CN110975760A

CN110975760A - Method for preparing nitrogen vacancy center in diamond in nondestructive and controllable manner

Info

Publication number: CN110975760A
Application number: CN201911105677.0A
Authority: CN
Inventors: 刘晓兵; 陈欣; 宋京岩; 李凤娇
Original assignee: Qufu Normal University
Current assignee: Qufu Normal University
Priority date: 2019-11-13
Filing date: 2019-11-13
Publication date: 2020-04-10
Anticipated expiration: 2039-11-13
Also published as: CN110975760B

Abstract

The invention discloses a method for preparing a nitrogen vacancy center in a diamond in a nondestructive and controllable manner, which reduces ferromagnetic defects in a synthetic diamond by selecting a non-metallic catalyst and a nitrogen source, synthesizes the content of nitrogen impurities in the diamond, accurately controls the formation type of the nitrogen vacancy in the diamond by controlling the matching of growth crystal orientation and temperature, adopts a high-temperature and high-pressure annealing technology to quickly and effectively adjust the type and the number of charges carried in the nitrogen vacancy in the diamond, and obtains a controllable NV⁰，NV^‑，N₂V and the like nitrogen vacancy centers, thereby effectively solving the problem that the further industrial application of the nitrogen vacancy controllable preparation technology is seriously limited due to the deficiency at present.

Description

Method for preparing nitrogen vacancy center in diamond in nondestructive and controllable manner

Technical Field

The invention belongs to the technical field of quantum science and technology and precision test materials, and particularly relates to a method for preparing a nitrogen vacancy center in diamond in a nondestructive and controllable manner.

Background

The quantum technology is an emerging interdisciplinary subject combining quantum theory and information theory, information is stored in quantum bits by utilizing quantum superposition and quantum entanglement effects, ultra-fast parallel computing capability is achieved, and the method has incomparable advantages of a traditional computer in the application fields of super computing, information processing, artificial intelligence, information safety and the like. In recent years, as quantum technology goes from theory to experiment, the quantum technology is successfully developed from laboratory research to practicality, so that the quantum technology has wide application prospects in the fields of national economy, science and technology and military, and is rapidly a research hotspot of current international quantum physics and information science. At present, quantum computer research based on photon and superconducting systems is still limited by the influence of extreme application environments. Therefore, a new material capable of manufacturing the qubit at room temperature is found, and the method has important scientific significance and practical application value for promoting the development of the quantum science and technology field.

The ultra-wideband gap of diamond allows its internal containment of many defects (-500), at least ten of which have been shown to exist as single quantum emitters, with single photon excitation wavelengths ranging from blue to the near infrared. Among the many candidate systems, the nitrogen-vacancy (N-V) center is the most specific single photon source at room temperature, and the presence of such defects makes diamond materials extremely valuable for qubit fabrication and is of great interest to numerous researchers.

The N-V centers are formed by a single substitutional nitrogen atom in the diamond in combination with vacancies in adjacent lattice sites. The optical particles excited by the N-V center can keep the superposition state of the qubits and can transfer information between quantum computing devices. The qubit made by this luminescent defect has the following characteristics at room temperature: (1) the electron spin decoherence time is long; (2) the fidelity of the quantum state is high; (3) can form a hyperfine interaction environment with surrounding nuclear spins. These characteristics can be used in the fields of quantum key distribution, quantum registration, quantum error correction, and the like, and are therefore considered to be excellent carriers with the highest potential for realizing quantum computation. In addition, the fluorescence excited by the N-V center is extremely sensitive to changes of environmental magnetic fields, electric fields, stress, temperature and the like, and can be used for detecting the change condition of electron spin. The traditional magnetic resonance imaging technology needs millions of spin information to capture a measurable signal, and the N-V center can easily detect a single target spin, so that the accuracy reaches the nanometer level. The unique characteristics enable the N-V center in the diamond to be used as a nano-size sensor and used in the fields of magnetic resonance imaging, high-precision weak magnetic detection and the like. Meanwhile, due to the non-toxicity and light resistance of the diamond material, the N-V center can also be used as an ideal biochemical probe material to be embedded into cells for scientific research and medical diagnosis.

Although the research work of the N-V center in the fields of quantum computation, high-spatial-resolution weak magnetic detection, high-precision detection and the like is greatly progressed at present. But its wide practical application from laboratory research is still severely limited by the following three aspects: firstly, the current laboratory research work mainly depends on natural diamonds, but the natural diamonds containing N-V centers in nature are rare, expensive and difficult to reproduce, and are not beneficial to moving to large-scale application; second, the N-V defects in natural diamonds are typically present in IIa diamond at concentrations well below 1 ppm; thirdly, the nanodiamond containing N-V centers for experimental research is mainly synthesized by an explosion method, and a large number of defects and other paramagnetic impurities exist inside, which causes the bytes generated by the N-V centers to be very unstable, i.e., the bytes can store quantum information, but are easily damaged by the influence of external environmental noise. Sometimes the storage time lasts only a millionth of a second at most, which means that in practical device applications quantum information cannot be stored. Meanwhile, the micro size of the device is limited, and the device can not meet the application requirements in the field of the current functional devices, which gradually becomes a bottleneck limiting the large-scale application of the device.

At present, defects are created on diamond crystal materials in a targeted mode by mainly using technologies such as focused ion beam milling, electron beam etching, angle etching, isotropic etching and the like internationally, vacancies are made in a mechanical mode, and nitrogen atoms are injected, and the technology gradually becomes an important means for preparing N-V centers. However, these techniques also present three major problems in producing N-V defects in diamond materials: firstly, when a target defect is formed on the surface of the diamond, crystal damage is usually caused, and the mechanical, optical and thermal stability of the material is seriously influenced; secondly, the control accuracy of such technical requirements is generally high (micrometer or nanometer scale), the production efficiency is low, and the method is not suitable for large-scale application of materials; third, the N-V defects produced are usually localized on the diamond surface and are difficult to achieve largeThe preparation of the block material with the size seriously limits the further industrial application of the N-V center. While the current research application is limited to NV only⁰And NV^-Defects, to other N-V centers (especially to monochromator N with higher thermal stability)₂V center) has been rarely addressed, which has severely limited research and application in this area, mainly due to the scarcity of natural diamonds containing such defects and the difficulty of preparing such defects in nanodiamond materials.

Therefore, the controllable preparation of the N-V center in the diamond growth process is realized, the diamond single crystal material with large size (several millimeters or even centimeter level), high quality and controllable N-V center concentration is obtained, and the method has extremely important research value and practical significance for preparing optical devices and promoting the N-V center to move to application.

Disclosure of Invention

Aiming at the problems in the application of the existing diamond N-V center, the invention provides an effective technical means for realizing the controllable preparation of the N-V center in the growth process of the diamond, improving the iron-nickel catalyst by using non-metallic elements such as sulfur, phosphorus, calcium and the like, regulating the nitrogen content in the diamond by adding a nitrogen removal agent and a non-metallic composite nitrogen source, controlling the growth orientation to regulate the internal nitrogen cavity type, and regulating the internal nitrogen cavity content and the carried charges by doping and annealing trace elements to obtain the diamond single crystal material with large size, high quality and controllable N-V center concentration.

In order to achieve the above purpose, the invention adopts the following technical scheme

Specifically, the method for preparing the nitrogen vacancy center in the diamond in a nondestructive and controllable manner comprises the following steps:

a method for preparing a nitrogen vacancy center in a diamond in a nondestructive and controllable manner comprises the following steps:

s1: preparation of diamond single crystals containing different nitrogen content cavity centers

(1) Synthesizing diamond: improving the Fe-Ni catalyst system, and synthesizing diamond single crystal by using graphite as a carbon source and keeping the temperature at 5.0-6.5GPa and 1350-;

(2) regulating and controlling the nitrogen content in the diamond: obtaining diamond single crystal containing 0-3000ppm nitrogen impurity by adjusting nitrogen content in diamond;

(3) controllable nitrogen hole type: respectively selecting {100} or {111} seed crystals, controlling a growth temperature interval, and synthesizing diamond single crystals containing different nitrogen cavity types;

s2: regulating the type of nitrogen hole center in diamond and the type of charge

(4) Adjusting defect type and charge transfer: adding trace elements into the high-pressure cavity to adjust the number of charges carried by nitrogen holes in the diamond monocrystal prepared in the step (3);

(5) annealing treatment: and (4) annealing the diamond single crystal synthesized in the step (4) at 5.0-6.0GPa and 1600-2000 ℃ to obtain the diamond single crystal containing the target nitrogen hole defects.

Preferably, the iron-nickel catalyst system improved in the step (1) adopts sulfur, phosphorus or calcium; the size of the synthesized diamond single crystal is 3-5 mm.

Preferably, the nitrogen source in step (2) is P₃N₅Or C₃N₃(NH₂)₃Concentration 0.1-1 wt.%; the nitrogen removing agent is aluminum foil or titanium sheet with the concentration of 0.1-1 wt.%.

Preferably, the diamond is controlled to grow according to 100 and 111 by controlling the orientation of the selected seed crystal and controlling the growth temperature in the step (3).

Preferably, the growth temperature control interval in the step (3) is 1400-1450 ℃ and is a {100} crystal growth interval; 1500 ℃ and 1550 ℃ are the {111} crystal growth interval.

Preferably, the trace element in step (4) is B, O or H.

Preferably, the defect type and charge transfer are adjusted by using a high-temperature high-pressure annealing experiment in the step (5).

Advantageous effects

(1) The invention synthesizes diamond monocrystal by using the temperature gradient growth technology, selects a proper diamond growth substrate, strictly controls the lifting process of the growth temperature, and ensures that the inside of a high-pressure synthesis cavity is internally provided withThe temperature field is stable for a long time, and the diamond crystal can be ensured to grow directionally according to the required crystal orientation strictly, thereby obtaining controllable NV⁰，NV^-，N₂V-isocentric high-quality large-size diamond single crystals. The technology of the invention can solve the problem of raw materials in the application research around the diamond N-V center at present, and has important scientific significance and application value for promoting and widening the application field of the N-V center.

(2) Compared with the prior art, the method has the advantages that the ferromagnetic defect in the synthetic diamond is reduced by selecting the non-metallic catalyst and the nitrogen source, the content of nitrogen impurities in the synthetic diamond is reduced, the formation type of nitrogen vacancies in the diamond is accurately controlled by controlling the matching of the growth crystal orientation and the temperature, the high-temperature high-pressure annealing technology is adopted to quickly and effectively adjust the type of the nitrogen vacancies in the diamond and realize charge transfer, and the controllable NV is obtained⁰，NV^-，N₂V, and the like nitrogen hole centers.

Drawings

FIG. 1 is a technical roadmap for the project;

FIG. 2 is a schematic diagram of a high pressure chamber assembly: (a) assembling by a film growth method; (b) assembling by a temperature gradient method; (c) assembling in a high-temperature annealing experiment;

FIG. 3 is a high temperature high pressure synthesis of nitrogen doped diamond single crystals: (a) the nitrogen impurity in the synthetic diamond in different catalyst systems changes with the temperature and the content. (b) The adjustment of nitrogen impurities in the synthetic diamond by an annealing experiment is that single substituted nitrogen atoms are gradually polymerized to form N under the conditions of 7.2GPa and 1800 DEG C₂Center and N₄V center. (c) In an iron carbonyl catalyst system, N₄V，NV₀，NV^-The centers are gradually increased along with the increase of the synthesis temperature in the growth process. (d) And (e) the preferred orientation of the N-V center in the {100} plane and the {111} plane in the synthetic diamond in the Fe-Ni-C system;

FIG. 4 is a graph of the distribution of NV centers within diamond crystals synthesized in different crystallographic orientations at elevated temperature: a is synthesized in a low-temperature growth interval [100 ]]Diamond single crystal, graph b is intermediate temperatureDegree interval synthetic [111]Diamond single crystal, panel c high temperature growth interval synthesis [111 ]]Diamond single crystal, white arrow in figure b indicates the diamond growth direction, figure d indicates the PL spectrum of selected region in a-c diagram, H3 indicates N₂V center (503 nm);

FIG. 5 shows the high pressure chamber containing N₂V-center diamond sample: b and c are optical and three-dimensional imaging photos of the indentation formed on the natural diamond anvil cell by the sample after the experiment is finished; d is a series of synthetic compounds containing different N₂Diamond raman spectroscopy at V center; e is pressure and N₂And V center Raman peak value correspondence.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the present invention is not limited to the following examples.

Means of experiment

① high-temperature high-pressure experiment, film growth method and temperature gradient method

The invention utilizes a film growth method (figure 2 a) to research the formation mechanism and preferred orientation of N-V center in the diamond growth process, and utilizes a temperature gradient method (figure 2 b) to synthesize large-size diamond single crystal. The non-metallic elements of sulfur, phosphorus, calcium, etc. are selected to improve the main catalyst (Fe-Ni) system, C₃N₃(NH₂)₃And P₃N₅And the like as nitrogen sources, and boron, oxygen, hydrogen, and the like as doping elements. The pressure during the experiment was calibrated based on the diamond-graphite phase equilibrium line of the catalyst system, and the temperature of the chamber was calibrated using a dual platinum rhodium type B thermocouple wire (Pt-Rh 30%/Pt-Rh 6%). The synthesis conditions are 5.0-6.5GPa, 1350-1850 ℃, the synthesis time is 10 minutes-60 hours, and the Ib diamond is used as a growth substrate to prepare the high-quality nitrogen-doped diamond monocrystal meeting the requirements of optical devices.

② calculation of electronic structure and formation energy based on first principle calculation of density functional theory

The method is based on the density functional theory, adopts the first principle to simulate the PAW pseudo potential method in software VASP, and more accurately calculates the electronic structure of the material, the adsorption energy of the crystal surface and the defect forming energy.

③ N-V center adjustment and Charge transfer Regulation HPHT annealing experiments

The diamond samples prepared in stage I were selected. The annealing experiment was performed using a cubic apparatus large cavity press under the conditions of 6.0-7.5 GPa and 1000-2500 deg.C (the cavity is shown in FIG. 2 c), and the annealing time was about two hours. The N-V center content and other impurity defect structures in the synthetic diamond are characterized by utilizing a variable temperature Raman, a femtosecond laser, a fluorescent near-infrared steady-state transient spectrometer, a photoelectric energy spectrum detection system, an extinction ratio tester and the like. And characterizing the working efficiency of the N-V center.

The following specifically describes the technical scheme of the present invention with reference to specific examples:

example 1

(1) Synthesizing diamond: selecting a sulfur-improved iron-nickel catalyst system, using high-purity flaky graphite as a carbon source, and keeping the temperature for 10 hours at 5.0GPa and 1850 ℃, wherein the size of the synthesized high-quality diamond monocrystal is 3-5 mm;

(2) regulating and controlling the nitrogen content in the diamond: adding 0.1wt.% of titanium sheet into the catalyst according to the mass ratio to obtain diamond single crystal with nitrogen concentration ranging from 0ppm to 1 ppm;

(3) controllable nitrogen hole type: selecting {100} crystal seeds respectively, controlling the growth temperature of diamond at 1400-1450 deg.C to obtain N₂{100} crystal with V center as the main;

(4) Adjusting defect type and charge transfer: the trace element is added into the high-pressure cavity to be the hydrogen element, so that the N in the diamond is adjusted₂The number of charges in the V center;

(5) annealing treatment: annealing the synthesized diamond single crystal at the temperature of 6.0GPa and 1800-2000 ℃ for 2 hours, naturally and slowly cooling to obtain the N with negative electricity₂ V center defect 100 diamond single crystal.

Example 2

(1) Synthesizing diamond: selecting nonmetallic elements such as phosphorus and the like to improve an iron-nickel catalyst system, using high-purity flaky graphite as a carbon source, and keeping the temperature for 10 hours at 5.0GPa and 1850 ℃, wherein the size of the synthesized high-quality diamond monocrystal is 3-5 mm;

(2) regulating and controlling the nitrogen content in the diamond: adding 0.1wt.% of C to a carbon source according to a mass ratio₃N₃(NH₂)₃Obtaining diamond single crystal with the nitrogen concentration range of 200-1000 ppm;

Example 3

A method for preparing a nitrogen vacancy center in a diamond in a nondestructive and controllable manner is characterized by comprising the following steps:

(1) Synthesizing diamond: selecting a sulfur non-metallic element to improve an iron-nickel catalyst system, and keeping the temperature for 40 hours at 6.0GPa and 1550 ℃ by using high-purity flaky graphite as a carbon source to synthesize a high-quality diamond monocrystal with the size of 3-5 mm;

(2) regulating and controlling the nitrogen content in the diamond: adding 1wt.% of titanium sheet into the catalyst according to the mass ratio to obtain diamond single crystals with the nitrogen concentration ranging from 0ppm to 1 ppm;

(3) controllable nitrogen hole type: selecting {100} crystal seed, controlling the growth temperature of diamond at 1500-⁰And NV^-A predominantly {100} crystal;

(4) Adjusting defect type and charge transfer: regulating the NV inside the diamond by adding trace elements as hydrogen elements into the high-pressure cavity⁰And NV^-The number of charges charged in the center;

(5) annealing treatment: annealing the synthesized diamond single crystal at 6.0GPa and 1600-1800 ℃ for 2 hours, naturally and slowly cooling, and regulating NV (nitrogen-induced degradation) in the prepared {100} diamond single crystal⁰And NV^-Ratio of centers to mass.

Example 4

(1) Synthesizing diamond: selecting a calcium element to improve an iron-nickel catalyst system, and keeping the temperature for 30 hours at 6.0GPa and 1550 ℃ by using high-purity flaky graphite as a carbon source to synthesize a high-quality diamond monocrystal with the size of 3-5 mm;

(2) regulating and controlling the nitrogen content in the diamond: adding 1wt.% of P into a carbon source according to the mass ratio₃N₅Obtaining diamond single crystal with the nitrogen concentration range of 200-1000 ppm;

(3) controllable nitrogen hole type: selecting {111} crystal seed to control diamond growthThe temperature is 1500-⁰And NV^-A predominantly centered {111} crystal;

(5) annealing treatment: annealing the synthesized diamond single crystal at 6.0GPa and 1600-1800 ℃ for 2 hours, naturally and slowly cooling, and regulating NV (nitrogen-induced degradation) in the prepared {111} diamond single crystal⁰And NV^-Ratio of centers to mass.

Performance detection

From examples 1 to 3 of the present invention, it can be found that N in diamond₂The increase of the concentration of the V center can effectively improve the mechanical property of the diamond. Example 1 preparation of Medium [100 ]]The diamond samples, which had relatively low mechanical properties, were found to contain N₂The V-centered diamond samples can be pressed into the natural diamond anvils in a high pressure experiment, demonstrating that such diamond materials possess higher hardness and compressibility than natural diamond anvils (fig. 5 a-c). In-situ test using high-pressure XRD and Raman showed that except for NV which has been extensively studied⁰And NV^-Center, N₂V-centers also show strong dependence and sensitivity to pressure and temperature, (fig. 5 e) making them a new candidate for high resolution precision sensing applications.

It was found from examples 3 to 4 of the present invention that NV is exhibited⁰And NV^-The centers of the diamond are regularly arranged in the {100} diamond, the concentration of the diamond can be controllably adjusted along with the nitrogen concentration in the synthetic environment, the controllable preparation in the range of 0-1000ppm can be realized, and the result can meet different requirements of scientific research and application fields.

Claims

1. A method for preparing a nitrogen vacancy center in a diamond in a nondestructive and controllable manner is characterized by comprising the following steps:

(2) regulating and controlling the nitrogen content in the diamond: obtaining diamond single crystal containing 0-3000ppm nitrogen impurity by adjusting the nitrogen content in the diamond;

2. The method of claim 1, wherein the step (1) of improving the Fe-Ni catalyst system comprises using sulfur, phosphorus or calcium; the size of the synthesized diamond single crystal is 3-5 mm.

3. The method according to claim 1, wherein the nitrogen source for adjusting the nitrogen content in the diamond in the step (2) is P₃N₅Or C₃N₃(NH₂)₃Concentration 0.1-1 wt.%; the nitrogen removing agent used for adjusting the nitrogen content in the diamond is aluminum foil or titanium sheet, and the concentration is 0.1-1 wt.%.

4. The method of claim 1, wherein the step (3) of controlling the diamond growth according to {100} and {111} by controlling the orientation of the selected seed crystal and controlling the growth temperature.

5. The method as claimed in claim 1, wherein the step (3) is performed by controlling the growth temperature range to 1400 ℃ and 1450 ℃ to {100} crystal growth range; 1500 ℃ and 1550 ℃ are the {111} crystal growth interval.

6. The method according to claim 1, wherein the trace element in step (4) is B, O or H.

7. The method of claim 1, wherein the step (5) utilizes a high temperature and high pressure annealing experiment to adjust defect type and charge transfer.