Synthetic single-crystal diamond and its manufacturing method

Abstract

This invention relates to a synthetic single-crystal diamond containing 100 ppm to 1500 ppm of nitrogen atoms. The synthetic single-crystal diamond comprises an aggregate containing one vacancy and 2 to 4 nitrogen atoms adjacent to that vacancy. Regarding the diagonal of the Knoop indentation in the <110> direction within the {001} plane of the synthetic single-crystal diamond, the ratio of the length b of the shorter diagonal to the length a of the longer diagonal, b / a, is 0.08 or less. The Knoop indentation is formed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9 N, by measuring the Knoop hardness of the synthetic single-crystal diamond in the <100> direction within the {001} plane.

Description

Technical Field

[0001] This invention relates to a synthetic single-crystal diamond and a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2020-113054, filed June 30, 2020. All contents described in that Japanese patent application are incorporated herein by reference. Prior Technology

[0002] Due to its high hardness, single-crystal diamonds are widely used in cutting tools, grinding tools, and wear-resistant tools. The single-crystal diamonds used in tools include both natural and synthetic diamonds.

[0003] Most natural diamonds contain aggregated nitrogen atoms (Type Ia) as impurities. When diamonds are used in tools, these aggregated nitrogen atoms in the diamond crystal prevent plastic deformation or crack propagation. Therefore, natural diamonds have higher mechanical strength. However, due to significant variations in quality and unstable supply, the use of natural diamonds for industrial purposes is limited.

[0004] On the other hand, synthetic diamonds, due to their certain quality and stable supply, can be widely used in the industrial field.

[0005] Synthetic diamonds typically contain isolated substituted nitrogen atoms (Ib type) as impurities. The higher the concentration of isolated substituted nitrogen atoms in a diamond crystal, the worse its mechanical properties tend to be. Therefore, when Ib type synthetic diamonds are used in tools, tip wear or chipping often occurs.

[0006] Furthermore, there are also synthetic diamonds that contain almost no nitrogen impurities (Type IIa). Because Type IIa synthetic diamonds do not contain impurities or crystal defects that prevent crack propagation, they are prone to tip chipping when used as tools.

[0007] Therefore, in synthetic diamonds, research has been conducted on techniques to improve wear resistance or damage resistance.

[0008] For example, Patent Document 1 (International Publication No. 2019 / 077888) discloses a synthetic single-crystal diamond with high hardness and excellent resistance to defects. [Previous Technical Documents] [Patent Literature]

[0009] [Patent Document 1] International Publication No. 2019 / 077888 Summary of the Invention

[0010] [The problem that this invention aims to solve] In recent years, due to the increasing demand for longer-lasting tools, there is a need for synthetic single-crystal diamonds with superior wear resistance and chip resistance.

[0011] Therefore, the purpose of this invention is to provide a synthetic single-crystal diamond with high hardness, high elastic recovery rate, and excellent resistance to defects.

[0012] The synthetic single-crystal diamond of this invention contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm, and The aforementioned synthetic single-crystal diamond comprises an aggregate containing one vacancy and any number of nitrogen atoms, ranging from two to four, adjacent to the vacancy. Regarding the aforementioned synthetic single-crystal diamond within the {001} plane <110> The ratio of the length b of the shorter diagonal to the length a of the longer diagonal in the Knoop indentation in the direction of the indentation is less than 0.08, and... The above-mentioned Knoop indentation was performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9 N on the synthetic single-crystal diamond in the {001} plane. <100> It is formed by measuring the Knoop hardness in the direction.

[0013] The method for manufacturing synthetic single-crystal diamond of the present invention is the same as the above-mentioned method for manufacturing synthetic single-crystal diamond, comprising: The first step involves synthesizing diamond single crystals using a solvent-metal temperature difference method. These diamond single crystals contain nitrogen atoms at a concentration of 100 ppm to 1500 ppm. Step 2 involves irradiating the aforementioned diamond single crystal with one or both of an electron beam and a particle beam with an energy of 100 MGy to 1000 MGy; and The third step involves applying a pressure of 5 GPa or higher and a temperature of 2300°C or higher but less than 2600°C to the diamond single crystal obtained after the second step for a period of 1 minute to 3600 minutes, thereby obtaining a synthetic single crystal diamond. [Effects of the Invention]

[0014] According to the present invention, a synthetic single-crystal diamond with high hardness, high elastic recovery rate, and excellent resistance to chipping can be provided. Simple Explanation of the Diagram

[0015] Figure 1 is a diagram used to illustrate Knoop indentation. Figure 2 is a schematic cross-sectional view showing an example of the sample chamber configuration used in the manufacture of synthetic single-crystal diamond according to one embodiment of the present invention. Implementation

[0016] [Description of Embodiments of the Invention] First, embodiments of the present invention will be described and illustrated. (1) The synthetic single-crystal diamond of this invention contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm, and The aforementioned synthetic single-crystal diamond comprises an aggregate containing one vacancy and any number of nitrogen atoms, ranging from two to four, adjacent to the vacancy. Regarding the aforementioned synthetic single-crystal diamond within the {001} plane <110> The ratio of the length b of the shorter diagonal to the length a of the longer diagonal in the Knoop indentation in the direction of the indentation is less than 0.08, and... The above-mentioned Knoop indentation was performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9 N on the synthetic single-crystal diamond in the {001} plane. <100> It is formed by measuring the Knoop hardness in the direction.

[0017] The synthetic single-crystal diamond of this invention has high hardness, high elastic recovery rate, and excellent resistance to chipping.

[0018] (2) Preferably, the infrared absorption spectrum of the above-mentioned synthetic single crystal diamond has an absorption peak in the range of wavenumber 1175±2 cm-1.

[0019] In this way, synthetic single-crystal diamonds can achieve higher hardness, greater elastic recovery rate, and excellent resistance to chipping.

[0020] (3) Preferably, in the fluorescence spectrum of the above-mentioned synthetic single crystal diamond, there is a emission peak in one or both of the following ranges: fluorescence wavelength 503±2 nm and fluorescence wavelength 510 nm to 530 nm.

[0021] In this way, synthetic single-crystal diamonds can achieve higher hardness, greater elastic recovery rate, and excellent resistance to chipping.

[0022] (4) Preferably, in the fluorescence spectrum of the above-mentioned synthetic single crystal diamond, there is a fluorescence peak in one or both of the following ranges: fluorescence wavelength 415±2 nm and fluorescence wavelength 420 nm to 470 nm.

[0023] In this way, synthetic single-crystal diamonds can achieve higher hardness, greater elastic recovery rate, and excellent resistance to chipping.

[0024] (5) Preferably, an absorption peak exists in the infrared absorption spectrum of the above-mentioned synthetic single crystal diamond in the range of wavenumber 1282±2 cm-1.

[0025] In this way, synthetic single-crystal diamonds can achieve higher hardness, greater elastic recovery rate, and excellent resistance to chipping.

[0026] (6) Preferably, the infrared absorption spectrum of the above-mentioned synthetic single crystal diamond has an absorption peak in the range of wavenumber above 1370 cm-1 and below 1385 cm-1.

[0027] In this way, synthetic single-crystal diamonds can achieve higher hardness, greater elastic recovery rate, and excellent resistance to chipping.

[0028] (7) The above-mentioned synthetic single-crystal diamond is within the {001} plane. <100> The ideal Knoop hardness in the direction is above 100 GPa.

[0029] In this way, synthetic single-crystal diamonds can have excellent wear resistance.

[0030] (8) In the destructive strength test of pressing a spherical diamond indenter with a front radius of 50 μm against the surface of the above-mentioned synthetic single crystal diamond at a load speed of 100 N / min, the crack initiation load is preferably above 17 N.

[0031] In this way, synthetic single-crystal diamonds can have excellent resistance to defects.

[0032] (9) The method for manufacturing synthetic single-crystal diamond of the present invention is the same as the above-mentioned method for manufacturing synthetic single-crystal diamond, comprising: The first step involves synthesizing diamond single crystals using a solvent-metal temperature difference method. These diamond single crystals contain nitrogen atoms at a concentration of 100 ppm to 1500 ppm. Step 2 involves irradiating the aforementioned diamond single crystal with one or both of an electron beam and a particle beam with an energy of 100 MGy to 1000 MGy; and The third step involves applying a pressure of 5 GPa or higher and a temperature of 2300°C or higher but less than 2600°C to the diamond single crystal obtained after the second step for a period of 1 minute to 3600 minutes, thereby obtaining a synthetic single crystal diamond.

[0033] This allows for the production of synthetic single-crystal diamonds with high hardness, high elastic recovery, and excellent resistance to defects.

[0034] [Details of the embodiments of the present invention] <The Forms in which Nitrogen Atoms Exist in Diamond Crystals> First, in order to deepen the understanding of the synthetic single-crystal diamond of the present invention, one of the main factors determining the properties of diamond will be explained, namely, the nitrogen atoms present in the crystal as impurities.

[0035] Nitrogen atoms in diamond crystals can be classified according to their form of existence as isolated substituted nitrogen atoms or aggregated nitrogen atoms, etc.

[0036] The so-called isolated substitutional nitrogen atom (C center) refers to a nitrogen atom that replaces a carbon atom in the diamond crystal as a unit of one atom, thus existing in the position of a carbon atom in the diamond crystal.

[0037] The inventors hypothesize that if a diamond crystal contains isolated substituted nitrogen atoms, it will generate local tensile stress in the surrounding lattice. This stress becomes the starting point for plastic deformation or failure, thereby reducing hardness and causing a decrease in wear resistance or damage resistance.

[0038] Synthetic single-crystal diamond containing isolated substituted nitrogen atoms exhibits an absorption peak near wavenumber 1130 cm⁻¹ (i.e., wavenumber 1130 ± 2 cm⁻¹) in its infrared absorption spectrum measured by Fourier transform infrared spectroscopy.

[0039] Because synthetic single-crystal diamonds containing isolated substituted nitrogen atoms possess unpaired electrons originating from nitrogen atoms, the concentration of isolated substituted nitrogen atoms can be determined using ESR (Electron Spin Resonance) analysis. In addition to detecting isolated substituted nitrogen atoms, ESR also detects signals such as crystal defects with unpaired electrons. In such cases, isolated substituted nitrogen atoms can be separated and detected based on the g-value or the relaxation time of the signal.

[0040] Aggregated nitrogen atoms refer to two or more nitrogen atoms that exist aggregated in diamond crystals.

[0041] The inventors hereby hypothesize that when a load is applied to a diamond crystal, the aggregated nitrogen atoms within the diamond crystal can suppress the plastic deformation or crack propagation that occurs at this time. Furthermore, the inventors hypothesize that if the diamond crystal contains aggregated nitrogen atoms, the diamond crystal's hardness increases, its elastic deformability increases, and its resistance to chipping improves.

[0042] Aggregated nitrogen atoms exist in A centers (nitrogen atom pairs), H3 centers (nitrogen 2-atom aggregation), N3 centers (nitrogen 3-atom aggregation), B centers (nitrogen 4-atom aggregation), and B' centers (small plates).

[0043] The term "A-center" (nitrogen atom pair) refers to a condensed aggregate containing two nitrogen atoms covalently bonded together, with each nitrogen atom replacing a carbon atom that constitutes the diamond crystal. Diamonds containing A-centers (nitrogen atom pairs) are called type IaA. Synthetic single-crystal diamonds containing A-centers (nitrogen atom pairs) exhibit an absorption peak near wavenumber 1282 cm⁻¹ (e.g., wavenumber 1282 ± 2 cm⁻¹) in their infrared absorption spectra measured by Fourier transform infrared spectroscopy.

[0044] An H3 center (nitrogen 2-atom condensation) refers to a condensation containing one vacancy and two nitrogen atoms adjacent to that vacancy, each nitrogen atom replacing a carbon atom that constitutes a diamond crystal. In this specification, "nitrogen atom adjacent to the vacancy" means the nitrogen atom with the shortest atomic distance to the carbon atom at the vacancy location (i.e., the nearest neighbor). The same meaning applies to the N3 center and B center described below.

[0045] Synthetic single-crystal diamond containing H3 centers (nitrogen 2-atom aggregates) exhibits emission peaks in the fluorescence spectrum obtained by irradiation with excitation light of approximately shorter than 500 nm, such as 325 nm, in one or both of the following ranges: near a fluorescence wavelength of 503 nm (e.g., 503 ± 2 nm) and between a fluorescence wavelength of 510 nm and 530 nm.

[0046] An N3 center (nitrogen 3-atom condensation) refers to a condensation containing one vacancy and three nitrogen atoms adjacent to that vacancy, with each nitrogen atom replacing a carbon atom that constitutes a diamond crystal.

[0047] Synthetic single-crystal diamonds containing N3 centers (condensation of nitrogen 3 atoms) exhibit emission peaks in the fluorescence spectrum obtained by irradiation with excitation light of approximately shorter than 410 nm, such as excitation light with a wavelength of 325 nm, in one or both of the following ranges: near a fluorescence wavelength of 415 nm (e.g., fluorescence wavelength 415 ± 2 nm) and fluorescence wavelengths above 420 nm and below 470 nm.

[0048] B-center (nitrogen 4-atom condensation) refers to a condensation containing one vacancy and four nitrogen atoms adjacent to that vacancy, with each nitrogen atom replacing a carbon atom that constitutes a diamond crystal.

[0049] Diamonds containing B centers (nitrogen 4-atom aggregates) are called type IaB. Synthetic single-crystal diamonds containing nitrogen 4-atom aggregates show an absorption peak near wavenumber 1175 cm⁻¹ (e.g., wavenumber 1175 ± 2 cm⁻¹) in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy.

[0050] B' centers (also known as small plates) are plate-like aggregates containing more than 5 nitrogen atoms and interlattice carbon, which enter the crystal as inclusions.

[0051] Diamonds containing a B' center (plate) are called IaB' type. Synthetic single-crystal diamonds containing a B' center (plate) exhibit absorption peaks in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy, with wavenumbers above 1358 cm⁻¹ and below 1385 cm⁻¹.

[0052] The inventors have conducted intensive research on condensed nitrogen atoms that can improve the properties of synthetic single-crystal diamonds. As a result, they have newly discovered that B-centers, H3-centers, and N3-centers exhibit less crystallization strain and greater structural stability. Furthermore, the inventors have newly discovered that by forming at least one of B-centers, H3-centers, and N3-centers in synthetic single-crystal diamonds, the hardness, elastic deformability, and resistance to chipping, among other mechanical properties, of synthetic single-crystal diamonds can be further improved, thus completing this invention.

[0053] Hereinafter, specific examples of the synthetic single-crystal diamond and its manufacturing method according to the present invention will be described with reference to the drawings. In the drawings of the present invention, the same reference numerals represent the same or equivalent parts. Furthermore, the dimensional relationships such as length, width, thickness, and depth may be appropriately varied to clarify and simplify the drawings, but do not necessarily represent the actual dimensional relationships.

[0054] In this specification, the term "A~B" refers to the upper and lower limits of a range (i.e., above A and below B). When no unit is specified in A, but only in B, the unit of A is the same as the unit of B.

[0055] In this specification, the term "surface orientation" which includes geometrically equivalent surface orientations is represented by {}, and the term "direction" which includes geometrically equivalent directions is represented by <>.

[0056] [Implementation Method 1: Synthesis of Single-Crystal Diamond] The synthetic single-crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm, and the synthetic single-crystal diamond comprises an aggregate containing one vacancy and any number of 2 to 4 nitrogen atoms adjacent to the vacancy. Regarding the synthetic single-crystal diamond in the {001} plane... <110> The ratio of the length b of the shorter diagonal to the length a of the longer diagonal in the Knoop indentation in the direction of the indentation is less than 0.08, and the Knoop indentation is performed according to JIS Z 2251:2009, at a temperature of 23℃±5℃ and a test load of 4.9 N on the synthetic single crystal diamond in the {001} plane. <100> It is formed by measuring the Knoop hardness in the direction.

[0057] The synthesized single-crystal diamond of this embodiment has high hardness, high elastic recovery rate, and excellent resistance to chipping. The reason for this is not clear, but it is speculated as described in (i) to (iii) below.

[0058] (i) The synthetic single-crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm. This allows the nitrogen atoms in the synthetic single-crystal diamond to easily aggregate. Therefore, this synthetic single-crystal diamond readily contains aggregated nitrogen atoms, resulting in greater elastic deformation and improved resistance to breakage.

[0059] (ii) The synthetic single-crystal diamond of this embodiment comprises an aggregate containing one vacancy and any number of nitrogen atoms, from two to four, adjacent to the vacancy. Therefore, the synthetic single-crystal diamond has higher hardness, greater elastic deformation, and improved resistance to chipping.

[0060] (iii) In the synthetic single-crystal diamond of this embodiment, the ratio of the diagonal of the Knoop indentation, b / a, is 0.08 or less. Therefore, the elastic deformability of this synthetic single-crystal diamond is relatively large. Furthermore, the relationship between the Knoop indentation and elastic deformability will be described below.

[0061] <Nitrogen concentration> The synthetic single-crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm (hereinafter also referred to as "nitrogen atom concentration"). If the nitrogen atom concentration is 100 ppm or higher, the nitrogen atoms in the synthetic single-crystal diamond tend to form aggregated nitrogen atoms. If the nitrogen atom concentration is 1500 ppm or lower, the synthetic single-crystal diamond can have higher hardness and excellent resistance to chipping.

[0062] The lower limit of nitrogen atom concentration in synthetic single-crystal diamond can be set to above 100 ppm, above 200 ppm, or above 300 ppm. The upper limit of nitrogen atom concentration in synthetic single-crystal diamond can be set to below 1500 ppm, below 1400 ppm, or below 1300 ppm. (The specific nitrogen atom concentration ranges from 100 ppm to 1500 ppm, 100 ppm to 1400 ppm, 100 ppm to 1300 ppm, 200 ppm to 1500 ppm, 200 ppm to 1400 ppm, 200 ppm to 1300 ppm, 300 ppm to 1500 ppm, 300 ppm to 1400 ppm, and 300 ppm to 1300 ppm.)

[0063] The nitrogen atom concentration in synthetic single-crystal diamonds can be determined by secondary ion mass spectrometry (SIMS).

[0064] <condensed nitrogen atoms> The synthesized single-crystal diamond of this embodiment includes an aggregate containing one vacancy and two to four nitrogen atoms adjacent to that vacancy. An example of an aggregate containing one vacancy and two nitrogen atoms adjacent to that vacancy is the H3 center (agglomeration of 2 nitrogen atoms). An example of an aggregate containing one vacancy and three nitrogen atoms adjacent to that vacancy is the N3 center (agglomeration of 3 nitrogen atoms). An example of an aggregate containing one vacancy and four nitrogen atoms adjacent to that vacancy is the B center (agglomeration of 4 nitrogen atoms).

[0065] The B-center, H3-center, and N3-center crystallization strains are relatively small, resulting in a stable structure. The synthetic single-crystal diamond of this embodiment contains at least one of the B-center, H3-center, and N3-center types, thus exhibiting high hardness, large elastic deformation, and excellent resistance to chipping.

[0066] (Center B) The synthetic single-crystal diamond of this embodiment preferably comprises a condensed mass (B-center (nitrogen 4-atom condensation)), wherein the condensed mass (B-center (nitrogen 4-atom condensation)) contains one vacancy and four nitrogen atoms adjacent to the vacancy. The presence of a B-center in the synthetic single-crystal diamond can be confirmed by measuring the infrared absorption spectrum using Fourier transform infrared spectroscopy. Specifically, the presence of an absorption peak near wavenumber 1175 cm⁻¹ (e.g., wavenumber 1175 ± 2 cm⁻¹) in the infrared absorption spectrum indicates that the synthetic single-crystal diamond contains a B-center.

[0067] (H3 Center) The synthetic single-crystal diamond of this embodiment preferably comprises an aggregate (H3 center (nitrogen 2-atom aggregate)), wherein the aggregate (H3 center (nitrogen 2-atom aggregate)) contains one vacancy and two nitrogen atoms adjacent to the vacancy. The presence of an H3 center in the synthetic single-crystal diamond can be confirmed by obtaining a fluorescence spectrum from excitation light with a wavelength of 325 nm. Specifically, if an emission peak is present in the fluorescence spectrum obtained by irradiating the synthetic single-crystal diamond with excitation light at a wavelength of 325 nm, and either within the fluorescence wavelength range of 503 ± 2 nm or within the fluorescence wavelength range of 510 nm to 530 nm, or both, it is determined that the synthetic single-crystal diamond contains an H3 center.

[0068] Furthermore, the peaks within the fluorescence wavelength range of 503 ± 2 nm correspond to the emission peaks of the zero phonon line at the center of H3, while the emission peaks within the fluorescence wavelength range of 510 nm to 530 nm correspond to the emission peaks of the sub-band (phonon sideband) at the center of H3. The emission peaks within the fluorescence wavelength range of 510 nm to 530 nm are observed in the form of more than one mountain-shaped peak within this range. At least one of these mountain-shaped peaks represents the maximum intensity within this range.

[0069] (N3 Center) The synthetic single-crystal diamond of this embodiment preferably comprises an aggregate (N3 center (nitrogen 3-atom aggregate)), wherein the aggregate (N3 center (nitrogen 3-atom aggregate)) contains one vacancy and three nitrogen atoms adjacent to the vacancy. The presence of an N3 center in the synthetic single-crystal diamond can be confirmed by obtaining the fluorescence spectrum from the excitation light at a wavelength of 325 nm. Specifically, if an emission peak exists in one or both of the fluorescence spectra obtained from the excitation light at a wavelength of 325 nm on the synthetic single-crystal diamond, within the fluorescence wavelength range of 415 ± 2 nm and the fluorescence wavelength range of 420 nm to 470 nm, the synthetic single-crystal diamond is deemed to contain an N3 center.

[0070] Furthermore, the peaks within the fluorescence wavelength range of 415 ± 2 nm correspond to the emission peaks of the zero phonon line at the center of N3, while the emission peaks within the fluorescence wavelength range of 420 nm to 470 nm correspond to the emission peaks of the sub-band (phonon sideband) at the center of N3. The emission peaks within the fluorescence wavelength range of 420 nm to 470 nm are observed in the form of more than one mountain-shaped peak within this range. At least one of these mountain-shaped peaks represents the maximum intensity within this range.

[0071] (A center (nitrogen atom pair)) The synthetic single-crystal diamond in this embodiment preferably contains A centers (nitrogen atom pairs). The A centers in the synthetic single-crystal diamond can suppress the propagation of cracks. Therefore, the synthetic single-crystal diamond can have excellent resistance to defects.

[0072] The presence of an A-center in a synthetic single-crystal diamond can be confirmed by using the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Specifically, if an absorption peak is found in the infrared absorption spectrum near a wavenumber of 1282 cm⁻¹ (e.g., 1282 ± 2 cm⁻¹), it is determined that the synthetic single-crystal diamond contains an A-center.

[0073] (B' Center (Small Board)) The synthetic single-crystal diamond of this embodiment preferably exhibits an absorption peak in the infrared absorption spectrum within the wavenumber range of 1370 cm⁻¹ to 1385 cm⁻¹. This absorption peak originates from the B' center (plate) in the synthetic single-crystal diamond.

[0074] If an absorption peak exists in the infrared absorption spectrum of synthetic single-crystal diamond in the range of wavenumbers from 1370 cm⁻¹ to 1385 cm⁻¹, then the size of the condensed mass of nitrogen atoms contained in the B' center (small plate) is moderate, which can prevent plastic deformation or crack propagation and is unlikely to become the starting point of damage. Therefore, synthetic single-crystal diamond can have high hardness and excellent strength.

[0075] Furthermore, generally speaking, synthetic single-crystal diamonds containing B' centers (plates) exhibit absorption peaks in their infrared absorption spectra between wavenumbers 1358 cm⁻¹ and 1385 cm⁻¹. However, if absorption peaks exist in the range below 1370 cm⁻¹ (above 1358 cm⁻¹ but below 1370 cm⁻¹), the aggregate of B' centers (plates) within the crystal is too large, becoming the starting point for destruction, which is undesirable. Therefore, it is preferable that no absorption peaks exist in the infrared absorption spectrum of synthetic single-crystal diamonds in the range above 1358 cm⁻¹ but below 1370 cm⁻¹.

[0076] (Other condensed nitrogen atoms) Agglomerated nitrogen atoms other than H3 centers, N3 centers, B centers, and B' centers do not significantly affect the mechanical properties of the synthesized single-crystal diamond. Therefore, the synthesized single-crystal diamond of this embodiment may also contain aggregated nitrogen atoms other than H3 centers, N3 centers, B centers, and B' centers.

[0077] <Isolated Substituted Nitrogen Atom> The synthetic single-crystal diamond of this embodiment preferably does not contain isolated substituted nitrogen atoms (C centers). Therefore, the synthetic single-crystal diamond of this embodiment can possess high hardness and excellent resistance to chipping.

[0078] The absence of isolated substituted nitrogen atoms in synthetic single-crystal diamond can be determined by using the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Single-crystal diamond containing isolated substituted nitrogen atoms exhibits a peak near wavenumber 1130 cm⁻¹ (i.e., wavenumber 1130 ± 2 cm⁻¹) in its infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Therefore, by confirming the absence of absorption peaks originating from isolated substituted nitrogen atoms in the wavenumber range of 1130 ± 2 cm⁻¹ in the infrared absorption spectrum of synthetic single-crystal diamond, it can be determined that it does not contain isolated substituted nitrogen atoms.

[0079] In the infrared absorption spectrum, a shoulder band exists in the wavenumber range of 1130 ± 2 cm⁻¹, representing the absorption spectrum of condensed nitrogen atoms other than isolated substituted nitrogen atoms. Whether this shoulder band originates from the absorption peak of isolated substituted nitrogen atoms is unclear. In this case, the presence or absence of isolated substituted nitrogen atoms can be determined by ESR analysis. When isolated substituted nitrogen atoms are absent in synthetic single-crystal diamond, unpaired electrons are also absent. Therefore, no signal is detected by ESR analysis of this type of synthetic single-crystal diamond. This confirms the absence of isolated substituted nitrogen atoms in synthetic single-crystal diamond.

[0080] <Infrared Absorption Spectroscopy> If C centers, A centers, B centers, and B' centers (small plates) exist in a diamond crystal, absorption peaks originating from each center can be observed in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Because the waveforms of each center overlap, the presence or quantity of each center cannot be determined solely by the intensity values ​​of each wavenumber. However, by comparing the relative intensities of each wavenumber and considering the approximate waveforms of each center, the presence or absence of each center can be determined, and a qualitative evaluation of the proportion of each center can be performed.

[0081] <The ratio of the diagonal of the Knoop indentation to b / a> Regarding the synthetic single-crystal diamond in this embodiment within the {001} plane <110> The ratio of the shorter diagonal length b to the longer diagonal length a in the Knoop indentation direction is b / a or less. This Knoop indentation is performed according to JIS Z 2251:2009, at a temperature of 23℃±5℃ and a test load of 4.9 N on the {001} plane of the synthetic single-crystal diamond. <100> It is formed by measuring the Knoop hardness in the direction.

[0082] The Knoop hardness test is known as one of the standards for expressing the hardness of industrial materials. As specified in JIS Z2251:2009, the Knoop indenter is pressed into the material being tested by applying a specific temperature and a specific load (test load) to determine the hardness of the material.

[0083] Here, the so-called Knoop indenter is a diamond indenter with a rhomboid prism shape on its bottom surface. Furthermore, for the diagonals of this rhomboid shape, the ratio of the shorter diagonal length b' to the longer diagonal length a', b' / a', is specified to be 0.141. Also, the so-called Knoop indentation refers to the mark left on the test material (in this embodiment, a synthetic single-crystal diamond) after the Knoop indenter is pressed under the aforementioned temperature and test load, and then released. In this embodiment, according to JIS Z 2251:2009, the indenter of the synthetic single-crystal diamond in the {001} plane is indented under the conditions of a temperature of 23℃±5℃ and a test load of 4.9 N. <100> Apply indentation in the direction of the indentation (Knoop indentation).

[0084] One characteristic of the synthetic single-crystal diamond in this embodiment is that the ratio of the diagonals of the Knoop indentation, b / a, is less than 0.08 and less than the ratio of the original Knoop indenter, b' / a' (0.141). This is because the material being tested (i.e., in this embodiment, the synthetic single-crystal diamond) moves elastically, and the indentation elastically recovers to its original shape (elastic recovery).

[0085] The above phenomenon is illustrated using Figure 1, which conceptually represents the Knoop indentation. For example, when the material being tested does not fully exhibit elastic recovery, the cross-section of the Knoop indenter and the Knoop indentation become equal in shape (the portion shown in Figure 1 as the "original Knoop indentation"). On the other hand, the synthetic single-crystal diamond of this embodiment readily undergoes elastic deformation in the direction of the arrow in the figure, thus its Knoop indentation becomes a rhombus shape as shown by the solid line in the figure. That is, if the recovery in the direction of the arrow in the figure increases, the value of b / a decreases. The smaller the value of b / a, the greater the elastic deformation.

[0086] The synthetic single-crystal diamond of this embodiment exhibits greater elastic deformation due to the ratio of the diagonal of the Knoop indentation (b / a) being less than 0.08. The greater the elastic deformation, the higher the toughness, thus resulting in a strong and tough synthetic single-crystal diamond.

[0087] The upper limit of the ratio of the diagonals of the Knoop indentation, b / a, is 0.08 or less, and can be set to 0.075 or less, 0.07 or less, 0.065 or less, or 0.06 or less. Since a smaller ratio of the diagonals of the Knoop indentation, b / a, results in greater elastic deformation, there is no need to specifically limit its lower limit. There are also cases where no plastic deformation or failure occurs at all; in such cases, b / a is 0, and the Knoop indentation is only a line along the longer diagonal. Therefore, the lower limit of the ratio of the diagonals of the Knoop indentation, b / a, can be set to 0 or more. The ratio of the diagonals of the Knoop indentation, b / a, can be set to 0 or more but less than 0.08, 0 or more but less than 0.075, 0 or more but less than 0.07, 0 or more but less than 0.065, or 0 or more but less than 0.06.

[0088] Knoop Hardness The synthetic single-crystal diamond in this embodiment is within the {001} plane. <100> Knoop hardness in the direction (hereinafter also referred to as "{001}") <100> The Knoop hardness is preferably above 100 GPa. {001} <100> Synthetic single-crystal diamonds with a Knoop hardness of 100 GPa or higher have a higher hardness than natural diamonds containing nitrogen, and also exhibit excellent wear resistance.

[0089] Synthetic single-crystal diamond {001} <100> The lower limit of Knoop hardness can be set to 105 GPa or higher, 110 GPa or higher, or 115 GPa or higher. Synthetic single-crystal diamond {001} <100> There is no specific upper limit to the Knoop hardness, but from a manufacturing perspective, it can be set to below 150 GPa, for example. (Regarding the synthesis of single-crystal diamonds {001}) <100> Knoop hardness can be set to 100 GPa or higher than 150 GPa, 105 GPa or higher than 150 GPa, 110 GPa or higher than 150 GPa, or 115 GPa or higher than 150 GPa.

[0090] For synthetic single-crystal diamonds {001} <100> The evaluation method for Knoop hardness (hereinafter also referred to as HK, with units of GPa) is explained. First, according to JIS Z 2251:2009, the Knoop hardness of synthetic single-crystal diamond in the {001} plane is evaluated under the conditions of a temperature of 23℃±5℃ and a test load of 4.9 N. <100> An indentation is applied in the direction of the indentation. The longer diagonal a (μm) of the obtained indentation is measured, and the Knoop hardness (HK) is calculated according to the following formula A.

[0091] HK = 14229 × 4.9 / a² (Formula A)

[0092] <Crack Occurrence Load> In the destructive strength test where a spherical diamond indenter with a front radius (R) of 50 μm is pressed against the surface of a synthetic single-crystal diamond at a load rate of 100 N / min, the crack initiation load of the synthetic single-crystal diamond in this embodiment is preferably 15 N or more. If the crack initiation load is 15 N or more, the synthetic single-crystal diamond has excellent destructive strength and chip resistance, and is less prone to tip chipping when used as a tool material.

[0093] The lower limit of the crack initiation load for synthetic single-crystal diamond can be set to 17 N or higher, 20 N or higher, 25 N or higher, or 30 N or higher. The upper limit of the crack initiation load is not specifically limited, but from a manufacturing point of view, it can be, for example, below 50 N. The crack initiation load for synthetic single-crystal diamond can be set to 15 N or higher but below 50 N, 17 N or higher but below 50 N, 20 N or higher but below 50 N, 25 N or higher but below 50 N, or 30 N or higher but below 50 N.

[0094] The specific method for the destructive strength test is as follows: A spherical diamond indenter with a front radius (R) of 50 μm is pressed against the sample, and a load is continuously applied to the sample at a loading rate of 100 N / min. The load at the instant the sample cracks (crack initiation load) is measured. At the instant the crack occurs, the measurement is performed using an AE (Acoustic Emission) sensor. A higher crack initiation load indicates higher sample strength and better resistance to damage.

[0095] If an indenter with a front radius (R) less than 50 μm is used as the testing indenter, the sample undergoes plastic deformation before cracking occurs, making it impossible to determine the correct strength for cracking. Furthermore, even if an indenter with a front radius (R) greater than 50 μm is used, the following problems exist: the required load increases until cracking occurs, and the contact area between the indenter and the sample increases, making the influence of the sample's surface finish on the measurement accuracy, or the influence of the crystal orientation of the single crystal, more significant. Therefore, in the destructive strength test of synthetic single-crystal diamond, it is preferable to use an indenter with a front radius (R) of 50 μm.

[0096] <Applications> In addition to being used in precision cutting tools or woodworking cutting machines, grinding stone dressing tools, wire drawing dies, engraving tools, waterjet nozzles, wire guides, and other wear-resistant tools, the synthetic single-crystal diamond of this embodiment can also be used in a wide range of tools.

[0097] [Implementation Method 2: Method for Manufacturing Synthetic Single-Crystal Diamonds] The following describes one example of the method for manufacturing a synthetic single-crystal diamond according to Embodiment 1. Furthermore, the synthetic single-crystal diamond of Embodiment 1 is not limited to that manufactured by the following method, but may also be manufactured by other methods.

[0098] The method for manufacturing synthetic single-crystal diamond of the present invention is the same as the method for manufacturing synthetic single-crystal diamond in Embodiment 1, comprising: a first step, wherein a diamond single crystal is synthesized by means of a solvent metal temperature difference method, wherein the diamond single crystal contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm; a second step, wherein the diamond single crystal is irradiated with one or both of an electron beam and a particle beam with an energy of 100 MGy to 1000 MGy; and a third step, wherein the diamond single crystal after the second step is subjected to a pressure of 5 GPa or more and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes, thereby obtaining a synthetic single-crystal diamond.

[0099] (Step 1) Diamond single crystals can be fabricated, for example, using a sample chamber with the configuration shown in Figure 2, by means of a temperature difference method.

[0100] As shown in Figure 2, in the sample chamber 10 used to manufacture diamond single crystal 1, an insulator 2, a carbon source 3, a solvent metal 4, and a seed crystal 5 are arranged within the space surrounded by a graphite heater 7, and a pressure medium 6 is arranged outside the graphite heater 7. The temperature difference method refers to the following synthesis method: a longitudinal temperature gradient is set inside the sample chamber 10, a carbon source 3 is arranged in the high-temperature section (Thigh), a diamond seed crystal 5 is arranged in the low-temperature section (Tlow), and a solvent metal 4 is arranged between the carbon source 3 and the seed crystal 5. Under conditions that are maintained above the melting temperature of the solvent metal 4 and above the pressure at which diamond is thermally stable, the diamond single crystal 1 is grown on the seed crystal 5.

[0101] Diamond powder is preferred as the carbon source 3. Alternatively, graphite or pyrolytic carbon may also be used. As the solvent metal 4, one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn), or alloys containing such metals, may be used.

[0102] Nitrogen sources such as iron nitride (Fe2N, Fe3N), aluminum nitride (AlN), phosphorus nitride (P3N4), silicon nitride (Si3N4), or organic nitrogen compounds such as melamine and sodium azide can be added alone or in mixtures to carbon source 3 or solvent metal 4. Alternatively, diamond or graphite containing a large amount of nitrogen can also be added as a nitrogen source. In this way, the synthesized diamond single crystal contains nitrogen atoms. At this time, the nitrogen atoms in the diamond single crystal mainly exist in the form of isolated substituted nitrogen atoms.

[0103] The nitrogen supply content in carbon source 3 or solvent metal 4 is adjusted so that the nitrogen atom concentration in the synthesized diamond single crystal is between 100 ppm and 1500 ppm. For example, in the carbon source, the nitrogen atom content from the nitrogen supply source can be set between 200 ppm and 3000 ppm. Furthermore, in the solvent metal, for example, when the solvent metal is an alloy containing iron-cobalt-nickel and the nitrogen supply source is Fe3N, the nitrogen supply source content can be set between 0.01% by mass and 0.2% by mass.

[0104] The solvent metal 4 may further include one or more elements selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), and platinum (Pt).

[0105] (Step 2) Secondly, the obtained diamond single crystal is irradiated with either or both of an electron beam and a particle beam with an energy of 100 MGy to 1000 MGy. This introduces lattice defects into the diamond single crystal, thereby creating vacancies.

[0106] If the irradiation energy is less than 100 MGy, there is a risk that the introduction of lattice defects will be insufficient. On the other hand, if the energy exceeds 1000 MGy, there is a risk of generating excessive vacancies, which could significantly reduce crystallinity. Therefore, the preferred energy is between 100 MGy and 1000 MGy.

[0107] As a particle beam, neutron rays or proton beams can be used. There are no particular limitations on the irradiation conditions as long as an energy of 100 MGy to 1000 MGy can be imparted to a single diamond crystal. For example, when using an electron beam, the irradiation energy can be set to 4.6 MeV to 4.8 MeV, the current to 2 mA to 5 mA, and the irradiation time to 30 hours to 45 hours.

[0108] (Step 3) Next, the diamond single crystal obtained after step 2 is subjected to a pressure of 5 GPa or higher and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes to obtain a synthetic single-crystal diamond. In this process, isolated substituted nitrogen atoms within the diamond single crystal condense through vacancy movement, thus becoming aggregated nitrogen atoms.

[0109] By setting the temperature of step 3 above 2300°C, the movement of nitrogen atoms in the diamond single crystal can be promoted, thus promoting the formation of aggregates. These aggregates contain one vacancy and any number of substituted nitrogen atoms (2 to 4) surrounding that vacancy. If the temperature of step 3 is below 2300°C, it is difficult to form such aggregates. From a cost or productivity standpoint, the upper limit of the temperature for step 3 is preferably below 2600°C.

[0110] On the other hand, heating a diamond single crystal to above 2300°C under normal pressure leads to graphitization. Through intensive research, the inventors have discovered that by applying a temperature of 2300°C to 2600°C for 1 to 3600 minutes under a high pressure of 5 GPa or higher, the movement of nitrogen atoms in the diamond single crystal can be promoted without graphitization.

[0111] The time for applying a temperature of 2300°C to 2600°C to a diamond single crystal under high pressure above 5 GPa is 1 minute to 3600 minutes. The time for applying a temperature of 2300°C to 2600°C to a diamond single crystal under high pressure above 5 GPa can be set to 60 minutes to 360 minutes. The pressure at this time can be set to 5 GPa to 20 GPa.

[0112] Performing step 2 and step 3 once each is considered one cycle, and this can be repeated two or more times. This promotes the aggregation of isolated substituted nitrogen atoms within a diamond single crystal.

[0113] [Postscript 1] The synthetic single-crystal diamond of the present invention may include a condensation mass (B-center (nitrogen 4-atom condensation)), wherein the condensation mass (B-center (nitrogen 4-atom condensation)) includes one vacancy and four nitrogen atoms present adjacent to the vacancy.

[0114] [Postscript 2] The synthetic single-crystal diamond of the present invention may include an aggregate (H3 center (nitrogen 2 atom aggregate)), wherein the aggregate (H3 center (nitrogen 2 atom aggregate)) includes one vacancy and two nitrogen atoms adjacent to the vacancy.

[0115] [Postscript 3] The synthetic single-crystal diamond of the present invention may include an aggregate (N3 center (nitrogen 3 atom aggregate)), wherein the aggregate (N3 center (nitrogen 3 atom aggregate)) includes one vacancy and three nitrogen atoms adjacent to the vacancy.

[0116] [Postscript 4] The synthetic single-crystal diamond of this invention may contain B centers and H3 centers.

[0117] [Postscript 5] The synthetic single-crystal diamond of this invention may contain B centers and N3 centers.

[0118] [Postscript 6] The synthetic single-crystal diamond of this invention may contain B centers, H3 centers, and N3 centers.

[0119] [Postscript 7] The synthetic single-crystal diamond of this invention preferably does not contain isolated substituted nitrogen atoms (C centers). This further improves the hardness and chip resistance of the synthetic single-crystal diamond.

[0120] [Postscript 8] Preferably, in the infrared absorption spectrum of the synthesized single-crystal diamond of the present invention, there is no absorption peak caused by the C center in the wavenumber range of 1130±2 cm⁻¹. This further improves the hardness and defect resistance of the synthesized single-crystal diamond. Furthermore, absorption caused by the A center or B center also exists in the wavenumber range of 1130±2 cm⁻¹.

[0121] [Postscript 9] Preferably, the infrared absorption spectrum of the synthesized single-crystal diamond of this invention does not contain any absorption peaks in the range of wavenumbers above 1358 cm⁻¹ but below 1370 cm⁻¹. This further improves the hardness and chip resistance of the synthesized single-crystal diamond.

[0122] [Postscript 10] The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 100 ppm and 1400 ppm. The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 100 ppm and 1300 ppm. The nitrogen atom concentration in the synthesized single-crystal diamond of this invention can be set to between 200 ppm and 1500 ppm. The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 200 ppm and 1400 ppm. The nitrogen atom concentration in the synthesized single-crystal diamond of this invention can be set to between 200 ppm and 1300 ppm. The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 300 ppm and 1500 ppm. The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 300 ppm and 1400 ppm. The nitrogen atom concentration in the synthetic single-crystal diamond of this invention can be set to between 300 ppm and 1300 ppm.

[0123] [Postscript 11] The ratio b / a of the diagonal of the Knoop indentation in the synthetic single-crystal diamond of this invention can be set to 0 or more and 0.08 or less. The ratio b / a of the diagonal of the Knoop indentation in the synthetic single-crystal diamond of this invention can be set to 0 or more and 0.075 or less. The ratio b / a of the diagonal of the Knoop indentation in the synthetic single-crystal diamond of this invention can be set to 0 or more and 0.07 or less. The ratio b / a of the diagonal of the Knoop indentation in the synthetic single-crystal diamond of this invention can be set to 0 or more and 0.065 or less. The ratio b / a of the diagonal of the Knoop indentation in the synthetic single-crystal diamond of this invention can be set to 0 or more and 0.06 or less.

[0124] [Postscript 12] The Synthetic Single-Crystal Diamond of the Invention {001} <100> The Knoop hardness can be set to between 100 GPa and 150 GPa. The Synthetic Single-Crystal Diamond of the Invention {001} <100> The Knoop hardness can be set to between 105 GPa and 150 GPa. The Synthetic Single-Crystal Diamond of the Invention {001} <100> The Knoop hardness can be set to between 110 GPa and 150 GPa. The Synthetic Single-Crystal Diamond of the Invention {001} <100> The Knoop hardness can be set to between 115 GPa and 150 GPa.

[0125] [Postscript 13] The cracking load of the synthetic single-crystal diamond of this invention can be set to 15 N or more and 50 N or less. The cracking load of the synthetic single-crystal diamond of the present invention can be set to 17 N or more and 50 N or less. The cracking load of the synthetic single-crystal diamond of this invention can be set to 20 N or more and 50 N or less. The cracking load of the synthetic single-crystal diamond of the present invention can be set to 25 N or more and 50 N or less. The cracking load of the synthetic single-crystal diamond of this invention can be set to 30 N or more and 50 N or less. [Example]

[0126] The embodiments are used to further illustrate this implementation. However, this implementation is not limited to these embodiments.

[0127] [The Production of Synthetic Single-Crystal Diamonds] <Sample 2, Sample 4~Sample 8> (Step 1) Diamond single crystals were synthesized using a sample chamber with the configuration shown in Figure 2 by means of a solvent metal temperature difference method.

[0128] An alloy containing iron, cobalt, and nickel was prepared as the solvent metal, and iron nitride (Fe3N) powder was added to it as a nitrogen supply source. The concentration of iron nitride in the solvent metal is shown in the "Concentration of iron nitride in solvent metal (mass %)" column of "Manufacturing Conditions" in Table 1. For example, in Sample 2, the concentration of iron nitride in the solvent metal was 0.02% by mass.

[0129] Diamond powder was used as the carbon source, and approximately 0.5 mg of diamond single crystal was used as the seed crystal. The temperature in the sample chamber was adjusted by a heater to create a temperature difference of several tens of degrees between the high-temperature section containing the carbon source and the low-temperature section containing the seed crystal. Based on this, an ultra-high pressure generator was used to control the pressure at 5.5 GPa and the temperature of the low-temperature section at 1370℃±10℃ (1360℃~1380℃) for 60 hours to synthesize diamond single crystals on the seed crystal.

[0130] (Step 2) Next, the obtained diamond single crystal was irradiated with an electron beam. The irradiation conditions were set as follows: irradiation line energy of 4.6 MeV, current of 2 mA, and irradiation time of 30 hours. These irradiation conditions impart an energy of 100 MGy to the diamond single crystal.

[0131] (Step 3) Next, the diamond single crystal irradiated with an electron beam is subjected to a high pressure of 6 GPa or higher (referred to as "high pressure" in Table 1) and the temperature listed in the "Step 3 (60 minutes)" column of "Manufacturing Conditions" in Table 1 for 60 minutes to obtain a synthetic single crystal diamond. For example, in Sample 2, a pressure of 6 GPa or higher (high pressure) and a temperature of 2350°C were applied to the diamond single crystal for 60 minutes.

[0132] <Sample 1> Sample 1 was synthesized as a diamond single crystal by the same first step as Sample 2. In Sample 1, steps 2 and 3 were not performed.

[0133] <Sample 3> Sample 3 was synthesized as a diamond single crystal by the same first step as Sample 4. In Sample 1, steps 2 and 3 were not performed.

[0134] [Table 1] Table 1 Sample No. Manufacturing conditions iron nitride concentration in solvent metal (quality%) Electron beam irradiation (100 MGy) Step 3 (60 minutes) 1 0.02 none none 2 0.02 have high pressure 2350℃ 3 0.08 none none 4 0.08 have high pressure 2350℃ 5 0.08 have high pressure 2450℃ 6 0.08 have High pressure 2600℃ 7 0.1 have high pressure 2450℃ 8 0.15 have high pressure 2450℃

[0135] <Evaluation> For the synthetic single-crystal diamonds of samples 2 and 4-8, and the diamond single crystals of samples 1 and 3 (hereinafter also referred to as "synthetic single-crystal diamonds / diamond single crystals"), nitrogen concentration was determined, fluorescence spectra were measured, infrared spectroscopy was analyzed, and {001} <100> Knoop hardness determination, Knoop indentation diagonal ratio b / a determination, and destructive strength test.

[0136] (Determination of nitrogen atom concentration) The nitrogen atom concentration in the synthetic single-crystal diamond / diamond single crystal of each sample was determined by SIMS analysis. The results are shown in the "Nitrogen Atom Concentration (ppm)" column of "Synthetic Single-Crystal Diamond / Diamond Single Crystal" in Table 2.

[0137] (fluorescence spectrum) After mirror polishing the surface of each sample of synthetic single-crystal diamond / diamond single crystal, it was irradiated with excitation light of wavelength 325 nm and the fluorescence spectrum was measured.

[0138] In the fluorescence spectrum, confirm whether there is a emission peak in the range of (a) to (d) below. (a) Within the range of fluorescence wavelength 415±2 nm (b) Fluorescence wavelengths between 420 nm and 470 nm (c) Within the range of fluorescence wavelength 503±2 nm (d) Fluorescence wavelengths between 510 nm and 530 nm The results are shown in Table 2 under “Fluorescence Spectrum” for “Synthetic Single Crystal Diamond / Diamond Single Crystal” in the columns “Emission Peak in the range of 415±2 nm”, “Subband of 420-470 nm”, “Emission Peak in the range of 503±2 nm”, and “Subband of 510-530 nm”.

[0139] When an emission peak is present in one or both of the following ranges: (a) fluorescence wavelength 415 ± 2 nm and (b) fluorescence wavelength 420 nm to 470 nm, the N3 center is set to "Present". When no emission peak is present in either of the above ranges, the N3 center is set to "None". The results are shown in the "N3 Center" column of "Fluorescence Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0140] When an emission peak is present in one or both of the following ranges: (c) fluorescence wavelength 503±2 nm and (d) fluorescence wavelength 510 nm to 530 nm, the H3 center is set to "Present". When no emission peak is present in either of the above ranges, the H3 center is set to "None". The results are shown in the "H3 Center" column of "Fluorescence Spectrum" under "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0141] (Infrared spectroscopy analysis) Each sample of synthetic single-crystal diamond / diamond single crystal was processed into a plate with a thickness of about 1 mm. After mirror polishing of the two light-transmitting surfaces, the absorbance in the infrared region was measured by Fourier transform infrared spectroscopy to produce an infrared absorption spectrum.

[0142] In the infrared absorption spectrum, apart from absorption caused by other centers, when an absorption peak exists at wavenumber 1282±2 cm⁻¹, center A is marked as "present"; when no absorption peak exists at wavenumber 1282±2 cm⁻¹, center A is marked as "absent". The results are shown in the "Center A" column of "Infrared Absorption Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0143] In the infrared absorption spectrum, apart from absorption caused by other centers, when an absorption peak exists at wavenumber 1175±2 cm⁻¹, center B is marked as "present"; when no absorption peak exists at wavenumber 1175±2 cm⁻¹, center B is marked as "absent". The results are shown in the "Center B" column of "Infrared Absorption Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0144] In the infrared absorption spectrum, apart from absorption caused by other centers, when an absorption peak exists at wavenumber 1130±2 cm⁻¹, the C center is marked as "present"; when no absorption peak exists at wavenumber 1130±2 cm⁻¹, the C center is marked as "absent". The results are shown in the "C center" column of "Infrared Absorption Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0145] In the infrared absorption spectrum, apart from absorption caused by other centers, when an absorption peak exists in the wavenumber range of 1370–1385 cm⁻¹, the B' center (small plate) is set to "present," and when no absorption peak exists in the wavenumber range of 1370–1385 cm⁻¹, the B' center (small plate) is set to "absent." The results are shown in the "B' center / small plate" column of "Infrared Absorption Spectroscopy" under "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0146] Furthermore, synthetic single-crystal diamond containing B' centers (platelets) exhibits absorption peaks in the infrared absorption spectrum between wavenumbers 1358 cm⁻¹ and 1385 cm⁻¹. However, if absorption peaks exist in the range below 1370 cm⁻¹ (above 1358 cm⁻¹ but below 1370 cm⁻¹), the aggregate of B' centers (platelets) within the crystal is too large, becoming the starting point for destruction, which is undesirable. In samples 1-8, no absorption peaks were found between wavenumbers 1358 cm⁻¹ and 1370 cm⁻¹.

[0147] As a reference value, when the absorbance caused by the phonons of diamond, i.e., the absorbance at wavenumber 2160 cm⁻¹, is set to 1, the absorbance values ​​at wavenumber 1282 cm⁻¹ (center A), 1175 cm⁻¹ (center B), 1130 cm⁻¹ (center C), the absorbance values ​​of the peaks between wavenumbers 1370 cm⁻¹ and 1385 cm⁻¹, and the absorbance values ​​of the peaks above wavenumber 1358 cm⁻¹ but not reaching the peak of wavenumber 1370 cm⁻¹ are calculated. The results are shown in the "Infrared Absorption Spectra" of "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2, specifically in the columns "I(1282) / I(2160)", "I(1175) / I(2160)", "I(1130) / I(2160)", "I(1370-1385) / I(2160)" and "I(1358-1370) / I(2160)".

[0148] Regarding I(1175) / I(2160), the value of I(1175) / I(2160) for sample 3, which has "no" B center, is greater than that for sample 2, which has "yes" B center. The reason is that since sample 3 has more nitrogen at its C center, the absorption at wavenumber 1175 cm⁻¹ in the shoulder band of the absorption spectrum originating from the C center is stronger, and it does not show that sample 3 contains a B center.

[0149] Regarding I(1130) / I(2160), the values ​​of I(1130) / I(2160) for samples 4 to 8, which have "no" C centers, are greater than those for sample 1, which has "present" C centers. This is because, since samples 4 to 8 have more nitrogen in their A and B centers, the absorption at wavenumber 1130 cm⁻¹ in the shoulder band of the absorption spectra originating from these A and B centers is stronger, and it does not indicate that samples 4 to 8 contain C centers.

[0150] (Knoop Hardness Measurement) For each sample, the synthetic single-crystal diamond / diamond single crystal in the {001} plane <100> An indentation was applied in the direction of the indentation with a load of 4.9 N. The length a (μm) of the longer diagonal of the obtained Knoop indentation was measured, and the Knoop hardness (HK) was calculated using the following formula A. Since the specific measurement method is described in Embodiment 1, it will not be repeated. The results are shown in Table 2 under "Synthetic Single Crystal Diamond / Diamond Single Crystal" under "{001}". <100> Knoop Hardness column. HK = 14229 × 4.9 / a² (Formula A)

[0151] (Determination of Knoop indentation (b / a)) Regarding the Knoop indentation obtained by the above Knoop hardness measurement, the length 'a' of the longer diagonal and the length 'b' of the shorter diagonal were measured, and the ratio b / a was calculated. The results are shown in Table 2, under "Synthetic Single Crystal Diamond / Diamond Single Crystal," under "b / a{001}". <110> The smaller the value of b / a, the greater the elastic deformation.

[0152] (Destructive Strength Test) A spherical diamond indenter with an R50 μm diameter was prepared. At room temperature (23°C), a load was continuously applied to each sample of synthetic single-crystal diamond / diamond single crystal at a loading rate of 100 N / min. The load at the instant the sample cracked (crack initiation load) was measured. Since the specific measurement method is described in Example 1, it will not be repeated here. A higher crack initiation load indicates higher sample strength and better resistance to defects. The results are shown in the "Crack Initiation Load" column of "Synthetic Single-Crystal Diamond / Diamond Single Crystal" in Table 2.

[0153] [Table 2] Table 2 Sample No. Synthetic single-crystal diamond / diamond single crystal Fluorescence spectrum Infrared absorption spectrum nitrogen atom concentration (ppm) {001} <110> Knoop Hardness (GPa) b / a {001} <110> Cracks occur load (N) emission peak in the range of 415±2 nm 420-470 nm sub-band N3 Center emission peak in the range of 503±2 nm 510-530 nm subband H3 Center I(1282) / I(2160) Center A I(1175) / I(2160) Center B I(1130) / I(2160) Center C I (1370-1385) / I(2160) I (1358-1370) / I(2160) B' Center / Small Board 1 none none none none none none 0.2 none 0.4 none 0.7 have 0 0 none 250 90 0.082 11 2 have have have have have have 0.9 have 0.6 have 0.3 none 0.001 0 have 250 102 0.075 17 3 none none none none none none 0.6 none 1.3 none 2.5 have 0 0 none 800 85 0.085 14 4 have have have have have have 1.8 have 2 have 0.9 none 0.005 0 have 800 118 0.072 20 5 have have have none none none 2.4 have 1.8 have 1.2 none 0.02 0 have 800 125 0.063 twenty three 6 have have have none none none 2.5 have 1.8 have 1.2 none 0.08 0 have 800 136 0.057 29 7 have have have none none none 2.7 have 1.6 have 1.1 none 0.1 0 have 1000 130 0.055 32 8 have have have none none none 3.7 have 2 have 1.3 none 0.15 0 have 1500 132 0.052 32

[0154] <Research> Samples 2 and 4-8 correspond to the Examples. Samples 1 and 3 correspond to the Comparative Examples. Compared with Samples 1 and 3 (Comparative Examples), Samples 2 and 4-8 (Examples) were found to have higher hardness, greater elastic deformation, and excellent resistance to damage.

[0155] As shown above, the embodiments and examples of the present invention have been described. However, it is initially intended that the above embodiments and examples may be appropriately combined or modified in various ways. It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and not limiting. The scope of this invention is not disclosed by the above embodiments and examples, but by the claims, and is intended to include all modifications within the scope and meaning of the claims.

[0156] 1: Diamond single crystal 2: Insulator 3: Carbon source 4: Solvent metal 5: Seed Crystal 6: Pressure medium 7: Graphite heater 10: Sample Chamber a: The length of the longer diagonal b: Length of the shorter diagonal Thigh: High-temperature section Tlow: low temperature part

Claims

1. A synthetic single-crystal diamond containing 100 ppm to 1500 ppm of nitrogen atoms, wherein the synthetic single-crystal diamond comprises an aggregate containing one vacancy and any number of 2 to 4 nitrogen atoms adjacent to the vacancy, wherein the ratio of the length b of the shorter diagonal to the length a of the longer diagonal in the <110> direction of the {001} plane of the synthetic single-crystal diamond is 0.08 or less, and the Knoop indentation is formed by measuring the Knoop hardness of the synthetic single-crystal diamond in the <100> direction of the {001} plane according to JIS Z 2251:2009 at a temperature of 23℃ ± 5℃ and a test load of 4.9 N.

2. The synthetic single-crystal diamond of claim 1, wherein an absorption peak exists in the infrared absorption spectrum of the synthetic single-crystal diamond in the range of wavenumber 1175±2 cm⁻¹.

3. The synthetic single-crystal diamond of claim 1 or 2, wherein the fluorescence spectrum of the synthetic single-crystal diamond contains a fluorescence peak in one or both of the following ranges: a fluorescence wavelength of 503±2 nm and a fluorescence wavelength of 510 nm to 530 nm.

4. The synthetic single-crystal diamond of claim 1 or 2, wherein the fluorescence spectrum of the synthetic single-crystal diamond contains a fluorescence peak in one or both of the following ranges: a fluorescence wavelength of 415 ± 2 nm and a fluorescence wavelength of 420 nm or more and 470 nm or less.

5. The synthetic single-crystal diamond of claim 1 or 2, wherein an absorption peak exists in the infrared absorption spectrum of the synthetic single-crystal diamond in the range of wavenumber 1282±2 cm⁻¹.

6. The synthetic single-crystal diamond of claim 1 or 2, wherein an absorption peak exists in the infrared absorption spectrum of the synthetic single-crystal diamond in the range of wavenumber from 1370 cm⁻¹ to 1385 cm⁻¹.

7. The synthetic single-crystal diamond of claim 1 or 2, wherein the Knoop hardness of the synthetic single-crystal diamond in the <100> direction within the {001} plane is 100 GPa or more.

8. The synthetic single-crystal diamond of claim 1 or 2, wherein in the destructive strength test of pressing a spherical diamond indenter with a front radius of 50 μm against the surface of the synthetic single-crystal diamond at a load rate of 100 N / min, the cracking load is 17 N or more.

9. A method for manufacturing a synthetic single-crystal diamond as claimed in any one of claims 1 to 8, comprising: The first step involves synthesizing a single diamond crystal using a solvent metal temperature difference method. The single diamond crystal contains nitrogen atoms at a concentration of 100 ppm to 1500 ppm. The second step involves irradiating the single diamond crystal with one or both of an electron beam and a particle beam with an energy of 100 MGy to 1000 MGy. The third step involves applying a pressure of 5 GPa or higher and a temperature of 2300°C to 2600°C to the single diamond crystal obtained after the second step for 1 minute to 3600 minutes, thereby obtaining a synthetic single-crystal diamond.

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