Diamond spin sensor

Abstract

A diamond spin sensor (100) includes a diamond containing an NV ‑ center having an electron spin, a transverse relaxation time of the electron spin determined by a Ramsey method is set to μsec, a concentration of the NV ‑ center in the diamond is set to Cppm, and a value α calculated using and C and by () 1 / 3 α < 2.5, a transverse relaxation time of the electron spin determined by a Hahn echo method is set to T2 μsec, T2 is 15 or more, and an average phase difference with respect to an entire surface of the diamond is 6 nm / mm or less.

Description

Technical Field

[0001] This disclosure relates to diamond spin sensors. This application claims priority to Japanese Patent Application No. 2024-027999, filed February 28, 2024. The entire contents of 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, consisting of nitrogen (N) substituted at a carbon (C) position in diamond and a vacancy (V) 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 NV center, but for convenience, will be referred to as the NV center below. When the charged NV center is excited by a laser with a wavelength of about 530 nm (i.e., green light), it emits fluorescence with a wavelength of about 635 nm (i.e., red light). The intensity of the fluorescence varies according to the spin state of the NV center, which varies according to magnetic resonance caused by the magnetic field applied to the NV center and microwave or radio waves, thus enabling it to be used as a magnetic sensor.

[0003] The detection utilizes a diamond containing an NV center as a diamond spin sensor, an optical system that transmits excitation light from a light source to the NV center, and a transmission line and microwave circuit that transmit microwaves from a power source to the NV center. Furthermore, an optical system is also used to focus fluorescence from the NV center and transmit it to a photodetector.

[0004] Methods for producing high-purity diamonds by reducing distortion and impurities in diamond crystals are known. For example, Patent Document 1 discloses that by adding getter materials such as titanium (Ti) to the raw material to target nitrogen, which is the largest impurity, it is possible to produce diamonds with low nitrogen content. Patent Document 2 discloses that by cutting a seed crystal from a diamond with a size of 3 mm or larger, and cutting the portion with fewer crystal defects to a size of less than 1 mm, and using this as a seed substrate for growth, it is possible to reduce crystal distortion.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 7-148426

[0008] Patent Document 2: Japanese Patent Application Publication No. 9-165295

[0009] Patent Document 3: International Publication No. 2022 / 210723

[0010] Patent Document 4: International Publication No. 2022 / 209512

[0011] Patent Document 5: International Publication No. 2016 / 013588 Summary of the Invention

[0012] One aspect of this disclosure relates to a diamond spin sensor comprising diamond, the diamond containing NV having electronic spin. - The center sets the transverse relaxation time of electron spin, determined using the Ramsey method, as... μsec, NV in diamond - The concentration at the center was set to Cppm, using and C through ( ) 1 / 3 The value α calculated by ×C is less than 2.5. The transverse relaxation time of the electron spin measured by the Hahn echo method is set to T2μsec. T2 is greater than 15, and the average phase difference over the entire surface of diamond is less than 6nm / mm. Attached Figure Description

[0013] Figure 1 This is a perspective view showing a diamond spin sensor according to an embodiment of the present disclosure.

[0014] Figure 2 This is a schematic diagram showing the crystal faces and orientations of diamond.

[0015] Figure 3 It shows the use Figure 1 The diagram shows the configuration of the apparatus used in the measurement of the diamond spin sensor.

[0016] Figure 4 It shows the use Figure 1 The timing diagram shown illustrates the timing of excitation light and electromagnetic wave irradiation, as well as the timing of emission light measurement, during the measurement of the diamond spin sensor.

[0017] 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).

[0018] Figure 6 This is a schematic diagram showing the NV center of a diamond.

[0019] Figure 7 It shows the method used for measurement Figure 1 The 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 emission light measurement.

[0020] Figure 8This is a graph showing the transverse relaxation time T2.

[0021] Figure 9 It shows the method used for measurement Figure 1 The transverse relaxation time of the diamond spin sensor shown The timing diagrams for the excitation light and electromagnetic wave irradiation timing, as well as the timing for the measurement of emitted light.

[0022] Figure 10 It shows the use of Figure 9 The graph shown is a time series diagram of the changes in fluorescence intensity.

[0023] Figure 11 This is a schematic diagram showing a diamond synthesis apparatus.

[0024] Figure 12 This is a schematic diagram illustrating a method for manufacturing seed crystals used in the synthesis of diamond.

[0025] Figure 13 It shows that from Figure 12 The diagram shows a method for synthesizing diamond by cutting a portion of the synthetic diamond and using it as a seed crystal.

[0026] Figure 14 It shows the ratio of use Figure 13 The diagram shows a method for synthesizing diamond with large seed crystals.

[0027] Figure 15 It is shown Figure 14 The top view of the synthetic diamond shown.

[0028] Figure 16 This is a top view showing a conventional synthetic diamond.

[0029] Figure 17 It is a diagram that shows the manufacturing conditions of the experimental samples in tabular form.

[0030] Figure 18 The graph presents the experimental results in tabular form. Detailed Implementation

[0031] [The technical problem this disclosure aims to solve]

[0032] Regarding sensors using diamond NV centers (also known as color centers), a longer spin transverse relaxation time T2 improves the sensor's sensitivity, thus being preferred. That is, a longer transverse relaxation time T2 increases the time for the resonant electromagnetic wave to act, thereby improving the sensor's sensitivity. A longer transverse relaxation time T2 affects the measurement sensitivity of DC (hereinafter referred to as DC) measurement objects (such as static magnetic fields). It also becomes longer, which is advantageous. This is to increase the transverse relaxation time T2 and the transverse relaxation time... For example, measures will be taken to reduce the amount of diamonds in the diamond. 13 The C content. Relative to the natural abundance ratio of the isotope, which is approximately 98.9%. 12 C does not have nuclear spin, while 13 C has a nuclear spin of 1 / 2. Therefore, when there is 13 At time C, the electron spin through the NV center and 13 The interaction of C's nuclear spins affects the transverse relaxation time T2 and the transverse relaxation time. Smaller. The synthesis rate decreased compared to the natural abundance. 13 Diamonds with a C content require the use of reduced... 13 The content of C and its effect 12 C uses a concentrated carbon source, which increases the number of steps involved in manufacturing such a carbon source. Therefore, the manufacturing cost of the diamond used in the sensor increases, leading to a higher product price.

[0033] When diamond exhibits strong luminescence intensity, signals are more easily detected, increasing the sensor's sensitivity. However, increasing the concentration of NV centers to enhance luminescence intensity creates an obstacle due to the large amount of spin-containing nitrogen, shortening the transverse relaxation time T2 (resulting in faster signal decay). Conversely, decreasing the concentration of NV centers in diamond is also effective in increasing the transverse relaxation time T2. However, fewer NV centers, the source of fluorescence, lead to weaker luminescence intensity. Thus, a trade-off exists between the transverse relaxation time T2 and the concentration of NV centers.

[0034] As disclosed in Patent Documents 1 and 2, high-purity diamond crystals with almost no impurities and defects are easy to manufacture. However, in order to use diamond containing NV centers that require nitrogen and defects (vacancies) as sensors, it is necessary to remove the distortions and impurities that are the scattering factors of fluorescence while leaving trace amounts of distortion and impurities. That is, a method is desired to reduce other impurities and distortions while leaving trace amounts of nitrogen and defects (vacancies) as impurities.

[0035] Therefore, the purpose of this disclosure is to provide a 13 A diamond spin sensor that maintains the natural abundance ratio of C content and can increase the transverse relaxation time T2 without reducing the concentration of NV centers.

[0036] [The Effects of This Disclosure]

[0037] According to this disclosure, it is possible to provide a 13 A diamond spin sensor that maintains the natural abundance ratio of C content and can increase the transverse relaxation time T2 without reducing the concentration of NV centers.

[0038] [Description of embodiments of this disclosure]

[0039] The embodiments of this disclosure are described below. At least some of the embodiments described below may be combined arbitrarily.

[0040] (1) The first aspect of this disclosure relates to a diamond spin sensor, comprising diamond containing NV having electron spin. - The center sets the transverse relaxation time of electron spin, determined using the Ramsey method, as... μsec, NV in diamond - The concentration at the center was set to Cppm, using and C through ( ) 1 / 3 The calculated value α is less than 2.5. The transverse relaxation time of the electron spin, determined using the Hahn echo method, is set to T2 μsec. Since T2 is greater than 15, the average phase difference across the entire diamond surface is less than 6 nm / mm. Therefore, in diamond... 13 The C content remains unchanged at its natural abundance ratio, which can achieve this without reducing NV. - The transverse relaxation time T2 is increased under the condition of high concentration at the center. Since it is not necessary to use [a specific method] when manufacturing diamond spin sensors... 12 C uses a concentrated carbon source, making it easier to manufacture and resulting in lower manufacturing costs and product prices. It should be noted that the transverse relaxation time is important for measuring alternating current (AC) objects (such as alternating magnetic fields). Even if it's small, it's not a problem.

[0041] (2) In (1) above, the value α can also be less than 0.25. Therefore, the transverse relaxation time... Or NV - The concentration at the center can become smaller, but the transverse relaxation time T2 can be maintained.

[0042] (3) In (1) or (2) above, NV - The concentration at the center can be above 0.002 ppm but less than 10 ppm, and the average phase difference can be below 2 nm / mm. This allows for an increase in the transverse relaxation time T2. Therefore, a sensor with higher sensitivity than before can be achieved.

[0043] (4) In any of (1) to (3) above, T2 can also be 250 or higher. Thus, a sensor with higher sensitivity than before can be realized.

[0044] (5) In any of (1) to (4) above, NV -The concentration at the center can also be above 0.002 ppm and below 0.3 ppm, thereby further increasing the transverse relaxation time T2 and enabling a sensor with higher sensitivity.

[0045] (6) In any of (1) to (5) above, It can also be above 0.05 and less than 0.8. Therefore, it will not affect the measurement of the AC target (such as alternating magnetic field).

[0046] (7) In any of (1) to (6) above, the half-width of the rocking curve of X-ray diffraction based on the dual-crystal method can also be less than 10 seconds. As a result, the transverse relaxation time T2 can be increased, and a sensor with high sensitivity can be realized.

[0047] (8) In any of (1) to (7) above, the half-width of the rocking curve of X-ray diffraction based on the dual-crystal method can also be less than 6 seconds. As a result, the transverse relaxation time T2 can be further increased, and a sensor with higher sensitivity can be realized.

[0048] (9) In any of (1) to (8) above, the number of dislocation defects in the diamond as a whole detected by X-ray morphology image can also be less than 10. As a result, the transverse relaxation time T2 can be increased, and a sensor with high sensitivity can be realized.

[0049] (10) In any of (1) to (9) above, the number of dislocation defects in the diamond as a whole detected by X-ray morphology image can also be 0. As a result, the transverse relaxation time T2 can be further increased, and a sensor with higher sensitivity can be realized.

[0050] (11) In any of (1) to (10) above, the concentration of isolated vacancies in diamond relative to NV - The concentration at the center can also be below 10%. This increases the transverse relaxation time T2, enabling the realization of a highly sensitive sensor.

[0051] (12) In (11) above, the proportion can also be less than 1%. As a result, the transverse relaxation time T2 can be further increased, and a sensor with higher sensitivity can be realized.

[0052] [Details of the embodiments of this disclosure]

[0053] In the following embodiments, the same reference numerals are used to refer to the same components. Their names and functions are also the same. Therefore, detailed descriptions of them are omitted.

[0054] 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 centers composed of nitrogen (N) and vacancies (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> or <010> direction. When the first face 102 is a (111) plane, the first side 104 is formed along the <1-10>, <10-1>, or <01-1> direction. It should be noted that the expression "-1" corresponds to the expression of a crystal direction with a line (horizontal line) above the 1.

[0055] 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 arbitrary and not limited to a rectangle. 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 (e.g., a pyramid with right angles on its lateral faces) where the first face 102 is a triangle (e.g., an equilateral triangle).

[0056] Reference Figure 2 In diamond, the (001) facet is a plane defined by points A5 to A8 (i.e., a plane passing through these four points). As described above, when the first facet 102 is the (001) facet, the diamond spin sensor 100 is implemented as, for example, a cube with points A1 to A8 as vertices. The <100> direction and <010> direction, which are possible directions for the first side 104, are the directions from point A1 to point A2 and from point A1 to point A4, respectively. For example, if the first facet 102 is a face with points A5 to A8 as vertices, then the first side 104 corresponds to a line segment connecting points A5 and A6, or a line segment connecting points A5 and A8.

[0057] (111) is a plane defined by points A5, A2, and A4. As described above, the first surface 102 can also be (111). In this case, the <1-10> direction, which is the possible direction of the first side 104, is the direction 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 <10-1> direction, which is the possible direction of the first side 104, is the direction 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 <01-1> direction, which is the possible direction of the first side 104, is the direction from point A1 toward point B3. That is, the first side 104 corresponds to the line segment connecting points A5 and A4.

[0058] Measurements using a diamond spin sensor 100, for example... 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.

[0059] The excitation light generating unit 210 is controlled by the control unit 230 to generate excitation light for exciting the NV center of the diamond spin sensor 100. The control unit 230 supplies a voltage to the excitation light generating unit 210 at predetermined timings 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., emitting light with a wavelength of 532 nm).

[0060] Filter 212 is an element used to separate the excitation light 204 incident from the excitation light generating unit 210 from the light emitted from the diamond spin sensor 100 (i.e., fluorescence). For example, filter 212 is a bandpass filter that cuts off (i.e. reflects) light with wavelengths below a specified wavelength while allowing light with wavelengths longer than the specified wavelength to pass through, or allows light with wavelengths within a specified wavelength range to pass through while cutting off (i.e. reflects) light with wavelengths outside the specified wavelength range. Generally, since the wavelength of the excitation light is shorter than that of the fluorescence, such a configuration is preferred. For example, filter 212 is a dichroic mirror with such a function.

[0061] A 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 and output from the excitation light generator 210 as possible into the end of the optical waveguide 216. The optical waveguide 216 includes a light-transmitting medium 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. Additionally, the optical waveguide 216 transmits the emitted 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.

[0062] The LPF (Long Pass Filter) 218 ​​is a long pass filter that allows light with wavelengths above a specified wavelength to pass through while blocking (e.g., reflecting) light with wavelengths shorter than the specified wavelength. The fluorescence 206, emitted as light from the diamond spin sensor 100, is red and passes through the LPF 218. However, the wavelength of the excitation light 204 output from the excitation light generator 210 is shorter than that of the fluorescence 206, and therefore does not pass through the LPF 218. Consequently, the excitation light 204 emitted from the excitation light generator 210 is detected by the photodetector 220 and becomes noise, thereby suppressing the decrease in detection sensitivity of the fluorescence 206, which is emitted as light from 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 control unit 230 acquires the output signal of the photodetector 220.

[0063] 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 formed including an electrical conductor or a microwave resonant circuit. 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, and are, for example... Figure 4 It is performed at regular intervals as shown.

[0064] Reference Figure 4 The control unit 230 controls the excitation light generating unit 210 to output excitation light within a predetermined time and period (e.g., time interval t1). The control unit 230 controls the electromagnetic wave generating unit 232 to output electromagnetic waves within a predetermined time and period (e.g., time interval t2). A suitable pulse sequence can be used appropriately within time interval t2. Thus, electromagnetic waves are irradiated onto the diamond along with the excitation light in a temporal and spatial combination. The control unit 230 receives the output signal from the input light detection unit 220 at a predetermined time (e.g., time interval t3) and stores it in the storage unit.

[0065] The NV center transitions from its ground state to an excited state by emitting green light (e.g., a 532nm laser) with wavelengths of 490nm–560nm, emitting red light (e.g., 635nm fluorescence) with wavelengths of 630nm–800nm, and then returns to its ground state. The NV center in the state of capturing an electron (i.e., NV...) - The magnetic quantum number m is formed under these conditions. s Given a spin triplet state of -1, 0, and +1, if a magnetic field exists, then m s The energy levels of the ±1 state split according to the magnetic field strength (i.e., Zeeman splitting). Irradiating the center of NV with microwaves at a frequency of 2.87 GHz causes m... s The state of =0 transitions to m s After reaching the ±1 state (i.e., electron spin resonance), the electron is excited by irradiating it with green light. As a result, the intensity of the observed emission decreases because the transition back to the ground state includes a non-emission transition (i.e., fluorescence). Therefore, a valley (i.e., a dip in the signal) is observed in the ODMR (Optically Detected Magnetic Resonance) spectrum.

[0066] As described above, the excitation light generating unit 210 and the electromagnetic wave generating unit 232 are controlled by the control unit 230 to measure, for example... Figure 5 The spectrum is as 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 center is the component along the axis (hereinafter referred to as the NV axis) through which the N and V vectors formed at the NV center of the diamond pass. That is, the angle between the magnetic field vector B and the NV axis is set as... Detected by diamond spin sensor 100 and Bcos The corresponding change in signal intensity (i.e. fluorescence intensity).

[0067] The above explanation illustrates the case where the magnetic field can be calculated from changes in the ODMR spectrum. However, it is known that the frequencies of the two resonant frequencies at the NV center are temperature-dependent in the range of 120K to 700K. Therefore, by measuring the frequency change at the center splitting at Δf using a diamond spin sensor 100, the temperature can be determined.

[0068] In the diamond spin sensor 100, the transverse relaxation time of the electron spin at the NV center is set as μsec, setting the concentration of NV centers (the ratio of the number of NV centers to the number of carbon atoms) in diamond to Cppm, and using and C through α=( ) 1 / 3 The calculated value of α using ×C is less than 2.5. Furthermore, setting the transverse relaxation time of the electron spin to T2μsec, where T2 is greater than or equal to 15, the average phase difference across the entire diamond surface, as discussed later, is less than 6nm / mm. Transverse relaxation time The transverse relaxation time T2 was determined using the Ramsey method (described later), and the Hahn echo method (described later). The concentration C of the NV centers was determined using electron spin resonance and other methods. Therefore, the concentration of NV centers in diamond... 13 By maintaining the natural abundance ratio of carbon (C), the transverse relaxation time (T2) can be increased without reducing the concentration of NV centers. Therefore, it is possible to suppress the decrease in luminescence intensity and achieve a sensor with higher sensitivity than before. Since it is not necessary to use [specific materials] during the fabrication of diamond spin sensors... 12 C uses a concentrated carbon source, making it easier to manufacture and resulting in lower manufacturing costs and product prices. It should be noted that the lateral relaxation time... A larger value is better for DC measurements (static magnetic fields, etc.), but it will not affect AC measurements (alternating magnetic fields, etc.). Therefore, for AC measurements (alternating magnetic fields, etc.), as long as the transverse relaxation time T2 can be maintained at a certain value, it is acceptable, even if the transverse relaxation time... Even if it's small, it's not a problem.

[0069] (Lateral relaxation time T2)

[0070] The Hahn echo method for determining transverse relaxation time T2 includes the electron spin echo method (hereinafter referred to as the spin echo method) as shown below. The spin echo method is a type of ESR (Electron Spin Resonance) measurement. In general ESR measurements, microwaves are continuously irradiated while an external magnetic field is applied and the absorption of microwaves is observed (CW (Continuous Wave)-ESR). In contrast, in the spin echo method, microwave pulses are used to excite electron spins, and the relaxation of electron spins is measured. The spin echo method can be used to determine the physical quantities of spin-lattice relaxation time T1 and spin-spin relaxation time T2. The spin-lattice relaxation time T1 is also called the longitudinal relaxation time T1. The transverse relaxation time T2 mentioned above refers to the spin-spin relaxation time T2.

[0071] In the spin echo method, microwaves are not applied continuously, but rather in multiple pulses that rotate the spin by θ°. The amount of spin rotation (i.e., the rotation angle θ) is determined by the intensity of the microwaves and the application time. In most cases, the operation is as follows: the spin is rotated by θ1° using a microwave pulse, placed for a time τ, and then further rotated by θ2° using a microwave pulse. For example, θ1 = 90°, θ2 = 180°.

[0072] Consider the action of spins in a rotating coordinate system rotating at a Larmor frequency. An initial pulse causes a uniform spin in the Z-axis direction (the direction of the magnetic field) to rotate θ1° towards the XY plane. All spins rotate in the same direction around the Z-axis; however, due to local magnetic field fluctuations, the rotational speeds of the individual spins around the Z-axis gradually become different after the initial θ1° rotation, and over time, the direction of each spin gradually deviates from its initial position. That is, the spins experience phase delay or lead. This dispersion increases proportionally to time τ (i.e., elapsed time). Then, when a microwave pulse rotating θ2° is applied, the dispersed spins rotate θ2° in the same direction as when the spins were initially rotated θ1°. After the θ2° rotation, all spins also rotate in the same direction around the Z-axis, again with different rotational speeds; slower-rotating spins rotate slowly, and faster-rotating spins rotate rapidly. However, the initial position of each spin's rotation around the Z-axis (the phase immediately after rotating θ2°) is opposite to that before rotating θ2°. That is, the spin with a slower rotation speed and a delayed phase becomes a leading phase, and the spin with a faster rotation speed and a leading phase becomes a delayed phase. Therefore, after rotating θ2°, the phase difference between the spins decreases over time. As a result, the spins become synchronized after time τ. Thus, a spin echo (hereinafter referred to as the echo) is detected as a spin-based signal.

[0073] In the determination of relaxation time in diamond NV centers, microwave pulses are applied in a manner such as 90°-τ-180°-τ-90° to read the fluorescence intensity based on the excited electron spin. The transverse relaxation time T2 is, for example, measured using... Figure 7 The pulse sequence shown is used for measurement in the spin echo method. The method of observing signals using such a pulse sequence is called the Hahn echo method. Pulses P1 and P3 are pulses that rotate the electron spin at the NV center by 90° (π / 2) as described above. Pulse P2 is a pulse that rotates the electron spin at the NV center by 180° (π) as described above. Pulses P1, P2, and P3 are applied to the diamond spin sensor 100 at equal time intervals τ.

[0074] As described above, spin echoes are generated through local fluctuations in the magnetic field, caused by inhomogeneities in the pulsed magnetic field, spin-nuclear interactions, and spin-spin dipole interactions. Furthermore, the relaxation time can be determined by the magnitude of the attenuation of the echo intensity (fluorescence intensity) as the time interval τ changes. That is, if... Figure 7 The pulse sequence shown is repeatedly measured for echoes, and the echo intensity (peak value of the echo signal) is plotted over time to obtain, for example... Figure 8 A chart like the one shown. In Figure 8 In the graph, the solid line schematically represents the measured value (fluorescence intensity). The vertical axis is represented by arbitrary units (au). The horizontal axis is 2τ (twice the time interval τ). The dashed line is a graph obtained by fitting the measured values ​​to an exponential function. The transverse relaxation time T2 is the value of τ in which the value of the exponential function becomes 1 / e of its initial value. That is, the transverse relaxation time T2 represents the duration of the measured signal; a longer transverse relaxation time T2 allows for signal measurement over a longer period.

[0075] Regarding diamond spin sensors, the more NV centers that generate fluorescence, the stronger the observed fluorescence intensity. However, if defects, distortions, and impurities other than nitrogen that constitute the NV centers are present in the diamond single crystal, the generated fluorescence will be scattered and absorbed by these defects, distortions, and impurities. Therefore, the more defects, distortions, 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, distortions, and impurities (other than nitrogen) (X represents the degree of defects, distortions, or impurities (other than nitrogen), I∝1 / X). It should be noted that the fluorescence intensity also depends on the surface roughness of the diamond spin sensor (hereinafter referred to as surface roughness), but the influence of surface roughness can be eliminated by polishing the surface.

[0076] The fewer the number of NV centers, the longer the transverse relaxation time T2. The transverse relaxation time T2 is also affected by defects, distortions, and impurities (excluding nitrogen) in the crystal, just like fluorescence intensity. Defects, distortions, and impurities (excluding nitrogen) in the crystal act as interferences on the transverse relaxation time T2, and it is considered that the transverse relaxation time T2 is inversely proportional to the amount of defects, distortions, and impurities (excluding nitrogen) (T2∝1 / X).

[0077] (lateral relaxation time) )

[0078] Lateral relaxation time Use, for example Figure 9The pulse sequence shown is used for measurement. Excitation light is irradiated onto the diamond spin sensor 100 at predetermined intervals (time interval t1) to initialize the electron spin state. Then, at time interval t2, pulses P1 and P2 are applied to the diamond spin sensor 100 sequentially at time intervals τ. Then, at time interval t3, excitation light is irradiated onto the diamond spin sensor 100, and the emitted light (i.e., fluorescence) from the NV center is measured. Pulses P1 and P2 are pulses that rotate the electron spin at the NV center by 90° (π / 2) as described above. The method of measuring the signal using such a pulse sequence is called the Ramsey method.

[0079] If the time interval τ is varied and repeated... Figure 9 The fluorescence intensity was measured using the pulse sequence shown, and the following results were obtained: Figure 10 The graph shows the vibration. The horizontal axis represents the time interval τ between pulses P1 and P2, and the vertical axis represents the measured value of fluorescence intensity (in arbitrary units). The frequency of the vibration is determined by the difference between the microwave frequency and the resonant frequency of the NV center. Figure 10 The vibrations shown in the graph decay exponentially. This is because the resonant frequency of the NV center is influenced by the external magnetic field, temperature, and the spin of impurities in the diamond. 13 This is caused by the interaction of C's nuclear spin, etc. The transverse relaxation time can be calculated from the vibrational decay, similar to the transverse relaxation time T2 mentioned above. .

[0080] The fewer the number of NV centers, the shorter the lateral relaxation time. The larger the lateral relaxation time. The transverse relaxation time is affected by defects, distortions, and impurities (excluding nitrogen) in the crystal. These defects, distortions, and impurities act as interferences, affecting the transverse relaxation time. The effect is considered to be the transverse relaxation time. It is inversely proportional to the amount of defects, distortions, and impurities (other than nitrogen). ∝1 / X). Therefore, the fewer defects, distortions, and impurities (other than nitrogen) in a diamond crystal, the shorter the transverse relaxation time. (μsec) and NV - The product of the central concentration C (%) is specifically α = ( ) 1 / 3 The larger ×C is.

[0081] Reduce diamond 13 The content of C, that is, the content of C 12 Concentrating C increases the transverse relaxation time. Effective. However, it will increase or decrease... 13The preparation of carbon sources with C content and other diamond manufacturing processes increase manufacturing costs. Therefore, it is preferable to adjust the manufacturing process based on the transverse relaxation time. (Unit: μsec) and NV - The value α calculated from the center concentration C (unit: ppm) is suppressed to be less than a specified value. As will be seen from the embodiments described later, even if the value α is less than the specified value, a diamond spin sensor with a transverse relaxation time T2 of 15 μsec or more can be achieved. That is, α can be made less than 2.5. Therefore, the average phase difference across the entire surface of the diamond spin sensor 100, as described later, is made less than 6 nm / mm. Thus, the diamond... 13 Maintaining the natural abundance ratio of C content allows for an increase in the transverse relaxation time T2 without reducing the concentration of NV centers, enabling a sensor with higher sensitivity. α is preferably less than 1.5, more preferably less than 0.5. α is further preferably less than 0.3. α can also be less than 0.25. α is even more preferably less than 0.2. Even with a small α, the transverse relaxation time T2 can be maintained.

[0082] As mentioned above, the value 'a' depends on the number, or concentration, of NV centers. Figure 1 In the diamond spin sensor 100 shown, as long as NV - By achieving a concentration of 0.002 ppm or higher and 10 ppm or lower at the center, a smaller value α than previously possible can be achieved. Furthermore, the average phase difference across the entire surface of the diamond spin sensor 100 (described later) can be reduced to 2 nm / mm or lower. This allows for an increase in the transverse relaxation time T2 in the diamond spin sensor. Consequently, a sensor with higher sensitivity than previously possible can be realized.

[0083] The concentration of NV centers can also be above 0.002 ppm and below 0.3 ppm. This allows for a further increase in the transverse relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0084] It should be noted that NV in diamond - The concentration of NV centers can be calculated, for example, based on measurements using electron spin resonance (CW-ESR). Alternatively, at low concentrations, measurements can be taken by observing individual NV centers using a fluorescence microscope and counting them. At high concentrations, for diamonds containing low concentrations of NV centers, a concentration-to-fluorescence intensity conversion rate can be determined, and the concentration can be calculated from the fluorescence intensity ratio using this conversion rate. 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.

[0085] The lateral relaxation time T2 is preferably 25 μsec or more, more preferably 80 μsec or more. The lateral relaxation time T2 can also be 250 μsec or more. The lateral relaxation time T2 is even more preferably 300 μsec or more. This enables the realization of a sensor with higher sensitivity.

[0086] Lateral relaxation time It can also be greater than 0.05 μsec and less than 0.8 μsec. Lateral relaxation time Preferably less than 0.6 μsec, more preferably less than 0.5 μsec, and even more preferably less than 0.25 μsec. Therefore, it will not affect the measurement of the target object (alternating magnetic field, etc.) of AC.

[0087] (Average phase difference)

[0088] The average phase difference is explained below. Diamond is inherently an isotropic crystal structure with an isotropic refractive index (dielectric constant). However, in reality, diamond single crystals contain defects and distortions, resulting in birefringence. When circularly polarized light is irradiated onto a birefringent diamond, a phase difference is generated between the two orthogonally polarized light rays (linearly polarized light), transforming it into elliptically polarized light, which is then output. The optical axis and phase difference can be determined from the directions 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 obtained by integrating along the direction in which light passes through the diamond (e.g., the thickness direction of the diamond). Therefore, the phase difference is normalized to, for example, the thickness of the diamond, i.e., expressed as the phase difference (unit: nm / mm) equivalent to a thickness of 1 mm. The phase difference is measured locally and is distributed two-dimensionally within the measured surface. Therefore, the phase difference is represented by the average value within the measured surface (hereinafter referred to as the average phase difference). It should be noted that the "average value" does not mean the phase difference per unit area, but rather the value obtained by averaging the phase differences obtained from multiple local measurements within the surface. In other words, it refers to the average of the frequency distribution of the phase difference within the surface.

[0089] The average phase difference across the entire surface of the diamond spin sensor 100 can be less than 6 nm / mm, as described above. Furthermore, the average phase difference across the entire surface of the diamond spin sensor 100 can also be less than 2 nm / mm, as described above. This allows for a further increase in the transverse relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0090] (Half-width of the oscillating curve)

[0091] In the X-ray diffraction using the twin-crystal method described later, the first crystal is used from the cut-out Figure 1Another diamond crystal, cut from the original crystal of the diamond spin sensor 100 shown, is used as the second crystal. Measurements are performed using CuKα rays in a parallel configuration on the (004) plane. The half-width (angle) of the rocking curve of the diamond spin sensor 100 obtained from the measurement can also be less than 10 arcsec. This increases the transverse relaxation time T2. Therefore, a sensor with higher sensitivity than before can be achieved. It should be noted that half-width refers to the full half-width.

[0092] 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 distortions. To improve detection accuracy, the twin-crystal method is used. In the twin-crystal method, two crystals are used: a spectroscopic crystal (first crystal) and a sample crystal (second crystal) as the evaluation object. X-rays from the X-ray source are irradiated onto the first crystal, causing the resulting diffracted X-rays to be incident on the second crystal, and the angle of the second crystal is changed. The diffracted X-rays are measured using a detector. Let ω represent the incident angle of the diffracted X-rays on the second crystal (the angle between the diffracted X-rays and the plane of the second crystal), and let 2θ represent the angle between the direction of the detector and the incident direction of the diffracted X-rays on the second crystal. The first crystal and the detector are fixed, and a center of rotation is set on the surface of the second crystal. When the second crystal is rotated, the angle 2θ is fixed, and only the incident angle ω is changed, thereby measuring the diffracted X-rays. Thus, the diffraction intensity distribution on a sphere centered at the origin in reciprocal 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 (angle) of the rocking curve is proportional to the degree of rocking of the crystal orientation. By using crystals cut from the same diamond single crystal in both the first and second crystals, the half-value width (angle) of the rocking curve sensitively reflects the quality of the crystal being measured.

[0093] In the diamond spin sensor 100, the half-width at half-maximum (WWHM) of the X-ray diffraction rocking curve based on the dual-crystal method is preferably less than 8 seconds, more preferably less than 7 seconds. The WWHM of the X-ray diffraction rocking curve based on the dual-crystal method can also be less than 6 seconds. The WWHM of the X-ray diffraction rocking curve based on the dual-crystal method is even more preferably less than 5 seconds. This allows for a further increase in the transverse relaxation time T2. Therefore, a sensor with higher sensitivity than previously possible can be achieved.

[0094] exist Figure 1 In the diamond spin sensor 100 shown, the concentration of isolated vacancies relative to NV -The concentration ratio at the center can also be below 10%. An isolated vacancy is a vacancy in which no nitrogen exists in its vicinity. Isolated vacancies can be uncharged or negatively charged. Therefore, the concentration ratio can be determined by the sum of the number of uncharged and negatively charged vacancies relative to NV. - The proportion of centers is calculated. This increases the transverse relaxation time T2, enabling the development of a highly sensitive sensor. The density (concentration) of vacancies is neutral isolated vacancies (V... 0 The density of ) and isolated negative charge vacancies (V - The total density of the isolated vacancies is calculated based on the integral absorption of light at wavelengths of 741 nm and 394 nm induced at liquid nitrogen temperature (wavelength integral of absorption coefficient: unit is meV×cm). -1 The calculation is performed using the integral absorption A and density β (unit: cm). -3 The proportionality coefficient k (k=A / β) is 1.2×10 -16 and 4.8×10 -16 Furthermore, when the density of vacancies cannot be calculated from the absorption coefficient of the visible region, it can be calculated using positron annihilation. By calibrating (proportional calculation) the relative value of the density obtained by positron annihilation with the value of the region from which the density can be obtained from the absorption coefficient, low-concentration regions can also be converted into density.

[0095] In the diamond spin sensor 100, the concentration of isolated vacancies relative to NV - The concentration of the center is preferably 5% or less, more preferably 3% or less. The concentration of isolated vacancies relative to NV... - The concentration at the center can also be below 1%. This allows for a further increase in the transverse relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0096] (Dislocation defect)

[0097] As described above, when the concentration of NV centers is above 0.01 ppm and below 1.0 ppm, it is sufficient that the overall dislocation defects of the diamond spin sensor 100 detected by X-ray topography images are less than 10. Dislocation defects refer to linear defects in diamond caused by one or more deviations in the crystal arrangement, resulting in a boundary with the non-deviation portion. Fewer dislocation defects in the diamond can increase the transverse relaxation time T2, enabling the realization of a highly sensitive sensor.

[0098] Growth sectors and dislocation defects in diamond can be detected by X-ray diffraction. Specifically, MoKα1 rays (characteristic X-rays of molybdenum with wavelength λ = 0.71 Å (0.071 nm)) are used as X-rays, and an X-ray morphology image formed by diffraction through the (220) plane of a single-crystal diamond is captured using a Landau camera. To obtain the overall dislocation defects in the diamond, an X-ray morphology image is captured in the entire diamond substrate, and linear defects are counted. To more easily determine the distribution of defects, it is preferable to process the sample into a thin plate with a thickness of about 0.5 mm. For example, the single-crystal diamond can be cut into a thin plate using a laser processing machine, and the cut surface can be flattened by polishing with a scaif polishing disc. Alternatively, a slit can be set on the X-ray source side to obtain an X-ray morphology image formed by diffraction rays from only a limited layer inside the sample (limited projection topography). Thus, for thicker samples, it is not necessary to process them into a thin plate to evaluate the presence or absence of defects.

[0099] The number of dislocation defects detected in the diamond as a whole using X-ray morphology images is preferably 8 or less, more preferably 7 or less, and even more preferably 3 or less. The number of dislocation defects detected in the diamond as a whole using X-ray morphology images can also be 0 (i.e., no dislocation defects are detected). This allows for a further increase in the transverse relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0100] (Manufacturing method of diamond spin sensor)

[0101] right Figure 1 The manufacturing method of the diamond spin sensor 100 shown will be described. Granular diamond is used as seed crystal, and synthetic diamond is produced by temperature difference under high pressure. A portion of the synthetic diamond is selected and cut out as seed crystals for subsequent processes.

[0102] Figure 11 The diagram shows the configuration of an apparatus for synthesizing diamond via a temperature difference method under high pressure. In the temperature difference method, crystals are grown using the difference in solubility of diamond relative to a solvent caused by a temperature difference. (Refer to...) Figure 11 A longitudinal temperature gradient is formed within a pressure medium 250 containing a graphite heater 252 and an insulating component 254. The insulating component 254 is placed in a high-temperature section, a seed crystal 300 is placed in a low-temperature section, and a solvent metal 258 is placed between them. The process is maintained at a temperature above the melting point of the solvent metal 258 and a pressure above the pressure at which diamond is thermally stable, thereby growing single-crystal diamond on the seed crystal 300. Diamond powder is preferably used as the carbon source 256. Alternatively, graphite or pyrolytic carbon can also be used as the carbon source 256. It should be noted that the carbon source 256 is not subjected to…12 Concentration of C, in carbon source 256 12 C and 13 The carbon ratio is the same as the natural abundance ratio. The solvent metal 258 uses one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn), or alloys containing these metals. By pressurizing the solvent metal 258 with external force through a pressure medium 250 (not shown) and heating it with a graphite heater 252, the pressure for thermodynamic stability of diamond and the temperature conditions for eutectic melting of the solvent metal 258 and carbon are achieved. Carbon melts from the carbon source 256 in the high-temperature section into the solvent metal 258 and diffuses to the low-temperature section below the solvent metal 258, where it grows on the seed crystal 300 to form synthetic diamond 302.

[0103] (First process)

[0104] First, a single-crystal diamond with a nitrogen concentration of less than 30 ppm is prepared. In the above-described method for synthesizing high-pressure single-crystal diamond, a single-crystal diamond with a nitrogen concentration of less than 30 ppm can be produced by adding a nitrogen getter to the solvent metal 258. Therefore, in the second step described later, a seed crystal with a single growth sector and fewer than 10 dislocation defects as detected by X-ray morphology can be cut.

[0105] The growth sector can be identified using a two-dimensional fluorescence image (area distribution image) of PL (Photo luminescence: a luminescent image formed by irradiation with ultraviolet light) or CL (Cathodo luminescence: a luminescent image formed by irradiation with an electron beam). That is, it can be determined based on whether the boundaries of regions with different fluorescence intensities are linear (see Patent Document 3).

[0106] Dislocations are measured, for example, by an etching test (see Patent Document 4). 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 ​​1000μm × 1000μm, and the number of pits per 1mm is obtained. 2 The number of pits. Pits refer to the pit-like depressions present on the surface of a single-crystal diamond. Pits correspond to dislocation defects. The pit-like depressions are quadrilaterals, rounded quadrilaterals, or roughly circular on the (100) face of a single-crystal diamond, and triangular, rounded triangulars, or roughly circular on the (111) face. The span of the pit-like depressions is approximately 1 μm to 50 μm. By measuring each 1 mm 2 The number of pits was magnified 100 times, and the number of pits per 1 cm was calculated.2 The number of pitting defects (dislocation density). It should be noted that linear pits are sometimes observed along with pitting defects on the surface of etched single-crystal diamond. Linear pits originate from stacking faults in single-crystal diamond. The number of linear pits is not included in the determination of dislocation defects.

[0107] Dislocations can also be detected by X-ray morphology (see Patent Document 5). In the case of transmission X-ray measurement using radiometric X-rays, 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, in the case of reflection measurement, X-rays with a wavelength of 0.96 Å (0.096 nm) can be 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 be changed for imaging. The measurement can also be performed using an X-ray diffraction apparatus in a laboratory system, for example, using a Mo-ray source to observe (111) diffraction and a Cu-ray source to observe (113) diffraction. A CCD (Charge Coupled Device) camera can also be used for the measurement, but a core plate is preferred for improving resolution. After developing the core plate, an image is acquired using an optical microscope, thereby enabling the identification and quantification of dislocations.

[0108] In the synthesis of single-crystal diamond using the temperature difference method, for example, the composition of the solvent metal 258 is set as 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 so that the temperature difference between the carbon source 256 and the seed crystal 300 is 10°C to 25°C, and the conditions of pressure 5.0 GPa to 5.5 GPa and temperature 1300°C to 1350°C are maintained for 80 hours to 250 hours. Therefore, referring to... Figure 12 Synthetic diamond 302 was synthesized from seed crystal 300. If the temperature difference exceeds 25°C, crystal growth becomes disordered, tending to result in the inability to observe growth traces on adjacent crystal faces. If the temperature difference is less than 10°C, the growth time required to grow crystals of the specified size becomes long, raising manufacturing costs. Furthermore, the temperature variation during the holding period is controlled within 3°C. This further improves crystallinity. If the temperature variation exceeds 3°C, growth becomes unstable, leading to crystal defects, distortions, and inclusions, thus reducing crystallinity.

[0109] (Second process)

[0110] Cutting diamond 304 (see reference) is produced from single-crystal diamond synthesized through the first process. Figure 12The seed facet of the diamond 304 used as the seed facet is preferably quadrilateral or octagonal, but is not limited to this. The size of the seed facet (e.g., the length of opposite sides) is preferably 0.3 mm or more and 3 mm or less. The seed facet 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 and finished to a surface roughness Ra of 20 nm or less. Then, it is preferable to cut into 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. Larger sizes are easier to avoid dislocation defects and obtain a single sector, which is preferred. When the diamond 304 is a cuboid and the plane of its seed facet is the (001) crystal plane, one side of the rectangle used as the seed facet is parallel to the <100> direction or the <010> direction. If the plane used as the seed face is the (111) crystal plane, then one side of the rectangle used as the seed face 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 face that has less damage can be obtained.

[0111] In single-crystal diamond synthesized using the temperature difference method, numerous dislocation defects exist along the principal face direction of the seed crystal and in directions deviating from its orientation by approximately X°. For example, when the principal face direction is the <001> direction, dislocation defects are abundant in the four directions with a deviation angle of approximately 35° (i.e., X=35): <112>, <-112>, <1-12>, and <-1-12>. Furthermore, when the principal face direction is the <111> direction, dislocation defects are abundant in the three directions with a deviation angle of approximately 19.5° (i.e., X=19.5): <112>, <121>, and <211>. In the above description of directions with a deviation angle of X°, when the principal face direction is inconsistent with either the <001> or <111> direction, the deviation angle will deviate somewhat, hence expressed as X°. When they are inconsistent, the deviation angle becomes the angle corrected from 35° or 19.5°. The individual sectors, excluding the deviation angles and the ±5° direction of the main face, contain high-quality crystals with few crystal defects. Furthermore, the boundaries between different sectors, such as the {001} sector and the {111} sector, exhibit significant crystal distortion, making them prone to defects. If the seed substrate is enlarged, the interval between deviation angles originating from the seed substrate increases, and the boundaries of different sectors shift towards the ends, thus increasing the size of the high-quality crystal. Here, the {abc} sector refers to the region where growth is stacked on the {abc} surface. For example, the {001} sector refers to the region where growth is stacked on the {001} surface. Therefore, in this second process, by cutting the diamond 304 from a single growth sector of the synthetic diamond 302 that is grown on the main face (excluding the ±5° direction of the seed crystal's main face growth), a seed crystal with few defects can be obtained.

[0112] If the seed substrate is enlarged, the size of the high-quality crystal can also be increased. For example, a seed crystal with fewer than 10 dislocations as detected by X-ray morphology can be cut. Single-crystal diamond synthesized using this seed crystal and subsequent processes has fewer defects and further reduced distortion. The single growth sector for synthesizing diamond 302 is a main face growth region other than ±5° of the seed crystal's main face growth direction, such as sector {001} or sector {111}. Alternatively, any crystallographically possible sector other than these (sector {113}, sector {115}, sector {110}, or sector {135}) can be used, as long as it is a single growth sector grown on a main face other than ±5° of the seed crystal's main face growth direction. When cutting a seed crystal, diamond 304, from synthetic diamond 302 can be used, it can be cut from a single sector or from two or more sectors, provided it does not contain areas with many dislocation defects. That is, the cut diamond 304 may or may not include sector boundaries. In single-crystal diamond, the region of each sector can be determined using a light-emitting image (ultraviolet-excited light-emitting image) formed by irradiation with ultraviolet light.

[0113] (Third process)

[0114] Using the seed crystals cut in the second process, diamond is synthesized via the temperature difference method as described above. That is, referring to... Figure 13 Using cut diamond 304 as seed crystal 310, synthetic diamond 312 is synthesized. This allows for the production of single-crystal diamonds with reduced crystal defects and distortion.

[0115] Specifically, refer to Figure 11 Diamond powder is used as the carbon source 256. Iron or cobalt, which have high solubility and good affinity for carbon, are used as the solvent metal 258. Depending on the synthesis conditions, trace amounts of nickel or manganese may be introduced into the diamond. The amount of boron impurities in the carbon source 256 and solvent metal 258 is controlled to be below 1 ppm. This allows the atomic number basis of boron (B) in the single-crystal diamond to 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 of nitrogen in the single-crystal diamond to be above 0.1 ppm and below 10 ppm. 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.

[0116] As conditions 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 pressure is maintained at 5.0 GPa or more and 5.5 GPa or less, and the temperature is maintained at 1300°C or more and 1350°C or less for 80 hours or more and 300 hours or less. If the temperature difference exceeds 25°C, the crystal growth becomes slightly disordered, and the growth of adjacent crystal planes is mostly not observed. In addition, by controlling the temperature change during the holding period to within 3°C, the crystallinity is further improved.

[0117] (Fourth process)

[0118] Synthetic diamond 312 synthesized through the third process (see reference) Figure 13 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.

[0119] (Fifth process)

[0120] An electron beam with an energy of 300 keV or higher and 1.2 MeV or lower is irradiated onto the cut diamond 318, which is cut from synthetic diamond 312 through the fourth process. This ionizes the orbital electrons of carbon atoms in the cut diamond 318, knocking out carbon nuclei and creating vacancies within the cut diamond 318. It should be noted that 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 (Noise, Vibration, and Acidity). - The quantity is in 1×10 18 cm -2 ~4×10 19 cm -2 It varies within a certain range.

[0121] (Sixth process)

[0122] The diamond 318 that has undergone the fifth process is annealed in a vacuum at a temperature of 1100°C or higher and 1400°C or lower for 0.1 hours or less and 0.5 hours or less. This causes the nitrogen in the diamond 318 to move, forming NV centers composed of nitrogen and vacancies.

[0123] In summary, using 12 C and 13 A carbon source 256 with the same C ratio as its natural abundance ratio can be used to manufacture a diamond spin sensor 100 that is larger than before and has an increased transverse relaxation time T2 without reducing the C concentration at the NV center. Therefore, it is possible to suppress the decrease in fluorescence intensity and realize a sensor with higher sensitivity.

[0124] The irradiation step in the fifth process and the annealing step in the sixth process can be repeated more than twice. This allows the desired amount of NV centers to be formed in the cut diamond 318.

[0125] As described above, a nitrogen getter is used in the third process. The nitrogen getter can contain any one of titanium (Ti), zirconium (Zr), hafnium (Hf), aluminum (Al), gallium (Ga), copper (Cu), silver (Ag), and gold (Au). This increases the transverse relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0126] As mentioned above, the diamond 318 cut can also include only one sector boundary, or no sector boundary at all. This increases the lateral relaxation time T2, enabling the realization of a sensor with higher sensitivity.

[0127] It should be noted that, referring to Figure 14 Alternatively, a larger seed crystal 320 can be used to perform the above synthesis steps (refer to the third step). For example, in the rectangular seed crystal 320, the length L of one side of the rectangle of the (001) crystal face or the (111) crystal face is 3 mm or more. As a result, the sector boundary 324, which is prone to impurities, can be moved away from the center 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. The cut diamond 328 is subjected to electron beam irradiation (fifth step) and annealing (sixth step) as described above. As a result, a larger diamond spin sensor 100 can be manufactured.

[0128] Figure 15 The image schematically illustrates the diamond synthesized as described above. Figure 15 It is a top view of the (001) plane. Figure 15 The left and right directions are <100> directions. The triangular regions at the four corners, i.e., sector 332, represent sector (111). The boundaries of different sectors become the boundaries of sectors with different impurity concentrations (refer to the dot pattern), thus forming distortion and introducing impurities. For example Figure 14 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 15 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, the entire sector 330, which is sector (111), can also be used as a seed crystal to fabricate a diamond spin sensor.

[0129] As a comparative example Figure 16 The image shows synthetic diamond used in NV's previous spin sensors. Figure 16 Is with Figure 15 Same top view. Sector 342 is sector (111). It can be seen that in Figure 16 In synthetic diamond, large sector boundaries with varying impurity concentrations are formed around the largest (001) sector 340 (refer to the dot pattern), making it impossible to cut out a sufficiently large area for a diamond spin sensor. This is because, as with sectors like (001) and (111), different sectors form boundaries.

[0130] Example 1

[0131] The effectiveness of the diamond spin sensor of this disclosure is demonstrated below through examples. Using multiple diamond spin sensors fabricated by the above manufacturing method, the transverse relaxation time T2 and... and NV center concentration C. Manufacturing conditions are shown in Figure 17 The measurement results are shown in Figure 17 and Figure 18 .

[0132] exist Figure 17 In this study, diamond seed crystals of a specified size cut from synthetic diamond produced as described above using a laser processing machine (refer to the second process) are shown as samples 1 to 8. For example, samples 1, 2, 5, and 6 are seed crystals of 3.0 mm × 3.0 mm × 1.0 mm. Sample 9 is a commercially available synthetic diamond (DNV-B14 manufactured by Element Six) produced by CVD (Chemical Vapor Deposition). It should be noted that samples 7 and 8 were cut from diamond produced under conditions of high nitrogen concentration and are positioned as comparative examples along with sample 9. Various crystals were cut from... Figure 17 The cutting is performed within the sector listed in the "Seed Crystal Cutting Sector" column. In the "Seed Crystal Cutting Sector" column, "(100)" refers to cutting from sector (100). Additionally, "(100) + (111)" refers to cutting in a manner that includes both sectors (100) and (111). X-ray morphology images were used to confirm the presence of defects in the obtained diamond seed crystal. The number of dislocation defects confirmed is shown in... Figure 17 In the "Dislocation Defects" section, the number of dislocation defects in samples 1 to 6 is very small compared to samples 7 and 8. This is because the nitrogen concentration in the diamond seed crystal is low.

[0133] Next, diamond crystals were grown on the aforementioned diamond seed crystal using a temperature difference method to obtain single-crystal diamonds for each sample (refer to step three). This is in Figure 17The results are shown as HPHT (High-Pressure High-Temperature). The carbon source used is diamond powder containing 100 ppm to 200 ppm nitrogen and 0.5 ppm to 1 ppm boron as impurities. The solvent metals used are high-purity iron (Fe) and cobalt (Co), with a solvent composition of Fe:Co = 55:45 (weight ratio). 1.75% by mass of titanium was added to the solvent metal. The conditions for the temperature difference method for each sample were as follows: titanium was used as the nitrogen getter; the temperature difference between the high-temperature section (carbon source) and the low-temperature section (seed crystal) was 23°C; the pressure was 5.3 GPa; the holding temperature of the low-temperature section was 1350°C; and the holding time was 150 hours.

[0134] Then, steps four through six described above are performed to fabricate multiple diamond spin sensors. The electron beam irradiation energy is 0.95 MeV, and the electron beam irradiation dose is 1 × 10⁻⁶. 18 cm -2 The annealing temperature was 950℃, and the annealing time was 60 minutes. The diamond cut through the fourth process is shown below. Figure 17 In the "Stering Method of Sensor Materials" section, regarding the "Location of Growth Sector," "above" indicates... Figure 15 The slash part, "upper + adjacent" indicates Figure 15 The dashed line represents the measured nitrogen concentration (unit: ppm) and NV. - The central concentration (unit: ppm) is shown in the "N Concentration" column and "NV" column, respectively. - In the "Concentration" column, the N concentration and NV concentration of samples 1 to 6 are shown. - The concentrations were all lower than those of samples 7 and 8.

[0135] The transverse relaxation time T2 and the transverse relaxation time were measured using a fabricated diamond spin sensor. The results are shown in Figure 18 Samples 1 to 9 and Figure 17 Same. Figure 18 In this context, phase difference represents the average phase difference over the entire surface (unit: nm / mm). Xrc represents the half-width of the rocking curve of X-ray diffraction (unit: arcsec). (V 0 +V - ) / NV - This refers to the sum of the number of uncharged isolated vacancies and the number of negatively charged isolated vacancies relative to NV. - The proportion of centers. α refers to the transverse relaxation time. (Unit: μsec) and NV - The central concentration C (unit: ppm) is determined by α = ( ) 1 / 3 The value calculated by ×C.

[0136] Depend on Figure 18 It can be seen that the product α of samples 1 to 6 is smaller than that of samples 7 to 9, enabling the achievement of a longer transverse relaxation time T2. NV - The central concentration has an impact on this. Specifically, the NV of samples 1 through 6... - The central concentration ratio of NV in samples 7 to 9 - The central concentration is low. Therefore, the transverse relaxation time T2 of samples 1 to 6 is longer than that of samples 7 to 9.

[0137] Regarding the product α, samples 1 to 6 all achieve α < 2.5. Sample 6 achieves α < 0.25. Regarding the transverse relaxation time T2, samples 1 to 6 all achieve T2 ≥ 15. Sample 6 achieves T2 ≥ 250. It can be seen from samples 1 to 6 that the smaller the product α, the longer the transverse relaxation time T2 can be achieved.

[0138] Regarding lateral relaxation time Samples 4 and 5 achieved times greater than 0.05 μsec and less than 0.8 μsec. Regarding NV... - The central concentration for samples 1 through 6 was above 0.002 ppm and below 10 ppm. Sample 6 achieved a concentration above 0.02 ppm and below 0.3 ppm. (Regarding V) 0 +V - ) / NV - Samples 1 through 6 all achieved less than 10%, and samples 1 and 6 achieved less than 1%.

[0139] Regarding the average phase difference across the entire surface, samples 1 through 6 all achieved an average phase difference below 6 nm / mm. Samples 1 and 6 achieved an average phase difference below 2 nm / mm. Regarding the half-width of the rocking curves from X-ray diffraction based on the dual-crystal method, samples 1 through 6 all achieved a half-width of less than 10 seconds. Samples 1, 5, and 6 achieved a half-width of less than 6 seconds. Regarding the number of dislocation defects (refer to...). Figure 17 Samples 1 through 6 all achieved fewer than 10 results, while samples 5 and 6 achieved 0 results.

[0140] The present disclosure has been described above by way of example, but the above embodiments are merely illustrative and the present disclosure is not limited to the above embodiments. The scope of the present disclosure is set forth in the claims based on the detailed description of the invention, and includes all modifications within the meaning and scope of the language used in the claims.

[0141] Explanation of reference numerals in the attached figures

[0142] 100: Diamond Spin Sensor

[0143] 102: First Page

[0144] 104: First side

[0145] 202: Electromagnetic wave irradiation section

[0146] 204: Excitation light

[0147] 206: Fluorescence

[0148] 210: Excitation Light Generator

[0149] 212: Filter

[0150] 214: Concentrating element

[0151] 216: Optical waveguide

[0152] 218: LPF

[0153] 220: Optical Detection Department

[0154] 230: Control Department

[0155] 232: Electromagnetic wave generation unit

[0156] 250: Pressure medium

[0157] 252: Graphite heater

[0158] 254: Insulating components

[0159] 256: Carbon source

[0160] 258: Solvent metal

[0161] 300, 310, 320: Seed Crystals

[0162] 302, 312, 322: Synthetic diamond

[0163] 304, 318, 328: Cutting diamonds

[0164] 314, 324: Sector boundaries

[0165] 316, 326, 330, 332, 340, 342: Sectors

[0166] A1, A2, A3, A4, A5, A6, A7, A8: points

[0167] C: Carbon

[0168] L: Length

[0169] N: Nitrogen

[0170] P1, P2, P3: Pulse

[0171] t, t1, t2, t3, τ: time intervals

[0172] V: Empty space

[0173] X, Y, Z: Axes

[0174] Δf: Frequency difference :angle.

Claims

1. A diamond spin sensor comprising diamond, said diamond containing NV with electron spin - center, Let the transverse relaxation time of the electron spin, determined using the Ramsey method, be defined as... μsec, the NV in the diamond - The concentration at the center was set to Cppm, using the aforementioned and the aforementioned C through ( ) 1 / 3 The value α calculated by ×C is less than 2.

5. The transverse relaxation time of the electron spin, determined using the Hahn echo method, is defined as T2 μsec, where T2 is 15 or more. The average phase difference across the entire surface of the diamond is less than 6 nm / mm.

2. The diamond spin sensor according to claim 1, wherein, The value α is less than 0.

25.

3. The diamond spin sensor according to claim 1 or 2, wherein, The NV - The concentration at the center is above 0.002 ppm and less than 10 ppm. The average phase difference is less than 2 nm / mm.

4. The diamond spin sensor according to any one of claims 1 to 3, wherein, The T2 is 250 or higher.

5. The diamond spin sensor according to any one of claims 1 to 4, wherein, The NV - The concentration at the center is above 0.002 ppm and less than 0.3 ppm.

6. The diamond spin sensor according to any one of claims 1 to 5, wherein, The It is greater than 0.05 and less than 0.

8.

7. The diamond spin sensor according to any one of claims 1 to 6, wherein, The half-width of the rocking curves of X-ray diffraction based on the dual-crystal method is less than 10 seconds.

8. The diamond spin sensor according to any one of claims 1 to 7, wherein, The half-width of the rocking curve based on the dual-crystal method of X-ray diffraction is less than 6 seconds.

9. The diamond spin sensor according to any one of claims 1 to 8, wherein, The diamond as a whole, detected by X-ray morphology imaging, has fewer than 10 dislocation defects.

10. The diamond spin sensor according to any one of claims 1 to 9, wherein, The diamond as a whole was found to have 0 dislocation defects using X-ray topography images.

11. The diamond spin sensor according to any one of claims 1 to 10, wherein, The concentration of isolated vacancies in the diamond relative to the NV - The concentration at the center is less than 10%.

12. The diamond spin sensor according to claim 11, wherein, The percentage is less than 1%.

Images