Diamond spin sensor and method of manufacturing the same

Abstract

A diamond spin sensor comprising diamond, the diamond containing NV with electron spin ‑ The color center is defined as follows: when the transverse relaxation time of the electron spin measured by the Hahn echo method is set to T2μsec, and the fluorescence intensity of the fluorescence emitted from the diamond by irradiating it with microwaves and lasers is expressed as the current value InA output from the Si-PIN diode that receives the fluorescence, the product of T2 and I is greater than 3000, the wavelength of the microwave is greater than or equal to 2.07GHz and less than 3.67GHz, the wavelength of the laser is greater than or equal to 520nm and less than 540nm, the power of the laser is 3mW, and the photosensitive sensitivity of the Si-PIN diode is greater than or equal to 0.36A / W and less than 0.44A / W at a wavelength of 600nm, and greater than or equal to 0.40A / W and less than 0.5A / W at a wavelength of 660nm.

Description

Technical Field

[0001] This disclosure relates to a diamond spin sensor and a method for manufacturing the same. This application claims priority to Japanese Application No. 2024-027998, filed February 28, 2024. All descriptions in that application are incorporated herein by reference. Background Technology

[0002] Diamond spin sensors using NV centers (hereinafter referred to as NV centers) are known. When the NV center, composed of nitrogen (N) at a substitutional position of carbon (C) in diamond and a void (V: vacancy) adjacent to that nitrogen, becomes negatively charged, its ground state becomes a triplet state (i.e., spin S = S = 1). The negatively charged NV center is denoted as NV. - The color center, but for convenience, will be abbreviated as NV color center below. When a charged NV color center is excited by a laser with a wavelength of approximately 530 nm (i.e., green light), it emits fluorescence with a wavelength of approximately 635 nm (i.e., red light). The intensity of the fluorescence varies depending on the spin state of the NV color center, which in turn varies according to the magnetic resonance between the magnetic field applied to the NV color center and the microwave or radio waves, thus enabling its use as a magnetic sensor.

[0003] In the detection, the following are used: a diamond substrate containing an NV color center as a diamond spin sensor, an optical system for transmitting excitation light from a light source and illuminating the NV color center, and a transmission line and microwave circuit for transmitting microwaves from a power source and illuminating the NV color center. Furthermore, an optical system is also used to focus fluorescence from the NV color center and transmit it to a photodetector.

[0004] Methods for manufacturing high-purity diamonds by reducing strain and impurities in diamond crystals are known. For example, Patent Document 1 discloses that nitrogen, which is the largest impurity, can be produced by adding getter materials such as titanium (Ti) to the raw materials, thereby reducing nitrogen content in the diamond. Patent Document 2 discloses that by cutting a portion of diamond with fewer crystal defects to a size of 1 mm or less from a diamond of size 3 mm or larger as a seed crystal, and using this as a seed crystal substrate for growth, the strain during crystallization can be reduced.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 7-148426; Patent Document 2: Japanese Patent Application Publication No. 9-165295; Patent Document 3: International Publication No. 2022 / 210696; Patent document 4: International Publication No. 2022 / 210723; Patent document 5: International Publication No. 2022 / 209512; Patent document 6: International Publication No. 2016 / 013588. Summary of the Invention

[0006] A diamond spin sensor, as described in one aspect of this disclosure, comprises diamond containing NVs with electron spin. - The color center is defined as follows: when the transverse relaxation time of the electron spin determined by the Hahn echo method is set to T2μsec, and the fluorescence intensity of the fluorescence emitted from the diamond by irradiating it with microwaves and lasers is expressed as the current value InA output from the Si-PIN diode that receives the fluorescence, the product of T2 and I is greater than 3000, the wavelength of the microwave is greater than or equal to 2.07GHz and less than 3.67GHz, the wavelength of the laser is greater than or equal to 520nm and less than 540nm, the power of the laser is 3mW, and the photosensitive sensitivity of the Si-PIN diode is greater than or equal to 0.36A / W and less than 0.44A / W at a wavelength of 600nm, and greater than or equal to 0.40A / W and less than 0.5A / W at a wavelength of 660nm. Attached Figure Description

[0007] Figure 1 This is a perspective view showing the diamond spin sensor according to an embodiment of the present disclosure.

[0008] Figure 2 This is a schematic diagram showing the crystal faces and orientations of diamond.

[0009] Figure 3 It means that it was used. Figure 1 The diagram shows the configuration of the apparatus used in the measurement of the diamond spin sensor.

[0010] Figure 4 It means that it was used. Figure 1 The diagram shows the timing of the excitation light and electromagnetic wave irradiation, as well as the timing of the radiation light measurement, during the measurement of the diamond spin sensor.

[0011] Figure 5 It is a graph that schematically shows the relationship between the observed signal intensity (i.e., fluorescence intensity) and the frequency of the electromagnetic wave (i.e., microwave).

[0012] Figure 6 This is a schematic diagram representing the NV color centers of diamond.

[0013] Figure 7 It is a stereoscopic diagram schematically representing the optical path of fluorescence radiated from the NV color center.

[0014] Figure 8 It indicates that it is used for measurement Figure 1The timing diagram shown is a time-series diagram of the transverse relaxation time T2 of the diamond spin sensor, including the timing of excitation light and electromagnetic wave irradiation, and the timing of radiation light measurement.

[0015] Figure 9 This is a graph representing the lateral relaxation time T2.

[0016] Figure 10 This is a schematic diagram showing the apparatus for synthesizing diamond.

[0017] Figure 11 This is a schematic diagram illustrating the manufacturing method of seed crystals used in the synthesis of diamond.

[0018] Figure 12 It means from Figure 11 The diagram shows a method for synthesizing diamond by cutting out a portion of the diamond as a seed crystal.

[0019] Figure 13 It indicates the use of ratio Figure 12 The diagram shows a method for synthesizing diamond with large seed crystals.

[0020] Figure 14 It means Figure 13 The top view of the synthetic diamond shown.

[0021] Figure 15 This is a top view showing a traditional synthetic diamond.

[0022] Figure 16 It is a diagram that shows the manufacturing conditions of the experimental samples in tabular form.

[0023] Figure 17 It is a graph that presents the experimental results in tabular form.

[0024] Figure 18 It is a graph representing the experimental results. Detailed Implementation

[0025] [The problem this disclosure aims to solve] Regarding sensors using diamond NV centers (also known as color centers), a longer spin-based transverse relaxation time T2 is preferred as it improves sensor sensitivity. That is, a longer transverse relaxation time T2 extends the time for the resonant electromagnetic wave to act, thus increasing sensor sensitivity. Furthermore, stronger luminescence intensity makes signal detection easier, resulting in higher sensor sensitivity. If the concentration of NV centers is increased to enhance luminescence intensity, the large amount of nitrogen with spin becomes an obstacle, shortening the transverse relaxation time T2 (leading to faster signal decay). Conversely, if the concentration of NV centers in diamond is reduced to prolong the transverse relaxation time T2, fewer NV centers serve as fluorescence sources, weakening luminescence intensity. Thus, there is a trade-off between transverse relaxation time T2 and fluorescence intensity, making it difficult to increase fluorescence intensity without reducing the transverse relaxation time T2. Conversely, it is also difficult to increase the transverse relaxation time T2 without reducing fluorescence intensity.

[0026] As disclosed in Patent Documents 1 and 2, high-purity diamond crystals with virtually no impurities or defects can be easily produced. However, in order to use diamond containing NV centers (necessary nitrogen and defects, pores) as a sensor, substances that contribute to fluorescence scattering must be removed while trace amounts of strain and impurities remain. In other words, a method is desired that reduces other impurities and strain while minimizing trace amounts of nitrogen and defects (pores) that are impurities.

[0027] Therefore, the purpose of this disclosure is to provide a diamond spin sensor and a method for manufacturing the same, which can increase fluorescence intensity without reducing transverse relaxation time, or increase transverse relaxation time without reducing fluorescence intensity.

[0028] [The Effects of This Disclosure] According to this disclosure, a diamond spin sensor and a method thereof can be provided that can increase fluorescence intensity without reducing transverse relaxation time, or can increase transverse relaxation time without reducing fluorescence intensity.

[0029] [Description of embodiments of this disclosure] The embodiments described herein are presented in an explanatory manner. At least some of the embodiments described below may be combined arbitrarily.

[0030] (1) The diamond spin sensor according to the first aspect of this disclosure comprises diamond, which contains NV having electron spin. -When the transverse relaxation time of electron spin, measured by the Hahn echo method, is defined as T2 μsec, and the fluorescence intensity of fluorescence emitted from diamond by irradiation with microwaves and lasers is expressed as the current value InA output from the Si-PIN diode receiving the fluorescence, the product of T2 and I is greater than 3000. The wavelength of the microwaves is 2.07 GHz or higher and 3.67 GHz or lower; the wavelength of the laser is 520 nm or higher and 540 nm or lower; the laser power is 3 mW; and the photosensitive sensitivity of the Si-PIN diode is 0.36 A / W or higher and 0.44 A / W or lower at a wavelength of 600 nm, and 0.40 A / W or higher and 0.5 A / W or lower at a wavelength of 660 nm. Therefore, it is possible to increase the fluorescence intensity without reducing the transverse relaxation time, or to increase the transverse relaxation time without reducing the fluorescence intensity.

[0031] (2) In (1) above, it is possible for the product of T2 and I to be greater than 10000. Thus, it is possible to further increase the fluorescence intensity without reducing the transverse relaxation time, or to further increase the transverse relaxation time without reducing the fluorescence intensity.

[0032] (3) The diamond spin sensor involved in the second aspect of this disclosure comprises diamond, which contains NV having electron spin. - Sex Heart, NV - The concentration of color centers is above 0.02 ppm and below 10 ppm, and the average phase difference across the diamond surface is below 6 nm / mm. Therefore, it is possible to increase fluorescence intensity without reducing transverse relaxation time, or to increase transverse relaxation time without reducing fluorescence intensity.

[0033] (4) In any of (1) to (3) above, the average phase difference of the diamond surface as a whole can be less than 4 nm / mm. As a result, the product of the transverse relaxation time T2 and the fluorescence intensity I can be increased, and a sensor with higher sensitivity can be realized.

[0034] (5) In any of (1) to (4) above, it is permissible for NV to... - The concentration of the color centers is above 0.02 ppm and below 1.2 ppm. This increases the product of the transverse relaxation time T2 and the fluorescence intensity I, enabling a sensor with higher sensitivity.

[0035] (6) The diamond spin sensor according to the third aspect of this disclosure comprises diamond, which contains NV having electron spin. - Sex Heart, NV -The concentration of the color center is above 0.02 ppm and below 10 ppm, and the half-width of the rocking curve based on the double-crystal method is below 8 seconds. Therefore, it is possible to increase the fluorescence intensity without reducing the transverse relaxation time, or to increase the transverse relaxation time without reducing the fluorescence intensity.

[0036] (7) In any of (1) to (4) and (6) above, NV - The concentration of the color center can be above 0.02 ppm and below 2 ppm, and the half-width of the rocking curve of X-ray diffraction based on the double-crystal method can be below 6 seconds. Therefore, it is possible to further increase the fluorescence intensity without reducing the transverse relaxation time, or to further increase the transverse relaxation time without reducing the fluorescence intensity.

[0037] (8) In any of (1) to (7) above, it is permissible for the concentration of isolated pores to be relative to NV. - The concentration of color centers is below 10%. This increases the product of the transverse relaxation time T2 and the fluorescence intensity I, enabling the realization of a sensor with higher sensitivity.

[0038] (9) In (8) above, it is possible that the concentration of isolated pores is relative to NV. - The concentration of color centers is less than 1%. This increases the product of the transverse relaxation time T2 and the fluorescence intensity I, enabling the realization of a sensor with higher sensitivity.

[0039] (10) A method for manufacturing a diamond spin sensor according to the fourth aspect of this disclosure, the method comprising: a synthesis step in which a rectangular surface having a (001) crystal plane or a (111) crystal plane is used as a seed crystal for synthesizing a diamond single crystal by means of a temperature difference method under a pressure of 5 GPa or higher; an irradiation step in which a cut diamond cut from the diamond single crystal synthesized by the synthesis step is irradiated with an electron beam of energy of 500 keV or higher and 1 MeV or lower; and an annealing step in which the cut diamond having undergone the irradiation step is annealed at a temperature of 1200°C or higher and 1400°C or lower for 0.1 hours or higher and 0.5 hours or lower, thereby generating a diamond spin sensor, wherein the nitrogen concentration of the seed crystal is 0.1 ppm or higher and 30 ppm or lower, and the linear dislocation defects of the seed crystal are 10 or less, and if the surface is a (001) crystal plane, one side of the rectangle is... <100> direction or <010> If the surface is a (111) crystal plane, then one side of the rectangle is parallel to the <1-10> direction, the <10-1> direction, or the <01-1> direction. Thus, it is possible to manufacture diamond spin sensors that increase fluorescence intensity without reducing transverse relaxation time, or increase transverse relaxation time without reducing fluorescence intensity.

[0040] (11) In (10) above, a nitrogen getter may be used in the synthesis step, the nitrogen getter being any one of titanium, zirconium, hafnium, aluminum, gallium, copper, silver, and gold. This increases the product of the transverse relaxation time T2 and the fluorescence intensity I, enabling a sensor with higher sensitivity.

[0041] (12) In (10) or (11) above, it is possible to cut the diamond with only one sector boundary or without a sector boundary. This increases the product of the lateral relaxation time T2 and the fluorescence intensity I, enabling a sensor with higher sensitivity.

[0042] [Details of the embodiments of this disclosure] In the following embodiments, the same reference numerals are used to refer to the same parts. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0043] Reference Figure 1The diamond spin sensor 100 disclosed herein is a cuboid having a first face 102 and a first side 104. The diamond spin sensor 100 may also be a cuboid with equal side lengths, i.e., a cube. The diamond spin sensor 100 is formed from a single diamond crystal containing NV color centers composed of nitrogen (N) and pores (V). The first face 102 is a crystal plane, for example, a (001) plane or a (111) plane. When the first face 102 is a (001) plane, the first side 104 is formed along the <100> direction or the <010> direction. When the first face 102 is a (111) plane, the first side 104 is formed along the <1-10> direction, the <10-1> direction, or the <01-1> direction. Furthermore, the marking "-1" corresponds to a marking indicating crystal orientation with a horizontal bar (line) above the 1.

[0044] Figure 1 The diagram shows a cuboid diamond spin sensor 100, but it is not limited to this. The shape of the first face 102 is not limited to a rectangle and is arbitrary. The first face 102 can also be a triangle, for example. In this case, the first side 104 corresponds to one side of the triangle. The solid shape of the diamond spin sensor 100 is not limited to a cuboid and can also be a pyramid (such as a prism or cone). For example, the diamond spin sensor 100 can also be a tetrahedron with the first face 102 being a triangle (e.g., an equilateral triangle) (e.g., a corner prism with right angles on the sides).

[0045] Reference Figure 2 The (001) plane in the diamond crystal is a plane defined by points A5 to A8 (i.e., a plane passing through these four points). As described above, when the first face 102 is the (001) plane, the diamond spin sensor 100 is implemented, for example, as a cube with points A1 to A8 as vertices. The possible directions of the first side 104 are... <100> direction and <010> The directions are the direction from point A1 toward point A2 and the direction from point A1 toward point A4, respectively. For example, if the first face 102 is a face with vertices from point A5 to point A8, then the first edge 104 corresponds to the line segment connecting point A5 and point A6, or the line segment connecting point A5 and point A8.

[0046] (111) plane is defined by points A5, A2, and A4. As described above, the first plane 102 can also be (111) plane. In this case, the possible direction of the first side 104, namely the <1-10> direction, is from point A1 toward point B1. That is, the first side 104 corresponds to the line segment connecting points A2 and A4. In addition, the possible direction of the first side 104, namely the <10-1> direction, is from point A1 toward point B2. That is, the first side 104 corresponds to the line segment connecting points A5 and A2. In addition, the possible direction of the first side 104, namely the <01-1> direction, is from point A1 toward point B3. That is, the first side 104 corresponds to the line segment connecting points A5 and A4.

[0047] Measurements using a diamond spin sensor 100, for example, by... Figure 3 The device shown performs the operation. The control unit 230 includes a CPU (Central Processing Unit) and a storage unit (neither shown). The processing performed by the control unit 230 is achieved by the CPU reading and executing programs pre-stored in the storage unit.

[0048] The excitation light generating unit 210 is controlled by the control unit 230 to generate excitation light for exciting the NV color centers of the diamond spin sensor 100. The control unit 230 supplies a voltage to the excitation light generating unit 210 at a predetermined timing to cause it to emit light. The excitation light 204 is green light (i.e., wavelength 490 nm to 560 nm). The excitation light 204 is, for example, a laser, and the excitation light generating unit 210 is, for example, a semiconductor laser (e.g., radiated light with a wavelength of 532 nm).

[0049] Filter 212 is an element used to separate the excitation light 204 incident from the excitation light generation unit 210 and the light (i.e., fluorescence) radiated from the diamond spin sensor 100. For example, filter 212 may be a filter that blocks (i.e. reflects) light with wavelengths below a predetermined wavelength while allowing light with wavelengths longer than the predetermined wavelength to pass through, or a bandpass filter that allows light with wavelengths within a predetermined wavelength range to pass through while blocking (i.e. reflects) light with wavelengths outside the predetermined wavelength range. Generally, the wavelength of the excitation light is shorter than that of the fluorescence, therefore such a structure is preferred. For example, filter 212 may be a dichroic mirror with this function.

[0050] The focusing element 214 focuses the excitation light 204 input from the filter 212. The focusing element 214 is, for example, a spherical lens. The focusing element 214 inputs as much of the excitation light diffused from the excitation light generating section 210 as possible into the end of the optical waveguide 216. The optical waveguide 216 contains a medium for transmitting light and transmits light bidirectionally. That is, the optical waveguide 216 has a first end and a second end, and transmits the excitation light 204 incident on the first end to the second end located near the diamond spin sensor 100. In addition, the optical waveguide 216 transmits the radiation light (i.e., fluorescence) of the diamond spin sensor 100 incident on the second end to the first end and outputs it. The optical waveguide 216 is, for example, an optical fiber.

[0051] The LPF (Long Pass Filter) 218 ​​is a long pass filter that allows light with wavelengths above a predetermined wavelength to pass through while blocking (e.g., reflecting) light with wavelengths smaller than the predetermined wavelength. The fluorescence 206, which is the radiation light of the diamond spin sensor 100, is red light and passes through the LPF 218. However, the excitation light 204 output from the excitation light generator 210 has a shorter wavelength and therefore does not pass through the LPF 218. As a result, the excitation light 204 radiated from the excitation light generator 210 is suppressed from being detected by the photodetector 220 and becomes noise, thus reducing the detection sensitivity of the fluorescence 206, which is the radiation light of the diamond spin sensor 100. The photodetector 220 generates and outputs an electrical signal corresponding to the incident light. The photodetector 220 is, for example, a photodiode. The output signal of the photodetector 220 is acquired by the control unit 230.

[0052] The electromagnetic wave irradiation unit 202 irradiates the diamond spin sensor 100 with electromagnetic waves (e.g., microwaves). The electromagnetic wave irradiation unit 202 is, for example, a coil or microwave resonant circuit containing an electrical conductor. The electromagnetic waves are supplied to the electromagnetic wave irradiation unit 202 from the electromagnetic wave generation unit 232 via, for example, a coaxial cable. The excitation light and electromagnetic wave irradiation of the diamond spin sensor 100 are controlled by the control unit 230, for example, in… Figure 4 The scheduled time is as shown.

[0053] Reference Figure 4 The control unit 230 controls the excitation light generating unit 210 to output excitation light at a predetermined time and for a predetermined period (e.g., time interval t1). The control unit 230 controls the electromagnetic wave generating unit 232 to output electromagnetic waves at a predetermined time and for a predetermined period (e.g., time interval t2). An appropriate pulse sequence can be used for the pulse sequence in time interval t2. Thus, the excitation light and electromagnetic waves are combined temporally and spatially to irradiate the diamond. The control unit 230 acquires the output signal of the input light detection unit 220 at a predetermined time (e.g., time interval t3) and stores it in the storage unit.

[0054] NV centers transition from the ground state to an excited state by emitting green light (e.g., 532 nm laser light) with wavelengths from 490 nm to 560 nm, emitting red light (e.g., 635 nm fluorescence) with wavelengths from 630 nm to 800 nm, and then return to the ground state. An NV center in a state where it has captured an electron (i.e., NV) - Under these conditions, the magnetic quantum number m is formed. s The spin triplet states are -1, 0, and +1. If a magnetic field is present, then m s The energy levels of the ±1 state split according to the magnetic field strength (i.e., Zeeman splitting). Irradiating the NV color center with microwaves at a frequency of 2.87 GHz causes m... s The state transition from 0 to m is... s After reaching the ±1 state (i.e., electron spin resonance), it is excited by irradiation with green light. Consequently, the migration back to the ground state includes the migration of non-radiative light (i.e., fluorescence), thus the observed intensity of radiative light decreases. Therefore, a trough (i.e., signal leakage) is observed in the ODMR (Optically Detected Magnetic Resonance) spectrum.

[0055] As described above, the control unit 230 controls the excitation light generating unit 210 and the electromagnetic wave generating unit 232 to, for example, measure... Figure 5 The spectrum shown. The interval between the two observed valleys, i.e., the frequency difference Δf, depends on the magnetic field strength (equivalent to Zeeman splitting) at the location of the diamond spin sensor 100. The control unit 230 can calculate the magnetic field based on the frequency difference Δf. (Refer to...) Figure 6 The magnetic field detected by the NV color center is the component that passes through the N and V axes (hereinafter referred to as the NV axis) formed in the NV color center of the diamond. That is, the angle between the magnetic field vector B and the NV axis is set as φ, and the change in signal intensity (i.e. fluorescence intensity) corresponding to Bcosφ is detected by the diamond spin sensor 100.

[0056] The above explains how the magnetic field can be calculated from changes in the ODMR spectrum. However, it is known that the frequencies of the two resonant frequencies of the NV color center are temperature-dependent in the range of 120K to 700K. Therefore, temperature measurement can be performed by using a diamond spin sensor 100 to measure the frequency changes of the centers that split into Δf.

[0057] In the diamond spin sensor 100, the transverse relaxation time of the electron spin of the NV color center, measured by the Hahn echo method described later, is set as T2 μsec, and the fluorescence intensity emitted from the diamond is set as InA (nanoamperes). The product α (α = T2 × I) of T2 (transverse relaxation time) and I (fluorescence intensity) is greater than 3000. Therefore, when using the diamond spin sensor 100 as a sensor, it is possible to increase the fluorescence intensity I without decreasing the transverse relaxation time T2, or to increase the transverse relaxation time T2 without decreasing the fluorescence intensity I. Thus, a sensor with higher sensitivity than before can be achieved.

[0058] Furthermore, the fluorescence intensity emitted from the diamond was measured as follows: The diamond spin sensor 100 was irradiated with microwaves (wavelength 2.87 ± 0.8 GHz (i.e., 2.07 GHz or higher and 3.67 GHz or lower)) and an excitation laser (wavelength 530 ± 10 nm (i.e., 520 nm or higher and 540 nm or lower) with a power of 3 mW). The fluorescence intensity emitted was then detected as a current value (nA) using a Si PIN photodiode (model name S 6967 (manufactured by Hamamatsu Photonics Co., Ltd.)). The diamond spin sensor 100 is, for example, a plate-shaped sensor made of diamond, with the upper and lower surfaces approximately parallel (parallelism (the angle between the two planes) within 1 degree) and a surface roughness Ra of 6 nm or less. The aforementioned laser is focused and irradiated from one side (upper or lower surface) of the diamond spin sensor 100 in this state within a diameter range of 400 μm, and the output current InA when the fluorescence radiated from the irradiated part is detected by a Si PIN photodiode is defined as the fluorescence intensity.

[0059] Reference Figure 7Fluorescence is emitted omnidirectionally (solid angle 4π(sr)) from the NV color center within the laser-irradiated area 240 (400 μm in diameter). The proportion of fluorescence emitted from the side where the Si PIN photodiode is disposed (e.g., the upper surface 100a of the diamond spin sensor 100) is constant relative to the total amount of radiated fluorescence. That is, fluorescence radiated from the irradiated area 240 with an incident angle to the upper surface 100a smaller than angle θ (the critical angle of the diamond spin sensor 100 disposed in the atmosphere) (e.g., fluorescence L1) is emitted from the upper surface 100a into the atmosphere. The output area 242 is a region on a sphere centered on the irradiated area 240, and fluorescence from the irradiated area 240 toward the output area 242 is emitted from the upper surface 100a. Other fluorescence (e.g., fluorescence L2 and fluorescence L3) is reflected from the upper surface 100a and is not released into the atmosphere. Considering the refractive index n (n = 2.4) of the diamond spin sensor 100, the angle θ is approximately 24.6°, and the solid angle of the output region 242 relative to the total solid angle is approximately 4.5%. Furthermore, if the transmittance of the diamond spin sensor 100 is set to 83%, the proportion of fluorescence emitted from the upper surface 100a is approximately 3.7% of the total fluorescence, a constant proportion. Therefore, as described above, by detecting the fluorescence emitted from the upper surface 100a using a Si PIN photodiode, even without detecting fluorescence radiated in all directions, the degree of fluorescence radiation of the diamond spin sensor 100 can be evaluated using the aforementioned fluorescence intensity.

[0060] Microwaves can also be applied to the diamond spin sensor 100 via a microwave resonant circuit (for example, see Patent Document 3). Furthermore, the Si PIN photodiode used for fluorescence detection is not limited to the aforementioned diode. The Si PIN photodiode with model name S 6967 has a photosensitive sensitivity of 0.40 (A / W) at a wavelength of 600 nm and a photosensitive sensitivity of 0.45 (A / W) at a wavelength of 660 nm; any photosensitive sensitivity of equivalent value is acceptable. For example, a Si PIN photodiode with a photosensitive sensitivity of 0.36 (A / W) or higher and 0.44 (A / W) or lower at a wavelength of 600 nm, and 0.40 (A / W) or higher and 0.50 (A / W) or lower at a wavelength of 660 nm can be used (e.g., model name S 6775 (manufactured by Hamamatsu Photonics Co., Ltd.)). Furthermore, the photosensitive sensitivity is calculated by dividing the magnitude of the photocurrent (A) by the energy of the incident light (W).

[0061] Lateral relaxation time T2, for example, using Figure 8The pulse sequence shown is used for measurement. The method of observing signals using such a pulse sequence is called the Hahn echo method or spin echo method. Pulses P1 and P3 are pulses that tilt the electron spin of the NV color center by 90° (π / 2). Pulse P2 is a pulse that reverses the electron spin of the NV color center by 180° (π). Pulses P1, P2, and P3 are applied to the diamond spin sensor 100 at equal time intervals τ. The tilted electron spins due to pulse P1 exhibit relaxation (a phenomenon where the phase velocity deviation among multiple electron spins increases) as time passes, attempting to return to their original state. Conversely, when pulse P2 is applied, the electron spins with faster phase velocities move to positions with delayed phase velocities, and the electron spins with slower phase velocities move to positions with advanced phase velocities. Therefore, the states of multiple electron spins change in the direction where the phases of each electron spin are consistent. Then, when pulse P3 is applied to detect the signal, the signal increases.

[0062] Repeatedly based on Figure 8 The measurement of the ESR (Electron Spin Resonance) signal of the pulse sequence shown, when plotting the signal intensity over time, yields, for example... Figure 9 The chart shown. Figure 9 In the graph, solid lines schematically represent measured values. The vertical axis is represented in arbitrary units (au). The horizontal axis is 2τ (twice the time interval τ). Dashed lines represent graphs obtained by fitting an exponential function to the measured values. The horizontal relaxation time T2 is the time τ when the value of the exponential function becomes 1 / e of its initial value. That is, the horizontal relaxation time T2 represents the duration of the measured signal; a longer horizontal relaxation time T2 allows for a longer measurement period.

[0063] Regarding diamond spin sensors, the greater the number of NV centers that produce fluorescence, the greater the observed fluorescence intensity. However, when defects, strain, and impurities other than nitrogen (which constitutes the NV centers) are present in the diamond single crystal, the generated fluorescence is scattered and absorbed by these impurities. Therefore, the more defects, strain, and impurities (other than nitrogen) there are, the lower the measured fluorescence intensity. That is, the measured fluorescence intensity I is considered to be inversely proportional to the amount of defects, strain, and impurities (other than nitrogen) (let X represent the degree of defects, strain, or impurities (other than nitrogen), from I∝1 / X). Furthermore, the fluorescence intensity also depends on the surface roughness Ra of the diamond spin sensor, but the effect of surface roughness Ra can be eliminated by polishing the surface.

[0064] The fewer the number of NV centers, the larger the transverse relaxation time T2. The transverse relaxation time T2, like fluorescence intensity, is affected by defects, strain, and impurities (excluding nitrogen) in the crystal. It is considered that defects, strain, and impurities (excluding nitrogen) in the crystal act as external interferences to the transverse relaxation time T2, and that T2 is inversely proportional to the amount of defects, strain, and impurities (excluding nitrogen) (T2∝1 / X). Therefore, the fewer defects, strain, and impurities (excluding nitrogen) in the diamond crystal, the larger the product α (T2×I) of the transverse relaxation time T2 and the fluorescence intensity I. Increasing the product α can lead to a sensor with higher sensitivity.

[0065] Through the embodiments described later, a diamond spin sensor with a larger product α of transverse relaxation time T2 (μsec) and fluorescence intensity I (nA) can be realized. That is, the product α of transverse relaxation time T2 and fluorescence intensity I can be greater than 6000. This enables a sensor with higher sensitivity. The product α can be greater than 10000, greater than 15000, or greater than 20000. The larger the product α, the higher the sensitivity of the sensor. In other words, in a diamond spin sensor, it is possible to further increase fluorescence intensity I without reducing transverse relaxation time T2, or to further increase transverse relaxation time T2 without reducing fluorescence intensity I.

[0066] As mentioned above, the product α of the transverse relaxation time T2 and the fluorescence intensity I depends on the number, i.e., the concentration (density), of the NV centers. Figure 1 In the diamond spin sensor 100 shown, if the concentration of NV centers (the ratio of the number of NV centers to the number of carbon atoms) is 0.02 ppm or more and 10 ppm or less, a larger product α than before can be achieved. Furthermore, the average phase difference across the entire surface of the diamond spin sensor 100 can be made 6 nm / mm or less. Therefore, in the diamond spin sensor, the fluorescence intensity I can be increased without decreasing the transverse relaxation time T2, or the transverse relaxation time T2 can be increased without decreasing the fluorescence intensity I. Thus, a sensor with higher sensitivity than before can be realized.

[0067] The concentration of NV color centers can be above 0.02 ppm and below 1.2 ppm. This allows for a larger product α, resulting in a sensor with higher sensitivity. The concentration of NV color centers can also be above 0.04 ppm and below 5 ppm. Furthermore, the concentration of NV color centers can be above 0.08 ppm and below 0.5 ppm.

[0068] Furthermore, the concentration of NV centers in diamond can be calculated, for example, based on measurements using electron spin resonance. Additionally, in the case of low concentrations, measurements can be taken by observing and counting individual NV centers using a fluorescence microscope. In the case of high concentrations, for diamonds containing low concentrations of NV centers, a conversion rate between concentration and fluorescence intensity is determined, and using this conversion rate, the concentration can be calculated based on the fluorescence intensity ratio. Furthermore, the concentration of NV centers can also be calculated based on the absorption coefficient at 637 nm in the absorption spectrum measured by UV-Vis absorption spectrophotometry.

[0069] The average phase difference is explained below. Diamond inherently possesses an isotropic crystal structure and an isotropic refractive index (dielectric constant). However, in reality, defects and strain exist within a single diamond crystal, and diamond exhibits birefringence. When circularly polarized light is irradiated onto a birefringent diamond, the two orthogonally polarized directions (linearly polarized light) produce a phase difference, resulting in elliptically polarized light output. The optical axis and phase difference can be determined from the orientation of the major and minor axes of the ellipse in the elliptically polarized light output from the diamond, as well as the ratio of the lengths of the major and minor axes. The measured phase difference is the value of the integral along the direction in which light passes through the diamond (e.g., the thickness direction of the diamond). Therefore, the phase difference is normalized, for example, by the thickness of the diamond, and is expressed as the phase difference converted to a thickness of 1 mm (single phase difference: nm / mm). The phase difference is measured locally, distributed two-dimensionally within the plane of measurement. Therefore, the phase difference is represented by the average value within the measurement plane (hereinafter referred to as the average phase difference). Furthermore, the "average value" does not refer to the phase difference per unit area, but rather to the value obtained by averaging the phase differences obtained from multiple local measurements within the plane, i.e., the average degree distribution of the phase difference within the plane.

[0070] The average phase difference across the entire surface of a diamond spin sensor can be less than 4 nm / mm. This allows for a larger product α, resulting in a sensor with higher sensitivity. Furthermore, the overall average phase difference across the surface of a diamond spin sensor can be less than 3 nm / mm, less than 2 nm / mm, or even less than 1 nm / mm. This again allows for a larger product α, resulting in a sensor with higher sensitivity.

[0071] The crystallinity of the diamond spin sensor 100 can be evaluated using a rocking curve. In the X-ray diffraction based on the dual-crystal method described later, the crystallization will be... Figure 1The diamond spin sensor 100 shown is used as a first crystal by cutting another diamond crystal from the original crystal, and the diamond spin sensor 100 is used as a second crystal. Measurements are performed using CuKα rays in a parallel configuration on the (004) plane. The half-width of the rocking curve of the diamond spin sensor 100 obtained from the measurement is less than 8 seconds. Therefore, a larger product α than before can be achieved. In the diamond spin sensor, the fluorescence intensity I can be increased without reducing the transverse relaxation time T2, or the transverse relaxation time T2 can be increased without reducing the fluorescence intensity I. Therefore, a sensor with higher sensitivity than before can be achieved. Furthermore, half-width refers to the full half-width.

[0072] The crystallinity of diamond can be evaluated by measuring the rocking curve in X-ray diffraction. The smaller the half-width of the rocking curve, the higher the crystallinity of the diamond, and the fewer crystal defects and strains. To improve detection accuracy, the twin-crystal method is used. In the twin-crystal method, two seed crystals are used: a spectroscopic crystal (first crystal) and a sample crystal (second crystal) as the evaluation object. X-rays from an X-ray source are irradiated onto the first crystal, causing the resulting diffracted X-rays to be incident on the second crystal, changing the angle of the second crystal. The diffracted X-rays are then measured using a detector. ω represents the incident angle of the diffracted X-rays onto the second crystal (the angle between the diffracted X-rays and the plane of the second crystal), and 2θ represents the angle between the direction of the detector and the incident direction of the diffracted X-rays onto the second crystal. If the first crystal and the detector are fixed, and a center of rotation is set on the surface of the second crystal, causing the second crystal to rotate, the diffracted X-rays can be measured by fixing the angle 2θ and only changing the incident angle ω. Thus, the diffraction intensity distribution on a sphere centered at the origin in reciprocal lattice space can be measured. By setting the horizontal axis to the incident angle ω and plotting the measured values ​​on the vertical axis, a rocking curve is obtained. The width of the rocking curve is proportional to the degree of fluctuation in the surface orientation. By using crystals cut from the same diamond single crystal as the first and second crystals, the half-value width of the rocking curve sensitively reflects the quality of the crystal being measured.

[0073] In the diamond spin sensor 100, the half-width at half-maximum (WHM) of the X-ray diffraction rocking curve based on the dual-crystal method can be less than 7 seconds. This allows for a larger product α, resulting in a sensor with higher sensitivity. Furthermore, the WHM of the X-ray diffraction rocking curve can be less than 6 seconds or less, or less than 5 seconds. This allows for a larger product α, resulting in a sensor with higher sensitivity.

[0074] exist Figure 1 In the diamond spin sensor 100 shown, the concentration of isolated pores relative to NV -The concentration of color centers can be below 10%. Isolated pores refer to pores in which nitrogen is absent from their surroundings. This allows for a larger product α than before, resulting in sensors with higher sensitivity. The density (concentration) of pores is that of neutral isolated pores (V0). 0 The density of ) and negatively charged isolated pores (V - The total density of the pores. The density of each isolated pore can be determined by the integral absorption of light at wavelengths of 741 nm and 394 nm induced at liquid nitrogen temperature (wavelength integral of absorption coefficient: unit meV×cm). -1 The integral absorption A is calculated using density β (unit: cm³). -3 The proportionality coefficient k (k=A / β) is 1.2×10 -16 and 4.8×10 -16 Furthermore, when the density of pores cannot be calculated from the absorption coefficient in the visible light region, it can be calculated using the positron annihilation method. The relative value of the density obtained by the positron annihilation method is calibrated (proportional calculation) based on the value of the region where the density is obtained using the absorption coefficient, thus allowing even regions with low concentrations to be converted into density.

[0075] In the diamond spin sensor 100, the concentration of isolated pores relative to NV - The concentration of color centers can be below 3%. Furthermore, in the diamond spin sensor 100, the concentration of isolated pores relative to NV... - The concentration of color centers can be below 1% or below 0.3%. This is achieved by reducing the concentration of isolated pores relative to NV. - The concentration ratio of color centers can achieve a larger product α than before, enabling sensors with higher sensitivity than ever before.

[0076] (Manufacturing method of diamond spin sensor) right Figure 1 The manufacturing method of the diamond spin sensor 100 shown will be described. Granular diamond is used as a seed crystal, and synthetic diamond is produced by temperature difference under high pressure. A portion of the synthetic diamond is sorted and cut out as a seed crystal for subsequent processes.

[0077] Figure 10 This diagram illustrates the configuration of an apparatus for synthesizing diamond under high pressure via a temperature difference method. In this method, crystal growth is achieved by utilizing the difference in solubility of diamond relative to a solvent, created by a temperature difference. (See reference...) Figure 10Within a pressure medium 250 equipped with a graphite heater 252 and an insulating member 254, a longitudinal temperature gradient is formed. The insulating member 254 is positioned at a high temperature, a seed crystal 300 is positioned at a low temperature, and a solvent metal 258 is positioned between them. Single-crystal diamond is grown on the seed crystal 300 under conditions above the melting temperature of the solvent metal 258 and a pressure above which the diamond is thermally stable. Diamond powder is preferably used as the carbon source 256. Alternatively, graphite or thermally decomposed carbon can also be used as the carbon source 256. The solvent metal 258 is a metal selected from iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn), or an alloy containing these metals. By pressurizing the pressure medium 250, which is subjected to external force from a high-pressure generator (not shown), and heating it with the graphite heater 252, the pressure for thermodynamically stabilizing the diamond and the temperature conditions for the eutectic melting of the solvent metal 258 and carbon are achieved. Carbon dissolves from the carbon source 256 in the high-temperature section into the solvent metal 258 and diffuses and is transported to the low-temperature section below the solvent metal 258. Crystals grow on the seed crystal 300 to form synthetic diamond 302.

[0078] (First process) First, a single-crystal diamond with a nitrogen concentration of 30 ppm or less is prepared. In the above-described method for synthesizing high-pressure single-crystal diamond, a single-crystal diamond with a nitrogen concentration of 30 ppm or less can be manufactured by adding a nitrogen getter to solvent metal 258. Therefore, in the second step described later, a seed crystal with a single growth sector and a reduced number of dislocations (10 or less) as detected by X-ray morphology can be cut. The growth sector can be identified by a two-dimensional fluorescence image (area distribution image) of PL (Photoluminescence: a light emission image based on ultraviolet irradiation) or CL (Cathodoluminescence: a light emission image based on electron beam irradiation). That is, it can be determined based on whether the boundaries of regions with different fluorescence intensities are linear (see Patent Document 4).

[0079] Dislocations are determined, for example, by an etching test (see Patent Document 5). The etching test is performed as follows: A single-crystal diamond is immersed in a molten potassium nitrate (KNO3) solution and heated at 600°C for 1 hour in a platinum crucible (etching). After slow cooling, the single-crystal diamond is removed, and the surface is observed at 50x magnification using an optical microscope. The number of pits is counted within a rectangular measurement area of ​​1000 μm × 1000 μm, allowing for the determination of the number of pits per 1 mm. 2The number of pits. Pit etch pits refer to the point-like depressions present on the surface of a single-crystal diamond. Pit etch pits correspond to dislocation defects. The point-like depressions are quadrilaterals, rounded quadrilaterals, or approximately circular on the (100) face of the single-crystal diamond, and triangular, rounded triangulars, or approximately circular on the (111) face. The diameter of the point-like depressions ranges from approximately 1 μm to 50 μm. By measuring each 1 mm 2 The number of dot-like etch pits was set to 100 times, and the calculation was performed for each 1cm. 2 The number of pits (dislocation density) is measured. Additionally, linear etch pits are sometimes identified along with pits on the surface of etched single-crystal diamond. Linear etch pits originate from stacking defects in the single-crystal diamond. The number of linear etch pits is not included in the determination of dislocation defects.

[0080] Dislocations can also be detected by X-ray morphology (see Patent Document 6). When measuring using X-rays of radiation in a transmission-type manner, for example, X-rays with a wavelength of 0.71 Å (0.071 nm) are used, and the measurement is performed using (220) diffraction with a diffraction angle of 2θ = 32.9°. Alternatively, when measuring using a reflection-type manner, for example, X-rays with a wavelength of 0.96 Å (0.096 nm) are used, and the measurement is performed using (113) diffraction with a diffraction angle of 2θ = 52.4°. The wavelength of the X-rays can also be changed, and the diffraction angle 2θ can also be changed for imaging. Measurements can be performed using a laboratory X-ray diffraction apparatus; for example, a Mo-ray source can be used to observe (111) diffraction, and a Cu-ray source can be used to observe (113) diffraction. A CCD (Charge Coupled Device) camera can also be used for measurement, but a nuclear plate is preferred for improving resolution. After developing the nuclear plate, an image is acquired using an optical microscope, thereby enabling the identification and quantification of dislocations.

[0081] In the synthesis of single-crystal diamond via temperature difference, for example, the solvent metal 258 has a composition of Fe / Co = 10 / 90 to 90 / 10 (mass ratio), and titanium (Ti) or aluminum (Al) of 1.5% to 3% by mass is added to the solvent metal as a nitrogen getter. The temperature gradient is adjusted such that the temperature difference between the carbon source 256 and the seed crystal 300 is 10°C to 25°C or more, and the conditions of a pressure of 5.0 GPa to 5.5 GPa and a temperature of 1300°C to 1350°C are maintained for 80 hours to 250 hours. Therefore, referring to... Figure 11Diamond 302 is synthesized from seed crystal 300. If the temperature difference exceeds 25°C, crystal growth becomes disordered, and there is a tendency to not see traces of micro-bevel growth. When the temperature difference is below 10°C, crystal growth to the predetermined size requires a long time, making manufacturing costs a problem. Furthermore, the temperature variation during holding is controlled within 3°C. This further improves crystallinity. When the temperature variation is greater than 3°C, growth becomes unstable, resulting in crystal defects, strain, and inclusions, thus reducing crystallinity.

[0082] (Second process) To be used as a seed crystal in the third process described later, cut diamond 304 (see reference) is cut from the single-crystal diamond synthesized in the first process. Figure 11 The seed crystal facet of the cut diamond 304, which serves as the seed crystal, is preferably quadrilateral or octagonal, but is not limited to this. The size of the seed crystal facet (e.g., the length of opposite sides) is preferably 0.3 mm or more and 3 mm or less. The seed crystal is cut into a plate shape with a thickness of about 0.5 mm to 1.0 mm by laser processing, and the surface of the plate is ground to achieve a surface roughness Ra of 20 nm or less. Then, it is preferable to cut a plate shape of about 0.3 mm × 0.3 mm × 0.3 mm to 3.0 mm × 3.0 mm × 1.0 mm by laser cutting. The larger the size, the more dislocation defects are avoided, and it is easier to obtain a single sector, so it is preferred. When the cut diamond 304 is rectangular and the plane serving as its seed crystal facet is the (001) crystal facet, one side of the rectangle serving as the seed crystal facet and <100> direction or <010> The directions are parallel. If the plane serving as the seed crystal is the (111) crystal plane, then one side of the rectangle serving as the seed crystal is parallel to the <1-10> direction, the <10-1> direction, or the <01-1> direction. As a result, the cutting allowance can be reduced, and a seed crystal with a seed crystal surface that has less damage can be obtained.

[0083] In single-crystal diamond synthesized via the temperature difference method, numerous dislocation defects exist along the principal plane direction of the seed crystal and in directions with an opening angle of approximately X° relative to its orientation. For example, in the principal plane direction... <001> In the case of direction, with an opening angle of approximately 35° (i.e., X = 35°), <112> There are many dislocation defects in the four directions: <-112>, <1-12>, and <-1-12>. Additionally, in the principal face direction... <111> In terms of direction, at an opening angle of approximately 19.5° (i.e., X = 19.5), <112> direction, <121> direction and <211> There are many dislocation defects in these three directions. In the above description of an opening angle of X°, in the principal plane direction and... <001> direction or <111> When the orientations are inconsistent, the opening angle shifts slightly, resulting in an X° deviation. When they are inconsistent, the opening angle becomes a correction from 35° or 19.5°. Aside from these opening angles and the ±5° of the main face orientation, a single sector generally contains a high-quality crystal with few defects. However, near the boundaries of different sectors, such as the boundary between the {001} sector and the {111} sector, there is more crystal strain, making it prone to defects. If the seed substrate is larger, the interval between the opening angles originating from the seed substrate widens, and the boundaries of different sectors shift towards the ends, thus increasing the size of a high-quality crystal. Here, the {abc} sector refers to the region grown on the {abc} surface, the region exposed at the outermost surface. For example, the {001} sector is the region grown on the {001} surface, the region exposed at the outermost surface. Therefore, in this second process, diamond 304 is cut from a single growth sector of the main face growth, excluding the growth direction of the main face of the seed crystal of synthetic diamond 302 by ±5°, thereby obtaining a seed crystal with fewer defects.

[0084] If the seed crystal substrate is enlarged, the size of the high-quality crystal can be increased. For example, it is possible to cut a seed crystal with fewer than 10 dislocations as detected by X-ray morphology. By using this seed crystal, the single-crystal diamond synthesized through subsequent processes has fewer defects and the strain is further reduced. The seed crystal for synthetic diamond 302 is a single growth sector growing on the main face, excluding the growth direction ±5° of the main face, such as the {001} sector or the {111} sector. In addition, even sectors that can exist crystallographically other than these ({113} sector, {115} sector, {110} sector, or {135} sector) are acceptable, as long as they are single growth sectors growing on the main face excluding the growth direction ±5° of the main face of the seed crystal. When cutting the cutting diamond 304, which serves as the seed crystal, from the synthetic diamond 302, it can be cut from one sector or in a manner that includes two or more sectors. That is, the cutting diamond 304 may or may not include sector boundaries. In single-crystal diamond, the regions of each sector can be determined by the luminescence pattern obtained by ultraviolet irradiation (ultraviolet-excited luminescence pattern).

[0085] (Third process) Using the seed crystals cut in the second process, diamond is synthesized via a temperature difference method as described above. That is, referring to... Figure 12 Using cut diamond 304 as seed crystal 310, synthetic diamond 312 is synthesized. This allows for the production of single-crystal diamond with reduced crystal defects and strain.

[0086] Specifically, refer to Figure 10 Diamond powder is used as the carbon source 256. Iron or cobalt, which has high solubility and affinity for carbon, is used as the solvent metal 258. Nickel or manganese is sometimes added in trace amounts to the diamond depending on the synthesis conditions. The amount of boron impurities in both the carbon source 256 and the solvent metal 258 is controlled to be below 1 ppm. Therefore, the atomic number basis content of boron (B) in the single-crystal diamond can be below 0.1 ppm. Titanium is added to the solvent metal 258 as a nitrogen getter. The concentration of added titanium is 1.5% by mass or more and 3% by mass or less. This allows the atomic number basis nitrogen content in the single-crystal diamond to be set to 0.1 ppm or more and 10 ppm or less. Aluminum can also be added as a nitrogen getter. In this case, an Fe-Al alloy can also be used as the solvent metal 258.

[0087] As a condition for the temperature difference method, for example, the temperature gradient is adjusted so that the temperature difference between the carbon source 256 and the seed crystal 300 is 10°C or more and 25°C or less, and the conditions of pressure 5.0 GPa or more and 5.5 GPa or less, and temperature 1300°C or more and 1350°C or less are maintained for 80 hours or more and 300 hours or less. If the temperature difference exceeds 25°C, the crystal growth becomes slightly disordered, and in most cases, micro-bevel growth is not visible. In addition, by controlling the temperature change during maintenance to within 3°C, the crystallinity is further improved.

[0088] (Fourth process) Synthetic diamond 312 synthesized through the third process (see reference) Figure 12 Cut the diamond 318. The diamond 318 is a region located within a single growth sector (e.g., sector 316) that does not include the sector boundary 314, and has fewer than 10 dislocations as detected by X-ray morphology. The cutting of the diamond 318 is performed using laser processing in the same manner as the second step described above.

[0089] (Fifth process) An electron beam with an energy of 300 keV or higher and 1.2 MeV or lower is irradiated onto the diamond 318 cut from synthetic diamond 312 via the fourth process. This ionizes the orbital electrons of the carbon atoms in the diamond 318, repelling the carbon nuclei and creating pores within the diamond 318. Alternatively, an electron beam with an energy of 500 keV or higher and 1 MeV or lower can also be used. The electron beam irradiation amount can be adjusted according to the desired NV (non-volatile organic compound) generation. - The quantity is 1×10 18 cm -2 Up to 4×10 19 cm -2 It varies within a certain range.

[0090] (Sixth process) The diamond 318 that has undergone the fifth process is annealed in a vacuum at a temperature of 1100°C to 1400°C for 0.1 hours to 0.5 hours. This causes the nitrogen in the diamond 318 to move, forming NV color centers based on nitrogen and pores.

[0091] Based on the above, a diamond spin sensor 100 can be manufactured that is larger than before, with increased fluorescence intensity I without reducing the transverse relaxation time T2, or with increased transverse relaxation time T2 without reducing fluorescence intensity I.

[0092] The irradiation step in the fifth process and the annealing step in the sixth process can be repeated more than twice. This allows for the formation of the desired amount of NV color centers in the cut diamond 318.

[0093] As described above, a nitrogen getter is used in the third process. The nitrogen getter may contain any one of titanium (Ti), zirconium (Zr), hafnium (Hf), aluminum (Al), gallium (Ga), copper (Cu), silver (Ag), and gold (Au). This increases the product of the transverse relaxation time T2 and the fluorescence intensity I, enabling a sensor with higher sensitivity.

[0094] As mentioned above, the cut diamond 318 can also contain only one sector boundary, or no sector boundary at all. This increases the product of the lateral relaxation time T2 and the fluorescence intensity I, enabling a sensor with higher sensitivity.

[0095] In addition, refer to Figure 13Alternatively, a larger seed crystal 320 can be used to perform the above-described synthesis steps. For example, in the seed crystal 320, which is a cuboid, the length L of one side of the rectangle with the (001) or (111) crystal plane is 3 mm or more. This allows the sector boundary 324, where impurities can easily enter, to be separated from the central part of the sector 326. Therefore, a larger cut diamond 328 can be cut from the sector 326 of the synthetic diamond 322 grown from the seed crystal 320. As described above, the cut diamond 328 is subjected to electron beam irradiation (fifth step) and annealing (sixth step). This allows the manufacture of a larger diamond spin sensor 100.

[0096] Figure 14 The diamond synthesized as described above is shown schematically. Figure 14 It is a top view of the (001) plane. Figure 14 The left and right directions are <100> directions. Sector 332, which forms a triangular region at the four corners, represents sector (111). The boundaries of different sectors become the boundaries of sectors with different impurity concentrations (reference point pattern), forming strain and introducing impurities. Figure 13 As shown, by increasing the size of the seed crystal, the region containing impurities can be located further outwards than the central region. Therefore, a larger region can be cut out, allowing for the fabrication of a larger diamond spin sensor. (Refer to...) Figure 14 A diagonal section within sector 330 can be cut out and used as a seed crystal to fabricate a diamond spin sensor. Alternatively, as shown by the dashed line, a larger seed crystal can be fabricated by cutting out a section that includes dislocation defects and two sector regions, and this seed crystal can be used to fabricate a diamond spin sensor. Furthermore, sector 330 as a (111) sector can also be used as a seed crystal to fabricate a diamond spin sensor.

[0097] As a comparative example, synthetic diamond used in previous NV spin sensors is shown in... Figure 15 . Figure 15 Is with Figure 14 The same top view. Sector 342 is sector (111). In Figure 15 In synthetic diamond, large sector boundaries with varying impurity concentrations are formed around the largest sector 340 (001), indicating that a sufficiently large area cannot be cut out for a diamond spin sensor. This is because different sectors, such as sector (001) and sector (111), form boundaries.

[0098] Example 1 The effectiveness of the diamond spin sensor disclosed herein is illustrated below through examples. Using multiple diamond spin sensors fabricated by the above-described manufacturing method, fluorescence intensity I and transverse relaxation time T2 were measured. Manufacturing conditions are shown below. Figure 16 The measurement results are shown in Figure 16 as well as Figure 17 .

[0099] Figure 16 In this study, samples 1 to 8 are shown as diamond seed crystals with dimensions of 3mm × 3mm × 0.8mm, 0.7mm × 0.7mm × 0.5mm, and 0.9mm × 0.9mm × 0.5mm (refer to the second process) cut from the synthetic diamond prepared as described above using a laser processing machine. Sample 9 is a commercially available product (DNV-B14 manufactured by Element Six) produced by CVD (Chemical Vapor Deposition). The diamond seed crystals were cut from... Figure 16 The cutting is performed within the sector recorded in the "Seed Crystal Cutting Sector" column. In the "Seed Crystal Cutting Sector" column, "(100)" means cutting from sector (100). In addition, "(100)+(111)" means cutting in a manner that includes both sector (100) and sector (111). The presence of defects in the obtained diamond seed crystal is confirmed by X-ray morphology images. The number of dislocation defects confirmed is shown in the figure. Figure 16 The "Dislocation Defect" section.

[0100] Next, diamond crystals are grown on the aforementioned diamond seed crystals using a temperature difference method to obtain single-crystal diamonds for each sample (refer to step three). This is in Figure 16 The method is represented by HPHT (High-Pressure High-Temperature). Diamond powder containing 100 ppm to 200 ppm nitrogen and 0.5 ppm to 1 ppm boron as impurities is used as the carbon source. High-purity iron (Fe) and cobalt (Co) are used as the solvent metal, with a solvent composition of Fe:Co = 55:45 (weight ratio). 1.75% by mass of titanium is added to the solvent metal. The conditions for the temperature difference method for each sample are as follows: titanium is used as the nitrogen getter; the temperature difference between the high-temperature section (carbon source) and the low-temperature section (seed crystal) is 23°C; the pressure is 5.3 GPa; and the holding temperature of the low-temperature section is 1350°C. The holding time is set to 150 hours.

[0101] Then, processes four through six described above are performed to fabricate multiple diamond spin sensors. The diamonds cut in process four are shown below. Figure 16 The section on "Cutting Method of Raw Materials for Sensors" displays the half-width (arcsec units) of the measured X-ray diffraction rocking curve in the "Xrc" column. Regarding "Location of Growth Sector," "Top" indicates... Figure 14 The slash part, "above + adjacent" indicates Figure 14 The dashed line represents the measured nitrogen concentration (ppm) and NV. -Color center concentration (ppm) is shown in the "N Concentration" column and "NV" column respectively. - "Concentration" column.

[0102] The fluorescence intensity I and transverse relaxation time T2 were measured using a fabricated diamond spin sensor. The results are presented in... Figure 17 Samples 1 to 9 and Figure 16 Same. Figure 17 In this context, fluorescence intensity I is expressed in nA units, and transverse relaxation time T2 is expressed in μsec units. Phase difference represents the average phase difference over the entire surface (nm / mm units). (V) 0 +V - ) / NV - This means that the sum of the number of uncharged isolated vias and the number of negatively charged isolated vias relative to NV - The proportion of color centers. Product α refers to the product of fluorescence intensity I and transverse relaxation time T2 (T2×I). NV - Concentration and the meaning of Xrc Figure 16 same.

[0103] Samples 1 and 6 produced by the trial production achieved a larger product α and a longer transverse relaxation time T2 than samples 7 to 9. The fluorescence intensity of sample 1 was greater than that of samples 7 to 9. The fluorescence intensity of samples 2 to 6 was similar to that of samples 7 to 9. (NV comparison) - From samples 1 to 3 with the same concentration, it can be seen that the smaller the phase difference and Xrc, the greater the fluorescence intensity I, transverse relaxation time T2, and product α. Comparing samples 1 and 6 with similar phase difference and Xrc values, it can be seen that reducing NV... - The concentration of NV increases, and the product α increases. However, by reducing NV... - At higher concentrations, fluorescence intensity decreases.

[0104] about Figure 17 Samples 1 to 9 shown are plotted with transverse relaxation time T2 and fluorescence intensity I. Figure 18 .exist Figure 18 In the graph, the horizontal axis represents the logarithm of fluorescence intensity I (nA units), and the vertical axis represents the logarithm of transverse relaxation time T2 (μsec units). The white circles labeled S1 to S9 correspond to... Figure 17 Samples 1 to 9.

[0105] Figure 18 The multiple straight lines shown represent graphs where the product α is 2300, 3000, 6000, 10000, and 15000 from bottom to top. Figure 18 In this context, since both axes are represented logarithmically, the graph of the constant product α of T2 and I is represented by a straight line. Figure 18In the diagram, S9 lies approximately on a straight line with product α = 2300. In contrast, the products α of S1 to S6 are all greater than 3000. Therefore, it can be seen that diamond spin sensors with fewer primary causes of fluorescence absorption and scattering can be fabricated. To suppress fluorescence absorption and scattering, materials with low phase difference, minimal influence from sector boundaries, low entrapment of impurities, few excess point defects (i.e., voids), and low interlattice nitrogen are preferred. That is, phase difference, nitrogen concentration, and NV... - The concentration of color centers, dislocation defects, and the half-width Xrc of the rocking curve are all within the above range, thereby enabling the realization of a diamond spin sensor that suppresses fluorescence absorption and scattering.

[0106] The present disclosure has been described above by way of example, but the above-described embodiments are illustrative and the present disclosure is not limited to the above-described embodiments. The scope of the present disclosure is defined by the claims based on the detailed description of the invention, and includes all modifications within the meaning and scope of the statements herein.

[0107] Explanation of reference numerals in the attached figures 100: Diamond spin sensor; 100a: upper surface; 102: First page; 104: First side; 202: Electromagnetic wave irradiation section; 204: Excitation light; 206: Fluorescence; 210: Excitation light-generating part; 212: Filter; 214: Concentrating element; 216: Optical waveguide; 218: LPF; 220: Optical Detection Department; 230: Control Department; 232: Electromagnetic wave generating unit; 240: Irradiation area; 242: Output area; 250: Pressure medium; 252: Graphite heater; 254: Insulating components; 256: Carbon source; 258: Solvent metal; 300, 310, 320: Seed crystals; 302, 312, 322: Synthetic diamond; 304, 318, 328: for cutting diamonds; 314, 324: Sector boundaries; 316, 326, 330, 332, 340, 342: sectors; A1, A2, A3, A4, A5, A6, A7, A8: points; C: Carbon; L: Length; N: Nitrogen; P1, P2, P3: Pulse; t, t1, t2, t3, τ: time intervals; V: Hole; X, Y, Z: axes; Δf: Frequency difference; φ, θ: Angles.

Claims

1. A diamond spin sensor, wherein, This diamond spin sensor contains diamond, which contains NVs with electron spin. - Lust, When the transverse relaxation time of the electron spin, determined by the Hahn echo method, is defined as T2 μsec, and the fluorescence intensity of the fluorescence emitted from the diamond by irradiating it with microwaves and lasers is represented by the current value InA output from the Si-PIN diode receiving the fluorescence, the product of T2 and I is greater than 3000. The wavelength of the microwave is above 2.07 GHz and below 3.67 GHz. The wavelength of the laser is above 520nm and below 540nm. The power of the laser is 3mW. The photosensitive sensitivity of the Si-PIN diode is above 0.36 A / W and below 0.44 A / W at a wavelength of 600 nm, and above 0.40 A / W and below 0.5 A / W at a wavelength of 660 nm.

2. The diamond spin sensor according to claim 1, wherein, The product of T2 and I is greater than 10000.

3. A diamond spin sensor, wherein, This diamond spin sensor contains diamond, which contains NVs with electron spin. - Lust, The NV - The concentration of color centers is above 0.02 ppm and below 10 ppm. The average phase difference of the diamond surface as a whole is less than 6 nm / mm.

4. The diamond spin sensor according to any one of claims 1 to 3, wherein, The average phase difference of the diamond surface as a whole is less than 4 nm / mm.

5. The diamond spin sensor according to any one of claims 1 to 4, wherein, The NV - The concentration of color centers is above 0.02 ppm and below 1.2 ppm.

6. A diamond spin sensor, wherein, This diamond spin sensor contains diamond, which contains NVs with electron spin. - Lust, The NV - The concentration of color centers is above 0.02 ppm and below 10 ppm. The half-width of the rocking curves of X-ray diffraction based on the dual-crystal method is less than 8 seconds.

7. The diamond spin sensor according to any one of claims 1 to 4 and claim 6, wherein, The NV - The concentration of color centers is above 0.02 ppm and below 2 ppm. The half-width of the rocking curves of X-ray diffraction based on the dual-crystal method is less than 6 seconds.

8. The diamond spin sensor according to any one of claims 1 to 7, wherein, The concentration of isolated pores relative to the NV - The concentration of color centers is less than 10%.

9. The diamond spin sensor according to claim 8, wherein, The concentration of isolated pores relative to the NV - The concentration of color centers is less than 1%.

10. A method for manufacturing a diamond spin sensor, wherein, The manufacturing method includes: Synthesis step, in which a rectangular surface having a (001) crystal plane or a (111) crystal plane is used as a seed crystal for synthesizing diamond, and diamond single crystal is synthesized under pressure of 5 GPa or higher by temperature difference method. The irradiation step involves irradiating the cut diamond cut from the diamond single crystal synthesized through the synthesis step with an electron beam of energy of 500 keV or more and 1 MeV or less. as well as The annealing step involves annealing the cut diamond, which has undergone the irradiation step, at a temperature between 1200°C and 1400°C for at least 0.1 hours and less than 0.5 hours, thereby generating a diamond spin sensor. The nitrogen concentration of the seed crystal is above 0.1 ppm and below 30 ppm, and The seed crystal has fewer than 10 linear dislocation defects. If the surface is a (001) crystal plane, then one side of the rectangle is parallel to... <100> direction or <010> The direction is parallel, If the surface is a (111) crystal plane, then one side of the rectangle is parallel to the <1-10> direction, the <10-1> direction, or the <01-1> direction.

11. The method for manufacturing a diamond spin sensor according to claim 10, wherein, In the synthesis step, a nitrogen getter is used. The nitrogen getter comprises any one of titanium, zirconium, hafnium, aluminum, gallium, copper, silver, and gold.

12. The method for manufacturing a diamond spin sensor according to claim 10 or 11, wherein, The cut diamond may contain only one sector boundary or no sector boundary.

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