[0039] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the thickness of the transition metal layer in step four is 5-90 nm, and the thickness of the anti-oxidation layer is 30-100 nm.

[0040] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the high-temperature annealing time in step 5 is 30 min to 3 h.

[0041] Example 1: This example describes a method for preparing shallow color centers by metallizing diamond with transition metals, implemented according to the following steps:

[0042] 1. Cleaning: The CVD diamond containing impurities was ultrasonically cleaned sequentially with deionized water, acetone and anhydrous ethanol, and then dried to obtain the cleaned diamond substrate.

[0043] II. Etching: Argon plasma was used to bombard the cleaned diamond surface for 15 minutes to remove the surface terminals and obtain the etched diamond substrate.

[0044] 3. Patterning process: The etched diamond substrate is patterned using photolithography to obtain a patterned diamond substrate.

[0045] IV. Transition metal deposition: A transition metal layer and an anti-oxidation layer are sequentially deposited on a patterned diamond substrate using magnetron sputtering to obtain a diamond substrate with a double-layer structure.

[0046] V. High-temperature annealing: The diamond substrate with a double-layer structure deposited was annealed at 900℃ for 30 minutes in an infrared vacuum annealing furnace under an argon atmosphere to obtain a metallized diamond substrate.

[0047] VI. Acid pickling: The metallized diamond substrate is immersed in aqua regia for 2 hours to remove the surface metal. After washing and drying, shallow color centers are obtained in the diamond.

[0048] The transition metal layer is a 20nm Ti layer, and the anti-oxidation layer is a 70nm Au layer.

[0049] In this embodiment, color centers were prepared at specific points on diamond. The photofluorescence spectra of the metallized region and the unmetallized blank region are shown in the attached figure. Figure 2 As shown, after transition metal metallization, the NV in the diamond lattice 0 NV - The fluorescence intensity of the color center and related phonon sidebands was significantly improved. (NV) - Taking the color center as an example, the change in its fluorescence intensity relative to the intensity of the first-order Raman peak of diamond with depth is shown in the attached figure. Figure 3 As shown, the enhanced NV color centers decay exponentially with depth according to Fick's first law, which proves that the increased color centers are mainly generated by vacancy diffusion and distributed on the diamond surface.

[0050] Example 2: This example differs from Example 1 in that the transition metal layer is a 20nm Sc layer and the anti-oxidation layer is a 70nm Au layer. In step five, an infrared vacuum annealing furnace is used to perform high-temperature annealing on the diamond substrate with the deposited double-layer structure in an argon atmosphere at a temperature of 600°C for 30 minutes.

[0051] The enhancement effect of this embodiment on the color center is similar to that of refractory metal Ti.

[0052] Comparative Example: This example demonstrates a method for metallizing diamond using platinum group metals, implemented according to the following steps:

[0053] 1. Cleaning: The CVD diamond containing impurities was ultrasonically cleaned sequentially with deionized water, acetone and anhydrous ethanol, and then dried to obtain the cleaned diamond substrate.

[0054] II. Etching: Argon plasma was used to bombard the cleaned diamond surface for 15 minutes to remove the surface terminals and obtain the etched diamond substrate.

[0055] 3. Patterning process: The etched diamond substrate is patterned using photolithography to obtain a patterned diamond substrate.

[0056] IV. Transition Metal Deposition: Transition metal Pt is deposited on a patterned diamond substrate using a vacuum deposition process to obtain a diamond substrate with the deposited transition metal.

[0057] V. High-temperature annealing: The diamond substrate with the transition metal deposited was annealed at 900℃ for 2 hours in an infrared vacuum annealing furnace under an argon atmosphere to obtain a metallized diamond substrate.

[0058] 6. Acid pickling: The metallized diamond substrate is immersed in aqua regia for 2 hours to remove the surface metal Pt. After washing and drying, Raman spectroscopy is performed.

[0059] Raman spectra of the metallized region and the unmetallized blank region are attached. Figure 4 As shown, it can be seen that, except for NV 0 NV - Apart from a very slight increase in the peak intensity at the color center, a peak at 1580 cm⁻¹ appeared in the metallized diamond. -1 The graphite peak indicates that Pt metallization of diamond can generate a large amount of graphite.

[0060] Since the precious metal Pt is not easily oxidized, there is no need to deposit an anti-oxidation layer. Although Pt can also generate vacancies and color centers in diamond metallization at high temperatures, compared with refractory metals Ti and rare earth metals Sc, which are transition metals described in this invention, Pt has higher inertness and requires a higher temperature for full metallization. Therefore, the increase in color center peak intensity at the current processing temperature of 900℃ is negligible. Furthermore, Pt is difficult to bond with diamond to form stable transition metal carbides. It can only diffuse into the diamond lattice in a metallic state to form a solid solution. After the free carbon atoms precipitate in the metallic Pt, a large amount of graphite is generated, which is the same as the graphite catalytic effect of ferrous metals (Fe, Co, Ni) on diamond at high temperatures. The formation of graphite will severely damage the diamond lattice and create an unstable lattice environment for the subsequent luminescence of color centers, which is not conducive to the quantum control of color centers.

Claims

1. A method for preparing shallow color centers by metallizing diamond with transition metals, characterized in that... The method for preparing shallow color centers by metallizing diamond with transition metals is implemented according to the following steps:

1. Cleaning: The diamond containing impurities is ultrasonically cleaned and dried to obtain the cleaned diamond substrate. II. Etching: Argon plasma is used to bombard and etch the surface of the cleaned diamond to obtain the etched diamond substrate.

3. Patterning process: The etched diamond substrate is patterned as needed using photolithography or masking processes to obtain a patterned diamond substrate. IV. Transition metal deposition: A transition metal layer and an anti-oxidation layer are sequentially deposited on a patterned diamond substrate using a vacuum coating process to obtain a diamond substrate with a double-layer structure. V. High-temperature annealing: The diamond substrate with a double-layer structure deposited is subjected to high-temperature annealing in an inert gas atmosphere at a temperature of 500-1200℃ to obtain a metallized diamond substrate. VI. Acid pickling: The metallized diamond substrate is immersed in a mixed strong acid solution to remove the surface metal and expose the underlying metallized diamond. After washing and drying, shallow color centers are obtained in the diamond. The transition metal layer is a rare earth metal or a refractory metal from group IIIB to group VIIB; the anti-oxidation layer is a noble metal.

2. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... The impurities in the diamond in step one are nitrogen impurities, silicon impurities, or germanium impurities.

3. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... The diamond containing impurities in step one is either high-temperature high-pressure diamond or chemical vapor deposition diamond.

4. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... In step one, deionized water, acetone, and anhydrous ethanol are used in sequence to ultrasonically clean the diamond containing impurities.

5. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... The etching time in step two is 10 minutes to 1 hour.

6. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... The vacuum coating process described in step three is either magnetron sputtering or electron beam evaporation.

7. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... In step three, patterning is performed to form a point matrix or a line matrix.

8. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... In step four, when the transition metal layer is a rare earth metal, the rare earth metal is Sc, Y, or La; when the transition metal layer is a refractory metal, the refractory metal is Ti, Ta, Mo, or W.

9. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... In step four, the thickness of the transition metal layer is 5–90 nm, and the thickness of the anti-oxidation layer is 30–100 nm.

10. The method for preparing shallow color centers by metallizing diamond with transition metals according to claim 1, characterized in that... In step five, the high-temperature annealing time is 30 minutes to 3 hours.

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