Synthetic single crystal diamond and method of manufacture thereof

Abstract

A synthetic single crystal diamond which is a synthetic single crystal diamond containing 100 ppm or more and 1500 ppm or less of nitrogen atoms, wherein the synthetic single crystal diamond contains an aggregate composed of one vacancy and any one number of two to four nitrogen atoms existing adjacent to the vacancy, a ratio b / a of a length of a shorter one of diagonal lines to a length of a longer one of diagonal lines in a Knoop indentation in a <110> direction in a {001} plane of the synthetic single crystal diamond is 0.08 or less, the Knoop indentation being formed in accordance with JIS Z 2251:2009, by measuring a Knoop hardness in a <100> direction in the {001} plane of the synthetic single crystal diamond under conditions that a temperature is 23°C ± 5°C and a test load is 4.9 N.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to synthetic single crystal diamond and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2020-113054 filed on June 30, 2020. The entire contents described in the Japanese Patent Application are incorporated herein by reference. BACKGROUND

[0002] Single crystal diamond is widely used for tools such as cutting tools, grinding tools, and wear-resistant tools because of its high hardness. Single crystal diamond used in tools is natural diamond or synthetic diamond.

[0003] In most natural diamonds, aggregated nitrogen atoms (type Ia) are contained as impurities. Aggregated nitrogen atoms in a diamond crystal can prevent the progress of plastic deformation and cracks that occur when the diamond is used as a tool. Therefore, the mechanical strength of natural diamond is high. However, the quality of natural diamond varies greatly, and the supply is unstable, so there are limitations in industrial use.

[0004] On the other hand, synthetic diamond is constant in quality and can be stably supplied, so it is widely used in the industrial field.

[0005] In general synthetic diamond, isolated substitution type nitrogen atoms (type Ib) are contained as impurities. The higher the concentration of isolated substitution type nitrogen atoms in a diamond crystal, the more the mechanical properties of the diamond deteriorate. Thus, in the case of using Ib type synthetic diamond as a tool, there is a tendency to easily produce wear and damage of the cutting edge.

[0006] In addition, in synthetic diamond, there is also synthetic diamond (type IIa) that contains almost no nitrogen impurities. Type IIa synthetic diamond does not contain impurities and crystal defects that prevent the progress of cracks, so in the case of being used as a tool, there is a tendency to easily produce damage of the cutting edge.

[0007] Thus, in synthetic diamond, techniques for improving wear resistance and damage resistance are being studied.

[0008] For example, Patent Literature 1 (International Publication No. 2019 / 077888) discloses synthetic single crystal diamond having high hardness and excellent damage resistance.

[0009] PRIOR ART DOCUMENTS

[0010] PATENT LITERATURE

[0011] Patent Literature 1: International Publication No. 2019 / 077888 SUMMARY

[0012] The synthetic single-crystal diamond of the present disclosure is a synthetic single-crystal diamond containing 100 ppm or more and 1500 ppm or less of nitrogen atoms, wherein

[0013] The synthetic single-crystal diamond contains an aggregate composed of one vacancy and any one number of two to four nitrogen atoms existing adjacent to the vacancy,

[0014] The ratio b / a of the length b of the shorter one of the diagonals to the length a of the longer one of the diagonals in the Knoop indentation in the <110> direction in the {001} face of the synthetic single-crystal diamond is 0.08 or less,

[0015] The Knoop indentation is formed by measuring the Knoop hardness in the <100> direction in the {001} face of the synthetic single-crystal diamond in accordance with JIS Z 2251:2009 under the conditions of a temperature of 23°C ± 5°C and a test load of 4.9 N.

[0016] The method of manufacturing the synthetic single-crystal diamond of the present disclosure is the above-described method of manufacturing the synthetic single-crystal diamond, wherein

[0017] The method of manufacturing the synthetic single-crystal diamond comprises:

[0018] The first step is a step in which a diamond single-crystal containing nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less on an atomic number basis is synthesized by a temperature difference method using a solvent metal;

[0019] The second step is a step in which one or both of an electron beam and a particle beam imparting an energy of 100 MGy or more and 1000 MGy or less are irradiated to the diamond single-crystal; and

[0020] The third step is a step in which a pressure of 5 GPa or more and a temperature of 2300°C or more and 2600°C or less for 1 minute or more and 3600 minutes or less are applied to the diamond single-crystal after the second step, to obtain a synthetic single-crystal diamond. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a diagram for explaining a Knoop indentation.

[0022] Figure 2 is a schematic cross-sectional view showing one example of a sample chamber configuration used in the manufacturing of a synthetic single-crystal diamond according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] [Problems to be Solved by the Present Disclosure]

[0024] Based on the increasing demand for longer tool life in recent years, there is a need for a synthetic single-crystal diamond with superior wear resistance and damage resistance.

[0025] 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 chipping.

[0026] [The Effects of This Disclosure]

[0027] According to this disclosure, a synthetic single-crystal diamond with high hardness, high elastic recovery rate, and excellent resistance to chipping can be provided.

[0028] [Description of embodiments of this disclosure]

[0029] First, embodiments of this disclosure will be described.

[0030] (1) The synthetic single-crystal diamond disclosed herein is a synthetic single-crystal diamond containing more than 100 ppm and less than 1500 ppm of nitrogen atoms, wherein,

[0031] The synthetic single-crystal diamond comprises an aggregate consisting of a cavity and any number of two to four nitrogen atoms adjacent to the cavity.

[0032] The {001} plane of the synthetic single-crystal diamond <110> The ratio of the length b of the shorter diagonal to the length a of the longer diagonal of the Knoop indentation in the direction of the indentation is less than 0.08.

[0033] The Knoop indentation was performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9N, on the {001} plane of the synthetic single-crystal diamond. <100> It is formed by measuring the Knoop hardness in the direction.

[0034] The synthetic single-crystal diamond disclosed herein has high hardness, high elastic recovery rate, and excellent resistance to chipping.

[0035] (2) Preferably, in the infrared absorption spectrum of the synthesized single-crystal diamond, the wavenumber is 1175±2cm. -1 Absorption peaks exist within the range.

[0036] This allows for the synthesis of single-crystal diamonds with higher hardness, greater elastic recovery, and excellent resistance to chipping.

[0037] (3) Preferably, in the fluorescence spectrum of the synthesized single crystal diamond, there is a fluorescence peak in one or both of the fluorescence wavelength range of 503±2nm and the fluorescence wavelength range of 510nm and 530nm.

[0038] This allows for the synthesis of single-crystal diamonds with higher hardness, greater elastic recovery, and excellent resistance to chipping.

[0039] (4) Preferably, in the fluorescence spectrum of the synthesized single crystal diamond, there is a fluorescence peak in one or both of the fluorescence wavelength range of 415±2nm and the fluorescence wavelength range of 420nm and 470nm.

[0040] This allows for the synthesis of single-crystal diamonds with higher hardness, greater elastic recovery, and excellent resistance to chipping.

[0041] (5) Preferably, in the infrared absorption spectrum of the synthesized single-crystal diamond, the wavenumber is 1282±2cm. -1 Absorption peaks exist within the range.

[0042] This allows for the synthesis of single-crystal diamonds with higher hardness, greater elastic recovery, and excellent resistance to chipping.

[0043] (6) Preferably, in the infrared absorption spectrum of the synthesized single-crystal diamond, at a wavenumber of 1370 cm⁻¹ -1 Above and 1385cm -1 Absorption peaks exist in the following range.

[0044] This allows for the synthesis of single-crystal diamonds with higher hardness, greater elastic recovery, and excellent resistance to chipping.

[0045] (7) Preferably, the {001} plane of the synthetic single-crystal diamond <100> The Knoop hardness in the direction is above 100 GPa.

[0046] This enables synthetic single-crystal diamond to possess excellent wear resistance.

[0047] (8) Preferably, in the destructive strength test of pressing a spherical diamond indenter with a front end radius of 50 μm onto the surface of the synthetic single crystal diamond at a load speed of 100 N / min, the load generated by cracking is 17 N or more.

[0048] This enables synthetic single-crystal diamond to possess excellent resistance to chipping.

[0049] (9) The method for manufacturing synthetic single-crystal diamond disclosed herein is the method for manufacturing synthetic single-crystal diamond described above, wherein,

[0050] The method for manufacturing the synthetic single-crystal diamond comprises:

[0051] In the first step, a diamond single crystal containing nitrogen atoms at a concentration of more than 100 ppm and less than 1500 ppm based on the atomic number is synthesized by using the temperature difference method of solvent metal.

[0052] The second step involves irradiating the diamond single crystal with one or both of an electron beam and a particle beam, each possessing an energy of 100 MGy or higher but less than 1000 MGy.

[0053] In the third step, a pressure of 5 GPa or more and a temperature of 2300°C or more and 2600°C or less are applied to the diamond single crystal after the second step for a period of more than 1 minute and less than 3600 minutes to obtain a synthetic single crystal diamond.

[0054] This allows for the production of synthetic single-crystal diamonds with high hardness, high elastic recovery rate, and excellent resistance to chipping.

[0055] [Details of the embodiments disclosed herein]

[0056] <The forms in which nitrogen atoms exist in diamond crystals>

[0057] First, in order to deepen the understanding of the synthetic single-crystal diamond disclosed herein, nitrogen atoms, which exist as impurities in the crystal and are one of the main factors determining the properties of diamond, will be explained.

[0058] Nitrogen atoms in diamond crystals can be classified according to their form of existence as isolated substituted nitrogen atoms, aggregated nitrogen atoms, etc.

[0059] An isolated substituted nitrogen atom (C center) refers to a nitrogen atom that exists in the position of a carbon atom in a diamond crystal, where a nitrogen atom replaces it by one atomic unit.

[0060] The inventors of this invention have a novel conception that if a diamond crystal contains isolated substituted nitrogen atoms, localized tensile stress is generated in the surrounding lattice, which becomes the starting point for plastic deformation and failure, reducing hardness and decreasing wear resistance and damage resistance.

[0061] Synthetic single-crystal diamond containing isolated substituted nitrogen atoms exhibits an infrared absorption spectrum at a wavenumber of 1130 cm⁻¹, as determined by Fourier transform infrared spectroscopy. -1 Nearby (i.e., wavenumber 1130±2cm) -1 It shows an absorption peak.

[0062] In synthetic single-crystal diamond containing isolated substituted nitrogen atoms, the concentration of these atoms can be determined using ESR (Electron Spin Resonance) analysis due to the presence of unpaired electrons originating from the nitrogen atoms. ESR can also detect signals from crystal defects that possess unpaired electrons in addition to isolated substituted nitrogen atoms. In such cases, isolated substituted nitrogen atoms can be separated and detected based on the g-value or the relaxation time of the signal.

[0063] Aggregated nitrogen atoms refer to nitrogen atoms that exist in a diamond crystal when two or more nitrogen atoms are aggregated together.

[0064] The inventors of this invention have a novel conception that aggregated nitrogen atoms in diamond crystals can suppress the progression of plastic deformation and cracking when a load is applied to the diamond crystal. Furthermore, the inventors have a novel conception that if a diamond crystal contains aggregated nitrogen atoms, the diamond crystal's hardness increases, its elastic deformability increases, and its resistance to chipping improves.

[0065] Aggregated nitrogen atoms exist in A centers (nitrogen 2-atom pairs), H3 centers (nitrogen 2-atom aggregates), N3 centers (nitrogen 3-atom aggregates), B centers (nitrogen 4-atom aggregates), and B' centers (platelets).

[0066] An A-center (nitrogen 2-pair) refers to an aggregate of two nitrogen atoms forming a covalent bond, with each nitrogen atom replacing a carbon atom that makes up the diamond crystal. Diamond containing an A-center (nitrogen 2-pair) is called type IaA. Synthetic single-crystal diamond containing an A-center (nitrogen 2-pair) exhibits an infrared absorption spectrum measured by Fourier transform infrared spectroscopy at a wavenumber of 1282 cm⁻¹. -1 Nearby (e.g., wavenumber 1282±2cm) -1 It shows an absorption peak.

[0067] The H3 center (nitrogen 2-atom aggregate) is an aggregate consisting of a hole and two nitrogen atoms adjacent to that hole, with each nitrogen atom replacing a carbon atom that constitutes the diamond crystal. In this specification, "nitrogen atom adjacent to the hole" refers to the nitrogen atom with the shortest interatomic distance to the carbon atom at the location of the hole (i.e., the nearest neighbor atom). The same meaning applies to the N3 center and B center described later.

[0068] Synthetic single-crystal diamond containing H3 centers (agglomeration of nitrogen 2 atoms) exhibits emission peaks in one or both of the following ranges when irradiated with excitation light of approximately shorter than 500 nm, such as 325 nm: near a fluorescence wavelength of 503 nm (e.g., 503 ± 2 nm) and between 510 nm and 530 nm.

[0069] The N3 center (nitrogen 3-atom aggregate) is an aggregate consisting of a hole and three nitrogen atoms adjacent to the hole, with each nitrogen atom replacing a carbon atom that makes up the diamond crystal.

[0070] Synthetic single-crystal diamond containing N3 centers (aggregates of nitrogen 3 atoms) exhibits emission peaks in one or both of the following ranges when irradiated with excitation light of approximately shorter than 410 nm, such as 325 nm: near a fluorescence wavelength of 415 nm (e.g., 415 ± 2 nm) and above a fluorescence wavelength of 420 nm and below 470 nm.

[0071] A B-center (nitrogen 4-atom aggregate) is an aggregate consisting of a hole and four nitrogen atoms adjacent to that hole, with each nitrogen atom replacing a carbon atom that makes up the diamond crystal.

[0072] Diamond containing B centers (agglomerates of nitrogen 4 atoms) is called type IaB. Synthetic single-crystal diamond containing agglomerates of nitrogen 4 atoms exhibits an infrared absorption spectrum at a wavenumber of 1175 cm⁻¹, as measured by Fourier transform infrared spectroscopy. -1 Nearby (e.g., wavenumber 1175±2cm) -1 It shows an absorption peak.

[0073] B' centers (also known as plate crystals) are plate-shaped aggregates composed of five or more nitrogen atoms and inter-lattice carbon, which are incorporated into the crystal as inclusions.

[0074] Diamond containing a B' center (lamellae) is called IaB' type. Synthetic single-crystal diamond containing a B' center (lamellae) shows an infrared absorption spectrum at a wavenumber of 1358 cm⁻¹ as measured by Fourier transform infrared spectroscopy. -1 Above and 1385cm -1 The absorption peaks are shown below.

[0075] The inventors of this invention conducted in-depth research on aggregated nitrogen atoms that can improve the properties of synthetic single-crystal diamond. As a result, they discovered that B-centers, H3-centers, and N3-centers exhibit less crystal strain and greater structural stability. Furthermore, they found that by forming at least one of B-centers, H3-centers, and N3-centers in synthetic single-crystal diamond, the mechanical properties of the synthetic single-crystal diamond, such as hardness, elastic deformability, and resistance to chipping, can be further improved, thus completing this disclosure.

[0076] Hereinafter, specific examples of the synthetic single-crystal diamond and its manufacturing method of the present disclosure will be described with reference to the accompanying drawings. In the accompanying drawings of the present disclosure, the same reference numerals denote the same or equivalent parts. In addition, the dimensional relationships of length, width, thickness, depth, etc. have been appropriately modified for the clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0077] In this specification, expressions such as "A~B" refer to the upper and lower limits of a range (i.e., above A and below B). When there is no unit recorded in A but only in B, the unit of A is the same as the unit of B.

[0078] In this specification, {} represents the general term for the plane orientation, which is equivalent to the plane orientation in crystal geometry, and <> represents the general term for the direction, which is equivalent to the direction in crystal geometry.

[0079] [Implementation Method 1: Synthesis of Single-Crystal Diamond]

[0080] The synthetic single-crystal diamond of this embodiment is a synthetic single-crystal diamond containing more than 100 ppm and less than 1500 ppm of nitrogen atoms. This synthetic single-crystal diamond comprises an aggregate, which is composed of a cavity and any number of two to four nitrogen atoms present adjacent to the cavity. The {001} facet of this synthetic single-crystal diamond... <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. This Knoop indentation is performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9N, on the {001} plane of the synthetic single-crystal diamond. <100> It is formed by measuring the Knoop hardness in the direction.

[0081] 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 yet clear, but it is speculated as described in (i) to (iii) below.

[0082] (i) The synthetic single-crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less based on the atomic number. As a result, the nitrogen atoms in the synthetic single-crystal diamond tend to aggregate. Therefore, this synthetic single-crystal diamond tends to contain aggregated nitrogen atoms, resulting in greater elastic deformation and improved resistance to chipping.

[0083] (ii) The synthetic single-crystal diamond of this embodiment comprises an aggregate consisting of a cavity and any number of two to four nitrogen atoms present adjacent to the cavity. Therefore, the synthetic single-crystal diamond has high hardness, high elastic deformation, and improved resistance to chipping.

[0084] (iii) In the synthetic single-crystal diamond of this embodiment, the ratio of the diagonals of the Knoop indentation, b / a, is 0.08 or less. Therefore, the synthetic single-crystal diamond exhibits greater elastic deformability. Furthermore, the relationship between the Knoop indentation and elastic deformability will be described later.

[0085] <Nitrogen concentration>

[0086] The synthetic single-crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less (hereinafter also referred to as "nitrogen atom concentration") based on the number of atoms. If the nitrogen atom concentration is 100 ppm or more, the nitrogen atoms in the synthetic single-crystal diamond tend to form aggregated nitrogen atoms. If the nitrogen atom concentration is 1500 ppm or less, the synthetic single-crystal diamond can have high hardness and excellent resistance to chipping.

[0087] The lower limit of nitrogen atom concentration in synthetic single-crystal diamond can be above 100 ppm, above 200 ppm, or above 300 ppm. The upper limit of nitrogen atom concentration in synthetic single-crystal diamond can be below 1500 ppm, below 1400 ppm, or below 1300 ppm. The nitrogen atom concentration in synthetic single-crystal diamond can be 100 ppm to below 1500 ppm, 100 ppm to below 1400 ppm, 100 ppm to below 1300 ppm, 200 ppm to below 1500 ppm, 200 ppm to below 1400 ppm, 200 ppm to below 1300 ppm, 300 ppm to below 1500 ppm, 300 ppm to below 1400 ppm, or 300 ppm to below 1300 ppm.

[0088] The nitrogen atom concentration in synthetic single-crystal diamond can be determined by secondary ion mass spectrometry (SIMS).

[0089] <Aggregated nitrogen atoms>

[0090] The synthetic single-crystal diamond of this embodiment comprises an aggregate consisting of one hole and any number of two to four nitrogen atoms adjacent to that hole. An example of an aggregate consisting of one hole and two nitrogen atoms adjacent to that hole is an H3 center (nitrogen 2-atom aggregate). An example of an aggregate consisting of one hole and three nitrogen atoms adjacent to that hole is an N3 center (nitrogen 3-atom aggregate). An example of an aggregate consisting of one hole and four nitrogen atoms adjacent to that hole is a B center (nitrogen 4-atom aggregate).

[0091] B-centered, H3-centered, and N3-centered crystals exhibit less strain and greater structural stability. The synthetic single-crystal diamond of this embodiment contains at least one of B-centered, H3-centered, and N3-centered types, thus possessing high hardness, large elastic deformation capacity, and excellent resistance to chipping.

[0092] (Center B)

[0093] The synthetic single-crystal diamond of this embodiment preferably comprises an aggregate (B-center (nitrogen 4-atom aggregate)) consisting of a cavity and four nitrogen atoms adjacent to the cavity. The presence of B-centers in the synthetic single-crystal diamond can be confirmed by measuring the infrared absorption spectrum using Fourier transform infrared spectroscopy. Specifically, when the infrared absorption spectrum shows a value of 1175 cm⁻¹... -1 Nearby (e.g., wavenumber 1175±2cm) -1 If an absorption peak is present, it is determined that the synthesized single-crystal diamond contains a B center.

[0094] (H3 Center)

[0095] The synthetic single-crystal diamond of this embodiment preferably comprises an aggregate (H3 center (nitrogen 2 atom aggregate)) consisting of a hole and two nitrogen atoms adjacent to the hole. The presence of H3 centers in the synthetic single-crystal diamond can be confirmed by fluorescence spectra obtained after irradiating it with excitation light at a wavelength of 325 nm. Specifically, if, in the fluorescence spectrum obtained by irradiating the synthetic single-crystal diamond with excitation light at a wavelength of 325 nm, there is an emission peak in one or both of the fluorescence wavelength ranges of 503 ± 2 nm and 510 nm or higher and 530 nm or lower, it is determined that the synthetic single-crystal diamond contains H3 centers.

[0096] Furthermore, the peaks within the fluorescence wavelength range of 503 ± 2 nm are emission peaks corresponding to the zero phonon line at the center of H3, while the emission peaks within the fluorescence wavelength range of 510 nm to 530 nm are emission peaks corresponding to the subband (phonon sideband) at the center of H3. The emission peaks within the fluorescence wavelength range of 510 nm to 530 nm are observed to be more than one mountain-shaped peak. At least one of these mountain-shaped peaks exhibits maximum intensity within this range.

[0097] (N3 Center)

[0098] The synthetic single-crystal diamond of this embodiment preferably comprises an aggregate (N3 center (nitrogen 3 atom aggregate)) consisting of a hole and three nitrogen atoms adjacent to the hole. The presence of N3 centers in the synthetic single-crystal diamond can be confirmed by the fluorescence spectrum obtained by irradiating the synthetic single-crystal diamond with excitation light at a wavelength of 325 nm. Specifically, if the fluorescence spectrum obtained by irradiating the synthetic single-crystal diamond with excitation light at a wavelength of 325 nm shows an emission peak in one or both of the following ranges: a fluorescence wavelength of 415 ± 2 nm and a fluorescence wavelength of 420 nm or higher and 470 nm or lower, it is determined that the synthetic single-crystal diamond contains N3 centers.

[0099] Furthermore, the peaks in the fluorescence wavelength range of 415 ± 2 nm correspond to the zero phonon line at the center of N3, while the emission peaks in the fluorescence wavelength range of 420 nm to 470 nm correspond to the subband (phonon sideband) at the center of N3. The emission peaks in the fluorescence wavelength range of 420 nm to 470 nm are observed as more than one mountain-shaped peak within this range. At least one of these mountain-shaped peaks exhibits the maximum intensity within this range.

[0100] (A center (nitrogen 2-atom pair))

[0101] The synthetic single-crystal diamond of this embodiment preferably contains A centers (nitrogen 2-atom pairs). The A centers in the synthetic single-crystal diamond can suppress crack propagation. Therefore, the synthetic single-crystal diamond can exhibit excellent resistance to chipping.

[0102] The presence of A-centers in synthetic single-crystal diamond can be confirmed by measuring the infrared absorption spectrum using Fourier transform infrared spectroscopy. Specifically, in this infrared absorption spectrum, at a wavenumber of 1282 cm⁻¹... -1 Nearby (e.g., 1282±2cm) -1 If an absorption peak is present, it is determined that the synthesized single-crystal diamond contains an A center.

[0103] (B' center (lamellae))

[0104] The synthetic single-crystal diamond of this embodiment preferably exhibits an infrared absorption spectrum at a wavenumber of 1370 cm⁻¹. -1 Above and 1385cm -1 Absorption peaks exist within the following range. These absorption peaks originate from the B' center (platelets) in synthetic single-crystal diamond.

[0105] If in the infrared absorption spectrum of synthetic single-crystal diamond, at a wavenumber of 1370 cm⁻¹ -1 Above and 1385cm -1 If an absorption peak exists within the following range, the size of the nitrogen atom aggregates contained in the B' center (platelet) is moderate, which can prevent the progression of plastic deformation and cracking, and is unlikely to become the starting point of failure. Therefore, synthetic single-crystal diamond can possess high hardness and excellent strength.

[0106] Furthermore, generally speaking, synthetic single-crystal diamond containing a B' center (lamellae) exhibits high infrared absorption spectra at wavenumber 1358 cm⁻¹. -1 Above and 1385cm -1 The following shows the absorption peaks. However, if the wavenumber is less than 1370 cm⁻¹, the absorption peaks will be smaller. -1 Range (wavenumber 1358cm) -1 The wavenumber is above and below 1370cm. -1 If an absorption peak is present, the B' center (lamellar) aggregates within the crystal are too large, becoming the starting point for destruction, and therefore are not preferred. Therefore, preferably, in the infrared absorption spectrum of synthesized single-crystal diamond, the peak is at a wavenumber of 1358 cm⁻¹. -1 The wavenumber is above and below 1370cm. -1 There are no absorption peaks within the range.

[0107] (Other aggregated nitrogen atoms)

[0108] Aggregated nitrogen atoms other than H3 centers, N3 centers, B centers, and B' centers do not have a significant impact on the mechanical properties of the synthesized single-crystal diamond. Therefore, the synthesized single-crystal diamond of this embodiment can contain aggregated nitrogen atoms other than H3 centers, N3 centers, B centers, and B' centers.

[0109] <Isolated Substituted Nitrogen Atom>

[0110] 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 have high hardness and excellent resistance to chipping.

[0111] The absence of isolated substituted nitrogen atoms in synthetic single-crystal diamond can be determined using infrared absorption spectra measured by Fourier transform infrared spectroscopy. Single-crystal diamond containing isolated substituted nitrogen atoms will exhibit an infrared absorption spectrum at a wavenumber of 1130 cm⁻¹. -1 Nearby (i.e., wavenumber 1130±2cm) -1 The peak was observed. Therefore, this was confirmed by observing the infrared absorption spectrum of the synthesized single-crystal diamond at a wavenumber of 1130 ± 2 cm⁻¹. -1 There are no absorption peaks originating from isolated substituted nitrogen atoms within the range, which indicates that it does not contain isolated substituted nitrogen atoms.

[0112] When in the infrared absorption spectrum, at a wavenumber of 1130±2cm -1 When there are shoulder peaks in the absorption spectra of aggregated nitrogen atoms other than isolated substituted nitrogen atoms within a certain range, and it is unclear whether these shoulder peaks originate from isolated substituted nitrogen atoms, ESR analysis can be used to determine the presence of isolated substituted nitrogen atoms. When isolated substituted nitrogen atoms are absent in synthetic single-crystal diamond, unpaired electrons are also absent. Therefore, no signal is detected in such synthetic single-crystal diamond during ESR analysis. Thus, it can be confirmed that isolated substituted nitrogen atoms are absent in synthetic single-crystal diamond.

[0113] <Infrared Absorption Spectroscopy>

[0114] If C centers, A centers, B centers, and B' centers (platelets) exist in a diamond crystal, absorption peaks originating from each center can be observed in the infrared absorption spectrum of the diamond crystal measured using Fourier transform infrared spectroscopy. Because the waveforms of each center overlap, the presence and quantity of each center cannot be determined solely based on the intensity values ​​at each wavenumber. On the other hand, by comparing the relative intensities at each wavenumber and considering the approximate waveforms of each center, it is possible to determine the presence or absence of each center and to qualitatively evaluate the content ratio of each center.

[0115] <The ratio of the diagonals of the Knoop indentation, b / a>

[0116] In this embodiment, the {001} plane of the synthesized single-crystal diamond <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. This Knoop indentation is performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9N on the {001} plane of the synthetic single-crystal diamond. <100> It is formed by measuring the Knoop hardness in the direction.

[0117] The above-mentioned Knoop hardness determination, as specified in JIS Z2251:2009, is known as one of the standards for expressing the hardness of industrial materials. The Knoop indenter is pressed against the material being tested at a predetermined temperature and under a predetermined load (test load) to determine the hardness of the material.

[0118] Here, a Knoop indenter refers to an indenter made of diamond with a diamond-shaped quadrangular prism base. Furthermore, within the diamond shape of its base, the ratio b' / a' of the length of the shorter diagonal (b') to the length of the longer diagonal (a') is specified as 0.141. Additionally, a Knoop indentation refers to the mark remaining at the point immediately after the Knoop indenter is released following pressing the material being tested (synthetic single-crystal diamond in this embodiment) under the aforementioned temperature and test load. In this embodiment, the mark is found in the {001} plane of the synthetic single-crystal diamond. <100> In the direction of the test, according to JIS Z 2251:2009, indentation (Knoop indentation) is applied at a temperature of 23℃±5℃ and a test load of 4.9N.

[0119] 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, which is smaller than the ratio b' / a' (0.141) of the original Knoop indenter. This is because the material being tested (i.e., the synthetic single-crystal diamond in this embodiment) moves elastically, and the indentation produces a recovery (elastic recovery) that attempts to elastically return to its original shape.

[0120] Using a conceptual representation of Knoop indentation Figure 1 The above phenomenon will be explained. For example, when the material being tested does not exhibit any elastic recovery, the cross-section of the Knoop indenter and the Knoop indentation have the same shape. Figure 1 (The portion shown in the figure is designated as the "original Knoop indentation"). On the other hand, the synthetic single-crystal diamond of this embodiment is prone to elastic deformation in the direction of the arrow in the figure, therefore its Knoop indentation is 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.

[0121] In the synthetic single-crystal diamond of this embodiment, since the ratio of the diagonals of the Knoop indentation, b / a, is less than 0.08, it exhibits greater elastic deformation. The greater the elastic deformation, the higher the toughness, thus resulting in a strong and tough synthetic single-crystal diamond.

[0122] The upper limit of the ratio of the diagonals of the Knoop indentation, b / a, is 0.08 or less, and can be 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 this case, b / a is 0, and the Knoop indentation is formed only along the longer diagonal. Therefore, the lower limit of the ratio of the diagonals of the Knoop indentation, b / a, can be 0 or more. The ratio of the diagonals of the Knoop indentation, b / a, can be 0 or more and 0.08 or less, 0 or more and 0.075 or less, 0 or more and 0.07 or less, 0 or more and 0.065 or less, or 0 or more and 0.06 or less.

[0123] Knoop Hardness

[0124] The {001} facet of the synthetic single-crystal diamond involved in this embodiment <100> Knoop hardness in the direction (hereinafter also denoted as "{001}") <100> The Knoop hardness is preferably 100 GPa or higher. {001} <100> Synthetic single-crystal diamonds with a Knoop hardness of 100 GPa or higher have higher hardness and better wear resistance than natural diamonds containing nitrogen.

[0125] {001} of synthetic single-crystal diamond <100> The lower limit of Knoop hardness can be above 105 GPa, above 110 GPa, or above 115 GPa. {001} is used for synthesizing single-crystal diamond. <100> There is no specific upper limit to the Knoop hardness; from a manufacturing perspective, it can be, for example, below 150 GPa. (The last part, "synthetic single-crystal diamond {001}", appears to be an unrelated fragment and is omitted from the translation.) <100> Knoop hardness can be above 100 GPa and below 150 GPa, above 105 GPa and below 150 GPa, above 110 GPa and below 150 GPa, or above 115 GPa and below 150 GPa.

[0126] {001} for synthetic single-crystal diamond <100> The evaluation method for Knoop hardness (hereinafter also denoted as HK, with units of GPa) will be explained. First, the Knoop hardness in the {001} plane of synthetic single-crystal diamond will be evaluated. <100> In the direction of the indentation, according to JIS Z 2251:2009, an indentation was applied at a temperature of 23℃±5℃ and a test load of 4.9N. The diagonal a (μm) of the longer side of the resulting indentation was measured, and the Knoop hardness (HK) was calculated using the following formula A.

[0127] HK = 14229 × 4.9 / a 2 Formula A

[0128] <Cracks generate load>

[0129] Preferably, in the synthetic single-crystal diamond of this embodiment, in a destructive strength test where a spherical diamond indenter with a front radius (R) of 50 μm is pressed onto the surface of the synthetic single-crystal diamond at a load rate of 100 N / min, the crack initiation load is 15 N or more. If the crack initiation load is 15 N or more, the synthetic single-crystal diamond exhibits excellent destructive strength and resistance to chipping, and is less prone to tip chipping when used as a tool material.

[0130] The lower limit of the crack induction load for synthetic single-crystal diamond can be 17N or higher, 20N or higher, 25N or higher, or 30N or higher. The upper limit of the crack induction load is not specifically limited, but from a manufacturing point of view, it can be, for example, below 50N. The crack induction load for synthetic single-crystal diamond can be 15N or higher and below 50N, 17N or higher and below 50N, 20N or higher and below 50N, 25N or higher and below 50N, or 30N or higher and below 50N.

[0131] 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 onto the specimen, and a load is applied to the specimen at a load rate of 100 N / min. The load at the instant the specimen cracks (cracking load) is measured. The instant of cracking is measured using an AE sensor. The greater the cracking load, the higher the strength of the specimen and the better its resistance to defects.

[0132] If an indenter with a front radius (R) less than 50 μm is used as the measuring indenter, the sample undergoes plastic deformation before cracking occurs, making it impossible to determine the accurate strength relative to the crack. Furthermore, even if a measuring indenter with a front radius (R) greater than 50 μm is used, the following problems arise: the load required to induce cracking increases, the contact area between the indenter and the sample increases, and the surface finish of the sample significantly affects the measurement accuracy, as does the crystal orientation of the single crystal. Therefore, in the destructive strength test of synthetic single-crystal diamond, an indenter with a front radius (R) of 50 μm is preferred.

[0133] <Application>

[0134] The synthetic single-crystal diamond of this embodiment can be used not only for cutting tools such as precision cutting lathe tools and woodworking tools, wear-resistant tools such as grinding wheel dressers, wire drawing dies, scribing tools, water jet orifices, and wire guides, but also for a wide range of other tools.

[0135] [Implementation Method 2: Method for Manufacturing Synthetic Single-Crystal Diamond]

[0136] The following describes an example of a method for manufacturing the synthetic single-crystal diamond according to Embodiment 1. Furthermore, the synthetic single-crystal diamond of Embodiment 1 is not limited to the manufacturing method described below, and can also be manufactured using other methods.

[0137] The method for manufacturing synthetic single-crystal diamond disclosed herein is a method for manufacturing synthetic single-crystal diamond according to Embodiment 1, comprising: a first step, wherein a diamond single crystal containing nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less based on atomic number is synthesized by using a solvent metal temperature difference method; 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 or more and 1000 MGy or less; and a third step, wherein the diamond single crystal after the second step is subjected to a pressure of 5 GPa or more for 1 minute or more and a temperature of 2300°C or more and 2600°C or less to obtain synthetic single-crystal diamond.

[0138] (First process)

[0139] Diamond single crystals, for example, can be used with... Figure 2 The sample chamber shown is fabricated using the temperature difference method.

[0140] like Figure 2 As shown, in the sample chamber 10 used to manufacture diamond single crystals 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 setting a longitudinal temperature gradient inside the sample chamber 10, with a high-temperature section (T...)... high Carbon source 3 is configured in the low-temperature section (T) low A synthesis method for growing a single diamond crystal 1 on a seed crystal 5, wherein a seed crystal 5 is prepared, a solvent metal 4 is prepared between a carbon source 3 and the seed crystal 5, and the conditions are maintained above the melting temperature of the solvent metal 4 and above the pressure that makes the diamond thermally stable.

[0141] Diamond powder is preferably used as the carbon source 3. Alternatively, graphite or pyrolytic carbon can 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 these metals, can be used.

[0142] In carbon source 3 or solvent metal 4, nitrides such as iron nitride (Fe2N, Fe3N), aluminum nitride (AlN), phosphorus nitride (P3N4), and silicon nitride (Si3N4), as well as organic nitrogen compounds such as melamine and sodium azide, can be added as nitrogen sources in the form of monomers or mixtures. Alternatively, diamond and graphite, which contain a large amount of nitrogen, can also be added as nitrogen sources. Thus, nitrogen atoms are present in the synthesized diamond single crystal. In this case, the nitrogen atoms in the diamond single crystal mainly exist as isolated substituted nitrogen atoms.

[0143] The content of the nitrogen supply source in the carbon source 3 or the solvent metal 4 is adjusted so that the concentration of nitrogen atoms in the synthesized diamond single crystal is 100 ppm or more and 1500 ppm or less. For example, in the carbon source, the content of nitrogen atoms originating from the nitrogen supply source can be 200 ppm or more and 3000 ppm or less. In addition, in the solvent metal, for example, when the solvent metal is an alloy composed of iron-cobalt-nickel and the nitrogen supply source is Fe3N, the content of the nitrogen supply source can be set to 0.01% by mass or more and 0.2% by mass or less.

[0144] Solvent metal 4 may also 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).

[0145] (Second process)

[0146] Next, 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 or higher but less than 1000 MGy. This introduces lattice defects into the diamond single crystal, forming holes.

[0147] If the irradiation energy is less than 100 mgy, there is a risk that the introduction of lattice defects may be insufficient. On the other hand, if the energy exceeds 1000 mgy, there is a risk that excessive holes may be generated, leading to a significant decrease in crystallinity. Therefore, the energy is preferably 100 mgy or more and 1000 mgy or less.

[0148] As the particle beam, neutron beams or proton beams can be used. As for the irradiation conditions, there are no particular limitations as long as the diamond single crystal can be irradiated with an energy of 100 MGy or higher and 1000 MGy or lower. For example, when using an electron beam, the irradiation energy can be 4.6 MeV or higher and 4.8 MeV or lower, the current can be 2 mA or higher and 5 mA or lower, and the irradiation time can be 30 hours or higher and 45 hours or lower.

[0149] (Third process)

[0150] Next, a pressure of 5 GPa or higher and a temperature of 2300°C or higher and 2600°C or lower are applied to the diamond single crystal after the second process for more than 1 minute and less than 3600 minutes to obtain synthetic single crystal diamond. As a result, isolated substituted nitrogen atoms in the diamond single crystal aggregate through hole movement to become aggregated nitrogen atoms.

[0151] By setting the temperature of the third process to 2300°C or higher, the movement of nitrogen atoms in the diamond single crystal is promoted, thereby promoting the formation of an aggregate consisting of a cavity and any number of two to four substituted nitrogen atoms surrounding the cavity. If the temperature of the third process is lower than 2300°C, it is difficult to form the aforementioned aggregate. From the viewpoint of cost and productivity, the upper limit of the temperature of the third process is preferably 2600°C or lower.

[0152] On the other hand, if a diamond single crystal is heated to above 2300°C under normal pressure, it will graphitize. The inventors of this invention, through in-depth research, have discovered that by applying a temperature of 2300°C to 2600°C for at least 1 minute and less than 3600 minutes under a high pressure of 5 GPa or more, it is possible to promote the movement of nitrogen atoms in the diamond single crystal without causing it to graphitize.

[0153] The time for applying a temperature of 2300°C to 2600°C under a high pressure of 5 GPa or higher to a diamond single crystal is 1 minute to 3600 minutes. The time for applying the temperature of 2300°C to 2600°C under a high pressure of 5 GPa or higher to a diamond single crystal can be set to 60 minutes to 360 minutes. The pressure at this time can be set to 5 GPa to 20 GPa.

[0154] The second and third processes can each be performed once as a cycle, and this cycle can be repeated two or more times. This promotes the aggregation of isolated substituted nitrogen atoms within the diamond single crystal.

[0155] [Postscript 1]

[0156] The synthetic single-crystal diamond disclosed herein may comprise an aggregate (B-center (nitrogen 4-atom aggregate)) consisting of a cavity and four nitrogen atoms present adjacent to the cavity.

[0157] [Postscript 2]

[0158] The synthetic single-crystal diamond disclosed herein may comprise an aggregate (H3 center (nitrogen 2 atom aggregate)) consisting of a cavity and two nitrogen atoms present adjacent to the cavity.

[0159] [Postscript 3]

[0160] The synthetic single-crystal diamond disclosed herein may comprise an aggregate (N3 center (N3 atom aggregate)) consisting of a cavity and three nitrogen atoms present adjacent to the cavity.

[0161] [Postscript 4]

[0162] The synthetic single-crystal diamond disclosed herein may contain both B-centers and H3-centers.

[0163] [Postscript 5]

[0164] The synthetic single-crystal diamond disclosed herein may contain both B-centers and N-3-centers.

[0165] [Postscript 6]

[0166] The synthetic single-crystal diamond disclosed herein may contain B centers, H3 centers, and N3 centers.

[0167] [Postscript 7]

[0168] The synthetic single-crystal diamond disclosed herein preferably does not contain isolated substituted nitrogen atoms (C centers). Therefore, the hardness and chip resistance of the synthetic single-crystal diamond are further improved.

[0169] [Postscript 8]

[0170] Preferably, in the infrared absorption spectrum of the synthetic single-crystal diamond disclosed herein, the wavenumber is 1130±2 cm⁻¹. -1 There are no absorption peaks centered at C within the range. Therefore, the hardness and chip resistance of the synthesized single-crystal diamond are further improved. Furthermore, at a wavenumber of 1130±2 cm⁻¹... -1 Absorption based on center A and center B also exists within the range.

[0171] [Postscript 9]

[0172] Preferably, in the infrared absorption spectrum of the synthetic single-crystal diamond disclosed herein, the wavelength is 1358 cm⁻¹. -1 The wavenumber is above and below 1370cm. -1 There are no absorption peaks within the specified range. Therefore, the hardness and chip resistance of the synthesized single-crystal diamond are further improved.

[0173] [Postscript 10]

[0174] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 100 ppm and below 1400 ppm.

[0175] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 100 ppm and below 1300 ppm.

[0176] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 200 ppm and below 1500 ppm.

[0177] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 200 ppm and below 1400 ppm.

[0178] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 200 ppm and below 1300 ppm.

[0179] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 300 ppm and below 1500 ppm.

[0180] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 300 ppm and below 1400 ppm.

[0181] The nitrogen atom concentration in the synthetic single-crystal diamond disclosed herein can be above 300 ppm and below 1300 ppm.

[0182] [Postscript 11]

[0183] The ratio of the diagonals of the Knoop indentation in the synthetic single-crystal diamond disclosed herein, b / a, can be greater than 0 and less than 0.08.

[0184] The ratio of the diagonals of the Knoop indentation in the synthetic single-crystal diamond disclosed herein, b / a, can be greater than 0 and less than 0.075.

[0185] The ratio of the diagonals of the Knoop indentation in the synthetic single-crystal diamond disclosed herein, b / a, can be greater than 0 and less than 0.07.

[0186] The ratio of the diagonals of the Knoop indentation in the synthetic single-crystal diamond disclosed herein, b / a, can be greater than 0 and less than 0.065.

[0187] The ratio of the diagonals of the Knoop indentation in the synthetic single-crystal diamond disclosed herein, b / a, can be greater than 0 and less than 0.06.

[0188] [Postscript 12]

[0189] The present disclosure relates to the synthesis of single-crystal diamond {001} <100> The Knoop hardness can be above 100 GPa and below 150 GPa.

[0190] The present disclosure relates to the synthesis of single-crystal diamond {001} <100> The Knoop hardness can be above 105 GPa and below 150 GPa.

[0191] The present disclosure relates to the synthesis of single-crystal diamond {001} <100> The Knoop hardness can be above 110 GPa and below 150 GPa.

[0192] The present disclosure relates to the synthesis of single-crystal diamond {001} <100> The Knoop hardness can be above 115 GPa and below 150 GPa.

[0193] [Postscript 13]

[0194] The cracking load of the synthetic single-crystal diamond disclosed herein can be above 15N and below 50N.

[0195] The cracking load of the synthetic single-crystal diamond disclosed herein can be above 17N and below 50N.

[0196] The cracking load generated by the synthetic single-crystal diamond disclosed herein can be above 20N and below 50N.

[0197] The cracking load of the synthetic single-crystal diamond disclosed herein can be above 25N and below 50N.

[0198] The cracking load generated by the synthetic single-crystal diamond disclosed herein can be above 30N and below 50N.

[0199] Example

[0200] This embodiment will be described in more detail through examples. However, this embodiment is not limited to these examples.

[0201] [Production of Synthetic Single-Crystal Diamond]

[0202] <Sample 2, Sample 4 to Sample 8>

[0203] (First process)

[0204] Use with Figure 2 The sample chamber shown was used to synthesize diamond single crystals by using the temperature difference method with solvent metal.

[0205] As the solvent metal, an alloy composed of iron, cobalt, and nickel was prepared, to which iron nitride (Fe3N) powder was added 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.

[0206] Diamond powder was used as the carbon source, and approximately 0.5 mg of a single diamond crystal was used as the seed crystal. The temperature inside the sample chamber was adjusted using a heater to create a temperature difference of several tens of degrees Celsius 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 was controlled within the range of 1370℃ ± 10℃ (1360℃~1380℃) for 60 hours to synthesize a single diamond crystal on the seed crystal.

[0207] (Second process)

[0208] Next, the obtained diamond single crystal was irradiated with an electron beam. The irradiation conditions were: beam energy of 4.6 MeV, current of 2 mA, and irradiation time of 30 hours. These are the irradiation conditions that impart 100 mgy energy to the diamond single crystal.

[0209] (Third process)

[0210] Next, the diamond single crystal irradiated with electron beam was subjected to a high pressure of 6 GPa or higher (referred to as "high pressure" in Table 1) and the temperature listed in the "Third Process (60 minutes)" column of "Manufacturing Conditions" in Table 1 for 60 minutes to obtain 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.

[0211] <Sample 1>

[0212] Sample 1 was synthesized with diamond single crystals through the same first process as Sample 2. In Sample 1, the second and third processes were not performed.

[0213] <Sample 3>

[0214] Sample 3 synthesized diamond single crystals through the same first process as Sample 4. In Sample 1, the second and third processes were not performed.

[0215] Table 1

[0216]

[0217] <Evaluation>

[0218] 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 spectrophotometry was performed, and {001} <100> The determination of Knoop hardness, the determination of the ratio of the diagonals of the Knoop indentation (b / a), and the destructive strength test.

[0219] (Determination of nitrogen atom concentration)

[0220] 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.

[0221] (fluorescence spectrum)

[0222] After mirror polishing the surface of each sample of synthetic single-crystal diamond / diamond single crystal, they were irradiated with excitation light at a wavelength of 325 nm, and the fluorescence spectrum was measured.

[0223] In the fluorescence spectrum, confirm the presence or absence of emission peaks in the ranges (a) to (d) below.

[0224] (a) Within the fluorescence wavelength range of 415±2nm

[0225] (b) Fluorescence wavelengths above 420 nm and below 470 nm

[0226] (c) Within the fluorescence wavelength range of 503±2nm

[0227] (d) Fluorescence wavelengths above 510 nm and below 530 nm

[0228] The results are shown in Table 2 under “Fluorescence Spectra” for “Synthetic Single Crystal Diamond / Diamond Single Crystal” in the columns “Emission Peak in the range of 415±2nm”, “420-470nm Subband”, “Emission Peak in the range of 503±2nm”, and “510-530nm Subband”.

[0229] An N3 center is defined as having a emission peak in one or both of the following ranges: (a) fluorescence wavelength 415±2 nm and (b) fluorescence wavelength 420 nm to 470 nm. An N3 center is defined as not having a emission peak in either range. The results are shown in the "N3 Center" column of "Fluorescence Spectroscopy" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0230] The presence of emission peaks in one or both of the following ranges is designated as "Present" H3 centers: (c) fluorescence wavelength 503±2 nm and (d) fluorescence wavelength 510 nm to 530 nm. The absence of emission peaks in either range is designated as "Negative" H3 centers. The results are shown in the "H3 Centers" column of "Fluorescence Spectra" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0231] (Infrared Spectroscopic Analysis)

[0232] The synthetic single-crystal diamond / diamond single crystal of each sample was processed into a plate with a thickness of about 1 mm. After grinding the two sides that allow light to pass through into a mirror surface, the absorbance in the infrared region was measured by Fourier transform infrared spectroscopy to produce an infrared absorption spectrum.

[0233] In addition to absorption based on other centers, the infrared absorption spectrum will show absorption at wavenumber 1282±2 cm⁻¹. -1 The presence of an absorption peak is designated as "present" at center A, with a wavenumber of 1282±2 cm⁻¹.-1 The absence of an absorption peak is marked as "None" A center. The results are shown in the "A Center" column of "Infrared Absorption Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0234] In addition to absorption based on other centers, the infrared absorption spectrum will show absorption at wavenumber 1175±2 cm⁻¹. -1 The presence of an absorption peak is designated as "present" at center B, with a wavenumber of 1175 ± 2 cm⁻¹. -1 The absence of an absorption peak is designated as "None" for the B center. The results are shown in the "B Center" column of the "Infrared Absorption Spectrum" section of "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0235] In addition to absorption based on other centers, the infrared absorption spectrum will show absorption at wavenumber 1130±2 cm⁻¹. -1 The presence of an absorption peak is designated as "present" at the C center, with a wavenumber of 1130 ± 2 cm⁻¹. -1 The absence of an absorption peak is marked as "None" C-center. The results are shown in the "C-center" column of "Infrared Absorption Spectrum" for "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0236] In addition to absorption based on other centers, the infrared absorption spectrum will show absorption at wavenumbers of 1370–1385 cm⁻¹. -1 The presence of an absorption peak is defined as "present" at the B' center (plate crystal), and the peak value will be between 1370 and 1385 cm⁻¹. -1 The absence of absorption peaks is marked as "None" for B' center (lamellae). The results are shown in the "B' center / lamellae" column of "Infrared Absorption Spectroscopy" in Table 2, under "Synthetic Single Crystal Diamond / Diamond Single Crystal".

[0237] Furthermore, synthetic single-crystal diamond containing a B' center (lamellae) exhibits high infrared absorption spectra at wavenumber 1358 cm⁻¹. -1 Above and 1385cm -1 The following shows the absorption peaks. However, if the wavenumber is less than 1370 cm⁻¹, the absorption peaks will be smaller. -1 Range (wavenumber 1358cm) -1 The wavenumber is above and below 1370cm. -1 The presence of absorption peaks indicates that the B' center (lamellae) aggregates within the crystal are too large, becoming the starting point for destruction, and therefore are not preferred. In samples 1-8, at a wavenumber of 1358 cm⁻¹... -1 The wavenumber is above and below 1370cm. -1 There is no absorption peak.

[0238] As a reference value, the phonon-based absorption of diamond, i.e., the wavenumber 2160 cm⁻¹, was calculated. -1 When the absorbance is set to 1, the wavenumber is 1282 cm⁻¹.-1 The absorbance value and wavenumber of (center A) are 1175 cm⁻¹. -1 The absorbance value and wavenumber of (center B) are 1130 cm⁻¹. -1 The absorbance value (C center) and wavenumber 1370 cm⁻¹ -1 Above and 1385cm -1 The following are the absorbance values ​​and wavenumbers of the peak 1358 cm⁻¹. -1 The wavenumber is above and below 1370cm. -1 The absorbance values ​​of the peaks are shown in Table 2 under “Infrared Absorption Spectra of Synthetic Single Crystal Diamond / Diamond Single Crystal” 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)”.

[0239] Regarding I(1175) / I(2160), the value of I(1175) / I(2160) is larger for sample 3 (without B centers) compared to sample 2 (with B centers). This is because sample 3 has more nitrogen in its C centers, resulting in a higher wavenumber of 1175 cm⁻¹ at the shoulder of the absorption spectrum originating from these C centers. -1 The strong absorption at that location does not necessarily mean that sample 3 contains a B center.

[0240] Regarding I(1130) / I(2160), compared to sample 1 which has a C-center, samples 4-8 which do not have a C-center have a larger I(1130) / I(2160) value. This is because samples 4-8 have more nitrogen in their A-centers and B-centers, thus resulting in a higher wavenumber of 1130 cm⁻¹ at the shoulder peak of the absorption spectrum originating from the aforementioned A-centers and B-centers. -1 The strong absorption at the point does not necessarily mean that samples 4 to 8 contain C centers.

[0241] (Knoop Hardness Measurement)

[0242] Within the {001} plane of the synthesized single-crystal diamond / diamond single crystal in each sample <100> An indentation was applied in the direction of the indentation with a load of 4.9 N. The length a (μm) of the diagonal of the longer side of the resulting Knoop indentation was measured, and the Knoop hardness (HK) was calculated using the following formula A. The specific measurement method is described in Embodiment 1, and therefore will not be repeated. The results are shown in Table 2 under “Synthetic Single Crystal Diamond / Diamond Single Crystal” “{001}”. <100> In the "Knoop Hardness" column.

[0243] HK = 14229 × 4.9 / a 2 Formula A

[0244] (Determination of Knoop indentation (b / a))

[0245] For the Knoop indentation obtained through the above Knoop hardness measurement, the length 'a' of the longer diagonal and the length 'b' of the shorter diagonal are measured, and the ratio b / a is calculated. The results are shown in Table 2, "Synthetic Single Crystal Diamond / Diamond Single Crystal," under "b / a{001}". <110> In the column, the smaller the value of b / a, the greater the elastic deformation.

[0246] (Destructive Strength Test)

[0247] A spherical diamond indenter with a radius of 50 μm was prepared. At room temperature (23°C), a load was 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 of crack initiation (crack initiation load) was measured. The specific measurement method is described in Example 1 and 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.

[0248]

[0249] <Inspection>

[0250] Samples 2 and 4 through 8 correspond to the Examples. Samples 1 and 3 correspond to the Comparative Examples. It can be confirmed that, compared with Samples 1 and 3 (Comparative Examples), Samples 2 and 4 through 8 (Examples) have higher hardness, greater elastic deformation, and excellent resistance to chipping.

[0251] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0252] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing embodiments and examples, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0253] Explanation of reference numerals in the attached figures

[0254] 1: Diamond single crystal; 2: Insulator; 3: Carbon source; 4: Solvent metal; 5: Seed crystal; 6: Pressure medium; 7: Graphite heater; 10: Sample chamber.

Claims

1. A synthetic single-crystal diamond, comprising nitrogen atoms of 100 ppm to 1500 ppm or more, wherein... The synthetic single-crystal diamond comprises an aggregate consisting of a cavity and any number of two to four nitrogen atoms adjacent to the cavity. The {001} plane of the synthetic single-crystal diamond <110> The ratio of the length b of the shorter diagonal to the length a of the longer diagonal of the Knoop indentation in the direction of the indentation is less than 0.

08. The Knoop indentation was performed according to JIS Z 2251:2009, under conditions of 23℃±5℃ and a test load of 4.9N, on the {001} plane of the synthetic single-crystal diamond. <100> It is formed by measuring the Knoop hardness in the direction.

2. The synthetic single-crystal diamond according to claim 1, wherein, In the infrared absorption spectrum of the synthesized single-crystal diamond, at a wavenumber of 1175±2 cm⁻¹ -1 Absorption peaks exist within the range.

3. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In the fluorescence spectrum of the synthesized single-crystal diamond, there are emission peaks in one or both of the fluorescence wavelength range of 503±2nm and the fluorescence wavelength range of 510nm and 530nm.

4. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In the fluorescence spectrum of the synthesized single-crystal diamond, there are emission peaks in one or both of the fluorescence wavelength range of 415±2nm and the fluorescence wavelength range of 420nm and above and 470nm and below.

5. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In the infrared absorption spectrum of the synthesized single-crystal diamond, at a wavenumber of 1282±2 cm⁻¹ -1 Absorption peaks exist within the range.

6. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In the infrared absorption spectrum of the synthesized single-crystal diamond, at a wavenumber of 1370 cm⁻¹ -1 Above and 1385cm -1 Absorption peaks exist within the following range.

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

8. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In a destructive strength test where a spherical diamond indenter with a front radius of 50 μm is pressed onto the surface of the synthetic single-crystal diamond at a load rate of 100 N / min, the cracking load exceeds 17 N.

9. The synthetic single-crystal diamond according to claim 1 or 2, wherein, In the infrared absorption spectrum of the synthesized single-crystal diamond, at a wavenumber of 1358 cm⁻¹ -1 The wavenumber is above and below 1370cm. -1 There are no absorption peaks within the range.

10. The synthetic single-crystal diamond according to claim 1 or 2, wherein, The nitrogen atom concentration in the synthetic single-crystal diamond is above 100 ppm and below 1300 ppm.

11. The synthetic single-crystal diamond according to claim 1 or 2, wherein, The nitrogen atom concentration in the synthetic single-crystal diamond is above 300 ppm and below 1300 ppm.

12. The synthetic single-crystal diamond according to claim 1 or 2, wherein, The ratio b / a is greater than 0 and less than 0.

075.

13. The synthetic single-crystal diamond according to claim 1 or 2, wherein, The {001} plane of the synthetic single-crystal diamond <100> The Knoop hardness in the direction is above 115 GPa and below 150 GPa.

14. A method for manufacturing synthetic single-crystal diamond, which is the method for manufacturing synthetic single-crystal diamond according to any one of claims 1 to 13, wherein, The method for manufacturing the synthetic single-crystal diamond comprises: In the first step, a diamond single crystal containing nitrogen atoms at a concentration of more than 100 ppm and less than 1500 ppm based on the atomic number is synthesized by using the temperature difference method of solvent metal. The second step involves irradiating the diamond single crystal with one or both of an electron beam and a particle beam, each possessing an energy of 100 MGy or higher but less than 1000 MGy. In the third step, a pressure of 5 GPa or more and a temperature of 2300°C or more and 2600°C or less are applied to the diamond single crystal after the second step for a period of more than 1 minute and less than 3600 minutes to obtain synthetic single crystal diamond.

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